Positron-emission tomography reporter gene expression imaging in rat myocardium.
BACKGROUND
This study examines the quantitative accuracy, detection sensitivity, and time course of imaging the expression of a mutant herpes simplex type-1 virus thymidine kinase (HSV1-sr39tk) PET reporter gene in rat myocardium by using the PET reporter probe 9-(4-[18F]-Fluoro-3-Hydroxymethylbutyl)-Guanine ([18F]-FHBG) and a small-animal PET (microPET).


RESULTS
In 40 rats, adenovirus expressing HSV1-sr39tk driven by a cytomegalovirus promoter (Ad-CMV-HSV1-sr39tk, 1x10(6) to 1x10(9) pfu) was injected through a thoracotomy directly into the left ventricular myocardium. After 3 days, myocardial perfusion was imaged with [13N]-ammonia for delineating the left ventricular myocardium, followed by imaging the expression of the reporter gene with intravenous [18F]-FHBG. The total myocardial [18F]-FHBG accumulation was quantified in percent of injected dose (%ID). Immunohistochemistry and autoradiography demonstrated HSV1-sr39tk enzyme (HSV1-sr39TK) and accumulation of [18F]-FHBG in the inoculated myocardium in 3 rats each. In 24 rats with various viral titers, the %ID was correlated with ex vivo well counting (r2=0.981, P<0.0001) and myocardial HSV1-sr39TK activity by tissue enzyme activity assay (r2=0.790, P<0.0001). Myocardial [18F]-FHBG accumulation was identified at viral titers down to 1x10(7) pfu. In 6 rats serially imaged up to day 17, myocardial [18F]-FHBG accumulation on microPET peaked on days 3 to 5 and was no longer identified on days 10 to 17.


CONCLUSIONS
HSV1-sr39tk reporter gene expression can be monitored with [18F]-FHBG and microPET in rat myocardium quantitatively and serially with high detection sensitivity. Cardiac PET reporter gene imaging offers the potential of monitoring the expression of therapeutic genes in cardiac gene therapy.
Inubushi
Masayuki
M
Department of Molecular and Medical Pharmacology, The Crump Institute for Molecular Imaging, University of California, Los Angeles 90095-1735, USA.
Wu
Joseph C
JC
Gambhir
Sanjiv S
SS
Sundaresan
Gobalakrishnan
G
Satyamurthy
Nagichettiar
N
Namavari
Mohammad
M
Yee
Simon
S
Barrio
Jorge R
JR
Stout
David
D
Chatziioannou
Arion F
AF
Wu
Lily
L
Schelbert
Heinrich R
HR
D000256:Adenoviridae / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D000818:Animals; D001345:Autoradiography; D005462:Fluorine Radioisotopes; D015774:Ganciclovir / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D015870:Gene Expression; D017930:Genes, Reporter; D006321:Heart / Q000000981:diagnostic imaging* / Q000502:physiology / Q000821:virology; D018259:Herpesvirus 1, Human / Q000201:enzymology / Q000235:genetics; D007150:Immunohistochemistry; D008297:Male; D023421:Models, Animal; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism*; D014055:Tomography, Emission-Computed; D014162:Transfection
C104325:9-((3-fluoro-1-hydroxy-2-propoxy)methyl)guanine; D005462:Fluorine Radioisotopes; D013937:Thymidine Kinase; D015774:Ganciclovir