Modification of uptake and antiproliferative effect of methylglyoxal bis(guanylhydrazone) by treatment with alpha-difluoromethylornithine in rodent cell lines with different sensitivities to methylglyoxal bis(guanylhydrazone)

Abstract

Uptake characteristics and growth-inhibitory effects of methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase, were investigated in 9L rat brain tumor cells and in V79 hamster lung cells. Proliferation of 9L cells was only slightly inhibited by treatment with 40 microM MGBG alone, but when used in combination with 0.5 mM alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, proliferation was much more effectively inhibited. The intracellular concentration of MGBG was approximately 2-fold higher 4 days after cells were treated with both DFMO and MGBG, either simultaneously or when MGBG was added after a 48-hr DFMO pretreatment, than that in cells treated with MGBG alone. Polyamine levels in DFMO- and MGBG-treated cells correlated with the antiproliferative effects of the drugs. Used either alone or in combination with 1 mM DFMO, 0.5 microM MGBG inhibited the growth of and eventually killed V79 cells. Simultaneous or sequential treatment with DFMO and MGBG increased intracellular concentrations of MGBG at 4 days by 2- and 3-fold, respectively, compared to treatment with MGBG alone. Intracellular polyamine levels did not correlate with the antiproliferative effect of the two drugs in V79 cells. In both cell lines, polyamines and MGBG share a common transport system. The net transport of polyamines and MGBG was more temperature dependent and up to 10-fold more active in V79 cells than in 9L cells. The Km and Vmax values for spermidine and MGBG measured 10 sec after addition (initial permeation) were not affected by DFMO pretreatment in either cell line. However, 1 hr after administration, the Vmax values for spermidine and MGBG uptake were doubled in V79 cells pretreated for 48 hr with DFMO; no significant change occurred in 9L cells. Mitochondrial function, assessed by pyruvate oxidation, was substantially impaired by MGBG in V79 cells but not in 9L cells when the intracellular concentrations of MGBG were equal in each cell line. Pretreatment with DFMO did not increase MGBG-induced inhibition of pyruvate oxidation in V79 cells. These results show that, compared with V79 cells, the decreased sensitivity of 9L cells to MGBG may be related to decreased intracellular MGBG accumulation but not to cellular permeation such as carrier transport. Results of measurements of both polyamine levels and mitochondrial function indicate that V79 cells may be more susceptible to nonpolyamine-dependent effects of MGBG than are 9L cells.