Abstract 3824: Investigating the role of allelic imbalance in pancreatic cancer aggressiveness, survival, and therapeutic resistance

Abstract Pancreatic ductal adenocarcinoma (PDAC) is driven by KRAS mutations in over 90% of cases. Targeted therapy has revolutionized the life of patients affected by solid malignancies. KRASi are beneficial to a subset of patients with KRAS mutations, who, however, soon develop resistance to this therapeutic strategy. We hypothesize that PDAC subpopulations with KRAS allelic imbalance, particularly those harboring loss of heterozygosity (LOH) at the KRAS locus (KRasG12D/LOH), exhibit enhanced aggressiveness, metastatic potential and poorer survival outcomes. We investigated the functional role of these subpopulations in tumor evolution, both naturally and under the selective pressure of KRAS inhibition. To test the main hypothesis, we developed a somatic mosaic genetically engineered mouse model (smGEMM) leveraging the CRISPR-Cas9 technology, and a reporter system engineered on murine chromosome 6 (R26RFCL-TdT) which is ∼30MB distant from the Kraswt and in trans with the KrasLSL-G12D latent mutant allele (KLOHPC): GFP+TdT+ cells retain the wild-type KRAS allele (KRasG12D/wt), while GFP+TdT- cells indicate LOH at the KRAS locus (KRasG12D/LOH). Preliminary findings reveal that KRasG12D/LOH subpopulations display pronounced chromosomal instability (CIN). Importantly, mice with tumors enriched in KRasG12D/LOH clones exhibited significantly worse survival compared to those dominated by KRasG12D/wt populations with poorly differentiated and highly metastatic phenotypes. Tumors enriched in KRasG12D/LOH clones tend to evolve under selective pressures, possibly contributing to resistance against targeted KRAS therapies.Genomic analysis of KRasG12D/LOH cancer cells highlights the presence of complex structural rearrangements, including chromothripsis, a catastrophic event associated with widespread chromosomal fragmentation and reassembly. This genomic instability, particularly prevalent in KRasG12D/LOH clones, is thought to accelerate tumor evolution, leading to the accumulation of subclonal drivers that fuel metastasis and disease progression.Using a multi-omics approach, including single-cell and spatial transcriptomics, we have observed that KRasG12D/LOH clones exhibit distinct molecular features compared to their KRasG12D/wt counterparts. This research sheds light on the critical role of KRAS allelic imbalance in driving tumor heterogeneity, chromosomal instability, and resistance to therapy in PDAC. Understanding these processes offers new insights into the biological mechanisms underlying the aggressive nature of pancreatic cancer and its ability to evade targeted therapies. Citation Format: Enrico Gurreri, Li Zhang, Hania Khan, Lisa Maria Mustachio, Ningping Feng, Tim Heffernan, Joseph R. Marszalek, Basturk Olca, David Klimstra, Stefano Sioletic, Alessandro Sgambato, Giampaolo Tortora, Giulio Draetta, Luigi Perelli, Giannicola Genovese. Investigating the role of allelic imbalance in pancreatic cancer aggressiveness, survival, and therapeutic resistance [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 3824.