Chemical engineering of cell penetrating antibodies

Accum™ Technology: A Novel Conjugable Primer for Onco-Immunotherapy

Compromised activity is a common impediment for biologics requiring endosome trafficking into target cells. In cancer cells, antibody-drug conjugates (ADCs) are trapped in endosomes or subsequently pumped extracellularly, leading to a reduction in intracellular accumulation. In subsets of dendritic cells (DCs), endosome-engulfed antigens face non-specific proteolysis and collateral damage to epitope immunogenicity before proteasomal processing and subsequent surface presentation. To bypass these shortcomings, we devised Accum™, a conjugable biotechnology harboring cholic acid (ChAc) and a nuclear localization signal (NLS) sequence for endosome escape and prompt nuclear targeting. Combined, these mechanisms culminate in enhanced intracellular accumulation and functionalization of coupled biologics. As proof-of-principle, we have biochemically characterized Accum, demonstrating its adaptability to ADCs or antigens in different cancer settings. Additionally, we have validated that endosome escape and nuclear routing are indispensable for effective intracellular accumulation and guaranteed target cell selectivity. Importantly, we have demonstrated that the unique mechanism of action of Accum translates into enhanced tumor cytotoxicity when coupled to ADCs, and durable therapeutic and prophylactic anti-cancer immunogenicity when coupled to tumor antigens. As more pre-clinical evidence accumulates, the adaptability, unique mechanism of action, and high therapeutic potency of Accum signal a promising transition into clinical investigations in the context of onco-immunotherapy.

Targeting the Virus Capsid as a Tool to Fight RNA Viruses

Several strategies have been developed to fight viral infections, not only in humans but also in animals and plants. Some of them are based on the development of efficient vaccines, to target the virus by developed antibodies, others focus on finding antiviral compounds with activities that inhibit selected virus replication steps. Currently, there is an increasing number of antiviral drugs on the market; however, some have unpleasant side effects, are toxic to cells, or the viruses quickly develop resistance to them. As the current situation shows, the combination of multiple antiviral strategies or the combination of the use of various compounds within one strategy is very important. The most desirable are combinations of drugs that inhibit different steps in the virus life cycle. This is an important issue especially for RNA viruses, which replicate their genomes using error-prone RNA polymerases and rapidly develop mutants resistant to applied antiviral compounds. Here, we focus on compounds targeting viral structural capsid proteins, thereby inhibiting virus assembly or disassembly, virus binding to cellular receptors, or acting by inhibiting other virus replication mechanisms. This review is an update of existing papers on a similar topic, by focusing on the most recent advances in the rapidly evolving research of compounds targeting capsid proteins of RNA viruses.

Intracellular delivery of therapeutic antibodies into specific cells using antibody-peptide fusions

Because of their favorable properties as macromolecular drugs, antibodies are a very successful therapeutic modality for interfering with disease-relevant targets in the extracellular space or at the cell membrane. However, a large number of diseases involve cytosolic targets and designing antibodies able to efficiently reach intracellular compartments would expand the antibody-tractable conditions. Here, we genetically fused cell penetrating peptides (CPPs) at various positions to an antibody targeting cancer cells, evaluated the developability features of the resulting antibody-peptide fusions and the ability of selected constructs to reach the cytosol. We first determined positions in the IgG structure that were permissive to CPP incorporation without destabilizing the antibody. Fusing CPPs to the C-terminus of the light chain and either before or after the hinge had the least effect on antibody developability features. These constructs were further evaluated for cell penetration efficiency. Two out of five tested CPPs significantly enhanced antibody penetration into the cytosol, in particular when fused before or after the hinge. Finally, we demonstrate that specific antibody binding to the cell surface target is necessary for efficient cell penetration of the CPP-antibody fusions. This study provides a solid basis for further exploration of therapeutic antibodies for intracellular targets.

A Novel Cell-Penetrating Antibody Fragment Inhibits the DNA Repair Protein RAD51

DNA damaging chemotherapies are successful in cancer therapy, however, the damage can be reversed by DNA repair mechanisms that may be up-regulated in cancer cells. We hypothesized that inhibiting RAD51, a protein involved in homologous recombination DNA repair, would block DNA repair and restore the effectiveness of DNA damaging chemotherapy. We used phage-display to generate a novel synthetic antibody fragment that bound human RAD51 with high affinity (K_D = 8.1 nM) and inhibited RAD51 ssDNA binding in vitro. As RAD51 is an intracellular target, we created a corresponding intrabody fragment that caused a strong growth inhibitory phenotype on human cells in culture. We then used a novel cell-penetrating peptide "iPTD" fusion to generate a therapeutically relevant antibody fragment that effectively entered living cells and enhanced the cell-killing effect of a DNA alkylating agent. The iPTD may be similarly useful as a cell-penetrating peptide for other antibody fragments and open the door to numerous intracellular targets previously off-limits in living cells.

Antibody Delivery for Intracellular Targets: Emergent Therapeutic Potential

Proteins have sparked fast growing interest as biological therapeutic agents for several diseases. Antibodies, in particular, carry an enormous potential as drugs owing to their remarkable target specificity and low immunogenicity. Although the market has numerous antibodies directed toward extracellular targets, their use in targeting therapeutically important intracellular targets is limited by their inability to cross cellular membrane. Realizing the potential for antibody therapy in disease treatment, progress has been made in the development of methods to deliver antibodies intracellularly. In this review, we address various platforms for delivery of antibodies and their merits and drawbacks.

Targeted Intracellular Delivery of Antibodies: The State of the Art

A dominant area of antibody research is the extension of the use of this mighty experimental and therapeutic tool for the specific detection of molecules for diagnostics, visualization, and activity blocking. Despite the ability to raise antibodies against different proteins, numerous applications of antibodies in basic research fields, clinical practice, and biotechnology are restricted to permeabilized cells or extracellular antigens, such as membrane or secreted proteins. With the exception of small groups of autoantibodies, natural antibodies to intracellular targets cannot be used within living cells. This excludes the scope of a major class of intracellular targets, including some infamous cancer-associated molecules. Some of these targets are still not druggable via small molecules because of large flat contact areas and the absence of deep hydrophobic pockets in which small molecules can insert and perturb their activity. Thus, the development of technologies for the targeted intracellular delivery of antibodies, their fragments, or antibody-like molecules is extremely important. Various strategies for intracellular targeting of antibodies via protein-transduction domains or their mimics, liposomes, polymer vesicles, and viral envelopes, are reviewed in this article. The pitfalls, challenges, and perspectives of these technologies are discussed.

NLS-Cholic Acid Conjugation to IL-5Rα-Specific Antibody Improves Cellular Accumulation and In Vivo Tumor-Targeting Properties in a Bladder Cancer Model

Receptor-mediated internalization followed by trafficking and degradation of antibody-conjugates (ACs) via the endosomal-lysosomal pathway is the major mechanism for delivering molecular payloads inside target tumor cells. Although a mainstay for delivering payloads with clinically approved ACs in cancer treatment and imaging, tumor cells are often able to decrease intracellular payload concentrations and thereby reduce the effectiveness of the desired application. Thus, increasing payload intracellular accumulation has become a focus of attention for designing next-generation ACs. We developed a composite compound (ChAcNLS) that enables ACs to escape endosome entrapment and route to the nucleus resulting in the increased intracellular accumulation as an interleukin-5 receptor α-subunit (IL-5Rα)-targeted agent for muscle invasive bladder cancer (MIBC). We constructed ⁶⁴Cu-A14-ChAcNLS, ⁶⁴Cu-A14-NLS, and ⁶⁴Cu-A14 and evaluated their performance by employing mechanistic studies for endosome escape coupled to nuclear routing and determining whether this delivery system results in improved ⁶⁴Cu cellular accumulation. ACs consisting of ∼20 ChAcNLS or NLS moieties per ⁶⁴Cu-A14 were prepared in good yield, high monomer content, and maintaining high affinity for IL-5Rα. Confocal microscopy analysis demonstrated ChAcNLS mediated efficient endosome escape and nuclear localization. ⁶⁴Cu-A14-ChAcNLS increased ⁶⁴Cu cellular accumulation in HT-1376 and HT-B9 cells relative to ⁶⁴Cu-A14 and ⁶⁴Cu-A14-NLS. In addition, we tested ⁶⁴Cu-A14-ChAcNLS in vivo to evaluate its tissue distribution properties and, ultimately, tumor uptake and targeting. A model of human IL-5Rα MIBC was developed by implanting NOD/SCID mice with subcutaneous HT-1376 or HT-B9MIBC tumors, which grow containing high and low IL-5Rα-positive tumor cell densities, respectively. ACs were intravenously injected, and daily blood sampling, biodistribution at 48 and 96 h, and positron emission tomography (PET) at 24 and 48 h were performed. Region of interest (ROI) analysis was also performed on reconstructed PET images. Pharmacokinetic analysis and biodistribution studies showed that ⁶⁴Cu-A14-ChAcNLS had faster clearance rates from the blood and healthy organs relative to ⁶⁴Cu-A14. However, ⁶⁴Cu-A14-ChAcNLS maintained comparable tumor accumulation relative to ⁶⁴Cu-A14. This resulted in ⁶⁴Cu-A14-ChAcNLS having superior tumor/normal tissue ratios at both 48 and 96 h biodistribution time points. Visualization of AC distribution by PET and ROI analysis confirmed that ⁶⁴Cu-A14-ChAcNLS had improved targeting of MIBC tumor relative to ⁶⁴Cu-A14. In addition, ⁶⁴Cu-A14 modified with only NLS had poor tumor targeting. This was a result of poor tumor uptake due to extremely rapid clearance. Thus, the overall findings in this model of human IL-5Rα-positive MIBC describe an endosome escape-nuclear localization cholic-acid-linked peptide that substantially enhances AC cellular accumulation and tumor targeting.

ChAcNLS, a Novel Modification to Antibody-Conjugates Permitting Target Cell-Specific Endosomal Escape, Localization to the Nucleus, and Enhanced Total Intracellular Accumulation

The design of antibody-conjugates (ACs) for delivering molecules for targeted applications in humans has sufficiently progressed to demonstrate clinical efficacy in certain malignancies and reduced systemic toxicity that occurs with standard nontargeted therapies. One area that can advance clinical success for ACs will be to increase their intracellular accumulation. However, entrapment and degradation in the endosomal-lysosomal pathway, on which ACs are reliant for the depositing of their molecular payload inside target cells, leads to reduced intracellular accumulation. Innovative approaches that can manipulate this pathway may provide a strategy for increasing accumulation. We hypothesized that escape from entrapment inside the endosomal-lysosomal pathway and redirected trafficking to the nucleus could be an effective approach to increase intracellular AC accumulation in target cells. Cholic acid (ChAc) was coupled to the peptide CGYGPKKKRKVGG containing the nuclear localization sequence (NLS) from SV-40 large T-antigen, which is termed ChAcNLS. ChAcNLS was conjugated to the mAb 7G3 (7G3-ChAcNLS), which has nanomolar affinity for the cell-surface leukemic antigen interleukin-3 receptor-α (IL-3Rα). Our aim was to determine whether 7G3-ChAcNLS increased intracellular accumulation while retaining nanomolar affinity and IL-3Rα-positive cell selectivity. Competition ELISA and cell treatment assays were performed. Cell fractionation, confocal microscopy, flow cytometry, and Western blot techniques were used to determine the level of antibody accumulation inside cells and in corresponding nuclei. In addition, the radioisotope copper-64 ((64)Cu) was also utilized as a surrogate molecular cargo to evaluate nuclear and intracellular accumulation by radioactivity counting. 7G3-ChAcNLS effectively escaped endosome entrapment and degradation resulting in a unique intracellular distribution pattern. mAb modification with ChAcNLS maintained 7G3 nM affinity and produced high selectivity for IL-3Rα-positive cells. In contrast, 7G3 ACs with the ability to either escape endosome entrapment or traffic to the nucleus was not superior to 7G3-ChAcNLS for increasing intracellular accumulation. Transportation of (64)Cu when complexed to 7G3-ChAcNLS also resulted in increased nuclear and intracellular radioactivity accumulation. Thus, ChAcNLS is a novel mAb functionalizing technology that demonstrates its ability to increase AC intracellular accumulation in target cells through escaping endosome entrapment coupled to nuclear trafficking.

A Cell Internalizing Antibody Targeting Capsid Protein (p24) Inhibits the Replication of HIV-1 in T Cells Lines and PBMCs: A Proof of Concept Study

There remains a need for newer therapeutic approaches to combat HIV/AIDS. Viral capsid protein p24 plays important roles in HIV pathogenesis. Peptides and small molecule inhibitors targeting p24 have shown to inhibit virus replication in treated cell. High specificity and biological stability of monoclonal antibodies (mAbs) make them an attractive contender for in vivo treatments. However, mAbs do not enter into cells, thus are restricted to target surface molecules. This also makes targeting intracellular HIV-1 p24 a challenge. A mAb specific to p24 that can internalize into the HIV-infected cells is hypothesized to inhibit the virus replication. We selected a mAb that has previously shown to inhibit p24 polymerization in an in vitro assay and chemically conjugated it with cell penetrating peptides (CPP) to generate cell internalizing anti-p24 mAbs. Out of 8 CPPs tested, κFGF-MTS -conjugated mAbs internalized T cells most efficiently. At nontoxic concentration, the κFGF-MTS-anti-p24-mAbs reduced the HIV-1 replication up to 73 and 49% in T-lymphocyte and PBMCs respectively. Marked inhibition of HIV-1 replication in relevant cells by κFGF-MTS-anti-p24-mAbs represents a viable strategy to target HIV proteins present inside the cells.

Cationic surface modification of gold nanoparticles for enhanced cellular uptake and X-ray radiation therapy

A challenge of X-ray radiation therapy is that high dose X-ray can damage normal cells and cause side effects. This paper describes a new nanoparticle-based method to reduce X-ray dose in radiation therapy by internalization of gold nanoparticles that are modified with cationic molecules into cancer cells. A cationic thiol molecule is synthesized and used to modify gold nanoparticles in a one-step reaction. The modified nanoparticles can penetrate cell membranes at high yield. By bring radio-sensitizing gold nanoparticles closer to nuclei where DNA is stored, the total X-ray dose needed to kill cancer cells has been reduced. The simulation of X-ray-gold nanoparticle interaction also indicates that Auger electrons contribute more than photoelectrons.

Single domain intrabodies against WASP inhibit TCR-induced immune responses in transgenic mice T cells

Intrabody technology provides a novel approach to decipher the molecular mechanisms of protein function in cells. Single domains composed of only the variable regions (V_H or V_L) of antibodies are the smallest recombinant antibody fragments to be constructed thus far. In this study, we developed transgenic (Tg) mice expressing the V_H or V_L single domains derived from a monoclonal antibody raised against the N-terminal domain of Wiskott–Aldrich syndrome protein (WASP), which is an adaptor molecule in immune cells. In T cells from anti-WASP V_H and V_L single domain Tg mice, interleukin-2 production induced by T cell receptor (TCR) stimulation were impaired, and specific interaction between the WASP N-terminal domain and the Fyn SH3 domain was strongly inhibited by masking the binding sites in WASP. These results strongly suggest that the V_H/V_L single domain intrabodies are sufficient to knockdown the domain function of target proteins in the cytosol.

Physical and biological properties of homophilic therapeutic antibodies

Homophilic antibodies have been discovered in mice and primates and can also be engineered. Compared to conventional antibodies, homophilic antibodies form lattices on targets leading to enhanced binding via polyvalent attachment. Previously, we have observed a paradoxical dose/potency effect with an engineered homophilic antibody against a human lung cancer tumor. Here, we have investigated some biophysical properties of homophilic antibodies and also studied the inhibition of human tumor growth in a xenograft model using homophilic Herceptin. Dimerization and viscosity of two homophilic antibodies are greater at physiological temperature than at 4°C. Similarly, binding to solid-phase antigen is greater at 37°C than at room temperature or 4°C. Dimer formation is higher at therapeutic concentration, supporting the notion that preformed dimers in solution are the effective molecular species responsible for polyvalent target binding and enhanced therapeutic potency.

Targeting antibodies to the cytoplasm

A growing number of research consortia are now focused on generating antibodies and recombinant antibody fragments that target the human proteome. A particularly valuable application for these binding molecules would be their use inside a living cell, e.g., for imaging or functional intervention. Animal-derived antibodies must be brought into the cell through the membrane, whereas the availability of the antibody genes from phage display systems allows intracellular expression. Here, the various technologies to target intracellular proteins with antibodies are reviewed.

Protective effects of anti-ricin A-chain antibodies delivered intracellularly against ricin-induced cytotoxicity

AIM: To evaluate the ability of anti-ricin A-chain antibodies, delivered intracellularly, to protect against ricin-induced cytotoxicity in RAW264.7 cells.

METHODS: Anti-deglycosylated ricin A-chain antibody and RAC18 anti-ricin A-chain monoclonal antibody were delivered intracellularly by encapsulating in liposomes or via conjugation with the cell-penetrating MTS-transport peptide. RAW264.7 cells were incubated with these antibodies either before or after ricin exposure. The changes in cytotoxicity were estimated by MTT assay. Co-localization of internalized antibody and ricin was evaluated by fluorescence microscopy.

RESULTS: Internalized antibodies significantly increased cell viability either before or after ricin exposure compared to the unconjugated antibodies. Fluorescence microscopy confirmed the co-localization of internalized antibodies and ricin inside the cells.

CONCLUSION: Intracellular delivery of antibodies to neutralize the ricin toxin after cellular uptake supports the potential use of cell-permeable antibodies for post-exposure treatment of ricin intoxication.

Structural conservation in band 4.1, ezrin, radixin, moesin (FERM) domains as a guide to identify inhibitors of the proline-rich tyrosine kinase 2

The nonreceptor focal adhesion kinases FAK and Pyk2 play a central role in the regulation of glioma cell proliferation and migration, making them attractive targets to improve clinical outcome. Noncatalytic targeting represents a novel approach to regulate the activity of these tyrosine kinases. A combination of site directed mutagenesis and molecular modeling was used to identify compounds that target the F3 module of the Pyk2 FERM domain. A protein pharmacophore model for the Pyk2 FERM/F3 module, generated utilizing the structural conservation of ligand-bound FERM domains with known 3D structures, was used to search the LeadQuest compound library. Compounds compliant with the model were tested for their ability to inhibit the binding of a monoclonal antibody that maps to a functional site on the F3 module. The highest scoring compound bound directly to the Pyk2 FERM domain, inhibited Pyk2 stimulated glioma migration, and provides the framework for the development of novel therapeutic agents to target the activity of the focal adhesion kinases.

The Pyk2 FERM domain as a target to inhibit glioma migration

The invasion of malignant glioma cells into the surrounding normal brain precludes effective clinical treatment. In this report, we investigated the role of the NH(2)-terminal FERM domain in the regulation of the promigratory function of Pyk2. We report that the substitution of residues that constitute a small cleft on the surface of the F3 module of the FERM domain do not significantly alter Pyk2 expression but result in the loss of Pyk2 phosphorylation. A monoclonal antibody, designated 12A10, specifically targeting the Pyk2 FERM domain was generated and recognizes an epitope located on the beta5C-alpha1C surface of the F3 module of the FERM domain. Amino acid substitutions in the F3 module that resulted in the loss of Pyk2 phosphorylation also inhibited the binding of 12A10, suggesting that the 12A10 epitope overlaps a site that plays a role in Pyk2 activity. Conjugation of 12A10 to a membrane transport peptide led to intracellular accumulation and inhibition of glioma cell migration in a concentration-dependent manner. A single chain Fv fragment of 12A10 was stable when expressed in the intracellular environment, interacted directly with Pyk2, reduced Pyk2 phosphorylation, and inhibited glioma cell migration in vitro. Stable intracellular expression of the 12A10 scFv significantly extended survival in a glioma xenograft model. Together, these data substantiate a central role for the FERM domain in regulation of Pyk2 activity and identify the F3 module as a novel target to inhibit Pyk2 activity and inhibit glioma progression.

Engineering a noncarrier to a highly efficient carrier peptide for noncovalently delivering biologically active proteins into human cells

Noncovalent protein delivery into cells via peptide carriers is an emerging concept. Only a handful of such peptides are known. To address various limitations associated with protein delivery for therapeutic purposes, a greater number of different delivery peptides would be required. No general method exists for creating such peptides. By combining a sequence of 16 lysine residues (K16) with the signal peptide (SP) sequence of Kaposi's fibroblast growth factor (K-FGF), we have synthesized a peptide (K16SP) that efficiently and noncovalently delivers functionally intact proteins (immunoglobulin G molecules, beta-galactosidase, and green fluorescent protein) into mammalian cells. The peptides K16 and SP each alone did not show any noncovalent protein-carrying capacity. K16SP appears to be nontoxic to cells and three to four times more efficient than a commercially available peptide reagent. Our approach offers proof-of-concept of a general strategy for creating a diverse array of peptide carriers for eventual therapeutic applications.

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.

Delivery of antibody-captured proteins into living cells using PTD-fused protein A

Protein transduction domain (PTD)-mediated protein delivery into animal cells is a useful technique for regulating cellular functions. Proteins captured by antibodies were delivered into living cells using an antibody/PTD-fused protein A complex. As a model protein, fluorescent-modified antibodies, captured by their respective primary antibody, were analyzed by fluorescence-activated cell sorting (FACS) which showed that the fluorescent-modified antibodies were directly delivered into cells. Peroxidase, captured by its specific antibody, was also delivered into cells and retained its activity.

Therapeutic applications of superantibodies

Superantibody technology represents a method to enhance the potency and utility of monoclonal antibodies. The blueprint for superantibody technology is taken from rare naturally occurring superantibodies with unique sequence regions, conferring specific biological functions not detected on most antibodies. In superantibody technology, peptides with specific amino acid sequences are crosslinked to antibodies using affinity-site-specific chemistry. Three types of superantibodies have been engineered: dimerizing superantibodies with enhanced effector potency, superantibodies with the ability to penetrate living cells and superantibodies as vaccines with built-in molecular adjuvant. Collectively, superantibody technology generates a new class of antibodies with higher levels of therapeutic potency.

Photo-activated affinity-site cross-linking of antibodies using tryptophan containing peptides

Affinity-based conjugation methods for antibodies can produce defined and reproducible conjugates. This requires that the target antibody has an affinity site for the ligand and that the ligand has a reactive site. These requirements are critical for the conjugation of antibodies designed for diagnostic and therapeutic application. Our laboratory has discovered a novel affinity of antibodies for the amino acid tryptophan using an azido derivative of tryptophan. Here we show that tryptophan without the azido group can be photo-cross-linked to antibodies. Biotinylated tryptophan peptides are photolysed into monoclonal and polyclonal antibodies and such biotinylated antibodies are used in avidin-based ELISA. With the simple and gentle tryptophan-affinity photo-conjugation of peptides, antibodies can be conjugated with peptides to enhance their potency and expand their targeting range.

Prevention of NF-kappaB activation in vivo by a cell-permeable NF-kappaB inhibitor peptide

The NF-kappaB/Rel transcription factor family plays a central role in coordinating the expression of a variety of genes that regulate stress responses, immune cell activation, apoptosis, proliferation, differentiation, and oncogenic transformation. Interventions that target the NF-kappaB pathway may be therapeutic for a variety of pathologies, especially immune/inflammatory diseases. Using membrane translocating sequence (MTS) technology, we developed a cell-permeable dominant inhibitor of NF-kappaB activation, termed IkappaBalpha-(DeltaN)-MTS. This molecule contains a 12-amino acid MTS motif attached to the COOH-terminal region of a nondegradable inhibitor protein [IkappaBalpha-(DeltaN)]. The recombinant protein enters cells and localizes in the cytoplasm. Delivery of the IkappaBalpha-(DeltaN)-MTS to cell lines and primary cells inhibited nuclear translocation of NF-kappaB proteins induced by cell activation. The protein also effectively inhibited NF-kappaB activation in vivo in two different animal models: NF-kappaB activation in response to skin wounding in mice and NF-kappaB activation in lungs after endotoxin treatment in sheep. Inhibition of NF-kappaB by the IkappaBalpha-(DeltaN)-MTS in the endotoxin model attenuated physiological responses to endotoxemia. These data demonstrate that activation of NF-kappaB can be inhibited using a recombinant protein designed to penetrate into cells. This technology may provide a new approach to NF-kappaB pathway-targeted therapies.

Proapoptotic activity of cell-permeable anti-Akt single-chain antibodies

We developed anti-Akt1 single-chain antibodies (scFv) by panning a mouse phage-displayed scFv recombinant antibody library. Recombinant scFv that bound glutathione S-transferase (GST)-Akt1 were screened for their ability to inhibit Akt activity in vitro in a kinase reaction containing human recombinant Akt1 and an Akt/serum glucocorticoid-inducible kinase (SGK) substrate. Michaelis-Menten analysis of kinase inhibition by a selected scFv was consistent with scFv-mediated competition with enzyme's substrate for the catalytic site of Akt. To generate a membrane-permeable version of the anti-Akt1 scFv, the scFv gene was subcloned into a GST expression vector carrying a membrane-translocating sequence (MTS) from Kaposi fibroblast growth factor. A purified GST-anti-Akt1-MTS fusion protein accumulated intracellularly in 293T, BT-474, and PyVmT cells in a dose- and time-dependent fashion. Intracellular accumulation correlated temporally with inhibition of p-Ser(473) Akt and GSK-3alpha/beta phosphorylation, suggesting that Ser(473) is an Akt autophosphorylation site. Phosphorylated (activated) phosphoinositide-dependent kinase 1, mitogen-activated protein kinase, p38, and HER2 (erbB2) were not affected, supporting Akt kinase specificity for the inhibitory scFv. Exogenously expressed constitutively active Akt2 and Akt3 were also inhibited in vitro by the anti-Akt1 fusion protein. Furthermore, GST-anti-Akt1-MTS induced apoptosis in three cancer cell lines that express constitutively active Akt. Finally, systemic treatment with the anti-Akt scFv reduced tumor volume and neovascularization and increased apoptosis in PyVmT-expressing transgenic tumors implanted in mouse dorsal window chambers. Thus, GST-anti-Akt1-MTS is a novel cell-permeable inhibitor of Akt, which selectively inhibits Akt-mediated survival in intact cells both in vitro and in vivo.

TransMabs: cell-penetrating antibodies, the next generation

Intracellular proteins are becoming attractive targets in diagnosis and for therapy such as in signal pathways, on enzymes, transcription factors and structural proteins. Antibodies have been used therapeutically for extracellular pathogens and for targeting cell-surface antigens. Antibodies normally do not pass easily through intact cellular or subcellular membranes in living cells. Methods to shuttle antibodies into living cells are either labour-intensive and/or compromise the structural and functional integrity of the cell or require the integration of genes for heavy and light chain production through gene therapy approaches. A new technology platform, 'SuperAntibody Technology', enables antibodies to be shuttled into living cells without harming them. Such cell-penetrating antibodies open new diagnostic and therapeutic windows. The term 'TransMabs' has been coined for these antibodies. Proof of principle has been achieved with a 17-amino acid peptide with membrane translocating properties, conjugated with anti-caspase-3 antibody. Such a TransMab inhibits significantly in vitro apoptosis-related events, such as caspase-3 activity, DNA fragmentation and spectrin cleavage. Anti-caspase-3 TransMab, therefore, could be utilised to inhibit apoptosis in a variety of diseases, such as Alzheimer's, Huntington's and Parkinson's. Unlike peptide inhibitors available at present, this TransMab is not expected to have invivo toxic side effects and can only target activated forms of the enzyme. This paper discusses the advantages and limitations of cell-penetrating antibodies (TransMabs) compared with existing small molecule drug development approaches.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Overview on the use of therapeutic antibodies in drug discovery

The number of therapeutic antibodies approved by regulatory agencies as novel drugs and the number of antibodies in development has increased significantly. The modular nature of antibody structure has enabled researchers to more predictably design therapeutic antibodies by choosing appropriate functional features most appropriate for a given antibody target and clinical indication. Advances in recombinant antibody technologies have allowed the routine generation of antibodies that can satisfy stringent drug design criteria, such as low immunogenicity, high affinity, target specificity, and commercially viable manufacturing methods. Engineering design opportunities exist for both the variable and the constant regions that encompass, in addition to antigen specificity and affinity, effector functions that mediate immune complex clearance or pharmacokinetics. These are discussed in the context of relevant in vivo and in vitro technologies, such as human IgG transgenic mice, phage display, and biologics manufacturing. Finally, therapeutic antibodies are compared with traditional drugs with respect to target class, selectivity, route of administration, intellectual property issues, and lead discovery and optimization.

Intracellular delivery of antibodies using TAT fusion protein A

Internalization of antibodies into mammalian cells is a useful method for analyzing and regulating cellular function. In this study, we developed a novel method for the delivery of antibodies into cells using the TAT-fused protein. This fusion protein consists of two functional domains, the protein transduction domain of HIV-1 TAT and the B domain of staphylococcal protein A (SpA), which has an ability to bind to the IgG. The TAT-SpA fusion protein was mixed with fluorescence-labeled rabbit IgG and added to cells. The internalization of antibody was analyzed using confocal microscopy and flow cytometry in living cells. As a result, fluorescence-labeled IgG with the TAT-SpA fusion protein was observed intracellularly. Flow cytometry results demonstrated time course and dose dependence relationships of antibody internalization. These results suggest that the TAT-SpA fusion protein can be a useful reagent for the delivery of antibody into cells.

Fibroblast growth factors in cancer: therapeutic possibilities

The fibroblast growth factor (FGF) family of signalling molecules and its receptors (FGFRs) contribute to normal developmental and physiological processes. However, the subversion of this powerful growth stimulatory pathway has been implicated in the generation of a variety of pathological conditions. This review focuses on the role of FGF/FGFRs in cancer. The case will be made that this signalling pathway is associated with and functionally important for the growth of some human tumours. As such, FGF/FGFRs can be viewed as rational therapeutic oncology targets and strategies used to inhibit these molecules are discussed. The therapeutic exploitation of tumour-associated FGFR expression to deliver toxins or antiproliferative signals to tumour cells is also reviewed, as is the use of FGFs as protein therapeutics to alleviate the side effects of cancer therapy.