Abstract 2870: Analysis of cancer cells response to radiotherapy activated NBTXR3 nanoparticles
Authors: Da Silva Jordan , Bienassis Celia , Paris Sebastien 
Published: March 2024

Abstract
In 2011, NBTXR3 emerged as the first-in-class radioenhancer used in clinical practice for treating patients with locally advanced soft tissue sarcoma (LA-STS). NBTXR3 became the first radioenhancer to receive CE mark approval after successfully completing a phase II/III clinical study for LA-STS with a doubling of the pCR rate in the NBTXR3 arm compared with the control arm. NBTXR3 nanoparticles consist of a functionalized core of hafnium oxide, a high atomic number element, specifically designed to amplify the effects of radiotherapy (RT) within cells without additional side effects on healthy tissues. Leveraging this physical mechanism, RT-activated NBTXR3 (NBTXR3+RT) has demonstrated superior efficacy in destroying tumor cells and controlling tumor growth in numerous preclinical models and in human, surpassing the effects of RT alone, while maintaining a favorable safety profile. Preclinical studies have revealed that the benefits of NBTXR3 extend beyond mere radioenhancement and improved cancer cell destruction. Specifically, NBTXR3 has been reported to possess immunomodulatory properties through 1) improved induction of DNA damage, leading to better activation of the cGAS-STING pathway, 2) promotion of immunogenic cell death, 3) enhancement of immunopeptidome presentation, 4) generation of an antitumor immune response leading to the production of an abscopal effect mediated by CD8+ cytotoxic lymphocytes. Notably, a series of recent studies using a two-tumor mouse model of anti-PD1-resistant lung cancer that the addition of NBTXR3 significantly improved the efficacy of various treatment regimens (RT+anti-PD1 and combinations with other check-point inhibitors) in terms of tumor growth, abscopal effect, and survival. It has been demonstrated that same benefits can be achieved when NBTXR3 was combined with proton therapy. Moreover, all these studies (X-ray and proton) reported a robust activation of the antitumor immune response, restoration of the effectiveness of anti-PD1 therapy, and the induction of memory response in cured mice. However, our understanding of the biological events leading to these effects remains limited. To address this question, we conducted a series of in vitro studies that employed cytometry, microscopy, and RNA sequencing on various cancer models, both human and murine. We reported that NBTXR3 nanoparticles primarily accumulate within lysosomes following their uptake by tumor cells, leading to the activation of genes associated with the biogenesis, structure, and contents of these organelles. Upon activation by RT, NBTXR3 within lysosomes induces lysosomal membrane permeabilization (LMP), resulting in an increase in lipid peroxidation, inducing regulation of fatty acid oxidation genes, and impacting mitochondrial genes expression, such as respirasome. These findings provide a deeper insight into the early biological effects of NBTXR3+RT in comparison to RT alone.
Citation Format: Jordan Da Silva, Celia Bienassis, Sebastien Paris. Analysis of cancer cells response to radiotherapy activated NBTXR3 nanoparticles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2870.