Comparison of [14C]FMAU, [3H]FEAU, [14C]FIAU, and [3H]PCV for monitoring reporter gene expression of wild type,and mutant herpes simplex virus type 1 thymidine kinase in cell culture

Purpose: To assess the optimal reporter probe/reporter gene combination for monitoring herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene expression, we compared the cellular uptake of 1-(2'-fluoro-2'-deoxy-D-arabinofuranosyl)-5-methyluracil (FMAU), 2-fluoro-2-deoxyarabinofuranosyl-5-ethyluracil (FEAU), 2'-fluoro-2-deoxy-beta-D-arabinofuranosyl-5-iodouracil (FIAU) and penciclovir (PCV) in both HSV1-tk and HSV1-sr39tk expressing cells. Procedures: For stably transfected cell studies, C6 rat glioma cells, C6 HSV1-tk transfectant, C6 mutant HSV1-sr39tk transfectant, rat Morris hepatoma cells (MH3924A), and MH3924A HSV1-tk transfectant cells were used. For adenoviral infection studies, C6 rat glioma cells were exposed to serial titers of AdCMV-HSV1-tk AdCMV-HSV1-sr39tk or AdCMV-fluc for 24 hours. These cells were incubated with [C-14]FMAU, [H-3]FEAU, [C-14]FIAU, and [H-3]PCV, and cellular uptake of radioactivity was measured. Results: [3 H]FEAU exhibited the highest or second highest accumulation and the most selectivity regardless of the mode of gene transfer for both HSV1-tk and mutant HSV1-sr39tk reporter genes. Conclusion: This combination of high accumulation and high selectivity for both HSV1-tk and HSV1-sr39tk makes suitably radiolabeled FEAU a promising candidate as a radiotracer for imaging HSV1-tk/HSV1-sr39tk gene expression in living subjects.