Figure 5.

PARP inhibition enhances the antitumor effects of irradiated tumor cells. (a) Inoculation of viable senescent B16SIY cells induced the greatest expression of IFN-γ in DNL when restimulated with tumor antigen gp100 in vitro as measured by ELISA (n = 6). (b) Injection of veliparib+IR treated senescent cells prevented the outgrowth of tumors after subsequent injection of untreated cells, suggesting systemic immune activation by senescent cells (n = 15–30). (c) Veliparib+IR treated cells prevented tumor formation more effectively than cells treated with 6 or 12 Gy alone. (d) Injection of flow-sorted cells revealed the antitumor effect was specific to large senescent cells (n = 10). (e) Repeated freeze-thawing reduced cell viability, with 3–5 cycles resulting in complete cellular destruction. (f) Freeze-thaw treatment markedly decreased the ability of irradiated or veliparib+IR treated cells to prevent tumor outgrowth, indicating a requirement for cell viability and/or integrity. ELISA, enzyme-linked immunosorbent assay; DNL, draining lymph node; FSC, forward scatter; IFN, interferon; IR, ionizing radiation; PARP, poly(ADP-ribose) polymerase; SSC, side scatter.