Highly potent inhibition of prostaglandin 15-hydroxydehydrogenase in-vitro and of prostaglandin inactivation in perfused lung by the new azobenzene analogue, Ph CL 28A

Abstract

Abstract The new azobenzene analogue Ph CL 28A (2-hydroxy-5-(3,5-dimethoxycarbonyl-benzoyl)-benzene acetic acid) potently inhibited prostaglandin 15-hydroxydehydrogenase (PGDH) in the nanomolar range in-vitro and inhibited prostaglandin inactivation in rat perfused lung at similar concentrations, and is the most potent PGDH inhibitor yet available. It was synthesized because electronegative substituents in the B ring of homosalazine enhance PGDH inhibitory potency. Ph CL 28A inhibited human placental PGDH non-competitively with regard both to substrate PGF2α (Ki = 18.7 ± 0.9 nM) and the NAD+ cofactor (Ki= 57.6 ± 2.9 nM); inhibition was greatly reduced at pH > 8.0. PhCL 28A hydrolyses spontaneously in alkali (t 1/2 at pH 9.0 = 45 h) to the less active dicarboxylic acid (IC50 human placental PGDH 1.6 μM versus 0.028 μm for Ph CL 28A). The new analogue is 1000 x more active than the parent compound sulphasalazine from which it derives. The IC50 values for five azobenzene analogues in rat perfused lung (Ph CL 28A = 72 nM) correlated strongly with those obtained using purified PGDH (r = 0.99), suggesting that they inhibit pulmonary prostaglandin degradation at the enzyme step rather than at the hypothetical carrier. The new compound will be a useful probe for PGDH structure and function.