Abstract C090: Elucidation of misp53-driven subtype specification and functions in pancreatic cancer
Authors: Urbach Laura , Wieland Lena , Penz Frederike , Klein Lukas , Appelhans Jennifer , Lenz Christof , Schneider Carolin , Günter Schneider , Schulz-Heddergott Ramona , Ellenrieder Volker , Heßmann Elisabeth , Singh Shiv K. 
Published: January 2024

Abstract
This study examines how mutations in the TP53 gene, specifically gain-of-function (GOF) mutations, impact the subtyping and stratification of pancreatic ductal adenocarcinoma (PDAC). In addition, it investigates the underlying mechanisms as well as the potential therapeutic implications.TP53 mutations/deletions are present in 60-75 % of cases in PDAC. The most common mutations are three specific hotspot missense mutations (misp53) found at codons R273H, R248W, and R175H. Several studies indicate that these misp53 mutants, despite losing their tumor suppressive function, acquire new oncogenic effects promoting disease aggressiveness and resistance to conventional therapies. Recent findings show that misp53 mutants are associated with a poorly differentiated metastatic subtype in PDAC. However, it is unclear how distinct misp53 mutants, such as misp53R273H, affect PDAC progression and therapy resistance and whether different mutants exert distinct functions. In this study, we explore misp53R273H- and misp53R248W-driven subtype-specificity and functions in PDAC aggressiveness by exploiting transcriptomics, genomic binding and regulation, controlled functional pathways and potential therapeutic targets. By combining cell line-based RNA- and ChIP-seq data we report that misp53R273H associates with and fuels basal-like (BL) neoplastic features by a potential regulation of cell cycle progression. Preclinical mouse models underpinned these findings by connecting misp53R273H tumors to metastatic spread. Generation of constitutive knockdown cell lines and corresponding overexpression assays could support these findings by bridging a loss of misp53R273H to the more favorable classical subtype properties. Of note, co-immunoprecipitation coupled to mass spectrometry analysis revealed misp53-specific and common hotspot mutant interaction partners: for instance, proteins of the group of chromatin remodelers or the ubiquitination pathway that could serve as a mechanistic foundation for misp53-specific functional outcomes. Further, implementation of a large-scale drug screen, flow cytometry and protein expression analyses revealed insights in the potential misp53-specific regulated pathways and therapeutic vulnerabilities, which strongly correlate to cell cycle progression and thus to the previous results. Integrating these findings with preclinical mouse studies, patient-derived xenograft cell lines and publicly available patient data sets strengthens the reported results and highlights their translational relevance. In conclusion, this study clearly demonstrates that hotspot misp53 mutants play a critical role in influencing PDAC subtype-specification and disease aggressiveness. In particular, misp53R273H was associated with BL aggressiveness and cell cycle progression. The ultimate aim of the study is to identify misp53 mutant-specific patient stratification to broaden individualized therapy options.
Citation Format: Laura Urbach, Lena Wieland, Frederike Penz, Lukas Klein, Jennifer Appelhans, Christof Lenz, Carolin Schneider, Schneider Günter, Ramona Schulz-Heddergott, Volker Ellenrieder, Elisabeth Heßmann, Shiv K. Singh. Elucidation of misp53-driven subtype specification and functions in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C090.