A Polymer Micelle Responding to the Protein Kinase A Signal

Applications and Mechanisms of Stimuli-Responsive Hydrogels in Traumatic Brain Injury

Traumatic brain injury (TBI) is a global neurotrauma with high morbidity and mortality that seriously threatens the life quality of patients and causes heavy burdens to families, healthcare institutions, and society. Neuroinflammation and oxidative stress can further aggravate neuronal cell death, hinder functional recovery, and lead to secondary brain injury. In addition, the blood–brain barrier prevents drugs from entering the brain tissue, which is not conducive to the recovery of TBI. Due to their high water content, biodegradability, and similarity to the natural extracellular matrix (ECM), hydrogels are widely used for the delivery and release of various therapeutic agents (drugs, natural extracts, and cells, etc.) that exhibit beneficial therapeutic efficacy in tissue repair, such as TBI. Stimuli-responsive hydrogels can undergo reversible or irreversible changes in properties, structures, and functions in response to internal/external stimuli or physiological/pathological environmental stimuli, and further improve the therapeutic effects on diseases. In this paper, we reviewed the common types of stimuli-responsive hydrogels and their applications in TBI, and further analyzed the therapeutic effects of hydrogels in TBI, such as pro-neurogenesis, anti-inflammatory, anti-apoptosis, anti-oxidation, and pro-angiogenesis. Our study may provide strategies for the treatment of TBI by using stimuli-responsive hydrogels.

Redox-responsive nanoparticles from disulfide bond-linked poly-(N-ε-carbobenzyloxy-l-lysine)-grafted hyaluronan copolymers as theranostic nanoparticles for tumor-targeted MRI and chemotherapy

Redox-responsive theranostic nanoparticles based on poly-(N-ε-carbobenzyloxy-l-lysine) (PZLL) grafted hyaluronan (HA) (HA-g-SS-PZLL) copolymers were constructed for hepatocellular carcinoma diagnosis and therapy. These hyaluronan derivatives formed nanoparticles via a self-assembly process in aqueous solution at low concentration. Theranostic nanoparticles were obtained after loading hydrophobic doxorubicin (DOX) and superparamagnetic iron oxide (SPIO) into the core of the nanoparticles via a dialysis method. Theranostic nanoparticles exhibited redox triggered DOX release behavior, and faster DOX released from theranostic nanoparticles was detected under a reducing environment compared with slow DOX release under a normal physiological environment. Confocal laser scanning microscopy (CLSM), flow cytometry and Prussian blue staining against HepG2 cells demonstrated that HA-g-SS-PZLL theranostic nanoparticles were capable of delivering DOX and SPIO into the cells. The analysis of the anticancer effect revealed that the HA-g-SS-PZLL theranostic nanoparticles shown higher cytotoxicity against HepG2 cells than DOX-loaded HA-g-PZLL nanoparticles. In vitro T₂ magnetic resonance imaging (MRI) results exhibited that theranostic nanoparticles showed a good contrast enhancement effect, and the r₂ relaxivity value was approximately 231 Fe mM^-1 s^-1. Finally, the theranostic nanoparticles acted as nanoprobes for HepG2 tumor-bearing BALB/c mice for in vivo MRI. Therefore, HA-g-SS-PZLL copolymers have great potential as theranostic nanoparticles for tumor-targeted diagnosis and treatment.

Isothermal kinase-triggered supramolecular assemblies as drug sensitizers

Protein kinases, the main regulators of a vast map of cellular processes, are the most attractive targets in drug discovery. Despite a few successful examples of protein kinase inhibitors, the drug discovery strategy of downregulating protein kinase activity has been quite limited and often fails even in animal models. Here, we utilize protein kinase A (PKA) activity to design PKA-triggered supramolecular assemblies with anticancer activities. Grafting a suitable peptide to PNIPAM raises the critical temperature of the LCST polymer above body temperature. Interestingly, the corresponding phosphorylated polymer has a critical temperature below body temperature, making this peptide-appended PNIPAM a suitable polymer for the PKA-triggered supramolecular assembly process. PKA-triggered assembly occurs selectively in PKA-upregulated MCF-7 cells, which disturbs the cytoskeleton and sensitizes cancer cells against doxorubicin. The chemosensitization is also observed in vivo to identify effective tumor inhibitors with satisfactory biocompatibility. Overall, this phosphorylation-induced (in principle, PKA-catalyzed) supramolecular assembly opens up a promising chemotherapy strategy for combating kinase-upregulated cancer.

A nonapeptide grafted LCST polymer undergoes enzymatic phosphorylation to assemble, which selectively disrupts PKA overexpressing cancer cells via kinetics targeting.

Comprehensive Insight into the Protein-Surface Biomolecular Interactions on a Smart Material: Complex Formation between Poly(N-vinyl Caprolactam) and Heme Protein

Proteins are naturally occurring biopolymers that exhibit a wide range of functional applications. Meticulous knowledge about biomolecular interactions between polymeric biomaterials and body fluids or proteins is essential for designing biospecific surfaces and understanding protein-polymer interactions beyond existing limitations. In this regard, we studied the comparative effect of heme proteins such as cytochrome c, myoglobin, and hemoglobin on the phase behavior of poly(N-vinyl caprolactam) (PVCL) aqueous solution and demonstrated various biomolecular interactions in the polymer-protein complex with the aid of various biophysical techniques. Absorption spectroscopy, steady-state fluorescence spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering studies, laser Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy were carried out at room temperature to examine the changes in absorbance, fluorescence intensity, molecular interactions, particle size, agglomeration behavior, and surface morphologies. Furthermore, differential scanning calorimetry studies were also performed to analyze conformational changes, coil to globule transition, and phase behavior in the presence of proteins. With the addition of heme proteins, the lower critical solution temperature of PVCL increases toward higher temperature. The present study may help in designing smart biomaterials and stimulate more novel concepts in polymer-protein interactions. It also helps in the development of a biomimetic polymer for "smart" applications such as pulsatile drug release systems and controlled bioadhesion by temperature-mediated hydrophilic/hydrophobic switching.

Responsive Polymers as Smart Nanomaterials Enable Diverse Applications

Responsive polymers undergo reversible or irreversible physical or chemical modifications in response to a change in environment or stimulus, e.g., temperature, pH, light, and magnetic or electric fields. Polymeric nanoparticles (NPs), which constitute a diverse set of morphologies, including micelles, vesicles, and core-shell geometries, have been successfully prepared from responsive polymers and have shown great promise in applications ranging from drug delivery to catalysis. In this review, we summarize pH, thermo-, photo-, and enzymatic responsiveness for a selection of polymers. We then discuss the formation of NPs made from responsive polymers. Finally, we highlight how NPs and other nanomaterials are enabling a wide range of smart applications with improved efficiency, as well as improved sustainability and recyclability of polymeric systems.

An insight on the role of photosensitizer nanocarriers for Photodynamic Therapy

Photodynamic therapy (PDT) is a modality of cancer treatment in which tumor cells are destroyed by reactive oxygen species (ROS) produced by photosensitizers following its activation with visible or near infrared light. The PDT success is dependent on different factors namely on the efficiency of the photosensitizer deliver and targeting ability. In this review a special attention will be given to the role of some drug delivery systems to improve the efficiency of tetrapyrrolic photosensitizers to this type of treatment.

Transiently thermoresponsive polymers and their applications in biomedicine

The focus of this review is on the class of transiently thermoresponsive polymers. These polymers are thermoresponsive, but gradually lose this property upon chemical transformation - often a hydrolysis reaction - in the polymer side chain or backbone. An overview of the different approaches used for the design of these polymers along with their physicochemical properties is given. Their amphiphilic properties and degradability into fully soluble compounds make this class of responsive polymers attractive for drug delivery and tissue engineering applications. Examples of these are also provided in this review.

Artificial Control of Gene Silencing Activity Based on siRNA Conjugation with Polymeric Molecule Having Coil-Globule Transition Behavior

A new strategy for controlling gene silencing activity of siRNA in the cell was developed in the present study. siRNA was linearly conjugated with PNIPAAm, where coil-globule transition of the conjugated PNIPAAm allows thermoresponsive exposure of the vicinal siRNA molecule; a coil form of PNIPAAm (T < LCST) inhibits siRNA interaction with gene silencing-related proteins due to the steric hindrance effect, while a globule form of PNIPAAm (T > LCST) allows a ready access of siRNA to gene silencing pathway. As a result, at T > LCST, PNIPAAm-siRNA elicited effective association of siRNA with a gene silencing-related protein of Ago2, while siRNA recruitment into the gene silencing pathway was significantly suppressed at T < LCST. Ultimately, gene silencing efficacy of PNIPAAm-siRNA was close to unconjugated siRNA at T > LCST (∼80%), while it was dramatically decreased to ∼20% at T < LCST, suggesting that coil-globule transition of the conjugated polymer can control the bioactivity of the vicinal siRNA molecule.

Novel pH-responsive polymeric micelles prepared through self-assembly of amphiphilic block copolymer with poly-4-vinylpyridine block synthesized by mechanochemical solid-state polymerization

We fabricated polymeric micelles containing 5-fluorouracil (5-FU) or fluorescein using the amphiphilic block copolymer, poly-4-vinylpyridine-b-6-O-methacryloyl galactopyranose. Although the polymeric micelles were stable at pH 7.4, they readily decomposed at pH 5, resulting in near complete release of 5-FU. Uptake of polymeric micelles containing fluorescein by HepG2 and HCT116 cells was also investigated. With both cell types, strong fluorescence was observed after a 12-h incubation, but the fluorescence weakened after 24 h of incubation. The fluorescein incorporated into the polymeric micelles was released into acidic organelles (endosome and/or lysosome), from which it diffused throughout the cell. The cytotoxicity of polymeric micelles containing 5-FU was evaluated against HepG2 cells using a CCK-8 assay. The results suggest that polymeric micelles containing 5-FU are more cytotoxic to HepG2 cells than free 5-FU.

Water soluble stimuli-responsive star copolymers with multiple encapsulation and release properties

Stimuli-responsive, water soluble, nontoxic, star-copolymers showing reversible encapsulation and release of hydrophobic dye/drug molecule with increasing temperature and decreasing pH.

Bioresponsive polymer-based nucleic acid carriers

Nucleic acid carriers need to possess multifunctionality for overcoming biological barriers, such as the stable encapsulation of nucleic acids in extracellular milieu, internalization by target cells, controlled intracellular distribution, and release of nucleic acids at the target site of action. To fulfill these stepwise functionalities, "bioresponsive" polymers that can alter their structure responding to site-specific biological signals are highly useful. Notably, pH, redox potential, and enzymatic activities vary along with microenvironments in the body, and thus, the responsiveness to these signals enables to construct nucleic acid carriers with programmed functionalities. This chapter describes the design of bioresponsive polymers that respond to various biological microenvironments for smart nucleic acids delivery.

Novel free-paclitaxel-loaded redox-responsive nanoparticles based on a disulfide-linked poly(ethylene glycol)-drug conjugate for intracellular drug delivery: synthesis, characterization, and antitumor activity in vitro and in vivo

To address the obstacles facing cancer chemotherapeutics, including toxicity, side effects, water insolubility, and lack of tumor selectivity, a novel stimuli-responsive drug-delivery system was developed based on paclitaxel-loaded poly(ethylene glycol)-disulfide-paclitaxel conjugate nanoparticles (PEG-SS-PTX/PTX NPs). The formulation emphasizes several benefits, including polymer-drug conjugates/prodrugs, self-assembled NPs, high drug content, redox responsiveness, and programmed drug release. The PTX-loaded, self-assembled NPs, with a uniform size of 103 nm, characterized by DLS, TEM, XRD, DSC, and (1)H NMR, exhibited excellent drug-loading capacity (15.7%) and entrapment efficiency (93.3%). PEG-SS-PTX/PTX NPs were relatively stable under normal conditions but disassembled quickly under reductive conditions, as indicated by their triggered-aggregation phenomena and drug-release profile in the presence of dithiothreitol (DTT), a reducing agent. Additionally, by taking advantage of the difference in the drug-release rates between physically loaded and chemically conjugated drugs, a programmed drug-release phenomenon was observed, which was attributed to a higher concentration and longer action time of the drugs. The influence of PEG-SS-PTX/PTX NPs on in vitro cytotoxicity, cell cycle progression, and cellular apoptosis was determined in the MCF-7 cell line, and the NPs demonstrated a superior anti-proliferative activity associated with PTX-induced cell cycle arrest in G2/M phase and apoptosis compared to their nonresponsive counterparts. Moreover, the redox-responsive NPs were more efficacious than both free PTX and the non-redox-responsive formulation at equivalent doses of PTX in a breast cancer xenograft mouse model. This redox-responsive PTX drug delivery system is promising and can be explored for use in effective intracellular drug delivery.

Temperature-responsive polymeric micelles for optimizing drug targeting to solid tumors

Targeting to solid tumors is the most challenging issue in the drug delivery field. To obtain the ideal pharmacodynamics of administrated drugs, drug carriers must suppress drug release and interactions with non-target tissues while circulating in the bloodstream, yet actively release the incorporated drug and interact with target cells after delivery to the tumor tissue. To handle this situation, stimuli-responsive drug carriers are extremely useful, because carriers change their physicochemical properties to control the drug release rate and interaction with cells in response to the surrounding environmental conditions or applied physical signals. The current review focuses on the strategy and availability of temperature-responsive (TR) polymeric micelles as a next-generation drug carrier. In particular, we discuss the unique properties of TR polymeric micelles, such as temperature-triggered drug release and intracellular uptake system. In addition, we explore the methodology for integrating other targeting systems into TR micelles to pursue the ideal pharmacodynamics in conjunction with thermal therapy as a future prospective of the TR system.

Nanodevices for studying nano-pathophysiology

Nano-scaled devices are a promising platform for specific detection of pathological targets, facilitating the analysis of biological tissues in real-time, while improving the diagnostic approaches and the efficacy of therapies. Herein, we review nanodevice approaches, including liposomes, nanoparticles and polymeric nanoassemblies, such as polymeric micelles and vesicles, which can precisely control their structure and functions for specifically interacting with cells and tissues. These systems have been successfully used for the selective delivery of reporter and therapeutic agents to specific tissues with controlled cellular and subcellular targeting of biomolecules and programmed operation inside the body, suggesting a high potential for developing the analysis for nano-pathophysiology.

Histidinylated poly-L-lysine-based vectors for cancer-specific gene expression via enhancing the endosomal escape

In this work, we synthesized a series of poly-L-lysine (PLL)-based polymers for gene delivery, by modifying the PLL with both cationic peptide and histidine. The peptide moieties serve as cationic centers for polyplex formation, and also as substrates for protein kinase Cα (PKCα), which is specifically activated in many types of cancer cells, to achieve cancer-specific gene expression. The histidine groups serve as buffering moieties to increase the ability of the plasmid DNA (pDNA)-polymer complex (polyplex) to escape the endosome and thus to promote expression of the pDNA in the transfected cells. The facile synthesis of the polymers proceeded by modifying the PLL with side-group-protected peptide and protected histidine, followed by deprotection of the functional groups. The synthesized polymers showed significant buffering capacity over the neutral to acidic pH range and showed less cytotoxicity in vitro compared with histidine-unmodified polymers. The polyplexes successfully showed PKCα-responsive gene expression immediately after their introduction into cancer cells and the gene expression continued for at least 24 h. These PLL-based carriers thus show promise for cancer-targeted gene therapy.

Cell division responsive peptides for optimized plasmid DNA delivery: the mitotic window of opportunity?

The delivery of plasmid DNA remains hard to achieve, especially due to the presence of the nuclear membrane barrier. During cell division, however, the nuclear membrane is temporarily disassembled. We evaluated two different strategies to optimize plasmid DNA delivery in dividing cells: 1) phosphorylation responsive peptides that release plasmid DNA preferentially during mitosis and 2) chromatin targeting peptides to anchor plasmid DNA in newly formed nuclei upon cell division. Peptide/DNA particles alone were not efficient in penetrating cells. Upon co-delivery with lipid-based carriers, however, transfection efficiency drastically improved when compared to controls. For the phosphorylation responsive peptides, the presence of the phosphorylation sequence slightly increased transfection efficiency. For the chromatin targeting peptides, however, the chromatin targeting sequence did not seem to be the main reason for the improvement of transfection efficiency when applied in living cells. In conclusion, the pre-condensation of plasmid DNA with peptides improves lipid based delivery, but the nature of the peptides (cell responsive or not) does not seem to be the main reason for the improvement. It seems that the nuclear entry of foreign plasmid DNA is still under tight control, even during the mitotic window of opportunity.

Enzyme-responsive polymeric assemblies, nanoparticles and hydrogels

Being responsive and adaptive to external stimuli is an intrinsic feature characteristic of all living organisms and soft matter. Specifically, responsive polymers can exhibit reversible or irreversible changes in chemical structures and/or physical properties in response to a specific signal input such as pH, temperature, ionic strength, light irradiation, mechanical force, electric and magnetic fields, and analyte of interest (e.g., ions, bioactive molecules, etc.) or an integration of them. The past decade has evidenced tremendous growth in the fundamental research of responsive polymers, and accordingly, diverse applications in fields ranging from drug or gene nanocarriers, imaging, diagnostics, smart actuators, adaptive coatings, to self-healing materials have been explored and suggested. Among a variety of external stimuli that have been utilized for the design of novel responsive polymers, enzymes have recently emerged to be a promising triggering motif. Enzyme-catalyzed reactions are highly selective and efficient toward specific substrates under mild conditions. They are involved in all biological and metabolic processes, serving as the prime protagonists in the chemistry of living organisms at a molecular level. The integration of enzyme-catalyzed reactions with responsive polymers can further broaden the design flexibility and scope of applications by endowing the latter with enhanced triggering specificity and selectivity. In this tutorial review, we describe recent developments concerning enzyme-responsive polymeric assemblies, nanoparticles, and hydrogels by highlighting this research area with selected literature reports. Three different types of systems, namely, enzyme-triggered self-assembly and aggregation of synthetic polymers, enzyme-driven disintegration and structural reorganization of polymeric assemblies and nanoparticles, and enzyme-triggered sol-to-gel and gel-to-sol transitions, are described. Their promising applications in drug controlled release, biocatalysis, imaging, sensing, and diagnostics are also discussed.

THERMOSENSITIVE NANOPARTICLES CONJUGATING WITH CD34 ANTIBODY AND ITS SOLUTION PEROPERTIES

Poly N-isopropylacrylamide (PNIPAAm) is a well-known temperature-sensitive polymer. When the temperature is higher than the lower critical solution temperature (LCST), PNIPAAm aquous solution is cloudy (phase separation occurred). In contrast, when the temperature is lower than the LCST, PNIPAAm is soluble in water (a homogeneous solution). The lower critical solution temperature (LCST) in aqueous solution of PNIPAAm was about 32~33°C. We prepared nano-scaled PNIPAAm particles containing carboxylic group on their surfaces by introducing acrylic acid monomer. The carboxylic groups were applied to conjugate with the amino group of the CD34 antibody. This immuno-conjugate can be applied on targeting the human CD34 positive cells, peripheral blood progenitor cells included, for cell purification and drug controlled release. In order to the active responding of controlled release of the conjugate in the body influenced by temperature, we hope to estimate the shifting of the gel-collapse temperature or cloud point of the immuno-conjugates by dynamic light scattering (DLS) and UV absorption. The results show that the gel-collapse temperature of the nano-particle was not significantly affected by the content of AA between 1.5~5 mol%. However, cloud point of the solution was elevated by the conjugation of CD34 antibody to 37°C. When CD34-conjugated particle was subsequently incorporated with recombinant FLT3-ligand, which is a smaller molecule compare to CD34 antibody, cloud point of the solution was not affected.

Stimuli-responsive polymers and their applications in nanomedicine

This review focuses on smart nano-materials built of stimuli-responsive (SR) polymers and will discuss their numerous applications in the biomedical field. The authors will first provide an overview of different stimuli and their corresponding, responsive polymers. By introducing myriad functionalities, SR polymers present a wide range of possibilities in the design of stimuli-responsive devices, making use of virtually all types of polymer constructs, from self-assembled structures (micelles, vesicles) to surfaces (polymer brushes, films) as described in the second section of the review. In the last section of this review the authors report on some of the most promising applications of stimuli-responsive polymers in nanomedicine. In particular, we will discuss applications pertaining to diagnosis, where SR polymers are used to construct sensors capable of selective recognition and quantification of analytes and physical variables, as well as imaging devices. We will also highlight some examples of responsive systems used for therapeutic applications, including smart drug delivery systems (micelles, vesicles, dendrimers...) and surfaces for regenerative medicine.

Intracellular partitioning of cell organelles and extraneous nanoparticles during mitosis

The nucleocytoplasmic partitioning of nanoparticles as a result of cell division is highly relevant to the field of nonviral gene delivery. We reviewed the literature on the intracellular distribution of cell organelles (the endosomal vesicles, Golgi apparatus, endoplasmic reticulum and nucleus), foreign macromolecules (dextrans and plasmid DNA) and inorganic nanoparticles (gold, quantum dot and iron oxide) during mitosis. For nonviral gene delivery particles (lipid- or polymer-based), indirect proof of nuclear entry during mitosis is provided. We also describe how retroviruses and latent DNA viruses take advantage of mitosis to transfer their viral genome and segregate their episomes into the host daughter nuclei. Based on this knowledge, we propose strategies to improve nonviral gene delivery in dividing cells with the ultimate goal of designing nonviral gene delivery systems that are as efficient as their viral counterparts but non-immunogenic, non-oncogenic and easy and inexpensive to prepare.

Thermosensitive polymeric micelles for targeted drug delivery

Thermosensitive polymers are characterized by temperature-dependent aqueous solution properties. Below their lower critical solution temperature they are in an expanded state and fully dissolved, while above it they are dehydrated and insoluble. This has been exploited for the development of polymeric micelles that can be formed or destabilized depending on the solution temperature. Many micelle forming thermosensitive polymers have been described in literature, among which poly(N-isopropylacrylamide) (pNIPAAm), Pluronics (triblock copolymers of polypropylene oxide middle block flanked by two polyethylene oxide blocks) and poly(hydroxypropyl methacrylamide-lactate) (p(HPMAm-Lacn)) are the most frequently studied and some drug-loaded formulations based on thermosensitive polymers have reached clinical trials. The first generation of micelles composed of thermosensitive polymers was based on mere hydrophobic interactions between polymer blocks, while more recently shell or core crosslinking was introduced, in order to improve their stability in the circulation after intravenous administration and therefore, the accumulation of their depot in diseased areas. Various formulations of drug-loaded micelles based on thermosensitive polymers have shown promising results in vitro, as well as in vivo. This review gives an overview of the most important recent developments regarding the design and synthesis of various types of thermosensitve polymers for drug delivery.

Protein kinase C alpha-specific peptide substrate graft-type copolymer for cancer cell-specific gene regulation systems

We recently proposed a novel gene regulation system responding to specifically and abnormally activated intracellular enzymes in diseased cells. In the present study, we focused on protein kinase C (PKC)alpha, which is hyper-activated in most tumor cells, as a trigger for transgene regulation. We prepared cationic copolymers comprising hydrophilic and neutral polymers in main chains and cationic peptide substrates with different contents in side chains. Our copolymer with high peptide content (>3 mol%) condensed with pDNA more weakly than with poly(L-lysine) (pLL) having a similar molecular weight, but gene suppression was nearly identical to that of pLL, probably due to the steric hindrance of the main chains in our copolymer. Steric hindrance of the main chains barely affected the phosphorylation reaction of the pendant peptide. In cell and mouse experiments, higher gene expression was observed in complexes of pDNA with copolymers pended PKC alpha-specific substrate peptide than that in complexes with negative copolymers pended peptide substituted phosphorylation site of serine residues with alanine. These results indicate that our system can recognize intracellular PKC alpha as a trigger to regulate transgene expression, and may be useful for tumor gene therapy.

Molecular mechanism of caspase-3-induced gene expression of polyplexes formed from polycations grafted with cationic substrate peptides

We previously reported a novel disease-site-specific gene targeting system that can release plasmid DNA (pDNA) from polymeric carriers responding to abnormally activated signal proteins in disease cells. In this study, the molecular mechanism of the gene targeting system responding to Caspase-3 activity was studied in detail. The polymeric carrier used was composed of a neutral main chain polymer and a grafted oligocationic peptide which contains the substrate sequence of Caspase-3. The polyplex formed from the polymeric carrier and pDNA was stable in physiological saline solution and protected from access of RNA polymerase and the transcriptional factors. These results indicate that the polyplex adopts a core-shell-like structure with a polyion complex core surrounded by neutral main chain polymers. In spite of the inert character of the polyplex to transcription, the polyplex afforded the access of Caspase-3 to the substrate peptide because the electrostatic interaction between each peptide and DNA is essentially weak. After the Caspase-3 reaction, the polyplex was weakened and then became available as a template for transcription.

Interactions between an anticancer drug and polymeric micelles based on biodegradable polyesters

Interactions between the anticancer drug quercetin and biodegradable polyesters within micelles were investigated by DSC, WAXD, and UV analyses. For micelles based on poly(ethylene glycol) methyl ether-block-poly(epsilon-caprolactone) (MPEG-PCL), DSC analysis indicated that the interactions were between the hydrophobic core and the drug within the micelle. For micelles based on poly(ethylene glycol) methyl ether-block-poly(L-lactide) (MPEG-PLLA), the interactions were between the hydrophobic core and the drug and between hydrophilic segments and the drug. WAXD results indicated that no crystalline phase of the drug was found in either of the micelle types. Based on the DSC and WAXD results, two probable micelle structures were proposed. The UV spectra revealed the presence of hydrogen bonding as the main interaction between the drug and the polyesters. In vitro studies demonstrated that quercetin release from micelles was sustained and was affected by the polymer-drug interaction.

Block copolymer micelles as delivery vehicles of hydrophobic drugs: Micelle–cell interactions

One-third of drugs in development are water insoluble and one-half fail in trials because of poor pharmacokinetics. Block copolymer micelles are nanosized particles that can solubilize hydrophobic drugs and alter their kinetics in vitro and in vivo. However, block copolymer micelles are not solely passive drug containers that simply solubilize hydrophobic drugs; cells internalize micelles. To facilitate the development of advanced, controlled, micellar drug delivery vehicles, we have to understand the fate of micelles and micelle-incorporated drugs in cells and in vivo. With micelle-based drug formulations recently reaching clinical trials, the impetus for answers is ever so strong and detailed studies of interactions of micelles and cells are starting to emerge. Most notably, the question arises: Is the internalization of block copolymer micelles carrying small molecular weight drugs an undesired side effect or a useful means of improving the effectiveness of the incorporated drugs?

Photocytotoxicity of mTHPC (temoporfin) loaded polymeric micelles mediated by lipase catalyzed degradation

PURPOSE

To study the in vitro photocytotoxicity and cellular uptake of biodegradable polymeric micelles loaded with the photosensitizer mTHPC, including the effect of lipase-catalyzed micelle degradation.

METHODS

Micelles of mPEG750-b-oligo(epsilon-caprolactone)5 (mPEG750-b-OCL5) with a hydroxyl (OH), benzoyl (Bz) or naphthoyl (Np) end group were formed and loaded with mTHPC by the film hydration method. The cellular uptake of the loaded micelles, and their photocytotoxicity on human neck squamous carcinoma cells in the absence and presence of lipase were compared with free and liposomal mTHPC (Fospeg).

RESULTS

Micelles composed of mPEG750-b-OCL5 with benzoyl and naphtoyl end groups had the highest loading capacity up to 30% (w/w), likely due to pi-pi interactions between the aromatic end group and the photosensitizer. MTHPC-loaded benzoylated micelles (0.5 mg/mL polymer) did not display photocytotoxicity or any mTHPC-uptake by the cells, in contrast to free and liposomal mTHPC. After dilution of the micelles below the critical aggregation concentration (CAC), or after micelle degradation by lipase, photocytotoxicity and cellular uptake of mTHPC were restored.

CONCLUSION

The high loading capacity of the micelles, the high stability of mTHPC-loaded micelles above the CAC, and the lipase-induced release of the photosensitizer makes these micelles very promising carriers for photodynamic therapy in vivo.

Triggered destabilisation of polymeric micelles and vesicles by changing polymers polarity: an attractive tool for drug delivery

Polymeric micelles and vesicles have emerged as versatile drug carriers during the past decades. Furthermore, stimuli-responsive systems are developed whose properties change after applying certain external triggers. Therefore, a triggered release of drugs from stimuli-sensitive micelles and vesicles has become an interesting challenge in the pharmaceutical field. Polymeric micelles or vesicles are mainly composed of amphiphilic block copolymers that are held together in water due to strong hydrophobic interactions between the insoluble hydrophobic blocks, thus forming a core-shell or bilayer morphology. Consequently, destabilisation of these assemblies is induced by increasing the polarity of the hydrophobic blocks. Preferably, this process should be the consequence of an external trigger, or take place in a certain time frame or at a specific location. A variety of mechanisms has recently been described to accomplish this transition, which will be reviewed in this paper. These mechanisms include the destabilisation of polymeric micelles and vesicles by temperature, pH, chemical or enzymatic hydrolysis of side chains, oxidation/reduction processes, and light.

Bio-nanocapsules for In vivo Pinpoint Drug Delivery

To maximize the beneficial effects and minimize the side effect of drugs, DDS (drug delivery system) has been attracted many researchers in the recent drug development. Especially, the in vivo pinpoint delivery system for drugs is very important and key technology for developing the next generations of anti-cancer drugs and gene therapies. Bio-nanocapsule (BNC) is recombinant yeast-derived hepatitis B virus surface antigen particle, which has been used as a recombinant hepatitis B vaccine for the last 20 years in the world. BNC can incorporate various materials (chemical compounds, proteins, genes, siRNA, etc) by the fusion with liposome, and deliver them to the organs and tissues in vivo specifically by the action of bio-recognition molecules on the BNC's surface. The transfection efficiency is significantly higher than that of liposome, because BNC harbors the complete set of hepatitis B virus infection machinery. Recently, we succeeded in the in vivo retargeting of BNC by displaying either antibody or homing peptide, less than 10 amino acid residues for in vivo targeting. BNC is a hybrid of liposome and virus, and very flexible system for in vivo retargeting. BNC might be very promising carriers in the next generation of DDS.

Functionalized micellar systems for cancer targeted drug delivery

Polymer micelles are rapidly becoming a powerful nanomedicine platform for cancer therapeutic applications due to their small size (10-100 nm), in vivo stability, ability to solubilize water insoluble anticancer drugs, and prolonged blood circulation times. Recent data from clinical trials with three micelle formulations have highlighted these and other pharmacokinetic advantages with reduced systemic toxicity and patient morbidity compared to conventional drug formulation. While the initial anti-tumor efficacy of these systems seems promising, a strong research impetus has been placed on micelle functionalization in order to achieve tumor targeting and site-specific drug release, with the hope of reaching a more pronounced tumor response. Hence, the purpose of this review is to draw attention to the new developments of multi-functional polymer micelles for cancer therapy with special focus on tumor targeting and controlled drug release strategies.

Intracellular signal-responsive artificial gene regulation

In gene therapy, in order to avoid serious side effects due to the unexpected expression of the transgene in non-target cells, transgenes have to be delivered only to the target cells. In response to this issue, many researchers have aimed at developing target cell-selective gene carriers using active targeting strategies. However, such methodology does not always work, because an ideal molecular marker, which is specific to the target disease cells, is not always available. In this study, we introduce a new concept regarding target disease cell-selective gene therapy (D-RECS). Here, we use intracellular signals, which are activated to an extraordinary degree only in the target disease cells, as a trigger for transgene expression using polymer-peptide conjugates. This strategy could actually activate gene expression in the target signal-activated cells only. Hyper-activation of certain intracellular signals has been reported in many diseases. Thus, this new strategy is expected to provide a powerful methodology for future gene therapy. In this review, the basic concept, some examples, and the molecular design of D-RECS carriers are introduced.