Author Correction: Conversion of human fibroblasts to angioblast-like progenitor cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A novel inhibitor of p75-neurotrophin receptor improves functional outcomes in two models of traumatic brain injury.

The p75 neurotrophin receptor is important in multiple physiological actions including neuronal survival and neurite outgrowth during development, and after central nervous system injury. We have discovered a novel piperazine-derived compound, EVT901, which interferes with p75 neurotrophin receptor oligomerization through direct interaction with the first cysteine-rich domain of the extracellular region. Using ligand binding assays with cysteine-rich domains-fused p75 neurotrophin receptor, we confirmed that EVT901 interferes with oligomerization of full-length p75 neurotrophin receptor in a dose-dependent manner. Here we report that EVT901 reduces binding of pro-nerve growth factor to p75 neurotrophin receptor, blocks pro-nerve growth factor induced apoptosis in cells expressing p75 neurotrophin receptor, and enhances neurite outgrowth in vitro Furthermore, we demonstrate that EVT901 abrogates p75 neurotrophin receptor signalling by other ligands, such as prion peptide and amyloid-ß. To test the efficacy of EVT901 in vivo, we evaluated the outcome in two models of traumatic brain injury. We generated controlled cortical impacts in adult rats. Using unbiased stereological analysis, we found that EVT901 delivered intravenously daily for 1 week after injury, reduced lesion size, protected cortical neurons and oligodendrocytes, and had a positive effect on neurological function. After lateral fluid percussion injury in adult rats, oral treatment with EVT901 reduced neuronal death in the hippocampus and thalamus, reduced long-term cognitive deficits, and reduced the occurrence of post-traumatic seizure activity. Together, these studies provide a new reagent for altering p75 neurotrophin receptor actions after injury and suggest that EVT901 may be useful in treatment of central nervous system trauma and other neurological disorders where p75 neurotrophin receptor signalling is affected.

Targeted identification of sialoglycoproteins in hypoxic endothelial cells and validation in zebrafish reveal roles for proteins in angiogenesis.

The formation of new vessels in the tumor, termed angiogenesis, is essential for primary tumor growth and facilitates tumor invasion and metastasis. Hypoxia has been described as one trigger of angiogenesis. Indeed, hypoxia, which is characterized by areas of low oxygen levels, is a hallmark of solid tumors arising from an imbalance between oxygen delivery and consumption. Hypoxic conditions have profound effects on the different components of the tumoral environment. For example, hypoxia is able to activate endothelial cells, leading to angiogenesis but also thereby initiating a cascade of reactions involving neutrophils, smooth muscle cells, and fibroblasts. In addition, hypoxia directly regulates the expression of many genes for which the role and the importance in the tumoral environment remain to be completely elucidated. In this study, we used a method to selectively label sialoglycoproteins to identify new membrane and secreted proteins involved in the adaptative process of endothelial cells by mass spectrometry-based proteomics. We used an in vitro assay under hypoxic condition to observe an increase of protein expression or modifications of glycosylation. Then the function of the identified proteins was assessed in a vasculogenesis assay in vivo by using a morpholino strategy in zebrafish. First, our approach was validated by the identification of sialoglycoproteins such as CD105, neuropilin-1, and CLEC14A, which have already been described as playing key roles in angiogenesis. Second, we identified several new proteins regulated by hypoxia and demonstrated for the first time the pivotal role of GLUT-1, TMEM16F, and SDF4 in angiogenesis.

Conversion of human fibroblasts to angioblast-like progenitor cells.

Lineage conversion of one somatic cell type to another is an attractive approach for generating specific human cell types. Lineage conversion can be direct, in the absence of proliferation and multipotent progenitor generation, or indirect, by the generation of expandable multipotent progenitor states. We report the development of a reprogramming methodology in which cells transition through a plastic intermediate state, induced by brief exposure to reprogramming factors, followed by differentiation. We use this approach to convert human fibroblasts to mesodermal progenitor cells, including by non-integrative approaches. These progenitor cells demonstrated bipotent differentiation potential and could generate endothelial and smooth muscle lineages. Differentiated endothelial cells exhibited neo-angiogenesis and anastomosis in vivo. This methodology for indirect lineage conversion to angioblast-like cells adds to the armamentarium of reprogramming approaches aimed at the study and treatment of ischemic pathologies.

Tumor vasculature is regulated by FGF/FGFR signaling-mediated angiogenesis and bone marrow-derived cell recruitment: this mechanism is inhibited by SSR128129E, the first allosteric antagonist of FGFRs.

Tumor angiogenesis is accompanied by vasculogenesis, which is involved in the differentiation and mobilization of human bone marrow cells. In order to further characterize the role of vasculogenesis in the tumor growth process, the effects of FGF2 on the differentiation of human bone marrow AC133(+) cells (BM-AC133(+)) into vascular precursors were studied in vitro. FGF2, like VEGFA, induced progenitor cell differentiation into cell types with endothelial cell characteristics. SSR128129E, a newly discovered specific FGFR antagonist acting by allosteric interaction with FGFR, abrogated FGF2-induced endothelial cell differentiation, showing that FGFR signaling is essential during this process. To assess the involvement of the FGF/FRGR signaling in vivo, the pre-clinical model of Lewis lung carcinoma (LL2) in mice was used. Subcutaneous injection of LL2 cells into mice induced an increase of circulating EPCs from peripheral blood associated with tumor growth and an increase of intra-tumoral vascular index. Treatment with the FGFR antagonist SSR128129E strongly decreased LL2 tumor growth as well as the intra-tumoral vascular index (41% and 50% decrease vs. vehicle-treated mice respectively, P < 0.01). Interestingly, SSR128129E treatment significantly decreased the number of circulating EPCs from the peripheral blood (53% inhibition vs. vehicle-treated mice, P < 0.01). These results demonstrate for the first time that the blockade of the FGF/FGFR pathway by SSR128129E reduces EPC recruitment during angiogenesis-dependent tumor growth. In this context, circulating EPCs could be a reliable surrogate marker for tumor growth and angiogenic activity.

Genetic evidence for a tumor suppressor role of HIF-2alpha.

The hypoxia-inducible transcription factors HIF-1alpha and HIF-2alpha are activated in hypoxic tumor regions. However, their role in tumorigenesis remains controversial, as tumor growth promoter and suppressor activities have been ascribed to HIF-1alpha, while the role of HIF-2alpha remains largely unknown. Here, we show that overexpression of HIF-2alpha in rat glioma tumors enhances angiogenesis but reduces growth of these tumors, in part by increasing tumor cell apoptosis. Moreover, siRNA knockdown of HIF-2alpha reduced apoptosis in hypoxic human malignant glioblastoma cells. Furthermore, inhibition of HIF by overexpression of a dominant-negative HIF transgene in glioma cells or HIF-2alpha deficiency in teratomas reduced vascularization but accelerated growth of these tumor types. These findings urge careful consideration of using HIF inhibitors as cancer therapeutic strategies.

Gas6 deficiency in recipient mice of allogeneic transplantation alleviates hepatic graft-versus-host disease.

Growth arrest-specific gene 6 (Gas6) is expressed in antigen-presenting cells and endothelial cells (ECs) but not in T cells. When wild-type (WT) or Gas6(-/-) mice received allogeneic non-T cell-depleted bone marrow cells, hepatic graft-versus-host disease (GVHD) was alleviated in Gas6(-/-) recipients regardless of donor genotype, but not in WT recipients. T-cell infiltration was more prominent and diffuse in WT than in Gas6(-/-) recipients' liver. When mice received 0.5 x 10(6) allogeneic T cells with T cell-depleted allogeneic bone marrow, clinical signs indicated that GVHD was less severe in Gas6(-/-) than in WT recipients, as shown by a significant improvement of the survival and reduced liver GVHD. These data demonstrate that donor cells were not involved in the protection mechanism. In addition, lack of Gas6 in antigen-presenting cells did not affect WT or Gas6(-/-) T-cell proliferation. We therefore assessed the response of WT or Gas6(-/-) ECs to tumor necrosis factor-alpha. Lymphocyte transmigration was less extensive through Gas6(-/-) than WT ECs and was not accompanied by increases in adhesion molecule levels. Thus, the lack of Gas6 in ECs impaired donor T-cell transmigration into the liver, providing a rationale for considering Gas6 pathway as a potential nonimmunosuppressive target to minimize GVHD in patients receiving allogeneic hematopoietic stem cell transplantation.

VEGF-B is dispensable for blood vessel growth but critical for their survival, and VEGF-B targeting inhibits pathological angiogenesis.

VEGF-B, a homolog of VEGF discovered a long time ago, has not been considered an important target in antiangiogenic therapy. Instead, it has received little attention from the field. In this study, using different animal models and multiple types of vascular cells, we revealed that although VEGF-B is dispensable for blood vessel growth, it is critical for their survival. Importantly, the survival effect of VEGF-B is not only on vascular endothelial cells, but also on pericytes, smooth muscle cells, and vascular stem/progenitor cells. In vivo, VEGF-B targeting inhibited both choroidal and retinal neovascularization. Mechanistically, we found that the vascular survival effect of VEGF-B is achieved by regulating the expression of many vascular prosurvival genes via both NP-1 and VEGFR-1. Our work thus indicates that the function of VEGF-B in the vascular system is to act as a "survival," rather than an "angiogenic" factor and that VEGF-B inhibition may offer new therapeutic opportunities to treat neovascular diseases.

Revascularization of ischemic tissues by PlGF treatment, and inhibition of tumor angiogenesis, arthritis and atherosclerosis by anti-Flt1.

The therapeutic potential of placental growth factor (PlGF) and its receptor Flt1 in angiogenesis is poorly understood. Here, we report that PlGF stimulated angiogenesis and collateral growth in ischemic heart and limb with at least a comparable efficiency to vascular endothelial growth factor (VEGF). An antibody against Flt1 suppressed neovascularization in tumors and ischemic retina, and angiogenesis and inflammatory joint destruction in autoimmune arthritis. Anti-Flt1 also reduced atherosclerotic plaque growth and vulnerability, but the atheroprotective effect was not attributable to reduced plaque neovascularization. Inhibition of VEGF receptor Flk1 did not affect arthritis or atherosclerosis, indicating that inhibition of Flk1-driven angiogenesis alone was not sufficient to halt disease progression. The anti-inflammatory effects of anti-Flt1 were attributable to reduced mobilization of bone marrow-derived myeloid progenitors into the peripheral blood; impaired infiltration of Flt1-expressing leukocytes in inflamed tissues; and defective activation of myeloid cells. Thus, PlGF and Flt1 constitute potential candidates for therapeutic modulation of angiogenesis and inflammation.

Role of PlGF in the intra- and intermolecular cross talk between the VEGF receptors Flt1 and Flk1.

Therapeutic angiogenesis is likely to require the administration of factors that complement each other. Activation of the receptor tyrosine kinase (RTK) Flk1 by vascular endothelial growth factor (VEGF) is crucial, but molecular interactions of other factors with VEGF and Flk1 have been studied to a limited extent. Here we report that placental growth factor (PGF, also known as PlGF) regulates inter- and intramolecular cross talk between the VEGF RTKs Flt1 and Flk1. Activation of Flt1 by PGF resulted in intermolecular transphosphorylation of Flk1, thereby amplifying VEGF-driven angiogenesis through Flk1. Even though VEGF and PGF both bind Flt1, PGF uniquely stimulated the phosphorylation of specific Flt1 tyrosine residues and the expression of distinct downstream target genes. Furthermore, the VEGF/PGF heterodimer activated intramolecular VEGF receptor cross talk through formation of Flk1/Flt1 heterodimers. The inter- and intramolecular VEGF receptor cross talk is likely to have therapeutic implications, as treatment with VEGF/PGF heterodimer or a combination of VEGF plus PGF increased ischemic myocardial angiogenesis in a mouse model that was refractory to VEGF alone.

The lectin-like domain of thrombomodulin confers protection from neutrophil-mediated tissue damage by suppressing adhesion molecule expression via nuclear factor kappaB and mitogen-activated protein kinase pathways.

Thrombomodulin (TM) is a vascular endothelial cell (EC) receptor that is a cofactor for thrombin-mediated activation of the anticoagulant protein C. The extracellular NH(2)-terminal domain of TM has homology to C-type lectins that are involved in immune regulation. Using transgenic mice that lack this structure (TM(LeD/LeD)), we show that the lectin-like domain of TM interferes with polymorphonuclear leukocyte (PMN) adhesion to ECs by intercellular adhesion molecule 1-dependent and -independent pathways through the suppression of extracellular signal-regulated kinase (ERK)(1/2) activation. TM(LeD/LeD) mice have reduced survival after endotoxin exposure, accumulate more PMNs in their lungs, and develop larger infarcts after myocardial ischemia/reperfusion. The recombinant lectin-like domain of TM suppresses PMN adhesion to ECs, diminishes cytokine-induced increase in nuclear factor kappaB and activation of ERK(1/2), and rescues ECs from serum starvation, findings that may explain why plasma levels of soluble TM are inversely correlated with cardiovascular disease. These data suggest that TM has antiinflammatory properties in addition to its role in coagulation and fibrinolysis.

The ternary complex of antithrombin-anhydrothrombin-heparin reveals the basis of inhibitor specificity.

Antithrombin, the principal physiological inhibitor of the blood coagulation proteinase thrombin, requires heparin as a cofactor. We report the crystal structure of the rate-determining encounter complex formed between antithrombin, anhydrothrombin and an optimal synthetic 16-mer oligosaccharide. The antithrombin reactive center loop projects from the serpin body and adopts a canonical conformation that makes extensive backbone and side chain contacts from P5 to P6' with thrombin's restrictive specificity pockets, including residues in the 60-loop. These contacts rationalize many earlier mutagenesis studies on thrombin specificity. The 16-mer oligosaccharide is just long enough to form the predicted bridge between the high-affinity pentasaccharide-binding site on antithrombin and the highly basic exosite 2 on thrombin, validating the design strategy for this synthetic heparin. The protein-protein and protein-oligosaccharide interactions together explain the basis for heparin activation of antithrombin as a thrombin inhibitor.

Role of Gas6 receptors in platelet signaling during thrombus stabilization and implications for antithrombotic therapy.

Mechanisms regulating thrombus stabilization remain largely unknown. Here, we report that loss of any 1 of the Gas6 receptors (Gas6-Rs), i.e., Tyro3, Axl, or Mer, or delivery of a soluble extracellular domain of Axl that traps Gas6 protects mice against life-threatening thrombosis. Loss of a Gas6-R does not prevent initial platelet aggregation but impairs subsequent stabilization of platelet aggregates, at least in part by reducing "outside-in" signaling and platelet granule secretion. Gas6, through its receptors, activates PI3K and Akt and stimulates tyrosine phosphorylation of the beta3 integrin, thereby amplifying outside-in signaling via alphaIIbbeta3. Blocking the Gas6-R-alphaIIbbeta3 integrin cross-talk might be a novel approach to the reduction of thrombosis.

Revascularization of ischemic tissues by PDGF-CC via effects on endothelial cells and their progenitors.

The angiogenic mechanism and therapeutic potential of PDGF-CC, a recently discovered member of the VEGF/PDGF superfamily, remain incompletely characterized. Here we report that PDGF-CC mobilized endothelial progenitor cells in ischemic conditions; induced differentiation of bone marrow cells into ECs; and stimulated migration of ECs. Furthermore, PDGF-CC induced the differentiation of bone marrow cells into smooth muscle cells and stimulated their growth during vessel sprouting. Moreover, delivery of PDGF-CC enhanced postischemic revascularization of the heart and limb. Modulating the activity of PDGF-CC may provide novel opportunities for treating ischemic diseases.

Life-threatening thrombosis in mice with targeted Arg48-to-Cys mutation of the heparin-binding domain of antithrombin.

Antithrombin (AT) inhibits thrombin and some other coagulation factors in a reaction that is dramatically accelerated by binding of a pentasaccharide sequence present in heparin/heparan-sulfate to a heparin-binding site on AT. Based on the involvement of R47 in the heparin/AT interaction and the frequent occurrence of R47 mutations in AT deficiency patients, targeted knock-in of the corresponding R48C substitution in AT in mice was performed to generate a murine model of spontaneous thrombosis. The mutation efficiently abolished the effect of heparin-like molecules on coagulation inhibition in vitro and in vivo. Mice homozygous for the mutation (AT(m/m) mice) developed spontaneous, life-threatening thrombosis, occurring as early as the day of birth. Only 60% of the AT(m/m) offspring reached weaning age, with further loss at different ages. Thrombotic events in adult homozygotes were most prominent in the heart, liver, and in ocular, placental, and penile vessels. In the neonate, spontaneous death invariably was associated with major thrombosis in the heart. This severe thrombotic phenotype underlines a critical function of the heparin-binding site of antithrombin and its interaction with heparin/heparan-sulfate moieties in health, reproduction, and survival, and represents an in vivo model for comparative analysis of heparin-derived and other antithrombotic molecules.

Long-term blockade of angiotensin AT1 receptors increases survival of obese Zucker rats.

Despite the well-documented effect of irbesartan, an angiotensin AT1 receptor antagonist, on diabetic nephropathy, its effect on mortality related to multiple metabolic risk factors is unknown. To address this question, obese fa/fa Zucker rats were submitted to a 13-month treatment by irbesartan (30 mg/kg/day p.o.). Vehicle-treated obese fa/fa Zucker rats exhibited an important mortality (72%), which was markedly reduced by irbesartan (22%, P<0.05). Mortality in control lean fa/+ rats attained 12%. Irbesartan diminished the elevation in urinary protein excretion, plasma creatinine and urea nitrogen levels, and reduced the extent of glomerular and tubulo-interstitial lesions together with a reduction of urinary monocyte chemoattractant protein-1 excretion in fa/fa Zucker rats. Irbesartan treatment prevented the rise in plasma total cholesterol, triglycerides and glucose levels, and partially corrected low-density lipoprotein/high-density lipoprotein (LDL/HDL) cholesterol ratio in fa/fa Zucker rats. Therefore, prolonged irbesartan treatment preserves renal function and metabolic profile, and substantially increases survival in obese fa/fa Zucker rats.

Effect of SR58611A, a potent beta-3 adrenoceptor agonist, on cutaneous wound healing in diabetic and obese mice.

In diabetic patients, impairment of wound healing is a serious problem which represents a significant health burden. The effect of a highly selective beta-3 adrenoceptor agonist, SR58611A, on wound healing was assessed in animal models of type II diabetes. In db/db diabetic mice, a daily oral treatment with SR58611A (1, 3 and 10 mg/kg/day for two weeks) significantly reduced hyperglycaemia from 3 mg/kg/day onwards. The compound also normalized wound healing, starting from the lowest dose tested (1 mg/kg/day). SR58611A did not affect wound healing of control (lean) mice. An oral anti-diabetic agent, devoid of affinity for beta-3 adrenoceptors, troglitazone (130 mg/kg/day p.o.), normalized glycaemia but did not improve wound healing in db/db mice. Local application of SR58611A (200 microg/day in db/db mice) did not affect wound healing. SR58611A also normalized glucose levels in ob/ob mice, but only slightly improved wound healing in this strain. Moreover, in 17-week old db/db mice (i.e. severely insulin resistant) and in streptozotocin-induced diabetic mice, SR58611A slightly decreased hyperglycaemia and did not affect wound healing. In conclusion, SR58611A improves wound healing in animal models of non-insulin-dependent diabetes. This effect is not related to its effect on glucose levels, but probably implicates systemic effects of the compound.

CEP-7055: a novel, orally active pan inhibitor of vascular endothelial growth factor receptor tyrosine kinases with potent antiangiogenic activity and antitumor efficacy in preclinical models.

Inhibition of the vascular endothelial growth factor VEGF-VEGF receptor (VEGF-R) kinase axes in the tumor angiogenic cascade is a promising therapeutic strategy in oncology. CEP-7055 is the fully synthetic orally active N,N-dimethyl glycine ester of CEP-5214, a C3-(isopropylmethoxy) fused pyrrolocarbazole with potent pan-VEGF-R kinase inhibitory activity. CEP-5214 demonstrates IC(50) values of 18 nM, 12 nM, and 17 nM against human VEGF-R2/KDR kinase, VEGF-R1/FLT-1 kinase, and VEGF-R3/FLT-4 kinase, respectively, in biochemical kinase assays. CEP-5214 inhibited VEGF-stimulated VEGF-R2/KDR autophosphorylation in human umbilical vein endothelial cells (HUVECs) with an IC (50) of approximately 10 nM and demonstrated an equivalent inhibition of murine FLK-1 autophosphorylation in transformed SVR endothelial cells. Evaluation of the antiangiogenic activity of CEP-5214 revealed a dose-related inhibition of microvessel growth ex vivo in rat aortic ring explant cultures and in vitro on HUVEC capillary-tube formation on Matrigel at low nanomolar concentrations. The antiangiogenic activity of CEP-5214 in these bioassays was observed in the absence of apparent cytotoxicity. Single-dose p.o. or s.c. administration of CEP-7055 or CEP-5214 to CD-1 mice at 23.8 mg/kg/dose b.i.d. resulted in a reversible inhibition of VEGF-R2/FLK-1 phosphorylation in murine lung tissues. Administration p.o. of CEP-7055 at 2.57 to 23.8 mg/kg/dose b.i.d. resulted in dose-related reductions in neovascularization in vivo in porcine aortic endothelial cell (PAEC)-VEGF/basic fibroblast growth factor-Matrigel implants in nude mice (maximum, 82% inhibition), significant reductions in granuloma formation (30%) and granuloma vascularity (42%) in a murine chronic inflammation-induced angiogenesis model, and significant and sustained (6 h) inhibition of VEGF-induced plasma extravasation in rats, with an ED(50) of 20 mg/kg/dose. Chronic p.o. administration of CEP-7055 at doses of 11.9 to 23.8 mg/kg/dose b.i.d. resulted in significant inhibition (50-90% maximum inhibition relative to controls) in the growth of a variety of established murine and human s.c. tumor xenografts in nude mice, including A375 melanomas, U251MG and U87MG glioblastomas, CALU-6 lung carcinoma, ASPC-1 pancreatic carcinoma, HT-29 and HCT-116 colon carcinomas, MCF-7 breast carcinomas, and SVR angiosarcomas. Significant antitumor efficacy was observed similarly against orthotopically implanted LNCaP human prostate carcinomas in male nude mice and orthotopically implanted renal carcinoma (RENCA) tumors in BALB/c mice, in terms of a significant reduction in the metastatic score and the extent of pulmonary metastases. These antitumor responses were associated with marked increases in tumor apoptosis, and significant reductions in intratumoral microvessel density (CD34 and Factor VIII staining) of 22-38% relative to controls depending on the specific tumor xenograft. The antitumor efficacy of chronic CEP-7055 administration was independent of initial tumor volume (in the ASPC-1 pancreatic carcinoma model) and reversible on withdrawal of treatment. Chronic p.o. administration of CEP-7055 in preclinical efficacy studies for periods of up to 65 days was well tolerated with no apparent toxicity or significant morbidity. Orally administered CEP-7055 has entered Phase I clinical trials in cancer patients.

Investigation of the selectivity of thrombin-binding aptamers for thrombin titration in murine plasma.

Detection of thrombin in plasma raises timely challenges to enable therapeutic management of thrombosis in patients under vital threat. Thrombin binding aptamers represent promising candidates as sensing elements for the development of real-time thrombin biosensors; however implementation of such biosensor requires the clear understanding of thrombin-aptamer interaction properties in real-like environment. In this study, we used Surface Plasmon Resonance technique to answer the questions of specificity and sensitivity of thrombin detection by the thrombin-binding aptamers HD1, NU172 and HD22. We systematically characterized their properties in the presence of thrombin, as well as interfering molecular species such as the thrombin precursor prothrombin, thrombin in complex with some of its natural inhibitors, nonspecific serum proteins, and diluted plasma. Kinetic experiments show the multiple binding modes of HD1 and NU172, which both interact with multiple sites of thrombin with low nanomolar affinities and show little specificity of interaction for prothrombin vs. thrombin. HD22, on the other hand, binds specifically to thrombin exosite II and has no affinity to prothrombin at all. While thrombin in complex with some of its inhibitors could not be recognized by any aptamer, the binding of HD1 and NU172 properties is compromised by thrombin inhibitors alone, as well as with serum albumin. Finally, the complex nature of plasma was overwhelming for HD1, but we define conditions for the thrombin detection at 10nM range in 100-fold diluted plasma by HD22. Consequently HD22 showed key advantage over HD1 and NU172, and appears as the only alternative to design an aptasensor.

P2Y receptor antagonists in thrombosis.

The dual role of P2Y1 and P2Y12 receptors in platelet aggregation by ADP has been firmly established, based on the action of selective inhibitors, gene targeting in mice and human genetic evidence. Both of these receptor subtypes constitute targets for antithrombotic agents, and compounds with a dual action might also be of interest. However, the agents currently on the market (ticlopidine and clopidogrel), or known to be in development (cangrelor, AZD-6140 and prasugrel), all target the P2Y12 receptor. The thienopyridines (ticlopidine, clopidogrel and prasugrel) irreversibly inactivate the P2Y12 receptor via the covalent binding of an active metabolite generated in the liver, while the other compounds are competitive antagonists. Cangrelor, an ATP derivative, is suitable for intravenous perfusion, whereas AZD-6140 is in clinical development as an orally active agent.