Abstract A104: Targeting RABL3 to disrupt KRAS trafficking and activity in pancreatic cancer
Authors: Jeong Woo-Jeong , Aney Katherine J. , Chen Ethan , Yang Annan , Uribe Giselle A. , Aguirre Andrew , Nissim Sahar 
Published: January 2024

Abstract
Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal cancers with limited treatment options. Nearly all PDAC harbors a KRAS mutation, and oncogenic KRAS signaling is a key driver. Localization of the KRAS protein to the plasma membrane is absolutely required for downstream tumorigenic activities, making trafficking of KRAS to the plasma membrane a compelling target for treatment. In a familial pancreatic cancer syndrome with a striking five cases of PDAC, we recently discovered a rare, inherited gain-of-function mutation in the gene RABL3 that impacts the kinetics of KRAS intracellular trafficking. RABL3 was found to indirectly interact with KRAS, and the familial RABL3 mutation accelerates trafficking of KRAS to the plasma membrane. Here, we present pre-clinical experiments evaluating the therapeutic potential of targeting RABL3 to disrupt KRAS trafficking and activity. To achieve inducible knockdown of RABL3, we have engineered KPCY cells (tumor cells derived from KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx1-Cre; Rosa26YFP/YFP mice) to express a doxycycline-inducible shRNA targeting RABL3. In vitro, RABL3 knockdown results in robust suppression of KPCY cell proliferation. Moreover, the knockdown of RABL3 abrogated tumor growth of KPCY cells in immune-competent subcutaneous and orthotopic pancreatic cancer mouse models. Single-cell transcriptome profiling of tumors revealed immune infiltration of T cells, B cells, macrophages, and dendritic cells following RABL3 knockdown, suggesting that RABL3 knockdown creates vulnerabilities seen with suppression of KRAS activity. Validating these findings in a human context, we find a significantly elevated level of RABL3 expression across multiple human PDAC cell lines, consistent with a driver role in PDAC and a critical role in regulating KRAS trafficking. Similarly, analysis of human datasets revealed elevated RABL3 transcript levels in PDAC TCGA specimens compared to matched normal tissue as well as in PDAC patient-derived organoids compared to the GTEx cohort of normal pancreas tissues. Furthermore, there is a trend for worse patient survival with higher RABL3 expression levels. Therefore, to evaluate the potential of RABL3 knockdown to improve the potency, efficacy, and toxicity when combined with other PDAC therapeutic targets, we are currently testing the impacts of RABL3 knockdown on the therapeutic profile of newly available small-molecular KRAS inhibitors. Our findings provide pre-clinical support for targeting RABL3 to disrupt KRAS intracellular trafficking and inhibit KRAS activity for the treatment of PDAC.
Citation Format: Woo-Jeong Jeong, Katherine J. Aney, Ethan Chen, Annan Yang, Giselle A. Uribe, Andrew Aguirre, Sahar Nissim. Targeting RABL3 to disrupt KRAS trafficking and activity 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 A104.