Hemolytic activity of pH-responsive polymer-streptavidin bioconjugates

Stimuli-responsive hydrogels: smart state of-the-art platforms for cardiac tissue engineering

Biomedicine and tissue regeneration have made significant advancements recently, positively affecting the whole healthcare spectrum. This opened the way for them to develop their applications for revitalizing damaged tissues. Thus, their functionality will be restored. Cardiac tissue engineering (CTE) using curative procedures that combine biomolecules, biomimetic scaffolds, and cells plays a critical part in this path. Stimuli-responsive hydrogels (SRHs) are excellent three-dimensional (3D) biomaterials for tissue engineering (TE) and various biomedical applications. They can mimic the intrinsic tissues' physicochemical, mechanical, and biological characteristics in a variety of ways. They also provide for 3D setup, adequate aqueous conditions, and the mechanical consistency required for cell development. Furthermore, they function as competent delivery platforms for various biomolecules. Many natural and synthetic polymers were used to fabricate these intelligent platforms with innovative enhanced features and specialized capabilities that are appropriate for CTE applications. In the present review, different strategies employed for CTE were outlined. The light was shed on the limitations of the use of conventional hydrogels in CTE. Moreover, diverse types of SRHs, their characteristics, assembly and exploitation for CTE were discussed. To summarize, recent development in the construction of SRHs increases their potential to operate as intelligent, sophisticated systems in the reconstruction of degenerated cardiac tissues.

Improvement of RG1-VLP vaccine performance in BALB/c mice by substitution of alhydrogel with the next generation polyphosphazene adjuvant PCEP

Current human papillomavirus (HPV) vaccines provide substantial protection against the most common HPV types responsible for oral and anogenital cancers, but many circulating cancer-causing types remain for which vaccine coverage is lacking. In addition, all current HPV vaccines rely on aluminum salt-based adjuvant formulations that function through unclear mechanisms with few substitutes available. In an effort to expand the toolbox of available adjuvants suitable for HPV vaccines, we compared the immunogenicity of the RG1-VLP (virus-like particle) vaccine in BALB/c mice when formulated with either the aluminum hydroxide adjuvant Alhydrogel or the novel polyphosphazene macromolecular adjuvant poly[di (carboxylatoethylphenoxy) phosphazene] (PCEP). PCEP-formulated RG1-VLPs routinely outperformed VLP/Alhydrogel in several measurements of VLP-specific humoral immunity, including consistent improvements in the magnitude of antibody (Ab) responses to both HPV16-L1 and the L2 RG1 epitope as well as neutralizing titers to HPV16 and cross-neutralization of pseudovirion (PsV) types HPV18 and HPV39. Dose-sparing studies indicated that RG1-VLPs could be reduced in dose by 75% and the presence of PCEP ensured activity comparable to a full VLP dose adjuvanted by Alhydrogel. In addition, levels of HPV16-L1 and -L2-specific Abs were achieved after two vaccinations with PCEP as adjuvant that were equivalent to or greater than levels achieved with three vaccinations with Alhydrogel alone, indicating that the presence of PCEP resulted in accelerated immune responses that could allow for a decreased dose schedule. Given the extensive clinical track record of polyphosphazenes, these data suggest that substitution of alum-based adjuvants with PCEP for the RG1-VLP vaccine could lead to rapid seropositivity requiring fewer boosts, the dose-sparing of commercial VLP-based vaccines, and the establishment of longer-lasting humoral responses to HPV.

Tracking gene expression, metabolic profiles, and biochemical analysis in the halotolerant basidiomycetous yeast Rhodotorula mucilaginosa EXF-1630 during benzo[a]pyrene and phenanthrene biodegradation under hypersaline conditions

Polyaromatic phenanthrene (Phe) and benzo[a]pyrene (BaP) are highly toxic, mutagenic, and carcinogenic contaminants widely dispersed in nature, including saline environments. Polyextremotolerant Rhodotorula mucilaginosa EXF-1630, isolated from Arctic sea ice, was grown on a huge concentration range -10 to 500 ppm- of Phe and BaP as sole carbon sources at hypersaline conditions (1 M NaCl). Selected polycyclic aromatic hydrocarbons (PAHs) supported growth as well as glucose, even at high PAH concentrations. Initially, up to 40% of Phe and BaP were adsorbed, followed by biodegradation, resulting in 80% removal in 10 days. While extracellular laccase, peroxidase, and un-specific peroxygenase activities were not detected, NADPH-cytochrome c reductase activity peaked at 4 days. The successful removal of PAHs and the absence of toxic metabolites were confirmed by toxicological tests on moss Physcomitrium patens, bacterium Aliivibrio fischeri, human erythrocytes, and pulmonary epithelial cells (A549). Metabolic profiles were determined at the midpoint of the biodegradation exponential phase, with added Phe and BaP (100 ppm) and 1 M NaCl. Different hydroxylated products were found in the culture medium, while the conjugative metabolite 1-phenanthryl-β-D-glucopyranose was detected in the medium and in the cells. Transcriptome analysis resulted in 870 upregulated and 2,288 downregulated transcripts on PAHs, in comparison to glucose. Genomic mining of 61 available yeast genomes showed a widespread distribution of 31 xenobiotic degradation pathways in different yeast lineages. Two distributions with similar metabolic capacities included black yeasts and mainly members of the Sporidiobolaceae family (including EXF-1630), respectively. This is the first work describing a metabolic profile and transcriptomic analysis of PAH degradation by yeast.

Polyphosphazenes enable durable, hemocompatible, highly efficient antibacterial coatings

Biocompatible antibacterial coatings are highly desirable to prevent bacterial colonization on a wide range of medical devices from hip implants to skin grafts. Traditional polyelectrolytes are unable to directly form coatings with cationic antibiotics at neutral pH and suffer from high degrees of antibiotic release upon exposure to physiological concentrations of salt. Here, novel inorganic-organic hybrid polymer coatings based on direct layer-by-layer assembly of anionic polyphosphazenes (PPzs) of various degrees of fluorination with cationic antibiotics (polymyxin B, colistin, gentamicin, and neomycin) are reported. The coatings displayed low levels of antibiotic release upon exposure to salt and pH-triggered response of controlled doses of antibiotics. Importantly, coatings remained highly surface active against Escherichia coli and Staphylococcus aureus, even after 30 days of pre-exposure to physiological conditions (bacteria-free) or after repeated bacterial challenge. Moreover, coatings displayed low (<1%) hemolytic activity for both rabbit and porcine blood. Coatings deposited on either hard (Si wafers) or soft (electrospun fiber matrices) materials were non-toxic towards fibroblasts (NIH/3T3) and displayed controllable fibroblast adhesion via PPz fluorination degree. Finally, coatings showed excellent antibacterial activity in ex vivo pig skin studies. Taken together, these results suggest a new avenue to form highly tunable, biocompatible polymer coatings for medical device surfaces.

Revealing Molecular-Level Interaction between a Polymeric Drug and Model Membrane Via Sum Frequency Generation and Microfluidics

Body fluids flow all over the body and affect the biological processes at biointerfaces. To simulate such a case, sum frequency generation (SFG) vibrational spectroscopy and a self-designed microfluidic chip were combined together to investigate the interaction between a pH-responsive polymeric drug, poly(α-propylacrylic acid) (PPAAc), and the model cell membranes in different liquid environments. By examining the SFG spectra under the static and flowing conditions, the drug-membrane interaction was revealed comprehensively. The interfacial water layer was screened as the key factor affecting the drug-membrane interaction. The interfacial water layer can prevent the side propyl groups on PPAAc from inserting into the model cell membrane but would be disrupted by numerous ions in buffer solutions. Without flowing, at pH 6.6, the interaction between PPAAc and the model cell membrane was strongest; with flowing, at pH 5.8, the interaction was strongest. Flowing was proven to substantially affect the interaction between PPAAc and the model cell membranes, suggesting that the fluid environment was of key significance for biointerfaces. This work demonstrated that, by combining SFG and microfluidics, new information about the molecular-level interaction between macromolecules and the model cell membranes can be acquired, which cannot be obtained by collecting the normal static SFG spectra.

The neuropilin-1 receptor mediates enhanced tumor delivery of H2K polyplexes

BACKGROUND

Promising plasmid-based treatments have limited value without an effective delivery system. Recently, the linear H2K with a repeating -KHHK- pattern was determined to be an effective plasmid carrier to tumor xenografts in vivo. Although unpacking of the H2K polyplex within the tumor may have a role, the mechanism for the enhanced efficacy remains unclear.

METHODS

After solid-phase synthesis of linear and branched histidine-lysine (HK) peptide carriers of plasmids, the peptides were compared for their ability to lyse endosomes with a red blood cell model and to transfect MDA-MB-435 xenografts in the presence or absence of neuropilin-1 receptor (NRP-1) antibodies. To examine stability, polyplexes were incubated with trypsin or NaCl and then analyzed by electrophoresis.

RESULTS

After screening peptides with a model for endosomal lysis at two pHs, the 33-mer H3K peptide lysed red blood cells effectively at the lower pH. Combining H3K and H2K peptides as carriers of plasmids expressing luciferase were more effective than H2K alone. Based on the repeating -KHHK- sequences of H2K, we studied whether the widespread gene expression in the tumor may be mediated by NRP-1. By blocking NRP-1 in tumor-bearing mice, luciferase activity in tumors delivered by HK polyplexes was reduced by 96%, whereas activity in normal tissues was minimally reduced.

CONCLUSIONS

Combining an endosomolytic peptide, H3K, with H2K polyplexes as a carrier further enhanced transfection in vivo. Moreover, the widespread distribution of H2K polyplexes is mediated by NRP-1, suggesting that transcytosis of these polyplexes through the tumor endothelium may lead to efficient transfection. Copyright © 2016 John Wiley & Sons, Ltd.

Formulation and characterization of poly(propylacrylic acid)/poly(lactic-co-glycolic acid) blend microparticles for pH-dependent membrane disruption and cytosolic delivery

Poly(lactic-co-glycolic acid) (PLGA) is widely used as a vehicle for delivery of pharmaceutically relevant payloads. PLGA is readily fabricated as a nano- or microparticle (MP) matrix to load both hydrophobic and hydrophilic small molecular drugs as well as biomacromolecules such as nucleic acids and proteins. However, targeting such payloads to the cell cytosol is often limited by MP entrapment and degradation within acidic endolysosomes. Poly(propylacrylic acid) (PPAA) is a polyelectrolyte polymer with the membrane disruptive capability triggered at low pH. PPAA has been previously formulated in various carrier configurations to enable cytosolic payload delivery, but requires sophisticated carrier design. Taking advantage of PPAA functionality, we have incorporated PPAA into PLGA MPs as a simple polymer mixture to enhance cytosolic delivery of PLGA-encapsulated payloads. Rhodamine loaded PLGA and PPAA/PLGA blend MPs were prepared by a modified nanoprecipitation method. Incorporation of PPAA into PLGA MPs had little to no effect on the size, shape, or loading efficiency, and evidenced no toxicity in Chinese hamster ovary epithelial cells. Notably, incorporation of PPAA into PLGA MPs enabled pH-dependent membrane disruption in a hemolysis assay, and a three-fold increased endosomal escape and cytosolic delivery in dendritic cells after 2 h of MP uptake. These results demonstrate that a simple PLGA/PPAA polymer blend is readily fabricated into composite MPs, enabling cytosolic delivery of an encapsulated payload. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1022-1033, 2018.

pH-Responsive Micelle-Based Cytoplasmic Delivery System for Induction of Cellular Immunity

(1) Background: Cytoplasmic delivery of antigens is crucial for the induction of cellular immunity, which is an important immune response for the treatment of cancer and infectious diseases. To date, fusogenic protein-incorporated liposomes and pH-responsive polymer-modified liposomes have been used to achieve cytoplasmic delivery of antigen via membrane rupture or fusion with endosomes. However, a more versatile cytoplasmic delivery system is desired for practical use. For this study, we developed pH-responsive micelles composed of dilauroyl phosphatidylcholine (DLPC) and deoxycholic acid and investigated their cytoplasmic delivery performance and immunity-inducing capability. (2) Methods: Interaction of micelles with fluorescence dye-loaded liposomes, intracellular distribution of micelles, and antigenic proteins were observed. Finally, antigen-specific cellular immune response was evaluated in vivo using ELIspot assay. (3) Results: Micelles induced leakage of contents from liposomes via lipid mixing at low pH. Micelles were taken up by dendritic cells mainly via macropinocytosis and delivered ovalbumin (OVA) into the cytosol. After intradermal injection of micelles and OVA, OVA-specific cellular immunity was induced in the spleen. (4) Conclusions: pH-responsive micelles composed of DLPC and deoxycholic acid are promising as enhancers of cytosol delivery of antigens and the induction capability of cellular immunity for the treatment of cancer immunotherapy and infectious diseases.

Biodegradable "Smart" Polyphosphazenes with Intrinsic Multifunctionality as Intracellular Protein Delivery Vehicles

A series of biodegradable drug delivery polymers with intrinsic multifunctionality have been designed and synthesized utilizing a polyphosphazene macromolecular engineering approach. Novel water-soluble polymers, which contain carboxylic acid and pyrrolidone moieties attached to an inorganic phosphorus-nitrogen backbone, were characterized by a suite of physicochemical methods to confirm their structure, composition, and molecular sizes. All synthesized polyphosphazenes displayed composition-dependent hydrolytic degradability in aqueous solutions at neutral pH. Their formulations were stable at lower temperatures, potentially indicating adequate shelf life, but were characterized by accelerated degradation kinetics at elevated temperatures, including 37 °C. It was found that synthesized polyphosphazenes are capable of environmentally triggered self-assembly to produce nanoparticles with narrow polydispersity in the size range of 150-700 nm. Protein loading capacity of copolymers has been validated via their ability to noncovalently bind avidin without altering biological functionality. Acid-induced membrane-disruptive activity of polyphosphazenes has been established with an onset corresponding to the endosomal pH range and being dependent on polymer composition. The synthesized polyphosphazenes facilitated cell-surface interactions followed by time-dependent, vesicular-mediated, and saturable internalization of a model protein cargo into cancer cells, demonstrating the potential for intracellular delivery.

Polymer-Based Protein Engineering: Synthesis and Characterization of Armored, High Graft Density Polymer-Protein Conjugates

Atom transfer radical polymerization (ATRP) from the surface of a protein can generate remarkably dense polymer shells that serve as armor and rationally tune protein function. Using straightforward chemistry, it is possible to covalently couple or display multiple small molecule initiators onto a protein surface. The chemistry is fine-tuned to be sequence specific (if one desires a single targeted site) at controlled density. Once the initiator is anchored on the protein surface, ATRP is used to grow polymers on protein surface, in situ. The technique is so powerful that a single-protein polymer conjugate molecule can contain more than 90% polymer coating by weight. If desired, stimuli-responsive polymers can be "grown" from the initiated sites to prepare enzyme conjugates that respond to external triggers such as temperature or pH, while still maintaining enzyme activity and stability. Herein, we focus mainly on the synthesis of chymotrypsin-polymer conjugates. Control of the number of covalently coupled initiator sites by changing the stoichiometric ratio between enzyme and the initiator during the synthesis of protein-initiator complexes allowed fine-tuning of the grafting density. For example, very high grafting density chymotrypsin conjugates were prepared from protein-initiator complexes to grow the temperature-responsive polymers, poly(N-isopropylacrylamide), and poly[N,N'-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate]. Controlled growth of polymers from protein surfaces enables one to predictably manipulate enzyme kinetics and stability without the need for molecular biology-dependent mutagenesis.

Molecular-Level Interactions of Polyphosphazene Immunoadjuvants and Their Potential Role in Antigen Presentation and Cell Stimulation

Two macromolecular immunoadjuvants, poly[di(carboxylatophenoxy)phosphazene], PCPP, and poly[di(carboxylatoethylphenoxy)phosphazene], PCEP, have been investigated for their molecular interactions with model and biopharmaceutically important proteins in solutions, as well as for their TLR stimulatory effects and pH-dependent membrane disruptive activity in cellular assays. Solution interactions between polyphosphazenes and proteins, including antigens and soluble immune receptor proteins, have been studied using Asymmetric Flow Field Flow Fractionation (AF4) and Dynamic Light Scattering (DLS) at near physiological conditions: phosphate buffered saline, pH 7.4. Polyphosphazenes demonstrated selectivity in their molecular interactions with various proteins, but displayed strong binding with all vaccine antigens tested in the present study. It was found that both PCPP and PCEP showed strong avidity to soluble immune receptor proteins, such as Mannose Receptor (MR) and certain Toll-Like Receptor (TLR) proteins. Studies on TLR stimulation in vitro using HEK293 cells with overexpressed human TLRs revealed activation of TLR7, TLR8, and TLR9 signaling pathways, albeit with some nonspecific stimulation, for PCPP and the same pathways plus TLR3 for PCEP. Finally, PCEP, but not PCPP, demonstrated pH-dependent membrane disruptive activity in the pH range corresponding to the pH environment of early endosomes, which may play a role in a cross-presentation of antigenic proteins.

Perspectives on Polymeric Gene Delivery

Research in the field of nonviral gene delivery is in the initial stages relative to the more commonly known viral systems. However, nonviral systems may, in the near future overcome some of the problems inherent to currently employed viral gene delivery systems. These problems range from limited payload capacity and general production issues to immune and toxic reactions, as well as the potential for catastrophic viral recombination. Self-assembling complexes of nucleic acids and synthetic polymers, commonly referred to as `polyplexes', are formed as the result of electrostatic interactions between the negatively charged phosphate groups of the DNA and the positively charged groups of the polycation. A wide array of polycations are available for such studies, including those with linear, branched, dendritic and block or graft copolymer architectures. These polycations vary greatly in chemical composition as well as the number of repeating units, providing for a wide range of different polyplexes that can be easily assembled. Some of the current gene delivery systems are described which serve as potential reagents in the field of polymer-based gene delivery.

Self-assembly of polyphosphazene immunoadjuvant with poly(ethylene oxide) enables advanced nanoscale delivery modalities and regulated pH-dependent cellular membrane activity

Water-soluble polyphosphazene polyacids, such as poly[di(carboxylatophenoxy)phosphazene] (PCPP), have been of significant interest due to their unique immunoadjuvant and vaccine delivery properties. We report that PCPP can spontaneously self-assemble into intermolecular complexes with common formulation excipients − polyethers in aqueous solutions at neutral pH through the establishment of hydrogen bonds. The resulting advanced PCPP delivery modalities can range from macromolecular assemblies at the nanoscale level to physically cross-linked hydrogels and the physical state can be modulated through varying polymer ratios and molecular weight of polyether. It has been demonstrated that such macromolecular complexes maintain protein-binding ability − a key characteristics of the delivery system. Importantly, the non-covalent modification of PCPP immunoadjuvant with polyethers introduces pH dependent membrane disruptive activity, which is not characteristic for PCPP itself, and is typically correlated to the ability of macromolecular carrier to facilitate endosomal escape. This can potentially affect the mechanism of immunoadjuvant action displayed by PCPP, afford means for its fine-tuning, as well as provide important insights for understanding the relationship between fundamental physico-chemical characteristics of polyphosphazene immunoadjuvants and their activity in vivo.

A biomimetic approach to hormone resistant prostate cancer cell isolation using inactivated Sendai virus (HVJ-E)

A versatile immobilization method of inactivated Sendai virus (HVJ-E) for metastatic prostate cancer cell isolation.

Release of proteins and enzymes from vesicular compartments by alternating magnetic fields

The magnetic release of catalytically active enzymes from vesicular compartments within aggregated nanomaterials has been demonstrated. These nanomaterials, magnetic nanoparticle-vesicle aggregates (MNPVs), were formed by the self-assembly of biotinylated silica-coated Fe3O4 nanoparticles, biotinylated vesicles and tetrameric avidin. The unique features of nanoscale magnetite allow adhesion between membranes to be combined with magnetically triggered transit of reagents across membranes. Adding short spacers between the adhesive biotin groups and the nanoparticle or vesicle surfaces was found to strengthen binding to avidin, with binding of avidin to biotinylated bilayers and biotinylated nanoparticles monitored by quartz crystal microgravimetry with dissipation (QCM-D). Three different reagents were released from the vesicle compartments of MNPVs by a pulse of alternating magnetic field, with the release of a dye modelling the release of small molecule substrates, and the release of cytochrome c modelling the release of biological polymers, such as enzymes. To confirm that enzymes could be released and maintain activity, trypsin was encapsulated and shown to digest casein after magnetically triggered release.

Role of polymeric endosomolytic agents in gene transfection: a comparative study of poly(L-lysine) grafted with monomeric L-histidine analogue and poly(L-histidine)

Endosomal entrapment is one of the main barriers that must be overcome for efficient gene expression along with cell internalization, DNA release, and nuclear import. Introducing pH-sensitive ionizable groups into the polycationic polymers to increase gene transfer efficiency has proven to be a useful method; however, a comparative study of introducing equal numbers of ionizable groups in both polymer and monomer forms, has not been reported. In this study, we prepared two types of histidine-grafted poly(L-lysine) (PLL), a stacking form of poly(L-histidine) (PLL-g-PHis) and a mono-L-histidine (PLL-g-mHis) with the same number of imidazole groups. These two types of histidine-grafted PLL, PLL-g-PHis and PLL-g-mHis, showed profound differences in hemolytic activity, cellular uptake, internalization, and transfection efficiency. Cy3-labeled PLL-g-PHis showed strong fluorescence in the nucleus after internalization, and high hemolytic activity upon pH changes was also observed from PLL-g-PHis. The arrangement of imidazole groups from PHis also provided higher gene expression than mHis due to its ability to escape the endosome. mHis or PHis grafting reduced the cytotoxicity of PLL and changed the rate of cellular uptake by changing the quantity of free ε-amines available for gene condensation. The subcellular localization of PLL-g-PHis/pDNA measured by YOYO1-pDNA intensity was highest inside the nucleus, while the lysotracker, which stains the acidic compartments was lowest among these polymers. Thus, the polymeric histidine arrangement demonstrate the ability to escape the endosome and trigger rapid release of polyplexes into the cytosol, resulting in a greater amount of pDNA available for translocation to the nucleus and enhanced gene expression.

Synthesis of pH-Responsive Nanocapsules via Inverse Miniemulsion Periphery RAFT Polymerization and Post-Polymerization Reaction

We report herein the versatility of inverse miniemulsion periphery RAFT polymerization (IMEPP) and postpolymerization reaction in producing pH-responsive nanocapsules with different functionalities. The robustness of the polymeric nanocapsules was confirmed by their ability to undergo reactions, be dried, and be redispersed in various solvents without any changes in size and core-shell morphology. Nanocapsules bearing carboxylic acid (COOH) functionalities were produced via hydrolysis, while nanocapsules bearing tertiary-amine (N-X₃) functionalities were synthesized via aminolysis. The responsive behavior of the nanocapsules was tested in aqueous solution with pHs ranging from 3 to 12. Nanocapsules with COOH functionalities were found to swell under basic conditions due to the deprotonated carboxylate ions. In contrast, nanocapsule with tertiary amine functionalities underwent swelling in acidic conditions.

Amphiphilic macromolecules on cell membranes: from protective layers to controlled permeabilization

Antimicrobial and cell-penetrating peptides have inspired developments of abiotic membrane-active polymers that can coat, penetrate, or break lipid bilayers in model systems. Application to cell cultures is more recent, but remarkable bioactivities are already reported. Synthetic polymer chains were tailored to achieve (i) high biocide efficiencies, and selectivity for bacteria (Gram-positive/Gram-negative or bacterial/mammalian membranes), (ii) stable and mild encapsulation of viable isolated cells to escape immune systems, (iii) pH-, temperature-, or light-triggered interaction with cells. This review illustrates these recent achievements highlighting the use of abiotic polymers, and compares the major structural determinants that control efficiency of polymers and peptides. Charge density, sp. of cationic and guanidinium side groups, and hydrophobicity (including polarity of stimuli-responsive moieties) guide the design of new copolymers for the handling of cell membranes. While polycationic chains are generally used as biocidal or hemolytic agents, anionic amphiphilic polymers, including Amphipols, are particularly prone to mild permeabilization and/or intracell delivery.

Intracellular routing in breast cancer cells of streptavidin-conjugated trastuzumab Fab fragments linked to biotinylated doxorubicin-functionalized metal chelating polymers

We describe the synthesis of a heterotelechelic metal-chelating polymer (Bi-MCP-Dox), a polyacrylamide with a number average degree of polymerization DPn = 50 (PDI = 1.2), with biotin (Bi) and doxorubicin (Dox) as functional chain ends and diethylenetriaminepentaacetic acid (DTPA) pendant groups as the binding sites for metal ions. We compared its behavior in cell-uptake experiments with a similar polymer (Bi-MCP) without Dox. These MCPs were complexed with trastuzumab Fab (tmFab) fragments covalently linked to streptavidin (SAv) to form tmFab-SAv-Bi-MCP-Dox and tmFab-SAv-Bi-MCP via the strong affinity between Bi and SAv. tmFab targets human epidermal growth factor receptor-2 (HER2), which is overexpressed on certain human breast cancer cells. Surface plasmon resonance (SPR) experiments with the extracellular domain (ECD) of HER2 showed that incorporation of the MCPs in these complexes had no significant effect on the association or dissociation rate with the HER2 ECD and the dissociation constants. The tmFab-complexed MCPs were subsequently labeled with (111)In (an Auger electron emitting radionuclide). Auger electrons can cause lethal DNA double strand breaks (DSBs) but only if they are emitted intracellularly and especially, in close proximity to the nucleus. To evaluate the cellular and nuclear uptake of tmFab-SAv-Bi-MCP-Dox, we incubated HER2+ SK-BR-3 human breast cancer cells with the complexes saturated with stable In(3+) and visualized their distribution by confocal fluorescence microscopy, monitoring the fluorescence of Dox. In parallel, we carried out cell fractionation studies on tmFab-SAv-Bi-MCP-Dox and on tmFab-SAv-Bi-MCP labeled with (111)In. Both radiolabeled complexes showed cell internalization and nuclear localization. We conclude that metal-chelating polymers with this composition appear to encourage internalization, nuclear uptake, and chromatin (DNA) binding of trastuzumab fragments modified with streptavidin in human breast cancer cells expressing HER2. Further study is needed to understand the impact of polymer charge on cellular uptake and distribution to intracellular compartments.

Assessment of cholesterol-derived ionic copolymers as potential vectors for gene delivery

A library of cholesterol-derived ionic copolymers were previously synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization as 'smart' gene delivery vehicles that hold diverse surface charges. Polyplex systems formed with anionic poly(methacrylic acid-co-cholesteryl methacrylate) (P(MAA-co-CMA)) and cationic poly(dimethylamino ethyl methacrylate-co-cholesteryl methacrylate) (Q-P(DMAEMA-co-CMA)) copolymer series were evaluated for their therapeutic efficiency. Cell viability assays, conducted on SHEP, HepG2, H460, and MRC5 cell lines, revealed that alterations in the copolymer composition (CMA mol %) affected the cytotoxicity profile. Increasing the number of cholesterol moieties in Q-P(DMAEMA-co-CMA) copolymers reduced the overall toxicity (in H460 and HepG2 cells) while P(MAA-co-CMA) series displayed no significant toxicity regardless of the CMA content. Agarose gel electrophoresis was employed to investigate the formation of stable polyplexes and determine their complete conjugation ratios. P(MAA-co-CMA) copolymer series were conjugated to DNA through a cationic linker, oligolysine, while Q-P(DMAEMA-co-CMA)-siRNA complexes were readily formed via electrostatic interactions at conjugation ratios beginning from 6:1:1 (oligolysine-P(MAA-co-CMA)-DNA) and 20:1 (Q-P(DMAEMA-co-CMA)-siRNA), respectively. The hydrodynamic diameter, ζ potential and complex stability of the polyplexes were evaluated in accordance to complexation ratios and copolymer composition by dynamic light scattering (DLS). The therapeutic efficiency of the conjugates was assessed in SHEP cells via transfection and imaging assays using RT-qPCR, Western blotting, flow cytometry, and confocal microscopy. DNA transfection studies revealed P(MAA-co-CMA)-oligolysine-DNA ternary complexes to be ineffective transfection vehicles that mostly adhere to the cell surface as opposed to internalizing and partaking in endosomal disrupting activity. The transfection efficiency of Q-P(DMAEMA-co-CMA)-GFP siRNA complexes were found to be polymer composition and N/P ratio dependent, with Q-2% CMA-GFP siRNA polyplexes at N/P ratio 20:1 showing the highest gene suppression in GFP expressing SHEP cells. Cellular internalization studies suggested that Q-P(DMAEMA-co-CMA)-siRNA conjugates efficiently escaped the endolysosomal pathway and released siRNA into the cytoplasm. The gene delivery profile, reported herein, illuminates the positive and negative attributes of each therapeutic design and strongly suggests Q-P(DMAEMA-co-CMA)-siRNA particles are extremely promising candidates for in vivo applications of siRNA therapy.

Efficient cytosolic delivery mediated by polymersomes facilely prepared from a degradable, amphiphilic, and amphoteric copolymer

To solve problems in polymersome preparation caused by liposolubility of copolymers and to improve the cytosolic delivery efficiency of polymersomes to drugs, a lipopolysaccharide-amine (LPSA) copolymer with amphotericity and amphiphilicity is developed. LPSA contains two hydrophilic oppositely charged blocks (anionic oxidized alginate (OA), cationic polyethyleneimine (PEI 1.8 k)) and one hydrophobic block (cholesteryl), where OA is the backbone and cholesteryl-grafted PEI is the side chain. The two hydrophilic blocks first guarantee that LPSA will dissolve in water, and then help polymersome formation via electrostatic interactions to generate water insoluble interpolyelectrolyte complexes, which supplement the hydrophobic part to reach the right hydrophilicity/hydrophobicity ratio, and thus realize a one-step self-assembly of polymersomes in water. Our results show LPSA nanopolymersomes (LNPs) have low cytotoxicity and degradability, and an excellent ability to enter cells. TEM observation demonstrates that LNPs are entrapped in endosomes after endocytosis, and are then released to cytosols because of their strong endosomal escape capacity. As an example of cytosolic delivery to bioactive molecules, pDNA is delivered in mesenchymal stem cells, and more than 95% of cells express a large target protein, indicating that LNPs have high cytosolic delivery efficiency. Our study provides a novel, easy, and universal method to design copolymers for the preparation of polymersomes as efficient cytosolic delivery nanocarriers.

Ex vivo red blood cell hemolysis assay for the evaluation of pH-responsive endosomolytic agents for cytosolic delivery of biomacromolecular drugs

Phospholipid bilayers that constitute endo-lysosomal vesicles can pose a barrier to delivery of biologic drugs to intracellular targets. To overcome this barrier, a number of synthetic drug carriers have been engineered to actively disrupt the endosomal membrane and deliver cargo into the cytoplasm. Here, we describe the hemolysis assay, which can be used as rapid, high-throughput screen for the cytocompatibility and endosomolytic activity of intracellular drug delivery systems. In the hemolysis assay, human red blood cells and test materials are co-incubated in buffers at defined pHs that mimic extracellular, early endosomal, and late endo-lysosomal environments. Following a centrifugation step to pellet intact red blood cells, the amount of hemoglobin released into the medium is spectrophotometrically measured (405 nm for best dynamic range). The percent red blood cell disruption is then quantified relative to positive control samples lysed with a detergent. In this model system the erythrocyte membrane serves as a surrogate for the lipid bilayer membrane that enclose endo-lysosomal vesicles. The desired result is negligible hemolysis at physiologic pH (7.4) and robust hemolysis in the endo-lysosomal pH range from approximately pH 5-6.8.

Stimuli-responsive polymers: biomedical applications and challenges for clinical translation

Over the past 25 years many interesting biomedical uses have been proposed for stimuli-responsive polymers, including uses in diagnostics, drug delivery, tissue engineering (regenerative medicine), and cell culture. This article briefly overviews the field of stimuli-responsive polymers and describes some of the most successful biomedical applications to date of such "smart" polymers. Other interesting potential applications are also discussed. The major barriers to future clinical translation of smart polymers are also critically discussed.

Poly(propylacrylic acid)-mediated serum stabilization of cationic lipoplexes

The serum instability associated with cationic lipoplexes represents one of the major obstacles for the in vivo delivery of nonviral gene therapy vectors. Recently, we have shown that poly(propylacrylic acid) (PPAA), a pH-sensitive polyanionic polymer, can significantly improve the in vitro serum stability of DOTAP lipoplexes and enhance transfection (Cheung et al., Bioconjug. Chem. 12, 906 (2001)). We investigated this serum-stabilizing effect provided by PPAA using methods to identify the specific serum proteins that interact with DOTAP/DNA and DOTAP/DNA/PPAA lipoplexes and determined their modes of interaction with these lipoplexes. Studies showed that only low-density lipoprotein (LDL) caused significant decondensation of DNA from lipoplexes lacking PPAA, but that fully condensed DNA was retained within lipoplexes incorporating PPAA. Another major factor in the loss of transfection activity was due to the reduced cellular uptake of DOTAP lipoplexes upon exposure to serum, with bovine serum albumin (BSA) and high-density lipoprotein (HDL) acting as major contributors to this reduction in vector internalization. In contrast, lipoplexes containing PPAA maintained high levels of uptake into cells in the presence of these proteins. Transfection results generally concurred with the mechanistic studies, suggesting that maintaining effective cellular delivery of intact lipoplexes in the presence of serum proteins is important to retain high transfection efficiencies. These results indicate that the addition of PPAA as a ternary component in DOTAP lipoplexes can overcome some of the serum-related deficiencies encountered with these lipoplexes to provide efficient transfection.

Delivery of intracellular-acting biologics in pro-apoptotic therapies

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide "stapling", cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.

RAFT-synthesized graft copolymers that enhance pH-dependent membrane destabilization and protein circulation times

Here we describe a new graft copolymer architecture of poly(propylacrylic acid) (polyPAA) that displays potent pH-dependent, membrane-destabilizing activity and in addition is shown to enhance protein blood circulation kinetics. PolyPAA containing a single telechelic alkyne functionality was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization with an alkyne-functional chain transfer agent (CTA) and coupled to RAFT polymerized poly(azidopropyl methacrylate) (polyAPMA) through azide-alkyne [3 + 2] Huisgen cycloaddition. The graft copolymers become membrane destabilizing at endosomal pH values and are active at significantly lower concentrations than the linear polyPAA. A biotin terminated polyPAA graft copolymer was prepared by grafting PAA onto polyAPMA polymerized with a biotin functional RAFT CTA. The blood circulation time and biodistribution of tritium labeled avidin conjugated to the polyPAA graft copolymer was characterized along with a clinically utilized 40kDa branched polyethylene glycol (PEG) also possessing biotin functionalization. The linear and graft polyPAA increase the area under the curve (AUC) over avidin alone by 9 and 12 times, respectively. Furthermore, polyPAA graft copolymer conjugates accumulated in tumor tissue significantly more than the linear polyPAA and the branched PEG conjugates. The collective data presented in this report indicate that the polyPAA graft copolymers exhibit robust pH-dependent membrane-destabilizing activity, low cytotoxicity, significantly enhanced blood circulation time, and increased tumor accumulation.

Efficient Intracellular Delivery of a Pro-Apoptotic Peptide With A pH-Responsive Carrier

A key challenge in developing protein therapeutics or imaging agents that work against cytosolic targets is the intracellular delivery barrier. Here, we show that the pH-responsive, membrane-destabilizing polymer, poly (propylacrylic acid) (PPAA), can strongly enhance target cell killing through the intracellular delivery of a functional proapoptotic peptide. The Bak BH3 peptide induces apoptosis via antagonization of suppressor targets such as Bcl-2 and Bcl-x(L). A genetically-engineered streptavidin that contains an N-terminal TAT peptide sequence was used to optimize the pinocytotic cell uptake of biotinylated BH3 peptide and end-biotinylated PPAA. Fluorescence microscopic analysis of DAPI-stained HELA cells was used to quantitate apoptosis. Approximately 30% of cells treated with TAT-SA:BH3 complexes revealed morphologically distinct nuclear condensation, a hallmark of apoptosis. The incorporation of biotinylated PPAA had the effect of markedly enhancing the killing effect of BH3 peptides by an additional 55% (p<0.001) to a total cell killing efficiency of 85%. Caspase-3 activity was up-regulated in a TAT-SA:BH3:PPAA dose-dependent manner. The induction of apoptosis with the TAT-SA:BH3:PPAA complex was abrogated with the L78A BH3 peptide, that had been previously shown to knock-out antagonization activity. The caspase and L78A peptide results demonstrate that the delivered BH3 is indeed working through the biologically relevant apoptosis signaling pathway. These studies establish the ability of PPAA to strongly enhance the intracellular delivery of a functional pro-apoptotic peptide. Together with the PPAA, the TAT-SA adaptor complex could prove useful as a carrier of peptide/protein cargo to cultured cells.

DNA-enzyme conjugate with a weak inhibitor that can specifically detect thrombin in a homogeneous medium

We present the DNA-assisted control of enzymatic activity for the detection of a target protein using a new type of DNA-enzyme conjugate. The conjugate is composed of an enzyme inhibitor to regulate enzyme activity and a DNA aptamer to be responsive toward the analyte protein. Glutathione S-transferase (GST) and thrombin were selected as a model enzyme and an analyte protein. A hexahistidine tag was genetically attached to the C terminus of the GST, and the 5' end of an oligonucleotide was conjugated with nitrilotriacetic acid (NTA) for the site-specific conjugation of the DNA with the GST based on a Ni(2+) complex interaction. We found that fluorescein acted as a weak inhibitor of GST and succeeded in the regulation of GST activity by increasing the local concentration of the weak inhibitor by the hybridization of a 3'-end fluorescein-modified DNA. The catalytic activity of the DNA aptamer-enzyme conjugate showed a dose-dependent response to thrombin, indicating that the GST activity was clearly recovered by the binding of the DNA aptamer to thrombin. The current system enables the sensitive and specific detection of thrombin simply by measuring the enzymatic activity in a homogeneous medium.

Delivery of basic fibroblast growth factor with a pH-responsive, injectable hydrogel to improve angiogenesis in infarcted myocardium

A pH- and temperature-responsive, injectable hydrogel has been designed to take advantage of the acidic microenvironment of ischemic myocardium. This system can improve therapeutic angiogenesis methods by providing spatio-temporal control of angiogenic growth factor delivery. The pH- and temperature-responsive random copolymer, poly(N-isopropylacrylamide-co-propylacrylic acid-co-butyl acrylate) (p[NIPAAm-co-PAA-co-BA]), was synthesized by reversible addition fragmentation chain transfer polymerization. This polymer was a liquid at pH 7.4 and 37 °C but formed a physical gel at pH 6.8 and 37 °C. Retention of biotinylated basic fibroblast growth factor (bFGF) between 0 and 7 days after injection into infarcted rat myocardium was 10-fold higher with hydrogel delivery versus saline. Following 28 days of treatment in vivo, capillary and arteriolar densities were increased 30-40% by polymer + bFGF treatment versus saline + bFGF or polymer-only controls. Treatment with polymer + bFGF for 28 days resulted in a 2-fold improvement in relative blood flow to the infarct region versus day 0, whereas saline + bFGF or polymer-only had no effect. Fractional shortening determined by echocardiography was significantly higher following treatment with polymer + bFGF (30 ± 1.4%) versus saline (25 ± 1.2%) and polymer alone (25 ± 1.8%). By responding to local changes in pH- and temperature in an animal model of ischemia, this hydrogel system provided sustained, local delivery of bFGF, improved angiogenesis, and achieved therapeutic effects in regional blood flow and cardiac function.

pH-dependent hemolysis of biocompatible imidazole-grafted polyaspartamide derivatives

A series of novel, pH-sensitive, endosomolytic polymers based on imidazole-grafted polyaspartamide were synthesized to characterize the pH-sensitive membrane fusion properties of red blood cells and their toxicity to L929 cells. All imidazole-containing polymers exhibited strong cationic characteristics under acidic conditions, as well as a high buffering effect in the pH range 5-7. In the presence of O-(2-aminoethyl)-O'-methylpolyethylene glycol and 1-(3-aminopropyl)imidazole-grafted polyaspartamide (MPEG/API-g-PASPAM) systems red blood cells agglutinated below pH 6.5 without any hemolytic effect. The octadecylamine, O-(2-aminoethyl)-O'-methylpolyethylene glycol and 1-(3-aminopropyl)imidazole-grafted polyaspartamide (C18/MPEG/API-g-PASPAM) systems, however, displayed considerable hemolytic behavior below pH 6.5, but no hemolysis occurred above this pH. It can be concluded from these results that not only the pH-sensitive imidazole group, but also the hydrophobic octadecyl chain plays a critical role in membrane fusion. The hypothetical mechanism of this fusion involves both ionic and hydrophobic interactions between the polymers and lipid bilayers.

Application of nanotechnologies for improved immune response against infectious diseases in the developing world

There is an urgent need for new strategies to combat infectious diseases in developing countries. Many pathogens have evolved to elude immunity and this has limited the utility of current therapies. Additionally, the emergence of co-infections and drug resistant pathogens has increased the need for advanced therapeutic and diagnostic strategies. These challenges can be addressed with therapies that boost the quality and magnitude of an immune response in a predictable, designable fashion that can be applied for wide-spread use. Here, we discuss how biomaterials and specifically nanoscale delivery vehicles can be used to modify and improve the immune system response against infectious diseases. Immunotherapy of infectious disease is the enhancement or modulation of the immune system response to more effectively prevent or clear pathogen infection. Nanoscale vehicles are particularly adept at facilitating immunotherapeutic approaches because they can be engineered to have different physical properties, encapsulated agents, and surface ligands. Additionally, nanoscaled point-of-care diagnostics offer new alternatives for portable and sensitive health monitoring that can guide the use of nanoscale immunotherapies. By exploiting the unique tunability of nanoscale biomaterials to activate, shape, and detect immune system effector function, it may be possible in the near future to generate practical strategies for the prevention and treatment of infectious diseases in the developing world.