Lung cancer is the leading cause of cancer-related deaths in the United States, and the 5-year survival rate of all lung cancer patients combined is only about 18%. The implementation of cancer immunotherapeutics for solid tumors such as lung cancers has shown great promise and provided the possibility for improved outcome in a small percentage of patients. However, the majority of patients show little to no response or acquire resistance during treatment with checkpoint inhibitors delivered as a monotherapy. Therefore, identifying resistance mechanisms and potential combination therapy approaches is a critical need to improve response rates to immune checkpoint inhibitors and patient prognosis. To address this, a clinically relevant in vivo shRNA dropout screen focused on genes encoding for FDA-approved drug targets (FDAome) was performed in epithelial and mesenchymal Kras/p53 (KP) mutant murine lung cancer cells. Mice were then treated with either isotype or anti- PD-1 antibody. Sequencing for the barcoded shRNAs revealed that Ntrk1 was significantly depleted from mesenchymal tumors challenged with PD-1 blockade compared to isotype treated tumors, suggesting it provides a survival advantage to these tumor cells when under immune system pressure. Preliminary data confirmed Ntrk1 transcript levels are upregulated in mesenchymal tumors treated with PD-1 inhibitors and cell lines derived from resistant tumors, and analysis of human NSCLC cell lines revealed that Ntrk1 mRNA levels correlate with a more aggressive, mesenchymal cell phenotype. Additionally, Ntrk1 overexpressing cells upregulate PD-L1 expression when co-cultured with splenocytes through upregulation of JAK signaling. Stable knockdown of Ntrk1 in mesenchymal murine KP mutant lung cancer cells reduced tumor growth in vivo and analysis of tumor- infiltrating T cell populations via flow cytometry showed that CD8+ T cell exhaustion was significantly reduced, whereas overexpression of Ntrk1 promoted CD8+ T cell exhaustion, thus decreasing effector status. These tumors also have an altered microenvironment, with upregulation of classically immunosuppressive cytokines such as IL-10. PD-1 protein levels were also significantly increased in Ntrk1-high human NSCLC cell lines, providing additional evidence that Ntrk1 may be a modulator of immune system functionality in human lung disease. The central hypothesis of the proposed work is that Ntrk1 upregulation causes acquired resistance to PD-1 blockade via aberrant JAK signaling and downstream CD8+ T cell dysfunction, thereby promoting tumor cell survival. A variety of powerful tools will be utilized to test this hypothesis, including time-lapse imaging of dynamic T cell-tumor cell interactions, genetically-engineered and syngeneic preclinical models of lung cancer to analyze immune subpopulations as a function of Ntrk1 expression, and IHC analyses of human NSCLC tissue samples. The goal of the proposed work is to provide strong evidence for a rational drug combination of Ntrk1 inhibitors with PD-1 blockade to be carried forward into the clinic to abrogate immune checkpoint blockade resistance and ultimately improve patient outcomes.
Therapeutic options that target and amplify a patient's natural immune system response to cancer within the body have dramatically revolutionized outcomes for a minority of lung cancer patients. However, many patients do not respond to these therapies or develop resistance, and thus there is a critical need to discover rational drug combinations to improve patient response to immunotherapies. The proposed work has identified one such potential avenue of resistance through Ntrk1 and therefore strives to provide compelling evidence to implement a rational combination therapy strategy with immune checkpoint inhibitors.