A Novel Self-Assembled Paclitaxel Nanodispersion Facilitates Rapid In-Vitro/In-Vivo Dissociation and Protein Binding

The study aims to prepare and characterize a novel paclitaxel (PtX) preconcentrate formulation using polymer and lipid excipients that forms nanodispersion upon dilution. The goal was to understand the mechanism of nanodispersion formation and its properties. The water-insoluble PtX was dissolved in organic solvents containing ethanol, polyethylene glycol (PEG400), povidone (PVP), caprylic acid (CA), and sodium cholesterol sulfate (CS). This formulation was diluted in 5% w/v dextrose medium to form PtX nanodispersion, which was assessed for particle size, stability, in-vitro/in-vivo dissociation and protein binding. Transmission electron microscopy (TEM), Small Angle Neutron Scattering (SANS), and Molecular Dynamics (MD) simulations were used to analyse the structure of the nanoparticles. The formulation was a clear, slightly yellow solution. The PtX nanodispersion displays particle size of ~ 100 nm with a zeta potential of -25, and the pH of 4.0. It displayed nearly spherical coacervate nanoparticles with a sponge-like structure, lacking internal structure order as revealed by TEM and SANS. MD simulations confirmed self-assembly of PtX and excipients forming nanoparticles. In vitro dissociation studies in simulated plasma demonstrated rapid dissociation of nanodispersion, releasing free PtX that immediately binds to plasma proteins. In vivo studies in rabbits corroborated these findings, showing rapid dissolution. The results present a novel formulation design that forms sponge-like coacervate nanoparticle due to complimentary interactions of the excipients that otherwise are unable to self-assemble under similar conditions of dilution. This alternative formulation solves the limitations of currently marketed PtX products and can provide its effective delivery in clinical settings.