Biochemical Pharmacology, Vol. 36, No. 17, pp. 2847-2853, 1987. 0006-2952/87 $3.00 + 0.00 Printed in Great Britain. ~) 1987. Pergamon Journals Ltd. INHIBITION OF RAT AORTA SEMICARBAZIDE-SENSITIVE AMINE OXIDASE BY 2-PHENYL-3-HALOALLYLAMINES AND RELATED COMPOUNDS GEOFFREY A. LYLES,* C. M. SUSAN MARSHALL, IAN A. MCDONALD,'~ PHILIPPE BEYt and MICHAEL G. PALEREYMANt Department of Pharmacology and Clinical Pharmacology, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, Scotland, U.K., and tMerrell Dow Research Institute, 2110 East Galbraith Road, Cincinnati, OH 45215, U.S.A. (Received 18 February i987; accepted 31 March 1987) Abstract--The inhibition of semicarbazide-sensitive amine oxidase (SSAO) in rat aorta homogenates by some 2-phenyl-3-haloaUylamines has been studied. Derivatives containing a fluorine atom were approximately three times more potent than the corresponding 3-chloroallylamines. These halogen- containing compounds were irreversible inhibitors of SSAO after preincubation with aorta homogenates; kinetic evidence for an initial competitive, reversible interaction (K~ around 0.4-0.6/~M) was found with two compounds (MDL 72145 and 72274). A similar Ki (approx. 0.7/~M) was obtained with 2- phenylallylamine (MDL 72200). However, this compound which lacks a halogen atom was a reversible inhibitor, even after preincubation. The use of a spectrophotometric assay to measure H202 production from amine metabolism demonstrated that MDL 72200 was a substrate (K,, = 1.4/*M) for SSAO, with a Vmax approximately five times smaller than that of benzylamine (K,, = 8.1/~M). Of particular interest in this study is the finding that (E)-2-phenyl-3-chloroallylamine(MDL 72274) is highly selective as an inhibitor of SSAO, compared with MAO-A or B activities, and may be a useful compound for investigating the importance of SSAO in animal tissues. The mitochondrial enzyme monoamine oxidase (MAO) exists in two forms called MAO-A and MAO-B, which have different substrate specificities and which can be distinguished by their relatively greater sensitivities towards inhibition by the ace- tylenic compounds clorgyline and deprenyl, respect- ively. As a consequence, the development of selec- tive inhibitors for these MAO subtypes has attracted considerable interest with the anticipation that this approach may provide therapeutic agents with more advantageous and safer pharmacological profiles compared with non-selective MAO inhibitors in cur- rent clinical use (see ref. 1 for review). The sel- ectivities and potential uses of a variety of new compounds, of considerably diverse chemical struc- ture, are currently under evaluation in a number of laboratories. One particular group of drugs acting as irreversible MAO inhibitors is a series of 2-phenyl- 3-haloallylamine derivatives [2]. Among these, the MAO-B selective properties of MDL 72145 [(E)-2- (3,4-dimethoxyphenyl)-3-fluoroallylamine] have been described in some detail [3, 4]. In addition to MAO-A and B, many animal tissues also contain a semicarbazide-sensitive amine oxidase (SSAO), with particularly high activity in blood ves- sels where the enzyme is associated predominantly with smooth muscle cells [5, 6]. Although the prop- erties of this enzyme are under continuing inves- tigation, its physiological role and the importance of its inhibition in oioo by various drugs remains unknown (reviewed in refs 7 and 8). * To whom correspondence should be addressed. !, We recently reported that MDL 72145 is a potent irreversible inhibitor of SSAO in rat aorta homo- genates at concentrations similar to or even below those required to produce MAO-B inhibition in other tissues [9]. In the current study we examined the inhibition of SSAO by related 2-phenyl-3-halo- allylamines. From the results obtained it appears that 2-phenyl-3-haloallylamines constitute a new class of inhibitor of SSAO, which may belong to the family of amine oxidases thought to contain copper and pyridoxal phosphate (or another carbonyl reagent- sensitive moiety) as cofactors (see ref. 10). In addition, we have identified one compound [(E)-2- phenyl-3-chloroallylamine, MDL 72274] with high potency and particular selectivity as an inhibitor of SSAO compared with MAO. Preliminary details of some of these findings have been reported previously [11]. MATERIALS AND METHODS Animals and chemicals. Adult male Wistar rats (200-500 g) were obtained from our Departmental breeding colony, Animal Services Unit, University of Dundee. (Methylene-14C)-benzylamine hydrochloride and (G-3H)-5-hydroxytryptamine creatinine sulphate were purchased from Amersham International PLC (Amersham, U.K.). The following drugs and reagents were obtained from Sigma (London) Chemical Co. (Poole, U.K.): 2,2'-azino-bis(3-ethyl- benzthiazolinesulphonic acid) (ABTS, diammonium salt), horseradish peroxidase (type II), and the 2847