Human lymphoma cells develop resistance to radiation in the presence of astrocytes in vitro

Background: Lymphomas growing in the central nervous system exhibit resistance to radiotherapy compared to lymphomas of the lymph nodes. Because astrocytes have been shown to reduce radiation-induced neuronal toxicity, this study hypothesized that astrocytes might protect lymphoma cells from radiation-induced cell killing. Materials and Methods: A human lymphoma cell line, H9, and normal human astrocytes were grown in culture, exposed to radiation and assessed for cell viability, radiation sensitivity, glutathione content, induction of apoptosis and cell-cycle distribution. Results: Cell survival assays demonstrated that H9 cells growing in an astrocyte-monolayer and also in an astrocyte-conditioned medium displayed radioresistance compared with H9 cells growing under standard conditions. The radioresistance correlated with accumulation of H9 cells in the G₂ phase of the cell cycle, suppression of radiation-induced apoptosis and coincided with a moderate increase in glutathione. Conclusion: The findings of this study suggest that astrocytes may play a role in the radioresistance exhibited by lymphomas of the central nervous system.