Influence of heparin mimetics on assembly of the FGF.FGFR4 signaling complex.

Fibroblast growth factor (FGF) signaling regulates mammalian development and metabolism, and its dysregulation is implicated in many inherited and acquired diseases, including cancer. Heparan sulfate glycosaminoglycans (HSGAGs) are essential for FGF signaling as they promote FGF.FGF receptor (FGFR) binding and dimerization. Using novel organic synthesis protocols to prepare homogeneously sulfated heparin mimetics (HM), including hexasaccharide (HM(6)), octasaccharide (HM(8)), and decasaccharide (HM(10)), we tested the ability of these HM to support FGF1 and FGF2 signaling through FGFR4. Biological assays show that both HM(8) and HM(10) are significantly more potent than HM(6) in promoting FGF2-mediated FGFR4 signaling. In contrast, all three HM have comparable activity in promoting FGF1.FGFR4 signaling. To understand the molecular basis for these differential activities in FGF1/2.FGFR4 signaling, we used NMR spectroscopy, isothermal titration calorimetry, and size-exclusion chromatography to characterize binding interactions of FGF1/2 with the isolated Ig-domain 2 (D2) of FGFR4 in the presence of HM, and binary interactions of FGFs and D2 with HM. Our data confirm the existence of both a secondary FGF1.FGFR4 interaction site and a direct FGFR4.FGFR4 interaction site thus supporting the formation of the symmetric mode of FGF.FGFR dimerization in solution. Moreover, our results show that the observed higher activity of HM(8) relative to HM(6) in stimulating FGF2.FGFR4 signaling correlates with the higher affinity of HM(8) to bind and dimerize FGF2. Notably FGF2.HM(8) exhibits pronounced positive binding cooperativity. Based on our findings we propose a refined symmetric FGF.FGFR dimerization model, which incorporates the differential ability of HM to dimerize FGFs.

The synthetic pentasaccharide fondaparinux: first in the class of antithrombotic agents that selectively inhibit coagulation factor Xa.

Fondaparinux (Arixtra), a synthetic pentasaccharide, is the first in a new class of antithrombotic agents that selectively inhibit coagulation factor Xa. In vitro experiments demonstrated that it is a selective inhibitor of factor Xa. In plasma, fondaparinux selectively binds to antithrombin, catalyzes factor Xa inhibition, and thereby inhibits thrombin generation. Its antithrombotic efficacy has been demonstrated in various animal models mimicking venous and arterial thrombosis. In humans, its pharmacokinetic profile is favorable, with a rapid onset of antithrombotic activity and an elimination half-life allowing a convenient once-daily dosing regimen. In several clinical trials, fondaparinux was more effective than the reference drug, enoxaparin, in preventing venous thromboembolism after hip fracture, major knee, and elective hip replacement surgeries. The overall reduction in the risk of venous thromboembolism ranged between 26.3 and 56.4%, depending on the trial. This superior efficacy was achieved without increasing the risk of clinically relevant bleeding. Fondaparinux also showed promising results in the treatment of patients with venous thromboembolism and acute coronary syndromes. Thus, it is now established that selective factor Xa inhibition is an efficient way to prevent venous thrombosis. The advent of fondaparinux offers an opportunity to improve substantially the management of venous thromboembolism.

First Synthetic Carbohydrates with the Full Anticoagulant Properties of Heparin.

A single disaccharide building block is required to obtain synthetic carbohydrates that reproduce the anticoagulant activity of heparin and inhibit thrombin (n>6) and/or factor Xa (n≥2; see reaction scheme). Thus, there is evidence that heparin fragments with at least 15 saccharide units are required for thrombin inhibition. Lev=levulinoyl.