V. Pierrefite-carle et al., Cytosine deaminase/5-fluorocytosine-based vaccination against liver tumors: Evidence of distant bystander effect, J NAT CANC, 91(23), 1999, pp. 2014-2019
Background: The cytosine deaminase gene of Escherichia coli converts the no
ntoxic compound 5-fluorocytosine into 5-fluorouracil (5-FU), thereby acting
as a suicide gene when introduced into cancer cells, killing the cells whe
n they are exposed to 5-fluorocytosine. We analyzed the efficacy of using c
ytosine deaminase-bearing cancer cells as an autologous tumor vaccine in a
rat model that mimics liver metastasis from colon carcinoma.
Methods: We introduced a plasmid vector containing the E. coli cytosine dea
minase gene into a BDM rat colon carcinoma cell line. Intrahepatic injectio
n of the modified cells in syngeneic animals generates a single experimenta
l liver "suicide tumor," We then analyzed the effect of 5-fluorocytosine tr
eatment in terms of regression of cytosine deaminase-expressing cells in vi
vo as well as protection against mild-type cancer cells.
Results: Treatment with 5-fluorocytosine induced regression of cytosine dea
minase-expressing (CD+) tumors, with seven of II treated animals being tumo
r free at the end of 30 days and a statistically significant difference in
tumor volumes bet between treated and control animals (two-sided P < .0001)
, Intrahepatic injection of CD+ cells followed by 5-fluorocytosine treatmen
t rendered the treated animals resistant to challenge with wild-type tumor
cells, with no (zero of seven) treated animals developing wild-type tumors
in contrast to all (four of four) control animals. Moreover, in animals wit
h established wild-type liver tumors, injection of CD+ tumor cells followed
by 5-fluorocytosine treatment produced a statistically significant increas
e in survival time (two-sided P < .0001). In vivo immunodepletion and immun
ohistologic analysis of experimental tumors indicate that natural killer ce
lls are the major immune component involved in this antitumor effect.
Conclusions and Implications: Taken together, these results suggest the pot
ential use of suicide gene-modified tumor cells as therapeutic vaccines aga
inst liver metastasis from colon carcinoma.