Targeting Invasive Glioma Cells
Name of the Trial
Phase I Trial of AZD7451, a Tropomyosin-Receptor Kinase (TRK) Inhibitor, for Adults with Recurrent Gliomas (NCI-12-C-0005). See the protocol summary.
Dr. Katharine McNeill, NCI Center for Cancer Research, and Dr. Howard Fine, New York University Cancer Institute
Why This Trial Is Important
Glioblastoma is the most common malignant brain tumor in adults, with about 12,000 new cases diagnosed each year in the United States. It is also one of the deadliest, with a median survival following diagnosis of about 14 months.
Surgery to remove as much of the tumor as possible is the standard primary treatment for glioblastoma. After surgery, doctors use radiation therapy and treatment with the chemotherapy drug temozolomide to try to delay the growth of the remaining cancer. Although these measures may delay disease progression for a while, they cannot prevent it, and death usually occurs within a few months. Currently, the only therapy that has proven effective in delaying death in patients with progressive glioblastoma is bevacizumab, which helps block the tumor's ability to induce the formation of new blood vessels.
Glioblastoma is particularly difficult to treat because of its highly invasive nature. Although the bulk of the tumor may be well defined, malignant cells have usually migrated away from the tumor by the time it is discovered. Some of these cells inevitably remain behind after surgery and, if left unchecked, will eventually kill the patient.
Progress in the treatment of glioblastoma has been hampered by the absence of preclinical tumor models that mimic the invasiveness of the cancer. However, NCI researchers recently developed new cell lines from a subset of glioblastoma tumor-initiating cells that more accurately replicate the invasiveness of human glioblastoma in animal models. Using the new models, they were able to determine that cells near the edge of glioblastoma tumors express a set of proteins that help make them highly invasive. Subsequently, they identified a compound that may be effective in blocking the function of one of these key proteins.
A protein called tropomyosin-receptor kinase, or Trk, is commonly found on brain cells and helps regulate the development, function, and survival of nerve cells. In glioblastoma, Trk is highly expressed on the cells around the edges of the tumor and on the infiltrative cells that have migrated away from the tumor mass, whereas those cells in the bulk of the tumor show lower levels of Trk expression. Doctors want to see if inhibiting the function of Trk will help block the invasiveness of glioblastoma cells and reduce the likelihood that the tumor will progress.
In this first-in-class phase I trial, patients with glioblastoma that has not responded to standard postoperative therapy or that has progressed will be treated with varying amounts of a Trk inhibitor called AZD7451 to determine the maximum tolerated dose and the side effects of this drug. Doctors will also look for signs of clinical activity.
“Regardless of the extent of tumor resection, there are always residual tumor cells because these cells are highly invasive and infiltrate normal brain tissue,” said Dr. Fine, former chief of NCI’s Neuro-Oncology Branch. “So surgery is never curative in this disease; some type of postoperative therapy is always required to try to address these remaining infiltrative tumor cells.
“We became interested in trying to study this invasive process in the laboratory in hopes of identifying new molecular targets for therapy,” he continued. “We were able to find that this molecule called Trk was expressed specifically on glioblastoma cells that were invading and [that] Trk was signaling to these tumor cells in a way that was important for the cells to move within the brain. Further, by inhibiting Trk we were able to shut off the invasive process in these models.”
The trial is taking place at the NIH Clinical Center in Bethesda, MD, and at the New York University Cancer Institute in New York City.