SFRP1-Silencing GapmeR-Loaded Lipid-Polymer Hybrid Nanoparticles for Bone Regeneration in Osteoporosis: Effect of Dosing and Targeting Strategy.

Introduction: Osteoporosis is a metabolic disorder characterized by the loss of bone mass and density. Nucleic acid-based therapies are among the most innovative approaches for osteoporosis management, although their effective delivery to bone tissue remains a challenge. In this work, SFRP1-silencing GampeR loaded-nanoparticles were prepared and functionalized with specific moieties to improve bone targeting and, consequently, therapeutic efficacy. SFRP1-silencing would promote osteoblastic differentiation by enhancing the WNT/β-catenin pathway and thus diminishing the progression of osteoporosis. Methods: A nucleic acid-based delivery system consisting of lipid-polymer hybrid nanoparticles (LPNPs) loading a GapmeR for SFRP1 silencing was developed and further functionalized with two bone-targeting moieties: a specific aptamer (Apt) for murine mesenchymal stem cells and an antiresorptive drug, namely alendronate (ALD). These systems were tested in vivo in osteoporotic mice at different dosage regimens to analyze dose dependence in bone-forming activity and potential toxicity. The quality of trabecular and cortical bone was assessed by both micro computed tomography (micro-CT) and histological and histomorphometric analyses. Early and late osteogenesis were quantified by immunohistochemistry. Results: Results showed that functionalizing LPNPs loaded with an SFRP1-silencing GapmeR using both Apt and ALD improved bone quality and enhanced osteogenesis following a dose-effect relationship, as revealed by micro-CT, histological and immunohistochemical analyses. In contrast, non-functionalized LPNPs did not produce these effects. Conclusion: These findings highlight the relevance of proper targeting and dosage in nucleic acid-based therapeutics, proving to be crucial for exerting their therapeutic effect: a deficient targeting strategy and/or dosage may result in the therapeutic failure of an adequate gene therapy agent.