U.S. patent application number 12/851222 was filed with the patent office on 2010-12-02 for protein synthesis required for long-term memory is induced by pkc activation on days preceding associative learning.
This patent application is currently assigned to BLANCHETTE ROCKEFELLER NEUROSCIENCES INSTITUTE. Invention is credited to Daniel L. Alkon.
Application Number | 20100303792 12/851222 |
Document ID | / |
Family ID | 37478854 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100303792 |
Kind Code |
A1 |
Alkon; Daniel L. |
December 2, 2010 |
PROTEIN SYNTHESIS REQUIRED FOR LONG-TERM MEMORY IS INDUCED BY PKC
ACTIVATION ON DAYS PRECEDING ASSOCIATIVE LEARNING
Abstract
The present invention provides methods of contacting a protein
kinase C (PKC) activator with a PKC activator in a manner
sufficient to stimulate the synthesis of proteins sufficient to
consolidate long-term memory. The present invention also provides
methods of contacting a protein kinase C (PKC) activator with a PKC
activator in a manner sufficient to downregulate PKC.
Inventors: |
Alkon; Daniel L.; (Bethesda,
MD) |
Correspondence
Address: |
MILBANK, TWEED, HADLEY & MCCLOY LLP
INTERNATIONAL SQUARE BUILDING, 1850 K STRET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
BLANCHETTE ROCKEFELLER
NEUROSCIENCES INSTITUTE
Morgantown
WV
|
Family ID: |
37478854 |
Appl. No.: |
12/851222 |
Filed: |
August 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11494636 |
Jul 28, 2006 |
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12851222 |
|
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60703501 |
Jul 29, 2005 |
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60728753 |
Oct 21, 2005 |
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Current U.S.
Class: |
424/94.5 |
Current CPC
Class: |
A61K 31/407 20130101;
A61P 25/00 20180101; A61K 31/437 20130101; A61P 43/00 20180101;
A61K 31/365 20130101; A61P 29/00 20180101; A61K 31/366 20130101;
A61P 25/28 20180101; A61K 31/4015 20130101; A61K 31/40
20130101 |
Class at
Publication: |
424/94.5 |
International
Class: |
A61K 38/45 20060101
A61K038/45; A61P 25/00 20060101 A61P025/00 |
Claims
1. A method comprising the step of contacting a PKC activator with
a protein kinase C (PKC) to stimulate the synthesis of proteins
sufficient to consolidate long term memory.
2. The method of claim 1, wherein said PKC activator is a
macrocyclic lactone.
3. The method of claim 1, wherein the PKC activator is a
benzolactam.
4. The method of claim 1, wherein the PKC activator is a
pyrrolidinone.
5. The method of claim 2, wherein the macrocyclic lactone is a
bryostatin.
6. The method of claim 5, wherein the bryostatin is bryostatin-1,
-2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16,
-17, or -18.
7. The method of claim 5, wherein the bryostatin is
bryostatin-1.
8. The method of claim 2, wherein the macrocyclic lactone is a
neristatin.
9. The composition of claim 8, wherein the neristatin is
neristatin-1.
10. The method of claim 1, wherein said contact activates PKC.
11. The method of claim 1, wherein said contact increases the
amount of PKC.
12. The method of claim 1, wherein said contact increases the
synthesis of PKC.
13. The method of claim 1, wherein said contact increases the
amount of calexcitin.
14. The method of claim 1, wherein said contact does not result in
substantial subsequent downregulation of PKC.
15. The method of claim 1, wherein the contacting of the PKC
activator with the PKC is repeated.
16. The method of claim 15, wherein the contacting of the PKC
activator with the PKC is repeated at regular intervals.
17. The method of claim 16, wherein the interval is between one
week to one month, one day and one week, or less than one hour and
24 hours.
18. The method of claim 17, wherein the interval is between one
week and one month.
19. The method of claim 17, wherein the interval is between one day
and one week.
20. The method of claim 17, wherein the interval is between less
than one hour and 24 hours.
21. The method of claim 1, wherein the contacting of the PKC
activator with the PKC is maintained for a fixed duration.
22. The method of claim 21, wherein the fixed duration is less than
24 hours.
23. The method of claim 21, wherein the fixed duration is less than
12 hours.
24. The method of claim 21, wherein the fixed duration is less than
6 hours.
25. The method of claim 21, wherein the fixed duration is less than
4 hours.
26. The method of claim 21, wherein the fixed duration is less than
2 hours.
27. The method of claim 21, wherein the fixed duration is between
about 2 and about 6 hours.
28. The method of claim 21, wherein the fixed duration is about 4
hours.
29. The method of claim 21, wherein said duration of said contact
is between about 1 and about 12 hours.
30. The method of claim 15, wherein said contact is repeated for a
period greater than one day.
31. The method of claim 15, wherein said contact is repeated for a
period between one day and one month.
32. The method of claim 15, wherein said contact is repeated for a
period between one day and one week.
33. The method of claim 15, wherein said contact is repeated for a
period between one week and one month.
34. The method of claim 15, wherein said contact is repeated for a
period between one month and six months.
35. The method of claim 15, wherein said contact is repeated for a
period of one month.
36. The method of claim 15, wherein said contact is repeated for a
period greater than one month.
37. A method comprising the step of contacting a PKC activator with
a protein kinase C (PKC) to downregulate PKC.
38. The method of claim 37, wherein said PKC activator is a
macrocyclic lactone.
39. The method of claim 37, wherein the PKC activator is a
benzolactam.
40. The method of claim 37, wherein the PKC activator is a
pyrrolidinone.
41. The method of claim 38, wherein the macrocyclic lactone is a
bryostatin.
42. The method of claim 41, wherein the bryostatin is bryostatin-1,
-2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16,
-17, or -18.
43. The method of claim 42, wherein the bryostatin is
bryostatin-1.
44. The method of claim 38, wherein the macrocyclic lactone is a
neristatin.
45. The composition of claim 38, wherein the neristatin is
neristatin-1.
46. The method of claim 37, wherein said contact produces
downregulation of PKC.
47. The method of claim 46, wherein said contact produces
substantial downregulation of PKC.
48. The method of claim 37, wherein said contact does not stimulate
the synthesis of PKC.
49. The method of claim 48, wherein said contact does not
substantially stimulate the synthesis of PKC.
50. The method of claim 37, wherein said contact decreases the
amount of PKC.
51. The method of claim 50, wherein said contact substantially
decreases the amount of PKC.
52. The method of claim 37, wherein said contact does not stimulate
the synthesis of calexcitin.
53. The method of claim 50, wherein said contact does not stimulate
the synthesis of calexitin.
54. The method of claim 37, wherein the contacting of the PKC
activator with the PKC is for a sustained period.
55. The method of claim 54, wherein the sustained period is between
less than one hour and 24 hours.
56. The method of claim 54, wherein the sustained period is between
one day and one week.
57. The method of claim 54, wherein the sustained period is between
one week and one month.
58. The method of claim 54, wherein the sustained period is between
less than one hour and 12 hours.
59. The method of claim 54, wherein the sustained period is between
less than one hour and 8 hours.
60. The method of claim 54, wherein the sustained period is between
less than one hour and 4 hours.
61. The method of claim 54, wherein the sustained period is about 4
hours.
62. The method of claim 37, wherein said contact produces sustained
downregulation of PKC.
63. The method of claim 1, further comprising the step of
inhibiting degradation of protein kinase C (PKC).
64. The method of claim 63, wherein said degradation is through
ubiquitination.
65. The method of claim 64, wherein said degradation is inhibited
by lactacysteine.
66. The method of claim 1, wherein the PKC is human.
67. The method of claim 1, wherein the PKC activator is provided in
the form of a pharmaceutical composition comprising the PKC
activator and a pharmaceutically acceptable carrier.
68. The method of claim 67, wherein the pharmaceutical composition
further comprises a PKC inhibitor.
69. The method of claim 68, wherein the PKC inhibitor inhibits PKC
in peripheral tissues.
70. The method of claim 68, wherein the PKC inhibitor selectively
inhibits PKC in peripheral tissues.
71. The method of claim 68, wherein the PKC inhibitor is a compound
that reduces myalgia associated with the administration of a PKC to
a subjects.
72. The method of claim 68, wherein the PKC inhibitor is a compound
that increases the tolerable dose of a PKC activator.
73. The method of claim 68, wherein the PKC inhibitor is vitamin E,
vitamin E analogs, vitamin E salts, calphostin C,
thiazolidinediones, ruboxistaurin or combinations thereof.
Description
PRIORITY OF INVENTION
[0001] This application is a continuation of U.S. application Ser.
No. 11,494,636, filed Jul. 28, 2006, which claims priority to U.S.
Provisional Application No. 60/703,501 filed Jul. 29, 2005 and U.S.
Provisional Application No. 60/728,753 filed on Oct. 21, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to methods of upregulating and
downregulating protein kinase C that are useful for enhancing
memory and the treatment of cell proliferative disorders.
BACKGROUND OF THE INVENTION
[0003] Various disorders and diseases exist which affect cognition.
Cognition can be generally described as including at least three
different components: attention, learning, and memory. Each of
these components and their respective levels affect the overall
level of a subject's cognitive ability. For instance, while
Alzheimer's Disease patients suffer from a loss of overall
cognition and thus deterioration of each of these characteristics,
it is the loss of memory that is most often associated with the
disease. In other diseases patients suffer from cognitive
impairment that is more predominately associated with different
characteristics of cognition. For instance, Attention Deficit
Hyperactivity Disorder (ADHD), focuses on the individual's ability
to maintain an attentive state. Other conditions include general
dementias associated with other neurological diseases, aging, and
treatment of conditions that can cause deleterious effects on
mental capacity, such as cancer treatments, stroke/ischemia, and
mental retardation.
[0004] The requirement of protein synthesis for long-term memory
has been demonstrated over several decades for a variety of memory
paradigms. Agranoff et al. (1967) Science 158: 1600-1601; Bergold
et al. (1990) Proc. Natl. Acad. Sci. 87:3788-3791; Cavallaro et al.
(2002) Proc. Natl. Acad. Sci. 99: 13279-16284; Crow et al. (1990)
Proc. Natl. Acad. Sci. 87: 4490-4494; Crow et al. (1999) J.
Neurophysiol. 82: 495-500; Epstein et al. (2003) Neurobiol. Learn.
Mem. 79: 127-131; Ezzeddine et al. (2003) J. Neurosci. 23:
9585-9594; Farley et al. (1991) Proc. Natl. Acad. Sci. 88:
2016-2020; Flexner et al. (1996) Proc. Natl. Acad. Sci. 55:
369-374; Hyden et al. (1970) Proc. Natl. Acad. Sci. 65: 898-904;
Nelson et al. (1990) Proc. Natl. Acad. Sci. 87: 269-273; Quattrone
et al. (2001) Proc. Natl. Acad. Sci. 98: 11668-11673; Zhao et al.
(1999) J. Biol. Chem. 274: 34893-34902; Zhao et al. (2000) FASEB J.
14: 290-300. Flexner originally showed that drug-induced inhibition
of protein synthesis (e.g., with 5-propyluracil or anisomycin)
blocked long-term memory when this inhibition occurred during a
critical time interval following the training paradigm. Flexner et
al. (1996) Proc. Natl. Acad. Sci. 55: 369-374. If protein synthesis
was inhibited before this critical time window or at any time after
this window, there was no effect on long-term memory. The identity
of the proteins essential for memory consolidation, the mechanisms
of their regulation, and their role in the consolidation of
long-term memory has remained a mystery.
[0005] In many species the formation of long-term associative
memory has also been shown to depend on translocation, and thus
activation, of protein kinase C (PKC) isozymes to neuronal
membranes. Initially, these PKC isozymes, when activated by a
combination of calcium and co-factors, such as diacylglycerol,
achieve a stable association with the inner aspect of the external
neuronal membrane and membranes of internal organelle, such as the
endoplasmic reticulum. PKC activation has been shown to occur in
single identified Type B cells of the mollusk Hermissenda (McPhie
et al. (1993) J. Neurochem. 60: 646-651), a variety of mammalian
associative learning protocols, including rabbit nictitating
membrane conditioning (Bank et al. (1988) Proc. Natl. Acad. Sci.
85: 1988-1992; Olds et al. (1989) Science 245: 866-869), rat
spatial maze learning (Olds et al. (1990) J. Neurosci. 10:
3707-3713), and rat olfactory discrimination learning, upon
Pavlovian conditioning. Furthermore, calexcitin (Nelson et al.
(1990) Science 247: 1479-1483), a high-affinity substrate of the
alpha isozyme of PKC increased in amount and phosphorylation
(Kuzirian et al. (2001) J. Neurocytol. 30: 993-1008) within single
identified Type B cells in a Pavlovian-conditioning-dependent
manner.
[0006] There is increasing evidence that the individual PKC
isozymes play different, sometimes opposing, roles in biological
processes, providing two directions for pharmacological
exploitation. One is the design of specific (preferably, isozyme
specific) inhibitors of PKC. This approach is complicated by the
fact that the catalytic domain is not the domain primarily
responsible for the isotype specificity of PKC. The other approach
is to develop isozyme-selective, regulatory site-directed PKC
activators. These may provide a way to override the effect of other
signal transduction pathways with opposite biological effects.
Alternatively, by inducing down-regulation of PKC after acute
activation, PKC activators may cause long term antagonism.
[0007] Following associative memory protocols, increased PKC
association with the membrane fractions in specific brain regions
can persist for many days (Olds et al. (1989) Science 245:
866-869). Consistent with these findings, administration of the
potent PKC activator bryostatin, enhanced rats spatial maze
learning (Sun et al. (2005) Eur. J. Pharmacol. 512: 45-51).
Furthermore, clinical trials with the PKC activator, bryostatin,
suggested (Marshall et al. (2002) Cancer Biology & Therapy 1:
409-416) that PKC activation effects might be enhanced by an
intermittent schedule of drug delivery. One PKC activator,
bryostatin, a macrolide lactone, activates PKC in sub-nanomolar
concentrations (Talk et al. (1999) Neurobiol. Learn. Mem. 72:
95-117). Like phorbol esters and the endogenous activator DAG,
bryostatin binds to the C1 domain within PKC and causes its
translocation to membranes, which is then followed by
downregulation.
[0008] The non-tumorigenic PKC activator, bryostatin, has undergone
extensive testing in humans for the treatment of cancer in doses
(25 .mu.g/m.sup.2-120 .mu.g/m.sup.2) known to cause initial PKC
activation followed by prolonged downregulation (Prevostel et al.
(2000) Journal of Cell Science 113: 2575-2584; Lu et al. (1998)
Mol. Biol. Cell 18: 839-845; Leontieva et al. (2004) J. Biol. Chem.
279:5788-5801). Bryostatin activation of PKC has also recently been
shown to activate the alpha-secretase that cleaves the amyloid
precursor protein (APP) to generate the non-toxic fragments soluble
precursor protein (sAPP) from human fibroblasts (Etcheberrigaray et
al. (2004) Proc. Natl. Acad. Sci. 101: 11141-11146). Bryostatin
also enhances learning and memory retention of the rat spatial maze
task (Sun et al. (2005) Eur. J. Pharmacol. 512: 45-51), learning of
the rabbit nictitating membrane paradigm (Schreurs and Alkon,
unpublished), and in a preliminary report, Hermissenda conditioning
(Scioletti et al. (2004) Biol. Bull. 207: 159). Accordingly,
optimal activation of PKC is important for many molecular
mechanisms that effect cognition in normal and diseased states.
[0009] Because the upregulation of PKC is difficult to achieve
without downregulation, and vice versa, methods of upregulation of
PKC while minimizing downregulation are needed to enhance the
cognitive benefits observed associated with PKC activation. The
methods and compositions of the present invention fulfill these
needs and will greatly improve the clinical treatment for
Alzheimer's disease and other neurodegenerative diseases, as well
as, provide for improved cognitive enhancement prophylactically.
The methods and compositions also provide treatment and/or
enhancement of the cognitive state through the modulation of
.alpha.-secretase.
SUMMARY OF THE INVENTION
[0010] This invention relates to a method of contacting a PKC
activator with protein kinase C in a manner sufficient to stimulate
the synthesis of proteins sufficient to consolidate long term
memory.
[0011] In one embodiment, the PKC activator is a macrocyclic
lactone. In one embodiment, the PKC activator is a benzolactam. In
one embodiment, the PKC activator is a pyrrolidinone. In a
preferred embodiment, the macrocyclic lactone is bryostatin. In a
more preferred embodiment, the bryostatin is bryostatin-1, -2, -3,
-4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16, -17, or
-18. In the most preferred embodiment, the bryostatin is
bryostatin-1.
[0012] In one embodiment, the macrocyclic lactone is neristatin. In
a preferred embodiment, the neristatin is neristatin-1.
[0013] In one embodiment, the contact activates PKC. In one
embodiment, the contact increases the amount of PKC. In one
embodiment, the contact increases the synthesis of PKC. In one
embodiment, the contact increases the amount of calexcitin. In one
embodiment, the contact does not result in substantial subsequent
deregulation of PKC.
[0014] In one embodiment, the contact is repeated. In another
embodiment, the contact is repeated at regular intervals. In
another embodiment, the interval is between one week to one month,
one day and one week, or less than one hour and 24 hours. In
another embodiment, the interval is between one week and one month.
In another embodiment, the interval is between one day and one
week. In another embodiment, the interval is between less than one
hour and 24 hours.
[0015] In one embodiment, the contact is maintained for a fixed
duration. In another embodiment, the fixed duration is less than 24
hours. In another embodiment, the fixed duration is less than 12
hours. In another embodiment, the fixed duration is less than 6
hours. In another embodiment, the fixed duration is less than 6
hours. In another embodiment, the fixed duration is less than 4
hours. In another embodiment, the fixed duration is less than 2
hours. In a preferred embodiment, the fixed duration is between
about 1 and 12 hours. In a more preferred embodiment, the fixed
duration is between about 2 and 6 hours. In the most preferred
embodiment, the fixed duration is about 4 hours.
[0016] In one embodiment, the contact is repeated for a period
greater than one day. In another embodiment, the contact is
repeated for a period between one day and one month. In another
embodiment, the contact is repeated for a period between one day
and one week. In another embodiment, the contact is repeated for a
period between one week and one month. In another embodiment, the
contact is repeated for a period between one month and six months.
In another embodiment, the contact is repeated for a period of one
month. In another embodiment, the contact is repeated for a period
greater than one month.
[0017] The invention relates to a method of contacting a PKC
activator with protein kinase C in a manner sufficient to
downregulate PKC.
[0018] In one embodiment, the PKC activator is a macrocyclic
lactone. In one embodiment, the PKC activator is a benzolactam. In
one embodiment, the PKC activator is a pyrrolidinone. In a
preferred embodiment, the macrocyclic lactone is bryostatin. In a
more preferred embodiment, the bryostatin is bryostatin-1, -2, -3,
-4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16, -17, or
-18. In the most preferred embodiment, the bryostatin is
bryostatin-1.
[0019] In one embodiment, the macrocyclic lactone is neristatin. In
a preferred embodiment, the neristatin is neristatin-1.
[0020] In one embodiment, the contact does not stimulate the
synthesis of PKC. In another embodiment, the contact does not
substantially stimulate the synthesis of PKC. In another
embodiment, the contact decreases the amount of PKC. In another
embodiment, the contact substantially decreases the amount of PKC.
In another embodiment, the contact does not stimulate the synthesis
of calexcitin.
[0021] In one embodiment, the contact is for a sustained period. In
one embodiment, the sustained period if between less than one hour
and 24 hours. In another embodiment, the sustained period is
between one day and one week. In another embodiment, the sustained
period is between one week and one month. In another embodiment,
the sustained period is between less than one hour and 12 hours. In
another embodiment, the sustained period is between less than one
hour and 8 hours. In another embodiment, the sustained period is
between less than one hour and 4 hours. In a preferred embodiment,
the sustained period is about 4 hours.
[0022] In one embodiment, the contact produces sustained
downregulation of PKC.
[0023] This invention relates to a method of contacting a PKC
activator with protein kinase C in a manner sufficient to stimulate
the synthesis of proteins sufficient to consolidate long term
memory, further comprising the step of inhibiting degradation of
PKC.
[0024] In one embodiment, the degradation is through
ubiquitination. In another embodiment, the degradation is inhibited
by lactacysteine. In another embodiment, the PKC is human.
[0025] This invention relates to a method of contacting a PKC
activator with protein kinase C in a manner sufficient to stimulate
the synthesis of proteins sufficient to consolidate long term
memory, wherein the PKC activator is provided in the form of a
pharmaceutical composition comprising the PKC activator and a
pharmaceutically acceptable carrier.
[0026] In one embodiment, the pharmaceutical composition further
comprises a PKC inhibitor. In another embodiment, the PKC inhibitor
is a compound that inhibits PKC in peripheral tissues. As used
herein, "peripheral tissues" means tissues other than brain. In
another embodiment, the PKC inhibitor is a compound that
preferentially inhibits PKC in peripheral tissues. In another
embodiment, the PKC inhibit is a compound that reduces myalgia
associated with the administration of a PKC activator to subjects
in need thereof. In another embodiment, the PKC inhibitor is a
compound that reduces myalgia produced in a subject treated with a
PKC activator. In another embodiment, the PKC inhibitor is a
compound that increases the tolerable dose of a PKC activator.
Specifically, PKC inhibitors include, for example, but are not
limited to vitamin E, vitamin E analogs, and salts thereof;
calphostin C; thiazolidinediones; ruboxistaurin, and combinations
thereof. As used herein, "vitamin E" means .alpha.-tocopherol (5,
7, 8-trimethyltocol); .beta.-tocopherol (5, 8-dimethyltocol;
.delta.-tocopherol (8-methyltocal); and .gamma.-tocopherol
(7,8-dimethyltocol), salts and analogs thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The patent or application file contains at least one
drawings executed in color. Copies of this patent or patent
application publication with color drawing(s) will be provided by
the Office upon request and payment of the necessary fee.
[0028] FIG. 1 depicts the effects of bryostatin on long term memory
acquisition, and shows that animals trained sub-optimally, but
treated with bryostatin, all demonstrate acquisitioned long-term
memory. Animals were trained with sub-optimal regimes of 4- and
6-paired CS/US training events (TEs) with bryostatin (0.25 ng/ml)
added during dark adaptation (10 min) prior to training and
remaining for 4 hours, or without Bryo (NSW controls); 9-paired TEs
and NSW served as the positive controls. Animals were tested with
the CS alone at 4 h, then at 24-h intervals. Animals trained
sub-optimally but treated with bryostatin all demonstrated
long-term retention (n=8-16 animals/condition/experiment; ANOVA,
p<0.01).
[0029] FIG. 2 depicts the effects of bryostatin on long-term memory
acquisition, and shows that randomized presentations of light and
rotation, either with or without bryostatin, produced no
conditioned response. Long-term memory (LTM) retention effects of
Bryostatin under control and antagonist experimental regimes.
Without Bryostatin (NSW), random, and paired CS/US training events
(TEs) did not generate LTM or elicit a CR when tested at 4 h.
Bryostatin (0.25 ng/ml in NSW) applied before 6-TE conditioning
(during 10 min dark adaptation) and for 4 hours thereafter produced
a positive CR (foot contraction; negative change in length), thus
indicating LTM was established. The antagonist, Ro-32 when applied
pre-training (during dark adaptation), blocked the effects of 6 TE
plus bryostatin, i.e. animals lengthened (positive length change)
with normal photaxis (n=4-8 animals/condition/experiment; ANOVA
differences, p<0.01).
[0030] FIG. 3 depicts the effects of bryostatin on long-term memory
acquisition, and shows that animals exposed to bryostatin for four
hours on two successive days, followed by two training events (TE)
on a third subsequent day, demonstrated acquisition of at least six
days of long-term memory. Two successive days of 4-h bryostatin
exposure (0.25 ng/ml) of animals coupled with 2-paired CS/US
training events produced at least 6 days of long-term retention
demonstrated by the CR (body length contraction) when tested with
the CS alone (n=16 animals/condition; ANOVA, p<0.01).
[0031] FIG. 4 depicts the effects of bryostatin on long term memory
acquisition, and shows that animals exposed to bryostatin for four
hours on three successive days, followed by two TE on a fourth
subsequent day, demonstrated acquisition of at least ninety-six
hours of long-term memory. Animals given three successive days of
4-h bryostatin exposure (0.25 ng/ml) followed one day later by
2-TEs, demonstrated long-term retention (LTR) measured over 96 h
post-training. Non-exposed animals (same as in FIG. 3) did not
demonstrate any behavioral modification (no CR to CS testing).
Anisomycin (ANI) (1 .mu.g/ml) administered immediately and
remaining for four hours post-training to animals receive the
three-day bryostatin treatments did not prevent long-term
retention. Thus the requirement for protein synthesis necessary to
generate LTR that is usually blocked by ANI when added
post-training was obviated by the three-day bryostatin treatment
(n=16 animals/condition; ANOVA, p<0.01).
[0032] FIG. 5 depicts the effects of bryostatin on long term memory
acquisition, and shows that exposure to bryostatin for 8 to 20
hours followed by two TE was not sufficient to acquire memory
equivalent to that achieved after a 4-hour exposure to bryostatin.
Effects of 20 hr Bryostatin (0.25 ng/ml) exposure on training. With
the sub-optimal 2-paired TE conditioning regime, retention was gone
in 48 hours. Retention of 4-paired TE conditioning with 20 h
pre-exposure to bryostatin persisted (n=8 animals/condition; ANOVA
at 48-h, p<0.01).
[0033] FIG. 6 depicts the effects of bryostatin on long term memory
acquisition, and shows that exposure to more than 1.0 ng/ml of
bryostatin inhibits acquisition of long-term memory. Retention
dose-response curves for 4- and 9-paired CS/US training events.
Bryostatin concentrations <0.50 ng/ml augment acquisition and
memory retention with sub-optimal (4 TE) training conditions. Those
concentrations had no demonstrable effects on retention performance
with 9-paired TEs. However, with all training conditions tested,
concentration .sup..gtoreq.1.0 ng/ml inhibited acquisition and
behavioral retention (n=16 animals/condition), presumably via PKC
down regulation.
[0034] FIG. 7 depicts the effects of bryostatin and anisomycin on
long-term memory acquisition, and shows that a single 4-hour
exposure to bryostatin together with 2 TE produced long-term memory
lasting hours that was entirely eliminated when anisomycin was
present during bryostatin exposure. Bryostatin and anisomycin
effects on behavioral acquisition and retention. Animals received
2-paired training events (TEs) and then tested for retention after
4 h. Bryostatin (0.25 ng/ml) applied in NSW to animals during the
10-min pre-training dark adaptation period and 4 h thereafter
demonstrated retention of the behavioral conditioning (foot
contraction (CR) and shortening in body length). NSW control
animals and those treated with bryostatin pre-training followed by
anisomycin (1.0 .mu.g/ml) immediately post-training showed no CR
with the foot lengthening in normal positive phototaxis (n=12
animals/condition/experiment, two-way ANOVA statistics,
p<0.01).
[0035] FIG. 8 depicts the effects of bryostatin and lactacysteine,
and shows that lactacysteine transformed the short-term memory
produced by the single bryostatin exposure (followed by 2 TE) to
long-term memory lasting many days. Behavioral effects of
bryostatin and lactacystin. Animals were incubated simultaneously
for 4 h with bryostatin (0.25 ng/ml) and lactacystin (10 .mu.M),
and then 24 hrs later were conditioned with 2-paired CS/US training
events (TEs). Animals were subsequently tested with CS alone at 4 h
post-training and then at 24-h intervals. Retention of the
conditioned behavior was persistent with the combined
bryostatin/lactacystin treatment; behavioral retention was lost by
bryostatin-only-treated animals after 24 h. Lactacystin-only
treated animals showed no acquisition or retention of behavioral
training (data not graphed). (n=28 animals, combined
byrostatin/lactacystin; n=20, bryostatin alone, n=16, lactacystin
alone).
[0036] FIG. 9 depicts the effects of PKC activation on calexcitin.
FIGS. (A, B) depict representative tissue sections from Hermissenda
eyes that were immunolabeled with the calexcitin polyclonal
antibody, 25U2. Positive claexcitin immunostaining occurred in
B-cell photoreceptors (*B-Cell) of animals that experienced paired
CS/USC associative conditioning with or without prior
administration of bryostatin (B). Random presentations of the two
stimuli (training events, TEs) did not produce behavioral
modifications nor a rise in calexcitin above normal background
levels (A); basement membrane and lens staining are artifact
associated with using vertebrate polyclonal antibodies. Differences
in staining intensities were measure using Image-J software and
recorded as gray-scale intensities (0-256; B-cell cytoplasm minus
tissue background).
[0037] FIG. (C) displays intensity measures for Hermissenda
conditioned with 9-random TEs (left bar) and animals treated with
two exposures on successive days to the PKC antagonist, bryostatin
(0.25 ng/ml), and then associatively conditioned with 2-paired TEs.
Activation of PKC from two exposures of bryostatin coupled with 2
TEs significantly increased calexcitin to levels associated with
9-paired TEs and consolidated (long-term) memory (n=4-8
animals/condition/replicate; t-test comparison, p<0.01).
[0038] Calexcitin immunostaining is sufficiently sensitive to
resolve boutons within synaptic of photic-vestibular neurites (D).
Arrows indicate arborization field between an interneuron (a), axon
from a contralateral neuron (b), and terminal boutons of neurites
from a putative photoreceptor (c). Scale bars=10 .mu.m; CPG,
cerebropleural ganglion.
[0039] FIG. 10a depicts the effect of bryostatin and training
events on calexcitin immunostaining. The figure shows calexcitin
increased within Type B cells with the number of training events.
Immuno-intensity measurements (as grey-scale intensity; 0-256) of
calexicitin (CE) antibody labeling as a function of bryostatin and
training regime. Randon traiming (4-TEs) without bryostatin yielded
slightly higher intensity measures than background. Bryostatin
administration increased the calexcitin levels fro both training
paradigms. With random training, when there was occasional overlap
(pairing) of the CS and US, as was the case here, it is not
unexpected that some rise in CE might occur (increase of 2.0).
However, calexcitin levels increased greater than 4.3.times.with
paired training (mean.+-.SE, N=5 animals/treatment. 4 RTE=random
control, 4 trials with random light and rotation; 6 PTE=paired
trials, 6 trials with paired light and rotation. (6 PTE-0 Bry vs. 6
PTE-0.25 Bry; p<0.001; 4 RTE-0.25 Bry vs. 6 PTE-0.25 Bry;
p<0.001 (t-test).
[0040] FIG. 10b depicts the effect of bryostatin alone calexcitin,
as shown by immunostaining. Bryostatin alone (without associative
conditioning) administered for 4-hr over each of 1, 2, and 3 days
progressively increased the levels of calexcitin in the
B-photoreceptors of Hermissenda when measured 24 hours after each
of the periods of bryostatin exposures. The calexcitin level after
3 bryostatin exposures followed by just 2-paired training events
(paired light and orbital shaking) raised that level even higher
with a significant concomitant length in the number of retention
days for the associative conditioning-induced behavioral
modification (n=16 animals/condition: ANOVA, p<0.01).
[0041] FIG. 11a depicts the effect of 4-hour bryostatin exposure,
on two consecutive days, followed 24 hours later by two training
events, on the intensity of calexcitin. The figure shows that
exposure to 4 hours of bryostatin on two consecutive days followed
24 hours later by 2 TEs are required to raise calexcitin levels to
the amount associated with consolidated long-term memory. Exposure
to 4-hr of bryostatin on two consecutive days followed 24 hours
later by 2-training events (2 TE) are required to raise calexcitin
levels to the amount associated with consolidated long-term memory,
Typically, 2-TEs with two bryostatin exposures produces retention
lasting more than one week (n=16 animals/condition; t-test,
p<0.01).
[0042] FIG. 11b depicts the effect of adding anisomycin after
bryostatin exposure on calexcitin. The figure shows that anisomycin
following 2 TE plus 3 days of 4 hour bryostatin exposures did not
reduce the calexcitin immunostaining. Priming with 4-hr exposures
to bryostatin over 3 consecutive days will induce calexcitin levels
required for consolidated memory. Anisomycin added immediately
after the 2-paired training events did not reduce this calexcitin
level and consolidated memory persists for many days (N=8
animals/condition; t-test, p>0.05, ns).
[0043] FIG. 12 depicts the effects of repeated 4-hour bryostatin
exposure on PKC activity, as measured by histone phosphorylation in
the cytosolic fraction. The figure shows bryostatin exposure on two
successive produces PKC activity significantly above control or
baseline levels. PKC activity in Hermissenda nervous systems
(cytosol) after bryostatin. Intact Hermissenda were exposed for 4
hour intervals to bryostatin (0.28 nM) on successive days under
conditions described ("Behavioral Pharmacology"). Histone
phosphorylation (See "Methods") in isolated circumesophageal
nervous systems was then measured in the cytosol fraction. PKC
activity measured both 10 minutes and 24 hours after the second of
two bryostatin exposures was significantly increased over baseline
levels (N=6, for each measurement).
[0044] FIG. 13 depicts the effects of repeated 4-hour bryostatin
exposure on PKC activity, as measured by histone phosphorylation in
the membrane fraction. The figure shows bryostatin exposure on two
successive produces PKC activity significantly above control or
baseline levels. PKC activity in Hermissenda nervous systems
(membrane) after bryostatin. As in FIG. 12, histone phosphorylation
was measured in the membrane fraction. PKC activity measured 24
hours after the second of two bryostatin exposures was
significantly increased over baseline (N=6) for each
measurement.
[0045] FIG. 14 depicts the effects of anisomycin on PKC activity.
The figure shows that the presence of anisomycin during each of
three successive days of bryostatin exposure reduced PKC activity
in both cytosolic and membrane fractions. Anisomycin reduces PKC
activity in Hermissenda. As in FIG. 12, 13 but with anisomycin (1.0
ng/ml) added together with each bryostatin (0.25 ng/ml) exposure.
Note that the anisomycin markedly reduced the PKC activity in both
the cytosolic and membrane fractions from the Hermissenda
circumesophagel nervous systems after exposure to bryostatin on
three successive days (N=3, for each measurement, p<0.01).
[0046] FIG. 15 depicts the effects of bryostatin on membrane-bound
PKC in hippocampal neurons. The figure shows that exposure of
cultured hippocampal neurons to a single activating dose of
bryostatin (0.28 nM) for 30 minutes produced a brief translocation
of PKC from the cytosol to the particulate fraction (approx 60%)
followed by a prolonged downregulation. A second exposure of up to
four hours after the first exposure significantly attenuates the
down regulation found four hours after a single bryostatin
exposure. Effect of bryostatin on membrane-bound PKC activity in
hippocampal cultured IGF/IR cells after 1) a single 30 min
exposure; or 2) two 30 min exposures separated by intervals of 30
min to 8 hr. A second exposure up to 4 hr after the first exposure
significantly attenuates the downregulation found 4 hr after a
single bryostatin exposure (N=6 for each measurement, *p<0.05,
**p<0.01).
[0047] FIG. 16 depicts the effects of repeated bryostatin exposure
on PKC activity. The figure shows that a second exposure after a 2-
to 4-hour delay eliminated the significant downregulation that a
single 30-minute bryostatin exposure produced, and that if the
second exposure was delayed until 4 hours after the first, activity
was increased above baseline, to a degree that was significantly
greater compared with a second exposure delivered after 2 hours or
less. Effect of bryostatin on cytosolic PKC activity in hippocampal
cultured IGF/IR cells after 1) a single 30 min exposure, or 2) two
30 min exposures separated by intervals of 30 min to 8 hr. PKC
activity was not altered in the cytosol the first 4 hours after
bryostatin exposure. By contrast, a second exposure to bryostatin
within 2 hr of the first induced a significant reduction of PKC
activity. However, if the second exposure was delayed until 4 hours
after the first, activity was increased above baseline, and was
significantly greater than activity measure in response to a second
exposure delivered after 1 or 2 hours (N=6 for each measurement,
*p<0.05, **p<0.01).
[0048] FIG. 17 depicts the effects of bryostatin on protein
synthesis. Rat IGF-IR cells were incubated for 30 minutes with 0.28
nM bryostatin for incubation times ranging from 1 to 79 hours.
[.sup.35S]Methionine (9.1 .mu.Ci) was then added to the medium
followed by analysis of radiolabel. A single 30-minute exposure to
0.28 nM bryostatin increased overall protein synthesis, as measured
by the incorporation of [.sup.35S]Methionine in the last half hour
before collecting the neurons, by 20% within 24 hours, increasing
to 60% by 79 hours after bryostatin exposure, but increasing
significantly less in the presence of the PKC inhibitor
Ro-32-0432.
DETAILED DESCRIPTION OF THE INVENTION
[0049] 1. Definitions
[0050] As used herein, "upregulating" or "upregulation" means
increasing the amount or activity of an agent, such as PKC protein
or transcript, relative to a baseline state, through any mechanism
including, but not limited to increased transcription, translation
and/or increased stability of the transcript or protein
product.
[0051] As used herein, "down regulating" or " down regulation"
means decreasing the amount or activity of an agent, such as PKC
protein or transcript, relative to a baseline state, through any
mechanism including, but not limited to decreased transcription,
translation and/or decreased stability of the transcript or protein
product.
[0052] As used herein, the term "pharmaceutically acceptable
carrier" means a chemical composition, compound, or solvent with
which an active ingredient may be combined and which, following the
combination, can be used to administer the active ingredient to a
subject. As used herein, "pharmaceutically acceptable carrier"
includes, but is not limited to, one or more of the following:
excipients; surface active agents; dispersing agents; inert
diluents; granulating and disintegrating agents; binding agents;
lubricating agents; preservatives; physiologically degradable
compositions such as gelatin; aqueous vehicles and solvents; oily
vehicles and solvents; suspending agents; dispersing or wetting
agents; emulsifying agents, demulcents; buffers; salts; thickening
agents; fillers; antioxidants; stabilizing agents; and
pharmaceutically acceptable polymeric or hydrophobic materials and
other ingredients known in the art and described, for example in
Genaro, ed. (1985) Remington's Pharmaceutical Sciences Mack
Publishing Co., Easton, Pa., which is incorporated herein by
reference.
[0053] The formulations of the pharmaceutical compositions
described herein may be prepared by any method known or hereafter
developed in the art of pharmacology. In general, such preparatory
methods include the step of bringing the active ingredient into
association with a carrier or one or more other accessory
ingredients, and then, if necessary or desirable, shaping or
packaging the product into a desired single- or multi-dose
unit.
[0054] Although the descriptions of pharmaceutical compositions
provided herein are principally directed to pharmaceutical
compositions which are suitable for ethical administration to
humans, it will be understood by the skilled artisan that such
compositions are generally suitable for administration to animals
of all sorts. Modification of pharmaceutical compositions suitable
for administration to humans in order to render the compositions
suitable for administration to various animals is well understood,
and the ordinarily skilled veterinary pharmacologist can design and
perform such modification with merely ordinary, if any,
experimentation. Subjects to which administration of the
pharmaceutical compositions of the invention is contemplated
include, but are not limited to, humans and other primates, and
other mammals.
[0055] 2. Alzheimer's Disease
[0056] Alzheimer's disease is associated with extensive loss of
specific neuronal subpopulations in the brain with memory loss
being the most universal symptom. (Katzman (1986) New England
Journal of Medicine 314: 964). Alzheimer's disease is well
characterized with regard to neuropathological changes. However,
abnormalities have been reported in peripheral tissue supporting
the possibility that Alzheimer's disease is a systematic disorder
with pathology of the central nervous system being the most
prominent. (Connolly (1998) Review, TiPS Col. 19: 171-77). For a
discussion of Alzheimer's disease links to a genetic origin and
chromosomes 1, 14, and 21 see St. George-Hyslop et al. (1987)
Science 235: 885; Tanzi et al. Review, Neurobiology of Disease
3:159-168; Hardy (1996) Acta Neuro! Scand: Supplement 165:
13-17.
[0057] Individuals with Alzheimer's disease are characterized by
progressive memory impairments, loss of language and visuospatial
skills and behavior deficits (McKhann et al. (1986) Neurology 34:
939-944). The cognitive impairment of individuals with Alzheimer's
disease is the result of degeneration of neuronal cells located in
the cerebral cortex, hippocampus, basal forebrain and other brain
regions. Histologic analyzes of Alzheimer's disease brains obtained
at autopsy demonstrated the presence of neurofibrillary tangles
(NFT) in perikarya and axons of degenerating neurons, extracellular
neuritic (senile) plaques, and amyloid plaques inside and around
some blood vessels of affected brain regions. Neurofibrillary
tangles are abnormal filamentous structures containing fibers
(about 10 nm in diameter) that are paired in a helical fashion,
therefore also called paired helical filaments. Neuritic plaques
are located at degenerating nerve terminals (both axonal and
dendritic), and contain a core compound of amyloid protein fibers.
In summary, Alzheimer's disease is characterized by certain
neuropathological features including intracellular neurofibrillary
tangles, primarily composed of cytoskeletal proteins, and
extracellular parenchymal and cerebrosvascular amyloid. Further,
there are now methods in the art of distinguishing between
Alzheimer's patents, normal aged people, and people suffering from
other neurodegenerative diseases, such as Parkinson's, Huntington's
chorea, Wernicke-Korsakoff or schizophrenia further described for
instance in U.S. Pat. No. 5,580,748 and U.S. Pat. No.
6,080,582.
[0058] While cellular changes leading to neuronal loss and the
underlying etiology of the disease remain under investigation the
importance of APP metabolism is well established. The two proteins
most consistently identified in the brains of patients with
Alzheimer's disease to play a role in the physiology or
pathophysiology of brain are .beta.-amyloid and tau. (See Selkoe
(2001) Physiological Reviews. 81:2). A discussion of the defects in
.beta.-amyloid protein metabolism and abnormal calcium homeostasis
and/or calcium activated kinases. (Etcheberrigaray et al.
Alzheimer's Reports Vol. Nos. 3, 5 & 6 pp 305-312; Webb et al.
(2000) British Journal of Pharmacology 130: 1433-52).
[0059] Alzheimer's disease (AD) is a brain disorder characterized
by altered protein catabolism. Altered protein phosphorylation has
been implicated in the formation of the intracellular
neurofibrillary tangles found in Alzheimer's disease. The
processing of the amyloid precursor protein (APP) determines the
production of fragments that later aggregate forming the amyloid
deposits characteristic of Alzheimer's disease (AD), known as
senile or AD plaques. A central feature of the pathology of
Alzheimer's disease is the deposition of amyloid protein within
plaques. Thus, APP processing is an early and key
pathophysiological event in AD.
[0060] Three alternative APP processing pathways have been
identified. The previously termed "normal" processing involves the
participation of an enzyme that cleaves APP within the A.beta.
sequence at residue Lys16 (or between Lys16 and Leu17; APP770
nomenclature), resulting in non-amyloidogenic fragments: a large
N-terminus ectodomain and a small 9 kDa membrane bound fragment.
This enzyme, yet to be fully identified, is known as
.alpha.-secretase. Two additional secretases participate in APP
processing. One alternative pathway involves the cleavage of APP
outside the A.beta. domain, between Met671 and Asp672 (by
.beta.-secretase) and the participation of the endosomal-lysomal
system. An additional cleavage site occurs at the carboxyl-terminal
end of the A.beta. portion, within the plasma membrane after amino
acid 39 of the A.beta. peptide. The secretase (.gamma.) action
produces an extracellular amino acid terminal that contains the
entire A.beta. sequence and a cell-associated fragment of .about.6
kDa. Thus, processing by .beta. and .gamma. secretases generate
potential amyloidogenic fragments since they contain the complete
A.beta. sequence. Several lines of evidence have shown that all
alternative pathways occur in a given system and that soluble
A.beta. may be a "normal product." However, there is also evidence
that the amount of circulating A.beta. in CSF and plasma is
elevated in patients carrying the "Swedish" mutation. Moreover,
cultured cells transfected with this mutation or the APP.sub.717
mutation, secrete larger amounts of A.beta.. More recently,
carriers of other APP mutations and PS1 and PS2 mutations have been
shown to secrete elevated amounts of a particular form, long (42-43
amino acids) A.beta..
[0061] Therefore, although all alternative pathways may occur
normally, an imbalance favoring amyloidogenic processing occurs in
familial and perhaps sporadic AD. These enhanced amyloidogenic
pathways ultimately lead to fibril and plaque formation in the
brains of AD patients. Thus, intervention to favor the
non-amyloidogenic, .alpha.-secretase pathway effectively shifts the
balance of APP processing towards a presumably non-pathogenic
process that increases the relative amount of sAPP compared with
the potentially toxic A.beta. peptides.
[0062] The PKC isoenzymes provides a critical, specific and rate
limiting molecular target through which a unique correlation of
biochemical, biophysical, and behavioral efficacy can be
demonstrated and applied to subjects to improve cognitive
ability.
[0063] Further with regard to normal and abnormal memory both
K.sup.+ and Ca.sup.2+ channels have been demonstrated to play key
roles in memory storage and recall. For instance, potassium
channels have been found to change during memory storage.
(Etcheberrigaray et al. (1992) Proc. Natl. Acad. Sci. 89: 7184;
Sanchez-Andres et al. (1991) Journal of Neurobiology 65: 796;
Collin et al. (1988) Biophysics Journal 55: 955; Alkon et al.
(1985) Behavioral and Neural Biology 44: 278; Alkon (1984) Science
226: 1037). This observation, coupled with the almost universal
symptom of memory loss in Alzheimer's patents, led to the
investigation of potassium channel function as a possible site of
Alzheimer's disease pathology and the effect of PKC modulation on
cognition.
[0064] 3. Protein Kinase C and Alzheimer's Disease
[0065] PKC was identified as one of the largest gene families of
non-receptor serine-threonine protein kinases. Since the discovery
of PKC in the early eighties by Nishizuka and coworkers (Kikkawa et
al. (1982) J. Biol. Chem. 257: 13341), and its identification as a
major receptor of phorbol esters (Ashendel et al. (1983) Cancer
Res., 43: 4333), a multitude of physiological signaling mechanisms
have been ascribed to this enzyme. The intense interest in PKC
stems from its unique ability to be activated in vitro by calcium
and diacylglycerol (and its phorbol ester mimetics), an effector
whose formation is coupled to phospholipid turnover by the action
of growth and differentiation factors.
[0066] The PKC gene family consists presently of 11 genes which are
divided into four subgrounds: 1) classical PKC.alpha.,
.beta..sub.1, .beta..sub.2 (.beta..sub.1 and .beta..sub.2 are
alternatively spliced forms of the same gene) and .gamma., 2) novel
PKC.delta., .epsilon., .eta. and .theta., 3) atypical PKC.zeta.,
.lamda., .eta. and and 4) PKC.mu.. PKC.mu. resembles the novel PKC
isoforms but differs by having a putative transmembrane domain
(reviewed by Blohe et al. (1994) Cancer Metast. Rev. 13: 411; Ilug
et al. (1993) Biochem J. 291: 329; Kikkawa et al. (1989) Ann. Rev.
Biochem. 58: 31). The .alpha., .beta..sub.1, .beta..sub.2, and
.gamma. isoforms are Ca.sup.2, phospholipid and
diacylglycerol-dependent and represent the classical isoforms of
PKC, whereas the other isoforms are activated by phospholipid and
diacylglycerol but are not dependent on CA.sup.2+. All isoforms
encompass 5 variable (V1-V5) regions, and the .alpha., .beta.,
.gamma. isoforms contain four (C1-C4) structural domains which are
highly conserved. All isoforms except PKC.alpha., .beta. and
.gamma. lack the C2 domain, and the .lamda., .eta. and isoforms
also lack nine of two cysteine-rich zinc finger domains in C1 to
which diacylglycerol binds. The C1 domain also contains the pseudo
substrate sequence which is highly conserved among all isoforms,
and which serves an auto regulatory function by blocking the
substrate-binding site to produce an inactive conformation of the
enzyme (House et al., (1987) Science 238: 1726).
[0067] Because of these structural features, diverse PKC isoforms
are thought to have highly specialized roles in signal transduction
in response to physiological stimuli (Nishizuka (1989) Cancer 10:
1892), as well as in neoplastic transformation and differentiation
(Glazer (1994) Protein Kinase C. J. F. Kuo, ed., Oxford U. Press
(1994) at pages 171-198). For a discussion of known PKC modulators
see PCT/US97/08141, U.S. Pat. Nos. 5,652,232; 6,043,270; 6,080,784;
5,891,906; 5,962,498; 5,955,501; 5,891,870 and 5,962,504.
[0068] In view of the central role that PKC plays in signal
transduction, PKC has proven to be an exciting target for the
modulation of APP processing. It is well established that PKC plays
a role in APP processing. Phorbol esters for instance have been
shown to significantly increase the relative amount of
non-amyloidogenic soluble APP (sAPP) secreted through PKC
activation. Activation of PKC by phorbol ester does not appear to
result in a direct phosphorylation of the APP molecule, however.
Irrespective of the precise site of action, phorbol-induced PKC
activation results in an enhanced or favored .alpha.-secretase,
non-amyloidogenic pathway. Therefore PKC activation is an
attractive approach for influencing the production of
non-deleterious sAPP and even producing beneficial sAPP and at the
same time reduce the relative amount of A.beta. peptides. Phorbol
esters, however, are not suitable compounds for eventual drug
development because of their tumor promotion activity. (Ibarreta et
al. (1999) NeuroReport Vol. 10, No. 5&6, pp 1034-40).
[0069] The present inventors have also observed that activation of
protein kinase C favors the .alpha.-secretase processing of the
Alzheimer's disease (AD) amyloid precursor protein (APP), resulting
in the generation of non-amyloidogenic soluble APP (sAPP).
Consequently, the relative secretion of amyloidogenic A.sub.1-40
and A.sub.1-42(3) is reduced. This is particularly relevant since
fibroblasts and other cells expressing APP and presenilin AD
mutations secrete increased amounts of total A.beta. and/or
increased ratios of A.sub.1-42(3)/A.sub.1-40. Interesting, PKC
defects have been found in AD brain (.alpha. and .beta. isoforms)
and in fibroblasts (.alpha.-isoform) from AD patients.
[0070] Studies have shown that other PKC activators (i.e.
benzolactam) with improved selectivity for the .alpha., .beta. and
.gamma. isoforms enhance sAPP secretion over basal levels. The sAPP
secretion in benzolactam-treated AD cells was also slightly higher
compared to control benzolactam-treated fibroblasts, which only
showed significant increases of sAPP secretion after treatment with
10 .mu.M BL. It was further reported that staurosporine (a PKC
inhibitor) eliminated the effects of benzolactam in both control
and AD fibroblasts while related compounds also cause a
.about.3-fold sAPP secretion in PC12 cells. The present inventors
have found that the use of bryostatin as a PKC activators to favor
non-amyloidogenic APP processing is of particular therapeutic value
since it is non-tumor promoting and already in stage II clinical
trials.
[0071] Alterations in PKC, as well alterations in calcium
regulation and potassium (K.sup.+) channels are included among
alterations in fibroblasts in Alzheimer's disease (AD) patients.
PKC activation has been shown to restore normal K.sup.+ channel
function, as measured by TEA-induced [Ca.sup.2+] elevations.
Further patch-clamp data substantiates the effect of PKC activators
on restoration of 113 psK.sup.+ channel activity. Thus PKC
activator-based restoration of K.sup.+ channels has been
established as an approach to the investigation of AD
pathophysiology, and provides a useful model for AD therapeutics.
(See, pending U.S. application Ser. No. 09/652,656, which is
incorporated herein by reference in its entirety.)
[0072] Of particular interest are macrocyclic lactones (i.e.
bryostatin class and neristatin class) that act to stimulate PKC.
Of the bryostatin class compounds, bryostatin-1 has been shown to
activate PKC and proven to be devoid of tumor promotion activity.
Bryostatin-1, as a PKC activator, is also particularly useful since
the dose response curve of bryostatin-1 is biphasic. Additionally,
bryostatin-1 demonstrates differential regulation of PKC isozymes,
including PKC.alpha., PKC.delta., and PKC.epsilon.. Bryostatin-1
has undergone toxicity and safety studies in animals and humans and
is actively being investigated as an anti-cancer agent.
Bryostatin-1's use in the studies has determined that the main
adverse reaction in humans is myalgia, limiting the maximum dose to
40 mg/m.sup.2. The present invention has utilized concentrations of
0.1 nM of bryostatin-1 to cause a dramatic increase of sAPP
secretion. Bryostatin-1 has been compared to a vehicle alone and to
another PKC activator, benzolactam (BL), used at a concentration
10,000 times higher. Bryostatin is currently in clinical trials as
an anti-cancer agent. The bryostatins are known to bind to the
regulatory domain of PKC and to activate the enzyme. Bryostatin is
an example of isozyme-selective activators of PKC. Compounds in
addition to bryostatins have been found to modulate PKC. (See, for
example, WO 97/43268; incorporated herein by reference in its
entirety).
[0073] Macrocyclic lactones, and particularly bryostatin-1 is
described in U.S. Pat. No. 4,560,774 (incorporated herein by
reference in its entirety). Macrocyclic lactones and their
derivatives are described elsewhere in the art for instance in U.S.
Pat. No. 6,187,568, U.S. Pat. No. 6,043,270, U.S. Pat. No.
5,393,897, U.S. Pat. No. 5,072,004, U.S. Pat. No. 5,196,447, U.S.
Pat. No. 4,833,257, and U.S. Pat. No. 4,611,066 (each of which are
incorporated herein by reference in their entireties). The above
patents describe various compounds and various uses for macrocyclic
lactones including their use as an anti-inflammatory or anti-tumor
agent. Other discussions regarding bryostatin class compounds can
be found in: Szallasi et al. (1994) Differential Regulation of
Protein Kinase C Isozymes by Bryostatin 1 and Phorbol 12-Myristate
13-Acetate in NIH 3T3 Fibroblasts, Journal of Biological Chemistry
269(3): 2118-24; Zhang et al. (1996) Preclinical Pharmacology of
the Natural Product Anticancer Agent Bryostatin 1, an Activator of
Protein Kinase C, Cancer Research 56: 802-808; Hennings et al.
(1987) Bryostatin 1, an activator of protein kinase C, inhibits
tumor promotion by phorbol esters in SENCAR mouse skin,
Carcinogenesis 8(9): 1343-46; Varterasian et al. (2000) Phase II
Trial of Bryostatin 1 in Patients with Relapse Low-Grade
Non-Hodgkin's Lymphoma and Chronic Lymphocytic Leukemia, Clinical
Cancer Research 6: 825-28; and Mutter et al. (2000) Review Article:
Chemistry and Clinical Biology of the Bryostatins, Bioorganic &
Medicinal Chemistry 8: 1841-1860 (each of which is incorporated
herein by reference in its entirety).
[0074] Myalgia is the primary side effect that limits the tolerable
dose of a PKC activator. For example, in phase II clinical trials
using bryostatin-1, myalgia was reported in 10 to 87% of all
treated patients. (Clamp et al. (2002) Anti-Cancer Drugs 13:
673-683). Doses of 20 .mu.g/m.sup.2 once per week for 3 weeks were
well tolerated and were not associated with myalgia or other side
effects. (Weitman et al. (1999) Clinical Cancer Research 5:
2344-2348). In another clinical study, 25 .mu.g/m2 of bryostatin-1
administered once per week for 8 weeks was the maximum tolerated
dose. (Jayson et al. (1995) British J. of Cancer 72(2): 461-468).
Another study reported that 50 .mu.g/m.sup.2 (a 1 hour i.v.
infusion administered once every 2 weeks for a period of 6 weeks)
was the maximum-tolerated dose. (Prendville et al. (1993) British
J. of Cancer 68(2): 418-424). The reported myalgia was cumulative
with repeated treatments of bryostatin-1 and developed several days
after initial infusion. Id. The deleterious effect of myalgia on a
patient's quality of life was a contributory reason for the
discontinuation of bryostatin-1 treatment. Id. The etiology of
bryostatin-induced myalgia is uncertain. Id.
[0075] The National Cancer Institute has established common
toxicity criteria for grading myalgia. Specifically, the criteria
are divided into five categories or grades. Grade 0 is no myalgia.
Grade 1 myalgia is characterized by mild, brief pain that does not
require analgesic drugs. In Grade 1 myalgia, the patient is fully
ambulatory. Grade 2 myalgia is characterized by moderate pain,
wherein the pain or required analgesics interfere with some
functions, but do not interfere with the activities of daily
living. Grade 3 myalgia is associated with severe pain, wherein the
pain or necessary analgesics severely interfere with the activities
of daily living. Grade 4 myalgia is disabling.
[0076] The compositions of the present invention increase the
tolerable dose of the PKC activator administered to a patient
and/or ameliorate the side effects associated with PKC activation
by attenuating the activation of PKC in peripheral tissues.
Specifically, PKC inhibitors inhibit PKC in peripheral tissues or
preferentially inhibit PKC in peripheral tissues. Vitamin E, for
example, has been shown to normalize diacylglycerol-protein kinase
C activation in the aorta of diabetic rats and cultured rat smooth
muscle cells exposed to elevated glucose levels. (Kunisaki et al.
(1994) Diabetes 43(11): 1372-1377). In a double-blind trial of
vitamin E (2000 IU/day) treatment in patients suffering from
moderately advanced Alzheimer's Disease, it was found that vitamin
E treatment reduced mortality and morbidity, but did not enhance
cognitive abilities. (Burke et al. (1999) Post Graduate Medicine
106(5): 85-96).
[0077] Macrocyclic lactones, including the bryostatin class were
originally derived from Bigula neritina L. While multiple uses for
macrocyclic lactones, particularly the bryostatin class are known,
the relationship between macrocyclic lactones and cognition
enhancement was previously unknown.
[0078] The examples of the compounds that may be used in the
present invention include macrocyclic lactones (i.e. bryostatin
class and neristatin class compounds). While specific embodiments
of these compounds are described in the examples and detailed
description, it should be understood that the compounds disclosed
in the references and derivatives thereof could also be used for
the present compositions and methods.
[0079] As will also be appreciated by one of ordinary skill in the
art, macrocyclic lactone compounds and their derivatives,
particularly the bryostatin class, are amenable to combinatorial
synthetic techniques and thus libraries of the compounds can be
generated to optimize pharmacological parameters, including, but
not limited to efficacy and safety of the compositions.
Additionally, these libraries can be assayed to determine those
members that preferably modulate .alpha.-secretase and/or PKC.
[0080] Synthetic analogs of bryostatin are also contemplated by the
present invention. Specifically, these analogues retain the
orientation of the C1-, C19-, C26-oxygen recognition domain as
determined by NMR spectroscopic comparison with bryostatin and
various degrees of PKC-binding affinity. The bryostatin analogues
disclosed and described in U.S. Pat. No. 6,624,189 (incorporated
herein by reference in its entirety) may also be used in the
methods of the present invention. Specifically, the bryostatin
analogues described by the genus of Formula I of U.S. Pat. No.
6,624,189 (column 3, lines 35-66) and the species of formulas
II-VII and 1998a and 1998b (column 8, lines 28-60) of U.S. Pat. No.
6,624,189 are PKC activators suitable for use in the methods of the
present invention.
[0081] There still exists a need for the development of methods for
the treatment for improved overall cognition, either through a
specific characteristic of cognitive ability or general cognition.
There also still exists a need for the development of methods for
the improvement of cognitive enhancement whether or not it is
related to specific disease state or cognitive disorder. The
methods and compositions of the present invention fulfill these
needs and will greatly improve the clinical treatment for
Alzheimer's disease and other neurodegenerative diseases, as well
as, provide for improved cognitive enhancement. The methods and
compositions also provide treatment and/or enhancement of the
cognitive state through the modulation of .alpha.-secretase.
EXAMPLES
Example 1
Behavioral Pharmacology
[0082] Bryostatin exposure--Specimens of Hermissenda Crassicornis
were maintained in artificial sea water (ASW) at 15.degree. for
three days in perforated 50-ml conical centrifuge tubes before
starting experiments. Bryostatin, purified from the marine bryozoan
Bugula neritina, was dissolved in EtOH and diluted to its final
concentration in ASW. Animals were incubated with bryostatin in ASW
for 4 hr, then rinsed with normal ASW. For selected experiments
lactacysteine (10 .mu.M) or anisomycin was added to the ASW.
[0083] Bryostatin effects on Hermissenda behavior and biochemistry
were produced by adding the drug to the bathing medium within an 8
cm long, 1 cm diameter test tube housing each individual
animal.
Example 2
Immunostaining Methods
[0084] Following experimental treatments and testing, animals were
rapidly decapitated, the central nervous systems (CNS) removed and
then fixed in 4% para-formaldehyde in 20 mM Tris-buffered (pH 8)
natural seawater (NSW; 0.2 .mu.m micropore-filtered). The CNSs were
then embedded in polyester wax (20), sectioned (6 .mu.m) and
immunostained using a biotinylated secondary antibody coupled to
avidin-bound microperoxidase (ABC method, Vector),
Aminoethylcarbazole (AEC) was used as the chromogen. The primary
polyclonal antibody (designated 25U2) was raised in rabbits from
the full length calexcitin protein extracted from squid optic
lobes. Gray-scale intensity measures were done from digital
photomicrographs on circumscribed cytoplasmic areas of the
B-photoreceptors minus the same background area (non-staining
neuropile).
Example 3
Protein Kinase C Assay
[0085] Cells were homogenized by sonication (5 sec, 25 W) in 100
.mu.l of 10 mM Tris-HCl pH 7.4 buffer containing 1 mM EGTA, 1 mM
PMSF, and 50 mM NaF. Homogenate was transferred to a polyallomer
centrifuge tube and was centrifuged at 100,000.times.g for 10 min
at 4.degree.. The supernatant was removed and immediately frozen on
dry ice. The particulate fraction was resuspended by sonication in
100 .mu.l of the same buffer and stored at -80.degree.. To measure
PKC, 10 .mu.l of cytosol or particulate fraction was incubated for
15 min at 37.degree. in the presence of 10 .mu.M histones, 4.89 mM
CaCI.sub.2, 1.2 .mu.g/.mu.l phosphatidyl-L-serine, 0.18 .mu.g/.mu.l
1.2-dioctanoyl-sn-glycerol, 10 mM MgCI.sub.2, 20 mM HEPES (pH 7.4),
0-8 mM EDTA, 4 mM EGTA, 4% glycerol, 8 .mu.g/ml aprotinin, 8
.mu.g/ml leupeptin, and 2 mM benzamidine. 0.5 .mu.Ci
[.gamma..sup.32P]ATP was added and .sup.32P-phosphoprotein
formation was measured by adsorption onto phosphocellulose as
described previously (25). This assay was used with slight
adjustments for either Hermissenda nervous system homogenates or
cultured mammalian neuron homogenates
Example 4
Cell Culture
[0086] Rat hippocampal H19-7/IGF-IR cells (ATCC) were plated onto
poly-L-lysine coated plates and grown at 35.degree. in DMEM/10% FCS
for several days until approx. 50% coverage was obtained. The cells
were then induced to differentiate into a neuronal phenotype by
replacing the medium with 5 ml N2 medium containing 10 ng/ml basic
fibroblast growth factor and grown in T-25 flasks at 39.degree. C.
(26). Various concentrations of bryostatin (0.01-1.0 nM) were then
added in 10 .mu.l aqueous solution. After a specified interval, the
medium was removed and the cells were washed with PBS, removed by
gentle scraping, and collected by centrifugation at 1000 rpm for 5
min.
Example 5
Behavioral Conditioning
[0087] Pavlovian conditioning of Hermissenda involves repeated
pairings of a neutral stimulus, light, with an unconditioned
stimulus, orbital shaking. (See, Lederhendler et al. (24) and
Epstein et al. (6)). A rotation/shaking stimulus excites the
statocyst hair cells and thereby elicits an unconditioned response:
a brisk contraction of the muscular undersurface called a foot,
accompanied by adherence or "clinging" to the surface that supports
the foot. Before conditioning, light elicits a weakly positive
phototaxis accompanied by lengthening of the foot. After sufficient
light-rotation pairings, light no longer elicits phototaxis, but
instead elicits a new response (24): the "clinging" and foot
shortening previously elicited only by the unconditional stimulus
(FIG. 1). Thus, the meaning of the unconditioned stimulus, rotation
or orbital shaking, has been transferred to the conditioned
stimulus and is manifested by a light-elicited foot contraction--a
negative change of foot length. This conditioned response to light
can last for weeks, is not produced by randomized light and
rotation, is stimulus-specific, and shares the other defining
characteristics of mammalian Pavlovian Conditioning.
Example 6
Bryostatin-Induced Prolongation of Associative Memory
[0088] Pavlovian conditioning of Hermissenda has well-defined
training parameters that produce progressively longer-lasting
retention of the learned conditioned response. Two training events
(2 TE) of paired light and orbital shaking (see "Methods"), for
example, induce a learned conditioned response (light-elicited foot
contraction or shortening) that persists without drug treatment for
approximately 7 minutes. Four to six training events (4-6 TE)
induce a conditioned response that persists up to several hours,
but disappears approximately by 1 day after training. Nine TE
produces long-term associative memory lasting many days and often
up to two weeks.
[0089] Animals were trained with sub-optimal regimes of 4- and
6-paired CS/US training events (TEs) with bryostatin (0.25 ng/ml)
added during dark adaptation (10 min) prior to training and
remaining for 4 hours, or without Bryo (NSW controls); 9-paired TEs
and NSW served as the positive controls. All animals were tested
with the CS alone at 4 h, then at 24-h intervals. Animals trained
sub-optimally but treated with bryostatin all demonstrated
long-term retention (n=8-16 animals/condition/experiment; ANOVA,
p<0.01).
[0090] Two TE plus bryostatin produced memory retention lasting
hours (vs. minutes without bryostatin), 4 TEs plus bryostatin
extended retention beyond 24 hours (FIG. 1), and 6 TE plus
bryostatin produced retention lasting 1 week or longer.
[0091] Without Bryostatin (NSW), random, and paired CS/US training
events (TEs) did not generate LTM or elicit a CR when tested at 4
h. Bryostatin (0.25 ng/ml in NSW) applied before 6-TE conditioning
(during 10 min dark adaptation) and for 4 hours thereafter produced
a positive CR (foot contraction; negative change in length), thus
indicating LTM was established. The antagonist, Ro-32 when applied
pre-training (during dark adaptation), blocked the effects of 6 TE
plus bryostatin, i.e. animals lengthened (positive length change)
with normal phototaxis (n=4-8 animals/condition/experiment; ANOVA
differences, p<0.01). Randomized presentations of light and
rotation, with or without bryostatin, produced no conditioned
response (FIG. 2), i.e., light-elicited foot-contraction. Thus,
bryostatin during and immediately following training prolonged
memory retention with sub-optimal training trials.
Example 7
Pre-Exposure to Bryostatin on Days Before Training Enhances Memory
Acquisition
[0092] Previous measurements (15, 17) have indicated that
learning-induced PKC association with neuronal membranes (i.e.,
translocation) can be sustained. Rabbit nictitating membrane
conditioning, rat spatial maze learning, maze learning, and rat
olfactory discrimination learning have all been found to be
accompanied by PKC translocation that lasts for days following
training. Hermissenda conditioning was followed for at least one
day after training by PKC translocation that could be localized in
single, identifiable Type B cells (15).
[0093] As already described, exposure to bryostatin for 4 hours
during and after training enhances memory retention produced by 2
TE from 6-8 minutes to several hours. However, a 4 hour exposure to
bryostatin on the day preceding training, as well as on the day of
the 2 TE prolonged memory retention for more than one day after
training. Two successive days of 4-h bryostatin exposure (0.25
ng/ml) of animals coupled with 2-paired CS/US training events
produced at least 6 days of long-term retention demonstrated by the
CR (body length contraction) when tested with the CS alone (n=16
animals/condition; ANOVA, p<0.01) (FIG. 3).
[0094] Animals given three successive days of 4-h bryostatin
exposure (0.25 ng/ml) followed one day later by 2-TEs, demonstrated
long-term retention (LTR) measured over 96 h post-training.
Non-exposed animals (same as in FIG. 3) did not demonstrate any
behavioral modification (no CR to CS testing). Anisomycin (ANI) (1
.mu.g/ml) administered immediately and remaining for four hours
post-training to animals receiving the three-day bryostatin
treatments did not prevent long-term retention. Thus the
requirement for protein synthesis necessary to generate LTR that is
usually blocked by ANI when added post-training was obviated by the
three-day bryostatin treatment (n=16 animals/condition; ANOVA,
p<0.01). A third day of exposure to the 4 hour interval of
bryostatin caused a similar enhanced retention of the Pavlovian
conditioned response (FIG. 4). The preceding results support the
view that two successive intervals of exposure to bryostatin cause
PKC activation and possibly synthesis of proteins critical for
long-term memory, with a minimum of concurrent and subsequent PKC
downregulation. This view was given further support by the
observation that a more prolonged interval of bryostatin exposure,
i.e. for 8 to 20 hours, followed by 2 TE (FIG. 5) was not
sufficient itself to produce memory retention equivalent to that
which accompanied the two 4 hour exposures on successive preceding
days. In these experiments, the effects of 20 hr bryostatin (0.25
ng/ml) exposure on training was observed. With the sub-optimal
2-paired TE conditioning regime, retention was gone in 48 hours.
Retention of 4-paired TE conditioning with 20 h pre-exposure to
bryostatin persisted (n=8 animals/condition; ANOVA at 48-h,
p<0.01). Sufficiently prolonged bryostatin exposure (e.g., 8-12
hours) is known in other cell systems to cause prolonged PKC
downregulation that may offset PKC activation and increase PKC
synthesis.
[0095] Similarly, sufficiently increased concentrations of
bryostatin ultimately blocked memory retention (FIG. 6) presumably
also because of PKC downregulation. Bryostatin concentrations
<0.50 ng/ml augment acquisition and memory retention with
sub-optimal (4 TE) training conditions. Those concentrations had no
demonstrable effects on retention performance with 9-paired TEs.
However, with all training conditions tested, concentration
.gtoreq.1.0 ng/ml inhibited acquisition and behavioral retention
(n=16 animals/condition), presumably via PKC downregulation.
Example 8
Pre-Exposure to Bryostatin Obviates the Requirement for Protein
Synthesis During Training
[0096] Animals received 2-paired training events (TEs) and then
tested for retention after 4 h. Bryostatin (0.25 ng/ml) applied in
NSW to animals during the 10-min pre-training dark adaptation
period and 4 h thereafter demonstrated retention of the behavioral
conditioning (foot contraction (CR) and shortening in body length).
NSW control animals and those treated with bryostatin pre-training
followed by anisomycin (1.0 .mu.g/ml) immediately post-training
showed no CR with the foot lengthening in normal positive
phototaxis (n=12 animals/condition/experiment, two-way ANOVA
statistics, p<0.01). A single 4 hour exposure to bryostatin
together with 2 TE produced long-term memory retention lasting
hours that was entirely eliminated when anisomycin was present
along with the bryostatin (FIG. 7). Similar blocking effects of
anisomycin were also observed with 6 TE plus bryostatin. Repeated
brief exposures to bryostatin, however, increase the net synthesis
of PKC, calexcitin, and other memory proteins and thus eliminate
the requirement for new synthesis during and after Pavlovian
conditioning--if PKC downregulation were sufficiently minimized.
Protein synthesis was blocked for 4 hours with anisomycin
immediately after 2 TE of animals that on each of 3 preceding days
had been first exposed to 4 hours of bryostatin. In this case,
anisomycin-induced blockade of protein synthesis did not prevent
memory retention that lasted many days (FIG. 4). By contrast, the
same 4 hour anisomycin treatment eliminated all memory retention
produced by 9 TE, a training regimen ordinarily followed by 1-2
weeks of memory retention (27). Finally, if 2 TE were given one day
after three successive days of 4 hour exposures to bryostatin that
was accompanied each time by anisomycin, long-term memory was
eliminated.
Example 9
Pre-Exposure to Proteasome Inhibition Enhances Bryostatin Effects
on Memory
[0097] Another means of enhancing and prolonging de novo synthesis
of PKC and other memory-related proteins is provided by blocking
pathways involved in protein degradation. One of these, the
ubiquitin-proteasome pathway (28-30), is known to be a major route
for degradation of the .alpha.-isozyme of PKC. Degradation of
PKC-.alpha. has been previously shown to be largely prevented by 20
.mu.M-5 Q.mu.M of the proteasome inhibitor, Lactacysteine.
[0098] Animals were incubated simultaneously for 4 h with
bryostatin (0.25 ng/ml) and lactacysteine (10 .mu./M), and then 24
hrs later were conditioned with 2-paired CS/US training events
(TEs). Animals were subsequently tested with the CS alone at 4 h
post-training and then at 24-h intervals. Retention of the
conditioned behavior was persistent with the combined
bryostatin/lactacysteine treatment; behavioral retention was lost
by bryostatin-only-treated animals after 24 h. Lactacysteine-only
treated animals showed no acquisition or retention of behavioral
training (data not graphed). (n=28 animals, combined
bryostatin/lactacysteine; n=20, bryostatin alone; n=16,
lactacysteine alone). Lactacysteine, in this case, transformed the
short-term memory produced by the single bryostatin exposure
(followed by 2 TE) to long-term memory lasting many days (FIG.
8).
Example 10
Calexcitin-Immunostaining Due to PKC Activation
[0099] Recently we showed that an immunostaining label of
calexcitin increased within single identified Type B cells during
acquisition and retention of Hermissenda conditioning (20). Many
previous findings have implicated a low molecular weight calcium
and GTP-binding protein, calexcitin, as a substrate for PKC
isozymes during Hermissenda conditioning (19). Calexcitin, now
completely sequenced in some animal species, and shown to have
significant homology with similar proteins in other species (31),
undergoes changes of phosphorylation during and after Hermissenda
Pavlovian conditioning. It is also a high affinity substrate for
the alpha-isozyme of PKC and a low affinity substrate for .beta.
and gamma (19).
[0100] Micrographs (A, B) depict representative tissue sections
from Hermissenda eyes that were immunolabeled with the calexcitin
polyclonal antibody, 25U2. Positive calexcitin immunostaining
occurred in B-cell photoreceptors (*B-Cell) of animals that
experienced paired CS/UCS associative conditioning with or without
prior administration of bryostatin (B). Random presentations of the
two stimuli (training events, TEs) did not produce behavioral
modifications nor a rise in calexcitin above normal background
levels (A); basement membrane and lens staining are artifact
associated with using vertebrate polyclonal antibodies. Differences
in staining intensities were measured and recorded as gray-scale
intensities (0-256; B-cell cytoplasm minus tissue background).
Graph (C) displays intensity measures for Hermissenda conditioned
with 9-random TEs (left bar) and animals treated with two exposures
on successive days to the PKC agonist, bryostatin (0.25 ng/ml), and
then associatively conditioned with 2-paired TEs. Activation of PKC
from two exposures of bryostatin coupled with 2 TEs significantly
increased calexcitin to levels associated with 9-paired TEs and
consolidated (long-term) memory (n=4-8 animals/condition/replicate;
t-test comparison, p<0.01).
[0101] Calexcitin immunostaining is sufficiently sensitive to
resolve boutons within synaptic fields of photic-vestibular
neurites (D). Arrows indicate arborization field between an
interneuron (a), axon from a contralateral neuron (b), and terminal
boutons of neurites from a putative photoreceptor (c). Scale
bars=10 .mu.m; CPG, cerebropleural ganglion (FIG. 9, 10).
[0102] This conditioning-induced calexcitin label increase
represents an increase in the actual amount of the protein since
the immunostaining antibody reacts with both the phosphorylated and
unphosphorylated forms of the protein. PKC, previously shown to
translocate within the same individual Type B cells, apparently
caused the conditioning-induced increase in the calexcitin label
since the specific PKC-blocker, Ro-32, prevented both learning and
learning-specific calexcitin increases in the Type B cell (see
above). Naive and/or randomized control training protocols produced
a small fraction of the training-induced calexcitin (CE)
immunostaining (FIG. 9).
[0103] Random training (4-TEs) without bryostatin yielded slightly
higher intensity measures than background. Bryostatin
administration increased the calexcitin levels for both training
paradigms. With random training, when there was occasional overlap
(pairing) of the CS and US, as was the case here, it is not
unexpected that some rise in CE might occur (increase of 2.0).
However, calexcitin levels increased greater than 4.3.times.with
paired training (mean.+-.SE, N=5 animals/treatment. 4 RTE=random
control, 4 trials with random light and rotation; 6 PTE=paired
trials, 6 trials with paired light and rotation. 6 PTE-0 Bry vs. 6
PTE-0.25 Bry: p<0.001; 4 RTE-0.25 Bry vs. 6 PTE-0.25 Bry;
p<0.001 (t-test). When sub-optimal training events (4-6 TE) were
used, the CE immunostaining (FIG. 10A) reached an intermediate
level of elevation. These sub-optimal regimes were insufficient to
produce memory retention lasting longer than 24 hours. As described
earlier, bryostatin administered during training with 6 TE induced
long-term memory retention (>1 week). Furthermore, bryostatin
plus 6 TE induced CE immunostaining comparable to that observed
after 9 TE.
[0104] Bryostatin in low doses (0.1-0.25 ng/ml) markedly enhanced
memory after 2, 4, or 6 training trials. Pavlovian conditioning
with 6 TE produced memory lasting many days with bryostatin, but
lasting only hours without bryostatin. This memory enhancement was
blocked by anisomycin or the PKC inhibitor, Ro-32. It is important
to note that CE immunostaining was greatly reduced 24 hours after 9
TE even though the memory persisted for more than 1 week
thereafter. More persistent CE immunostaining resulted, however,
from repeated bryostatin exposures on days preceding minimal
training (2 TE).
[0105] Bryostatin alone (without associative conditioning)
administered for 4-hr over each of 1, 2, and 3 days progressively
increased the levels of calexcitin in the B-photoreceptors of
Hermissenda when measured 24 hours after each of the periods of
bryostatin exposures. Twenty-four hours after 1 bryostatin exposure
for four hours, CE immunostaining was not elevated (FIG. 10B).
Twenty-four hours after 2 bryostatin exposures, 1 on each of two
successive days showed greater residual CE immunostaining. The
calexcitin level after 3 bryostatin exposures followed by just
2-paired training events (paired light and orbital shaking) raised
that level even higher with a significant concomitant length in the
number of retention days for the associative conditioning-induced
behavioral modification (n=16 animals/condition: ANOVA, p<0.01).
With 2 TE on the subsequent day after these three exposures, CE
immunostaining 24 hours later approached the levels previously
observed immediately following 9 TE (FIG. 10B). Thus, CE
immunostaining following these three days of 4 hour bryostatin
exposure followed by minimal training (2 TE) showed a greater
persistence than did the training trials alone. This persistence of
newly synthesized calexcitin is consistent with the biochemical
observations indicating enhanced protein synthesis induced by
bryostatin.
[0106] Exposure to 4-hr of bryostatin on two consecutive days
followed 24 hours later by 2-training events (2 TE) are required to
raise calexcitin levels to the amount associated with consolidated
long-term memory. Typically, 2-TEs with two bryostatin exposures
produces retention lasting more than one week (n=16
animals/condition; t-test, p<0.01). Priming with 4-hr exposures
to bryostatin over 3 consecutive days will induce calexcitin levels
required for consolidated memory. Anisomycin added immediately
after the 2-paired training events did not reduce this calexcitin
level and consolidated memory persists for many days (N=8
animals/condition; t-test, p>0.05, ns). (FIGS. 11 A, B).
[0107] It is noteworthy that the Ro-32 inhibition of PKC
immediately after bryostatin plus training did not prevent
long-term memory induction, while this inhibition during the
training plus bryostatin did prevent memory consolidation. In
contrast, anisomycin during training with and without bryostatin
did not prevent long-term memory, while anisomycin after training
with and without bryostatin completely blocked memory formation.
Therefore, PKC activation during training is followed by protein
synthesis required for long-term memory. Thus, once PKC activation
is induced to sufficient levels, the required protein synthesis is
an inevitable consequence. Consistently, bryostatin-induced PKC
activation on days prior to training is sufficient, with minimal
training trials, to cause long-term memory. Furthermore, this
latter long-term memory does not require protein synthesis
following the training (and PKC activation on preceding days).
Again, prior PKC activation was sufficient to produce that protein
synthesis necessary for subsequent long-term memory formation. One
of those proteins whose synthesis is induced by bryostatin-induced
PKC activation as well as conditioning trials is calexcitin--as
demonstrated by the immunostaining labeling. The other protein is
PKC itself.
Example 11
Effect of Bryostatin on PKC Activity
[0108] Bryostatin is known to transiently activate PKC by
increasing PKC association with the cellular membrane fraction. A
variety of associative memory paradigms have also been demonstrated
to cause increased PKC association with neuronal membranes. We
tested, therefore, the possibility that repeated exposures of
Hermissenda to bryostatin (i.e., 4 hour exposures, exactly as with
the training protocols) might also induce prolonged PKC
activation.
[0109] Intact Hermissenda were exposed for 4 hour intervals to
bryostatin (0.28 nM) on successive days under conditions described
("Behavioral Pharmacology"). Histone phosphorylation (See
"Methods") in isolated circumesophageal nervous systems was then
measured in the cytosol fraction. PKC activity measured both 10
minutes and 24 hours after the second of two bryostatin exposures
was significantly increased over baseline levels (N=6, for each
measurement). (FIG. 12, 13). Thus, the quantity of PKC in both
fractions was apparently increased, but not the ratio of the PKC in
the membrane to that in the cytosolic fraction. These results
demonstrate that the bryostatin pre-exposure causes an effect on
PKC somewhat different from learning itself. After an initial
activation (via translocation), this bryostatin effect is most
likely due to increased synthesis of PKC, consistent with the
increased levels of calexcitin induced by bryostatin, but not
directly correlated with repeated bryostatin exposure.
[0110] As in FIG. 12, 13 but with anisomycin (1.0 ng/ml) added
together with each bryostatin (0.25 ng/ml) exposure. Note that the
anisomycin markedly reduced the PKC activity in both the cytosolic
and membrane fractions from the Hermissenda circumesophageal
nervous systems after exposure to bryostatin on three successive
days (N=3, for each measurement, p<0.01) (FIG. 14).
[0111] To further examine biochemical consequences of repeated
exposures to bryostatin, rat hippocampal neurons were studied after
they had been immortalized by retroviral transduction of
temperature sensitive tsA5CSV40 large T antigen (25). These
differentiate to have a neuronal phenotype when induced by basic
fibroblast growth factor in N2 medium (26) and express a normal
complement of neuronal proteins, including PKC.
[0112] Exposure of cultured hippocampal neurons to a single
activating dose of bryostatin (0.28 nM) for 30 minutes produced a
brief translocation of PKC from the cytosol to the particulate
fraction (approx 60%) followed by a prolonged downregulation (FIG.
15). Both the initial PKC activation and subsequent downregulation
have been previously described and were confirmed by measurement of
PKC activity in membrane and cytosol. Exposing the cultured
hippocampal neurons to one 30-minute period of bryostatin, followed
by a second 30-minute exposure, at intervals ranging from 30
minutes to 8 hours, caused the membrane-bound PKC to rebound more
quickly. Thus, a second exposure after a 2- to 4-hour delay
eliminated the significant downregulation that a single bryostatin
exposure produced (FIG. 16). In the cytoplasmic fraction, no
significant alteration of PKC activity was detected within the
first 4 hours after bryostatin exposure. In contrast, if cells were
exposed to bryostatin twice within a 2-hour period, there was a
significant reduction of PKC activity in response to the second
exposure. However, if the second exposure was delayed until 4 hours
after the first, activity was increased above baseline, to a degree
that was significantly greater compared with a second exposure
delivered after 2 hours or less (FIG. 16).
[0113] These results are consistent with the interpretation that
the initial bryostatin activation of PKC followed by downregulation
(28-30) leads to increased synthesis (via de novo protein
synthesis) of PKC isozymes (as well as calexcitin, described
earlier). In fact, we found here that a single 30-minute exposure
to 0.28 nM bryostatin increased overall protein synthesis (FIG.
17), measured by incorporation of .sup.35-S Methionine in the last
1/2 hour before collecting the neurons, by 20% within 24 h,
increasing to 60% by 79 hours after the bryostatin exposure. This
prolonged and profound increase of protein synthesis induced by
bryostatin was partially blocked when the PKC inhibitor Ro-32 was
also present (FIG. 17).
[0114] Abundant observations indicate that sufficient
bryostatin-induced PKC activation leads, inevitably, to progressive
PKC inactivation and subsequent downregulation. Sufficient doses of
bryostatin (greater than 1.0 ng/ml) actually inhibited Pavlovian
conditioning. This was most likely due to PKC downregulation that
characterized the behavioral results with high bryostatin
concentrations. PKC activation induced by bryostatin has been shown
to be downregulated by two distinct pathways. One that is also
induced by phorbol ester involves ubiquitination and subsequent
proteolytic degradation through the proteasome pathway. The second
mechanism of downregulation, not induced by phorbol ester, involves
movement through caveolar compartments and degradation mediated by
phosphatase PP1 and PP2A. With sufficient concentrations and/or
durations of PKC activators, the PKC degrading pathways create a
deficit of PKC that stimulates de novo synthesis of PKC, PKC
synthesis cannot compensate for inactivation and down regulation,
thereby causing depletion of available PKC of 95% or more.
* * * * *