UNC5B promotes EMT and metastasis of pancreatic adenocarcinomas and expresses different isoforms that impact sensitivity to Netrin-1 blockade

Abstract The axonal guidance receptor UNC5B is considered to be a tumor suppressor because it promotes apoptosis in the absence of its protein ligand, NTN1. But we find that UNC5B is not a tumor suppressor of pancreatic ductal adenocarcinomas (PDAC), and instead promotes metastasis. In TCGA data, UNC5B expression associates with poor patient outcome. In vivo, pancreatic cancer metastasis was completely eliminated by knocking out UNC5B from the genetically engineered KPC mouse model of PDACs, and was reduced upon knockout of UNC5B in a splenectomy model of liver metastasis. An inhibitor of NTN1, NP137, also reduced metastasis in vivo. In vitro, knockout of UNC5B from mesenchymal pancreatic cell lines was sufficient to reduce many metastatic traits including invasiveness, EMT, and aerobic glycolysis. YAP1 is a known target of UNC5B and was overexpressed in high UNC5B expressing cell lines, which were sensitive to the YAP1 inhibitor CA3. NP137 is currently in clinical trial for several tumor types and we have been investigating which patients might respond best to this drug. Using an antibody (D9M7Z) that recognizes an epitope in UNC5B that overlaps with the caspase-3 cleavage site that is critical for UNC5B's apoptotic functions, we found two isoforms in murine and human PDACs: one isoform that contains the caspase-3-containing epitope as well as a previously-unreported isoform that to lack it. Cells expressing the caspase-3 site were much more sensitive to NP137. We also discovered genetic alterations in patient samples that induce expression of UNC5B. For instance, UNC5B was recurrently amplified in PDACs and these amplifications were highly focal to the UNC5B locus; also, UNC5B expression was increased by mutations of ARID1A, a component of the SWI/SNF transcription complex that is recurrently mutated in pancreatic adenocarcinomas. ARID1A mutations caused cell lines to become mesenchymal, but the cells returned to an epithelial phenotype upon knockout of UNC5B. In current and future clinical trials, NP137 may particularly benefit patients with tumors that harbor mutations in ARID1A or ARID1B, focal amplifications of UNC5B, and/or high expression of the caspase-3-containing isoform of UNC5B. Citation Format: Chris R. Harris, Orjola Prela, Lan Wang, Anthony Casabianca, Wade Narrow, Zachary Sechrist, Tracy Withers, Cory Shields, Asra Asad, Aram Hezel, Darren Carpizo. UNC5B promotes EMT and metastasis of pancreatic adenocarcinomas and expresses different isoforms that impact sensitivity to Netrin-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1286.