Genetic Therapy Inc. announced Tuesday that it has begun thefirst human clinical trials of gene therapy to treat brain cancerat the National Institutes of Health (NIH), using GTI's vectorsystem.

GTI's vector systems are being used to transfer the gene for anenzyme called thymidine kinase into dividing tumor cells.

"What we're putting in are producer cells, the cells thatproduce the vectors," GTI spokesman Marc Schneebaum said.For surgically accessible tumors, the tumor is "debulked," or cutout, and producer cells are injected into the tumor bed. Forsurgically inaccessible tumors, a microscopic needle deliversthe producer cells through the skull and into the tumor bed.

Schneebaum said it's too early to know whether the debulkingof the tumor affects the success of the treatment.

When the cells express the enzyme thymidine kinase, theybecome susceptible to the anti-viral drug ganciclovir. Duringthe trial, ganciclovir is administered to destroy tumor cells thathave expressed the enzyme, as well as the cells used toproduce the original vector.

One of the major advantages of GTI's vector system in braincancer, said Schneebaum, is that only dividing tumor cells --not healthy brain cells -- will be transduced and take up thegene.

The trial is approved for 20 patients, but currently only one isunder treatment, Schneebaum told BioWorld. "The idea is totreat three patients, assess the therapy, and then proceed withthe remaining patients," he said, adding that the companyexpects the trials to be completed next year.

GTI's brain cancer trial is focusing on the most common form ofbrain tumor, primary glioma brain tumor, a fatal disease thatgenerally results in death nine months after diagnosis,according to the company, and for which other treatmentshaven't worked.

This is the Gaithersburg, Md., company's 12th gene therapytrial and the first trial that applies an in vivo gene therapyapproach for brain cancer in which the trial protocol does notrequire the removal of patient cells or subsequentreintroduction of those cells.

-- Michelle Slade Associate Editor

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