The goal of this application is to develop strains of the bacterium, Salmonella typhimurium (S. typhimurium), that can target and cure prostate cancer without affecting normal organs. The bacteria to be developed in this application are the first that can kill tumors by themselves. Previously, other strains of bacteria have been tested in preclinical mouse models and in cancer patients in a Phase I clinical trial. These other bacteria did not kill tumor cells.

The hypothesis of this application is that virulent strains of S. typhimurium, that are mutated to require specific amino acids, can target and kill primary and metastatic tumors. Our hypothesis is that the tumor can supply the bacteria the amino acids they require and the normal tissues cannot. The specific amino-acid requirements of the bacteria allow them to grow in and kill the tumor without toxicity to the host. We have previously demonstrated that an amino-acid-requiring virulent S. typhimurium variant A1 selectively kills a human prostate tumor growing in mice (Zhao et al. Proc. Natl. Acad. Sci. USA 102, 755-760, 2005). We will develop in the present application strains of S. typhimurium that will have the capability to broadly target primary and metastatic prostate cancer.

Strains of S. typhimurium are genetically tagged with the jellyfish protein, green fluorescent protein (GFP), which makes the bacteria fluorescent. The fluorescent bacteria are treated with a mutagen to generate amino-acid-requiring strains. The strains are then tested for their specific amino acid requirements. The selected bacterial strains are then tested for virulence in prostate tumor cells in vitro. Efficacy is determined by imaging the targeting of the amino-acid-requiring GFP-expressing S. typhimurium strains on red-fluorescent-protein (RFP)-expressing tumors in mice. Having the green fluorescent bacteria and red fluorescent tumors enables visualization of tumor-targeting by the bacteria in the living animal. Strains requiring different amino acids will be tested for efficacy against a series of human and mouse prostate cancer tumors in mouse models.

The bacterial strains to be developed in this application are the first that can target and kill tumors by themselves. This is due to the bacteria being engineered to require specific amino acids that tumors, as opposed to normal tissue, supply to the bacteria. The amino acid-requiring bacteria maintain their virulence and therefore can kill the targeted tumors and metastases but do not affect normal tissues since they cannot continuously grow in normal tissue. After the grant period, methodology will be developed to determine specific effective S. typhimurium auxotrophic strains for individual patients.

This application addresses a major need for prostate cancer, the effective treatment of metastatic cancer. The researchers will interact with various advocacy groups to disseminate information of the novel approach this application is taking to target and cure metastatic prostate cancer with specially engineered bacteria.