Cell binding and internalization by filamentous phage displaying a cyclic Arg-Gly-Asp-containing peptide

An RGD-oligolysine peptide: a prototype construct for integrin-mediated gene delivery

We have synthesized a linear, bifunctional peptide that comprises an integrin-targeting domain containing an arginine-glycine-aspartic acid tripeptide motif and a DNA-binding moiety consisting of a short stretch of 16 lysine residues. This peptide can form distinctive, condensed complexes with DNA and is capable of mediating its delivery and expression in a variety of mammalian cells in culture. Internalization is mediated by cell surface integrin receptors via a mechanism that is known to be phagocytic. We have analyzed the relationship between DNA and peptide and have investigated the conditions suitable for optimal gene delivery. The formation of condensed peptide DNA complexes leads to resistance to nuclease degradation. The level of reporter gene expression obtained is dependent on the peptide-to-DNA ratio and is enhanced in the presence of the endosomal buffer chloroquine, polyethyleneimine, and deactivated adenovirus during gene delivery. Under optimal conditions the levels of reporter gene expression obtained approach or even exceed those obtained with DNA delivered with the commercial liposome Lipofectamine. The ability to produce an efficient gene delivery system using small, easily modified, and well-defined constructs that have no constraint of particle size demonstrates the advantages of integrin-targeting peptides for gene transfer.

Creating and engineering human antibodies for immunotherapy

Targeting in immunotherapy has traditionally been achieved by using monoclonal rodent antibodies. Despite gene-engineering, there are many problems and limitations associated with the non-human origin, the targeting specificity and the binding strength of these molecules. Now these issues may be addressed in a more rational way, by designing and then shaping, in vitro, the desired human antibodies. This review addresses how this may be achieved by the selection of monoclonal human antibodies from phage display libraries and the engineering of affinity and specificity thereafter. Phage display of antibody fragments has allowed access to large collections of different phage antibodies, created by cloning antibody V-genes from B-cells. Antibodies against any type of antigen may be derived from such repertoires, by rounds of enrichment on antigen and re-amplification. This review presents the state of the art in rational antibody design and creation. It will highlight the strengths of this increasingly important field, which will aid in the generation of tailor-made targeting entities for immunotherapy.

Lipid-mediated enhancement of transfection by a nonviral integrin-targeting vector

Nonviral vectors consisting of integrin-targeting peptide/DNA (ID) complexes have the potential for widespread application in gene therapy. The transfection efficiency of this vector, however, has been limited by endosomal degradation. We now report that lipofectin (L) incorporated into the ID complexes enhances integrin-mediated transfection, increasing luciferase expression by more than 100-fold. The transfection efficiency of Lipofectin/Integrin-binding peptide/DNA (LID) complexes, assessed by beta-galactosidase reporter gene expression and X-gal staining, was improved from 1% to 10% to over 50% for three different cell lines, and from 0% to approximately 25% in corneal endothelium in vitro. Transfection complexes have been optimized with respect to their transfection efficiency and we have investigated their structure, function, and mode of transfection. Both ID and LID complexes formed particles, unlike the fibrous network formed by lipofectin/DNA complexes (LD). Integrin-mediated transfection by LID complexes was demonstrated by the substantially lower transfection efficiency of LKD complexes in which the integrin-biding peptide was substituted for K16 (K). Furthermore, the transfection efficiency of complexes was shown to be dependent on the amount of integrin-targeting ligand in the complex. Finally, a 34% reduction in integrin-mediated transfection efficiency by LID complexes was achieved with a competing monoclonal antibody. The role of lipofectin in LID complexes appears, therefore, to be that of a co-factor, enhancing the efficiency of integrin-mediated transfection. The mechanism of enhancement is likely to involve a reduction in the extent of endosomal degradation of DNA.

Cancer treatment by targeted drug delivery to tumor vasculature in a mouse model

In vivo selection of phage display libraries was used to isolate peptides that home specifically to tumor blood vessels. When coupled to the anticancer drug doxorubicin, two of these peptides-one containing an alphav integrin-binding Arg-Gly-Asp motif and the other an Asn-Gly-Arg motif-enhanced the efficacy of the drug against human breast cancer xenografts in nude mice and also reduced its toxicity. These results indicate that it may be possible to develop targeted chemotherapy strategies that are based on selective expression of receptors in tumor vasculature.

Towards gene therapy of mitochondrial disorders

Mitochondrial disorders are characterized by protein deficiencies affecting the structure and function of mitochondria. The protein deficiencies are caused by mutations either in a nuclear gene or in the mitochondrial genome. Most current approaches to gene therapy of mitochondrial diseases aim at expression of the corrective gene sequence by nuclear/cytoplasmic expression. However, the mitochondrial genome and its autonomous expression system offer the potential of an alternative gene therapy strategy: the introduction of nuclear gene sequences into the mitochondrial genome and their expression by the mitochondrial gene expression system. In addition to its potential for gene therapy, the introduction and expression of an exogenous gene in mitochondria would provide an invaluable tool towards the understanding of mitochondrial genome expression and its regulation.

Accessibility of peptides displayed on filamentous bacteriophage virions: susceptibility to proteinases

The genome of the filamentous bacteriophage fd has been engineered so that small peptides can be inserted into the exposed N-terminal segment of pVIII, the major protein of the virus capsid. Most small peptides can be displayed on all 2700 copies of pVIII (a recombinant virion), but larger peptides can be displayed only in virions in which modified and wild-type proteins are intermingled (hybrid virions). Peptides displayed in this way are highly immunogenic and capable of interacting with receptors and other ligands. The physical accessibility of the displayed peptides was tested by examining their susceptibility to digestion with proteinases. Potential cleavage sites in peptides displayed on recombinant or hybrid virions were in general found to be accessible to trypsin and chymotrypsin; and the density of incorporation of peptides in the virion had no effect on the susceptibility to cleavage. However, peptide bonds towards the C-terminal end of an insert, located approximately 47 residues or fewer from the C-terminus of the coat protein, were protected from digestion, presumably because of their proximity to the bulk viral surface. These results have important implications for the design and optimization of peptide display systems using filamentous bacteriophages.

Targeting DNA to cells with basic fibroblast growth factor (FGF2)

Ligand-mediated targeting of DNA was validated by condensing a plasmid DNA encoding the beta-galactosidase (beta-gal) gene with a basic fibroblast growth factor (FGF2) that was first chemically conjugated to polylysine (K). The conditions that gave optimal binding of this FGF2 to DNA also generated the highest level of beta-gal expression when added to FGF2 target cells like COS-1, 3T3, baby hamster kidney (BHK), or endothelial cells. This beta-gal activity increased in a time- and dose-dependent manner and was dependent on the inclusion of FGF2 in the complex. FGF receptor specificity was demonstrated by competition of the complex with FGF2 and heparin, and by the failure of cytochrome c or histone H1 to mimic the gene-targeting effects of FGF2. The expression of beta-gal was also endosome dependent because chloroquine increased beta-gal expression 8-fold and endosome disruptive peptides increased expression of beta-gal 26-fold. Taken together these findings establish that DNA can be introduced into cells through the high affinity FGF receptor complex, and while its efficiency will require significant enhancements to achieve sustained and elevated transgene expression, the possibility that the technique could be used to deliver DNAs encoding cytotoxic molecules is discussed.

Total modification of the bacteriophage lambda tail tube major subunit protein with foreign peptides

The bacteriophage lambda has been shown previously to tolerate a high multiplicity of peptide additions to the C-terminus of the major tail tube subunit protein (gpV, the product of the V gene). However, it was not clear whether all gpV copies within a functional virion could tolerate such modification. Complementation tests with phage bearing either V gene amber mutations or a precisely deleted V gene were used to test the extent of possible tail tube peptide display. Expression of plasmid-encoded gpV fused C-terminally with certain foreign peptides allowed rescue of such V gene-defective phage to essentially wild-type levels. After extensive purification such phage were shown by sensitive Western blotting to contain only the modified form of gpV. Peptide-modified gpV could also form indefinite tail tube polymeric structures (polytubes).

A recombinant, arginine-glycine-aspartic acid (RGD) motif from foot-and-mouth disease virus binds mammalian cells through vitronectin and, to a lower extent, fibronectin receptors

The cell-binding abilities of a recombinant, RGD-containing peptide from foot-and-mouth disease virus (FMDV) have been characterized in HeLa and BHK cells. This peptide represents the aa sequence of the solvent-exposed G-H loop of protein VP1 which is involved in cell recognition and infection. The efficiency of the viral motif in promoting cell attachment and spreading is comparable to that shown by fibronectin or vitronectin. Cell binding is inhibited by a monoclonal antibody directed against a viral, RGD-involving B-cell epitope and also by sera against vitronectin (alpha V beta 3/beta 5) and fibronectin (alpha 5 beta 1) receptors. In addition, a synthetic RGD peptide, which is a ligand for both integrins, prevents the cell binding mediated by the FMDV domain. These data demonstrate that the FMDV RGD motif is a potent ligand for cell-receptor integrins and sufficient to promote cell attachment to susceptible cells mainly through the vitronectin receptor.

Phage display of proteins

Phage display of proteins continues to be an important technology with a variety of applications. In the past year, advances have been made in coupling rational protein design with the power of the display selection process. In addition to the widely used filamentous phage, other bacteriophage surface expression systems have now been developed, some of which may be of particular use for the selection of surface-display cDNA clones.

Toward cell-targeting gene therapy vectors: selection of cell-binding peptides from random peptide-presenting phage libraries

Ideal gene therapy vectors would be delivered intravenously to transfect only specific cells. Existing vectors only transfect cells in vivo in a manner determined by blood flow and the site of introduction. As a general and systematic approach for generating cell-targeting ligands for gene therapy vectors, we have used peptide-presenting phage libraries to select peptides that bind and enter several different cell types. Because of their small size, cell-binding peptides such as these could be incorporated into biological or physical gene therapy vectors. In addition, peptide-presenting phage themselves may also be candidates for gene therapy vectors.

Mammalian cell binding and transfection mediated by surface-modified bacteriophage lambda

Bacteriophage lambda virions whose tail tube major subunit (V) proteins are modified with a cyclizable Arg-Gly-Asp (RGD) peptide are able to promote the binding of certain mammalian cells to a solid surface. This effect was shown to be specific by peptide competition experiments, and control phage lacking the RGD peptide showed no significant cellular interaction. RGD-modified but not control phage bearing a reporter gene could transfect COS cells at a significant frequency. Phage-mediated transfection therefore benefits when the efficiency of only one step in the multi-stage uptake process is improved.

Phage display: protein engineering by directed evolution

Phage display of proteins has become an important tool for protein engineering. Over the past year, the versatility of the technology has expanded to include the development of DNA-binding proteins with novel specificities, energetics of protein folding and directed evolution of antibodies. In addition, display of expressed cDNA libraries opens an exciting opportunity for studying protein-protein interactions.