Adenosine 2A Receptor Activation Amplifies Ibrutinib Antiplatelet Effect; Implications in Chronic Lymphocytic Leukemia

SIMPLE SUMMARY: A significant number of patients with chronic lymphocytic leukemia (CLL) have an increased risk of bleeding. This risk is further increased when taking ibrutinib, a new effective therapy for CLL. Platelets are the key player in haemostasis and thrombosis. In this study, we first characterized platelet function in untreated stable CLL patients in comparison to age-matched healthy volunteers. Using ex vivo platelets from healthy volunteers, we then investigated a possible mechanism of platelet dysfunction induced by a combination of a CLL-derived factor (adenosine) and ibrutinib. We found that therapeutic concentration of ibrutinib did not affect platelet activation response to collagen. However, the presence of adenosine switched off a central platelet activation pathway leading to increased antiplatelet activity of ibrutinib. Larger studies are needed to draw a correlation between adenosine, platelet function and ibrutinib-associated bleeding in CLL patients. ABSTRACT: Chronic lymphocytic leukemia patients have an increased bleeding risk with the introduction of Bruton tyrosine kinase (BTK) inhibitors. BTK is a signaling effector downstream of the platelet GPVI receptor. Innate platelet dysfunction in CLL patients and the contribution of the leukemia microenvironment to the anti-platelet effect of BTK inhibitors are still not well defined. Herein, we investigated platelet function in stable, untreated CLL patients in comparison to age-matched healthy subjects as control. Secondly, we proposed a novel mechanism of platelet dysfunction via the adenosinergic pathway during BTK inhibitor therapy. Our data indicate that the nucleotidase that produces adenosine, CD73, was expressed on one-third of B-cells in CLL patients. Inhibition of CD73 improved platelet response to ADP in the blood of CLL patients ex vivo. Using healthy platelets, we show that adenosine 2A (A2A) receptor activation amplifies the anti-platelet effect of ibrutinib (10 nM). Ibrutinib plus an A2A agonist—but not ibrutinib as a single agent—significantly inhibited collagen (10 µg/mL)-induced platelet aggregation. Mechanistically, A2A activation attenuated collagen-mediated inhibition of p-VASP and synergized with ibrutinib to inhibit the phosphorylation of AKT, ERK and SYK kinases. This manuscript highlights the potential role of adenosine generated by the microenvironment in ibrutinib-associated bleeding in CLL patients.