Abstract 2630: Inhibition of angiogenesis contributes to enhanced radiation response in tumors following MDM2 inhibition by AMG 232

Abstract

Abstract MDM2-p53 interaction and downstream signaling impacts cellular response to DNA damage. AMG 232 is a potent small molecule inhibitor that blocks the interaction of MDM2 and p53. We previously elucidated the capacity of AMG 232 to augment radiation response across a spectrum of human tumor cell lines and xenografts. In the current study, we examine the capacity of AMG 232 to inhibit angiogenesis and assess the resultant impact on AMG 232-induced radiosensitivity. We first examined the impact of AMG 232 on the growth and radiosensitivity of human umbilical vein endothelial (HUVEC) and dermal lymphatic endothelial cells (HDLEC). We found that AMG 232 inhibited the proliferation of both endothelial cell types in a dose dependent manner. Importantly, treatment with AMG 232 significantly reduced angiogenesis-related tube formation in both endothelial cell types. Using clonogenic survival analysis, we identified that treatment with AMG 232 significantly enhanced radiosensitivity. Immunoblot analysis showed that combined treatment with AMG 232 and radiation resulted in a profound impact on molecules involved in cell cycle progression, DNA damage repair, and apoptosis signaling, including FoxM1, ATM/ATR, CHK2, Rad51, and Bax. Flow cytometric analysis also showed a significant cell cycle arrest in G2/M phase with an increase of DNA damage related γH2AX level at 48 hrs following radiation and AMG 232 treatment. In H460 and SJSA-1 tumor xenografts, we found a markedly increased antitumor capacity of AMG 232 when combined with radiation. Immunohistochemical analysis revealed a significant reduction of cellular proliferation and vascular density in both tumor types following combined treatment of AMG 232 and radiation. Taken together, these findings reveal the potential anti-angiogenic capacity of AMG 232 that may contribute to augmentation of radiation response previously observed in tumor xenograft studies. A detailed investigation is in progress to examine changes in the tumor microenvironment following AMG 232 and radiation treatment, including hypoxia and vascular normalization, to assess their respective impact on tumor response to radiation. Citation Format: Lauryn R. Werner, Shyhmin Huang, Eric A. Armstrong, Fang Ma, Jude Canon, Paul M. Harari. Inhibition of angiogenesis contributes to enhanced radiation response in tumors following MDM2 inhibition by AMG 232. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2630. doi:10.1158/1538-7445.AM2015-2630