Gamma camera imaging of HSV-tk gene expression with [131I]-FIAU: Clinical applications in gene therapy

Develop a method to image gene expression that can be used to monitor successful gene transduction in patients. Currently there are no noninvasive ways to define the extent and spatial location of gene transduction or the level of gene expression in targeted organs or tumors. Wild-type RF2 s.c. tumors were produced by implantation of 10{sup 6} cells into both flanks of Sprague Dawley R-Nu rats. Following a 46 day growth period, the left and right flank tumors reached a 5x4x3 and 3x2x1 cm size. The left tumor was inoculated with 10{sup 6} gp-STK-A2 retroviral vector-producer cells (10{sup 6}-10{sup 7} cfu/ml) in 100 {mu}l of media to induce in vivo transduction with HSV-tk gene. No carrier added 2`-fluoro-1-{beta}-D-arabinofuranosyl-5-[131I]-iodo-uracil [131I]-FIAU was synthesized and 2.8 mCi was injected i.v. 14 days after gp-STK-A2 cell inoculation. Gamma camera imaging was performed in vivo at 4,24 and 36 hours post [131I]-FIAU injection with a dual-headed gamma camera. The 24 and 36 hour images showed specific localization of retained radioactivity only in the transduced tumors. These results were confirmed using quantitative autoradiography (QAR) of the same tumors. QAR also showed significantly higher levels of retained radioactivity (>1% dose/g) in the transduced tumor than in other nontransducedmore » areas (<0.03 %dose/g). The transduced tumor tissue had microscopic features typical of subcutaneously growing RG2 glioma and non vector-producer cells could be identified. Gene therapy trials in patients would benefit greatly from a noninvasive measure and image that could define the location, magnitude and persistence of gene expression overtime. HSV-tk and FIAU can be used as a {open_quotes}marker gene{close_quotes} - {open_quotes}marker substrate{close_quotes} combination for PET ([124-I]) or possibly SPECT ([123-I]) imaging.« less