Optimizing Platelet GPVI Inhibition versus Haemostatic Impairment by the Btk Inhibitors Ibrutinib, Acalabrutinib, ONO/GS-4059, BGB-3111 and Evobrutinib

Abstract

Ibrutinib and acalabrutinib are approved for B cell malignancies and novel Bruton's tyrosine kinase (Btk) inhibitors undergo clinical testing also in B cell-driven autoimmune disorders. Btk in platelets mediates platelet activation via glycoprotein (GP) VI, which is crucial for atherosclerotic plaque-induced platelet thrombus formation. This can be selectively inhibited by Btk inhibitors. Since patients on second-generation Btk inhibitors apparently show less bleeding than patients on ibrutinib, we compared the effects of ibrutinib and four novel irreversible Btk inhibitors on GPVI-dependent platelet aggregation in blood and in vitro bleeding time. Low concentrations of collagen which induced the same low degree of GPVI-mediated platelet aggregation as atherosclerotic plaque material were applied. IC50 values for collagen (0.2–0.5 µg/mL)-induced platelet aggregation after 15-minute pre-incubation were: ibrutinib 0.12 µM, BGB-3111 0.51 µM, acalabrutinib 1.21 µM, ONO/GS-4059 1.20 µM and evobrutinib 5.84 µM. Peak venous plasma concentrations of ibrutinib (0.5 µM), acalabrutinib (2 µM) and ONO/GS-4059 (2 µM) measured after anti-proliferative dosage inhibited collagen-induced platelet aggregation, but did not increase PFA-200 closure time on collagen/epinephrine. Closure times were moderately increased by 2- to 2.5-fold higher concentrations of these inhibitors, but not by BGB-3111 (1 µM) and evobrutinib (10 µM). Prolonging platelet drug exposure to 60 minutes lowered IC50 values of any Btk inhibitor for GPVI-mediated aggregation by several fold, and 5- to 10-fold below anti-proliferative therapeutic drug plasma levels. In conclusion, low blood concentrations of ibrutinib and the novel Btk inhibitors suffice for GPVI selective platelet inhibition relevant for atherothrombosis but do not impair primary haemostasis.

Relative Selectivity of Covalent Inhibitors Requires Assessment of Inactivation Kinetics and Cellular Occupancy: A Case Study of Ibrutinib and Acalabrutinib

“…However, when properly adjusted for clinical exposure, covalent binding mechanism, and enzymatic activity, our data and those of other groups (Bye et al, 2017) now indicate that ibrutinib and acalabrutinib have similar selectivity between BTK and TEC. This similar selectivity is consistent with a recent study suggesting that platelet inhibition and potential hemorrhagic risk predicted by in vitro closure time are likelyclass effects across five BTK inhibitors: ibrutinib, zanubrutinib, acalabrutinib, tirabrutinib, and evobrutinib (Denzinger et al, 2019). Furthermore, recent mechanistic investigations of the effects of ibrutinib and acalabrutinib on platelet functions suggested that polymorphism of drug efflux pumps might sensitize some patients toward platelet aggregation impairment more than others (Series et al, 2019).…”

Selective inhibition of thromboinflammation in COVID-19 by Btk inhibitors

“…As we reported recently, FcγRIIA-stimulated platelet activation (aggregation, secretion, and P-selectin expression) and formation of platelet-neutrophil aggregates were completely suppressed by low concentrations of various Btk-inhibitors in vitro and by a single low oral dose of ibrutinib for several days ex vivo [13]. Further platelet-mediated mechanisms of vascular thrombosis, that are also blocked by Btk-inhibitors, are the activation of platelet glycoprotein (GP) VI by collagen exposed after endothelial injury and of GPIb by von Willebrand factor expressed on inflamed endothelium [14,15,16,17,18,19,20].…”

“…One must, however, be aware that patients treated with the irreversible covalent Btk-inhibitors ibrutinib, acalabrutinib, or zanubrutinib for B-cell malignancies show adverse reactions such as infections (grade 3 and higher in 18%-24% of the treated patients, mostly pneumonia) and frequently (50%) mild bleeding events [33,34,35]. One explanation for the latter might be the inhibition of the homologous kinase Tec in addition to Btk in platelets by these Btk-inhibitors [14,15].…”

“…Perhaps the higher Btk-expression of autoreactive B-cells or the necessity to reach sessile B-cells in lymph nodes requires higher drug concentrations. If antiviral antibody producing, clonal expanding memory B-cells of COVID-19 patients [42] behave similar to autoreactive B-cells concerning Btk-expression and drug pharmacodynamics a preferential inhibition of platelet activation (via their CLEC-2, FcγRIIA, GPVI and GPIb receptors) and monocyte and neutrophil activation, and hence thromboinflammation might be achievable by using low doses of selective Btk-inhibitors [7,13,15,16].…”

Platelets and cancer… the plot doesn’t always thicken

“…Understanding the functional impacts of ibrutinib is also proving critical. Advances in our understanding suggest the potential for repurposing as specific atherosclerosis inhibitor as low concentrations impede glycoprotein (GP) VI mediated platelet aggregation without impacting primary haemostasis 8,9 . There are also clinical trials of BTK inhibitors underway in immune and inflammatory disorders, including immune thrombocytopenic purpura.…”