Experiments at the Pioneer Valley Life Sciences Institute (PVLSI) at Baystate Medical Center in Springfield, Mass., reported in a recent British Journal of Cancer, confirm that University of Massachusetts Amherst chemical engineer Neil Forbes' delivery and trigger system has for the first time successfully placed TRAIL, a cancer-fighting protein, directly into solid tumors and on cue, turned it on. The treatment improved the 30-day survival time of mice with mammary tumors from 0 to 100 percent.
"This is a first step, but it's the first time we've controlled delivery to the tumors and the first time we've been able to turn on production of a cytotoxic protein and kill tumors from within. With more work we should be able to fine-tune our methods," says Forbes. "As an engineer, what I've designed is transport and deployment, that is, a way to get the army in position plus a switch to signal those troops to arm themselves and attack."
It's been known for about 10 years that common bacteria such as Salmonella and Escherichia favor the microenvironment of solid tumors, says Forbes. When others engineered a non-pathogenic strain of Salmonella, Forbes saw an opportunity. He began to design a "troop transport" of sorts, which would be controllable in location and time, to attack tumor cells at the same time it is less harmful to patients.
Forbes designed experiments that were carried out by PVLSI surgical oncologist Sabha Ganai, who received her doctorate for the work. They report dramatic success in delivering millions of the bacterium, S. typhimurium, into mouse mammary tumors and triggering them to start producing tumor necrosis factor-related apoptosis-inducing ligand, or TRAIL, a peptide toxic to cancer cells. It selectively causes tumor cell death, or apoptosis, with minimal host toxicity, that is, without harming normal cells.
They began by engineering the salmonella to include the gene for TRAIL so that it gets expressed under control of the RecA promoter. Then Ganai injected 2 million S. typhimurium cells that carried the engineered RecA promoter and TRAIL gene into groups of genetically identical mice with mammary tumors, that is, breast cancer. The RecA promoter activates when cells experience DNA damage from any cause. In this case, Ganai and Forbes use a very low dose, 2 Grey, of gamma radiation to switch on RecA.