A sharp fluctuation in peripheral blood cells shortly after dasatinib administration

Thrombopoietin Levels During Tyrosine Kinase Inhibitor Therapy for Chronic Myeloid Leukemia

BACKGROUND AND OBJECTIVE

Although it is well known that platelet depletion is one of the major adverse events related to tyrosine kinase inhibitor (TKI) therapy, the effect of TKIs on thrombopoietin (TPO), a stimulating factor for thrombopoiesis, has not been examined to date. In this study, we investigated the effect of TKIs on the levels of plasma TPO concentration in patients with well-controlled chronic myeloid leukemia receiving imatinib or dasatinib and those in treatment-free remission (TFR).

METHODS

Blood samples for blood cell counts and plasma TPO levels were obtained from 23 dasatinib-treated patients before and 1 h after intake, 11 patients treated with imatinib before and 2 h after intake, and nine TFR patients. Levels of plasma TPO were determined by using enzyme-linked immunosorbent assays.

RESULTS

Levels of TPO were significantly inversely correlated with platelet counts in the entire cohort (r = - 0.568, p < 0.0001). Dasatinib intake, but not imatinib, significantly reduced platelet counts after intake (p = 0.0009 in dasatinib and p = 0.5431 in imatinib). However, imatinib and dasatinib intake increased the levels of TPO in these patients (p = 0.0024, dasatinib; p = 0.0098, imatinib).

CONCLUSIONS

Our study results suggest that neither dasatinib nor imatinib therapy inhibits TPO production. Rather, transient increases in TPO levels seen with these two treatments might be a result of the decrease in TPO clearance these TKIs confer. However, further investigations are required to clarify the effect of TKIs on thrombopoiesis.

Direct effect of dasatinib on signal transduction pathways associated with a rapid mobilization of cytotoxic lymphocytes

It has been shown that an increase in cytotoxic lymphocyte counts in the peripheral blood occurs rapidly after taking dasatinib, but the underlying mechanism is not yet elucidated. To investigate the influence of dasatinib on signal transduction pathways, we investigated the changes in JAK-STAT, mitogen-activated protein kinase (MAPK), and AKT in cytotoxic lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), before and after dasatinib treatment in chronic myeloid leukemia patients. Among a total of 30 patients, 18 were treated with dasatinib, nine with imatinib, and three with nilotinib. At constitutive levels, the expression of phosphorylated proteins, pSTAT1, pSTAT3, and pERK in NK cells and pSTAT3 in CTLs, was significantly higher in dasatinib-treated patients. Among the patients evaluated, only dasatinib-treated patients showed inhibition of multiple signaling pathways after taking a tyrosine kinase inhibitor. The magnitude of pERK and pAKT inhibition was closely associated with an increase in NK cells and CTLs, respectively, after taking a tyrosine kinase inhibitor. Those responses were more evident in patients with cytomegalovirus IgG positivity. In this study, we demonstrated for the first time, the influence of dasatinib on cell events in cytotoxic lymphocytes in vivo and explained the possible underlying mechanism that results in lymphocyte mobilization after dasatinib treatment.

Principal component analysis uncovers cytomegalovirus-associated NK cell activation in Ph+ leukemia patients treated with dasatinib

Dasatinib treatment markedly increases the number of large granular lymphocytes (LGLs) in a proportion of Ph⁺ leukemia patients, which associates with a better prognosis. The lymphocytosis is predominantly observed in cytomegalovirus (CMV)-seropositive patients, yet detectable CMV reactivation exists only in a small fraction of patients. Thus, etiology of the lymphocytosis still remains unclear. Here, we identified NK cells as the dominant LGLs expanding in dasatinib-treated patients, and applied principal component analysis (PCA) to an extensive panel of NK cell markers to explore underlying factors in NK cell activation. PCA displayed phenotypic divergence of NK cells that reflects CMV-associated differentiation and genetic differences, and the divergence was markedly augmented in CMV-seropositive dasatinib-treated patients. Notably, the CMV-associated highly differentiated status of NK cells was already observed at leukemia diagnosis, and was further enhanced after starting dasatinib in virtually all CMV-seropositive patients. Thus, the extensive characterization of NK cells by PCA strongly suggests that CMV is an essential factor in the NK cell activation, which progresses stepwise during leukemia and subsequent dasatinib treatment most likely by subclinical CMV reactivation. This study provides a rationale for the exploitation of CMV-associated NK cell activation for treatment of leukemias.

Real-time analysis of imatinib- and dasatinib-induced effects on chronic myelogenous leukemia cell interaction with fibronectin

Attachment of stem leukemic cells to the bone marrow extracellular matrix increases their resistance to chemotherapy and contributes to the disease persistence. In chronic myelogenous leukemia (CML), the activity of the fusion BCR-ABL kinase affects adhesion signaling. Using real-time monitoring of microimpedance, we studied in detail the kinetics of interaction of human CML cells (JURL-MK1, MOLM-7) and of control BCR-ABL-negative leukemia cells (HEL, JURKAT) with fibronectin-coated surface. The effect of two clinically used kinase inhibitors, imatinib (a relatively specific c-ABL inhibitor) and dasatinib (dual ABL/SRC family kinase inhibitor), on cell binding to fibronectin is described. Both imatinib and low-dose (several nM) dasatinib reinforced CML cell interaction with fibronectin while no significant change was induced in BCR-ABL-negative cells. On the other hand, clinically relevant doses of dasatinib (100 nM) had almost no effect in CML cells. The efficiency of the inhibitors in blocking the activity of BCR-ABL and SRC-family kinases was assessed from the extent of phosphorylation at autophosphorylation sites. In both CML cell lines, SRC kinases were found to be transactivated by BCR-ABL. In the intracellular context, EC50 for BCR-ABL inhibition was in subnanomolar range for dasatinib and in submicromolar one for imatinib. EC50 for direct inhibition of LYN kinase was found to be about 20 nM for dasatinib and more than 10 µM for imatinib. Cells pretreated with 100 nM dasatinib were still able to bind to fibronectin and SRC kinases are thus not necessary for the formation of cell-matrix contacts. However, a minimal activity of SRC kinases might be required to mediate the increase in cell adhesivity induced by BCR-ABL inhibition. Indeed, active (autophosphorylated) LYN was found to localize in cell adhesive structures which were visualized using interference reflection microscopy.

Rapid and sustained increase of large granular lymphocytes and rare cytomegalovirus reactivation during dasatinib treatment in chronic myelogenous leukemia patients

We retrospectively investigated increases in large granular lymphocytes (LGL) in peripheral blood during dasatinib treatment in 25 chronic myelogenous leukemia patients. Fifteen of 25 patients (60 %) showed an increase in LGL. All 15 of these patients also showed an increase in NK cells, and 11 showed an increase in CD8(+) T cells. High frequencies of clonal rearrangements of TCR-β, -γ, and -δ genes were observed in LGL (+) patients, and at lower frequencies in LGL (-) patients as well. Clinical responses were favorable for all. With respect to their newly obtained complete molecular response after dasatinib treatment, LGL (+) patients showed higher response rates than did LGL (-) patients. In contrast, pleural effusions were more commonly observed in LGL (+) patients (60 %) than in LGL (-) patients (20 %). LGL counts significantly increased at 2 h after oral intake of dasatinib in all 25 patients. This was not observed in treatment with imatinib or nilotinib. Cytomegalovirus (CMV) C7-HRP tests were negative in all patients. Serum CMV-IgM antibodies were positive in only 2 of 25 patients without symptom of infection. Thus, LGL lymphocytosis during dasatinib treatment may be correlated with favorable molecular response, and with increased incidence of pleural effusions. In the clinical setting, CMV reactivation appears uncommon.