Abstract
Autosomal dominant osteopetrosis type 2 (ADO2) is a rare inherited bone disorder characterised by dense but brittle bones. It displays striking phenotypic variability, with the most severe symptoms, including blindness and bone marrow failure. Disease management largely relies on symptomatic treatment since there is no safe and effective treatment. Most ADO2 cases are caused by heterozygous loss-of-function mutations in the CLCN7 gene, which encodes an essential Cl−/H+ antiporter for proper bone resorption by osteoclasts. Thus, siRNA-mediated silencing of the mutant allele is a promising therapeutic approach, but targeting bone for first-in-human translation remains challenging. Here, we demonstrate the utility of silicon-stabilised hybrid lipid nanoparticles (sshLNPs) as a next-generation nucleic acid nanocarrier capable of delivering allele-specific siRNA to bone. Using a Clcn7G213R knock-in mouse model recapitulating one of the most common human ADO2 mutations and based on the 129S genetic background (which produces the most severe disease phenotype amongst current models), we show substantial knockdown of the mutant allele in femur when siRNA targeting the pathogenic variant is delivered by sshLNPs. We observed lower areal bone mineral density in femur and reduced trabecular thickness in femur and tibia, when siRNA-loaded sshLNPs were administered subcutaneously (representing the most relevant administration route for clinical adoption and patient adherence). Importantly, sshLNPs have improved stability over conventional LNPs and enable ‘post hoc loading’ for point-of-care formulation. The treatment was well tolerated, suggesting that sshLNP-enabled gene therapy might allow successful clinical translation of essential new treatments for ADO2 and potentially other rare genetic bone diseases.
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Acknowledgements
A.M. is supported by the ‘Piano Operativo Nazionale (PON) Ricerca Innovazione’ (FSE-REACT EU D.M.1062).
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M.E., I.A., R.G.-O., and D.A. contributed to in vivo study design, study conduct, data analysis, and data interpretation. A.T. and A.M. designed the siRNA and contributed to assay development. S.S.-S., F.M.S., N.T.-P., A.D., P.B.-R., and L.I. contributed to study design and assay development; designed, produced, and evaluated the sshLNPs; and performed in vitro assays and organ analyses. All authors contributed to drafting and revision of the manuscript.
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S.S.-S. is CEO and shareholder of SiSaf Ltd. F.M.S., A.D., N.T.-P., and P.B.-R. are employees of SiSaf Ltd. A.T., A.M., L.I., and M.E. served or serve as consultants of SiSaf Ltd.
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Saffie-Siebert, S., Alam, I., Sutera, F.M. et al. Effect of Allele-Specific Clcn7G213R siRNA Delivered Via a Novel Nanocarrier on Bone Phenotypes in ADO2 Mice on 129S Background. Calcif Tissue Int (2024). https://doi.org/10.1007/s00223-024-01222-3
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DOI: https://doi.org/10.1007/s00223-024-01222-3