Increased chemosensitivity of IDH1-mutated gliomas due to impairment of RPA1-mediated DNA repair

Isocitrate dehydrogenase 1 (IDH1) mutation, resulting in the expression of mutant IDH1 (mIDH1), is the most common genetic abnormality in low-grade gliomas and is recognized as a biological marker for better patient prognosis and a robust response to temozolomide (TMZ). To investigate the possible mechanisms of chemosensitivity differences between wild-type (WT) IDH1 and IDH1-mutated gliomas, we conducted immunoprecipitation–mass spectrometry (IP-MS) and coimmunoprecipitation (co-IP) in glioma cells expressing wild-type IDH1 and mIDH1 to identify the specific protein that directly interacts with mIDH1, namely, replication protein A1 (RPA1). Increased expression of RPA1 was significantly associated with low TMZ responsiveness and worse prognosis. Subsequently, we demonstrated that overexpression of RPA1, an essential functional factor in DNA damage repair (DDR), increased TMZ resistance in glioma cells, while treatment with an RPA1 inhibitor (HAMNO) sensitized glioma cells to TMZ both in vitro and in vivo. Moreover, TMZ induced a greater degree of general DNA damage in glioma cells coexpressing mIDH1 and RPA1 than in those coexpressing wild-type IDH1 and RPA1, indicating RPA1 dysfunction in IDH1-mutant glioma cells. Further, mIDH1 directly bound to the DNA binding domain (DBD-A) of RPA1 and then suppressed its binding to single-stranded DNA (ssDNA), consequently leading to blockade of the downstream ATR/CHK1 DNA repair signalling pathway, failure of DNA repair and apoptosis. Taken together, our findings reveal a novel molecular mechanism involved in the chemosensitivity of IDH-mutated gliomas and suggest that targeting RPA1-related DNA repair is a promising therapeutic strategy to increase the TMZ response of IDH1-mutant gliomas. Moreover, the combination of TMZ and (1Z)-1-[(2-hydroxyanilino)methylidene] naphthalen-2-one (HAMNO) may be a clinically effective treatment strategy.