Promoting remyelination in multiple sclerosis

The greatest unmet need in multiple sclerosis (MS) are treatments that delay, prevent or reverse progression. One of the most tractable strategies to achieve this is to therapeutically enhance endogenous remyelination; doing so restores nerve conduction and prevents neurodegeneration. The biology of remyelination-centred on the activation, migration, proliferation and differentiation of oligodendrocyte progenitors-has been increasingly clearly defined and druggable targets have now been identified in preclinical work leading to early phase clinical trials. With some phase 2 studies reporting efficacy, the prospect of licensed remyelinating treatments in MS looks increasingly likely. However, there remain many unanswered questions and recent research has revealed a further dimension of complexity to this process that has refined our view of the barriers to remyelination in humans. In this review, we describe the process of remyelination, why this fails in MS, and the latest research that has given new insights into this process. We also discuss the translation of this research into clinical trials, highlighting the treatments that have been tested to date, and the different methods of detecting remyelination in people.

Lesion remyelinating activity of GSK239512 versus placebo in patients with relapsing-remitting multiple sclerosis: a randomised, single-blind, phase II study

Histamine H₃ receptor blockade may enhance lesion remyelination in multiple sclerosis (MS). The efficacy (using a magnetic resonance imaging marker of myelination, magnetisation transfer ratio [MTR]), safety and pharmacokinetics of GSK239512, a potent and brain penetrant H₃ receptor antagonist/inverse agonist on lesion remyelination in relapsing-remitting MS (RRMS) were assessed. This was a phase II, randomised, parallel-group, placebo-controlled, double-blind (sponsor-unblinded), international, multicentre study (NCT01772199). Patients aged 18-50 with RRMS, receiving intramuscular interferon-β1a or glatiramer acetate, were randomised 1:1 to once-daily oral GSK239512 or placebo, up-titrated over 4-5 weeks to a maximum tolerable dose up to 80 µg and maintained until Week 48. The co-primary endpoints were mean changes in post-lesion MTR in gadolinium-enhanced (GdE) or Delta-MTR defined lesions from pre-lesion values. Adverse events (AE) and withdrawals were monitored. Of the 131 patients randomised, 114 patients completed the study (GSK239512, n = 51; placebo, n = 63) and 27 (GSK239512) and 28 (placebo) patients contributed lesions to the primary analysis. GSK239512 was associated with positive effect sizes of 0.344 [90% confidence interval (CI) 0.018, 0.671] and 0.243 (90% CI -0.112, 0.598) for adjusted mean changes in the normalised MTR for GdE and Delta-MTR lesions, respectively. The overall incidence of AEs was similar between GSK239512 and placebo during the treatment phase although some AEs including insomnia were more common with GSK239512, particularly during the titration period. A small but positive effect of GSK239512 on remyelination was observed. MTR assessment represents a promising method for detecting lesion remyelination in RRMS.

Sample sizes for lesion magnetisation transfer ratio outcomes in remyelination trials for multiple sclerosis

BACKGROUND

Enhancing remyelination in MS might improve function and protect axons from future damage. Lesion magnetisation transfer ratio (MTR) is sensitive to myelin content, and may be a useful measure for trials evaluating potential remyelinating agents.

OBJECTIVE

Estimating sample sizes required for a parallel group, placebo-controlled trial in MS using change in mean MTR of all T2lesions as a primary outcome measure.

METHODS

The primary sample size calculation was derived from data from a natural history study of relapsing remitting MS (n=18). The MTR values observed in demyelinated and remyelinated lesions in an ex vivo study were used to estimate the effect of remyelination on lesion MTR. The ex vivo data were also used to independently calculate sample sizes in order to inform the robustness of the in vivo estimates.

RESULTS

Calculations suggest that 30% remyelination of T2 lesions could be detected with 80% power in 38 (95% confidence interval 12-96) patients per arm based on the in vivo data, and in 66 per arm based on the ex vivo data.

CONCLUSION

The sample sizes derived are in a range that makes MTR a feasible outcome measure for proof-of-concept trials of putative therapies achieving remyelination in MS lesions.

Periventricular magnetisation transfer abnormalities in early multiple sclerosis

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Periventricular-MTR gradients are present from the earliest stage of MS and become steeper in advanced disease.

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Lower MTR in periventricular-NAWM was positively associated with reduced cortical-mean-thickness.

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MTR in periventricular-lesions scaled with cortical-mean-thickness, while non-periventricular lesions were unrelated.

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These findings suggest a common pathophysiologic mechanism between CSF-adjacent cortical and periventricular areas.

Objective

Recent studies suggested that CSF-mediated factors contribute to periventricular (PV) T2-hyperintense lesion formation in multiple sclerosis (MS) and this in turn correlates with cortical damage. We thus investigated if such PV-changes are observable microstructurally in early-MS and if they correlate with cortical damage.

Methods

We assessed the magnetisation transfer ratio (MTR) in PV normal-appearing white matter (NAWM) and in MS lesions in 44 patients with a clinically isolated syndrome (CIS) suggestive of MS and 73 relapsing-remitting MS (RRMS) patients. Band-wise MTR values were related to cortical mean thickness (CMT) and compared with 49 healthy controls (HCs). For each band, MTR changes were assessed relative to the average MTR values of all HCs.

Results

Relative to HCs, PV-MTR was significantly reduced up to 2.63% in CIS and 5.37% in RRMS (p < 0.0001). The MTR decreased towards the lateral ventricles with 0.18%/mm in CIS and 0.31%/mm in RRMS patients, relative to HCs. In RRMS, MTR-values adjacent to the ventricle and in PV-lesions correlated positively with CMT and negatively with EDSS.

Conclusion

PV-MTR gradients are present from the earliest stage of MS, consistent with more pronounced microstructural WM-damage closer to the ventricles. The positive association between reduced CMT and lower MTR in PV-NAWM suggests a common pathophysiologic mechanism. Together, these findings indicate the potential use of multimodal MRI as refined marker for MS-related tissue changes.

Sulcal and gyral crown cortical grey matter involvement in multiple sclerosis: A magnetisation transfer ratio study

BACKGROUND

Histopathology has demonstrated extensive cortical grey matter (GM) demyelination in multiple sclerosis (MS), and suggests that sulcal folds may be preferentially affected, particularly in progressive MS. This has not been confirmed in vivo, and it is not known if it is relevant to clinical status.

OBJECTIVES

To determine sulcal and gyral crown magnetisation transfer ratio (MTR) in MS cortical GM, and the MTR associations with clinical status.

METHODS

We measured sulcal and gyral crown cortical GM MTR values in 61 MS patients and 32 healthy controls. Disability was measured using Expanded Disability Status Scale and Multiple Sclerosis Functional Composite scores.

RESULTS

MTR values were reduced in sulcal and gyral crown regions in all MS subtypes, more so in secondary progressive (SP) MS than relapsing remitting (RR) MS, and similarly in primary progressive (PP) MS and RRMS. Sulcal MTR was lower than gyral crown MTR in controls, PPMS and RRMS patients, but not in SPMS. MTR correlated with clinical status in RRMS and SPMS, but not PPMS.

CONCLUSIONS

Cortical pathology, as reflected by MTR, is present in all MS subtypes and most pronounced in SPMS. A preferential disease effect on sulcal cortical regions was not observed. Cortical MTR abnormalities appear to be more clinically relevant in relapse-onset rather than progressive-onset MS.

Disability in progressive MS is associated with T2 lesion changes

BACKGROUND

Progressive multiple sclerosis (MS) is characterised by diffuse changes on brain magnetic resonance imaging (MRI), which complicates the use of MRI as a diagnostic and prognostic marker. The relationship between MRI measures (conventional and non-conventional) and clinical disability in progressive MS therefore warrants further investigation.

OBJECTIVE

To investigate the relationship between clinical disability and MRI measures in patients with progressive MS.

METHODS

Data from 93 primary and secondary progressive MS patients who had participated in 3 phase 2 clinical trials were included in this cross-sectional study. From 3T MRI baseline scans we calculated total T2 lesion volume and analysed magnetisation transfer ratio (MTR) and the diffusion tensor imaging indices fractional anisotropy (FA) and mean diffusivity (MD) in T2 lesions, normal-appearing white matter (NAWM) and cortical grey matter. Disability was assessed by the Expanded Disability Status Scale (EDSS) and the MS functional composite.

RESULTS

T2 lesion volume was associated with impairment by all clinical measures. MD and MTR in T2 lesions were significantly related to disability, and lower FA values correlated with worse hand function in NAWM. In multivariable analyses, increasing clinical disability was independently correlated with increasing T2 lesion volumes and MTR in T2 lesions.

CONCLUSION

In progressive MS, clinical disability is related to lesion volume and microstructure.