In vivo comparison of IVDU and IVFRU in HSV1-TK gene expressing tumor bearing rats

(E)-5-(2-Iodovinyl)-2′-deoxyuridine (IVDU) and (E)-5-(2-iodovinyl)-2′-fluoro-2′-deoxyuridine (IVFRU) are potential substrates of Herpes Simplex Virus type 1thymidine kinase (HSV-TK). In the present study, cellular uptake of radioiodinated substrates was found to be low in wild type MCA cells, but high in HSV-TK gene expressing cells. The carrier-free substrates, in particular, showed higher cellular uptake than carrier-added compounds. Biodistribution showed that the %ID/g of the MCA-TK/MCA tumor ratio of IVDU injected at 1, 4, and 24 h were 1.1, 0.9 and 1.3, and those of IVFRU were 1.7, 1.7 and 1.8 respectively. Therefore, both IVDU and IVFRU could possibly be used as radiopharmaceuticals to evaluate reporter gene expression. However, IVFRU was more specific and stable than IVDU for selective non-invasive imaging of HSV-TK expression.