Tumor amplified protein expression therapy: Salmonella as a tumor-selective protein delivery vector

Attenuated strains of Salmonella typhimurium, VNP20009 and YS7212, when inj ected systemically to tumor-bearing mice, accumulated preferentially in tum ors at levels at least 200-fold and, more commonly, 1000-fold greater than in other normal tissues. This selectivity occurred in subcutaneously implan ted murine tumors, including B16F10 melanoma, M27 lung carcinoma, and colon 38 carcinoma. The preferential accumulation was also manifested in animals bearing human tumor xenografts, including Lex, C8186, DLD1, SW620, HCT116, HTB177, DU145, MDA-MB-231, and Caki. Four to five days after a single IV i njection of 1 x 10(6) colony-forming unit (cfu)/mouse, we routinely detecte d VNP20009 proliferation and accumulation at levels ranging from 1 x 10(8) to 2 x 10(9) cfu/g tumor. The amount of VNP20009 accumulated in the liver r anged from 3 x 10(4) to 2 x 10(6) cfu/g. The distribution of Salmonella in tumors was homogenous; YS7212 could be detected from the periphery to the i nterior portion of the tumors. Using mice with various immunodeficiencies, we also discovered the same preferential accumulation of Salmonella in tumo rs implanted in these mice. The use of Salmonella as a protein delivery vec tor was shown by IV administration of the bacteria expressing either green fluorescent protein (GFP) or cytosine deaminase (CD) into tumor-bearing mic e. GFP and CD were detected in tumors, but not in livers, taken from mice i noculated with Salmonella carrying these genes. Bacteria accumulation and C D expression persisted in the tumors for up to 14 days after a single bolus IV administration of bacteria to tumor-bearing mice.