A Human-Derived Reporter Gene for Noninvasive Imaging in Humans: Mitochondrial Thymidine Kinase Type 2

Abstract

A human-derived intrinsically nonimmunogenic reporter gene was tested for PET imaging of different molecular–genetic processes for potential clinical use. Methods: The human mitochondrial thy-midine kinase type 2 (hTK2) reporter gene truncated at the N ter-minus (DhTK2), alone or fused with green fluorescent protein (GFP), was used for preclinical evaluation in a mouse model. The levelsof enzymatic activity ofDhTK2 andDhTK2 GFP proteins were assessed using radiotracer accumulation and prodrug acti-vation assays in vitro and in subcutaneous tumors grown from the corresponding cell lines in nude mice. Kinetic analyses of 124I-29-fluoro-29-deoxy-1-b-D-b-arabinofuranosyl-5-iodouracil (FIAU), 18F-29-fluoro-29-deoxy-1-b-D-b-arabinofuranosyl-5-ethyluracil (FEAU), or 18F-9-(4-18F-fluoro-3-hydroxymethylbutyl)guanine (FHBG) up-take in tumors and biodistribution studies were performed. Results: DhTK2 was successfully expressed in the cytoplasm of transduce