Cytotoxicity of Methylglyoxal Bis(guanylhydrazone) in Combination With α-Difluoromethylornithine Against HeLa Cells and Mouse L1210 Leukemia

Abstract

The cytotoxicity was determined for a combination of α-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG) in HeLa cells in culture and in an experimental animal tumor system, L1210 leukemia in (C57BL/6J × DBA/2J)F1 mice. DFMO (2.5 mM) was found to be cytotoxic to HeLa cells. DFMO treatment for 96 hours killed about 50% of the cells as measured by a cloning assay. MGBG at a concentration of 25 µM for 4 hours killed only 40% of the cells, whereas after DFMO pretreatment, the same dose killed nearly 100% of the cells. Coincidental with this increase ih cell killing was a threefold increase in the uptake of [U-14C]MGBG in DFMO-treated cells compared to the uptake in control cells. While the mechanisms of cellular uptake of DFMO and [U-14C]- MGBG appear to be different, an inverse correlation was observed between the intracellular levels of polyamines and the uptake of [U-14C]MGBG. Furthermore, exogenously added polyamines inhibited the uptake of [U-14C]MGBG, which suggests a common mode of entry of these compounds into mammalian cells. Studies with mouse L1210 leukemia also showed a threefold to sixfold increase in the uptake of [U-14C]MGBG by tumor cells from DFMO-treated leukemic mice. A therapeutic potentiation was obtained with respect to an increase in the life-span of the tumor-bearing mice treated with MGBG combined with DFMO. DFMO (2% in the drinking water) had little effect on the increase in life-span (10%). MGBG at 25 mg/kg and 50 mg/kg increased survival by 1.9-3.0 days. However, a combination of DFMO and MGBG increased survival by 4.8-5.4 days. In toto, these observations suggest that cancer chemotherapeutic schedules involving a combination of MGBG and DFMO may be uniquely effective.