PARP-1 inhibitor MK-4827 in combination with radiation as a treatment strategy for metastatic neuroblastoma.

Abstract

9559 Background: Metastatic neuroblastoma continues to carry a dismal prognosis. Radiation is an important part of the treatment for these patients and PARP inhibitors have been shown to radio-sensitize cancer cells. We hypothesize that the PARP inhibitor MK-4827 will radio-sensitize neuroblastoma cells and lead to a survival benefit in an in vivo model of metastatic neuroblastoma. Methods: Clonogenic survival assays were performed in four human neuroblastoma cell lines [Kelly, NB1691, SY5Y, Tet21(Myc-N expressed) and Tet21 (Myc-N suppressed)] with MK-4827 as a single agent and in combination with radiation. PARP activity in the presence of MK-4827 was assessed at varying concentrations and time points by a PARP activity assay (Trevigen, Inc.) as well as by western blot analysis of Poly-ADP-ribose. Phosphorylated H2AX, a marker of DNA strand breaks, was determined by FACS. In vivo activity of MK-4827 as a single agent and in combination with radiation was assessed in a murine metastatic neuroblastoma model using luciferase modified NB1691 cells. Survival benefit was assessed by Kaplan-Meier estimates. Results: Clonogenic survival assays revealed dose-dependent cytotoxic effects in all neuroblastoma cell lines with IC50 values ranging from 13-38 nM, an effect that was significantly enhanced by radiation. Maximal PARP inhibition of approximately 60% was obtained within 1 hour of MK-4827 administration, and was sustained for 48 hours. Phosphorylated H2AX remained elevated for significantly longer time periods in cells treated with MK-4827 and radiation compared to radiation treatment alone. Mice treated with a combination of MK-4827 and radiation showed significantly reduced tumor burden (p<0.01) and longer survival (p<0.01) compared to mice treated with MK-4827 as single agent. Conclusions: The PARP inhibitor MK-4827 cooperates with radiation to enhance cell death of neuroblastoma cells in vitro. Combination of MK-4827 with radiation decreases tumor burden and prolongs survival in a metastatic neuroblastoma model in vivo. MK-4827 in combination with radiation appears to be a promising new therapy for treatment of metastatic neuroblastoma.