Diethylglyoxal bis(guanylhydrazone): a novel highly potent inhibitor of S-adenosylmethionine decarboxylase with promising properties for potential chemotherapeutic use.

Diethylglyoxal bis(guanylhydrazone) (DEGBG), a novel analog of the antileukemic agent methylglyoxal bis(guanylhydrazone) (MGBG) was synthesized. It was found to be the most powerful inhibitor of yeast S-adenosylmethionine decarboxylase (AdoMetDC) so far studied (Ki approx. 9 nM). This property, together with the finding that the compound is a weaker inhibitor of intestinal diamine oxidase than are MGBG and its glyoxal, ethylglyoxal and ethylmethylglyoxal analogs, makes the compound a promising candidate as a polyamine antimetabolite for chemotherapy studies. DEGBG was also found to potentiate the antiproliferative effect of the ornithine decarboxylase inhibitor alpha-difluoromethyl ornithine against mouse L1210 leukemia cells in vitro. DEGBG increased several-fold the intracellular putrescine concentration of cultured L1210 cells, just as MGBG and its ethylglyoxal analog are known to do. The results strongly suggest that DEGBG is worth further studies. Combined with previous studies, they also made possible the construction of some empirical rules concerning the structure-activity relationships of bis(guanylhydrazone) type inhibitors of AdoMetDC. The identity of DEGBG was confirmed by a single-crystal X-ray analysis and by 1H- and 13C-NMR spectroscopy. It consisted of the same isomer as MGBG and several of its analogs are known to consist of.