Accurate and Safe Tumor Targeting of Orally-administered Salmonella typhimurium A1-R Leads to Regression of an Aggressive Fibrosarcoma in Nude Mice.

Background/aim: Salmonella typhimurium A1-R has been shown to target and inhibit many types of cancers in mouse models without continuous infection of normal tissue. The objective of the present study was to determine the effective dose of orally-administered Salmonella typhimurium A1-R, expressing-green fluorescent protein (GFP), on an HT1080 human-fibrosarcoma nude-mouse model.

Materials and methods: The HT1080-human- fibrosarcoma nude-mouse models were randomized into the following three groups: G1: untreated control; G2: Oral Salmonella typhimurium A1-R (5×10⁷ colony forming units [CFU]/body, twice a week, 2 weeks); G3: Oral Salmonella typhimurium A1-R (3.3×10⁸ CFU/body, twice a week, 2 weeks). Each group comprised five mice. Body weight and tumor volume were measured twice a week. The number of colonies of Salmonella typhimurium A1-R-GFP in excised tumors and excised livers in groups G2 and G3 were determined on day 3, day 7 and 14 by growth on agar plates. Tukey-Kramer analysis was used to examine the relationships between variables. Statistically-significant results are defined as those with p≤0.05.

Results: Salmonella typhimurium A1-R was administered orally at a dose of 3.3×10⁸ CFU, which successfully regressed the HT1080 tumor in nude mice. However, this effect was not observed at a lower dose of 5×10⁷ CFU. After administering Salmonella typhimurium A1-R at 3.3×10⁸ CFU, tumors and liver tissues were harvested, homogenized, and cultured on days 3, 7 and 14. Resulting GFP-expressing Salmonella typhimurium A1-R colonies were then counted. The number of GFP-bacterial colonies derived from excised tumors at intervals of 3, 7, and 14 days increased over time post-administration of oral GFP-Salmonella typhimurium. Conversely, the number of GFP-Salmonella typhimurium A1-R colonies that could be grown from excised livers decreased over time, following oral administration of GFP-Salmonella typhimurium. Additionally, the GFP-bacterial colonies grown from the excised tumors were significantly larger than those grown from the excised livers.

Conclusion: The present study showed that an aggressive fibrosarcoma could be regressed by orally-administered Salmonella typhimurium A1-R which accurately targeted tumors without continuous growth in normal organs. The present results suggested the potential of orally-administered Salmonella typhimurium A1-R as a probiotic to treat aggressive soft-tissue sarcoma.