Effect of inhibitors of S-Adenosylmethionine decarboxylase on polyamine content and growth of L1210 cells

Abstract

Analogues of S-adenosylmethionine that were designed as inhibitors of S-adenosylmethionine decarboxylase were tested for their abilities to inhibit the purified enzyme from rat prostate. The most potent inhibitors were 5'-deoxy-5'-[N-methyl-N-[2-(aminooxy)ethyl]amino]adenosine (MAOEA) and 5'-deoxy-5'-[N-methyl-N-(3-hydrazinopropyl)amino]adenosine (MHZPA), which had I50 values of 400 nM and 70 nM, respectively, when added directly to the assay medium under standard conditions. These compounds were irreversible inactivators of the enzyme, and more than 95% of the activity was lost within 15 min of exposure to 5 microM MAOEA or 0.5 microM MHZPA. Both inhibitors led to a large reduction in the content of decarboxylated S-adenosylmethionine in L1210 cells and to a substantial decrease in the production of 5'-(methylthio)adenosine by these cells. These results are consistent with their bringing about an inhibition of S-adenosylmethionine decarboxylase activity in the cell which leads to a reduction in the synthesis of spermidine and spermine. Analysis of the polyamine content in L1210 cells exposed to 100 microM MAOEA or 50 microM MHZPA showed that this was the case and that putrescine levels were greatly increased while spermidine and spermine content declined. The combined application of 100 microM MAOEA and 5 mM alpha-(difluoromethyl)ornithine (an ornithine decarboxylase inhibitor) to L1210 cells completely prevented the synthesis of putrescine, spermidine, and spermine for up to 48 h. The reduction in polyamine content brought about by MHZPA or MAOEA could be partially prevented by the addition of decarboxylated S-adenosylmethionine to the culture medium. These inhibitors also brought about an inhibition of cell growth which could be reversed by the addition of spermidine.(ABSTRACT TRUNCATED AT 250 WORDS)