Summary. Background: Based on in vitro and animal data, PI3Kb is given an important role in platelet adhesion and aggregation but its role in insulin signaling is unclear. Objective: To strengthen the PI3Kb target validation using the novel, short-acting inhibitor AZD6482. Methods and results: AZD6482 is a potent, selective and ATP competitive PI3Kb inhibitor (IC 50 0.01 lM). A maximal anti-platelet effect was achieved at 1 lM in the in vitro and ex vivo tests both in dog and in man. In dog, in vivo AZD6482 produced a complete antithrombotic effect without an increased bleeding time or blood loss. AZD6482 was well tolerated in healthy volunteers during a 3-h infusion. The ex vivo anti-platelet effect and minimal bleeding time prolongation in the dog model translated well to data obtained in healthy volunteers. AZD6482 inhibited insulin-induced human adipocyte glucose uptake in vitro (IC 50 of 4.4 lM). In the euglycemic hyperinsulinemic clamp model, in rats, glucose infusion rate was not affected at 2.3 lM but reduced by about 60% at a plasma exposure of 27 lM. In man, the homeostasis model analysis (HOMA) index increased by about 10-20% at the highest plasma concentration of 5.3 lM. Conclusions: This is the first human target validation for PI3Kb inhibition as anti-platelet therapy showing a mild and generalized antiplatelet effect attenuating but not completely inhibiting multiple signaling pathways with an impressive separation towards primary hemostasis. AZD6482 at Ôsupra-therapeuticÕ plasma concentrations may attenuate insulin signaling, most likely through PI3Ka inhibition.

This is the first reported crystal structure of a complex formed between a serpin and a serpin inhibitor. The localisation of the inhibitory peptide in the complex strongly supports the theory that molecules binding in the space between beta strands 3A and 5A of a serpin are able to prevent insertion of the reactive-centre loop into beta sheet A, thereby abolishing the ability of the serpin to irreversibly inactivate its target enzyme. The characterisation of the two binding sites for the peptide inhibitor provides a solid foundation for computer-aided design of novel, low molecular weight PAI-1 inhibitors.

• In the clinic, all oral antiplatelet medicines have a risk of bleeding complications.• We present an antidote for ticagrelor that reverses its antiplatelet effect in human platelet-rich plasma and its bleeding effect in mice.Ticagrelor is a direct-acting reversibly binding P2Y 12 antagonist and is widely used as an antiplatelet therapy for the prevention of cardiovascular events in acute coronary syndrome patients. However, antiplatelet therapy can be associated with an increased risk of bleeding. Here, we present data on the identification and the in vitro and in vivo pharmacology of an antigen-binding fragment (Fab) antidote for ticagrelor. The Fab has a 20 pM affinity for ticagrelor, which is 100 times stronger than ticagrelor's affinity for its target, P2Y 12 . Despite ticagrelor's structural similarities to adenosine, the Fab is highly specific and does not bind to adenosine, adenosine triphosphate, adenosine 59-diphosphate, or structurally related drugs. The antidote concentration-dependently neutralized the free fraction of ticagrelor and reversed its antiplatelet activity both in vitro in human platelet-rich plasma and in vivo in mice. Lastly, the antidote proved effective in normalizing ticagrelor-dependent bleeding in a mouse model of acute surgery. This specific antidote for ticagrelor may prove valuable as an agent for patients who require emergency procedures. (Blood. 2015;125(22):3484-3490)

A novel low-molecular-weight inhibitor, AR-H029953XX, was developed from a known fibrinolytic compound, flufenamic acid, which prevented complex formation of human plasminogen activator inhibitor type 1 (PAI-1) with tissue plasminogen activator (tPA) by inhibition of PAI-1. To explore the binding site for AR-H029953XX, mutants of human PAI-1 were constructed by site-directed mutagenesis and were then expressed in CHO cells, purified, activated, and characterized. (1) PAI-1 with mutations in the reactive center loop: L1-PAI-1 (P10, Ser337Glu) had stability and activity similar to those of wild-type PAI-1 (wt-PAI-1), and L2-PAI-1 (P12, Ala335Glu) was highly stable but was a substrate for tPA. (2) PAI-1 with mutations near the binding epitope for the strongly inhibiting monoclonal antibody CLB-2C8: C1-PAI-1 (Phe114Glu), C2-PAI-1 (Val121Phe), C3-PAI-1 (Arg76Glu/Arg115Glu/Arg118Glu), and C4-PAI-1 (Arg115Glu) were all comparable in activity and stability to wt-PAI-1. AR-H029953XX (Ki = 25 microM) prevented complex formation between tPA and active wt-PAI-1 as well as that with mutants L1-, L2-, C1-, C2-, and C4-PAI-1. AR-H029953XX also inhibited binding of these PAI-1 variants to the antibody CLB-2C8, as measured by surface plasmon resonance. In contrast, AR-H029953XX had almost no inhibitory effect on the complex formation of tPA with C3-PAI-1. Moreover, AR-H029953XX had no effect on the binding rate of CLB-2C8 to C3-PAI-1, or on the binding to latent PAI-1 or to cleaved L2-PAI-1. The binding site of AR-H029953XX thus appears to be located in the neighborhood of the postulated epitope for CLB-2C8, near residues Arg76 and/or Arg118. This specific domain of the PAI-1 molecule might thus also be important for the mechanism of inhibitory activity toward tPA. Moreover, the structure of this region in active PAI-1 has to be different from the corresponding regions in latent and cleaved PAI-1.