Potentiation of CCNU toxicity by AF-2 in V79 spheroids: implications for mechanisms of chemosensitization.

Spheroids of Chinese hamster V79-171 cells were incubated for 1.5 hr. with 0-10 micrograms/ml of the nitrofuran AF-2 (a potent radiosensitizer and hypoxic cell cytotoxin) under 1-10% oxygen, then exposed to 0-3 micrograms/ml CCNU for a further 30 minutes in the presence of the AF-2 and a fluorescent bisbenzimide stain. Single cells from the disaggregated spheroids were then sorted by a dual laser cell sorter for subsequent analyses of clonogenicity. Two sorting criteria were intercompared: sorting on the basis of cell position in the spheroid (defined by the bisbenzimide uptake), or on the basis of the bound AF-2 (which is itself fluorescent). These studies indicated chemosensitization was not observed in the absence of AF-2 toxicity, cellular oxygen content modified AF-2 toxicity more than AF-2 potentiation of CCNU toxicity, and cellular susceptibility to intracellular AF-2 dominated the net response.