Stem cells have been produced that can release chemicals that kill cancer cells, offering a path to fight particularly hard to access tumors.
Stem cells have become a focus of medical research for their capacity to turn into the cells that make up the body's organs. They also can be engineered to produce Pseudomonas exotoxin (PE), a chemical toxic to brain tumors cells.
PE can already be produced outside the body and administered as a way of fighting brain cancer, but this approach has been found to have limitations. Dr. Khalid Shah of Harvard Medical School said, “Cancer-killing toxins have been used with great success in a variety of blood cancers, but they don't work as well in solid tumors because the cancers aren't as accessible and the toxins have a short half-life."
To get round this problem, Shah wanted to find a way to keep on producing the anti-cancer agents, preferably while having reached into the tumors' core.
In Stem Cells, Shah has announced success, at least with mice.
“A few years ago we recognized that stem cells could be used to continuously deliver these therapeutic toxins to tumors in the brain, but first we needed to genetically engineer stem cells that could resist being killed themselves by the toxins,” Shah says. “Now, we have toxin-resistant stem cells that can make and release cancer-killing drugs.”
PE will kill any cell it can get inside, but other labs have succeeded in making it and other cytotoxins enter cancer cells but be resisted by normal cells.
Shah has gone a step further, preventing the PE from acting while it is inside the stem cell that produces it. “We tested these stem cells in a clinically relevant mouse model of brain cancer, where you resect the tumors and then implant the stem cells encapsulated in a gel into the resection cavity,” Shah says. “After doing all of the molecular analysis and imaging to track the inhibition of protein synthesis within brain tumors, we do see the toxins kill the cancer cells and eventually prolonging the survival in animal models of brain tumors.”
Before moving to trials in humans, Shah wants to develop therapies where the PE-producing stem cells operate in conjunction with other cancer-fighting stem cells his lab has produced.
Earlier this year Shah announced the use of stem cells carrying biological, rather than chemical weaponry. That project successfully used stem cells that transport the herpes virus to brain cancers in mice.