THE CYTOTOXICITY OF MELPHALAN AND ITS RELATIONSHIP TO PH, HYPOXIA ANDDRUG UPTAKE

In the present in vitro studies we examined the effect of hypoxia and acidic pH, two important consequences of reduced blood flow in vivo, o n the cototoxicity of melphalan treatment in Chinese hamster V79-WNRE and SiHa human tumor cells. Cells were exposed to various concentratio ns of melphalan for 1 hr at 37 degrees C under oxic or hypoxic conditi ons, pH 6.6 or 7.4, and cell survival was measured. The cytotoxicity o f melphalan was potentiated by both low pH and hypoxia, in both cell l ines. The overall potentiation, expressed as an enhancement ratio (ER) , from both hypoxia and low pH was 3.5 in V79-WNRE and 2.9 in SiHa cel ls. The potentiation of cell killing produced by hypoxia alone (ER(Hyp )) ranged from 1.4 to 1.9, and was greater in V79-WNRE than in SiHa ce lls. The potentiation from low pH (ER(pH)) was approximately 2 in both cell lines. HPLC analysis showed substantial intracellular accumulati on of melphalan in both cell lines. Hypoxia and reduced pH further enh anced uptake of melphalan but this was not sufficient by itself to acc ount for eh increased potentiation of cytotoxicity observed under thos e conditions.