Human target validation of phosphoinositide 3‐kinase (PI3K)β: effects on platelets and insulin sensitivity, using AZD6482 a novel PI3Kβ inhibitor

Abstract

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.

Inhibition of PI3Kβ Signaling with AZD8186 Inhibits Growth of PTEN-Deficient Breast and Prostate Tumors Alone and in Combination with Docetaxel

“…PI3Kb mediates GPCR receptor signaling, regulating thrombinand ADP-mediated platelet aggregation (13,14), as well as LPA receptor-mediated signals via the small GTPase rac (15). Consistent with this, AZD8186 inhibits ADP-induced human platelet aggregation with a mean IC 50 value of 186 nmol/L (Fig.…”

Discovery and functional characterization of a neomorphic PTEN mutation

“…Contrary to current dogma, these observations suggest that PTEN can also act as an oncogene as well as a tumor suppressor. Lastly, we demonstrate that cells expressing this mutant allele are sensitive to treatment with PI3K inhibitors that are currently undergoing clinical testing (25,26). These results add another layer to the findings of PTEN lossof-function and dominant-negative mutations implicated with tumorigenesis (cf.…”

Platelet PI3Kβ and GSK3 regulate thrombus stability at a high shear rate

“…This is consistent with the fact that inhibition of PI3Kb does not induce a bleeding phenotype. 6,10,12,13 During thrombus growth there is a local restriction of the lumen of the vessel leading to an increase in shear rate and an elevation of the tensile forces on formed interplatelet bonds. Our in vivo experiments on mesenteric arterioles are consistent with the notion that a certain degree of instability is a normal feature of arterial thrombus formation, as nearly 30% of massive thrombi (.28 000 mm 2 ) are subject to platelet emboli shedding.…”

“…Heparinized human blood was treated with the selective PI3Kb inhibitor AZD6482 13 and was perfused over a collagen matrix at 1500 seconds 21 for 2 minutes followed by application of a pathological shear rate of 4000 seconds 21 . Although thrombi from untreated blood remained stable and kept growing at pathological shear rate, inhibition of PI3Kb led to thrombi instability ( Figure 1A right).…”

“…6,10,11 Because PI3Kb inhibition prevents occlusive thrombus formation in mice, rats, and dogs with a limited increase in bleeding risk and acceptable safety in humans, this kinase has been proposed as a potential antithrombotic drug target. 12,13 However, the role of platelet PI3Kb in integrated in vivo or ex vivo models of thrombosis on high shear-rate condition remains incompletely documented.…”