PEG-SS-PPS:  Reduction-Sensitive Disulfide Block Copolymer Vesicles for Intracellular Drug Delivery

Abstract

Under appropriate conditions, block copolymeric macroamphiphiles will self-assemble in water to form vesicles, referred to as polymersomes. We report here polymersomes that can protect biomolecules in the extracellular environment, are taken up by endocytosis, and then suddenly burst within the early endosome, releasing their contents prior to exposure to the harsh conditions encountered after lysosomal fusion. Specifically, block copolymers of the hydrophile poly(ethylene glycol) (PEG) and the hydrophobe poly(propylene sulfide) (PPS) were synthesized with an intervening disulfide, PEG17-SS-PPS30. Polymersomes formed from this block copolymer were demonstrated to disrupt in the presence of intracellular concentrations of cysteine. In cellular experiments, uptake, disruption, and release were observed within 10 min of exposure to cells, well within the time frame of the early endosome of endolysosomal processing. This system may be useful in cytoplasmic delivery of biomolecular drugs such as peptides, proteins, oligonucleotides, and DNA.

Materials engineering for immunomodulation

“…On the one hand, low-T g polymers have the advantage of being readily formed at normal production temperatures, thus approaching equilibrium micelle size and shape; on the other hand, higher-T g hydrophobic block compositions (T g >37 °C) or crystalline hydrophobic polymers (T m >37 °C) self-assemble at supraphysiological temperatures for very stable use at 37 °C, below T g or T m . Micelle, and also polymersome 35 (see below), processability can thus be engineered by manipulating any of the mat erial parameters mentioned above to exploit the equilibrium nature of the materials, as well as by slowing the dissociation rate to suit practical use. Biologically derived molecules may also readily self-assemble, as can be observed in virus-like particles, which are now in clinical use.…”

“…Earlier in the processes of endolysosomal processing, endocytosed nanoparticles encounter a reductive environment. Self-assembling block co-polymers with architecture PEG-SS-PPS, that is with a reducible disulphide connection between the hydrophobic and hydrophilic blocks, have been shown to destabilize within 15 min of endocytosis in a macrophagelike cell line (a model of APCs), releasing the contents of the polymersomes within the early endosome 35 . Linear multiblock co-polymers have also been developed; they consist of DNA-binding peptides that are flanked on each side by a cysteine residue and polymerized by oxidation in vitro 50 .…”

“…With regard to reduction, the polymer fragments produced by reduction of the PEG-SS-PPS block co-polymers mentioned above apparently possessed sufficient surface activity to disrupt the endosomal membrane, making the payload available within the endosome within 15 min but within the cytosol within 2 h (ref. 35). Triggers sensitive to pH are more commonly sought.…”

Poly(ethylene glycol) with Observable Shedding

“…[7] In another example, Cerritelli et al observed faster cytoplasm release of calcein from NPs formed using PEG-SS-poly(propylene sulfide) copolymers when compared with a non-cleavable formulation. [8] However, so far, assays to evaluate PEG shedding are end-point focused and yield no information of PEG shedding process during NP-cell interactions. In addition, these functional assays are unique to the delivery of the specific payloads, and thus may not be generalized across NP systems.…”

“…Both conjugation and deprotection reactions are confirmed by the ninhydrin test. The resin is then reacted with amine-reactive OG488 dyes to assemble (8). Since the thiol of cystine is protected by a trityl group, thiol deprotection and resin cleavage can thus be carried out in a single TFA treatment.…”