Zinc-65 imaging of rat brain tumors

The uptake of zinc, an essential nutrient, is critical for cell proliferation. On the basis of the idea that zinc uptake can be an index of viability in proliferating cells, tumor imaging with ⁶⁵Zn was performed using autoradiography. After s.c. implantation of ascites hepatoma (AH7974F) cells into the dorsum, 1 h after i.v. injection of ⁶⁵ZnCl₂,⁶⁵Zn uptake in the tumor was higher than in the brain tissue but lower than in the liver, which suggests that brain tumors can be positively imaged with ⁶⁵Zn. After implantation of AH7974F cells into the periaqueductal gray, 1 h after i.v. injection of ⁶⁵ZnCL₂, ⁶⁵Zn uptake in the tumor was ∼10 times higher than in other brain regions. After implantation of C6 glioma cells into the hippocampus, ⁶⁵Zn uptake in the tumor was also much higher than in other brain regions. The present findings demonstrate that brain tumors can be imaged with radioactive zinc. To compare brain tumor imaging with ⁶⁵Zn with that of [¹⁸F]fluorodeoxyglucose (FDG), which is widely used for the diagnosis of brain tumors, ¹⁴C-FDG imaging of the C6 glioma was performed in the same manner. ¹⁴C-FDG uptake in the tumor was ∼1.5 times higher than in the contralateral region in which ¹⁴C-FDG uptake was relatively high. It is likely that zinc uptake is more specific for brain tumors than is FDG uptake, which suggests that there is great potential for the use of ^69mZn, a short half-life γ emitter, in the diagnosis of brain tumors.