High Drug Loading, Reversible Disulfide Core-Cross-Linked Multifunctional Micelles for Triggered Release of Camptothecin.

Nanomedicines in polymeric therapeutics present a potential treatment for cancers. However, their clinical effectiveness still has room to be improved. Herein, reduction-responsive reversibly core-cross-linked micelles based on the poly(ethylene glycol)-dihydrolipoic acid (MeO-PEG2k-DHLA) conjugate were developed for triggered intracellular release of camptothecin (CPT). Coupling two molecules of dihydrolipoic acid (DHLA) to methyl-terminated PEG (Mw 2000) through a labile ester bond was performed by solution-phase condensation reaction. Due to the amphiphilic property, the MeO-PEG2k-DHLA conjugate formed micelles that were readily cross-linked with disulfide formation dispersed in water. These sole cross-linked micelles were 74.9 nm in hydrodiameter, as analyzed by dynamic light scattering (DLS). The nanostructures demonstrated excellent stability against extensive dilution, while rapidly dissociating under 10 mM glutathione (GSH), highlighting their potential for drug delivery. Interestingly, CPT was modified with a disulfide linkage and subsequently conjugated to the MeO-PEG2k-DHLA polymer scaffold. Core-cross-linking of the micelles achieved high drug loading of CPT (31.81%, wt %) and demonstrated that CPT release at pH 7.4 was significantly declined by cross-linking (i.e., less than 15% release in 24 h), whereas more than 90% of CPT was released under 10 mM GSH condition. In vitro cellular uptake and MTT assays showed that CPT-conjugated MeO-PEG2k-DHLA micelles were effectively internalized into tumor cells to induce the cytotoxic effects against HepG-2 and MCF-7 cells. Importantly, in vivo pharmacokinetics analysis demonstrated the nanoscale feature of micelles makes CPT to present longer retention time, resulting in a higher accumulation at tumor sites. Taken together, the disulfide core-cross-linked MeO-PEG2k-DHLA multifunctional micelles with high drug loading and excellent stability are potential candidates for tumor-targeting drug delivery.