Engineering Salmonella for lung cancer therapy
Initial Award Abstract
Tumors contain hypoxic and acidic regions that hinder the delivery of therapeutics to cancer cells. These conditions reduce the effectiveness of radiation and chemotherapeutic agents and select for cancer cells that are more aggressive, metastatic (acquire the ability to migrate), and resistant to therapies. Ironically, this metabolically compromised microenvironment provides a place where Salmonella can grow anaerobically and where it accumulates 1000-fold compared to the rest of the body. This ability of Salmonella to accumulate in tumors may be due to the bacteria sensing the tumor environment and expressing genes that are not normally expressed in normal tissue.
We will use Salmonella-based therapy to treat lung tumors and metastasis. Salmonella mutant strains are already approved for use in humans to deliver protein vaccines. These strains are slowly and completely eliminated from the host normal tissue. As our first goal, we will improve upon these strains. We have a collection of mutants from almost all Salmonella genes. These mutants will be mixed and put into human lung tumors growing in mice. The Salmonella mutants that can survive in tumors but not in the rest of the mouse will be identified using a high-throughput strategy we have devised that can look at all mutants, simultaneously.
Bacteria can be engineered to carry genes that encode proteins useful in therapy, such as an enzyme that converts a non-toxic drug to cytotoxic drug, capable of killing the tumor. To limit the side-effect of the drug in normal tissue, we need a system that only turns on the enzyme when bacteria reach the tumor. A “promoter” is a DNA sequence that ensures that a gene is on in particular circumstances where they are needed by the organism. We will find promoters that are only on in tumors as our second goal: We will make a library of all the Salmonella genome so that it can turn on a green protein if that particular part of the genome carries a promoter. We will put a mixture of Salmonella, each carrying one of this library of all possible regions that could be promoters, into lung tumors in mice and also into normal tissue. We will look for bacteria that turn green in tumors and do not turn green in the rest of the body using a machine that can sort 1000 green Salmonella per second. The promoters identified among these green Salmonella will be used for future delivery of therapeutic proteins.
Finally, a Salmonella mutant with growth that is restricted to tumors (our first goal) and tumor-specific promoters controlling production of a therapeutic protein (our second goal) can be combined into the same Salmonella therapeutic strain: This is our third goal. Such a combination of the most selective growth in tumors, and expression of therapeutic genes only in tumors, will be a powerful tool to deliver and express therapeutic molecules in lung tumors and their metastases. Thus, we will use the power of genetics to engineer an improved Salmonella anti-cancer therapy.
This is the first time that high-throughput methods will be used to simultaneously observe the effect of thousands of mutations on Salmonella growth in tumor and tissues. This is also the first time that a screen of all Salmonella promoters will be performed to find those that are used more extensively in tumors than in normal tissues. |
|Salmonella promoters preferentially activated inside tumors
|Periodical: Cancer Research
|Authors: Arrach, N, Zhao, M., Porwollik, S., Hoffman, R., McCllelland, M.,