Selective S1PR1/S1PR5 Modulation Impacts Neurologic Architecture/Function By Improving Kinematic Gait and Protecting from Neuronal Breaks in a Demyelinating Mouse Model

Background: Ozanimod, an oral, once-daily immunomodulator that selectively targets sphingosine-1-phosphate receptor 1 (S1P_R1) and S1P_R5, has shown therapeutic benefit in clinical trials of relapsing multiple sclerosis. Ozanimod down-regulates S1P_R1, retaining autoreactive lymphocytes in peripheral lymphoid tissues, and penetrates the blood-brain barrier, potentially conferring CNS benefits via S1P_R1 and S1P_R5.

Objectives: To assess the effects of ozanimod on motor function using the cuprizone mouse model.

Methods: C57BL/6 mice were treated concurrently with cuprizone (to demyelinate brain axons) and ozanimod (RPC1063; 0.1, 0.3, or 1 mg/kg orally once daily), ozanimod surrogate (RP-101074; 1 mg/kg orally once daily), or vehicle for 3–6 weeks. Motor function was assessed by kinematic gait analysis. Histological analysis of demyelinated neurons in the corpus callosum was assessed by SMI-32 staining to detect neuronal breaks and ovoid formation.

Results: Ozanimod improved functional assessment as evaluated by a kinematic gait analysis. Compared with vehicle-treated mice, those treated with ozanimod exhibited significant improvements in multiple parameters of gait analysis including tail-tip height, hind-limb jerk, and fore-limb trajectory. Overall kinematic gait score improved significantly in ozanimod-treated cuprizone mice vs. vehicle-treated cuprizone mice (P=0.0063, P=0.0086, and P=0.027 for ozanimod 0.1, 0.3, and 1.0 mg/kg, respectively). In an attempt to understand how S1P_R1/S1P_R5 modulation leads to improvements in kinematic gait, the effects of an ozanimod surrogate RP-101074 following cuprizone-induced demyelination were also examined. Histological analysis demonstrated reduced neuronal breaks and less neuronal ovoid formation when mice were treated with RP-101074 vs. vehicle (32 vs. 124 SMI-32–positive ovoids per 250,000 µm²; P<0.0001).

Conclusions:

Mice treated with ozanimod or its surrogate demonstrated improved functional capabilities and reduced neuronal breaks following cuprizone-induced demyelination. This work provides support that modulation of S1P_R1/S1P_R5 may potentially directly preserve CNS integrity and improve gait as shown through improved tail strength and hind-limb and fore-limb fluidity.