Abstract 5645: Targeting transcription-replication conflict for selective chemotherapy in glioblastoma

Abstract The current standard of care for glioblastoma (GBM) is surgical intervention followed by a combination of temozolomide (TMZ) and radiation therapy. Only 5% GBM patients survive more than five years despite aggressive therapeutic treatment. A significant hurdle to develop target-based therapies for GBM is the complexity and diversity of the disease. Genomic and epigenetic profiling has found a broad range mutational and transcriptional events across this histologically diverse disease. A hallmark of GBM is genomic instability, which is a key factor in its progression and complexity. The fast growing and aggressive GBM cells demand rapid DNA replication and hypertranscription, leading to enhanced transcription-replication conflicts (TRCs). A major source of genomic instability, TCR causes lethal double stranded DNA breaks (DSBs) if not resolved properly. We hypothesize that enhanced TRC is a weak link and a promising target for treating GBM. Proliferating cell nuclear antigen (PCNA) is a key component of DNA replication machinery and plays an essential role in the DNA replication and repair. Through a rational drug design, we identified a small molecule PCNA inhibitor, AOH1996, which selectively kills cancer cells. Mechanistically, AOH1996 enhances the interaction between PCNA and the largest subunit of RNA polymerase II, RPB1, and dissociates PCNA from actively transcribed chromatin regions. By interfering with TRC resolution as evidenced by induction of R-loop levels in cancer cells, AOH1996 induces DSBs in a transcription-dependent manner. Orally administrable and metabolically stable, AOH1996 can freely pass the blood brain barrier and enter brain tumors. Here, we report that it selectively kills GBM cells as a monotherapy or in combination with TMZ but causes no discernable side effects. Importantly, AOH1996 targets a cancer specific region of PCNA that is a highly conserved through evolution and influences the activity of broad cellular processes that are essential to the growth and survival of cancer cells. GBM cancer cells are, therefore, less likely to develop resistance to AOH1996 through mutagenesis in PCNA. If combined with the existing chemotherapeutic regime and inhibitors of DNA repair pathways, AOH1996 may provide a new and unique therapeutic avenue for exploiting this cancer-selective vulnerability to deliver a durable response in GBM. Citation Format: Long Gu, Robert J. Hickey, Linda H. Malkas. Targeting transcription-replication conflict for selective chemotherapy in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5645.