Remibrutinib (LOU064) inhibits neuroinflammation driven by B cells and myeloid cells in preclinical models of multiple sclerosis.

BACKGROUND: Bruton's tyrosine kinase (BTK) is a key signaling node in B cell receptor (BCR) and Fc receptor (FcR) signaling. BTK inhibitors (BTKi) are an emerging oral treatment option for patients suffering from multiple sclerosis (MS). Remibrutinib (LOU064) is a potent, highly selective covalent BTKi with a promising preclinical and clinical profile for MS and other autoimmune or autoallergic indications. METHODS: The efficacy and mechanism of action of remibrutinib was assessed in two different experimental autoimmune encephalomyelitis (EAE) mouse models for MS. The impact of remibrutinib on B cell-driven EAE pathology was determined after immunization with human myelin oligodendrocyte glycoprotein (HuMOG). The efficacy on myeloid cell and microglia driven neuroinflammation was determined in the RatMOG EAE. In addition, we assessed the relationship of efficacy to BTK occupancy in tissue, ex vivo T cell response, as well as single cell RNA-sequencing (scRNA-seq) in brain and spinal cord tissue. RESULTS: Remibrutinib inhibited B cell-dependent HuMOG EAE in dose-dependent manner and strongly reduced neurological symptoms. At the efficacious oral dose of 30 mg/kg, remibrutinib showed strong BTK occupancy in the peripheral immune organs and in the brain of EAE mice. Ex vivo MOG-specific T cell recall response was reduced, but not polyclonal T cell response, indicating absence of non-specific T cell inhibition. Remibrutinib also inhibited RatMOG EAE, suggesting that myeloid cell and microglia inhibition contribute to its efficacy in EAE. Remibrutinib did not reduce B cells, total Ig levels nor MOG-specific antibody response. In brain and spinal cord tissue a clear anti-inflammatory effect in microglia was detected by scRNA-seq. Finally, remibrutinib showed potent inhibition of in vitro immune complex-driven inflammatory response in human microglia. CONCLUSION: Remibrutinib inhibited EAE models by a two-pronged mechanism based on inhibition of pathogenic B cell autoreactivity, as well as direct anti-inflammatory effects in microglia. Remibrutinib showed efficacy in both models in absence of direct B cell depletion, broad T cell inhibition or reduction of total Ig levels. These findings support the view that remibrutinib may represent a novel treatment option for patients with MS.

Central Versus Peripheral Drug Exposure Ratio, a Key Differentiator for Siponimod Over Fingolimod?

INTRODUCTION: Siponimod, a potent and selective sphingosine-1-phosphate (S1P1,5) agonist, is the only therapeutic agent that has shown efficacy against disability progression, decline in cognitive processing speed, total brain volume loss, gray matter atrophy and signs of demyelination in patients with secondary progressive multiple sclerosis (SPMS). Although the pathophysiology of progression in SPMS and primary progressive MS (PPMS) is thought to be similar, fingolimod, the prototype S1P1,3,45 agonist, failed to show efficacy against disability progression in PPMS. Differentiating siponimod from fingolimod at the level of their central effects is believed to be the key to a better understanding of the underlying characteristics that could make siponimod uniquely efficacious in progressive MS (PMS). METHODS: Here, we compared the central vs. peripheral dose-dependent drug exposures for siponimod and fingolimod in healthy mice and mice with experimental autoimmune encephalomyelitis (EAE). RESULTS: Siponimod treatment achieved dose-dependent efficacy and dose-proportional increases in steady-state drug blood levels, with a central nervous system (CNS)/blood drug-exposure ratio (CNS/bloodDER) of ~ 6 in both healthy and EAE mice. In contrast, fingolimod treatments achieved dose-proportional increases in fingolimod and fingolimod-phosphate blood levels, with respective CNS/bloodDER that were markedly increased (≥ threefold) in EAE vs. healthy mice. CONCLUSION: If proven to have translational value, these observations would suggest that CNS/bloodDER may be a key differentiator for siponimod over fingolimod for clinical efficacy in PMS.

Increased Remyelination and Proregenerative Microglia Under Siponimod Therapy in Mechanistic Models.

BACKGROUND AND OBJECTIVES: Siponimod is an oral, selective sphingosine-1-phosphate receptor-1/5 modulator approved for treatment of multiple sclerosis. METHODS: Mouse MRI was used to investigate remyelination in the cuprizone model. We then used a conditional demyelination Xenopus laevis model to assess the dose-response of siponimod on remyelination. In experimental autoimmune encephalomyelitis-optic neuritis (EAEON) in C57Bl/6J mice, we monitored the retinal thickness and the visual acuity using optical coherence tomography and optomotor response. Optic nerve inflammatory infiltrates, demyelination, and microglial and oligodendroglial differentiation were assessed by immunohistochemistry, quantitative real-time PCR, and bulk RNA sequencing. RESULTS: An increased remyelination was observed in the cuprizone model. Siponimod treatment of demyelinated tadpoles improved remyelination in comparison to control in a bell-shaped dose-response curve. Siponimod in the EAEON model attenuated the clinical score, reduced the retinal degeneration, and improved the visual function after prophylactic and therapeutic treatment, also in a bell-shaped manner. Inflammatory infiltrates and demyelination of the optic nerve were reduced, the latter even after therapeutic treatment, which also shifted microglial differentiation to a promyelinating phenotype. DISCUSSION: These results confirm the immunomodulatory effects of siponimod and suggest additional regenerative and promyelinating effects, which follow the dynamics of a bell-shaped curve with high being less efficient than low concentrations.