Proteolysis: A Biological Process Adapted in Drug Delivery, Therapy, and Imaging

Expanding the chemical repertoire of protein-based polymers for drug-delivery applications

Expanding the chemical repertoire of natural and artificial protein-based polymers (PBPs) can enable the production of sequence-defined, yet chemically diverse, biopolymers with customized or new properties that cannot be accessed in PBPs composed of only natural amino acids. Various approaches can enable the expansion of the chemical repertoire of PBPs, including chemical and enzymatic treatments or the incorporation of unnatural amino acids. These techniques are employed to install a wide variety of chemical groups-such as bio-orthogonally reactive, cross-linkable, post-translation modifications, and environmentally responsive groups-which, in turn, can facilitate the design of customized PBP-based drug-delivery systems with modified, fine-tuned, or entirely new properties and functions. Here, we detail the existing and emerging technologies for expanding the chemical repertoire of PBPs and review several chemical groups that either demonstrate or are anticipated to show potential in the design of PBP-based drug delivery systems. Finally, we provide our perspective on the remaining challenges and future directions in this field.

Novel strategies to improve tumour therapy by targeting the proteins MCT1, MCT4 and LAT1

Poor selectivity, potential systemic toxicity and drug resistance are the main challenges associated with chemotherapeutic drugs. MCT1 and MCT4 and LAT1 play vital roles in tumour metabolism and growth by taking up nutrients and are thus potential targets for tumour therapy. An increasing number of studies have shown the feasibility of including these transporters as components of tumour-targeting therapy. Here, we summarize the recent progress in MCT1-, MCT4-and LAT1-based therapeutic strategies. First, protein structures, expression, relationships with cancer, and substrate characteristics are introduced. Then, different drug targeting and delivery strategies using these proteins have been reviewed, including designing protein inhibitors, prodrugs and nanoparticles. Finally, a dual targeted strategy is discussed because these proteins exert a synergistic effect on tumour proliferation. This article concentrates on tumour treatments targeting MCT1, MCT4 and LAT1 and delivery techniques for improving the antitumour effect. These innovative tactics represent current state-of-the-art developments in transporter-based antitumour drugs.

Predicting monoclonal antibody pharmacokinetics following subcutaneous administration via whole-body physiologically-based modeling

Use of the subcutaneous (SC) route for administering monoclonal antibodies (mAbs) to treat chronic conditions has been hindered because of an incomplete understanding of fundamental mechanisms controlling mAb absorption from the SC site, and due to the limited translatability of preclinical studies. In this paper, we report on the development and evaluation of a whole-body physiologically-based model to predict mAb pharmacokinetics following SC administration. The circulatory model is based on the physiological processes governing mAb transport and includes two mAb-specific parameters representing differences in pinocytosis rate and the diffusive/convective transport rates among mAbs. At the SC administration site, two additional parameters are used to represent mAb differences in lymphatic capillary uptake and in pre-systemic clearance. Model development employed clinical intravenous (IV) plasma PK data from 20 mAbs and SC plasma PK data from 12 of these mAbs, as obtained from the literature. The resulting model reliably described both the IV and SC measured plasma concentration data. In addition, a metric based on the positive charge across the mAb's complementarity determining region vicinity was found to positively correlate with the model-based estimates of the mAb-specific parameter governing organ/tissue pinocytosis transport and with estimates of the mAb's SC lymphatic capillary clearance. These two relationships were incorporated into the model and accurately predicted the SC PK profiles of three out of four separate mAbs not included in model development. The whole-body physiologically-based model reported herein, provides a platform to characterize and predict the plasma disposition of monoclonal antibodies following SC administration in humans.

Membrane functionalization in artificial cell engineering

Bottom-up synthetic biology aims to construct mimics of cellular structure and behaviour known as artificial cells from a small number of molecular components. The development of this nascent field has coupled new insights in molecular biology with large translational potential for application in fields such as drug delivery and biosensing. Multiple approaches have been applied to create cell mimics, with many efforts focusing on phospholipid-based systems. This mini-review focuses on different approaches to incorporating molecular motifs as tools for lipid membrane functionalization in artificial cell construction. Such motifs range from synthetic chemical functional groups to components from extant biology that can be arranged in a ‘plug-and-play’ approach which is hard to replicate in living systems. Rationally designed artificial cells possess the promise of complex biomimetic behaviour from minimal, highly engineered chemical networks.

Overcoming Hurdles in Nanoparticle Clinical Translation: The Influence of Experimental Design and Surface Modification

Nanoparticles are becoming an increasingly popular tool for biomedical imaging and drug delivery. While the prevalence of nanoparticle drug-delivery systems reported in the literature increases yearly, relatively little translation from the bench to the bedside has occurred. It is crucial for the scientific community to recognize this shortcoming and re-evaluate standard practices in the field, to increase clinical translatability. Currently, nanoparticle drug-delivery systems are designed to increase circulation, target disease states, enhance retention in diseased tissues, and provide targeted payload release. To manage these demands, the surface of the particle is often modified with a variety of chemical and biological moieties, including PEG, tumor targeting peptides, and environmentally responsive linkers. Regardless of the surface modifications, the nano-bio interface, which is mediated by opsonization and the protein corona, often remains problematic. While fabrication and assessment techniques for nanoparticles have seen continued advances, a thorough evaluation of the particle's interaction with the immune system has lagged behind, seemingly taking a backseat to particle characterization. This review explores current limitations in the evaluation of surface-modified nanoparticle biocompatibility and in vivo model selection, suggesting a promising standardized pathway to clinical translation.

Cathepsin-sensitive nanoscale drug delivery systems for cancer therapy and other diseases

Cathepsins are an important category of enzymes that have attracted great attention for the delivery of drugs to improve the therapeutic outcome of a broad range of nanoscale drug delivery systems. These proteases can be utilized for instance through actuation of polymer-drug conjugates (e.g., triggering the drug release) to bypass limitations of many drug candidates. A substantial amount of work has been witnessed in the design and the evaluation of Cathepsin-sensitive drug delivery systems, especially based on the tetra-peptide sequence (Gly-Phe-Leu-Gly, GFLG) which has been extensively used as a spacer that can be cleaved in the presence of Cathepsin B. This Review Article will give an in-depth overview of the design and the biological evaluation of Cathepsin-sensitive drug delivery systems and their application in different pathologies including cancer before discussing Cathepsin B-cleavable prodrugs under clinical trials.

pH-Responsive Emulsions with β-Cyclodextrin/Vitamin E Assembled Shells for Controlled Delivery of Polyunsaturated Fatty Acids

Lipid-based delivery systems (LBDSs) are widely applied in pharmaceuticals and health care because of the increased bioavailability of lipophilic components when they are coadministered with high-fat meals. However, how to accurately control their in vivo release and stability is still challenging. Here, after introducing the simple esterification and coprecipitation, we created the dual-functional composite ODS-β-CD-VE by the coassembly of β-cyclodextrin (β-CD), octadecenyl succinic anhydride (ODSA), and vitamin E (VE). The resulting dual-functional particle presented a uniform sheetlike shape and nanometer size. In addition, its chemical structure was clarified in detail via nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Benefiting from the antioxygenation of VE, lipid oxidation in the ODS-β-CD-VE-stabilized Pickering emulsion was effectively inhibited. Meanwhile, pH-induced protonation/deprotonation of carboxyl groups guaranteed that the emulsions kept steady at pH ≤4 but were unsteady under neutral conditions. In this way, the lipids contained in the emulsion were protected from gastric juice and then digested and accurately released as n-3 polyunsaturated fatty acids (PUFA) in the simulated intestine environment. This strategy sheds some light on the rational and efficient construction of LBDSs for nutrient supplements and even pharmaceuticals in a living digestive tract.

Sensors for Proteolytic Activity Visualization and Their Application in Animal Models of Human Diseases

Various sensors designed for optical and photo(opto)acoustic imaging in living systems are becoming essential components of basic and applied biomedical research. Some of them including those developed for determining enzyme activity in vivo are becoming commercially available. These sensors can be used for various fluorescent signal detection methods: from whole body tomography to endoscopy with miniature cameras. Sensor molecules including enzyme-cleavable macromolecules carrying multiple quenched near-infrared fluorophores are able to deliver their payload in vivo and have long circulation time in bloodstream enabling detection of enzyme activity for extended periods of time at low doses of these sensors. In the future, more effective "activated" probes are expected to become available with optimized sensitivity to enzymatic activity, spectral characteristics suitable for intraoperative imaging of surgical field, biocompatibility and lack of immunogenicity and toxicity. New in vivo optical imaging methods such as the fluorescence lifetime and photo(opto)acoustic imaging will contribute to early diagnosis of human diseases. The use of sensors for in vivo optical imaging will include more extensive preclinical applications of experimental therapies. At the same time, the ongoing development and improvement of optical signal detectors as well as the availability of biologically inert and highly specific fluorescent probes will further contribute to the introduction of fluorescence imaging into the clinic.

Towards Developing Bioresponsive, Self-Assembled Peptide Materials: Dynamic Morphology and Fractal Nature of Nanostructured Matrices

(Arginine-alanine-aspartic acid-alanine)₄ ((RADA)₄) nanoscaffolds are excellent candidates for use as peptide delivery vehicles: they are relatively easy to synthesize with custom bio-functionality, and assemble in situ to allow a focal point of release. This enables (RADA)₄ to be utilized in multiple release strategies by embedding a variety of bioactive molecules in an all-in-one "construct". One novel strategy focuses on the local, on-demand release of peptides triggered via proteolysis of tethered peptide sequences. However, the spatial-temporal morphology of self-assembling nanoscaffolds may greatly influence the ability of enzymes to both diffuse into as well as actively cleave substrates. Fine structure and its impact on the overall effect on peptide release is poorly understood. In addition, fractal networks observed in nanoscaffolds are linked to the fractal nature of diffusion in these systems. Therefore, matrix morphology and fractal dimension of virgin (RADA)₄ and mixtures of (RADA)₄ and matrix metalloproteinase 2 (MMP-2) cleavable substrate modified (RADA)₄ were characterized over time. Sites of high (glycine-proline-glutamine-glycine+isoleucine-alanine-serine-glutamine (GPQG+IASQ), CP1) and low (glycine-proline-glutamine-glycine+proline-alanine-glycine-glutamine (GPQG+PAGQ), CP2) cleavage activity were chosen. Fine structure was visualized using transmission electron microscopy. After 2 h of incubation, nanofiber networks showed an established fractal nature; however, nanofibers continued to bundle in all cases as incubation times increased. It was observed that despite extensive nanofiber bundling after 24 h of incubation time, the CP1 and CP2 nanoscaffolds were susceptible to MMP-2 cleavage. The properties of these engineered nanoscaffolds characterized herein illustrate that they are an excellent candidate as an enzymatically initiated peptide delivery platform.

Modular Synthesis of Bioreducible Gene Vectors through Polyaddition of N,N'-Dimethylcystamine and Diglycidyl Ethers

Bioreducible, cationic linear poly(amino ether)s (PAEs) were designed as promising gene vectors. These polymers were synthesized by the reaction of a disulfide-functional monomer, N,N'-dimethylcystamine (DMC), and several different diglycidyl ethers. The resulting PAEs displayed a substantial buffer capacity (up to 64%) in the endosomal acidification region of pH 7.4⁻5.1. The PAEs condense plasmid DNA into 80⁻200 nm sized polyplexes, and have surface charges ranging from +20 to +40 mV. The polyplexes readily release DNA upon exposure to reducing conditions (2.5 mM DTT) due to the cleavage of the disulfide groups that is present in the main chain of the polymers, as was demonstrated by agarose gel electrophoresis. Upon exposing COS-7 cells to polyplexes that were prepared at polymer/DNA w/w ratios below 48, cell viabilities between 80⁻100% were observed, even under serum-free conditions. These polyplexes show comparable or higher transfection efficiencies (up to 38%) compared to 25 kDa branched polyethylenimine (PEI) polyplexes (12% under serum-free conditions). Moreover, the PAE-based polyplexes yield transfection efficiencies as high as 32% in serum-containing medium, which makes these polymers interesting for gene delivery applications.

A Transformable Chimeric Peptide for Cell Encapsulation to Overcome Multidrug Resistance

Multidrug resistance (MDR) remains one of the biggest obstacles in chemotherapy of tumor mainly due to P-glycoprotein (P-gp)-mediated drug efflux. Here, a transformable chimeric peptide is designed to target and self-assemble on cell membrane for encapsulating cells and overcoming tumor MDR. This chimeric peptide (C₁₆ -K(TPE)-GGGH-GFLGK-PEG₈ , denoted as CTGP) with cathepsin B-responsive and cell membrane-targeting abilities can self-assemble into nanomicelles and further encapsulate the therapeutic agent doxorubicin (termed as CTGP@DOX). After the cleavage of the Gly-Phe-Leu-Gly (GFLG) sequence by pericellular overexpressed cathepsin B, CTGP@DOX is dissociated and transformed from spherical nanoparticles to nanofibers due to the hydrophilic-hydrophobic conversion and hydrogen bonding interactions. Thus obtained nanofibers with cell membrane-targeting 16-carbon alkyl chains can adhere firmly to the cell membrane for cell encapsulation and restricting DOX efflux. In comparison to free DOX, 45-time higher drug retention and 49-fold greater anti-MDR ability of CTGP@DOX to drug-resistant MCF-7R cells are achieved. This novel strategy to encapsulate cells and reverse tumor MDR via morphology transformation would open a new avenue towards chemotherapy of tumor.

Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents

We review recent advances in the design and application of excited-state intramolecular proton-transfer (ESIPT) based fluorescent probes. These sensors and imaging agents (probes) are important in biology, physiology, pharmacology, and environmental science.

Intelligent "Peptide-Gathering Mechanical Arm" Tames Wild "Trojan-Horse" Peptides for the Controlled Delivery of Cancer Nanotherapeutics

Cell-penetrating peptides (CPPs), also called "Trojan-Horse" peptides, have been used for facilitating intracellular delivery of numerous diverse cargoes and even nanocarriers. However, the lack of targeting specificity ("wildness" or nonselectivity) of CPP-nanocarriers remains an intractable challenge for many in vivo applications. In this work, we used an intelligent "peptide-gathering mechanical arm" (Int PMA) to curb CPPs' wildness and enhance the selectivity of R₉-liposome-based cargo delivery for tumor targeting. The peptide NGR, serving as a cell-targeting peptide for anchoring, and peptide PLGLAG, serving as a substrate peptide for deanchoring, were embedded in the Int PMA motif. The Int PMA construct was designed to be sensitive to tumor microenvironmental stimuli, including aminopeptidase N (CD13) and matrix metalloproteinases (MMP-2/9). Moreover, Int PMA could be specifically recognized by tumor tissues via CD13-mediated anchoring and released for cell entry by MMP-2/9-mediated deanchoring. To test the Int PMA design, a series of experiments were conducted in vitro and in vivo. Functional conjugates Int PMA-R₉-poly(ethylene glycol) (PEG)₂₀₀₀-distearoylphosphatidyl-ethanolamine (DSPE) and R₉-PEG₂₀₀₀-DSPE were synthesized by Michael addition reaction and were characterized by thin-layer chromatography and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The Int PMA-R₉-modified doxorubicin-loaded liposomes (Int PMA-R₉-Lip-DOX) exhibited a proper particle diameter (approximately 155 nm) with in vitro sustained release characteristics. Cleavage assay showed that Int PMA-R₉ peptide molecules could be cleaved by MMP-2/9 for completion of deanchoring. Flow cytometry and confocal microscopy studies indicated that Int PMA-R₉-Lip-DOX can respond to both endogenous and exogenous stimuli in the presence/absence of excess MMP-2/9 and MMP-2/9 inhibitor (GM6001) and effectively function under competitive receptor-binding conditions. Moreover, Int PMA-R₉-Lip-DOX generated more significant subcellular dispersions that were especially evident within endoplasmic reticulum (ER) and Golgi apparatus. Notably, Int PMA-R₉-Lip-DOX could induce enhanced apoptosis, during which caspase 3/7 might be activated. In addition, Int PMA-R₉-Lip-DOX displayed enhanced in vitro and in vivo antitumor efficacy versus "wild" R₉-Lip-DOX. On the basis of investigations at the molecular level, cellular level, and animals' level, the control of Int PMA was effective and promoted selective delivery of R₉-liposome cargo to the target site and reduced nonspecific uptake. This Int PMA-controlled strategy based on aminopeptidase-guided anchoring and protease-triggered deanchoring effectively curbed the wildness of CPPs and bolstered their effectiveness for in vivo delivery of nanotherapeutics. The specific nanocarrier delivery system used here could be adapted using a variety of intelligent designs based on combinations of multifunctional peptides that would specifically and preferentially bind to tumors versus nontumor tissues for tumor-localized accumulation in vivo. Thus, CPPs have a strong advantage for the development of intelligent nanomedicines for targeted tumor therapy.

Metal-bound claMP Tag inhibits proteolytic cleavage

Biologics can be an improvement to small molecule drugs, providing high specificity for an identified target, lowering toxicity and limiting side effects. To achieve effective delivery, the biologic must have sufficient time to reach the target tissue. A prolonged half-life in the circulating environment is desired, but often serum stability is limited by proteases. Proteolysis in the serum causes degradation and inactivation as the biologic is fragmented and more rapidly cleared from the body. To improve the circulating half-life, large, hydrophilic polymers may be conjugated or stable fusion tags may be engineered to increase the effective size of the peptide and to hinder degradation by proteases. Improved resistance to proteases is essential for effective delivery. Here, a proof of concept study is presented using a metal-binding tripeptide tag known as the claMP Tag to create an inline conjugate and the ability of the tag to inhibit proteolysis was examined.

Preparation of intravenous injection nanoformulation via co-assemble between cholesterylated gemcitabine and cholesterylated mPEG: enhanced cellular uptake and intracellular drug controlled release

The objective of this study was to prepare the CHS-mPEG/CHS-dFdC nanoformulation could be administrated through intravenous injection in nude mice. Particularly, CHS-mPEG was selected to co-assemble with CHS-dFdC to improve the prodrug concentration and enhance the stability of nanoformulation. The nanoformulation could be prepared by codissolution-coprecipitation. All of the nanoformulations kept stable in PBS at 4 °C or simulative human plasma at 37 °C. As molar ratios of CHS-mPEG₁₉₀₀/CHS-dFdC increased from 0.1/1 to 2/1, the weight concentration of CHS-dFdC increased from 2.5 to 15 mg/mL. It was found the optimal CHS-mPEG₁₉₀₀/CHS-dFdC nanoformulation displayed controlled drug release in simulative lysosome condition. The amount of released dFdC reached up to 90% within 10 h. It also exhibited enhanced cellular uptake ability, 7-folds higher than that of dFdC during 2.5 h incubation. And it showed superior cytotoxicity resulted from the enhanced cellular uptake ability on BxPC-3 cells.

Neural tissue engineering: Bioresponsive nanoscaffolds using engineered self-assembling peptides

Rescuing or repairing neural tissues is of utmost importance to the patient's quality of life after an injury. To remedy this, many novel biomaterials are being developed that are, ideally, non-invasive and directly facilitate neural wound healing. As such, this review surveys the recent approaches and applications of self-assembling peptides and peptide amphiphiles, for building multi-faceted nanoscaffolds for direct application to neural injury. Specifically, methods enabling cellular interactions with the nanoscaffold and controlling the release of bioactive molecules from the nanoscaffold for the express purpose of directing endogenous cells in damaged or diseased neural tissues is presented. An extensive overview of recently derived self-assembling peptide-based materials and their use as neural nanoscaffolds is presented. In addition, an overview of potential bioactive peptides and ligands that could be used to direct behaviour of endogenous cells are categorized with their biological effects. Finally, a number of neurotrophic and anti-inflammatory drugs are described and discussed. Smaller therapeutic molecules are emphasized, as they are thought to be able to have less potential effect on the overall peptide self-assembly mechanism. Options for potential nanoscaffolds and drug delivery systems are suggested.

STATEMENT OF SIGNIFICANCE

Self-assembling nanoscaffolds have many inherent properties making them amenable to tissue engineering applications: ease of synthesis, ease of customization with bioactive moieties, and amenable for in situ nanoscaffold formation. The combination of the existing knowledge on bioactive motifs for neural engineering and the self-assembling propensity of peptides is discussed in specific reference to neural tissue engineering.

Induced Neural Differentiation of MMP-2 Cleaved (RADA)4 Drug Delivery Systems

(RADA)₄ self-assembling peptides (SAPs) are promising for neural nanoscaffolds with on-demand drug delivery capabilities due to their automated synthesis, in-situ assembly, and potential for interaction with and release of biomolecules. Neuroinflammation cued on-demand drug release, due to up-regulated proteases, may well be vital in the treatment of several neurological diseases. In these conditions, releasing neurotrophic growth factors (NTFs) could potentially lead to neuroprotection and neurogenesis. As such, (RADA)₄ was made with the high and low activity matrix metalloproteinase 2 (MMP-2) cleaved sequences, GPQG+IASQ (CP1) and GPQG+PAGQ (CP2), the brain-derived NTF secretion stimulating peptide MVG (DP1) and the ciliary NTF analogue DGGL (DP2). PC-12 cell culture was performed to assess bioactive substrate cell adhesion and NTF specific neuronal differentiation. The laminin-derived IKVAV peptide, known for neural cell attachment and interaction, was tethered to (RADA)₄-IKVAV and mixed in increasing increments with (RADA)₄ for this purpose. With 1 nanomolar MMP-2 treatment, product formation was observed to increase over a three day period, with (RADA)₄/(RADA)₄-CP1/CP2 mixture, however there was little difference between groups. Smaller CP1/CP2 concentrations displayed comparable (RADA)₄ nanoscale morphology to higher concentrations. Acetylcholine esterase and neural differentiation was observed over 3 days with 1 nM MMP-2 treatment according to the following makeup: 8/1/1 (RADA)4/(RADA)4-IKVAV/(RADA)4-CP1/CP2-DP1/DP2. Signalling gradually increased in all groups, and neurite outgrowth was visible after three days.

Anticancer nanoparticulate polymer-drug conjugate

We review recent progress in polymer-drug conjugate for cancer nanomedicine. Polymer-drug conjugates, including the nanoparticle prepared from these conjugates, are designed to release drug in tumor tissues or cells in order to improve drugs' therapeutic efficacy. We summarize general design principles for the polymer-drug conjugate, including the synthetic strategies, the design of the chemical linkers between the drug and polymer in the conjugate, and the in vivo drug delivery barriers for polymer-drug conjugates. Several new strategies, such as the synthesis of polymer-drug conjugates and supramolecular-drug conjugates, the use of stimulus-responsive delivery, and triggering the change of the nanoparticle physiochemical properties to over delivery barriers, are also highlighted.

Substrate-based near-infrared imaging sensors enable fluorescence lifetime contrast via built-in dynamic fluorescence quenching elements

Enzymatic activity sensing in fluorescence lifetime (FLT) mode with "self-quenched" macromolecular near-infrared (NIR) sensors is a highly promising strategy for in vivo imaging of proteolysis. However, the mechanisms of FLT changes in such substrate-based NIR sensors have not yet been studied. We synthesized two types of sensors by linking the near-infrared fluorophore IRDye 800CW to macromolecular graft copolymers of methoxy polyethylene glycol and polylysine (MPEG-gPLL) with varying degrees of MPEGylation and studied their fragmentation induced by trypsin, elastase, plasmin and cathepsins (B,S,L,K). We determined that the efficiency of such NIR sensors in FLT mode depends on sensor composition. While MPEG-gPLL with a high degree of MPEGylation showed rapid (τ1/2=0.1-0.2 min) FLT increase (Δτ=0.25 ns) upon model proteinase-mediated hydrolysis in vivo, lower MPEGylation density resulted in no such FLT increase. Temperature-dependence of fluorescence de-quenching of NIR sensors pointed to a mixed dynamic/static-quenching mode of MPEG-gPLL-linked fluorophores. We further demonstrated that although the bulk of sensor-linked fluorophores were de-quenched due to the elimination of static quenching, proteolysis-mediated deletion of a fraction of short (8-10kD) negatively charged fragments of highly MPEGylated NIR sensor is the most likely event leading to a rapid FLT increase phenomenon in quenched NIR sensors. Therefore, the optimization of "built-in" dynamic quenching elements of macromolecular NIR sensors is a potential avenue for improving their response in FLT mode.

In Vitro and in Vivo Demonstration of Photodynamic Activity and Cytoplasm Imaging through TPE Nanoparticles

We synthesized novel tetraphenylethene (TPE) conjugates, which undergo unique self-assembly to form spherical nanoparticles that exhibited aggregation induced emission (AIE) in the near-infrared region. These nanoparticles showed significant singlet oxygen generation efficiency, negligible dark toxicity, rapid cellular uptake, efficient localization in cytoplasm, and high in vitro photocytotoxicity as well as in vivo photodynamic activity against a human prostate tumor animal model. This study demonstrates, for the first time, the power of the self-assembled AIE active tetraphenylethene conjugates in aqueous media as a nanoplatform for future therapeutic applications.

Peptide-substituted phthalocyanine photosensitizers: design, synthesis, photophysicochemical and photobiological studies

Activatable molecular beacons were synthesized bearing phthalocyanine, peptide sequence and fluorophore groups. The phototoxicity and cytotoxicity of the systems were studied against the cervical cancer cell line named HeLa for evaluation of their suitability for photodynamic therapy.

Development of gelatin nanoparticles conjugated with phytohemagglutinin erythroagglutinating loaded with gemcitabine for inducing apoptosis in non-small cell lung cancer cells

Fluorescent gelatin nanoparticles (GNPs) conjugated with PHA-E and carried gemcitabine were synthesized by nanoprecipitation for targeting and treatment of NSCLC cells.

Development of PEGylated peptide probes conjugated with (18)F-labeled BODIPY for PET/optical imaging of MT1-MMP activity

Since the processing activity of the matrix metalloproteinase MT1-MMP regulates various cellular functions such as motility, invasion, growth, differentiation and apoptosis, precise in vivo evaluation of MT1-MMP activity in cancers can provide beneficial information for both basic and clinical studies. For this purpose, we designed a cleavable Positron Emission Tomography (PET)/optical imaging probe consisting of BODIPY650/665 and polyethylene glycol (PEG) conjugated to opposite ends of MT1-MMP substrate peptides. We used in vitro and in vivo fluorescence experiments to select suitable substrate peptide sequences and PEG sizes for the MT1-MMP probes and obtained an optimized structure referred to here as MBP-2k. Radiofluorinated MBP-2k ([(18)F]MBP-2k) was then successfully synthesized via an (18)F-(19)F isotopic exchange reaction in BODIPY650/665. After intravenous injection into mice with xenografted tumors, [(18)F]MBP-2k showed significantly higher accumulation in HT1080 tumors with high MT1-MMP activity than in A549 tumors that have low MT1-MMP activity. Moreover, PET images showed better contrast in HT1080 tumors. These results show that [(18)F]MBP-2k can be used as a hybrid PET/optical imaging agent and is a promising probe for non-invasive monitoring of MT1-MMP activity in cancers. This probe may also efficiently combine targeted tumor imaging with image-guided surgery that could be beneficial for patients in the future.

Silica nanoparticle-based dual imaging colloidal hybrids: cancer cell imaging and biodistribution

In this study, fluorescent dye-conjugated magnetic resonance (MR) imaging agents were investigated in T mode. Gadolinium-conjugated silica nanoparticles were successfully synthesized for both MR imaging and fluorescence diagnostics. Polyamine and polycarboxyl functional groups were modified chemically on the surface of the silica nanoparticles for efficient conjugation of gadolinium ions. The derived gadolinium-conjugated silica nanoparticles were investigated by zeta potential analysis, transmission electron microscopy, inductively coupled plasma mass spectrometry, and energy dispersive x-ray spectroscopy. MR equipment was used to investigate their use as contrast-enhancing agents in T₁ mode under a 9.4 T magnetic field. In addition, we tracked the distribution of the gadolinium-conjugated nanoparticles in both lung cancer cells and organs in mice.

pH-Responsive and near-infrared-emissive polymer nanoparticles for simultaneous delivery, release, and fluorescence tracking of doxorubicin in vivo

Dextran modified with pendant acetals is used to load doxorubicin (DOX) and a near-infrared-emissive conjugated polymer (BTTPF), and this aims to provide selective drug release at therapeutic targets including tumors. The BTTPF is applicable to tracking the anticancer drug release through the change of Förster resonance energy transfer efficiency between doxorubicin and BTTPF during degradation of the nanoparticles in vivo.

Bioresponsive probes for molecular imaging: concepts and in vivo applications

Molecular imaging is a powerful tool to visualize and characterize biological processes at the cellular and molecular level in vivo. In most molecular imaging approaches, probes are used to bind to disease-specific biomarkers highlighting disease target sites. In recent years, a new subset of molecular imaging probes, known as bioresponsive molecular probes, has been developed. These probes generally benefit from signal enhancement at the site of interaction with its target. There are mainly two classes of bioresponsive imaging probes. The first class consists of probes that show direct activation of the imaging label (from "off" to "on" state) and have been applied in optical imaging and magnetic resonance imaging (MRI). The other class consists of probes that show specific retention of the imaging label at the site of target interaction and these probes have found application in all different imaging modalities, including photoacoustic imaging and nuclear imaging. In this review, we present a comprehensive overview of bioresponsive imaging probes in order to discuss the various molecular imaging strategies. The focus of the present article is the rationale behind the design of bioresponsive molecular imaging probes and their potential in vivo application for the detection of endogenous molecular targets in pathologies such as cancer and cardiovascular disease.

Enhancement of anti-tumor activity of hybrid peptide in conjugation with carboxymethyl dextran via disulfide linkers

To improve the anti-tumor activity of EGFR2R-lytic hybrid peptide, we prepared peptide-modified dextran conjugates with the disulfide bonds between thiolated carboxymethyl dextran (CMD-Cys) and cysteine-conjugated peptide (EGFR2R-lytic-Cys). In vitro release studies showed that the peptide was released from the CMD-s-s-peptide conjugate in a concentration-dependent manner in the presence of glutathione (GSH, 2μM-2mM). The CMD-s-s-peptide conjugate exhibited a similar cytotoxic activity with free peptide alone against human pancreatic cancer BxPC-3 cells in vitro. Furthermore, it was shown that the CMD-s-s-peptide conjugates were highly accumulated in tumor tissue in a mouse xenograft model using BxPC-3 cells, and the anti-tumor activity of the conjugate was more effective than that of the free peptide. In addition, the plasma concentrations of peptide were moderately increased and the elimination half-life of the peptide was prolonged after intravenous injection of CMD-s-s-peptide conjugates. These results demonstrated that the conjugate based on thiolated CMD polymer would be potentially useful carriers for the sustained release of the hybrid peptide in vivo.

Redox-responsive polymer-drug conjugates based on doxorubicin and chitosan oligosaccharide-g-stearic acid for cancer therapy

Here, a biodegradable polymer-drug conjugate of doxorubicin (DOX) conjugated with a stearic acid-grafted chitosan oligosaccharide (CSO-SA) was synthesized via disulfide linkers. The obtained polymer-drug conjugate DOX-SS-CSO-SA could self-assemble into nanosized micelles in aqueous medium with a low critical micelle concentration. The size of the micelles was 62.8 nm with a narrow size distribution. In reducing environments, the DOX-SS-CSO-SA could rapidly disassemble result from the cleavage of the disulfide linkers and release the DOX. DOX-SS-CSO-SA had high efficiency for cellular uptake and rapidly released DOX in reductive intracellular environments. In vitro antitumor activity tests showed that the DOX-SS-CSO-SA had higher cytotoxicity against DOX-resistant cells than free DOX, with reversal ability up to 34.8-fold. DOX-SS-CSO-SA altered the drug distribution in vivo, which showed selectively accumulation in tumor and reduced nonspecific accumulation in hearts. In vivo antitumor studies demonstrated that DOX-SS-CSO-SA showed efficient suppression on tumor growth and relieved the DOX-induced cardiac injury. Therefore, DOX-SS-CSO-SA is a potential drug delivery system for safe and effective cancer therapy.

Surface charge-reversible polyelectrolyte complex nanoparticles for hepatoma-targeting delivery of doxorubicin

Polymeric nanoparticles are greatly advancing the field of nanomedicine due to their ability for targeted and controlled drug release.

An authentic imaging probe to track cell fate from beginning to end

Accurate tracing of cell viability is critical for optimizing delivery methods and evaluating the efficacy and safety of cell therapeutics. A nanoparticle-based cell tracker is developed to image cell fate from live to dead. The particle is fabricated from two types of optically quenched polyelectrolytes, a life indicator and a death indicator, through electrostatic interactions. On incubation with cells, the fabricated bifunctional nanoprobes are taken up efficiently and the first colour is produced by normal intracellular proteolysis, reflecting the healthy status of the cells. Depending on the number of coated layers, the signal can persist for several replication cycles. However, as the cells begin dying, the second colour appears quickly to reflect the new cell status. Using this chameleon-like cell tracker, live cells can be distinguished from apoptotic and necrotic cells instantly and definitively.

Engineered nanoparticles for drug delivery in cancer therapy

In medicine, nanotechnology has sparked a rapidly growing interest as it promises to solve a number of issues associated with conventional therapeutic agents, including their poor water solubility (at least, for most anticancer drugs), lack of targeting capability, nonspecific distribution, systemic toxicity, and low therapeutic index. Over the past several decades, remarkable progress has been made in the development and application of engineered nanoparticles to treat cancer more effectively. For example, therapeutic agents have been integrated with nanoparticles engineered with optimal sizes, shapes, and surface properties to increase their solubility, prolong their circulation half-life, improve their biodistribution, and reduce their immunogenicity. Nanoparticles and their payloads have also been favorably delivered into tumors by taking advantage of the pathophysiological conditions, such as the enhanced permeability and retention effect, and the spatial variations in the pH value. Additionally, targeting ligands (e.g., small organic molecules, peptides, antibodies, and nucleic acids) have been added to the surface of nanoparticles to specifically target cancerous cells through selective binding to the receptors overexpressed on their surface. Furthermore, it has been demonstrated that multiple types of therapeutic drugs and/or diagnostic agents (e.g., contrast agents) could be delivered through the same carrier to enable combination therapy with a potential to overcome multidrug resistance, and real-time readout on the treatment efficacy. It is anticipated that precisely engineered nanoparticles will emerge as the next-generation platform for cancer therapy and many other biomedical applications.

In vivo Overhauser-enhanced MRI of proteolytic activity

There is an increasing interest in developing novel imaging strategies for sensing proteolytic activities in intact organisms in vivo. Overhauser-enhanced MRI (OMRI) offers the possibility to reveal the proteolysis of nitroxide-labeled macromolecules thanks to a sharp decrease of the rotational correlation time of the nitroxide moiety upon cleavage. In this paper, this concept is illustrated in vivo at 0.2 T using nitroxide-labeled elastin orally administered in mice. In vitro, this elastin derivative was OMRI-visible and gave rise to high Overhauser enhancements (19-fold at 18 mm nitroxide) upon proteolysis by pancreatic porcine elastase. In vivo three-dimensional OMRI detection of proteolysis was carried out. A keyhole fully balanced steady-state free precession sequence was used, which allowed 3D OMRI acquisition within 20 s at 0.125 mm(3) resolution. About 30 min after mouse gavage, proteolysis was detected in the duodenum, where Overhauser enhancements were 7.2 ± 2.4 (n = 7) and was not observed in the stomach. Conversely, orally administered free nitroxides or pre-digested nitroxide-labeled elastin were detected in the mouse's stomach by OMRI. Combined with specific molecular probes, this Overhauser-enhanced MRI technique can be used to evaluate unregulated proteolytic activities in various models of experimental diseases and for drug testing.

Undesired versus designed enzymatic cleavage of linkers for liver targeting

A design for the selective release of drug molecules in the liver was tested, involving the attachment of a representative active agent by an ester linkage to various 2-substituted 5-aminovaleric acid carbamates. The anticipated pathway of carboxylesterase-1-mediated carbamate cleavage followed by lactamization and drug release was frustrated by unexpectedly high sensitivity of the ester linkage toward hydrolysis by carboxylesterase-2 and other microsomal components.

Synthesis, characterization and antimicrobial activity of conjugates based on fluoroquinolon-type antibiotics and gelatin

Different fluoroquinolon-type antibiotics were conjugated to gelatin with the aim to synthesize biomacromolecules with antimicrobial properties. The covalent linkage of the antibiotic was performed by a radical process involving the residues in the side chains of gelatin able to undergo oxidative modifications. The conjugation of antibiotic moieties onto the protein structure was confirmed by FT-IR, UV-Vis, fluorescence, and calorimetric analyses. Biocompatibility tests were performed on human bone marrow mesenchymal stromal cells and the antibacterial properties of bioactive polymers were investigated by appropriate tests against Klebsiella pneumoniae and Escherichia coli. With regard to the tests conducted in the presence of E. coli, a minimum inhibitory concentration (MIC) ranging from 0.05 to 0.40 μg mL(-1) was recorded, while in the presence of K. pneumoniae this concentration varies from 0.10 to 1.60 μg mL(-1). In all the conjugates, the drug moieties retain their biological activity and the MIC values are lower than the resistance parameters of fluoroquinolon-type antibiotics versus Enterobacteriacae. The collected data suggest a broad range of applications, from biomedical to pharmaceutical and food science for all conjugates.

A new colorimetric strategy for monitoring caspase 3 activity by HRP-mimicking DNAzyme–peptide conjugates

A new colorimetric method is designed for the detection of caspase 3 activity by HRP-mimicking DNAzyme–peptide conjugates.