Tiny Factories Placed in Brain Make Tumor-Strangling Drug
Dec. 29, 2000 -- After removing brain tumors, surgeons soon may leave something in their place: miniature drug factories.
These factories -- now being tested in animals -- aren't built with bricks. They instead consist of living cells genetically engineered to manufacture one or more antitumor drugs. A shell of seaweed-based gel protects the cells against attack by the immune system. Meanwhile, tiny pores in the shell let in the nutrients needed to sustain the cells. They also allow the antitumor drugs to seep out and attack tumor cells left behind after surgery.
"This could be a new type of delivery system for the treatment of tumors -- it doesn't just have to be brain tumors," Harvard Medical School researcher Rona S. Carroll, PhD, tells WebMD. "It is a novel drug delivery system."
Carroll's team was one of two independent research groups to announce successful treatment of animal brain tumors using the tiny factories to produce a drug known as endostatin. Endostatin prevents tumors from growing the new blood vessels they need to survive. However, this tumor-strangling drug only lasts a very short time in the human body -- and the natural blood barrier that protects the brain blocks most of this drug from getting to where it is needed.
The two groups -- the Harvard team and a group led by Tracy-Ann Read, MSc, and Rolf Bjerkvig, PhD, from the University of Bergen, Norway -- each placed endostatin-making cells inside the tiny microcapsules. The Harvard team put the capsules near tumors previously implanted under the skin of mice that lacked working immune systems. The Norwegian team put the capsules into the brains of rats with intact immune systems and, at the same time, implanted human brain tumors.
Both teams found that the miniscule endostatin factories reduced tumor growth by more than two-thirds. The Harvard team saw existing tumors shrink to nearly a quarter of their original size after three weeks -- and the microcapsules are able to keep working for about six months.
The technique is not yet ready for human use, although similar microcapsules are being tested as small insulin factories in diabetic patients. However, Carroll can envision use of the endostatin-making cells during brain cancer surgery.
"From neurosurgeons' point of view, they want to remove as much of a tumor as they can," says Carroll, who teaches neurosurgery at Brigham and Women's Hospital in Boston. "They can get the tumor out, but there are cells [left behind] -- that's what kills the patient. What we hope is that, at the time of surgery, they would be able to put the capsules in the tumor bed, and the endostatin would stop the tumor from regrowing."