Abstract 2414: Early biological impacts of radiotherapy-activated NBTXR3 nanoparticles

Abstract

Abstract Since many decades, radiotherapy (RT) is worldwide used and crucial therapeutic approach for the treatment of cancers. Nowadays, about 50% of cancer patients will receive radiotherapy during their treatment. Nevertheless, the use of RT is limited by the damage induced by ionizing radiation on healthy tissues. To overcome this constraint, we have developed high electron density of functionalized hafnium oxide nanoparticles (NBTXR3), allowing a high probability of interaction with incoming ionizing radiation, increasing energy dose deposit within cells. Many preclinical data have shown that RT-activated NBTXR3 (NBTXR3+RT) increase cancer cell destruction as well as better control treated tumor growth, compared to RT alone. In clinic, the benefit of NBTXR3+RT compared to RT alone has been demonstrated for patients with locally advanced Soft Tissue Sarcoma, in the randomized controlled phase II/III Act.in.Sarc study (NCT02379845). We also demonstrated in preclinical settings that, beyond the destruction of tumor cells, NBTXR3+RT was also able to induce an antitumor immune response capable to produce a significant abscopal effect, linked to the increase of CD8 infiltrates in tumors. It has been recently reported that NBTXR3+RT can also restore anti-PD1 efficacy in an anti-PD1 resistant mouse model. At the cancer cell level, we reported that NBTXR3+RT could modulate the immunopeptidome of cancer cells, induce the activation of the cGAS-STING pathway and increase the expression of ICD biomarkers. All these data indicate that NBTXR3+RT has the ability to transform the tumor into an in situ vaccine more efficiently than RT alone and could have important implications for the use of NBTXR3+RT in combination with immunotherapy. Nevertheless, we currently have relatively few elements on the early cellular events that could trigger or explain the above reported performances of NBTXR3+RT, compared to RT alone. To address this question, we have carried out a series of in vitro studies (cytometry, microscopy) on different cancer models (human and murine). We have thus identified that the vast majority of NBTXR3 nanoparticles are located in lysosomes after endocytosis by tumor cells. Once activated by RT, we detected lysosomal membrane permeabilization (LMP) only in cells treated with NBTXR3+RT, but not in cells only treated by RT. Following LMP, we measured a significant increase of in lipid peroxidation. These first elements allow a better understanding of the early biological consequences induced by NBTXR3+RT, compared to RT alone. Citation Format: Jordan Da Silva, Célia Bienassis, Sebastien Paris. Early biological impacts of radiotherapy-activated NBTXR3 nanoparticles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2414.