Dasatinib-Induced Platelet Dysfunction.

Dasatinib is efficacious and safe in patients (pts) with chronic myelogenous leukemia (CML) after imatinib failure. However, dasatinib therapy has been linked to bleeding in some pts, typically affecting mucosal surfaces. We analyzed the effect of dasatinib on basic coagulation tests and platelet aggregation function in 55 pts with CML in chronic phase at diagnosis (1), >8 weeks after tyrosine kinase inhibitor (TKI) discontinuation (3), or during therapy with the ABL/SRC inhibitors dasatinib (n=27) and bosutinib (n=12), or the aminopyrimidine derivatives imatinib (n=8) and nilotinib (n=4). Median age was 54 yrs (range, 22–80), WBC 5.5 ×10⁹/L (range, 2.1–58.5), hemoglobin 12.2 g/dL (range, 9.7–15.1), and platelets 230 ×10⁹/L (range, 80–746). Only 2 pts (both on imatinib and warfarin) had abnormal basic coagulation parameters (prolonged prothrombin time [PT]). In the remainder 53 pts, the median PT time was 11.6 sec (9.8–13), activated partial thromboplastin time (aPTT) 28.5 sec (range, 21–33.9), and fibrinogen level 495 mg/dL (range, 336–700), suggesting an intact secondary hemostasis. To evaluate the primary hemostasis status, platelet aggregation was measured by turbidometry in 1 mL of platelet-rich plasma upon stimulation with 5 μM of ADP, 1 μg/ml of collagen, 1 μM of epinephrine, 1 mM arachidonic acid, or 8 μL of ristocetin by using a Whole Blood Lumi-Aggregometer (Chrono-Log Corporation, Havertown, PA). Aggregation was expressed as the maximal percent change in light transmittance from baseline using platelet-poor plasma as a reference. Five (9%) patients (2 bosutinib, 1 nilotinib, and 2 imatinib) were on aspirin and showed an aspirin-like effect (decreased platelet aggregation with arachidonic acid [AA] and epinephrine [Epi]). Patients off-TKI or untreated had a normal platelet aggregation test. Results on the remaining 46 assessable patients demonstrate that dasatinib is strongly associated platelet aggregation defects, particularly an aspirin-like effect, when compared with other TKIs.

Platelet function analysis by PFA-100 showed that addition of dasatinib (400 nM) to fresh whole blood obtained from a healthy volunteer rapidly induced platelet dysfunction. Closure times were prolonged from 100 sec (baseline) to >300 sec in response to Epi (normal <160 sec) but not in response to ADP (from 72 to 84 sec, normal <120 sec) after 30 min incubation. In summary, our data indicate that dasatinib does not interfere with secondary hemostasis. Rather, it inhibits platelet function in an aspirin-like manner. This effect, while independent, can be additive to dasatinib-induced thrombocytopenia and may account for the bleeding diathesis observed in pts with CML receiving dasatinib.