Purpose: To improve radiation based immunotherapy via tumor vasculature targeted gold nanoparticles for the treatment of highly immunosuppressive triple negative breast cancer.
Methods: In vitro studies to optimize radiation dose with tumor vasculature targeted gold nanoparticles (AuNP-RGD) were conducted by quantifying dsDNA break accumulation within the cytosol, which is a characteristic of immunologic cell death. Further, mice were inoculated with immunosuppressive murine triple negative breast cancer. Mice were treated with AuNP-RGD along with 10 Gy radiation 24 h post-nanoparticles. Local tumor and systemic immune responses were quantified 7 days post-radiation therapy. Mouse tumor and spleen were resected and stained for immunosuppressive cells, including regulatory T-cells, myeloid derived suppressor cells, and M2 polarized macrophages, as well as immune activating cells, including cytotoxic T-cells and M1 polarized macrophages.
Results: In vitro dsDNA breaks increased significantly with the addition of targeted gold nanoparticles between 10-15 Gy directly further in vivo work. Tumor vasculature targeted gold nanoparticles boosted local radiation dose in vivo and led to a shift in the tumor local microenvironment towards more anti-tumor lymphocyte infiltration as well as an overall systemic lymphocyte shift 7 days post-radiation therapy. Locally, there was a decrease in infiltrating pro-tumor regulatory T-cells as well as a decrease in myeloid derived suppressor cells (MDSCs) and M2 polarized macrophages. Relative to those shifts, there was an increase in infiltration of anti-tumor M1 polarized macrophages tilting the spectrum of immune response towards a more favorable tumor suppressive environment. Systemic effects within the spleen indicated increase in active cytotoxic T-cells and decrease in MDSCs.
Conclusion: Although gold nanoparticles have been studied in the past as radiosensitizers to boost local radiation, the novel approach to a tumor vasculature directed response opens up a unique immunological therapy component for previously highly immunosuppressive tumors such as triple negative breast cancer.