Abstract 6209: O6-methylguanine as the junction of MGMT and PARP1-mediated repair pathways

Temozolomide is the first-choice DNA alkylating agent and has been commonly used in oncology over the last several decades. The cytotoxicity that temozolomide elicits through the methylation of guanine and adenine residues often becomes the limiting factor in effective treatment. Despite growing evidence of dysregulated alkylating DNA damage repair as a driving force of genome instability leading to cancer, neurological diseases, and premature aging, little is currently known about the coordinated role of PARP1 and MGMT (O6-methylguanine methyltransferase) enzymes in the repair of temozolomide-induced methylated DNA lesions. A major PARP1 function in DNA damage is facilitation of repair of the methylated DNA lesions, N6-methyladenine and N7-methylguanine, via base excision repair (BER); while MGMT restores guanine in O6-methylguanine (O6meG), the most cytotoxic adduct, by a one-step catalysis. It is generally thought that BER and MGMT represent two distinct mechanisms for removing DNA damage induced by alkylating agents; however, using a number of advanced cell-free and cell-based approaches, we provided evidence for direct (DNA-independent) and indirect (through PARylation) interaction between PARP1 and MGMT and demonstrated a functional crosstalk between these repair pathways. Particularly, O6meG repair activity is increased once PARP1 PARylates MGMT. Further, longer (more clinically relevant) exposure to temozolomide induced stronger MGMT PARylation in cells, indicating that the PARP1-MGMT interaction is important for enhanced O6meG repair and cell survival. As PARP1-MGMT complex forms in a variety of cancer cell types, our findings have strong implications for the development of an effective cancer therapy for cells dependent on PARP1 and MGMT mediated DNA repair. Citation Format: Jodie D. Cropper, Dauren S. Alimbetov, Kevin T. Brown, Andrew Robles, Rostislav I. Likhotvorik, James T. Guerra, Yidong Chen, Youngho Kwon, Raushan T. Kurmasheva. O6-methylguanine as the junction of MGMT and PARP1-mediated repair pathways. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6209.