Antitumor activities and mechanisms of action of harringtonine and homoharringtonine

The antitumor activities and the mechanisms of action of harringtonine and homoharringtonine, alkaloids isolated from cephalotaxus hainanensis Li, were compared to those of vincristine. The results obtained were as follows: Harringtonine and homoharringtonine Significantly inhibited the growth of L1210 cells in culture. The IC50 values were similar to that of vincristine. Harringtonine and homoharringtonine had little effects on changes in the DNA histograms of FL cells at any concentrations, which suggesting that these drugs prolong the duration of each phase of the cell cycle evenly. Harringtonine and homoharringtonine had only a minor effect in arresting P388 cells in mitosis. Harringtonine significantly inhibited the DNA synthesis of P388 leukemia cells in culture, while vincristine weakly inhibited RNA and DNA synthesis. The successive treatment with harringtonine and homoharringtonine were as effective as the successive treatment with vincristine against P388 and L1210 leukemia, while both drugs were ineffective against Lewis lung carcinoma.     

Small-dose Harringtonine induces complete remission in patients with acute promyelocytic leukemia

Small-dose Harringtonine (1-3 mg infused during 4-5 hr) was used as a single agent to treat 10 patients with acute promyelocytic leukemia. Every patient received one to three courses, each lasting 13-81 days (mean 33 days). The interval between courses (i.e., interruptions) was 5-11 days. During treatment, marrow aplasia occurred in one patient and hypoplasia in three. Pancytopenia occurred in all 10 patients. Complete remission was achieved in seven patients (70%) and cytoreduction in two. In vitro studies showed that, although Harringtonine produced a decrease in leukemic cells in all five series of marrow cultures from five patients, there was only one wherein the decrease was accompanied by a simultaneous absolute increase in differentiated myeloid cells. Considerable discrepancy existed between the culture results and clinical responses. These results seem to suggest that the therapeutic effect of Harringtonine on acute promyelocytic leukemia originates chiefly from cytotoxicity.     

Targeting Hsp90 by 17-AAG in leukemia cells: mechanisms for synergistic and antagonistic drug combinations with arsenic trioxide and Ara-C.

17-Allylamino-17-demethoxygeldanamycin (17-AAG) is a new anticancer agent currently in clinical trials. The ability of 17-AAG to abrogate the function of heat-shock protein Hsp90 and modulate cellular sensitivity to anticancer agents has prompted recent research to use this compound in drug combination therapy. Here we report that 17-AAG has striking opposite effects on the activity of arsenic trioxide (ATO) and ara-C. Combination of 17-AAG with ATO exhibited a synergistic effect in leukemia cells, whereas coincubation of 17-AAG and ara-C showed antagonistic activity. Mechanistic studies revealed that ATO exerted cytotoxic action by reactive oxygen species generation, and activated Akt survival pathway. 17-AAG abrogated Akt activation and enhanced the activity of ATO. In contrast, treatment of leukemia cells with 17-AAG caused a G1 arrest, a decrease in DNA synthesis and reduced ara-C incorporation into DNA, leading to antagonism. The ability of 17-AAG to enhance the antileukemia activity of ATO was further demonstrated in primary leukemia cells isolated from patients with acute myeloid leukemia and chronic lymphocytic leukemia, including cells from refractory patients. Our data suggest that combination of 17-AAG and ATO may be an effective therapeutic regimen. Caution should be exercised in using 17-AAG together with ara-C, as their combination effects are schedule dependent.     

Alemtuzumab in chronic lymphocytic leukemia

Alemtuzumab is a humanized monoclonal antibody specific for CD52, a glycosylphosphatidylinositol-anchored, lymphocyte-surface glycoprotein. Administration of alemtuzumab to patients with chronic lymphocytic leukemia depletes normal and neoplastic lymphocytes from the blood, spleen and marrow, but appears to be less effective in resolving lymphadenopathy. Owing to its activity in clearing leukemia cells of patients who are refractory to purine analogs, such as fludarabine, alemtuzumab became the first and only monoclonal antibody approved by the US FDA and other regulatory authorities for the treatment of chronic lymphocytic leukemia. Here we review the results of clinical studies evaluating the activity and safety of alemtuzumab when used alone or in combination with other antileukemia agents for the treatment of this disease.     

DETERMINATION OF SERUM HARRINGTONINE IN PATIENTS WITH ANLL AND ITS CLINICAL IMPLICATION

Harringtonine(H) level in serum was quantified by high-performance liquid chromatographic (HPLC) technique and its pharmacokinetic parameters were determined in 11 patients with ANLL after 4 hours continuous infusion of 4 mg of H. 74 serum samples over the range of H administered 1-6 mg/d were also determined, the dose of H administered paralleled the mean serum H concentration, but the highest concentration were 1.6-7 folds higher than the lowest under the same doses. It seems that the dosage of harringtonine must be individualized in order to achieve better antileukemia effect. It was found that under the similar serum H concentration the marrow blast decrease index (MBDI) in types M4 and M5 of ANLL is much more greater than in M2 after the first course of chemotherapy and in 3 patients of M2, the serum H level and the MBDI show positive correlation.     

Hematopoietic growth factors and leukemia.

Hematopoietic growth factors, particularly granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor, can be used as supportive agents to enhance bone marrow recovery after the administration of myelosuppressive chemotherapy given for nonmyeloid neoplasms. The use of these agents in the treatment of acute myeloid leukemia and myelodysplastic syndrome poses novel opportunities and challenges due to their direct effects on the neoplastic cells, which represent the transformed counterparts of normal hematopoietic stem cells. The interaction between hematopoietic growth factors and leukemic progenitor cells bearing a specific receptor for a given agent would be expected to result in proliferation, although maturation induction could occur. Hematopoietic growth factors have been employed as primary differentiating agents in myelodysplastic syndrome and as supportive agents after chemotherapy in acute myeloid leukemia. In either case, close monitoring for evidence of leukemic stimulation is required. Alternatively, pretreatment with colony-stimulating factors could induce cell cycling, thereby making the leukemic cells more susceptible to S-phase-specific chemotherapeutic agents, such as cytarabine.     

Gemtuzumab ozogamicin in the treatment of acute myeloid leukemia

Options for treatment of poor-prognosis or relapsed acute myeloid leukemia (AML) remain limited. Gemtuzumab ozogamicin (Mylotarg, Wyeth-Ayerst, Philadelphia, PA) is an immunoconjugate composed of recombinant humanized murine anti-CD33 antibody linked to calicheamicin, a potent cytotoxic agent. Phase II trials have shown the efficacy of gemtuzumab ozogamicin in the treatment of relapsed AML. Trials exploring this agent in other CD33+ hematologic malignancies and in combination with other agents for AML are ongoing. Gemtuzumab ozogamicin is associated with acceptable toxicity as a single agent. However, the incidence of veno-occlusive disease of the liver remains a concern when this agent is used in combination with chemotherapy or in the context of hematopoietic stem cell transplant.     

老年急性髓细胞白血病的临床特点

根据老年急性髓细胞白血病的临床特点,寻求治疗老年急性髓细胞性白血病的有效措施。回顾性分析25例老年急性髓细胞白血病的临床资料,治疗按个体差异分为姑息治疗组、小剂量HA化疗组及标准剂量联合化疗组,并对其治疗效果进行比较。老年急性髓细胞白血病,具有独特的生物学及临床特征;姑息治疗组3例,CR率为0;小剂量HA化疗组7例,CR率28.6%;标准剂量联合化疗组15例,CR率33.3%。标准剂量联合化疗组的CR率及平均存活期均高于小剂量HA化疗组,而诱导期死亡率则低于小剂量HA化疗组,但其差异均无统计学意义。对老年急性髓细胞性白血病的化学治疗应个体化,并辅以积极的综合治疗,才能有望提高疗效。     

全反式维甲酸治疗APL诱发高白细胞症的临床观察

为了提高全反式维甲酸（ATRA）治疗急性早幼粒细胞白血病（APL）诱发高白细胞症的疗效，对21例APL在ATRA治疗中出现的高白细胞症进行观察，并用羟基脲或三尖杉酯碱治疗。结果显示：对白细胞上升较迟峰值较低的普通组高白细胞症患者用羟基脲治疗有效，而对白细胞上并迅速且峰值较高的严重组高白细胞症患者用三尖杉酯碱治疗有较好的疗效。     

SOHO State of the Art Updates and Next Questions: Harnessing Apoptosis in AML

The treatment landscape for acute myeloid leukemia has expanded significantly in the past 5 years with the approval of several therapeutic small molecules. While agents such as FLT3 inhibitors and IDH inhibitors are restricted for patients with specific mutations, the selective BCL-2 inhibitor venetoclax combined with a hypomethylating agent or low-dose cytarabine was approved after demonstrating frontline efficacy across a molecularly heterogenous group of patients. Currently, venetoclax is being investigated in combination with multiple other therapies as the role of the intrinsic apoptotic pathway in acute myeloid leukemia continues to be explored.     

羟基喜树碱治疗慢性粒细胞白血病临床观察

本文报告国产羟基喜树碱(下称羟喜)治疗慢性粒细胞白血病11例结果。提示羟喜剂量6～8mg/m/日,连续用药30天,可使白细胞逐渐下降,完全缓解4/11,部分缓解5/11,无骨髓抑制及严重毒副作用,是一种安全、有效治疗慢性粒细胞白血病新药。对复治患者,尤其是长期服用马利兰产生耐药或毒副作用严重者,可优先选用羟喜。本文对用药途径,间隙时间及维持用药等进行了讨论。     

Azacitidine Use for Myeloid Neoplasms

Azacitidine and decitabine are hypomethylating agents frequently used interchangeably to treat myeloid neoplasms in different settings. Azacitidine is metabolized intracellularly into decitabine. Hypomethylating agents work by inhibiting DNA methyltransferases, causing demethylation of aberrantly methylated promoter regions of genes involved in the pathogenesis of myeloid neoplasms. Azacitidine was the first agent approved by the US Food and Drug Administration for treatment of myelodysplastic syndrome in 2004, after which, the use of azacitidine in other myeloid neoplasms increased significantly. It is a well tolerated agent and can be safely administered in the outpatient setting, which makes it an attractive choice for patients as well as physicians. In this review we summarize the published literature about the use of azacitidine in myeloid neoplasms, and shed the light on some ongoing trials.     

Farnesyltransferase inhibitors in acute myeloid leukemia and myelodysplastic syndromes

Farnesyltransferase inhibitors were initially developed as Ras inhibitors as they inhibit the prenylation necessary for Ras activation. It is clear now that their mechanism of action is more complex and probably involves other proteins unrelated to Ras. At least 3 drugs within this family have been investigated in acute myeloid leukemia, myelodysplastic syndromes, and other leukemias. These are tipifarnib (R115777, Zarnestra), lonafarnib (SCH66336, Sarasar), and BMS-214662. The first 2 are administered orally, whereas BMS-214662 is given intravenously. These drugs are at different stages of development, and design of treatment schedules and methodology of the available studies are very different. Although most of the information is still preliminary, these agents have demonstrated clear evidence of clinical activity in these diseases and very favorable toxicity profiles. Several studies are still ongoing to better define the efficacy of these agents in the treatment of leukemias, as well as to determine the best schedules, the role of combination with other agents, and the role of these agents in different settings, such as the management of minimal residual disease. It is very possible that these agents will soon find their way to the ranks of established agents for the management of myeloid malignancies     

Identification of 6-benzylthioinosine as a myeloid leukemia differentiation-inducing compound

As the pathophysiology of acute myelogenous leukemia (AML) involves a block of myeloid maturation, a desirable therapeutic strategy is to induce leukemic cell maturation to increase the efficacy and to avoid the side effects of traditional chemotherapeutics. Through a compound library screen, 6-benzylthioinosine (6BT) was identified as a promising differentiation-inducing agent. 6BT induces monocytic differentiation of myeloid leukemia cell lines such as HL-60 and OCI-AML3, as well as primary patient samples as evidenced by morphology, immunophenotyping, and nitroblue tetrazolium reduction. Not only can 6BT induce differentiation but a subset of AML cell lines such as MV4-11 and HNT34 instead undergo 6BT-mediated cell death. Despite inducing cell death in some leukemic cells, 6BT exhibits extremely low toxicity on several nonmalignant cells such as fibroblasts, normal bone marrow, and endothelial cells. This toxicity profile may relate to the function of 6BT as an inhibitor of the nucleoside transporter, ent1, which is thought to prevent it from entering many cell types. In contrast, 6BT likely enters at least some leukemic cell lines as shown by its requirement for phosphorylation for its differentiation activity. 6BT is also able to synergize with currently used myeloid differentiation agents such as ATRA and decitabine. Early studies indicate that the mechanism of action of this compound may involve ATP depletion that leads to growth inhibition and subsequent differentiation. Besides in vitro activity, 6BT also shows the ability to impair HL-60 and MV4-11 tumor growth in nude mice. 6BT is a promising new monocytic differentiation agent with apparent leukemic cell-specific activity.     

Novel therapies for patients with chronic myeloid leukemia

The most immediate issues that will have a major impact on the long-term survival of patients with chronic myeloid leukemia is the optimal use of imatinib mesylate (Gleevec, Novartis) and the development of effective therapies for those patients who are intolerant of, or become resistant to, optimal doses of this agent. Of the multiple new agents that are currently being developed for patients with chronic myeloid leukemia, most are being investigated in patients who have developed resistance to imatinib, which is a confounding factor in itself. The mechanisms of action of novel agents are diverse and they may have a variably synergistic therapeutic relationship with imatinib. The complete blockade of the intracellular pathways that are triggered by Bcr-Abl, combined with successful reversal of apoptotic and/or angiogenic abnormalities in chronic myeloid leukemia, may well lead to a cure for the majority of patients.     

Novel therapies for patients with chronic myeloid leukemia

The most immediate issues that will have a major impact on the long-term survival of patients with chronic myeloid leukemia is the optimal use of imatinib mesylate (Gleevec^®, Novartis) and the development of effective therapies for those patients who are intolerant of, or become resistant to, optimal doses of this agent. Of the multiple new agents that are currently being developed for patients with chronic myeloid leukemia, most are being investigated in patients who have developed resistance to imatinib, which is a confounding factor in itself. The mechanisms of action of novel agents are diverse and they may have a variably synergistic therapeutic relationship with imatinib. The complete blockade of the intracellular pathways that are triggered by Bcr-Abl, combined with successful reversal of apoptotic and/or angiogenic abnormalities in chronic myeloid leukemia, may well lead to a cure for the majority of patients.     

Advances in the management of acute promyelocytic leukemia and other hematologic malignancies with arsenic trioxide

Acute promyelocytic leukemia (APL), once considered the most devastating subtype of acute myeloid leukemia, is now the most treatable of all subtypes as a result of intensive research into its molecular pathogenesis. This research has led to a rational approach to treatment in which the use of the differentiating agent all-trans-retinoic acid (ATRA) has proven to be effective first-line treatment for inducing complete remission. Arsenic trioxide (ATO) is currently used to treat relapsed disease, further enhancing survival rates in a patient population for which limited salvage options exist. This review discusses the molecular mechanisms responsible for development of APL and the evolution of treatment options over the last three decades, including the major advances using ATRA and ATO in the last 12 years. The mechanism of action of ATO is also described in view of this agent's potential for broader therapeutic application in a variety of hematologic malignancies.     

Treatment of childhood acute myeloid leukemia

Childhood acute myeloid leukemia is rare, but accounts for a significant number of malignancy-related deaths in this age group. However, the prognosis has improved over past decades, and survival rates of 60% and above have been reported. Still, this implies that more than a third of children and adolescents die from this disease. Moreover, treatment is intensive, and quality of life and late effects are worrying issues. Therefore, there is a need for further improved treatment of pediatric acute myeloid leukemia. This review describes several important developments in this respect, such as improved diagnostics, prognostic factors, subgroup-directed and tailored treatment, and targeted therapy. In addition, background information is provided and current treatment strategies are described, as well as the late effects of treatment. Most groups now have risk-group adapted protocols, with allogeneic stem cell transplantation often being reserved for the higher risk group. Even in these cases, the benefit of stem cell transplantation has not been demonstrated beyond reasonable doubt with current high-intensive chemotherapy. Similarly, the use of cranial irradiation for CNS prophylaxis and maintenance treatment does not seem to be indicated in general. Subgroup-directed treatment has become a reality for acute myeloid leukemia in young children with Down's syndrome and in acute promyelocytic leukemia. In addition to tailoring therapy according to biologic features and especially monitoring treatment by measurements of minimal residual disease, targeted therapy for subgroups with activating mutations in receptor tyrosine kinases will further optimize the treatment of pediatric acute myeloid leukemia. Together with the development of many novel agents that have different mechanisms of action than the currently available anticancer agents, and improved supportive care, it is realistic that the prognosis of acute myeloid leukemia in children and adolescents will improve further in the next 5-10 years.     

Increased error-prone NHEJ activity in myeloid leukemias is associated with DNA damage at sites that recruit key nonhomologous end-joining proteins

Double strand breaks (DSBs) are considered the most lethal form of DNA damage for eukaryotic cells, and misrepair of DSB can cause cell death, chromosome instability, and cancer. Nonhomologous end-joining (NHEJ) is a major mechanism for the repair of DSBs. We previously reported that the cancer predisposition Bloom's syndrome and myeloid leukemias demonstrate increased NHEJ activity and consequent misrepair. In this study, we link this increased NHEJ activity and infidelity to ongoing or induced DNA damage at sites that recruit key NHEJ proteins. We show here that in myeloid leukemia cells and normal hemopoietic cells, agents that induce DSBs produce an up to 2-fold increase in this DSB misrepair activity, whereas an alkylating agent produces little or no increases. Furthermore, NHEJ overactivity after induction of DSBs is dependent on the presence of Ku70/Ku86. We also present data to explain the constitutively activated NHEJ in myeloid leukemias. Using an immunofluorescence-based assay for DNA damage, myeloid leukemias demonstrate constitutive DNA damage in the absence of treatment with DSB-inducing agents compared with normal hemopoietic cells. Importantly, damaged foci from myeloid leukemia and normal cells colocalize with NHEJ proteins Ku70 and Ku86. These data suggest that the generation of increased constitutive DNA damage may be a common pathway for the creation of NHEJ-dependent genomic instability.     

Treatment of childhood acute myeloid leukemia

Childhood acute myeloid leukemia is rare, but accounts for a significant number of malignancy-related deaths in this age group. However, the prognosis has improved over past decades, and survival rates of 60% and above have been reported. Still, this implies that more than a third of children and adolescents die from this disease. Moreover, treatment is intensive, and quality of life and late effects are worrying issues. Therefore, there is a need for further improved treatment of pediatric acute myeloid leukemia. This review describes several important developments in this respect, such as improved diagnostics, prognostic factors, subgroup-directed and tailored treatment, and targeted therapy. In addition, background information is provided and current treatment strategies are described, as well as the late effects of treatment. Most groups now have risk-group adapted protocols, with allogeneic stem cell transplantation often being reserved for the higher risk group. Even in these cases, the benefit of stem cell transplantation has not been demonstrated beyond reasonable doubt with current high-intensive chemotherapy. Similarly, the use of cranial irradiation for CNS prophylaxis and maintenance treatment does not seem to be indicated in general. Subgroup-directed treatment has become a reality for acute myeloid leukemia in young children with Down’s syndrome and in acute promyelocytic leukemia. In addition to tailoring therapy according to biologic features and especially monitoring treatment by measurements of minimal residual disease, targeted therapy for subgroups with activating mutations in receptor tyrosine kinases will further optimize the treatment of pediatric acute myeloid leukemia. Together with the development of many novel agents that have different mechanisms of action than the currently available anticancer agents, and improved supportive care, it is realistic that the prognosis of acute myeloid leukemia in children and adolescents will improve further in the next 5–10 years.