Solid Phase Extraction as an Innovative Separation Method for Measuring Free and Entrapped Drug in Lipid Nanoparticles

Contrary to physical characterization techniques for nanopharmaceuticals (shape, size and zeta-potential), the techniques to quantify the free and the entrapped drug remain very few and difficult to transpose in routine analytical laboratories. The application of Solid Phase Extraction (SPE) technique was investigated to overcome this challenge. The separation of free and entrapped drug by SPE was quantitatively validated by High Performance Liquid Chromatography. The developed protocol was implemented to characterize cyclosporine A-loaded 120 nm-sized lipid nanoparticles (LNPs, LipidotA (R)) dispersed in aqueous buffer. The colloidal stability was assessed by Dynamic Light Scattering (DLS). Validation experiments demonstrated suitable linearity, repeatability, accuracy and specificity to quantify residual free, entrapped and total drug. For the investigated LNPs, the method revealed a very limited shelflife of the formulation when stored in an aqueous buffer at 5A degrees C and even more at elevated temperature. Nevertheless, the DLS measurements confirmed the stability of nanoparticles during SPE in a suitable concentration range. SPE, when successfully validated, represents a valuable tool for drug development and quality control purposes of lipid-based nanopharmaceuticals in an industrial environment.