Encapsulation and Covalent Binding of Molecular Payload in Enzymatically Activated Micellar Nanocarriers

Abstract

The high selectivity and often-observed overexpression of specific disease-associated enzymes make them extremely attractive for triggering the release of hydrophobic drug or probe molecules from stimuli-responsive micellar nanocarriers. Here we utilized highly modular amphiphilic polymeric hybrids, composed of a linear hydrophilic polyethylene glycol (PEG) and an esterase-responsive hydrophobic dendron, to prepare and study two diverse strategies for loading of enzyme-responsive micelles. In the first type of micelles, hydrophobic coumarin-derived dyes were encapsulated noncovalently inside the hydrophobic core of the micelle, which was composed of lipophilic enzyme-responsive dendrons. In the second type of micellar nanocarrier the hydrophobic molecular cargo was covalently linked to the end-groups of the dendron through enzyme-cleavable bonds. These amphiphilic hybrids self-assembled into micellar nanocarriers with their cargo covalently encapsulated within the hydrophobic core. Both types of micelles were highly responsive toward the activating enzyme and released their molecular cargo upon enzymatic stimulus. Importantly, while faster release was observed with noncovalent encapsulation, higher loading capacity and slower release rate were achieved with covalent encapsulation. Our results clearly indicate the great potential of enzyme-responsive micellar delivery platforms due to the ability to tune their payload capacities and release rates by adjusting the loading strategy.

Supramolecular Translation of Enzymatically Triggered Disassembly of Micelles into Tunable Fluorescent Responses

“…This is in www.chemeurj.org good agreement with our previous work on esterase-responsive PEG-dendronh ybrids. [34] The very weak fluorescence of the fluorescein-labeled hybrid 1F at 525 nm (excited at 470 nm) increased rapidly upon addition of the enzyme ( Figure 5a). The excellentc orrelation with the HPLC data (Figure 5b)i ndicates that, as hypothesized, the enzymatic hydrolysis of the micelle-forming amphiphilic hybrids leads to the formation of hydrophilic hybridst hat disassemble and diffuse away from each other.T his physical separation halts the selfquenching of the dyes and thus turns on their strong intrinsic fluorescence.…”

“…This approach was basedo nu tilizing the formation of coumarin-derived excimers within the dendritic structuresi norder to achieve ar ed-shifto f the emitted fluorescences pectra before the enzymatic stimuli. [34] The polymericp latform was based on amphiphilic block co-polymers of al inear polyethylene glycol (PEG) chain as the hydrophilic block and ad endron with lipophilic coumarin dyes as enzymatically cleavable end-groups, serving as the hydrophobic block. In aqueous solution, such amphiphilic hybrids self-assemble into micelles with aP EG shell and ah ydrophobic core consisting of the lipophilic dendrons.…”

“…[35] Using coumarin derivatives as covalently bound hydrophobic end-groups, we showed the ability of our micelle to reportt heir disassembly by changing their fluorescence spectrau pon enzymatic hydrolysis of the dyes, which diminished the ability of the dyes to form excimers after they were released from the polymeric platform. [34] Althought he covalent binding of the dye though an enzymatically cleavable bond and its incorporationa sp art of the enzyme-responsive moiety, either by modification of the electronic conjugation of the dyes or their ability to form excimers, allow the generation of spectralc hanges in response to the enzymatic activation,t hese approaches might also be highly limited. It is clear that the requirementt hat the dye will serve as the enzymatic substrate may hamper the generalityo f these approaches in cases that the structuralp roperties of the dye are substantially different than those of the naturals ubstrate of the target enzyme and hence the dye might not be recognized or manipulated by the activating enzyme.…”

Photo‐Cross‐Linked Dual‐Responsive Hollow Capsules Mimicking Cell Membrane for Controllable Cargo Post‐Encapsulation and Release

“…One of the first bioinspired functions of artificial cell membrane to be investigated in self‐assembled systems was the ability to respond to internal stimuli such as the presence of biomolecules and enzymes,9, 10, 11, 12, 13, 14, 15 redox conditions,16, 17, 18 or ionic strength19 and pH20, 21, 22, 23 of the environment and external stimuli such as light24, 25 or temperature26, 27 to control the transport behaviors. Most of these “smart” systems developed were used to elicit cargo release by a single stimulus 28…”

Propagation of Enzyme‐Induced Surface Events inside Polymer Nanoassemblies for a Fast and Tunable Response

“…However, enzyme‐responsive nanoassemblies do not typically capture these features, in particular the fast kinetics that are characteristic of small‐molecule substrates. This has been mainly attributed to the limited accessibility of hydrophobic substrates that are deeply buried in amphiphilic assemblies ,. We and others have shown that unimer–aggregate equilibria, between the amphiphilic molecular constituents and their assemblies, play a critical role in determining the reaction rates because the enzymatic reaction is favored to occur in the unimer state where access to the substrate functionalities is better .…”