Abstract
Abstract Purpose: Glioblastoma multiforme (GBM) is the most common primary brain tumor in the USA. Standard treatment for primary GBM includes surgical resection, followed by concurrent chemotherapy and radiotherapy (RT). As a result of the major role RT plays in the treatment of GBM, there is much interest in identifying the determinants of radiosensitivity to improve the efficacy of clinically tolerable radiation doses. Also, presence of GBM stem cells within tumor makes it remarkably resistant to current radio- and chemotherapies. Here we have studied DNA repair genes as a determinant of radiosensitivity in GBM. Materials and Methods: We performed a small interfering RNA (siRNA) screen of 206 genes involved in DNA damage repair to identify genes whose knockdown can increase tumor sensitivity to RT. siRNA screens were performed in two different GBM tumor cells; U251 and U87-MG and in one GBM stem cell line, GBAM1. At 72 hrs, after transfection, cells were irradiated for 24 hrs. As a marker of DNA damage and repair, γH2AX activity was analyzed by ELISA after 24 hrs in unirradiated and irradiated cells. Results: We identified several genes which upon downregulation increased radiosenstiivity of GBM tumor cells. The various genes includes DNA double strand break repair genes, genes involved in translesion DNA synthesis and DNA damage signaling genes. Nevertheless, we observed differences between GBM tumor cells and stem cells. In tumor cells, some of the radiosensitizer genes were BRCA2, PHB, PTCH, SMC5, ERCC5 and POL G. On the other hand, GBM stem cells showed radiosensitization with downregulation of RFC1, UBE2A, RPA1 RAD54L, XPA, FANCL and TOP2A genes. There was one gene common between GBM tumor cells and stem cells, REV1L. Rev1-like protein is as a scaffold that recruits DNA polymerases involved in translesion DNA synthesis (TLS) of damaged DNA. This is an ongoing study. We are further validating role of some of these targets in both tumor cells and stem cells. Conclusions: We observed inherent differences in radiosensitivity between GBM tumor cells and stem cells. Identification of tumor cell specific and stem cell specific targets may help us in determining better treatment options for GBM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A105.
Published Version
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