The Promise of Integrins as Effective Targets for Anticancer Agents

Venom peptides in cancer therapy: An updated review on cellular and molecular aspects

Based on the high incidence and mortality rates of cancer, its therapy remains one of the most vital challenges in the field of medicine. Consequently, enhancing the efficacy of currently applied treatments and finding novel strategies are of great importance for cancer treatment. Venoms are important sources of a variety of bioactive compounds including salts, small molecules, macromolecules, proteins, and peptides that are defined as toxins. They can exhibit different pharmacological effects, and in recent years, their anti-tumor activities have gained significant attention. Several different compounds are responsible for the anti-tumor activity of venoms, and peptides are one of them. In the present review, we discuss the possible anti-tumor activities of venom peptides by highlighting molecular pathways and mechanisms through which these molecules can act effectively. Venom peptides can induce cell death in cancer cells and can substantially enhance the efficacy of chemotherapy and radiotherapy. Also, the venom peptides can mitigate the migration of cancer cells via suppression of angiogenesis and epithelial-to-mesenchymal transition. Notably, nanoparticles have been applied in enhancing the bioavailability of venom peptides and providing targeted delivery, thereby leading to their elevated anti-tumor activity and potential application for cancer therapy.

Isolation of an Anti-Tumour Disintegrin: Dabmaurin-1, a Peptide Lebein-1-Like, from Daboia mauritanica Venom

In the soft treatment of cancer tumours, consequent downregulation of the malignant tissue angiogenesis constitutes an efficient way to stifle tumour development and metastasis spreading. As angiogenesis requires integrin–promoting endothelial cell adhesion, migration, and vessel tube formation, integrins represent potential targets of new therapeutic anti–angiogenic agents. Our work is a contribution to the research of such therapeutic disintegrins in animal venoms. We report isolation of one peptide, named Dabmaurin–1, from the hemotoxic venom of snake Daboia mauritanica, and we evaluate its potential anti–tumour activity through in vitro inhibition of the human vascular endothelial cell HMECs functions involved in tumour angiogenesis. Dabmaurin–1 altered, in a dose–dependent manner, without any significant cytotoxicity, HMEC proliferation, adhesion, and their mesenchymal migration onto various extracellular matrix proteins, as well as formation of capillary–tube mimics on Matrigel^TM. Via experiments involving HMEC or specific cancers cells integrins, we demonstrated that the above Dabmaurin–1 effects are possibly due to some anti–integrin properties. Dabmaurin–1 was demonstrated to recognize a broad panel of prooncogenic integrins (αvβ6, αvβ3 or αvβ5) and/or particularly involved in control of angiogenesis (α5β1, α6β4, αvβ3 or αvβ5). Furthermore, mass spectrometry and partial N–terminal sequencing of this peptide revealed, it is close to Lebein–1, a known anti–β1 disintegrin from Macrovipera lebetina venom. Therefore, our results show that if Dabmaurin–1 exhibits in vitro apparent anti–angiogenic effects at concentrations lower than 30 nM, it is likely because it acts as an anti–tumour disintegrin.

PAMAM-cRGD mediating efficient siRNA delivery to spermatogonial stem cells

Background

Spermatogonial stem cells (SSCs) are the cornerstone of sperm production and thus perpetual male fertility. In clinics, transplantation of patient’s own SSCs into testes is a promising technique to restore fertility when male germ cells have been depleted by gonadotoxic therapies. Auto-transplantation of genetically modified SSCs even has the potential to treat male infertility caused by genetic mutations. However, SSCs are refractory to transfection approaches. Poly(amidoamine) (PAMAM) dendrimers have the unique three-dimensional architecture, surface charge, and high density of surface groups that are suitable for ligand attachment, thereby facilitating target delivery. The goal of this study was to elucidate whether PAMAM dendrimers can efficiently deliver short interfering RNAs (siRNAs) to SSCs.

Methods and results

We introduced cyclic arginine-glycine-aspartic acid (cRGD) peptides to the fifth generation of PAMAM dendrimers (G5) to generate PAMAM-cRGD dendrimers (G5-cRGD). The characterization of G5-cRGD was detected by Fourier transform infrared spectroscope (FTIR), transmission electron microscope (TEM), and the Cell Counting Kit-8 (CCK-8) assay. Confocal microscopy and flow cytometry were used to evaluate the delivery efficiency of siRNA by G5-cRGD to SSCs. The results showed that G5-cRGD encompassing siRNA could self-assemble into spherical structures with nanoscale size and possess high transfection efficiency, excellent endosomal escape ability, and low cytotoxicity, superior to a commercial transfection reagent Lipofectamine® 2000. Moreover, we demonstrated that G5-cRGD efficiently delivered siRNAs and triggered gene silencing.

Conclusions

This study thus provides a promising nanovector for siRNA delivery in SSCs, facilitating the future clinical application of SSC auto-transplantation with genetically modified cells with a hope to cure male infertility that is caused by genetic disorders.

Anticancer effects of alloxanthoxyletin and fatty acids esters - In vitro study on cancer HTB-140 and A549 cells

Alloxanthoxyletin, a natural occurring pyranocoumarin isolated from a number of plant sources, such as family of Rutaceae, and its synthetic derivatives show cytotoxic and antitumor activities. In the present study new eleven esters of alloxanthoxyletin and fatty acids were synthesized and evaluated for their anticancer toxicity. The structures of the compounds were confirmed by Proton Nuclear Magnetic Resonance (¹H NMR), Carbon-13 Nuclear Magnetic Resonance (¹³C NMR) and High Resolution Mass Spectrometry (HRMS) analyses. For all compounds 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the cytotoxic effect on human melanoma cells (HTB-140), human epithelial lung carcinoma cells (A549) and human keratinocyte line (HaCaT). For the most active compounds (8-11) lactate dehydrogenase (LDH) assay to assess the level of cell damage as well as migration inhibition assay were performed. To explain the basic mechanism of cell death induction, the effect of derivatives 8-11 on early and late apoptosis in Annexin V-FITC/7-AAD flow cytometry analysis was investigated. The results indicate that human melanoma cells (HTB-140) and human epithelial lung carcinoma cells (A549) were more sensitive to new alloxanthoxyletin derivatives exposure compared to human keratinocytes (HaCaT). Both, the cytotoxicity and the migration tests showed a concentration-dependent inhibition of cell growth, although with a different degree of efficacy. Tested compounds induced apoptosis in cancer cells, however, derivatives 8, 9, 10 and 11 were found to be much more potent inducers of early apoptosis in HTB-140 cells than in A549 and HaCaT cells. To establish the potent mechanism of action of alloxanthoxyletin derivatives 8, 9, 10 and 11 on HaCaT, A549 and HTB-140 cells, the level of IL-6 was measured. Our results indicate, that tested compounds significantly decrease the release of IL-6 for all cancer cell lines.

RhoA and Rac1 play independent roles in lysophosphatidic acid-induced ovarian cancer chemotaxis

Lysophosphatidic acid (LPA), which is a bioactive phospholipid existing at high level in ascites and plasma of ovarian cancer patients, is known to be involved in cell survival, proliferation, adhesion, and migration. Small guanosine triphosphatases (GTPases) such as RhoA and Rac1 are intracellular signaling molecules which affect morphology and chemotactic behavior of cells. In this research, we first investigated roles of RhoA and Rac1 in the LPA-induced chemotaxis of SKOV3 human ovarian cancer cells using a multilevel microfluidic platform. The multilevel microfluidic device was fabricated by a rapid prototyping method based on soft lithography using multi-layered adhesive tapes. This platform allows us to conduct the on-chip chemotaxis assays in conventional biology laboratories without any huge and expensive equipment for fabrication and fluidic manipulation. Based on image-based analysis of single cell trajectories in the microfluidic device, the chemotaxis of SKOV3 cells could be quantitatively analyzed in two independent parameters-migration speed and directional persistence. Inhibition of the RhoA/ROCK pathways reduced the directional persistence, not the migration speed, of the cells, while only the migration speed was decreased when the activity of Rac1/PAK pathways was suppressed. These results suggest that RhoA and Rac1 signaling pathways potentially play independent roles in the chemotactic migration of SKOV3 ovarian cancer cells in the linear and stable LPA concentration gradient. Our microfluidic platform would provide a rapid, low cost, easy-to-use, and versatile way for research of cancer cell migration which is crucial for tumor metastasis.

Parathyroid hormone-related protein (PTHrP) modulates adhesion, migration and invasion in bone tumor cells

Parathyroid-hormone-related protein (PTHrP) has been shown to be an important factor in osteolysis in the setting of metastatic carcinoma to the bone. However, PTHrP may also be central in the setting of primary bone tumors. Giant cell tumor of bone (GCT) is an aggressive osteolytic bone tumor characterized by osteoclast-like giant cells that are recruited by osteoblast-like stromal cells. The stromal cells of GCT are well established as the only neoplastic element of the tumor, and we have previously shown that PTHrP is highly expressed by these cells both in vitro and in vivo. We have also found that the stromal cells exposed to a monoclonal antibody to PTHrP exhibited rapid plate detachment and quickly died in vitro. Therefore, PTHrP may serve in an autocrine manner to increase cell proliferation and promote invasive properties in GCT. The purpose of this study was to use transcriptomic microarrays and functional assays to examine the effects of PTHrP neutralization on cell adhesion, migration and invasion. Microarray and proteomics data identified genes that were differentially expressed in GCT stromal cells under various PTHrP treatment conditions. Treatment of GCT stromal cells with anti-PTHrP antibodies showed a change in the expression of 13 genes from the integrin family relative to the IgG control. Neutralization of PTHrP reduced cell migration and invasion as evidenced by functional assays. Adhesion and anoikis assays demonstrated that although PTHrP neutralization inhibits cell adhesion properties, cell detachment related to PTHrP neutralization did not result in associated cell death, as expected in mesenchymal stromal cells. Based on the data presented herein, we conclude that PTHrP excreted by GCT stromal cells increases bone tumor cell local invasiveness and migration.

A novel dendritic nanocarrier of polyamidoamine-polyethylene glycol-cyclic RGD for "smart" small interfering RNA delivery and in vitro antitumor effects by human ether-à-go-go-related gene silencing in anaplastic thyroid carcinoma cells

The application of RNA interference techniques is promising in gene therapeutic approaches, especially for cancers. To improve safety and efficiency of small interfering RNA (siRNA) delivery, a triblock dendritic nanocarrier, polyamidoamine-polyethylene glycol-cyclic RGD (PAMAM-PEG-cRGD), was developed and studied as an siRNA vector targeting the human ether-à-go-go-related gene (hERG) in human anaplastic thyroid carcinoma cells. Structure characterization, particle size, zeta potential, and gel retardation assay confirmed that complete triblock components were successfully synthesized with effective binding capacity of siRNA in this triblock nanocarrier. Cytotoxicity data indicated that conjugation of PEG significantly alleviated cytotoxicity when compared with unmodified PAMAM. PAMAM-PEG-cRGD exerted potent siRNA cellular internalization in which transfection efficiency measured by flow cytometry was up to 68% when the charge ratio (N/P ratio) was 3.5. Ligand-receptor affinity together with electrostatic interaction should be involved in the nano-siRNA endocytosis mechanism and we then proved that attachment of cRGD enhanced cellular uptake via RGD-integrin recognition. Gene silencing was evaluated by reverse transcription polymerase chain reaction and PAMAM-PEG-cRGD-siRNA complex downregulated the expression of hERG to 26.3% of the control value. Furthermore, gene knockdown of hERG elicited growth suppression as well as activated apoptosis by means of abolishing vascular endothelial growth factor secretion and triggering caspase-3 cascade in anaplastic thyroid carcinoma cells. Our study demonstrates that this novel triblock polymer, PAMAM-PEG-cRGD, exhibits negligible cytotoxicity, effective transfection, “smart” cancer targeting, and therefore is a promising siRNA nanocarrier.

Supramolecular hydrogels formed by the conjugates of nucleobases, Arg-Gly-Asp (RGD) peptides, and glucosamine

Here we report the generation of a novel class of supramolecular hydrogelators based on the integration of nucleobase, Arg-Gly-Asp (RGD) peptides, and glucosamine in a single molecule. These novel small molecule hydrogelators self-assemble in water to form stable supramolecular nanofibers/hydrogels and exhibit useful biostability. This approach provides a new opportunity for systematic exploration of the self-assembly of small biomolecules by varying any individual segment to generate a large array of supramolecular hydrogels for biological functions and for biomedical applications.

Supramolecular hydrogels formed by the conjugates of nucleobases, Arg-Gly-Asp (RGD) peptides, and glucosamine

Here we report the generation of a novel class of supramolecular hydrogelators based on the integration of nucleobase, Arg-Gly-Asp (RGD) peptides, and glucosamine in a single molecule. These novel small molecule hydrogelators self-assemble in water to form stable supramolecular nanofibers/hydrogels and exhibit useful biostability. This approach provides a new opportunity for systematic exploration of the self-assembly of small biomolecules by varying any individual segment to generate a large array of supramolecular hydrogels for biological functions and for biomedical applications.

High-amylose resistant starch increases hormones and improves structure and function of the gastrointestinal tract: a microarray study

BACKGROUND/AIMS

Type 2 resistant starch from high-amylose maize (HAM-RS2) is associated with increased fermentation, increased expression of proglucagon (gene for GLP-1) and peptide YY (PYY) genes in the large intestine, and improved health. To determine what other genes are up- or downregulated with feeding of HAM-RS2, a microarray was performed.

METHODS

Adult, male Sprague Dawley rats were fed one of the following three diets for a 4-week study period: cornstarch control (CC, 3.74 kcal/g), dietary energy density control (EC, 3.27 kcal/g), and 30% HAM-RS2 (RS, 3.27 kcal/g). Rat microarray with ∼27,000 genes and validation of 94 representative genes with multiple qPCR were used to determine gene expression in total RNA extracts of cecal cells from rats. The RS versus EC comparison tested effects of fermentation as energy density of the diet was controlled.

RESULTS

For the RS versus EC comparison, 86% of the genes were validated from the microarray and the expression indicates promotion of cell growth, proliferation, differentiation, and apoptosis. Gut hormones GLP-1 and PYY were increased.

CONCLUSIONS

Gene expression results predict improved structure and function of the GI tract. Production of gut hormones may promote healthy functions beyond the GI tract.

Integrin alpha9beta1: Unique signaling pathways reveal diverse biological roles

Integrins are transmembrane heterodimeric receptors responsible for transducing and modulating signals between the extracellular matrix and cytoskeleton, ultimately influencing cell functions such as adhesion and migration. Integrin alpha9beta1 is classified within a two member sub-family of integrins highlighted in part by its specialized role in cell migration. The importance of this role is demonstrated by its regulation of numerous biological functions including lymphatic valve morphogenesis, lymphangiogenesis, angiogenesis and hematopoietic homeostasis. Compared to other integrins the signaling mechanisms that transduce alpha9beta1-induced cell migration are not well described. We have recently shown that Src tyrosine kinase plays a key proximal role to control alpha9beta1 signaling. Specifically it activates inducible nitric oxide synthase (iNOS) and in turn nitric oxide (NO) production as a means to transduce cell migration. Furthermore, we have also described a role for FAK, Erk and Rac1 in alpha9beta1 signal transduction. Here we provide an over view of known integrin alpha9beta1 signaling pathways and highlight its roles in diverse biological conditions.

Can anti-migratory drugs be screened in vitro? A review of 2D and 3D assays for the quantitative analysis of cell migration

The aim of the present review is to detail and analyze the pros and cons of in vitro tests available to quantify the anti-migratory effects of anti-cancer drugs for their eventual use in combating the dispersal of tumor cells, a clinical need which currently remains unsatisfied. We therefore briefly sum up why anti-migratory drugs constitute a promising approach in oncology while at the same time emphasizing that migrating cancer cells are resistant to apoptosis. To analyze the pros and cons of the various in vitro tests under review we also briefly sum up the molecular and cellular stages of cancer cell migration, an approach that enables us to argue both that no single in vitro test is sufficient to characterize the anti-migratory potential of a drug and that standardization is needed for the efficient quantitative analysis of cell locomotion in a 3D environment. Before concluding our review we devote the final two parts (i) to the description of new prototypes which, in the near future, could enter the screening process with a view to identifying novel anti-migratory compounds, and (ii) to the anti-migratory compounds currently developed against cancer, with particular emphasis on how these compounds were selected before entering the clinical trial phase.

Peptide Motifs for Cell-Surface Intervention

The discovery of new antimicrobial and anticancer drugs, and overcoming the problem of resistance to current anti-infective and anticancer drug therapies require innovation in the pharmaceutical and scientific research community. A further challenge of drug design is to make the therapeutic agent specific, long lasting, of minimal toxicity, and affordable. Microbial and cancer cell surfaces present molecular features that can differentially prefocus drugs within the human host. This property can localize drugs near cell-surface targets, thereby reducing opportunities for adverse effects, or the emergence of drug resistance caused by intracellular drug and target modification and by the induction of drug efflux pumps. The solubility demands on cell-surface targeting drugs should also be less stringent than for those drugs requiring transmembrane transport or internalization in order to reach intracellular targets. Cationic peptides have provided an increasingly important research focus in this regard. Although the cationic antimicrobial peptides are distributed widely in nature and provide localized primary defenses against microbial attack, the susceptibility of L-peptides to proteolysis and the known properties of successful antimicrobials have led to a focus on circularized peptides, D,L-peptides, and peptides containing unusual amino acids. New on the scene as lead antifungal agents are D-octapeptides and their derivatives that were developed from a combinatorial library produced through solid-phase peptide synthesis protocols. These peptides contain an amidated C-terminal tri-arginine motif, which confers membrane impermeability and focuses the peptides near the fungal cell surface. To date, the octapeptides and their derivatives also require some aromaticity, preferably the indole ring of tryptophan. In some cases, a single 4-methoxy-2,3,6-trimethylbenzenesulfonyl moiety remaining on the peptide after incomplete cleavage of the peptide from the solid phase produces a peptide with activity, whereas the parent shows little or no activity in the screen. Recent research advances that support the polycationic cell surface approach include the RGD (Arg-Gly-Asp) tripeptide and its mimetics, as well as aminoglycoside arginine drugs (e.g. neomycin coupled to small arginine polymers) and prodrugs. In the case of polycationic peptides, D-peptides could be used for intravenous injection and direct-surface drug applications, but mimetics will probably be needed for oral delivery.

Emerging views of integrin signaling: implications for prostate cancer

Integrins are heterodimeric transmembrane cellular receptors that link the cell to its underlying substratum. Alterations in integrin expression and signaling have been implicated in many aspects of tumorigenesis and metastasis including cell survival, migration, and invasion. In prostate cancer, the progression from normal to metastatic cells is accompanied by changes in the repertoire of integrins expressed and up-regulation of key adhesion-dependent signaling pathways. Recent work from several laboratories indicates the emergence of new mechanisms for the regulation of growth and migratory pathways by integrin engagement. These pathways are likely to provide novel sites of therapeutic intervention for the treatment of prostate cancer.

Functional proteomic screens reveal an essential extracellular role for hsp90 alpha in cancer cell invasiveness

Tumour cell invasiveness is crucial for cancer metastasis and is not yet understood. Here we describe two functional screens for proteins required for the invasion of fibrosarcoma cells that identified the molecular chaperone heat shock protein 90 (hsp90). The hsp90 alpha isoform, but not hsp90 beta, is expressed extracellularly where it interacts with the matrix metalloproteinase 2 (MMP2). Inhibition of extracellular hsp90 alpha decreases both MMP2 activity and invasiveness. This role for extracellular hsp90 alpha in MMP2 activation indicates that cell-impermeant anti-hsp90 drugs might decrease invasiveness without the concerns inherent in inhibiting intracellular hsp90.