R), and oxytocin receptor, respectively] contrasting with AVP's lack of selectivity, especially versus the V 2 R (selectivity ratio of 1:18:0.2:92; human V 1a R EC 50 ϭ 0.24 nM). This activity and selectivity profile was confirmed in radioligand binding assays. FE 202158 was a potent vasoconstrictor in the isolated rat common iliac artery ex vivo (EC 50 ϭ 3.6 nM versus 0.8 nM for AVP) and reduced rat ear skin blood flow after intravenous infusion in vivo (ED 50 ϭ 4.0 versus 3.4 pmol/kg/min for AVP). The duration of its vasopressor effect by intravenous bolus in rats was as short as AVP at submaximally effective doses. FE 202158 had no V 2 R-mediated antidiuretic activity in rats by intravenous infusion at its ED 50 for reduction of ear skin blood flow, in contrast with the pronounced antidiuretic effect of AVP. Thus, FE 202158 seems suitable for treatment of conditions where V 1a R activity is desirable but V 2 R activity is potentially deleterious, such as vasodilatory hypotension in septic shock. In addition to the desirable selectivity profile, its shortacting nature should allow dose titration with rapid onset and offset of action to optimize vasoconstriction efficacy and safety.
Objective To test the selectivity and degree of functional agonism of Ocelot Bio’s dual agonist/antagonist molecule, OCE-205, at the vasopressin 1a receptor (V1aR). Methods Cells expressing human (h) or rat V1a, V1b, V2, or oxytocin receptors (OTR) were incubated with varying concentrations of OCE-205 or with arginine vasopressin (AVP), and responses were measured with fluorescence or reporter gene assays. In addition, human resistance arteries were exposed to increasing concentrations of OCE-205, and the resulting contractility was measured. Results The mean efficacy of OCE-205 at hV1aR was 39% of the maximal possible effect (MPE), with a mean EC50 of 0.71 nM. Above 1 nM OCE-205, the percent maximal possible effect (%MPE) plateaued. The EC50 was much higher at hV1bR (134 nM), hV2R (420 nM), and OTR (6.9 nM), indicating selectivity for hV1aR. Results at rat receptors were similar. OCE-205 produced 40.0% of maximal depolarization-induced contraction, demonstrating functional partial agonism. Conclusion The dual agonist/antagonist structure of OCE-205 thus allows it to act as a highly selective partial agonist at vasopressin V1aR at therapeutically relevant concentrations.
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