Imaging the expression of successful gene transduction has been demons
trated in vivo for the first time by using an appropriate combination
of ''marker gene'' and ''marker substrate'' in an experimental animal
model, The herpes simplex virus 1 thymidine kinase (ASV1-tk) gene was
selected as an example of a marker gene, and the recombinant STK retro
virus containing HSV1-tk was used to transduce RG2 glioma cells in vit
ro and in vivo, HG2TK(+) cell lines expressing the HSV1-tk gene and th
ree potential marker substrates for the HSV1-TK enzyme were evaluated.
Radiolabeled -2'-fluoro-2'deoxy-1-beta-D-arabinofuranosyluracil (FLAU
) was shown to be a substantially better marker substrate for the HSV1
-TK enzyme than 5-iodo-2'-deoxyuridine or ganciclovir, The magnitude o
f FIAU accumulation in different RG2TK(+) clones corresponded to their
sensitivity to ganciclovir and to the level of HSV1-tk mRNA expressio
n, Imaging the expression of HSV1-tk in transduced RG2 tumor cells was
demonstrated in animals using quantitative autoradiography; 2-[C-14]F
IAU accumulation was shown to be high in HG2TK(+) brain tumors growing
in one hemisphere and very low in nontransduced RG2 tumors in the con
tralateral hemisphere, Transduction of RG2 tumor cells with the HSV-tk
gene in vivo resulted in tumors which accumulated FIAU to high levels
and produced clearly defined images, Given the level of FIAU accumula
tion in the transduced tumors, it is likely that a clinically applicab
le method for imaging HSV1-tk gene expression can be implemented using
existing clinical imaging techniques.