Spatial analysis of nanoparticle distribution in human breast xenografts reveals nanoparticles targeted to cancer cells localized with tumor-associated stromal cells.

The biological influence of physicochemical parameters of "targeted" nanoparticles on their delivery to cancer tumors remains poorly understood. A comparative analysis of nanoparticle distributions in tumors following systemic delivery across several models can provide valuable insights. Methods: Bionized nanoferrite nanoparticles (iron oxide core coated with starch), either conjugated with a targeted anti-HER2 antibody (BH), or unconjugated (BP), were intravenously injected into athymic nude or NOD-scid gamma (NSG) female mice bearing one of five human breast cancer tumor xenografts growing in a mammary fat pad. Tumors were harvested 24 hours after nanoparticle injection, fixed, mounted, and stained. We performed detailed histopathology analysis by comparing spatial distributions of nanoparticles (Prussian blue) with various stromal cells (CD31, SMA, F4/80, CD11c, etc.) and the target antigen-expressing (HER2) tumor cells. Results: Only BH nanoparticles were retained in tumors and generally concentrated in the tumor periphery, with nanoparticle content diminishing towards the tumor interior. Nanoparticle distribution correlated strongly with specific stromal cells within each tumor type, which varied among tumor types and between mouse strains. Weak or no correlation between nanoparticle distribution and HER2 positive cells, or CD31 cells was observed. Conclusion: Antibody-labeled nanoparticles were retained across all tumors, irrespective of presence of the "target" antigen. Though presence of antibody on nanoparticles correlated with retention, non-cancerous host stromal cells were responsible for their retention in the tumor microenvironment. This study highlights gaps in our understanding of the complex biological interplay between disease and host immune biology, and the need to account for the influence of underlying aberrant tumor biology as factors determining nanoparticle fate in vivo.

Nanoparticle interactions with immune cells dominate tumor retention and induce T cell-mediated tumor suppression in models of breast cancer.

The factors that influence nanoparticle fate in vivo following systemic delivery remain an area of intense interest. Of particular interest is whether labeling with a cancer-specific antibody ligand ("active targeting") is superior to its unlabeled counterpart ("passive targeting"). Using models of breast cancer in three immune variants of mice, we demonstrate that intratumor retention of antibody-labeled nanoparticles was determined by tumor-associated dendritic cells, neutrophils, monocytes, and macrophages and not by antibody-antigen interactions. Systemic exposure to either nanoparticle type induced an immune response leading to CD8+ T cell infiltration and tumor growth delay that was independent of antibody therapeutic activity. These results suggest that antitumor immune responses can be induced by systemic exposure to nanoparticles without requiring a therapeutic payload. We conclude that immune status of the host and microenvironment of solid tumors are critical variables for studies in cancer nanomedicine and that nanoparticle technology may harbor potential for cancer immunotherapy.