Potential future clinical applications for the GPIIb/IIIa antagonist, abciximab in thrombosis, vascular and oncological indications

Identification of Podoplanin Aptamers by SELEX for Protein Detection and Inhibition of Platelet Aggregation Stimulated by C-Type Lectin-like Receptor 2

Tumor cell-induced platelet aggregation (TCIPA) is a mechanism for the protection of tumor cells in the bloodstream and the promotion of tumor progression and metastases. The platelet C-type lectin-like receptor 2 (CLEC-2) can bind podoplanin (PDPN) on a cancer cell surface to facilitate TCIPA. Selective blockage of PDPN-mediated platelet-tumor cell interaction is a plausible strategy for inhibiting metastases. In this study, we aimed to screen for aptamers, which are the single-stranded DNA oligonucleotides that form a specific three-dimensional structure, bind to specific molecular targets with high affinity and specificity, bind to PDPN, and interfere with PDPN/CLEC-2 interactions. The systematic evolution of ligands by exponential enrichment (SELEX) was employed to enrich aptamers that recognize PDPN. The initial characterization of ssDNA pools enriched by SELEX revealed a PDPN aptamer designated as A1 displaying parallel-type G-quadruplexes and long stem-and-loop structures and binding PDPN with a material with a dissociation constant (Kd) of 1.3 ± 1.2 nM. The A1 aptamer recognized both the native and denatured form of PDPN. Notably, the A1 aptamer was able to quantitatively detect PDPN proteins in Western blot analysis. The A1 aptamer could interfere with the interaction between PDPN and CLEC-2 and inhibit PDPN-induced platelet aggregation in a concentration-dependent manner. These findings indicated that the A1 aptamer is a candidate for the development of biosensors in detecting the levels of PDPN expression. The action by A1 aptamer could result in the prevention of tumor cell metastases, and if so, could become an effective pharmacological agent in treating cancer patients.

Bleeding and Thrombosis in Multiple Myeloma: Platelets as Key Players during Cell Interactions and Potential Use as Drug Delivery Systems

Multiple myeloma (MM) is a hematological malignancy originated in the bone marrow and characterized by unhindered plasma cell proliferation that results in several clinical manifestations. Although the main role of blood platelets lies in hemostasis and thrombosis, platelets also play a pivotal role in a number of other pathological conditions. Platelets are the less-explored components from the tumor microenvironment in MM. Although some studies have recently revealed that MM cells have the ability to activate platelets even in the premalignant stage, this phenomenon has not been widely investigated in MM. Moreover, thrombocytopenia, along with bleeding, is commonly observed in those patients. In this review, we discuss the hemostatic disturbances observed in MM patients and the dynamic interaction between platelets and myeloma cells, along with present and future potential avenues for the use of platelets for diagnostic and therapeutic purposes.

Integrins as attractive targets for cancer therapeutics

Integrins are transmembrane receptors that have been implicated in the biology of various human physiological and pathological processes. These molecules facilitate cell–extracellular matrix and cell–cell interactions, and they have been implicated in fibrosis, inflammation, thrombosis, and tumor metastasis. The role of integrins in tumor progression makes them promising targets for cancer treatment, and certain integrin antagonists, such as antibodies and synthetic peptides, have been effectively utilized in the clinic for cancer therapy. Here, we discuss the evidence and knowledge on the contribution of integrins to cancer biology. Furthermore, we summarize the clinical attempts targeting this family in anti-cancer therapy development.

Identification of a novel platelet antagonist that binds to CLEC-2 and suppresses podoplanin-induced platelet aggregation and cancer metastasis

Podoplanin (PDPN) enhances tumor metastases by eliciting tumor cell-induced platelet aggregation (TCIPA) through activation of platelet C-type lectin-like receptor 2 (CLEC-2). A novel and non-cytotoxic 5-nitrobenzoate compound 2CP was synthesized that specifically inhibited the PDPN/CLEC-2 interaction and TCIPA with no effect on platelet aggregation stimulated by other platelet agonists. 2CP possessed anti-cancer metastatic activity in vivo and augmented the therapeutic efficacy of cisplatin in the experimental animal model without causing a bleeding risk. Analysis of the molecular action of 2CP further revealed that Akt1/PDK1 and PKCμ were two alternative CLEC-2 signaling pathways mediating PDPN-induced platelet activation. 2CP directly bound to CLEC-2 and, by competing with the same binding pocket of PDPN in CLEC-2, inhibited PDPN-mediated platelet activation. This study provides evidence that 2CP is the first defined platelet antagonist with CLEC-2 binding activity. The augmentation in the therapeutic efficacy of cisplatin by 2CP suggests that a combination of a chemotherapeutic agent and a drug with anti-TCIPA activity such as 2CP may prove clinically effective.

Interaction between circulating cancer cells and platelets: clinical implication

Metastasis is the main cause of cancer-associated mortality. During this complicated process, some cancer cells, also called circulating tumor cells (CTCs), detach from primary sites, enter bloodstream and extravasate at metastatic site. Thrombocytosis is frequently observed in patients with metastatic cancers suggesting the important role of platelets in metastasis. Therefore this review focuses on how platelets facilitate the generation of CTCs, protect them from various host attacks, such as immune assaults, apoptosis and shear stress, and regulate CTCs intravasation/extravasation. Platelet-derived cytokines and receptors are involved in this cascade. Identification the mechanisms underlie platelet-CTCs interactions could lead to the development of new platelet-targeted therapeutic strategy to reduce metastasis.

Feasibility of polyelectrolyte-driven Fab fragment separation

The use of antigen-binding fragments (Fabs) as biotherapeutic agents is gaining interest and thus requires development of adequate purification strategies aimed at separating Fabs from other proteins. Thus, the feasibility of using a copolymer for separation of Fabs from monoclonal antibodies (mAbs) and fragment constant regions (Fcs) was evaluated, employing a blend of purified solutions of these proteins. The use of a copolymer exerting both hydrophobic as well as anionic properties resulted in high precipitation yields for both the mAb and Fc fragment, even at ionic strength of 150 mM NaCl. On the contrary, Fabs exhibited reduced precipitation yields upon copolymer addition. These observations are attributed to differences in protein physicochemical parameters, allowing mAbs and Fcs to be precipitated via conjoint electrostatic and hydrophobic interactions. In contrast, Fabs were mainly precipitated via electrostatic interactions, being reduced at higher ionic strength. This finding was corroborated by hydrophobicity analysis using 2-p-toluidinonaphthalene-6-sulfonate, showing enhanced hydrophobicity of Fcs compared to mAbs alone, while Fabs exhibited the lowest hydrophobicity. Within the context of increasing demand for Fabs as therapeutic proteins, these results may open up a simpler purification strategy for this protein class, potentially also to be implemented within the context of polymer-driven protein purification during fermentation.

Strategies to inhibit tumor associated integrin receptors: rationale for dual and multi-antagonists

The integrins are a family of 24 heterodimeric transmembrane cell surface receptors. Involvement in cell attachment to the extracellular matrix, motility, and proliferation identifies integrins as therapeutic targets in cancer and associated conditions: thrombosis, angiogenesis, and osteoporosis. The most reported strategy for drug development is synthesis of an agent that is highly selective for a single integrin receptor. However, the ability of cancer cells to change their integrin repertoire in response to drug treatment renders this approach vulnerable to the development of resistance and paradoxical promotion of tumor growth. Here, we review progress toward development of antagonists targeting two or more members of the Arg-Gly-Asp (RGD) binding integrins, notably αvβ3, αvβ5, αvβ6, αvβ8, α5β1, and αIIbβ3, as anticancer therapeutics.

Expression and characterization of an enantioselective antigen-binding fragment directed against α-amino acids

This work describes the design and expression of a stereoselective Fab that possesses binding properties comparable to those displayed by the parent monoclonal antibody. Utilizing mRNA from hybridoma clones that secrete a stereoselective anti-l-amino acid antibody, a corresponding biotechnologically produced Fab was generated. For that, appropriate primers were designed based on extensive literature and databank searches. Using these primers in PCR resulted in successful amplification of the VH, VL, CL and CH1 gene fragments. Overlap PCR was utilized to combine the VH and CH1 sequences and the VL and CL sequences, respectively, to obtain the genes encoding the HC and LC fragments. These sequences were separately cloned into the pEXP5-CT/TOPO expression vector and used for transfection of BL21(DE3) cells. Separate expression of the two chains, followed by assembly in a refolding buffer, yielded an Fab that was demonstrated to bind to l-amino acids but not to recognize the corresponding d-enantiomers.

siRNA-mediated silencing of integrin β3 expression inhibits the metastatic potential of B16 melanoma cells

Integrins comprise a large family of αβ heterodimeric cell-surface receptors that mediate diverse processes involved in cell-cell and cell-matrix interactions such as cellular adhesion and migration, cell survival and differentiation. It is now well documented that integrins play a crucial role in cancer metastasis and angiogenesis. The β3 integrins appear to have an important stimulatory role in tumour progression and metastasis and, thus, have been often proposed as potential targets for cancer diagnosis and therapy. In this study, we evaluated the in vitro and in vivo properties of B16 mouse melanoma cells with low expression of integrin β3. Proliferation rate, adhesive properties and the ability to migrate and metastasize were studied. Over 90% inhibition of integrin β3 expression was achieved as a result of the transfection with siRNA. No changes in the proliferation rate were observed in siRNA-transfected B16 cells; however, they showed impaired ability to bind to fibronectin. Moreover, inhibition of integrin β3 expression caused almost complete impairment of the ability of B16 cells to migrate through matrigel and metastasize. The mean number of lung metastatic colonies in mice inoculated intravenously with B16 expressing low levels of integrin β3 was decreased to 14 colonies compared to 101 in the control group. These results provide evidence for a direct role of integrin β3 in the adhesion, migration and metastasis processes of mouse melanoma cells and point to the potential therapeutic advantages of siRNAs.

Vascular integrins: therapeutic and imaging targets of tumor angiogenesis

Cells, including endothelial cells, continuously sense their surrounding environment and rapidly adapt to changes in order to assure tissues and organs homeostasis. The extracellular matrix (ECM) provides a physical scaffold for cell positioning and represents an instructive interface allowing cells to communicate over short distances. Cell surface receptors of the integrin family emerged through evolution as essential mediators and integrators of ECM-dependent communication. In preclinical studies, pharmacological inhibition of vascular integrins suppressed angiogenesis and inhibited tumor progression. alpha(V)beta(3) and alpha(V)beta(5) were the first integrins targeted to suppress tumor angiogenesis. Subsequently, additional integrins, in particular alpha(1)beta(1), alpha(2)beta(1), alpha(5)beta(1), and alpha(6)beta(4), emerged as potential therapeutic targets. Integrin inhibitors are currently tested in clinical trials for their safety and antiangiogenic/antitumor activity. In this chapter, we review the role of integrins in angiogenesis and present recent advances in the use of integrin antagonists as potential therapeutics in cancer and discuss future perspectives.

Cell adhesion molecules: role and clinical significance in cancer

There is a growing body of evidence suggesting that alterations in the adhesion properties of neoplastic cells endow them with an invasive and migratory phenotype. Indeed, changes in the expression or function of cell adhesion molecules have been implicated in all steps of tumor progression, including detachment of tumor cells from the primary site, intravasation into the blood stream, extravasation into distant target organs, and formation of the secondary lesions. This review presents recent data regarding the role of cell adhesion molecules in tumor development and progress with concern to their clinical exploitation as potential biomarkers in neoplastic diseases.

Vascular Integrins in Tumor Angiogenesis: Mediators and Therapeutic Targets

The notion that tumor angiogenesis may have therapeutic implications in the control of tumor growth was introduced by Dr. Judah Folkman in 1971. The approval of Avastin in 2004 as the first antiangiogenic systemic drug to treat cancer patients came as a validation of this visionary concept and opened new perspectives to the treatment of cancer. In addition, this success boosted the field to the quest for new therapeutic targets and antiangiogenic drugs. Preclinical and clinical evidence indicate that vascular integrins may be valid therapeutic targets. In preclinical studies, pharmacological inhibition of integrin function efficiently suppressed angiogenesis and inhibited tumor progression. alphaVbeta3 and alphaVbeta5 were the first vascular integrins targeted to suppress tumor angiogenesis. Subsequent experiments revealed that at least four additional integrins (i.e., alpha1beta1, alpha2beta1, alpha5beta1, and alpha6beta4) might be potential therapeutic targets. In clinical studies low-molecular-weight integrin inhibitors and anti-integrin function-blocking antibodies demonstrated low toxicity and good tolerability and are now being tested in combination with radiotherapy and chemotherapy for anticancer activity in patients. In this article the authors review the role of integrins in angiogenesis, present recent development in the use of alphaVbeta3 and alpha5beta1 integrin antagonists as potential therapeutics in cancer, and discuss future perspectives.

The role of platelet activation in tumor metastasis

Platelets are highly reactive components of the circulatory system, which exert not only haemostatic activity but also contribute to the modulation of various pathological conditions including inflammation, atherosclerosis and cancer metastasis through the release of cytokines, chemokines and the presentation of several adhesion molecules. During cancer metastasis, the formation of platelet-tumor cell aggregates in the circulation facilitates immune evasion and the microvascular arrest of tumor cells at distant sites. Several adhesion molecules, such as integrins and glycoproteins, were shown to be involved in this process. Recent findings indicate that P-selectin is another main mediator of platelet-tumor cell interactions. Other effects of activated platelets on cancer progression are associated with a release of platelet-derived factors stimulating tumor growth and angiogenesis. Any interference in platelet-tumor cell interactions resulted in attenuation of cancer metastasis. The well recognized, albeit not fully characterized function of platelets during cancer progression defines platelets as potential targets for cancer therapy. Specifically, the rapid expression of P-selectin on the cell surface of activated platelets and its strong association with metastasis provide a rationale for P-selectin inhibition as an antimetastatic treatment.

Integrin alpha(v)beta(3)-Targeted Cancer Therapy

Anti-angiogenesis is a promising strategy for the treatment of cancer. Integrins, consisting of two noncovalently bound transmembrane alpha and beta subunits, are an important molecular family involved in tumor angiogenesis. The blockade of integrin signaling has been demonstrated to be efficient to inhibit tumor growth, angiogenesis, and metastasis. Among all the integrins, alpha(v)beta(3) seems to be the most important one during tumor angiogenesis. The inhibition of integrin alpha(v)beta(3) signaling with antibodies, peptides, peptidomimetics, and other antagonists has great potential in the treatment of cancer. In addition, integrin alpha(v)beta(3) is highly expressed on activated endothelial cells, new-born vessels as well as some tumor cells, but is not present in resting endothelial cells and most normal organ systems, making it a suitable target for anti-angiogenic therapy. In this article we will review the role of integrin alpha(v)beta(3) in angiogenesis, present recent progress in the use of integrin alpha(v)beta(3) antagonists and integrin-targeted delivery systems as potential cancer therapeutics, and discuss future perspectives.

[Functional arginine-containing amino acid sequences in peptides and proteins]

L-arginine is a source of nitrogen oxide and plays a great role in a number of other biochemical processes. Functions and prospects for practical application of five groups of arginine-containing amino acid sequences and synthetic polyarginine sequences are considered. The physiological characteristics of well-known arginine-containing peptides, such as RGD peptides, kyotorphin, and tuftsin, are described in detail. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http://www.maik.ru

Platelet adhesion onto immobilized fibrinogen under arterial and venous in-vitro flow conditions does not significantly differ between men and women

Background

Gender-related differences in incidence of arterial thrombosis have been a focus of interest for years. The platelet integrin αIIbβ3 is primarily responsible for the interaction between platelets and fibrinogen and consecutive thrombus growth. In this study, we evaluated platelet adhesion onto immobilized fibrinogen under venous and arterial flow conditions in men and women.

Methods

Platelets in whole anticoagulated blood were labelled with the fluorescence dye Mepacrine and perfused through the rectangular flow chamber over glass cover slips coated with fibrinogen (shear rates of 50 s^-1, 500 s^-1 and 1500 s^-1). A fluorescence laser-scan microscope was used for visualisation and quantification of platelet adhesion at 15 seconds, 1 and 5 minutes after the start of perfusion.

Results

During perfusion, the platelet adhesion linearly increased in regard to exposition time and shear rate. After five minutes of perfusion the platelet adhesion onto immobilized fibrinogen showed no significant gender related difference, neither at 50 s^-1 nor at 500 s^-1 and 1500 s^-1 (p > 0.05), respectively. No significant difference in platelet adhesion onto immobilized fibrinogen, in regard to the menopausal status, was either observed (p > 0.05).

Conclusion

In our in vitro experimental system, hormonal differences between men and women did not influence platelet adhesion onto immobilized fibrinogen, neither under venous nor under arterial rheological conditions.

Concentration-dependent effect of abciximab on platelets and neutrophils in a model of cardiopulmonary bypass

Abciximab is a GPIIb/IIIa antagonist used in percutaneous coronary interventions to avoid platelet activation, thrombosis and inflammation. We investigated whether abciximab influenced platelet activation and platelet interaction with neutrophils and polyvinyl chloride (PVC) in a cardiopulmonary bypass (CPB) model. Isolated platelets, preincubated with and without 0.1-20 μg/mL of abciximab, were resuspended with neutrophils in plasma and recirculated by a roller pump. Platelet, but not neutrophil adhesion to PVC was inhibited by abciximab. Only high doses of abciximab reduced platelet aggregation size, but simultaneously increased platelet-neutrophil aggregation. Abciximab had no effect on platelet CD62P expression or degranulation, but platelet activation on platelet-neutrophil aggregates increased with high doses. Only low doses inhibited neutrophil degranulation. The concentration-dependent effect of abciximab on platelet-neutrophil interaction reduces its usefulness and stresses the dependency on experimental design in the evaluation of abciximab. Our study does not support the use of abciximab alone in CPB. However, incorporation of surface-coating the biomaterial with abciximab may be an interesting option.

Mechanisms of heparin induced anti-cancer activity in experimental cancer models

BACKGROUND

Retrospective analyses of clinical trials and prospective clinical studies have suggested that heparins may have an effect on cancer survival. This putative anti-cancer activity of heparins is supported by data from studies in animal tumour models.

OBJECTIVE

To clarify the various potential mechanisms of heparin anti-cancer activity we evaluated the data from pre-clinical studies in which heparins have been tested as anti-cancer therapy.

METHODS

Pre-clinical studies, published between 1960 and 2005 were assessed. Data were collected on the type and dose of heparin used, duration of exposure to heparin, interval between heparin administration and cancer cell inoculation, and the animal tumour model used. In addition, a distinction was made in the analysis between heparin effects on the primary tumour or on established metastases and effects on the metastatic potential of infused cells.

RESULTS

Heparins seemed to affect the formation of metastasis rather than the growth of primary tumours. Chemically modified heparins with no or limited anticoagulant activity also showed anti-metastatic properties. Possible mechanisms to explain the effects on the process of metastases include inhibition of blood coagulation, inhibition of cancer cell-platelet and -endothelial interactions by selectin inhibition and inhibition of cell invasion and angiogenesis.

CONCLUSION

The anti-cancer activity of heparins depends more on inhibition of metastasis formation than on the effects on primary tumour growth. These effects are probably related to both coagulation and non-coagulation dependent factors. For a definitive proof of the anti-cancer activity of heparins in the clinic, prospective randomized trials especially in patients with early metastatic disease or in the adjuvant setting are urgently needed.

Genetic variation in platelet integrin alphabeta (GPIIb/IIIa) and the metastatic potential of renal cell carcinoma

OBJECTIVE

To explore whether genetic polymorphisms in platelet receptors known to be associated with platelet activity have any association with haematogenous metastases in renal cell carcinoma (RCC), as platelets and their fibrinogen receptors may be central to haematogenous cancer spread, in addition to various adhesive proteins on both platelets and tumour cells on themselves.

PATIENTS AND METHODS

The glycoprotein alpha(IIb)beta3 (GPIIb/IIIa) is the main fibrinogen receptor on platelets, with GPIb-IX-V and GPIa/IIa being the von Willebrand Factor and collagen receptors, respectively. In a cross-sectional survey of 128 men treated for RCC (55 with disseminated disease and 73 with a local disease), they were genotyped using DNA extracted from freshly drawn blood, and central clinical data were recorded.

RESULTS

The frequency of possessing the GPIIIaPl(A2) allele among patients with metastatic RCC was 43.6%, and with local disease was 24.7% (P = 0.024). The frequencies of the different alleles of the GIB-IX-V, C3550T and GPIa/IIa C807T polymorphisms did not differ between the groups. In a stepwise logistic regression (metastatic vs local RCC) the Pl(A2) allele remained a significant risk factor, with an odds ratio of 2.7 (95% confidence interval, 1.1-6.5; P = 0.02).

CONCLUSION

The prothrombotic Pl(A2) allele of platelet fibrinogen receptor GPIIb/IIIa increased the risk of metastases in RCC in men.

Integrins: Molecular targets in cancer therapy

Integrins are cell surface adhesion molecules coupling the extracellular environment to the cytoskeleton as well as receptors for transmitting signals important for cell migration, invasion, proliferation, and survival. At least six integrin inhibitors are being evaluated in clinical trials for cancer. Currently, patients with melanoma and glioblastoma multiforme benefit from Vitaxin (MedImmune, Gaithersburg, MD) or cilengitide treatment, respectively. Many phase II trials are being or have been conducted with these two compounds (the most advanced). Surprisingly, despite the broad theoretical impact of such molecules on integrin function, and thus on pathology, the clear identification of discrete clinical niches for their use remains to be defined. Possible reasons for this are discussed in this review. The parallel development of integrin antagonists as imaging tools for patient selection may accelerate the discovery of new avenues for their use.

Ligand-mimetic anti-aIIbβ3 antibody PAC-1 inhibits tyrosine signaling, proliferation and lung colonization of melanoma cells

Beta3 integrin expression is the hallmark of melanoma and may serve as a potential therapeutic target. While alphav beta3 integrin expression seems to be constitutive in melanoma, ectopic expression of platelet-alphaIIb beta3 is dependent on progression. B16a murine melanoma is a suitable model for studies on alphaIIb beta3 treatment strategies since alphav beta3 is not expressed in this cell line. Here we have used a ligand-mimetic anti-alphaIIb beta3 monoclonal antibody, PAC-1, to test the biological consequences of alphaIIb beta3 modulation in melanoma cells. We have previously reported that in B16a cells FAK is constitutively active and tyrosine-phosphorylated. Upon PAC-1 binding to the surface alphaIIb beta3, which is in the active conformation, FAK became dephosphorylated through a process of PKC-dependent phosphatase activation. Furthermore, PAC-1 binding to B16a cells induced a significant decrease in phosphotyrosine-positive melanoma cells within 30 min. Treatment of B16a cells in vitro with PAC-1 significantly inhibited proliferation by decreasing the mitotic index but not affecting apoptotic rate. Incubation of B16a cells with PAC-1 decreased their lung colonization potential, suggesting a profound alteration in their biological behavior under the effect of this antibody. These preclinical data suggest that the ectopic expression of alphaIIb beta3 in melanoma cells can be exploited as a novel target of antibody therapy of melanoma.

Platelet-Mimicry of Cancer Cells: Epiphenomenon with Clinical Significance

Stem cell mimicry of cancer cells has been known for a long time and is considered to be responsible for ectopic gene expressions. The stem cell characteristics of tumor cells are shown to be involved in epithelial-mesenchymal transition and in the phenomenon of vascular mimicry. Certain cancer types acquire a geno-phenotype closely resembling the platelets and express several megakaryocytic genes (adhesion receptors alpha IIb beta 3, thrombin receptor and PECAM/CD 31 and/or platelet-type 12-LOX) able to activate the coagulation cascade or the platelets themselves. Here we define these potentials as platelet mimicry of cancer cells typical of pancreatic, breast, prostate, colorectal and urogenital cancers and melanoma. Data all support that platelet mimicry of certain cancer types is an important factor in their hematogenous dissemination and provides an attractive therapeutic target. Besides the long-available preclinical data, clinical trials have only recently provided evidence that targeting platelet mimicry of cancers is an efficient way to prevent tumor progression. The systematic discovery of the markers of platelet mimicry in various cancer types and their molecular targeting may provide new supportive therapeutic modalities for the management of the progressing disease.

Breast adenocarcinoma cell adhesion to the vascular subendothelium in whole blood and under flow conditions: effects of alphavbeta3 and alphaIIbbeta3 antagonists

Tumour cell adhesion to vascular extracellular matrix (ECM), an important step of metastatic progression, is promoted by platelets. The aim of our study was to investigate, in whole blood under venous and arterial shear conditions, the respective role of tumour cell alphavbeta3 and platelet alphaIIbbeta3 integrins in MDA-MB-231 breast adenocarcinoma cell adhesion to human umbilical vein endothelial cell ECM. For that purpose, blood containing MDA-MB-231 cells was incubated with non-peptide antagonists specific for platelet alphaIIbbeta3 (lamifiban) or tumour cell alphavbeta3 (SB-273005). At 300 s(-1), each antagonist used alone did not modify tumour cell adhesion, whereas, at 1500 s(-1), tumour cell adhesion was decreased by 25% in presence of lamifiban indicating a role of platelet alphaIIbbeta3 at higher shear rate. However, a combination of SB-273005 and lamifiban, or c7E3 Fab (a potent inhibitor of both alphaIIbbeta3 and alphavbeta3) inhibited tumour cell adhesion by 40-45%, at either shear rate applied, indicating a cooperation between these two integrins in MDA-MB-231 cell adhesion to ECM, as well as the participation of other adhesive receptors on tumour cells and/or platelets. Thus, efficient anti-metastatic therapy should target multiple receptors on tumour cells and platelets.

Platelet--cancer interactions: mechanisms and pharmacology of tumour cell-induced platelet aggregation

During haematogenous metastasis, cancer cells migrate to the vasculature and interact with platelets resulting in tumour cell-induced platelet aggregation (TCIPA). We review: 1. The biological and clinical significance of TCIPA; 2. Molecular mechanisms involved in platelet aggregation by cancer cells; 3. Strategies for pharmacological regulation of these interactions. We conclude that pharmacological regulation of platelet-cancer cell interactions may reduce the impact of TCIPA on cancer biology.

Noncardiac applications of glycoprotein IIb/IIIa inhibitors

Platelet activation and aggregation have become increasingly recognized as the primary processes involved in the cascade that leads to thrombus formation in atherosclerotic vascular disease. Glycoprotein IIb/IIIa receptor inhibitors (GPI) favorably impact thrombus formation and distal embolization by inhibiting the final common pathway of platelet aggregation. Glycoprotein IIb/IIIa inhibitors have been used effectively in a wide variety of clinical scenarios including unstable angina, non-ST segment elevation myocardial infarction, ST segment elevation myocardial infarction, and low and high risk percutaneous coronary interventions with and without intracoronary stenting, however there is limited data regarding the use of these potent antiplatelet agents in the setting of extracardiac vascular disease. This article will review the non-cardiac applications of glycoprotein IIb/IIIa inhibitors in the setting of acute ischemic stroke, carotid and vertebral angioplasty and stenting, acute critical limb ischemia, and percutaneous interventions in peripheral arterial occlusive disease.

Purification of Fab fragments from a monoclonal antibody papain digest by Gradiflow electrophoresis

Fab fragments isolated from papain digests of monoclonal antibodies have a wide variety of uses in analytical and in both in vivo and in vitro diagnostic applications. A novel, non-affinity method which uses the Gradiflow to purify Fab fragments from the papain digest of a mouse IgG1 anti-c-myc monoclonal antibody is described. The Gradiflow is a preparative electrophoresis instrument that uses polyacrylamide membranes of known pore size to separate proteins in solution in their native state under mild pH conditions by charge or size. The Fab and Fc fragments from the papain digestion were characterized using isoelectric focusing (IEF) and non-reducing SDS-PAGE in conjunction with IEF and Western blot. There were three Fab isoforms with p [Formula: see text] between pH 6.5 and 7.4 while the Fc had a range of isoforms between 6.1 and 6.3. Both Fab and Fc fragments had similar [Formula: see text] of 50kDa. A charge-based purification strategy was developed to obtain a high purity Fab preparation after 10min, confirmed by Western blot and chemiluminescence analyses. A small quantity of residual undigested IgG1 remained and was removed using a size-based separation. The efficiency of the separation despite the narrow pH range between Fab and Fc suggests that this technique may be an alternative to protein A or G affinity separation of Fc and Fab monoclonal antibody fragments from papain digests of monoclonal antibodies.

Molecular pathology of tumor metastasis III. Target array and combinatorial therapies

Therapy of tumor progression and the metastatic disease is the biggest challenge of clinical oncology. Discovery of the diverse molecular pathways behind this complex disease outlined an approach to better treatment strategies. The development of combined cytotoxic treatment protocols has produced promising results but no breakthrough in the clinical management of metastatic disease. The multiple - specific and non-specific pathways and cellular targets of tumor progression are outlined in this review. Such an approach, individually designed for various cancer types, may have a better chance to treat or even cure cancer patients with progressive disease.

The Promise of Integrins as Effective Targets for Anticancer Agents

This review will briefly describe integrin function, address why integrins are attractive targets for chemotherapeutic drug design, and discuss some ongoing studies aimed at inhibiting integrin activity. Integrins are cell surface heterodimeric receptors. They modulate many cellular processes including: growth, death (apoptosis), adhesion, migration, and invasion by activating several signaling pathways. Many potential chemotherapeutic agents target integrins directly (eg, polypeptides, monoclonal antibodies, adenovirus vectors). These agents may be clinically useful in controlling the metastatic spread of cancer.

Right atrial thrombus treated successfully with abciximab and heparin

We report here a case of right atrial thrombus diagnosed by echocardiography in a 25-year-old female patient with Hodgkin's disease receiving chemotherapy and heparin. After 24 hours therapy with the glycoprotein IIb/IIIa receptor antagonist (abciximab) with concomitant heparin the complete dissolution of the thrombus could be demonstrated by transesophageal echocardiography. To our knowledge this case represents the first use of abciximab in right atrial thrombosis.