Hypoxia imaging with 18F-FAZA PET/CT predicts radiotherapy response in esophageal adenocarcinoma xenografts

Abstract

Background: Esophageal cancer is an aggressive disease with poor survival rates. A more patient-tailored approach based on predictive biomarkers could improve outcome. We aimed to predict radiotherapy (RT) response by imaging tumor hypoxia with F-18-FAZA PET/CT in an esophageal adenocarcinoma (EAC) mouse model. Additionally, we investigated the radiosensitizing effect of the hypoxia modifier nimorazole in vitro and in vivo. Methods: In vitro MTS cell proliferation assays (OACM5 1.C SC1, human EAC cell line) were performed under normoxic and hypoxic (< 1%) conditions: control (100 mu L PBS), nimorazole, irradiation (5, 10 or 20 Gy) with or without nimorazole. In vivo, subcutaneous xenografts were induced in nude mice (OACM5 1.C SC1). Treatment was given daily for 5 consecutive days: (A) control (600 mu l NaCl 0.9% intraperitoneally (IP)) (N = 5, n = 7), (B) RT (5 Gy/d) (N = 11, n = 20), (C) combination (nimorazole (200 mg/kg/d IP) 30 min before RT) (N = 13, n = 21). N = number of mice, n = number of tumors. F-18-FAZA PET/CT was performed before treatment and tumor to background (T/B) ratios were calculated. Relative tumor growth was calculated and tumor sections were examined histologically (hypoxia, proliferation). Results: A T/B= 3.59 on pre-treatment F-18-FAZA PET/CT was predictive for worse RT response (sensitivity 92.3%, specificity 71.4%). Radiation was less effective in hypoxic tumors (T/B = 3.59) compared to normoxic tumors (T/B < 3.59) (P = 0.0025). In vitro, pre-treatment with nimorazole significantly decreased hypoxic radioresistance (P < 0.01) while in vivo, nimorazole enhanced the efficacy of RT to suppress cancer cell proliferation in hypoxic tumor areas (Ki67, P = 0.064), but did not affect macroscopic tumor growth. Conclusions: Tumor tissue hypoxia as measured with F-18-FAZA PET/CT is predictive for RT response in an EAC xenograft model. The radiosensitizing effect of nimorazole was questionable and requires further investigation