Proteasome inhibition in myelodysplastic syndromes and acute myelogenous leukemia cell lines.

In this work, effects of bortezomib on apoptosis, clonal progenitor growth, cytokine production, and NF-κB expression in patients with MDS with cytopenias requiring transfusion support are examined. Bortezomib increased apoptosis in marrow mononuclear cells but had no effects on CFU-GM, BFU-E, or CFU-L content. No consistent effects on NF-κB activation in vivo were noted. To further define the role of bortezomib in AML and MDS, we examined it in combination with several targeted agents and chemotherapeutic agents in vitro. Combinations with arsenic trioxide, sorafenib, and cytarabine demonstrated synergistic in vitro effects in AML cell lines.

Effects of AMD3100 on transmigration and survival of acute myelogenous leukemia cells.

Acute myelogenous leukaemia (AML) blasts transmigrate in response to SDF-1alpha. AMD3100, a novel bicyclam molecule which inhibits stromal-derived factor (SDF)-1alpha/CXCR4 interactions, inhibited the transmigration of AML blasts and inhibited outgrowth of leukemia colony forming units. AMD3100 did not abrogate stroma-mediated protection from cytarabine-mediated apoptosis, except in the case of one promyelocytic leukemic sample tested, and it did not influence adhesion of blasts to endothelial monolayers. When AML blasts were pretreated with AMD3100, the positive effects of SDF-1alpha on NOD/SCID engraftment were diminished. This work confirms that AML is influenced by the SDF-1alpha/CXCR4 axis and demonstrates that disruption of this axis by the bicyclam AMD3100 can influence AML microenvironmental interactions.

Flavonoid effects on normal and leukemic cells.

Quercetin and flavopiridol, both flavonoids which influence oxidative milieu, proliferation, and apoptosis of various cell types, were examined for their effects on acute myelogenous leukemic cells and normal progenitors. Both quercetin and flavopiridol inhibited the growth and viability of various acute myelogenous leukemia (AML) cell lines and AML blasts isolated afresh from patients with AML of various subtypes. The effects on inhibition of proliferation and decreased viability were also significant in normal CD34+ cells isolated from normal marrow donors. In certain AML cases, the effects of flavopiridol appeared to be mediated through activation of caspase 3, offering one possible mechanism for the apoptosis evident after exposure to flavopiridol as measured by annexin V expression. These flavonoid compounds might find use in various therapeutic settings in AML.

A phase I study of decitabine and rapamycin in relapsed/refractory AML.

A phase I study utilizing decitabine (DAC) followed by the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, in patients with relapsed/refractory adult AML was undertaken to assess safety and feasibility. Patients received DAC 20mg/m(2) intravenously daily for 5 days followed by rapamycin from day 6 to day 25 at doses of 2 mg, 4 mg, and 6 mg/day in a standard 3+3 dose escalation design. Twelve patients completed treatment for safety evaluation. Maximum tolerated dose (MTD) was not reached, and except for grade 3 mucositis in 4 patients, no other significant unexpected non-hematologic toxicities have occurred indicating safety of this regimen. This trial is registered at clinical trials.gov as NCT00861874.

Cytotoxicity of algae extracts on normal and malignant cells.

Algae preparations are commonly used in alternative medicine. We examined the effects of algae extracts on normal hematopoietic cells and leukemia cells. Ethanol extracts were prepared of Dunaliella salina (Dun), Astaxanthin (Ast), Spirulina platensis (Spir), and Aphanizomenon flos-aquae (AFA). Cell viability effects were completed by Annexin staining. Ast and AFA inhibited HL-60 and MV-4-11 whereas Dun and Spir had no effect. Primary AML blasts demonstrated increased apoptosis in AFA. Primary CLL cells showed apoptosis at 24 hours after exposure to Dun, Ast, Spir, and AFA. High AFA concentrations decreased viability of normal marrow cells. Normal CD34+ viability was inhibited by Dun. Dun and AFA inhibited BFU-E, but all extracts inhibited CFU-GM. Cell-cycle analysis of AML cell lines showed G0/G1 arrest in the presence of AFA. These data suggest that algae extracts may inhibit AML cell lines and leukemia blasts, but they may also have potential inhibitory effects on normal hematopoiesis.

Acute myelogenous leukemia--microenvironment interactions: role of endothelial cells and proteasome inhibition.

How leukemia progenitors interact with marrow microenvironment components is poorly understood. In this work, the effects of endothelial coculture on acute myelogenous leukemia (AML) blast survival is examined as are the effects of endothelial coculture on the impact of a cytotoxic agent such as cytarabine. Similar to marrow stromal cells, endothelial cells are able to increase survival and proliferation of AML blasts and to partially protect against cytarabine effects. The proteasome inhibitor, bortezomib, has inhibitory effects in multiple myeloma in part through effects on marrow stromal cells. Bortezomib has been found to inhibit AML blast survival. Such inhibition is less, however, in the presence of endothelial monolayers. Furthermore, AML blast transmigration through human umbilical vein endothelial cells is inhibited by bortezomib. These studies demonstrate that AML is subject to influence of endothelial cells and of agents such as bortezomib which have potential impact on AML interaction with the microenvironmental niche.