Synergistic Chemo-Immunotherapy Using pH-Responsive Nanoparticles in Breast Cancer Treatment: In Vitro and In Vivo Studies

Recent research underscores the pivotal role of the heterogeneous multicellular interactome within the tumor microenvironment (TME) in tumor progression and survival. Tumor-associated macrophages (TAMs), among other nonmalignant cells in the TME, promote an immunosuppressive environment, fostering tumor cell survival, proliferation, and resistance. Hence, combining chemotherapy with immunomodulatory agents to transition TAMs to an immunostimulatory phenotype holds immense therapeutic potential. The present study focuses on developing tumor-responsive nanoparticles (NPs) for combined chemo-immunotherapy using resiquimod (RSQ), a TLR 7/8 agonist as an immunomodulator, and paclitaxel (PTX) as chemotherapeutics. A pH-responsive NP known as PHNP, tailored with a star-shaped PLGA conjugated with poly histidine, was engineered to selectively deliver a consistent ratio of PTX and RSQ directly to the tumor site. In vitro studies demonstrate enhanced drug release at pH 6.4, increased penetration in tumor spheroids, and increased cytotoxic efficacy against breast cancer cells. Furthermore, PHNPs activate macrophages for antitumor activity. In vivo studies demonstrated a notable rise in plasma AUC and improved delivery of drugs to the tumor using PHNPs, resulting in enhanced effectiveness against tumor growth in a mouse orthotopic breast cancer model. Notably, PHNP treatment elevated intratumoral ROS and apoptosis levels and inhibited lung metastasis. Overall, this study underscores the potential of the PTX and RSQ combination as a prospective combined chemo-immunotherapeutic modality.