A new pyrimidine-specific reporter gene: a mutated human deoxycytidine kinase suitable for PET during treatment with acycloguanosine-based cytotoxic drugs

In this article, we describe a series of new human-derived reporter genes based on human deoxycytidine kinase (dCK) suitable for clinical PET. Native dCK and its mutant reporter genes were tested in vitro and in vivo for their phosphorylation of pyrimidine- and acycloguanosine-based radiotracers including 2'-deoxy-2'-fluoroarabinofuranosylcytosine, 2'-fluoro-2'-deoxyarabinofuranosyl-5-ethyluracil (FEAU), penciclovir, and 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine (FHBG) and clinically applied antiviral and anticancer drugs. Cells transduced with dCK mutant reporter genes showed high in vitro and in vivo uptake of pyrimidine-based radiopharmaceuticals ((18)F-FEAU) comparable to that of herpes simplex virus type-1 thymidine kinase (HSV1-tk)-transduced cells. These mutants did not phosphorylate acycloguanosine-based radiotracers ((18)F-FHBG) or antiviral drugs (ganciclovir). Furthermore, the mutants displayed suicidal activation of clinically used pyrimidine-based prodrugs (cytarabine, gemcitabine). The mutants of human dCK can be used as pyrimidine-specific PET reporter genes for imaging with (18)F-FEAU during treatment with acycloguanosine-based antiviral drugs. Additionally, the prosuicidal activity of these reporters with pyrimidine-based analogs will allow for the safe elimination of transduced cells.