Summary

Background: Hafnium oxide, an electron-dense material, was designed at the nanoscale to increase the radiation dose deposited from within the cancer cells: “Hot spot” of energy deposit where the nanoparticles are when exposed to radiation therapy (RT). Preclinical studies have demonstrated increase of cancer cells killing in vitro and marked antitumor efficacy in vivo with presence of these nanoparticles (HfO2-NP) exposed to RT, when compared to RT alone. […]

Material and Methods: CT26 (murine colorectal cancer cells) were subcutaneously injected in the flank of BALB/c mice. Once the mean tumors volume reached 115±30 mm3, tumors were intratumor injected with HfO2-NP and irradiated with 2Gyx3 or 4Gyx3, or irradiated only. Tumors were collected 5 days after the last RT fraction and analyzed for immune cell infiltrates by immunohistochemistry (2Gyx3 and 4Gyx3) and cytokines content by flow cytometry (2Gyx3). […]

Results: In mice bearing CT26 tumors, a marked increase of cytokines content and immune cell infiltrates was observed with HfO2-NP + 2Gyx3 when compared to RT alone. The tumor immune cell infiltrates were
further enhanced with HfO2-NP + 4Gyx3. In mice inoculated with 4T1 cells treated with HfO2-NP + 40Gy, a marked increase of immune cell infiltrate (CD8+) was observed in tumors when compared to tumors in mice inoculated with 4T1 cells treated with 40Gy and control.

Conclusions: These in vivo data generated from CT26 and 4T1 tumor models suggest that HfO2-NP + RT triggers immunogenic conversion of the tumor microenvironement when compared to RT alone. HfO2-NP treatment may represent a therapeutical approach for broad applications since it does not rely on any molecular characteristics of the tumor.