Transactivating transcriptional activator-mediated drug delivery

Effect of Cholesterol on Biomimetic Membrane Curvature and Coronavirus Fusion Peptide Encapsulation

Biomimetic cubic phases can be used for protein encapsulation in a variety of applications such as biosensors and drug delivery. Cubic phases with a high concentration of cholesterol and phospholipids were obtained herein. It is shown that the cubic phase structure can be maintained with a higher concentration of biomimetic membrane additives than has been reported previously. Opposing effects on the curvature of the membrane were observed upon the addition of phospholipids and cholesterol. Furthermore, the coronavirus fusion peptide significantly increased the negative curvature of the biomimetic membrane with cholesterol. We show that the viral fusion peptide can undergo structural changes leading to the formation of hydrophobic α-helices that insert into the lipid bilayer. This is of high importance, as a fusion peptide that induces increased negative curvature as shown by the formation of inverse hexagonal phases allows for greater contact area between two membranes, which is required for viral fusion to occur. The cytotoxicity assay showed that the toxicity toward HeLa cells was dramatically decreased when the cholesterol or peptide level in the nanoparticles increased. This suggests that the addition of cholesterol can improve the biocompatibility of the cubic phase nanoparticles, making them safer for use in biomedical applications. As the results, this work improves the potential for the biomedical end-use applications of the nonlamellar lipid nanoparticles and shows the need of systematic formulation studies due to the complex interplay of all components.

Enhanced efficiency of generating human-induced pluripotent stem cells using Lin28-30Kc19 fusion protein

Induced pluripotent stem cells (iPSCs) have intrinsic properties, such as self-renewal ability and pluripotency, which are also shown in embryonic stem cells (ESCs). The challenge of improving the iPSC generation efficiency has been an important issue and there have been many attempts to develop iPSC generation methods. In this research, we added Lin28, known as one of the reprogramming factors, in the form of a soluble recombinant protein from E. coli to improve the efficiency of human iPSC (hiPSC) generation, in respect of alkaline phosphatase (AP)-positive colonies. To deliver Lin28 inside the cells, we generated a soluble Lin28-30Kc19 fusion protein, with 30Kc19 at the C-terminal domain of Lin28. 30Kc19, a silkworm hemolymph-derived protein, was fused due to its cell-penetrating and protein-stabilizing properties. The Lin28-30Kc19 was treated to human dermal fibroblasts (HDFs), in combination with four defined reprogramming factors (Oct4, Sox2, c-Myc, and Klf4). After 14 days of cell culture, we confirmed the generated hiPSCs through AP staining. According to the results, the addition of Lin28-30Kc19 increased the number and size of generated AP-positive hiPSC colonies. Through this research, we anticipate that this recombinant protein would be a valuable material for increasing the efficiency of hiPSC generation and for enhancing the possibility as a substitute of the conventional method.

Engineered Sumoylation-Deficient Prdx6 Mutant Protein-Loaded Nanoparticles Provide Increased Cellular Defense and Prevent Lens Opacity

Aberrant Sumoylation-mediated protein dysfunction is involved in a variety of oxidative and aging pathologies. We previously reported that Sumoylation-deficient Prdx6K^{(lysine)122/142R(Arginine)} linked to the TAT-transduction domain gained stability and protective efficacy. In the present study, we formulated wild-type TAT-HA-Prdx6^WT and Sumoylation-deficient Prdx6-loaded poly-lactic-co-glycolic acid (PLGA) nanoparticles (NPs) to further enhance stability, protective activities, and sustained delivery. We found that in vitro and subconjuctival delivery of Sumoylation-deficient Prdx6-NPs provided a greater protection of lens epithelial cells (LECs) derived from human and Prdx6^-/--deficient mouse lenses against oxidative stress, and it also delayed the lens opacity in Shumiya cataract rats (SCRs) than TAT-HA-Prdx6^WT-NPs. The encapsulation efficiencies of TAT-HA-Prdx6-NPs were ≈56%-62%. Dynamic light scattering (DLS) and atomic force microscopy (AFM) analyses showed that the NPs were spherical, with a size of 50-250 nm and a negative zeta potential (≈23 mV). TAT-HA-Prdx6 analog-NPs released bioactive TAT-HA-Prdx6 (6%-7%) within 24 h. Sumoylation-deficient TAT-HA-Prdx6-NPs provided 35% more protection by reducing the oxidative load of LECs exposed to H₂O₂ compared to TAT-HA-Prdx6^WT-NPs. A subconjuctival delivery of TAT-HA-Prdx6 analog-NPs demonstrated that released TAT-HA-Prdx6^K122/142R could reduce lens opacity by ≈60% in SCRs. Collectively, our results demonstrate for the first time that the subconjuctival delivery of Sumoylation-deficient Prdx6-NPs is efficiently cytoprotective and provide a proof of concept for potential use to delay cataract and oxidative-related pathobiology in general.

Impact Of Penetratin Stereochemistry On The Oral Bioavailability Of Insulin-Loaded Solid Lipid Nanoparticles

Purpose

This study evaluated the stereoisomeric effect of L- and D-penetratin—cell-penetrating peptides (CPPs)—incorporated insulin-loaded solid lipid nanoparticles (INS-SLNs) on the bioavailability (BA) of oral insulin (INS).

Methods

Insulin-loaded solid nanoparticles, L-penetratin-INS-SLNs (LP-INS-SLNs), and D-penetratin-INS-SLNs (DP-INS-SLNs) were formulated by double emulsification. The developed SLNs were evaluated for particle size, zeta potential (ZP), and drug encapsulation and subjected to differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and evaluated for stability against enzymatic degradation in rat intestinal fluid. Finally, the SLNs were administered to rats to evaluate the BA of INS-SLNs that contained L- and D-penetratin.

Results

The mean particle size, PDI, and ZP values of INS-SLNs, LP-INS-SLNs, and DP-INS-SLNs ranged from 618.5 to 973.0 nm, 0.227 to 0.734, and −17.0 to −23.7 mV, respectively. The encapsulation efficiency (%EE) and drug loading (%DL) of INS-SLNs, LP-INS-SLNs, and DP-INS-SLNs ranged from 59.03% to 67.42% and from 1.62% to 1.82%, respectively. Differential scanning calorimetry and FTIR analyses indicated that INS was successfully encapsulated in SLNs. Enzymatic degradation of DP-INS-SLNs was slower in intestinal fluid, and the half-life (t_1/2) was significantly prolonged, compared to all other SLNs. The pharmacological availability (PA) and BA of orally administered LP-INS-SLNs, which were the most effective SLNs, were 13.1% and 15.7% relative to s.c. administration, respectively.

Conclusion

Penetratin stereochemistry significantly impacted oral BA of INS-SLNs, which are promising carriers for oral INS administration.

Exploring the role of peptides in polymer-based gene delivery

Polymers are widely studied as non-viral gene vectors because of their strong DNA binding ability, capacity to carry large payload, flexibility of chemical modifications, low immunogenicity, and facile processes for manufacturing. However, high cytotoxicity and low transfection efficiency substantially restrict their application in clinical trials. Incorporating functional peptides is a promising approach to address these issues. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we systematically summarize the role of peptides in polymer-based gene delivery, and elaborate how to rationally design polymer-peptide based gene delivery vectors.

STATEMENT OF SIGNIFICANCE

Polymers are widely studied as non-viral gene vectors, but suffer from high cytotoxicity and low transfection efficiency. Incorporating short, bioactive peptides into polymer-based gene delivery systems can address this issue. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we highlight the peptides' roles in polymer-based gene delivery, and elaborate how to utilize various functional peptides to enhance the transfection efficiency of polymers. The optimized peptide-polymer vectors should be able to alter their structures and functions according to biological microenvironments and utilize inherent intracellular pathways of cells, and consequently overcome the barriers during gene delivery to enhance transfection efficiency.

Protein transduction domain can enhance the humoral immunity and cross-protection of HPV16L2 peptide vaccines

Due to type-specificity, commercially available human papillomavirus (HPV) vaccines are only effective against homologous HPV serotypes, providing limited protection. Recent studies have highlighted the role of HPV minor capsid protein (known as L2) in inducing cross-protection. The N-terminal peptides of L2 contain conserved cross-response epitopes that can induce neutralizing antibodies against heterogeneous HPVs. However, when compared with L1, these peptides have lower immunogenicity, which limits the application of these vaccines. The protein transduction domain (PTD), located in the Tat protein of human immunodeficiency virus, facilitates delivery of DNA, peptides, proteins and virus particles into cells by unknown mechanisms, and has been reported to enhance immunogenicity of several antigens. In the present study, two peptides derived from the N-terminal of HPV16L2 were chosen as model antigens and constructed a series of L2 peptide vaccines by either fusing or mixing with PTD. Subsequently their immunogenicity was evaluated. The results indicated that the L2 peptides fused with PTD show considerably enhanced humoral immunity. In particular, they increased the titer of cross-neutralizing antibodies, while L2 peptides that had only been mixed with PTD induced only small cross-protection responses. Overall, the data suggest that fusion of L2 peptides with PTD significantly enhances their cross-protection and may be a promising strategy for the development of broad-spectrum HPV prophylactic vaccines.

Delivery of cancer therapeutics to extracellular and intracellular targets: Determinants, barriers, challenges and opportunities

Advances in molecular medicine have led to identification of worthy cellular and molecular targets located in extracellular and intracellular compartments. Effectiveness of cancer therapeutics is limited in part by inadequate delivery and transport in tumor interstitium. Parts I and II of this report give an overview on the kinetic processes in delivering therapeutics to their intended targets, the transport barriers in tumor microenvironment and extracellular matrix (TME/ECM), and the experimental approaches to overcome such barriers. Part III discusses new concepts and findings concerning nanoparticle-biocorona complex, including the effects of TME/ECM. Part IV outlines the challenges in animal-to-human translation of cancer nanotherapeutics. Part V provides an overview of the background, current status, and the roles of TME/ECM in immune checkpoint inhibition therapy, the newest cancer treatment modality. Part VI outlines the development and use of multiscale computational modeling to capture the unavoidable tumor heterogeneities, the multiple nonlinear kinetic processes including interstitial and transvascular transport and interactions between cancer therapeutics and TME/ECM, in order to predict the in vivo tumor spatiokinetics of a therapeutic based on experimental in vitro biointerfacial interaction data. Part VII provides perspectives on translational research using quantitative systems pharmacology approaches.

Neuroprotective effect of TAT PTD-Ngb fusion protein on primary cortical neurons against hypoxia-induced apoptosis

Hypoxic-ischemic injury increases neuroglobin (Ngb) expression in the brain. In our previous study, we have generated a transactivator-of-transcription protein-transduction domain-neuroglobin fusion protein (TAT PTD-Ngb) that successfully mediated exogenous Ngb expression in the primary neurons. In this study, we further investigated the role of TAT PTD-Ngb in protecting neurons against hypoxia-induced apoptosis and explored the possible mechanism. The primary cultured neurons were divided into four groups: (1) the normal group (no hypoxic injury); (2) the vehicle group (vehicle treatment and hypoxia injury); (3) the TAT PTD-Ngb group (TAT PTD-Ngb treatment and hypoxia injury); and (4) the Ngb group (Ngb treatment and hypoxia injury). Translocation of TAT PTD-Ngb into neurons was detected using fluorescent immunostaining against His-tag as early as 30 min after incubation. MTT assay showed that the TAT PTD-Ngb group had significantly increased cell viability compared to the vehicle or Ngb group after hypoxia. The result of transmission electron microscopy (TEM) also displayed rescued ultrastructure in TAT PTD-Ngb neurons compared to that of apoptotic neurons. In addition, TAT PTD-Ngb neurons showed significantly increased expression of anti-apoptotic Bcl-2 protein and decreased activities of caspase-3 and caspase-9 in response to hypoxia. These results suggest that TAT PTD-Ngb fusion protein protects primary cortical neurons against hypoxia-induced injury possibly through suppressing mitochondria apoptotic pathway.

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.

Complexes of streptavidin-fused antigens with biotinylated antibodies targeting receptors on dendritic cell surface: a novel tool for induction of specific T-cell immune responses

The choice of tools that enable efficient targeting of exogenous antigens (Ag) for processing and presentation by professional Ag-presenting cells (APC) remains limited. This represents, indeed, a bottleneck in development of vaccines inducing specific T-cell responses. Here, we describe a novel strategy of Ag delivery into APCs. The Ag of choice is fused to the N- or C-terminus of streptavidin (SA) and tetrameric Ag-SA or SA-Ag fusion proteins are produced in E. coli and purified by 2-Iminobiotin-Agarose affinity chromatography. Alternatively, Ag-SA proteins are purified from urea extracts of E. coli inclusion bodies and refolded in vitro into functional tetramers. Complexes with biotinylated antibodies targeting cell surface receptors are formed and used to deliver the Ags of choice for processing and presentation by APCs and induction of Ag-specific CD4+ and CD8+ T-cell responses in vitro and in vivo.

Oxidative stress in apoptosis and cancer: an update

The oxygen paradox tells us that oxygen is both necessary for aerobic life and toxic to all life forms. Reactive oxygen species (ROS) touch every biological and medical discipline, especially those involving proliferative status, supporting the idea that active oxygen may be increased in tumor cells. In fact, metabolism of oxygen and the resulting toxic byproducts can cause cancer and death. Efforts to counteract the damage caused by ROS are gaining acceptance as a basis for novel therapeutic approaches, and the field of prevention of cancer is experiencing an upsurge of interest in medically useful antioxidants. Apoptosis is an important means of regulating cell numbers in the developing cell system, but it is so important that it must be controlled. Normal cell death in homeostasis of multicellular organisms is mediated through tightly regulated apoptotic pathways that involve oxidative stress regulation. Defective signaling through these pathways can contribute to both unbalance in apoptosis and development of cancer. Finally, in this review, we discuss new knowledge about recent tools that provide powerful antioxidant strategies, and designing methods to deliver to target cells, in the prevention and treatment of cancer.

Delivery of nanomedicines to extracellular and intracellular compartments of a solid tumor

Advances in molecular medicines have led to identification of promising targets on cellular and molecular levels. These targets are located in extracellular and intracellular compartments. The latter include cytosol, nucleus, mitochondrion, Golgi apparatus and endoplasmic reticulum. This report gives an overview on the barriers to delivering nanomedicines to various target sites within a solid tumor, the experimental approaches to overcome such barriers, and the potential utility of nanotechnology.

Successful TAT-mediated enzyme replacement therapy in a mouse model of mitochondrial E3 deficiency

Medicine today offers no cure for patients suffering from mitochondrial disorders, such as lipoamide dehydrogenase (LAD; also known as E3) deficiency, and treatment is limited to symptomatic care. LAD is one of the components of the α-ketoacid dehydrogenase complexes, which are mitochondrial multienzyme complexes crucial for the metabolism of carbohydrates and amino acids. Recently, we tested the therapeutic approach for treating mitochondrial disorders whereby the activity of multicomponent complexes in the mitochondria is restored by TAT-mediated enzyme replacement therapy (ERT). The LAD deficiency disease was used before as a proof-of-principle in vitro, in patients' cells, utilizing the TAT-LAD fusion protein. In this report, we present successful TAT-mediated ERT in an in vivo mouse model using E3-deficient mice. We demonstrate the delivery of TAT-LAD into E3-deficient mice tissues and that a single administration of TAT-LAD results in a significant increase in the enzymatic activity of the mitochondrial multienzyme complex pyruvate dehydrogenase complex within the liver, heart and, most importantly, the brain of TAT-LAD-treated E3-deficient mice. We believe that this TAT-mediated ERT approach could change the management of mitochondrial disorders and of other metabolic diseases in modern medicine.

The delivery of HBcAg via Tat-PTD enhances specific immune response and inhibits Hepatitis B virus replication in transgenic mice

Recent studies have indicated that the therapeutic vaccine based on enhancement of HBV-specific cytotoxic T-lymphocyte (CTL) activity may lead to viral clearance in chronically infected individuals. It is demonstrated that protein transduction domains (PTD) from HIV-1-Tat protein is able to enter cells when combined with exogenous antigens and induce specific CTL responses. We have previously testified that the expressed and purified fusion protein containing Tat-PTD47-57 and HBcAg could enter cytoplasm of dendritic cells, and enhance T cells response to generate HBcAg-specific CTLs efficiently in vitro. In the present study, we evaluated HBcAg-specific immune responses of PTD-HBcAg fusion protein in BALB/c mice and antiviral immunity in HBV transgenic mice. The studies showed that PTD-HBcAg not only induced significantly higher antibody responses, but also increased production of cytokine (IFN-gamma, IL-2, IL-4 and IL-10) compared to HBcAg alone and PBS. Moreover, PTD-HBcAg fusion protein increased significantly the percentages of IFN-gamma+CD8+ T cells and HBcAg-specific (CTL) responses. Also, enhancement of immune response induced by fusion protein reduced HBV DNA and HBsAg levels and decreased the expression of HBsAg in liver tissue of HBV transgenic mice. In conclusion, PTD-HBcAg fusion protein could enhance not only cell immune response but also humoral immune response, and induce robust specific CTL activity and therapeutic effects in HBV transgenic mice.

Tat-Mediated Peptide Intervention in Analgesia and Anesthesia

Membrane-permeable peptide carriers are attractive drug delivery tools. Among such carriers, the protein transduction domain (PTD) of the human immunodeficiency virus-type 1 Tat protein is most frequently used and has been successfully shown to deliver a large variety of cargoes. The Tat PTD can facilitate the uptake of large, biologically active molecules into mammalian cells, and recent studies have shown that it can mediate the delivery of different cargoes into tissues throughout a living organism. Given that the Tat PTD-mediated delivery is size-independent, this technology could make previously non-applicable large molecules usable to modulate biological function in vivo and treat human diseases. It is likely that the peptide carrier-mediated intracellular delivery process encompasses multiple mechanisms, but endocytic pathways are the predominant internalization routes. Tat PTD has been successfully used in preclinical models for the study of cancer, ischemia, inflammation, analgesia, and anesthesia. Our recent studies have shown that intraperitoneally injected fusion Tat peptide Tat-PSD-95 PDZ2 can be delivered into the spinal cord to dose-dependently disrupt protein-protein interactions between PSD-95 and NMDA receptors. This peptide significantly inhibits chronic inflammatory pain and reduces the threshold for halothane anesthesia. The ability of the Tat PTD to target any cell is advantageous in some respects. However, the drug delivery system will be more attractive if we can modify the Tat PTD to deliver cargo only into desired organs to avoid possible side effects.

"Soft" calcium crosslinks enable highly efficient gene transfection using TAT peptide

PURPOSE

Typically, low molecular weight cationic peptides or polymers exhibit poor transfection efficiency due to an inability to condense plasmid DNA into small nanoparticles. Here, efficient gene delivery was attained using TAT/pDNA complexes containing calcium crosslinks.

METHODS

Electrostatic complexes of pDNA with TAT or PEI were studied with increasing calcium concentration. Gel electrophoresis was used to determine DNA condensation. The morphology of the complexes was probed by transmission electron microscopy. Transfection efficiency was assessed using a luciferase reporter plasmid. The accessibility of phosphate and amine groups within complexes was evaluated to determine the effect of calcium on structure.

RESULTS

TAT/pDNA complexes were condensed into small, 50-100 nm particles by optimizing the concentration of calcium. Complexes optimized for small size also exhibited higher transfection efficiency than PEI polyplexes in A549 cells. TAT and TAT complexes displayed negligible cytotoxicity up to 5 mg/mL, while PEI exhibited high cytotoxicity, as expected. Probing the TAT-Ca/pDNA structure suggested that calcium interacted with both phosphate and amine groups to compact the complexes; however, these "soft" crosslinks could be competitively disrupted to facilitate DNA release.

CONCLUSION

Small and stable TAT-Ca/pDNA complexes were obtained via "soft" calcium crosslinks leading to sustained gene expression levels higher than observed for control PEI gene vectors. TAT-Ca/pDNA complexes were stable, maintaining particle size and transfection efficiency even in the presence of 10% of FBS. TAT-Ca complexes offer an effective vehicle offering potential for translatable gene delivery.

TAT-based drug delivery system--new directions in protein delivery for new hopes?

There has been great progress in the use of TAT-based drug delivery systems for the delivery of different macromolecules into cells in vitro and in vivo, thus circumventing the bioavailability barrier that is a problem for so many drugs. There are many advantages to using this system, such as the ability to deliver these cargoes into all types of cells in culture and into all organs in vivo. This system can even deliver cargoes into the brain across the blood-brain barrier. In addition, the ability to target specific intracellular sub-localizations such as the nuclei, the mitochondria and lysosomes further expands the possibilities of this drug delivery system to the development of sub-cellular organelle-targeted therapy. The therapeutic applications seem almost unlimited, and the use of the TAT-based delivery system has extended from proteins to a large variety of cargoes such as oligonucleotides, imaging agents, low molecular mass drugs, nanoparticles, micelles and liposomes. In this review the most recent advances in the use of the TAT-based drug delivery system will be described, mainly discussing TAT-mediated protein delivery and the use of the TAT system for enzyme replacement therapy.

Recent developments in peptide-based nucleic acid delivery

Despite the fact that non-viral nucleic acid delivery systems are generally considered to be less efficient than viral vectors, they have gained much interest in recent years due to their superior safety profile compared to their viral counterpart. Among these synthetic vectors are cationic polymers, branched dendrimers, cationic liposomes and cell-penetrating peptides (CPPs). The latter represent an assortment of fairly unrelated sequences essentially characterised by a high content of basic amino acids and a length of 10–30 residues. CPPs are capable of mediating the cellular uptake of hydrophilic macromolecules like peptides and nucleic acids (e.g. siRNAs, aptamers and antisense-oligonucleotides), which are internalised by cells at a very low rate when applied alone. Up to now, numerous sequences have been reported to show cell-penetrating properties and many of them have been used to successfully transport a variety of different cargos into mammalian cells. In recent years, it has become apparent that endocytosis is a major route of internalisation even though the mechanisms underlying the cellular translocation of CPPs are poorly understood and still subject to controversial discussions. In this review, we will summarise the latest developments in peptide-based cellular delivery of nucleic acid cargos. We will discuss different mechanisms of entry, the intracellular fate of the cargo, correlation studies of uptake versus biological activity of the cargo as well as technical problems and pitfalls.

Intracellular delivery of nanoparticles via the HIV-1 tat peptide

Functionalized nanoparticles are heralded as part of the future with regards to targeted cell and nuclear delivery. However, direct intracellular and intranuclear delivery has, until recently, been difficult to achieve owing to the impermeable nature of the plasma and nuclear membranes. During the past 15 years, a range of peptides, termed cell-penetrating peptides (CPPs), which have the ability to translocate into living cells, have been discovered. Thus, in more recent years, the combination of CPPs with nanoparticles, enabling CPP-mediated cell delivery, has opened up many avenues of research. This review discusses the use of various CPPs, focusing on tat peptide, to functionalize nanoparticles and the possible move from the laboratory to the clinic.

Methodological and cellular aspects that govern the internalization mechanisms of arginine-rich cell-penetrating peptides

Peptides including HIV-1 Tat peptide and oligoarginines represent arginine-rich membrane-permeable vectors that attain efficient intracellular delivery of bioactive molecules. The importance of the arginine residues or their guanidino functions is now appreciated for efficient internalization of the Tat peptide, and based on this, various novel arginine/guanidino-rich vectors have now been developed. However, molecular detail of their method(s) of internalization are still debated. This review summarizes our current understandings of endocytic and non-endocytic aspects of internalization of arginine-rich peptide vectors. We highlight the possibility of simultaneous employment of multiple internalization pathways, the contribution of which is dependent on a number of factors. Similarities and dissimilarities among the internalization methods of typical peptide vectors and other guanidino-rich vectors including branched-chain, beta-peptide, and sugar-based vectors, are also discussed.

Cellular internalization and distribution of arginine-rich peptides as a function of extracellular peptide concentration, serum, and plasma membrane associated proteoglycans

The exact mechanisms by which arginine-rich cell-penetrating peptides enter cells are still the subject of debate. Here, we have analyzed in detail the effects of serum and extracellular concentration on the internalization of oligoarginines (R n; n = 4, 8, 12, 16). The presence of serum in the incubation medium had a major influence on the uptake of R12 and R16 peptides but did not affect the uptake of R4 and R8 significantly. Incubation of cells at 37 degrees C with R12 and R16 peptides in serum-containing medium showed that the majority of labeling was confined to punctate endocytic structures. Performing the same experiments in serum-free media led to a dramatic increase in cytosolic labeling, and similarly diffuse R12 and R16 labeling was observed in cells treated with peptides at 4 degrees C. This suggests, in both cases, that the peptides were entering via a nonendocytic mechanism. Further studies on R12 peptide suggest that the initiation of nonendocytic uptake and cytosolic labeling is also dependent on serum concentration and extracellular peptide concentration. At relatively low concentrations, the peptide labels endocytic structures, but upon raising the peptide concentration, the fraction labeling the cytosol increases dramatically and this accompanies a nonlinear increase in total cellular fluorescence. Membrane-associated proteoglycans also contribute to increasing the peptide concentration at the cell surface by enhancing their recruitment via electrostatic interactions. These results demonstrate that uptake mechanisms of these compounds are highly dependent on both the presence of serum and the effective extracellular peptide concentration.

A review of stimuli-responsive nanocarriers for drug and gene delivery

Nanotechnology has shown tremendous promise in target-specific delivery of drugs and genes in the body. Although passive and active targeted-drug delivery has addressed a number of important issues, additional properties that can be included in nanocarrier systems to enhance the bioavailability of drugs at the disease site, and especially upon cellular internalization, are very important. A nanocarrier system incorporated with stimuli-responsive property (e.g., pH, temperature, or redox potential), for instance, would be amenable to address some of the systemic and intracellular delivery barriers. In this review, we discuss the role of stimuli-responsive nanocarrier systems for drug and gene delivery. The advancement in material science has led to design of a variety of materials, which are used for development of nanocarrier systems that can respond to biological stimuli. Temperature, pH, and hypoxia are examples of "triggers" at the diseased site that could be exploited with stimuli-responsive nanocarriers. With greater understanding of the difference between normal and pathological tissues and cells and parallel developments in material design, there is a highly promising role of stimuli-responsive nanocarriers for drug and gene delivery in the future.

Enhancement of gene transfer using YIGSR analog of Tat-derived peptide

Cell penetrating peptide based gene carriers are notably known for low level of gene transfer. To remedy this, as laminin receptor (LR) has been previously linked to tumor metastasis, the LR-binding domain (YIGSR) as well as a scrambled sequence (SGIYR) were added to Tat-derived peptide sequence (YIGSR-Tat and SGIYR-Tat respectively). Peptides cellular uptake was assessed with high-LR (HT1080) and low-LR (HT29) cell lines by flow cytometry. Their ability to form complexes with DNA was examined using YOPRO-1 fluorescence assay and their transfection efficiencies evaluated using a luciferase reporter gene assay. DNA complexes were formed at (+/-) charge ratios as low as 2:1. While no conclusion could be drawn on the effect of YIGSR sequence on peptides uptake in both cell lines, a significant improvement in gene transfection in HT1080 cells was achieved using YIGSR-Tat compared to Tat and SGIYR-Tat. Additionally this increased efficiency was inhibited by excess free YIGSR. No significant difference in transfection efficiency was observed between Tat, SGIYR-Tat and YIGSR-Tat based complexes in HT29 cells. These studies demonstrate that attachment of receptor-binding ligand (YIGSR) to Tat-derived peptide can improve the efficiency of gene transfer in LR-positive cells (HT1080).

Nanotechnology-based delivery systems in HIV/AIDS therapy

The therapeutic efficacy of anti-HIV agents is often hampered by poor bioavailability and lack of drug penetration in infected target tissues and cells. Using different types of nanotechnology-based delivery systems, it is possible to engineer strategies that can improve the therapeutic efficacy in HIV/AIDS by delivering drugs to cellular and anatomical viral reservoirs. The rationale for the use of nanocarrier systems relies on the fact that different types of therapeutic payloads can be encapsulated and the systemic pharmacokinetics and distribution are dictated by the properties of the nanocarriers rather than the drugs. The versatility of nanoplatforms can be further exploited in a formulation that has enhanced oral bioavailability, protects against degradation upon oral or systemic administration and prolongs the residence time at the target site. Nanocarriers can facilitate lymphatic transport, delivery across the blood–brain barrier, and efficient internalization in cells by nonspecific or receptor-mediated endocytosis. In this review, we will address the role of nanotechnology-based delivery systems in improving the delivery efficiency of anti-HIV drugs to cellular and anatomical sites of interest. Specific published examples will be highlighted with emphasis on the role of polymeric nanoparticle micelles, liposomes and nanoemulsions in improving delivery efficiency.

The taming of the cell penetrating domain of the HIV Tat: myths and realities

Protein transduction with cell penetrating peptides over the past several years has been shown to be an effective way of delivering proteins in vitro and now several reports have also shown valuable in vivo applications in correcting disease states. An impressive bioinspired phenomenon of crossing biological barriers came from HIV transactivator Tat protein. Specifically, the protein transduction domain of HIV Tat has been shown to be a potent pleiotropic peptide in protein delivery. Various approaches such as molecular modeling, arginine guanidinium head group structural strategy, multimerization of PTD sequence and phage display system have been applied for taming of the PTD. This has resulted in identification of PTD variants which are efficient in cell membrane penetration and cytoplasmic delivery. In spite of these state of the art technologies, the dilemma of low protein transduction efficiency and target specific delivery of PTD fusion proteins remains unsolved. Moreover, some misconceptions about PTD of Tat in the literature require considerations. We have assembled critical information on secretory, plasma membrane penetration and transcellular properties of Tat and PTD using molecular analysis and available experimental evidences.