RGD peptide in cancer targeting: Benefits, challenges, solutions, and possible integrin-RGD interactions

RGD peptide can be found in cell adhesion and signaling proteins, such as fibronectin, vitronectin, and fibrinogen. RGD peptides' principal function is to facilitate cell adhesion by interacting with integrin receptors on the cell surface. They have been intensively researched for use in biotechnology and medicine, including incorporation into biomaterials, conjugation to medicinal molecules or nanoparticles, and labeling with imaging agents. RGD peptides can be utilized to specifically target cancer cells and the tumor vasculature by engaging with these integrins, improving drug delivery efficiency and minimizing adverse effects on healthy tissues. RGD-functionalized drug carriers are a viable option for cancer therapy as this focused approach has demonstrated promise in the future. Writing a review on the RGD peptide can significantly influence how drugs are developed in the future by improving our understanding of the peptide, finding knowledge gaps, fostering innovation, and making drug design easier.

FITC-Labeled RGD Peptides as Novel Contrast Agents for Functional Fluorescent Angiographic Detection of Retinal and Choroidal Neovascularization

The development of choroidal neovascularization (CNV) is a crucial factor in the pathophysiology and prognosis of exudative age-related macular degeneration (AMD). Therefore, the detection of CNV is essential for establishing an appropriate diagnosis and treatment plan. Current ophthalmic imaging techniques, such as fundus fluorescent angiography and optical coherence tomography, have limitations in accurately visualizing CNV lesions and expressing CNV activity, owing to issues such as excessive dye leakage with pooling and the inability to provide functional information. Here, using the arginine-glycine-aspartic acid (RGD) peptide's affinity for integrin α_vβ₃, which is expressed in the neovascular endothelial cells in ocular tissues, we propose the use of fluorescein isothiocyanate (FITC)-labeled RGD peptide as a novel dye for effective molecular imaging of CNV. FITC-labeled RGD peptides (FITC-RGD₂), prepared by bioconjugation of one FITC molecule with two RGD peptides, demonstrated better visualization and precise localization of CNV lesions than conventional fluorescein dyes in laser-induced CNV rodent models, as assessed using various imaging techniques, including a commercially available clinical fundus camera (Optos). These results suggest that FITC-RGD₂ can serve as an effective novel dye for the diagnosis of neovascular retinal diseases, including AMD, by enabling early detection and treatment of disease occurrence and recurrence after treatment.

Use of Chitosan from Southern King Crab to Develop Films Functionalized with RGD Peptides for Potential Tissue Engineering Applications

Southern King Crab (SKC) represents an important fishery resource that has the potential to be a natural source of chitosan (CS) production. In tissue engineering, CS is very useful to generate biomaterials. However, CS has a lack of signaling molecules that facilitate cell-substrate interaction. Therefore, RGD (arginine-glycine-aspartic acid) peptides corresponding to the main integrin recognition site in extracellular matrix proteins have been used to improve the CS surface. The aim of this study was to evaluate in vitro cell adhesion and proliferation of CS films synthesized from SKC shell wastes functionalized with RGD peptides. The FTIR spectrum of CS isolated from SKC shells (SKC-CS) was comparable to commercial CS. Thermal properties of films showed similar endothermic peaks at 53.4 and 53.0 °C in commercial CS and SKC-CS, respectively. The purification and molecular masses of the synthesized RGD peptides were confirmed using HPLC and ESI-MS mass spectrometry, respectively. Mouse embryonic fibroblast cells showed higher adhesion on SKC-CS (1% w/v) film when it was functionalized with linear RGD peptides. In contrast, a cyclic RGD peptide showed similar adhesion to control peptide (RDG), but the highest cell proliferation was after 48 h of culture. This study shows that functionalization of SKC-CS films with linear or cyclic RGD peptides are useful to improve effects on cell adhesion or cell proliferation. Furthermore, our work contributes to knowledge of a new source of CS to synthesize constructs for tissue engineering applications.

Enzymatic Late-Stage Halogenation of Peptides

The late-stage site-selective derivatisation of peptides has many potential applications in structure-activity relationship studies and postsynthetic modification or conjugation of bioactive compounds. The development of orthogonal methods for C-H functionalisation is crucial for such peptide derivatisation. Among them, biocatalytic methods are increasingly attracting attention. Tryptophan halogenases emerged as valuable catalysts to functionalise tryptophan (Trp), while direct enzyme-catalysed halogenation of synthetic peptides is yet unprecedented. Here, it is reported that the Trp 6-halogenase Thal accepts a wide range of amides and peptides containing a Trp moiety. Increasing the sequence length and reaction optimisation made bromination of pentapeptides feasible with good turnovers and a broad sequence scope, while regioselectivity turned out to be sequence dependent. Comparison of X-ray single crystal structures of Thal in complex with d-Trp and a dipeptide revealed a significantly altered binding mode for the peptide. The viability of this bioorthogonal approach was exemplified by halogenation of a cyclic RGD peptide.

RGD Nanoarrays with Nanospacing Gradient Selectively Induce Orientation and Directed Migration of Endothelial and Smooth Muscle Cells

Directed migration of cells through cell-surface interactions is a paramount prerequisite in biomaterial-induced tissue regeneration. However, whether and how the nanoscale spatial gradient of adhesion molecules on a material surface can induce directed migration of cells is not sufficiently known. Herein, we employed block copolymer micelle nanolithography to prepare gold nanoarrays with a nanospacing gradient, which were prepared by continuously changing the dipping velocity. Then, a self-assembly monolayer technique was applied to graft arginine-glycine-aspartate (RGD) peptides on the nanodots and poly(ethylene glycol) (PEG) on the glass background. Since RGD can trigger specific cell adhesion via conjugating with integrin (its receptor in the cell membrane) and PEG can resist protein adsorption and nonspecific cell adhesion, a nanopattern with cell-adhesion contrast and a gradient of RGD nanospacing was eventually prepared. In vitro cell behaviors were examined using endothelial cells (ECs) and smooth muscle cells (SMCs) as a demonstration. We found that SMCs exhibited significant orientation and directed migration along the nanospacing gradient, while ECs exhibited only a weak spontaneously anisotropic migration. The gradient response was also dependent upon the RGD nanospacing ranges, namely, the start and end nanospacings under a given distance and gradient. The different responses of these two cell types to the RGD nanospacing gradient provide new insights for designing cell-selective nanomaterials potentially used in cell screening, wound healing, etc.

Evidence That β1-Integrin Is Required for the Anti-Viability and Anti-Proliferative Effect of Resveratrol in CRC Cells

The β1-integrin receptor is broadly expressed on tumor and other cells in the tumor microenvironment (TME), and is an unfavorable prognostic factor for cancers. Nature-derived resveratrol has preventive and apoptotic effects on tumors, but whether resveratrol can exert its suppressive actions on TME-induced tumorigenesis through β1-integrin on the surface of CRC cells is still unknown. HCT116 or SW480 cells were exposed to inhibitory antibodies against β1-integrin, bacitracin (selective β1-integrin inhibitor), integrin-binding RGD (Arg-Gly-Asp) peptide, and/or resveratrol. We evaluated the anti-tumor actions and signaling impacts of resveratrol in colorectal cancer (CRC)-TME. We found that resveratrol completely altered the β1-integrin distribution pattern and expression on the surface of CRC cells in TME. Moreover, resveratrol down-regulated CRC cell proliferation, colony formation, viability, and up-regulated apoptosis in a concentration-dependent way. These actions of resveratrol were antagonized mainly by inhibitory antibodies against β1-integrin but not β5-integrin, and by an integrin-binding RGD peptide but not by RGE peptide, and by bacitracin in TME. Similarly, resveratrol-blocked TME-induced p65-NF-kB and its promoted gene markers linked to proliferation (cyclin D1), invasion (focal adhesion kinase, FAK), or apoptosis (caspase-3), were largely abrogated by anti-β1-integrin or RGD peptide, suggesting that β1-integrin is a potential transmission pathway for resveratrol/integrin down-stream signaling in CRC cells. The current results highlight, for the first time, the important gateway role of β1-integrins as signal carriers for resveratrol on the surfaces of HCT116 and SW480 cells, and their functional cooperation for the modulatory effects of resveratrol on TME-promoted tumorigenesis.

Impact of Different [Tc(N)PNP]-Scaffolds on the Biological Properties of the Small cRGDfK Peptide: Synthesis, In Vitro and In Vivo Evaluations

Background: The [^99mTc][Tc(N)(PNP)] system, where PNP is a bisphosphinoamine, is an interesting platform for the development of tumor ‘receptor-specific’ agents. Here, we compared the reactivity and impact of three [Tc(N)(PNP)] frameworks on the stability, receptor targeting properties, biodistribution, and metabolism of the corresponding [^99mTc][Tc(N)(PNP)]-tagged cRGDfK peptide to determine the best performing agent and to select the framework useful for the preparation of [^99mTc][Tc(N)(PNP)]-housing molecular targeting agents. Methods: cRGDfK pentapeptide was conjugated to Cys and labeled with each [Tc(N)(PNP)] framework. Radioconjugates were assessed for their lipophilicity, stability, in vitro and in vivo targeting properties, and performance. Results: All compounds were equally synthetically accessible and easy to purify (RCY ≥ 95%). The main influences of the synthon on the targeting peptide were observed in in vitro cell binding and in vivo. Conclusions: The variation in the substituents on the phosphorus atoms of the PNP enables a fine tuning of the biological features of the radioconjugates. ws[^99mTc][Tc(N)(PNP3OH)]– and [^99mTc][Tc(N)(PNP3)]– are better performing synthons in terms of labeling efficiency and in vivo performance than the [^99mTc][Tc(N)(PNP43)] framework and are therefore more suitable for further radiopharmaceutical purposes. Furthermore, the good labeling properties of the ws[^99mTc][Tc(N)(PNP3OH)]– framework can be exploited to extend this technology to the labeling of temperature-sensitive biomolecules suitable for SPECT imaging.

Membranes Prepared from Recombinant RGD-Silk Fibroin as Substrates for Human Corneal Cells

A recombinant formulation of silk fibroin containing the arginine–glycine–aspartic acid (RGD) cell-binding motif (RGD-fibroin) offers potential advantages for the cultivation of corneal cells. Thus, we investigated the growth of corneal stromal cells and epithelial cells on surfaces created from RGD-fibroin, in comparison to the naturally occurring Bombyx mori silk fibroin. The attachment of cells was compared in the presence or absence of serum over a 90 min period and analyzed by quantification of dsDNA content. Stratification of epithelial cells on freestanding membranes was examined by confocal fluorescence microscopy and optimized through use of low molecular weight poly(ethylene glycol) (PEG; 300 Da) as a porogen, the enzyme horseradish peroxidase (HRP) as a crosslinking agent, and stromal cells grown on the opposing membrane surface. The RGD-fibroin reduced the tendency of stromal cell cultures to form clumps and encouraged the stratification of epithelial cells. PEG used in conjunction with HRP supported the fabrication of more permeable freestanding RGD-fibroin membranes, that provide an effective scaffold for stromal–epithelial co-cultures. Our studies encourage the use of RGD-fibroin for corneal cell culture. Further studies are required to confirm if the benefits of this formulation are due to changes in the expression of integrins, components of the extracellular matrix, or other events at the transcriptional level.

Enlargement, Reduction, and Even Reversal of Relative Migration Speeds of Endothelial and Smooth Muscle Cells on Biomaterials Simply by Adjusting RGD Nanospacing

Although many tissue regeneration processes after biomaterial implantation are related to migrations of multiple cell types on material surfaces, available tools to adjust relative migration speeds are very limited. Herein, we put forward a nanomaterial strategy to employ surface modification with arginine-glycine-aspartate (RGD) nanoarrays to tune in vitro cell migration using endothelial cells (ECs) and smooth muscle cells (SMCs) as demonstrated cell types. We found that migrations of both cell types exhibited a nonmonotonic trend with the increase of RGD nanospacing, yet with different peaks-74 nm for SMCs but 95 nm for ECs. The varied sensitivities afford a facile way to regulate the relative migration speeds. Although ECs migrated at a speed similar to SMCs on a non-nano surface, the migration of ECs could be controlled to be significantly faster or slower than SMCs simply by adjusting the RGD nanospacing. This study suggests a potential application of surface modification of biomaterials on a nanoscale level.

[68Ga]Ga-DFO-c(RGDyK): Synthesis and Evaluation of Its Potential for Tumor Imaging in Mice

Angiogenesis has a pivotal role in tumor growth and the metastatic process. Molecular imaging was shown to be useful for imaging of tumor-induced angiogenesis. A great variety of radiolabeled peptides have been developed to target αvβ3 integrin, a target structure involved in the tumor-induced angiogenic process. The presented study aimed to synthesize deferoxamine (DFO)-based c(RGD) peptide conjugate for radiolabeling with gallium-68 and perform its basic preclinical characterization including testing of its tumor-imaging potential. DFO-c(RGDyK) was labeled with gallium-68 with high radiochemical purity. In vitro characterization including stability, partition coefficient, protein binding determination, tumor cell uptake assays, and ex vivo biodistribution as well as PET/CT imaging was performed. [⁶⁸Ga]Ga-DFO-c(RGDyK) showed hydrophilic properties, high stability in PBS and human serum, and specific uptake in U-87 MG and M21 tumor cell lines in vitro and in vivo. We have shown here that [⁶⁸Ga]Ga-DFO-c(RGDyK) can be used for αvβ3 integrin targeting, allowing imaging of tumor-induced angiogenesis by positron emission tomography.

Elucidating the Surface Functionality of Biomimetic RGD Peptides Immobilized on Nano-P(3HB-co-4HB) for H9c2 Myoblast Cell Proliferation

Biomaterial scaffolds play crucial role to promote cell proliferation and foster the regeneration of new tissues. The progress in material science has paved the way for the generation of ingenious biomaterials. However, these biomaterials require further optimization to be effectively used in existing clinical treatments. It is crucial to develop biomaterials which mimics structure that can be actively involved in delivering signals to cells for the formation of the regenerated tissue. In this research we nanoengineered a functional scaffold to support the proliferation of myoblast cells. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] copolymer is chosen as scaffold material owing to its desirable mechanical and physical properties combined with good biocompatibility, thus eliciting appropriate host tissue responses. In this study P(3HB-co-4HB) copolymer was biosynthesized using Cupriavidus malaysiensis USMAA1020 transformant harboring additional PHA synthase gene, and the viability of a novel P(3HB-co-4HB) electrospun nanofiber scaffold, surface functionalized with RGD peptides, was explored. In order to immobilize RGD peptides molecules onto the P(3HB-co-4HB) nanofibers surface, an aminolysis reaction was performed. The nanoengineered scaffolds were characterized using SEM, organic elemental analysis (CHN analysis), FTIR, surface wettability and their in vitro degradation behavior was evaluated. The cell culture study using H9c2 myoblast cells was conducted to assess the in vitro cellular response of the engineered scaffold. Our results demonstrated that nano-P(3HB-co-4HB)-RGD scaffold possessed an average fiber diameter distribution between 200 and 300 nm, closely biomimicking, from a morphological point of view, the structural ECM components, thus acting as potential ECM analogs. This study indicates that the surface conjugation of biomimetic RGD peptide to the nano-P(3HB-co-4HB) fibers increased the surface wettability (15 ± 2°) and enhanced H9c2 myoblast cells attachment and proliferation. In summary, the study reveals that nano-P(3HB-co-4HB)-RGD scaffold can be considered a promising candidate to be further explored as cardiac construct for building cardiac construct.

Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

Integrins are a family of cell surface receptors crucial to fundamental cellular functions such as adhesion, signaling, and viability, deeply involved in a variety of diseases, including the initiation and progression of cancer, of coronary, inflammatory, or autoimmune diseases. The natural ligands of integrins are glycoproteins expressed on the cell surface or proteins of the extracellular matrix. For this reason, short peptides or peptidomimetic sequences that reproduce the integrin-binding motives have attracted much attention as potential drugs. When challenged in clinical trials, these peptides/peptidomimetics let to contrasting and disappointing results. In the search for alternative utilizations, the integrin peptide ligands have been conjugated onto nanoparticles, materials, or drugs and drug carrier systems, for specific recognition or delivery of drugs to cells overexpressing the targeted integrins. Recent research in peptidic integrin ligands is exploring new opportunities, in particular for the design of nanostructured, micro-fabricated, cell-responsive, stimuli-responsive, smart materials.

Structure-Activity Relationship of RGD-Containing Cyclic Octapeptide and αvβ3 Integrin Allows for Rapid Identification of a New Peptide Antagonist

The αvβ3 integrin, a receptor for many extracellular matrix proteins with RGD-sequence motif, is involved in multiple physiological processes and highly expressed in tumor cells, therefore making it a target for cancer therapy and tumor imaging. Several RGD-containing cyclic octapeptide (named LXW analogs) were screened as αvβ3 antagonists with dramatically different binding affinity, and their structure–activity relationship (SAR) remains elusive. We performed systematic SAR studies and optimized LXW analogs to improve antagonistic potency. The NMR structure of LXW64 was determined and docked to the integrin. Structural comparison and docking studies suggested that the hydrophobicity and aromaticity of the X7 amino acid are highly important for LXW analogs binding to the integrin, a potential hydrophobic pocket on the integrin surface was proposed to play a role in stabilizing the peptide binding. To develop a cost-efficient and fast screening method, computational docking was performed on LXW analogs and compared with in vitro screening. A consistency within the results of both methods was found, leading to the continuous optimization and testing of LXW mutants via in silico screening. Several new LXW analogs were predicted as the integrin antagonists, one of which—LXZ2—was validated by in vitro examination. Our study provides new insight into the RGD recognition specificity and valuable clues for rational design of novel αvβ3 antagonists.

Size-Dependent Cellular Uptake of RGD Peptides

Monomeric RGD peptides show unspecific fluid-phase uptake in cells, whereas multimeric RGD peptides are thought to be internalized by integrin-mediated endocytosis. However, a potential correlation between uptake mechanism and molecular mass has been neglected so far. A dual derivatization of peptide c(RGDw(7Br)K) was performed to investigate this. A fluorescent probe was installed by chemoselective Suzuki-Miyaura cross-coupling of the 7-bromotryptophan and a poly(ethylene glycol) (PEG) linker was attached to the lysine residue. Flow cytometry and live cell imaging confirmed unspecific uptake of the small, non-PEGylated peptide, whereas the PEG5000 peptide conjugate unveiled a selective internalization by M21 cells overexpressing αv β3 and no uptake in αv -deficient M21L cells.

Peptide-Functionalized Nanostructured Microarchitectures Enable Rapid Mechanotransductive Differentiation

Microenvironmental factors play critical roles in regulating stem cell fate, providing a rationale to engineer biomimetic microenvironments that facilitate rapid and effective stem cell differentiation. Three-dimensional (3D) hierarchical microarchitectures have been developed to enable rapid neural differentiation of multipotent human mesenchymal stromal cells (HMSCs) via mechanotransduction. However, low cell viability during long-term culture and poor cell recovery efficiency from the architectures were also observed. Such problems hinder further applications of the architectures in stem cell differentiation. Here, we present improved 3D nanostructured microarchitectures functionalized with cell-adhesion-promoting arginylglycylaspartic acid (RGD) peptides. These RGD-functionalized architectures significantly upregulated long-term cell viability and facilitated effective recovery of differentiated cells from the architectures while maintaining high differentiation efficiency. Efficient recovery of highly viable differentiated cells enabled the downstream analysis of morphology and protein expression to be performed. Remarkably, even after the removal of the mechanical stimulus provided by the 3D microarchitectures, the recovered HMSCs showed a neuron-like elongated morphology for 10 days and consistently expressed microtubule-associated protein 2, a mature neural marker. RGD-functionalized nanostructured microarchitectures hold great potential to guide effective differentiation of highly viable stem cells.

Preclinical Evaluation of Radiolabeled Peptides for PET Imaging of Glioblastoma Multiforme

In this study, we have compared four ⁶⁸Ga-labeled peptides (three Arg-Gly-Asp (RGD) peptides and substance-P) with two ¹⁸F-tracers clinically approved for tumor imaging. We have studied in vitro and in vivo characteristics of selected radiolabeled tracers in a glioblastoma multiforme tumor model. The in vitro part of the study was mainly focused on the evaluation of radiotracers stability under various conditions. We have also determined in vivo stability of studied ⁶⁸Ga-radiotracers by analysis of murine urine collected at various time points after injection. The in vivo behavior of tested ⁶⁸Ga-peptides was evaluated through ex vivo biodistribution studies and PET/CT imaging. The obtained data were compared with clinically used ¹⁸F-tracers. ⁶⁸Ga-RGD peptides showed better imaging properties compared to ¹⁸F-tracers, i.e., higher tumor/background ratios and no accumulation in non-target organs except for excretory organs.

Synthesis and Biological Evaluation of RGD⁻Cryptophycin Conjugates for Targeted Drug Delivery

Cryptophycins are potent tubulin polymerization inhibitors with picomolar antiproliferative potency in vitro and activity against multidrug-resistant (MDR) cancer cells. Because of neurotoxic side effects and limited efficacy in vivo, cryptophycin-52 failed as a clinical candidate in cancer treatment. However, this class of compounds has emerged as attractive payloads for tumor-targeting applications. In this study, cryptophycin was conjugated to the cyclopeptide c(RGDfK), targeting integrin αvβ₃, across the protease-cleavable Val-Cit linker and two different self-immolative spacers. Plasma metabolic stability studies in vitro showed that our selected payload displays an improved stability compared to the parent compound, while the stability of the conjugates is strongly influenced by the self-immolative moiety. Cathepsin B cleavage assays revealed that modifications in the linker lead to different drug release profiles. Antiproliferative effects of Arg-Gly-Asp (RGD)⁻cryptophycin conjugates were evaluated on M21 and M21-L human melanoma cell lines. The low nanomolar in vitro activity of the novel conjugates was associated with inferior selectivity for cell lines with different integrin αvβ₃ expression levels. To elucidate the drug delivery process, cryptophycin was replaced by an infrared dye and the obtained conjugates were studied by confocal microscopy.

Biocompatibility of Small-Diameter Vascular Grafts in Different Modes of RGD Modification

Modification with Arg-Gly-Asp (RGD) peptides is a promising approach to improve biocompatibility of small-calibre vascular grafts but it is unknown how different RGD sequence composition impacts graft performance. Here we manufactured 1.5 mm poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) grafts modified by distinct linear or cyclic RGD peptides immobilized by short or long amine linker arms. Modified vascular prostheses were tested in vitro to assess their mechanical properties, hemocompatibility, thrombogenicity and endothelialisation. We also implanted these grafts into rat abdominal aortas with the following histological examination at 1 and 3 months to evaluate their primary patency, cellular composition and detect possible calcification. Our results demonstrated that all modes of RGD modification reduce ultimate tensile strength of the grafts. Modification of prostheses does not cause haemolysis upon the contact with modified grafts, yet all the RGD-treated grafts display a tendency to promote platelet aggregation in comparison with unmodified counterparts. In vivo findings identify that cyclic Arg-Gly-Asp-Phe-Lys peptide in combination with trioxa-1,13-tridecanediamine linker group substantially improve graft biocompatibility. To conclude, here we for the first time compared synthetic small-diameter vascular prostheses with different modes of RGD modification. We suggest our graft modification regimen as enhancing graft performance and thus recommend it for future use in tissue engineering.

An RGD-Containing Peptide Derived from Wild Silkworm Silk Fibroin Promotes Cell Adhesion and Spreading

Arginine-Glycine-Aspartate (RGD) tripeptide can promote cell adhesion when present in the amino acid of proteins such as fibronectin. In order to demonstrate the bioactivity of an RGD-containing silk protein, a gene encoding the RGD motif-containing peptide GSGAGGRGDGGYGSGSS (⁻RGD⁻) derived from nonmulberry silk was designed and cloned, then multimerised and inserted into a commercial pGEX expression vector for recombinant expression of (⁻RGD⁻)n peptides. Herein, we focus on two glutathione-S-transferase (GST)-tagged fusion proteins, GST⁻(⁻RGD⁻)₄ and GST⁻(⁻RGD⁻)₈, which were expressed in Escherichia coli BL21, purified by GST affinity chromatography, and analyzed with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MS). Target peptides (⁻RGD⁻)₄ and (⁻RGD⁻)₈ (6.03 and 11.5 kDa) were cleaved from the GST-tag by thrombin digestion, as verified with MS and SDS-PAGE. Isoelectric point analysis confirmed that target peptides were expressed and released in accordance with the original design. Target peptides self-assembled into a mainly α-helical structure, as determined by circular dichroism spectroscopy. Furthermore, (⁻RGD⁻)₄ and (⁻RGD⁻)₈ modified mulberry silk fibroin films were more effective for rapid cell adhesion, spreading and proliferative activity of L929 cells than some chemically synthesized RGD peptides modified and mulberry silk lacking the RGD motif.

Biodistribution and toxicity assessment of intratumorally injected arginine-glycine-aspartic acid peptide conjugated to CdSe/ZnS quantum dots in mice bearing pancreatic neoplasm

Quantum dots (QDs) conjugated with arginine-glycine-aspartic acid (RGD) peptides (which are integrin antagonists) are novel nanomaterials with the unique optical property of high molar extinction coefficient, and they have potential utility as photosensitizers in photodynamic therapy (PDT). Our group previously demonstrated significant benefits of using PDT with QD-RGD on pancreatic tumor cells. This study aimed to evaluate the biodistribution and toxicity of QD-RGD in mice prior to in vivo application. Mice with pancreatic neoplasms were intratumorally injected with varying doses of QD-RGD, and the biodistribution 0-24 h post injection was compared to that in control mice (intravenously injected with unconjugated QD). Various tissue samples were collected for toxicity analyses, which included inductively coupled plasma mass spectrometry (ICP-MS) to assess Cd²⁺ concentrations and hematoxylin-eosin staining for histopathological examination. Fluorescent imaging revealed relatively sufficient radiant efficiency in mice under specific conditions. The ICP-MS and HE data showed no significant signs of necrosis due to Cd²⁺ release by QDs. The mice survived well and had no apparent weakness or weight loss during the 4 weeks post injection. These findings provide novel insights into the biodistribution of QD-RGD and encourage profound in vivo studies regardless of safety concerns. These findings alleviate safety concerns and provide novel insights into the biodistribution of QD-RGD, offering a solid foundation for comprehensive in vivo studies.

In Vivo Characterization of 4 68Ga-Labeled Multimeric RGD Peptides to Image αvβ3 Integrin Expression in 2 Human Tumor Xenograft Mouse Models

α_vβ₃ integrins play an important role in angiogenesis and cell migration in cancer and are highly expressed on the activated endothelial cells of newly formed blood vessels. Here, we compare the targeting characteristics of 4 ⁶⁸Ga-labeled multimeric cyclic arginine-glycine-aspartate (RGD)-based tracers in an α_vβ₃ integrin-expressing tumor model and a tumor model in which α_vβ₃ integrin is expressed solely on the neovasculature. Methods: Female BALB/c nude mice were subcutaneously injected with SK-RC-52 (α_vβ₃ integrin-positive) or FaDu (α_vβ₃ integrin-negative) tumor cells. ⁶⁸Ga-labeled DOTA-(RGD)₂, TRAP-(RGD)₃, FSC-(RGD)₃, or THP-(RGD)₃ was intravenously administered to the mice (0.5 nmol per mouse, 10-20 MBq), followed by small-animal PET/CT imaging and ex vivo biodistribution studies 1 h after injection. Nonspecific uptake of the tracers in both models was determined by coinjecting an excess of unlabeled DOTA-(RGD)₂ (50 nmol) along with the radiolabeled tracers. Results: Imaging and biodistribution data showed specific uptake in the tumors for each tracer in both models. Tumor uptake of ⁶⁸Ga-FSC-(RGD)₃ was significantly higher than that of ⁶⁸Ga-DOTA-(RGD)₂, ⁶⁸Ga-TRAP-(RGD)₃, or ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 model but not in the FaDu model, in which ⁶⁸Ga-FSC-(RGD)₃ showed significantly higher tumor uptake than ⁶⁸Ga-TRAP-(RGD)₃ Most importantly, differences were also observed in normal tissues and in tumor-to-blood ratios. Conclusion: All tracers showed sufficient targeting of α_vβ₃ integrin expression to allow for tumor detection. Although the highest tumor uptake was found for ⁶⁸Ga-FSC-(RGD)₃ and ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 and FaDu models, respectively, selection of the optimal tracer for specific diagnostic applications also depends on tumor-to-blood ratio and uptake in normal tissues; these factors should therefore also be considered.

Conformational Equilibrium of Human Platelet Integrin Investigated by Three-Dimensional Electron Cryo-Microscopy

Integrins are bidirectional transmembrane receptors that play central roles in hemostasis and arterial thrombosis. They have been subject to structural studies for many years, in particular using X-ray crystallography, nuclear magnetic resonance spectroscopy, and two-dimensional negative stain electron microscopy. Despite considerable progress, a full consensus on the molecular mechanism of integrin activation is still lacking. Three-dimensional reconstructions of full-length human platelet integrin α_IIbβ₃ in lipid-bilayer nanodiscs obtained by electron cryo-microscopy and single-particle reconstruction have shed new light on the activation process. These studies show that integrin α_IIbβ₃ exists in a continuous conformational equilibrium ranging from a compact nodular conformation similar to that obtained in crystal structures to a fully extended state with the leg domains separated. This equilibrium is shifted towards the extended conformation when extracellular ligands, cytosolic activators and lipid-bilayer nanodiscs are added. Addition of cytosolic activators and extracellular ligands in the absense of nanodiscs produces significantly less dramatic shifts, emphasizing the importance of the membrane bilayer in the activation process.

A Systematic Comparative Evaluation of 68Ga-Labeled RGD Peptides Conjugated with Different Chelators

Purpose

The present paper reports a systematic study on the effect of bifunctional chelators (BFC) namely, NOTA, DOTA, and DTPA, on the radiochemical formulation, in vitro stability, and in vivo biological properties of ⁶⁸Ga-labeled RGD peptide derivatives.

Methods

The three RGD conjugates namely, NOTA-Bn-E-[c(RGDfk)]₂, DOTA-Bn-E-[c(RGDfk)]₂, and DTPA-Bn-E-[c(RGDfk)]₂ were radiolabeled with ⁶⁸Ga and the radiolabeling was optimized with respect to the ligand amount, radiolabeling time, and temperature. Further, the ⁶⁸Ga complexes were assessed for their in vitro and in vivo stabilities. The biodistribution studies of the three radiolabeled conjugates were carried out in C57BL/6 mice bearing melanoma tumor at 30 min and 1 h post-adimistration.

Results

NOTA-Bn-E-[c(RGDfk)]₂ could be radiolabeled with ⁶⁸Ga at room temperature while DOTA-Bn-E-[c(RGDfk)]₂ and DTPA-Bn-E-[c(RGDfk)]₂ were radiolabeled at high temperature. ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ was found to be the most kinetically rigid in in vitro stability assay. The uptake of the three radiolabeled peptide conjugates in melanoma tumor was comparable at 1 h post-administration (NOTA; DOTA; DTPA (% I.D./g):: 2.78 ± 0.38; 3.08 ± 1.1; 3.36 ± 0.49). However, the tumor/background ratio of ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ was the best amongst the three radiotracers. ⁶⁸Ga-complexes of NOTA-Bn-E-[c(RGDfk)]₂ and DOTA-Bn-E-[c(RGDfk)]₂ showed excellent in vivo stability while ⁶⁸Ga-DTPA-Bn-E-[c(RGDfk)]₂ showed significant metabolic degradation.

Conclusion

These studies show that ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ would be the most appropriate ⁶⁸Ga-labeled radiotracer and the most amenable for kit formulation.

Comparison of Ga-68-Labeled Fusarinine C-Based Multivalent RGD Conjugates and [(68)Ga]NODAGA-RGD-In Vivo Imaging Studies in Human Xenograft Tumors

PURPOSE

Multimeric arginine-glycine-aspartic acid (RGD) peptides have advantages for imaging integrin αvβ3 expression. Here, we compared the in vitro and in vivo behavior of three different Ga-68-labeled multimeric Fusarinine C-RGD (FSC-RGD) conjugates, whereby RGD was coupled directly, via a succinic acid or PEG linker (FSC(RGDfE)3, FSC(succ-RGD)3, FSC(Mal-RGD)3). The positron emission tomography/X-ray computed tomography (PET/CT) imaging properties were further compared using [(68)Ga]FSC(succ-RGD)3 with the monomeric [(68)Ga]NODAGA-RGD in a murine tumor model.

PROCEDURE

FSC-RGD conjugates were labeled with Ga-68, and stability properties were studied. For in vitro characterization, the partition coefficient, integrin αvβ3 binding affinity, and cell uptake were determined. To characterize the in vivo properties, biodistribution studies and microPET/CT were carried out using mice bearing either human M21/M21-L melanoma or human U87MG glioblastoma tumor xenografts.

RESULTS

All FSC-RGD conjugates were quantitatively labeled with Ga-68 within 10 min at RT. The [(68)Ga]FSC-RGD conjugates exhibited high stability and hydrophilic character, with only minor differences between the different conjugates. In vitro and in vivo studies showed enhanced integrin αvβ3 binding affinity, receptor-selective tumor uptake, and rapid renal excretion resulting in good imaging properties.

CONCLUSIONS

The type of linker between FSC and RGD had no pronounced effect on targeting properties of [(68)Ga]FSC-RGD trimers. In particular, [(68)Ga]FSC(succ-RGD)3 exhibited improved properties compared to [(68)Ga]NODAGA-RGD, making it an alternative for imaging integrin αvβ3 expression.

Probing the contractile vacuole as Achilles' heel of the biotrophic grapevine pathogen Plasmopara viticola

The causative agent of Grapevine Downy Mildew, the oomycete Plasmopara viticola, poses a serious threat to viticulture. In the current work, the contractile vacuole of the zoospore is analysed as potential target for novel plant protection strategies. Using a combination of electron microscopy, spinning disc confocal microscopy, and video differential interference contrast microscopy, we have followed the genesis and dynamics of this vacuole required during the search for the stomata, when the non-walled zoospore is exposed to hypotonic conditions. This subcellular description was combined with a pharmacological study, where the functionality of the contractile vacuole was blocked by manipulation of actin, by Na, Cu, and Al ions or by inhibition of the NADPH oxidase. We further observe that RGD peptides (mimicking binding sites for integrins at the extracellular matrix) can inhibit the function of the contractile vacuole as well. Finally, we show that an extract from Chinese liquorice (Glycyrrhiza uralensis) proposed as biocontrol for Downy Mildews can efficiently induce zoospore burst and that this activity depends on the activity of NADPH oxidase. The effect of the extract can be phenocopied by its major compound, glycyrrhizin, suggesting a mode of action for this biologically safe alternative to copper products.

Cyclic-RGD penta-peptides cRGDyK derivatized with cyclopentadienyl complexes of technetium and rhenium as radiopharmaceutical probes

The present study reports the syntheses of half-sandwich complexes of the type [M(η⁵ -C₅ H₄ CONH-R)(CO)₃ ] (M═Re,^99m Tc;R═cyclic RGD peptide (cRGDyK) for potential imaging of α_v β₃ integrin expression. The ^99m Tc complex was prepared directly from the reaction of [^99m Tc(OH₂ )₃ (CO)₃ ]⁺ with cRGDyK, doubly conjugated to Thiele's acid [(C₅ H₅ COOH)₂ ] in water. This approach extends the viability of metal-mediated retro Diels-Alder reactions for the preparation of small molecules such as linear tripeptides to a more complex cyclic peptide carrying a [(η⁵ -C₅ H₄ )^99m Tc(CO)₃ ] tag. The Diels-Alder product [(C₅ H₅ CONH-cRGDyK)₂ ] was prepared from Thiele's acid via double peptide coupling. The Re-complex [Re(η⁵ -C₅ H₄ CONH-cRGDyK)(CO)₃ ] was obtained by attaching [Re(η⁵ -C₅ H₄ COOH)(CO)₃ ] directly to the N-terminus of cRGDyK. The identity of the ^99m Tc-complex is confirmed by chromatographic comparison with the corresponding rhenium complex, fully characterized by spectroscopic techniques.

Effects of arginine-glycine-aspartic acid peptide-conjugated quantum dots-induced photodynamic therapy on pancreatic carcinoma in vivo

Quantum dots (QDs) conjugated with integrin antagonist arginine-glycine-aspartic acid (RGD) peptides (QDs-RGD) are novel nanomaterials with a unique optical property: a high molar extinction coefficient. Previously, we have shown that QDs-RGD demonstrate a photodynamic therapy (PDT) effect as new photosensitizers for the pancreatic cancer cell line SW1990 in vitro. Here, we investigate the application of QDs-RGD in mice bearing pancreatic tumors using PDT. To ensure that more photosensitizers accumulated in tumors, QDs-RGD were injected intratumorally. After selection of an adequate dosage for injection from analyses of biodistribution images captured by an IVIS system, PDT was initiated. Three groups were created according to different PDT procedures. In group 1, mice were injected with QDs-RGD intratumorally, and an optical fiber connected to a laser light was inserted directly into the tumor. Irradiation was sustained for 20 min with a laser light (630 nm) at 100 mW/cm2. In group 2, the laser optical fiber was placed around, and not inserted into, tumors. In group 3, PDT was conducted as in group 1 but without injection of QDs-RGD. After 28 days of observation, tumors on the back of mice in group 1 grew slowly (V/V0 =3.24±0.70) compared with the control groups, whose tumors grew quickly, and the mean V/V0 reached 6.08±0.50 (group 2) and 7.25±0.82 (group 3). Histology of tumor tissues showed more necrotic tissues, more inflammatory cells, and less vascular tissue in the PDT group than those in the control groups. These results suggest that QDs-RGD-mediated PDT, with illumination using an optical fiber inserted directly into the tumor, can inhibit the growth of SW1990 tumors with high efficiency in nude mice.

Sulfonation of Tyrosine as a Method To Improve Biodistribution of Peptide-Based Radiotracers: Novel 18F-Labeled Cyclic RGD Analogues

Control of the biodistribution of radiolabeled peptides has proven to be a major challenge in their application as imaging agents for positron emission tomography (PET). Modification of peptide hydrophilicity in order to increase renal clearance has been a common endeavor to improve overall biodistribution. Herein, we examine the effect of site-specific sulfonation of tyrosine moieties in cyclic(RGDyK) peptides as a means to enhance their hydrophilicity and improve their biodistribution. The novel sulfonated cyclic(RGDyK) peptides were conjugated directly to 4-nitrophenyl 2-[¹⁸F]fluoropropionate, and the biodistribution of the radiolabeled peptides was compared with that of their nonsulfonated, clinically relevant counterparts, [¹⁸F]GalactoRGD and [¹⁸F]FPPRGD2. Site-specific sulfonation of the tyrosine residues was shown to increase hydrophilicity and improve biodistribution of the RGD peptides, despite contributing just 79 Da toward the MW, compared with 189 Da for both the "Galacto" and mini-PEG moieties, suggesting this may be a broadly applicable approach to enhancing biodistribution of radiolabeled peptides.

Conjugation with RGD Peptides and Incorporation of Vascular Endothelial Growth Factor Are Equally Efficient for Biofunctionalization of Tissue-Engineered Vascular Grafts

The blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) has recently been considered promising for vascular tissue engineering. However, it was shown that PHBV/PCL grafts require biofunctionalization to achieve high primary patency rate. Here we compared immobilization of arginine-glycine-aspartic acid (RGD)-containing peptides and the incorporation of vascular endothelial growth factor (VEGF) as two widely established biofunctionalization approaches. Electrospun PHBV/PCL small-diameter grafts with either RGD peptides or VEGF, as well as unmodified grafts were implanted into rat abdominal aortas for 1, 3, 6, and 12 months following histological and immunofluorescence assessment. We detected CD31⁺/CD34⁺/vWF⁺ cells 1 and 3 months postimplantation at the luminal surface of PHBV/PCL/RGD and PHBV/PCL/VEGF, but not in unmodified grafts, with the further observation of CD31⁺CD34-vWF⁺ phenotype. These cells were considered as endothelial and produced a collagen-positive layer resembling a basement membrane. Detection of CD31⁺/CD34⁺ cells at the early stages with subsequent loss of CD34 indicated cell adhesion from the bloodstream. Therefore, either conjugation with RGD peptides or the incorporation of VEGF promoted the formation of a functional endothelial cell layer. Furthermore, both modifications increased primary patency rate three-fold. In conclusion, both of these biofunctionalization approaches can be considered as equally efficient for the modification of tissue-engineered vascular grafts.

Development of peptide-functionalized synthetic hydrogel microarrays for stem cell and tissue engineering applications

Synthetic polymer microarray technology holds remarkable promise to rapidly identify suitable biomaterials for stem cell and tissue engineering applications. However, most of previous microarrayed synthetic polymers do not possess biological ligands (e.g., peptides) to directly engage cell surface receptors. Here, we report the development of peptide-functionalized hydrogel microarrays based on light-assisted copolymerization of poly(ethylene glycol) diacrylates (PEGDA) and methacrylated-peptides. Using solid-phase peptide/organic synthesis, we developed an efficient route to synthesize methacrylated-peptides. In parallel, we identified PEG hydrogels that effectively inhibit non-specific cell adhesion by using PEGDA-700 (M. W.=700) as a monomer. The combined use of these chemistries enables the development of a powerful platform to prepare peptide-functionalized PEG hydrogel microarrays. Additionally, we identified a linker composed of 4 glycines to ensure sufficient exposure of the peptide moieties from hydrogel surfaces. Further, we used this system to directly compare cell adhesion abilities of several related RGD peptides: RGD, RGDS, RGDSG and RGDSP. Finally, we combined the peptide-functionalized hydrogel technology with bioinformatics to construct a library composed of 12 different RGD peptides, including 6 unexplored RGD peptides, to develop culture substrates for hiPSC-derived cardiomyocytes (hiPSC-CMs), a cell type known for poor adhesion to synthetic substrates. 2 out of 6 unexplored RGD peptides showed substantial activities to support hiPSC-CMs. Among them, PMQKMRGDVFSP from laminin β4 subunit was found to support the highest adhesion and sarcomere formation of hiPSC-CMs. With bioinformatics, the peptide-functionalized hydrogel microarrays accelerate the discovery of novel biological ligands to develop biomaterials for stem cell and tissue engineering applications.

STATEMENT OF SIGNIFICANCE

In this manuscript, we described the development of a robust approach to prepare peptide-functionalized synthetic hydrogel microarrays. Combined with bioinformatics, this technology enables us to rapidly identify novel biological ligands for the development of the next generation of functional biomaterials for stem cell and tissue engineering applications.

Improved Pharmacokinetics Following PEGylation and Dimerization of a c(RGD-ACH-K) Conjugate Used for Tumor Positron Emission Tomography Imaging

Improving the in vivo pharmacokinetics (PK) of positron emission tomography (PET) radiotracers is of critical importance to tumor diagnosis and therapy. In the case of peptide-based radiotracers, the modification and addition of a linker or spacer functional group often offer faster in vivo pharmacokinetic behavior. In this study, the authors introduced two new PEGlyated dimeric c(RGD-ACH-K) conjugates, in which an aminocyclohexane carboxylic acid (ACH) is inserted into the ring chain of the cyclic RGD peptides, with a common bifunctional chelator (DOTA or NOTA) used for labeling with radiometals (including ⁶⁸Ga and ⁶⁴Cu). The addition of polyethylene glycol (PEG) and dimerization of c(RGD-ACH-K) affected the PK of the renal system and the tumor-targeting ability, relative to unmodified molecule. As a result, both ⁶⁴Cu-DOTA-E[c(RGD-ACH-K)]₂ (complex 1) and ⁶⁴Cu-NOTA-E[c(RGD-ACH-K)]₂ (complex 2) exhibited specific tumor-targeting properties relative to tumor-blocking control group, most likely resulting from improved in vivo tumor imaging. The in vivo tumor-to-blood ratio of the ⁶⁴Cu(NOTA) complex shows better PET imaging than that of the ⁶⁴Cu(DOTA) complex, which should lead to improved dosimetry and increased suitability for noninvasive monitoring of tumor growth or tumor-targeted radionuclide therapy.

αvβ3- or α5β1-Integrin-Selective Peptidomimetics for Surface Coating

Engineering biomaterials with integrin-binding activity is a very powerful approach to promote cell adhesion, modulate cell behavior, and induce specific biological responses at the surface level. The aim of this Review is to illustrate the evolution of surface-coating molecules in this field: from peptides and proteins with relatively low integrin-binding activity and receptor selectivity to highly active and selective peptidomimetic ligands. In particular, we will bring into focus the difficult challenge of achieving selectivity between the two closely related integrin subtypes αvβ3 and α5β1. The functionalization of surfaces with such peptidomimetics opens the way for a new generation of highly specific cell-instructive surfaces to dissect the biological role of integrin subtypes and for application in tissue engineering and regenerative medicine.

Bioabsorbable Bypass Grafts Biofunctionalised with RGD Have Enhanced Biophysical Properties and Endothelialisation Tested In vivo

Small diameter arterial bypass grafts are considered as unmet clinical need since the current grafts have poor patency of 25% within 5 years. We have developed a 3D scaffold manufactured from natural and synthetic biodegradable polymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(𝜀-caprolactone) (PCL), respectively. Further to improve the biophysical properties as well as endothelialisation, the grafts were covalently conjugated with arginine-glycine-aspartic acid (RGD) bioactive peptides. The biophysical properties as well as endothelialisation of PHBV/PCL and PCL 2 mm diameter bypass grafts were assessed with and without biofunctionalisation with RGD peptides in vitro and in vivo. Morphology of the grafts was assessed by scanning electron microscopy, whereas physico-mechanical properties were evaluated using a physiological circulating system equipped with a state of art ultrasound vascular wall tracking system. Endothelialisation of the grafts in vitro and in vivo were assessed using a cell viability assay and rat abdominal aorta replacement model, respectively. The biofunctionalisation with RGD bioactive peptides decreased mean fiber diameter and mean pore area in PHBV/PCL grafts; however, this was not the case for PCL grafts. Both PHBV/PCL and PCL grafts with RGD peptides had lower durability compared to those without; these durability values were similar to those of internal mammary artery. Modification of PHBV/PCL and PCL grafts with RGD peptides increased endothelial cell viability in vitro by a factor of eight and enhanced the formation of an endothelial cell monolayer in vivo 1 month postimplantation. In conclusion, PHBV/PCL small-caliber graft can be a suitable 3D scaffold for the development of a tissue engineering arterial bypass graft.

Installing multifunctionality on titanium with RGD-decorated polyurethane-polyurea roxithromycin loaded nanoparticles: toward new osseointegrative therapies

A novel class of polyurethane-polyurea nanoparticles (PUUa NPs) to install multifunctionality on biomaterials is presented. Biofunctionalization of titanium with roxithromycin loaded RGD-decorated PUUa NPs results in an outstanding improvement of osteoblast adhesion and strong suppression of bacterial attachment. This strategy represents a powerful approach to enhance the osseointegration of implant materials.

Arg-Gly-Asp-D-Phe-Lys peptide-modified PEGylated dendrimer-entrapped gold nanoparticles for targeted computed tomography imaging of breast carcinoma

AIM

To investigate cyclo (Arg-Gly-Asp-D-Phe-Lys) peptide (RGD)-modified PEGylated dendrimer-entrapped gold nanoparticles (PEGylated Au DENPs-RGD) for targeted computed tomography (CT) imaging of breast carcinomas.

MATERIALS & METHODS

PEGylated Au DENPs-RGD were synthesized and characterized. Then, the PEGylated Au DENPs-RGD for targeted CT imaging were investigated using the MDA-MB-435 cell line, an integrin-rich breast carcinoma cells, and mice with MDA-MB-435 xenograft tumors. Finally, silver enhancement staining and integrin αvβ3 immunohistochemistry of the tumors were performed.

RESULTS

The synthesized PEGylated Au DENPs-RGD were spherical, water dispersible and biocompatible nanoprobes with a gold nanoparticle core size of 2.8 nm. Due to the presence of the Au nanoparticles, the PEGylated Au DENPs-RGD displayed a higher x-ray attenuation intensity than Omnipaque at the same Au or I concentrations. The conjugated RGD ligand can specifically identify and target overexpressed integrin receptors on MDA-MB-435 cells. After intravenous injection, these nanoprobes accumulated in the targeted area of mice with MDA-MB-435 xenograft tumors, which enabled the tumor to be detected by CT imaging. The histological results confirmed the imaging results.

CONCLUSION

The PEGylated Au DENPs-RGD can be used as targeted nanoprobes with good biocompatibility for targeted CT imaging and diagnosis of integrin-positive tumors.

Biomimetic Hybrid Nanofiber Sheets Composed of RGD Peptide-Decorated PLGA as Cell-Adhesive Substrates

In biomedical applications, there is a need for tissue engineering scaffolds to promote and control cellular behaviors, including adhesion, proliferation and differentiation. In particular, the initial adhesion of cells has a great influence on those cellular behaviors. In this study, we concentrate on developing cell-adhesive substrates applicable for tissue engineering scaffolds. The hybrid nanofiber sheets were prepared by electrospinning poly(lactic-co-glycolic acid) (PLGA) and M13 phage, which was genetically modified to enhance cell adhesion thru expressing RGD peptides on their surface. The RGD peptide is a specific motif of extracellular matrix (ECM) for integrin receptors of cells. RGD peptide-decorated PLGA (RGD-PLGA) nanofiber sheets were characterized by scanning electron microscopy, immunofluorescence staining, contact angle measurement and differential scanning calorimetry. In addition, the initial adhesion and proliferation of four different types of mammalian cells were determined in order to evaluate the potential of RGD-PLGA nanofiber sheets as cell-adhesive substrates. Our results showed that the hybrid nanofiber sheets have a three-dimensional porous structure comparable to the native ECM. Furthermore, the initial adhesion and proliferation of cells were significantly enhanced on RGD-PLGA sheets. These results suggest that biomimetic RGD-PLGA nanofiber sheets can be promising cell-adhesive substrates for application as tissue engineering scaffolds.

Toxicity assessment of repeated intravenous injections of arginine-glycine-aspartic acid peptide conjugated CdSeTe/ZnS quantum dots in mice

Background

Nanotechnology-based near-infrared quantum dots (NIR QDs) have many excellent optical properties, such as high fluorescence intensity, good fluorescence stability, and strong tissue-penetrating ability. Integrin αvβ3 is highly and specifically expressed in tumor angiogenic vessel endothelial cells of almost all carcinomas. Recent studies have shown that NIR QDs linked to peptides containing the arginine–glycine–aspartic acid (RGD) sequence (NIR QDs-RGD) can specifically target integrin αvβ3 expressed in endothelial cells of tumor angiogenic vessels in vivo, and they offer great potential for early cancer diagnosis, in vivo tumor imaging, and tumor individualized therapy. However, the toxicity profile of NIR QDs-RGD has not been reported. This study was conducted to investigate the toxicity of NIR QDs-RGD when intravenously administered to mice singly and repeatedly at the dose required for successful tumor imaging in vivo.

Materials and methods

A NIR QDs-RGD probe was prepared by linking NIR QDs with the maximum emission wavelength of 800 nm (QD800) to the RGD peptide (QD800-RGD). QD800-RGD was intravenously injected to BALB/C mice once or twice (200 pmol equivalent of QD800 for each injection). Phosphate-buffered saline solution was used as control. Fourteen days postinjection, toxicity tests were performed, including complete blood count (white blood cell, red blood cell, hemoglobin, platelets, lymphocytes, and neutrophils) and serum biochemical analysis (total protein, albumin, albumin/globulin, aspartate aminotransferase, alanine aminotransferase, and blood urea nitrogen). The coefficients of liver, spleen, kidney, and lung weight to body weight were measured, as well as their oxidation and antioxidation indicators, including superoxide dismutase, glutathione, and malondialdehyde. The organs were also examined histopathologically.

Results

After one or two intravenous injections of QD800-RGD, as compared with control, no significant differences were observed in the complete blood count; biochemical indicators of blood serum, organ coefficient, and oxidation and antioxidation indicators; and no cell necrosis or inflammation were seen in the liver, spleen, kidney, or lung through histopathological examination.

Conclusion

Our data demonstrate that the single and repeated intravenous injection of QD800-RGD at a dose needed for successful tumor imaging in vivo is not toxic to mice. Our work lays a solid foundation for further biomedical applications of NIR QDs-RGD.

Tumor targeting RGD conjugated bio-reducible polymer for VEGF siRNA expressing plasmid delivery

Targeted delivery of therapeutic genes to the tumor site is critical for successful and safe cancer gene therapy. The arginine grafted bio-reducible poly (cystamine bisacrylamide-diaminohexane, CBA-DAH) polymer (ABP) conjugated poly (amido amine) (PAMAM), PAM-ABP (PA) was designed previously as an efficient gene delivery carrier. To achieve high efficacy in cancer selective delivery, we developed the tumor targeting bio-reducible polymer, PA-PEG1k-RGD, by conjugating cyclic RGDfC (RGD) peptides, which bind αvβ3/5 integrins, to the PAM-ABP using polyethylene glycol (PEG, 1 kDa) as a spacer. Physical characterization showed nanocomplex formation with bio-reducible properties between PA-PEG1k-RGD and plasmid DNA (pDNA). In transfection assays, PA-PEG1k-RGD showed significantly higher transfection efficiency in comparison with PAM-ABP or PA-PEG1k-RAD in αvβ3/5 positive MCF7 breast cancer and PANC-1 pancreatic cancer cells. The targeting ability of PA-PEG1k-RGD was further established using a competition assay. To confirm the therapeutic effect, the VEGF siRNA expressing plasmid was constructed and then delivered into cancer cells using PA-PEG1k-RGD. PA-PEG1k-RGD showed 20-59% higher cellular uptake rate into MCF7 and PANC-1 than that of non-targeted polymers. In addition, MCF7 and PANC-1 cancer cells transfected with PA-PEG1k-RGD/pshVEGF complexes had significantly decreased VEGF gene expression (51-71%) and cancer cell viability (35-43%) compared with control. These results demonstrate that a tumor targeting bio-reducible polymer with an anti-angiogenic therapeutic gene could be used for efficient and safe cancer gene therapy.

Improvement of pharmacokinetic and antitumor activity of PEGylated liposomal doxorubicin by targeting with N-methylated cyclic RGD peptide in mice bearing C-26 colon carcinomas

Cyclic Arg-Gly-Asp (cRGD) pentapeptides engrafted liposomes have attracted considerable attention for targeting integrin receptors on tumor vasculature. In this study PEGylated liposomal doxorubicin (PLD) was decorated with three cRGD peptides including Arg-Gly-Asp-D-Tyr-Cys (RGDyC), Arg-Gly-Asp-D-Phe-Lys (RGDfK) and Arg-Gly-Asp-D-Phe-[N-Methyl]Lys (RGDf[N-Met]K). The in vitro liposome-cell-association and cytotoxicity experiments demonstrated the RGD-PLDs capability of internalization into integrin expressing HUVEC cells via receptor mediated endocytosis. The biodistribution studies revealed that decreasing the hydrophilicity of the peptide greatly reduces the RGD-PLDs blood clearance rate and increases their localization in C-26 colon carcinoma tumor model. Meanwhile, the most selective version, RGDf[N-Met]K, which has intermediate hydrophilicity revealed the lowest unwanted interactions with other integrin presenting sites, further localization in tumor, and lower doxorubicin (Dox) side effects. RGDf[N-Met]K-PLD demonstrated a superior control of tumor growth and increased the survival of mice. In this study, we introduced RGDf[N-Met]K for the first time, as a promising ligand for active targeting of liposomes to solid tumor which merits further investigations.

Specific uptake of 99mTc-NC100692, an αvβ3-targeted imaging probe, in subcutaneous and orthotopic tumors

INTRODUCTION

The αvβ3 integrin, which is expressed by angiogenic epithelium and some tumor cells, is an attractive target for the development of both imaging agents and therapeutics. While optimal implementation of αvβ3-targeted therapeutics will require a priori identification of the presence of the target, the clinical evaluation of these compounds has typically not included parallel studies with αvβ3-targeted diagnostics. This is at least partly due to the relatively limited availability of PET radiopharmaceuticals in comparison to those labeled with (99m)Tc. In an effort to begin to address this limitation, we evaluated the tumor uptake of (99m)Tc-NC100692, a cyclic RGD peptide that binds to αvβ3 with ~1-nM affinity, in an αvβ3-positive tumor model as well as its in vivo specificity.

METHODS

MicroSPECT imaging was used to assess the ability of cilengitide, a therapeutic with high affinity for αvβ3, to block and displace (99m)Tc-NC100692 in an orthotopic U87 glioma tumor. The specificity of (99m)Tc-NC100692 was quantitatively evaluated in mice bearing subcutaneous U87MG tumors, by comparison of the biodistribution of (99m)Tc-NC100692 with that of the non-specific structural analogue (99m)Tc-AH-111744 and by blocking uptake of (99m)Tc-NC100692 with excess unlabeled NC100692.

RESULTS

MicroSPECT imaging studies demonstrated that uptake of (99m)Tc-NC100692 in the intracranial tumor model was both blocked and displaced by the αvβ3-targeted therapeutic cilengitide. Biodistribution studies provided quantitative confirmation of these imaging results. Tumor uptake of (99m)Tc-NC100692 at 1h post-injection was 2.8 ± 0.7% ID/g compared to 0.38 ± 0.1% ID/g for (99m)Tc-AH-111744 (p < 0.001). Blocking (99m)Tc-NC100692 uptake by pre-injecting the mice with excess unlabeled NC100692 reduced tumor uptake by approximately five-fold, to 0.68 ± 0.3% ID/g (p = 0.01).

CONCLUSION

These results confirm that (99m)Tc-NC100692 does, in fact, target the αvβ3 integrin and may, therefore, be useful in identifying patients prior to anti-αvβ3 therapy as well as monitoring the response of these patients to therapy.

Influence of PEGylation and RGD loading on the targeting properties of radiolabeled liposomal nanoparticles

Purpose

Liposomes have been proposed to be a means of selectively targeting cancer sites for diagnostic and therapeutic applications. The focus of this work was the evaluation of radiolabeled PEGylated liposomes derivatized with varying amounts of a cyclic arginyl–glycyl–aspartic acid (RGD) peptide. RGD peptides are known to bind to α_vβ₃ integrin receptors overexpressed during tumor-induced angiogenesis.

Methods

Several liposomal nanoparticles carrying the RGD peptide targeting sequence (RLPs) were synthesized using a combination of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, cholesterol, diethylenetriaminepentaacetic acid-derivatized lipids for radiolabeling, a polyethylene glycol (PEG) building block, and a lipid-based RGD building block. Relative amounts of RGD and PEG building blocks were varied. In vitro binding affinities were determined using isolated α_vβ₃ integrin receptors incubated with different concentrations of RLPs in competition with iodine-125-labeled cyclo-(-RGDyV-). Binding of the indium-111-labeled RLPs was also evaluated. Biodistribution and micro single photon emission computed tomography/computed tomography imaging studies were performed in nude mice using different tumor xenograft models.

Results

RLPs were labeled with indium-111 with high radiochemical yields. In vitro binding studies of RLPs with different RGD/PEG loading revealed good binding to isolated receptors, which was dependent on the extent of RGD and PEG loading. Binding increased with higher RGD loading, whereas reduced binding was found with higher PEG loading. Biodistribution showed increased circulating time for PEGylated RLPs, but no dependence on RGD loading. Both biodistribution and micro single photon emission computed tomography/computed tomography imaging studies revealed low, nonspecific tumor uptake values.

Conclusion

In this study, RLPs for targeting angiogenesis were described. Even though good binding to α_vβ₃ integrin receptors was found in vitro, the balance between PEGylation and RGD loading clearly requires optimization to achieve targeting in vivo. These data form the basis for future development and provide a platform for the investigation of multimodal approaches.

Integrin targeted delivery of gene therapeutics

Integrins have become key targets for molecular imaging and for selective delivery of anti-cancer agents. Here we review recent work concerning the targeted delivery of antisense and siRNA oligonucleotides via integrins. A variety of approaches have been used to link oligonucleotides to ligands capable of binding integrins with high specificity and affinity. This includes direct chemical conjugation, incorporating oligonucleotides into lipoplexes, and use of various polymeric nanocarriers including dendrimers. The ligand-oligonucleotide conjugate or complex associates selectively with the integrin, followed by internalization into endosomes and trafficking through subcellular compartments. Escape of antisense or siRNA from the endosome to the cytosol and nucleus may come about through endogenous trafficking mechanisms, or because of membrane disrupting capabilities built into the conjugate or complex. Thus a variety of useful strategies are available for using integrins to enhance the pharmacological efficacy of therapeutic oligonucleotides.