Clinical trials in multiple sclerosis

Although the first comprehensive description of multiple sclerosis was by Jean-Martin Charcot in 1868, there were no FDA-approved disease-modifying therapies for multiple sclerosis until 1993. In the 30 years since the approval of interferon beta-1b in 1993, there has been extensive progress in the development of disease-modifying therapies for multiple sclerosis. At present, there are 20 FDA-approved disease-modifying therapies. Although most advances have been made in the treatment of relapsing-remitting multiple sclerosis (RRMS), there has been some progress in the treatment of primary progressive multiple sclerosis (PPMS), notably with the approval of ocrelizumab in 2017. Multiple sclerosis remains an active area of drug development, with several ongoing clinical trials for both RRMS and PPMS.

It is widely accepted that clinical trials should fulfill standards for methodological quality, assuring an objective estimate of treatment effects. The quality of clinical trials is now frequently evaluated according to the CONSORT statement (02). Adequate randomization eliminates selection bias, and blinding prevents ascertainment bias. Randomization is a crucial component of high-quality clinical trials (02), particularly when testing medications, such as interferons or immunosuppressants, with well-known side effects that can bias reliability of blinding (88). Trials have also heightened the need to ensure matching (which is not assured by randomization or blinding); treatment arms with unmatched baseline demographics or disease characteristics may lead to skewed and uninterpretable results.

As the best-described biomarker for multiple sclerosis disease activity (31), MRI has proven crucial in clinical trial design, albeit not yet as a surrogate primary endpoint in pivotal phase III trials. Most pivotal clinical trials in multiple sclerosis are designed with annualized relapse rate or other relapse-related metrics as the primary outcome. This approach leads to a wide acceptance of relapse prevention as a drug efficacy marker. Disability progression is also a crucial metric. However, clinical trials rarely accept disability progression prevention as a primary outcome, reserving disability metrics (such as EDSS – Expanded Disability Status Scale) for secondary clinical outcomes. For this reason, clinical trials studying RRMS tend to be relatively short (often up to 24 months). Long-term outcomes are becoming increasingly important in terms of identifying impact on disability progression and for ensuring safety. Confirmed disability progression over 12 weeks is the standard metric used to evaluate disease-modifying therapies in secondary progressive multiple sclerosis (SPMS) and primary progressive multiple sclerosis (PPMS). It is important to note that EDSS measurements are often primarily impacted by a patient’s ambulatory status, thus, limiting some evaluation of disability in other domains. Despite cautions against comparing results among clinical trials, evidence-based medicine principles allow clinically meaningful conclusions to be drawn from clinical trials and simplified comparison of results from different trials (94). The relative effectiveness of a drug can be compared using both the risk ratio and risk reduction relative to the control group. Side effects of treatment, including infections, liver injury, infusion reactions, and other adverse events, can also be compared between the treatment and placebo groups.

Current treatment of multiple sclerosis is focused on three aspects: (1) treatment of relapses; (2) long-term disease-modifying treatment; and (3) symptomatic treatment. For a detailed discussion on symptomatic therapy of multiple sclerosis, please consult the relevant MedLink article, Multiple sclerosis: treatment of its symptoms. In this article, we evaluate major clinical trials for disease-modifying therapies in RRMS, PPMS, and radiologically isolated syndrome (RIS) after reviewing foundational studies on the treatment of relapses. Although a major focus of research, there are no FDA-approved therapies for remyelination or other restorative targets, and prospects for therapeutic development along these lines is not discussed here.

Treatment of acute relapses

Relapses (exacerbations, attacks, or flares) are a hallmark of multiple sclerosis and are often associated with functional impairments leading to decreased quality of life. Although symptoms from relapses can remit to some degree, relapses are a significant contributor to the development of disability. Even when relapse-associated symptoms ultimately improve or resolve, the time course for this is often slow (over months) and is associated with functional impairment for an extended period. Given the acuity and unpredictability of onset and prospects for recovery, relapses are a major concern for most patients. In addition to the use of high-efficacy disease-modifying therapies to limit relapses, much effort has been focused on identifying relapses and optimizing use of acute therapies to aid in recovery.

The generally accepted definition of a multiple sclerosis relapse is a new or worsening neurologic deficit lasting 24 hours or longer in the absence of fever, infection, or other contributory neurologic or medical concern. Relapse symptoms are dependent on the CNS localization of new or reactivated inflammatory lesions.

New or worsened inflammatory lesions typically result in motor or sensory (including visual) deficits. These lesions often involve the optic nerve; up to 50% of patients have optic neuritis at some point during their disease course. Other areas of involvement include the spinal cord, brainstem, and cerebellum, in addition to the cerebrum. Although MRI lesions are most common in the cerebrum, most new MRI lesions in this location tend to be asymptomatic. This is in stark opposition to lesions within the spinal cord or optic nerve, where there is thought to be less neurologic reserve, and injury directly attributes clinical symptoms.

When a patient has acute or subacute onset of neurologic symptoms, it is always important to rule out recrudescence or pseudo-relapses (also termed pseudoexacerbations or pseudoflares). These are symptoms that mimic relapses but do not have new underlying damage to the nervous system. Pseudorelapses are thought to be decompensation of the nervous system that has previously been injured (from multiple sclerosis) secondary to an acute insult, such as infection, extreme weather, overexertion, and other insults. Uhthoff phenomenon identifies recrudescence that occurs in the setting of increased temperature, whether that be internal temperature (fevers) or elevated ambient temperature (such as from hot weather, hot showers, or hot tub use). Overheating is thought to shorten action potential duration, leading to electrochemical transmission failure along demyelinated axons. Infections, particularly urinary tract infections, should always be considered in patients having recrudescence. This is important as patients with multiple sclerosis may have neurogenic bladder or be on immunosuppressive therapies that increase the risk of urinary tract infections. Other infections, including respiratory infections, are also common. A thorough evaluation for infection is recommended prior to treating any potential relapse with steroids. Notably, a patient cannot be identified as having recrudescence if there are neurologic symptoms they have never had in the past.

Reasons to treat relapses include strong evidence that treatment of relapses can shorten the time for a patient to reach their post-relapse baseline as well as more limited evidence that treatment of a relapse can reduce the interval risk of subsequent clinical events.

A milestone in the treatment of relapses was a well-designed, controlled, double-blind, multicenter (arguably the first multicenter clinical trial in multiple sclerosis) clinical trial that was reported in 1970 (90). Patients were randomly assigned to either adrenocorticotropic hormone gel or placebo gel. A total of 197 patients were enrolled from 10 centers throughout United States. This study was also the first to introduce the Disability Status Scale (DSS), which later and with minor modification became well known as EDSS (Expanded Disability Status Scale). In this study, a treatment regimen of 40 units of adrenocorticotropic hormone gel given as intramuscular injections twice daily for 7 days, then 20 units twice daily for 4 days, and 20 units twice daily for 3 days had beneficial effects in comparison to the similarly administered placebo gel. These data led to broad acceptance of adrenocorticotropic hormone as a treatment for relapses and eventually to the FDA approval of adrenocorticotropic hormone in 1978.

Studies in the 1980s shifted focus to the use of intravenous methylprednisolone as the preferred treatment option for relapse, in part due to ease of access and lower cost. Several studies were done comparing intravenous methylprednisolone to adrenocorticotropic hormone (01; 08; 69; 100) and to placebo (27; 70). The dosages used in these studies differ from as low as methylprednisolone 40 mg/day (69) to 500 mg/day (70), 15 mg/kg/day intravenously, and 1000 mg per day (27; 100). Lower dosages were found to be ineffective (69), and dosages from 500 to 1000 mg of intravenous methylprednisolone per day became widely accepted. The length of treatment also varied in these studies, and the consensus on how long the relapse should be treated transformed over the years. Although back in 1960s to 1980s it was common practice to treat multiple sclerosis exacerbation for 4 weeks and even for up to 35 days (89; 90; 69), significantly shorter courses of 3 to 7 days were subsequently found to be quite adequate (70; 100).

Oral steroids at the equivalent dose are noninferior to the intravenous route (60). Thus, oral high-dose steroids are an excellent option for those patients who cannot obtain intravenous steroids and those who would not otherwise be hospitalized.

Practical recommendations. Accurate identification of multiple sclerosis relapses versus recrudescence is essential. Although mild relapses may not require treatment (87), there is a consensus that moderate to severe multiple sclerosis exacerbations with disabling symptoms should be treated using systemic steroids (preferably corticosteroids). There is no consensus as to how early steroid treatment must be initiated to be effective, but it is generally thought that it should be started as early as possible from symptom onset. That said, it has been suggested that relapse treatment can be successfully initiated even as late as 1 to 2 months into a relapse (38).

Intravenous administration of high-dose methylprednisolone at 1000 mg per day for 3 to 5 days is the gold standard of management of moderate to severe relapses. Oral prednisone 1250 mg per day for 3 to 5 days is considered noninferior and can be more easily used in the outpatient setting. This method can be optimal for those with poor access to infusion centers or limited hours at infusion centers and is more cost effective. However, it should not be used in those with dysphagia or aspiration risk. Note that methylprednisolone at the 1000 mg dose can also be taken orally, although it is not always easily accessible.

In general, data do not support oral steroid tapers as offering additional benefit (83). However, some clinicians may choose to offer oral steroid tapers for those patients with severe attacks, larger lesions, or incomplete recovery.

For patients with disabling multiple sclerosis relapse symptoms not responding to treatment with adrenocorticotropic hormone or a course of intravenous or oral corticosteroids, plasma exchange should be considered (106; 58; 21).

Treatment of disease activity and progression

There are currently 20 FDA-approved disease-modifying therapies for multiple sclerosis. Each class will be explored based on evidence from clinical trials.

INJECTABLE DISEASE-MODIFYING THERAPIES

Interferon beta

In the 1980s, successful evaluation of intrathecal interferon beta (50) opened the way to the development of more convenient treatment protocols and eventually the first FDA-approved therapy for relapsing multiple sclerosis.

In 1993, the Interferon beta-1b Multiple Sclerosis Study Group trial was published (03; 81), which eventually led to FDA approval. The study included 372 patients with EDSS scores of 0 to 5.5 and at least two relapses in the preceding 2 years. Patients were randomized to receive placebo or interferon beta-1b (50 or 250 µg subcutaneously every other day) for 2 years. The average duration of multiple sclerosis since diagnosis was 8 years. Interferon beta-1b at a dose of 250 µg (8 million units), when compared to placebo, reduced the annualized relapse rate over 2 years of follow-up (-34%; p< 0.0001), the primary endpoint of the study. It also reduced the median number of new, recurrent, or enlarging lesions on MRI (-83%; p< 0.009).

The Prevention of Relapses and Disability by Interferon beta-1a Subcutaneously in Multiple Sclerosis Study (PRISMS) was a multicenter and controlled trial, which led to eventual approval of this compound. A total of 560 patients with an EDSS score between 1.0 and 5.0 and at least two relapses in the preceding 2 years were randomized to 2-year treatment with placebo or interferon beta-1a (22 or 44 µg subcutaneously three times weekly) (06; 62). Interferon beta-1a at a dose of 44 µg, three times weekly, reduced relapse rate (-32%; p< 0.005) and reduced the confirmed 1.0-point EDSS progression rate (-30%; p< 0.05), the median number of T2 active lesions (-78%; p< 0.0001), and the median volume of T2 MRI disease burden (-14.7%; p< 0.0001) when compared with placebo.

Pharmacological and clinical studies point to a dose-dependent response for interferon-beta. This may be relevant to the fact that the serum concentration of interferon beta-induced biological markers is dose-dependent; in addition, the markers are maintained at higher levels for longer periods when several administrations per week are used, rather than a single weekly dose (108; 98; 22).

Clinical trials in relapsing-remitting multiple sclerosis have also demonstrated dose-dependent effects on both clinical and MRI outcomes (81; 04; 06; 07). Evidence-based medicine measures calculated from the published controlled trials that led to the approval of the various interferon beta formulations show that multiple weekly administrations of interferon beta significantly decrease the risk of a disease event compared with placebo. In addition, interferon beta-1a 30 µg weekly reduced rates of sustained disability progression on EDSS as well as relapse rates when compared to placebo (49).

A multicenter trial, involving 802 patients with an EDSS score of 2.0 to 5.5 and at least three relapses in the past 3 years, compared 30 to 60 µg of intramuscular interferon beta-1a, given once a week (10). The primary clinical outcome was EDSS sustained progression rate. Thirty micrograms and 60 µg were equally effective on all clinical outcomes, even after stratification of patients according to various clinical or MRI baseline characteristics. The authors concluded that there is a ceiling effect for weekly interferon, whose efficacy does not increase over a certain dose; below a threshold dose, there might be a dose-response curve, but above this threshold, efficacy does not increase. An alternative explanation could be that this ceiling effect can be overcome if interferon beta is given with a multiple weekly administration per week protocol.

Two major studies, INCOMIN and EVIDENCE, support the hypothesis that the dose and dosing schedule have a major impact on the clinical efficacy of beta interferon. They also corroborate pharmacological and preclinical data favoring frequent high-dose administration of beta interferon.

INCOMIN directly compared the clinical and MRI efficacy of interferon beta-1b (250 µg every other day subcutaneously) to once weekly interferon beta-1a (30 µg intramuscularly) (29). INCOMIN was a controlled study where 188 patients, with an EDSS score between 1.0 and 3.5 and at least two relapses in the preceding 2 years, were randomized, with allocation concealment, to treatment with either drug for 2 years. INCOMIN is the only multicenter trial examining interferon beta for the treatment of multiple sclerosis not sponsored by drug companies, with funding coming via institutional sources instead.

Over the 2 years, every-other-day interferon beta-1b increased the proportion of patients without relapses (primary clinical endpoint) (42%; p=0.03), without new T2 lesions at MRI (primary MRI endpoint) (112%; p< 0.0003), and without confirmed 1.0 score EDSS progression (25%; p< 0.005); it slowed time to confirmed disability progression (p< 0.01) when compared to once-weekly interferon beta-1a. The trial was well-designed, but the blinded assessment was limited to the MRI analysis, which was performed on a subset of patients. Ascertainment bias introduced by the open-label clinical evaluation was probably marginal because clinical results were consistent with MRI results. A double-blind study design is, of course, the gold standard for clinical trials. The problem is that when using drugs with very well-characterized side effects such as interferons, beta blockers, or others, the reliability of blinding is controversial. A review from the Cochrane group comparing controlled trials of interferon in relapsing-remitting multiple sclerosis concluded that such trials could be considered as single-blind trials at best (88). Risk ratios and absolute risk reductions with every-other-day interferon beta-1b compared to once weekly interferon beta-1a were all statistically significant and were similar to those observed for multiple weekly injection interferon beta formulations compared to placebo in the pivotal trials. Number needed to treat values were low, statistically significant, and fell within the range of those calculated from published data from all previous controlled trials of type I interferons in multiple sclerosis (88).

Another study comparing interferon beta-1a, 44 µg subcutaneously, three times weekly (n=339) and interferon beta-1a, 30 µg intramuscularly once weekly (n=338) (80) was the EVIDENCE trial (Evidence for Interferon Dose Effect: European – North American Comparative Efficacy); this was a multicenter, prospective, randomized, assessor-blinded study. The initial phase of the study was 24 weeks, with patients having the option to remain on study medication for up to 48 weeks. At 24 weeks, interferon beta-1a given at 44 µg three times weekly had a significantly greater effect than at 30 µg once weekly on several relapse-related outcomes. Significantly more patients were relapse-free with the three times weekly dosing schedule at 44 µg (74.9%) than with once weekly dosing at 30 µg (63.3%; p=0.022). In addition, 44 µg of interferon beta-1a reduced the risk of suffering a first relapse by 30% and increased the number of patients free from new T2 lesions by 30%. At 48 weeks, clinical and MRI effects still favored the high-dose, three times weekly interferon beta-1a, although the difference between the two groups became less pronounced.

Both studies, however, do have some methodological drawbacks that should be highlighted. EVIDENCE only lasted 1 year, with limited findings reaching significance at the second 6-month mark (ie, relapse rate). Although INCOMIN was of longer duration (2 years), there was limited power as well as matching of patients in both arms (ie, those on once weekly interferon beta-1a were older, more likely to be male, and with longer disease duration and more enhancing lesions on baseline MRI). Still, greater age at disease onset and male sex are associated with an adverse outcome according to a population-based study (107). This might suggest a poorer prognosis for patients treated with interferon beta-1a and, therefore, bias the results in favor of interferon beta-1b.

Because most published trials report only 2 to 3 years of follow-up, the question of whether efficacy persists over time is yet to be answered. Due to gradual patient accrual and a long period for analysis and FDA submission, some patients in the pivotal trial of every-other-day 250 µg interferon beta-1b were followed up for up to 4 to 5 years (04). The 30% relapse rate reduction observed in the pivotal trial was maintained through to year 5, although significance was lost, likely because of the reduced sample size. With treatment, the median volume of T2 disease burden did not significantly change from baseline in each of the 5 years and was always significantly lower than that observed in placebo-treated patients.

Following the 2-year placebo-controlled study, the PRISMS trial was continued for an additional 2 years. Placebo-treated patients were re-randomized to receive either 22 µg or 44 µg three times weekly interferon beta-1a (86). On years 3 and 4 of follow-up, the high dose was more effective than the low dose at reducing relapse rate (p< 0.03), increasing time to EDSS confirmed progression (p< 0.05), and reducing MRI disease burden and T2 lesion activity (p< 0.001). Comparing the high-dose to the low-dose arm, relapse rate was reduced by 5% during the first 2 years of the trial (p = not significant) and by 21% during years 3 and 4 (p< 0.03).

All the above-mentioned long-term studies are, however, either open-label extensions of randomized control trials (86), or post-hoc analysis on small patients’ cohorts not reaching statistical significance (04), and as such may not be very reliable. The Cochrane review concluded, in fact, that interferon has a certain effect in relapsing-remitting multiple sclerosis in reducing relapses and disability during the first year of treatment, but the clinical effect beyond the first year of treatment is not clear (33).

However, according to the analysis of clinical outcomes of the original treatment groups 16 years after the pivotal IFNB-1b trial, there was a reduction in long-term disability, and mortality rates among patients originally treated with IFNB-1b were lower than in the original placebo group (18.3% for placebo vs. 8.3% for IFNB-1b 50 mcg and 5.4% for IFNB-1b 250 mcg) (30). Furthermore, a randomized cohort study 21 years after the start of the pivotal IFNB-1b trial reported that hazard rate of death was reduced by 46.8% among patients treated with IFNB-1b 250 mcg compared with placebo (42).

Most of the side effects associated with interferon beta use are most likely to occur during the first 3 to 6 months of treatment and are likely to decline in frequency thereafter (104). It is possible that a low-dose, once-weekly beta interferon regimen might offer some benefits with respect to patient compliance. INCOMIN study showed that the frequency of some side effects (eg, abnormal liver enzymes, local skin reactions, occurrence of neutralizing anti-interferon antibodies) was greater in the high-dose, high-frequency regimens. Most side effects are mild to moderate in intensity. Liver function alterations disappear in most patients within a few months (28); local skin reactions to interferon beta tend to decline with improved injection technique (101).

During treatment, some patients develop antibodies against interferon beta. Neutralizing antibodies (NAbs) to interferon beta may affect its biological availability and the production of interferon-induced biological markers (91; 23; 20; 102; 09). Neutralizing antibodies may also impact interferon beta clinical and MRI efficacy. However, the NAbs data remain somewhat controversial: whereas some studies find a detrimental effect of neutralizing antibodies on treatment response (05; 91; 96; 66; 37; 54), others did not (06; 29; 80). Long-term evaluations show that the impact of NAbs on clinical outcomes might be delayed for between 3 and 4 years (86). It is worth noting that neutralizing antibodies frequency is lower for intramuscular interferon beta 1a (which has been associated with the lowest frequency of NAbs, 2% to 6%) (49; 80) compared to subcutaneous interferon beta 1a (12% to 25%) (06; 80) and interferon beta 1b (22% to 38%) (05; 29; 96).

Strategies to reduce the occurrence of NAbs have been studied. The addition of 1 g methylprednisolone each month to interferon beta therapy was well tolerated and reduced the development of NAbs by over 50% (85). Another approach is to increase the interferon beta dose. The PRISMS study, which compared the efficacy of 22 or 44 µg interferon beta 1a subcutaneously three times per week in patients with relapsing-remitting multiple sclerosis, showed that NAbs frequency was significantly lower in patients treated with the higher dose (06; 37). The OPTimization of Interferon for MS (OPTIMS) study, a multicenter, prospective trial investigating outcomes with two interferon beta-1b doses, 250 or 375 µg, administered subcutaneously every other day, showed that NAbs-positive patients treated with 375 µg interferon beta 1b had a significantly greater probability of NAbs disappearance (hazard ratio: 3.41; 95% confidence interval: 1.78 – 6.43; p < 0.01) (26).

There is a lack of consensus on whether a single weekly administration of interferon beta is less effective than higher dose, more frequent injections of either interferon beta-1a or beta-1b. Patient preference and resulting adherence to prescribed therapy is important to weigh against presented evidence suggesting that interferon beta given by more frequent injections is more effective than once-weekly injections. Arguments that NAbs against interferon beta-1b deleteriously affect the eventual course of multiple sclerosis must be evaluated in long-term studies.

Glatiramer acetate

Randomized trials. The first large, controlled trial included 251 patients with an EDSS score between 0 and 5.5 and at least two relapses in the preceding 2 years, randomized to receive either placebo or 20 mg glatiramer acetate subcutaneous daily for up to 3 years (51). At 2 years, glatiramer acetate reduced relapse rate (-29%; p=0.007), the primary endpoint, and slowed unconfirmed 1.5-point EDSS progression (-28%; p=0.037), compared to placebo. No MRI outcome measures were assessed as part of this trial.

A second trial was undertaken to evaluate MRI measures (18). It involved 249 patients with EDSS scores between 0 and 5.0, at least one relapse in the previous 2 years, and one gadolinium-enhancing lesion on the screening MRI. Patients were randomized to receive either placebo or 20 mg glatiramer acetate for 9 months with MRIs completed monthly. Glatiramer acetate reduced the total number of enhancing lesions (the primary endpoint) (-35%; p=0.001), relapse rate (-33%; p=0.012), and the median change in T2 disease burden (-8.3%; p=0.0011). The effect on MRI-enhancing lesions was delayed until 6 months after starting treatment. Consequently, the compound was approved.

Another multicenter randomized study evaluated the efficacy, safety, and tolerability of glatiramer acetate 40 mg daily versus the approved 20 mg formulation given for 9 months (15). The trial enrolled 229 patients with EDSS scores of 0 to 5.0, no previous use of glatiramer acetate, at least one relapse in the previous year, and 1 to 15 gadolinium-enhancing lesions on a screening MRI. Of them, 90 were randomly assigned to glatiramer acetate 20 mg (n=44), or 40 mg (n=46). The primary efficacy endpoint was the total number of enhancing lesions at months 7, 8, and 9, and it showed a trend favoring the 40 mg dose (38% relative reduction, p = 0.090). The clinical endpoints were statistically significant in favor of the 40 mg dose: relapse-free subjects (p=0.018) and time to first relapse (p=0.037). The results suggest a trend for higher efficacy of the 40 mg dose over the 20 mg dose in reducing MRI activity. The 40 mg dose was significantly more effective than the standard dose on clinical endpoints (clinical relapses, time to first relapse).

Although the 20 mg dose of glatiramer acetate appears to be sufficient to provide meaningful efficacy, there is hope that a higher dose (40 mg) at less frequent dosing intervals may be able to demonstrate even greater convenience. Based on several open-label, small-scale (30 to 68 subjects) studies (30 to 68 subjects) that demonstrated relatively comparable efficacy of the standard daily dosing glatiramer acetate to alternate days or twice weekly, a large scale, multinational multicenter double-blinded placebo-controlled trial of glatiramer acetate 40 mg three times a week versus placebo was designed. In the phase III, Glatiramer Acetate Low-Frequency Administration (GALA) study, there was a 34.4% reduction in annualized relapse rate (ARR) as compared to placebo (p< 0.0001). Additionally, there was a 34.4% reduction in the cumulative number of new and enlarging T2 lesions (p< 0.0001) and a 44.8% reduction in the cumulative number of gadolinium-enhancing legions (p< 0.0001). At 12 months, there was no significant difference in percent change of brain volume between glatiramer acetate and placebo. Discontinuation rates among the glatiramer acetate and placebo patient cohorts were comparable. The overall frequency of adverse events in the two arms was comparable; the most reported adverse events were injection-site reactions, headaches, and nasopharyngitis.

Glatiramer acetate is usually well-tolerated. Short-lived local skin reactions are common. Lipoatrophy can be very disfiguring and is thought to be permanent, which should be taken into consideration. It is important that patients be aware of the possibility of lipoatrophy, be able to identify it, and discontinue injecting in areas where it is identified. Glatiramer acetate 40 mg daily showed the same safety profile as the 20 mg formulation (15).

Persistence of glatiramer acetate efficacy over time, comparative trials, and treatment protocol. A report on the extended open-label use (approximately 5.8 years) of glatiramer acetate in 152 patients initially enrolled in the placebo-controlled study has been published (52). The authors reported a reduction in relapse rate of almost 70% and stabilization of the EDSS score during follow-up. However, the overall dropout rate was high (40%), possibly resulting in a self-selected cohort of patients that responded well to therapy. During this long-term open-label follow-up period, relapse rates were similar in those patients receiving active treatment from the beginning of the trial as well as in those initially randomized to placebo.

Another extended, open-label use, multicenter study (going back to approximately 13.6 years) of glatiramer acetate in 100 patients initially enrolled in the placebo-controlled study has been published (35). For ongoing patients, annual relapse rates (ARRs) maintained a decline from 1.12 +/- 0.82 at baseline to 0.25 +/- 0.34 per year; 57% had stable or improved EDSS scores (change 0.5 or fewer points); 65% had not transitioned to secondary progressive multiple sclerosis (SPMS); 38%, 18%, and 3% reached EDSS 4, 6, and 8. The authors also reported the results of a follow-up MRI scan from 135 patients remaining in the open-label follow-up, obtained after an average of 4 years' treatment (109). This enabled a comparison of gadolinium-enhancing lesion frequency in a group of patients receiving glatiramer acetate for approximately 4 years with the group that had remained on active treatment since the trials began (about 6.7 years). In patients receiving active treatment for a shorter period, the risk of having enhancing lesions was 2.5 times higher, suggesting that the full benefit of glatiramer on this MRI finding occurs after many years of treatment. Gadolinium enhancement is, however, a short-lived and highly dynamic phenomenon and might be a controversial endpoint in a study where only one MRI scan was obtained after 4 years of treatment. Of note, the T2 disease burden, an MRI parameter that better reflects accumulated disease activity, was similar in both groups. As previously discussed, open-label extension studies may have statistical bias and be difficult to interpret.

A Cochrane systematic review assessed efficacy of glatiramer acetate by pooling together data from four published individual trials (73). Authors tried to get raw patient data from the original trials from the company producing glatiramer, but they did not receive any answer. Authors used intent-to-treat analysis and calculated the risk ratio with the fixed effect model for most outcomes (disability progression at 2 years, EDSS change at 2 years, and proportion of patients with relapses), using a random model only in case of outcomes with a significant heterogeneity (mean number of relapses at 1 and 2 years). Glatiramer acetate did not seem better than placebo either in preventing clinical progression or in reducing the number of relapse-free patients at 2 years. For the mean number of relapses, the weighted mean difference showed no significant decrease of relapse at 1 and 2 years.

Another systematic review, instead of analyzing the various studies individually, pooled raw patient data from the original trials provided by the company producing glatiramer (67). They claimed that glatiramer was able to reduce relapse rate by 28% compared to placebo over a 2-year follow-up. Martinelli Boneschi and colleagues used data from only three of the four published studies on this topic and did not specify criteria for study selection. They used multivariate regression analysis and did not mention either intention to treat analysis or evaluation of data heterogeneity. Finally, they evaluated only continuous outcomes (annualized relapse rate and time to first relapse). It should be noted that dichotomous outcome, such as the proportion of patients who were relapse free (the outcome used in the analysis of Munari and colleagues) instead of relapse rate (used by Martinelli Boneschi and colleagues) is a more sensitive outcome measure (67; 73). A few patients with many relapses might, in fact, disproportionately affect the overall relapse rate, while they proportionally affect the number of relapse-free patients, being always counted as one patient with relapses independently from the number of relapses. Martinelli Boneschi and colleagues did not assess the heterogeneity among studies; that was not, therefore, considered in their multivariate analysis (71).

There were two head-to-head studies conducted between glatiramer and interferon products: REGARD and BEYOND. REGARD was designed based on the preconceived expectation that interferon beta-1a 44 mcg three times a week is superior to daily glatiramer acetate 20 mg. In this direct head-to-head comparison trial, there did not appear to be meaningful differences between interferon beta-1a 44 mcg three times a week and glatiramer acetate 20 mg daily (68). Similarly, BEYOND (a trial that aimed to demonstrate superiority of double-dose interferon beta-1b over the standard dose of 250 mcg and over glatiramer acetate 20 mg daily) did not demonstrate meaningful differences between interferon beta-1b and glatiramer acetate in respect to the primary outcome of the study (relapse risk) (77); however, the rater-blinded, post hoc analysis on new MRI lesion evolution into permanent “black holes,” a marker of irreversible tissue damage, provided Class III evidence that interferon beta-1b is associated with a reduction in MRI permanent “black holes” formation and evolution compared with glatiramer acetate between years 1 and 2 of treatment (32).

Furthermore, it should be noted that based on CombiRx study data, the arms of glatiramer acetate monotherapy and combined glatiramer acetate and IFN-beta-1a IM weekly did not show statistically significant difference in respect to the primary outcome (annualized relapse rate). (CombiRx study was an NIH-funded clinical trial comparing several arms: (1) IFN-beta-1a intramuscular weekly monotherapy; (2) glatiramer acetate subcutaneous monotherapy; (3) combination therapy of IFN-beta-1a intramuscular weekly and glatiramer acetate subcutaneous daily.) This evidence indicates that adding IFN-beta-1A intramuscular weekly to glatiramer acetate did not provide any additional benefit (64).

Ofatumumab

Ofatumumab is an anti-CD20 monoclonal antibody that was approved by the FDA in 2020. Unlike ocrelizumab and ublituximab, which are infusions, ofatumumab is a 20 mg, every-4-week subcutaneous injection that follows three weekly 20 mg loading doses. The identical phase III, randomized, double-blind trials ASCLEPIOS I and II were published in 2020 (45). Taken together, these studies enrolled 1882 patients with RRMS and compared ofatumumab to teriflunomide 14 mg daily. The primary outcome, annual relapse rate, was 0.11 and 0.10 in the ofatumumab groups in each study, respectively, with reductions of -0.11 (95% CI: -0.16 to -0.06, p< 0.001) and -0.15 (95% CI: -0.20 to -0.09). Confirmed disability progression at 12 weeks was reduced in the ofatumumab groups (HR: 0.66, p=0.002): 10.9% with ofatumumab versus 15% with teriflunomide. Injection reactions were seen in 20.2% of patients receiving ofatumumab (15% in the teriflunomide group with placebo injections); 2.5% of the ofatumumab groups had serious infections. An extension study to 3.5 years did not identify additional safety concerns (46).

ORAL DISEASE-MODIFYING THERAPIES

Sphingosine 1-phosphate receptor modulator (S1Ps)

Fingolimod. Fingolimod was approved by the FDA in 2010 for the treatment of relapsing forms of multiple sclerosis after the pivotal study demonstrating its efficacy in reducing the frequency of clinical exacerbations and delaying the accumulation of physical disability. Fingolimod is metabolized by sphingosine kinase to the active metabolite, fingolimod-phosphate. Fingolimod-phosphate is a sphingosine 1-phosphate receptor modulator and binds with high affinity to sphingosine 1-phosphate receptors 1, 3, 4, and 5. Fingolimod-phosphate blocks the capacity of lymphocytes to egress from lymph nodes, substantially reducing the number of lymphocytes in peripheral blood. The efficacy of this drug was shown by two studies: the TRANSFORMS study (11) and the FREEDOMS study (57). After FDA approval, the FREEDOMS II trial confirmed the results of the FREEDOMS trial.

In the 12-month TRANSFORMS trial, 1292 patients with relapsing-remitting multiple sclerosis were randomly assigned in a double-dummy, double-blind design to fingolimod 1.25 mg oral daily, fingolimod 0.5 mg oral daily, or interferon beta-1a 30 mcg intramuscular weekly. A total of 1153 patients (89%) completed the study. The annualized relapse rate was significantly lower in both groups receiving fingolimod--0.20 (95% confidence interval [CI], 0.16 to 0.26) in the 1.25-mg group and 0.16 (95% CI: 0.12 to 0.21) in the 0.5-mg group--than in the interferon group (0.33, 95% CI: 0.26 to 0.42, P< 0.001 for both comparisons). MRI findings supported the primary outcome results. No significant differences were seen among the study groups with respect to progression of disability. Two fatal infections occurred in the group that received the 1.25 mg dose of fingolimod: disseminated primary varicella zoster and herpes simplex encephalitis. Other adverse events among patients receiving fingolimod were nonfatal herpesvirus infections, bradycardia and atrioventricular block, hypertension, macular edema, skin cancer, and elevated liver-enzyme levels.

In the 24-month FREEDOMS study, 1272 patients with relapsing-remitting multiple sclerosis were randomly assigned in a double-blind design to one of three groups: fingolimod 1.25 mg oral daily, fingolimod 0.5 mg oral daily, or matching placebo oral daily. A total of 1033 of the 1272 patients (81.2%) completed the study. The annualized relapse rate was 0.18 with 0.5 mg of fingolimod, 0.16 with 1.25 mg of fingolimod, and 0.40 with placebo (P< 0.001 for either fingolimod dose vs. placebo). Fingolimod at doses of 0.5 mg and 1.25 mg significantly reduced the risk of disability progression over the 24-month period (hazard ratio, 0.70 and 0.68, respectively; p=0.02 vs. placebo, for both comparisons). The cumulative probability of disability progression (confirmed after 3 months) was 17.7% with 0.5 mg of fingolimod, 16.6% with 1.25 mg of fingolimod, and 24.1% with placebo. Both fingolimod doses were superior to placebo with regard to MRI-related measures (number of new or enlarged lesions on T2-weighted images, gadolinium-enhancing lesions, and brain-volume loss; P< 0.001 for all comparisons at 24 months). Causes of study discontinuation and adverse events related to fingolimod included bradycardia and atrioventricular conduction block at the time of fingolimod initiation, macular edema, elevated liver-enzyme levels, and mild hypertension.

In 2012, FREEDOMS II randomized 1083 patients with relapsing-remitting multiple sclerosis to fingolimod 0.5 mg, 1.25 mg, or placebo in a 1:1:1 ratio. Participants were treated for 24 months. Three-fourths of the participants had undergone prior treatment with other disease-modifying treatments. Approximately 72% of patients enrolled in the trial completed this study. Fingolimod administered at a daily dose of 0.5 mg significantly reduced the annualized relapse rate by 48% compared with placebo (p< 0.001) and increased the percentage of patients free of multiple sclerosis relapse at the end of 24 months compared with placebo (71.5% vs. 52.7%, respectively). Brain atrophy was significantly reduced with daily treatment of 0.5 mg of fingolimod versus placebo at month 24: 33% reduction in brain volume versus placebo (p< 0.001). The effect on brain volume was seen as early as 6 months (39% reduction) and was consistent at 12 months (40% reduction) and 24 months. 
Although numerically fewer patients treated with 0.5 mg of fingolimod experienced disability progression, as measured by change in Expanded Disability Status Scale (EDSS), this difference did not reach statistical significance. However, functional impairments, as measured by the Multiple Sclerosis Functional Composite (MSFC), was significantly less at month 24 in the group treated with fingolimod daily dose of 0.5 mg versus placebo (p=0.012). Fingolimod, administered at 0.5 mg, was superior to placebo on all MRI assessments of gadolinium-enhancing lesions and new or newly enlarging T2 lesions.

The most common adverse events reported in the clinical trials were headache, influenza, diarrhea, back pain, liver transaminase elevations, and cough. The side-effect profiles seen in both phase III pivotal trials (FREEDOMS and TRANSFORMS) were similar.

Siponimod. Siponimod was approved by the FDA for relapsing multiple sclerosis. Like fingolimod, siponimod is a modulator of the sphingosine-1-phosphate receptor with specific affinity for S1PR types 1 and 5. The BOLD study tested two patient cohorts sequentially, separated by an interim analysis at 3 months. The primary endpoint was dose-response, assessed by percentage reduction in number of unique active lesions at 3 months for siponimod versus placebo. In cohort 1, 188 patients were allocated (1:1:1:1) to receive once-daily siponimod 10 mg, 2 mg, or 0.5 mg, or placebo for 6 months. In cohort 2, 109 patients were allocated (4:4:1) to siponimod 1.25 mg, siponimod 0.25 mg, or placebo once-daily for 3 months. The study showed a dose-response relation across the five doses of siponimod (p=0.0001), with reductions in unique active lesions at 3 months compared with placebo of 35% (95% CI: 17-57) for siponimod 0.25 mg (51 patients included in the primary endpoint analysis), 50% (29 to 69) for siponimod 0.5 mg (43 patients), 66% (48 to 80) for siponimod 1.25 mg (42 patients), 72% (57 to 84) for siponimod 2 mg (45 patients), and 82% (70 to 90) for siponimod 10 mg (44 patients). The highest incidence of adverse events was noted in patients receiving siponimod 10 and 2 mg daily. Cardiac adverse events including bradycardia, bradyarrhythmia, and atrioventricular conduction delays were noted when treatment was started without dose titration. Increases in liver transaminases were also observed in a dose-dependent manner. However, incidence of infections was not related to dose (95). Siponimod use is dependent on the CYP2C9 genotype, and this must be tested prior to use as it impacts safety and titration schedules. Siponimod is contraindicated with the CYP2C9 * 3/* 3 genotype, whereas daily dosing is 1 mg in patients with CYP2C9 * 1/* 3 or * 2/* 3 genotypes (25).

An extension of the BOLD study was conducted and designed to assess the efficacy and safety of siponimod for up to 24 months. Patients taking siponimod continued at the originally assigned dose, and patients taking placebo were rerandomized to the five siponimod doses. Of the 252 patients, 184 (73%) entered the extension; 159 (86.4%) completed the dose-blinded extension. The incidence of adverse events was similar across treatment groups (10 mg: 87.9%; 2 mg: 89.7%; 1.25 mg: 88.4%; 0.5 mg: 96.6%; and 0.25 mg: 84.0%). Reductions in mean (95% CI) gadolinium-enhancing T1 lesion counts from the last BOLD assessment were sustained in the 10 mg, 2 mg, 1.25 mg, and 0.5 mg dose groups. Similarly, both the annualized relapse rate (95% CI) and number of new or newly enlarging T2 lesions (95% CI) were significantly lower in the three highest dose cohorts compared to the two lower dose cohorts up to 24 months (56).

Ozanimod. Ozanimod is an oral therapy that was approved by the FDA in 2020. Ozanimod is a sphingosine-1-phosphate receptor modulator with selective binding to receptor subtypes 1 and 5. Ozanimod was evaluated in the phase III SUNBEAM and RADIANCE trials (13; 19). SUNBEAM compared ozanimod with interferon beta-1a in patients with relapsing multiple sclerosis over 12 months. Patients had an EDSS of 5.0 or less as well as either one relapse within 12 months or one relapse within 24 months and an enhancing lesion on MRI within 12 months. In this study, 1346 patients were enrolled, and treatment groups were ozanimod 1 mg daily, ozanimod 0.5 mg daily, or interferon beta-1a 30 μg weekly. The primary endpoint was annualized relapse rate: 0.35 for interferon beta-1a, 0.24 (95% CI: 0.19–0.31) for ozanimod 0.5 mg, and 0.18 (95% CI: 0.14–0.24) for ozanimod 1 mg. When compared to interferon beta-1a, both ozanimod 0.5 mg (0.69, 95% CI: 0.55–0.86) and ozanimod 1 mg (0.24, 95% CI: 0.19–0.31, p=0.0013) showed reduction based on rate ratio. No clinically significant arrythmias or heart blocks were noted. RADIANCE was a similar study with a 24-month follow-up, again comparing interferon beta-1a and ozanimod at either 0.5 or 1 mg daily dosing. Similar outcomes were achieved. Treatment discontinuation was highest in the interferon beta-1a group.

Ponesimod. Ponesimod is a sphingosine-1-phosphate receptor modulator that acts exclusively on receptor subtype 1. The OPTIUUM trial evaluated the efficacy of ponesimod in comparison to teriflunomide 14 mg daily in patients with relapsing multiple sclerosis; an EDSS of 5.5 or less; and active disease evidenced by one or more relapses within 12 months, two or more relapses within 24 months, or one or more gadolinium-enhancing lesions on MRI within 6 months (55). In this study, 1133 patients were enrolled, and patients were followed for 108 weeks; the primary outcome was annualized relapse rate. The ponesimod group had an annualized relapse rate of 0.202 compared to 0.290 for the teriflunomide group, with a reduction in annualized relapse rate of 30.5% (rate ratio 0.695; 99% CI: 0.536–0.902; p< 0.001). Ponesimod reduced active lesions on MRI by 56% (1.405 vs. 3.164; p< 0.001). Extension studies are ongoing.

Fumarates

Dimethyl fumarate. Dimethyl fumarate was approved by the FDA for relapsing multiple sclerosis in April 2013. According to the proposed mechanism of action, it inhibits expression of proinflammatory adhesion molecules and cytokines and causes activation of Nrf2 pathways. Dimethyl fumarate’s efficacy has been studied in two pivotal phase III trials: DEFINE and CONFIRM (36; 41). Both DEFINE and CONFIRM were 2-year trials that enrolled more than 1200 subjects. In addition to the three arms of the DEFINE trial (dimethyl fumarate 240 mg BID; dimethyl fumarate 240 mg TID; and placebo), CONFIRM included another comparator arm: daily subcutaneous glatiramer acetate. The incidence of serious infections was similar across treatment groups in both trials. The most common tolerability side effects of dimethyl fumarate are flushing and gastrointestinal symptoms, including abdominal cramps and diarrhea. In DEFINE, the annualized relapse rate was decreased 53% (when compared to placebo) with 240 mg BID dosing (p< 0.001), with an 85% decrease in new or enlarging T2 MRI lesions and a 90% decrease in gadolinium-enhancing lesions. When comparing dimethyl fumarate 240 mg BID to placebo in CONFIRM, the annualized relapse rate was decreased 44% (p< 0.001), with T2 MRI lesions and gadolinium-enhancing lesions reduced 71% and 57%, respectively (p< 0.001).

Diroximel fumarate. Diroximel fumarate was approved by the FDA in 2019. Like dimethyl fumarate, it is a prodrug that is metabolized to the active form, monomethyl fumarate. However, due to differences in chemical structure, it carries a lower risk of gastrointestinal side effects (74). The EVOLVE-MS-1 was an open-label, single arm 2-year trial evaluating long-term safety and efficacy. Patients 18 to 65 years of age with a diagnosis of relapsing remitting multiple sclerosis (based on 2010 McDonald criteria) with an expanded disability status scale less than 6 and no relapses within 30 days of enrollment were eligible for inclusion. Adverse events occurred in 84.6% (589 out of 696) of patients; the majority were mild (31.2%; 217 out of 696) or moderate (46.8%; 326 out of 696) in severity. Overall treatment discontinuation was 14.9%, 6.3% due to adverse events and less than 1% due to gastrointestinal system adverse events (75).

Monomethyl fumarate. Monomethyl fumarate was approved by the FDA in April 2020. Monomethyl fumarate is the sole active metabolite of dimethyl fumarate and diroximel fumarate and was approved based on bioequivalence data.

Other oral disease-modifying therapies

Teriflunomide. Teriflunomide was approved by the FDA for the treatment of relapsing forms of multiple sclerosis in 2012. Teriflunomide, an immunomodulatory agent with anti-inflammatory properties, inhibits dihydroorotate dehydrogenase, a mitochondrial enzyme involved in de novo pyrimidine synthesis. Teriflunomide is the active metabolite of leflunomide, which was previously approved by the FDA for rheumatoid arthritis. The efficacy of teriflunomide was demonstrated in TEMSO, a double-blind, placebo-controlled study that evaluated once-daily doses of teriflunomide 7 mg and 14 mg in patients with relapsing forms of multiple sclerosis over 108 weeks (76). All patients had a definite diagnosis of multiple sclerosis exhibiting a relapsing clinical course, with or without progression, and had experienced at least one relapse over the year preceding the trial or at least two relapses over the 2 years preceding the trial. Subjects had not received interferon beta for at least 4 months or any other preventive multiple sclerosis medications for at least 6 months before entering the study, nor were these medications permitted during the study. Neurologic evaluations were performed at screening every 12 weeks until week 108 and at unscheduled visits for suspected relapse. MRI was performed at screening at weeks 24, 48, 72, and 108. The primary endpoint was annualized relapse rate.

In this study, 1088 patients were randomized to receive 7 mg (n=366) or 14 mg (n=359) of teriflunomide or placebo (n=363). At entry, patients had an EDSS score of 5.5 or lower. The mean age of the study population was 37.9 years, the mean disease duration was 5.33 years, and the mean EDSS at baseline was 2.68. A total of 91.4% had RRMS, and 8.6% had a progressive form of multiple sclerosis with relapses. The mean time on placebo was 631 days, on teriflunomide 7 mg was 635 days, and on teriflunomide 14 mg was 627 days.

The annualized relapse rate was significantly reduced in patients treated with either 7 or 14 mg of teriflunomide compared to patients who received placebo. There was a consistent reduction of the annualized relapse rate noted in subgroups defined by sex, age group, prior multiple sclerosis therapy, and baseline disease activity. The time to disability progression sustained for 12 weeks (as measured by at least a 1-point increase from baseline EDSS of 5.5 or less or a 0.5-point increase from baseline EDSS greater than 5.5) was statistically significantly reduced only in the teriflunomide 14 mg group compared to placebo. The effect of teriflunomide was assessed on several MRI variables, including the total lesion volume of T2 and hypointense T1 lesions. The change in total lesion volume from baseline was significantly lower in the 7 and 14 mg groups than in the placebo group. Patients in both teriflunomide groups had significantly fewer gadolinium-enhancing lesions per T1-weighted scan than those in the placebo group.

Although the FDA approval of teriflunomide was based on TEMSO, a second phase III, placebo-controlled trial of teriflunomide 7 mg and 14 mg has been reported (TOWER). The results of TOWER are consistent with those seen in TEMSO. In terms of annualized relapse rate, there was a 22.3% reduction (p=0.02) in the teriflunomide 7 mg arm and a 36.3% reduction (p< 0.0001) in the teriflunomide 14 mg arm, compared to placebo. In terms of 12-week sustained accumulation of physical disability, there was a statistically significant 31.5% (p=0.0442) reduction for teriflunomide 14 mg, but reduction was not significant for teriflunomide 7 mg, as compared to placebo.

A phase III, multinational, randomized parallel-group study (TENERE) was designed as a superiority trial to compare the effectiveness, defined as time to failure (first occurrence of confirmed relapse or permanent treatment discontinuation for any reason, whichever came first), and tolerability of oral teriflunomide 7 mg daily (n=109) or oral teriflunomide 14 mg daily (n=111) versus subcutaneous interferon beta-1a 44 mcg, three times weekly (n=104) (103). The results of this trial did not reveal any statistical differences in the primary composite endpoint: 48.6% for teriflunomide 7 mg, 42.3% for interferon beta-1a 44 mcg, and 37.8% for teriflunomide 14 mg. The adjusted annualized relapse rate over 96 weeks of treatment was 0.41 with teriflunomide 7 mg, 0.26 with teriflunomide 14 mg, and 0.22 with interferon beta-1a 44 mcg. There was no significant difference for teriflunomide 14 mg versus interferon beta-1a 44 mcg, but teriflunomide 7 mg was associated with a higher risk of relapse than interferon beta-1a 44 mcg (89.7%, p=0.03). Greater treatment satisfaction (p=0.02) and fewer discontinuations were observed with both doses of teriflunomide compared with interferon beta-1a 44 mcg. There was also a statistically significant lower adjusted mean change from baseline to week 48 in the fatigue impact scale score for the teriflunomide 7 mg arm as compared to the interferon beta-1a 44 mcg arm (p=0.03) but not for the teriflunomide 14 mg arm as compared to the interferon beta-1a 44 mcg arm (p=0.18).

The most common adverse events reported in the clinical trials were alanine aminotransferase increase, nasopharyngitis, alopecia (hair thinning), nausea, diarrhea, and paresthesias. Teriflunomide has a black box warning label about fetotoxicity and is contraindicated in pregnancy. In placebo-controlled studies, peripheral neuropathy, including both polyneuropathy and mononeuropathy (eg, carpal tunnel syndrome), was reported more frequently in patients taking teriflunomide than in patients taking placebo. Because teriflunomide may take up to 2 years (average of 8 months) to be cleared after discontinuation, elimination can be accelerated by the use of cholestyramine, particularly in those with unintended pregnancies on teriflunomide.

Cladribine. Cladribine is a synthetic deoxyadenosine analogue that was approved by the FDA for relapsing multiple sclerosis based on the CLARITY study, which examined the efficacy of cladribine using rate of relapse at 96 weeks as its primary endpoint (39). In the study, 1326 patients were randomly assigned in an approximate 1:1:1 ratio to receive one of two cumulative doses of cladribine tablets (either 3.5 or 5.25 mg/kg) or matching placebo, given in two or four courses for the first 48 weeks, then in two courses starting at week 48 and week 52 (for a total of 8 to 20 days per year). Among patients who received cladribine tablets (either 3.5 or 5.25 mg/kg), there was a significantly lower annualized rate of relapse than in the placebo group (0.14 and 0.15, respectively, vs. 0.33; p< 0.001 for both comparisons), a higher relapse-free rate (79.7% and 78.9%, respectively, vs. 60.9%; p< 0.001 for both comparisons), a lower risk of 3-month sustained progression of disability (hazard ratio for the 3.5 mg/kg group: 0.67, 95% CI: 0.48–0.93, p=0.02; hazard ratio for the 5.25 mg/kg group: 0.69, 95% CI: 0.49–0.96, p=0.03), and significant reductions in the brain lesion count on MRI (p< 0.001 for all comparisons). Adverse events that were more frequent in the cladribine groups included lymphocytopenia (21.6% in the 3.5 mg/kg group and 31.5% in the 5.25 mg/kg group vs. 1.8%) and herpes zoster (8 patients and 12 patients, respectively, vs. no patients).

A post hoc and subgroup analysis of the CLARITY study showed that treatment with cladribine increased the proportion of patients showing NEDA-3 (no evidence of disease activity) over a 96-week period. Freedom from disease activity is commonly defined using three clinical and radiographic parameters: absence of relapses, absence of new MRI lesions over a specified period, and absence of sustained change in EDSS over a 3-month period (40). Of the 1326 patients enrolled in the CLARITY study, 1192 were assessed for disease activity at 24, 48, and 96 weeks. These patients were analyzed based on treatment group as well as subgroups, including age, prior treatment status, disease duration, number of relapses in the previous 12 months, EDSS score, T1 Gd-enhancing lesions, T2 lesion volume, and patients with high disease activity. Over 24 weeks, 266 (67%) of 395 patients in the cladribine 3.5 mg/kg group and 283 (70%) of 406 in the cladribine 5.25 mg/kg group were free from disease activity versus 145 (39%) of 373 in the placebo group (95% CI: 2.46–4.46 for the 3.5 mg/kg group; 95% CI: 2.73–4.97 for the 5.25 mg/kg group; both p< 0.0001). Over 48 weeks, 208 (54%) of 384 patients in the cladribine 3.5 mg/kg group and 222 (56%) of 396 patients in the cladribine 5.25 mg/kg group were free from disease activity versus 86 (24%) of 360 patients in the placebo group (95% CI: 2.77–5.22 for the 3.5 mg/kg group; 95% CI: 3.02–5.66 for the 5.25 mg/kg group; both p< 0.0001). Over 96 weeks, 178 (44%) of 402 patients in the cladribine 3.5 mg/kg group and 189 (46%) of 411 patients in the cladribine 5.25 mg/kg group were free from disease activity versus 60 (16%) of 379 patients in the placebo group (95% CI: 3.05–6.02 for the 3.5 mg/kg group; 95% CI: 3.29–6.48 for the 5.25 mg/kg group; both p< 0.0001). The effects of cladribine tablets on freedom from disease activity were significant across all patient subgroups.

INFUSION DISEASE-MODIFYING THERAPIES

Natalizumab

Natalizumab was approved by the FDA in 2004 for the treatment of relapsing forms of multiple sclerosis based on the demonstrated reduction of the frequency of clinical exacerbations and the delay in accumulation of physical disability. Natalizumab is a recombinant humanized IgG4k monoclonal antibody. The efficacy of this drug was shown in two studies: AFFIRM (84) and SENTINEL (92). These were randomized, double-blind, placebo-controlled trials involving more than 2000 subjects who were enrolled if they had at least one relapse during the prior year and an EDSS score between 0 and 5.0. MRI scans were performed at baseline and after 1 year, analyzing T1-weighted enhancing lesions and T2-weighted hyperintense lesions.

In the AFFIRM study, 942 patients who had not received any treatment during the previous 6 months were randomized to receive either natalizumab (300 mg intravenously) or placebo every 4 weeks for 28 months. The median age was 37 years, with a median disease duration of 5 years. After 24 months of treatment, there was a significant reduction in the annualized relapse rate (-68%; p< 0.001) and in sustained disability progression risk (-42%; p< 0.001). There was also an increase of relapse-free patients (-21%; p< 0.001) in the natalizumab group compared with the placebo.

In the SENTINEL study, 1171 patients who had experienced one or more relapses during the prior year of treatment with interferon beta-1a once weekly (30 mcg intramuscularly) were randomized to receive natalizumab (300 mg intravenously) or placebo every 4 weeks for 28 months (while continuing interferon beta-1a 30 mcg once-weekly treatment). The median age was 39 years, and the median disease duration was 7 years. At 24 months, there was a significant decrease in relapse rate (54%; p< 0.001) and a significantly increased proportion of patients who remained relapse-free (54% vs. 32%; p< 0.001) in the natalizumab plus interferon beta-1a group compared to the placebo plus interferon beta-1a group.

The most frequent originally reported serious side effects, even if uncommon, were infections, hypersensitivity reactions (anaphylactic reactions, mostly during the first hours after the infusion), fever, low blood pressure, headache, and depression.

In 2005, natalizumab was voluntarily withdrawn from the market by the manufacturing company based on a report of two cases of progressive multifocal leukoencephalopathy, one of which was fatal (59). This opportunistic infection of the CNS is caused by reactivation of clinically latent JC polyomavirus, which infects oligodendrocytes and leads to multifocal demyelination. This can lead to significant morbidity as well as mortality. In the past, progressive multifocal leukoencephalopathy typically occurred in the context of a severe immunodepression, such as in patients with HIV/AIDS, hematological malignancy, or post-organ transplantation. After natalizumab was withdrawn from the market, a third case of progressive multifocal leukoencephalopathy was reported in a patient with Crohn disease who had also received other immunosuppressive drugs. A careful retrospective analysis of all the patients involved in the clinical studies did not find any new progressive multifocal leukoencephalopathy cases. After such analyses, the FDA approved a supplemental license application for the reintroduction of natalizumab as monotherapy treatment for relapsing forms of multiple sclerosis in 2006. However, the post-marketing experience was significant for more progressive multifocal leukoencephalopathy cases occurring in the setting of natalizumab monotherapy.

Three factors have been established as aids in risk stratification for patients with multiple sclerosis on natalizumab at risk for developing progressive multifocal leukoencephalopathy: (1) presence of antibodies to the JC virus (JCV Abs); (2) length of treatment with natalizumab (over 2 years); and (3) prior exposure to immunosuppressants. In late 2012, a second-generation enzyme-linked immunosorbent assay (ELISA), StatifyJCV, was made available to aid in determining prior exposure to the JC virus (105).

The NOVA study compared the standard every-4-week dosing of natalizumab for RRMS and 6-week extended-interval dosing to evaluate efficacy. Due to the thought that extended-interval dosing may allow for increased immunosurveillance and reduced risk of progressive multifocal leukoencephalopathy, extended-interval dosing had been explored for safety purposes but had not been prospectively evaluated for efficacy. This was best evaluated by a retrospective cohort study utilizing the TOUCH safety database of patients positive for JC virus, with a relative risk reduction of 94% (93). NOVA enrolled 499 patients with at least 12 months on natalizumab without relapse and no missed doses within 3 months. Patients were randomized 1:1 to natalizumab every 6 weeks or to the standard every-4-week dosing. The primary outcome was new or enlarging T2 lesions on MRI at week 72. Mean new or enlarging T2 lesions at week 72 were 0.20 (95% CI: 0.07–0.63) in the every-6-weeks group and 0.05 (95% CI: 0.01–0.22) in the every-4-weeks group, with a mean lesion ratio of 4.24 (95% CI: 0.86–20.85; p=0.076). Two patients in the every-6-weeks group drove the mean lesion count with 25 or more new or enlarging lesions. There was one case of asymptomatic progressive multifocal leukoencephalopathy in the extended-interval dosing arm and no cases in the once every 4 weeks arm. The study was not powered to assess the risk of progressive multifocal leukoencephalopathy, and 21% of patients in the extended-interval dosing group and 19% of patients in the every-4-weeks group had JCV Abs in the serum (34). Taken together, extending natalizumab dosing from every 4 weeks to every 6 weeks is a reasonable option based on the available safety and efficacy data.

In August 2023, the FDA approved natalizumab-sztn, a biosimilar for natalizumab, on the basis of the Antelope phase III randomized controlled trial (Hemmer at al 2023). Biosimilars have previously been approved for rituximab, but this is the first biosimilar directly approved for the treatment of relapsing multiple sclerosis.

Alemtuzumab

Alemtuzumab is a humanized monoclonal antibody that binds to CD52 found on T cells, B cells, and monocytes (16). Two pivotal phase III trials demonstrated the robust efficacy of alemtuzumab: CARE-MS I and CARE-MS II (12; 17). In both trials, intravenous alemtuzumab was infused daily for 5 days with no repeat dosing until the second year, when there were an additional 3 days of infusions. The comparator arm was subcutaneous interferon beta-1a 44 mcg three times a week (and no placebo arm). CARE-MS I enrolled treatment-naive multiple sclerosis patients, whereas CARE-MS II enrolled treatment-experienced multiple sclerosis patients who had a history of at least one relapse after at least 6 months on one of their prior therapies. In both CARE-MS I and II, adverse events included thyroid disorders, immune thrombocytopenic purpura, other humoral autoimmune diseases, and infections (mostly respiratory). The annualized relapse ratio was 0.18 with alemtuzumab compared to 0.39 with interferon beta-1a in CARE-MS I (p< 0.001) and 0.26 compared to 0.50 in CARE-MS II (p< 0.001).

Ocrelizumab

Ocrelizumab is a monoclonal anti-CD20 monoclonal antibody—a B-cell depleting therapy—that was approved by the FDA in April 2017 for the treatment of both RRMS and PPMS. Ocrelizumab went through several trials: OPERA I and OPERA II (RRMS), which ran side by side, and ORATORIO (PPMS). In the OPERA I and II trials, 821 and 835 patients were respectively randomized to receive either intravenous ocrelizumab every 26 weeks or a subcutaneous interferon beta-1a injection three times a week for 96 weeks (44). In OPERA I and OPERA II, the annualized relapse rate was 46% and 47% lower, respectively, in the ocrelizumab group as compared to the interferon beta-1a group. The disability progression measured by EDSS was lower in the ocrelizumab group than in the interferon beta-1a group at 12 weeks (9.1% vs. 13.6%, 95% CI: 0.45 to 0.81, p< 0.001) and at 24 weeks (6.9% vs. 10.5%, 95% CI: 0.43 to 0.84, p=0.003). In OPERA I and OPERA II, the mean number of new gadolinium-enhancing lesions was 94% and 95% lower, respectively, in the ocrelizumab group as compared to the interferon beta-1a group.

Infections occurred in about 56.9% of patients on ocrelizumab and in 54.3% of patients on interferon beta-1a in OPERA I. A similar trend was observed in OPERA II. Upper respiratory infections, nasopharyngitis, and urinary tract infections were the most common infectious manifestations in both groups. Urinary tract infections were more common in patients on ocrelizumab (15.2%) than in patients on interferon beta-1a therapy (10.5%). Herpes virus infections occurred more commonly in patients on ocrelizumab (5.9%) than in patients on interferon beta-1a (3.4%) across both trials. In both trials, one third of patients (34% to 37%) in the ocrelizumab arm developed infusion reactions, most of which were mild to moderate and only one being a case of life-threatening bronchospasm, which resolved with symptomatic treatment. Over the course of both trials, four cases of malignancies (renal cell carcinoma, melanoma, and two invasive ductal breast cancers) occurred in the ocrelizumab groups and two (mantle cell lymphoma, squamous cell carcinoma in the chest) in the interferon beta-1a groups (44). As a result, the FDA issued a warning that the medication may be associated with a risk of malignancies. However, pooled data from multiple studies of ocrelizumab for multiple sclerosis involving 5680 patients with 18,218 years of treatment with ocrelizumab do not suggest an increased risk of malignancy in treated patients (47).

Ublituximab

Ublituximab is a glycoengineered chimeric monoclonal antibody with a novel epitope on CD20 resulting in higher antibody-dependent cell-mediated cytotoxicity than ocrelizumab or ofatumumab. Similar to ocrelizumab, ublituximab is an every-6-month intravenous infusion; however, it can be administrated in 60 minutes compared to the more extended duration of ocrelizumab infusion.

The identical phase III, randomized, double-blind trials ULTIMATE I and II were completed in 2022 (97). Taken together, these studies enrolled 1089 patients with RRMS with two or more relapses in the prior 2 years or one relapse in the prior year or one or more gadolinium-enhancing lesions. In ULTIMATE I and II, ublituximab had strong clinical effect in comparison to the active comparator teriflunomide, with annualized relapse rates of 0.08 and 0.09 or reductions of 59% and 49%, respectively. Contrast-enhancing lesions on MRI were reduced by 97% and 96%, and new or enlarging T2 lesions by 92% and 90%, respectively. Ublituximab was well tolerated; infusion reactions were predominantly mild and seen with the first infusion. Ublituximab was approved by the FDA in late 2022 and entered the market in 2023.

Treatment of primary progressive multiple sclerosis (PPMS)

PPMS is defined as progressive symptoms with disability progression over at least 12 months, without clinical relapse and having at least two of the following: one or more characteristic brain lesions, two or more characteristic spine lesions, or oligoclonal bands in the CSF (99). Although clinical trials for RRMS had relatively early success, the first (and only) disease-modifying therapy approved for PPMS was ocrelizumab in 2017. In the phase 3 ORATORIO trial, 732 patients with PPMS were randomized in a two to one fashion to receive ocrelizumab or placebo over 120 weeks (72). The percentage of patients with confirmed disability progression at 12 weeks served as the primary endpoint of the trial. At 12 weeks, 39.3% of the patients in the placebo arm reached the primary point, whereas only 32.9% of the patients in the ocrelizumab arm were confirmed to have disability progression. At 24 weeks, confirmed disability progression occurred in 35.7% of patients on placebo and 29.6% of patients on ocrelizumab. At 120 weeks, the performance of the 25-foot walks worsened by 38.9% in those on ocrelizumab versus 55.1% on placebo (72). No opportunistic infections occurred during the duration of the trial.

Four cases of breast cancer were recorded in 237 women in the ocrelizumab arm over the course of 2.3 years, whereas no cases were reported in the placebo group. To date, it is not known whether these cases were incidental or if these were in some way associated with the use of ocrelizumab. An FDA warning states that the medication may be associated with a risk of malignancies; however, pooled data from multiple studies of ocrelizumab for multiple sclerosis involving 5680 patients with 18,218 years of treatment with ocrelizumab do not suggest an increased risk of malignancy in treated patients (47).

Treatment of secondary progressive multiple sclerosis (SPMS)

Similar to the treatment of PPMS, treatment of progression in SPMS has been challenging. Although disease-modifying therapies approved for RRMS may continue to limit relapses, patients with SPMS also have slow worsening of disability and can experience this decline without clinical relapses (65). When considering therapeutic benefit in the SPMS population, it is important to consider clinical benefits from reducing relapses in those with active SPMS (defined by still having overt inflammatory activity, clinically manifest by relapses) versus implications of reducing slow progression without relapses.

Siponimod was approved for RRMS in 2019 and underwent further evaluation in a dedicated study of SPMS. In the EXPAND study, 1651 patients were randomly assigned (1105 to the siponimod group and 546 to the placebo group) (53). Out of the 1651 patients, 1645 patients were included in the analyses (1099 in the siponimod group and 546 in the placebo). At baseline, the mean time since first multiple sclerosis symptom was 16.8 years (SD 8.3), and the mean time since conversion to SPMS was 3.8 years (SD 3.5); 1055 (64%) patients had not relapsed in the previous 2 years, and 918 (56%) of 1651 needed walking assistance. Nine hundred and three (82%) patients receiving siponimod and 424 (78%) patients receiving placebo completed the study. Two hundred eighty-eight (26%) of 1096 patients receiving siponimod and 173 (32%) of 545 patients receiving placebo had 3-month confirmed disability progression (hazard ratio: 0.79, 95% CI: 0.65–0.95, relative risk reduction: 21%, p=0.013). Adverse events among patients taking siponimod included lymphopenia, increased liver transaminase concentration, bradycardia and bradyarrhythmia at treatment initiation, macular edema, hypertension, varicella zoster reactivation, and convulsions. Initial dose titration mitigated cardiac first-dose side effects. Frequency of infection, malignancy, and death did not significantly differ between the two groups.

Treatment of radiologically isolated syndrome

Radiologically isolated syndrome is defined by radiological findings consistent with multiple sclerosis on MRI for a patient without symptoms typical of multiple sclerosis. The first randomized controlled trial for the treatment of radiologically isolated syndrome was completed with the intent to delay or prevent the onset of first relapse. Eighty-seven patients were enrolled, with the key inclusion criteria meeting the 2009 Okuda radiologically isolated syndrome criteria. MRI anomalies were highly suggestive of CNS demyelination, with at least three of the following four features: 1) nine or more T2-weighted hyperintense lesions or one or more gadolinium-enhancing lesions; 2) three or more periventricular lesions; 3) one or more juxtacortical lesions; and 4) one or more infratentorial lesions (79). MRIs were evaluated by a central site. Participants were randomized to either dimethyl fumarate with 240 mg BID maintenance dosing or identical-appearing placebo. Demographics, adverse events, and rates of discontinuation were similar in each group. Time to first clinical relapse was the primary outcome as evaluated on intention to treat analysis. The hazard ratio for dimethyl fumarate versus placebo was 0.18 (95% CI: 0.05–0.63, p=0.007). No patients developed evidence of progression. MRI activity, as measured by new or enlarging T2 lesions at 96 weeks, was lower in the dimethyl fumarate group when adjusting for baseline gadolinium-enhancing lesion count. MRIs were not re-baselined after starting treatment (78). An additional study utilizing teriflunomide 14 mg daily versus placebo also demonstrated delay in time to first clinical event in patients with radiologically isolated syndrome meeting the Okuda criteria (HR: 0.37, 95% CI: 0.16–0.84; p=0.02) (61). Thus, teriflunomide provides another evidence-based disease-modifying therapy option for patients with radiologically isolated syndrome.

The treatment of radiologically isolated syndrome will continue to evolve. Of note, the MAGNIMS criteria have proposed using a definition for radiologically isolated syndrome less stringent than the Okuda criteria, with patients needing to meet only radiological dissemination in space criteria and be without typical multiple sclerosis symptoms (24). This may facilitate even earlier treatment but must be balanced with prognostic uncertainty and potential safety implications.

The future of multiple sclerosis treatment

The aforementioned therapies represent a great deal of progress in the treatment of multiple sclerosis, particularly regarding relapsing disease. Treatment of PPMS remains a major challenge. Although ocrelizumab was the first therapy approved for PPMS, its efficacy is relatively modest in comparison to its impact on relapsing multiple sclerosis. Similarly, treatment for secondary progressive multiple sclerosis is limited in options and in efficacy.

There are multiple strategies in development that aim to modulate pathways involved in CNS inflammation. Most prominent are small molecules targeting Bruton tyrosine kinase (BTK). At present, there are BTK inhibitors in clinical trials, including for relapsing and progressive multiple sclerosis. Other potential avenues for treatment include use of other immunosuppressive agents, such as alternative B-cell depletion strategies or, longer-term, modulation of immune system regulatory mechanisms via cell-based therapies (82; 63).

Beyond modification of the disease process itself, neuroprotective and neurorestorative (remyelination) therapies remain active areas of development. Ongoing efforts in this area include both the study of small molecules (such as clemastine for recovery from optic neuritis) and mesenchymal stem cells (43; 14).

Conclusions

The last 30 years of drug development in multiple sclerosis have revolutionized the treatment of a potentially devastating disease. Although there are many challenges remaining, including optimizing the selection and safety of disease-modifying therapy and treatment of progressive disease, patients now have an array of options that can make a real impact on the course of multiple sclerosis.

As we become more adept at managing the inflammatory components of multiple sclerosis, there is a need to shift our focus to manage, prevent, and potentially reverse the neurodegenerative aspects of multiple sclerosis.