DNA alkylating agents including temozolomide (TMZ) and 1,3-bis[2- chloroethyl]-1-nitroso-urea (BCNU) are the most common form of chemotherapy in the treatment of gliomas. Despite their frequent use, the therapeutic efficacy of these agents is limited by the development of resistance. Previous studies suggest that the mechanism of this resistance is complex and involves multiple DNA repair pathways. To better define the pathways contributing to the mechanisms underlying glioma resistance, we tested the contribution of the Fanconi anemia (FA) DNA repair pathway. TMZ and BCNU treatment of FA-proficient cell lines led to a dose- and time-dependent increase in FANCD2 mono-ubiquitination and FANCD2 nuclear foci formation, both hallmarks of FA pathway activation. The FA-deficient cells were more sensitive to TMZ/BCNU relative to their corrected, isogenic counterparts. To test whether these observations were pertinent to glioma biology, we screened a panel of glioma cell lines and identified one (HT16) that was deficient in the FA repair pathway. This cell line exhibited increased sensitivity to TMZ and BCNU relative to the FA-proficient glioma cell lines. Moreover, inhibition of FA pathway activation by a small molecule inhibitor (curcumin) or by small interference RNA suppression caused increased sensitivity to TMZ/BCNU in the U87 glioma cell line. The BCNU sensitizing effect of FA inhibition appeared additive to that of methyl-guanine methyl transferase inhibition. The results presented in this paper underscore the complexity of cellular resistance to DNA alkylating agents and implicate the FA repair pathway as a determinant of this resistance.
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Acknowledgement We would like to thank Richard Kennedy and Sonya Wang for critical reading of this manuscript. We are grateful to Yuko Hasegawa for her technical assistance in the experiments involving MGMT treatment. This work is supported by NIH grant R01HL52725 and a grant from the Accelerated Brain Cancer Cure Foundation. CC is supported by a postdoctoral fellowship from the Damon Runyon Research Foundation (DRG-101-04). TT is a Searle Scholar and a V Scholar.
- 1,3-Bis[2-chloroethyl]-1-nitroso-urea (BCNU)
- DNA repair
- Fanconi anemia (FA)
- Glioma therapeutics
- Temozolomide (TMZ)