Abstract IA-08: Syndecan 1 is a therapeutic target for KRAS-driven pancreatic cancer

Abstract KRAS inhibitors targeting G12C mutation have been approved by FDA for the treatment of non-small cell lung cancers and have shown promising clinical responses in pancreatic ductal adenocarcinoma (PDAC). RAS inhibitors targeting additional KRAS mutations or multiple RAS isoforms are under clinical development. Although targeting KRAS exhibits anti-tumor effect in PDAC, majority of tumors inevitably develop resistant disease, as is the case for most targeted therapies. In this new era of targeting KRAS driven cancer, understanding mechanisms driving this resistance to RAS targeted therapies and further devising combination strategies to overcome it have become a necessary, though challenging, task to achieve long term disease control. To tackle this problem, we employed various in vitro and in vivo preclinical model systems to explore the development of resistance to both genetic and pharmacological KRAS blockade. Our previous work identified the membrane proteoglycan Syndecan 1 (SDC1) as a KRAS downstream surrogate whose cell surface localization is tightly controlled by oncogenic KRAS signaling and is critical for KRAS-driven tumor development. Here, our analysis of KRAS driven genetically engineered PDAC mouse model and human pancreatic or colorectal cancer (CRC) cells with KRASG12C mutation discovered that, while cell surface SDC1 is reduced upon acute genetic or pharmacological inhibition of oncogenic KRAS, plasma membrane SDC1 is recovered in tumor cells that become resistant to KRAS inhibition (KRAS-bypass cells). Surface localization of SDC1 leads to the activation of multiple receptor tyrosine kinases (RTKs) and macropinocytosis, resulting in the resistance to KRAS blockade. We further identified that the recovery of plasma membrane SDC1 in KRAS-bypass cells is driven by YAP1 oncogene, which induces the downregulation of ARF6 GAPs, leading to the activation of ARF6, a small GTPase required for SDC1 membrane recycling. To therapeutically targeting SDC1, we have successfully developed a monoclonal antibody (22B mAb), which exhibits remarkable sensitivity and specificity for human SDC1. Our results indicate that 22B mAb exerts substantial inhibition of PDAC cell growth in vitro and desirable tumor inhibitory effects in vivo in murine PDAC tumors and human PDAC cell-derived xenograft tumors. Importantly, our 22B mAb synergizes with KRAS inhibitors, chemotherapy, or immunotherapy, resulting in significantly enhanced therapeutic effects. Taken together, our study identified SDC1 as a functional driver for the bypass of KRAS-dependence and therapeutically targeting SDC1 with a novel mAb will overcome the acquired resistance to KRAS targeted therapy. As such, our research yields important new insights in the fields of cancer biology regarding mechanisms of resistance employed by human cancers, and identifies new actionable therapeutic targets and approaches to overcome resistance to KRAS inhibition. Citation Format: Mitsunobu Takeda, Zecheng Yang, Madeline S Theardy, Alexey Sorokin, Oluwadara Coker, Shuaitong Chen, Long T Vien, Laura Bover, Haoqiang Ying, Scott Kopetz, Wantong Yao. Syndecan 1 is a therapeutic target for KRAS-driven pancreatic cancer abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr IA-08.