Dasatinib Remodels the Tumor Microenvironment and Sensitizes Small Cell Lung Cancer to Immunotherapy

Effective strategies to reinvigorate the immune system are needed to improve outcomes in small cell lung cancer (SCLC). Targeting Src family kinases with dasatinib (Dasa) can elicit immunomodulatory effects in some cancer types. Here, we explored the potential of combining Dasa with immune checkpoint blockade in SCLC. While the SCLC models were refractory to anti-PD-1 or anti-CTLA4 monotherapy, anti-PD-1 and anti-CTLA4 combination immunotherapy (ITc) induced a significant antitumor response. Further, the Dasa+ITc combination was superior to ITc or Dasa alone. Dasa+ITc activity was mediated by CD4+ T cells, MHC-II+ antigen presenting cells (APCs), and natural killer (NK) cells, as depletion of these populations impeded the combination treatment antitumor efficacy. Increased tumor infiltration of CD4+ and CD8+ T cells, NK cells, M1-like macrophages, and CD11c+ APCs and a reduction of regulatory T cells (Tregs) and M2-like macrophages were found in Dasa+ITc-treated mice. Dasa increased CCL5 in NK cells and reduced Treg cell conversion from CD4+ lymphocytes. Dasa+ITc therapy elicited robust antitumor efficacy in 3D co-cultures of immune and SCLC cells. In vivo experiments showed that CCL5 was necessary for the Dasa+ITc response. In SCLC immunotherapy-treated patients, a gene signature including CD4, CIITA, and tumor mutational burden predicted good prognosis. On-treatment CCL5 plasma levels were increased only in patients with long progression-free survival, and pre-treatment secretomics identified cytokines related to myeloid cells significantly associated with poor prognosis. In summary, combining Dasa with immunotherapy represents a strategy to treat SCLC, with CCL5 as a cytokine that could serve to monitor response.