[Siponimod: a new view at the therapy of secondary progressive multiple sclerosis]

The mitochondriogenic but not the immunosuppressant effects of mTOR inhibitors prompt neuroprotection and delay disease evolution in a mouse model of progressive multiple sclerosis

INTRODUCTION

Purportedly, the progression of multiple sclerosis (MS) occurs when neurodegenerative processes due to derangement of axonal bioenergetics take over the autoimmune response. However, a clear picture of the causative interrelationship between autoimmunity and axonal mitochondrial dysfunction in progressive MS (PMS) pathogenesis waits to be provided.

METHODS

In the present study, by adopting the NOD mouse model of PMS, we compared the pharmacological effects of the immunosuppressants dexamethasone and fingolimod with those of mTOR inhibitors rapamycin and everolimus that, in addition to immunosuppression, also regulate mitochondrial functioning. Female Non-Obese Diabetic (NOD) mice were immunized with MOG35-55 and treated with drugs to evaluate functional, immune and mitochondrial parameters during disease evolution.

RESULTS

We found that dexamethasone and fingolimod did not affect the pattern of progression as well as survival. Conversely, mTOR inhibitors rapamycin and everolimus delayed disease progression and robustly extended survival of immunized mice. The same effects were obtained when treatment was delayed by 30 days after immunization. Remarkably, dexamethasone and fingolimod prompted the same degree of immunosuppression of rapamycin within both spleen and spinal cord of mice. However, only rapamycin prompted mitochondriogenesis by increasing mitochondrial content, and expression of several mitochondrial respiratory complex subunits, thereby preventing mtDNA reduction in the spinal cords of immunized mice. These pharmacodynamic effects were not reproduced in healthy NOD mice, suggesting a disease context-dependent pharmacodynamic effect.

DISCUSSION

Data corroborate the key role of mitochondriogenesis to treatment of MS progression, and for the first time disclose the translational potential of mTOR inhibitors in PMS therapy.

Siponimod for multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a chronic immune-mediated disease of the central nervous system, with an unpredictable course. Current MS therapies such as disease-modifying therapies focus on treating exacerbations, preventing new exacerbations and avoiding the progression of disability. Siponimod (BAF312) is an oral treatment, a selective sphingosine-1-phosphate (S1P) receptor modulator, for the treatment of adults with relapsing forms of MS including active, secondary progressive MS with relapses.

OBJECTIVES

To assess the benefits and adverse effects of siponimod as monotherapy or combination therapy versus placebo or any active comparator for people diagnosed with MS.

SEARCH METHODS

On 18 June 2020, we searched the Cochrane Multiple Sclerosis and Rare Diseases of the CNS Trials Register, which contains studies from CENTRAL, MEDLINE and Embase, and the trials registry databases ClinicalTrials.gov and WHO International Clinical Trials Registry Platform (ICTRP). We also handsearched relevant journals and screened the reference lists of published reviews and retrieved articles and searched reports (2004 to June 2020) from the MS societies in Europe and America.

SELECTION CRITERIA

We included randomised parallel controlled clinical trials (RCTs) that evaluated siponimod, as monotherapy or combination therapy, versus placebo or any active comparator in people with MS. There were no restrictions on dose or administration frequency.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. We discussed disagreements and resolved them by consensus among the review authors. Our primary outcomes wereworsening  disability , relapse and adverse events, and secondary outcomes were annualised relapse rate, gadolinium-enhancing lesions, new lesions or enlarged pre-existing lesions and mean change of brain volume. We independently evaluated the certainty of evidence using the GRADE approach. We contacted principal investigators of included studies for additional data or confirmation of data.

MAIN RESULTS

Two studies (1948 participants) met our selection criteria, 608 controls and 1334 treated with siponimod. The included studies compared siponimod with placebo. Overall, all studies had a high risk of bias due to selective reporting and attrition bias.  Comparing siponimod administered at a dose of 2 mg to placebo, we found that siponimod may reduce the number of participants with disability progression at six months (56 fewer people per 1000; risk ratio (RR) 0.78, 95% confidence interval (CI) 0.65 to 0.94; 1 study, 1641 participants; low-certainty evidence) and annualised relapse rate (RR 0.43, 95% CI 0.34 to 0.56; 2 studies, 1739 participants; low-certainty evidence). But it might lead to little reduction in the number of participants with new relapse (166 fewer people per 1000; RR 0.38, 95% CI 0.15 to 1.00; 1 study, 94 participants; very low-certainty evidence). We observed no evidence of a difference   due to adverse events for siponimod at 2 mg compared to placebo (14 more people per 1000; RR 1.52, 95% CI 0.85 to 2.71; 2 studies, 1739 participants, low-certainty evidence). In addition, due to the high risk of inaccurate magnetic resonance imaging (MRI) data in the two included studies, we could not combine data for active lesions on MRI scans. Both studies had high attrition bias resulting from the unbalanced reasons for dropouts among groups and high risk of bias due to conflicts of interest. Siponimod may reduce the number of gadolinium-enhancing T1-weighted lesions at two years of follow-up (RR 0.14, 95% CI 0.10 to 0.19; P < 0.0001; 1 study, 1641 participants; very low-certainty evidence). There may be no evidence of a difference between groups in the number of participants with at least one serious adverse event excluding relapses (113 more people per 1000; RR 1.80, 95% CI 0.37 to 8.77; 2 studies, 1739 participants; low-certainty evidence) at six months. No data were available regarding cardiac adverse events. In terms of safety profile, the most common adverse events associated with siponimod were headache, back pain, bradycardia, dizziness, fatigue, influenza, urinary tract infection, lymphopenia, nausea, alanine amino transferase increase and upper respiratory tract infection. These adverse events have dose-related effects and rarely led to discontinuation of treatment.

AUTHORS' CONCLUSIONS

Based on the findings of the RCTs included in this review, we are uncertain whether siponimod interventions are beneficial for people with MS. There was low-certainty evidence to support that siponimod at a dose of 2 mg orally once daily as monotherapy compared with placebo may reduce the annualised relapse rate and the number of participants who experienced disability worsening, at 6 months. However, the certainty of the evidence to support the benefit in reducing the number of people with a relapse is very low.  The risk of withdrawals due to adverse events requires careful monitoring of participants over time. The duration of all studies was less than 24 months, so the efficacy and safety of siponimod over 24 months are still uncertain, and further exploration is needed in the future. There is no high-certainty data available to evaluate the benefit on MRI outcomes. We assessed the certainty of the body of evidence for all outcomes was low to very low, downgraded due to serious study limitations, imprecision and indirectness. We are uncertain whether siponimod is beneficial for people with MS. More new studies with robust methodology and longer follow-up are needed to evaluate the benefit of siponimod for the management of MS and to observe long-term adverse effects. Also, in addition to comparing with placebo, more new studies are needed to evaluate siponimod versus other therapeutic options.