Gene Signature-Based Drug Screening Reveals Ponatinib Enhances Immunotherapy Efficacy in Triple-Negative Breast Cancer by Reversing MDSC-Mediated Immunosuppressive Tumor Microenvironment.

The infiltration of myeloid-derived suppressor cells (MDSCs) is critical for the establishment of immunosuppressive tumor microenvironment (TME), yet no approved therapies specifically block it. Here, we employed a gene signature-based drug screening approach to identify potential agents for reversing MDSC-mediated immunosuppression in triple-negative breast cancer (TNBC). Transcriptomic analysis of 73,326 tumor samples and 190,588 single cells revealed C-X-C motif ligand 1 (CXCL1) and CXCL2 as the key gene signature of MDSC infiltration. Combining this gene signature with high-throughput sequencing-based high-throughput screening (HTS²), we identified ponatinib as a potential inhibitor of MDSC infiltration. By employing multiple preclinical models, we demonstrated that ponatinib blocks MDSC infiltration and reverses the immunosuppressive TME, thus inhibiting TNBC growth in a TME-dependent manner, and significantly enhances anti-programmed cell death-ligand 1 (PD-L1) immunotherapy efficacy. Mechanistically, ponatinib directly inhibits p38α kinase activity, reducing signal transducer and activator of transcription 1 (STAT1) phosphorylation at Ser⁷²⁷ and suppressing CXCL1 and CXCL2 expression in cancer cells, thereby blocking MDSC infiltration. Our findings establish ponatinib as a novel inhibitor of MDSC-mediated immunosuppressive TME and underscore its therapeutic potential in combination with immune checkpoint blockade for TNBC treatment.