Agonist-induced activation of the S1P receptor 2 constitutes a novel osteoanabolic therapy for the treatment of osteoporosis in mice

Background and purpose: Osteoporosis is a worldwide epidemic but pharmacological agents to stimulate new bone formation are scarce. We have shown that increasing tissue levels of sphingosine-1-phosphate (S1P) by blocking its degradation by the S1P lyase has pronounced osteoanabolic effect in mouse osteoporosis models by stimulating osteoblast differentiation through the S1P receptor 2 (S1P2). However, S1P lyase inhibitors have side effects complicating potential clinical use. Here, we tested whether direct S1P2 engagement by the S1P2 agonist CYM5520 exerted osteoanabolic potential in estrogen deficiency-induced osteopenia in mice. We compared its efficacy to LX2931, a novel S1P lyase inhibitor currently tested in rheumatoid arthritis.

Experimental approach: CYM5520, LX2931 or vehicle were administered to ovariectomized mice for 6 weeks beginning 5 weeks after ovariectomy, Bone mass, cellular composition and mechanical strength were assessed by microCT, histomorphometry and three point bending tests. Plasma markers of bone metabolism were analyzed by ELISA.

Key results: Therapeutic treatment with CYM5520 and LX2931 clearly increased long bone and vertebral bone mass to impressive 3-5 fold over vehicle in osteopenic ovariectomized mice. As expected, lymphopenia was a side effect of LX2931, whereas none occurred with CYM5520. Consistent with an osteoanabolic effect, CYM5520 increased osteoblast number, osteoid surface and Alkaline Phosphatase area 2-3 fold over vehicle. Plasma concentrations of the osteoanabolic marker procollagen I C-terminal propeptide were also elevated by CYM5520 and LX2931. LX2931 but not yet CYM5520 increased cortical thickness and mechanical strength without affecting mineral density.

Conclusion and implications: Treatment with a pharmacological S1P2 agonist corrected ovariectomy-induced osteopenia in mice by inducing new bone formation thus constituting a novel osteoanabolic approach to osteoporosis.