Combining 5-azacitidine with the E-selectin antagonist uproleselan is an effective strategy to augment responses in myelodysplasia and acute myeloid leukaemia.

The interaction of acute myeloid leukaemic (AML) blasts with the bone marrow (BM) microenvironment is a major determinant governing disease progression and resistance to treatment. The constitutive expression of E-selectin in the vascular compartment of BM, a key endothelial cell factor, directly mediates chemoresistance via E-selectin ligand/receptors. Despite the success of hypomethylating agent (HMA)-containing regimens to induce remissions in older AML patients, the development of primary or secondary resistance is common. We report that following treatment with 5-azacitidine, promoter regions regulating the biosynthesis of the E-selectin ligands, sialyl Lewis X, become further hypomethylated. The resultant upregulation of these gene products, in particular α(1,3)-fucosyltransferase VII (FUT7) and α(2,3)-sialyltransferase IV (ST3GAL4), likely causes functional E-selectin binding. When combined with the E-selectin antagonist uproleselan, the adhesion to E-selectin is reversed and the survival of mice transplanted with AML cells is prolonged. Finally, we present clinical evidence showing that BM myeloid cells from higher risk MDS and AML patients have the potential to bind E-selectin, and these cells are more abundant in 5-azacitidine-non-responsive patients. The collective data provide a strong rationale to evaluate 5-azacitidine in combination with the E-selectin antagonist, uproleselan, in this patient population.

Targeting hematologic malignancies by inhibiting E-selectin: A sweet spot for AML therapy?

E-selectin, a cytoadhesive glycoprotein, is expressed on venular endothelial cells and mediates leukocyte localization to inflamed endothelium, the first step in inflammatory cell extravasation into tissue. Constitutive marrow endothelial E-selectin expression also supports bone marrow hematopoiesis via NF-κB-mediated signaling. Correspondingly, E-selectin interaction with E-selectin ligand (sialyl Lewisx) on acute myeloid leukemia (AML) cells leads to chemotherapy resistance in vivo. Uproleselan (GMI-1271) is a carbohydrate analog of sialyl Lewisx that blocks E-selectin binding. A Phase 2 trial of MEC chemotherapy combined with uproleselan for relapsed/refractory AML showed a median overall survival of 8.8 months and low (2%) rates of severe oral mucositis. Clinical trials seek to confirm activity in AML and mitigation of neutrophil-mediated adverse events (mucositis and diarrhea) after intensive chemotherapy. In this review we summarize E-selectin biology and the rationale for uproleselan in combination with other therapies for hematologic malignancies. We also describe uproleselan pharmacology and ongoing clinical trials.

A randomized clinical trial of the efficacy and safety of rivipansel for sickle cell vaso-occlusive crisis.

The efficacy and safety of rivipansel, a predominantly E-selectin antagonist, were studied in a phase 3, randomized, controlled trial for vaso-occlusive crisis (VOC) requiring hospitalization (RESET). A total of 345 subjects (204 adults and 141 children) were randomized and 320 were treated (162 with rivipansel, 158 with placebo) with an IV loading dose, followed by up to 14 additional 12-hourly maintenance doses of rivipansel or placebo, in addition to standard care. Rivipansel was similarly administered during subsequent VOCs in the Open-label Extension (OLE) study. In the full analysis population, the median time to readiness for discharge (TTRFD), the primary end point, was not different between rivipansel and placebo (-5.7 hours, P = .79; hazard ratio, 0.97), nor were differences seen in secondary end points of time to discharge (TTD), time to discontinuation of IV opioids (TTDIVO), and cumulative IV opioid use. Mean soluble E-selectin decreased 61% from baseline after the loading dose in the rivipansel group, while remaining unchanged in the placebo group. In a post hoc analysis, early rivipansel treatment within 26.4 hours of VOC pain onset (earliest quartile of time from VOC onset to treatment) reduced median TTRFD by 56.3 hours, reduced median TTD by 41.5 hours, and reduced median TTDIVO by 50.5 hours, compared with placebo (all P < .05). A similar subgroup analysis comparing OLE early-treatment with early-treatment RESET placebo showed a reduction in TTD of 23.1 hours (P = .062) and in TTDIVO of 30.1 hours (P = .087). Timing of rivipansel administration after pain onset may be critical to achieving accelerated resolution of acute VOC. Trial Registration: Clinicaltrials.gov, NCT02187003 (RESET), NCT02433158 (OLE).

E-selectin inhibitor is superior to low-molecular-weight heparin for the treatment of experimental venous thrombosis.

BACKGROUND: This study evaluated E-selectin inhibition with GMI-1271 (Uproleselan [GMI]) alone and in combination with the standard of care low-molecular-weight heparin (LMWH) to improve vein recanalization, decrease vein wall inflammation and protect against adverse bleeding in a primate model. We sought to examine this novel treatment of venous thrombosis. METHODS: Using a well-documented primate animal model, iliac vein thrombosis was induced by balloon occlusion of the iliac vein for 6 hours. Starting on day 2 after thrombosis, animals began treatment in two phases. In phase one, nontreated controls received no treatment (n = 5) vs animals treated with the E-selectin inhibitor GMI, 25 mg/kg, subcutaneous (SC), once daily (n = 4) for 21 days (previously published data). In phase two, animals were treated with GMI plus a combination of LMWH 1.5 mg/kg or 40 mg (GMI + LMWHc) SC once daily (n = 8) for 19 days; and animals treated with LMWH 1.5 mg/kg or 40 mg (LMWHc) SC once daily (n = 6) for 19 days. Animals were evaluated by magnetic resonance venography for vein recanalization and inflammation by gadolinium extravasation, duplex ultrasound, coagulation tests (thromboelastography, bleeding time, prothrombin time, activated partial thromboplastin time, fibrinogen) and complete blood count at baseline, days 2, 7, 14, and 21 at euthanasia. Statistical analysis included using unpaired t test with Welch's correction for direct comparisons and one-way analysis of variance for comparison between the groups. RESULTS: Percent vein recanalization by magnetic resonance venography was highest in the GMI alone group followed by GMI + LMWHc, both significantly different from control. On ultrasound examination, animals treated with GMI alone had no decrease in open vein lumen by day 21, whereas decreases were observed in groups GMI + LMWHc (-26%), LMWHc (-27%), and controls (-80%). Vein wall inflammation decreased significantly in all treated groups. Intimal fibrosis and intimal thickness was best preserved in the GMI alone group. An analysis of total vein wall collagen revealed a trend in all treatment groups of decreasing vein wall collagen. No clinically significant bleeding events were noted in any group. The LMWH groups trended to have prolonged coagulation test values, whereas E-selectin inhibition with GMI did not cause clinically significant changes in coagulation measures. CONCLUSIONS: Treatment with E-selectin inhibition results in improved vein recanalization, a decrease in vein wall inflammation and vein wall intimal thickness and fibrosis, with no changes in markers of coagulation. E-selectin inhibition with GMI alone is superior to E-selectin inhibition combined with LMWH, LMWH alone, and no treatment in this deep vein thrombosis model of iliac vein thrombosis.

Phase 1/2 study of uproleselan added to chemotherapy in patients with relapsed or refractory acute myeloid leukemia.

Uproleselan (GMI-1271) is a novel E-selectin antagonist that disrupts cell survival pathways, enhances chemotherapy response, improves survival in mouse xenograft and syngeneic models, and decreases chemotherapy toxicity in vivo. A phase 1/2 study evaluated the safety, tolerability, and antileukemic activity of uproleselan (5-20 mg/kg) with MEC (mitoxantrone, etoposide, and cytarabine) among patients with relapsed/refractory (R/R) acute myeloid leukemia (AML). Among the first 19 patients, no dose-limiting toxicities were observed. The recommended phase 2 dose (RP2D) was 10 mg/kg twice daily. An additional 47 patients with R/R AML were treated with uproleselan at the RP2D plus MEC. At the RP2D, the remission rate (complete response [CR]/CR with incomplete count recovery [CRi]) was 41% (CR, 35%), and the median overall survival (OS) was 8.8 months. In a separate cohort, 25 newly diagnosed patients age ≥60 years received uproleselan at the RP2D plus cytarabine and idarubicin (7 + 3). In these frontline patients, the CR/CRi rate was 72% (CR, 52%), and the median OS was 12.6 months. The addition of uproleselan was associated with low rates of oral mucositis. E-selectin ligand expression on leukemic blasts was higher in patients with relapsed vs primary refractory AML and in newly diagnosed older patients with high-risk cytogenetics and secondary AML. In the R/R cohort, E-selectin expression >10% was associated with a higher response rate and improved survival. The addition of uproleselan to chemotherapy was well tolerated, with high remission rates, low induction mortality, and low rates of mucositis, providing a strong rationale for phase 3 randomized confirmatory studies. This trial was registered at www.clinicaltrials.gov as #NCT02306291.

Targeting Neutrophil Adhesive Events to Address Vaso-Occlusive Crisis in Sickle Cell Patients.

Neutrophils are essential to protect the host against invading pathogens but can promote disease progression in sickle cell disease (SCD) by becoming adherent to inflamed microvascular networks in peripheral tissue throughout the body. During the inflammatory response, leukocytes extravasate from the bloodstream using selectin adhesion molecules and migrate to sites of tissue insult through activation of integrins that are essential for combating pathogens. However, during vaso-occlusion associated with SCD, neutrophils are activated during tethering and rolling on selectins upregulated on activated endothelium that line blood vessels. Recently, we reported that recognition of sLex on L-selectin by E-selectin during neutrophil rolling initiates shear force resistant catch-bonds that facilitate tethering to endothelium and activation of integrin bond clusters that anchor cells to the vessel wall. Evidence indicates that blocking this important signaling cascade prevents the congestion and ischemia in microvasculature that occurs from neutrophil capture of sickled red blood cells, which are normally deformable ellipses that flow easily through small blood vessels. Two recently completed clinical trials of therapies targeting selectins and their effect on neutrophil activation in small blood vessels reveal the importance of mechanoregulation that in health is an immune adaption facilitating rapid and proportional leukocyte adhesion, while sustaining tissue perfusion. We provide a timely perspective on the mechanism underlying vaso-occlusive crisis (VOC) with a focus on new drugs that target selectin mediated integrin adhesive bond formation.

Endothelial E-selectin inhibition improves acute myeloid leukaemia therapy by disrupting vascular niche-mediated chemoresistance.

The endothelial cell adhesion molecule E-selectin is a key component of the bone marrow hematopoietic stem cell (HSC) vascular niche regulating balance between HSC self-renewal and commitment. We now report in contrast, E-selectin directly triggers signaling pathways that promote malignant cell survival and regeneration. Using acute myeloid leukemia (AML) mouse models, we show AML blasts release inflammatory mediators that upregulate endothelial niche E-selectin expression. Alterations in cell-surface glycosylation associated with oncogenesis enhances AML blast binding to E-selectin and enable promotion of pro-survival signaling through AKT/NF-κB pathways. In vivo AML blasts with highest E-selectin binding potential are 12-fold more likely to survive chemotherapy and main contributors to disease relapse. Absence (in Sele-/- hosts) or therapeutic blockade of E-selectin using small molecule mimetic GMI-1271/Uproleselan effectively inhibits this niche-mediated pro-survival signaling, dampens AML blast regeneration, and strongly synergizes with chemotherapy, doubling the duration of mouse survival over chemotherapy alone, whilst protecting endogenous HSC.

Use of GMI-1271, an E-selectin antagonist, in healthy subjects and in 2 patients with calf vein thrombosis.

BACKGROUND: There is an unmet need for antithrombotic treatments for venous thromboembolic disease that do not increase bleeding risk. Selectins are cell adhesion molecules that augment thrombosis by activating immune cells to initiate the coagulation cascade. GMI-1271, a potent small-molecule E-selectin antagonist, has been shown in mouse models to decrease thrombus burden with a low risk of bleeding. METHODS: A first-in-human study of GMI-1271 was conducted to assess its safety, tolerability, and pharmacokinetic (PK) profile. As a secondary end point, biomarkers of coagulation, cell adhesion, and leukocyte/platelet activation were evaluated. Aims 1 and 2 were performed in healthy volunteers and evaluated single and multiple doses of the study drug, respectively. Aim 3 included 2 patients with isolated calf-level deep vein thrombosis (DVT). RESULTS: GMI-1271 showed consistent PK parameters for doses ranging from 2 to 40 mg/kg. Plasma levels increased in a linear manner with respect to dose, while clearance, volume of distribution, and half-life were not dose dependent. No accumulation was seen with multiple consecutive doses. No serious adverse events (grade 3 or 4) were reported. Biomarker analysis demonstrated a trend in reduction of soluble E-selectin (sEsel) levels with GMI-1271 exposure, while exposure did not impact laboratory testing of coagulation. Two patients with calf vein DVT were treated with GMI-1271 and demonstrated rapid improvement of symptoms after 48 hours, with repeat ultrasound showing signs of clot resolution. CONCLUSIONS: We demonstrate that GMI-1271 is safe in healthy volunteers and provide proof of concept that an E-selectin antagonist is a potential therapeutic approach to treat venous thrombosis.

Bone vascular niche E-selectin induces mesenchymal-epithelial transition and Wnt activation in cancer cells to promote bone metastasis.

How disseminated tumour cells engage specific stromal components in distant organs for survival and outgrowth is a critical but poorly understood step of the metastatic cascade. Previous studies have demonstrated the importance of the epithelial-mesenchymal transition in promoting the cancer stem cell properties needed for metastasis initiation, whereas the reverse process of mesenchymal-epithelial transition is required for metastatic outgrowth. Here we report that this paradoxical requirement for the simultaneous induction of both mesenchymal-epithelial transition and cancer stem cell traits in disseminated tumour cells is provided by bone vascular niche E-selectin, whose direct binding to cancer cells promotes bone metastasis by inducing mesenchymal-epithelial transition and activating Wnt signalling. E-selectin binding activity mediated by the α1-3 fucosyltransferases Fut3/Fut6 and Glg1 are instrumental to the formation of bone metastasis. These findings provide unique insights into the functional role of E-selectin as a component of the vascular niche critical for metastatic colonization in bone.

Determination of Glycolipid Ligands of Carbohydrate-Binding Proteins Directly on Thin Layer Chromatograms.

Determination of a glycolipid ligand can quickly reveal the carbohydrate epitope recognized by carbohydrate-binding proteins (CBP) which may include antibodies, lectins, toxins, and virulence factors. Thin layer chromatography (TLC) is a simple, well-known, and heavily used method to separate glycolipids based on their migration through a thin layer of chromatography media, usually silica gel, coated on the surface of a rigid plate. Reacting carbohydrate-binding proteins directly on a TLC plate of separated glycolipids is a powerful technique to quickly determine functional carbohydrate epitopes present in an entire glycolipid extract of a target cell type or tissue.

P- and E-selectin receptor antagonism prevents human leukocyte adhesion to activated porcine endothelial monolayers and attenuates porcine endothelial damage.

BACKGROUND: Alongside the need to develop more effective and less toxic immunosuppression, the shortage of human organs available for organ transplantation is one of the major hurdles facing the field. Research into xenotransplantation, as an alternative source of organs, has unveiled formidable challenges. Porcine lungs perfused with human blood rapidly sequester the majority of circulating neutrophils and platelets, which leads to inflammation and organ failure within hours, and is not significantly attenuated by genetic modifications to the pig targeted to diminish antibody binding and complement and coagulation cascade activation. METHODS: Here, we model the interaction of freshly isolated human leukocytes with xenotransplanted vasculature under physiologic flow conditions using microfluidic channels coated with porcine endothelial cells. Both isolated human neutrophils and whole human blood were perfused over transgenic pig aortic endothelial cells that had been activated with rhTNF-α or rhIL-4 using the BioFlux system. Novel compounds GMI-1271 and rPSGL1.Fc were tested as E- and P- selectin antagonists, respectively. Cellular adhesion and rolling events were tracked using FIJI (imageJ). RESULTS: Porcine endothelium activated with either rhTNF-α or rhIL-4 expressed high amounts of selectins, to which isolated human neutrophils readily rolled and tethered. Both E-and P-selectin antagonism significantly reduced the number of neutrophils rolling and rolling distance in a dose-dependent manner, with near total inhibition at higher doses (P < .001). Similarly, with whole human blood, selectin blocking compounds exhibited dose-dependent inhibition of prevalent leukocyte adhesion and severe endothelial injury (Untreated: 394 ± 97 PMNs/hpf, 57 ± 6% loss EC; GMI1271+rPSGL1.Fc: 23 ± 9 PMNs/hpf, 8 ± 6% loss EC P < .01). CONCLUSIONS: Selectin blockade may be useful as part of an integrated strategy to prevent neutrophil-mediated organ xenograft injury, especially during the early time points following reperfusion.

Selectin catch-bonds mechanotransduce integrin activation and neutrophil arrest on inflamed endothelium under shear flow.

E-selectin extends from the plasma membrane of inflamed endothelium and serves to capture leukocytes from flowing blood via long-lived catch-bonds that support slow leukocyte rolling under shear stress. Its ligands are glycosylated with the tetrasaccharide sialyl Lewisx (sLex), which contributes to bond affinity and specificity. E-selectin-mediated rolling transmits signals into neutrophils that trigger activation of high-affinity ß2-integrins necessary for transition to shear-resistant adhesion and transendothelial migration. Rivipansel is a glycomimetic drug that inhibits E-selectin-mediated vaso-occlusion induced by integrin-dependent sickle-red blood cell-leukocyte adhesion. How Rivipansel antagonizes ligand recognition by E-selectin and blocks outside-in signaling of integrin-mediated neutrophil arrest while maintaining rolling immune-surveillance is unknown. Here, we demonstrate that sLex expressed on human L-selectin is preferentially bound by E-selectin and, on ligation, initiates secretion of MRP8/14 that binds TLR4 to elicit the extension of ß2-integrin to an intermediate affinity state. Neutrophil rolling over E-selectin at precise shear stress transmits tension and catch-bond formation with L-selectin via sLex, resulting in focal clusters that deliver a distinct signal to upshift ß2-integrins to a high-affinity state. Rivipansel effectively blocked formation of selectin catch-bonds, revealing a novel mechanotransduction circuit that rapidly converts extended ß2-integrins to high-affinity shear-resistant bond clusters with intracellular adhesion molecule 1 on inflamed endothelium.

E-selectin inhibition with GMI-1271 decreases venous thrombosis without profoundly affecting tail vein bleeding in a mouse model.

Selectins, such as E-selectin (CD62E), function in venous thrombosis by binding and activating immune cells to initiate the coagulation cascade. GMI-1271 is a small molecule antagonist that inhibits E-selectin activity. Here we determine whether inhibition of E-selectin is sufficient to decrease acute venous thrombosis and associated inflammatory events in both prophylactic and treatment protocols without significantly affecting haemostasis. Male C57BL/6 mice underwent surgery for experimental thrombosis induction and were harvested at peak thrombus formation in our animal model, two days post induction. Groups included non-thrombosed true controls, shams, controls, and prophylactic or treatment groups of GMI-1271 (10 mg/kg intraperitoneal BID (twice a day) and low-molecular-weight heparin (LMWH, Lovenox 6 mg/kg subcutaneously (SC), once a day (SID). Compared with control animals, prophylaxis or treatment with LMWH and GMI-1271 in a dose-dependent manner significantly decreased thrombosis. GMI-1271 significantly lowered tail bleeding times when compared to LMWH. GMI-1271 and LMWH prophylactically administered significantly decreased vein wall neutrophil cell extravasation. However, all treatment and prophylactic therapies significantly decreased vein wall monocyte extravasation versus controls. GMI-1271 prophylactic therapy significantly decreased intra-thrombus cell counts versus control animals and other treatment groups. Immunohistochemistry confirmed that both treatments with GMI-1271 and LMWH significantly decreased activated leukocyte migration. GMI-1271 therapy significantly decreased thrombus weight and resulted in significantly lower bleeding times than LMWH. GMI-1271 treated mice showed decreased local and systemic inflammatory effects while modulating neutrophil activation, suggesting that GMI-1271 is a viable therapeutic candidate for venous thrombosis prophylaxis and treatment.

E-Selectin Inhibition Mitigates Splenic HSC Activation and Myelopoiesis in Hypercholesterolemic Mice With Myocardial Infarction.

OBJECTIVE: Atherosclerosis is a chronic disease characterized by lipid accumulation in the arterial wall. After myocardial infarction (MI), atherosclerotic plaques are infiltrated by inflammatory myeloid cells that aggravate the disease and increase the risk of secondary myocardial ischemia. Splenic myelopoiesis provides a steady flow of myeloid cells to inflamed atherosclerotic lesions after MI. Therefore, targeting myeloid cell production in the spleen could ameliorate increased atherosclerotic plaque inflammation after MI. APPROACH AND RESULTS: Here we show that MI increases splenic myelopoiesis by driving hematopoietic stem and progenitor cells into the cell cycle. In an atherosclerotic mouse model, E-selectin inhibition decreased hematopoietic stem and progenitor cell proliferation in the spleen after MI. This led to reduced extramedullary myelopoiesis and decreased myeloid cell accumulation in atherosclerotic lesions. Finally, we observed stable atherosclerotic plaque features, including smaller plaque size, reduced necrotic core area, and thicker fibrous cap after E-selectin inhibition. CONCLUSIONS: Inhibiting E-selectin attenuated inflammation in atherosclerotic plaques, likely by reducing leukocyte recruitment into plaques and by mitigating hematopoietic stem and progenitor cell activation in the spleen of mice with MI.

Randomized phase 2 study of GMI-1070 in SCD: reduction in time to resolution of vaso-occlusive events and decreased opioid use.

Treatment of vaso-occlusive crises (VOC) or events in sickle cell disease (SCD) remains limited to symptom relief with opioids. Animal models support the effectiveness of the pan-selectin inhibitor GMI-1070 in reducing selectin-mediated cell adhesion and abrogating VOC. We studied GMI-1070 in a prospective multicenter, randomized, placebo-controlled, double-blind, phase 2 study of 76 SCD patients with VOC. Study drug (GMI-1070 or placebo) was given every 12 hours for up to 15 doses. Other treatment was per institutional standard of care. All subjects reached the composite primary end point of resolution of VOC. Although time to reach the composite primary end point was not statistically different between the groups, clinically meaningful reductions in mean and median times to VOC resolution of 41 and 63 hours (28% and 48%, P = .19 for both) were observed in the active treatment group vs the placebo group. As a secondary end point, GMI-1070 appeared safe in acute vaso-occlusion, and adverse events were not different in the two arms. Also in secondary analyses, mean cumulative IV opioid analgesic use was reduced by 83% with GMI-1070 vs placebo (P = .010). These results support a phase 3 study of GMI-1070 (now rivipansel) for SCD VOC. This trial was registered at www.clinicaltrials.gov as #NCT01119833.

Phase 1 study of the E-selectin inhibitor GMI 1070 in patients with sickle cell anemia.

BACKGROUND: Sickle cell anemia is an inherited disorder of hemoglobin that leads to a variety of acute and chronic complications. Abnormal cellular adhesion, mediated in part by selectins, has been implicated in the pathophysiology of the vaso-occlusion seen in sickle cell anemia, and selectin inhibition was able to restore blood flow in a mouse model of sickle cell disease. METHODS: We performed a Phase 1 study of the selectin inhibitor GMI 1070 in patients with sickle cell anemia. Fifteen patients who were clinically stable received GMI 1070 in two infusions. RESULTS: The drug was well tolerated without significant adverse events. There was a modest increase in total peripheral white blood cell count without clinical symptoms. Plasma concentrations were well-described by a two-compartment model with an elimination T1/2 of 7.7 hours and CLr of 19.6 mL/hour/kg. Computer-assisted intravital microscopy showed transient increases in red blood cell velocity in 3 of the 4 patients studied. CONCLUSIONS: GMI 1070 was safe in stable patients with sickle cell anemia, and there was suggestion of increased blood flow in a subset of patients. At some time points between 4 and 48 hours after treatment with GMI 1070, there were significant decreases in biomarkers of endothelial activation (sE-selectin, sP-selectin, sICAM), leukocyte activation (MAC-1, LFA-1, PM aggregates) and the coagulation cascade (tissue factor, thrombin-antithrombin complexes). Development of GMI 1070 for the treatment of acute vaso-occlusive crisis is ongoing. TRIAL REGISTRATION: ClinicalTrials.gov NCT00911495.

Implications of the E-selectin S128R mutation for drug discovery.

The C-type lectin E-selectin mediates the rolling of circulating leukocytes on vascular endothelial cells during the inflammatory process. In numerous studies, the S128R mutation of the E-selectin was associated with cardiovascular and autoimmune diseases. There is evidence that the S128R E-selectin mutation leads to a loss in ligand specificity, thus increasing leukocyte recruitment. Apart from the natural tetrasaccharide ligand sialyl Lewis(x) (sLe(x)), it has previously been proposed that non-fucosylated carbohydrates also bind to S128R E-selectin. To evaluate the therapeutic potential of the antagonism of the E-selectin mutant, ligand specificity was reinvestigated on a molecular basis. We determined the ligand specificity of wild-type and S128R E-selectin in a target-based competitive assay, a glycan array screen and cell-based binding assays under static and flow conditions. Regarding ligand-specificity, the binding properties of S128R E-selectin were identical to those of wt E-selectin, i.e., no mutant-specific binding of 3'-sialyl-N-acetyllactosamine, heparin, fetuin and K562 cells was observed. Additionally, the binding affinities of glycomimetic E-selectin antagonists were identical for wt and S128R E-selectin. Overall, the previous reports on carbohydrate ligand promiscuity of S128R E-selectin could not be confirmed.