Positron emission tomography (PET) imaging of tumor hypoxia provides valuable information for
cancer treatment planning. Two types of PET tracers,
nitroimidazole compounds and [62,64Cu]
copper-
diacetyl-bis[N(4)-methylthio-
semicarbazone] (
Cu-ATSM), have been used for imaging hypoxic
tumors. High accumulation of these tracers in
tumors was shown to predict poor prognosis. Both similar and different intratumoral distributions of these PET tracers have been reported with some studies questioning the dependence of the
Cu-ATSM accumulation on
hypoxia. In the present study, we compared the intratumoral distribution and cellular uptake of 1-(5-fluoro-5-deoxy-α-D-arabinofuranosyl)-2-nitroimidazole (FAZA) and
Cu-ATSM. Intratumoral distributions of FAZA and
Cu-ATSM compared by double tracer autoradiography in xenografts of 8 cancer cell lines and 3 cancer tissue originated spheroids (CTOSs) showed that only a limited overlap was observed between the regions with high levels of FAZA and
Cu-ATSM accumulation in all the xenografts. Immunohistochemistry in the regions enriched with FAZA and
Cu-ATSM in xenografts demonstrated that
pimonidazole adducts were in regions that accumulated high levels of FAZA, while HIF-1α was in areas enriched with either tracer. In addition, we examined the cellular uptake of FAZA and
Cu-ATSM at different levels of
oxygen concentration in 4 cell lines and revealed that cellular uptake of FAZA was increased with the decrease of
oxygen concentration from 20 to 2 and from 2 to 1%, while the
Cu-ATSM uptake increased with the decrease of
oxygen concentration from 20 to 2%, but did not increase with the decrease from 2 to 1%. Our findings indicate that intratumoral distributions of FAZA and
Cu-ATSM were essentially non-overlapping and although
hypoxia affects the buildup of both tracers, the accumulation of
Cu-ATSM occurred at milder
hypoxia compared to the conditions required for the accumulation of FAZA. Therefore, accumulation levels of FAZA and
Cu-ATSM may be considered as independent
biomarkers.