Abstract LB475: Capture the early benign-to-malignant transition of colon cancer in the mouse

Abstract Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide, with an increasing incidence and mortality rate among younger patients. Although various risk factors have been identified, they remain insufficient to fully explain the rise of early-onset CRC. While genetic driver mutations are necessary for tumorigenesis, they alone are not sufficient to drive malignant transformation CRC. This is evident as these mutations are often present in histologically normal tissue. A critical unresolved question is: why do some benign polyps progress to malignant CRC while others remain non-invasive? Studying this phenomenon in human patients is challenging, as the earliest stages of benign-to-malignant transition are difficult to capture and cannot be functionally interrogated. To address this, we developed a new genetically engineered mouse model that recapitulates the stepwise-progression of colon cancer by combining in vivo CRISPR-Cas9 editing in the distal colon and an inducible “split-Cre” system. This allows us to decouple tumor initiating events from those that drive malignant progression. Benign adenomas are induced via colonoscopy guided injection of lentivirus expressing single guide RNA against the Apc gene (mutated in ∼80% of human CRC). Recombination of Kras LSL-G12D and Trp53 flox/flox alleles (modeling the most common drivers of advanced CRC in humans) is spatiotemporally controlled via an inducible split Cre-recombinase system, with C-terminal Cre (CreC) delivered in the initiating lentivirus and N-terminal Cre (CreN), fused to a destabilization domain (dd) and Estrogen Receptor T2 (ERT2), expressed from an internal ribosome entry site (IRES) following the stop codon of the endogenous Epcam gene (conferring epithelial specificity). We have validated that this model can capture the full histological spectrum of CRC benign-to-malignant progression: benign adenoma, intramucosal carcinoma, early invasion, and adenocarcinoma-in-adenoma with extensive histological and transcriptional intratumoral heterogeneity. In many of these Apc knockout polyps, we also observe multiple distinct regions with Kras G12D recombination alone and in combination with Trp53 knockout, recapitulating the polyclonal mutational heterogeneity of early CRC in humans. We have performed 10x Visium HD spatial transcriptomics analysis on these samples to elucidate the earliest transcriptional changes associated with stepwise Kras G12D and Trp53 loss-of-function mutations and benign-to-malignant transition. Through comprehensive tumor kinetics and spatial transcriptomic analyses, we seek to uncover deeper insights into the earliest tumor intrinsic and microenvironmental mechanisms underlying CRC benign-to-malignant transition. This approach holds significant potential to inform strategies for CRC early detection and prevention. Citation Format: Yihan Qin, Daniel Zhang, Nikita Persaud, Nischal Bhandari, Zakeria Aminzada, Colin McLaughlin, Song Han, Alex Liu, Rodrigo Romero, Santiago Naranjo, Claire Regan, William Rideout III, Alexander Cicala, Karen Yee, Jonathan Preall, Semir Beyaz, Sepideh Gholami, Zhen Zhao, Tyler Jacks, Peter M. Westcott. Capture the early benign-to-malignant transition of colon cancer in the mouse [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB475.