Abstract 614: Src family kinase inhibition demonstrates antitumor activity in vitro and in patient-derived xenograft models of human cholangiocarcinoma

Abstract Background: Cholangiocarcinoma (CCA) is a lethal and heterogenous malignancy of the biliary tree characterized by perineural invasion. About 85% of CCA show activation of YAP signaling, which promotes proliferation, anti-apoptosis, and therapeutic resistance. YAP signaling is mediated by Src family kinases (SFK) by phosphorylation of YAP (pYAPy357). NXP900 is a first-in-class, highly selective, SFK inhibitor with a novel mechanism of action which locks SFK in its closed and inhibited conformation, in contrast to other Src inhibitors such as dasatinib. A phase 1a study of NXP900 in patients with advanced solid tumors was recently initiated. Here, we examined treatment responses of CCA to NXP900 in vitro and in vivo. Methods: Cell viability was determined in seven CCA cell lines by CellTiter-Glo. Cell death and apoptosis were assayed by PI/Hoechst and Caspase-Glo 3/7 assay. CalcuSyn software was used to determine synergistic drug effects. Immunoblot analysis, RT-PCR, and IF staining of YAP localization were used to evaluate YAP knockdown. Clones of human CCA cell lines resistant to NXP900 were generated through escalating exposure to NXP900 over 6 months. Five patient-derived xenograft (PDX) tumors were expanded into flanks of NOD/SCID mice. Tumor bearing mice were randomized 1: 1 with 5 mice per arm and treated with vehicle or NXP900 (40 mg/kg) once daily for up to 4 weeks. To determine drivers of sensitivity and resistance, predicted sensitivity scores based on tumor growth were linked to multi-omics (RNA seq and phospho-proteomics) of our PDX models. Results: All cell lines were sensitive to NXP900 with IC50 values between 7nM-15µM; IC50’s of resistant clones were 1000 times higher. NXP900 induced more cell death compared to vehicle, which appeared to be through apoptosis. NXP900 inhibited pSrc, decreased pYAPy357, and upregulated inactive pYAPs127. Correspondingly, decreased YAP target gene (Cyr61, NUAK, and CTGF) levels and a nuclear-to-cytoplasmic translocation were observed. NXP900/GemCis combination therapy increased cell death demonstrated a synergistic effect (Combination Indices 1) at all concentrations. In our PDX models, treatment was associated with a significant decrease in tumor growth in 3 models (mean fold change 3. 1 vs. 14. 2; 1. 0 vs. 7. 6; 1. 4 vs. 2. 6). The major resistant signature was the TRK signaling network, involved in nerve growth factor binding activity, while drivers of sensitivity included the SRC network. Conclusion: NXP900 demonstrated therapeutic activity in vitro and in human PDX models. We are currently performing multi-omic approaches in NXP900 sensitive and resistant cell lines to unravel determinants of activity and resistance. Additional in vivo studies will be performed to determine effects of NXP900/GemCis and NXP900/anti-PDL-1 combination therapy. Citation Format: Hendrien Kuipers, Jennifer L. Tomlinson, Danielle M. Carlson, Amro M. Abdelrahman, Erik Jessen, Jack W. Sample, Nathan W. Werneburg, Hannah E. Stumpf, Mark J. Truty, Sumera I. Ilyas, Gregory J. Gores, Rory L. Smoot. Src family kinase inhibition demonstrates antitumor activity in vitro and in patient-derived xenograft models of human cholangiocarcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 614.