^99mTc-EC-guanine: Synthesis, biodistribution, and tumor imaging in animals

Purpose. DNA markers are useful in assessing cell proliferation. The purpose of this study was to synthesize ^99mTc-ethylenedicysteine- guanine (EC-Guan) for evaluation of cell proliferation. Methods. Tumor cells were incubated with ^99mTc-EC-Guan for cell cycle analysis. Prostate tumor cells that were overexpressing the HSV thymidine kinase gene, or various tumor cells were incubated with ^99mTc-EC-Guan at 0.5-2 h. Thymidine incorporation assays were performed in lung cancer cells incubated with EC-Guan at 0.1-1 mg/well. Tissue distribution, autoradiography, and planar scintigraphy of ^99mTc-EC-Guan and ^99mTc-EC (control) were determined in tumor-bearing rodents at 0.5-4 h. Results. Cell culture assays indicated that EC-Guan was incorporated in DNA, and there was no significant uptake difference between HSVTK overexpressed and normal groups. Biodistribution and scintigraphic imaging studies of ^99mTc-EC-Guan showed increased tumor/tissue count density ratios as a function of time. Conclusions. Our results indicate that ^99mTc-EC-Guan may be useful as a tumor proliferation imaging agent.