Imaging adenoviral-mediated herpes virus thymidine kinase gene transfer and expression in vivo

The feasibility of noninvasive imaging of adenoviral-mediated herpes virus type one thymidine kinase (HSV1-tk) gene transfer and expression was assess ed in a well-studied, animal model of metastatic colon carcinoma of the liv er. Tumors were produced. in syngeneic BALB/c mice by intrahepatic injectio n of colon carcinoma cells (MCA-26). Seven days later, three different dose s (3 x 10(8), 1 x 10(8), and 3 x 10(7) plaque-forming units (pfu) of the re combinant adenoviral vector ADV, Rous sarcoma virus (RSV)-tk bearing the HS V1-tk gene were administered by intratumoral injection in separate groups o f mice. Two control groups of tumor-bearing mice received intratumoral inje ctions of the control adenoviral vector (MR) images of mice were obtained b efore administering the virus and provided an anatomical reference of hepat ic tumor localization Eighteen h after the virus injection, one group of an imals was given i.v. injections of 300 mu Ci of no-carrier-added 5-[I-131]- 2'-fluoro-1-beta-D-arabinofuranosyl uracil (FIAU) and imaged 24 h later wit h a gamma camera, In some animals, the tumors were sampled and processed fo r histology and quantitative autoradiography (QAR), The gamma camera images demonstrated highly specific localization of [I-131]FIAU-derived radioacti vity to the area of ADV.RSV-Lk-injected tumors in the liver, which was conf irmed by coregistering the gamma camera and T2-weighted MR images. There wa s no accumulation of [I-131]FIAU-derived radioactivity in tumors that were injected with the control vector or injection solution alone, A more precis e distribution of radioactivity in the area of transfected tumor was obtain ed by histological and QAR comparisons, A heterogeneous pattern of radioact ivity distribution in transfected tumors was observed. A punctate pattern o f radioactivity distribution was observed in peritumoral liver tissue in an imals given injections of 3 x 10(8) and 1 x 10(8) pfu of ADV.RSV-tk but not in animals given injections of 3 x 10(7) pfu nor in control animals, A QAR -microscopic comparison showed that the punctate areas of radioactivity col ocalized with cholangial ducts, The level of [I-131]FIAU-derived radioactiv ity accumulation (HSV1-tk expression) in the transfected tumors was viral d ose-dependent, The viral dose-dependency of radioactivity accumulation mas more pronounced in peritumoral liver, which was confirmed by reverse transc ription-PCR analysis. h separate group of tumor-bearing animals received di fferent doses of ADV,RSV-tk vector followed by treatment with ganciclovir ( GCV), 10 mg/kg i.p. b.i.d. for 6 days. The ADV,RSV-tk transfected tumors si gnificantly regressed with GCV treatment; the control tumors continued to g row. During the GCV treatment, the levels of liver transaminases (ALT and A ST) were significantly increased in animals that received injections of 3 x 10(8) and 1 x 10(8) pfu of ADV.RSV-tk but not in animals that received inj ections of 3 x 10(7) pfu and in control animals, The observed liver toxicit y confirms the results of gamma camera and QAR imaging, which demonstrated an unwanted spread of ADV.RSV-tk vector and HSV1-tk expression in peritumor al and remote liver tissue at higher doses. These and our previous results indicate that noninvasive imaging of adenoviral-mediated HSV1-tk gene expre ssion is feasible for monitoring cancer gene therapy in patients.