Multi-kinetic analysis reveals drug release and structural dissociation behaviors of paclitaxel-loaded polymeric micelles

Polymeric micelles (PMs) may undergo structural dissociation with concurrent release and redistribution of payload and carrier material, processes that are difficult to resolve by conventional bulk pharmacokinetic analysis. Here, paclitaxel (PTX)-loaded methoxy poly(ethylene glycol)-poly(D,L-lactide) (mPEG-PLA) PMs were used to investigate the multi-kinetic interplay among drug payload, copolymer material, and PM particles during serum incubation and after intravenous administration. Serum was separated by gradient density ultracentrifugation (GDUC) into lipoprotein-rich, PM-density, and lipoprotein-deficient serum (LPDS) fractions. PTX and mPEG-PLA in each fraction were quantified by LC–Q-TOF/MS, whereas PM particles in the validated PM-density fraction were assessed by ACQ1-based fluorescence bioimaging. During in vitro serum incubation, separated PMs largely maintained their initial PTX-to-micelle ratio; released PTX redistributed mainly to LPDS, while part of the mPEG-PLA shifted toward HDL and LPDS. After intravenous administration, the PTX-to-micelle ratio declined rapidly, whereas mPEG-PLA and PM-associated fluorescence persisted longer, revealing early drug–carrier uncoupling. These findings demonstrate that PTX release, carrier–material redistribution, and PM disposition are interconnected but asynchronous. Fraction-resolved integration of PTX pharmacokinetics, mPEG-PLA materiokinetics, and PM particokinetics provides mechanistic information beyond bulk pharmacokinetics or particle tracking alone and offers a practical framework for evaluating drug-loaded PM formulations. A refined gradient density ultracentrifugation strategy integrating LC–Q-TOF/MS and ACQ fluorescence imaging enables fraction-resolved analysis of paclitaxel, carrier material, and polymeric micelles. Comparative multi-kinetic analysis reveals distinct drug–carrier behaviors during serum incubation and systemic circulation, highlighting asynchronous drug release, carrier redistribution, and particle disposition. Download: Download high-res image (300KB) Download: Download full-size image