Abstract 2610: AMG 232, a small molecular inhibitor of MDM2 augments radiation response in human tumors harboring wild-type p53

Abstract

Abstract Activation of p53 is an attractive therapeutic target in radiation oncology because of its tumor-suppressor activity. AMG 232 is an effective p53 activator via inhibition of p53 interaction with its primary negative regulator, MDM2. In the current study, we examine the capacity of AMG 232 to augment radiation response in a variety of human tumors derived from lung, breast, colorectal, melanoma and sarcoma. We first examined the anti-proliferative effect of AMG 232 and confirmed a dose-dependent growth inhibition following AMG 232 treatment across a panel of 7 cell lines harboring wild type p53. In addition, the lack of growth inhibition in a p53 null cell line H1299 confirmed the p53-dependent anti-proliferative effect of AMG 232. Using clonogenic survival analysis, we identified that treatment with AMG 232 significantly enhanced radiosensitivity in all cell lines tested. Immunoblot analysis revealed the capacity of AMG 232 to inhibit radiation-induced DNA damage repair via inhibition of ATM, DNAPK-DNA ligase IV and BRCA1-Rad51/52 pathways. Flow cytometric analysis also showed a significant accumulation of cell populations in G2/M phase and a strong increase in γH2AX expression at 48 hrs following 2 Gy of radiation and AMG 232 treatment. Consistently, AMG 232 was shown to activate 1433σ that blocked G2/M progression via inhibiting CDC2. Further imaging studies to detect senescence-associated β-galactosidase activity identified that combined treatment of AMG 232 and radiation significantly induced a senescence phenotype. These results suggest that AMG 232 augments radiation response via the induction of cell cycle arrest and/or senescence followed by cell death, likely reflecting inhibitory effects on DNA damage repair. In addition to increased apoptotic cell death following the combination treatment, we found that autophagy-related cell death may also be contributing to AMG 232-induced radiosensitivity. Finally, in a variety of human tumor xenograft models, we confirmed that the combination of AMG 232 and radiation resulted in a significant delay in tumor regrowth and superior anti-tumor efficacy than treatment with drug or radiation alone. Taken together, these data reveal the strong capacity of AMG 232 to augment radiation response across a variety of tumor types. These promising results provide a basis for the further investigation of MDM2 antagonists combined with radiation as a novel treatment approach in cancer therapy. Citation Format: Lauryn Werner, Shyhmin Huang, Eric A. Armstrong, Dave Francis, Tao Osgood, Jude Canon, Paul M. Harari. AMG 232, a small molecular inhibitor of MDM2 augments radiation response in human tumors harboring wild-type p53. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2610. doi:10.1158/1538-7445.AM2014-2610