Use of a novel and highly selective oxytocin receptor antagonist to characterize uterine contractions in the rat

Abstract

Spontaneous and induced uterine contractions in the rat were found to be inhibited by a novel and selective oxytocin receptor antagonist GSK221149A (3R,6R)-3-Indan-2-yl-1-[(1R)-1-(2-methyl-1,3-oxazol-4-yl)-2-morpholin-4-yl-2-oxoethyl]-6-[(1S)-1-methylpropyl]-2,5-piperazinedione. GSK221149A displayed nanomolar affinity (K(i) = 0.65 nM) for human recombinant oxytocin receptors with >1,400-fold selectivity over human V1a, V1b, and V2 receptors. GSK221149A had similar affinity (K(i) = 4.1 nM) and selectivity for native oxytocin receptors from rat and produced a functional, competitive block of oxytocin-induced contractions in isolated rat myometrial strips with a pA(2) value of 8.18. Intravenous administration of GSK221149A produced a dose-dependent decrease in oxytocin-induced uterine contractions in anesthetized rats with an ID(50) = 0.27 +/- 0.60 mg/kg (corresponding plasma concentrations were 88 ng/ml). Oral administration of GSK221149A (5 mg/kg) was effective in inhibiting oxytocin-induced uterine contractions after single and multiple (4-day) dosing. Spontaneous uterine contractions in late-term pregnant rats (19-21 days gestation) were significantly reduced by intravenous administration of 0.3 mg/kg of GSK221149A. These results provide further evidence that selective oxytocin receptor antagonism may offer an effective treatment for preterm labor.

The design of orally bioavailable 2, 5‐diketopiperazine oxytocin antagonists: from concept to clinical candidate for premature labor

“…GSK221149A is greater than 15-fold more potent than atosiban with a far superior selectivity profile with respect to vasopressin receptors. 41 The OTR selectivity for 74 vs. these receptors is 418,000 for hV1a, 415,000 for hV1b, and 41,400 for hV2). A further measure of the potency of our lead OT antagonist 74 was established by its functional OT antagonist activity (fpK i ) in whole cells (by the FLIPR assay 27 ).…”

“…7). 41 Uterine activity was measured as an integral of force Intravenous administration of GSK221149A to late-term pregnant rats significantly reduced spontaneous uterine contractions in a dose-dependent manner (Fig. 8).…”

“…In particular 74 was prepared as the major isomer from the acid 45 (R 1 5 2-Me-4-oxazole, R 2 5 CH(S)MeCH 2 Me) by activation with benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate followed by the addition of morpholine and subsequent column chromatography yielded homo-chiral GSK221149A. 41 …”

Oxytocin and Myometrial Contractility in Labor

“…In addition, spontaneous uterine contractions in late-term pregnant rats (at 19-21 days gestation) were significantly reduced by intravenous administration of GSK221149A at a dose of 0.3 mg/kg. In vitro experiments using Chinese hamster ovary (CHO) cell membranes expressing human OT receptors or human V1a, V1b, or V2 receptors, and human endothelial kidney (HEK) cells expressing rat oxytocin receptors showed that GSK221149A also has a higher affinity for human and rat oxytocin receptors than for V1a and V2 receptors (McCafferty et al, 2007). GSK221149A is over 15-fold more potent compared to atosiban for the OTR (Borthwick and Liddle, 2011).…”

Oxytocin receptor ligands: a survey of the patent literature

“…Oxytocin OTR (h) COS-7 0.7 OT [25] OTR (h) CHO 0.5 OTA [55] OTR (r) CHO 1.9 OTA [55] V1AR (h) CHO 123 OTA [55] V1AR (r) CHO 120 OTA [30] V1AR (r) COS-7 845 LVA [110] V1BR (h) CHO 1782 OTA [111] V2R (h) CHO 1544 OTA [55] V2R (r) CHO 3500 OTA [30] [Arg 8 ]-vasopressin OTR (h) COS-7 6.5 OT [25] OTR (h) CHO 1.7 OTA [112] OTR (r) CHO 1.7 OTA [112] V1AR (h) CHO 1.1 AVP [112] V1AR (r) CHO 2.6 AVP [112] V1BR (h) CHO 0.7 AVP [112] V1BR (r) CHO 3.3 AVP [112] V2R (h) COS-7 0.6 OT [25] V2R (h) CHO 1.2 AVP [112] V2R (r) CHO 0.5 AVP [112] Carbetocin OTR (h) COS-7 7.1 OT [25] OTR (r) Uterus 2.0 § OT [36] V1AR (r) Uterus 7.2 § AVP [36] V2R (r) Kidney 61.3 § AVP [36] Peptide antagonists OTR (h) Rec Ltk 895 OTA [50] OTR (h) Uterus 775 OTA [50] OTR (h) UtSMC 561 OTA [50] OTR (h) CHO 81 OTA [55] OTR (h) CHO 11 OT [47] OTR (h) HEK293 27 OTA [55] OTR (r) Uterus 215 OTA [50] OTR (r) CHO 76 OTA [55] OTR (r) CHO 32 OT [47] V1AR (h) CHO 0.15 AVP [47] V1AR (r) Liver 1059 AVP [50] V1AR (r) Liver 310 AVP [47] V1BR (h) CHO 44 AVP [47] V1BR (r) CHO 241 AVP [50] V2R (h) CHO 330 AVP [47] V2R (r) Kidney > 1000 AVP [50] V2R (r) Kidney 29 AVP [47] Barusiban OTR (r) Breast 8.9 OT [41] ...…”