University, Company Test Gene Transfer Cancer Treatment

Toca 511 trial patient in surgery (UC San Diego School of Medicine)

University of California in San Diego and biopharmaceutical company Tocagen Inc., also in San Diego, are testing a new type of brain cancer treatment that injects a viral vector directly into a tumor. Viral vectors use viruses to deliver genetic material into cells, and in this case, the vectors intend to target the cancerous cells while leaving healthy cells intact.

The test is part of a phase 1 clinical trial of Tocagen’s retroviral replicating vector technology. The patients have glioblastoma, a type of brain cancer considered among the most fatal. The late Senator Ted Kennedy was a glioblastoma victim. The current standard of care includes surgically removing as much of the tumor as possible, followed by radiation therapy and chemotherapy, although the tumor usually recurs.

The alternative viral vector treatment developed by Tocagen, known as Toca 511, delivers a cytosine deaminase (CD) gene selectively to cancer cells, in combination with the anti-fungal drug flucytosine in tablet form. After Toca 511 spreads through the cancerous tumor, those cancer cells expressing the CD gene — and only those cells — convert flucytosine into the anti-cancer drug 5-fluorouracil that kills the cancer cells. Patients in this trial receive cycles of oral Toca FC each month for up to six months.

Clark Chen, director of stereotactic and radiosurgery at UCSD’s cancer center, administered Toca 511 into the first patients who have participated in this clinical trial in San Diego. “We fused the patient’s CT scan to their MRI and used neuro-navigation software to calculate exactly where in the tumor we needed to place the injection of Toca 511,” says Chen. “The patients were given the injection and discharged from the hospital the day after the procedure.”

The phase 1 trial’s objective is to test the treatments’ safety and tolerability, looking specifically for toxicity in the blood or elsewhere related to the Toca 511 or flucytosine after two months. The secondary outcome measure of the trial is the percentage of subjects who have not progressed or died after six months.

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