Abstract 2417: Mutant p53 and oncogenic KRAS converge on CREB1 to drive pancreatic cancer metastasis

Pancreatic ductal adenocarcinoma (PDAC) is almost uniformly fatal and characterized by early metastasis. Oncogenic KRAS mutations prevail in 95% of PDAC tumors and co-occur with genetic alterations in the TP53 tumor suppressor in nearly 70% of patients. Most p53 alterations are missense mutations that exhibit gain-of-function phenotypes that include increased invasiveness and metastasis. However, the extent of direct cooperation or synergism between KRAS effectors and mutant p53 remain undefined. To study how KRAS effectors and mutant p53 cooperate to drive PDAC development, we developed a novel somatic model that expresses mutant KRAS and p53 only in pancreas tumor cells, leaving the tumor microenvironment and immune system intact. PDAC genetically engineered mouse models (GEMMs) were generated by crossing a conditional oncogenic KRasG12D (K) allele with a conditional null p53 allele (Pfl) or a novel, conditional knock-in mutant p53R172H allele (Pwm) that selectively expresses mutant p53 in tumor cells while preserving wildtype p53 expression in all other animal cells. The incidence of metastatic lesions in the liver and lungs of KPwmC mice was over 2-fold greater (p=.03) relative to KPflC mice. Through orthogonal analyses of this model and human PDAC samples, we show that oncogenic KRAS effectors phosphorylate and activate cyclic AMP responsive element binding protein 1 (CREB1), allowing physical interactions with mutant p53 to transcriptionally upregulate the pro-metastatic transcription factor, FOXA1, which enhances β-catenin stabilization and activity. Targeting KRAS and mutant p53 cooperativity through pharmacologic inhibition of CREB1 dramatically dampens FOXA1 expression and PDAC metastasis. Our findings demonstrate a direct, mechanistic link between key oncogenic KRAS signaling elements and mutant p53 that result in a broad, multiplexed activation of cancer-associated transcriptional networks. Moreover, we identify CREB1 as a viable therapeutic strategy to undermine oncogenic KRAS and mutant p53 cooperation to mitigate PDAC metastasis. Citation Format: Michael Paul Kim, Xinqun Li, Jenying Deng, Yun Zhang, Bingbing Dai, Kendra Allton, Tara Hughes, Christian Siangco, Jithesh Augustine, Yaan Kang, Joy M. McDaniel, Shunbin Xiong, Eugene Koay, Florencia McAllister, Christopher Bristow, Timothy Heffernan, Anirban Maitra, Bin Liu, Michelle Barton, Amanda Wasylischen, Jason Fleming, Guillermina lozano. Mutant p53 and oncogenic KRAS converge on CREB1 to drive pancreatic cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2417.