Norikazu Imai

Energy metabolism of leukemia cells: glycolysis versus oxidative phosphorylation.

For generation of energy, cancer cells utilize glycolysis more vigorously than oxidative phosphorylation in mitochondria (Warburg effect). We examined the energy metabolism of four leukemia cell lines by using glycolysis inhibitor, 2-deoxy-d-glucose (2-DG) and inhibitor of oxidative phosphorylation, oligomycin. NB4 was relatively sensitive to 2-DG (IC50: 5.75 mM), consumed more glucose and produced more lactate (waste product of glycolysis) than the three other cell lines. Consequently, NB4 was considered as a “glycolytic” leukemia cell line. Dependency on glycolysis in NB4 was confirmed by the fact that glucose (+) FCS (−) medium showed more growth and survival than glucose (−) FCS (+) medium. Alternatively, THP-1, most resistant to 2-DG (IC50: 16.14 mM), was most sensitive to oligomycin. Thus, THP-1 was recognized to be dependent on oxidative phosphorylation. In THP-1, glucose (−) FCS (+) medium showed more growth and survival than glucose (+) FCS (−) medium. The dependency of THP-1 on FCS was explained, at least partly, by fatty acid oxidation because inhibitor of fatty acid β-oxidation, etomoxir, augmented the growth suppression of THP-1 by 2-DG. We also examined the mechanisms by which THP-1 was resistant to, and NB4 was sensitive to 2-DG treatment. In THP-1, AMP kinase (AMPK), which is activated when ATP becomes limiting, was rapidly phosphorylated by 2-DG, and expression of Bcl-2 was augmented, which might result in resistance to 2-DG. On the other hand, AMPK phosphorylation and augmentation of Bcl-2 expression by 2-DG were not observed in NB4, which is 2-DG sensitive. These results will facilitate the future leukemia therapy targeting metabolic pathways.

Disease-specific expression of VEGF and its receptors in AML cells: possible autocrine pathway of VEGF/type1 receptor of VEGF in t(15;17) AML and VEGF/type2 receptor of VEGF in t(8;21) AML

Various angiogenic factors, such as vascular endothelial growth factor (VEGF) and an associated molecule, placenta growth factor (PlGF), are thought to be important for normal and malignant hematopoiesis. This study examined mRNA expression of VEGF, PlGF and receptors for these molecules in AML cells and identified the disease-specific patterns of expression. AML M3 having t(15;17) abnormality showed highest expression of VEGF and VEGF receptor type 1 (VEGFR1), suggesting the autocrine pathway of VEGF-VEGFR1. Then, t(8;21) AML demonstrated augmented expression of VEGF and VEGF receptor type 2 (VEGFR2), suggesting VEGF-VEGFR2 autocrine pathway. Then, addition of VEGFR2 kinase inhibitor in Kasumi-1, a t(8;21) AML cell line, resulted in marked inhibition of cell growth, although growth inhibitory effect of R2 kinase inhibitor to HL-60 was marginal. In addition, cell cycle analysis study showed S-phase cell population reduction by R2 kinase inhibitor in Kasumi-1, but not in HL-60. This observation is thought to be the rationale for novel molecular target therapy directed to angiogenic molecules.

Placenta growth factor stimulates the growth of philadelphia chromosome positive acute lymphoblastic leukemia cells by both autocrine and paracrine pathways

Abstract:  Vascular endothelial growth factor (VEGF) and its associated molecule, placenta growth factor (PlGF) are now known to support normal hematopoiesis, and leukemia cell growth. In this study, expression of VEGF and PlGF in acute lymphoblastic leukemia (ALL) cells was examined by real time reverse transcription‐polymerase chain reaction in 20 patient samples. Expression of PlGF was more intense in Philadelphia chromosome positive (Ph+) ALL than in Ph− ALL cases. On the other hand, expression level of VEGF was not different between Ph+ and Ph− cases. Then, PlGF was added to the two ALL cell lines, CRL1929 (Ph+), and Nalm6 (Ph−). The PlGF stimulated the growth of CRL1929 in time‐ and dose‐dependent manners, although the growth of Nalm6 was not affected by PlGF. The growth stimulation of CRL1929 by PlGF was confirmed by the increase of S phase cells. And the growth promoting effect of PlGF on CRL1929 was cancelled by simultaneous addition of VEGFR1/Fc (which binds to PlGF and abrogates its function), but was not cancelled by VEGFR2/Fc (which does not bind to PlGF). Then, addition of VEGFR1/Fc to the simple culture of CRL1929 demonstrated growth inhibitory effect. These observations demonstrated that PlGF stimulates the growth of Ph+ ALL cells by both autocrine and paracrine pathways. Finally, PlGF‐VEGFR1 loop might be a therapeutic target to improve the prognosis of Ph+ ALL.

Growth inhibition of AML cells with specific chromosome abnormalities by monoclonal antibodies to receptors for vascular endothelial growth factor

By using neutralizing monoclonal antibodies to vascular endothelial growth factor receptor type 1 (VEGFR1) and VEGFR2, we have shown that acute myelogenous leukemia (AML) cells with specific chromosome abnormalities are dependent on VEGF/VEGFR system. AML with t(8;21) is the most dependent subtype on VEGF with both VEGFR1 and VEGFR2. t(15;17)AML cells depend on VEGF with VEGFR1. AML cells with 11q23 abnormalities showed variable dependence on VEGF. The growth of t(11;19)AML cells are most extensively inhibited by anti-VEGFR1 antibody. Then, the growth of Kasumi-1, a t(8;21) cell line was suppressed by either anti-VEGFR1 antibody (p=0.0022) or anti-VEGFR2 antibody (p=0.0029) in a dose-dependent manner. The growth of NB4, a t(15;17) cell line was more potently suppressed by anti-VEGFR1 antibody (p=0.0111) than by anti-VEGFR2 antibody (p=0.0477). These results are quite concordant with the results of clinical samples with t(8;21) or t(15;17). In addition, anti-VEGFR2 monoclonal antibody significantly potentiated the growth inhibitory effect of idarubicin for Kasumi-1. As for downstream signals, we have shown that VEGFR2 transduce growth and survival signals through phosphorylation of Akt and MEK in leukemia cells (Kasumi-1). However, VEGFR1 transduce growth and survival signals through pathways other than MEK and Akt (NB4), although Akt phosphorylation may account for some of the VEGFR1 signals (Kasumi-1). Finally, our data suggested that autocrine pathway of VEGF and VEGFRs observed in AML cells with specific chromosomal translocations have contributed to leukemogenesis as activated signaling of receptor tyrosine kinase.

t(8;21) acute myeloid leukaemia cells are dependent on vascular endothelial growth factor (VEGF)/VEGF receptor type2 pathway and phosphorylation of Akt.

Several anti‐angiogenic drugs have recently been clinically tested for haematological malignancies. To improve the efficacy of molecular target therapy against angiogenic molecules in acute myeloid leukaemia (AML), we examined the dependency of AML cells on the vascular endothelial growth factor (VEGF)/VEGF receptor type2 (VEGFR2) system by using VEGFR2 kinase inhibitor. Nineteen patient AML samples were cultured with or without VEGFR2 kinase inhibitor. All four t(8;21) viable AML cells showed significant reductions when treated with VEGFR2 kinase inhibitor, although VEGFR2 kinase inhibitor did not affect the cell proliferation of five t(15;17) AML samples. Other AML cases showed variable responses. VEGFR2 kinase inhibitor greatly suppressed the growth of Kasumi‐1, a t(8;21) cell line in a dose‐dependent manner through induction of apoptosis, but did not show any significant influence on NB4, a t(15;17) cell line. In addition, VEGFR2 kinase inhibitor potentiated the growth inhibitory effect of cytarabine in Kasumi‐1. Finally, it was shown that the Akt phosphorylation was augmented by VEGF165 in Kasumi‐1, which was abrogated by VEGFR2 kinase inhibitor. NB4 showed undetectable Akt phosphorylation even with VEGF165. These data demonstrated that t(8;21) AML cells are dependent on VEGF through VEGFR2, resulting in the phosphorylation of Akt.

Aortic thrombus in a patient with myeloproliferative thrombocytosis, successfully treated by pharmaceutical therapy: a case report

IntroductionThrombosis in myeloproliferative thrombocytosis occurs usually in the microvessels and medium-sized arteries and veins and only rarely in the aorta. Aortic thrombosis is usually treated with thrombectomy. Reported here is a rare case that was treated pharmacologically.Case presentationA 60-year-old Japanese woman presented with numbness of both lower extremities. Her platelet count was 1787 × 103/μl. Through bone marrow examination, we diagnosed her condition as myelodysplastic and/or myeloproliferative disorder-unclassifiable. Abdominal ultrasonography and computed tomographic scan revealed aortic thrombosis. Her platelet count was controlled with hydroxyurea and ranimustine. Aspirin and ticlopidine improved the numbness in both lower limbs on the second day. Aortic thrombosis was not observed in a computed tomographic scan on the seventh day.ConclusionFor aortic thrombosis, surgical management is usually adopted, but pharmacological management is also an option because of its immediate curative effects.

Aplastic anaemia associated with a Philadelphia chromosome and monosomy 7 during immunosuppressive therapy.

Abstract: We describe a patient who presented with aplastic anaemia associated with the Philadelphia (Ph1) chromosome during immunosuppressive therapy and who subsequently developed myelodysplastic syndrome (MDS) with monosomy 7. Initially the patient had hypocellular fatty marrow without leukaemic blasts or dysplastic features. Chromosome analysis showed 46, XY, t(9;22)(q34;q11) during immunosuppressive therapy, but no leukaemic transformation was detected. The patient showed gradual haematologic improvement and became transfusion independent. Thereafter, bone marrow dysplasia with monosomy 7 progressed following transfusion independence. These findings indicate that multiple cytogenetic evolutions occur in aplastic anaemia during immunosuppressive therapy, and that Ph1 chromosome may play a role in bone marrow suppression rather than development of leukaemia.