Interaction of DLL3-targeting CAR-T cells with the JAK1 inhibitor in treating small cell lung cancer.

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Background: Small cell lung cancer (SCLC) is an aggressive malignancy with limited effective treatment options. DLL3-targeted CAR-T therapy represents a promising immunotherapeutic strategy, but its efficacy is often hampered by tumor intrinsic aggressiveness and CAR-T cell exhaustion. The JAK-STAT signaling pathway is closely associated with tumor proliferation, survival, and immune regulation. However, whether JAK1 inhibition can enhance the anti-tumor activity of DLL3 CAR-T cells against SCLC remains unclear. Methods: Human SCLC cell lines were treated with JAK1 inhibitor alone or in combination with DLL3 CAR-T cells. In vitro assays included Western blot, qPCR, Annexin/PI apoptosis assay, flow cytometry, CCK-8 proliferation assay, Transwell migration and invasion assay, and soft agar colony formation assay. CAR-T cell exhaustion and memory phenotype were evaluated by flow cytometry and RNA-sequencing. Tumor cell killing efficiency was assessed in co-culture system and flow cytometry. Anti-tumor efficacy in vivo was evaluated in NSG mice bearing SCLC subcutaneous xenografts. Results: In vitro, JAK1 inhibition significantly induced apoptosis in SCLC cells, and suppressed cell proliferation, migration, invasion, and colony formation. Notably, JAK1 inhibition reduced the exhaustion phenotype and enhanced the memory-like phenotype of CAR-T cells, as validated by flow cytometry and RNA-seq. In co-culture killing assays, the combination of JAK1 inhibitor and DLL3 CAR-T cells further reduced the proportion of viable tumor cells compared with CAR-T treatment alone. In NSG mouse xenograft models, both CAR-T monotherapy and JAK1 inhibitor monotherapy inhibited tumor growth, while their combination resulted in significantly greater suppression of subcutaneous tumor growth. Conclusions: JAK1 inhibition exerts direct anti-tumor effects on SCLC cells by inhibiting proliferation, migration, invasion, and inducing apoptosis. Furthermore, JAK1 inhibition enhances the anti-tumor function of DLL3 CAR-T cells by mitigating CAR-T exhaustion and promoting memory formation. These preclinical findings support the combination of JAK1 inhibition with DLL3 CAR-T therapy as a novel and promising strategy for the treatment of SCLC.