The gram-negative facultative anaerobic bacteria Salmonella enterica serovar Typhimurium (hereafter S. Typhimurium) has always been considered as one candidate of anti-
tumor agents or vectors for delivering
drug molecules. In this study, we compared several widely studied S. Typhimurium strains in their anti-
tumor properties aiming to screen out the best one for further optimization and use in
cancer therapy. In terms of the motility, virulence and anti-
tumor efficacy, the three strains 14028, SL1344, and
UK-1 were similar and obviously better than LT-2, and
UK-1 showed the best phenotypes among them. Therefore, the strain
UK-1 (D) was selected for the following studies. Its auxotrophic mutant strain (D1) harboring ∆aroA and ∆purM mutations was further optimized through the modification of
lipid A structure, generating a new strain named D2 with stronger immunostimulatory activity. Finally, the ∆asd derivative of D2 was utilized as one live vector to deliver anti-
tumor molecules including the
angiogenesis inhibitor endostatin and apoptosis inducer TRAIL and the therapeutic and toxic-side effects were evaluated in mouse models of colon
carcinoma and
melanoma. After intraperitoneal
infection, engineered Salmonella bacteria equipped with
endostatin and/or TRAIL significantly suppressed the
tumor growth and prolonged survival of
tumor-bearing mice compared to PBS or bacteria carrying the empty plasmid. Consistently, immunohistochemical studies confirmed the colonization of Salmonella bacteria and the expression of anti-
tumor molecules inside
tumor tissue, which were accompanied by the increase of cell apoptosis and suppression of
tumor angiogenesis. These results demonstrated that the beneficial anti-
tumor efficacy of attenuated S. Typhimurium bacteria could be improved through delivery of
drug molecules with powerful anti-
tumor activities.