Evaluation of 131/123I-5-iodo-2′-deoxycytidine as a novel proliferation probe in a tumor mouse model

• N.c.a. [123I]ICdR and [123I]IUdR can be prepared from their organotin precursors.
• Both SPECT imaging and biodistribution show specific tumor uptake of [123I]ICdR.
• [123I]ICdR is a plausible SPECT probe for imaging tumor proliferation.
• Metabolic instability of [123I]IUdR in vivo limits its clinical application.

This study evaluated a radioiodinated deoxycytidine analog, 131I-5-iodo-2′-deoxycytidine ([131I]ICdR), as a novel proliferation probe and compared it with 131I-5-iodo-2′-deoxyuridine ([131I]IUdR) in a NG4TL4 sarcoma-bearing mouse model. As an imaging agent, the biological characteristics of [123I]IUdR is not satisfactory due to its metabolic instability and short biological half-life in vivo. With [123I]ICdR/SPECT it was possible to clearly delineate the tumor lesion at 1 h post-injection (tumor-to-muscle ratio 7.74) in tumor-bearing mice. The results of biodistribution were consistent with those observed in scintigraphic imaging. This study demonstrated that [131I]ICdR is a more promising SPECT probe than [131I]IUdR for imaging proliferation.