TAT peptide on the surface of liposomes affords their efficient intracellular delivery even at low temperature and in the presence of metabolic inhibitors

Cationic membrane peptides: atomic-level insight of structure-activity relationships from solid-state NMR

Many membrane-active peptides, such as cationic cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs), conduct their biological functions by interacting with the cell membrane. The interactions of charged residues with lipids and water facilitate membrane insertion, translocation or disruption of these highly hydrophobic species. In this review, we will summarize high-resolution structural and dynamic findings towards the understanding of the structure-activity relationship of lipid membrane-bound CPPs and AMPs, as examples of the current development of solid-state NMR (SSNMR) techniques for studying membrane peptides. We will present the most recent atomic-resolution structure of the guanidinium-phosphate complex, as constrained from experimentally measured site-specific distances. These SSNMR results will be valuable specifically for understanding the intracellular translocation pathway of CPPs and antimicrobial mechanism of AMPs, and more generally broaden our insight into how cationic macromolecules interact with and cross the lipid membrane.

The six amino acid antimicrobial peptide bLFcin6 penetrates cells and delivers siRNA

Cell-penetrating peptides (CPPs) are a new class of vectors with high pharmaceutical potential to deliver bioactive cargos into cells. Here, we characterized bLFcin(6) , a six amino acid peptide derived from bovine lactoferricin, as a CPP. Uptake of bLFcin(6) was measured by flow cytometry. The ability to delivery siRNA was analyzed in HeLa cells. bLFcin(6) exhibited concentration-dependent uptake and intracellular distribution. Below 7.5 μm, uptake of bLFcin(6) was significantly lower than uptake of TAT (P < 0.05) because bLFcin(6) has fewer cationic amino acids. Compared to CPP(5) (RLRWR) and CPP(6) (PFVYLI), bLFcin(6) had a significantly higher internalization ratio above 2.5 μm because it has two tryptophan residues. Uptake of bLFcin(6) starts with an ionic cell-surface interaction. It is then rapidly internalized by lipid raft-dependent macropinocytosis, followed by release from macropinosomes into the cytosol and nucleus. Moreover, bLFcin(6) formed stable electrostatic complexes with siRNA and delivered siRNA into cells, resulting in significant knockout activity at both the mRNA and protein levels. The knockout activity of siRNA delivered by bLFcin(6) was similar to that mediated by TAT, although knockout by bLFcin(6) required a higher molar ratio. In this study, bLFcin(6) was tested for its ability to act as an siRNA-delivering CPP.

Cell penetrating peptide tethered bi-ligand liposomes for delivery to brain in vivo: Biodistribution and transfection

Targeted nano-particulate systems hold extraordinary potential for delivery of therapeutics across blood brain barrier (BBB). In this work, we investigated the potential of novel bi-ligand (transferrin-poly-l-arginine) liposomal vector for delivery of desired gene to brain, in vivo. The in vivo evaluation of the delivery vectors is essential for clinical translation. We followed an innovative approach of combining transferrin receptor targeting with enhanced cell penetration to design liposomal vectors for improving the transport of molecules into brain. The biodistribution profile of 1, 1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine iodide(DiR)-labeled liposomes was evaluated in adult rats after single intravenous injection at dose of 15.2μmoles of phospholipids/kg body weight. We demonstrated that bi-ligand liposomes accumulated in rat brain at significantly (p<0.05) higher concentrations as compared to the single-ligand (transferrin) or plain liposomes. In addition, the bi-ligand liposomes resulted in increased expression of β-galactosidase(β-gal) plasmid in rat brain tissue in comparison to the single-ligand liposomes. Histological examination of the transfected tissues did not show any signs of tissue necrosis or inflammation. Hemolysis assay further authenticated the biocompatibility of bi-ligand liposomes in blood up to 600 nmoles of phospholipids/1.4×10(7) erythrocytes. The findings of this study provide important and detailed information regarding the distribution of bi-ligand liposomes in vivo and accentuate their ability to demonstrate improved brain penetration and transfection potential over single-ligand liposomes.

Immunoconjugates and long circulating systems: origins, current state of the art and future directions

Significant progress has been made recently in the area of immunoconjugated drugs and drug delivery systems (DDS). The immuno-modification of either the drug or DDS has proven to be a very promising approach that has significantly improved the targeted accumulation in pathological sites while decreasing its undesirable side effects in healthy tissues. The arrangement for both prolonged life in the circulation and specific target recognition represents another potent strategy in the development of immuno-targeted systems. The longevity of immuno-targeted DDS such as immunoliposomes and immunomicelles improves their targetability even in the presence of the additional passive accumulation in areas with a compromised vasculature. The added use of the immuno-targeted systems takes advantage of the specific microenvironment of pathological sites including lowered pH, increased temperature, and variation in the enzymatic activity. "Smart" stimulus-responsive systems combine different valuable functionalities including PEG-protection, targeting antibody, cell-penetration, and stimulus-sensitive functions. In this review we examined the evolution, current status and future directions in the area of therapeutical immunoconjugates and long-circulating immuno-targeted DDS.

Liposomal drug delivery systems: from concept to clinical applications

The first closed bilayer phospholipid systems, called liposomes, were described in 1965 and soon were proposed as drug delivery systems. The pioneering work of countless liposome researchers over almost 5 decades led to the development of important technical advances such as remote drug loading, extrusion for homogeneous size, long-circulating (PEGylated) liposomes, triggered release liposomes, liposomes containing nucleic acid polymers, ligand-targeted liposomes and liposomes containing combinations of drugs. These advances have led to numerous clinical trials in such diverse areas as the delivery of anti-cancer, anti-fungal and antibiotic drugs, the delivery of gene medicines, and the delivery of anesthetics and anti-inflammatory drugs. A number of liposomes (lipidic nanoparticles) are on the market, and many more are in the pipeline. Lipidic nanoparticles are the first nanomedicine delivery system to make the transition from concept to clinical application, and they are now an established technology platform with considerable clinical acceptance. We can look forward to many more clinical products in the future.

Transactivating-transduction protein-polyethylene glycol modified liposomes traverse the blood-spinal cord and blood-brain barriers

Naive liposomes can cross the blood-brain barrier and blood-spinal cord barrier in small amounts. Liposomes modified by a transactivating-transduction protein can deliver antibiotics for the treatment of acute bacterial infection-induced brain inflammation. Liposomes conjugated with polyethylene glycol have the capability of long-term circulation. In this study we prepared transactivating-transduction protein-polyethylene glycol-modified liposomes labeled with fluorescein isothiocyanate. Thus, liposomes were characterized by transmembrane, long-term circulation and fluorescence tracing. Uptake, cytotoxicity, and the ability of traversing blood-spinal cord and blood-brain barriers were observed following coculture with human breast adenocarcinoma cells (MCF-7). Results demonstrated that the liposomes had good biocompatibility, and low cytotoxicity when cocultured with human breast adenocarcinoma cells. Liposomes could traverse cell membranes and entered the central nervous system and neurocytes through the blood-spinal cord and blood-brain barriers of rats via the systemic circulation. These results verified that fluorescein isothiocyanate-modified transactivating-transduction protein-polyethylene glycol liposomes have the ability to traverse the blood-spinal cord and blood-brain barriers.

Structural characterization of a peptoid with lysine-like side chains and biological activity using NMR and computational methods

N-substituted glycine oligomers or peptoids with charged side chains are a novel class of cell penetrating peptide mimetics and have been shown to serve as drug delivery agents. Here, we investigated by NMR spectroscopy and quantum chemical calculations whether a Rhodamine B labelled peptoid [RhoB(Spiro)-Ahx]-[But](6A)NH(2) with lysine-like side chains adopts structural motifs similar to regular peptides. Due to a low chemical shift dispersion, high resolution structure determination with conventional NMR-derived distance restraints and J-couplings was not possible. Instead, a combined assignment and structure refinement strategy using the QM/MM force field COSMOS-NMR was developed to interpret the highly ambiguous chemical shift and distance constraints and obtain a medium resolution three-dimensional structural model. This allowed us to select for the all cis-amide conformation of the peptide with a pseudo-helical arrangement of extended side chains as a faithful representative structure of [RhoB(Spiro)-Ahx]-[But](6A)NH(2). We tested the biological activity of the peptoid by live-cell imaging, which showed that the cellular uptake of the peptoid was comparable to conventional cell-penetrating peptides.

Enhancing the Cellular Delivery of Nanoparticles using Lipo-Oligoarginine Peptides

Nanoparticles have great potential as nanotherapeutics, delivery vectors, and molecular imaging agents due to their flexible properties. Although intracellular and nuclear delivery of nanoparticles is desirable for therapeutic applications, it remains a challenge. Cell penetrating peptides (CPPs) are a powerful tool for the intracellular delivery of various cargoes. Here we report that functionalization of nanoparticles with a myristoylated oligoarginine CPP promoted cellular uptake without increased toxicity. It was evidenced that the myristoylated CPP is much more effective in transporting nanoparticles than the unmodified CPPs.

Chemical modification allows phallotoxins and amatoxins to be used as tools in cell biology

Phallotoxins inhibit the dynamics of microfilaments in cells and lead to apoptosis. Due to poor cellular uptake these effects cannot be studied in live cells, even at millimolar toxin concentrations, nor can phalloidin be used for the elimination of tumor cells. Uptake is greatly enhanced by conjugation of phallotoxins to either lipophilic or polycationic moieties, such as oleic acid, polylysine, or Tat-peptide. These conjugates were lethally toxic for cells, e.g., mouse fibroblasts or Jurkat leukemia cells, in the micromolar range. Uptake into cells starts with the attachment of the toxin conjugates to the plasma membrane, followed by endocytosis and, in most cases, cleavage of the toxin from the carrier. Interestingly, the internalization rate of phalloidin into cells was also significantly increased by the fluorescent moiety tetramethylrhodaminyl, as well as by high molecular weight methoxy-polyethyleneglycol, two compounds unknown so far for their uptake-mediating activity. Conjugation to carriers as investigated in this work will allow the use of phallotoxins in experimental cell biology and possibly in tumor therapy. The findings obtained with phallotoxins could be applied also to the family of amatoxins, where α-amanitin, for example, when conjugated to oleic acid was more than 100-fold more toxic for cells than the native toxin. This suggests the possibility of a more general use of the moieties examined here to enhance the uptake of hydrophilic peptides, or drugs, into live cells.

Detecting and destroying cancer cells in more than one way with noble metals and different confinement properties on the nanoscale

Today, 1 in 2 males and 1 in 3 females in the United States will develop cancer at some point during their lifetimes, and 1 in 4 males and 1 in 5 females in the United States will die from the disease. New methods for detection and treatment have dramatically improved cancer care in the United States. However, as improved detection and increasing exposure to carcinogens has led to higher rates of cancer incidence, clinicians and researchers have not balanced that increase with a similar decrease in cancer mortality rates. This mismatch highlights a clear and urgent need for increasingly potent and selective methods with which to detect and treat cancers at their earliest stages. Nanotechnology, the use of materials with structural features ranging from 1 to 100 nm in size, has dramatically altered the design, use, and delivery of cancer diagnostic and therapeutic agents. The unique and newly discovered properties of these structures can enhance the specificities with which biomedical agents are delivered, complementing their efficacy or diminishing unintended side effects. Gold (and silver) nanotechnologies afford a particularly unique set of physiological and optical properties which can be leveraged in applications ranging from in vitro/vivo therapeutics and drug delivery to imaging and diagnostics, surgical guidance, and treatment monitoring. Nanoscale diagnostic and therapeutic agents have been in use since the development of micellar nanocarriers and polymer-drug nanoconjugates in the mid-1950s, liposomes by Bangham and Watkins in the mid-1960s, and the introduction of polymeric nanoparticles by Langer and Folkman in 1976. Since then, nanoscale constructs such as dendrimers, protein nanoconjugates, and inorganic nanoparticles have been developed for the systemic delivery of agents to specific disease sites. Today, more than 20 FDA-approved diagnostic or therapeutic nanotechnologies are in clinical use with roughly 250 others in clinical development. The global market for nano-enabled medical technologies is expected to grow to $70-160 billion by 2015, rivaling the current market share of biologics worldwide. In this Account, we explore the emerging applications of noble metal nanotechnologies in cancer diagnostics and therapeutics carried out by our group and by others. Many of the novel biomedical properties associated with gold and silver nanoparticles arise from confinement effects: (i) the confinement of photons within the particle which can lead to dramatic electromagnetic scattering and absorption (useful in sensing and heating applications, respectively); (ii) the confinement of molecules around the nanoparticle (useful in drug delivery); and (iii) the cellular/subcellular confinement of particles within malignant cells (such as selective, nuclear-targeted cytotoxic DNA damage by gold nanoparticles). We then describe how these confinement effects relate to specific aspects of diagnosis and treatment such as (i) laser photothermal therapy, optical scattering microscopy, and spectroscopic detection, (ii) drug targeting and delivery, and (iii) the ability of these structures to act as intrinsic therapeutic agents which can selectively perturb/inhibit cellular functions such as division. We intend to provide the reader with a unique physical and chemical perspective on both the design and application of these technologies in cancer diagnostics and therapeutics. We also suggest a framework for approaching future research in the field.

Molecular basis for nanoscopic membrane curvature generation from quantum mechanical models and synthetic transporter sequences

We investigate the physical origin of peptide-induced membrane curvature by contrasting differences between H-bonding interactions of prototypical cationic amino acids, arginine (Arg) and lysine (Lys), with phosphate groups of phospholipid heads using quantum mechanical (QM) calculations of a minimum model and test the results via synthetic oxaorbornene-based transporter sequences without the geometric constraints of polypeptide backbones. QM calculations suggest that although individual Lys can in principle coordinate two phosphates, they are not able to do so at small inter-Lys distances without drastic energetic penalties. In contrast, Arg can coordinate two phosphates down to less than 5 Å, where guanidinium groups can stack "face to face". In agreement with these observations, poly-Lys cannot generate the nanoscale positive curvature necessary for inducing negative Gaussian membrane curvature, in contrast to poly-Arg. Also consistent with QM calculations, polyguanidine-oxanorbornene homopolymers (PGONs) showed that curvature generation is exquisitely sensitive to the guanidinium group spacing when the phosphate groups are near close packing. Addition of phenyl or butyl hydrophobic groups into guanidine-oxanorbornene polymers increased the amount of induced saddle-splay membrane curvature and broadened the range of lipid compositions where saddle-splay curvature was induced. The enhancement of saddle-splay curvature generation and relaxation of lipid composition requirements via addition of hydrophobicity is consistent with membrane activity profiles. While PGON polymers displayed selective antimicrobial activity against prototypical (Gram positive and negative) bacteria, polymers with phenyl and butyl groups were also active against red blood cells. Our results suggest that it is possible to achieve deterministic molecular design of pore-forming peptides.

Immunomicelles for advancing personalized therapy

Personalized medicine, which ultimately seeks to afford tailored therapeutic regimens for individual patients, is quickly emerging as a new paradigm in the diagnosis and treatment of diseases. The idea of casting aside generic treatments in favor of patient-centric therapies has become feasible owing to advances in nanotechnology and drug delivery coupled with an enhanced knowledge of genomics and an understanding of disease at the molecular level. This review highlights polymeric immunomicelles as a class of nanocarriers that have the potential to combine diagnosis, targeted drug therapy, as well as imaging and monitoring of therapeutic response, to render a personalized approach to the management of disease. Smart multi-functional immunomicelles, as the next generation of nanocarriers, are poised for facilitating personalized cancer treatment. This review provides an assessment of immunomicelles as tools for advancing personalized therapy of diseases, with cancer being the major focus.

The use and importance of liposomes in positron emission tomography

Among different imaging modalities, Positron Emission Tomography (PET) gained importance in routine hospital practice depending on ability to diagnose diseases in early stages and tracing of therapy by obtaining metabolic information. The combination of PET with Computed Tomography (CT) forms hybrid imaging modality that gives chance to obtain better images having higher resolution by fusing both functional and anatomical images in the same imaging modality at the same time. Therefore, better contrast agents are essentially needed. The advance in research about developing drug delivery systems as specific nanosized targeted systems gained an additional importance for obtaining better diagnosis and therapy of different diseases. Liposomes appear to be more attractive drug delivery systems in delivering either drugs or imaging ligands to target tissue or organ of diseases with higher accumulation by producing in nano-scale, long circulating by stealth effect and specific targeting by modifying with specific ligands or markers. The combination of positron emitting radionuclides with liposomes are commonly in research level nowadays and there is no commercially available liposome formulation for PET imaging. However by conjugating positron emitter radionuclide with liposomes can form promising diagnostic agents for improved diagnosis and following up treatments by increasing image signal/contrast in the target tissue in lower concentrations by specific targeting as the most important advantage of liposomes. More accurate and earlier diagnosis of several diseases can be obtained even in molecular level with the use of stable and effectively radiolabeled molecular target specific nano sized liposomes with longer half-lived positron emitting radionuclides.

A MSLN-targeted multifunctional nanoimmunoliposome for MRI and targeting therapy in pancreatic cancer

Pancreatic cancer is a highly lethal disease with a 5-year survival rate less than 5% due to the lack of an early diagnosis method and effective therapy. To provide a novel early diagnostic method and targeted therapy for pancreatic cancer, a multifunctional nanoimmunoliposome with high loading of ultrasmall superparamagnetic iron oxides (USPIOs) and doxorubicin (DOX) was prepared by transient binding and reverse-phase evaporation method, and was conjugated with anti-mesothelin monoclonal antibody by post-insertion method to target anti-mesothelin-overexpressed pancreatic cancer cells. The in vitro and in vivo properties of this anti-mesothelin antibody-conjugated PEGlyated liposomal DOX and USPIOs (M-PLDU; and PEGlyated nanoimmunoliposome without antibody conjugation [PLDU]) were evaluated both in human pancreatic cancer cell line Panc-1 cell and in a pancreatic cancer xenograft animal model. Results showed that M-PLDUs were spherical and uniform with a diameter about ∼180 nm, with a zeta potential of about −28∼−30 mV, and had good efficacy encapsulating DOX and USPIOs. The in vitro study demonstrated that M-PLDUs possessed good magnetic resonance imaging (MRI) capability with a transverse relaxivity (r²) of about 58.5 mM^–1 · s^–1. Confocal microscopy showed more efficient uptake of M-PLDU in Panc-1 cells by antibody-mediated targeting. Methyl thiazolyl tetrazolium assay results showed significant inhibitory effect of M-PLDU against Panc-1 cells (half-maximal inhibitory concentration, 1.95 μM). The in vivo imaging study showed that the tumor signal intensity (SI) dropped significantly about 4 hours after intravenous injection of M-PLDU. The decrease in tumor SI induced by M-PLDUs (ΔSI = 145.98 ± 20.45) or PLDUs (ΔSI = 75.69 ± 14.53) was much more significant than that by free USPIOs (ΔSI = 42.78 ± 22.12; P < 0.01). The in vivo antitumor study demonstrated that compared with FD (free DOX) and PLDU, M-PLDU possessed higher inhibitory effect on tumor growth and the tissue distribution assay further proved that M-PLDUs could selectively accumulate in the tumor xenograft. These results indicated that M-PLDU not only well retained the inherent MRI capability of USPIOs, but significantly improved the targeting distribution of USPIOs and therapeutic agents in pancreatic tumor tissues. They may serve as a promising theranostic nanomedicine not only for early detection but also for MRI-monitored targeting therapy of human pancreatic cancer.

Microenvironments and different nanoparticle dynamics in living cells revealed by a standard nanoparticle

For quantitative analysis of nanoparticle diffusions and submicro-environments in living cells, use of newly synthesized silica-based fluorescent nanoparticle (Si-FNP) as a standard nanoprobe is successfully demonstrated. The appropriate characteristics of a standard probe were fully analyzed in vitro by single molecule detection, transmission electron microscopy, and dynamic light scattering. Using fluorescence correlation analysis in single living cells, we quantitatively compared the diffusional properties of the standard Si-FNP with a diameter of 50 nm, peptide coated Si-FNP, streptavidin coated Qdot, and GFP molecule which have different sizes and surface properties. The result demonstrates that the standard Si-FNP without coat is minimally trapped in the vesicles in the process of cellular endocytosis. Interestingly, a large proportion of Si-FNP introduced into the cells by electroporation diffuses freely in the cells during a cell cycle suggesting free diffusing NPs are hardly trapped in the vesicles. The simple but highly sensitive method will provide insight into strategies to understanding the hydrodynamic process of nanoparticle delivery into living cells as well as the cellular microenvironment in the view of submicro-size.

Cell-penetrating properties of the transactivator of transcription and polyarginine (R9) peptides, their conjugative effect on nanoparticles and the prospect of conjugation with arsenic trioxide

Cell-penetrating peptides (CPPs) are short chains of amino acids with the distinct ability to cross cell plasma membranes. They are usually between seven and 30 residues in length. The mechanism of action is still a highly debated subject among researchers; it seems that a commonality between all CPPs is the presence of positively charged residues within the amino acid chain. Polyarginine and the transactivator of transcription peptide are two widely used CPPs. One distinct application of these CPPs is the ability to further enhance the therapeutic properties of a range of different agents. One group of agents of particular importance are nanoparticles (NPs). Most NPs have no mechanism for cellular uptake. Hence, by conjugating CPPs to NPs, the amount of NPs taken up by cells can be increased, and therefore, the therapeutic benefits can be maximized. Some examples of this will be explored further in this review. In addition to CPPs, the concept of conjugation with the anticancer drug arsenic trioxide is reviewed and the prospect of transactivator of transcription-conjugated arsenic trioxide albumin microspheres is also discussed. Recent locked nucleic acid technology to stabilize nucleotides (RNA or DNA) aptamer complexes able to target cancer cells more specifically and selectively to kill tumour cells and spare normal body cells. NPs tagged with modified locked nucleic acid-aptamers have the potential to kill cancer cells more specifically and effectively while sparing normal cells.

Size matters: gold nanoparticles in targeted cancer drug delivery

Cancer is the current leading cause of death worldwide, responsible for approximately one quarter of all deaths in the USA and UK. Nanotechnologies provide tremendous opportunities for multimodal, site-specific drug delivery to these disease sites and Au nanoparticles further offer a particularly unique set of physical, chemical and photonic properties with which to do so. This review will highlight some recent advances, by our laboratory and others, in the use of Au nanoparticles for systemic drug delivery to these malignancies and will also provide insights into their rational design, synthesis, physiological properties and clinical/preclinical applications, as well as strategies and challenges toward the clinical implementation of these constructs moving forward.

Antinuclear antibodies with nucleosome-restricted specificity for targeted delivery of chemotherapeutic agents

Circulating antinuclear autoantibodies (ANAs) are well known to accompany various pathological conditions and can be artificially induced by immunization. Research and clinical data permit us to hypothesize a definite connection between cancer and ANAs. Based on the available data, my group's research suggested that exogenous ANAs may be used as anticancer therapeutics. Among these ANAs, nucleosome-specific ANAs may be particularly useful. Advances in cancer immunotherapy with monoclonal antibodies re-emphasized the role of humoral immunity in neoplasia control. The development of a universal antibody targeting diverse cancers is of clear importance. We showed that certain natural ANAs recognize the surface of numerous tumor cells but not normal cells via cell surface-bound nucleosomes originating from the apoptotically dying neighboring tumor cells, mediate antibody-dependent cellular cytotoxicity of tumor cells in vitro and inhibit the development of murine tumor in syngeneic mice. A single monoclonal antinuclear nucleosome-specific autoantibody, mAb 2C5, specifically recognizes multiple unrelated human tumor cell lines and accumulates at a high tumor-to-normal cell ratio in various human tumors in nude mice. Immunotherapy with mAb 2C5 resulted in significant suppression of the growth of several human tumors. In addition, mAb 2C5, when used in subtherapeutic quantities, can serve as a highly efficient specific ligand to target various drug- or diagnostic agent-loaded pharmaceutical nanocarriers, such as liposomes and polymeric micelles, to various tumors. Here, the data (accumulated predominantly in our laboratory over several years) on mAb 2C5-mediated tumor targeting of chemotherapeutic agents is reviewed.

Peptide targeted lipid nanoparticles for anticancer drug delivery

Encapsulating anticancer drugs in nanoparticles has proven to be an effective mechanism to alter the pharmacokinetic and pharmacodynamic profiles of the drugs, leading to clinically useful cancer therapeutics like Doxil and DaunoXome. Underdeveloped tumor vasculature and lymphatics allow these first-generation nanoparticles to passively accumulate within the tumor, but work to create the next-generation nanoparticles that actively participate in the tumor targeting process is underway. Lipid nanoparticles functionalized with targeting peptides are among the most often studied. The goal of this article is to review the recently published literature of targeted nanoparticles to highlight successful designs that improved in vivo tumor therapy, and to discuss the current challenges of designing these nanoparticles for effective in vivo performance.

Efficient intracellular delivery of nucleic acid pharmaceuticals using cell-penetrating peptides

Over the last 20 years, researchers have designed or discovered peptides that can permeate membranes and deliver exogenous molecules inside a cell. These peptides, known as cell-penetrating peptides (CPPs), typically consist of 6-30 residues, including HIV TAT peptide, penetratin, oligoarginine, transportan, and TP10. Through chemical conjugation or noncovalent complex formation, these structures successfully deliver bioactive and membrane-impermeable molecules into cells. CPPs have also gained attention as an attractive vehicle for the delivery of nucleic acid pharmaceuticals (NAPs), including genes/plasmids, short oligonucleotides, and small interference RNAs and their analogues, due to their high internalization efficacy, low cytotoxicity, and flexible structural design. In this Account, we survey the potential of CPPs for the design and optimization of NAP delivery systems. First, we describe the impact of the N-terminal stearylation of CPPs. Endocytic pathways make a major contribution to the cellular uptake of NAPs. Stearylation at the N-terminus of CPPs with stearyl-octaarginine (R8), stearyl-(RxR)(4), and stearyl-TP10 prompts the formation of a self-assembled core-shell nanoparticle with NAPs, a compact structure that promotes cellular uptake. Researchers have designed modifications such as the addition of trifluoromethylquinoline moieties to lysine residues to destabilize endosomes, as exemplified by PepFect 6, and these changes further improve biological responsiveness. Alternatively, stearylation also allows implantation of CPPs onto the surface of liposomes. This feature facilitates "programmed packaging" to establish multifunctional envelope-type nanodevices (MEND). The R8-MEND showed high transfection efficiency comparable to that of adenovirus in non-dividing cells. Understanding the cellular uptake mechanisms of CPPs will further improve CPP-mediated NAP delivery. The cellular uptake of CPPs and their NAP complex involves various types of endocytosis. Macropinocytosis, a mechanism which is also activated in response to stimuli such as growth factors or viruses, is a primary pathway for arginine-rich CPPs because high cationic charge density promotes this endocytic pathway. The use of larger endosomes (known as macropinosomes) rather than clathrin- or caveolae-mediated endocytosis has been reported in macropinocytosis which would also facilitate the endocytosis of NAP nanoparticles into cells.

Endothelial dysfunction and systemic hypertension by selective cGMP-dependent protein kinase I inhibition using novel cell-penetrating peptide delivered in vivo

BACKGROUND AND OBJECTIVE

Nitric oxide (NO) and related nitrovasodilators regulate blood pressure by activation of soluble guanylate cyclase, elevation of cyclic guanosine monophosphate (cGMP), and activation of cGMP-dependent protein kinase (cGPK). Despite the progress of our understanding of the NO/cGMP mediated vasorelaxation, partly through conventional cGPK knock-out mice, the role of cGPK remains unclear. In particular, the downstream target(s) of the kinase are not well defined. We hypothesized that highly selective inhibitors of cGPK delivered in vivo in adult may elucidate the role of the kinase in vasorelaxation and regulation of blood pressure.

METHODS AND RESULTS

We have adopted a newly developed method of TAT-mediated protein transduction to study NO/cGMP signaling pathways in mice. In vitro, TAT-cGPK inhibitor peptide blocked autophosphorylation of the kinase. The effect of cGPK inhibition on murine blood pressure (BP) was investigated by continuous infusion of 100 μg of the inhibitor into the internal jugular vein over 72 hours. In 8 animals infused with the inhibitor, the mean BP increased by 38 ± 24/31 ± 30 mm Hg (from 108 ± 14/92 ± 19 to 145 ± 13/123 ± 19 mm Hg) whereas in 8 animals injected with either saline (4) or TAT-green fluorescent protein (4), the BP remained the same (from 117 ± 21/101 ± 26 to 119 ± 22/96 ± 30 mm Hg); P=0.001. Ex vivo, using vascular ring assays, NO-dependent relaxation in murine aortas harvested from animals administered with TAT-cGPK inhibitor was inhibited by 25% (sham 76 ± 11%, inhibitor 51 ± 13%).

CONCLUSION

We demonstrated that highly specific peptide inhibitor of cGPK induced adult murine hypertension through inhibition of nitric oxide mediated relaxation.

Effects of serum adsorption on cellular uptake profile and consequent impact of titanium dioxide nanoparticles on human lung cell lines

Exposure to fetal bovine serum (FBS) is shown herein to reduce the aggregate size of titanium dioxide (TiO(2)) nanoparticles, affecting uptake and consequent effect on A549 and H1299 human lung cell lines. Initially, the cellular uptake of the FBS-treated TiO(2) was lower than that of non-FBS-treated TiO(2). Expulsion of particles was then observed, followed by a second phase of uptake of FBS-treated TiO(2), resulting in an increase in the cellular content of FBS-treated TiO(2), eventually exceeding the amount by cells exposed to non-FBS-treated TiO(2). Surface adsorbed vitronectin and the clathrin-mediated endocytosis pathway were shown to regulate the uptake of TiO(2) into A549 cells, while the endocytosis mechanism responsible remains elusive for H1299. Intriguingly, nystatin treatment was shown to have the unexpected effect of increasing nanoparticle uptake into the A549 cells via an alternate endocytic pathway. The surface adsorbed serum components were found to provide some protection from the cytotoxic effect of endocytosed TiO(2) nanoparticles.

Beyond the imaging: limitations of cellular uptake study in the evaluation of nanoparticles

Poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) conjugated to a cell-penetrating peptide, TAT, was used to increase intracellular delivery of paclitaxel (PTX) to multi-drug resistant (MDR) cells. Efficient cellular uptake of the TAT-conjugated PLGA NPs was observed; however, it did not translate to increased killing of MDR cells. An investigation of drug release kinetics in phosphate-buffered saline containing Tween 80 led us to suspect that a significant fraction of the loaded PTX was released before efficient cellular uptake could occur. These results indicate that the increased cellular uptake of NPs does not always mean an enhanced drug effect and that it is critical to control both the location of NPs and the drug release from NPs together. Based on this study, we propose that two prevalent practices in NP research be reconsidered: first, the utility of a new NP system should be tested beyond the imaging level. Second, NP release kinetics should be monitored in a medium that can reflect the complexity of biological environment rather than a simple buffered saline.

Matrix metalloprotease 2-responsive multifunctional liposomal nanocarrier for enhanced tumor targeting

A novel "smart" multifunctional drug delivery system was successfully developed to respond to the up-regulated matrix metalloprotease 2 (MMP2) in the tumor microenvironment and improve cancer cell-specific delivery of loaded drugs. The system represents a surface-functionalized liposomal nanocarrier, for which two functional polyethylene glycol (PEG)-lipid conjugates were synthesized and characterized. The functionalized liposome was further modified with the tumor cell-specific antinucleosome monoclonal antibody (mAb 2C5). In the resulting system, several drug delivery strategies were combined in the same nanocarrier in a simple way and coordinated in an optimal fashion. The functions of the nanocarrier include (i) the hydrophilic and flexible long PEG chains to prevent nanocarrier nonspecific interactions and prolong its circulation time; (ii) a nanoscale size of the system that allows for its passive tumor targeting via the enhanced permeability and retention (EPR) effect; (iii) a mAb 2C5 to allow for the specific targeting of tumor cells; (iv) a matrix metalloprotease 2-sensitive bond between PEG and lipid that undergoes cleavage in the tumor by the highly expressed extracellular MMP2 for the removal of PEG chains; (v) cell-penetrating peptide (TATp) triggering of the enhanced intracellular delivery of the system after long-chain PEG removal and exposure of the previously hidden surface-attached TATp. It is shown that such a design can enhance the targetability and internalization of nanocarriers in cancer cells.

Molecular mechanisms in the dramatic enhancement of HIV-1 Tat transduction by cationic liposomes

Human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat) protein possesses a unique membrane-transduction property. Interestingly, Tat transduction could be dramatically increased 1000-fold based on LTR-transactivation assay when complexed with cationic liposomes (lipo-Tat), compared with Tat alone. Therefore, underlining mechanisms were explored further. Microscopy and flow cytometry showed that this effect was associated with enhanced membrane binding, large particle formation (1-2 μm) and increased intracellular uptake of Tat fluorescent proteins. Using pharmacological assays and immune colocalizations, it was found that lipid raft-dependent endocytosis and macropinocytosis were major pathways involved in lipo-Tat uptake, and actin-filaments played a major role in intracellular trafficking of lipo-Tat to the nucleus. Furthermore, we found that the Tat hydrophobic domain (aa 36-47) mediated formation of two positively charged molecules into lipo-Tat complexes via hydrophobic bonds, based on LTR-transactivation inhibition assay. Thus, the hydrophobic domain may play an important role in Tat protein uptake and be useful for intracellular delivery of biomacromolecules if coupled together with Tat basic peptide, a cell-penetrating peptide.

Interaction of α-synuclein and a cell penetrating fusion peptide with higher eukaryotic cell membranes assessed by ¹⁹F NMR

We show that fluorine NMR can be used to monitor the insertion and change in conformation of a ¹⁹F-labeled cell-penetrating peptide upon interacting with the cellular plasma membrane. α-Synuclein and a construct comprising a cell-penetrating peptide covalently attached to its N-terminus were studied. Important information about the interaction of the proteins with CHO-K1 cells was obtained by monitoring the diminution of ¹⁹F resonances of 3-fluoro-l-tyrosine labeled proteins. For α-synuclein, a decrease in the resonance from position 39 was observed indicating that only the N-terminal third region of the protein interacts with plasma membrane. However, when the fusion construct was incubated with the cells, a decrease in the resonance from the fusion peptide region was noted with no change in the resonances from α-synuclein region. Longer incubation, studied by using confocal fluorescence microscopy, revealed that the fusion construct translocates into the cells, but α-synuclein alone did not cross the membrane in significant amounts.

Effects of the TAT peptide orientation and relative location on the protein transduction efficiency

To understand the protein transduction domain (PTD)-mediated protein transduction behavior and to explore its potential in delivering biopharmaceutic drugs, we prepared four TAT-EGFP conjugates: TAT(+)-EGFP, TAT(-)-EGFP, EGFP-TAT(+) and EGFP-TAT(-), where TAT(+) and TAT(-) represent the original and the reversed TAT sequence, respectively. These four TAT-EGFP conjugates were incubated with HeLa and PC12 cells for in vitro study as well as injected intraperitoneally to mice for in vivo study. Flow cytometric results showed that four TAT-EGFP conjugates were able to traverse HeLa and PC12 cells with almost equal transduction efficiency. The in vivo study showed that the TAT-EGFP conjugates could be delivered into different organs of mice with different transduction capabilities. Bioinformatic analyses and CD spectroscopic data revealed that the TAT peptide has no defined secondary structure, and conjugating the TAT peptide to the EGFP cargo protein would not alter the native structure and the function of the EGFP protein. These results conclude that the sequence orientation, the spatial structure, and the relative location of the TAT peptide have much less effect on the TAT-mediated protein transduction. Thus, the TAT-fused conjugates could be constructed in more convenient and flexible formats for a wide range of biopharmaceutical applications.

Photochemical internalisation of a macromolecular protein toxin using a cell penetrating peptide-photosensitiser conjugate

Photochemical internalisation (PCI) is a site-specific technique for improving cellular delivery of macromolecular drugs. In this study, a cell penetrating peptide, containing the core HIV-1 Tat 48-57 sequence, conjugated with a porphyrin photosensitiser has been shown to be effective for PCI. Herein we report an investigation of the photophysical and photobiological properties of a water soluble bioconjugate of the cationic Tat peptide with a hydrophobic tetraphenylporphyrin derivative. The cellular uptake and localisation of the amphiphilic bioconjugate was examined in the HN5 human head and neck squamous cell carcinoma cell line. Efficient cellular uptake and localisation in endo/lysosomal vesicles was found using fluorescence detection, and light-induced, rupture of the vesicles resulting in a more diffuse intracellular fluorescence distribution was observed. Conjugation of the Tat sequence with a hydrophobic porphyrin thus enables cellular delivery of an amphiphilic photosensitiser which can then localise in endo/lysosomal membranes, as required for effective PCI treatment. PCI efficacy was tested in combination with a protein toxin, saporin, and a significant reduction in cell viability was measured versus saporin or photosensitiser treatment alone. This study demonstrates that the cell penetrating peptide-photosensitiser bioconjugation strategy is a promising and versatile approach for enhancing the therapeutic potential of bioactive agents through photochemical internalisation.

Exploring transduction mechanisms of protein transduction domains (PTDs) in living cells utilizing single-quantum dot tracking (SQT) technology

Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and to identify the rate-limiting steps. Because of technical limitations for imaging PTD behavior on cells with conventional fluorescent-dyes, how PTDs enter the cells has been a topic of much debate. Utilizing quantum dots (QDs), we recently tracked the behavior of PTD that was derived from HIV-1 Tat (TatP) in living cells at the single-molecule level with 7-nm special precision. In this review article, we initially summarize the controversy on TatP entry mechanisms; thereafter, we will focus on our recent findings on single-TatP-QD tracking (SQT), to identify the major sequential steps of intracellular delivery in living cells and to discuss how SQT can easily provide direct information on TatP entry mechanisms. As a primer for SQT study, we also discuss the latest findings on single particle tracking of various molecules on the plasma membrane. Finally, we discuss the problems of QDs and the challenges for the future in utilizing currently available QD probes for SQT. In conclusion, direct identification of the rate-limiting steps of PTD entry with SQT should dramatically improve the methods for enhancing transduction efficiency.

Enhanced activity of cyclic transporter sequences driven by phase behavior of peptide-lipid complexes

We demonstrate that recent observed increases in cell permeation activity of cyclic peptides via transporter sequences is due to the underlying phase behavior of peptide-lipid complexes and its relation to the topological requirement of membrane permeation. We also show how these effects can be amplified by incorporating hydrophobicity in these sequences.

Simultaneous detection of infectious human echoviruses and adenoviruses by an in situ nuclease-resistant molecular beacon-based assay

A multiplex methodology using two nuclease-resistant molecular beacons that target specific genomic regions of adenovirus 2 and echovirus 17 during simultaneous infection in A549 cells is presented. Using fluorescence microscopy, visualization of enteroviral and adenoviral replication was possible within 3 h postinfection.

Multifunctional PEGylated 2C5-immunoliposomes containing pH-sensitive bonds and TAT peptide for enhanced tumor cell internalization and cytotoxicity

pH-sensitive PEGylated (with PEG-PE) long-circulating liposomes (HSPC:cholesterol and Doxil®), modified with cell-penetrating TAT peptide (TATp) moieties and cancer-specific mAb 2C5 were prepared. A degradable pH-sensitive hydrazone bond between a long shielding PEG chains and PE (PEG(2k)-Hz-PE) was introduced. TATp was conjugated with a short PEG(1k)-PE spacer and mAb 2C5 was attached to a long PEG chain (2C5-PEG(3.4k)-PE). The "shielding" effect of TATp by long PEG chains was investigated using three liposomal models. At normal pH, surface TATp moieties are "hidden" by the long PEG chains. Upon the exposure to lowered pH, this multifunctional carrier exposes TATp moieties after the degradation of the hydrazone bond and removal of the long PEG chains. Enhanced cellular uptake of the TATp-containing immunoliposomes was observed in vitro after pre-treatment at lowered pH (using flow cytometry and fluorescence microscopy techniques). The presence of mAb 2C5 on the liposome surface further enhanced the interaction between the carrier and tumor cells but not normal cells. Furthermore, multifunctional immuno-Doxil® preparation showed increased cellular cytotoxicity of B16-F10, HeLa and MCF-7 cells when pre-incubated at lower pH, indicating TATp exposure and activity. In conclusion, a multifunctional immunoliposomal nanocarrier containing a pH-sensitive PEG-PE component, TATp, and the cancer cell-specific mAb 2C5 promotes enhanced cytotoxicity and carrier internalization by cancer cells and demonstrates the potential for intracellular drug delivery after exposure to lowered pH environment, typical of solid tumors.