Chemotherapeutic drugs have been shown to be promising for the treatment of tumors, however, they are associated with several disadvantages including low aqueous solubility, non-specificity, and poor plasma stability. Hence, they accumulate in the health organs and create several adverse effects. Drug encapsulated stimuli-responsive nanoparticles bearing redox-responsive disulfide linkages have emerged as promising delivery vehicle to address these limitations. A glutathione (GSH) responsive disulfide-based drug delivery system based on a polyethylene glycol methyl ether (PEGME) and a polydisulfide (PDS) diblock copolymer has been developed. The cyclic lactone containing a disulfide link, 1,4,5-oxadithiepan-2-one, was prepared using a thiol-free method utilizing the reaction of 2-bromoethyl bromoacetate with sodium disulfide. Ring-opening polymerization (ROP) of 1,4,5-oxadithiepan-2-one using 1-butanol in the presence of Sn(oct)2 generated the homopolymer PDS whereas the diblock copolymer PEGME-b-PDS was obtained when PEGME was used as a macroinitiator. In aqueous solution, PEGME-b-PDS self-assembled into spherical-shaped micelles with a hydrodynamic radius of 146 and 116 nm as measured by Field-emission Scanning Electron Microscopy (FESEM) and Dynamic Light Scattering (DLS), respectively. At pH = 7.4, a Doxorubicin (DOX) loaded PEGME-b-PDS micelle showed a cumulative release of ∼98.2, ∼9.9, and ∼1.9 % in presence of 2 mM, 2 μM DTT and in absence of DTT, respectively clearly demonstrating the redox responsiveness of the PDS block. The best fit of kinetic data using with the Korsmeyer-Peppas model suggests a Fickian diffusion as well as chain-relaxation controlled drug release process. DOX loaded micelles and free DOX displayed similar cytotoxicity towards both 4T1 and MCF-7 cells indicating that the encapsulation inside the micelle did not affect the anticancer efficacy of the drug. The drug loaded micelle showed higher cellular uptake than free DOX in both 4T1 and MCF-7 lines and lower cellular uptake than free DOX in 3T3-L1 cell lines. This polymeric micellar nanoparticle may be further exploited for encapsulation of other hydrophobic drugs.
Read full abstract