Identification of FGF receptor-binding peptides for cancer gene therapy

Targeting Protein-Protein Interfaces with Peptides: The Contribution of Chemical Combinatorial Peptide Library Approaches

Protein-protein interfaces play fundamental roles in the molecular mechanisms underlying pathophysiological pathways and are important targets for the design of compounds of therapeutic interest. However, the identification of binding sites on protein surfaces and the development of modulators of protein-protein interactions still represent a major challenge due to their highly dynamic and extensive interfacial areas. Over the years, multiple strategies including structural, computational, and combinatorial approaches have been developed to characterize PPI and to date, several successful examples of small molecules, antibodies, peptides, and aptamers able to modulate these interfaces have been determined. Notably, peptides are a particularly useful tool for inhibiting PPIs due to their exquisite potency, specificity, and selectivity. Here, after an overview of PPIs and of the commonly used approaches to identify and characterize them, we describe and evaluate the impact of chemical peptide libraries in medicinal chemistry with a special focus on the results achieved through recent applications of this methodology. Finally, we also discuss the role that this methodology can have in the framework of the opportunities, and challenges that the application of new predictive approaches based on artificial intelligence is generating in structural biology.

Peptide-based delivery of therapeutics in cancer treatment

Current delivery strategies for cancer therapeutics commonly cause significant systemic side effects due to required high doses of therapeutic, inefficient cellular uptake of drug, and poor cell selectivity. Peptide-based delivery systems have shown the ability to alleviate these issues and can significantly enhance therapeutic loading, delivery, and cancer targetability. Peptide systems can be tailor-made for specific cancer applications. This review describes three peptide classes, targeting, cell penetrating, and fusogenic peptides, as stand-alone nanoparticle systems, conjugations to nanoparticle systems, or as the therapeutic modality. Peptide nanoparticle design, characteristics, and applications are discussed as well as peptide applications in the clinical space.

Tumor-Associated Fibroblast-Targeting Nanoparticles for Enhancing Solid Tumor Therapy: Progress and Challenges

Even though nanoparticle drug delivery systems (nanoDDSs) have improved antitumor efficacy by delivering more drugs to tumor sites compared to free and unencapsulated therapeutics, achieving satisfactory distribution and penetration of nanoDDSs inside solid tumors, especially in stromal fibrous tumors, remains challenging. As one of the most common stromal cells in solid tumors, tumor-associated fibroblasts (TAFs) not only promote tumor growth and metastasis but also reduce the drug delivery efficiency of nanoparticles through the tumor's inherent physical and physiological barriers. Thus, TAFs have been emerging as attractive targets, and TAF-targeting nanotherapeutics have been extensively explored to enhance the tumor delivery efficiency and efficacy of various anticancer agents. The purpose of this Review is to opportunely summarize the underlying mechanisms of TAFs on obstructing nanoparticle-mediated drug delivery into tumors and discuss the current advances of a plethora of nanotherapeutic approaches for effectively targeting TAFs.

All Good Things Must End: Termination of Receptor Tyrosine Kinase Signal

Receptor tyrosine kinases (RTKs) are membrane receptors that regulate many fundamental cellular processes. A tight regulation of RTK signaling is fundamental for development and survival, and an altered signaling by RTKs can cause cancer. RTKs are localized at the plasma membrane (PM) and the major regulatory mechanism of signaling of RTKs is their endocytosis and degradation. In fact, RTKs at the cell surface bind ligands with their extracellular domain, become active, and are rapidly internalized where the temporal extent of signaling, attenuation, and downregulation are modulated. However, other mechanisms of signal attenuation and termination are known. Indeed, inhibition of RTKs’ activity may occur through the modulation of the phosphorylation state of RTKs and the interaction with specific proteins, whereas antagonist ligands can inhibit the biological responses mediated by the receptor. Another mechanism concerns the expression of endogenous inactive receptor variants that are deficient in RTK activity and take part to inactive heterodimers or hetero-oligomers. The downregulation of RTK signals is fundamental for several cellular functions and the homeostasis of the cell. Here, we will review the mechanisms of signal attenuation and termination of RTKs, focusing on FGFRs.

Cyclodextrins-Peptides/Proteins Conjugates: Synthesis, Properties and Applications

Cyclodextrins (CDs) are a family of macrocyclic oligosaccharides mostly composed of six, seven, or eight α-D-glucopyranose units with α-1,4-glycosidic bonds to form toroidal structures. The CDs possess a hydrophilic exterior and hydrophobic interior with the ability to form an inclusion complex, especially with hydrophobic molecules. However, most existing studies are about conjugation CDs with peptide/protein focusing on the formation of new systems. The CD-peptide/protein can possess new abilities; particularly, the cavity can be applied in modulation properties of more complexed proteins. Most studies are focused on drug delivery, such as targeted delivery in cell-penetrating peptides or co-delivery. The co-delivery is based mostly on polylysine systems; on the other hand, the CD-peptide allows us to understand biomolecular mechanisms such as fibryllation or stem cell behaviour. Moreover, the CD-proteins are more complexed systems with a focus on targeted therapy; these conjugates might be controllable with various properties due to changes in their stability. Finally, the studies of CD-peptide/protein are promising in biomedical application and provide new possibilities for the conjugation of simple molecules to biomolecules.

Potential anticancer activity of a new pro-apoptotic peptide-thioctic acid gold nanoparticle platform

Targeted nanoparticle platforms designed to induce cell death by apoptosis can bypass the resistance mechanisms of cancer cells. With this in mind we have constructed a new cancer-targeting peptide-functionalized nanoparticle using gold nanoparticles (AuNPs) and a thioctic acid-DMPGTVLP peptide (TA-peptide) conjugate. Morphological analysis of the nanoparticles by transmission electron microscopy showed average diameters of about 3.52 nm and 26.2 nm for the AuNP core and shell, respectively. Strong affinity toward the nucleolin receptors of breast cancer cell lines MCF-7 and T47D was observed for the TA-peptide gold nanoparticles (TAP@AuNPs) based on IC₅₀ values. Furthermore, the nanoparticles showed excellent hemocompatibility. Quantitative results of atomic absorption showed improved uptake of TAP@AuNPs. Treatment of the cells with TAP@AuNPS resulted in greater release of cytochrome c following caspase-3/7 activation compared with free TA-peptide. The cytosolic level of adenosine triphosphate for TAP@AuNPs was higher than in controls. Higher anti-tumor efficiency was observed for TAP@AuNPs than TA-peptide compared with phosphate-buffered saline after intratumoral injection in tumor-bearing mice. It can be concluded that the design and development of a receptor-specific peptide-AuNP platform will be valuable for theranostic applications in cancer nanomedicine.

Hitting the Target but Missing the Point: Recent Progress towards Adenovirus-Based Precision Virotherapies

More people are surviving longer with cancer. Whilst this can be partially attributed to advances in early detection of cancers, there is little doubt that the improvement in survival statistics is also due to the expansion in the spectrum of treatments available for efficacious treatment. Transformative amongst those are immunotherapies, which have proven effective agents for treating immunogenic forms of cancer, although immunologically "cold" tumour types remain refractive. Oncolytic viruses, such as those based on adenovirus, have great potential as anti-cancer agents and have seen a resurgence of interest in recent years. Amongst their many advantages is their ability to induce immunogenic cell death (ICD) of infected tumour cells, thus providing the alluring potential to synergise with immunotherapies by turning immunologically "cold" tumours "hot". Additionally, enhanced immune mediated cell killing can be promoted through the local overexpression of immunological transgenes, encoded from within the engineered viral genome. To achieve this full potential requires the development of refined, tumour selective "precision virotherapies" that are extensively engineered to prevent off-target up take via native routes of infection and targeted to infect and replicate uniquely within malignantly transformed cells. Here, we review the latest advances towards this holy grail within the adenoviral field.

Nanomedicine as a putative approach for active targeting of hepatocellular carcinoma

The effectiveness of chemotherapy in hepatocellular carcinoma (HCC) is restricted by chemo-resistance and systemic side effects. To improve the efficacy and safety of chemotherapeutics in HCC management, scientists have attempted to deliver these drugs to malignant tissues using targeted carriers as nanoparticles (NPs). Among the three types of NPs targeting (active, passive, and stimuli-responsive), active targeting is the most commonly investigated in HCC treatment. Despite the observed promising results so far, clinical research on nanomedicine targeting for HCC treatment still faces many challenges.These include batch-to-batch physicochemical properties' variations, limiting large scale production and insufficient data on human and environmental toxicities. This review summarized the characteristics of different nanocarriers, ligands, targeted receptors on HCC cells and provided recommendations to overcome the challenges, facing this novel line of treatment for HCC.

Identification of a peptide antagonist of the FGF1-FGFR1 signaling axis by phage display selection

Overexpression of fibroblast growth factor receptor 1 (FGFR1) is a common aberration in lung and breast cancers and has necessitated the design of drugs targeting FGFR1‐dependent downstream signaling and FGFR1 ligand binding. To date, the major group of drugs being developed for treatment of FGFR1‐dependent cancers are small‐molecule tyrosine kinase inhibitors; however, the limited specificity of these drugs has led to increasing attempts to design molecules targeting the extracellular domain of FGFR1. Here, we used the phage display technique to select cyclic peptides F8 (ACSLNHTVNC) and G10 (ACSAKTTSAC) as binders of the fibroblast growth factor 1 (FGF1)–FGFR1 interface. ELISA and in vitro cell assays were performed to reveal that cyclic peptide F8 is more effective in preventing the FGF1–FGFR1 interaction, and also decreases FGF1‐induced proliferation of BA/F3 FGFR1c cells by over 40%. Such an effect was not observed for BA/F3 cells lacking FGFR1. Therefore, cyclic peptide F8 can act as a FGF1–FGFR1 interaction antagonist, and may be suitable for further development for potential use in therapies against FGFR1‐expressing cancer cells.

Peptide-based gene delivery vectors

Gene therapy as a strategy for disease treatment requires safe and efficient gene delivery systems that encapsulate nucleic acids and deliver them to effective sites in the cell.

Identification of Novel Single-Domain Antibodies against FGF7 Using Phage Display Technology

Fibroblast growth factor 7 (FGF7) is a member of the fibroblast growth factor (FGF) family of proteins. FGF7 is of stromal origin and produces a paracrine effect on epithelial cells. In the current investigation, we aimed to identify new single-domain antibodies (sdAbs) against FGF7 using phage display technology. The vector harboring the codon-optimized DNA sequence for FGF7 protein was transformed into Escherichia coli BL21 (DE3) pLysS, and then the protein was expressed at the optimized condition. Enzyme-linked immunosorbent assay, circular dichroism spectropolarimetry, and in vitro scratch assay experiments were used to confirm the proper folding and functionality of the purified FGF7 protein. The purity of the produced FGF7 was 92%, with production yield of 3.5 mg/L of culture. Panning against the purified FGF7 was performed, and the identified single-domain antibodies showed significant affinity. Further investigation on one of the selected sdAb displaying phage clones showed concentration-dependent binding to FGF7. The selected sdAb can be used for developing novel tumor-suppressing agents where inhibition of FGF7 is required.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Ligand-based targeted therapy: a novel strategy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver cancer with high morbidity and mortality worldwide. Chemotherapy is recommended to patients with intermediate or advanced stage cancer. However, the conventional chemotherapy yields low desired response rates due to multidrug resistance, fast clearance rate, nonspecific delivery, severe side effects, low drug concentration in cancer cells, and so on. Nanoparticle-mediated targeted drug delivery system can surmount the aforementioned obstacles through enhanced permeability and retention effect and active targeting as a novel approach of therapeutics for HCC in recent years. The active targeting is triggered by ligands on the delivery system, which recognize with and internalize into hepatoma cells with high specificity and efficiency. This review focuses on the latest targeted delivery systems for HCC and summarizes the ligands that can enhance the capacity of active targeting, to provide some insight into future research in nanomedicine for HCC.

Aberrant Splicing in Cancer: Mediators of Malignant Progression through an Imperfect Splice Program Shift

Although the efforts to understand the genetic basis of cancer allowed advances in diagnosis and therapy, little is known about other molecular bases. Splicing is a key event in gene expression, controlling the excision of introns decoded inside genes and being responsible for 80% of the proteome amplification through events of alternative splicing. Growing data from the last decade point to deregulation of splicing events as crucial in carcinogenesis and tumor progression. Several alterations in splicing events were observed in cancer, caused by either missexpression of or detrimental mutations in some splicing factors, and appear to be critical in carcinogenesis and key events during tumor progression. Notwithstanding, it is difficult to determine whether it is a cause or consequence of cancer and/or tumorigenesis. Most reviews focus on the generated isoforms of deregulated splicing pattern, while others mainly summarize deregulated splicing factors observed in cancer. In this review, events associated with carcinogenesis and tumor progression mainly, and epithelial-to-mesenchymal transition, which is also implicated in alternative splicing regulation, will be progressively discussed in the light of a new perspective, suggesting that splicing deregulation mediates cell reprogramming in tumor progression by an imperfect shift of the splice program.

Incorporation of Peptides Targeting EGFR and FGFR1 into the Adenoviral Fiber Knob Domain and Their Evaluation as Targeted Cancer Therapies

Oncolytic virotherapies based on adenovirus 5 (Ad5) hold promise as adjunctive cancer therapies; however, their efficacy when delivered systemically is hampered by poor target cell specificity and preexisting anti-Ad5 immunity. Ovarian cancer represents a promising target for virotherapy, since the virus can be delivered locally into the peritoneal cavity. Both epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor 1 (FGFR1) are overexpressed in the majority of human tumors, including ovarian cancer. To generate adenoviral vectors with improved tumor specificity, we generated a panel of Ad5 vectors with altered tropism for EGFR and FGFR, rather than the natural Ad5 receptor, hCAR. We have included mutations within AB loop of the viral fiber knob (KO1 mutation) to preclude interaction with hCAR, combined with insertions in the HI loop to incorporate peptides that bind either EGFR (peptide YHWYGYTPQNVI, GE11) or FGFR1 (peptides MQLPLAT, M*, and LSPPRYP, LS). Viruses were produced to high titers, and the integrity of the fiber protein was validated by Western blotting. The KO1 mutation efficiently ablated hCAR interactions, and significantly increased transduction was observed in hCAR^low/EGFR^high cell lines using Ad5.GE11, while transduction levels using Ad5.M* or Ad5.LS were not increased. In the presence of physiological concentrations of human blood clotting factor X (hFX), significantly increased levels of transduction via the hFX-mediated pathway were observed in cell lines, but not in primary tumor cells derived from epithelial ovarian cancer (EOC) ascites samples. Ad5-mediated transduction of EOC cells was completely abolished by the presence of 2.5% serum from patients, while, surprisingly, incorporation of the GE11 peptide resulted in significant evasion of neutralization in the same samples. We thus speculate that incorporation of the YHWYGYTPQNVI dodecapeptide within the fiber knob domain may provide a novel means of circumventing preexisting Ad5 immunity that warrants further investigation.

Low molecular weight polyethylenimine as a transgenic vector for tumor gene therapy

We constructed a polymer composed of a series of small molecule polyethylenimine (PEI) using 4-arm polyethylenimine (PEG) as a core for tumor gene therapy. N,N'-carbonyldiimidazole and N-succinimidyl-3-(2-pyridyldithio) propionate were used as chemical connecting reagents to synthesize 4-arm PEG-PEI2000 and 4-arm PEG-PEI2000-MC11. Chemical characterization was performed using (1)H-NMR. The retardation effect of polymers on plasmid DNA was observed using electrophoretic mobility shift and MTT assays to test the toxicity of the polymers. The gene delivery capability of 4-arm PEG-PEI2000 and 4-arm PEG-PEI2000-MC11, and the effect of MC11 were determined by an in vitro gene delivery experiment with human hepatoma HepG2 cells. At a N:P ratio of 3, the 4-arm PEG-PEI2000 could retard successfully plasmid DNA with low toxicity. In experiments in vitro, when the N:P ratio was 30, the gene delivery efficiency of 4-arm PEG-PEI2000 in HepG2 cells was five times that of PEI2000; After connecting ligand MC11, however, the gene delivery efficiency was twice as great. Free MC11 effectively inhibited the gene delivery efficiency of the 4-arm PEG-PEI2000-MC11. Four-arm PEG-PEI2000 has low toxicity and high gene delivery efficiency, and is an effective gene delivery vector after linking ligand MC11.

Identification of a novel peptide that blocks basic fibroblast growth factor-mediated cell proliferation

Basic fibroblast growth factor (bFGF) has been implicated in tumor growth via interactions with its receptors (FGFRs) on the cell surface and therefore, bFGF/FGFRs are considered essential targets for cancer therapy. Herein, a consensus heptapeptide (LSPPRYP) was identified for the first time from a phage display heptapeptide library after three sequential rounds of biopanning against FGFR-expressing cells with competitive displacement of phage by bFGF, followed by subtraction of non-specific binding by FGFR-deficient cells. Phage bearing LSPPRYP showed high levels of binding to Balb/c 3T3 cells expressing high-affinity bFGF-binding FGFR (bFGFR), but not to the cells that do not express bFGFR (Cos-7), or express a very low affinity bFGFR (HaCat). The selected-phage-derived peptide synthesized by solid phase method using a rapid and practical Fmoc strategy was found to specifically compete with bFGF for binding to its receptors, inhibit bFGF-stimulated cell proliferation by inducing cell cycle arrest, and block bFGF-induced activation of Erk1 and Erk2 kinase in B16-F10 melanoma cells. Importantly, treatment of melanoma-bearing mice with the synthetic peptide significantly suppressed tumor growth. The results demonstrate a strong anticancer activity of the isolated bFGFR-binding peptide (and its future derivatives), which may have great potential for cancer therapy.

Vascular-homing peptides for targeted drug delivery and molecular imaging: meeting the clinical challenges

The vasculature of each organ expresses distinct molecular signatures critically influenced by the pathological status. The heterogeneous profile of the vascular beds has been successfully unveiled by the in vivo phage display, a high-throughput tool for mapping normal, diseased, and tumor vasculature. Specific challenges of this growing field are targeted therapies against cancer and cardiovascular diseases, as well as novel bioimaging diagnostic tools. Tumor vasculature-homing peptides have been extensively evaluated in several preclinical and clinical studies both as targeted-therapy and diagnosis. To date, results from several Phase I and II trials have been reported and many other trials are currently ongoing or recruiting patients. In this review, advances in the identification of novel peptide ligands and their corresponding receptors on tumor endothelium through the in vivo phage display technology are discussed. Emphasis is given to recent findings in the clinical setting of vascular-homing peptides selected by in vivo phage display for the treatment of advanced malignancies and their altered vascular beds.

Differential effects of a soluble or immobilized VEGFR-binding peptide

Regulating endothelial cell behavior is a key step in understanding and controlling neovascularization for both pro-angiogenic and anti-angiogenic therapeutic strategies. Here, we characterized the effects of a covalently immobilized peptide mimic of vascular endothelial growth factor, herein referred to as VEGF receptor-binding peptide (VR-BP), on human umbilical vein endothelial cell (HUVEC) behavior. Self-assembled monolayer arrays presenting varied densities of covalently immobilized VR-BP and varied densities of the fibronectin-derived cell adhesion peptide Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) were used to probe for changes in HUVEC attachment, proliferation and tubulogenesis. In a soluble form, VR-BP exhibited pro-angiogenic effects in agreement with previous studies, indicated by increases in HUVEC proliferation. However, when presented to cells in an insoluble context, covalently immobilized VR-BP inhibited several pro-angiogenic HUVEC behaviors, including attachment and proliferation, and also inhibited HUVEC response to soluble recombinant VEGF protein. Furthermore, substrates with covalently immobilized VR-BP also modulated HUVEC tubulogenesis when a matrigel overlay assay was used to provide cells with a pseudo-three dimensional environment. Taken together, these results demonstrate that the context in which ligands are presented to cell surface receptors strongly influences their effects, and that the same ligand can be an agonist or an antagonist depending on the manner of presentation to the cell.

Landscape phages and their fusion proteins targeted to breast cancer cells

Breast cancer is a leading cause of death among women in the USA. The efficacy of existing anticancer therapeutics can be improved by targeting them through conjugation with ligands binding to cellular receptors. Recently, we developed a novel drug targeting strategy based on the use of pre-selected cancer-specific 'fusion pVIII proteins' (fpVIII), as targeting ligands. To study the efficiency of this approach in animal models, we developed a panel of breast cancer cell-binding phages as a source of targeted fpVIIIs. Two landscape phage peptide libraries (8-mer f8/8 and 9-mer f8/9) were screened to isolate 132 phage variants that recognize breast carcinoma cells MCF-7 and ZR-75-1 and internalize into the cells. When tested for their interaction with the breast cancer cells in comparison with liver cancer cells HepG2, human mammary cells MCF-10A cells and serum, 16 of the phage probes selectively interacted with the breast cancer cells whereas 32 bound both breast and liver cancer cells. The most prominent cancer-specific phage DMPGTVLP, demonstrating sub-nanomolar Kd in interaction with target cells, was used for affinity chromatography of cellular membrane molecules to reveal its potential binding receptor. The isolated protein was identified by direct sequencing as cellular surface nucleolin. This conclusion was confirmed by inhibition of the phage-cell interaction with nucleolin antibodies. Other prominent phage binders VPTDTDYS, VEEGGYIAA, and DWRGDSMDS demonstrate consensus motifs common to previously identified cancer-specific peptides. Isolated phage proteins exhibit inherent binding specificity towards cancer cells, demonstrating the functional activity of the selected fused peptides. The selected phages, their peptide inserts and intact fusion proteins can serve as promising ligands for the development of targeted nanomedicines and their study in model mice with xenograft of human cells MCF-7 and ZR-75-1.

FGF receptor-mediated gene delivery using ligands coupled to PEI-β-CyD

A novel vector with high gene delivery efficiency and special cell-targeting ability was developed using a good strategy that utilized low-molecular-weight polyethylenimine (PEI; molecular weight: 600 KDa [PEI600]) crosslinked to β-cyclodextrin (β-CyD) via a facile synthetic route. Fibroblast growth factor receptors (FGFRs) are highly expressed in a variety of human cancer cells and are potential targets for cancer therapy. In this paper, CY11 peptides, which have been proven to combine especially with FGFRs on cell membranes were coupled to PEI-β-CyD using N-succinimidyl-3-(2-pyridyldithio) propionate as a linker. The ratios of PEI600, β-CyD, and peptide were calculated based on proton integral values obtained from the (1)H-NMR spectra of the resulting products. Electron microscope observations showed that CY11-PEI-β-CyD can efficiently condense plasmid DNA (pDNA) into nanoparticles of about 200 nm, and MTT assays suggested the decreased toxicity of the polymer. Experiments on gene delivery efficiency in vitro showed that CY11-PEI-β-CyD/pDNA polyplexes had significantly greater transgene activities than PEI-β-CyD/pDNA in the COS-7 and HepG2 cells, which positively expressed FGFR, whereas no such effect was observed in the PC-3 cells, which negatively expressed FGFR. Our current research indicated that the synthesized nonviral vector shows improved gene delivery efficiency and targeting specificity in FGFR-positive cells.

Dual-targeting non-viral vector based on polyethylenimine improves gene transfer efficiency

Polyethylenimine (PEI) is the polymer most commonly used for transferring plasmids into eukaryotes, but its gene-transfer efficiency is lower compared to viral vectors. Receptors targeting PEI combined with ligands can enhance efficiency of gene transfer into the corresponding receptor-positive cells. Using the double-receptor-mediated pathway of viral infection, in this study we synthesized a novel non-viral vector based on PEI combined with two peptides recognizing FGF receptors (peptide YC25) and integrins (peptide CP9) on the cell surface. The dual targeting vector showed a physicochemical character similar to that of PEI, such as pDNA formation, particle size, zeta potential and lower toxicity. In vitro gene transfer showed that the dual-receptor targeted vector (YC25-PEI-CP9) exhibited a markedly higher transgene efficiency in cell lines with positive expression of FGF receptors and integrins, compared with single-peptide-modified PEI or unmodified PEI. In the cells with only integrin-positive expression, YC25-PEI-CP9 mediated a higher transgene expression than PEI but lower than CP9-PEI. The corresponding free peptides could inhibit the transgene efficiency of the peptide-coupled PEI. In vivo gene transfer in tumor-bearing nude mice also demonstrated that the dual-targeting vectors showed a significantly enhanced transfection efficiency in tumors with positive expression of FGF receptors and integrins. The synthesized polymer YC25-PEI-CP9 has the prospect to act as a novel kind of non-viral vector in gene therapy.

Ag-bearing liposomes engrafted with peptides that interact with CD11c/CD18 induce potent Ag-specific and antitumor immunity

Dendritic cells (DCs) play key role in eliciting antigen (Ag)-specific immune responses, and crucial to this is the uptake of Ag via surface receptors including the heterodimeric integrin CD11c/CD18. Here we report that CD11c/CD18-interacting peptides can be used as targeting moieties to deliver liposomal Ag to antigen presenting cells (APCs) and elicit Ag-specific and antitumor immunity. Two peptides of sequence related to human ICAM-4 and previously reported to bind CD11c/CD18, and a 12-mer cyclic peptide previously identified by phage display to bind CD11c/CD18, were produced synthetically, and tested for their ability to target liposomal Ag. The three peptides were designed to contain a shorter spacer to reduce steric hindrance, and a His-tag to enable engraftment onto liposomes incorporated with chelator lipid. Our results show that the three peptides, denoted as p17, p18 and p30, promote strong binding of liposomes to CD11c(+) and CD11b(+) cells in vitro and in vivo. Vaccination of mice with Ag-bearing liposomes engrafted with the peptides, particularly p18 and p30, induced Ag-specific T cell priming and antibody production. Importantly, the vaccination of C57BL/6 mice with syngeneic B16-OVA-derived plasma membrane vesicles (PMVs) engrafted with p18 and p30 peptide showed dramatic antitumor responses, inhibiting tumor growth/metastasis in both the lung and subcutaneous tumor models, with a high proportion of the mice apparently being "cured" of their tumors. The engraftment of p18 and p30 peptides onto liposomes and PMVs, thus provides an effective means to target Ags to DCs in vivo, for the development of effective cancer vaccines and immunotherapies.

Exploiting Surface Plasmon Resonance (SPR) Technology for the Identification of Fibroblast Growth Factor-2 (FGF2) Antagonists Endowed with Antiangiogenic Activity

Angiogenesis, the process of new blood vessel formation, is implicated in various physiological/pathological conditions, including embryonic development, inflammation and tumor growth. Fibroblast growth factor-2 (FGF2) is a heparin-binding angiogenic growth factor involved in various physiopathological processes, including tumor neovascularization. Accordingly, FGF2 is considered a target for antiangiogenic therapies. Thus, numerous natural/synthetic compounds have been tested for their capacity to bind and sequester FGF2 in the extracellular environment preventing its interaction with cellular receptors. We have exploited surface plasmon resonance (SPR) technique in search for antiangiogenic FGF2 binders/antagonists. In this review we will summarize our experience in SPR-based angiogenesis research, with the aim to validate SPR as a first line screening for the identification of antiangiogenic compounds.

Ligand-directed cancer gene therapy to angiogenic vasculature

Gene therapy strategies in cancer have remained an active area of preclinical and clinical research. One of the current limitations to successful trials is the relative transduction efficiency to produce a therapeutic effect. While intratumoral injections are the mainstay of many treatment regimens to date, this approach is hindered by hydrostatic pressures within the tumor and is not always applicable to all tumor subtypes. Vascular-targeting strategies introduce an alternative method to deliver vectors with higher local concentrations and minimization of systemic toxicity. Moreover, therapeutic targeting of angiogenic vasculature often leads to enhanced bystander effects, improving efficacy. While identification of functional and systemically accessible molecular targets is challenging, approaches, such as in vivo phage display and phage-based viral delivery vectors, provide a platform upon which vascular targeting of vectors may become a viable and translational approach.

Identification of oligopeptide binding to colon cancer cells separated from patients using laser capture microdissection

The development of intravascular conjugates that efficiently deliver genes or drugs to tumors is limited by the lack of efficacious targeting ligands. Small targeting peptides, such as those iterated by phage display technology, offer enormous potential for these applications. The majority of reports published to date have focused on the identification of peptides isolated for their ability to bind to human cancer cell lines in vitro, and have failed to account for the loss of polarization and de-differentiation of such cells from their in vivo state. Here, we report a novel approach for the identification of peptides capable of binding specifically to cancer cells derived from clinically resected human colon cancer. In this strategy, laser capture microdissection (LCM) is performed on a surgically resected colon cancer specimen to separate only cancer cells from the specimen. Subsequently, biopanning was performed on the LCM-selected colon cancer cells to identify peptide sequences that bound specifically to them. A peptide containing the SPT motif was selected as the most promising consensus sequence binding specifically to the LCM-selected colon cancer cells. Phage clones displaying the SPT motif demonstrated 9-fold higher binding to colon cancer cells derived from a patient than insertless phage (p < 0.05), while, recovery of the SPT phage from the colon cancer cell lines DLD-1 and HCT-15 was 7-fold higher than that of the control insertless phage (p < 0.05). The binding of SPT phage to colon cancer cells from the patient was confirmed by immunofluorescence. Additionally, a synthesized SPT-containing peptide (SPTKSNS) showed binding activity in the absence of mitogenic effects on colon cancer cells in vitro. In summary, we have introduced LCM into a biopanning procedure and identified a small peptide that binds preferentially to colon cancer cells derived from a clinically resected sample. This procedure could be applicable for the design of customized cancer cell targeting methodologies using clinical biopsy samples from human subjects.

Progress in developing cationic vectors for non-viral systemic gene therapy against cancer

Initially, gene therapy was viewed as an approach for treating hereditary diseases, but its potential role in the treatment of acquired diseases such as cancer is now widely recognized. The understanding of the molecular mechanisms involved in cancer and the development of nucleic acid delivery systems are two concepts that have led to this development. Systemic gene delivery systems are needed for therapeutic application to cells inaccessible by percutaneous injection and for multi-located tumor sites, i.e. metastases. Non-viral vectors based on the use of cationic lipids or polymers appear to have promising potential, given the problems of safety encountered with viral vectors. Using these non-viral vectors, the current challenge is to obtain a similarly effective transfection to viral ones. Based on the advantages and disadvantages of existing vectors and on the hurdles encountered with these carriers, the aim of this review is to describe the "perfect vector" for systemic gene therapy against cancer.

Phage peptide display

Molecular imaging is at the forefront in the advancement of in-vivo diagnosis and monitoring of cancer. New peptide-based molecular probes to facilitate cancer detection are rapidly evolving. Peptide-based molecular probes that target apoptosis, angiogenesis, cell signaling and cell adhesion events are in place. Bacteriophage (phage) display technology, a molecular genetic approach to ligand discovery, is commonly employed to identify peptides as tumor-targeting molecules. The peptide itself may perhaps have functional properties that diminish tumor growth or metastasis. More often, a selected peptide is chemically synthesized, coupled to a radiotracer or fluorescent probe, and utilized in the development of new noninvasive molecular imaging probes. A myriad of peptides that bind cancer cells and cancer-associated antigens have been reported from phage library selections. Phage selections have also been performed in live animals to obtain peptides with optimal stability and targeting properties in vivo. To this point, few in-vitro, in-situ, or in-vivo selected peptides have shown success in the molecular imaging of cancer, the notable exception being vascular targeting peptides identified via in-vivo selections. The success of vasculature targeting peptides, such as those with an RGD motif that bind alpha(v)beta(3)integrin, may be due to the abundance and expression patterns of integrins in tumors and supporting vasculature. The discovery of molecular probes that bind tumor-specific antigens has lagged considerably. One promising means to expedite discovery is through the implementation of selected phage themselves as tumor-imaging agents in animals.

Bacteriophage biopanning in human tumour biopsies to identify cancer-specific targeting ligands

Intravenous targeting of anticancer agents should improve both efficacy and therapeutic index. However, rational design of targeting constructs requires detailed definition of receptor targets and must take account of polarised tissue architecture that may restrict access to chosen receptors from the bloodstream. Bacteriophage biopanning provides a solution to this problem, identifying targeting sequences by functional selection rather than design, although reiterative panning in polarized human tumours has not previously been attempted. Here, we report an ex vivo, intra-arterial method for biopanning in freshly-resected human tumours, enabling reiterative selection of oligopeptide sequences capable of intravascular targeting to human colorectal tumours. Significant consensus was observed after two rounds of panning in tumours from different patients, and lead sequences demonstrated tumour targeting in samples from unrelated patients. This novel approach may be applicable to a wide range of settings, thus enabling iteration of consensus targeting sequences for tumour imaging and selective delivery of anticancer agents.

Identification of an Oligopeptide Binding to Hepatocellular Carcinoma

OBJECTIVES

We carried out identification of a small peptide binding to human hepatocellular carcinoma (HCC) cells with the aim of applying the peptide for future HCC-targeted therapy or imaging.

METHODS

The biopanning technique using phage peptide display libraries was performed on HCC cells in vitro, and a phage clone expressing the HCC-binding peptide motif was selected. The binding activity of the selected phage was evaluated by plaque infection assay and immunofluorescence on cell lines. In addition, the binding activity of the peptide-expressing phage was investigated using HCC specimens derived from patients who had undergone hepatectomy for HCC.

RESULTS

A heptapetide, Thr-Thr-Pro-Arg-Asp-Ala-Tyr (TTPRDAY), was identified as a motif binding to HCC. TTPRDAY bound specifically to HCC cells in comparison with other cancer cells, and the binding to HCC cells was also confirmed by immunofluorescence. In addition, the synthesized TTPRDAY peptide showed binding activity and a non-mitogenic effect on HCC cells in vitro. TTPRDAY-presenting phage showed more significant binding to HCC cells derived from specimens obtained from actual patients than to non-cancerous liver tissue.

CONCLUSION

The motif TTPRDAY, identified by the biopanning technique, shows significant binding to HCC cells.

FGF Receptor-mediated Gene Delivery using Ligands Coupled to Polyethylenimine

To obtain new nonviral vectors with high gene delivery efficiency and special cell targeting ability, an attractive strategy is to link ligands to polyethylenimine (PEI). Fibroblast growth factor receptors (FGFRs) are highly expressed on a variety of human cancer cells and are potential targets for cancer gene therapy. In this study, the peptides NH2-Met-Gln-Leu-Pro-Leu-Ala-ThrGly-Gly-Gly-Cys-COOH (MC11) which have been proved to combine specially with the FGFR on cell membrane are coupled to PEI using N-Succinimidyl-3-(2-pyridyldithio) propionate (SPDP) as a linker with different molar ratios (1 : 0.3, 1 : 0.75, 1 : 1.5, and 1 : 3.0) and the new polymer PEI-MC11 is verified by a series of physicochemical methods including 1H-NMR and FTIR. The agarose gel electrophoresis assay, particle size test, zeta potential test, and electron microscope observation show that PEI-MC11 can efficiently condense plasmid DNA into nanoparticles with about 200 nm in diameter and with positive surface charge at the suitable N/P ratio. The MTT assay suggests the decreased toxicity of the polymers. The results of the gene delivery efficiency in vitro show that PEI-MC11/pDNA polyplexes have significantly greater transgene activity than PEI/pDNA in COS-7 and HepG2 cells which express FGFR positively, while no such effect is observed in PC3 cells which have negative FGFR. The enhanced gene delivery efficiency of PEI-MC11 can be blocked by the co-culture of free peptides MC11 before the gene delivery procedure. The synthesized nonviral vector based on PEI with the targeting peptides MC11 for binding FGFR has improved efficiency of gene delivery and targeting specificity in FGFR positive cells. It may have potential application in cancer gene therapy.

Identification of oligopeptides binding to peritoneal tumors of gastric cancer

This is a report of in vivo intraperitoneal biopanning, and we successfully identified a novel peptide to target the multiple peritoneal tumors of gastric cancer. A phage display library was injected directly into the abdominal cavity of mice bearing peritoneal tumors of human gastric cancer, and phages associated with the tumors were subsequently reclaimed from isolated samples. The tumor-associated phages were amplified and the biopanning cycle was repeated five times to enrich for high affinity tumor-selective binding peptides. Finally, a tri-peptide motif, KLP, which showed homology with laminin 5 (a ligand for alpha3beta1 integrin), was identified as a binding peptide for peritoneal tumors of gastric cancer. Phage clones displaying the sequence KLP showed 64-fold higher binding to peritoneal tumors than control phage and were preferentially distributed in tumors rather than in normal organs after intraperitoneal injection into mice. In addition, the KLP phages were more likely to bind to cancer cells in malignant ascites derived from a patient with recurrent gastric cancer. Synthesized peptide containing the motif KLP (SWKLPPS) also showed a strong binding activity to peritoneal tumors without cancer growth effect. Liposomes conjugated with SWKLPPS peptide appeared significantly more often in tumors than control liposomes after intraperitoneal injection into mice. Furthermore, modification of liposomes with SWKLPPS peptide enhanced the antitumor activity of adriamycin on gastric cancer cells. The peptide motif KLP seems a potential targeting ligand for the treatment of peritoneal metastasis of gastric cancer.

Importin beta: a novel autoantigen in human autoimmunity identified by screening random peptide libraries on phage

By screening random peptide libraries (RPLs) with sera of Type 1 diabetes (T1D) patients, we previously identified 5 disease-specific 'mimotopes' displayed on phages (phagotopes). We already characterised 1 phagotope (CH1p), as an epitope of human osteopontin, an autoantigen expressed within the somatostatin cells of human islets. In this paper, we report the characterization of the second phagotope, 195Dyn, by immunohistochemistry, Western Blotting and screening of a human islet cDNA library using rabbit anti-195Dyn antibodies. The 195Dyn mimotope was detected in human islets. The screening of a lambdagt11 cDNA library from human islets has identified a clone, which corresponded to human importin beta. ELISA detected autoantibodies against this protein in sera of around 60% of TD1 patients and in 30% of patients affected by other autoimmune diseases. In summary, RPLs technology proved again successful in identifying another novel autoantigen (importin beta), whose significance in the autoimmune process remains to be fully elucidated.

Designing scaffolds of peptides for phage display libraries

Phage display is a powerful method for the discovery of peptide ligands that are used for analytical tools, drug discovery, and target validations. Phage display technology can produce a huge number of peptides and generate novel peptide ligands. Recently, phage display technology has successfully managed to create peptide ligands that bind to pharmaceutically difficult targets such as the erythropoietin receptor. As a result of the structural analysis of their ligands, we found that the conformational design of peptides in library is important for selecting high-affinity ligands that bind to every target from a phage peptide library. Key issues concern constraints on the conformation of peptides on the phage and the development of chemically synthesized peptides derived from peptides on phage. This review discusses studies related to the conformation of peptides selected from phage display peptide libraries in addition to the conversion from peptides to non-peptides.

Targeted polymers for gene delivery

Over the past decade, significant research has been done in the area of polymer-mediated gene delivery. Synthesis of new polymers and modifications to existing polymers has resulted in polyplexes with improved in vitro and in vivo transfection efficiencies. Targeting has been an important aspect of this research, and various strategies for obtaining selective and enhanced gene delivery to the target site have been evaluated. This review covers the different aspects involved in polyplex targeting. Development of targeted polyplexes involves a careful consideration of the target site, the targeting ligand and the physicochemical properties of the polyplex itself. The need to redirect the polyplexes by using the 'shield and target' approach by reducing nonspecific interactions with negatively charged components, while conferring specificity by incorporating targeting ligands, is discussed. Basic chemistry involved in modifying polymers is covered and examples of targeting strategies used for tissue-specific gene delivery are discussed. Targeting is also discussed in the broader context of developing safe and effective polymeric vectors for in vivo gene delivery. Maximum benefit of targeting can be obtained when it is used as part of a multi-functional complex containing elements designed to improve gene delivery and reduce overall toxicity of the polyplex.

Combinatorial discovery of tumor targeting peptides using phage display

Peptides possess appropriate pharmacokinetic properties to serve as cancer imaging or therapeutic targeting agents. Currently, only a small number of rationally-derived, labeled peptide analogues that target only a limited subset of antigens are available. Thus, finding new cancer targeting peptides is a central goal in the field of molecular targeting. Novel tumor-avid peptides can be efficiently identified via affinity selections using complex random peptide libraries containing millions of peptides that are displayed on bacteriophage. In vitro and in situ affinity selections may be used to identify peptides with high affinity for the target antigen in vitro. Unfortunately, it has been found that peptides selected in vitro or in situ may not effectively target tumors in vivo due to poor peptide stability and other problems. To improve in vivo targeting, methodological combinatorial chemistry innovations allow selections to be conducted in the environment of the whole animal. Thus, new targeting peptides with optimal in vivo properties can be selected in vivo in tumor-bearing animals. In vivo selections have been proven successful in identifying peptides that target the vasculature of specific organs. In addition, in vivo selections have identified peptides that bind specifically to the surface of or are internalized into tumor cells. In the future, direct selection of peptides for cancer imaging may be expedited using genetically engineered bacteriophage libraries that encode peptides with intrinsic radiometal-chelation or fluorescent sequences.

Cyclic peptides selected by phage display mimic the natural epitope recognized by a monoclonal anti-colicin A antibody

A 10-mer random peptide library displayed on filamentous bacteriophage was used to determine the molecular basis of the interaction between the monoclonal anti-colicin A antibody 1C11 and its cognate epitope. Previous studies established that the putative epitope recognized by 1C11 antibody is composed of amino acid residues 19-25 (RGSGPEP) of colicin A. Using the phage display technique it was confirmed that the epitope of 1C11 antibody was indeed restricted to residues 19-25 and the consensus motif RXXXPEP was identified. Shorter consensus sequences (RXXPEP, RXXEP, KXXEP) were also selected. It was also demonstrated that the disulfide bond found in one group of the selected peptides was crucial for 1C11 antibody recognition. It was shown that cyclization of the peptides by disulfide bond formation could result in a structure that mimics the natural epitope of colicin A.

Clinical development of gene therapy for colorectal cancer

Colorectal cancer (CRC) is the second most common type of malignancy in Western nations. Improvements in surgical and radiotherapeutic techniques and the increased availability of new cytotoxic drugs have improved outcome, but 50% of patients still die from recurrent or metastatic disease. Several features of its natural history render CRC a good candidate for gene therapy. Techniques include gene replacement, virus-directed enzyme-prodrug therapy, immune manipulation and virotherapy, all of which have entered clinical trials.

Gene therapy for colorectal cancer

Colorectal cancer is an important public health problem worldwide. Gene therapy has therapeutic potential for patients with advanced or recurrent colorectal cancer, incurable by conventional treatments. To date, many strategies of gene therapy have been explored, including mutant gene correction, prodrug activation, immune stimulation and genetically-modified oncolytic viruses. Although the preclinical results of gene therapy for colorectal cancer have shown promise, gene therapy is still at an early stage of clinical development and has not yet shown a significant therapeutic benefit for patients. The main obstacles for introduction of gene therapy to patients are poor targeting selectivity of the vectors and inefficient gene transfer. As the science supporting tumour-selective vectors evolves, gene therapy may expand rapidly in the clinical practice of colorectal cancer treatment.