Porcupine inhibition is a promising pharmacological treatment for severe sclerosteosis pathologies

Sclerosteosis, an ultra-rare disorder characterised by high bone mass (HBM) and skeletal overgrowth, leads to facial paralysis, hearing loss and raised intracranial pressure, which is currently managed only through high-risk surgery. Sclerosteosis is caused by SOST mutations and loss of functional sclerostin, a protein that suppresses osteogenesis by antagonising Wnt/β-catenin signalling. Herein, using in vitro and in vivo approaches, we explore whether LGK974, another potent Wnt inhibitor that targets porcupine (PORCN, Wnt-specific acyltransferase), is a promising sclerosteosis therapeutic. In vitro assays showed that 100 nmol/L LGK974 significantly reduced osteoblast alkaline phosphatase (ALP) activity/mineralisation, decreased Wnt/osteoblast marker (Axin2, Runx2 and Ocn) expression, and downregulated ossification and the Wnt signalling pathway, without affecting osteoclast numbers/resorption. To assess in vivo effects, 6-week-old male and female Sost deficient (Sost^-/-) mice received LGK974 for 4 weeks and right hindlimbs were subjected to 20 N peak loading to assess mechanoadaptive interactions. µCT revealed significant reductions in vertebral trabecular number and lower cortical bone volume in loaded and non-loaded tibiae in male and female LGK974-treated Sost^-/- mice. Interestingly, the target engagement biomarker Axin2 was only significantly reduced in male vertebrae, which may indicate differences in male and female response to LGK974. This study also shows that PORCN inhibition may effectively limit characteristic HBM and skeletal overgrowth in sclerosteosis patients at sites with severe pathology.