UCLA

NELL-1 is an osteogenic, secretory molecule previously shown to enhance bone regeneration in multiple rodent and ovine orthopedic defect models. Excitingly, we have recently shown that systemic delivery of NELL-1 induces robust bone formation in healthy and osteoporotic mice; however, like other cytokine therapies, NELL-1 has a relatively short half-life requiring a frequent dosing schedule (q2d). Here, we investigate the potential of PEGylation, a chemical process of adding polyethylene glycol (PEG), to improve NELL-1's pharmacokinetics, while maintaining bioactivity. Three different PEGylation patterns (5K-linear, 20K-linear, and 40K-branched) were covalently attached to NELL-1. First, thermostability and bioactivity of PEG-NELL-1 was compared to unmodified NELL-1 in vitro. Next, we evaluated the biological half-life and osteogenic potential of systemically administered PEG-NELL-1 (5K-linear, 1.25mg/kg, i.v., q4d and q7d) in healthy mice. To monitor the changes in bone mineral density (BMD) and bone turnover rate in vivo, dual-energy X-ray absorptiometry (DXA) and microPET/CT bone scans was performed weekly. Animals were sacrificed after four weeks of treatment for microCT and histological analyses. PEGylation was observed to improve thermostability and biological half-life, while retaining in vitro bioactivity of NELL-1 protein comparable to unmodified NELL-1. In vivo, systemic PEG-NELL-1 therapy significantly increased femoral and lumbar BMD as well as bone turnover rate at overall skeletal sites after four weeks of treatment. MicroCT confirmed significant increases in trabecular BMD and fractional bone volume in PEG-NELL-1-treated groups. Further, immunohistochemistry revealed an increase in osteocalcin expression, while TRAP staining showed a reduction in osteoclast number in PEG-NELL-1 groups. Collectively, PEGylation significantly extends NELL-1's half-life, while retaining osteoinductive potential. Thus, PEG-NELL-1 holds promise for non-invasive, wide clinical application for the treatment of osteopenic disorders.