Independence of drug action on mitochondria and polyamines in L1210 leukemia cells treated with methylglyoxal-bis(guanylhydrazone).

The relationship between inhibition of polyamine biosyn thesis and interference with mitochondria! structure and func tion by the antitumor agent, methylglyoxal-bis(guanylhydrazone) (MGBG), was examined by studying the temporal sequence of events relevant to these two drug actions. In ascites L1210 cells treated in vivo with a single dose of MGBG (75 mg/kg), significant inhibition of pyruvate utilization, used here as a measure of mitochondrial function, occurred within 1 hr after initiation of drug treatment and continued to decrease for 24 hr. Ultrastructural damage to mitochondria, in the form of swelling, was first apparent in 50% of the cells after 6 hr of treatment and in > 90% of the cells after 20 hr. Inhibition of Sadenosylmethionine decarboxylase, a key enzyme in spermidine and spermine biosynthesis, occurred within 1 hr of drug treatment. Enzyme levels increased dramatically after 8 hr of treatment as a result of MGBG stabilization of the enzyme. Beginning at 8 hr, ornithine decarboxylase, the enzyme re sponsible for putrescine synthesis, increased slightly and con tinued to rise slowly during the next 16 hr. As a consequence of S-adenosylmethionine decarboxylase inhibition by MGBG, intracellular putrescine pools began to accumulate after 2 hr of treatment and increased rapidly after 12 hr. In contrast, sperm ine pools decreased slowly after 4 hr while spermidine pools decreased even more slowly. However, even after 24 hr, sig nificant amounts of both polyamines were still present intracellularly. Since MGBG-induced changes in mitochondrial function pre cede significant alterations in polyamine pools, it is concluded that the two effects are separable. This conclusion is further supported by the finding that, in cultured L1210 cells treated with a-methylornithine at concentrations which effectively in hibited putrescine and spermidine biosynthesis, the mitochon drial ultrastructure was unaffected. Results of the present study raise the possibility that MGBG interference with mitochondrial function might be responsible for the early antiproliferative action of the drug.