Abstract PS4-04-28: Multifunctional lipid nanoparticles remodeling tumor immune microenvironment for breast cancer chemio-immunotherapy

Abstract Background: Breast cancer is one of the most common malignant tumors worldwide, and its treatment faces challenges such as the complexity of the immune microenvironment and the side effects associated with conventional therapies. Doxorubicin (DOX) is often confronted with issues of resistance and significant side effects, while Resiquimod (R848) has been shown to enhance anti-tumor immune responses. This study presents a liposome-based nanodrug delivery platform that combines the advantages of liposomes with the protective properties of chitosan, aiming to co-deliver DOX and R848 to target tumor cells and tumor-associated macrophages (TAMs), thereby improving the therapeutic efficacy in breast cancer treatment. Methods: In this study, folic acid (FA) and chitosan (CS) were conjugated to form an FA-CS complex for incorporation into liposomes, enhancing their stability and targeting ability. FA-CS-R848/DOX@Lip liposomes were prepared via the rotary evaporation method, and their morphology, particle size, and zeta potential were characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The drug encapsulation efficiency, loading capacity, and in vitro release were assessed. In vivo, a mouse breast cancer xenograft model was established to evaluate the anti-tumor efficacy and biocompatibility of the drug delivery system. Flow cytometry was used to quantify immune cell populations in the tumor immune microenvironment, including CD8+ T cells, TAMs, regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs), to analyze changes in the immune response. Results: FA-CS-R848/DOX@Lip liposomes were successfully prepared with a particle size of approximately 211 nm and a zeta potential of 5.3 mV. The encapsulation efficiencies of R848 and DOX were found to exceed 80% and 70%, respectively, with drug loading capacities of 6.8% and 4.6%. Drug release studies indicated that the release profile of FA-CS-R848/DOX@Lip liposomes was relatively slow. Cellular uptake assays demonstrated significantly higher uptake efficiency in RAW 264.7 macrophages and EO771 tumor cells compared to non-targeted liposomes. Cytotoxicity evaluations showed that FA-CS-R848/DOX@Lip exhibited superior anti-tumor activity, effectively inducing tumor cell death while simultaneously stimulating immune responses. In vivo experiments revealed that FA-CS-R848/DOX@Lip significantly inhibited tumor growth, while maintaining favorable biocompatibility and safety profiles. Flow cytometry analysis indicated a notable increase in the proportion of CD8+ T cells with enhanced functionality, as well as a significant shift in the M1/M2 ratio of TAMs and a reduction in the numbers of Tregs and MDSCs. Collectively, these results suggest that this nanodelivery platform effectively activates immune responses and remodels the tumor immune microenvironment. Conclusion: The FA-CS-R848/DOX@Lip liposomes developed in this study synergistically combine the cytotoxic effects of DOX with the immune activation properties of R848, achieving a cooperative interaction between chemotherapy and immunotherapy. This delivery platform effectively targets tumor cells and TAMs, significantly enhancing anti-tumor immune responses while overcoming the limitations of conventional therapies. By optimizing the drug delivery system and enabling precise immune modulation, FA-CS-R848/DOX@Lip represents a novel and effective strategy for breast cancer treatment. This study provides a theoretical foundation for the combined application of chemotherapy and immunotherapy, offering promising prospects for advancing therapeutic approaches in other cancer types. Citation Format: H. Fang, W. Jiang. Multifunctional lipid nanoparticles remodeling tumor immune microenvironment for breast cancer chemio-immunotherapy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-04-28.