Abstract B106: A minimal driver pair for a spontaneous high-grade serous ovarian cancer mouse model: Myc and p53-R270H

Abstract Genetically engineered mouse models (GEMM) have fundamentally changed how ovarian cancer etiology, early detection, and treatment can be understood. One challenge of the last decade has been to provide evidence for which cells are responsible for the origin of epithelial ovarian cancer. Different promoters, including Pax8, Lgr5, Ogvp1, and others have allowed for expression of transgenes in specific epithelial compartments in mice. Ovgp1 has been shown to be specific for fallopian tube epithelium (FTE), which most HGSOC is now thought to originate from. Pairing Ovgp1 with multiple homozygous deletions of powerful tumor suppressors like Brca1, Trp53, Rb1, and Nf1 yields murine disease after a year of age. However, human tumors do not contain homozygous deletions of these many tumor suppressors. Others have utilized Pax8 to knock out Trp53 and Pten to yield tumors at 3-8 months of age, but human tumors rarely have PTEN knockouts and Pax8 drives kidney and thyroid expression as well. We postulated that it is possible to strictly mimic human HGSOC genetics in a mouse model and nonetheless drive oncogenesis within the lifespan of a mouse. Here, we describe the OvTrpMyc model, Trp53em1JdelTg (Ovgp1-Trp53*R270H-Myc), in which p53-R270H and Myc expression are driven by the Ovgp1 promoter. The transgene was inserted at the endogenous Trp53 locus, predicting that this design would allow for loss of the opposing wild-type chromosome 11 (syntenic to chromosome 17 in humans) to better mimic human HGSOC genetics. This model generated lethal disease at a median of 15. 6 months of age. Dissected metastatic tumors were peritoneal and expressed Pax8, consistent with human disease. Immunohistochemical staining of the fallopian tube, ovary, and uterus indicated clear nuclear staining of p53 and Myc on the FTE. Notably, pockets of intraepithelial metastases expressing p53 and Myc were also found on the uterine epithelium. Cells grown ex vivo from uterus or fallopian tube dissections were analyzed for transcriptomes. RNA-seq revealed a clustering of these extracted cancer cells with human HGSOC and p53 mutant serous endometrial cancers. Loss of heterozygosity at the p53 locus was universal in these ex vivo grown cancer cells, as was extensive aneuploidy. The OvTrpMyc model requires only a single transgene for its breeding strategy, better enabling cancer detection, prevention, and treatment experiments. Taken together, the OvTrpMyc model of p53-R270H mutation and Myc expression driven by Ovgp1 is sufficient to recapitulate cancer hallmarks of HGSOC and, surprisingly, p53 mutant serous uterine cancer as well. Citation Format: Joe R Delaney. A minimal driver pair for a spontaneous high-grade serous ovarian cancer mouse model: Myc and p53-R270H abstract. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₂): Abstract nr B106.