Abstract 5434: A novel combination therapy for lung squamous cell carcinoma

Abstract Lung cancer is the leading cause of cancer deaths in the US. Non-small cell lung cancer (NSCLC) accounts for ~80% of lung cancer cases and is further classified into adenocarcinoma (LUAD), squamous cell carcinoma (LUSC), and large cell carcinoma. New approaches targeting pathways in NSCLC have emerged, resulting in encouraging new treatments that benefit LUAD patients, but very few advances have been made in the treatment options for LUSC which accounts for ~30% of lung cancer cases. NSCLCs, including LUSCs, contain a sub-population of cells that exhibit properties of cancer stem cells (CSCs) and are responsible for tumor initiation, maintenance, therapeutic resistance, and relapse. Therefore, CSCs must be effectively targeted to elicit long lasting therapeutic results in LUSC patients. Our studies have shown that: 1) PKCι is an oncogene and prognostic marker in LUSC; 2) copy number gains (CNGs) of the PKCι gene (PRKCI) drives overexpression of PKCι in 90% of LUSCs; 3) PKCι phosphorylates SOX2, and controls SOX2-mediated transcriptional activation of Hedgehog Acyl Transferase, resulting in Hedgehog (Hh) pathway activation that drives a CSC phenotype in LUSC cells; and 4) the FDA approved compound Auranofin (ANF) is a potent inhibitor of oncogenic PKCι. In this study, we assessed the effect of ANF in combination with the Hh pathway inhibitor, LDE225, on LUSC CSCs and tumor growth. Cell viability, sphere formation and soft agar assays were used to assess the effects of ANF and LDE225 alone or in combination on the growth of LUSC CSCs with PRKCI CNGs or LUAD and LUSC CSCs without PRKCI CNG to determine if PRKCI CNG can be used to predict response to ANF and LDE225 and test the selectivity of response for LUSC. The effects of ANF and LDE225 on the levels of PKCι-Hh signaling components was assessed by qPCR and western blotting. Finally, the efficacy of ANF and LDE225 in combination was evaluated in human primary LUSC patient-derived xenograft (PDX) models that harbor PRKCI CNGs and the ability of PKCι-Hh signaling intermediates to serve as biomarkers of PKCι-Hh pathway inhibition was validated in vivo. We observed a dose-dependent decrease in cell proliferation, clonal expansion and transformed growth in CSCs treated with ANF and LDE225 alone. ANF and LDE225 combined treatment of LUSC CSCs with PRKCI CNGs (but not LUAD or LUSC CSCs without PRKCI CNG) synergistically inhibited CSC phenotypes based on results of combination index analysis. Furthermore, treatment of LUSC PDX models with ANF and LDE225 in combination had a synergistic effect on tumor growth inhibition. Lastly, ANF and LDE225 treatment led to inhibition of PKCι-Hh signaling intermediates demonstrating the on-target effects of treatment. Our data indicate that a PKCι-Hh vertical blockade strategy of combined ANF and LDE225 effectively targets LUSC CSCs and blocks tumor growth in vivo and provides compelling rationale to develop this novel combination strategy further in clinical trials. Citation Format: Dania Alqasrawi, Ryan Argo, Christine Ratliff Rang, Prita Pandya, Skyeler Klinge, Jennifer Lindemann, Nyla Searl, Alan Fields, Verline Justilien. A novel combination therapy for lung squamous cell carcinoma 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 5434.