Cytotoxic effect of RA233 on hypoxic B16 melanoma cells in vitro

The pyrimido-pyrimidine derivative RA233 was found to selectively kill cultured mouse B16 melanoma cells after prolonged hypoxia. At the optimum cytotoxic concentration (100 microM), RA233 reduced cell clonogenicity by about 80% when administered during long-term hypoxia of 4 days. Comparable cytotoxicity was also evident when RA233 was present only during re-oxygenation following 4 days of hypoxia. RA233 treatment during both hypoxia and re-oxygenation resulted in the greatest cytotoxicity, with only about 1% of cells surviving such treatment. By contrast, the hypoxic cell sensitizer misonidazole was cytotoxic only when administered during hypoxia. RA233 appears to be a unique hypoxic cell sensitizer that kills long-term hypoxic tumor cells principally during re-oxygenation.