LAUSR

Targeted therapies, such as EGFR inhibitors, have improved survival for patients with non-small cell lung cancer (NSCLC). Overall cure rates remain low due to eventual development of resistance. Osimertinib is a third-generation EGFR inhibitor that overcomes T790M-mediated resistance to earlier generation EGFRi. However, resistance to osimertinib has also emerged through mechanisms that are EGFR-dependent and EGFR-independent. To uncover novel strategies to overcome osimertinib resistance, we explored androgen receptor (AR) antagonists in combination with osimertinib as recent studies have demonstrated AR inhibition enhanced TKI-targeted therapy. For these experiments, we utilized lab-derived osimertinib-resistant PC9-AR and HCC827-AR NSCLC cell lines and matching parental lines in both in vitro and in vivo model systems. Clonogenic assays revealed that darolutamide in combination with osimertinib synergistically suppressed clonal growth in resistant cell lines. Similar results were observed with the combination of enzalutamide and osimertinib. Given this result, we next wanted to establish whether the promising in vitro activity of this combination translates into antitumor efficacy in vivo. Mice bearing either HCC827AR or PC9AR xenografts were treated orally daily with both drugs. At the doses administered, neither drug alone had antitumor activity. However, the combination significantly delayed tumor growth by more than 60%. We confirmed this ability to reverse resistance as a class effect using a different AR antagonist, enzalutamide in PC9AR-bearing mice. Significant tumor growth inhibition was observed with the combination of enzalutamide and osimertinib. To investigate the mechanism by which this combination may reverse osimertinib-resistance, RNA-seq studies were performed following drug exposure in vitro using parental and resistant cell lines under various experimental conditions. Comparison of gene expression profiles between parental and resistant cell lines under different therapeutic pressure and pathway enrichment analysis revealed important differentially expressed genes pointing plausible activated pathways that underline osimertinib resistance. AR antagonists have the potential to reverse EGFR inhibitor resistance in treatment of EGFR-mutant NSCLC. Citation Format: John C. Schmitz, Guojing Zhang, Zhentao Liu, Yufei Huang, Gabriel Sica, Shi-Yong Sun, Taofeek K. Owonikoko. Darolutamide reverses osimertinib resistance in non-small cell lung cancer [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 1752.