RO1138452 and RO3244794: characterization of structurally distinct, potent and selective IP(prostacyclin) receptor antagonists

1 Prostacyclin (PGI(2)) possesses various physiological functions, including modulation of nociception, inflammation and cardiovascular activity. Elucidation of these functions has been hampered by the absence of selective IP receptor antagonists. 2 Two structurally distinct series of IP receptor antagonists have been developed: 4,5-dihydro-1H-imidazol-2-yl)-[4-(4-isopropoxy-benzyl)-phenyl]-amine (RO1138452) and R-3-(4-fluoro-phenyl)-2[5-(4-fluoro-phenyl)-benzofuran-2-ylmethoxycarbonylamino]-propionic acid (RO3244794). 3 RO1138452and RO3244794 display high affinity for IP receptors. In human platelets, the receptor affinities (pK(i)) were 9.3 +/- 70.1 and 7.77 +/- 0.03, respectively; in a recombinant IP receptor system, pK(i) values were 8.77 +/- 0.06 and 6.97 +/- 0.1, respectively. 4 Functional antagonism of RO1138452and RO3244794 was studied by measuring inhibition of carbaprostacyclin-induced cAMP accumulation in CHO-K1 cells stably expressing the human IP receptor. The antagonist affinities (pK(i)) of RO1138452and RO3244794 were 9.07 +/- 0.06 and 8.57 +/- 0.11, respectively. 5 Selectivity profiles for RO1138452and RO3244794 were determined via a panel of receptor binding and enzyme assays. RO1138452 displayed affinity at I-2 (8.3) and PAF (7.9) receptors, while RO3244794 was highly selective for the IP receptor: pKi values for EP1 (< 5), EP3 (5.38), EP4 (5.74) and TP (5.09). 6 RO1138452(1-10 mg kg(-1), i.v.) and RO3244794 (1-30 mg kg(-1), i.v.) significantly reduced cetic acid-induced abdominal constrictions. RO1138452(3-100 mg kg(-1), p.o.) and RO3244794 (0.3-30 mg kg(-1), p.o.) significantly reduced carrageenan-induced mechanical hyperalgesia and edema formation. RO3244794 (1 and 10 mg kg(-1), p.o.) also significantly reduced chronic joint discomfort induced by monoiodoacetate. 7 These data suggest that RO1138452and RO3244794 are potent and selective antagonists for both human and rat IP receptors and that they possess analgesic and anti-inflammatory potential.