Attenuated salmonella have been reported to be capable of both selectively growing in
tumors and expressing exogenous genes for
tumor-targeted
therapy. As
6-methoxypurine 2'-deoxyriboside (MoPdR) is similar to
6-methylpurine 2'-deoxyriboside in structure, we aimed to evaluate the antitumoral effect of the Escherichia coli
purine nucleoside phosphorylase (
ePNP) gene, using an attenuated salmonella-mediated delivery system, in combination with MoPdR. A novel mutant serovar Typhimurium (SC36) was used to carry the pEGFP-C1-ePNP vector that contains an
enhanced green fluorescent protein and an
ePNP gene under the control of the cytomegalovirus promoter. The function of the
ePNP expression vector was confirmed in vitro using the enzymic conversion of MoPdR into methoxypurine. We also observed a high bystander effect induced by the
ePNP/MoPdR system with a very low proportion (1%) of
ePNP-positive cells and 5 microg/mL MoPdR, although the growth of parental cells was affected appreciably by MoPdR. The killing effect and increased apoptosis induced by SC36 carrying the
ePNP expression vector (SC/
ePNP) were detected by cytotoxicity assay and
propidium iodide staining flow cytometry analysis, in combination with MoPdR. SC/
ePNP was given orally to mice bearing mammary
carcinomas, and its antitumor effect was evaluated. SC/
ePNP plus MoPdR significantly inhibited
tumor growth by approximately 86.6-88.7% and prolonged the survival of
tumor-hosting mice. Our data support the view that MoPdR combined with the
ePNP gene could be used in gene-directed
enzyme prodrug therapy. Attenuated salmonella could be a promising strategy to improve
ePNP/MoPdR bystander killing due to its preferential accumulation and anticancer activity in
tumors.