Abstract 6117: Dose, dose rate, and linear energy transfer influence tumor immunologic and DNA damage response following alpha- and beta-emitting radionuclides
Authors: Sheehan-Klenk Julia , Kerr Caroline P. , Nguyen Thanh P. , Grudzinski Joseph J. , Adam David , Powers Maria , Sriramaneni Raghava N. , Clark Paul A. , Hernandez Reinier , Bednarz Bryan , Weichert Jamey P. , Morris Zachary S. 
Published: June 2023

Abstract
Background: The low response rate to immunotherapies in poorly immunogenic cancers highlights the potential for combination therapies that propagate an anti-tumor response in metastatic settings. Targeted radionuclide therapy (TRT) can deliver radiation to metastatic tumor sites. In preclinical studies, combining low dose TRT with immune checkpoint blockade augments the anti-tumor immune response, promoting the immune susceptibility of metastatic disease sites. Radionuclides differ in their physical properties such as emission type, linear energy transfer (LET), half-life, and tissue range. In this study, clinically relevant α- and β-emitting radionuclides (225Ac, 90Y, 177Lu) were compared in vitro in MOC2 head and neck squamous cell carcinoma and B78 melanoma. We hypothesized that the unique physical properties of radionuclides would differentially impact the quantity and accumulation over time of double stranded DNA breaks, mirroring the timing of effects on tumor cell immune susceptibility markers.
Methods: MOC2 or B78 cells were grown in culture and treated with external beam radiation (EBRT), or culture media containing 90Y, 177Lu, or 225Ac delivering continuous radiation at activity levels using GEANT4 Monte Carlo to deliver 12 Gy (MOC2) and 4 Gy (B78) to the cell monolayer. Cells were harvested, and cDNA was isolated for RT-qPCR one, three, and seven days after the start of irradiation. Additional cells treated in this manner were fixed and stained with DAPI/γ-H2AX antibody for confocal microscopy at the same timepoints. γ-H2AX foci/cell were quantified manually using ImageJ.
Results: γ-H2AX foci counts/cell increased significantly and accumulated over time following treatment with 225Ac, but not with 90Y or 177Lu. EBRT, 90Y, and 225Ac, but not 177Lu, upregulated expression of immune response associated genes (Fas, Pdl1, Mhc1) compared to non-irradiated controls. In cells treated with EBRT every 24h at doses mimicking the interval dose delivered by continuous exponential decay of 90Y and 225Ac, but not 177Lu, the time course and magnitude of Fas and Pdl1 expression phenocopied that of these radionuclides.
Conclusions: DNA damage accumulation and the timing of immunomodulation are modified by the dose, dose-rate, and LET of radiation emitted from a given radionuclide. Understanding the effects of radionuclide therapies on cancer cell immunogenicity could enable rational design of clinical trials that investigate the integration of TRT and immunotherapies into the clinical care of patients with metastatic cancers.
Citation Format: Julia Sheehan-Klenk, Caroline P. Kerr, Thanh P. Nguyen, Joseph J. Grudzinski, David Adam, Maria Powers, Raghava N. Sriramaneni, Paul A. Clark, Reinier Hernandez, Bryan Bednarz, Jamey P. Weichert, Zachary S. Morris. Dose, dose rate, and linear energy transfer influence tumor immunologic and DNA damage response following alpha- and beta-emitting radionuclides [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 6117.