Hypoxia marker pimonidazole accumulation and glucose transporter-1 expression are strongly correlated in rodent breast cancers

Objectives Glucose transporter-1 (GLUT-1) is one of the hypoxic markers regulated, in part, by Hypoxia-inducible factor-1 (HIF-1). FDG uptake partially depends on the amount of GLUT-1 expression. We examined correlation between hypoxia as assessed by pimonidazole accumulation, GLUT-1 expression and FDG uptake.

Methods Rats bearing syngeneic mammary tumor (RMT) were prepared. A well-established hypoxia marker, pimonidazole (60mg/kg) was injected i.p. six hours before sacrifice. 14C-deoxy-d-glucose (10μCi) and a perfusion marker, Hoechst 33342 (10mg/kg) were injected i.v. two hours and one minute before sacrifice, respectively. We removed the tumors and made sections of three or four different parts of each tumor. Autoradiography for 14C and immunofluorescent staining using a confocal microscope were performed with the same frozen sections. The images of the distribution of the three tracers and GLUT1 staining were quantitatively assessed for density in the tumor sections using ImageJ. Correlation of the tracers was analyzed.

Results Pimonidazole and GLUT-1 showed a strong positive correlation (r=0.70, p<0.000001), and pimonidazole accumulation and Hoechst 33342 assessment of perfusion showed a weak negative correlation (r=-0.297, p<0.000001). GLUT-1 and 14C-deoxy-d-glucose uptake did not show a clear positive correlation (r=-0.02, p=0.489) but high 14C-deoxy-d-glucose uptake was associated with high GLUT-1 expression or high perfusion.

Conclusions Hypoxic areas as assessed by pimonidazole accumulation and high GLUT-1 expression were strongly correlated. On the other hand, GLUT-1 and FDG uptake did not show a clear correlation in our experimental system. Our result confirmed that GLUT-1 expression is an excellent hypoxic marker and also suggested that GLUT-1 expression and FDG accumulation may show a simple positive correlation only in limited conditions, possibly due to limitations of FDG delivery by blood flow in high GLUT1 expressing severely hypoxic areas of tumors