Abstract 435: The role of HIF-1 and Notch pathway in radio-resistance of non small lung cancer cell lines.

Abstract

Abstract Background: Notch pathway regulates cell-fate determination in multi-cellular organisms and aberrant activation of Notch pathway has been reported in tumorigenesis of many cancers. We previously reported that Notch3 and its downstream effector, HEY1, were upregulated by radiation in non-small cell lung cancer (NSCLC) cell lines. Furthermore, we demonstrated that g-secretase-inhibitor (GSI), when combined with radiation therapy significantly suppressed the growth of lung cancer cells compared to either GSI or radiation alone by a potential mechanism that GSI suppressed radiation-induced Notch activation and its resultant radio-resistance. Since the expression of Notch was reported to be activated via HIF under hypoxia, we, in this study, hypothesized that HIF would be involved in radiation-induced Notch activation in NSCLC and thus HIF inhibitor (YC-1) would have an anti-tumor effect when combined with radiation therapy as is the case with GSI. Materials and Methods: Two Notch-expressing lung cancer cell lines (H460 and H1793) were used. We first examined, by Western Blotting (WB) and real time RT-PCR, the changes in expressions of HIF-1 and Notch family after treatment by radiation under hypoxia. We then repeated the same experiment while using SiRNA targeting HIF-1, in an attempt to examine the role of HIF-1 on Notch pathway and its downstream proteins. Finally, we investigated an antitumor effect of YC-1, using a MTT proliferation assay and a clonogenic assay, when combined with radiation treatment. Results: Under hypoxia, treatment by radiation up-regulated protein expression of HIF-1 at 6 hours and that of Notch3 as well at 24 hours, but not of other Notch family. As expected, specific suppression of HIF-1 by siRNA down-regulated Notch3 activation associated with radiation; however, did not affect other Notch family and its downstream effectors, including HES1. An anti-tumor effect of YC-1 was evident only when radiation treatment was concurrently applied, but not when sequentially applied, in the growth of lung cancer cells and also colony formation. Conclusions: Radiation-induced up-regulations of HIF-1 and Notch pathway may be therapeutic targets for more effective radiation therapy in NSCLC. Citation Format: Yasuyuki Ikezawa, Jun Sakakibara-Konishi, Hidenori Mizugaki, Satoshi Ooizumi, Masaharu Nishimura. The role of HIF-1 and Notch pathway in radio-resistance of non small lung cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 435. doi:10.1158/1538-7445.AM2013-435