U.S. patent application number 10/037791 was filed with the patent office on 2002-07-18 for method of simultaneously enhancing analgesic potency and attenuating dependence liability caused by morphine and other bimodally-acting opioid agonists.
Invention is credited to Crain, Stanley M., Shen, Ke-Fei.
Application Number | 20020094947 10/037791 |
Document ID | / |
Family ID | 46254970 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094947 |
Kind Code |
A1 |
Crain, Stanley M. ; et
al. |
July 18, 2002 |
METHOD OF SIMULTANEOUSLY ENHANCING ANALGESIC POTENCY AND
ATTENUATING DEPENDENCE LIABILITY CAUSED BY MORPHINE AND OTHER
BIMODALLY-ACTING OPIOID AGONISTS
Abstract
This invention relates to a method for selectively enhancing the
analgesic potency of a bimodally-acting opioid agonist such as
morphine and simultaneously attenuating anti-analgesia,
hyperalgesia, hyperexcitability, physical dependence and/or
tolerance effects associated with the administration of the
bimodally-acting opioid agonist. The method of the present
invention comprises administering to a subject an analgesic or
sub-analgesic amount of a bimodally-acting opioid agonist such as
morphine and an amount of an excitatory opioid receptor antagonist
such as naltrexone or nalmefene effective to enhance the analgesic
potency of the bimodally-acting opioid agonist and attenuate the
anti-analgesia, hyperalgesia, hyperexcitability, physical
dependence and/or tolerance effects of the bimodally-acting opioid
agonist.
Inventors: |
Crain, Stanley M.; (Leonia,
NJ) ; Shen, Ke-Fei; (Flushing, NY) |
Correspondence
Address: |
Craig J. Arnold
Amster, Rothstein & Ebenstein
90 Park Avenue
New York
NY
10016
US
|
Family ID: |
46254970 |
Appl. No.: |
10/037791 |
Filed: |
January 3, 2002 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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10037791 |
Jan 3, 2002 |
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09585517 |
Jun 1, 2000 |
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6362194 |
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09585517 |
Jun 1, 2000 |
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09094977 |
Jun 16, 1998 |
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6096756 |
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09094977 |
Jun 16, 1998 |
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08759590 |
Dec 3, 1996 |
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5767125 |
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08759590 |
Dec 3, 1996 |
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08276966 |
Jul 19, 1994 |
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5512578 |
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08276966 |
Jul 19, 1994 |
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08097460 |
Jul 27, 1993 |
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5472943 |
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08097460 |
Jul 27, 1993 |
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07947690 |
Sep 21, 1992 |
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Current U.S.
Class: |
514/285 ;
514/18.3; 514/18.4; 514/18.5; 514/282 |
Current CPC
Class: |
Y10S 514/812 20130101;
A61K 31/00 20130101; G01N 33/9486 20130101; G01N 2500/10 20130101;
G01N 33/94 20130101; A61K 31/485 20130101; A61K 31/135 20130101;
A61K 38/33 20130101; A61K 31/135 20130101; A61K 2300/00 20130101;
A61K 31/4468 20130101; A61K 31/485 20130101; A61K 2300/00 20130101;
A61K 38/33 20130101; A61K 38/33 20130101; A61K 31/485 20130101;
A61K 31/4468 20130101; A61K 31/485 20130101; A61K 31/485 20130101;
A61K 31/485 20130101 |
Class at
Publication: |
514/2 ;
514/282 |
International
Class: |
A61K 038/33; A61K
031/485 |
Claims
What is claimed is:
1. A method for selectively enhancing the analgesic potency of a
bimodally-acting opioid agonist and simultaneously attenuating
anti-analgesia, hyperalgesia, hyperexcitability, physical
dependence and/or tolerance effects associated with the
administration of the bimodally-acting opioid agonist, said method
comprising administering to a subject an analgesic or sub-analgesic
amount of a bimodally-acting opioid agonist and an amount of
nalmefene effective to enhance the analgesic potency of the
bimodally-acting opioid agonist and attenuate the anti-analgesia,
hyperalgesia, hyperexcitability, physical dependence and/or
tolerance effects of the bimodally-acting opioid agonist.
2. The method of claim 1 wherein the bimodally-acting opioid
agonist is selected from the group consisting of morphine, codeine,
fentanyl analogs, pentazocine, buprenorphine, methadone,
enkephalins, dynorphins, endorphins and similarly acting opioid
alkaloids and opioid peptides.
3. The method of claim 2 wherein the bimodally-acting opioid
agonist is morphine.
4. The method of claim 2 wherein the bimodally-acting opioid
agonist is codeine.
5. The method of claim 2 wherein the bimodally-acting opioid
agonist is methadone.
6. The method of claim 1 wherein the amount of nalmefene
administered is 1000-10,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
7. The method of claim 1 wherein the amount of nalmefene
administered is 10,000-1,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
8. The method of claim 1 wherein the mode of administration is
selected from the group consisting of oral, sublingual,
intramuscular, subcutaneous, intravenous and transdermal.
9. A method for treating pain in a subject comprising administering
to the subject an analgesic or sub-analgesic amount of a
bimodally-acting opioid agonist and an amount of nalmefene
effective to enhance the analgesic potency of the bimodally-acting
opioid agonist and attenuate anti-analgesia, hyperalgesia,
hyperexcitability, physical dependence and/or tolerance effects of
the bimodally-acting opioid agonist.
10. The method of claim 9 wherein the bimodally-acting opioid
agonist is selected from the group consisting of morphine, codeine,
fentanyl analogs, pentazocine, methadone, buprenorphine,
enkephalins, dynorphins, endorphins and similarly acting opioid
alkaloids and opioid peptides.
11. The method of claim 10 wherein the bimodally-acting opioid
agonist is morphine.
12. The method of claim 10 wherein the bimodally-acting opioid
agonist is codeine.
13. The method of claim 10 wherein the bimodally-acting opioid
agonist is methadone.
14. The method of claim 9 wherein the amount of nalmefene
administered is 1000-10,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
15. The method of claim 9 wherein the amount of nalmefene
administered is 10,000-1,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
16. The method of claim 9 wherein the mode of administration is
selected from the group consisting of oral, sublingual,
intramuscular, subcutaneous, intravenous and transdermal.
17. A method for treating an opiate addict comprising administering
to the opiate addict an amount of nalmefene effective to attenuate
physical dependence caused by a bimodally-acting opioid agonist and
enhance the analgesic potency of a bimodally-acting opioid
agonist.
18. The method of claim 17 wherein nalmefene is coadministered with
an analgesic or sub-analgesic amount of a bimodally-acting opioid
agonist.
19. The method of claim 18 wherein the bimodally-acting opioid
agonist is selected from the group consisting of morphine, codeine,
fentanyl analogs, pentazocine, buprenorphine, methadone,
enkephalins, dynorphins, endorphins and similarly acting opioid
alkaloids and opioid peptides.
20. The method of claim 19 wherein the bimodally-acting opioid
agonist is methadone.
21. The method of claim 19 wherein the bimodally-acting opioid
agonist is buprenorphine.
22. The method of claim 18 wherein the amount of nalmefene
administered is 1000-10,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
23. The method of claim 18 wherein the amount of nalmefene
administered is 10,000-1,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered.
24. The method of claim 17 wherein the mode of administration is
selected from the group consisting of oral, sublingual,
intramuscular, subcutaneous, intravenous and transdermal.
25. A composition comprising an analgesic or sub-analgesic amount
of a bimodally-acting opioid agonist and an amount of nalmefene
effective to enhance the analgesic potency of the bimodally-acting
opioid agonist and attenuate the anti-analgesia, hyperalgesia,
hyperexcitability, physical dependence and/or tolerance effects of
the bimodally-acting opioid agonist in a subject administered the
composition.
26. The composition of claim 25 wherein the bimodally-acting opioid
agonist is selected from the group consisting of morphine, codeine,
fentanyl analogs, pentazocine, methadone, buprenorphine,
enkephalins, dynorphins, endorphins and similarly acting opioid
alkaloids and opioid peptides.
27. The composition of claim 26 wherein the bimodally-acting opioid
agonist is morphine.
28. The composition of claim 26 wherein the bimodally-acting opioid
agonist is codeine.
29. The composition of claim 26 wherein the bimodally-acting opioid
agonist is methadone.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of copending application Ser.
No. 08/276,966, filed Jul. 19, 1994, which is a
continuation-in-part of application Ser. No. 08/097,460, filed Jul.
27, 1993, currently pending, which is a continuation-in-part of
application Ser. No. 07/947,690, filed Sep. 19, 1992, now
abandoned, the contents of which are hereby incorporated by
reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a method of enhancing the
analgesic (inhibitory) effects of bimodally-acting opioid agonists,
including morphine, codeine and other clinically used opioid
analgesics, while at the same time attenuating anti-analgesia,
physical dependence, tolerance, hyperexcitability, hyperalgesia,
and other undesirable (excitatory) side effects typically caused by
chronic use of bimodally-acting opioid agonists.
[0003] "Bimodally-acting opioid agonists" are opioid agonists that
bind to and activate both inhibitory and excitatory opioid
receptors on nociceptive neurons which mediate pain. Opioid
analgesia results from activation by opioid agonists of inhibitory
opioid receptors on neurons in the nociceptive (pain) pathways of
the peripheral and central nervous systems. The undesirable side
effects, including anti-analgesic actions, hyperexcitability and
hyperalgesia, the development of physical dependence, and some
types of tolerance result from sustained activation by
bimodally-acting opioid agonists of excitatory opioid receptors on
neurons in the nociceptive (pain) pathways of the peripheral and
central nervous systems.
[0004] In the instant invention, a very low dose of a selective
excitatory opioid receptor antagonist, an opioid which binds to and
acts as an antagonist to excitatory but not inhibitory opioid
receptors on nociceptive neurons which mediate pain, is combined
with a dose of a bimodally-acting opioid agonist so as to enhance
the degree of analgesia (inhibitory effects) and attenuate the
undesired side effects (excitatory effects).
BACKGROUND OF THE INVENTION
[0005] Morphine or other bimodally-acting opioid agonists are
administered to relieve severe pain due to the fact that they have
analgesic effects mediated by their activation of inhibitory opioid
receptors on nociceptive neurons (see North, Trends Neurosci., Vol.
9, pp. 114-117 (1986) and Crain and Shen, Trends Pharmacol. Sci.,
Vol. 11, pp. 77-81 (1990)).
[0006] However, morphine and other bimodally-acting opioid agonists
also activate opioid excitatory receptors on nociceptive neurons,
which attenuate the analgesic potency of the opioids and result in
the development of physical dependence and increased tolerance (see
Shen and Crain, Brain Res., Vol. 597, pp. 74-83 (1992)), as well as
hyperexcitability, hyperalgesia and other undesirable (excitatory)
side effects. As a result, a long-standing need has existed to
develop a method of both enhancing the analgesic (inhibitory)
effects of bimodally-acting opioid agonists and blocking or
preventing undesirable (excitatory) side effects caused by such
opioid agonists. The present invention satisfies this need.
SUMMARY OF THE INVENTION
[0007] This present invention is directed to a method for
selectively enhancing the analgesic potency of a bimodally-acting
opioid agonist and simultaneously attenuating anti-analgesia,
hyperalgesia, hyperexcitability, physical dependence and/or
tolerance effects associated with the administration of the
bimodally-acting opioid agonist. The method comprises administering
to a subject an analgesic or sub-analgesic amount of a
bimodally-acting opioid agonist and an amount of an excitatory
opioid receptor antagonist effective to enhance the analgesic
potency of the bimodally-acting opioid agonist and attenuate the
anti-analgesia, hyperalgesia, hyperexcitability, physical
dependence and/or tolerance effects of the bimodally-acting opioid
agonist.
[0008] The present invention also provides a method for treating
pain in a subject comprising administering to the subject an
analgesic or sub-analgesic amount of a bimodally-acting opioid
agonist and an amount of an excitatory opioid receptor antagonist
effective to enhance the analgesic potency of the bimodally-acting
opioid agonist and attenuate anti-analgesia, hyperalgesia,
hyperexcitability, physical dependence and/or tolerance effects of
the bimodally-acting opioid agonist.
[0009] The present invention further provides a method for treating
an opiate addict comprising administering to the opiate addict an
amount of an excitatory opioid receptor antagonist either alone or
in combination with a bimodally-acting opioid agonist effective to
attenuate physical dependence caused by a bimodally-acting opioid
agonist and enhance the analgesic potency of a bimodally-acting
opioid agonist.
[0010] Finally, the present invention provides a composition
comprising an analgesic or sub-analgesic amount of a
bimodally-acting opioid agonist and an amount of an excitatory
opioid receptor antagonist effective to enhance the analgesic
potency of the bimodally-acting opioid agonist and attenuate the
anti-analgesia, hyperalgesia, hyperexcitability, physical
dependence and/or tolerance effects of the bimodally-acting opioid
agonist in a subject administered the composition.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 represents the structural formulae of the
bimodally-acting opioid agonist morphine and the excitatory opioid
receptor antagonists naloxone, naltrexone and nalmefene. Naltrexone
is the N-cyclopropylmethyl congener of naloxone. Nalmefene is the
6-methylene derivative of naltrexone (Hahn, E. F., et al. J. Med.
Chem. 18:259-262 (1975)).
[0012] FIG. 2 represents the direct inhibitory effect of etorphine
on the action potential duration (APD) of nociceptive types of
sensory neurons and the blocking effect of etorphine on the
excitatory response (APD prolongation) elicited by morphine. Acute
application of low (pM-nM) concentrations of etorphine to naive
dorsal root ganglion (DRG) neurons elicits dose-dependent,
naloxone-reversible inhibitory shortening of the APD. In contrast,
morphine and other bimodally-acting opioid agonists elicit
excitatory APD prolongation at these low concentrations which can
be selectively blocked by <pM levels of etorphine, resulting in
unmasking of potent inhibitory APD shortening by nM morphine.
[0013] FIG. 3 represents dose-response curves of different opioids,
showing that etorphine and dihydroetorphine elicit only inhibitory
dose-dependent shortening of the APD of DRG neurons at all
concentrations tested (fM-.mu.M). In contrast, dynorphin A (as well
as morphine and other bimodally-acting opioids) elicit
dose-dependent excitatory APD prolongation at low concentrations
(fM-nM) and requires much higher concentrations (about 0.1-1 .mu.M)
to shorten the APD, thereby resulting in a bell-shaped,
dose-response curve.
[0014] FIGS. 4A and 4B represent the selective blocking of
excitatory APD-prolonging effects elicited by morphine in DRG
neurons by co-administration of a low (pM) concentration of
diprenorphine, thereby unmasking potent dose-dependent inhibitory
APD shortening by low concentrations of morphine (comparable to the
inhibitory potency of etorphine). In contrast, co-treatment with a
higher (nM) concentration of DPN blocks both inhibitory as well as
excitatory opioid effects.
[0015] FIG. 5 represents similar selective blocking of excitatory
APD-prolonging effects elicited by morphine in DRG neurons when
co-administered with a low (pM) concentration of naltrexone,
thereby unmasking potent inhibitory APD shortening by low
concentrations of morphine. In contrast, a higher (.mu.M)
concentration of naltrexone blocks both inhibitory as well as
excitatory opioid effects.
[0016] FIG. 6 represents the assay procedure used to demonstrate
that selective antagonists at excitatory opioid receptors prevents
development of tolerance/dependence during chronic co-treatment of
DRG neurons with morphine.
[0017] FIG. 7 represents a comparison of the antinociceptive
potency of .sup.-1 mg/kg morphine administered (i.p.) to mice
alone, 10 ng/kg naltrexone administered (i.p.) to mice alone, and a
combination of 1 mg/kg morphine and 10 ng/kg naltrexone
administered (i.p.) to mice. Shown are the time-response curves for
1 mg/kg morphine (x); 1 mg/kg morphine and 10 ng/kg naltrexone
(NTX) (.quadrature.); 10 ng/kg naltrexone (.box-solid.), in a
warm-water (55.degree. C.) tail-flick test. Twenty-five mice were
used per dosing group (10 animals for NTX alone). Injection of 10
ng of NTX per kg alone did not elicit analgesic effects. **,
Statistically significant difference between individual morphine
vs. morphine plus naltrexone time points: P<0.01.
[0018] FIG. 8 represents a comparison of the percentage of mice
showing naloxone-precipitated withdrawal jumping (i) 3-4 hours
after injection with morphine alone (100 mg/kg, s.c.), and morphine
(100 mg/kg, s.c.) plus naltrexone (10 .mu.g/kg, s.c.) (acute
physical dependence assay); and (ii) 4 days after increasing daily
injections with morphine alone (20-50 mg/kg, s.c.), and morphine
(20-50 mg/kg, s.c.) plus naltrexone (10 Ag/kg, s.c.) (chronic
physical dependence assay). **, Statistically significant
difference from control morphine alone group: P<0.01; **,
P<0.001.
[0019] FIG. 9 represents a comparison of the antinociceptive
potency of morphine administered (i.p.) to mice alone, and morphine
administered (i.p.) to mice in combination with various ultra-low
doses of nalmefene (NMF). Shown are the time-response curves for 3
mg/kg morphine (); 3 mg/kg morphine and 100 ng/kg nalmefene
(.quadrature.); 3 mg/kg morphine and 10 ng/kg nalmefene (x); and 3
mg/kg morphine and 1 ng/kg nalmefene (.diamond.) in a warm-water
(55.degree. C.) tail-flick test. Ten mice were used per dosing
group.
[0020] FIG. 10 represents a comparison of the percentage of mice
showing naloxone-precipitated withdrawal jumping 4 hours after
injection (acute physical dependence assay) with a 100 mg/kg (s.c.)
dose of morphine (Mor) alone or in combination with 1 or 10
.mu.g/kg (s.c.) dose of nalmefene (NMF) or 10 .mu.g/kg (s.c.) dose
of naltrexone (NTX). Additional injections of nalmefene (1 or 10
.mu.g/kg, s.c.) or naltrexone (10 .mu.g/kg, s.c.) were made 90
minutes after the initial injections. **, Statistically significant
difference from control morphine alone group: P<0.01; ***,
P<0.001.
DETAILED DESCRIPTION OF THE INVENTION
[0021] As used herein, the term "opioid" refers to compounds which
bind to specific opioid receptors and have agonist (activation) or
antagonist (inactivation) effects at these receptors, such as
opioid alkaloids, including the agonist morphine and the antagonist
naloxone, and opioid peptides, including enkephalins, dynorphins
and endorphins. The term "opiate" refers to drugs derived from
opium or related analogs.
[0022] "Bimodally-acting opioid agonists" are opioid agonists that
bind to and activate both inhibitory and excitatory opioid
receptors on nociceptive neurons which mediate pain. Activation of
inhibitory receptors by said agonists causes analgesia. Activation
of excitatory receptors by said agonists results in anti-analgesia,
hyperexcitability, hyperalgesia, as well as development of physical
dependence, tolerance and other undesirable side effects.
[0023] Bimodally-acting opioid agonists suitable for use in the
present invention may be identified by measuring the opioid's
effect on the action potential duration (APD) of dorsal root
ganglion (DRG) neurons in tissue cultures. In this regard,
bimodally-acting opioid agonists are compounds which elicit
prolongation of the APD of DRG neurons at pM-nM concentrations
(i.e. excitatory effects), and shortening of the APD of DRG neurons
at .mu.M concentrations (i.e. inhibitory effects). Suitable
bimodally-acting opioid agonists include but are not limited to
morphine, codeine, fentanyl analogs, pentazocine, buprenorphine,
methadone, enkephalins, dynorphins, endorphins and similarly acting
opioid alkaloids and opioid peptides. For purposes of treating
pain, morphine and codeine are preferred. Buprenorphine and
methadone are preferred for treating opioid addiction.
[0024] "Excitatory opioid receptor antagonists" are opioids which
bind to and act as antagonists to excitatory but not inhibitory
opioid receptors on nociceptive neurons which mediate pain. That
is, excitatory opioid receptor antagonists are compounds which bind
to excitatory opioid receptors and selectively block excitatory
opioid receptor functions of nociceptive types of DRG neurons at
1,000 to 10,000-fold lower concentrations than are required to
block inhibitory opioid receptor functions in these neurons.
[0025] Excitatory opioid receptor antagonists suitable for use in
the present invention may also be identified by measuring their
effect on the action potential duration (APD) of dorsal root
ganglion (DRG) neurons in tissue cultures. In this regard,
excitatory opioid receptor antagonists are compounds which
selectively block prolongation of the APD of DRG neurons (i.e.
excitatory effects) but not the shortening of the APD of DRG
neurons (i.e. inhibitory effects) elicited by a bimodally-acting
opioid receptor agonist. Suitable excitatory opioid receptor
antagonists of the invention include nalmefene, naltrexone,
naloxone, etorphine and dihydroetorphine, as well as similarly
acting opioid alkaloids and opioid peptides. Preferred excitatory
opioid receptor antagonists are nalmefene and naltrexone because of
their longer duration of action as compared to naloxone and their
greater bioavailability after oral administration.
[0026] The bimodally-acting opioid agonists and the excitatory
opioid receptor antagonists for use in the present invention may in
the form of free bases or pharmaceutically acceptable acid addition
salts thereof. Examples of suitable acids for salt formation
include but are not limited to methanesulfonic, sulfuric,
hydrochloric, glucuronic, phosphoric, acetic, citric, lactic,
ascorbic, maleic, and the like.
[0027] The excitatory opioid receptor antagonist alone, or in
combination with the bimodally-acting opioid agonist, may be
administered to a human or animal subject by known procedures
including but not limited to oral, sublingual, intramuscular,
subcutaneous, intravenous, and transdermal modes of administration.
When a combination of these compounds are administered, they may be
administered together in the same composition, or may be
administered in separate compositions. If the bimodally-acting
opioid agonist and the excitatory opioid receptor antagonist are
administered in separate compositions, they may be administered by
similar or different modes of administration, and may be
administered simultaneously with one another, or shortly before or
after the other.
[0028] The bimodally-acting opioid agonists and the excitatory
opioid receptor antagonists may be formulated in compositions with
a pharmaceutically acceptable carrier. The carrier must be
"acceptable" in the sense of being compatible with the other
ingredients of the formulation and not deleterious to the recipient
thereof. Examples of suitable pharmaceutical carriers include
lactose, sucrose, starch, talc, magnesium stearate, crystalline
cellulose, methyl cellulose, carboxymethyl cellulose, glycerin,
sodium alginate, gum arabic, powders, saline, water, among others.
The formulations may conveniently be presented in unit dosage and
may be prepared by methods well-known in the pharmaceutical art, by
bringing the active compound into association with a carrier or
diluent, as a suspension or solution, and optionally one or more
accessory ingredients, e.g. buffers, flavoring agents, surface
active agents, and the like. The choice of carrier will depend upon
the route of administration.
[0029] For oral and sublingual administration, the formulation may
be presented as capsules, tablets, powders, granules or a
suspension, with conventional additives such as lactose, mannitol,
corn starch or potato starch; with binders such as crystalline
cellulose, cellulose derivatives, acacia, corn starch or gelatins;
with disintegrators such as corn starch, potato starch or sodium
carboxymethyl-cellulose; and with lubricants such as talc or
magnesium stearate.
[0030] For intravenous, intramuscular, or subcutaneous
administration, the compounds may combined with a sterile aqueous
solution which is preferably isotonic with the blood of the
recipient. Such formulations may be prepared by dissolving solid
active ingredient in water containing physiologically compatible
substances such as sodium chloride, glycine, and the like, and
having a buffered pH compatible with physiological conditions to
produce an aqueous solution, and rendering said solution sterile.
The formulations may be present in unit or multi-dose containers
such as sealed ampoules or vials.
[0031] For transdermal administration, the compounds may be
combined with skin penetration enhancers such as propylene glycol,
polyethylene glycol, isopropanol, ethanol, oleic acid,
N-methylpyrrolidone, and the like, which increase the permeability
of the skin to the compounds, and permit the compounds to penetrate
through the skin and into the bloodstream. The compound/enhancer
compositions also may be combined additionally with a polymeric
substance such as ethylcellulose, hydroxypropyl cellulose,
ethylene/vinylacetate, polyvinyl pyrrolidone, and the like, to
provide the composition in gel form, which can be dissolved in
solvent such as methylene chloride, evaporated to the desired
viscosity, and then applied to backing material to provide a
patch.
[0032] When the excitatory opioid receptor antagonist is used in
combination with the bimodally-acting opioid agonist, the amount of
the bimodally-acting opioid agonist administered may be an
analgesic or sub-analgesic amount. As used herein, an "analgesic"
amount is amount of the bimodally-acting opioid agonist which
causes analgesia in a subject administered the bimodally-acting
opioid agonist alone, and includes standard doses of the agonist
which are typically administered to cause analgesia (e.g, mg
doses). A "sub-analgesic" amount is an amount which does not cause
analgesia in a subject administered the bimodally-acting opioid
agonist alone, but when used in combination with the excitatory
opioid receptor antagonist, results in analgesia. The amount of the
excitatory opioid receptor antagonist is an amount effective to
enhance the analgesic potency of the bimodally-acting opioid
agonist and attenuate the anti-analgesia, hyperalgesia,
hyperexcitability, physical dependence and/or tolerance effects of
the bimodally-acting opioid agonist. Based on studies of
nociceptive DRG neurons in culture and in vivo mouse studies, the
amount of the excitatory opioid receptor administered may be
between about 1000 and about 10,000,000 fold less, and preferably
between about 10,000 and 1,000,000 fold less than the amount of the
bimodally-acting opioid agonist administered. The optimum amounts
of the bimodally-acting opioid agonist and the excitatory opioid
receptor antagonist administered will of course depend upon the
particular agonist and antagonist used, the carrier chosen, the
route of administration, and the pharmacokinetic properties of the
subject being treated.
[0033] When the excitatory opioid receptor antagonist is
administered alone (i.e. for treating an opioid addict), the amount
of the excitatory opioid receptor antagonist administered is an
amount effective to attenuate physical dependence caused by a
bimodally-acting opioid agonist such as morphine and enhance the
analgesic potency of the bimodally-acting opioid agonist. That is,
the amount of the excitatory opioid receptor antagonist is an
amount which blocks the excitatory effects (i.e. physical
dependence) of the bimodally-acting opioid agonist without blocking
the inhibitory effects (i.e. analgesic effects) of the
bimodally-acting opioid agonist. This amount is readily
determinable by one skilled in the art.
[0034] The present invention is described in the following examples
which are set forth to aid in the understanding of the invention,
and should not be construed to limit in any way the invention as
defined in the claims which follow thereafter.
EXAMPLE 1
Etorphine and Dihydroetorphine Act as Potent Selective Antagonists
at Excitatory Opioid Receptors on DRG Neurons Thereby Enhancing
Inhibitory Effects of Bimodally-Acting Opioid Agonists
[0035] Methods: The experiments described herein were carried out
on dorsal root ganglion (DRG) neurons in organotypic explants of
spinal cord with attached DRGs from 13-day-old fetal mice after 3
to 5 weeks of maturation in culture. The DRG-cord explants were
grown on collagen-coated coverslips in Maximow depression-slide
chambers. The culture medium consisted of 65% Eagle's minimal
essential medium, 25% fetal bovine serum, 10% chick embryo extract,
2 mM glutamine and 0.6% glucose. During the first week in vitro the
medium was supplemented with nerve growth factor (NGF-7S) at a
concentration of about 0.5 .mu.g/ml, to enhance survival and growth
of the fetal mouse DRG neurons.
[0036] In order to perform electrophysiologic procedures, the
culture coverslip was transferred to a recording chamber containing
about 1 ml of Hanks' balanced salt solution (BSS). The bath
solution was supplemented with 4 mM Ca.sup.2+ and 5 mM Ba.sup.2+
(i.e., Ca, Ba/BSS) to provide a prominent baseline response for
pharmacological tests. Intracellular recordings were obtained from
DRG perikarya selected at random within the ganglion. The
micropipettes were filled with 3 M KCl (having a resistance of
about 60-100 megohms) and were connected via a chloridized silver
wire to a neutralized input capacity preamplifier (Axoclamp 2A) for
current-clamp recording. After impalement of a DRG neuron, brief (2
msec) depolarizing current pulses were applied via the recording
electrode to evoke action potentials at a frequency of 0.1 Hz.
Recordings of the action potentials were stored on a floppy disc
using the P-clamp program (Axon Instruments) in a microcomputer
(IBM AT-compatible).
[0037] Drugs were applied by bath perfusion with a manually
operated, push-pull syringe system at a rate of 2-3 ml/min.
Perfusion of test agents was begun after the action potential and
the resting potential of the neuron reached a stable condition
during >4 minute pretest periods in control Ca, Ba/BSS.
Opioid-mediated changes in the APD were considered significant if
the APD alteration was >10% of the control value for the same
cell and was maintained for the entire test period of 5 minutes.
The APD was measured as the time between the peak of the APD and
the inflection point on the repolarizing phase. The following drugs
were used in this and the following Examples: etorphine,
diprenorphine and morphine (gifts from Dr. Eric Simon);
dihydroetorphine (gift from Dr. B.-Y. Qin, China and United
Biomedical, Inc.); naloxone (Endo Labs); naltrexone, DADLE,
dynorphin and other opioid peptides (Sigma).
[0038] Opioid alkaloids and peptides were generally prepared as 1
mM solutions in H.sub.2O and then carefully diluted with BSS to the
desired concentrations, systematically discarding pipette tips
after each successive 1-10 or 1-100 dilution step to ensure
accuracy of extremely low (fM-pM) concentrations.
[0039] Results: Intracellular recordings were made from small- and
medium-size DRG neuron perikarya (about 10-30 .mu.m in diameter)
which generate relatively long APDs (greater than 3 msec in Ca/Ba
BSS) and which show characteristic responsiveness to opioid
agonists and other properties of primary afferent nociceptive
neurons as occur in vivo. Acute application of selective inhibitory
opioid receptor agonists, e.g., etorphine, to these DRG neurons
shortens the APD in 80-90% of the cells tested, whereas low
concentrations of bimodally-acting (excitatory/inhibitory) opioids,
e.g., morphine, dynorphin, enkephalins, prolong the APD in these
same cells. Relatively small numbers of large DRG neurons (about
30-50 .mu.m in diameter) survive in DRG-cord explants (about
10-20%) and show much shorter APDs (about 1-2 msec in Ca/Ba BSS),
with no clear-cut inflection or "hump" on the falling phase of the
spike. The APD of these large DRG neurons is not altered by
exogenous opioids.
[0040] The opioid responsiveness of DRG neurons was analyzed by
measuring the opioid-induced alterations in the APD of DRG
perikarya. A total of 64 DRG neurons (from 23 DRG-cord explants)
were studied for sensitivity to progressive increases in the
concentration of etorphine (n=30) or dihydroetorphine (n=38).
Etorphine rapidly and dose-dependently shortened the APD in
progressively larger fractions of DRG cells at concentrations from
1 fM (30% of cells; n=26) to 1 uM (80% of cells; n=16) (see FIGS. 2
and 3).
[0041] FIG. 2 shows that acute application of low (pM-nM)
concentrations of etorphine to naive DRG neurons elicits
dose-dependent, naloxone-reversible inhibitory shortening of the
action potential duration (APD). In contrast, dynorphin (and many
other bimodally-acting opioid agonists, e.g., morphine, DADLE)
elicit excitatory APD prolongation at these low concentrations (see
FIG. 3), which can be selectively blocked by <pM levels of
etorphine, as well as by diprenorphine or naltrexone (see FIGS. 4
and 5). FIG. 2A record 1 shows the action potential (AP) generated
by a DRG neuron in balanced salt solution containing 5 mM Ca.sup.2+
and 5 mM Ba.sup.2+ (BSS). AP response in this record (and in all
records below) is evoked by-a brief (2 msec) intracellular
depolarizing current pulse. FIG. 2A records 2-5 show that APD is
not altered by bath perfusion with 1 fM etorphine (Et) but is
progressively shortened in 1 pM, 1 nM and 1 .mu.M concentrations (5
minute test periods). FIG. 2A record 6 shows that APD returns to
control value after transfer to BSS (9 minute test). FIG. 2B
records 1 and 2 show that APD of another DRG neuron is shortened by
application of 1 nM etorphine (2 minute test). FIG. 2B record 3
shows that APD returns to control value after transfer to 10 nM
naloxone (NLX). FIG. 2B records 4 and 5 show that APD is no longer
shortened by 1 nM or even 1 .mu.M etorphine when co-perfused with
10 nM naloxone (5 minute test periods).
[0042] FIG. 2C records 1 and 2 show that APD of another DRG neuron
is prolonged by application of 3 nM morphine. FIG. 2C record 3
shows that APD returns to control value by 5 minutes after washout.
FIG. 2C record 4 shows that application of 1 pM etorphine does not
alter the APD. FIG. 2C record 5 shows that APD is no longer
prolonged by 3 nM morphine when co-perfused with 1 pM etorphine and
instead is markedly shortened to a degree which would require a
much higher morphine concentration in the absence of etorphine.
Similar. results were obtained by pretreatment with 1 pM
diprenorphine (see FIG. 4), with 1 pM naltrexone (FIG. 5) or 1 pM
naloxone. Records in this and subsequent Figures are from DRG
neurons in organotypic DRG-spinal cord explants maintained for 3-4
weeks in culture.
[0043] FIG. 3 shows dose-response curves demonstrating that
etorphine (Et) (.quadrature.) and dihydroetorphine (DHE)
(.diamond.) elicit only inhibitory dose-dependent shortening of the
APD of DRG neurons at all concentrations tested (fM-.mu.M). In
contrast, dynorphin A (1-13) (Dyn) (X) (as well as morphine and
other bimodally-acting opioids) elicits dose-dependent excitatory
APD prolongation at low concentrations (fM-nM) and generally
requires much higher concentrations (about 0.1-1 .mu.M) to shorten
the APD, thereby resulting in a bell-shaped dose-response curve.
Data were obtained from 11 neurons for the etorphine tests, 13 for
the DHE tests and 35 for the dynorphin tests; 5, 8 and 9 neurons
were tested (as in FIG. 2) with all four concentrations of
etorphine, DHE and dynorphin, respectively (from fM to .mu.M). For
sequential dose-response data on the same neuron, the lowest
concentrations (e.g., 1 fM) were applied first.
[0044] Dihydroetorphine was even more effective (n=38; FIG. 3).
Naloxone (10 nM) prevented the etorphine- and
dihydroetorphine-induced APD shortening which was previously
elicited in the same cells (n=12; FIG. 2B). These potent inhibitory
effects of etorphine and dihydroetorphine on DRG neurons at low
concentrations are in sharp contrast to the excitatory
APD-prolonging effects observed in similar tests with morphine and
a wide variety of mu, delta and kappa opioids. None of the DRG
neurons tested with different concentrations of etorphine or
dihydroetorphine showed prominent APD prolongation.
[0045] The absence of excitatory APD-prolonging effects of
etorphine and dihydroetorphine on DRG neurons could be due to low
binding affinity of these opioid agonists to excitatory opioid
receptors. Alternatively, these opioids might bind strongly to
excitatory receptors, but fail to activate them, thereby
functioning as antagonists. In order to distinguish between these
two modes of action, DRG neurons were pretreated with etorphine at
low concentrations (fM-pM) that evoked little or no alteration of
the APD. Subsequent addition of nM concentrations of morphine,
DAGO, DADLE or dynorphin to etorphine-treated cells no longer
evoked the usual APD prolongation observed in the same cells prior
to exposure to etorphine (n=11; see FIG. 2C). This
etorphine-induced blockade of opioid excitatory effects on DRG
neurons was often effective for periods up to 0.5-2 hours after
washout (n=4).
[0046] These results demonstrate that etorphine, which has been
considered to be a "universal" agonist at mu, delta and kappa
opioid receptors (see Magnan et al., Naunyn-Schmiedeberg's Arch.
Pharmacol., Vol. 319, pp. 197-205 (1982)), has potent antagonist
actions at mu, delta and kappa excitatory opioid receptors on DRG
neurons, in addition to its well-known agonist effects at
inhibitory opioid receptors. Pretreatment with dihydroetorphine
(fM-pM) showed similar antagonist action at excitatory opioid
receptor mediating nM opioid-induced APD prolongation (n=2).
Furthermore, after selective blockade of opioid excitatory
APD-prolonging effects by pretreating DRG neurons with low
concentrations of etorphine (fM-pM), which showed little or no
alteration of the APD, fM-nM levels of bimodally-acting opioids now
showed potent inhibitory APD-shortening effects (5 out of 9 cells)
(see FIG. 2C and FIG. 4). This is presumably due to unmasking of
inhibitory opioid receptor-mediated functions in these cells after
selective blockade of their excitatory opioid receptor functions by
etorphine.
EXAMPLE 2
Diprenorphine, Naloxone and Naltrexone, at Low Concentrations, Also
Show Potent Selective Antagonist Action at Excitatory Opioid
Receptors
[0047] Drug tests: Mouse DRG-cord explants, grown for >3 weeks
as described in Example 1, were tested with the opioid antagonists
diprenorphine, naltrexone and naloxone. Electrophysiological
recordings were made as in Example 1.
[0048] Results: The opioid receptor antagonists naloxone and
diprenorphine were previously shown to block, at nM concentrations,
both inhibitory APD shortening of DRG neurons by .mu.M opioid
agonists as well as excitatory APD prolongation by nM opioids.
Tests at lower concentrations have revealed that pM diprenorphine,
as well as pM naloxone or naltrexone, act selectively as
antagonists at mu, delta and kappa excitatory opioid receptors,
comparable to the antagonist effects of pM etorphine and
dihydroetorphine. In the presence of pM diprenorphine, morphine
(n=7) and DAGO (n=7) no longer elicited APD prolongation at low
(pM-nM) concentrations (see FIG. 4A). Instead, they showed
progressive dose-dependent APD shortening throughout the entire
range of concentrations from fM to .mu.M (see FIG. 4B), comparable
to the dose-response curves for etorphine and dihydroetorphine (see
FIG. 3 and FIG. 2C). This unmasking of inhibitory opioid
receptor-mediated APD-shortening effects by pM diprenorphine
occurred even in the presence of 10-fold higher concentrations of
morphine (see FIG. 4A, records 11 vs. 5).
[0049] FIG. 4 shows that excitatory APD-prolonging effects elicited
by morphine in DRG neurons are selectively blocked by
co-administration of a low (pM) concentration of diprenorphine,
thereby unmasking potent dose-dependent inhibitory APD shortening
by low concentrations of morphine. FIG. 4A records 1-4 show that
APD of a DRG neuron is progressively prolonged by sequential bath
perfusions with 3 fM, 3 pM and 3 .mu.M morphine (Mor). FIG. 4A
record 5 shows that APD of this cell is only slightly shortened
after increasing morphine concentration to 3 pM. FIG. 4A records 6
and 7 show that after transfer to 355, the APD is slightly
shortened during pretreatment for 17 minutes with 1 pM
diprenorphine (DPN). FIG. 4A records 8-11 show that after the APD
reached a stable value in DPN, sequential applications of 3 fM, 3
pM, 3 nM and 3 .mu.M Mor progressively shorten the APD, in contrast
to the marked APD prolongation evoked by these same concentrations
of Mor in the absence of DPN (see also FIG. 2C). FIG. 4B
dose-response curves demonstrate similar unmasking by 1 pM DPN of
potent dose-dependent inhibitory APD shortening by morphine
(.quadrature.) in a group of DRG neurons (n=7), all of which showed
only excitatory APD prolongation responses when tested prior to
introduction of DPN (X). Note that the inhibitory potency of
morphine in the presence of pM DPN becomes comparable to that of
etorphine and dihydroetorphine (see FIG. 3). In contrast,
pretreatment with a higher (nM) concentration of DPN blocks both
inhibitory as well as excitatory effects of morphine ().
[0050] FIG. 5 shows that excitatory APD-prolonging effects elicited
by morphine in DRG neurons (O) are also selectively blocked by
co-administration of a low (pM) concentration of naltrexone (NTX),
thereby unmasking potent dose-dependent inhibitory APD shortening
by low concentrations or morphine (X). In contrast, pretreatment
with a higher (.mu.M) concentration of NTX blocks both inhibitory
as well as excitatory effects of morphine (.quadrature.) (similar
blockade occurs with 1 nM NTX). These dose-response curves are
based on data from 18 neurons, all of which showed only excitatory
APD prolongation responses when tested prior to introduction of
NTX. The inhibitory potency of morphine in the presence of pM NTX
becomes comparable to that of etorphine and dihydroetorphine (see
FIG. 3).
EXAMPLE 3
Chronic Co-treatment of DRG Neurons with Morphine and
Ultra-low-dose Naloxone or Naltrexone Prevents Development of
Opioid Excitatory Supersensitivity ("Dependence") and Tolerance
[0051] Co-administration of ultra-low (pM) concentrations of
naloxone or naltrexone during chronic treatment of DRG neurons with
.mu.M levels of morphine was effective in preventing development of
opioid excitatory supersensitivity and tolerance which generally
occurs after sustained exposure to bimodally-acting opioids. Acute
application of fM dynorphin A-(1-13) or fM morphine (n=21), as well
as 1 nM naloxone (n=11), to DRG neurons chronically exposed to 1
.mu.M morphine together with 1 pM naloxone or naloxone or
naltrexone (for 1-10 weeks) did not evoke the usual excitatory APD
prolongation observed in chronic morphine-treated cells tested
after washout with BSS (see FIG. 6). Furthermore, there was no
evidence of tolerance to the usual inhibitory effects of .mu.M
opioids (n=6) (FIG. 6).
[0052] These results are consonant with previous data that blockade
of sustained opioid excitatory effects by cholera toxin-B sub-unit
during chronic morphine treatment of DRG neurons prevents
development of tolerance and dependence. (See Shen and Crain, Brain
Res., Vol. 597, pp. 74-83 (1992)). This toxin sub-unit selectively
interferes with GM1 ganglioside regulation of excitatory opioid
receptor functions (see Shen and Crain, Brain Res., Vol. 531, pp.
1-7 (1990) and Shen et al., Brain Res., Vol. 559, pp. 130-138
(1991)).
[0053] Similarly, in the presence of pM etorphine, chronic .mu.M
morphine-treated DRG neurons did not develop signs of tolerance or
dependence. FIG. 6 outlines the assay procedure used for testing
the effectiveness of these and other antagonists at excitatory
opioid receptors in preventing development of tolerance/dependence
during chronic co-treatment of DRG neurons with morphine.
EXAMPLE 4
Excitatory Opioid Receptor Antagonists Enhance Analgesic Potency
and Reduce Dependence Liability and Other Side Effects of Morphine
when Administered in Combination with Morphine
[0054] Electrophysiological studies on DRG neurons in culture
indicated that pretreatment with low fM-pM concentrations of
naltrexone, naloxone, diprenorphine, etorphine or dihydroetorphine
is remarkably effective in blocking excitatory APD-prolonging
effects of morphine or other bimodally-acting opioid agonists by
selective antagonist actions at mu, delta and kappa excitatory
opioid receptors on these cells. In the presence of these selective
excitatory opioid receptor antagonists, morphine and other
clinically used bimodally-acting opioid agonists showed markedly
increased potency in evoking the inhibitory effects on the action
potential of sensory neurons which are generally considered to
underlie opioid analgesic action in vivo.
[0055] These bimodally-acting opioid agonists became effective in
shortening, instead of prolonging, the APD at pM-nM (i.e.,
10.sup.-12-10.sup.-9 M) concentrations, whereas 0.1-1 .mu.M (i.e.,
10.sup.-7-10.sup.-6 M) levels were generally required to shorten
the APD (FIGS. 4B and 5). Selective blockade of the excitatory side
effects of these bimodally-acting opioid agonists eliminates the
attenuation of their inhibitory effectiveness that would otherwise
occur. Hence, according to this invention, the combined use of a
relatively low dose of one of these selective excitatory opioid
receptor antagonists, together with morphine or other
bimodally-acting mu, delta or kappa opioid agonists, will markedly
enhance the analgesic potency of said opioid agonist, and render
said opioid agonist comparable in potency to etorphine or
dihydroetorphine, which, when used alone, are >1000 times more
potent than morphine in eliciting analgesia.
[0056] Co-administration of one of these excitatory opioid receptor
antagonists at low (pM) concentration (10.sup.-12 M) during chronic
treatment of sensory neurons with 10.sup.-6 M morphine or other
bimodally-acting opioid agonists (>1 week in culture) prevented
development of the opioid excitatory supersensitivity, including
naloxone-precipitated APD-prolongation, as well as the tolerance to
opioid inhibitory effects that generally occurs after chronic
opioid exposure. This experimental paradigm was previously utilized
by the inventors on sensory neurons in culture to demonstrate that
co-administration of 10.sup.-7 M cholera toxin-B sub-unit, which
binds selectively to GM1 ganglioside and thereby blocks excitatory
GM1-regulated opioid receptor-mediated effects, but not opioid
inhibitory effects (see Shen and Crain, Brain Res., Vol. 531, pp.
1-7 (1990)), during chronic opioid treatment prevents development
of these plastic changes in neuronal sensitivity that are
considered to be cellular manifestations related to opioid
dependence/addiction and tolerance in vivo (see Shen and Crain,
Brain Res., Vol. 597, pp. 74-83 (1992)).
EXAMPLE 5
Cotreatment of Mice with Morphine Plus Ultra Low Dose Naltrexone
Enhances opioid Antinociceptive Potency
[0057] Antinociceptive effects of opioids were measured using a
warm-water tail flick assay similar to methods described in Horan,
P. J., et al. J. Pharmacol. Exp. Ther. 264:1446-1454 (1993). In
this regard, each mouse was inserted into a plastic restraining
device that permitted the tail to be dipped into a water bath
maintained at 55.degree. C. The latency to a rapid tail flick was
recorded; mice with control latencies >5 seconds were excluded
from these tests and a 10 second cutoff was used to minimize tissue
damage. Six sequential control tests were made, each with a 10
minute interval. The latencies of the last four tests were averaged
to provide a control value. Percent antinociception was calculated
according to the formula: 100.times.[(test latency
control-latency)/10-control latency)]. Differences between
treatment groups were examined for statistical significance by
means of ANOVA with Neuman-Keuls tests.
[0058] Untreated mice showed tail-flick latencies of 2.15.+-.0.4
seconds (mean.+-.SD; n=58). Cotreatment of mice with 10 mg of
morphine per kg plus a 1000-fold lower dose of naltrexone (10
.mu.g/kg, i.p.) resulted in moderate attenuation and no significant
enhancement of the analgesic potency of morphine injected alone. In
contrast, cotreatment of mice with 1 mg of morphine per kg plus a
100,000 fold lower dose of naltrexone (10 ng/kg, i.p.) demonstrated
that in the presence of this extremely low dose of naltrexone, the
peak values of tail-flick latencies at 1 hour were maintained
during the subsequent hour, whereas the antinociceptive effects of
morphine alone rapidly decreased during this same period.
Furthermore, a remarkable degree of antinociception was maintained
for >1.5 hours after the effects of 1 mg of morphine per kg
alone were no longer detectable (n=25; FIG. 7). The marked
enhancement of the analgesic potency of morphine in mice during
cotreatment with 10 ng of naltrexone per kg is quite consonant with
the unmasking of potent inhibitory effects of 1 pM-1 nM morphine in
DRG neurons in vitro by cotreatment with 1 pM naltrexone.
EXAMPLE 6
Cotreatment of Mice with Morphine Plus Low-Dose Naltrexone
Attenuates Withdrawal Jumping Behavior
Acute Physical Dependence Assays
[0059] Acute physical dependence was assessed by recording
naloxone-precipitated withdrawal jumping behavior in mice that had
been injected 3-4 hours earlier with a 100 mg/kg (s.c.) dose of
morphine (Horan, P. J., et al. supra; Yano, I. and Takemori, A. E.
Res. Commun. Chem. Pathol. Pharmacol. 16:721-733 (1977); Sofuoglu,
M., et al. J. Pharmacol. Exp. Ther. 254:841-846 (1990),
administered alone or together with a low dose of naltrexone. Each
mouse was placed individually in a tall container and the number of
abrupt, stereotyped jumps was recorded during a 15 minute period
after administration of naloxone (10 mg/kg, i.p.). Differences
between treatment groups were examined for statistical significance
by means of X.sup.2 tests.
[0060] Three to four hours after the administration of a high dose
of morphine (100 mg/kg, s.c.), injection of naloxone (10 mg/kg,
i.p.) evoked characteristic withdrawal jumping behavior. About 67%
of these treated mice (n=30) showed 5-100 robust jumps during a 15
minute test period (n=30; FIG. 8), whereas jumping behavior was
observed in only 10-20% of untreated mice. On the other hand, after
cotreatment of mice with a 10,000-fold lower dose of naltrexone (10
.mu.g/kg) administered 15 minutes prior to and together with 100 mg
of morphine per kg, the incidence of naloxone-precipitated jumping
behavior was markedly reduced to only 23% of the treated animals
(n=30); FIG. 8). The mice were routinely pretreated with naltrexone
to ensure antagonist binding to excitatory opioid receptors prior
to their possible long-lasting activation by morphine. An
additional injection of naltrexone (10 .mu.g/kg, s.c.) was made 2
hours after administration of morphine plus naltrexone, because
this antagonist has been reported to have a much shorter duration
of action in mice, in contrast to humans.
[0061] Antinociceptive tail-flick tests on naive mice were made in
order to show that this effect of 10 .mu.g of naltrexone per kg was
mediated primarily by blocking excitatory, rather than inhibitory,
opioid receptor functions. Cotreatment of mice with 100 mg of
morphine per kg plus 10 .mu.g of naltrexone per kg (i.p.) did not
significantly attenuate the potent (supramaximal) analgesic effect
of 100 mg of morphine per kg injected alone. In both groups of
treated mice, tail-flick latencies rapidly increased to the peak
cutoff value of 10 seconds.
Chronic Physical Dependence and Tolerance Assays
[0062] Chronic physical dependence was assessed by similar
naloxone-precipitated withdrawal jumping behavior tests as
described above in mice that had been injected for four days (twice
daily) with increasing doses of morphine (20-50 mg/kg, s.c.), alone
or together with a low dose of naltrexone. On the fifth day, the
animals were primed with morphine (10 mg/kg) and challenged 1 hour
later with naloxone (10 mg/kg, i.p.), as in previous chronic
morphine-dependence assays (Sofuoglu, M., et al. J. Pharmacol. Exp.
Ther. 254:841-846 (1990); Brase, D. B., et al. J. Pharmacol. Exp.
Ther. 197:317-325 (1976); Way, E. L. and Loh, H. H. Ann. N.Y. Acad.
Sci. 281:252-261 (1976)). Differences between treatment groups were
examined for statistical significance by means of X.sup.2
tests.
[0063] About 60% of the treated mice showed stereotyped jumping as
observed in the acute dependence tests (n=30; FIG. 8). By contrast,
after cotreatment of mice with 10 .mu.g of naltrexone per kg (s.c.)
administered 15 minutes prior to and together with each of the
morphine injections indicated above, naloxone-precipitated jumping
occurred in only 13% of the mice (n=30; FIG. 8). Tail-flick assays
on naive mice showed that cotreatment with 20 mg of morphine per kg
plus 10 .mu.g of naltrexone per kg did not significantly attenuate
the analgesic effect of 20 mg of morphine per kg injected alone. In
similar- chronic cotreatment tests using a 10-fold lower dose of
naltrexone (1 .mu.g/kg), withdrawal jumping was still markedly
attenuated from 60% down to 30% of the mice (n=30; data not shown).
These results demonstrate that chronic cotreatment with morphine
plus 50,000- to 5,000-fold lower doses of naltrexone significantly
decreased development of physical dependence.
[0064] Tail-flick assays on some of these chronic cotreated mice at
1 day after drug withdrawal showed that opioid tolerance was also
partially attenuated. Acute injection of 1 mg of morphine per kg
resulted in a much larger degree of antinociception in chronic
morphine plus 10 ng of naltrexone per kg cotreated mice (15%.+-.3%,
n=10; time to peak effect at 30 minutes), as compared to chronic
morphine-treated mice (3%.+-.2% at 30 minutes, n=10; peak effect of
7%.+-.1$ at 60 minutes) (data not shown).
EXAMPLE 7
Cotreatment of Mice with Morphine Plus Low-Dose Nalmefene Enhances
Opioid Antinociceptive Potency
[0065] Mice were injected (i.p.) with 3 mg/kg morphine alone, and 3
mg/kg morphine in combination with 30,000-fold lower dose of
nalmefene (100 ng/kg, i.p.), 300,000-fold lower dose of nalmefene
(10 ng/kg, i.p.) and 3,000,000-fold lower dose of nalmefene (1
ng/kg, i.p.). Ten mice were used per dosing group. Antinociceptive
effects of opioids were measured using a warm-water tail flick
assay as described above. The results are presented in FIG. 9.
Co-treatment of mice with ultra-low doses of nalmefene (NLF)
enhances morphine's antinociceptive potency, in contrast to the
characteristic attenuation of morphine analgesia by higher doses of
nalmefene. Co-treatment with 1 ng/kg nalmefene was as effective as
10 ng/kg naltrexone in enhancing morphine antinociceptive potency
(compare FIGS. 7 and 9).
EXAMPLE 8
Cotreatment of Mice with Morphine Plus Low-Dose Nalmefene
Attenuates Withdrawal Jumping Behavior
Acute Physical Dependence Assays
[0066] Mice were injected with a 100 mg/kg (s.c.) dose of morphine,
administered either alone or in combination with 1 or 10 .mu.g/kg
(s.c.) dose of nalmefene or 10 .mu.g/kg (s.c.) dose of naltrexone
(as control), followed by additional injections of nalmefene (1 or
10 .mu.g/kg, s.c.) or naltrexone (10 .mu.g/kg, s.c.) 90 minutes
after the initial injections. Acute physical dependence was
assessed by recording naloxoneprecipitated withdrawal jumping
behavior in mice 4 hours after the initial injections. The results
are presented in FIG. 10. Co-treatment of mice for 4 hours with
morphine plus the low dose nalmefene (NLF; n=40) or naltrexone
(NTX; n=30) attenuates naloxone-precipitated withdrawal-jumping in
the acute physical dependence assays. These results demonstrate
that co-treatment with nalmefene is as effective as naltrexone in
attenuating morphine dependence liability. Tests with 1 .mu.g/kg
nalmefene (n=10) indicate that nalmefene may even be more effective
than naltrexone in attenuating morphine dependence liability.
[0067] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of various aspects of the
invention. Thus, it is to be understood that numerous modifications
may be made in the illustrative embodiments and other arrangements
may be devised without departing from the spirit and scope of the
invention.
* * * * *