Experimental therapy K-9 restores lost vision and mobility in MS mice

An experimental therapy called kamuvudine-9 (K-9) reversed established paralysis and vision loss in a mouse model of multiple sclerosis (MS), offering hope for treatments that can restore lost function rather than just prevent future damage.

“Most MS therapies are aimed at preventing the next attack. What’s remarkable is that K-9 not only prevented further neurological deterioration, but animals recovered function they had already lost,” Jayakrishna Ambati, MD, co-author of the study at the University of Virginia, said in a university news story.

The therapy was derived from a common class of antiviral medications known as nucleoside reverse transcriptase inhibitors (NRTIs). Beyond the animal findings, real-world insurance data showed that people taking these antivirals had lower rates of MS and fewer disease flare-ups.

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Experimental therapy shows dual protection

“These findings provide a rationale for further investigating K-9 for treating MS,” researchers wrote in the study “The nucleoside analog kamuvudine-9 shows protective and therapeutic efficacy in a mouse model of multiple sclerosis,” which was published in Science Translational Medicine. The work was funded by the National Institutes of Health (NIH).

“The remarkable reversal of some of MS’s most severe complications in animals, taken together with this drug’s promising safety profile, present a very compelling translational pathway,” Michael F. Chiang, MD, director of NIH’s National Eye Institute, said in a press release.

MS is an inflammatory disease that causes damage to the nervous system. A complex of inflammatory molecules known as the inflammasome has been implicated in the progression of MS. Normally, the inflammasome acts as a molecular alarm system, detecting infectious invaders and rallying the immune system to attack them. However, in MS, the inflammasome may become chronically activated, leading to prolonged inflammation that drives disease processes.

NRTIs are a class of antiviral medications used to treat HIV and hepatitis B. These medications block the replication of these viruses, but they have also been found to inhibit the inflammasome, and in a recent study, NRTIs preserved vision in a mouse model of eye damage. Because vision loss is also a common problem in MS and the inflammasome is implicated in the disease, researchers hypothesized that NRTI treatment may offer benefits in MS.

K-9 was derived from NRTIs by essentially removing the parts of the medication that have antiviral effects, while preserving the inflammasome-inhibiting components. The goal was to minimize neurological and muscular side effects that are associated with NRTIs, making the therapy safer.

The researchers tested K-9 in mice with experimental autoimmune encephalitis, a lab-induced immune disorder used to model MS. The treatment reversed paralysis and vision loss while preserving myelin, the fatty covering around nerves that is damaged in MS, as well as nerve fibers in the brain and spinal cord. K-9 also reduced levels of neurofilament light chain (NfL), a marker of nerve damage that indicates disease activity in MS.

Real-world data supports human trials

The researchers then analyzed MS rates in three groups of human patients taking NRTIs: those taking these medications to manage HIV or hepatitis B infection, or those taking NRTIs as preexposure prophylaxis to reduce the risk of contracting HIV. In all three groups, the use of NRTIs was associated with lower MS risk. In a cohort of MS patients, individuals taking NRTIs tended to have fewer disease flares.

“Though NRTIs are different molecules, they too block inflammasome activation and the signal we detected here is exactly what we would expect to see if K-9 does one day prove effective in humans,” Ambati said.

Collectively, these data support K-9 or other NRTI derivatives as potential MS treatments. The researchers called for further research examining this medication class in MS.

“When [the reversal of paralysis and vision loss in animal models] is considered together with the preservation of nerve tissue, the NfL response and the human epidemiologic findings, we believe there is a compelling rationale to test this approach in patients,” Ambati said.