Abstract
Evaluating a new probe for monitoring gene expression for the gene therapy efficacy was dealt with in the study. The radiolabeled nucleoside analogue, 5-123I-iodo-2’-hydroxy-2’- deoxy-1-β-D- arabinofuranosyl-uracil ([123I]IaraU), was proposed to be a substrate for imag-ing HSV1-tk expression. Methods: The rat prostate cancer cell line Tramp-C1 was trans-duced with HSV1-sr39tk and IL-3. The transduced Tramp referred as Tramp-C1/IL3-tk to-gether with the Tramp-C1 as a control was employed for the test of in vitro uptake of [123I]IaraU. Tramp-C1/IL3-tk cells as well as the Tramp-C1 cells were subcutaneously inocu-lated to produce the xenografts in C57BL/6J mice. Biodistribution study was carried out for the animals after being [123I]IaraU injected for 6h and 24h. The animals were microSpect/CT imaged after 1h postinjection. Results: The cytotoxicity of IaraU was surveyed on Tramp-C1/IL3-tk and Tramp-C1. There was no significant difference between the tk trans-duced and the wild-type cells. The CC50 of IaraU was 309.7μM for Tramp-IL3-tk and 363.9μM for Tramp-C1. The cell uptake for Tramp-C1/IL3-tk by [123I]IaraU was slightly greater than Tramp-C1 after incubation for 8 h. The cell internalization test showed that Tramp-C1/IL3-tk cells trapped [123I]IaraU in the cytoplasm. For in vivo trial, Tramp-C1/IL3-tk and Tramp-C1 were inoculated subcutaneously into the left and right flank of C57BL/6J mice separately. After the xenograft was generated, [123I]IaraU was injected via tail vein for biodistribution study and microSpect/CT imaging. The biodistribution results showed that GI tract retention at 6h, and metabolized from the body at 24h. The imaging showed early (1h) ambiguous localization of [123I]IaraU in Tramp-C1/IL3-tk xenograft, and no accumulation in the Tramp-C1 xenograft. Simultaneously, the image showed significant and apparent retention of [123I]IaraU in GI tract. Conclusion: [123I]IaraU has not sufficiently evidenced as an efficacious gene probe for monitoring the gene expression in the HSV1-sr39tk system from the study.