RGD-based strategies for selective delivery of therapeutics and imaging agents to the tumour vasculature

During the past decade, RGD-peptides have become a popular tool for the targeting of drugs and imaging agents to alphavbeta3-integrin expressing tumour vasculature. RGD-peptides have been introduced by recombinant means into therapeutic proteins and viruses. Chemical means have been applied to couple RGD-peptides and RGD-mimetics to liposomes, polymers, peptides, small molecule drugs and radiotracers. Some of these products show impressive results in preclinical animal models and a RGD targeted radiotracer has already successfully been tested in humans for the visualization of alphavbeta3-integrin, which demonstrates the feasibility of this approach. This review will summarize the structural requirements for RGD-peptides and RGD-mimetics as ligands for alphavbeta3. We will show how they have been introduced in the various types of constructs by chemical and recombinant techniques. The importance of multivalent RGD-constructs for high affinity binding and internalization will be highlighted. Furthermore the in vitro and in vivo efficacy of RGD-targeted therapeutics and diagnostics reported in recent years will be reviewed.     

急性肾功能衰竭的治疗进展

目的：探讨急性肾功能衰竭的治疗。方法：复习有关急性肾功能衰竭的治疗文献，作一总结。结果：使用人工合成三肽序列（RGD）的多肽、生长因子、心房利钠因子和人工肾小管治疗急性肾功能衰竭都取得了较好的疗效。结论：这些新的治疗可望改善急性肾衰的预后和降低死亡率。     

In vitro characterization of peptide-modified p(AAm-co-EG/AAc) IPN-coated titanium implants.

Interpenetrating polymer networks (IPNs) of poly(acrylamide-co-ethylene glycol/acrylic acid) [p(AAm-co-EG/AAc)] functionalized with an -Arg-Gly-Asp- containing peptide derived from rat bone sialoprotein [bsp-RGD(15)] were grafted to titanium implants in an effort to modulate osteoblast behavior in vitro. Surface characterization data were consistent with the presence of an IPN, and ligand density measurements established that the range of peptide density on the modified implants spanned three orders of magnitude (0.01-20 pmol/cm2). In vitro biological characterization of the modified implants employing the primary rat calvarial osteoblast (RCO) model resulted in the identification of a critical ligand density (0.01RGD(15) modified implants compared to the base titanium and other control surfaces. The observed effects were attributed to specific interactions with bsp-RGD(15) and support the concept that peptide-modified implants can enhance the kinetics of differentiation of the cells they contact. These results suggest that in vivo biological performance evaluation of these biomimetic implant surfaces is merited.     

靶向寡肽溶栓剂

对靶向寡肽溶栓剂P6A(ARPAK)及其衍生物、RGD肽及含有自由基伪肽的靶向溶栓作用进行综述。P6A是纤溶酶原的降解产物之一,具有增加血管通透性和溶栓作用。P6A的衍生物及P6A代谢产物具有更强的溶栓作用。血栓形成中,RGD序列是纤维蛋白原与血小板结合的关键序列。将RGD序列与溶栓寡肽结合,构成了具有靶向溶栓作用的杂交寡肽。在溶栓治疗中,血流再灌注生成的大量自由基会对组织造成损伤,将自由基清除剂与溶栓寡肽结合可得到具有溶栓和自由基清除双向功能的溶栓伪肽。因为溶栓处是产生大量自由基的部位,所以含自由基清除剂的溶栓伪肽可将自由基清除剂带到自由基堆积部位,体现了靶向内涵。     

The improvement of calvarial bone healing by durable nanogel-crosslinked materials

Abstract

Different approaches have been developed to improve the scaffold properties that provide structural support and biological interaction to achieve the desired environment for tissue regeneration. We previously reported that addition of human fibroblast growth factor 18 (hFGF18) to acryloyl group-modified cholesterol-bearing pullulan (CHPOA) nanogel-crosslinked (NanoClik) hydrogels that contain human bone morphogenetic protein 2 (hBMP2) stabilized bone healing in mouse calvarial defect model. In this study, we evaluated the use of disc-shaped dried nanogel-crosslinked gel as carriers of growth factors in order to seek possible clinical application in future. Both conventionally-dried NanoClik disc and nanogel-crosslinked porous (NanoCliP) disc made by freeze-drying that contained the growth factors induced bone healing but not as much as with NanoClik hydrogel application but addition of RGD peptides (RGD-NanoCliP disc) improved the healing. All type of discs showed the same biphasic ovalbumin-Alexa Fluor 488 protein release profile in vitro, an initial burst followed by a gradual sustained release more than one week, which was confirmed in vivo. Histological analysis showed remarkable new bone formation with more calcification in RGD-NanoCliP disc with the growth factors and the osteogenesis appeared to begin in the dura mater in contact with the disc. These observations suggest: (1) the fitness of the durable discs to the bone defect is a critical factor for bone healing, which is supplemented by addition of RGD peptides, (2) the porosity is suitable for osteoblast recruitment, (3) growth factor release pattern of the CHPOA nanogel based gels is ideal for bone healing.     

RGD多肽化学修饰聚苯乙烯培养板的细胞相容性研究

目的 考察RGD多肽化学修饰聚苯乙烯培养板细胞相容性研究.方法 采用高锰酸钾硫酸溶液对聚苯乙烯表面进行氧化反应,生成羧基位点；水溶性碳二亚胺活化羧基,接枝明胶、胶原和RGD多肽.用红外光谱、X-射线光电子能谱(XPS)、动态接触角等研究了RGD化学修饰聚苯乙烯的变化,并考察了RGD化学修饰聚苯乙烯后细胞相容性的变化.结果 XPS结果证实了聚苯乙烯表面N原子的引入,RGD是共价键合在聚苯乙烯表面的.动态接触角下降显著,证明修饰表面的亲水性能提高.在修饰后的聚苯乙烯培养板种植入表皮细胞,结果显示提高了细胞的黏附和增殖能力.结论 聚苯乙烯表面进行RGD化学修饰,有利于提高细胞在其表面的黏附和增殖能力,有望为免疫磁珠分离得到的高纯度内皮祖细胞提供良好的培养介质.     

Biomolecular modification of p(AAm-co-EG/AA) IPNs supports osteoblast adhesion and phenotypic expression

Interpenetrating polymer networks (IPNs) were designed to resist materials fouling caused by non-specific protein adsorption, and indiscriminate cell or bacterial adhesion. These IPNs were thin adherent films ( ~ 20 nm) comprised of acrylamide (AAm), ethylene glycol (EG), and acrylic acid (AA) grafted to either silicon waters or quartz substrates via photoinitiated free radical polymerization. These networks were further modified to promote specific cell adhesion by tethering bioactive groups such as peptides that mimic cell-binding domains found on extracellular matrix molecules. As a specific example of biomolecular surface engineering, peptides from the cell-binding domain of bone sialoprotein were tethered to a p(AAm-co-EG/AA) IPN to control cell behavior at the surface. The networks were characterized by contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy to convey information on IPN wettability, thickness, and chemistry. The surface characterization data supported the theory that the PEG/AA layer formed an IPN with the underlying p(AAm) network, and after graft modification of this IPN with diamino PEG (PEG(NH₂)₂), the PEG(NH₂)₂ chains were enriched at the surface. Rat calvarial osteoblasts attached to Arg-Gly-Asp (RGD) modified IPNs at levels significantly greater than on clean quartz, Arg-Gly-Glu (RGE) modified, or the PEG(NH₂)₂ modified IPN, with or without serum in the media. Cells maintained in media containing 15% fetal bovine serum (FBS) proliferated, exhibited nodule formation, and generated sheets of mineralized extracellular matrix (ECM) with the addition on β-glycerophosphate to the media. Cell adhesion and mineralized ECM formation were specifically dependent on the peptide sequence present at the surface.     

HepaRG culture in tethered spheroids as an in vitro three‐dimensional model for drug safety screening

Conventional two‐dimensional (2D) monolayer cultures of HepaRG cells allow in vitro maintenance of many liver‐specific functions. However, cellular dedifferentiation and functional deterioration over an extended culture period in the conventional 2D HepaRG culture have hampered its applications in drug testing. To address this issue, we developed tethered spheroids of HepaRG cells on Arg–Gly–Asp (RGD) and galactose‐conjugated substratum with an optimized hybrid ratio as an in vitro three‐dimensional (3D) human hepatocyte model. The liver‐specific gene expression level and drug metabolizing enzyme activities in HepaRG‐tethered spheorids were markedly higher than those in 2D cultures throughout the culture period of 7 days. The inducibility of three major cytochrome P450 (CYP) enzymes, namely CYP1A2, CYP2B6 and CYP3A4, was improved in both mRNA and activity level in tethered spheroids. Drug‐induced cytotoxic responses to model hepatotoxins (acetaminophen, chlorpromazine and ketoconazole) in tethered spheroids were comparable to 2D cultures as well as other studies in the literature. Our results suggested that the HepaRG‐tethered spheroid would be an alternative in vitro model suitable for drug safety screening. Copyright © 2014 John Wiley & Sons, Ltd.     

Integrin and extracellular matrix interactions regulate engraftment of transplanted hepatocytes in the rat liver

BACKGROUND & AIMS: Recognition and circumvention of the hepatic endothelial barrier is critical in the engraftment of transplanted cells. We examined whether interactions between integrin and extracellular matrix component receptors could be manipulated for improving transplanted cell engraftment and liver repopulation. METHODS: Fischer 344 rat hepatocytes were transplanted into syngeneic dipeptidyl peptidase IV-deficient rats. Coating of cells or of liver sinusoids with natural collagen, natural laminin, or an engineered fibronectin-like polymer was studied with analysis of cell engraftment and liver repopulation using histologic and molecular assays. Focal adhesion complexes were identified by vinculin immunostaining. The role of integrin receptors in cell engraftment was analyzed with RGD peptide inhibition assays. RESULTS: Coating of cells with extracellular matrix components before transplantation did not enhance cell engraftment. In contrast, intraportal infusion of collagen or fibronectin-like polymer in recipients prior to cell transplantation increased cell engraftment. Adherence of transplanted cells to the hepatic endothelium resulted in rapid activation of vinculin-containing focal adhesion complexes. Superior cell engraftment in animals treated with fibronectin-like polymer was RGD sensitive, verifying the integrin-dependent nature of this process. Moreover, studies in the retrorsine-partial hepatectomy rat model showed that intraportal infusion of the fibronectin-like polymer before cell transplantation significantly accelerated liver repopulation. CONCLUSIONS: Integrin-extracellular matrix component interactions can be manipulated for enhancing cell engraftment in the liver. Such mechanisms will be relevant for engraftment of other cell types and for strategies concerning liver-directed cell therapy.     

Possible Involvement of Altered RGD Sequence in Reduced Adhesive and Spreading Activities of Advanced Glycation End Product-Modified Fibronectin to Vascular Smooth Muscle Cells

Although fibronectin (FN) modified by advanced glycation end products (AGEs) has been shown to contribute to the development of diabetic vascular complications through its reduced adhesive activity to vascular cells, little is known about changes in the cell binding domain of AGE-modified FN. Here we examined the mechanism of reduced adhesive and spreading activities of AGE-modified FN to vascular smooth muscle cells (SMCs), particularly the contribution of modification of Arg-Gly-Asp (RGD) sequence. Incubation with glucose caused not only the formation of N-carboxymethyllysine and pentosidine, but also polymerization of FN in a dose- and time-dependent manner. AGE-modified FN had significantly low adhesive and spreading activities to cultured SMCs. On the other hand, multimeric FN formed by disulfide bonds did not show any effect on either cell adhesion or spreading. The adhesive activity of type I collagen, one of the RGD sequence-containing proteins, to SMCs also decreased by AGE-modification. The inhibitory effect of AGE-modification on cell adhesion was significantly greater in type I collagen than in FN. Although the extent of AGE-modification of type I collagen was indistinguishable from that of FN, AGE-modification decreased the arginine content of type I collagen by 69.5% and of FN by 30.6%, compared with their non-glycated forms. The addition of RGD peptides caused a decrease in adhesion of SMCs to non-glycated FN, but not to AGE-modified FN. Modification of RGD sequence with glyoxal eliminated its inhibitory effect on cell adhesion. Our results suggest that a marked decrease in adhesive and spreading activities of AGE-modified FN to SMCs might largely be due to a modification of its RGD sequence by AGE, thus suggesting a potential link between AGE modification of FN and the pathogenesis of diabetic angiopathy.