Raltegravir is an antiretroviral medicine currently used to treat HIV, under the brand name Isentress. It was investigated for its potential in treating relapsing-remitting multiple sclerosis (RRMS) patients in a small clinical trial sponsored by Merck, but failed to show benefits.

This drug’s potential as a MS treatment now appears to be on hold.

How Raltegravir works

In MS, the immune system mistakenly attacks the myelin sheath (a protective layer that surrounds nerve fibers), causing damage and inflammation in the brain and spinal cord. The underlying trigger of these immune system attacks on the nervous system is not entirely known, although some evidence suggests that, in some cases, they can be due to the activation of human endogenous retroviruses (HERVs).

HERVs are a family of viruses present in the human genome. They are similar to retroviruses, such as HIV, but are generally inactive or present at levels too low to be considered a threat. Research has shown that HERVs that become active may be involved in MS pathology. For example, a subset called multiple sclerosis-associated retroviral element, or MSRV, has been found in high levels in MS lesions. Once active, MSRV produces a protein called MSRV-envelope protein (MSRV-Env) that can induce an inflammatory response and prevent the development of oligodendrocytes (cells that produce and repair myelin).

Other viruses, such as the Epstein-Barr virus (EBV), are also suggested to influence the heightened immune response seen in MS. 

Because of a possible viral link to the disease, Merck decided to investigate whether the HIV drug, Raltegravir, could treat MS. The drug inhibits a viral protein called integrase, which is essential to inserting a virus into the genome to promote its replication. 

Raltegravir in clinical trials

A Phase 2b proof-of-concept trial called INSPIRE (NCT01767701) aimed to determine whether Raltegravir might be effective in easing disease progression in RRMS patients. About 23 participants took Raltegravir for three months and underwent monthly MRI scans to assess changes in the number of MS lesions present in the brain. Results, however, found that Raltegravir failed to be of benefit; no changes were seen in the development of lesions and no improvements in the level of disability or quality of life were reported in treated patients.

Currently, there are no updates concerning Raltegravir’s future as an MS treatment and no further clinical tests are being planned.

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