An allylamine derivative (MDL 72145) with potent irreversible inhibitory actions on rat aorta semicarbazide-sensitive amine oxidase

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Abstract
(E)-2-(3, 4-dimethoxyphenyl)-3-fluoroallylamine (MDL 72145) was found to be an extremely potent inhibitor of the semicarbazide-sensitive amine oxidase (SSAO) in rat aorta homogenates. Considerable inhibition, which was not reversed by dialysis, could be produced under appropriate in-vitro conditions at drug concentrations around 10 nM. The pseudo first order kinetics for time-dependent inhibition by MDL 72145 (10–100 nM) were found to be consistent with a bimolecular reaction between enzyme and inhibitor with a rate constant for this step of 2 times 106 min−1 M−1. A similar rate of inhibition under an oxygen atmosphere to that obtained under nitrogen was produced upon incubation of enzyme with inhibitor, suggesting that oxidation of the inhibitor to an active metabolite was not required for its activity. Incubation of homogenates for very short periods (1 min) with inhibitor (0.05-0.5 μM) and benzylamine (1–10 μM) as substrate indicated non-competitive kinetics for the early interaction of enzyme with the drug. Benzylamine (50 μM), but not pyridoxal phosphate (100 μM), was able to protect SSAO from inhibition by 10 nM MDL 72145. However, pyridoxal phosphate alone appeared to produce some irreversible inhibition of the enzyme. Dialysis against buffer containing 50 μM or 1 mM benzylamine was unable to reactivate SSAO inhibited by 10 nM MDL 72145. It is concluded that MDL 72145 irreversibly inhibits SSAO by acting at, or near, the substrate binding site, but the exact nature of the complex formed remains to be identified.