Human pharmacokinetic and dosimetry studies of [(18)F]FHBG: a reporter probe for imaging herpes simplex virus type-1 thymidine kinase reporter gene expression

J Nucl Med. 2001 Aug;42(8):1225-34.


9-[4-[(18)F]fluoro-3-(hydroxymethyl)butyl]guanine ([(18)F]FHBG) has been used as a reporter probe to image expression of herpes simplex virus type-1 thymidine kinase (HSV1-tk) reporter gene in living animals. Our aim was to study the kinetics, biodistribution, stability, dosimetry, and safety of [(18)F]FHBG in healthy human volunteers, preparatory to imaging patients undergoing HSV1-tk gene therapy.

Methods: [(18)F]FHBG was synthesized with a specific activity of 37,000--444,000 GBq/mmol and a radiochemical purity > 99%. Ten healthy volunteers consented to participate in the study. A transmission scan was obtained before bolus injection of 70.3--229.4 MBq [(18)F]FHBG into a hand vein, followed by dynamic PET imaging with 4 consecutive emission scans. Warmed hand-vein blood was withdrawn at various times after injection for blood time--activity measurements. Electrocardiography, blood pressure, and blood and urine pharmacologic parameters were measured before and after injection of the [(18)F]FHBG tracer (n = 5). The stability of [(18)F]FHBG in the urine was analyzed. Attenuation-corrected images were reconstructed using the ordered-subsets expectation maximization algorithm. Image region-of-interest time-activity data were used with the MIRD program to estimate absorbed radiation dosages.

Results: [(18)F]FHBG had rapid blood clearance; only 8.42% +/- 4.76% (mean +/- SD) of the peak blood activity remained at approximately 30 min. The average ratio of plasma activity to whole-blood activity during the study was 0.91 +/- 0.04. Penetration of [(18)F]FHBG across the blood-brain barrier was not observed. The primary routes of clearance were renal and hepatobiliary. High activities were observed in the bladder, gut, liver, and kidneys, but <0.0002% of the injected dose per gram was observed in other tissues. In the urine, 83% of activity 180 min after injection was stable [(18)F]FHBG. Blood and urine pharmacologic parameters did not change significantly after injection of the [(18)F]FHBG tracer. The bladder absorbed the highest radiation dose.

Conclusion: [(18)F]FHBG has the desirable in vivo characteristics of stability, rapid blood clearance, low background signal, biosafety, and acceptable radiation dosimetry in humans. This study forms the foundation for using [(18)F]FHBG in applications to monitor HSV1-tk reporter gene expression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Calibration
  • Female
  • Gene Expression Regulation, Enzymologic / genetics*
  • Genes, Reporter*
  • Guanine* / adverse effects
  • Guanine* / analogs & derivatives
  • Guanine* / pharmacokinetics
  • Herpesvirus 1, Human / enzymology*
  • Humans
  • Image Processing, Computer-Assisted
  • Male
  • Radiometry
  • Radiopharmaceuticals* / adverse effects
  • Radiopharmaceuticals* / pharmacokinetics
  • Thymidine Kinase / biosynthesis
  • Thymidine Kinase / genetics*
  • Tissue Distribution
  • Tomography, Emission-Computed


  • 9-(4-fluoro-3-hydroxymethylbutyl)guanine
  • Radiopharmaceuticals
  • Guanine
  • Thymidine Kinase