P08.45 Inhibition of homologous recombination resensitizes temozolomide-resistant glioma cells to temozolomide

Abstract

Introduction: TMZ is a DNA-methylating agent. TMZ-induced O6-methylguanine adducts, in the absence of repair by O6-methylguanine DNA methyltransferase (MGMT), mispair with thymine during the next DNA replication cycle, leading to futile DNA mismatch repair by the mismatch repair system, formation of double strand breaks (DSBs) and eventual cell death of glioma cell lines. Several mechanisms have been proposed about the acquisition of resistance to TMZ in gliomas, such as changes of expression of MGMT, mismatch repair, nucleotide excision repair and homologous recombination. In this study we revealed a mechanism associated with the resistance to TMZ in glioma cell lines and a way to resensitize the temozolomide-resistant glioma cells to TMZ. Materials and Methods: The effect of TMZ was measured by colony formation assay. The cell cycle distributions were analyzed by FACS. The levels of DSBs were measured by immunofluorescence study using anti-gamma H2AX antibody. Results: Several clones of U251 cells resistant to TMZ were obtained. FACS analyses showed several patterns of cell cycle distributions of the cells treated with TMZ. A clone showed G2 arrest at day3 and this arrest was abrogated sooner compared to the G2 arrest of original U251. TMZ-induced DSBs in the resistant cells were rapidly disappeared compared to those in U251 cells. By suppression of Rad51, which was major factor associated with homologous recombination, the resistant cells were resensitized to TMZ. Conclusions: These results suggested that inhibition of homologous recombination may be a viable means to resensitize some kinds of temozolomide-resistant gliomas to TMZ.