In vivo effects of imatinib mesylate on human haematopoietic progenitor cells

Apoptotic profiling of chronic myeloid leukaemia patients' platelets ex vivo before and after treatment with Imatinib

Chronic myeloid leukaemia (CML) is a malignancy of the haematopoietic stem cells. The first line of treatment for CML, especially in developing countries, remains the first-generation tyrosine kinase inhibitor, Imatinib. Patients with CML are frequently diagnosed with platelet abnormalities. However, the specific mechanism of platelet abnormalities in CML remains unclear and poorly understood. The aim of this study was therefore to determine the apoptotic profiles of CML patients ex vivo on platelets before and after treatment with Imatinib. Blood samples of healthy volunteers and CML patients at diagnosis and after 6 months treatment with Imatinib were collected. Platelet counts, viability and activation were determined. Results showed that CML patients' platelet counts were elevated upon diagnosis and these levels statistically significantly decreased after 6 months of treatment. Platelet activation was significantly increased after 6 months of treatment compared to levels at diagnosis (P-value < .05). Similarly, platelet apoptosis was also increased after 6 months of treatment. Abnormalities in platelet functioning found in this study may partly be due to clonal proliferation of haematopoietic cells in CML patients, specifically of megakaryocyte precursors as well as the inhibition of platelet tyrosine kinase's and the inhibition of platelet-derived growth factor.

Incidence of Clinically Significant (≤10 g/dL) Late Anemia in Elderly Patients with Newly Diagnosed Chronic Myeloid Leukemia Treated with Imatinib

BACKGROUND

In elderly patients with chronic myeloid leukemia (CML) responsive to imatinib, the incidence of clinically significant (CS) late chronic anemia is still unknown.

MATERIALS AND METHODS

To highlight this issue, we revised retrospectively 81 CML patients aged >60 years treated at our Institution with front-line imatinib for at least 24 months in durable complete cytogenetic response (CCyR). CS late chronic anemia was defined as the presence of persistent (>6 months) and otherwise unexplained Hb levels ≤10 g/dL, which occurred >6 months from imatinib start.

RESULTS

A condition of CS late chronic anemia occurred in 22 out of 81 patients (27.2%) at different intervals from imatinib start. Seven out of 22 patients (31.8%) needed packed red cell transfusions during the follow-up. At diagnosis, patients who developed CS late chronic anemia were significantly older and had a lower Hb median level. Six out of 22 patients with CS late chronic anemia received subcutaneous recombinant alpha-erythropoietin (EPO) at the standard dosage of 40,000 IU weekly: all 6 patients achieved an erythroid response. A significantly worse event-free survival (EFS) in patients with untreated CS late chronic anemia was observed (p = 0.012).

CONCLUSIONS

CS late chronic anemia during long-term treatment with imatinib is a common complication in responsive elderly patients, with worse EFS if untreated. Results with EPO are encouraging, but larger studies are warranted to define its role.

Renal dysfunction and anemia associated with long-term imatinib treatment in patients with chronic myelogenous leukemia

Knowledge of the toxicity profile of long-term treatment with imatinib is limited. In the present study, we sought to evaluate renal function and hemoglobin levels during long-term imatinib treatment. Eighty-two patients with chronic myelogenous leukemia in chronic phase who had been on imatinib for over 5 years were retrospectively analyzed. The mean estimated glomerular filtration rate (eGFR) was significantly decreased over 5 years (77 ± 17 to 62 ± 14 ml/min/1.73m², P < 0.001). Higher age and lower eGFR value at initiation of imatinib were significantly associated with development of renal dysfunction by multivariate analyses. Mean hemoglobin levels also significantly decreased over the 5-year period (12.9 ± 1.7 to 12.4 ± 1.3 g/dl, P < 0.01). The rate of decrease in eGFR correlated significantly with hemoglobin levels (correlation coefficient = - 0.249, P < 0.05). Serum erythropoietin (EPO) levels did not increase in 16 patients with both renal dysfunction and anemia (median, 31.9 mIU/ml). In patients who participated in a clinical trial of imatinib discontinuation, mean eGFR (50.0 ± 6.5 to 56.0 ± 10.2 ml/min/1.73m², P < 0.05) and hemoglobin levels (12.0 ± 1.7 to 14.0 ± 1.6 g/dl, P < 0.01) improved significantly at 1 year after discontinuation. These findings suggest that long-term imatinib results in a partially reversible continuous decline in renal function and decreased hemoglobin levels.

Feasibility of treatment discontinuation in chronic myeloid leukemia in clinical practice: results from a nationwide series of 236 patients

Over half of chronic myeloid leukemia (CML) patients in deep molecular response do not lose the major molecular response (MMR) after stopping treatment with tyrosine kinase inhibitors (TKI). This strategy is safe in clinical trials, but its applicability in the real-life setting remains unsettled. We describe the outcomes after TKI discontinuation in a nationwide series of 236 CML patients. Median follow-up from treatment discontinuation was 21.5 months and 5 patients died from CML-unrelated causes. TKI therapy was reinitiated due to MMR loss (n = 52), increase ≥ 1 log in BCR-ABL transcript level without losing MMR (n = 12), patient preference (n = 2), and withdrawal syndrome (n = 1). Treatment-free remission rate at 4 years was 64% (95% confidence interval, CI: 55%–72%). Cumulative incidence of molecular recurrence at 3 years was 33% (95% CI: 26%–38%). TKI treatment for < 5 years and MR4.5 duration shorter than 4 years were both associated with higher incidence of molecular recurrence. No patient had disease progression. Response status at last control was: MR4.5 (n = 196), MR4 (n = 15), MMR (n = 14), complete cytogenetic response (n = 10), and other (n = 1). A significant increase in Hb and cholesterol levels was observed after imatinib withdrawal. Our results demonstrate that TKI treatment discontinuation is feasible in real-life clinical practice.

Platelet Dysfunction in Patients with Chronic Myeloid Leukemia: Does Imatinib Mesylate Improve It?

Objective:

The aim of this study was to investigate the effects of imatinib mesylate on platelet aggregation and adenosine triphosphate (ATP) release in chronic myeloid leukemia patients.

Materials and Methods:

Platelet aggregation and ATP release induced by 5.0 mM adenosine diphosphate, 0.5 mM arachidonic acid, 1.0 mg/mL ristocetin, and 2 µg/mL collagen were studied by whole blood platelet lumi-aggregometer in 20 newly diagnosed chronic myeloid leukemia patients before and after imatinib mesylate treatment.

Results:

At the time of diagnosis, 17/20 patients had abnormal platelet aggregation results; 8 (40%) had hypoactivity, 6 (30%) had hyperactivity, and 3 (15%) had mixed hypo- and hyperactivity. Repeat platelet aggregation studies were performed after a mean of 19 months (min: 5 months-max: 35 months) in all patients who received imatinib mesylate during this period. After therapy, 18/20 (90%) patients had abnormal laboratory results; 12 (60%) had hypoactive platelets, 4 (20%) had mixed hypo- and hyperactive platelets, and 2 (10%) had hyperactive platelets. Three of the 8 patients with initial hypoactivity remained hypoactive, while 2 developed a mixed picture, 2 became hyperactive, and 1 normalized. Of the 6 patients with initial hyperactivity, 4 became hypoactive and 2 developed a mixed pattern. All of the 3 patients with initial hypo- and hyperactivity became hypoactive. Finally, 2 of the 3 patients with initial normal platelets became hypoactive while 1 remained normal. There was a significant decrease in ristocetin-induced platelet aggregation after therapy (p<0.001), while platelet aggregation and secretion induced by other agonists showed no difference after treatment (p>0.05).

Conclusion:

These findings indicate that a significant proportion of chronic myeloid leukemia patients have different patterns of platelet function abnormalities and imatinib mesylate has no effect on these abnormalities, with a significant impairment in ristocetin-induced platelet aggregation.

Change of health-related profiles after Imatinib cessation in chronic phase chronic myeloid leukemia patients

The aim of this study was to investigate the changes in health-related profiles including quality-of-life (HRQoL) in the chronic myeloid leukemia (CML) patients who discontinued imatinib (IM). An HRQoL survey composed of 43 parameters about IM-related adverse events (AEs), physical health-related and mental health-related was provided at baseline and 6 months post-discontinuation. A total of 55 patients with a sustained UMRD over 6 months were analyzed. Although the majority of IM-related AEs were significantly improved, unexpectedly pruritus and musculoskeletal pain worsen or newly develop in 29.1% and 21.8% of patients, respectively. The improvements in physical and mental health condition were variable in individual patients. In addition, rapid restorations of the hematological and biochemical parameters were observed. The results showed the changes of HRQoL and laboratory tests in treatment-off patients and the necessity of continuing physical and mental support for some patients in tyrosine kinase inhibitor (TKI)-off studies.

Incidence of persistent/late chronic anemia in newly diagnosed patients with chronic myeloid leukemia responsive to imatinib

In patients with chronic myeloid leukemia (CML) responsive to imatinib, it is still unknown whether the long-lasting treatment could induce the appearance of a persistent/late chronic anemia. To highlight this issue, we revised 128 patients with CML (M/F 64/64, median age at diagnosis 56.9 years, interquartile range 43.0-69.3) treated at our Institution with 1st line imatinib for at least 36 months and in stable complete cytogenetic response. At the 36th month of imatinib, a chronic anemia (Hb < 12 g/dl for > 6 months) was present in 38/128 patients (29.6%): the anemia was moderate (Hb > 8 ≤ 10 g/dl) in 12 patients (9.3%) and mild (Hb > 10 < 12 g/dl) in 26 patients (20.3%). All patients with persistent/late chronic anemia had a low reticulocyte count and 8/38 a condition of iron deficiency without clinical and instrumental signs of chronic blood loss. Four out of 38 patients (10.5%) needed red cell transfusions during the follow-up. At a landmark analysis from the 36th month of imatinib treatment, cumulative 4-year overall survival (OS) for patients with chronic anemia was 94.4% (CI 95% 83.8-100) compared to 93.5% (CI 95% 87.2-99.8) for patients without chronic anemia (P = 0.617). In conclusion, the occurrence of a late chronic anemia during long-lasting treatment with imatinib has been observed in about 30% of our responsive patients: its occurrence does not seem to affect OS, but its real impact should be evaluated on a larger cohort of patients.

CD34(+)/CD38(-) stem cells in chronic myeloid leukemia express Siglec-3 (CD33) and are responsive to the CD33-targeting drug gemtuzumab/ozogamicin

BACKGROUND

CD33 is a well-known stem cell target in acute myeloid leukemia. So far, however, little is known about expression of CD33 on leukemic stem cells in chronic leukemias.

DESIGN AND METHODS

We analyzed expression of CD33 in leukemic progenitors in chronic myeloid leukemia by multi-color flow cytometry and quantitative polymerase chain reaction. In addition, the effects of a CD33-targeting drug, gemtuzumab/ozogamicin, were examined.

RESULTS

As assessed by flow cytometry, stem cell-enriched CD34(+)/CD38(-)/CD123(+) leukemic cells expressed significantly higher levels of CD33 compared to normal CD34(+)/CD38(-) stem cells. Moreover, highly enriched leukemic CD34(+)/CD38(-) cells (>98% purity) displayed higher levels of CD33 mRNA. In chronic phase patients, CD33 was found to be expressed invariably on most or all stem cells, whereas in accelerated or blast phase of the disease, the levels of CD33 on stem cells varied from donor to donor. The MDR1 antigen, supposedly involved in resistance against ozogamicin, was not detectable on leukemic CD34(+)/CD38(-) cells. Correspondingly, gemtuzumab/ozogamicin produced growth inhibition in leukemic progenitor cells in all patients tested. The effects of gemtuzumab/ozogamicin were dose-dependent, occurred at low concentrations, and were accompanied by apoptosis in suspension culture. Moreover, the drug was found to inhibit growth of leukemic cells in a colony assay and long-term culture-initiating cell assay. Finally, gemtuzumab/ozogamicin was found to synergize with nilotinib and bosutinib in inducing growth inhibition in leukemic cells.

CONCLUSIONS

CD33 is expressed abundantly on immature CD34(+)/CD38(-) stem cells and may serve as a stem cell target in chronic myeloid leukemia.

Identification and isolation from either adult human bone marrow or G-CSF-mobilized peripheral blood of CD34(+)/CD133(+)/CXCR4(+)/ Lin(-)CD45(-) cells, featuring morphological, molecular, and phenotypic characteristics of very small embryonic-like (VSEL) stem cells

OBJECTIVE

Recently, we demonstrated that normal human bone marrow (hBM)-derived CD34(+) cells, released into the peripheral blood after granulocyte colony-stimulating factor mobilization, contain cell subpopulations committed along endothelial and cardiac differentiation pathways. These subpopulations could play a key role in the regeneration of post-ischemic myocardial lesion after their direct intracardiac delivery. We hypothesized that these relevant cells might be issued from very small embryonic-like stem cells deposited in the BM during ontogenesis and reside lifelong in the adult BM, and that they could be mobilized into peripheral blood by granulocyte colony-stimulating factor.

MATERIALS AND METHODS

Samples of normal hBM and leukapheresis products harvested from cancer patients after granulocyte colony-stimulating factor mobilization were analyzed and sorted by multiparameter flow cytometry strategy. Immunofluorescence and reverse transcription quantitative polymerase chain reaction assays were performed to analyze the expression of typical pluripotent stem cells markers.

RESULTS

A population of CD34(+)/CD133(+)/CXCR4(+)/Lin(-) CD45(-) immature cells was first isolated from the hBM or from leukapheresis products. Among this population, very small (2-5 μm) cells expressing Oct-4, Nanog, and stage-specific embryonic antigen-4 at protein and messenger RNA levels were identified.

CONCLUSIONS

Our study supports the hypothesis that very small embryonic-like stem cells constitute a "mobile" pool of primitive/pluripotent stem cells that could be released from the BM into the peripheral blood under the influence of various physiological or pathological stimuli. In order to fully support that hBM- and leukapheresis product-derived very small embryonic-like stem cells are actually pluripotent, we are currently testing their ability to differentiate in vitro into cells from all three germ layers.

Platelet-derived growth factor enhances platelet recovery in a murine model of radiation-induced thrombocytopenia and reduces apoptosis in megakaryocytes via its receptors and the PI3-k/Akt pathway

BACKGROUND

Platelet-derived growth factor is involved in the regulation of hematopoiesis. Imatinib mesylate, a platelet-derived growth factor receptor inhibitor, induces thrombocytopenia in a significant proportion of patients with chronic myeloid leukemia. Although our previous studies showed that platelet-derived growth factor enhances megakaryocytopoiesis in vitro, the in vivo effect of platelet-derived growth factor in a model of radiation-induced thrombocytopenia has not been reported.

DESIGN AND METHODS

In this study, we investigated the effect of platelet-derived growth factor on hematopoietic stem/progenitor cells and platelet production using an irradiated-mouse model. We also explored the potential molecular mechanisms of platelet-derived growth factor on thrombopoiesis in M-07e cells.

RESULTS

Platelet-derived growth factor, like thrombopoietin, significantly promoted the recovery of platelets and the formation of bone marrow colony-forming unit-megakaryocyte in irradiated mice. Histology confirmed the protective effect of platelet-derived growth factor, as shown by an increased number of hematopoietic stem/progenitor cells and a reduction of apoptosis. In a megakaryocytic apoptotic model, platelet-derived growth factor had a similar anti-apoptotic effect as thrombopoietin on megakaryocytes. We also demonstrated that platelet-derived growth factor activated the PI3-k/Akt signaling pathway, while addition of imatinib mesylate reduced p-Akt expression.

CONCLUSIONS

Our findings show that platelet-derived growth factor enhances platelet recovery in mice with radiation-induced thrombocytopenia. This radioprotective effect is likely to be mediated via platelet-derived growth factor receptors with subsequent activation of the PI3-k/Akt pathway. We also provide a possible explanation that blockage of platelet-derived growth factor receptors may reduce thrombopoiesis and play a role in imatinib mesylate-induced thrombocytopenia.

Targeting breast cancer stem cells

The cancer stem cell (CSC) hypothesis postulates that tumors are maintained by a self-renewing CSC population that is also capable of differentiating into non-self-renewing cell populations that constitute the bulk of the tumor. Although, the CSC hypothesis does not directly address the cell of origin of cancer, it is postulated that tissue-resident stem or progenitor cells are the most common targets of transformation. Clinically, CSCs are predicted to mediate tumor recurrence after chemo- and radiation-therapy due to the relative inability of these modalities to effectively target CSCs. If this is the case, then CSC must be efficiently targeted to achieve a true cure. Similarities between normal and malignant stem cells, at the levels of cell-surface proteins, molecular pathways, cell cycle quiescence, and microRNA signaling present challenges in developing CSC-specific therapeutics. Approaches to targeting CSCs include the development of agents targeting known stem cell regulatory pathways as well as unbiased high-throughput siRNA or small molecule screening. Based on studies of pathways present in normal stem cells, recent work has identified potential "Achilles heals" of CSC, whereas unbiased screening provides opportunities to identify new pathways utilized by CSC as well as develop potential therapeutic agents. Here, we review both approaches and their potential to effectively target breast CSC.

Plerixafor inhibits chemotaxis toward SDF-1 and CXCR4-mediated stroma contact in a dose-dependent manner resulting in increased susceptibility of BCR-ABL+ cell to Imatinib and Nilotinib

Despite Imatinib's remarkable success in chronic myelogenous leukemia treatment, monotherapy frequently causes resistance, underlining the rationale for combination chemotherapy. A potential approach would be interrupting the SDF-1/CXCR4 axis using the selective CXCR4 antagonist Plerixafor (previously AMD3100), as this axis has been reported to provide survival-enhancing effects to myeloid progenitor cells. By efficient CXCR4 blocking in the CXCR4(+)/BCR-ABL(+) cell line BV-173, plerixafor (1-100 muM) significantly inhibits SDF-1alpha-mediated chemotaxis and cell migration toward the murine stroma cell line FBMD-1. Furthermore, plerixafor also significantly (10-100 muM) increased the detachment rate of SDF-1-mediated/VCAM-1-associated cell adherence under shear stress. Using a stroma-dependent coculture assay, plerixafor sensitized BCR-ABL(+) cells toward tyrosine kinase inhibitor therapy. Because the level of cell killing nearly reached that of samples cultured without stroma, a cell-cell interaction disruption seems to improve the efficacy of BCR-ABL-targeting drugs. In addition, we could show that exposure of BCR-ABL(+) cells to Imatinib or Nilotinib induced an increase in surface CXCR4 expression. Our data suggest that for BCR-ABL(+) leukemia, the selective blocking of the SDF-1/CXCR4 axis by plerixafor is a potential mechanism to overcome the protective effect of the bone marrow environment, thereby increasing the therapeutic potency of anti-BCR-ABL drugs and the therapeutic window.

Dasatinib inhibits progenitor cell proliferation from polycythaemia vera

BACKGROUND

A mutation of Janus kinase 2 V617F is present in most patients with polycythaemia vera (PV). However, it is generally believed that JAK2(V617F) is not the sole molecular abnormality in PV. Since dasatinib is currently evaluated in patients with PV, it is of interest to study the effects of dasatinib on the growth of clonal progenitor cells in vitro.

DESIGN AND METHODS

Peripheral blood mononuclear cells from patients with PV, chronic myeloid leukaemia (CML) and controls were exposed to dasatinib (0.1 to 500 nm mL(-1)). Colony growth was stimulated by interleukin-3, granulocyte-macrophage colony-stimulating factor and erythropoietin. Endogenous erythroid colony (EEC) growth was investigated without exogenous cytokines. Real-time PCR was performed to assess the percentage of JAK2(V617F) cells.

RESULTS

10 nm of dasatinib suppressed EEC growth from PV by 89% (P = 0.002). This inhibition was dose dependent and occurred at pharmacological concentrations. Erythroid and myeloid colony growth was also significantly suppressed in the presence of exogenous cytokines. When compared to PV the inhibition of stimulated colony growth was significantly less pronounced in controls but tended to be more vigorous in CML. Interestingly, despite the potent inhibition of PV cells real-time PCR revealed that the numbers of JAK2(V617F) transcripts did not decrease upon exposure to dasatinib.

CONCLUSION

This study shows a marked inhibition of the proliferative capacity of progenitor cells from PV. Although JAK2(V617F) transcript levels did not decrease upon exposure to dasatinib, the drug might suppress PV progenitors through inhibition of a yet undefined molecular target.