cis-1-[4-(Hydroxymethyl)-2-cyclopenten-1-yl]-5-iodovinyluracil as a new imaging agent for HSV-TK reporter gene

Objectives While IVDU is an effective substrate for HSV-TK, it is not suitable for in vivo study because of C-N glycocidic bond cleavage by thymidine phosphorylase. A carbocyclic IVDU analogue, ddIVDU, is synthesized and possesses greater metabolic stability due to replacement of the furanose oxygen with carbon.

Methods A carbocyclic iodonucleoside analogue, cis-1-[4-(hydroxymethyl)-2-cyclopenten-1-yl]-5-iodovinyluracil (ddIVDU) was synthesized from cyclopentadiene and glyoxylic acid as starting materials in 10 steps. The synthetic route for precursor employed cyclopentadiene as a starting material and proceed in good yield through 9 steps which contain hetero Diels-Alder reaction and Pd(0)-catalyzed coupling reaction as key reactions. For cytotoxicity analysis, MCA and MCA-TK (HSV-TK positive) cells were treated with various concentration of IVDU, ddIVDU, and GCV. Cytotoxicity was measured by the MTS methods. For in vitro uptake study, MCA and MCA-TK cells were incubated with 1uCi of [¹²⁵I]IVDU and [¹²⁵I]ddIVDU. The accumulation of each agent was measured after various incubation times.

Results IVDU and GCV were more toxic than ddIVDU in MCA-TK cells. But, in MCA cells, ddIVDU was more toxic than IVDU. Cell uptake of [¹²⁵I]IVDU was higher than [¹²⁵I]ddIVDU in MCA-TK cell. And also, higher accumulation of [¹²⁵I]ddIVDU was observed more in the acid-insoluble fraction than the acid-soluble fraction of MCA-TK cell lysates. By contrast with [¹²⁵I]ddIVDU, [¹²⁵I]IVDU showed high accumulation in the acid-soluble fraction.

Conclusions These results revealed that metabolic stability of ddIVDU was improved than IVDU.