Controlling of N-alkylpolyamine analogue metabolism by selective deuteration

Abstract

Replacing protium with deuterium is an efficient method to modulate drug metabolism. N-alkylated polyamine analogues are polyamine antimetabolites with proven anticancer efficacy. We have characterized earlier the preferred metabolic routes of N¹,N¹²-diethylspermine (DESpm), N¹-benzyl-N¹²-ethylspermine (BnEtSpm) and N¹,N¹²-dibenzylspermine (DBSpm) by human recombinant spermine oxidase (SMOX) and acetylpolyamine oxidase (APAO). Here, we studied the above analogues, their variably deuterated counterparts and their metabolites as substrates and inhibitors of APAO, SMOX, semicarbazide-sensitive amine oxidase (SSAO), diamine oxidase (DAO) and monoamine oxidases. We found that targeted deuteration efficiently redirected the preferable cleavage site and suppressed reaction rate by APAO and SMOX in vitro We found a three- to six-fold decline in V_max with moderate variable effect on K_m when deuterium was located at the preferred hydrogen abstraction site of the analogue. We also found some of the metabolites to be potent inhibitors of DAO and SSAO. Surprisingly, analogue deuteration did not markedly alter the anti-proliferative efficacy of the drugs in DU145 prostate cancer cells, while in mouse embryonic fibroblasts, which had higher basal APAO and SMOX activities, moderate effect was observed. Interestingly, the anti-proliferative efficacy of the analogues did not correlate with their ability to suppress polyamine biosynthetic enzymes, induce spermidine/spermine-N¹-acetyltransferase or deplete intracellular polyamine levels, but correlated with their ability to induce SMOX. Our data show that selective deuteration of N-alkyl polyamine analogues enables metabolic switching, offering the means for selective generation of bioactive metabolites inhibiting, e.g. SSAO and DAO, thus setting a novel basis for in vivo studies of this class of analogues.

Keywords: deuterium; flavin-dependent amine oxidoreductases; kinetic isotope effect; metabolic switching; polyamines; spermine oxidase.