Dual-tracer autoradiographic analysis of glucose metabolism and hypoxia in orthotopic and PDX tumor models.

Background and purpose: Quantification/mapping of tumor hypoxia may guide pretreatment decision-making in radiation oncology. Hypoxia-selective positron emission tomography (PET) tracers, like 18F-fluoroazomycin arabinoside (FAZA), allow assessment of hypoxia, but since hypoxia stimulates glycolysis, fluorodeoxyglucose (FDG) and hypoxia-PET may provide overlapping/similar information. Clinical dual-tracer PET studies are highly complex and remain inconclusive. Accordingly, we developed dual-tracer autoradiography techniques to allow high-resolution assessment of the spatial coupling of FAZA and 14C-2DG (FDG-analogue), without the time-separation and co-registration-related inaccuracies intrinsic to PET. Patient/material and methods: Orthotopic lung adenocarcinomas were induced in CRISPR/Cas9 knock-in mice. Mammary adenocarcinomas developed spontaneously in transgenic mice overexpressing ErbB2 (Her2). Patient-derived-xenografts (PDX) were established in immunocompromised mice using biopsies from oropharyngeal cancer patients. Tumor growth was followed by MRI/Caliper measurements. Mice were administered with FAZA (~40 MBq)/14C-2DG (37 kBq)/pimonidazole and sacrificed. Tumor cryosections were analyzed for FAZA/14C-2DG using dual-tracer autoradiography followed by histological stainings. Complementary autoradiograms were co-registered and covered by a square-grid (0.5 × 0.5 mm), and Pearson correlation coefficients (R) were calculated.

Results/interpretation: Hypoxic sub-volumes (FAZA/pimonidazole) were commonly present. A reasonable spatial overlap between FAZA and 14C-2DG was observed in most lung and oropharyngeal tumors with R typically exceeding 0.55. In the breast tumor model, the extent of overlap between FAZA and 14C-2DG varied widely with R ranging from 0.03 to 0.82, which may relate to intertumor mutational differences in this Her2+ oncogene-driven model. Our results suggest a putative role for FDG-PET to identify hypoxic foci and guide dose-escalation.