Abstract 2938: In vivo assessment of the combination of the JAK1 selective inhibitor itacitinib with first- and second-generation EGFR inhibitors in models of non-small cell lung cancer

Non-small cell lung cancers (NSCLC) make up the majority of lung cancers, and are predominantly driven by aberrant kinase pathway signaling. Oncogenic mutations leading to activation of the epidermal growth factor receptor (EGFR) have been identified in a substantial fraction of NSCLC patients, leading to EGFR-targeted therapies such as erlotinib that have improved patient outcome. However, inhibition of EGFR consistently leads to drug resistance through multiple pathways, creating a therapeutic need in NSCLC. One particular route to resistance of EGFR inhibitors is activation of pathways that can bypass the need for signaling through the EGFR, such as the JAK/STAT pathway. To explore the impact of JAK/STAT pathway modulation on EGFR inhibitor resistance, combination efficacy studies evaluating the JAK1 selective inhibitor itacitinib with either erlotinib or the EGFR T790M mutant inhibitor osimertinib, were conducted in xenograft models of activated and erlotinib resistant NSCLC. The HCC827 xenograft (EGFR-activating deletion in exon 19) model was very sensitive to both erlotinib and osimertinib, while the NCI-H1975 xenograft (EGFR T790M/L858R) model responded only to osimertinib. Itacitinib was efficacious in the HCC827 model, while only marginal tumor growth inhibition was observed with itacitinib in the NCI-H1975 model despite both models having detectable levels of pSTAT3. The combination of itacitinib with either erlotinib or osimertinib inhibited tumor growth to a greater degree than monotherapies in the HCC827 model. Despite marginal single agent efficacy from itacitinib in the NCI-H1975 model, itacitinib enhanced the efficacy of osimertinib at several dose levels in this model. Importantly, itacitinib and erlotinib administration had synergistic efficacy in this erlotinib-resistant model, indicating that JAK1 specific signaling may be a critical bypass mechanism for resistance to EGFR inhibitors. Downstream of EGFR, both erlotinib and osimertinib inhibited different signaling pathways when combined with itacitinib in the NCI-H1975 model: STAT signaling was regulated by erlotinib, while the AKT/S6 and ERK pathways were regulated by osimertinib. An analysis of possible upstream activators of signaling pathways relevant to NSCLC survival revealed that IL-6, MCP-1 and IL-8 levels were altered in H1975 tumors from mice treated with the combination of itacitinib and osimertinib, and to a lesser extent with the combination of itacitinib and erlotinib. These data demonstrate the potential utility of the JAK1 specific inhibitor itacitinib in EGFR activated NSCLC, or for patients with EGFR mutations who are no longer responsive to a first generation EGFR inhibitor such as erlotinib. The combination of itacitinib and osimertinib is currently in a Phase I/II study (NCT02917993). Citation Format: Matthew C. Stubbs, Xiaoming Wen, Chu-Biao Xue, Taisheng Huang, Wenqing Yao, Brian Metcalf, Reid Huber, Peggy Scherle, Bruce Ruggeri. In vivo assessment of the combination of the JAK1 selective inhibitor itacitinib with first- and second-generation EGFR inhibitors in models of non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2938.