AL-8810: a novel prostaglandin F2 alpha analog with selective antagonist effects at the prostaglandin F2 alpha (FP) receptor

A novel analog of prostaglandin F(2alpha) [AL-8810; (5Z, 13E)-(9S, 11S,15R)-9,15-dihydroxy-11-fluoro-15-(2-indanyl)-16,17,18,19, 20-pentanor-5,13-prostadienoic acid] has been discovered with uniquely low efficacy (E(max)) at the endogenous prostaglandin F(2alpha) receptors (FP receptors) of A7r5 rat thoracic aorta smooth muscle cells and Swiss mouse 3T3 fibroblasts, as assayed by stimulation of Phospholipase C activity. AL-8810 has weak agonist potency (EC(50)) of 261 +/- 44 nM (n = 3) and E(max) = 19% (relative to the full FP receptor agonist cloprostenol) in A7r5 cells and EC(50) of 186 +/- 63 nM (n = 3) and E(max) = 23% in 3T3 fibroblasts. AL-8810 exhibited properties of an apparent competitive antagonist, i.e., produced parallel dextral shifts of the agonist concentration-response curves and no significant suppression of the maximal agonist-induced response, when the potent, selective FP receptor agonist fluprostenol was used. The inhibition parameters of AL-8810 were: pA(2) = 6.68 +/- 0.23 and 6.34 +/- 0.09 (n = 3-4) for A7r5 cells and 3T3 cells, respectively, with Schild slopes ranging from 0.80 to 0.92. AL-8810 concentration-dependently antagonized the response to 100 nM fluprostenol (K(i) = 426 +/- 63 nM; n = 5) in A7r5 cells. However, even at 10 microM concentration, AL-8810 did not significantly inhibit functional responses of TP, DP, EP(2), EP(4), receptor subtypes in various cell lines. AL-8810 also did not antagonize the Phospholipase C-coupled V(1)-vasopressin receptor in A7r5 cells. These results suggest that AL-8810 is a unique, selective antagonist at the FP receptor, a heretofore unavailable pharmacological tool that should be valuable for studying FP receptor-mediated functional responses in complex biological systems.