A four-stage process that identified a hydroxypropyl beta cyclodextrin and polysorbate containing formulation that eliminated aggregation of recombinant human NELL-1 after exposure to extrinsic stresses

Abstract Background Recombinant human NELL-1 (rhNELL-1) is a potent osteogenic protein with therapeutic potential in regenerative medicine. A stable formulation is essential to prevent aggregation during production, filling, storage, and clinical use. Methodology A four-stage rational formulation strategy was used: (1) identify intrinsic aggregation risks of rhNELL-1; (2) screen polysorbate- and cyclodextrin-based formulations to enhance colloidal and conformational stability; (3–4) test lead candidates under agitation, freeze/thaw, pH shifts, and elevated temperature. Analytical techniques included PEG challenge, differential scanning fluorimetry (DSF), isothermal chemical denaturation (ICD), and dynamic light scattering (DLS). Aggregation was assessed via visible particles (VP), opalescence, subvisible particles (SVP, Micro Flow Imaging), SDS-PAGE, and ultra-high performance size exclusion chromatography (UP-SEC). Results rhNELL-1 was prone to self-association via hydrophobic and electrostatic interactions. Polysorbate 20 (PS20) and hydroxypropyl beta cyclodextrin (HPB-LB-BCD) improved protein stability. PS20 markedly reduced VP and SVP formation. While HPB-LB-BCD alone did not further reduce SVP beyond PS20, it enhanced thermal stress resistance. PS20 was more effective under agitation. Conclusions Two lead formulations containing potassium phosphate/Tris buffer, sorbitol, PS20, and HPB-LB-BCD demonstrated strong resistance to aggregation under multiple stresses. PS20 mitigated interfacial stress, while HPB-LB-BCD suppressed solution-phase aggregation, especially at high temperatures. This systematic approach offers a framework for stabilizing other aggregation-prone proteins.