ESTRO 2022 - Abstract Book

S518

Abstract book

ESTRO 2022

1 Radboud University Medical Center, Radiation oncology, Nijmegen, The Netherlands; 2 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 3 Radboud University Medical Center, Medical Imaging, Nijmegen, The Netherlands Purpose or Objective Limited diffusion of oxygen into remote tumor areas and oxygen consumption through oxidative phosphorylation (OXPHOS) leads to hypoxia in most solid tumors. This scarcity of oxygen is known to induce radioresistance, but can also have a disrupting effect on the anti-tumor immune response. Therefore, we investigated the potential of OXPHOS inhibition to relieve tumor hypoxia by decreasing the oxygen consumption. Furthermore, we developed a radiolabeled antibody which recognizes murine CAIX ([ 111 In]In-DTPA-mCAIX), an enzyme upregulated by cancer cells under chronic hypoxic conditions, to monitor chronic hypoxia in syngeneic mouse models. Materials and Methods Several syngeneic murine cell lines and tumor models on a C57Bl/6 background were used (B16ova, MOC1, MC38 and GL261). In vitro oxygen consumption of these tumor cells was measured using the Agilent XF Seahorse Analyzer before and after treatment with the OXPHOS inhibitor IACS-010759. The in vivo tumor microenvironment of B16ova and MOC1 tumors, treated (10mg/kg IACS-010759) and vehicle-treated (0.5% methylcellulose), was characterized by immunohistochemistry. The biodistribution of [ 111 In]In-DTPA-mCAIX was measured by ex vivo radioactivity counting and in vivo SPECT imaging comparing different antibody doses and time points post injection. Intratumoral distribution of tracer uptake was visualized using autoradiography. Image analysis was performed by parametric mapping and zonal analysis in ImageJ. Results The data show that mitochondrial complex I inhibitor IACS-010759 inhibited oxygen consumption in a dose dependent manner in several tumor cell lines in vitro . Furthermore, diffusion limited hypoxia in vivo is reduced up to 200µm from perfused blood vessels by IACS-01079 treatment (10mg/kg) in MOC1 and B16ova tumors (fig 1). This can be visualized by staining pimonidazole as well as CAIX. In vitro, [In 111 ]-DTPA-mCAIX showed specific binding to B16ova cells when cultured at 1% O 2 (9.3±1.2%), but not to cells cultured at 20% O 2 (0.8±0.04%). In vivo, CAIX expression could be visualized by SPECT using [In 111 ]-DTPA-mCAIX. Radiotracer uptake in the tumor was significantly higher compared with uptake of isotype control tracer [In 111 ]-DTPA-IgG1 (34.6±5.8 vs. 13.4±2.7 %ID/g) (fig 2F). Autoradiography and immunohistochemistry of tumor sections showed a strong spatial correlation of CAIX with [In 111 ]-DTPA-mCAIX (r=0.72±0.11) and not with [In 111 ]-DTPA-IgG1 (-0.16±0.33)(fig 2A-E).