Effects of bleomycin on Burkitt lymphoma cells grown in vitro and in vivo.

The effects of bleomycin (BLM) on the survival of Burkitt lymphoma cells grown in vitro and in vivo were studied. Cells at the early plateau phase in culture were much more resistant to BLM than at the exponential phase. The late plateau-phase cells showed the highest sensitivity to the drug among the three phases of growth. After exposure to BLM, no recovery in survival was found for the cells in culture. Burkitt tumor in nude mice grew exponentially with about a threefold longer cell cycle time than the cells in culture, but the age-distribution of cells in the tumor was similar to that of the exponentially growing culture. The cells in the tumor were killed by BLM in a biphasic manner and did not show any significant recovery in survival after an injection of the drug, as found with the cells in culture. These findings indicate a deficiency in the repair of potentially lethal damage in Burkitt cells induced by BLM; this may be one of the reasons for the high sensitivity of the lymphoma to the drug.