Monitoring vascular normalization induced by antiangiogenic treatment with 18F‐fluoromisonidazole‐PET

BACKGROUND Rationalization of antiangiogenics requires biomarkers. Vascular re-normalization is one widely accepted mechanism of action for this drug class. The interstitium of tumors with abnormal vasculature is hypoxic. We sought to track vascular normalization with (18)F-misonidazole ([18F]-FMISO, a probe that detects hypoxia) PET, in response to window-of-opportunity (WoO) treatment with the antiangiogenic dovitinib. METHODS Two patient-derived pancreas xenografts (PDXs; Panc215 and Panc286) and the spontaneous breast cancer model MMTV-PyMT were used. Animals were treated during 1 week of WoO treatment with vehicle or dovitinib, preceded and followed by [18F]-FMISO-PET, [18F]-FDG-PET, and histologic assessment (dextran extravasation, hypoxia and microvessel staining, and necrosis, cleaved caspase-3 and Ki67 measurements). After WoO treatment, gemcitabine (pancreas)/adriamycin (breast) or vehicle was added and animals were treated until the humane endpoint. Tumor growth inhibition (TGI) and survival were the parameters studied. RESULTS [18F]-FMISO SUV did not change after dovitinib-WoO treatment compared to vehicle-WoO (0.54 vs. 0.6) treatment in Panc215, but it decreased significantly in Panc286 (0.58 vs. 1.18; P < 0.05). In parallel, 10-KDa perivascular dextran extravasation was not reduced with dovitinib or vehicle-WoO treatment in Panc215, but it was reduced in Panc286. Whereas the addition of dovitinib to gemcitabine was indifferent in Panc215, it increased TGI in Panc286 (TGI switched from -59% to +49%). [18F]-FMISO SUV changes were accompanied by an almost 100% increase in interstitial gemcitabine delivery (665-1260 ng/mL). The results were validated in the PyMT model. CONCLUSIONS [18F]-FMISO accurately monitored vascular re-normalization and improved interstitial chemotherapy delivery.