Biodistribution and Genetic Stability of the Novel Antitumor Agent VNP20009, a Genetically Modified Strain ofSalmonella typhimurium

Abstract

VNP20009 is a genetically modified strain of Salmonella typhimurium possessing an excellent safety profile, including genetically stable attenuated virulence (a deletion in the purI gene), reduction of septic shock potential (a deletion in the msbB gene), and antibiotic susceptibility. VNP20009 is genetically stable after multiple generations in vitro and in vivo. In mice, VNP20009 is rapidly cleared from the blood from a peak level of 1x104 cfu/mL to undetectable levels in 24 h. In tumor-bearing mice, VNP20009 accumulates preferentially in tumors over livers at a ratio of 1000&rcolon;1. In nonhuman primates, VNP20009 was also rapidly cleared from the blood, from a peak level of 1.0x106 cfu/mL to undetectable levels in 24 h. VNP20009 was detected in the liver, spleen, and bone marrow of monkeys; the amount decreased over time, and VNP20009 was cleared from all organs by day 41; no VNP20009 could be detected in the urine or feces of the monkeys. VNP20009 is genetically stable after many generations of growth (>140) both in vitro and in vivo.

Plasmid-based Survivin shRNA and GRIM-19 carried by attenuated Salmonella suppresses tumor cell growth

“…Thus, anti-tumor genes vectored by Salmonella can be functionally transferred to mammalian cells for anti-tumor therapy. 46 The resulting nutritional requirements of Salmonella were apparently met within the tumor environment where the bacteria replicated/concentrated to at least 1000-fold over their level in normal tissues. Preferential replication allows the bacteria to produce and deliver a variety of anticancer therapeutic agents at high concentrations directly within the tumor, while minimizing toxicity to normal tissues.…”

EGFR‐targeted Chimeras of Pseudomonas ToxA released into the extracellular milieu by attenuated Salmonella selectively kill tumor cells

“…Because Salmonella localize to tumors at substantially greater concentrations than other tissues, expression of a toxin is inherently tumor-specific by virtue of the tumor-localized replication of the bacteria (Pawelek et al, 1997). However, Salmonella can still be found in other tissues such as liver, spleen and bone marrow (Clairmont et al, 2000), and thus it is not yet apparent if toxicity to these tissues from a bacterial protein toxin would be significant. An example of an additional, independent tumor localization mechanism for expression by a tumor-targeted Salmonella is the use of a hypoxic promoter, which has bacterial targeting as a primary localization mechanism and the cooccurrence of hypoxia as a second targeting mechanism and was used for expression of the cytotoxic protein HlyE (ClyA) (Ryan et al, 2009).…”

Antitumor Effects in Mice of the Intravenous Injection of Attenuated Salmonella Typhimurium

“…In an attempt to increase the applicability of Salmonella organisms for cancer treatment, Salmonella typhimurium was genetically engineered to improve tumor targeting as well as to reduce toxicity (3)(4)(5)(6)(7). Chromosomal deletion of the purI gene creates a requirement for an external source of adenine, and deletion of the msbB gene prevents the addition of a terminal myristyl group to the lipid-A domain of lipopolysaccharide and thus, markedly diminishes its capacity to induce tumor necrosis factor-α production compared with the parental Salmonella.…”

“…Chromosomal deletion of the purI gene creates a requirement for an external source of adenine, and deletion of the msbB gene prevents the addition of a terminal myristyl group to the lipid-A domain of lipopolysaccharide and thus, markedly diminishes its capacity to induce tumor necrosis factor-α production compared with the parental Salmonella. These deletions were genetically stable and increased the LD 50 in mice by approximately 10,000 fold (5). These modified bacteria were reported to selectively grow in transplanted tumors in mice and result in reduced tumor growth (3).…”