Synergistic antitumor efficacy of suicide/ePNP gene and 6-methylpurine 2′-deoxyriboside via Salmonella against murine tumors

Abstract

Some anaerobes and facultative anaerobes have been used in tumor-specific gene therapy by reason of their selective growth in tumors. In this work, we aimed to evaluate the anticancer efficacy of attenuated Salmonella typhimurium as a carrier to deliver the Escherichia coli purine nucleoside phosphorylase (ePNP) gene for GDEPT (gene-directed enzyme-prodrug therapy). A live attenuated purine-auxotrophic strain of S. typhimurium (SC36) was used to carry the pEGFP-C1-ePNP vector that contains a green fluorescent protein (GFP) and an ePNP gene under the control of the human cytomegalovirus (CMV) promoter. The function of the ePNP expression vector was confirmed in vitro using the enzymic conversion of 6-methylpurine 2 0 -deoxyriboside (MePdR) into 6-methylpurine. We also observed a high bystander effect induced by the ePNP/MePdR system with a very low proportion (1%) of ePNP-positive cells. The killing effect and increased apoptosis induced by SC/ePNP (SC36 carrying the ePNP expression vector) infection were detected by cytotoxicity assay and PI staining flow cytometry analysis, in combination with MePdR administration. Furthermore, SC/ePNP was administered orally into mice bearing melanomas or pulmonary tumors, and its anti-tumor effect was evaluated. When the tumor was huge (500 mm 3 ) at the beginning of MePdR administration, SC/ePNP plus MepdR significantly inhibited tumor growth by about 59-80% and prolonged survival of mice. Complete tumor regression and long-term cure were achieved by MePdR administration, even when the tumor was large (100 mm 3 ) at the beginning of MePdR treatment. Our data support a hopeful view that tumor-targeting SC36 could improve antitumor efficacy of the ePNP/MePdR system due to its preferential accumulation and anticancer activity in tumors.

Inhibitory Effects of the AttenuatedSalmonella typhimuriumContaining the IL-2 Gene on Hepatic Tumors in Mice

“…It demonstrated that the recombinant attenuated S. typhimurium containing a eukaryotic expression plasmid could transform the exogenous gene into the tissues of mice and be expressed in these tissues. Attenuated S. typhimurium is one of the prevalent bacterial vectors in gene therapy and oral DNA vaccines, which could transfer multiple exogenous gene into host cells effectively [20, 21]. In vivo, live attenuated S. typhimurium strains penetrate into the intestinal epithelial barrier via M cells and macrophages, and reach the Peyer's patches, gain access to the gut-associated lymphoid tissue, migrate to the mesenteric lymph nodes (MLNs) and disseminate to the liver and spleen [22].…”

Bacteria as vectors for gene therapy of cancer

“…In more recent years, tumor-specific replication following IV administration has been demonstrated for numerous bacterial species, including Bifidobacterium, Salmonella, Escherichia coli, Vibrio cholerae and Listeria monocytogenes. [21][22][23][24][25] This facet permits the use of even non-invasive strains expressing heterologous genes to achieve tumor localised expression and secretion of therapeutics ( Fig. 1).…”

“…21,[45][46][47] Salmonella is the most widely studied genus for bactofection with numerous studies demonstrating therapeutic expression and anti-tumor efficacy. 23,24,48,49 Preclinical trials utilizing various attenuated, replication incompetent strains of salmonellae delivered by direct intratumoral or systemic administration have achieved impressive anti-tumor responses using a range of therapeutic approaches. Vaccination strategies involving bactofection of antigen presenting cells (APC) using replication deficient mutants of S. typhimurium and other strains have also shown significant successes in the treatment of cancer and infectious diseases (see below).…”

Draft genome sequences of Salmonella Oslo isolated from seafood and its laboratory generated auxotrophic mutant

“…However, its therapeutic potential as an anti-cancer agent remain unexplored. Among more than 2500 NTS serovars, S. Typhimurium VNP20009 [2][3][4], an auxotrophic mutant strain of S. Typhimurium A1-R [5,6], has been successfully studied and was even tested in phase I clinical trial for the treatment of solid tumors [7]. Many features of Salmonella namely the ability to thrive in hypoxic environment of the tumor, to induce innate immune response against tumor or its bactofection, and ability to release anticancer genes within tumor were found to be favorable for tumor regression in animal models [8][9][10].…”