Two drugs already on the market -- an antifungal and a steroid -- may potentially take on new roles as treatments for multiple sclerosis. According to a study published in Nature today, researchers discovered that these drugs may activate stem cells in the brain to stimulate myelin producing cells and repair white matter, which is damaged in multiple sclerosis. The study was partially funded by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health.
Specialized cells called oligodendrocytes lay down multiple layers of a fatty white substance known as myelin around axons, the long "wires" that connect brain cells. Myelin acts as an insulator and enables fast communication between brain cells. In multiple sclerosis there is breakdown of myelin and this deterioration leads to muscle weakness, numbness and problems with vision, coordination and balance.
"To replace damaged cells, the scientific field has focused on direct transplantation of stem cell-derived tissues for regenerative medicine, and that approach is likely to provide enormous benefit down the road. We asked if we could find a faster and less invasive approach by using drugs to activate native nervous system stem cells and direct them to form new myelin. Our ultimate goal was to enhance the body's ability to repair itself," said Paul J. Tesar, Ph.D., associate professor at Case Western Reserve School of Medicine in Cleveland, and senior author of the study.
It is unknown how myelin-producing cells are damaged, but research suggests they may be targeted by malfunctioning immune cells and that multiple sclerosis may start as an autoimmune disorder. Current therapies for multiple sclerosis include anti-inflammatory drugs, which help prevent the episodic relapses common in multiple sclerosis, but are less effective at preventing long-term disability. Scientists believe that therapies that promote myelin repair might improve neurologic disability in people with multiple sclerosis.
Adult brains contain oligodendrocyte progenitor cells (OPCs), which are stem cells that generate myelin-producing cells. OPCs are found to multiply in the brains of multiple sclerosis patients as if to respond to myelin damage, but for unknown reasons they are not effective in restoring white matter. In the current study, Dr. Tesar wanted to see if drugs already approved for other uses were able to stimulate OPCs to increase myelination.
OPCs have been difficult to isolate and study, but Dr. Tesar and his colleagues, in collaboration with Robert Miller, Ph.D., professor at George Washington University School of Medicine and Health Sciences in Washington, D.C., developed a novel method to investigate these cells in a petri dish. Using this technique, they were able to quickly test the effects of hundreds of drugs on the stem cells.
The compounds screened in this study were obtained from a drug library maintained by NIH's National Center for Advancing Translational Sciences (NCATS). All are approved for use in humans. NCATS and Dr. Tesar have an ongoing collaboration and plan to expand the library of drugs screened against OPCs in the near future to identify other promising compounds.
Dr. Tesar's team found that two compounds in particular, miconazole (an antifungal) and clobetasol (a steroid), stimulated mouse and human OPCs into generating myelin-producing cells.
Next, they examined whether the drugs, when injected into a mouse model of multiple sclerosis, could improve re-myelination. They found that both drugs were effective in activating OPCs to enhance myelination and reverse paralysis. As a result, almost all of the animals regained the use of their hind limbs. They also found that the drugs acted through two very different molecular mechanisms.
"The ability to activate white matter cells in the brain, as shown in this study, opens up an exciting new avenue of therapy development for myelin disorders such as multiple sclerosis," said Ursula Utz, Ph.D., program director at the NINDS.
Dr. Tesar and his colleagues caution that more research is needed before miconazole and clobetasol can be tested in multiple sclerosis clinical trials. They are currently approved for use as creams or powders on the surfaces of the body but their safety administered in other forms, such as injections, in humans is unknown.
"Off-label use of the current forms of these drugs is more likely to increase other health concerns than alleviate multiple sclerosis symptoms. We are working tirelessly to ready a safe and effective drug for clinical use," Dr. Tesar said.
NIH/National Institute of Neurological Disorders and Stroke