Organelle-Level Trafficking and Metabolism Kinetics for Redox-Responsive Paclitaxel Prodrug Nanoparticles Characterized by Experimental and Modeling Analysis

Redox-responsive self-assembled prodrug nanoparticles have received extensive attention for their high loading efficiency and environmentally responsive properties. However, the intracellular metabolism and transportation kinetics were poorly understood, which limited the rational design and development of this delivery system. Herein, tetraphenylporphyrin-paclitaxel (TxP) prodrugs with thioether, disulfide, and dicarbon linkers (TsP, TssP, and TccP) were synthesized and self-assembled as nanoparticles. The redox responsiveness was investigated both in the simulated medium and in tumor cells via mass spectrometry. TxP NP and PTX concentrations in 4T1 whole cells, endosomal systems, and cytoplasm over time were quantified by UPLC-MS/MS and modeled using the nonlinear mixed effect (NLME) approach. Cytotoxicity was studied in 4T1 and MCF-7 cell lines, and antitumor efficacy was analyzed in 4T1 tumor-bearing mice. Mass spectrometry identified both oxidative and reductive metabolites in redox simulants for TssP NPs and TsP NPs. In 4T1 cells, only reductive metabolites for TssP NPs were detected, while both oxidative and reductive metabolites for TsP NPs were detected. The developed subcellular pharmacokinetic model suggested that the estimated metabolism rates of TxP NPs in endosomal systems were 10 to 27 times of the rates in cytoplasm, indicating that endosomal systems were the dominant place for intracellular metabolism. These rates were numerically higher for TsP NPs than TssP NPs in endosomal systems (1.7-fold) and the cytoplasm (2.5-fold). The internalization of nanoparticles was identified to be slow (k_max,int, 0.015 h^-1) and saturable. The transportation rate constant across the endosomal membranes was fast for PTX (27.1 h^-1) and slow for TxP NPs (0.098 h^-1). TsP and TssP NPs had comparable in vivo antitumor efficacy, which was higher than that of TccP NPs. This study quantified the organelle-level transportation and metabolism kinetics for three prodrug nanoparticles with redox-responsive or inert linkers using a combined experimental and modeling approach. These findings and the modeling framework might inform future studies for redox-responsive prodrug design and drug delivery systems.