PROJECT SUMMARY/ABSTRACT Patients with gastrointestinal (GI) metastases in the peritoneal cavity suffer high morbidity, chemotherapy resistance, and decreased overall survival. The molecular mechanism and phenotypic features that facilitate peritoneal metastasis are poorly understood, although mucin-expressing tumors exhibit especially high predilection for peritoneal spread. Preliminary analyses determined in a pan-cancer patient cohort that mucinous GI tumors are highly enriched in a specific mutation in GNAS that leads to pathogenic gain-of- function in the encoded G protein alpha subunit (GNAS). GNAS mutations are associated with pancreatic and small cell lung tumor development, yet the pathogenic mechanism mobilized by GNAS to facilitate metastasis is unknown. Preliminary data demonstrates that patients with GNAS-mutated GI cancers exhibit increased burden of peritoneal metastases, decreased response to first-line chemotherapy, and poor overall survival. Analysis of tumor DNA and RNA from independent groups of patient tumors shows that mutated GNAS may operate within a distinct gene-regulatory network that activates PI3K and MAPK signaling. The PI and collaborators established GNAS-mutated, patient-derived-organoids (PDOs) and a peritoneal metastasis mouse model to evaluate the hypothesis that GNAS is a key molecular driver that governs the signaling pathway involved in metastatic peritoneal seeding and growth. To test this hypothesis, the study will (1) define the GNAS-induced gene regulatory networks and phenotypic features that facilitate tumor progression in patient peritoneal metastasis and CRISPR-Cas9 gene- edited PDOs and (2) determine the impact of GNAS modulation on metastasis distribution and pathogenicity in vivo using xenograft metastatic models. Investigations will integrate multi-omic analyses with PDO experimental validation to improve the fundamental understanding of metastasis and validate GNAS signaling as a therapeutically-relevant target. The applicant, Dr. Michael Foote, is a rising Assistant Attending in the GI Oncology Service at Memorial Sloan Kettering Cancer Center (MSKCC). Dr. Foote has defined a 5-year plan to integrate his background in targeted drug development and computational bioinformatics with new expertise in experimental modeling and molecular biology. Dr. Foote will be mentored by a complementary advisory committee led by Dr. Luis Diaz, an international expert in genomics with a strong background in training successful independent physician scientists. Dr. Foote’s development plan includes supportive workshops and mentoring from an advisory committee of experts in molecular biology, cell signaling, and bioinformatics at MSKCC, a world-renowned translational center of excellence. Completion of the project goals will facilitate new therapeutic approaches for treating metastatic GI cancer and Dr. Foote’s development into an independent physician scientist and expert leader in GI metastasis.

PROJECT NARRATIVE Patients with gastrointestinal (GI) cancers that metastasize to the peritoneal cavity suffer high morbidity and mortality and have few effective treatment options. Mutations in the GNAS gene are associated with higher rates of peritoneal metastasis, as well as decreased responses to chemotherapy in many GI cancers. The study will investigate the impact of GNAS mutations on tumor molecular signaling cascades and tumor progression, improve fundamental knowledge of tumor peritoneal metastasis, and evaluate GNAS inhibition as a new promising treatment strategy for the large number of patients with metastatic GI cancers.