U.S. patent application number 13/619238 was filed with the patent office on 2013-03-21 for stabilized mutant opsin proteins.
This patent application is currently assigned to Regents of the University of Minnesota. The applicant listed for this patent is Shalesh Kaushal, Vladimir Kuksa, Syed M. Noorwez, Krzysztof Palczewski. Invention is credited to Shalesh Kaushal, Vladimir Kuksa, Syed M. Noorwez, Krzysztof Palczewski.
Application Number | 20130072443 13/619238 |
Document ID | / |
Family ID | 33029969 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130072443 |
Kind Code |
A1 |
Palczewski; Krzysztof ; et
al. |
March 21, 2013 |
STABILIZED MUTANT OPSIN PROTEINS
Abstract
Methods and compositions for stabilizing opsin protein in a
vertebrate visual system are provided by administration of
opsin-binding synthetic retinoids.
Inventors: |
Palczewski; Krzysztof; (Bay
Village, OH) ; Kaushal; Shalesh; (Gainesville,
FL) ; Kuksa; Vladimir; (Seattle, WA) ;
Noorwez; Syed M.; (Gainesville, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Palczewski; Krzysztof
Kaushal; Shalesh
Kuksa; Vladimir
Noorwez; Syed M. |
Bay Village
Gainesville
Seattle
Gainesville |
OH
FL
WA
FL |
US
US
US
US |
|
|
Assignee: |
Regents of the University of
Minnesota
Minneapolis
MN
University of Washington
Seattle
WA
|
Family ID: |
33029969 |
Appl. No.: |
13/619238 |
Filed: |
September 14, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13217128 |
Aug 24, 2011 |
|
|
|
13619238 |
|
|
|
|
10801078 |
Mar 15, 2004 |
|
|
|
13217128 |
|
|
|
|
60455182 |
Mar 14, 2003 |
|
|
|
Current U.S.
Class: |
514/20.8 |
Current CPC
Class: |
A61K 31/435 20130101;
A61P 27/10 20180101; A61K 9/0048 20130101; A61K 31/695 20130101;
A61K 38/1709 20130101; A61P 27/02 20180101; Y10S 514/912 20130101;
A61K 31/07 20130101; A61K 31/382 20130101; A61K 31/11 20130101 |
Class at
Publication: |
514/20.8 |
International
Class: |
A61K 38/17 20060101
A61K038/17 |
Goverment Interests
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under grant
numbers EY008061 and EY009339 awarded by the National Institutes of
Health. The government has certain rights in the invention.
Claims
1-34. (canceled)
35. A method of treating retinitis pigmentosa due to mutant opsin,
comprising: administering an opsin-binding synthetic retinoid to an
eye of a human subject, wherein the eye of the human subject has a
mutant opsin protein and the opsin-binding synthetic retinoid binds
to and stabilizes the mutant opsin protein.
36. The method of claim 35, wherein the opsin-binding synthetic
retinoid is a synthetic cis retinoid.
37. The method of claim 35, wherein the opsin-binding synthetic
retinoid is a derivative of 11-cis retinal, a derivative of
9-cis-retinal or is 9-cis-retinal.
38. The method of claim 35, wherein the opsin-binding synthetic
retinoid is not 9-cis-retinal or 11-cis-retinal.
39. The method of claim 35, wherein the opsin-binding synthetic
retinoid is a synthetic 11-cis-retinal or 9-cis-retinal that has a
formula according to one of formulae I, II, III, IV, V, VI, VII,
VIII, IX, X, XI, XII, and XIII.
40. The method of claim 35, wherein the mutant opsin is a Class I,
Class II or Class III mutant.
41. The method of claim 35, wherein the mutant opsin comprises an
amino acid substitution, insertion or deletion in the
N-terminus.
42. The method of claim 41, wherein the mutant opsin comprises a
substitution of proline 23 by histidine.
43. The method of claim 35, wherein administering comprises
administering the opsin-binding synthetic retinoid in a
pharmaceutically acceptable vehicle.
44. The method of claim 35, wherein the opsin-binding synthetic
retinoid is administered orally or locally.
45. The method of claim 35, wherein the opsin-binding synthetic
retinoid is administered by eye drops, intraocular injection or
periocular injection.
46. A method of treating retinitis pigmentosa due to a mutant
opsin, comprising: administering an opsin-binding synthetic
retinoid to an eye of a human subject, wherein the eye of a human
subject has a mutant opsin protein and, wherein the opsin-binding
synthetic retinoid is a synthetic 11-cis-retinal or 9-cis-retinal
that has a formula according to one of formulae I, II, III, IV, V,
VI, VII, VIII, IX, X, XI, XII, and XIII and binds to and stabilizes
the mutant opsin protein.
47. The method of claim 46, wherein the opsin-binding synthetic
retinoid is not 9-cis-retinal or 11-cis-retinal.
48. A pharmaceutical ophthalmological composition for the use in
treating retinitis pigmentosa due to a mutant opsin protein of an
eye in a human subject, comprising: an opsin-binding synthetic
retinoid, wherein when the opsin-binding synthetic retinoid is
administered to the human subject it binds and stabilizes the
mutant opsin protein; and, a pharmaceutically acceptable
vehicle.
49. The pharmaceutical ophthalmological composition of claim 48,
wherein the composition is formulated for local administration to
the eye by eye drops or injection.
50. The pharmaceutical ophthalmological composition of claim 48,
wherein the composition is formulated for systemic administration
to the eye by oral dosage form or injection.
51. The pharmaceutical ophthalmological composition of claim 48,
wherein the composition further comprises isotonizing agents,
buffering agents, surfactants, stabilizing agents or
preservatives.
52. The pharmaceutical ophthalmological composition of claim 48,
wherein the composition is administered prophylactically.
53. The pharmaceutical ophthalmological composition of claim 48,
wherein the composition is administered therapeutically.
54. The method of claim 48, wherein the opsin-binding synthetic
retinoid is not 9-cis-retinal or 11-cis-retinal.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/217,128 filed Aug. 24, 2011, pending, which is a
continuation of U.S. application Ser. No. 10/801,078 filed Mar. 15,
2004, abandoned, which claims the benefit of U.S. Provisional
Patent Application No. 60/455,182, filed Mar. 14, 2003, the
disclosures of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0003] A diminished visual acuity or total loss of vision may
result from a number of eye diseases or disorders caused by
dysfunction of tissues or structures in the anterior region of the
eye and/or posterior region of the eye. The eye is divided
anatomically into an anterior and posterior segment. The anterior
segment includes the cornea, anterior chamber, iris and ciliary
body (anterior choroid), posterior chamber and crystalline lens.
The posterior segment includes the retina with optic nerve, choroid
(posterior choroid) and vitreous. The posterior portion of the
eyeball supports the retina, choroid and associated tissues.
[0004] Protein conformational disorders are a set of inherited
human diseases in which mutant proteins are misfolded. Protein
conformation disorders can affect proteins of the vertebrate visual
system and cause dysfunction of tissues or structures within the
eye. For example, misfolded proteins can aggregate, causing damage
within cells expressing the mutant protein. Certain types of
retinitis pigmentosa are associated with protein conformational
disorders. For example, many opsin mutants associated with
retinitis pigmentosa are misfolded and retained within the
cell.
[0005] Rhodopsin (Rh) is the visual pigment protein of the rod cell
and belongs to a large family of transmembrane G protein-coupled
receptors, which are involved in numerous physiological functions.
This superfamily of membrane glycoprotein receptors is
characterized by seven transmembrane .alpha.-helices that are
anchored within the lipid bilayer. Rhodopsin is composed of opsin,
the apoprotein, which is bound to chromophore. In contrast to other
G protein-coupled receptors, which respond to diffusible ligands,
rhodopsin responds to light. The chromophore in rhodopsin,
11-cis-retinal, is a covalently bound reverse agonist that yields a
distinct UV-visible spectrum with a max of approximately 500 nm.
Rhodopsin is approximately 40,000 daltons. The crystal structure of
rhodopsin has been previously elucidated.
[0006] In recent years, more than 100 opsin mutants have been
linked to various genetic forms of retinitis pigmentosa, the most
common form of hereditary retinal degeneration. Retinitis
pigmentosa leads to photoreceptor death and subsequent severe loss
of peripheral and night vision. These opsin mutants account for
nearly 50% of all the autosomal dominant retinitis pigmentosa cases
with the most common being a substitution of Proline 23 to
Histidine (P23H), which accounts for approximately 10% of all
retinitis pigmentosa cases.
[0007] Although opsin mutants display distinct biochemical
features, the mutant phenotypes fall mainly into three basic
classes. Class I mutants are expressed at nearly wild-type levels
and form stable pigment with 11-cis-retinal in the dark. The
associated amino acid substitutions cluster at the C terminus of
rhodopsin and disrupt vectorial transport to the rod outer segment.
Some mutants also inefficiently activate transducin. Class II
mutants do not bind 11-cis-retinal and are retained in the
endoplasmic reticulum. Class II mutants, like P23H, form small
amounts of pigment and mainly remain in the endoplasmic reticulum
or form aggresomes. These mutants are typically targeted for
degradation by the ubiquitin proteasome system Other phenotypic
properties associated with opsin amino acid substitutions may
include the destabilization of the structure formed within the rod
outer segment by mutated rhodopsin molecules or the disruption of
other biological processes unique to the rod outer segment.
[0008] Patients with the P23H substitution usually have milder
disease progression than those harboring other rhodopsin mutations.
Based on the crystal structure of rhodopsin. Proline 23 is located
in the N-terminal tail within one of the .beta.-strands that make
up an integral part of the N-terminal plug. The plug keeps the
chromophore in its proper position, and mutations within this
region result in improper folding of opsin and poor binding of the
chromophore. P23H-opsin forms the pigment poorly, does not acquire
the Golgi-related glycosylation, and is retained within the cell,
collectively providing evidence that it is misfolded.
[0009] There is currently no effective treatment for protein
conformational disorders of vertebrate visual systems. The present
invention satisfies this and other needs.
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention provides methods of restoring or
stabilizing photoreceptor function in a vertebrate visual system
comprising a mutant opsin protein. Mutant opsin proteins can be
stabilized by contacting the mutant protein with an opsin-binding
synthetic retinoid. The mutant opsin protein binds to the synthetic
retinoid, which stabilizes the mutant opsin protein and/or
ameliorates the effects of the mutant opsin protein on the
vertebrate visual system.
[0011] In one aspect, a method is provided for restoring
photoreceptor function in a vertebrate eye having a mutant opsin
protein. The method generally includes administering to the
vertebrate an effective amount of an opsin-binding synthetic
retinoid in a pharmaceutically acceptable vehicle. The
opsin-binding synthetic retinoid binds to and stabilizes the opsin
protein in the eye. The opsin-binding synthetic retinoid can be,
for example, an 11-cis-7-ring retinal, a 9-cis-7-ring retinal,
cycloheptatrienylidene 11-cis-locked retinal or
cycloheptatrienylidene 9-cis-locked retinal. The opsin-binding
synthetic retinoid also can be, for example, a synthetic retinoid
of formula I, II, IV, V, VI, VII, VIII, IX, X, XI, XII or XIII. In
another embodiment, the opsin-binding synthetic retinoid is a
9-cis-fused retinal. The mutant opsin protein can be, for example,
a Pro23His mutant opsin protein.
[0012] The opsin-binding synthetic retinoid can be locally
administered to the eye. For example, the opsin-binding synthetic
retinoid can be locally administered by eye drops, intraocular
injection or periocular injection. The opsin-binding synthetic
retinoid also can be orally administered to a subject comprising
the vertebrate eye.
[0013] In another aspect, a method is provided for stabilizing
mutant opsin protein. The method generally includes contacting the
mutant opsin protein with an opsin-binding synthetic retinoid for
an amount of time sufficient for the formation of a stabilized
opsin/synthetic retinoid complex. The opsin-binding synthetic
retinoid can be, for example, a synthetic retinoid of formula I,
II, III, IV, V, VI, VII, VIII, IX, X, XI, XII or XIII. In certain
embodiments, the opsin-binding synthetic retinoid is a 9-cis-locked
retinal, an 11-cis-locked retinal, an 11-cis-7-ring retinal or a
9-cis-ring retinal. In certain other embodiments, the opsin-binding
synthetic retinoid is cycloheptatrienylidene 11-cis-locked retinal
or cycloheptatrienylidene 9-cis-locked retinal. The mutant opsin
protein can be, for example, a Pro23His mutant opsin protein.
[0014] In yet another aspect, a method of ameliorating loss of
photoreceptor function in a vertebrate eye is provided. The method
generally includes prophylactically administering an effective
amount of an opsin-binding synthetic retinoid in a pharmaceutically
acceptable vehicle to a vertebrate eye comprising a mutant opsin
protein having a reduced affinity for 11-cis-retinal. The synthetic
retinoid binds to and stabilizes the mutant opsin protein.
[0015] The opsin-binding synthetic retinoid can be orally
administered to a vertebrate. The opsin-binding synthetic retinoid
also can be locally administered to the vertebrate eye.
[0016] The opsin-binding synthetic retinoid can be, for example, a
synthetic retinoid of formula I, II, III, IV, V, VI, VII, VIII, IX,
X, XI, XII or XIII. In certain embodiments, the opsin-binding
synthetic retinoid can be a 9-cis-7-ring retinal, an 11-cis-7-ring
retinal, cycloheptatrienylidene 11-cis-locked retinal or
cycloheptatrienylidene 9-cis-locked retinal. The mutant opsin
protein can, for example, have mutation (e.g., an amino acid
substitution, deletion, insertion, or the like) in the N-terminal
plug. For example, the mutant opsin protein can be a Pro23His
mutant opsin protein.
[0017] In yet another aspect, an ophthalmologic composition
including an opsin-binding synthetic retinoid in a pharmaceutically
acceptable vehicle is provided. The opsin-binding synthetic
retinoid can be, for example, a synthetic retinoid of formula I,
II, III, IV, V, VI VII, VIII, IX, X, XI, XII or XIII. The
opsin-binding synthetic retinoid can be, for example, a
9-cis-7-ring retinal, an 11-cis-7-ring retinal,
cycloheptatrienylidene 11-cis-locked retinal or
cycloheptatrienylidene 9-cis-locked retinal.
[0018] In a related aspect, an oral dosage form including an
opsin-binding synthetic retinoid in a pharmaceutically acceptable
vehicle is provided. The opsin-binding synthetic retinoid can be,
for example, a synthetic retinoid of formula I, II, III, IV, V, VI,
VII, VIII, IX, X, XI, XII or XIII. The opsin-binding synthetic
retinoid can be, for example, a 9-cis-7-ring retinal, an
11-cis-7-ring retinal, cycloheptatrienylidene 11-cis-locked retinal
or cycloheptatrienylidene 9-cis-locked retinal.
[0019] In yet another aspect, a method of identifying an
opsin-binding synthetic retinoid to stabilize a mutant opsin
protein is provided. The method generally includes providing an
expression system for the expression of a mutant opsin protein,
contacting the mutant opsin protein with a synthetic retinoid for a
time sufficient and in suitable conditions for the binding of the
synthetic retinoid by the mutant opsin protein; and detecting
whether the mutant opsin protein binds the synthetic retinoid to
form a stable mutant opsin protein/synthetic retinoid complex. The
expression system can be, for example, a eukaryotic cell line
expressing the mutant opsin protein. The synthetic retinoid can be,
for example, administered to cell culture media in which the
eukaryotic cell line is cultured. The opsin-binding synthetic
retinoid can be, for example, a synthetic retinoid of formula I,
II, III, IV, V, VI, VII, VIII, IX, X, XI, XII or XIII.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A-1B. Models of rhodopsin and structures of
7-locked-retinals, FIG. 1A, two-dimensional model of rhodopsin.
White letters on a black background indicate a mutation associated
with retinitis pigmentosa. Proline 23 is shown by a black
background and the designation "P23," FIG. 1B, chemical structures
of the four 11-cis-7-ring retinal isomers. Carbon atom numbering is
as accepted in retinoid nomenclature.
[0021] FIGS. 2A-2F. Pigment formation when the chromophores were
added to harvested cell membranes or provided during biosynthesis.
FIG. 2A, regeneration of wild-type rhodopsin in cell membranes with
11-cis-retinal, 11-cis-6-ring retinal, and 11-cis-7-ring retinal.
FIG. 2B, lack of regeneration of P23H-rhodopsin in cell membranes
with 11-cis-retinal, 11-cis-6-ring retinal, and 11-cis-7-ring
retinal. FIG. 2C, regeneration of wild-type rhodopsin with
11-cis-6-ring retinal, 11-cis-7-ring retinal, and 11-cis-retinal
when retinals were added during biosynthesis. FIG. 2D, regeneration
of P23H-rhodopsin with 11-cis-7-ring retinal and 11-cis-retinal,
but not with 11-cis-6-ring retinal, when retinals were added during
biosynthesis. Insets in FIGS. 2C and 2D, acid denaturation of
purified 7-rhodopsin and 11-cis-7-ring-P23H-rhodopsin,
respectively. FIG. 2E, elution of 7-rhodopsin at pH 6.0 and pH 7.0.
FIG. 2F, elution of 7-P23H-rhodopsin at pH 6.0 and 7.0.
[0022] FIGS. 3A-3D. Photosensitivity of 7-rhodopsin and
7-P23H-rhodopsin in detergent and in cell membrane. FIG. 3A,
purified 7-rhodopsin is stable to light in detergent. FIG. 3B,
purified 7-P23H-rhodopsin was bleached after 5 minutes of exposure
to light in detergent. FIGS. 3B, 3C and D, 7-rhodopsin and
7-P23H-rhodopsin in cell membranes were not bleached by light.
Insets, changes in absorption at 494 nm as a function of time.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides methods of restoring or
stabilizing photoreceptor function in a vertebrate visual system
having a mutant opsin protein. Mutant opsin proteins can be
stabilized by contacting the mutant protein with an opsin-binding
synthetic retinoid. The mutant opsin protein binds to the synthetic
retinoid, which stabilizes the mutant opsin protein and/or
ameliorates the effects of the mutant opsin protein on the
vertebrate visual system. An opsin-binding synthetic retinoid can
be administered prophylactically or therapeutically to a vertebrate
to prevent or reduce damage to the eye associated with the mutant
opsin protein. Suitable vertebrates include, for example, human and
non-human vertebrates. Suitable non-human vertebrates include, for
example, mammals, such as dogs, cats, horses and other domesticated
animals.
[0024] The mutant opsin protein has one or more amino acid
substitutions, deletions, insertions and/or other mutations that
affect nascent protein folding, stability, degradation,
localization, or the like. Mutant opsin proteins can be, for
example, a class I, class II or class III opsin mutant. Typically,
the mutant opsin protein exhibits reduced affinity for
11-cis-retinal and/or does not form a stable complex with
11-cis-retinal. In certain embodiments, the opsin mutant is a class
III mutant. The opsin mutant also can be, for example, associated
with a dominant retinitis pigmentosa condition. In additional
embodiments, the opsin mutant comprises an amino acid substitution,
insertion and/or deletion in the N-terminal plug of opsin, which
results in reduced affinity for 11-cis-retinal. In an exemplary
embodiment, the opsin mutant is a Pro23His mutant in human opsin.
In additional embodiments, the opsin mutant is a Phe45Leu mutant, a
Gly51Val mutant, a Gly51Arg mutant, a Leu125Arg mutant, a Gly114Val
mutant, a Gly114Asp mutant, an Ala164Glu mutant, or the like, in
human opsin.
[0025] The opsin-binding synthetic retinoids are retinals derived
from 11-cis-retinal or 9-cis-retinal, or are 9-cis-retinal. In
certain embodiments, the "synthetic retinoid" is a "synthetic cis
retinoid." Synthetic retinoids according to the present invention
can bind to an opsin mutant, and function as an chaperone, or opsin
agonist. As used herein, the term "chaperone" refers to a molecule
or compound that helps a nascent polypeptide chain fold into the
proper conformation, stabilizes the folding protein, protects the
nascent polypeptide from making premature or nonproductive
contacts, and/or protects the protein from improper
modification.
[0026] In certain additional embodiments, the synthetic retinoid
restores function (e.g., photoreception) to the mutant opsin when
it is part of an opsin/synthetic retinoid complex, whereby the
mutant opsin/synthetic retinoid complex can respond to photons.
[0027] Synthetic retinoids include 11-cis-retinal derivatives or
9-cis-retinal derivatives such as, for example, the following:
acyclic retinals; retinals with modified polyene chain length, such
as trienoic or tetraenoic retinals; retinals with substituted
polyene chains, such as alkyl, halogen or heteratom-substituted
polyene chains; retinals with modified polyene chains, such as
trans- or cis-locked polyene chains, or with, for example, allene,
alkane, alkene or alkyne modifications; and retinals with ring
modifications, such as heterocyclic, heteroaromatic or substituted
cycloalkane or cycloalkene rings.
[0028] In certain embodiments, the synthetic retinoid can be a
retinal of the following formula I:
##STR00001##
R and R1 can be independently selected from linear, iso-, sec-,
tert- and other branched alkyl groups as well as substituted alkyl
groups, substituted branched alkyl, hydroxyl, hydroalkyl, amine,
amide, or the like. R and R1 can independently be lower alkyl,
which means straight or branched alkyl with 1-6 carbon atom(s) such
as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl,
pentyl, hexyl, or the like. Suitable substituted alkyls and
substituted branch alkyls include, for example, alkyls, branched
alkyls and cyclo-alkyls substituted with oxygen, hydroxyl,
nitrogen, amide, amine, halogen, heteroatom or other groups.
Suitable heteroatoms include, for example, sulfur, silicon, and
fluoro- or bromo-substitutions.
[0029] In certain additional embodiments, R or R1 can be a
cyclo-alkyl such as, for example, hexane, cyclohexene, benzene as
well as substituted cyclo-alkyl. Suitable substituted cyclo alkyl
include, for example, cyclo-alkyls substituted with oxygen,
hydroxyl, nitrogen, amide, amine, halogen, heteroatom or other
groups. Suitable heteroatoms include, for example, sulfur, silicon,
and fluoro- or bromo-substitutions.
[0030] The synthetic retinoid also can be a derivative of an
11-cis-retinal or 9-cis-retinal that has a modified polyene chain
length of the following formula II:
##STR00002##
[0031] The polyene chain length can be extended by 1, 2, or 3
alkyl, alkene or alkylene groups. According to formula II, each n
and n.sub.1 can be independently selected from 1, 2, or 3 alkyl,
alkene or alkylene groups, with the proviso that the sum of the n
and n.sub.1 is at least 1.
[0032] The synthetic retinoid also can be a derivative of an
11-cis-retinal or 9-cis-retinal that has a substituted polyene
chain of the following formulas, respectively, IIIa and IIIb:
##STR00003##
[0033] Each of R1 to R9 can be independently selected from
hydrogen, alkyl, branched alkyl, cyclo-alkyl, halogen, a
heteroatom, hydroxyl, hydroxyalkyl, amine, amide, or the like.
Suitable alkyls include, for example, methyl, ethyl, propyl,
substituted alkyl (e.g., alkane with hydroxyl, hydroalkyl, amine,
amide) or the like. Suitable branched alkyl can be, for example,
isopropyl, isobutyl, substituted branched alkyl, or the like.
Suitable cyclo-alkyls can include, for example, cyclohexane,
cycloheptane, and other cyclic alkanes as well as substituted
cyclic alkanes sac substituted cyclohexane or substituted
cycloheptane. Suitable halogens include, for example, bromine,
chlorine, fluorine, or the like. Suitable heteroatoms include, for
example, sulfur, silicon, and fluoro- or bromo-substitutions.
Suitable substituted alkyls, substituted branch alkyls and
substituted cyclo-alkyls include, for example, alkyls, branched
alkyls and cyclo-alkyls substituted with oxygen, hydroxyl,
nitrogen, amide, amine, halogen, a heteroatom or other groups. In
exemplary embodiments, the synthetic retinoid is
9-ethyl-11-cis-retinal, 7-methyl-11-cis-retinal,
13-desmethyl-11-cis-retinal, 11-cis-10-F-retinal,
11-cis-10-Cl-retinal, 11-cis-10-methyl-retinal,
11-cis-10-ethyl-retinal, 9-cis-10-Cl-retinal,
9-cis-10-methyl-retinal, 9-cis-10-ethyl-retinal,
11-cis-12-F-retinal, 11-cis-12-Cl-retinal,
11-cis-12-methyl-retinal, 11-cis-10-ethyl-9-cis-12-F-retinal,
9-cis-12-methyl-retinal, 11-cis-14-F-retinal,
11-cis-14-methyl-retinal, 11-cis-14-ethyl-retinal,
9-cis-14-F-retinal, 9-cis-14-methyl-retinal,
9-cis-14-ethyl-retinal, or the like.
[0034] The synthetic retinoid further can be derivative of an
11-cis-retinal or 9-cis-retinal that has a modified ring structure.
Suitable examples include, for example, derivatives containing ring
modifications, aromatic analogs and heteroaromatic analogs of the
following formulae IV, V and VI, respectively:
##STR00004##
[0035] Each of R1 to R5 or R6, as applicable, can be independently
selected from hydrogen, alkyl, substituted alkyl, hydroxyl,
hydroalkyl, amine, amide, halogen, a heteratom, or the like,
Suitable alkyls include, for example, methyl, ethyl, propyl,
isopropyl, butyl, isobutyl or the like. Suitable halogens include,
for example, bromine, chlorine, fluorine, or the like. Suitable
heteroatoms include, for example, sulfur, silicon, or nitrogen. In
addition, X can be a heteroatoms, such as, for example, sulfur,
silicon, or nitrogen.
[0036] The synthetic retinoid can further be a derivative of an
11-cis-retinal or 9-cis-retinal that has a modified polyene chain.
Suitable derivatives include, for example, those with a trans/cis
locked configuration. 6s-locked analogs, as well as modified
allene, alkene, alkyne or alkylene groups in the polyene chain. In
one example, the derivative is an 11-cis-locked analog of the
following formula VII:
##STR00005##
[0037] R can be, for example, hydrogen, methyl or other lower
alkane or branched alkane, or a heteroatom. n can be 0 to 4. m plus
1 equals 1, 2 or 3.
[0038] In a specific embodiment, the synthetic retinoid is a
11-cis-locked analog of the following formula VIII:
##STR00006##
n can be 1 to 4.
[0039] In certain exemplary embodiments, the synthetic retinoid is
9,11,13-tri-cis-7-ring retinal, 11,13-cis-7-ring retinal,
11-cis-7-ring retinal or 9,11-di-cis-7-ring retinal.
[0040] In another example, the synthetic retinoid is a 6s-locked
analog of formula IX. R1 and R2 can be independently selected from
hydrogen, methyl and other lower alkyl and substituted lower alkyl.
R3 can be independently selected from an alkene group at either of
the indicated positions.
##STR00007##
[0041] In other embodiments, the synthetic retinoid can be a
9-cis-ring-fused derivative, such as, for example, those shown in
formulae X-XII.
[0042] In yet another embodiment, the synthetic retinoid is of the
following formula XIII.
##STR00008##
[0043] Each of R1 to R15 can be independently selected from
hydrogen, alkyl, branched alkyl, halogen, hydroxyl, hydroxyalkyl,
amine, amide, a heteroatom, or the like. Suitable alkyls include,
for example, methyl, ethyl, propyl, substituted alkyl (e.g., alkyl
with hydroxyl, hydroxyalkyl, amine, amide), or the like. Suitable
branched alkyl can be, for example, isopropyl, isobutyl,
substituted branched alkyl, or the like. Suitable halogens include,
for example, bromine, chlorine, fluorine, or the like. Suitable
heteroatoms include, for example, sulfur, silicon, and fluoro- or
bromo-substitutions. Suitable substituted alkyls and substituted
branch alkyls include, for example, alkyls and branched alkyls
substituted with oxygen, hydroxyl, nitrogen, amide, amine, halogen,
heteroatom or other groups. Each of n and n.sub.1 can be
independently selected from 1, 2, or 3 alkyl, alkene or alkylene
groups, with the proviso that the sum of the n and n.sub.1 is at
least 1. In addition, R11-R12 and/or R13-R14 can comprise an alkene
group in the cyclic carbon ring. In certain embodiments, R5 and R7
together can form a cyclo-alkyl, such as a five, six, seven or
eight member cyclo-alkyl or substituted cyclo-alkyl, such as, for
example, those shown in formulae VII, VIII, X, XI and XII.
[0044] In additional embodiments, the synthetic retinoid also can
be 9-cis-retinal. Alternatively, 11-cis-retinal can be used.
[0045] Methods of making synthetic retinoids are disclosed in, for
example, the following references: Anal. Biochem. 272:232-42
(1999); Angew. Chem. 36:2089-93 (1997); Biochemistry 14:3933-41
(1975); Biochemistry 21:384-93 (1982); Biochemistry 28:2732-39
(1989); Biochemistry 33:408-16 (1994); Biochemistry 35:6257-62
(1996); Bioorganic Chemistry 27:372-82 (1999); Biophys. Chem.
56:31-39 (1995); Biophys. 56:1259-65 (1989); Biophys. J. 83:3460-69
(2002); Chemistry 7:4198-204 (2001); Chemistry (Europe) 5:1172-75
(1999); FEBS 158:1 (1983); J. American Chem. Soc. 104:3214-16
(1982); J. Am. Chem. Soc. 108:6077-78 (1986): J. Am. Chem. Soc.
109:6163 (1987); J. Am. Chem. Soc. 112:7779-82 (1990); J. Am. Chem.
Soc. 119:5758-59 (1997); J. Am. Chem. Soc. 121:5803-04 (1999); J.
American Chem. Soc. 123:10024-29 (2001); J. American Chem. Soc.
124:7294-302 (2002); J. Biol. Chem. 276:26148-53 (2001); J. Biol.
Chem. 277:42315-24 (2004); J. Chem. Soc.-Perkin T. 1:1773-77
(1997); J. Chem. Soc.-Perkin T. 1:2430-39 (2001); J. Org. Chem.
49:649-52 (1984); J. Org. Chem. 58:3533-37 (1993); J. Physical
Chemistry B 102:2787-806 (1998); Lipids 8:558-65; Photochem.
Photobiol. 13:259-83 (1986); Photochem. Photobiol. 44:803-07
(1986); Photochem. Photobiol. 54:969-76 (1991); Photochem.
Photobiol. 60:64-68 (1994); Photochem. Photobiol. 65:1047-55
(1991); Photochem. Photobiol. 70:111-15 (2002); Photochem.
Photobiol. 76:606-615 (2002); Proc. Natl Acad. Sci. USA 88:9412-16
(1991); Proc. Natl Acad. Sci. USA 90:4072-76 (1993); Proc. Natl
Acad. Sci. USA 94:13442-47 (1997); and Proc. R. Soc. Lond. Series
B, Biol. Sci. 233(1270): 55-76 1988) (the disclosures of which are
incorporated by reference herein).
[0046] Opsin-binding synthetic retinoids can be identified by an
expression system expressing a mutant opsin protein. Suitable
expression systems can include, for example, in vitro or in vivo
systems. Suitable in vitro systems include for example, coupled
transcription-translation systems. Suitable in vivo systems
include, for example, animal models and cells expressing a mutant
opsin protein. For example, cells of a vertebrate visual system can
be adapted for culture in vitro, or recombinant cell lines
expressing an opsin protein can be used.
[0047] Suitable non-human animal models include rat, mouse, primate
systems. Such animal models can be prepared, for example, by
promoting homologous recombination between a nucleic acid encoding
an opsin in its chromosome and an exogenous nucleic acid encoding a
mutant opsin. In one aspect, homologous recombination is carried
out by transforming embryo-derived stem (ES) cells with a vector
containing an opsin gene, such that homologous recombination
occurs, followed by injecting the ES cells into a blastocyst, and
implanting the blastocyst into a foster mother, followed by the
birth of the chimeric animal (see, e.g., Capecchi, Science
244:1288-92 (1989)). The chimeric animal can be bred to produce
additional transgenic animals.
[0048] Also, recombinant cell lines expressing a mutant opsin
protein can be used. The cell lines are typically stable cell lines
expressing the mutant opsin protein. Synthetic retinoid can be
added to the cell culture media, and the cells are cultured for a
suitable period of time to allow the production of opsin/rhodopsin.
Opsin and/or rhodopsin can be isolated (e.g., by immunoaffinity).
Isolated protein samples are examined to determine the amount of
pigment formed, and absorbance maxima.
[0049] Recombinant cell lines expressing mutant opsin protein can
be prepared by, for example, introducing an expression construct
encoding a mutant opsin protein into a suitable cell line. Methods
of introducing nucleic acids into vertebrate cells are disclosed
in, for example, Sambrook et al., Molecular Cloning: A Laboratory
Manual, Cold Spring Harbor Laboratory Press (Cold Spring Harbor,
N.Y., 2001) (the disclosure of which is incorporated by reference
herein). The expression construct typically includes a promoter
operably linked to a nucleic acid encoding a mutant opsin protein,
and optionally a termination signal(s). Nucleic acids encoding
opsin can be obtained, for example, by using information from a
database (e.g., a genomic or cDNA library), by polymerase chain
reaction, or the like. For example opsin encoding nucleic acids can
be obtained by hybridization. (See generally Sambrook et al.
(supra).) In a specific embodiment, an opsin encoding nucleic acid
can be obtained by hybridization under conditions of low, medium or
high stringency.
[0050] In certain embodiments, opsin encoding nucleic acids can be
obtained under conditions of high stringency hybridization. By way
of example, and not limitation, procedures using conditions of high
stringency are as follows: Prehybridization of filters containing
DNA is carried out for 8 hours to overnight at 65.degree. C. in
buffer composed of 6.times.SSC, 50 mM Tris-HCl (pH 7.5), 1 mM EDTA,
0.02% PVP, 0.02% Ficoll, 0.02% BSA, and 500 .mu.g/ml denatured
salmon sperm DNA. Filters are hybridized for 48 hours at 65.degree.
C. in prehybridization mixture containing 100 .mu.g/ml denatured
salmon sperm DNA and 5-20.times.10.sup.6 cpm of .sup.32P-labeled
probe. Washing of filters is done at 65.degree. C. for 1 hour in a
solution containing 2.times.SSC, 0.01% PVP, 0.01% Ficoll, and 0.01%
BSA. This is followed by a wash in 0.1.times.SSC at 50.degree. C.
for 45 minutes before autoradiography. Other conditions of high
stringency which can be used are well known in the art. (See
generally Sambrook et al. (supra).)
[0051] The expression construct can optionally include one or more
origins of replication and/or selectable marker(s) (e.g., an
antibiotic resistance gene). Suitable selectable markers include,
for example, those conferring resistance to ampicillin,
tetracycline, neomycin, G418, and the like. Suitable cells lines
include, for example, HEK293 cells, T-REx.TM.-293 cells, CHO cells
and other cells or cell lines.
[0052] The UV-visible spectra of rhodopsin mutants (comprising
mutant opsin and a synthetic retinoid) can be monitored to
determine whether the synthetic retinoid has formed a Schiff base
with the mutant opsin protein. For example, acid-denatured,
purified protein can be analyzed to determine whether an absorbance
maxima of approximately 440 nm is present, providing evidence that
the synthetic retinoid forms a Schiff base with the mutant opsin
protein. In additional embodiments, hydroxylamine treatment can be
used to confirm the Schiff's base is sequestered from the external
environment (infra).
[0053] Suitable opsin-binding synthetic retinoids also can be
selected by molecular modeling of rhodopsin and opsin mutants. The
coordinates for rhodopsin crystal structure are available from the
Protein Data Bank (1HZX) (Teller et al., Biochemistry 40:7761-72
(2001)). The effects of amino acid substitutions on the structure
of rhodopsin, and on the contacts between opsin and 11-cis-retinal,
or a synthetic retinoid, can be determined by molecular
modeling.
[0054] In an exemplary embodiment, the coordinates for the
rhodopsin crystal structure from the Protein Data Bank (1HZX)
(Teller et al., Biochemistry 40:7761-72 (2001)) are used to
generate a computer model. As appropriate, amino acid substitutions
can be introduced into the rhodopsin crystal structure. The
addition of hydrogen atoms and optimization can be done, for
example, using Insight II (Insightll release 2000, Accelrys, Inc.,
San Diego, Calif.). Crystallographic water can be removed, and
water molecules introduced based on the accessible space in the
extracellular region. Typically, no minimization is performed
before water is added. A water layer (e.g., 5 .ANG. thick) can be
used to coat the extracellular part of rhodopsin as well as
residues in contact with polar phospholipids heads. All of the
water molecules can be allowed to move freely, as is the
extracellular half of rhodopsin, with retinal. If no water cap is
put on the cytoplasmic part of rhodopsin, this part of the molecule
can be frozen to prevent degradation of the model.
[0055] In certain embodiments, a water cap is put on the
extracellular part of rhodopsin (together with that part buried in
membrane in contact with polar heads of phospholipids). Water and
the extracellular part of rhodopsin can be allowed to move and the
movement modeled at any suitable frequency. For example, the
movement of the modeled rhodopsin can be modeling at 100 ps
simulations.
[0056] Opsin-binding synthetic retinoids are contacted with a
mutant opsin protein under conditions suitable and for a period of
time sufficient for the formation of a mutant opsin
protein/synthetic retinoid complex. The stability of the mutant
opsin/synthetic retinoid complex can be determined by methods
described herein or as known to the skilled artisan. The mutant
opsin in the mutant opsin/synthetic retinoid complex is stabilized
when it exhibits increased stability (e.g., increased affinity for
the synthetic retinoid as compared with 11-cis-retinal, is less
sensitive to hydroxylamine, exhibits less accumulation in
aggresomes, or the like), as compared with the mutant opsin protein
associated with 11-cis-retinal.
[0057] In certain embodiments, the mutant opsin protein is Pro23His
opsin (i.e., having a proline to histidine amino acid substitution
in opsin protein at position 23). The opsin-binding synthetic
retinoid can be contacted with the mutant opsin protein in vitro or
in vivo. For example, the mutant opsin protein can be synthesized
in an in vitro translation system (e.g., a wheat germ or
reticulocyte lysate expression system) and the synthetic retinoid
added to the expression system. In additional embodiments, the
mutant opsin protein can be contacted with the mutant opsin protein
ex vivo, and then the complex can be administered to a vertebrate
eye.
[0058] As used herein, "prophylactic" and "prophylactically" refer
to the administration of a synthetic retinoid to prevent
deterioration or further deterioration of the vertebrate visual
system, as compared with a comparable vertebrate visual system not
receiving the synthetic retinoid. The term "restore" refers to a
long-term (e.g., as measured in weeks or months) improvement in
photoreceptor function in a vertebrate visual system, as compared
with a comparable vertebrate visual system not receiving the
synthetic retinoid. The term "stabilize" refers to minimization of
additional degradation in a vertebrate visual system, as compared
with a comparable vertebrate visual system not receiving the
synthetic retinoid.
[0059] Opsin-binding synthetic retinoids can be administered to a
vertebrate eye having mutant opsin protein. In certain aspects, the
vertebrate eye is characterized as having an inherited retinal
disease, such as, for example, Retinitis Pigmentosa, in which there
is a defect in opsin gene or opsin protein. In certain embodiments,
the mutant opsin protein has a P23H amino acid substitution. In
other embodiments, the mutant opsin protein has an amino acid
substitution or other mutation in the N-terminal plug of opsin. The
synthetic retinoid binds to and stabilizes the opsin protein.
Typically, the stabilized opsin protein can be incorporated into
the membrane rather than forming an aggregate.
[0060] Synthetic retinoids can be administered to human or other
non-human vertebrates. Synthetic retinoids can be delivered to the
eye by any suitable means, including, for example, oral or local
administration. Modes of local administration can include, for
example, eye drops, intraocular injection or periocular injection.
Periocular injection typically involves injection of the synthetic
retinoid into the conjunctiva or to the tennon (the fibrous tissue
overlying the eye). Intraocular injection typically involves
injection of the synthetic retinoid into the vitreous. In certain
embodiments, the administration is non-invasive, such as by eye
drops or oral dosage form.
[0061] Synthetic retinoids can be formulated for administration
using pharmaceutically acceptable vehicles as well as techniques
routinely used in the art. A vehicle is selected according to the
solubility of the synthetic retinoid. Suitable ophthalmological
compositions include those that are administrable locally to the
eye, such as by eye drops, injection or the like. In the case of
eye drops, the formulation can also optionally include, for
example, isotonizing agents such as sodium chloride, concentrated
glycerin, and the like; buffering agents such as sodium phosphate,
sodium acetate, and the like; surfactants such as polyoxyethylene
sorbitan mono-oleate (also referred to as Polysorbate 80), polyoxyl
stearate 40, polyoxyethylene hydrogenated castor oil, and the like;
stabilization agents such as sodium citrate, sodium edentate, and
the like; preservatives such as benzalkonium chloride, parabens,
and the like; and other ingredients. Preservatives can be employed,
for example, at a level of from about 0.001 to about 1.0%
weight/volume. The pH of the formulation is usually within the
range acceptable to ophthalmologic formulations, such as within the
range of about pH 4 to 8.
[0062] For injection, the synthetic retinoid can be provided in an
injection grade saline solution, in the form of an injectable
liposome solution, or the like. Intraocular and periocular
injections are known to those skilled in the art and are described
in numerous publications including, for example, Ophthalmic
Surgery: Principles of Practice, Ed., G. L. Spaeth, W. B. Sanders
Co., Philadelphia, Pa., U.S.A., pages 85-87 (1990).
[0063] Suitable oral dosage forms include, for example, tablets,
pills, sachets, or capsules of hard or soft gelatin,
methylcellulose or of another suitable material easily dissolved in
the digestive tract. Suitable nontoxic solid carriers can be used
which include, for example, pharmaceutical grades of mannitol,
lactose, starch, magnesium stearate, sodium saccharin, talcum,
cellulose, glucose, sucrose, magnesium carbonate, and the like.
(See, e.g., Remington "Pharmaceutical Sciences", 17 Ed. Gennaro
(ed.). Mack Publishing Co. Easton, Pa. (1985)).
[0064] The doses of the synthetic retinoids can be suitably
selected depending on the clinical status, condition and age of the
subject, dosage form and the like. In the case of eye drops, a
synthetic retinoid can be administered, for example, from about
0.01 mg, about 0.1 mg, or about 1 mg, to about 25 mg, to about 50
mg, to about 90 mg per single dose. Eye drops can be administered
one or more times per day, as needed. In the case of injections,
suitable doses can be, for example, about 0.0001 mg, about 0.001
mg, about 0.01 mg, or about 0.1 mg, to about 10 mg, to about 25 mg,
to about 50 mg, or to about 90 mg of the synthetic retinoid, one to
four times per week. In other embodiments, about 1.0 to about 30 mg
of synthetic retinoid can be administered one to three times per
week.
[0065] Oral doses can typically range from about 1.0 to about 1000
mg, one to four times, or more, per day. An exemplary dosing range
for oral administration is from about 10 to about 250 mg one to
three times per day.
[0066] The following examples are provided merely as illustrative
of various aspects of the invention and shall not be construed to
limit the invention in any way.
EXAMPLES
Example 1
[0067] The present study demonstrates that P23H-opsin can be
induced to properly fold by providing cells with a seven-membered
ring variant of 11-cis-retinal during opsin biosynthesis. The
affinity and selectivity of mutant opsin for 11-cis-7-ring retinal
can be explained based on the crystal structure of rhodopsin.
Methods and Materials
[0068] Synthesis of 11-cis-7-Ring Retinals: Synthesis of
11-cis-7-ring retinals was performed as described previously with
some modifications (Fujimoto et al., Chirality 14:340-46 (2002);
Akito et al., J. Am. Chem. 102:6370-72 (1980); Caldwell et al., J.
Org. Chem. 58:3533-37 (1993). All of the reactions were performed
in a dried nitrogen atmosphere unless otherwise specified.
2-Cycloheptenone was first converted into allyl acetate by
N-bromosuccinimide bromination in CCl.sub.4 followed by treatment
with KOAc in hexamethylphosphoramide. Purified
4-acetoxy-2-cycloheptenone (46% from 2-cycloheptenone) was
subjected to a Horner-Emmons reaction with diethyl
(2-cyanoethyl)phosphonate, which gave an isomeric mixture of two
trans/cis (E/Z) cyanoacetates in a 2:1 ratio. The mixture was
hydrolyzed with K.sub.2CO.sub.3 in MeOH:H.sub.2O (5:1), and then
the hydroxy group of the resulting allylic alcohol was protected
with tert-butyldimethylsilyl chloride in pyridine (80% from
cycloheptenonyl acetate). The resulting cyano compound was reduced
with diisobutylaluminium hydride in CH.sub.2Cl.sub.2 to an aldehyde
and purified by flash chromatography on a silica gel (63%).
.beta.-Cyclocitral was reduced with NaBH.sub.4 to
.beta.-cyclogeraniol and then reacted with triphenylphosphine
hydrobromide in MeOH over 3 days to afford
.beta.-cyclogeranyltriphenylphosphonium bromide after the removal
of solvent and drying of the residue in vacuum. Wittig reaction of
the silylated aldehyde with an excess of phosphonium salt in the
presence of potassium tert-butoxide and a catalytic amount of
18-crown-6 in methylene chloride at ambient temperature afforded
protected cyclic alcohol in 75% yield. The tert-butyldimethylsilyl
protecting group was removed by treatment with tetrahutylammonium
fluoride in dry THF, and the resulting alcohol was oxidized with
MnO.sub.2 in CH.sub.2Cl.sub.2 to a mixture of two (E/Z) cyclic
ketones (2:1 ratio) in 96% yield. This mixture was condensed with
triethyl phosphonoacetate under Horner-Emmons conditions, followed
by lithium aluminum hydride reduction of the resulting isomeric
mixture of ethyl 7-ring retinoates and oxidation of retinols with
MnO.sub.2 (86%) in CH.sub.2Cl.sub.2.
[0069] The following isomers were used: isomer 1 (FIG. 1B),
9,11,13-tri-cis-7-ring retinal: 1.04 (s, 6H, 2.times.CH.sub.3-1),
1.45-1.50 (m, 2H, CH.sub.2-2), 1.59-1.67 (m, 2H, CH.sub.2-3), 1.74
(s, 3H, CH.sub.3-5), 1.90 (m, 2H, J 6.74 Hz, CH.sub.2-22), 1.97 (s,
3H, CH.sub.3-9), 2.03 (t, 2H, CH.sub.2-4), 2.46 (t, 2H, J 7.26 Hz,
CH.sub.2-20), 2.51 (t, 2H, J 6.74 Hz, CH.sub.2-21), 5.78 (d, 1H, J
7.78 Hz, H-14), 6.20 (d, 1H, J 11.42 Hz, H-7), 6.54 (d, 1H, J 11.42
Hz, H-8), 6.95 (d, 1H, J 16.08 Hz, H-12), 7.08 (d, 1H, J 16.08 Hz,
H-11), 10.11 (d, 1H, J 7.78 Hz, H-15); isomer 2 (FIG. 1B),
11,13-di-cis-7-ring retinal: 1.04 (s, 6H, 2.times.CH.sub.3-1),
1.47-1.50 (m, 2H, CH.sub.2-2), 1.60-1.67 (m, 2H, CH.sub.2-3), 1.73
(s, 3H, CH.sub.3-5), 1.86 (m, 2H, J 6.74 Hz, CH.sub.2-22), 2.00 (s,
3H, CH.sub.3-9), 2.04 (t, 2H, CH.sub.2-4), 2.45 (t, 2H, J 7.27 Hz,
CH.sub.2-20), 2.54 (t, 2H, J 6.74 Hz, CH.sub.2-21), 5.79 (d, 1H, J
7.78 Hz, H-14), 6.32 (d, 1H, J 16.08 Hz, H-7), 6.52 (d, 1H, J 16.08
Hz, H-8), 7.02 (m, 2H, H-11, H-12), 10.12 (d, 1H, J 7.78 Hz, H-15);
isomer 3 (FIG. 1B), 11-cis-7-ring retinal: 1.04 (s, 6H,
2.times.CH.sub.3-1), 1.44-1.52 (m, 2H, CH.sub.2-2), 1.57-1.67 (m,
2H, CH.sub.2-3), 1.74 (s, 3H, CH.sub.3-5), 1.86 (m, 2H, J 6.74 Hz,
CH.sub.2-22), 2.00 (s, 3H, CH.sub.3-9), 2.04 (t, 2H, CH.sub.2-4),
2.58 (t, 2H, J 6.75 Hz, CH.sub.2-20), 2.87 (t, 2H, J 6.75 Hz,
CH.sub.2-21), 5.93 (d, 1H, J 8.3 Hz, H-14), 6.22 (d, 1H, J 11.42
Hz, H-12), 6.32 (d, 1H, J 16.08 Hz, H-7), 6.52 (d, 1H, J 16.08 Hz,
H-8), 6.91 (s, 1H, J 11.42 Hz, H-11), 10.03 (d, 1H, J 7.79 Hz,
H-15); and isomer 4 (FIG. 1B), 9,11-di-cis-7-ring retinal: 1.04 (s,
6H, 2.times.CH.sub.3-1), 1.44-1.52 (m, 2H, CH.sub.2-2), 1.57-1.67
(m, 2H, CH.sub.2-3), 1.74 (s, 3H, CH.sub.3-5), 1.86 (m, 2H, J 6.74
Hz, CH.sub.2-22), 2.00 (s, 3H, CH.sub.3-9), 2.04 (t, 2H,
CH.sub.2-4), 2.58 (t, 2H, J 6.75 Hz, CH.sub.2-20), 2.87 (t, 2H, J
6.75 Hz, CH.sub.2-21), 5.93 (d, 1H, J 8.3 Hz, H-14), 6.17 (d, 1H, J
11.41 Hz, H-12), 6.21 (d, 1H, J 16.08 Hz, H-7), 6.53 (d, 1H, J
16.08 Hz, H-8), 6.98 (s, 1H, J 11.41 Hz, H-11), 10.03 (d, 1H, J
7.78 Hz, H-15).
[0070] Cell Lines and Growth Conditions:
[0071] For the construction and selection of tetracycline-inducible
opsin cell lines, an invitrogen T-REx.TM. system was used. Briefly,
nucleic acids encoding wild-type opsin and the P23H mutant were
excised as EcoRI-NotI (fragments from pMT4 and then cloned into the
EcoRI-NotI site within the polylinker of pcDNA4. Using
opsin-specific forward and reverse primers, the entire gene was
sequenced for verification. These plasmids were then separately
transfected by calcium-phosphate precipitation into T-REx.TM.-293
cells that already stably expressed the tetracycline repressor;
these cells were routinely grown under blasticidin selection. After
transfection, zeocin was added to the culture medium, and surviving
colonies of cells were isolated and subsequently expanded into
larger 6-well plates. Each of these clones was exposed to
tetracycline, and 48 hours after induction, the cells were
harvested and solubilized with 1% DM. Separately, uninduced cells
were also solubilized. The samples were run on SDS-PAGE and
immunoblotted with the monoclonal antibody 1D4. Cell lines were
chosen on the basis of production of the least amount of opsin
(i.e., nondetectable opsin levels on immunoblots) in the absence of
tetracycline and moderate amounts of opsin in the presence of the
drug. HEK293 cells were grown in Dulbecco's modified Eagle's medium
containing high glucose (Invitrogen) at 37.degree. C. in the
presence of 5.0% CO.sub.2. In all of the studies, the cells were
harvested after 48 hours of induction with tetracycline (1
.mu.g/ml).
[0072] Cell Culture and Regeneration:
[0073] The cells were washed three times with PBS, harvested, and
incubated with different analogs of 11-cis-retinal (50 .mu.M) for
45 minutes at 4.degree. C. The cells were then lysed with 1.0%
n-dodecyl-maltoside (DM) (Anatrace) in the presence of protease
inhibitors (complete protease inhibitor mixture tablets; Roche
Molecular Biochemicals) and centrifuged at 36,000 rpm in a Beckman
ultracentrifuge for 30 minutes at 4.degree. C. The supernatant was
incubated with 1D4-coupled CNBr-activated Sepharose 4B (Pharmacia
Corp.) beads overnight. The beads were then washed three times with
PBS containing 0.1% DM. Bound pigments were eluted off the beads
using 0.1 mM synthetic peptide (last 9 amino acid residues of the C
terminus of rhodopsin) in 0.1% DM. In studies when retinoids (50
.mu.M) were added during biosynthesis, a Me.sub.2SO solution of
retinoids (10 .mu.l of 100 mM) was added directly to the cell
culture medium after 2 and 24 hours of induction. The cells were
harvested at 48 hours and lysed with 1.0% DM. Pigment was purified
by immunoaffinity chromatography. The UV-visible spectra of the
eluted pigment samples were then recorded on a Perkin Elmer Lambda
800 UV-visible spectrophotometer in the range of 250-650 nm.
[0074] SDS Gel Electrophoresis and Immunoblotting:
[0075] The samples were loaded on 10% SDS-polyacrylamide gels and
transferred to Immunoblotting-NC membrane (Millipore) according to
established protocols. The membranes were blocked with blocking
buffer (Licor) for 1 hour incubated at room temperature with 1D4
antibody (1:1000) for 1 hour. The membranes were then washed with
PBS containing 0.1% Tween 20 and then incubated for 1 hour at room
temperature with IRDye800.TM.-conjugated affinity purified goat
anti-mouse IgG (Licor), diluted 1:5000. The membranes were then
washed with PBS containing Tween 20 and scanned using an Odyssey
Infrared imager (Licor).
[0076] Glycosylation Status:
[0077] Purified 7-rhodopsin and 7-P23H-rhodopsin (rhodopsin and
P23H-rhodopsin regenerated with 11-cis-7-ring retinal,
respectively) were treated with N-glycanase according to the
manufacturer's recommendations (Glyko). The samples were incubated
at 37.degree. C. for 16 hours and then loaded onto a 10%
polyacrylamide gel. The immunoblots were developed as described
above.
[0078] Photosensitivity Studies:
[0079] Whole cells expressing wild-type and P23H-opsin treated with
11-cis-7-ring retinals were harvested and exposed for 20 minutes to
light emitted from a Fiber-Lite, MI 150, High Intensity Illuminator
(Dolan-Jenner). The cells were then washed and then lysed with 1.0%
DM as described above. In a separate study, immunoaffinity purified
7-rhodopsin and 7-P23H-rhodopsin samples were exposed to light from
Fiber-Lite, and UV-visible spectra were recorded at different
times.
[0080] Hydroxylamine Sensitivity:
[0081] Whole cells expressing wild-type and P23H-opsin treated with
11-cis-7-ring retinals were harvested and treated with 500 mM
neutral solution of hydroxylamine for 45 min. The cells were
thoroughly washed with PBS to remove all traces of hydroxylamine.
Rhodopsin was then purified, and spectra were taken. In a separate
study, purified 7-rhodopsin and 7-P23H-rhodopsin were treated with
20 mM neutral hydroxylamine, and UV-visible spectra were recorded
at different times.
[0082] Thermostability of Pigments and Acid Hydrolysis:
[0083] Purified 7-rhodopsin and 7-P23H-rhodopsin were incubated at
37.degree. C., and the spectra were recorded at indicated times. In
acid treatment studies, purified 7-rhodopsin and 7-P23H-rhodopsin
were treated with 100 mM sulfuric acid, and spectra were
recorded.
[0084] HPLC Analysis of Retinoids:
[0085] A 450 .mu.l aliquot of either purified 7-rhodopsin, purified
7-P23H-rhodopsin, or cell medium were treated with 50 .mu.l of 10%
SDS and 100 .mu.l of 1 M NH.sub.2OH (freshly prepared, pH 7.5). The
mixture was kept at room temperature for 30 min, and then 400 .mu.l
of MeOH and 400 .mu.l of hexane were added. The mixture was shaken
on a vortex for 5 minutes and centrifuged at 14,000 rpm to separate
layers. The hexane layer was collected. Another 400 .mu.l of hexane
was added to the aqueous layer, and extraction was repeated.
Combined hexane layers were dried down and redissolved in 120 .mu.l
of hexane, and 100 .mu.l fractions were analyzed by normal phase
HPLC as previously described.
[0086] Immunocytochemistry:
[0087] HEK293 cells expressing wild-type rhodopsin or P23H-opsin
under a tetracycline-inducible promoter were cultured in Dulbecco's
modified Eagle's medium (Invitrogen). The cells were attached to
glass bottom microwell dishes (MatTek Corp.) with Cell-Tak (Becton
Dickinson Labware). Expression of opsin or P23H-opsin was induced
by the addition of 1 .mu.g/ml tetracycline as recommended by the
manufacturer's protocol (Invitrogen). The cells were treated with
50 .mu.M 11-cis-7-ring retinal 2 hours after induction. The cells
were harvested after 24 hours and fixed with 4% paraformaldehyde
(Fisher) in PBS (136 mM NaCl, 11.4 mM sodium phosphate, pH 7.4) for
10 minutes and washed by PBS. To block nonspecific labeling, the
cells were incubated in 1.5% normal goat serum (Vector Lab., Inc.)
in PBST (136 mM NaCl, 11.4 mM sodium phosphate, 0.1% Triton X-100,
pH 7.4) for 15 minutes at room temperature. The cells were
incubated overnight at 4.degree. C. in purified 1D4 antibody
diluted with PBST. The sections were rinsed in PBST and incubated
with indocarbocyanine (Cy3)-conjugated goat anti-mouse IgG (Jackson
ImmunoResearch Lab., Inc.) and Hoechst 33342 dye (Molecular
Probes). The cells were rinsed in PBST and mounted in 50 .mu.l of
2% 1,4-diazabicyclo-[2.2.2]octane (Sigma) in 90% glycerol to retard
photobleaching. For confocal imaging, the cells were analyzed on a
Zeiss LSM510 laser scanning microscope (Carl Zeiss, Inc.).
[0088] Protein Simulation and Modeling:
[0089] Coordinates for rhodopsin were taken from the Protein. Data
Bank (1HZX) (Teller et al., Biochemistry 40:7761-72 (2001). The
addition of hydrogen atoms and all of the optimizations were done
in Insight II (InsightII release 2000, Accelrvs, Inc., San Diego,
Calif.). Crystallographic water was removed, and water molecules
were introduced based on the accessible space in the extracellular
region. No minimization was performed before water was added.
[0090] A water layer (5 .ANG. thick) was used to coat the
extracellular part of rhodopsin as well as residues in contact with
polar phospholipids heads. All of the water molecules were allowed
to move freely, as was the extracellular half of rhodopsin, which
contains P23H and retinal. Because no water cap was put on the
cytoplasmic part of rhodopsin, this part of the molecule was frozen
to prevent degradation of the model.
Results
[0091] The chromophore of rhodopsin, 11-cis-retinal, plays a
central role in the photoactivation process and is also important
for the stabilization of the receptor. For example, rhodopsin is
stable for months in mild detergents, although opsin precipitates
in a few hours. The chromophore may also induce a proper folding of
rhodopsin mutants. The P23H amino acid substitution may destabilize
the native chromophore-accepting conformation of opsin, leading to
aberrant folding and subsequent aggregation. However, an analog of
11-cis-retinal may facilitate native-like folding of P23H-opsin and
therefore play the role of pharmacological chaperone. Recently,
wild-type opsin was regenerated with 11-cis-7-ring retinal
(7-rhodopsin), containing a chromophore with a seven-membered ring
to prevent isomerization around the C11=C12 double bond (FIG. 1B),
is very stable in vivo and in vitro. In contrast, bleaching of the
wild-type opsin regenerated with 11-cis-6-ring retinal
(6-rhodopsin), which contains a more rigid chromophore, produces
multiple isomers with modest changes in protein conformations.
These results reveal that 11-cis-7-ring retinals, particularly
isomer 3 (FIG. 1B), are easily accepted into the binding site of
opsin and provide additional contact sites by virtue of the
seven-membered ring and the 9-methyl group with the protein moiety.
Because of its intrinsic flexibility, this analog could potentially
influence/affect protein folding during biosynthesis, which is
particularly important for those mutant proteins that fold less
efficiently. The binding pocket of wild-type opsin adopts specific
conformations that allow it to bind preferentially certain
retinoids.
[0092] 11-cis-7-Ring Retinal Chaperone Folding of P23H-opsin:
[0093] Rhodopsin is regenerated with 11-cis-7-ring retinals in the
harvested membranes (FIG. 2B), whereas only a small amount of
pigment was formed when membranes containing P23H-opsin were
treated with 11-cis-retinal, 11-cis-6-ring retinal, or
11-cis-7-ring retinal after the cells were harvested (FIG. 2B). If
the mutant proteins are structurally unstable, it was proposed that
the addition of retinal during the course of protein biosynthesis
might induce a more native-like folding of the protein and its
subsequent stabilization.
[0094] The first studies utilized 11-cis-locked versions of
11-cis-retinal in stable cell lines expressing wild-type and
P23H-opsin. The UV-visible spectra of the immunoaffinity purified
samples from 11-cis-6- or 11-cis-7-ring retinals provided to the
cells during biosynthesis showed that both retinals recombined with
wild-type opsin (FIG. 2C). Supporting this prediction, P23H-opsin
formed significant amounts of pigment when 11-cis-7-ring retinal
was added during biosynthesis (FIG. 2D). The max of the pigment was
approximately 490.+-.3 nm, unlike the wild-type protein (with a max
of approximately 500.+-.3 nm) (FIG. 2, C and D). The UV-visible
spectra with a max of approximately 440 nm of acid-denatured
purified 7-P23H-rhodopsin (FIG. 2D, inset) provided evidence that
the chromophore forms a Schiff base with rescued P23H-opsin. No
significant pigment was seen when 11-cis-6-ring retinal, which is
photoisomerable along C9- and C13-C.dbd.C double bonds, was added
to P23H-opsin-expressing cells (FIG. 2D). Furthermore,
11-cis-9-demethyl-7-ring retinal was also ineffective in pigment
formation with P23H-opsin. These studies illustrate unique
specificity of the binding interaction between 11-cis-7-ring
retinal and P23H-opsin.
[0095] Immunoblots showed that the rescued P23H-opsin had a high
molecular weight and a Golgi-associated glycosylation pattern
similar to the wild-type protein, suggesting that the protein is
sufficiently folded to proceed along the secretory pathway. This is
in striking contrast to P23H -opsin that was not treated with
11-cis-7-ring retinal during P23H-opsin biosynthesis, Purified
7-rhodopsin and 7-P23H-rhodopsin were efficiently deglycosylated by
N-glycanase, and the mutant protein spontaneously aggregated,
forming high molecular weight aggregates).
[0096] In control studies, 9-cis-retinal and 11-cis-retinal were
tested for proper folding of P23H-opsin. It should also be noted
that 9-cis-retinal promoted transport of P23H-opsin to the cell
surface. 11-cis-retinal was also observed to induce the in vivo
folding and stabilization of P23H-opsin forming visual pigments
(499 nm and 492 nm, for rhodopsin and P23H-rhodopsin, respectively)
(FIG. 2, C and D). Moreover, these pigments also acquired a mature
state of glycosylation. 11-cis-retinoids are unstable in vitro and
in vivo and rapidly undergo "reverse isomerization.". Therefore,
locked analogs were used throughout the rest of this study.
[0097] Properties and Stability of 7-P23H-Rhodopsin:
[0098] When the mixture of the four 7-ring retinal isomers (FIG.
1B) was added to cells expressing opsin and P23H-opsin during
biosynthesis, both wild-type opsin and P23H-opsin selectively bound
only isomer 3. These observations further support the extraordinary
specificity of wild-type and P23H-opsin for binding this
11-cis-retinal isomer. Addition of 11-cis-retinal to cell membranes
containing either wild-type or P23H-opsin that were already treated
with the 11-cis-7-ring retinal during their biosynthesis did not
lead to its substitution after photobleaching, as measured
spectrophotometrically and by retinoid analysis of the bound
chromophores. 7-Rhodopsin, purified in the detergent, is stable to
light (FIG. 3A), whereas purified 7-P23H-rhodopsin undergoes
bleaching under the same conditions (FIG. 3B). In contrast, both
rhodopsins are stable in the membranes of HEK293 cells (FIG. 3, C
and D). This result suggests that, in detergent, the chromophore in
7-P23H-rhodopsin is more flexible, thus allowing
photoisomerization. The mechanism by which 7-P23H-rhodopsin
undergoes bleaching in detergent most likely involves isomerization
of isomer 3 to three other isomers and its subsequent hydrolysis.
The membranes apparently stabilized 7-P23H-rhodopsin, thus
preventing isomerization of its bound chromophore. In tissue
culture samples, small amounts of non-rhodopsin-bound retinals
eluted between 30 and 40 minutes and remained in equilibrium with
the vast majority of retinols, governed by the redox potential of
the cells.
[0099] To further characterize the rescued protein, the affinity
bound 7-rhodopsin and 7-P23H-rhodopsin were eluted under conditions
that selectively released only the folded form of the protein (10
mM phosphate, pH 6.0). The spectra of the ciliates (FIG. 2, E and
F) and the corresponding immunoblots indicated that approximately
80% of 7-P23H-rhodopsin folded to form pigment. Additionally,
immunoblots of these eluates demonstrated that both contained a
mature glycosylated band and unglycosylated bands; however, only
the material eluted at pH 6.0 had the Golgi-specific glycosylation
pattern.
[0100] The structure of the rescued protein was also probed by
determining its sensitivity to neutral hydroxylamine.
7-P23H-rhodopsin is resistant to hydroxylamine treatment when
embedded in the lipid bilayer of HEK293 cells, suggesting that the
rescued protein adopts a conformation that sequesters the Schiff
base linkage within the protein and protects it from chemical
modification. Unlike the purified wild-type protein, the mutant
chromophore is accessible to hydroxylamine in detergent (0.1% DM),
as evidenced by the formation of the retinaloximes
(max=approximately 360 nm). These data imply that the structure of
7-P23H-rhodopsin is less tightly packed than that of the
7-rhodopsin. Finally, the temperature stability of the purified
7-rhodopsin and 7-P23H-rhodopsin was studied. There was no change
in the amount of chromophore after incubation of 7-rhodopsin at
either 4.degree. C. or 37.degree. C. However, for the rescued
7-P23H-rhodopsin, there is time-dependent thermal bleaching that is
accelerated by increased temperature, with a half-life of
approximately 4 minutes at 37.degree. C. and 10 days at 4.degree.
C. in the detergent solution.
[0101] Localization of the Rescued 7-Locked-P23H-Rhodopsin:
[0102] Immunofluorescence microscopy demonstrated that P23H-opsin
is retained intracellularly, predominantly in a perinuclear
distribution with punctuated fluorescence consistent with
aggresomes. In contrast, the rescued 7-P23H-rhodopsin is
predominantly found in a diffuse pattern with significantly greater
staining at the cell surface similar to the 7-rhodopsin and
wild-type opsin, which are found predominantly at the plasma
membrane. In summary, this result indicates that the rescued
P23H-rhodopsin was not only correctly glycosylated and formed a
pigment but was also correctly routed to the cell membranes.
Discussion
[0103] Protein Conformational Disorders:
[0104] Dominantly inherited diseases can result from (a)
haploinsufticiency of a gene, e.g., as for the melanocortin-4
receptor; (b) constitutive activity (gain of function) in some
opsin mutants or lack of activity because of somatic mutation; and
(c) loss of function because of mutant protein misfolding and
aggregation. The diseases caused by misfolded proteins are known as
protein conformational disorders and include Alzheimer's disease.
Huntington's disease, Parkinson's disease, diabetes insipidus,
cystic fibrosis, prion disease, emphysema, dominant cataracts, and
oculopharyngeal muscular dystrophy. Gene delivery is one method of
correcting haploinsufficiency. Constitutive activity has been
successfully blocked by reverse agonist-like compounds, and
conformation and function can be rescued by small chemical agents.
The medically most prevalent forms of dominant disorders are the
protein conformational disorders. Although they are the most
challenging to treat, some successes have been reported. Examples
include the rescue of misfolded cystic fibrosis transmembrane
regulator (CFTR) variant F508 and the Z-variant of 1-antitrypsin.
In the instance of CFTR, the osmolytes glycerol and
trimethylamino-oxide have been used. The protein acquires mature
glycosylation and is transported to the cell surface where it pumps
Cl ions. The chemical chaperone 4-phenylbutyric acid mediated a
marked increase in secretion of .alpha..sub.1-antitrypsin. Recent
studies, however, suggest that the rescued protein is less stable
than the wild-type. Other approaches to inducing the folding of
proteins have been developed. For example, mini-chaperones that
prevent .beta.-sheet formation prevent toxic aggregation of
amyloid-.beta. found in Alzheimer's disease and the PrP protein
associated with prion disease.
[0105] P23H Rescue:
[0106] This study demonstrates that P23H-opsin can be induced to
properly fold and be stabilized with a seven-membered locked ring
version of 11-cis-retinal, the inverse agonist of opsin.
Furthermore, this model system provides a quantitative means to
study the folding of this membrane protein. The rescued
7-P23H-rhodopsin contains a Schiff base linkage with Lys296,
producing pigment with a max of approximately 490 nm (FIG. 2D) that
can be used as a quantitative measure of the amount of correctly
folded protein. Using chromatographic conditions that selectively
elute the folded form of the protein, 11-cis-7-ring retinal leads
to the rescue of approximately 80% of the P23H-opsin. This study
also demonstrated that the rescued protein is not only folded but
also proceeds along the secretory pathway. Like the wild-type
protein, the rescued protein acquires the heterogeneous
glycosylation associated with oligosaccharide processing within the
Golgi apparatus. Clearly, the protein is of a sufficiently
native-like conformation and is not sequestered by the cellular
quality control apparatus, at least that which exists at the level
of endoplasmic reticulum.
[0107] Furthermore, the rescued protein is structurally different
from the wild-type protein. The detergent-purified protein is
light-sensitive, displays thermal instability, and is sensitive to
neutral hydroxylamine. The bleaching of detergent-solubilized
7-P23H-rhodopsin occurs because of isomerization of double bonds
along the polyene chain of the chromophore producing a mixture of
isomers. However, in the membranes of the HEK cells,
7-P23H-rhodopsin is stable, and therefore, it is expected this
pigment will also be stable in vivo.
[0108] Chemical and Structural Considerations of the Rescue:
[0109] The mutant P23H protein is less stable because it is
misfolded and is thus retained intracellularly. The rescue effect
with 11-cis-7-ring retinal leads to increased amounts of the
correctly folded mutant and is extraordinarily specific as shown by
the lack of activity observed with several structural homologs
(11-cis-9-demethyl-ring retinal and 11-cis-6-ring retinal).
However, unlike the wild-type protein, purified 7-P23H-rhodopsin
appears to be in a less compact conformation, as evidenced by its
sensitivity to neutral hydroxylamine in detergent. It was also
observed that the rescued protein spontaneously releases the locked
retinoid over time. Previous studies have demonstrated that
11-cis-7-ring retinal is inherently more flexible than
11-cis-6-ring retinal. The rigidity of 11-cis-6-ring retinal may
not allow the P23H-opsin binding pocket to accept this chromophore.
Alternatively, P23H-opsin may bind 11-cis-6-ring retinal but that
the resulting protein is less stable and maybe more susceptible to
water-assisted hydrolysis of the Schiff base linkage, as it is in
the case of 9-cis-retinal.
[0110] These molecular modeling studies provide an explanation for
the defect caused by P23H mutation. Two alterations appear to be
present in P23H mutant: (a) The mutation disrupts ionic
interactions of Pro23, Gln182, and Glu184 on the tip of the plug
between helices 4 and 5. Mutation of Pro to His leads to formation
of conjugated hydrogen bonding that exposes the chromophore-binding
site. This interaction stiffens the plug and possibly opens the
binding site of opsin, allowing water to hydrolyze the Schiff base
between the retinal chromophore and .gamma.-amino group of Lys296.
This prediction is consistent with a hipsochromic shift in the
absorption maximum of the chromophore and accessibility to
hydrolysis in the presence or absence of hydroxylamine. (b) There
is a hydrophilic channel in the interior of the protein that could
accommodate water molecules (FIG. 1E). In the model, rhodopsin was
soaked with water on the external side, only including the part of
the membranes that is charged and without constraints imposed on
water molecules. During simulation, a route was established where
water molecules drifted from one side to another (cytoplasmic).
This route was along helix II and partly along helices I and III.
The key residue facilitating this transport was Thr93 on helix II
(close to Glu113). Collectively, these two effects may alter the
electronic/dipole environment around the retinal, explaining the
nearly 10-nm blue shift.
[0111] In summary, this study has shown using a cell culture model
system that the retinitis pigmentosa mutant P23H-opsin can be
induced to properly fold by providing cells with a seven-membered
ring variant of 11-cis-retinal during opsin biosynthesis.
Furthermore, the remarkable affinity and selectivity of mutant
opsin for 11-cis-7-ring retinal on the basis of the crystal
structure of rhodopsin.
[0112] The previous examples are provided to illustrate but not to
limit the scope of the claimed inventions. Other variants of the
inventions will be readily apparent to those of ordinary skill in
the art and encompassed by the appended claims. All publications,
patents, patent applications and other references cited herein are
hereby incorporated by reference.
* * * * *