In Vivo Cancer Gene Therapy by Adenovirus-mediated Transfer of a Bifunctional Yeast Cytosine Deaminase/Uracil Phosphoribosyltransferase Fusion Gene
2000
Direct transfer of prodrug activation systems into tumors was
demonstrated to be an attractive method for the selective in
vivo elimination of tumor cells. However, most current suicide
gene therapy strategies are still handicapped by a poor efficiency of
in vivo gene transfer and a limited bystander cell
killing effect. In this study, we describe a novel and highly potent
suicide gene derived from the Saccharomyces cerevisiae
cytosine deaminase ( FCY1 ) and uracil
phosphoribosyltransferase genes ( FUR1 ). This suicide
gene, designated FCU1 , encodes a bifunctional chimeric
protein that combines the enzymatic activities of FCY1
and FUR1 and efficiently catalyzes the direct conversion
of 5-FC, a nontoxic antifungal agent, into the toxic metabolites
5-fluorouracil and 5-fluorouridine-5′-monophosphate, thus bypassing the
natural resistance of certain human tumor cells to 5-fluorouracil.
Unexpectedly, although the uracil phosphoribosyltransferase activity of
FCU1 was equivalent to that encoded by
FUR1 , its cytosine deaminase activity was 100-fold
higher than the one encoded by FCY1 . As a consequence,
tumor cells transduced with an adenovirus expressing
FCU1 (Ad-FCU1) were sensitive to concentrations of 5-FC
1000-fold lower than the ones used for cells transduced with a
vector expressing FCY1 (Ad-FCY1). Furthermore,
bystander cell killing was also more effective in cells transduced with
Ad-FCU1 than in cultures infected with Ad-FCY1 or Ad-FUR1, alone or in
combination. Finally, intratumoral injections of Ad-FCU1 into allo- or
xenogeneic tumors implanted s.c. into mice, with concomitant systemic
administration of 5-FC, led to substantial delays in tumor growth.
These unique properties make of the FCU1 /5-FC prodrug
activation system a novel and powerful candidate for cancer gene
therapy strategies.
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