Full-length proteins attached to the HIV tat protein transduction domain are neither transduced between cells, nor exhibit enhanced immunogenicity

Direct protein delivery into intact Arabidopsis cells for genome engineering

Intracellular delivery of biomolecules is a prerequisite for genetic techniques such as recombinant engineering and genome editing. Realizing the full potential of this technology requires the development of safe and effective methods for delivering protein tools into cells. In this study, we demonstrated the spontaneous internalization of exogenous proteins into intact cells and root tissue of whole plants of Arabidopsis thaliana. We termed this internalization phenomenon as protein Delivery Independent of Vehicles or Equipment (DIVE), which efficiently delivered genome engineering proteins including Cre recombinase and zinc-finger nucleases (ZFN) into plant cells. Using protein DIVE, we achieved less toxic protein delivery than electroporation with up to 94% efficiency in Arabidopsis cell culture and 19% genome modification in Arabidopsis plants that was maintained in regenerated tissue. This work illustrates the potential of protein DIVE for a wide range of applications, including genome engineering in plants.

A Step-by-Step Guide for the Production of Recombinant Fluorescent TAT-HA-Tagged Proteins and their Transduction into Mammalian Cells

Investigating the function of target proteins for functional prospection or therapeutic applications typically requires the production and purification of recombinant proteins. The fusion of these proteins with tag peptides and fluorescently derived proteins allows the monitoring of candidate proteins using SDS-PAGE coupled with western blotting and fluorescent microscopy, respectively. However, protein engineering poses a significant challenge for many researchers. In this protocol, we describe step-by-step the engineering of a recombinant protein with various tags: TAT-HA (trans-activator of transduction-hemagglutinin), 6×His and EGFP (enhanced green fluorescent protein) or mCherry. Fusion proteins are produced in E. coli BL21(DE3) cells and purified by immobilized metal affinity chromatography (IMAC) using a Ni-nitrilotriacetic acid (NTA) column. Then, tagged recombinant proteins are introduced into cultured animal cells by using the penetrating peptide TAT-HA. Here, we present a thorough protocol providing a detailed guide encompassing every critical step from plasmid DNA molecular assembly to protein expression and subsequent purification and outlines the conditions necessary for protein transduction technology into animal cells in a comprehensive manner. We believe that this protocol will be a valuable resource for researchers seeking an exhaustive, step-by-step guide for the successful production and purification of recombinant proteins and their entry by transduction within living cells. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: DNA cloning, molecular assembly strategies, and protein production Basic Protocol 2: Protein purification Basic Protocol 3: Protein transduction in mammalian cells.

A Method for Electroporation of Cre Recombinase Protein into Intact Nicotiana tabacum Cells

The Cre/lox recombination system has become a powerful technology for gene function analysis in a broad spectrum of cell types and organisms. In our previous report, Cre protein had been successfully delivered into intact Arabidopsis thaliana cells using electroporation. To expand the feasibility of the method of protein electroporation to other plant cells, here we attempt the protein electroporation into tobacco-derived BY-2 cells, one of the most frequently used plant cell lines for industrial production. In this study, we successfully deliver Cre protein into BY-2 cells with intact cell walls by electroporation with low toxicity. Targeted loxP sequences in the BY-2 genome are recombined significantly. These results provide useful information for genome engineering in diverse plant cells possessing various types of cell walls.

Potential of cell-penetrating peptides (CPPs) in delivery of antiviral therapeutics and vaccines

Viral infections are a great threat to human health. Currently, there are no effective vaccines and antiviral drugs against the majority of viral diseases, suggesting the need to develop novel and effective antiviral agents. Since the intracellular delivery of antiviral agents, particularly the impermeable molecules, such as peptides, proteins, and nucleic acids, are essential to exert their therapeutic effects, using a delivery system is highly required. Among various delivery systems, cell-penetrating peptides (CPPs), a group of short peptides with the unique ability of crossing cell membrane, offer great potential for the intracellular delivery of various biologically active cargoes. The results of numerous in vitro and in vivo studies with CPP conjugates demonstrate their promise as therapeutic agents in various medical fields including antiviral therapy. The CPP-mediated delivery of various antiviral agents including peptides, proteins, nucleic acids, and nanocarriers have been associated with therapeutic efficacy both in vitro and in vivo. This review describes various aspects of viruses including their biology, pathogenesis, and therapy and briefly discusses the concept of CPP and its potential in drug delivery. Particularly, it will highlight a variety of CPP applications in the management of viral infections.

Nanolipoprotein-Mediated Her2 Protein Transfection Induces Malignant Transformation in Human Breast Acinar Cultures

Her2 overexpression is associated with an aggressive form of breast cancer and malignant transformation. We demonstrate in this work that nanolipoprotein particles (NLPs) synthesized in a cell-free manner can be used to transfer Her2 protein into the membrane of nonmalignant cells in 3D culture in a nontoxic and facile manner. With NLP-mediated Her2 protein delivery, we observed an increased probability of nonmalignant cells forming apolar nongrowth-arrested tumor-like structures. The NLP delivery system alone or Her2-NLPs plus the Her2 inhibitor trastuzumab showed no effect on the acinar organization rate, indicating that Her2 signaling is key to this process. Transcriptomics revealed essentially no effect of empty NLPs compared to untreated cells, whereas Her2-NLPs versus either untreated or empty-NLP-treated cells revealed upregulation of several factors associated with breast cancer. Pathway analysis also suggested that known nodes downstream of Her2 were activated in response to Her2-NLP treatment. This demonstrates that Her2 protein delivery with NLPs is sufficient for the malignant transformation of nonmalignant cells. Thus, this system offers a new model for studying cell surface receptor signaling without genomic modification or transformation techniques.

The Utilization of Cell-Penetrating Peptides in the Intracellular Delivery of Viral Nanoparticles

Viral particles (VPs) have evolved so as to efficiently enter target cells and to deliver their genetic material. The current state of knowledge allows us to use VPs in the field of biomedicine as nanoparticles that are safe, easy to manipulate, inherently biocompatible, biodegradable, and capable of transporting various cargoes into specific cells. Despite the fact that these virus-based nanoparticles constitute the most common vectors used in clinical practice, the need remains for further improvement in this area. The aim of this review is to discuss the potential for enhancing the efficiency and versatility of VPs via their functionalization with cell-penetrating peptides (CPPs), short peptides that are able to translocate across cellular membranes and to transport various substances with them. The review provides and describes various examples of and means of exploitation of CPPs in order to enhance the delivery of VPs into permissive cells and/or to allow them to enter a broad range of cell types. Moreover, it is possible that CPPs are capable of changing the immunogenic properties of VPs, which could lead to an improvement in their clinical application. The review also discusses strategies aimed at the modification of VPs by CPPs so as to create a useful cargo delivery tool.

A method using electroporation for the protein delivery of Cre recombinase into cultured Arabidopsis cells with an intact cell wall

Genome engineering in plants is highly dependent on the availability of effective molecular techniques. Despite vast quantities of research, genome engineering in plants is still limited in terms of gene delivery, which requires the use of infectious bacteria or harsh conditions owing to the difficulty delivering biomaterial into plant cells through the cell wall. Here, we describe a method that uses electroporation-mediated protein delivery into cultured Arabidopsis thaliana cells possessing an intact cell wall, and demonstrate Cre-mediated site-specific recombination. By optimizing conditions for the electric pulse, protein concentration, and electroporation buffer, we were able to achieve efficient and less-toxic protein delivery into Arabidopsis thaliana cells with 83% efficiency despite the cell wall. To the best of our knowledge, this is the first report demonstrating the electroporation-mediated protein delivery of Cre recombinase to achieve nucleic acid-free genome engineering in plant cells possessing an intact cell wall.

Delivery of Soluble Heme Oxygenase 1 Cell-Penetrating Peptide into Liver Cells in in vitro and ex vivo Models of Cold Ischemia

BACKGROUND/PURPOSE

Liver transplantation is the treatment of choice in patients with end-stage liver disease. During liver transplantation, ischemia-reperfusion injury (IRI) occurs, which is an inevitable consequence of the transplantation process. To reduce the extent of cellular injury, one of the proteins that have been extensively investigated is heme oxygenase 1 (HO-1), which plays an important role in protecting the organs against IRI. The aim of this study was to introduce an active and functional HO-1 protein conjugated to a cell-penetrating peptide (CPP) in vitro and ex vivo into liver cells in hypothermic and anoxic conditions and to assert its cytoprotective effects.

METHODS

We generated an enzymatically active soluble (s)HO-1-CPP recombinant protein. The ability of the sHO-1-CPP protein to penetrate McA-RH7777, Clone 9, and Hep G2 cells, primary hepatocytes, and Kupffer and human umbilical vein endothelial cells in vitro, as well as its ability to penetrate a whole liver ex vivo under hypothermic and anoxic conditions, was assessed. An in vitro hypoxia-reoxygenation (HR) model was used to determine the cytoprotective effect of the sHO-1-CPP protein.

RESULTS

We showed that our recombinant protein sHO-1-CPP can cross cell membranes into rodent and human liver cells in vitro, and the results were further validated ex vivo, where rodent livers were perfused with an organ preservation solution supplemented with sHO-1-CPP under anoxic and hypothermic conditions. Immunohistochemistry revealed an intracellular localization of sHO-1-CPP in zones 1-3 of the perfused livers. The CPP did not exert any significant toxicity on the cells. Treating cells with sHO-1-CPP showed significant cytoprotection in the in vitro HR model.

CONCLUSIONS

Our findings show that the recombinant protein sHO-1-CPP can be successfully delivered to cells of a whole organ in an ex vivo hypothermic and anoxic perfusion model and that it provides cytoprotection to hepatocytes in an in vitro HR model. These results hold great potential for future repair and protection of donor organs. Future experiments are planned to confirm these data in in vivo models of IRI.

Intracellular targeting with engineered proteins

If the isolation, production, and clinical use of insulin marked the inception of the age of biologics as therapeutics, the convergence of molecular biology and combinatorial engineering techniques marked its coming of age. The first wave of recombinant protein-based drugs in the 1980s demonstrated emphatically that proteins could be engineered, formulated, and employed for clinical advantage. Yet despite the successes of protein-based drugs such as antibodies, enzymes, and cytokines, the druggable target space for biologics is currently restricted to targets outside the cell. Insofar as estimates place the number of proteins either secreted or with extracellular domains in the range of 8000 to 9000, this represents only one-third of the proteome and circumscribes the pathways that can be targeted for therapeutic intervention. Clearly, a major objective for this field to reach maturity is to access, interrogate, and modulate the majority of proteins found inside the cell. However, owing to the large size, complex architecture, and general cellular impermeability of existing protein-based drugs, this poses a daunting challenge. In recent years, though, advances on the two related fronts of protein engineering and drug delivery are beginning to bring this goal within reach. First, prompted by the restrictions that limit the applicability of antibodies, intense efforts have been applied to identifying and engineering smaller alternative protein scaffolds for the modulation of intracellular targets. In parallel, innovative solutions for delivering proteins to the intracellular space while maintaining their stability and functional activity have begun to yield successes. This review provides an overview of bioactive intrabodies and alternative protein scaffolds amenable to engineering for intracellular targeting and also outlines advances in protein engineering and formulation for delivery of functional proteins to the interior of the cell to achieve therapeutic action.

The grafting of universal T-helper epitopes enhances immunogenicity of HIV-1 Tat concurrently improving its safety profile

Extracellular Tat (eTat) plays an important role in HIV-1 pathogenesis. The presence of anti-Tat antibodies is negatively correlated with disease progression, hence making Tat a potential vaccine candidate. The cytotoxicity and moderate immunogenicity of Tat however remain impediments for developing Tat-based vaccines. Here, we report a novel strategy to concurrently enhance the immunogenicity and safety profile of Tat. The grafting of universal helper T-lymphocyte (HTL) epitopes, Pan DR Epitope (PADRE) and Pol₇₁₁ into the cysteine rich domain (CRD) and the basic domain (BD) abolished the transactivation potential of the Tat protein. The HTL-Tat proteins elicited a significantly higher titer of antibodies as compared to the wild-type Tat in BALB/c mice. While the N-terminal epitope remained immunodominant in HTL-Tat immunizations, an additional epitope in exon-2 was recognized with comparable magnitude suggesting a broader immune recognition. Additionally, the HTL-Tat proteins induced cross-reactive antibodies of high avidity that efficiently neutralized exogenous Tat, thus blocking the activation of a Tat-defective provirus. With advantages such as presentation of multiple B-cell epitopes, enhanced antibody response and importantly, transactivation-deficient Tat protein, this approach has potential application for the generation of Tat-based HIV/AIDS vaccines.

Amelioration of radiation-induced skin injury by HIV-TAT-mediated protein transduction of RP-1 from Rana pleurade

Radiation-induced reactive oxygen species (ROS) can damage DNA and most other biological macromolecules in skin and radiation-induced skin injury is a serious concern for radiation therapy. Skin possesses an extremely efficient antioxidant system, which is conferred by two systems: antioxidant enzymes and small molecules that can scavenge ROS by donating electrons. Amphibian skin is a multifunctional organ, which protects against dangers of various oxidative stresses. Recently, a small peptide called RP-1 was isolated from the skin secretions of Rana pleurade, which shows strong antioxidant activity. However, this RP-1 peptide is limited because its inability to across the cell membrane. Protein transduction domains (PTDs) have demonstrated high efficiency for facilitating the internalization of both homologous and heterogeneous proteins into cells. This study aims to elucidate the protective effects of a HIV-TAT (TAT) PTD-coupled RP-1 fusion protein (TAT-RP1) on radiation-induced skin injury in vitro and in vivo. The synthesized fusion TAT-RP1 peptide can be incorporated into human keratinocyte HaCaT cells in a dose- and time-dependent manner without cytotoxicity. We then evaluated the protective role of TAT-RP1 against ionizing radiation. TAT-RP1 supplementation increased anti-superoxide anion ability of HaCaT cells and decreased HaCaT cell radiosensitivity to irradiation. Moreover, TAT-RP1 was able to penetrate the skin of rats, entering epidermis as well as the dermis of the subcutaneous layer in skin tissue. Topical spread of TAT-RP1 promoted the amelioration of radiation-induced skin damage in rats. These results suggest that TAT-RP1 has potential as a protein therapy for radiation-induced skin injury.

Replacement of the C6ORF66 assembly factor (NDUFAF4) restores complex I activity in patient cells

Disorders of the oxidative phosphorylation (OXPHOS) system frequently result in a severe multisystem disease with the consequence of early childhood death. Among these disorders, isolated complex I deficiency is the most frequently diagnosed, accounting for one-third of all cases of respiratory chain deficiency. We chose to focus on complex I deficiency, caused by mutation in the assembly factor chromosome 6, open reading frame 66 (C6ORF66; NADH dehydrogenase [ubiquinone] complex I assembly factor 4 [NDUFAF4]) protein. We used the approach of cell- and organelle-directed protein/enzyme replacement therapy, with the transactivator of transcription (TAT) peptide as the moiety delivery system. This step will enable us to deliver the wild-type assembly factor C6ORF66 into patient cells and their mitochondria, leading to the proper assembly and function of complex I and, as a result, to a functional OXPHOS system. We designed and constructed the TAT-ORF fusion protein by gene fusion techniques, expressed the protein in an Escherichia coli expression system and highly purified it. Our results indicate that TAT-ORF enters patients' cells and their mitochondria rapidly and efficiently. TAT-ORF is biologically active and led to an increase in complex I activity. TAT-ORF also increased the number of patient cells and improved the activity of their mitochondria. Moreover, we observed an increase in ATP production, a decrease in the content of mitochondria and a decrease in the level of reactive oxygen species. Our results suggest that this approach of protein replacement therapy for the treatment of mitochondrial disorders is a promising one.

Cell permeable cocaine esterases constructed by chemical conjugation and genetic recombination

Cocaine esterase (CocE) is the most efficient cocaine-metabolizing enzyme tested in vivo to date, displaying a rapid clearance of cocaine and a robust protection against cocaine's toxicity. Two potential obstacles to the clinical application of CocE, however, lie in its proteolytic degradation and induced immune response. To minimize these potential obstacles, we attempted nondisruptive cell encapsulation by creating a cell permeable form of CocE, which was achieved by covalently linking a thermally stable CocE mutant (dmCocE) with cell penetrating peptides (CPPs). Two types of CPPs, Tat and the low molecular weight protamine (LMWP), were used in this study. Two types of disulfide-bridged chemical conjugates, Tat-S-S-dmCocE and LMWP-S-S-dmCocE, were synthesized and then purified by heparin affinity chromatography. In addition, four recombinant CPP-dmCocE fusion proteins, Tat-N-dmCocE, LMWP-N-dmCocE, dmCocE-C-Tat, and dmCocE-C-LMWP, were constructed, expressed in Escherichia coli, and purified as soluble proteins. Among these six CPP-dmCocE variants, LMWP-S-S-dmCocE showed the highest cocaine-hydrolyzing activity, and dmCocE-C-Tat had the highest production yield. To evaluate their cellular uptake behavior, a covalently linked fluorophore (FITC) was utilized to visualize the cellular uptake of all six CPP-dmCocE variants in living HeLa cells. All the six variants exhibited cellular uptake, but their intracellular distribution phenotypes differed. While the chemical conjugates showed primarily cytoplasmic distribution, which was likely due to the reduction of the disulfide linkage between CPP and dmCocE, all the other four recombinant fusion proteins displayed both nuclear and cytoplasmic localization, with dmCocE-C-CPP exhibiting higher cytoplasmic distribution during cellular uptake. Based on a balanced consideration of essentials for clinical application, including parameters such as high cocaine-hydrolyzing efficiency, large production yield, major cytoplasmic distribution, etc., the dmCocE-C-Tat fusion protein seems to be the best candidate from this investigation. Further in vivo studies of the cell-encapsulated dmCocE-C-Tat in hydrolyzing cocaine and alleviating immunogenicity and proteolytic degradation in established, clinically relevant mouse models are currently underway in our laboratories. Findings from this research are not only useful for developing other new CPP-CocE constructs but also valuable for establishing a nondisruptive cell-encapsulation technology for other protein therapeutics that are known to be immunogenic for direct clinical application.

Adenovirus with hexon Tat-protein transduction domain modification exhibits increased therapeutic effect in experimental neuroblastoma and neuroendocrine tumors

Adenovirus serotype 5 (Ad5) is widely used as an oncolytic agent for cancer therapy. However, its infectivity is highly dependent on the expression level of coxsackievirus-adenovirus receptor (CAR) on the surfaces of tumor cells. Furthermore, infected cells overproduce adenovirus fiber proteins, which are released prior to cell lysis. The released fibers block CAR on noninfected neighboring cells, thereby preventing progeny virus entry. Our aim was to add a CAR-independent infection route to Ad5 to increase the infectivity of tumor cells with low CAR expression and prevent the fiber-masking problem. We constructed Ad5 viruses that encode the protein transduction domain (PTD) of the HIV-1 Tat protein (Tat-PTD) in hypervariable region 5 (HVR5) of the hexon protein. Tat-PTD functions as a cell-penetrating peptide, and Tat-PTD-modified Ad5 showed a dramatic increased transduction of CAR-negative cell lines compared to unmodified vector. Moreover, while tumor cell infectivity was severely reduced for Ad5 in the presence of fiber proteins, it was only marginally reduced for Tat-PTD-modified Ad5. Furthermore, because of the sequence alteration in the hexon HVR, coagulation factor X-mediated virus uptake was significantly reduced. Mice harboring human neuroblastoma and neuroendocrine tumors show suppressed tumor growths and prolonged survival when treated with Tat-PTD-modified oncolytic viruses. Our data suggest that modification of Ad5 with Tat-PTD in HVR5 expands its utility as an oncolytic agent.

Expressed cell-penetrating peptides can induce a bystander effect, but passage through the secretory pathway reduces protein transduction activity

Despite advances in vector technology, inefficient gene transfer still limits clinical efficacy of cancer gene therapy. Cell-penetrating peptides (CPPs), such as the basic domain of the transactivator of transcription (Tat) protein of HIV-1, are internalized by intact cells and have been used to deliver purified recombinant proteins. A combination of gene therapy with protein transduction technology could induce a strong bystander effect and represent a platform to deliver proteins to target cells. However, whether expressed CPP can facilitate intercellular trafficking, i.e., a bystander effect, is controversial. Our data suggest that expressed fusion proteins that contain the basic domain of Tat do not induce a detectable bystander effect. However, Tat-fusion proteins that also contain a secretory signal peptide (SP) can induce a bystander effect in vitro, although the in vivo effect is small. Surprisingly, despite the presence of a SP, the bystander effect does not seem to be related to secretion of the fusion protein. In fact, Tat-fusion proteins are secreted very inefficiently, and protein transduction seems largely mediated by fusion proteins that are released by cell lysis. Modification of Tat can improve secretion efficacy and prevent cleavage by the endoprotease furin, but passage through the secretory pathway is associated with reduced transduction activity of Tat-fusion proteins.

Efficient and targeted delivery of siRNA in vivo

RNA interference (RNAi) has been regarded as a revolutionary tool for manipulating target biological processes as well as an emerging and promising therapeutic strategy. In contrast to the tangible and obvious effectiveness of RNAi in vitro, silencing target gene expression in vivo using small interfering RNA (siRNA) has been a very challenging task due to multiscale barriers, including rapid excretion, low stability in blood serum, nonspecific accumulation in tissues, poor cellular uptake and inefficient intracellular release. This minireview introduces major challenges in achieving efficient siRNA delivery in vivo and discusses recent advances in overcoming them using chemically modified siRNA, viral siRNA vectors and nonviral siRNA carriers. Enhanced specificity and efficiency of RNAi in vivo via selective accumulations in desired tissues, specific binding to target cells and facilitated intracellular trafficking are also commonly attempted utilizing targeting moieties, cell-penetrating peptides, fusogenic peptides and stimuli-responsive polymers. Overall, the crucial roles of the interdisciplinary approaches to optimizing RNAi in vivo, by efficiently and specifically delivering siRNA to target tissues and cells, are highlighted.

Cell-targeting and cell-penetrating peptides for delivery of therapeutic and imaging agents

This review will discuss the basic concepts concerning the use of cell-targeting peptides (CTPs) and cell-penetrating peptides (CPPs) in the context of nanocarrier technology. It deals with the discovery and subsequent evolution of CTPs and CPPs, issues concerning their interactions with cells and their biodistribution in vivo, and their potential advantages and disadvantages as delivery agents. The article also briefly discusses several specific examples of the use of CTPs or CPPs to assist in the delivery of nanoparticles, liposomes, and other nanocarriers.

Design of a bioactive cell-penetrating peptide: when a transduction domain does more than transduce

The discovery of cell-penetrating peptides (CPPs) has facilitated delivery of peptides into cells to affect cellular behavior. Previously, we were successful at developing a phosphopeptide mimetic of the small heat shock-like protein HSP20 . Building on this success we developed a cell-permeant peptide inhibitor of mitogen-activated protein kinase-activated protein kinase 2 (MK2). It is well documented that inhibition of MK2 may be beneficial for a myriad of human diseases including those involving inflammation and fibrosis. During the optimization of the activity and specificity of the MK2 inhibitor (MK2i) we closely examined the effect of cell-penetrating peptide identity. Surprisingly, the identity of the CPP dictated kinase specificity and functional activity to an extent that rivaled that of the therapeutic peptide. The results reported herein have wide implications for delivering therapeutics with CPPs and indicate that judicious choice of CPP is crucial to the ultimate therapeutic success.

Cloning, expression, purification, distribution and kinetics characterization of the bacterial beta-galactosidase fused to the cytoplasmic transduction peptide in vitro and in vivo

Cytoplasmic transduction peptide (CTP) offers exciting therapeutic opportunities for the treatment of many diseases caused by cytoplasmic functional molecules. It can transduce large, biologically active proteins into the cytoplasmic compartment of several mammalian cells. However, other intriguing features of CTP, including its activity in vitro, and distribution and tissue infiltration abilities in vivo, remain to be explored. The present study was initiated to (1) further confirm the cytoplasmic localization preference and the enzymatic activity of the transduced CTP-beta-gal in vitro and (2) examine the kinetics and tissue distribution of the CTP-beta-gal fusion protein in mice. A CTP-beta-gal fusion protein was expressed in Escherichia coli and either transduced into BaF3-BCR/ABL cells or administered intravenously into female Balb/C mice at a dose of 100 microg per mouse. Its localization in BaF3-BCR/ABL cells was evaluated by immunocytochemistry and in situ X-gal staining, and its distribution in various tissues was analyzed both by in situ X-gal staining and quantitative enzymatic activity assay. beta-Galactosidase enzyme activity was observed in BaF3-BCR/ABL cells and in all tissues tested, with peak activity occurring at 15 min in most tissues and at 24h in brain. These data will not only allow rational selection of delivery schedules for therapeutic CTP, but will also aid the use of CTP fusion protein transduction in the development of protein therapeutics targeting the cytoplasmic compartment both in vitro and in vivo.

MDV-1 VP22: a transporter that can selectively deliver proteins into cells

The tegument protein VP22 of Marek's disease virus (MDV) was previously shown to be able to travel between cells. To further characterize the transport property of VP22 and assess whether it can be used for protein delivery, we investigated the subcellular localization of VP22 fused to five heterologous proteins, including green fluorescent protein, nucleoprotein of avian influenza virus, bovine IFN-gamma, F protein of Newcastle disease virus and VP2 protein of infectious bursa disease virus. The transport of these fusion proteins in monolayer cells was assayed by immunofluorescence assay. The results showed that all except VP2 could be delivered by VP22 of MDV serotype 1 (MDV-1), at different efficiencies. After being transported to surrounding cells, VP22 fused to avian influenza nucleoprotein, bovine IFN-gamma, or to F was localized in the nucleus. Our data suggest that VP22 of MDV-1 can be used as transport tool in protein delivery and that the original localization of cargo proteins may be changed after transport by MDV-1 VP22. Finally, infectious bursa disease VP2 protein could not be transported by MDV-1 VP22.

Endocytosis and membrane potential are required for HeLa cell uptake of R.I.-CKTat9, a retro-inverso Tat cell penetrating peptide

Cell-penetrating peptides (CPPs) can enter many types of cells and have become useful tools for introducing a variety of cargo such as exogenous peptides, proteins, and nucleic acids into cultured cells in vitro. Tat CPPs derived from the HIV-1 Tat protein are the most widely used among the arginine-rich CPPs. Even though CPPs hold considerable promise for drug delivery, poor biological stability and high in vivo clearance may limit their effectiveness for delivering cargo. Therefore, we utilize a retro-inverso form of a Tat peptide, R.I.-CKTat9, which is proteolytically stable. In the current study, the cellular entry mechanism of this arginine-rich CPP is investigated. Fluorescently labeled R.I.-CKTat9 entered HeLa cells in a concentration- and energy-dependent manner demonstrating both diffuse and punctate (vesicular) appearance inside the cells. The labeled R.I.-CKTat9 colocalized with labeled transferrin in the punctate structure, suggesting that the peptide enters HeLa cells by clathrin-dependent endocytosis. Incubation of cells with an isotonic/high K(+) buffer (KPBS) or an NH(4)Cl solution abolished the diffuse but not the punctate fluorescence, suggesting that membrane potential plays a critical role. This result also suggests that the flux originates from the endosome, not the extracellular space, and relies on the acidity of the endosome. Impairment of clathrin-mediated endocytosis by RNAi with clathrin heavy chain function and endocytosis inhibitors greatly reduced or completely abolished both diffuse and punctate fluorescence, further supporting a single route of endocytosis and subsequent endosomal escape. Since cells in the mitotic (M) phase shut down endocytosis but maintain plasma membrane potential, this property was used to further confirm the endocytic mechanism. Direct measurement of plasma membrane potential confirmed its persistence in M phase arrested HeLa cells. Consistent with our working hypothesis, these cells did not show any vesicular nor diffuse fluorescence of labeled R.I.-CKTat9, providing compelling evidence for the sequential steps of endocytosis and endosomal escape. Binding of labeled R.I.-CKTat9 to the surface of HeLa cells at 0 degrees C was reduced under the mildly acidic conditions of early endosomes, suggesting an acidity-dependent endosomal escape mechanism. Overall, these results indicate that both endocytosis and membrane potential are required for R.I.-CKTat9 entry into HeLa cells and suggest that translocation occurs at the endosomal membrane.

Secretion and uptake of TAT-fusion proteins produced by engineered mammalian cells

BACKGROUND

Intracellular signaling can be regulated by the exogenous addition of physiological protein inhibitors coupled to the TAT protein transduction domain. Thus far experiments have been performed with purified inhibitors added exogenously to cells in vitro or administered in vivo. Production of secretable TAT-fusion proteins by engineered mammalian cells, their uptake, and route of entry has not been thoroughly investigated. Such methodology, if established, could be useful for transplantation purposes.

METHODS

Secretion of TAT-fusion proteins from transfected mammalian cells was achieved by means of a signal peptide. Cell uptake and subcellular localization of TAT-fusion proteins were determined by immunoblotting and confocal microscopy.

RESULTS

Engineered TAT-fusion proteins were secreted with variable efficiency depending on the nature of the protein fused to the TAT peptide. Secreted proteins were able to transduce unmanipulated cells. Their mechanism of entry into cells partly involves lipid rafts and a portion of the internalised protein is directed to the Golgi.

CONCLUSIONS

Generation of secretable TAT-coupled inhibitors of signaling pathways, able to transduce other cells can be achieved.

GENERAL SIGNIFICANCE

These results provide key information that will assist in the design of TAT-inhibitors and engineered cells in order to regulate cell function within tissues.

Efficient siRNA delivery with non-viral polymeric vehicles

Sequence-specific gene silencing using small interfering RNA (siRNA) provides a potent and specific method for gene expression, thus is now being evaluated in clinical trials as a novel therapeutic strategy. As a results, there has been a significant surge of interest in the application of siRNA in therapeutics as a means of silencing the specific gene function. However, for siRNA technology to be valuable and effective, the development of efficient siRNA delivery strategy is essential for improving biological activities such as stability, cellular uptake, sequence-specificity, devoid of nonspecific knockdown and toxic side effects. Accordingly, a number of delivery systems, both viral and nonviral, have been reported and some of them successfully used for the introduction of siRNA into cells both in vitro and in vivo. Here, we discuss the current understanding of synthetic siRNA delivery mechanism and strategies of siRNA delivery by non-viral polymeric vehicles which are currently used in vitro and in vivo.

Cellular uptake mechanisms and potential therapeutic utility of peptidic cell delivery vectors: progress 2001-2006

Cell delivery vectors (CDVs) are short amphipathic and cationic peptides and peptide derivatives, usually containing multiple lysine and arginine residues. They possess inherent membrane activity and can be conjugated or complexed with large impermeable macromolecules and even microscopic particles to facilitate cell entry. Various mechanisms have been proposed but it is now becoming clear that the main port of entry into cells of such CDV constructs involves adsorptive-mediated endocytosis rather than direct penetration of the plasma membrane. It is still unclear, however, how and to what extent CDV constructs are capable of exiting endosomal compartments and reaching their intended cellular site of action, usually the cytosol or the nucleus. Furthermore, although many CDVs can mediate cellular uptake of their cargo and appear comparatively non-toxic to cells in tissue culture, the utility of CDVs for in vivo applications remains poorly understood. Whatever the mechanisms of cell entry and disposition, the overriding question as far as potential pharmacological application of CDV conjugates is concerned is whether or not a therapeutic margin can be achieved by their administration. Such a margin will only result if the intracellular concentration in the target tissues necessary to elicit the biological effect of the CDV cargo can be achieved at systemic CDV exposure levels that are non-toxic to both target and bystander cells. It is proposed that the focus of CDV research now be shifted from mechanistic in vitro studies with labeled but otherwise unconjugated CDVs to in vivo pharmacological and toxicological studies using CDV-derivatized and other cationized forms of inherently non-permeable macromolecules of true therapeutic interest.

Tat peptide-mediated intracellular delivery of pharmaceutical nanocarriers

Cell-penetrating peptides (CPPs) including TAT peptide (TATp) have been successfully used for intracellular delivery of a broad variety of cargoes including various nanoparticulate pharmaceutical carriers (liposomes, micelles, nanoparticles). Here, we will consider the main results in this area, with a special emphasis on TATp-mediated delivery of liposomes and DNA. We will also address the development of "smart" stimuli-sensitive nanocarriers, where cell-penetrating function can be activated by the decreased pH only inside the biological target minimizing thus the interaction of drug-loaded nanocarriers with non-target cells.

Intracellular delivery of peptides via association with ubiquitin or SUMO-1 coupled to protein transduction domains

Background

We previously developed small hybrid proteins consisting of SUMO-1 linked to an heptapeptide fused to the Tat protein transduction domain (PTD). The heptapeptide motif was selected from a library of random sequences to specifically bind HIV-1 regulatory proteins Tat or Rev. These constructs, named SHP, are able to enter primary lymphocytes and some of them inhibit HIV-1 replication. Considering these positive results and other data from the literature, we further tested the ability of ubiquitin or SUMO-1 linked to various PTD at their N-terminus to deliver within cells proteins or peptides fused downstream of their diglycine motif. In this system it is expected that the intracellular ubiquitin or SUMO-1 hydrolases cleave the PTD-Ub or PTD-SUMO-1 modules from the cargo polypeptide, thereby allowing its delivery under an unmodified form.

Results

Several bacterial expression vectors have been constructed to produce modular proteins containing from the N- to the C-terminus: the FLAG epitope, a cleavage site for a protease, a PTD, human ubiquitin or SUMO-1, and either GFP or the HA epitope. Nine different PTDs were tested, including the Tat basic domain, wild type or with various mutations, and stretches of arginine or lysine. It was observed that some of these PTDs, mainly the Tat PTD and seven or nine residues long polyarginine motifs, caused association of the hybrid proteins with cells, but none of these constructs were delivered to the cytosol. This conclusion was derived from biochemical and immunofluorescence studies, and also from the fact that free cargo protein resulting from cleavage by proteases after ubiquitin or SUMO-1 was never observed. However, in agreement with our previous observations, mutation of the diglycine motif into alanine-arginine, as in the SHP constructs, allows cytosol entry demonstrated by immunofluorescence observations on living cells and by cell fractionation analyses. This process results from a non-endocytic pathway.

Conclusion

Our observations indicate that fusion of SUMO-1 to a peptide-PTD module allows generation of a stable hybrid protein that is easily produced in bacteria and which efficiently enters into cells but this property necessitates mutation of the diglycine motif at the end of SUMO-1, thereby impairing delivery of the peptide alone.

On The Biomedical Promise of Cell Penetrating Peptides: Limits Versus Prospects

The cell membrane poses a substantial hurdle to the use of pharmacologically active biomacromolecules that are not per se actively translocated into cells. An appealing approach to deliver such molecules involves tethering or complexing them with so-called cell penetrating peptides (CPPs) that are able to cross the plasma membrane of mammalian cells. The CPP approach is currently a major avenue in engineering delivery systems that are hoped to mediate the non-invasive import of problematic cargos into cells. The large number of different cargo molecules that have been efficiently delivered by CPPs ranges from small molecules to proteins and even liposomes and particles. With respect to the involved mechanism(s) there is increasing evidence for endocytosis as a major route of entry. Moreover, in terms of intracellular trafficking, current data argues for the transport to acidic early endosomal compartments with cytosolic release mediated via retrograde delivery through the Golgi apparatus and the endoplasmic reticulum. The focus of this review is to revisit the performance of cell penetrating peptides for drug delivery. To this aim we cover both accomplishments and failures and report on new prospects of the CPP approach. Besides a selection of successful case histories of CPPs we also review the limitations of CPP mediated translocation. In particular, we comment on the impact of (i) metabolic degradation, (ii) the cell line and cellular differentiation state dependent uptake of CPPs, as well as (iii) the regulation of their endocytic traffic by Rho-family GTPases. Further on, we aim at the identification of promising niches for CPP application in drug delivery. In this context, as inspired by current literature, we focus on three principal areas: (i) the delivery of antineoplastic agents, (ii) the delivery of CPPs as antimicrobials, and (iii) the potential of CPPs to target inflammatory tissues.

Myristoyl-based transport of peptides into living cells

Translocation of membrane-impermeant molecules to the interior of living cells is a necessity for many biochemical investigations. Myristoylation was studied as a means to introduce peptides into living cells. Uptake of a myristoylated, fluorescent peptide was efficient in the B lymphocyte cell line BA/F3. In contrast, this cell line was resistant to uptake of a cell-penetrating peptide derived from the TAT protein. In BA/F3 cells, membrane association was shown to be rapid, reaching a maximum within 30 min. Cellular uptake of the peptide lagged the membrane association but occurred within a similar time frame. Experiments performed at 37 versus 4 degrees C demonstrated profound temperature dependence in the cellular uptake of myristoylated cargo. Myristoylated peptides with either positive or negative charge were shown to load efficiently. In contrast to TAT-conjugated cargo, pyrenebutyrate did not enhance cellular uptake of the myristoylated peptide. The myristoylated peptide did not adversely affect cell viability at concentrations up to 100 muM. This assessment of myristoyl-based transport provides fundamental data needed in understanding the intracellular delivery of myristoylated peptide cargoes for cell-based biochemical studies.

Enhanced purification of cell-permeant Cre and germline transmission after transduction into mouse embryonic stem cells

Continuous expression of Cre recombinase has the potential to yield toxic side effects in various cell types, thereby limiting applications of the Cre/loxP system for conditional mutagenesis. In this study, we investigate the potential of Cre protein transduction to overcome this limitation. COS-7, CV1-5B, and mouse embryonic stem (ES) cells treated with cell-permeant Cre (HTNCre) maintain a normal growth behavior employing Cre concentrations sufficient to induce recombination in more than 90% of the cells, whereas continuous application of high doses resulted in markedly reduced proliferation. HTNCre-treated ES cells maintain a normal karyotype and are still able to contribute to the germline. Moreover, we present an enhanced HTNCre purification protocol that allows the preparation of a concentrated glycerol stock solution, thereby enabling a considerable simplification of the Cre protein transduction procedure. The protocol described here allows rapid and highly efficient conditional mutagenesis of cultured cells.

Cell Penetrating Peptides: Intracellular Pathways and Pharmaceutical Perspectives

Cell penetrating peptides, generally categorized as amphipathic or cationic depending on their sequence, are increasingly drawing attention as a non-invasive delivery technology for macromolecules. Delivery of a diverse set of cargo in terms of size and nature ranging from small molecules to particulate cargo has been attempted using different types of cell penetrating peptides (CPPs) in vitro and in vivo. However, the internalization mechanism of CPPs is an unresolved issue to date, with dramatic changes in view regarding the involvement of endocytosis as a pathway of internalization. A key reason for the lack of consensus on the mechanism can be attributed to the methodology in deciphering the internalization mechanism. In this review, we highlight some of the methodology concerns, focus more on the internalization pathway and also provide a novel perspective about the intracellular processing of CPPs, which is a crucial aspect to consider when selecting a cell penetrating peptide as a drug delivery system. In addition, recent applications of cell penetrating peptides for the delivery of small molecules, peptides, proteins, oligonucleotides, nanoparticles and liposomes have been reviewed.

Pretreatment with PTD-calbindin D 28k alleviates rat brain injury induced by ischemia and reperfusion

Calcium toxicity remains the central focus of ischemic brain injury. Calcium channel antagonists have been reported to be neuroprotective in ischemic animal models but have failed in clinical trials. Rather than block the calcium channels, calbindin proteins can buffer excessive intracellular Ca2+, and as a result, maintain the calcium homeostasis. In the present study, we investigated the effect of calbindin D 28k (CaBD) in ischemic brain using the novel technique protein transduction domain (PTD)-mediated protein transduction. We generated PTD-CaBD in Escherichia coli, tested its biologic activity in N-methyl-D-aspartate (NMDA)- and oxygen-glucose deprivation (OGD)-induced hippocampal injury models, and examined the protection of the fusion protein using a rat brain focal ischemia model. Infarct volume was determined using 2,3,5-triphenyl-tetrazolium chloride staining; neuronal injury was examined using terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) staining and cleaved caspase-3 assay. The results showed that the PTD-CaBD was efficiently delivered into Cos7 cells, hippocampal slice cells, and brain tissue. Pretreatment with PTD-CaBD decreased intracellular free calcium concentration and reduced cell death in NMDA- or OGD-exposed hippocampal slices (P<0.05). Intraperitoneal administration of PTD-CaBD before transient middle cerebral artery occlusion decreased brain infarct volume (280+/-47 versus 166+/-70 mm3, P<0.05), and improved neurologic outcomes compared with the control. Further studies showed that, compared with the control animals, PTD-CaBD decreased TUNEL (58%+/-7% versus 29%+/-3%, P<0.05)- and cleaved caspase-3 (62+/-4/field versus 31+/-6/field, P<0.05)-positive cells in the ischemic boundary zone. These results indicate that systemic administration of PTD-CaBD could attenuate ischemic brain injury, suggesting that PTD-mediated protein transduction might provide a promising and effective approach for the therapies of brain diseases, including cerebral ischemia.

Recent advances in rational gene transfer vector design based on poly(ethylene imine) and its derivatives

The continually increasing wealth of knowledge about the role of genes involved in acquired or hereditary diseases renders the delivery of regulatory genes or nucleic acids into affected cells a potentially promising strategy. Apart from viral vectors, non-viral gene delivery systems have recently received increasing interest, due to safety concerns associated with insertional mutagenesis of retro-viral vectors. Especially cationic polymers may be particularly attractive for the delivery of nucleic acids, since they allow a vast synthetic modification of their structure enabling the investigation of structure-function relationships. Successful clinical application of synthetic polycations for gene delivery will depend primarily on three factors, namely (1) an enhancement of the transfection efficiency, (2) a reduction in toxicity and (3) an ability of the vectors to overcome numerous biological barriers after systemic or local administration. Among the polycations presently used for gene delivery, poly(ethylene imine), PEI, takes a prominent position, due to its potential for endosomal escape. PEI as well as derivatives of PEI currently under investigation for DNA and RNA delivery will be discussed. This review focuses on structure-function relationships and the physicochemical aspects of polyplexes which influence basic characteristics, such as complex formation, stability or in vitro cytotoxicity, to provide a basis for their application under in vivo conditions. Rational design of optimized polycations is an objective for further research and may provide the basis for a successful cationic polymer-based gene delivery system in the future.

Conditional mutagenesis by cell-permeable proteins: potential, limitations and prospects

The combination of two powerful technologies, the Cre/loxP recombination system and the protein transduction technique, holds great promise for the advancement of biomedical and genome research by enabling precise and rapid control over mutation events. Protein transduction is a recently developed technology to deliver biologically active proteins directly into mammalian cells. It involves the generation of fusion proteins consisting of the cargo molecule to be delivered and a so-called protein transduction domain. Recently, the derivation of cell permeable variants of the DNA recombinase Cre has been reported. Cre is a site-specific recombinase that recognizes 34 base pair loxP sites and has been widely used to genetically engineer mammalian cells in vitro and in vivo. Recombinant cell-permeable Cre recombinase was found to efficiently induce recombination of loxP-modified alleles in various mammalian cell lines. Here we review recent advances in conditional expression and mutagenesis employing cell-permeable Cre proteins. Moreover, this review summarizes recent findings of studies aimed at deciphering the molecular mechanism of the cellular uptake of cell-permeable fusion proteins.

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.

TAT-mediated intracellular delivery of purine nucleoside phosphorylase corrects its deficiency in mice

Defects in purine nucleoside phosphorylase (PNP) enzyme activity result in abnormal nucleoside homeostasis, severe T cell immunodeficiency, neurological dysfunction, and early death. Protein transduction domain (PTD) can transfer molecules into cells and may help restore PNP activity in cases of PNP deficiency. However, long-term use of PTD to replace enzymes in animal models or patients has not previously been described. We fused human PNP to the HIV-TAT PTD and found that the fusion with TAT changed the retention and distribution of PNP in PNP-deficient mice. TAT induced rapid intracellular delivery of PNP into tissues, including the brain, prevented urinary excretion of PNP, and protected PNP from neutralizing antibodies, resulting in significant extension of the enzyme's biological activity in vivo. Frequent TAT-PNP injections in PNP-deficient mice corrected the metabolic disorder and immune defects with no apparent toxicity. TAT-PNP remained effective over 24 weeks of treatment, resulting in continued improvement in immune function and extended survival. Our data demonstrate that TAT changes the properties of PNP in vivo and that long-term intracellular delivery of PNP by TAT corrects PNP deficiency in mice. We provide evidence to promote further use of PTD to treat diseases that require repeated intracellular enzyme or protein delivery.

Cholesteryl Oligoarginine Delivering Vascular Endothelial Growth Factor siRNA Effectively Inhibits Tumor Growth in Colon Adenocarcinoma

Vascular endothelial growth factor (VEGF) is a multifunctional angiogenic growth factor that is a primary stimulant of the development and maintenance of a vascular network in the vascularization of solid tumors. It has been reported that a blockade of VEGF-mediated angiogenesis is a powerful method for tumor regression. RNA interference represents a naturally occurring biological strategy for inhibition of gene expression. In mammalian systems, however, the in vivo application of small interfering RNA (siRNA) is severely limited by the instability and poor bioavailability of unmodified siRNA molecules. In this study, we tested the hypothesis that a hydrophobically modified protein transduction domain, cholesteryl oligo-d-arginine (Chol-R9), may stabilize and enhance tumor regression efficacy of the VEGF-targeting siRNA. The noncovalent complexation of a synthetic siRNA with Chol-R9 efficiently delivered siRNA into cells in vitro. Moreover, in a mouse model bearing a subcutaneous tumor, the local administration of complexed VEGF-targeting siRNA, but not of scrambled siRNA, led to the regression of the tumor. Hence, we propose a novel and simple system for the local in vivo application of siRNA through Chol-R9 for cancer therapy.

Emerging vectors and targeting methods for nonviral gene therapy

Until recently, nonviral vectors were outside the mainstream of gene transfer technology. Recent problems in clinical trials using viral vectors renewed interest in these methods. The clinical usefulness of nonviral methods is still hindered by their relatively low gene delivery/transgene expression efficiencies. Vectors must navigate a series of obstacles before the therapeutic gene can be expressed. This review considers these barriers and the properties of components of nonviral vectors that are essential for nucleic acid transfer. Although developments of new physical methods (hydrodynamic delivery, ultrasound, electroporation) have made a significant impact on gene transfer efficiency, various chemical carriers (lipids and polymers) have been shown to achieve high-level gene delivery and functional expression. Success of nonviral gene targeting will depend not only on the efficacy, but also safety of this methodology, and this aspect is also discussed. Understanding problems associated with nonviral targeting can also help in designing better viral vectors. In fact, interplay between viral and nonviral technologies should lead to a continued refinement of both methodologies.

Nuclear-targeted minicircle to enhance gene transfer with non-viral vectors in vitro and in vivo

BACKGROUND

To develop more efficient non-viral vectors, we have previously described a novel approach to attach a nuclear localisation signal (NLS) to plasmid DNA, by generating a fusion protein between the tetracycline repressor protein TetR and an SV40 NLS peptide (TetR-NLS). The high affinity of TetR for the DNA sequence tetO is used to bind the NLS to DNA. We have now investigated the ability of this system displaying the SV40 NLS or HIV-1 TAT peptide to enhance nuclear import of a minimised DNA construct more suitable for in vivo gene delivery: a minicircle.

METHODS

We have produced a new LacZ minicircle compatible with the TetR system. After transfection of the minicircle in combination with TetR-NLS or TetR-TAT using different transfection agents, we first measured beta-galactosidase activity in vitro. We then used a special delivery technique, in which DOTAP/cholesterol liposomes and DNA/protein complexes are sequentially injected intravenously, to evaluate the activity of this system in vivo.

RESULTS

In vitro results showed a 30-fold increase in transfection efficiency of the nuclear-targeted minicircle compared to normal plasmid lipofection. Results on cell cycle arrested cells seem to indicate a different mechanism between the TetR-NLS and TetR-TAT. Finally, we demonstrate a more than 6-fold increase in beta-galactosidase expression in the mouse lung using the minicircle and the TetR-TAT protein. This increase is specific for the peptide sequence and is not observed with the control protein TetR.

CONCLUSIONS

Our results indicate that the combination of a minicircle DNA construct with a TetR nuclear-targeting system is able to potentiate gene expression of non-viral vectors.

Medium-sized peptides as built in carriers for biologically active compounds

A growing number of oligopeptides of natural and/or synthetic origin have been described and considered as targeting structures for delivery bioactive compounds into various cell types. This review will outline the discovery of peptide sequences and the corresponding mid-sized oligopeptides with membrane translocating properties and also summarize de novo designed structures possessing similar features. Conjugates and chimera constructs derived from these sequences with covalently attached bioactive peptide, epitope, oligonucleotide, PNA, drug, reporter molecule will be reviewed. A brief note will refer to the present understanding on the uptake mechanism at the end of each section.

Tat8-TK/GCV suicide gene therapy induces pancreatic tumor regression in vivo

Suicide gene therapy using the herpes simplex virus thymidine kinase (TK) gene in combination with ganciclovir (GCV) has been shown to produce therapeutic, but limited, efficacy because of poor gene transfer efficiency and reduced bystander effect. Here we report that fusion of TK to an eight-amino acid peptide from the basic domain of the human immunodeficiency virus (HIV) Tat protein significantly increases the cytotoxic efficacy of the TK/GCV system in pancreatic cancer cells. We demonstrate that Tat8-TK protein is released from the intracellular compartment of Tat8-TK-expressing cells to the extracellular medium after GCV treatment. Interestingly, we show that this conditioned medium is then able to mediate cytotoxicity of wildtype cultures, suggesting the internalization of the Tat8-TK protein. Moreover, a strong antitumoral effect of Tat8-TK/GCV treatment could be achieved by two different in vivo approaches. Tumors injected with NIH 3T3/Tat8-TK cells attached to microcarriers (MC+Tat8-TK) and treated with GCV led to a 35.6% reduction in the initial tumor volume and to 50% tumor eradication. Furthermore, electrogene transfer of TK or Tat8-TK followed by administration of high doses of GCV led to an overall statistically significant reduction in tumor growth. However, the reduction in initial tumor volume was statistically significant only for the Tat8-TK group (59.5% reduction). Moreover, in this group 50% complete tumor eradication was achieved. When moderate doses of GCV were administered, the overall reduction in tumor growth was statistically significant only in the Tat8-TK group. Therefore, our results suggest that fusion of TK to the Tat8 peptide enhances TK/GCV suicide gene therapy.

Transactivating transcriptional activator-mediated drug delivery

Cell-penetrating peptides (CPPs) are peptide vectors that can traverse through the plasma membrane barrier without breaching the integrity of the cell, and deliver various cargoes inside cell. The range of cargoes that can be delivered intracellularly by CPPs encompasses a broad variety of hydrophilic molecules, such as peptides, proteins, antibodies, imaging agents, DNA and even nanosized entities, including polymer-based systems, solid nanoparticles and liposomes. Multiple studies have focused on CPPs such as transactivating transcriptional activator peptide (TATp), penetratin, VP22, transportan and synthetic oligoarginines because of their high inherent potential as intracellular delivery vectors. However, the TATp remains the most popular CPP used for a variety of purposes. This review article attempts to bring together the available data on TAT-mediated intracellular uptake of a broad range of molecules and nanoparticles. It also considers potential practical applications of this approach.

Genetic fusion of proteins to the SIV Tat protein enhances their immunogenicity

The potential of genetically fusing recombinant proteins to the simian immunodeficiency virus (SIV) Tat protein has been investigated. The recombinant SIV Tat protein was initially expressed in very low amounts in E. coli, but optimization of the coding sequence for translation in the bacterial host significantly improved protein expression. Whilst fusion of SIV Tat to an experimental antigen (GST) facilitated the binding of the antigen to cell surfaces it did not appear to facilitate the transport of the protein into the cytosol. The immunogenicity of GST was significantly enhanced, in the absence of adjuvants, when fused to SIV Tat, with the induction of IgG1 and IgG2a antibodies indicative of a Th1 response being induced. However, no evidence was obtained that such an immunization scheme efficiently induced a CTL response.