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.