Abstract 3046: Cathepsin B and uPAR downregulation sensitizes glioma initiating cells to radiation induced cell cycle arrest

Abstract

Abstract Ionizing radiation is the standard treatment for glioblastoma multiforme (GBM). Radiation and chemoresistance have been attributed to a small population of cells known as glioma stem cells (GSCs) or glioma initiating cells (GICs). In the present study, we studied the effect of ionizing radiation on the progression of cell cycle of glioma initiating cells, non glioma initiating cells (non-GICs), and the respective parental cell lines (U251 and U87). Initial experiments showed that GICs were resistant to lower doses of radiation (3 and 5 Gy) as compared to parental and non-GICs. Radiation dosage of 10 Gy induced significant G2/M arrest as early as 12 and 24 hours in non-GICs (U251 and U87) and parental cell lines (U251 and U87), respectively and a low percentage of GICs were observed in the G2/M phase 48 hours after radiation. Apart from cathepsin B and uPAR, expression levels of cyclin B1, pcdc2, pchk2 and pERK were also elevated when cells were exposed to radiation. shRNA-mediated simultaneous knockdown of cathepsin B and uPAR (pCU) decreased radiation-induced expression of cyclin B1, pcdc2, pchk2 and pERK and induced apoptosis. Further, immunoblot analysis indicated that cathepsin B and uPAR downregulation reduced the expression of neural stem cell markers, such as CD133, Sox-2 and Bmi-1. Activation of pERK played an important role in inducing the G2/M arrest of GICs of both cell lines as its inhibition induced cell differentiation and sensitized the cells to radiation. Irradiation induced aggressive tumors in vivo and the knockdown of uPAR and cathepsin B significantly decreased radiation-induced tumor growth. Thus, these results indicate that uPAR and cathepsin B downregulation sensitized GICs to ionizing radiation and targeting these proteins could be an efficient approach to eradicate tumors, particularly GICs in the tumor bulk. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3046. doi:1538-7445.AM2012-3046