Antitumor Effect of VNP20009, an Attenuated Salmonella, in Murine Tumor Models

Abstract

VNP2000 9, a genetically modified strain of Salmonella typhii?Wrium with deletions in the msbB and purl loci, exhibited antitumor activities when given systemically to tumor-bearing mice. VNP2000 9 inhibited the growth of subcutaneously implanted B16F10 murine melanoma, and the human tumor xenografts Lox, DLD-1, A549, WiDr, HTB177, and MDA MB-231. A single intravenous injection of VNP20009 , at doses ranging from 1 x Hf to 3 x 106 cfulrnouse, produced tumor growth inhibitions of 57-95%. Tumor volume doubling time, another indicator for tumor growth inhibition, also significantly increased in mice treated with VNP2000 9. Using mice with immune system deficiencies, we also demon• strated that the antitumor effects of VNP20009 did not depend on the presence ofT and B cells. In addition, VNP20009 , given intravenously, inhibited the growth of lung metastases in mice. Only live bacteria showed the antitumor effect.

Pilot trial of genetically modified, attenuated Salmonella expressing the E. coli cytosine deaminase gene in refractory cancer patients

“…14,15 Despite its substantial attenuation, VNP20009 effectively colonized syngeneic, spontaneous, and human tumors in mice, formed high tumor-to-normal tissue ratios (range from 250 : 1 to 25,000 : 1 compared to liver), and inhibited tumor growth. 14,15,[19][20][21] Recently, a phase I clinical trial involving 25 patients, who received intravenous infusion of VNP20009, defined a maximum tolerated dose of 3 Â 10 8 CFU/m 2 . 22 Colonization of tumor was detected in three patients however, objective tumor regression was not observed.…”

Positron emission tomography (PET) imaging of tumor-localized Salmonella expressing HSV1-TK

“…24 VNP20009 is ''unarmed'', containing no additional anticancer genes, but is oncolytic and inhibits tumor growth in animal models. 16 Of note, very high levels of bacteria can be found in murine tumors with very low to nil numbers of bacteria are found in normal tissues. 16,17,25 This differential in the biodistribution of the bacteria offers the basis for therapy and imaging.…”

“…16 Of note, very high levels of bacteria can be found in murine tumors with very low to nil numbers of bacteria are found in normal tissues. 16,17,25 This differential in the biodistribution of the bacteria offers the basis for therapy and imaging. The mechanism of this preferential replication is unknown, but may involve decreases in immune functions within tumors as well as other factors such as increased availability of nutrients.…”

“…13 The localization in and around the necrotic areas probably reflects oncolysis and tumor necrosis formation mediated by the bacteria. 16 This phenomenon may be facilitated by a type III secretion mechanism, 19 a complex bacterial system for introduction of bacterial proteins directly into mammalian cells using needle-like projections from the bacterial surface, which can result in the induction of apoptosis. [20][21][22] The Salmonella vector, VNP20009, is modified by a partial deletion in the msbB gene that results in the loss of myristylate from the lipopolysaccharide in the cell wall.…”

“…1 Currently, Bifidobacterium, 2-4 Clostridium, [5][6][7][8][9][10][11][12] Salmonella [13][14][15][16][17] and Vibrio 18 are under investigation as tumor-selective bacterial vectors in preclinical models. In order to determine the efficiency of targeting in a human clinical trial, detection of the vectors is necessary.…”