May 7, 2012
New clues to how brain cancer cells migrate and invade
Johns Hopkins findings hint at why certain brain cancers are so deadly
Johns Hopkins researchers have discovered that a protein that transports sodium, potassium and chloride may hold clues to how glioblastoma, the most common and deadliest type of brain cancer, moves and invades nearby healthy brain tissue.
The findings, reported in May in the journal PLoS Biology, also suggest that an inexpensive FDA-approved drug already on the market could slow movement of glioblastoma cells and contain their spread.
“The biggest challenge in brain cancer is the migration of cancer cells. We can’t control it,” said study leader Alfredo Quinones-Hinojosa, an associate professor of neurosurgery and oncology at the Johns Hopkins University School of Medicine. “If we could catch these cells before they take off into other parts of the brain, we could make malignant tumors more manageable, and improve life expectancy and quality of life. This discovery gives us hope and brings us closer to a cure.”
Glioblastoma, which is diagnosed in roughly 10,000 Americans each year, is so aggressive that the average life expectancy after diagnosis is just 15 months, Quinones-Hinojosa says. The cancer spreads to healthy brain tissue so quickly and completely that surgical cures are virtually impossible, and advances in radiation and chemotherapy have been slow in coming.
In a search for ways to prevent or limit the spread, and stop lethal recurrence, of the tumor, the Johns Hopkins researchers focused on a protein called NKCC1 in human tumor cells in the laboratory and in tumor cells injected into mice.
NKCC1 transports sodium, potassium and chloride ions and regulates cell volume.
Quinones-Hinojosa and his team found that cells with more NKCC1 appeared to move farther because the protein made it easier for tumor cells to grab onto other cells and tissues in the brain and propel themselves through tissue. The more of this protein in the tumor cell, they discovered, the faster the glioblastoma cells were able to travel. When NKCC1 was absent, they noted, the cells had larger focal adhesions, which allow for Velcro-like attachment to surrounding cells. Larger adhesions, they found, appear to keep the cells more anchored in place, while smaller ones make cells more mobile and allow for more migration.
In their experiments, the researchers blocked the protein and were able to slow the migration of the tumor cells. Less mobility, Quinones-Hinojosa says, means less invasion of surrounding tissue.
To block the channel, the team used the diuretic bumetanide, a simple water pill routinely used to reduce swelling and fluid retention caused by various medical problems. Added to tumor cells in the laboratory, or to human tumor cells in mice, the drug blocked the NKCC channel and slowed the pace of cell movement.
If the cells were made less invasive, Quinones-Hinojosa notes, tumors also would be easier to remove surgically.
The researchers were also able to correlate human tumor grade with levels of NKCC1. Less-aggressive tumors, they discovered, had smaller amounts of the protein, while more-aggressive tumors had more. This suggests that NKCC1 may not only contribute to the increased invasiveness of higher-grade tumors but also serve as a potential marker for diagnosis.
Other Johns Hopkins researchers involved in the study are Tomas Garzon-Muvdi, Paula Schiapperelli, Collette ap Rhys, Hugo Guerrero-Cazares, Christopher Smith, Deok-Ho Kim, Lyonel Kone, Harrison Farber, Daneille Y. Lee, Steven S. An and Andre Levchenko.