Specific Tumor Localization of Immunogenic Lipid-Coated Mesoporous Silica Nanoparticles following Intraperitoneal Administration in a Mouse Model of Serous Epithelial Ovarian Cancer

SIMPLE SUMMARY: Ovarian tumors mobilize a heterogenous population of myeloid cells. While these cells initially contribute to anti-tumor immunity, as cancer progresses, they switch from immunostimulatory to immunosuppressive. Ovarian cancer is most frequently restricted to the peritoneal cavity, negating the need for systemic delivery of therapeutics. With a goal of targeting and activating myeloid cells in the tumor microenvironment, this study sought to determine which nanoparticle characteristics enhance uptake by myeloid cells in vitro and in vivo using an animal model of ovarian cancer. Lipids coating a mesoporous silica core were optimized for surface charge, formulation, and inclusion of immunogenic monophosphoryl lipid A. Benefits of a mesoporous core include opportunities for loading with additional therapeutics, such as antigens to direct immune responses or other therapeutic payloads that facilitate anti-cancer immune responses. ABSTRACT: Immunogenic lipid-coated mesoporous silica nanoparticles (ILM) present pathogen-associated molecular patterns (PAMPs) on the nanoparticle surface to engage pathogen-associated receptors on immune cells. The mesoporous core is capable of loading additional immunogens, antigens or drugs. In this study, the impact of lipid composition, surface potential and intercalation of lipophilic monophosphoryl lipid A (MPL-A) in the lipid coat on nanoparticle properties and cellular interactions is presented. Loading and retention of the model antigen ovalbumin into the mesoporous silica core were found to be similar for all nanoparticle formulations, with presentation of ova peptide (SIINFEKL) by major histocompatibility complex (MHC) evaluated to facilitate the selection of an anionic nanoparticle composition. ILM were able to induce lysosomal tubulation and streaming of lysosomes towards the cell surface in dendritic cells, leading to an enhanced surface presentation of MHC. Myeloid cells robustly internalized all ILM formulations; however, non-myeloid cells selectively internalized cationic ILM in vitro in the presence of 20% serum. Interestingly, ILM administration to the peritoneal cavity of mice with disseminated ovarian cancer resulted in selective accumulation of ILM in tumor-associated tissues (>80%), regardless of nanoparticle surface charge or the presence of MPL-A. Immunofluorescence analysis of the omental tumor showed that ILMs, regardless of surface charge, were localized within clusters of CD11b(+) myeloid cells 24 h post administration. Selective uptake of ILMs by myeloid cells in vivo indicates that these cells outcompete other cell populations in the ovarian tumor microenvironment, making them a strong target for therapeutic interventions.