Cyclin‐dependent kinase inhibitors enhance programmed cell death protein 1 immune checkpoint blockade efficacy in triple‐negative breast cancer by affecting the immune microenvironment

ABSTRACT Background Clinical studies on programmed death‐ligand 1 (PD‐L1) immune checkpoint inhibitors for treating triple‐negative breast cancer (TNBC) have shown unsatisfactory efficacy due to low tumor‐infiltrating lymphocyte (TIL) levels. Inhibitors targeting cyclin‐dependent kinase (CDK) proteins can affect the immune microenvironment, increase TIL levels, and promote antitumor immunity, thus providing a new direction for TNBC treatment strategies. Methods The authors tested three CDK inhibitors on the TNBC cell lines MDA‐MB‐231 and 4T1 and validated their antitumor effects and impact on the immune microenvironment using multiple detection methods. They verified the efficacy and immune‐related mechanisms of different combination therapy experiments in a 4T1 cell‐transplanted BALB/c mouse model. Results Treatment with CDK inhibitors for 72 hours inhibited cell proliferation, clone formation, migration, and cell‐cycle arrest and induced apoptosis in human breast cancer MDA‐MB‐231 cells and mouse breast cancer 4T1 cells. CDK inhibitors suppressed DNA methylation by downregulating DNMT1, DNMT3a, and DNMT3b expression. These three inhibitors promoted the secretion of various chemokines, enhanced tumor cell antigen presentation, and increased PD‐L1 expression. CDK inhibitors improved the efficacy of immunotherapy in animal models and increased TIL levels. Conclusions Combination therapy with CDK and PD‐L1 immune checkpoint inhibitors affects the immune microenvironment, promotes antitumor immunity, and improves the efficacy of immunotherapy for TNBC.