Counteracting temozolomide resistance in glioblastoma multiforme (GBM) through suppression of the base excision repair (BER) pathway

Background Glioblastoma Multiforme (GBM) is an aggressive cerebral cancer. Standard chemotherapeutic of GBM is Temozolomide; a DNA alkylating agent. Patients relapse mostly due to recurrence of resistant tumour. GBM resistance may involve DNA repair pathways that become hyperactivated, my project seeks to understand the molecular underpinnings of GBM resistance and recurrence in order to identify novel treatment paradigms that may serve to counteract drug-resistant GBM. Methods and Materials TMZ sensitive/resistant GBM models with nuclear fluorescent were generated, and resistance was validated with growth, DNA damage and death assays. Furthermore, RNA/protein expressions were compared to identify modifications in TMZ-resistant cells; significant changes were investigated via RNAi experiment. Data indicated that base excision repair featured prominently; showing enhanced DNA repair activity in TRR. As poly ADP-ribose polymerase (PARP) plays a pivotal role in BER signaling, PARP inhibitors (PARPi) were used in cell-based assays to evaluate the relative contribution of BER to TMZ resistance in GBM. Results TRR cells demonstrated robust performance toward TMZ in terms of growth, tolerance against DNA damage and resistance to TMZ-induced cell death. With RNA /protein analysis assays, XRCC1-mediated BER expression and activity was found enhanced, and further stimulated under subsequent treatment of TMZ indicating a plastic response to de novo DNA damage despite acquired resistance. Validation studies of XRCC1 knockdown in TRR and over-expression in SG suggested XRCC1 plays a critical role in TMZ-resistance. Furthermore, effects of 4 independent PARP inhibitors/trappers (PARPi/PARPt) were tested on this cell model to study the efficacy of chemical-mediated BER inhibition as a co-treatment strategy to re-sensitize TRR toward TMZ. PARPi/PARPt demonstrated cooperativity with TMZ, displaying growth suppression, enhanced DNA damage, and increased cell death in TRR. Conclusion In my study, base excision repair pathway was ...