Detection of hypoxia in human squamous cell carcinoma by EF5 binding

Localization and quantitation of 2-nitroimidazole drug binding in low pO(2) tumors is a technique that can allow the assessment of hypoxia as a predic tive assay. EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3,-pentafluoroprop yl) acetamide] is such a drug, and it has been shown to be predictive of ra diation response in rodent tumors. Using fluorescence immunohistochemical t echniques, we provide data on the presence. distribution, and levels of EF5 binding as a surrogate fur hypoxia in human head and neck and uterine cerv ix squamous cell cancers (SCCs), Six patients with SCC were studied. Four p atients had head and neck tumors. and two had uterine cervix cancers. The i ncubation of fresh tissue cubes in EF3 under hypoxic conditions ("reference binding") demonstrated that all tumors were capable of binding drug, and t hat this binding varied by a factor of 2.9-fold (174.5-516.1) on an absolut e fluorescence scale. In the five patients treated at the lowest drug doses (9 mg/kg), in situ binding was quantitatable. For all six patients, the ma ximum rate of in situ binding varied by a factor of 6.7 between the Lowest and highest binding tumor (24.8-160.3) on an absolute fluorescence scale. I n tumors with high binding regions, intratumoral heterogeneity was large, e xtending from minimal fluorescence (<1%) up to 88.6% of reference binding. In tumors with minimal binding, there was little intratumoral heterogeneity . These studies demonstrate substantial heterogeneity of in situ binding be tween and within individual squamous cell tumors.