Immunostimulatory effects of IL-12 targeted pH-responsive nanoparticles in macrophage-enriched 3D immuno-spheroids in vitro model

Metastatic colorectal cancer (CRC) has the dismal 5-year survival rate of only 14%, and immunotherapies fail to improve the patient outcome. One reason for the poor response rate is the slightly acidic (~ 6.5) immunosuppressive microenvironment. Interleukin 12 (IL-12) is a highly potent pro-inflammatory cytokine that can stimulate tumor immune cells and reverse immunosuppression by inducing interferon gamma (IFN-γ) expression. However, its clinical applications are hindered by systemic side effects. In this study, we developed pH-responsive polymeric nanoparticles (NPs) encapsulating IL-12 to enhance its therapeutic efficacy into the tumor microenvironment (TME). IL-12-loaded pH-responsive NPs induced antitumoral pro-inflammatory response in macrophages at pH ~ 6.5, determined by increased IFN-γ levels and nitric oxide (NO) release, without affecting metabolic activity. In contrast, IL-12-loaded pH non-responsive PLGA NPs showed much lower macrophage activation. To validate the specificity and efficacy in a complex immune-rich microenvironment, we developed a novel CRC 3D immuno-spheroid by incorporating human monocyte-derived macrophages with tumor cells in collagen, mimicking CRC spatial organization and extracellular matrix. The interaction of IL-12 pH-responsive NPs induced macrophage polarization, by providing a reduction of M2-like markers (CD14 + CD163+) while increasing pro-inflammatory M1-like counterparts (CD14 + CD86+). Moreover, IL-12 pH-responsive NPs increased IFN-γ levels and reduced anti-inflammatory IL-10 secretion. Overall, this study provides two major findings (1) a pH-responsive NP system to effectively deliver IL-12 to the TME and reprogram local macrophages into pro-inflammatory phenotype; (2) a macrophage-enriched human 3D immuno-spheroid in vitro system as a tool to test the effectivity of immunomodulatory NPs.