Intracellular Delivery of Colloidally Stable Core-Cross-Linked Triblock Copolymer Micelles with Glutathione-Responsive Enhanced Drug Release for Cancer Therapy

Abstract

Design and development of amphiphilic block copolymer-based nanocarriers exhibiting enhanced colloidal stability upon dilution in the blood and cellular glutathione-responsive rapid drug release is highly desired for tumor-targeting chemotherapy. Herein, we report a novel ABA-type triblock copolymer consisting of a hydrophilic central poly(ethylene glycol) block and two terminal hydrophobic blocks of a polymethacrylate having pendant disulfides (PHMssEt), thus PHMssEt-b-PEG-b-PHMssEt (ssTP). Aqueous self-assembly and the following disulfide-exchange reaction of the resulting ssTP allow for formation of core-cross-linked micelles (CCMs) through the formation of new disulfide linkages, retaining enhanced colloidal stability in physiological conditions and in the presence of proteins. Further, they exhibit reduction-responsive enhanced release of encapsulated drugs in response to cellular concentrations of glutathione in cancer cells, confirmed by dynamic light scattering and spectroscopic analysis. Combined with these results, in vitro (cells) and in vivo (mouse model) biological results suggest that ssTP-based CCMs are effective candidates as intracellular nanocarriers targeting tumors for cancer therapy.

Fabrication of Core Crosslinked Polymeric Micelles as Nanocarriers for Doxorubicin Delivery: Self-Assembly, In Situ Diselenide Metathesis and Redox-Responsive Drug Release

“…On the other hand, CCMs showed an increase in D h of the micellar structure from 156.57 ± 4.42 to 464.55 ± 3.15 nm ( Figure S5C) which may be ascribed to the dissolution and swelling of the crosslinked cores by DMF. Consistent with previous reports, CCMs retained their core-shell architecture in the presence of 10-fold DMF as compared to their precursors (NCMs) [12,15]. These scenarios further confirmed the success of the core crosslinking and the extra stability of CCMs under harsh conditions [27].…”

“…A similar trend was noticed when DOX@CCMs were treated with BSA (171.78 ± 2.21) ( Figure S5B). The presence of mPEG shell may prevent the adsorption and interaction of protein on the surface of the micelles [15,38]. Moreover, the presence of core crosslinking makes the micellar aggregate resistant to BSA triggered micellar disassembly [53].…”

“…This significant difference emanated from the intracellular drug-releasing behavior of DOX@NCMs and DOX@CCMs. The lack of covalent crosslinking in the core of DOX@NCMs expected to cause abrupt micellar swelling/disassembly, pronounced DOX release [15], and better apoptotic effect (IC 50 = 3.80 µg/mL) when exposed to intracellular reduced GSH and H 2 O 2 of HeLa cells ( Figure S8C). On the other hand, the covalent diselenide crosslinking in DOX@CCMs requires a relatively long period of time to cleave Se-Se bonds and release a therapeutically sufficient amount of DOX to inhibit proliferation of HeLa cells.…”

“…Despite the aforementioned appealing attributes of PMs as carriers of CAs, only a few micellar formulations advance beyond the preclinical development stage [13]. This may be attributed to the poor thermodynamic stability of PMs due to their non-specific interaction with blood protein components, and failure to withstand a subclassification of compressive, tensile, and shear stresses in vivo which leads to premature release of their cargo and non-specific biodistribution upon intravenous administration [14][15][16][17]. To circumvent the in vivo instability of PMs, covalent crosslinking of the micellar shell or core were often employed [10].…”

“…As the former suffered from aggregation, reduced stealthiness and weakened EPR effect [18][19][20][21], core crosslinking has attracted considerable attention in the fabrication of stable PMs intended for anticancer drug delivery applications (DDAs) [22][23][24]. To achieve the on-demand release of CAs in the region of interest, stimuli-responsive core crosslinking agents with dynamic covalent bonds (DCBs) are in high demand [10,12,15,25]. In this regard, S-S and Se-Se bonds containing PMs [23,26,27] have shown preferential sensitivity towards tumor tissue redox signals (2-10 mM reduced glutathione (GSH) and 1 mM H 2 O 2 ) over extracellular cancer environments (2-10 µM reduced GSH and 20 nM H 2 O 2 ) [17,28,29].…”