LET-dependent bystander effects caused by irradiation of human prostate carcinoma cells with X rays or alpha particles.

Radiation-induced bystander effects have been demonstrated in both normal and tumor cells using a variety of different radiation qualities. Literature reports are contradictory, however, on whether there is an LET dependence of the bystander effect. This study investigated the ability of DU-145 human prostate carcinoma cells irradiated with either alpha particles or 250 kVp X rays to cause medium-mediated bystander effects in unirradiated populations of DU-145 cells or in AG01522 human fibroblasts. The end points measured in both of the bystander cell lines were micronucleus formation, gamma-H2AX focus induction, and the surviving fraction. The incidence of micronuclei increased 1.5-2.0-fold in both tumor and fibroblast bystander cells after 4 h of co-culture with DU-145 tumor cells that had been directly irradiated with either alpha particles or X rays. Only the AG01522 fibroblasts showed bystander effects for the gamma-H2AX focus (a 1.5-fold increase) and surviving fraction (a decrease to 0.8) end points when co-cultured with X-irradiated tumor cells. Alpha-particle irradiation of DU-145 tumor cells produced no decrease in the surviving fraction and no increase in gamma-H2AX focus induction in co-cultured bystander cells of either cell line. These results indicate that there are LET-dependent differences in the signal released from DU-145 human prostate carcinoma cells and that, for some end points, bystander AG01522 fibroblasts and bystander DU-145 prostate carcinoma cells respond differently to the same medium-mediated signal.