Development of a Rationally Designed siRNA-Based Therapeutic Targeting PD-L1 in Triple-Negative Breast Cancer

In triple-negative breast cancer (TNBC), immune checkpoint pathways play a central role in tumor immune evasion. Programmed death protein 1 (PD-1) is an inhibitory receptor expressed on T cells, while its ligand, programmed death-ligand 1 (PD-L1), is commonly expressed on tumor cells and cells within the tumor microenvironment. Their interaction suppresses T-cell activation and promotes immune escape. In this study, we evaluated the potential of small interfering RNA (siRNA) to silence PD-L1 expression in TNBC. Transcriptomic analysis of GEO datasets revealed consistent upregulation of CD274 (PD-L1) in TNBC samples. Three siRNA candidates were designed and evaluated in MDA-MB-231 cells. All siRNAs significantly reduced CD274 expression (>70%), as determined by RT-qPCR. Immunofluorescence analysis confirmed a reduction in PD-L1 protein levels (54.3 vs. 98.7 a.u.), while MTT assays demonstrated preserved cell viability at the working concentration (100 pM), supporting a non-cytotoxic and specific gene-silencing effect. These findings highlight PD-L1 as a viable molecular target and support siRNA-mediated silencing as a promising therapeutic strategy in TNBC.