Pharmacological profile of T-0632, a novel potent and selective CCKA receptor antagonist, in vitro.

The pharmacological profile of a new CCKA receptor antagonist, T-0632 [sodium (S)-3-[1-(2-fluorophenyl)-2,3-dihydro-3-[(3-isoquinolinyl)-carbonyl] amino-6-methoxy-2-oxo-1-H-indole]propanoate], was examined in in vitro studies and compared with those of L-364,718 [3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1, 4-benzodiazepine-3-yl)-1H-indole-2-carboxamide] and loxiglumide [D,L-4-(3,4-dichlorobenzoylamino)-5-(N-3-methoxypropyl-pentylam ino)-5- oxopentanoic acid]. T-0632 inhibited the specific binding of [125I]CCK-8 to rat pancreatic CCKA receptor in a concentration-dependent and competitive manner. The Ki value of T-0632 for the CCKA receptor was estimated to be 0.24 nM, which was 23 000-fold less than the Ki value (5600 nM) for guinea pig CCKB receptor. L-364,718 and loxiglumide were 1500- and 64-fold selective for CCKA over CCKB receptor, respectively. T-0632, L-364,718 and loxiglumide inhibited CCK-8 (100 pM)-stimulated amylase release from rat pancreatic acini in a concentration-dependent manner with IC50 values of 5.0 nM, 5.0 nM and 3.0 microM, respectively. In the isolated rabbit gallbladder smooth muscle, T-0632 and loxiglumide competitively inhibited CCK-8-induced contraction with pA2 values of 8.5 and 7.0, respectively. However, L-364,718 showed an apparent non-competitive antagonism. The IC50 values of T-0632, L-364,718 and loxiglumide for CCK-8 (30 nM)-induced contraction were 31 nM, 4.9 nM and 1300 nM, respectively. The inhibitory effects of T-0632 and loxiglumide in gallbladder smooth muscle were readily reversible, but L-364,718 showed a long-lasting inhibition. These results suggest that T-0632 is a potent, reversible and more selective CCKA receptor antagonist compared with L-364,718 and loxiglumide.