Immunophenotypic features of acute myeloid leukaemia patients exhibiting high FLT3 expression not associated with mutations.

FMS-related tyrosine kinase 3 (FLT3) mutations are found in 30% of cases of acute myeloid leukaemia (AML). In addition, recent studies have lead to the identification of about 10-15% of AML patients displaying high expression of FLT3, not associated with mutations of the receptor (FLT3 Wild-type High, FLT3WTH). These AMLs, as well as those displaying internal tandem duplication (ITD) are associated with an unfavourable prognosis. However, the biological features of these AMLs are poorly characterized. The present study explored the immunophenotypic features of FLT3WTH AMLs in 94 de novo cases of AML. The levels of FLT3 expression, as assessed by flow cytometry and FLT3 mutational status, was used to identify four AML subgroups: FLT3WTH (14/94); FLT3 Wild-type low (FLT3WTL, 48/94); FLT3 internal tandem duplication (FLT3ITD 26/94); FLT3 aspartic acid 835 (FLT3D835, 6/94). FLT3WTH and FLT3ITD were characterized by: high white blast cell counts; predominance of M4 and M5 French-American-British classification subtypes and associated expression of myelo-monocytic markers; high expression of CD123 and TRAIL-Rs; high expression of receptors for angiogenic growth factors. Addition of FLT3 Ligand to human CD34(+) or monocytic cells stimulated CD123 and TRAIL-R expression. These findings are of potential value for the development of new therapeutic strategies.

Bone marrow-derived progenitors are greatly reduced in patients with severe COPD and low-BMI.

Chronic obstructive pulmonary disease (COPD) patients have reduced circulating hemopoietic progenitors. We hypothesized that severity of COPD parallels the decrease in progenitors and that the reduction in body mass index (BMI) could be associated with more severe bone marrow dysfunction. We studied 39 patients with moderate to very severe COPD (18 with low-BMI and 21 with normal-BMI) and 12 controls. Disease severity was associated to a greater reduction in circulating progenitors. Proangiogenetic and inflammatory markers correlated with disease severity parameters. Compared to normal-BMI patients, low-BMI patients showed: greater reduction in circulating progenitors; higher VEGF-A, VEGF-C, HGF, Ang-2, TNF-alpha, IL-6 and MCP-1 levels. Furthermore, among patients with similar pulmonary impairment, those who displayed low-BMI had a more markedly reduced number of CD34(+) cells and late endothelial progenitors. We show that the reduction in hematopoietic and endothelial progenitor cells correlates with COPD severity. Our findings also indicate that, in severe low-BMI COPD patients, bone marrow function seems to be further impaired and may lead to reduced reparative capacity.

Colocalization of the VEGF-R2 and the common IL-3/GM-CSF receptor beta chain to lipid rafts leads to enhanced p38 activation.

Previous studies suggested an important role for vascular endothelial growth factor (VEGF) and its receptors in postnatal haemopoiesis. However, it is unclear how VEGF receptor (VEGFR) signalling could interact with that issued from the activation of haematopoietic growth factor receptors. To elucidate this point we explored VEGF-R2 and granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) membrane localization and cell signalling in TF1-KDR cells (TF1 leukaemic cells that overexpress VEGF-R2/KDR). Activation of either GM-CSFR or VEGF-R2 was shown to determine the migration of both receptor elements (VEGF-R2 and the common beta-chain of the GM-CSFR) to lipid rafts. The study of receptor phosphorylation showed that GM-CSF induced the phosphorylation of its own receptor and the transphosphorylation of VEGF-R2; on the other hand, VEGF triggered the phosphorylation of its receptor and transphosphorylated the beta-chain of the GM-CSFR. Co-stimulation of TF1-KDR cells with both GM-CSF and VEGF-A resulted in massive migration of both the common GM-CSFR beta-chain and VEGF-R2 to lipid rafts and sustained p38 mitogen-activated protein kinase activation. Disruption of lipid rafts inhibited the capacity of both GM-CSF and VEGF-A to activate p38. Experiments with specific p38 inhibitors showed that p38 activation was required to sustain the VEGF- and GM-CSF-dependent proliferation of TF1-KDR and the survival of primary acute myeloid leukaemia blasts.

Interleukin (IL)-3/granulocyte macrophage-colony stimulating factor/IL-5 receptor alpha and beta chains are preferentially expressed in acute myeloid leukaemias with mutated FMS-related tyrosine kinase 3 receptor.

The common beta chain subunit (beta(c)), also known as CDw131, shared by the interleukin-3 (IL-3), granulocytic macrophage colony-stimulating factor (GM-CSF) and IL-5 receptors, is required for high-affinity ligand binding and signal transduction. The present study explored the expression of CDw131 in 105 de novo cases of acute myeloid leukaemia (AML). The levels of CDw131 expression were used to identify two AML subgroups characterized by low (75/105) and high (30/105) expression of this receptor chain. It was observed that (i) the level of CDw131 expression strictly correlated with the level of CD116 (GM-CSFalpha receptor chain) and CD123 (IL-3Ralpha chain); (ii) AMLs with high CDw131 expression were characterized by low CD34 expression and usually high CD11b, CD14 expression; (iii) AMLs with high CDw131 expression frequently co-expressed receptors for angiogenic growth factors (vascular endothelial growth factor R2, Tie-2); (iv) AMLs with high CDw131 expression were more cycling than those with low CDw131 expression; (v) AMLs with high CDw131 frequently displayed Feline Murine Sarcoma (FMS-related) tyrosine kinase 3 (FLT3) internal tandem duplication and constitutively activated Signal Transducer and Activator of Transcription-5 (STAT5). In conclusion, the analysis of the level of CDw131 expression enabled the identification of a subset of AMLs characterized by a high cycling status, the expression of myelo-monocytic markers, mutated FLT3 and the co-expression of receptors for angiogenic growth factors. These findings are of value for the development of new therapeutic strategies for the treatment of these AMLs.

Resistance of acute myeloid leukemic cells to the triterpenoid CDDO-Imidazolide is associated with low caspase-8 and FADD levels.

The synthetic triterpenoid CDDO-Im-induced apoptosis of patient-derived AML blasts: 11/25 AMLs were highly sensitive, while the remaining were moderately sensitive to CDDO-Im. The addition of TRAIL significantly potentiated the cytotoxic effect of CDDO-Im, through mechanisms involving the induction of TRAIL-R1/TRAIL-R2 and downmodulation of TRAIL-R3/TRAIL-R4. Biochemical studies showed that CDDO-Im: induced a rapid and marked GSH depletion and antioxidants (GSH or NAC) completely inhibited its pro-apoptotic effect; sequentially activated caspase-8, -9 and -3; caspase inhibitors partially protected AML blasts from CDDO-Im-induced apoptosis; resistance of AML blasts to CDDO-Im-induced apoptosis correlated with low caspase-8/FADD and high Bcl-X(L) expression in leukemic blasts.

M4 and M5 acute myeloid leukaemias display a high sensitivity to Bortezomib-mediated apoptosis.

The present study explored the sensitivity of leukaemic blasts derived from 30 acute myeloid leukaemia (AML) patients to Bortezomib. Bortezomib induced apoptosis of primary AML blasts: 18/30 AMLs were clearly sensitive to the proapoptotic effects of Bortezomib, while the remaining cases were moderately sensitive to this molecule. The addition of tumour necrosis factor-related-apoptosis-inducing ligand, when used alone, did not induce apoptosis of AML blasts and further potentiated the cytotoxic effects of Bortezomib. The majority of AMLs sensitive to Bortezomib showed immunophenotypic features of the M4 and M5 French-American-British classification subtypes and displayed myelomonocytic features. All AMLs with mutated FLT3 were in the Bortezomib-sensitive group. Biochemical studies showed that: (i) Bortezomib activated caspase-8 and caspase-3 and decreased cellular FLICE [Fas-associated death domain (FADD)-like interleukin-1beta-converting enzyme]-inhibitory protein (c-FLIP) levels in AML blasts; (ii) high c-FLIP levels in AML blasts were associated with low Bortezomib sensitivity. Finally, analysis of the effects of Bortezomib on leukaemic cells displaying high aldehyde dehydrogenase activity suggested that this drug induced in vitro killing of leukaemic stem cells. The findings of the present study, further support the development of Bortezomib as an anti-leukaemic drug and provide simple tools to predict the sensitivity of AML cells to this drug.

Expression of Tie-2 and other receptors for endothelial growth factors in acute myeloid leukemias is associated with monocytic features of leukemic blasts.

We investigated the expression of Tie-2 in primary blasts from 111 patients with acute myeloid leukemia (AML) to evaluate a possible linkage between the expression of this receptor and the immunophenotypic and biologic properties of leukemic blasts. Tie-2 was expressed at moderate and high levels in 39 and 23 of 111 AMLs, respectively. The analysis of the immunophenotype clearly showed that Tie-2 expression in AML was associated with monocytic features. Interestingly, Tie-2 expression on AML blasts was associated with concomitant expression of other receptors for endothelial growth factors, such as vascular endothelial growth factor receptor 1 (VEGF-R1), -R2, and -R3. Tie-2(+) AMLs were characterized by high blast cell counts at diagnosis, a high frequency of Flt3 mutations, and increased Flt3 expression. The survival of Tie-2(+) AMLs is sustained through an autocrine pattern involving Angiopoietin-1 and Tie-2, as suggested by experiments showing induction of apoptosis in Tie-2(+) AMLs by agents preventing the binding of angiopoietins to Tie-2. Finally, the in vitro growth of Tie-2(+) AMLs in endothelial culture medium supplemented with VEGF and angiopoietins resulted in their partial endothelial differentiation. These observations suggest that Tie-2(+) AMLs pertain to a mixed monocytic/endothelial lineage, derived from the malignant transformation of the normal counterpart represented by monocytic cells expressing endothelial markers. The autocrine angiopoietin/Tie-2 axis may represent a promising therapeutic target to improve the outcome of patients with monocytic AML. Disclosure of potential conflicts of interest is found at the end of this article.

Podocalyxin is expressed in normal and leukemic monocytes.

We have investigated the expression of podocalyxin in primary cultures of leukemic blast cells from 73 patients with acute myeloid leukemia. Podocalyxin was expressed at moderate levels in 15 patients and at high levels in 13 patients. The analysis of membrane markers showed that Podocalyxin expression in leukemic blasts was associated with a monocytic immunophenotype. Cases of podocalyxin-positive acute myelogenous leukemia had high blast cell counts at diagnosis and elevated CD123, CD135, VLA-4 and CXCR4 expression, features associated with poor prognosis. Podocalyxin expression in leukemic blasts was coupled with the concomitant expression of VEGF-R1, -R2, -R3 and Tie-2, the capacity to release VEGF-A and angiopoietin1 and the ability to differentiate into endothelial cells under appropriate culture conditions. These findings show that podocalyxin is a marker of acute myeloid leukemia with a monocytic phenotype and suggest that podocalyxin-positive cases of acute myeloid leukemia originate from the malignant transformation of progenitors common to the myeloid and endothelial lineages. These observations suggest a possible relationship between the monocytic lineage and podocytes.