Reinforcement of Solid Lipid Nanoparticles for Targeted PD-L1 Downregulation in Breast Cancer

Abstract Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype characterized by the absence of targetable receptors and limited therapeutic options. Its inherently low immunogenicity necessitates strategies to enhance its susceptibility to immune attack. This study aimed to enhance the antitumor immune response by inducing downregulation of the programmed death ligand 1 (PD-L1), thereby increasing cancer cell recognition and activating tumor-specific immunity. To this end, a targeted solid lipid nanoparticle (tSLN) system was developed for the precise delivery of CRISPR/Cas9 plasmids to achieve functional PD-L1 downregulation. The SLN formulation comprised a cetyl palmitate core stabilized with cationic and PEGylated lipids. Functionalization with the tumor-penetrating peptide iRGD yielded tSLN, which demonstrated good colloidal stability, serum protection of the CRISPR cargo, and minimal cytotoxicity. In vitro studies in two breast cancer subtypes, the luminal MCF-7 and the triple-negative 4T1 line, confirmed greater transfection efficiency and PD-L1 knockdown by tSLN:Crispr/PD-L1 relative to non-targeted controls. In an orthotopic 4T1 mouse model, systemic administration of tSLN:Crispr/PD-L1 significantly inhibited tumor growth and metastasis while enhancing T cell infiltration, and was more effective than standard chemotherapy (paclitaxel) in this model. The targeted approach also exhibited a favorable short-term safety profile, with no organ toxicity detected over the treatment period. These findings underscore the potential of SLN-mediated CRISPR delivery as an immunomodulatory strategy for breast cancer, and particularly for TNBC.