Mitochondrial effects of the guanidino group-containing cytostatic drugs, m-iodobenzylguanidine and methylglyoxal bis (guanylhydrazone)

The involvement of mitochondrial damage in the antiproliferative effects of m-iodobenzylguanidine [MIBG] and methylglyoxal bis (guanylhydrazone) [methylGAG] was studied in human neuroblastoma SK-N-SH, mouse neuroblastoma N 1E115 and mouse lymphosarcoma S49 cells. Proliferation of SK-N-SH cells was insensitive to MIBG (100 μM gave 15% inhibition), but sensitive to methylGAG ( ic 50 = 50 μ M) . MIBG and methlyGAG were approximately equitoxic to N 1E115 cells ( ic 50 of 92 and 87 μM, respectively). S49 cells were most sensitive to both MIBG ( ic 50 = 11 μ M) and methylGAG ( ic 50 = 5 μ M) . In isolated sonicated mitochondria, MIBG inhibited respiration at complex I of the respiratory chain ( ec 50 = 0.5 mM) , whereas methylGAG was much less effective ( ec 50 > 15 mM ). In intact cells, MIBG at 31 μM impaired mitochondrial respiration and stimulated the glycolytic flux. In contrast, equimolar concentrations of methylGAG had no effect on oxygen consumption, ATP content, glucose consumption and lactate production. MethylGAG significantly increased putrescine levels in N 1E115 and S49 cells within 12 hr via inhibition of S-adenosylmethionine decarboxylase. No such effects were seen in SK-N-SH cells for up to 48 hr. Equimolar concentrations of MIBG had no effect on the putrescine levels in the various cell lines, suggesting that MIBG did not inhibit S-adenosylmethionine decarboxylase. It is concluded that the antiproliferative mechanisms of the guanidino compounds are essentially different. MIBG inhibited mitochondrial respiration at complex I with concomitant stimulation of the glycolytic flux but was essentially without effect on polyamine levels. On the other hand, cytotoxicity of methylGAG was not associated with mitochondrial dysfunction.