Antagonists of G-protein-coupled receptor

[0002] (a) Field of the Invention

[0003] The invention relates to G-protein-coupled receptor antagonists which bind to the intracellular molecular interface between the receptor for PGF_2α (FP receptor) and the G-protein.

[0004] (b) Description of Prior Art

[0005] Prostaglandins are derived from the oxygenation of arachidonic acid by prostaglandin synthases. Prostaglandins mediate a wide variety of physiological actions, such as vasomotricity, sleep/wake cycle, intestinal secretion, lipolysis, glomerular filtration, mast cell degranulation, neurotransmission, platelet aggregation, leuteolysis, myometrial contraction and labor, inflammation and arthritis, patent ductus arteriosus, cell growth and differentiation. Prostanoids mediate their actions through binding to distinct receptors which belong to the super family of rhodopsin-like seven transmembrane helical receptors. These receptors are coupled to heterotrimeric G-proteins consisting of α, β and γ subunits which, upon activation, elicit alterations in cell calcium, initiate phosphoinositide hydrolysis or promotion or repression of cyclic adenosine monophosphate synthesis (Strader, C. D., et al., Ann. Rev. Biochem. 63: 101-132, 1994).

[0006] Of the five pharmacologically distinct prostanoid receptors for E₂, I₂, D₂, TxA₂and F_2α and their many isoforms, the receptor for PGF_2α, also called FP receptor, shows limited tissue distribution, predominantly expressed in corpora leutea, uterine myometrium, trabecular meshwork of the eye, and to a lesser extent in vascular smooth muscle. Initiation of labor is marked by tremendous rise in PGF_2α levels and increased uterine contractility. The wide spread use of PGF_2α analogues to induce labor in veterinary industry points to the primary role of PGF_2α and its receptor in parturition. This is underscored by the fact that mice lacking the FP receptor fail to undergo labor (Sugimoto, Y., et al., Science, 277: 81-83, 1997).

[0007] In face of escalating costs incurred as a result of premature births and associated complications to the neonate, such as intraventricular hemorrhage, bronchopulmonary displasia and periventricular leukomalacia leading to cerebral palsy, prolongation of gestation by arresting premature labor is an effective preventive therapy. The relative success of nonsteroidal anti-inflammatory drugs as a short term therapy toward prevention of premature labor is based on their inhibitory actions upon the synthesis of prostaglandins, particularly PGE₂and PGF_2α. However, inhibition of the former is associated with serious complications to the fetus such as the closure of ductus arteriosus, renal failure and pulmonary hypertension. At another level, PGF_2α has been attributed a major role in dysmenorrhea, a condition which afflicts 5%-7% of premenopausal women. A pre-menstrual increase in PGF_2α levels resulting in myometrial spasms underlies the pathogenesis of this disorder. Lack of effective antagonists of FP receptor for extended therapy hampered the advances in preventing premature labor and associated sequelae.

[0008] Human FP receptor is a 45 kDa integral membrane glycoprotein, consisting of 359 amino acids and shares only 47% sequence identity with EP1 receptor, and to a lesser extent with other prostanoid receptors (Abramovitz, M., et al., J. Biol. Chem., 269: 2632-2636, 1994). Binding of PGF_2α to FP receptor is followed by the activation of G_αqβγ complex, increased GTP binding by the G_αqsubunit, stimulation of phospholipase β activity, release of inositol phosphates, increased intracellular calcium and subsequent signal transduction phenomena ultimately leading to smooth muscle contraction. The FP receptor is the only efficacious target for development of therapeutic drugs since a few G_α-proteins catalyze the actions of hundreds of G-protein coupled receptors, thus targets downstream from the receptor are essentially of little use.

[0009] Antagonists of FP receptors directed to the ligand binding site could be of limited use since ligand based inhibitors show cross reactivity with other prostanoid receptors; their efficacy will be compromised in face of tremendous increase in PGF_2α concentrations in myometrium at the onset of labor; and the basal activity of the receptors in the absence of ligand limits the use of ligand-based inhibitors.

[0010] It would be highly desirable to be provided with antagonists of FP receptors which do not cross-react with other prostanoid receptors and which are effective even in the absence of a ligand.

[0011] One aim of the present invention is to provide antagonists of FP receptors which do not cross-react with other prostanoid receptors and which are effective even in the absence of a ligand.

[0012] Another aim of the present invention is to provide inhibitors of FP receptors devised by a novel strategy to target the intracellular surface of the receptor at which the cytoplasmic domains of the FP receptor and the G_qprotein interact.

[0013] In accordance with the present invention there is provided a receptor prostanoid receptor antagonist which binds to an intracellular molecular interface between a receptor and a G_α-protein, wherein said antagonist has a first amino acid sequence coding for a third or fourth intracellular domain, or a part thereof, and a second amino acid sequence coding for α-helices of a G_α protein, whereby when bound to the intracellular molecular interface, said antagonist hampers signal transduction from said receptor.

[0014] The receptor is preferably the PGF_2α receptor of prostaglandin.

[0015] The antagonist of the present invention preferably comprises an amino acid sequence derived from the sequence of at least one of the prostaglandin F_2α receptor and the associated protein G_αq. More preferably, the antagonist of the present invention consist in is an amino acid sequence of the FP receptor selected from the group consisting of RVKFKSQQHR QGRSHHLEM (SEQ ID NO:3) and RKAVLKNLYK LASQCCGVHV ISLHIWELSS IKNSLKVAAI SESPVAEKSA ST (SEQ ID NO:4).

[0016] In accordance with the present invention there is also provided a method for preventing premature delivery of fetus comprising the step of administering to a female in need of such a treatment a therapeutically effective amount of a G-protein-coupled receptor antagonist which binds to an intracellular molecular interface between a receptor and a G-protein, wherein the antagonist, when bound to the intracellular molecular interface, hampers the transduction of a signal, thereby reducing contractions.

[0017] In accordance with the present invention there is also provided a method for preventing and/or treating dysmenorrhea comprising the step of administering to a female in need of such a treatment a therapeutically effective amount of a G-protein-coupled receptor antagonist which binds to an intracellular molecular interface between a receptor and a G-protein, wherein the antagonist, when bound to the intracellular molecular interface, hampers the transduction of a signal thereby reducing pain associated with contractions.

[0018] FIGS. 1A and 1B illustrate the inhibitory effects of PCP-1 and PCP-2 on FP receptor function upon stimulation with PGF_2α or PGE₂in accordance with one embodiment of the present invention;

[0019] FIG. 2A illustrates the effects of G_αq-derived peptides on FP receptor function; and

[0020] FIG. 2B illustrates a dose-response of PCP-4 on PGF_2α receptor function.

[0021] In accordance with the present invention, there is provided a new class of G-protein-coupled receptor antagonists which bind to the intracellular molecular interface between the receptor and the G-protein, thus hampering signal transduction.

[0022] Hence, a novel strategy to target the intracellular surface of the receptor at which the cytoplasmic domains of FP receptor and Gq protein interact was designed. By preventing the binding of Gq protein to FP receptor with the inhibitors of the present invention, derived from both the FP receptor and Gq protein, FP receptor function in the presence of its ligand was diminished. Furthermore, the specificity of the inhibitors of the present invention is demonstrated by analyzing the function of a highly related prostaglandin receptor, EP1.

[0023] Cell Culture

[0024] A549 lung carcinoma cells (ATCC Accession No.: CCL185, American Type Culture Collection, Rockville, Md. 20852) were cultured in Dulbecco's modified Eagles medium (DMEM) with 10% fetal bovine serum (FBS) and antibiotics, penicillin (10 U/ml) and streptomycin (10 μg/ml) in a humidified atmosphere containing 5% CO₂at 37° C. The cells were trypsinized and plated in 6-well tissue culture dishes at 2×10⁵cells/well, a day before commencing the experiments.

[0025] Cloning FP Receptor Intracellular Domains

[0026] The DNA fragments 5′AGA GTT AAA TTT AAA AGT CAG CAG CAC AGA CAA GGC AGA TCT CAT CAT TTG GAA ATG 3′ (SEQ ID NO:1) and 5′ CGA AAG GCT GTC CTT AAG AAT CTC TAT AAG CTT GCC AGT CAA TGC TGT GGA GTG CAT GTC ATC AGC TTA CAT ATT TGG GAG CTT AGT TCC ATT AAA AAT TCC TTA AAG GTT GCT GCT ATT TCT GAG TCA CCA GTT GCA GAG AAA TCA GCA AGC ACC 3′ (SEQ ID NO:2), encoding the intracellular domains of the FP receptor having the following amino acid sequences: RVKFKSQQHR QGRSHHLEM (SEQ ID NO:3) (PCP-1) and RKAVLKNLYK LASQCCGVHV ISLHIWELSS IKNSLKVAAI SESPVAEKSA ST (SEQ ID NO:4) (PCP-2) were cloned by RT-PCR. Total mRNA from human foreskin fibroblasts were prepared by acid phenol-guanidine isothiocyanate method (Chomczynski, P., and Sacchi, N., Anal. Biochem., 162: 156-159, 1987).

[0027] Reverse transcription followed by amplification of the cDNAs using the gene-specific primers pcp 1.1: 5′ GCG TCT AGA ATC AGA GTT AAA TTT AAA AGT CAG 3′ (SEQ ID NO:5), pcp 1.2: 5′ GCG TCT AGA CTA CAT TTC CAA ATG ATG 3′ (SEQ ID NO:6) pcp 2.1: 5′ CGC TCT AGA ATG CGA AAG GCT GTC CTT AAG 3′ (SEQ ID NO:7) and pcp 2.2: 5′ GCG TCT GAG CTA GGT GCT TGC TGA TTT CTC 3′ (SEQ ID NO:8), derived from the human FP receptor sequence (Abramovitz, M., et al., J. Biol. Chem., 269: 2632-2636, 1994) and Taq™ polymerase (GIBCO Life Technologies, Burlington, ON) were conducted as described by Peri et al. (Peri, K. G., et al., J. Biol. Chem., 270: 24615-24620, 1995). Briefly, two micrograms of total RNA was reverse transcribed using 400 U of M-MLV reverse transcriptase and 10 μg/ml random hexamers, in a 50 μl reaction containing 50 mM Tris-HCl, pH 8.3, 75 mM KC1, 3 mM MgCl₂, 10 mM DTT, and 0.5 mM each of dCTP, dGTP, dATP and dTTP, for 1 h, at 42° C. An aliquot of the cDNA (equivalent to 1 μg of RNA) was amplified using 1.5 U Taq DNA polymerase in a 100 μl reaction buffer containing 20 mM Tris-HCl, pH 8.4, 50 mM KC1, 1.5 mM MgC1₂, 0.2 mM each of dCTP, dGTP, dATP and dTTP, and 0.5 μM each of the primers, for 35 cycles (each cycle was 94° C., 1 min.; 50° C., 1 min.; and 72° C., 1 min.).

[0028] The PCR products were digested with Xba I restriction enzyme (GIBCO Life Technologies, Burlington, ON) and cloned into the Xba I site of pRC-CMV vector (Invitrogen, Calif.). Multiple plasmid clones were sequenced using the T7 sequencing kit (Pharmacia, Baie D'Urfe, PQ) to verify the sequence of the cDNAs.

[0029] Cell Transfection and Selection of G418-Resistant Clones

[0030] The expression plasmids carrying the third (PCP-1) and the fourth (PCP-2) intracellular domains were introduced into A549 cells using Transfectamine lipid (GIBCO Life Technologies, Burlington, ON). Three (3) micrograms of DNA and 16 μg of lipid were mixed in 200 μl of water and incubated at room temperature for 45 min. Then, the lipid-DNA complexes were diluted with 0.8 ml of Opti-MEM™ (GIBCO Life Technologies, Burlington, ON). The cells were washed twice with Hank's Balanced Salt Solution and incubated with lipid-DNA complexes for 6 hours. An equal volume of DMEM with 20% FBS was added and the cells were kept in the incubator overnight. On the next day, the medium was replaced with DMEM containing 10% FBS and antibiotics and incubated for another 24 hours.

[0031] On the following day, the cells were trypsinized and plated in 100 mm cell culture dishes at 1×10⁴cells/ml in DMEM containing 10% FBS, antibiotics and 1 mg/ml of G418 (GIBCO Life Technologies, Burlington, ON). The G418 containing medium was replaced every 3 days. G418-resistant colonies were trypsinized and pooled for further analysis. The expression of PCP-1 and PCP-2 peptides was tested by analyzing mRNA expression using RNase protection assays as described by Peri et al. (Peri, K. G., et al., J. Biol. Chem., 270: 24615-24620, 1995). More particularly, total RNA was isolated using acid phenol guanidine isothiocyanate is method (Chomczynski, P., and Sacchi, N., Anal. Bio-chem., 162: 156-159, 1987). Aliquots of total RNA (10 μg) were mixed with 5×10⁵cpm of [³²P]-labeled cRNA probes (synthesized from pIL3 and pIL4 plasmids which are expression plasmids encoding PCP-1 and PCP-2 peptides, using a commercial in vitro transcription kit sold by Promega, Madison, Wis.) in a solution containing 80% (v/v) formamide, 40 mM PIPES, pH 6.8 and 0.4 M NaCl and incubated overnight at 50° C. On the next day, the hybrids are digested with RNase A (10 μg/ml) and RNase T1 (250 U/ml) in a solution containing 10 mM Tris-HCl, pH 7.5, 1 mM EDTA and 0.3 M NaCl for 30 min. at 25° C. Proteinase K (10 μg) and sarcosyl (1%) were added and the incubation continued for another 30 min. at 37° C. The precipitation of RNA hybrids and resolution of labeled RNAs on urea-polyacrylamide gels were done exactly as described by Peri et al. (Peri, K. G., et al., J. Biol. Chem., 270: 24615-24620, 1995).

[0032] Phosphoinositide Hydrolysis

[0033] The cells in 6-well dishes (5×10⁵/well) were incubated with [³H]-myo inositol (1 μCi/ml of 10 Ci/mmol specific activity: Amersham Canada, Mississauga, ON) for 24 hours in DMEM containing 5% FBS and antibiotics to label the inositol phospholipids. The cells were washed with DMEM containing 50 mM LiCl twice and incubated in the same medium for 15 min. Then the cells were stimulated with 1 μM of PGF_2α or PGE₂for 30 min. The cells were washed with phosphate-buffered saline (PBS) once and the reactions were stopped by adding 0.4 ml of ice-cold methanol. The cells were scraped, collected into 1.5 ml microfuge tubes, 0.4 ml of water and 0.4 ml of chloroform were added, vortexed vigorously for 30 sec. and centrifuged at 14,000×g for 10 min. The aqueous layer was applied to Dowex™ AG1-X8 (formate form) ion-exchange columns (Bio-Rad, Mississauga, ON). The inositol phosphates were eluted with increasing concentrations of ammonium formate in 0.1 M formic acid exactly as described by Berridge et al.

[0034] Introduction of Peptides into Cells

[0035] The saponin treatment of cells on ice with peptides was conducted exactly as described by Johnson et al. (Johnson, J. A., et al., Circ. Res., 79: 10086-10099, 1996). Briefly, the media from cells (at 80% confluence) in 6-well dishes was removed and saved. The cells were treated with 2 ml of room temperature PBS for 2 min. followed by ice-cold PBS for an additional 2 min. on ice. The cells were then incubated for 10 min. in 2 ml of freshly prepared permeabilization buffer (20 mM HEPES, pH 7.4, 10 mM EGTA, 140 mM KCl, 50 μg/ml saponin, 6 mM ATP and 5 mM oxalic acid) containing varying concentrations of peptides, PCP-3 and PCP-4. The cells were washed gently four times on ice with 2 ml of ice-cold PBS each time. The cells. were incubated for 20 min. in the fifth wash on ice. The cells were then successively incubated for 2 min. with 2 ml of PBS at room temperature and at 37° C. The conditioned media was returned to the cells and they were allowed to recover for 30 min. before determining phosphoinositide hydrolysis in response to prostaglandins.

[0036] Discussion

[0037] In accordance with the present invention, a novel strategy of utilizing intracellular interface between the FP receptor and the G_αqprotein as a target for designing inhibitors of FP receptor function was used. This method can be generalized to all G-protein-coupled receptors. Peptides derived from the intracellular domains of FP receptors (PCP-1 and PCP-2) and the αN and αC helices of Gq-protein (PCP-3 and PCP-4 respectively) were found to be effective inhibitors of FP receptor.

[0038] The present invention will be more readily understood by referring to the following examples which are given to illustrate the invention rather than to limit its scope.

[0039] Effects of Intracellular Expression of PCP-1 and PCP-2 Peptides on FP Receptor Function

[0040] Cell lines expressing the peptides, PCP-1 and PCP-2, were stimulated with 1 μM PGF_2α and PGE₂for 30 min. and the inositol phosphates were measured by anion exchange chromatography as described by Berridge et al. (Berridge, M. J., et al., Biochem. J., 212: 473-482, 1983). Briefly, the medium was discarded and the inositol triphosphate (IP3) synthesis was stopped by adding 0.6 ml ice-cold methanol. The cells were scraped and collected into polypropylene tubes. Distilled water (0.5 ml) and chloroform (0.6 ml) were added and vigorously vortexed for 2 min. The phases were separated by centrifugation at 6000×g for 10 min. The aqueous phase was applied to AG-1X-8 (Formate form) anion exchange columns (1 ml bed volume) and free inositol was eluted with 10 ml of water, followed by 60 mM ammonium formate in 0.1 M formic acid. Then, the inositol phosphates were eluted with 5 ml of 1.2 M ammonium formate in 0.1 M formic acid. After adding 3 volumes of scintillation cocktail (Optiphase-HiSafe III™), the eluates were counted by scintillation spectrophotometry.

[0041] As shown in FIG. 1A, expression of either PCP-1 or PCP-2 inhibited ligand-stimulated phosphoinositide hydrolysis (n=3). Both PCP-1 and PCP-2 were stably expressed intracellularly. The cells were labeled with ³H-myo inositol for 24 hours and stimulated with 1 μM of PGF_2α or PGE₂for 30 min. Inositol phosphates were separated by ion exchange chromatography and determined by scintillation counting. Data are expressed as fold stimulation in phosphoinositide hydrolysis over unstimulated controls. On the other hand, stimulation of a related prostaglandin receptor expressed in these cells (with which FP receptor shows highest sequence identity among all G-protein-coupled receptors), EP1, with PGE₂did not affect inositol phosphate generation by this receptor (FIG. 1B). Both EP1 and FP receptors are coupled to Gq-class of G-proteins and generate inositol phosphates upon stimulation with ligands. The inhibition of FP receptor by ectopically expressed PCP-1 and PCP-2 peptides is specific and these peptides will be modified to produce smaller and more diffusible inhibitors of FP function.

[0042] Effects of PCP-3 and PCP-4 Peptides of Human Gq Protein on FP Receptor Function

[0043] The second component of interaction between the FP receptor and G-protein is the domain of Gq which is composed of αN and αC helices (Lambright, D. G., et al., Nature, 379: 311-319, 1996). Peptides CLSEEAKEAR RINDEIERQL RRDKRDARRE-NH2 (SEQ ID NO:9) (PCP-3) and KDTILQLNLK EYNLV-NH₂(SEQ ID NO:10) (PCP-4), corresponding to αN and αC helices, respectively, were chemically synthesized using F moc chemistry and introduced transiently into permeabilized A549 cells. The cells were stimulated with PGF_2α, as described above and inositol phosphate synthesis was measured. The results are expressed as fold stimulation of phosphoinositide hydrolysis by the ligand (n=3). Both αN and αC helical peptides of Gq protein inhibited agonist-induced activation of FP receptor, whereas a control peptide (poly aspartic acid, Asp6) did not is affect the receptor function (FIG. 2A). PCP-3 and PCP-4, at 100 μM, were introduced into ³H-myo inositol-labeled permeabilized A549 cells and stimulated with 1 μM PGF_2α for 30 min. Inositol phosphates were separated by ion exchange chromatography and determined by scintillation counting. A dose-response of αC peptide on FP receptor revealed a half maximal inhibitory concentration of 50 μM of peptide under these conditions (FIG. 2B). In FIG. 2B, data are expressed as fold-stimulation by PGF_2α over control cells not treated with peptide.

[0044] While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.