Adaptive immunity is required for durable responses to alectinib in murine models of EML4-ALK lung cancer

Purpose Lung cancers bearing oncogenic EML4-ALK fusions respond to targeted tyrosine kinase inhibitors (TKIs; e.g. alectinib), with variation in the degree of shrinkage and duration of treatment (DOT). We previously demonstrated a positive association of a TKI-induced interferon gamma (IFNγ) transcriptional response with DOT in EGFR-mutant lung cancers. Herein, we used murine models of EML4-ALK lung cancer to test a role for host immunity in the therapeutic response to alectinib. Experimental Design Three murine EML4-ALK cell lines (EA1, EA2, EA3) were implanted orthotopically into the lungs of immunocompetent and immunodeficient mice and treated with alectinib. Tumor volumes were serially measured by μCT. Immune cell content was measured by flow cytometry, multispectral immunofluorescence and CyTOF. Transcriptional responses to alectinib were assessed by RNAseq and secreted chemokines were measured by ELISA. Results All cell lines were sensitive to alectinib in vitro . EA1 and EA3 tumors retained residual disease that rapidly progressed upon termination of treatment while EA2 tumors were eliminated by TKI treatment. Alectinib induced inflammatory transcriptional programs and multiple chemokines in all cell lines while untreated tumors exhibited distinct baseline chemokine expression patterns and content of CD8+ T cells and myeloid subsets. When propagated in immune-deficient mice, all three cell line-derived lung tumor models exhibited significant shrinkage followed by prompt progression despite continuous alectinib treatment. Conclusions The findings support an hypothesis that host and TKI-stimulated production of chemokines by tumor cells promotes functional engagement of adaptive immune cells within the tumor microenvironment that enhances the durability and depth of TKI response. Statement of Translational Relevance Patients with metastatic lung cancer harboring ALK fusions are treated with targeted tyrosine kinase inhibitors (TKI) in the first line setting. Despite bearing the same driver oncogene, patients experience a range of tumor burden reduction and variable amounts of residual disease. Residual disease burden associates with patient survival and contributes to the emergence of drug resistance yielding treatment failure. The factors mediating this differential response to TKI and residual disease are incompletely understood. Our group has developed a panel of murine ALK driven lung cancer cell lines that reproducibly show differences in the depth and duration of response when implanted into immunocompetent mice. Data using this model indicate that the presence of CD8+ T cells is a major contributor to the depth and duration of response. These models will be critical in developing rational combination therapies to augment the immune microenvironment engagement along with TKIs to improve outcomes for these patients.