Evaluation of 123I-ICdR as a novel SPECT proliferation probe in a sarcoma-bearing mouse model

Objectives This study evaluated a radioiodinated deoxycytidine analogue, 5-iodo-2'-deoxycytidine (123I-ICdR), as a novel proliferation probe and compared with that of 18F-FLT in a NG4TL4 sarcoma-bearing mouse model.

Methods Starting from 5-tributylstannyl-2'-deoxycytidine, 123I-ICdR was prepared with high radiochemical yield (≧85%, decay corrected) and radiochemical purity (≧95%). 18F-FLT was prepared according to the literature. Biological characterization studies including cellular uptake, biodistribution, and scintigraphic imaging were performed.

Results The uptake of 123I-ICdR and 18F-FLT in NG4TL4 cell culture kept increasing with time. The cell-to-medium ratio of 123I-ICdR was 75.37±3.23 at 8 h incubation and that of 18F-FLT was 78.67±7.82 at 2 h incubation. Biodistribution studies revealed significant tumor uptake after administration of both 131I-ICdR (3.46±0.07, 3.78±0.07, 4.85±0.17 and 2.32±0.27 %ID/g at 1, 2, 4 and 8 h p.i.) and 18F-FLT (7.68±0.98, 7.63±1.61, 6.61±1.02 and 6.48±1.25 %ID/g at 10, 30, 60 and 120 min p.i.) in NG4TL4 sarcoma-bearing mice. Increasing tumor-to-muscle ratio (T/M of 25.77 at 8 h p.i. for 131I-ICdR and 6.11 at 2 h p.i. for 18F-FLT) indicated specific retention in tumor and rapid clearance from normal organs. Scintigraphic imaging of sarcoma-bearing mice after 123I-ICdR and 18F-FLT injection also showed apparent radioactivity accumulation in tumor and the normal organs with fast proliferation (e.g. intestine).

Conclusions This study successfully prepared 123I-ICdR with high radiochemical yield and purity. The results of biological characterization demonstrated that 123I-ICdR is a promising tumor detection SPECT probe, at least as good as 18F-FLT for PET