Fluorogenic Enzyme-Responsive Micellar Nanoparticles

Enzyme-Responsive Nanoparticles for the Targeted Delivery of an MMP Inhibitor to Acute Myocardial Infarction

Herein, we have developed a drug-loaded matrix metalloproteinase (MMP)-responsive micellar nanoparticle (NP) intended for minimally invasive intravenous injection during the acute phase of myocardial infarction (MI) and prolonged retention in the heart for small-molecule drug delivery. Peptide-polymer amphiphiles (PPAs) bearing a small-molecule MMP inhibitor (MMPi), PD166793, were synthesized via ring-opening metathesis polymerization (ROMP) and formulated into spherical micelles by transitioning to aqueous solution. The resulting micellar NPs underwent MMP-induced aggregation, demonstrating enzyme responsiveness. Using a rat MI model, we observed that these NPs were capable of successfully extravasating into the infarcted region of the heart where they were retained due to the active, enzyme-mediated targeting, remaining detectable after 1 week post administration without increasing macrophage recruitment. Furthermore, in vitro studies show that these NPs demonstrated successful drug release following MMP treatment and maintained drug bioactivity as evidenced by comparable MMP inhibition to free MMPi. This work establishes a targeted NP platform for delivering small-molecule therapeutics to the heart after MI, opening possibilities for myocardial infarction treatment.

Enzyme-Responsive Nanoparticles for Dexamethasone Targeted Delivery to Treat Inflammation in Diabetes

Diabetes is a global epidemic accompanied by impaired wound healing and increased risk of persistent infections and resistance to standard treatments. Therefore, there is an immense need to develop novel methods to specifically target therapeutics to affected tissues and improve treatment efficacy. This study aims to use enzyme-responsive nanoparticles for the targeted delivery of an anti-inflammatory drug, dexamethasone, to treat inflammation in diabetes. These nanoparticles are assembled from fluorescently-labeled, dexamethasone-loaded peptide-polymer amphiphiles. The nanoparticles are injected in vivo, adjacent to labeled collagen membranes sub-periosteally implanted on the calvaria of diabetic rats. Following their implantation, collagen membrane resorption is linked to inflammation, especially in hyperglycemic individuals. The nanoparticles show strong and prolonged accumulation in inflamed tissue after undergoing a morphological switch into microscale aggregates. Significantly higher remaining collagen membrane area and less inflammatory cell infiltration are observed in responsive nanoparticles-treated rats, compared to control groups injected with free dexamethasone and non-responsive nanoparticles. These factors indicate improved therapeutic efficacy in inflammation reduction. These results demonstrate the potential use of enzyme-responsive nanoparticles as targeted delivery vehicles for the treatment of diabetic and other inflammatory wounds.

The Yin and Yang of the protein corona on the delivery journey of nanoparticles

Nanoparticles-based drug delivery systems have attracted significant attention in biomedical fields because they can deliver loaded cargoes to the target site in a controlled manner. However, tremendous challenges must still be overcome to reach the expected targeting and therapeutic efficacy in vivo. These challenges mainly arise because the interaction between nanoparticles and biological systems is complex and dynamic and is influenced by the physicochemical properties of the nanoparticles and the heterogeneity of biological systems. Importantly, once the nanoparticles are injected into the blood, a protein corona will inevitably form on the surface. The protein corona creates a new biological identity which plays a vital role in mediating the bio-nano interaction and determining the ultimate results. Thus, it is essential to understand how the protein corona affects the delivery journey of nanoparticles in vivo and what we can do to exploit the protein corona for better delivery efficiency. In this review, we first summarize the fundamental impact of the protein corona on the delivery journey of nanoparticles. Next, we emphasize the strategies that have been developed for tailoring and exploiting the protein corona to improve the transportation behavior of nanoparticles in vivo. Finally, we highlight what we need to do as a next step towards better understanding and exploitation of the protein corona. We hope these insights into the "Yin and Yang" effect of the protein corona will have profound implications for understanding the role of the protein corona in a wide range of nanoparticles.

Chemical design and synthesis of macromolecular profluorescent nitroxide systems as self-reporting probes

The objective of this mini-review article is to highlight the importance of the chemical design towards the synthesis of polymeric profluorescent nitroxides applicable as self-reporting probes.

Tunning Intermolecular Interaction of Peptide-Conjugated AIEgen in Nano-Confined Space for Quantitative Detection of Tumor Marker Secreted from Cells

Determining the expression level of biomarkers is crucial for disease diagnosis. However, the low abundance of biomarkers in the early stage makes the detection extremely difficult by traditional aggregation-induced emission (AIE)-based fluorescent probes. Here, by tuning the intermolecular interaction, a two steps-based MP/NPs-SLIPS sensing system is designed for ultrasensitive detection of the tumor marker matrix metalloproteinase-2 (MMP-2). During the sensing process, aggregation of AIE residual could be intensified through the electrostatic absorption by negatively charged nanoparticles (NPs), as well as the confined space formed by the self-assembly of NPs to photonic crystals (PCs) on slippery lubricant-infused porous substrates (SLIPS). The fluorescent signals obviously increased with a strengthened aggregation degree, which contributes to improved sensitivity. Thus, the limit of detection is decreased to 3.7 ng/mL for MP/NPs-SLIPS sensing system, which could be used for detecting the MMP-2 secreted by tumor cells directly. This strategy also demonstrated its potential applications as high-throughput detection devices and will be of significance for the ultrasensitive analysis of biomarkers.

Bioresponsive nanomedicines based on dynamic covalent bonds

Trends in the development of modern medicine necessitate the efficient delivery of therapeutics to achieve the desired treatment outcomes through precise spatiotemporal accumulation of therapeutics at the disease site. Bioresponsive nanomedicine is a promising platform for this purpose. Dynamic covalent bonds (DCBs) have attracted much attention in studies of the fabrication of bioresponsive nanomedicines with an abundance of combinations of therapeutic modules and carrier function units. DCB-based nanomedicines could be designed to maintain biological friendly synthesis and site-specific release for optimal therapeutic effects, allowing the complex to retain an integrated structure before accumulating at the disease site, but disassembling into individual active components without compromising function in the targeted organs or tissues. In this review, we focus on responsive nanomedicines containing dynamic chemical bonds that can be cleaved by various specific stimuli, enabling achievement of targeted drug release for optimal therapy in various diseases.

Poly(peptide): Synthesis, Structure, and Function of Peptide-Polymer Amphiphiles and Protein-like Polymers

In this Account, we describe the organization of functional peptides as densely arrayed side chains on polymer scaffolds which we introduce as a new class of material called poly(peptide). We describe two general classes of poly(peptide): (1) Peptide-Polymer Amphiphiles (PPAs), which consist of block copolymers with a dense grouping of peptides arrayed as the side chains of the hydrophilic block and connected to a hydrophobic block that drives micelle assembly, and (2) Protein-like Polymers (PLPs), wherein peptide-brush polymers are composed from monomers, each containing a peptide side chain. Peptides organized in this manner imbue polymers or polymeric nanoparticles with a range of functional qualities inherent to their specific sequence. Therefore, polymers or nanoparticles otherwise lacking bioactivity or responsiveness to stimuli, once linked to a peptide of choice, can now bind proteins, enter cells and tissues, have controlled and switchable biodistribution patterns, and be enzyme substrates (e.g., for kinases, phosphatases, proteases). Indeed, where peptide substrates are incorporated, kinetically or thermodynamically driven morphological transitions can be enzymatically induced in the polymeric material. Synergistically, the polymer enforces changes in peptide activity and function by virtue of packing and constraining the peptide. The scaffold can protect peptides from proteolysis, change the pharmacokinetic profile of an intravenously injected peptide, increase the cellular uptake of an otherwise cell impermeable therapeutic peptide, or change peptide substrate activity entirely. Moreover, in addition to the sequence-controlled peptides (generated by solid phase synthesis), the polymer can carry its own sequence-dependent information, especially through living polymerization strategies allowing well-defined blocks and terminal labels (e.g., dyes, contrast agents, charged moieties). Hence, the two elements, peptide and polymer, cooperate to yield materials with unique function and properties quite apart from each alone. Herein, we describe the development of synthetic strategies for accessing these classes of biomolecule polymer conjugates. We discuss the utility of poly(peptide)-based materials in a range of biomedical applications, including imaging of diseased tissues (myocardial infarction and cancer), delivering small molecule drugs to tumors with high specificity, imparting cell permeability to otherwise impermeable peptides, protecting bioactive peptides from proteolysis in harsh conditions (e.g., stomach acid and whole blood), and transporting proteins into traditionally difficult-to-transfect cell types, including stem cells. Poly(peptide) materials offer new properties to both the constituent peptides and to the polymers, which can be tuned by the design of the oligopeptide sequence, degree of polymerization, peptide arrangement on the polymer backbone, and polymer backbone chemistry. These properties establish this approach as valuable for the development of peptides as medicines and materials in a range of settings.

Enzyme-Induced Kinetic Control of Peptide-Polymer Micelle Morphology

In this paper, experiment and simulation were combined to provide a view of the molecular rearrangements underlying the equilibrium and nonequilibrium transitions occurring in stimuli-responsive block copolymer amphiphile self-assemblies. Three block copolymer amphiphiles were prepared, each consisting of a hydrophilic peptide brush, responsive to proteolytic enzymes, and containing one of three possible hydrophobic blocks: (1) poly(ethyl acrylate), (2) poly(styrene), or (3) poly(lauryl acrylate). When assembled, they generate three spherical micelles each responsive to the addition of the bacterial protease, thermolysin. We found core-block-dependent phase transitions in response to the hydrophilic block being truncated by the stimulus. In one example, we found an unexpected, well-defined, pathway-dependent spherical micelle to vesicle phase transition induced by enzymatic stimulus.

An oxygen self-sufficient NIR-responsive nanosystem for enhanced PDT and chemotherapy against hypoxic tumors

The efficacy of photodynamic therapy and chemotherapy is largely limited by oxygen deficiency in the hypoxic tumor microenvironment. To solve these problems, we fabricated a novel NIR-responsive nanosystem which could co-deliver oxygen and anticancer drug DOX. An oxygen self-sufficient amphiphile (F-IR780-PEG) was first synthesized and subsequently utilized to load anticancer drug DOX to form nanoparticles (F/DOX nanoparticles). Due to the high oxygen capacity of such nanoparticles, the hypoxic tumor microenvironment was greatly modulated after these nanoparticles reached the tumor region, and the results revealed that hypoxia-inducible factor α (HIF-1α) was down-regulated and the expression of P-glycoprotein (P-gp) was then reduced, which were in favor of chemotherapy. Under light irradiation at 808 nm, IR780 could efficiently produce singlet oxygen to damage cancer cells by photodynamic therapy (PDT). Simultaneously, the IR780 linkage could be cleaved by singlet oxygen generated by itself and resulted in DOX release, which further caused cell damage by chemotherapy. With the combination of PDT and chemotherapy, F/DOX nanoparticles showed remarkable therapeutic efficacy under in vitro and in vivo conditions. Furthermore, the F/DOX nanoparticles are favorable for imaging-guided tumor therapy due to the inherent fluorescence properties of IR780. We thus believe that the synergistic treatment described here leads to an ideal therapeutic approach to hypoxic tumors.

Tumor Retention of Enzyme-Responsive Pt(II) Drug-Loaded Nanoparticles Imaged by Nanoscale Secondary Ion Mass Spectrometry and Fluorescence Microscopy

In nanomedicine, determining the spatial distribution of particles and drugs, together and apart, at high resolution within tissues, remains a major challenge because each must have a different label or detectable feature that can be observed with high sensitivity and resolution. We prepared nanoparticles capable of enzyme-directed assembly of particle therapeutics (EDAPT), containing an analogue of the Pt(II)-containing drug oxaliplatin, an 15N-labeled monomer in the hydrophobic block of the backbone of the polymer, the near-infrared dye Cy5.5, and a peptide that is a substrate for tumor metalloproteinases in the hydrophilic block. When these particles reach an environment rich in tumor associated proteases, the hydrophilic peptide substrate is cleaved, causing the particles to accumulate through a morphology transition, locking them in the tumor extracellular matrix. To evaluate the distribution of drug and EDAPT carrier in vivo, the localization of the isotopically labeled polymer backbone was compared to that of Pt by nanoscale secondary ion mass spectrometry (NanoSIMS). The correlation of NanoSIMS with super-resolution fluorescence microscopy revealed the release of the drug from the nanocarrier and colocalization with cellular DNA within tumor tissue. The results confirmed the dependence of particle accumulation and Pt(II) drug delivery on the presence of a Matrix Metalloproteinase (MMP) substrate and demonstrated antitumor activity. We conclude that these techniques are powerful for the elucidation of the localization of cargo and carrier, and enable a high-resolution assessment of their performance following in vivo delivery.

Self-Assembled Fluorescent Organic Nanomaterials for Biomedical Imaging

Fluorescent nanomaterials, self-assembled from building blocks through multiple intermolecular interactions show diversified structures and functionalities, and are potential fluorescence contrast agents/probes for high-performance biomedical imaging. Self-assembled nanomaterials exhibit high stability, long circulation time, and targeted biological distribution. This review summarizes recent advances of self-assembled nanomaterials as fluorescence contrast agents/probes for biomedical imaging. The self-assembled nanomaterials are classified into two groups, i.e., ex situ and in situ construction of self-assembled nanomaterials. The advantages of ex situ as well as in situ constructed nanomaterials for biomedical applications are discussed thoroughly. The directions of future developments for self-assembled nanomaterials are provided.

Micellar Stability in Biological Media Dictates Internalization in Living Cells

The dynamic nature of polymeric assemblies makes their stability in biological media a crucial parameter for their potential use as drug delivery systems in vivo. Therefore, it is essential to study and understand the behavior of self-assembled nanocarriers under conditions that will be encountered in vivo such as extreme dilutions and interactions with blood proteins and cells. Herein, using a combination of fluorescence spectroscopy and microscopy, we studied four amphiphilic PEG-dendron hybrids and their self-assembled micelles in order to determine their structure-stability relations. The high molecular precision of the dendritic block enabled us to systematically tune the hydrophobicity and stability of the assembled micelles. Using micelles that change their fluorescent properties upon disassembly, we observed that serum proteins bind to and interact with the polymeric amphiphiles in both their assembled and monomeric states. These interactions strongly affected the stability and enzymatic degradation of the micelles. Finally, using spectrally resolved confocal imaging, we determined the relations between the stability of the polymeric assemblies in biological media and their cell entry. Our results highlight the important interplay between molecular structure, micellar stability, and cell internalization pathways, pinpointing the high sensitivity of stability-activity relations to minor structural changes and the crucial role that these relations play in designing effective polymeric nanostructures for biomedical applications.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Enzyme-Targeted Nanoparticles for Delivery to Ischemic Skeletal Muscle

The targeted delivery of enzyme-responsive nanoparticles to specific tissues can be a valuable, minimally invasive approach for imaging or drug delivery applications. In this study, we show for the first time enzyme-directed assembly of intravenously (IV) delivered nanoparticles in ischemic skeletal muscle, which has applications for drug delivery to damaged muscle of the type prevalent in peripheral artery disease (PAD). Specifically, micellar nanoparticles are cleavable by matrix metalloproteinases (MMPs), causing them to undergo a morphological switch and thus aggregate in tissues where these enzymes are upregulated, like ischemic muscle. Here, we demonstrated noninvasive in vivo imaging of these IV-injected nanoparticles through near-infrared dye labeling and in vivo imaging (IVIS) particle tracking in a rat hindlimb ischemia model. Polymer peptide amphiphilic nanoparticles were synthesized and optimized for both MMP cleavage efficiency and near-IR fluorescence. Nanoparticles were injected 4 days after unilateral hindlimb ischemia and were monitored over 28 days using IVIS imaging. Nanoparticles targeted to ischemic muscle over healthy muscle, and ex vivo biodistribution analysis at 7 and 28 days post-injection confirmed targeting to the ischemic muscle as well as off target accumulation in the liver and spleen. Ex vivo histology confirmed particle localization in ischemic but not healthy muscle. Altering the surface charge of the nanoparticles through addition of zwitterionic dye species resulted in improved targeting to the ischemic muscle. To our knowledge, this is the first study to demonstrate the targeted delivery and long term retention of nanoparticles using an enzyme-directed morphology switch. This has implications for noninvasive drug delivery vehicles for treating ischemic muscle, as no minimally invasive, non-surgical options currently exist.

Balancing the intermolecular forces in peptide amphiphiles for controlling self-assembly transitions

While the influence of alkyl chain length and headgroup size on self-assembly behaviour has been well-established for simple surfactants, the rational control over the pH- and concentration-dependent self-assembly behaviour in stimuli responsive peptides remains an elusive goal. Here, we show that different amphiphilic peptides can have similar self-assembly phase diagrams, providing the relative strengths of the attractive and repulsive forces are balanced. Using palmitoyl-YYAAEEEEK(DO3A:Gd)-NH2 and palmitoyl-YAAEEEEK(DO3A:Gd)-NH2 as controls, we show that reducing hydrophobic attractive forces through fewer methylene groups in the alkyl chain will lead to a similar self-assembly phase diagram as increasing the electrostatic repulsive forces via the addition of a glutamic acid residue. These changes allow creation of self-assembled MRI vehicles with slightly different micelle and nanofiber diameters but with minimal changes in the spin-lattice T1 relaxivity. These findings reveal a powerful strategy to design self-assembled vehicles with different sizes but with similar self-assembly profiles.

Stimuli-Regulated Smart Polymeric Systems for Gene Therapy

The physiological condition of the human body is a composite of different environments, each with its own parameters that may differ under normal, as well as diseased conditions. These environmental conditions include factors, such as pH, temperature and enzymes that are specific to a type of cell, tissue or organ or a pathological state, such as inflammation, cancer or infection. These conditions can act as specific triggers or stimuli for the efficient release of therapeutics at their destination by overcoming many physiological and biological barriers. The efficacy of conventional treatment modalities can be enhanced, side effects decreased and patient compliance improved by using stimuli-responsive material that respond to these triggers at the target site. These stimuli or triggers can be physical, chemical or biological and can be internal or external in nature. Many smart/intelligent stimuli-responsive therapeutic gene carriers have been developed that can respond to either internal stimuli, which may be normally present, overexpressed or present in decreased levels, owing to a disease, or to stimuli that are applied externally, such as magnetic fields. This review focuses on the effects of various internal stimuli, such as temperature, pH, redox potential, enzymes, osmotic activity and other biomolecules that are present in the body, on modulating gene expression by using stimuli-regulated smart polymeric carriers.

Enzyme-Responsive Nanoparticles for the Treatment of Disease

Nanomedicine for cancer therapy seeks to treat malignancies through the selective accumulation of therapeutics in diseased tissue. Nanoparticles offer the convenience of high drug loading capacities and can be readily decorated with targeting moieties, drugs, and/or diagnostics. Our lab has pioneered a new tissue targeting strategy where enhanced accumulation of nanomaterials occurs as a result of morphology changes to the material in response to overexpressed enzymes in diseased tissues. Herein, we describe the general strategy for the preparation of these enzyme-responsive nanoparticles (ER-NPs) for therapeutic applications.

An Amylase-Responsive Bolaform Supra-Amphiphile

An amylase-responsive bolaform supra-amphiphile was constructed by the complexation between β-cyclodextrin and a bolaform covalent amphiphile on the basis of host-guest interaction. The bolaform covalent amphiphile could self-assemble in solution, forming sheet-like aggregates and displaying weak fluorescence because of aggregation-induced quenching. The addition of β-cyclodextrin led to the formation of the bolaform supra-amphiphile, prohibiting the aggregation of the bolaform covalent amphiphile and accompanying with the significant recovery of fluorescence. Upon the addition of α-amylase, with the degradation β-cyclodextrin, the fluorescence of the supra-amphiphile would quench gradually and significantly, and the quenching rate linearly correlated to the concentration of α-amylase. This study enriches the field of supra-amphiphiles on the basis of noncovalent interactions, and moreover, it may provide a facile way to estimate the activity of α-amylase.

Towards a new FRET system via combination of pyrene and perylene bisimide: synthesis, self-assembly and fluorescence behavior

A new fluorescent derivative of cholesterol, N,N'-(N-(2-(3β-cholest-5-en-3yl-formamido)ethyl) pyrene-1-sulfonamido)ethyl perylene-3,4:9,10-tetracarboxylic acid bisimide (CPPBI), was designed and synthesized. In the design, pyrene (Py) and perylene bisimide (PBI) were specially chosen as the energy donor and the acceptor, respectively. Fluorescence studies revealed that (1) CPPBI shows a strong tendency to form supra-molecular assemblies, (2) the assemblies possess a high efficiency of fluorescence resonance energy transfer (FRET) via intermolecular interactions, and (3) the profile and position of its fluorescence emission are highly dependent upon the nature of its medium, but the medium shows little effect on the efficiency of the energy transfer, suggesting that the chromophores including both Py and PBI units enjoy some rotational and/or translational mobility in the aggregated state of the compound. Temperature- and concentration-dependent (1)H NMR spectroscopy studies revealed that both hydrogen-bonding and π-π stacking play a great role in stabilizing the assemblies of the compound, and confirmed the existence of π-π stacking between the Py moieties and between the PBI residues of the compound, of which the donor and the acceptor may have arranged in an appropriate orientation and at a suitable distance which are the key factors to determine the FRET efficiency. Moreover, the CPPBI-based film possesses unusual photochemical stability, and its emission is sensitive to the presence of some organic vapors, in particular aniline.

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

The need for advanced fluorescent imaging and delivery platforms has motivated the development of smart probes that change their fluorescence in response to external stimuli. Here a new molecular design of fluorescently labeled PEG-dendron hybrids that self-assemble into enzyme-responsive micelles with tunable fluorescent responses is reported. In the assembled state, the fluorescence of the dyes is quenched or shifted due to intermolecular interactions. Upon enzymatic cleavage of the hydrophobic end-groups, the labeled polymeric hybrids become hydrophilic, and the micelles disassemble. This supramolecular change is translated into a spectral response as the dye-dye interactions are eliminated and the intrinsic fluorescence is regained. We demonstrate the utilization of this molecular design to generate both Turn-On and spectral shift responses by adjusting the type of the labeling dye. This approach enables transformation of non-responsive labeling dyes into smart fluorescent probes.

Therapeutic Enzyme-Responsive Nanoparticles for Targeted Delivery and Accumulation in Tumors

An enzyme-responsive, paclitaxel-loaded nanoparticle is described and assessed in vivo in a human fibrosarcoma murine xenograft. This work represents a proof-of-concept study demonstrating the utility of enzyme-responsive nanoscale drug carriers capable of targeted accumulation and retention in tumor tissue in response to overexpressed endogenous enzymes.

Enzyme-responsive polymer assemblies constructed through covalent synthesis and supramolecular strategy

Enzyme-responsive polymer assemblies have continually gained progress through the introduction of new enzymes and the development of new strategies for their preparation. In addition, kinetic studies will pave the way for tuning the response rate in a controlled manner.

Probing peptide amphiphile self-assembly in blood serum

There has been recent interest in designing smart diagnostic or therapeutic self-assembling peptide or polymeric materials that can selectively undergo morphological transitions to accumulate at a disease site in response to specific stimuli. Developing approaches to probe these self-assembly transitions in environments that accurately amalgamate the diverse plethora of proteins, biomolecules, and salts of blood is essential for creating systems that function in vivo. Here, we have developed a fluorescence anisotropy approach to probe the pH-dependent self-assembly transition of peptide amphiphile (PA) molecules that transform from spherical micelles at pH 7.4 to nanofibers under more acidic pH's in blood serum. By mixing small concentrations of a Ru(bipy)3(2+)-tagged PA with a Gd(DO3A)-tagged PA having the same lipid-peptide sequence, we showed that the pH dependence of self-assembly is minimally affected and can be monitored in mouse blood serum. These PA vehicles can be designed to transition from spherical micelles to nanofibers in the pH range 7.0-7.4 in pure serum. In contrast to the typical notion of serum albumin absorbing isolated surfactant molecules and disrupting self-assembly, our experiments showed that albumin does not bind these anionic PAs and instead promotes nanofibers due to a molecular crowding effect. Finally, we created a medium that replicates the transition pH in serum to within 0.08 pH units and allows probing self-assembly behavior using conventional spectroscopic techniques without conflicting protein signals, thus simplifying the development pathway from test tube to in vivo experimentation for stimuli-responsive materials.

Peptides displayed as high density brush polymers resist proteolysis and retain bioactivity

We describe a strategy for rendering peptides resistant to proteolysis by formulating them as high-density brush polymers. The utility of this approach is demonstrated by polymerizing well-established cell-penetrating peptides (CPPs) and showing that the resulting polymers are not only resistant to proteolysis but also maintain their ability to enter cells. The scope of this design concept is explored by studying the proteolytic resistance of brush polymers composed of peptides that are substrates for either thrombin or a metalloprotease. Finally, we demonstrate that the proteolytic susceptibility of peptide brush polymers can be tuned by adjusting the density of the polymer brush and offer in silico models to rationalize this finding. We contend that this strategy offers a plausible method of preparing peptides for in vivo use, where rapid digestion by proteases has traditionally restricted their utility.

Labelling Polymers and Micellar Nanoparticles via Initiation, Propagation and Termination with ROMP

In this paper we compare and contrast three approaches for labelling polymers with functional groups via ring-opening metathesis polymerization (ROMP). We explored the incorporation of functionality via initiation, termination and propagation employing an array of novel initiators, termination agents and monomers. The goal was to allow the generation of selectively labelled and well-defined polymers that would in turn lead to the formation of labelled nanomaterials. Norbornene analogues, prepared as functionalized monomers for ROMP, included fluorescent dyes (rhodamine, fluorescein, EDANS, and coumarin), quenchers (DABCYL), conjugatable moieties (NHS esters, pentafluorophenyl esters), and protected amines. In addition, a set of symmetrical olefins for terminally labelling polymers, and for the generation of initiators in situ is described.

Programmed hydrolysis of nanoassemblies by electrostatic interaction-mediated enzymatic-degradation

Electrostatic interaction-mediated enzymatic-hydrolysis of poly(lactide)-containing nanoscale assemblies is described. At physiological pH, degradable core-shell morphologies with charged shells can readily attract or repel enzymes carrying opposite or similar charges, respectively.

Optimising the enzyme response of a porous silicon photonic crystal via the modular design of enzyme sensitive polymers

The incorporation of a versatile and tuneable polymer–peptide network into the pores of porous silicon photonic crystals improves the selectivity of porous silicon optical biosensors to detect certain types of matrix metalloproteinase enzymes.

Enzyme-directed assembly of nanoparticles in tumors monitored by in vivo whole animal imaging and ex vivo super-resolution fluorescence imaging

Matrix metalloproteinase enzymes, overexpressed in HT-1080 human fibrocarcinoma tumors, were used to guide the accumulation and retention of an enzyme-responsive nanoparticle in a xenograft mouse model. The nanoparticles were prepared as micelles from amphiphilic block copolymers bearing a simple hydrophobic block and a hydrophilic peptide brush. The polymers were end-labeled with Alexa Fluor 647 dyes leading to the formation of labeled micelles upon dialysis of the polymers from DMSO/DMF to aqueous buffer. This dye-labeling strategy allowed the presence of the retained material to be visualized via whole animal imaging in vivo and in ex vivo organ analysis following intratumoral injection into HT-1080 xenograft tumors. We propose that the material is retained by virtue of an enzyme-induced accumulation process whereby particles change morphology from 20 nm spherical micelles to micrometer-scale aggregates, kinetically trapping them within the tumor. This hypothesis is tested here via an unprecedented super-resolution fluorescence analysis of ex vivo tissue slices confirming a particle size increase occurs concomitantly with extended retention of responsive particles compared to unresponsive controls.

Redox-responsive, core-cross-linked micelles capable of on-demand, concurrent drug release and structure disassembly

We developed camptothecin (CPT)-conjugated, core-cross-linked (CCL) micelles that are subject to redox-responsive cleavage of the built-in disulfide bonds, resulting in disruption of the micellar structure and rapid release of CPT. CCL micelles were prepared via coprecipitation of disulfide-containing CPT-poly(tyrosine(alkynyl)-OCA) conjugate and monomethoxy poly(ethylene glycol)-b-poly(tyrosine(alkynyl)-OCA), followed by cross-linking of the micellar core via azide-alkyne click chemistry. CCL micelles exhibited excellent stability under physiological conditions, while they underwent rapid dissociation in reduction circumstance, resulting in burst release of CPT. These redox-responsive CCL micelles showed enhanced cytotoxicity against human breast cancer cells in vitro.

Polymerization of a peptide-based enzyme substrate

Polymers of norbornenyl-modified peptide-based enzyme substrates have been prepared via ring-opening metathesis polymerization (ROMP). Peptides displayed on water-soluble homopolymers retain the ability to be enzymatically processed by a disease-associated enzyme. In contrast, when the peptides are densely arrayed on a nanoparticle derived from a self-assembled amphiphilic block-copolymer, they function with reduced activity as enzymatic substrates.

Enzyme-directed assembly of a nanoparticle probe in tumor tissue

Enzyme-directed assembly in vivo: A targeting strategy is demonstrated, which leads to an active accumulation of nanoparticles by virtue of an assembly event specific to endogenous, enzymatic biochemical signals associated with tumor tissue. The viability of this approach is examined through a proof-of-concept study showing enzyme-directed particle targeting and accumulation in human xenograft tumors in mice following intravenous injection, and the retention of particles is demonstrated within tumors for extended periods of time.

Gold nanocluster-based electrochemically controlled fluorescence switch surface with prussian blue as the electrical signal receptor

A highly robust electrochemically controlled fluorescence switch based on ultrasmall Au nanoclusters has been designed by the aid of the electrochemical redox reaction of prussian blue.