Abstract 2506: Preclinical evaluation of sorafenib in combination with ionizing radiation in metastatic breast cancer model
Authors: Heravi Mitra , Muanza Thierry , Tomic Nada , Liang LiHeng , Holmes Joseph , DeBlois François , Radzioch Danuta 
Published: June 2012

Abstract
Sorafenib tosylate (Bay 54-9085) is an oral, small molecule multikinase inhibitor of several targets including RAF/MEK/ERK signaling, vascular endothelial growth factor receptor-2 (VEGFR-2), VEGFR-3, and platelet derived growth factor receptor-beta (PDGFR-b). Sorafenib has shown clinical efficacy in solid tumors such as renal cell and hepatocellular carcinomas. Retrospective analysis of breast cancer patients has shown an unfavorable prognosis in patients with high expression level of VEGF, indicating that VEGF could be associated with efficacy of chemotherapy and radiotherapy. It has also been shown that radiation resistance is partially due to tumor cell production of angiogenic cytokines, particularly VEGF that protects endothelial cells through survival pathways. The aim of this study is to investigate if radiation response is enhanced through inhibition of p-VEGFR2/PDGFR-b by Sorafenib and if the combination of Sorafenib and radiation will increase the treatment response in a metastatic breast cancer model.
Mouse metastatic mammary cancer cells, 4T1 were used in this study. Clonogenic assay was performed to assess the radiomodulating effect of Sorafenib. In addition, cell cycle analysis and annexin-V binding assay were performed 24 and 48 hrs post treatment respectively. To confirm our in vitro data, a tumor growth delay assay was completed in a syngeneic mouse model.
Western blot analysis showed strong dose dependent inhibition of ERK1/2 phosphorylation by sorafenib. Our clonogenic assay showed a supra-additive effect of Sorafenib (7.5 μM) and radiation (4 Gy) with a dose enhancement factor (DEF) of 1.81. Sorafenib in combination with radiation demonstrated a significant G2/M cell cycle arrest (p&lt;0.0001). Moreover, annexin-V staining assay showed a significant increase in the level of apoptosis in cells treated with both sorafenib and radiation (p&lt;0.0004). Our in vivo results strongly suggest that radiation prolongs the anti tumor activity of sorafenib. In addition, tumor growth was delayed when radiation was combined with sorafenib concurrently (tumor growth delay was increased from 10.5 days in irradiated group to 18 days in combined treatment group).
Our results demonstrate that sorafenib increases both the level of apoptosis and the sensitivity of 4T1 cancer cells to radiation. The higher potency of sorafenib combined with radiation can be partially due to the strong cell cycle arrest at G2/M phase. Moreover, our in vivo results show that sorafenib in combination with radiation exhibit a superior tumor growth control. Overall, our findings suggest that greater treatment response may be achieved when sorafenib is combined with radiation. More studies are being conducted to investigate the optimal schedule for this combination.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2506. doi:10.1158/1538-7445.AM2011-2506