Laser Surgery Opens Blood-Brain Barrier to Chemotherapy

A laser probe has been used to open the brain’s protective cover, enabling delivery of chemotherapy drugs to patients with glioblastoma — the most common and aggressive form of brain cancer.

In a pilot study conducted by the Washington University School of Medicine in St. Louis, Mo., 14 patients with glioblastoma underwent minimally invasive laser surgery to treat a recurrence of their tumors. Heat from the laser was already known to kill brain tumor cells but, unexpectedly, the researchers found that the technology penetrated the blood-brain barrier.

"The laser treatment kept the blood-brain barrier open for four to six weeks, providing us with a therapeutic window of opportunity to deliver chemotherapy drugs to the patients," said neurosurgery professor Eric Leuthardt, MD, who also treats patients at Barnes-Jewish Hospital. "This is crucial because most chemotherapy drugs can't get past the protective barrier, greatly limiting treatment options for patients with brain tumors.

Washington University neurosurgeon Dr. Eric C. Leuthardt and others have discovered another benefit of laser surgery for patients with glioblastomas, one of the most difficult cancers to treat. In addition to killing the tumors with heat, the technology bypasses the brain's protective cover to allow for up to six weeks of chemotherapy. Courtesy of Robert Boston.

The team is still closely following the patients, though early results indicate they are doing better on average, in terms of survival and clinical outcomes, than what the researchers would expect with other treatment methods.

Glioblastomas are one of the most difficult cancers to treat. Most patients diagnosed with this type of brain tumor survive just 15 months, according to the American Cancer Society.

The research is part of a larger phase II clinical trial that will involve 40 patients. Twenty patients were enrolled in the pilot study, 14 of whom were found to be suitable candidates for the minimally invasive laser surgery, a technology that Leuthardt helped pioneer.

The laser technology was approved by the FDA in 2009 as a surgical tool to treat brain tumors. The Washington team’s research marks the first time the laser has been shown to disrupt the blood-brain barrier, which shields the brain from harmful toxins but inadvertently blocks potentially helpful drugs, such as chemotherapy.

As part of the trial, doxorubicin, a widely used chemotherapy, was delivered intravenously to 13 patients in the weeks following the laser surgery. Preliminary data indicate that 12 patients showed no evidence of tumor progression during the short, 10-week time frame of the study. One patient experienced tumor growth before chemotherapy was delivered; the tumor in another patient progressed after chemotherapy was administered, the researcher reported.

The laser surgery was well-tolerated by the patients in the trial; most went home one to two days afterward, and none experienced severe complications. The surgery was performed while a patient lies in an MRI scanner, providing the neurosurgical team with a real-time look at the tumor. Using an incision of only 3 mm, a neurosurgeon robotically inserted the laser to heat up and kill brain tumor cells at a temperature of about 150 °F.

"The laser kills tumor cells, which we anticipated," said Leuthardt. "But, surprisingly, while reviewing MRI scans of our patients, we noticed changes near the former tumor site that looked consistent with the breakdown of the blood-brain barrier."

Leuthardt confirmed and further studied these imaging findings with study co-author Dr. Joshua Shimony, a professor of radiology at Washington University.

The researchers, including co-corresponding author Dr. David Tran, a neuro-oncologist now at the University of Florida, performed follow-up testing, which showed that the degree of permeability through the blood-brain barrier peaked one to two weeks after surgery but that the barrier remained open for up to six weeks.

Other successful attempts to breach the barrier have left it open for only a short time — about 24 hours — not long enough for chemotherapy to be consistently delivered, or have resulted in only modest benefits, the researchers said. The laser technology leaves the barrier open for weeks — long enough for patients to receive multiple treatments with chemotherapy. Further, the laser only opens the barrier near the tumor, leaving the protective cover in place in other areas of the brain. This has the potential to limit the harmful effects of chemotherapy drugs in other areas of the brain, the researchers said.

The findings also suggest that other approaches, such as cancer immunotherapy — which harnesses cells of the immune system to seek out and destroy cancer — could also be useful for patients with glioblastomas.

The researchers are planning another clinical trial that combines the laser technology with chemotherapy and immunotherapy, as well as trials to test targeted cancer drugs that normally can't breach the blood-brain barrier.

The research was published in Plos One (doi: 10.1371/journal.pone.0148613).