Stem cells are strongly attracted towards cancer cells, so it is hoped that as well as homing in on the main tumour, they will also be drawn to secondary growths, or metastases. This will enable higher doses of drug to be delivered to cancer cells while minimising the risk of side effects in the rest of the body.
A team led by Karen Aboody at the City of Hope Beckman Research Institute in Duarte, California, used neural stem cells originally derived from human fetuses which had been genetically engineered to produce cytosine deaminase. This is an enzyme that converts a drug called 5-fluorocytosine (5-FC) into an active chemotherapy drug, 5-fluorouracil (5-FU), but only in the immediate vicinity of the stem cell.
The team then injected the modified stem cells into the brains of mice with glioma, an aggressive form of brain cancer. The animals were subsequently given 5-FC. Treated mice saw a 70 per cent reduction in tumour mass compared with untreated animals. "In effect, we're allowing a much higher dose of chemo to be localised to the tumour site," says Aboody, who presented the results in May at an international brain tumour conference in Travemünde, Germany.
The US Food and Drug Administration has granted Aboody approval to carry out a safety trial of the therapy in up to 20 patients with recurrent glioma, for whom life expectancy is just three to six months. The stem cells will be injected into the tumour cavity following surgery to reduce its mass, and then given four days to home in on any remaining cancer cells. Patients will then be treated with daily 5-FC for one week.
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