Platelet Function Prior to Ibrutinib Treatment Is More Severely Impaired in Chronic Lymphocytic Leukemia Than in Mantle Cell Lymphoma

INTRODUCTION. Ibrutinib is an oral small-molecule drug that irreversibly inhibits Bruton's tyrosine kinase and thus suppresses proliferation of B cells. Ibrutinib therapy in chronic lymphocytic leukemia (CLL) and in mantle cell lymphoma (MCL) is associated with frequent bleeding complications that were reported to be more severe in CLL. This difference was suggested to be related to differential adenosine diphosphate (ADP) disruption by CD39, expressed by tumor cells. Here we investigate platelet functional activity in CLL and MCL patients before initiation of ibrutinib.

MATERIALS. Fifty one adult patients with relapsed and refractory CLL and MCL and 20 healthy donors were included in the study. Platelet functional activity was characterized by flow cytometry before and after activation with SFLLRN plus collagen-related peptide. Levels of CD42b, CD61, CD62P, PAC1, annexin V binding, and mepacrine release were determined. Aggregation with collagen, ADP and ristocetin were measured.

RESULTS. Among 36 CLL patients 25 (69%) were men, the median age was 66 (range, 31 to 83 years) and 23 (64%) had a refractory disease. In 34 previously treated patients the median number of prior treatments was 2 (range, 1 - 6). Two CLL patients with del (17p) received ibrutinib as a first line. In a group of MCL patients (n=15) there were 12 men (80%), the median age was 63 years (range, 49-79). Seven (54%) patients had a high MIPI score. The median number of previous chemotherapy lines in MCL patients was 1 (range, 1 - 6). Lymphocyte count before initiation of ibrutinib was significantly higher in CLL group (median 17,5 х 10⁹/L range 0,48 - 189,7) compared to MCL group (median 1,75 х 10⁹/L, range 0,35 - 6,59, p=0,037). Initial platelets count was also different being lower in CLL than in MCL patients (127 х 10⁹/L (15 - 248) versus 186 х 10⁹/L (63 - 311), p=0,005). Platelets of untreated patients with CLL had statistically significant impairments in their responses compared to those with MCL. Specifically, they had decreased integrin activation in response to stimulation (46±19% versus 73±18%; for healthy donors, 100±17%), and relative mepacrine release (2.9±0.9 versus 3.5±0.8; healthy, 4.0±0.7). P-selectin release was impaired milder (77±17% versus 92±14%; healthy, 100±10%), and procogulant platelet formation impairment was not statistically significant (8±6% versus 12±7%; healthy, 12±3%). In control experiments, addition of MeS-AMP and MRS2179, selective inhibitors of ADP receptors, had comparable effects on the healthy donor platelets. Aggregation in response to ADP was dramatically impaired in CLL compared with MCL (24±18% versus 42±16%), as well as that in response to collagen (47±23% versus 72±13%). Upon ibrutinib treatment, further decrease of PAC1 binding and procoagulant platelets formation almost to the level of resting platelets were observed; activation with SFLLRN alone produced a similar result with donor platelets.

CONCLUSIONS. Patients with CLL and MCL have initially impaired response of platelets. The defects of platelet function in CLL is much greater suggesting a possible explanation of the different clinical severity.