Research in multiple sclerosis may find new pathways to interact with the disease, improve function, curtail attacks, or limit the progression of the underlying disease. Many treatments already in clinical trials involve drugs that are used in other diseases or medications that have not been designed specifically for multiple sclerosis. There are also trials involving the combination of drugs that are already in use for multiple sclerosis. Finally, there are also many basic investigations that try to understand the disease better and in the future may help to find new treatments.
Research directions on MS treatments include investigations of MS pathogenesis and heterogeneity; research of more effective, convenient, or tolerable new treatments for RRMS; creation of therapies for the progressive subtypes; neuroprotection strategies; and the search for effective symptomatic treatments.
Separated variants
Several previous MS variants have been recently separated from MS after the discovery of a specific auto-antibody, specially autoantibodies against AQP4, MOG and Neurofascin proteins.
Previously recognized variants of MS like Optic-Spinal MS is now classified as a phenotype of the anti-AQP4 spectrum, and some tumefactive cases of MS as anti-MOG associated encephalomyelitis. Some researchers think that there could exist also an overlapping between Anti-NMDA receptor encephalitis cases and neuromyelitis optica or acute disseminated encephalomyelitis.
The following previous MS variants are now considered apart from MS:
Optic-Spinal MS: Now it is considered inside the Anti-AQP4 diseases spectrum. Anti-MOG associated MS and some cases of tumefactive multiple sclerosis currently considered inside the anti-MOG spectrum. Anti-neurofascin associated MS and CIDP: Some Anti-neurofascin demyelinating diseases were previously considered a subtype of Multiple Sclerosis but now they are considered a separate entity, as it happened before to anti-MOG and anti-AQP4 cases. Around 10% of MS cases are now thought to be anti-Neurofascin disease in reality.Marcus Vinicius, Magno Goncalves, Yara Dadalti Fragoso, The involvement of anti-neurofascin 155 antibodies in central and peripheral demyelinating diseases, Neuroimmunol Neuroinflammation, 8 Apr 2019;6:6.10.20517/2347-8659.2019.08 Anti-neurofascin autoantibodies have been reported in atypical cases of MS and CIDP, and a whole spectrum of Anti-neurofascin demyelinating diseases has been proposed. Some cases of CIDP are reported to be produced by auto-antibodies against several neurofascin proteins. These proteins are present in the neurons and four of them have been reported to produce disease: NF186, NF180, NF166 and NF155. Antibodies against Neurofascins NF-155 can also appear in MS and NF-186 could be involved in subtypes of MS yielding an intersection between both conditions. Summarising, autoantibodies against several neurofascins can produce MS: neurofascin186 (NF186), neurofascin155 (NF155), contactin 1 (CNTN1), contactin associated protein 1 (CASPR1) and gliomedin. All of them nodal and paranodal proteins. Anti-TNF associated MS: Several anti-TNF drugs like adalimumab are commonly prescribed by a number of autoimmune conditions. Some of them have been reported to produce a CNS-demyelination compatible with, and by current knowledge indistinguishable from, standard MS. Several other monoclonal antibodies like pembrolizumab,Marzia Anita Lucia Romeo et al, Multiple sclerosis associated with pembrolizumab in a patient with non-small cell lung cancer, Journal of Neurology, pp 1–4, 04 October 2019 nivolumab and infliximab have been also reported to produce MS artificially. This has given birth to the Anti-TNF-α therapy-associated demyelinating disorders. The reactions have been diverse according to the source of the disease. Some of these cases can be classify as ADEM, using the confluent demyelination as barrier between both conditions. In most cases, the damage fulfills all pathological diagnostic criteria of MS and can therefore be classified as MS in its own right. The lesions were classified as pattern II in the Lassman/Lucchinetti system. Some lesions also showed Dawson fingers, which is supposed to be a MS-only feature. LHON-associated MS: Also a previous subtype of MS associated to LHON has been described (LHON-MS). It is a presentation of LHON with MS-like CNS damage. It used to satisfy McDonalds definition for MS, but after demonstration that LHON can produce this kind of lesions, the "no better explanation" requirement does not hold anymore. It is not due to auto-antibodies, but to defective mitochondria instead. The symptoms of this higher form of the disease include loss of the brain's ability to control the movement of muscles, tremors, and cardiac arrhythmia. and the lack of muscular control.
Treatments
Advancements during the last decades have led to the recent approval of several oral drugs. In March 2019 for example the Food and Drug Administration approved cladribine tablets (Mavenclad) to treat relapsing forms of multiple sclerosis (MS) in adults, to include relapsing-remitting disease and active secondary progressive disease. These drugs are expected to gain in popularity and frequency of use at the expense of previously existing therapies.
Further oral drugs are still under investigation, the most notable example being laquinimod, which was announced in August 2012 to be the focus of a third phase III trial after mixed results in the previous ones. Early trials of the female sex hormone estriol, led in part by Rhonda Voskuhl, have generated interest in reducing symptoms in women with RRMS. Similarly, several other studies are aimed to improve efficacy and ease of use of already existing therapies through the use of novel preparations.
Such is the case the PEGylated version of interferon-β-1a, that has a longer life than normal interferon and therefore it is being studied if given at less frequent doses has a similar efficacy than the existing product. Peginterferon beta-1a was approved for use in the United States in August 2014.
Preliminary data have suggested that mycophenolate mofetil, an anti-rejection immunosuppressant medication, might have benefits in people with multiple sclerosis. However, a systematic review found that the limited evidence available was insufficient to determine the effects of mycophenolate mofetil as an add‐on therapy for interferon beta-1a in people with RRMS.
Monoclonal antibodies, which are biological drugs of the same family as natalizumab, have also raised high levels of interest and research. Alemtuzumab, daclizumab and CD20 monoclonal antibodies such as rituximab, ocrelizumab and ofatumumab have all shown some benefit and are under study as potential treatments for MS. Nevertheless, their use has also been accompanied by the appearance of potentially dangerous adverse effects, most importantly opportunistic infections. Related to these investigations is the recent development of a test against JC virus antibodies which might help to predict what patients are at a greater risk of developing progressive multifocal leukoencephalopathy when taking natalizumab. While monoclonal antibodies are probably going to have some role in the treatment of the disease in the future, it is believed that it will be small due to the risks associated to them.
Another research strategy is to evaluate the combined effectiveness of two or more drugs. The main rationale for polytherapy in MS is that the involved treatments target different mechanisms of the disease and therefore, their use is not necessarily exclusive. Moreover, synergies, in which a drug potentiates the effect of another, are also possible. Nevertheless, there can also appear important drawbacks such as antagonizing mechanisms of action or potentiation of deleterious secondary effects. While there have been several clinical trials of combined therapy none has shown positive enough effects to merit the consideration as a viable treatment for MS.
Regarding neuroprotective and regenerative treatments such as stem cell therapy, while their research is considered of high importance at the moment they are only a promise of future therapeutic approaches. Likewise, there are not any effective treatments for the progressive variants of the disease. Many of the newest drugs as well as those under development are probably going to be evaluated as therapies for PPMS or SPMS, and their improved effectiveness when compared with previously existing drugs may eventually lead to a positive result in these groups of patients.
Disease-modifying drugs
Disease-modifying drugs represent possible interventions able to modify the natural course of the disease instead of targeting the symptoms or the recovery from relapses. Over a dozen clinical trials testing potential therapies are underway, and additional new treatments are being devised and tested in animal models.
New drugs must pass several clinical trials in order to get approved by regulatory agencies. Phase III is normally the last testing phase and when results are as expected a formal approval request is submitted to the regulator. Phase III programs consist of studies on large patient groups (300 to 3,000 or more) and are aimed at being the definitive assessment of how effective and safe a test drug will be. It is the last stage of drug development and is followed by a submission to the appropriate regulatory agencies (e.g., European Medicines Agency (EMEA) for the European Union, the Food and Drug Administration (FDA) for the United States, Therapeutic Goods Administration (TGA) for Australia, etc.) to obtain approval for marketing. Treatment in MS phase III studies is usually two years per patient.
Relapsing-remitting MS
Currently there are several ongoing phase III trials, and there are also some drugs that are waiting for approval after finishing theirs. The following drugs, at least, are also in phase III (for a complete list see Multiple sclerosis drug pipeline):
Tovaxin (injectable) A vaccine against self T-Cells, which consist of attenuated autoreactive T cells. It is developed by Opexa Therapeutics, (previously known as PharmaFrontiers), and finished a phase IIb September 2008, failing its primary target though in March 2008 was still performing well. After several financial troubles, a phase III trial was granted in 2011.
Secondary progressive variants
Relapsing-Onset variants (RO), even when they turn into progressive, have proved easier to treat than Progressive-Onset variants. Though difficult to treat, Secondary progressive and Progressive-Relapsing are easier to treat than PPMS. Only mitoxantrone has been approved for them, but there is nothing for PPMS. At this moment several therapies are under research:
Cyclophosphamide (trade name Revimmune) is currently in Phase III for secondary progressive MS. It was also studied for RRMS but the company does not pursue actively this path. After a 2006 study for refractory cases it showed good behaviour Later, a 2007 open label study found it equivalent to mitoxantrone and in 2008 evidence appeared that it can reverse disability. Simvastatin has shown brain atrophy reduction in secondary progressive MS. Masitinib, a tyrosine kinase inhibitor, is in late-stage testing for the treatment of patients with secondary and primary progressive MS (PPMS). It is a twice-daily oral medication that targets mast cells and inhibits several biochemical processes.14 Ibudilast: MediciNova, Inc., announced that MN-166 (ibudilast) has been approved for "fast track" development by the U.S. Food and Drug Administration (FDA) as of 2016, as a potential treatment for progressive multiple sclerosis (MS). Progressive MS in this case means both the primary progressive (PPMS) and secondary progressive (SPMS) forms of the disease.
Treatment for Primary Progressive variants