The herpes simplex virus type 1 thymidine kinase (HSV1-tk) positron emission tomography (PET) reporter gene (PRG) or its mutant HSV1-sr39tk are used to investigate intracellular molecular events in cultured cells and to image intracellular molecular events and cell trafficking in living subjects. The expression of these PRGs can be imaged using 18F- or 124I-radiolabeled acycloguanosine or pyrimidine analog PET reporter probes (PRPs). This protocol describes the procedures for imaging HSV1-tk or HSV1-sr39tk PRG expression in living subjects with the acycloguanosine analog 9-4-[18F]fluoro-3-(hydroxymethyl)butyl]guanine ([18F]FHBG). [18F]FHBG is a high-affinity substrate for the HSV1-sr39TK enzyme with relatively low affinity for mammalian TK enzymes, resulting in improved detection sensitivity. Furthermore, [18F]FHBG is approved by the US Food and Drug Administration as an investigational new imaging agent and has been shown to detect HSV1-tk transgene expression in the liver tumors of patients. MicroPET imaging of each small animal can be completed in approximately 1.5 h, and each patient imaging session takes approximately 3 h.
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The authors acknowledge the following funding sources: NIH grants NCI ICMIC P50 CA114747, SAIRP R24 CA92865, P50 CA86306, R01 CA82214-01; DOE contract DE-FC03-87ER60615; RSNA Postdoctoral Fellowship in Basic Radiological Sciences.
The authors declare no competing financial interests.
Shown is a mouse microPET dynamic image set taken over the course of 60 min after injection of the tracer [18F]FHBG via tail-vein. The mouse was injected via tail-vein with 1 × 109 plaque forming units of a replication deficient adenovirus carrying the HSV1-sr39tk reporter gene 48 h prior to the small animal PET imaging study. The tracer quickly distributes out of the blood and clears via the renal system into the bladder. Tracer is a so slowly extracted from the blood and is trapped in hepatocytes that express the HSV1-sr39tk reporter gene. Some tracer also clear via the hepatobiliary system into the gastro-intestinal tract. (MPG 1098 kb)
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Yaghoubi, S., Gambhir, S. PET imaging of herpes simplex virus type 1 thymidine kinase (HSV1-tk) or mutant HSV1-sr39tk reporter gene expression in mice and humans using [18F]FHBG. Nat Protoc 1, 3069–3074 (2006). https://doi.org/10.1038/nprot.2006.459
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