High and low dose rate irradiation have opposing effects on cytokine gene expression in human glioblastoma cell lines

Effects of radiation on five cytokine expressing human glioblastoma cell lines were studied. In comparison to unirradiated controls, IL-1β and IL-6 mRNAs were generally reduced after low (LDR, 1.0 cGy/min) and very low (VLDR, 0.35 cGy/min) dose rate irradiation. In contrast, high (HDR, 200 cGy/min) and intermediate (IDR, 4.1 cGy/min) dose rates increased steady-state levels of IL-1β and IL-6 mRNAs. The surviving fraction was generally inversely proportional to the dose rate; however, these glioma cells were unusually susceptible to LDR. In the two cell lines tested, IDR was less cytotoxic than either HDR or LDR irradiation. Although cytokine gene expression had no clear effect on radiation survival in vitro, autologous cytokines conld be important to radiation response in vivo by affecting immune response, tumour stroma, vasculature or surrounding tissues. Adjusting dose rates to account for inverse dose rate effects and altered gene expression may be a useful stategy in optimising radiation therapy of glioblastomas.