Virus-associated tumor imaging by induction of viral gene expression

Purpose: EBV and other herpesviruses are associated with a variety of malignancies. The EBV thymidine kinase (TK) is either not expressed or is expressed at very low levels in EBV-associated tumors. However, EBV-TK expression can be induced in vitro with several chemotherapeutic agents that promote viral lytic induction. The goal of this study is to image EBV-associated tumors by induction of viral TK expression with radiolabeled 2′-fluoro-2′-deoxy-β-D-5-iodouracil-arabinofuranoside (FIAU). Experimental Design: Immunoblot, luciferase reporter assay, and in vitro assay with [¹⁴C] FIAU were used to show the effects of bortezomib on the induction of lytic gene expression of EBV-associated tumor cells. In vivo imaging and ex vivo biodistribution studies with [¹²⁵I] FIAU on EBV-associated tumors were done to visualize and confirm, respectively, the EBV(+) tumor-specific effects of bortezomib. Results: In vitro assays with [¹⁴C] FIAU and ex vivo biodistribution studies with [¹²⁵I] FIAU showed that uptake and retention of radiolabeled FIAU was specific for cells that express EBV-TK. Planar gamma imaging of EBV(+) Burkitt's lymphoma xenografts in severe combined immunodeficient mice showed [¹²⁵I] FIAU localization within tumors following treatment with bortezomib. Conclusions: These results indicate the feasibility of imaging chemotherapy-mediated viral lytic induction by radiopharmaceutical-based techniques such as single photon emission computed tomography and positron emission tomography.