An overview on the role of FLT3-tyrosine kinase receptor in acute myeloid leukemia: biology and treatment.

Hematopoiesis, the process by which the hematopoietic stem cells and progenitors differentiate into blood cells of various lineages, involves complex interactions of transcription factors that modulate the expression of downstream genes and mediate proliferation and differentiation signals. Despite the many controls that regulate hematopoiesis, mutations in the regulatory genes capable of promoting leukemogenesis may occur. The FLT3 gene encodes a tyrosine kinase receptor that plays a key role in controlling survival, proliferation and differentiation of hematopoietic cells. Mutations in this gene are critical in causing a deregulation of the delicate balance between cell proliferation and differentiation. In this review, we provide an update on the structure, synthesis and activation of the FLT3 receptor and the subsequent activation of multiple downstream signaling pathways. We also review activating FLT3 mutations that are frequently identified in acute myeloid leukemia, cause activation of more complex downstream signaling pathways and promote leukemogenesis. Finally, FLT3 has emerged as an important target for molecular therapy. We, therefore, report on some recent therapies directed against it.

Medium adsorbance fraction of reticulocyte and myeloperoxidase index may individuate a patient subset with a low risk of chemotherapy-related neutropenia.

In neoplastic patients chemotherapy frequently involves severe myeloid suppression. Sometimes myeloid suppression is the main cause of therapy recycling delay with severe and prolonged neutropenia, anaemia and thrombocytopenia. Our study aimed to verify whether there is a correlation between reticulocyte fractions, reticulocyte indices, myeloperoxidase index (MPXI) and post-chemotherapy myelopoietic function and severe post-chemotherapy neutropenia. A cohort of 112 patients was identified, 30 with lymphoma or myeloma and 82 with solid neoplasms with bone marrow micrometastases. The patients were treated with chemotherapy (CT). After CT, 60 patients had neutropenia (ANC <500/mcl) for a median of 7 days (range 3-21). Before CT, myelopoietic function was assessed by the above-mentioned parameters using a hematologic automated analyzer. We assigned patients with an MPXI-positive value and medium adsorbance fraction of reticulocyte (MFR) >10.7% a score of 1, and a score of 0 was assigned to the remaining patients. Patients with a score of 1 showed a lower number of neutropenic events (only 9 out of 36 patients) than those with a score of 0 (51 out of 76 patients), p<0.0001. MPXI and MFR may be used in the assessment of myelopoiesis before CT administration, independently of the type of tumor, CT regimen and number of CT cycle, with the aim of identifying a patient subset with a lower risk of developing neutropenia post-CT.

Monitoring of FLT3 phosphorylation status and its response to drugs by flow cytometry in AML blast cells.

FLT3 mutation and overexpression in most acute myeloid leukaemia (AML) patients make this tyrosine kinase receptor an attractive therapeutic target. FLT3 kinase inhibitors are actually in clinical trials, thus it is critical to develop a reproducible and standardized method for screening of FLT3 activation and for monitoring its inhibition in response to drug in AML patients. We developed a flow cytometry method to analyse phosphorylated FLT3 (P-FLT3) in samples with <10(5) cells. The method was first validated in FLT3 wild-type (HL60/WT) and mutant (MV4-11/ITD(+)) as well as FLT3 negative (K562) cell lines. The method also proved to be reproducible in AML patient samples. Analysis was performed after exposure to drugs (CEP-701 and SU11657), in vitro and in vivo. In response to increasing drug concentrations, there was a linear reduction in P-FLT3. Intracellular flow cytometry analysis correlated with Western blot and XTT assays; flow cytometry data also correlated with FLT3 mutational status. The results highlight a rapid method to detect P-FLT3 protein at the single cell level by flow cytometry which enables an accurate assessment of FLT3 kinase activity in blast cells in response to novel tyrosine kinase inhibitors.

Superiority of thalidomide and dexamethasone over vincristine-doxorubicindexamethasone (VAD) as primary therapy in preparation for autologous transplantation for multiple myeloma.

The aim of the present study was to compare thalidomide-dexamethasone (Thal-Dex) and vincristine-doxorubicin-dexamethasone (VAD) as primary therapy in preparation for autologous peripheral blood stem-cell (PBSC) transplantation for multiple myeloma (MM). For this purpose, we performed a retrospective matched case-control analysis of 200 patients who entered 2 consecutive studies from 1996 to 2004 and received Thal-Dex (n = 100) or VAD (n = 100) administered for 4 months before collection of PBSCs and autologous transplantation. Matching criteria included age, clinical stage, and serum beta2-microglobulin levels. In comparison with VAD, Thal-Dex resulted in a significantly higher response rate (52% versus 76%, respectively; P < .001) and effected more profound reduction in myeloma cell mass of both immunoglobulin G (IgG; P = .02) and IgA (P = .03) type. More frequent toxicities included nonfatal deep vein thrombosis with Thal-Dex (15%) and granulocytopenia with VAD (12%). In each of the 2 treatment groups, 91% of patients proceeded to PBSC mobilization. The median number of collected CD34+ cells was 7.85 x 10(6)/kg in the Thal-Dex group and 10.5 x 10(6)/kg in the control group. Thal-Dex may be considered an effective and relatively well-tolerated oral alternative to the more complex VAD regimen as front-line therapy for MM patients who are candidates for subsequent autologous transplantation.