NIMG-45REAL-TIME PET IMAGING DEMONSTRATES TUMOR ACCUMULATION AND OXYGENATION BY OMX-4.80P, AN OXYGEN CARRIER ENGINEERED FOR THE TREATMENT OF GLIOBLASTOMA

BACKGROUND: Hypoxia is a hallmark of glioblastoma (GB) and is correlated with tumor progression and decreased overall survival. OMX-4.80P is a protein oxygen carrier engineered for the treatment of GB in combination with radiotherapy. Prior studies in rodent GB models demonstrated that OMX-4.80P accumulates within intracranial tumors and reduces tumor hypoxia—as assessed by immunohistochemical and ELISA methods—and enhances tumor killing by radiotherapy. To support clinical evaluation of OMX-4.80P in patients, this report describes non-invasive positron emission tomography (PET) imaging to assess both OMX-4.80P tumor accumulation and oxygen delivery. METHODS: To assess its biodistribution, OMX-4.80P was labelled with 89Zr using a desferrioxamine (DFO) chelator. Either 89Zr-DFO-OMX-4.80P or free 89Zr was administered intravenously to both nude mice bearing H460 subcutaneous xenografts, as well as to Fischer rats bearing intracranial F98 tumors. OMX-4.80P distribution was assessed by PET, and by measuring radioactivity in major organs using a gamma counter. To assess OMX-4.80P-mediated changes in tumor hypoxia in the same tumor models, tumor:brain signal ratio of the hypoxia marker fluoromisonidazole (18F-FMISO) was assessed before and after treatment with OMX-4.80P by performing scans on two consecutive days. RESULTS: While free 89Zr was present mainly in the bones, 89Zr-DFO-OMX-4.80P was not, suggesting that the label is stable in vivo. As expected, 89Zr-DFO-OMX-4.80P accumulated in both subcutaneous and intracranial tumors, and in the clearance organs (liver, kidneys, spleen). Furthermore, 18F-FMISO levels, as measured by tumor:brain ratios, were decreased by u003e2 fold after either intravenous or intratumoral injection of OMX-4.80P, in both subcutaneous and intracranial tumors demonstrating OMX-4.80P-mediated tumor oxygenation activity. CONCLUSIONS: PET-based approaches are a feasible method for assessing OMX-4.80P distribution and oxygenation. These methods will be developed as biomarkers of OMX-4.80P activity in a planned Phase 1 clinical trial in newly diagnosed GB patients.