A combination of temsirolimus,an allosteric mTOR inhibitor,with clofarabine as a new therapeutic option for patients with acute myeloid leukemia

Signaling through the phosphatidylinositol 3-kinase (PI3K) pathway and its downstream effectors, Akt and mechanistic target of rapamycin (mTOR), is aberrantly activated in acute myeloid leukemia (AML) patients, where it contributes to leukemic cell proliferation, survival, and drug-resistance. Thus, inhibiting mTOR signaling in AML blasts could enhance their sensitivity to cytotoxic agents. Preclinical data also suggest that allosteric mTOR inhibition with rapamycin impaired leukemia initiating cells (LICs) function. In this study, we assessed the therapeutic potential of a combination consisting of temsirolimus [an allosteric mTOR complex 1 (mTORC1) inhibitor] with clofarabine, a nucleoside analogue with potent inhibitory effects on both ribonucleotide reductase and DNA polymerase. The drug combination (CLO-TOR) displayed synergistic cytotoxic effects against a panel of AML cell lines and primary cells from AML patients. Treatment with CLO-TOR induced a G₀/G₁-phase cell cycle arrest, apoptosis, and autophagy. CLO-TOR was pro-apoptotic in an AML patient blast subset (CD34⁺/CD38⁻/CD123⁺), which is enriched in putative leukemia initiating cells (LICs). In summary, the CLO-TOR combination could represent a novel valuable treatment for AML patients, also in light of its efficacy against LICs.     

The phosphatidylinositol 3-kinase/Akt/mTOR signaling network as a therapeutic target in acute myelogenous leukemia patients

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling axis plays a central role in cell proliferation, growth, and survival under physiological conditions. However, aberrant PI3K/Akt/mTOR signaling has been implicated in many human cancers, including acute myelogenous leukemia (AML). Therefore, the PI3K/Akt/mTOR network is considered as a validated target for innovative cancer therapy. The limit of acceptable toxicity for standard polychemotherapy has been reached in AML. Novel therapeutic strategies are therefore needed. This review highlights how the PI3K/Akt/mTOR signaling axis is constitutively active in AML patients, where it affects survival, proliferation, and drug-resistance of leukemic cells including leukemic stem cells. Effective targeting of this pathway with small molecule kinase inhibitors, employed alone or in combination with other drugs, could result in the suppression of leukemic cell growth. Furthermore, targeting the PI3K/Akt/mTOR signaling network with small pharmacological inhibitors, employed either alone or in combinations with other drugs, may result in less toxic and more efficacious treatment of AML patients. Efforts to exploit pharmacological inhibitors of the PI3K/Akt/mTOR cascade which show efficacy and safety in the clinical setting are now underway.     

Advancing treatment of acute myeloid leukemia: the future of FLT3 inhibitors

Introduction: Mutations of the FLT3 gene are among most common genetic abnormalities occurring in acute myeloid leukemia (AML) and are associated with dismal prognosis. Tremendous effort has been devoted to developing clinically effective FLT3 inhibitors. First generation inhibitors consisted of multi-kinase inhibitors (sorafenib, lestaurtinib, midostaurin), which blocked FLT3 as well as multiple other kinase receptors. The failure of these agents to induce durable responses led to the development of second generation FLT3 tyrosine kinase inhibitors (quizartinib, crenolinib, gilteritinib) exhibiting high potency and specificity for mutant FLT3 kinases and sustained in vivo FLT3 inhibition. These myriad FLT3 inhibitors possess diverse kinase inhibitory properties, toxicity profiles, and pharmacokinetics, which impact on their incorporation into therapeutic regimens.

Areas covered: This article reviews the medical literature on current and future FLT3 inhibitors for AML therapy. We provide algorithms for which kinase inhibitor should be utilized for different FLT3 mutations (ITD±TKD) and clinical scenarios (de novo, relapsed/refractory, fit vs. unfit) and discuss novel FLT3 targeted therapeutic approaches.

Expert commentary: Integration of clinically active FLT3 inhibitors into all stages of therapy for all individuals with FLT3 mutant AML promises to significantly improve outcomes for this poor prognosis disease.     

PI3K信号通路在急性髓细胞白血病治疗及耐药性调节中作用的研究进展

PI3K-AKT-mTOR通路是人体内重要的信号通路之一,其在控制细胞生长、分化、凋亡和自噬等方面都发挥着重要作用。近年来研究发现,PI3K-AKT-mTOR信号通路与急性髓系白血病（acute myeloid leukemia,AML）的发生发展密切相关。以PI3K-AKT-mTOR 通路为靶点的AML治疗也取得了很大进步。本文就PI3K-AKT-mTOR信号通路的组成、表达、调控以及该信号通路相关抑制剂在AML中的研究进展进行综述,并对今后的研究方向进行展望。     

Pharmacological targeting of the PI3K/mTOR pathway alters the release of angioregulatory mediators both from primary human acute myeloid leukemia cells and their neighboring stromal cells

Acute myeloid leukemia (AML) is a heterogeneous and aggressive malignancy with poor overall survival. Constitutive as well as cytokine-initiated activation of PI3K/Akt/mTOR signaling is a common feature of AML patients, and inhibition of this pathway is considered as a possible therapeutic strategy in AML. Human AML cells and different stromal cell populations were cultured under highly standardized in vitro conditions. We investigated the effects of mTOR inhibitors (rapamycin and temsirolimus) and PI3K inhibitors (GDC-0941 and 3-methyladenin (3-MA)) on cell proliferation and the constitutive release of angioregulatory mediators by AML and stromal cells.Primary human AML cells were heterogeneous, though most patients showed high CXCL8 levels and detectable release of CXCL10, Ang-1, HGF and MMP-9. Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent. Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators. PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.     

Two hits are better than one: targeting both phosphatidylinositol 3-kinase and mammalian target of rapamycin as a therapeutic strategy for acute leukemia treatment

Phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) are two key components of the PI3K/Akt/mTOR signaling pathway. This signal transduction cascade regulates a wide range of physiological cell processes, that include differentiation, proliferation, apoptosis, autophagy, metabolism, motility, and exocytosis. However, constitutively active PI3K/Akt/mTOR signaling characterizes many types of tumors where it negatively influences response to therapeutic treatments. Hence, targeting PI3K/Akt/mTOR signaling with small molecule inhibitors may improve cancer patient outcome. The PI3K/Akt/mTOR signaling cascade is overactive in acute leukemias, where it correlates with enhanced drug-resistance and poor prognosis. The catalytic sites of PI3K and mTOR share a high degree of sequence homology. This feature has allowed the synthesis of ATP-competitive compounds targeting the catalytic site of both kinases. In preclinical models, dual PI3K/mTOR inhibitors displayed a much stronger cytotoxicity against acute leukemia cells than either PI3K inhibitors or allosteric mTOR inhibitors, such as rapamycin. At variance with rapamycin, dual PI3K/mTOR inhibitors targeted both mTOR complex 1 and mTOR complex 2, and inhibited the rapamycin-resistant phosphorylation of eukaryotic initiation factor 4E-binding protein 1, resulting in a marked inhibition of oncogenic protein translation. Therefore, they strongly reduced cell proliferation and induced an important apoptotic response. Here, we reviewed the evidence documenting that dual PI3K/mTOR inhibitors may represent a promising option for future targeted therapies of acute leukemia patients.     

DNA甲基化靶向药物在急性髓系白血病中的应用

DNA甲基化和组蛋白甲基化是急性髓系白血病（acute myeloid leukemia,AML）表观遗传学调控的常见模式,针对甲基化过程的靶向治疗包括DNA甲基转移酶抑制剂、甲基化调节蛋白抑制剂及组蛋白甲基化调控蛋白抑制剂,其中DNA甲基转移酶（DNA methyltransferase,DNMT）抑制剂阿扎胞苷、地西他滨已上市进入临床,针对甲基化调节蛋白IDH1/2抑制剂也已进入Ⅱ期临床研究。此外,针对组蛋白甲基化调控蛋白EZH2、LSD1抑制剂也显示出良好体外抗白血病活性,部分已进入Ⅰ期临床研究,为AML的治疗提供新的选择。      

PI3K/Akt/mTOR通路抑制剂对白血病细胞株增殖及其PHLPP表达的影响

目的:观察PI3K/Akt/mTOR通路抑制剂wortmannin或rapamycin对白血病细胞株增殖及其PHLPP(PH domainleucine-rich repeat protein phosphatase)蛋白表达的影响。方法:以不同浓度的wortmannin或rapamycin分别作用于人类髓细胞白血病细胞系K562、HL-60,采用WST-1法检测细胞的增殖活性,AnnexinⅤ-FITC双染流式细胞术检测细胞凋亡,Westernblotting法检测细胞中p-Akt、Akt、PHLPP蛋白的表达。结果:Wortmannin以时间以及剂量依赖方式抑制K562、HL-60细胞的增殖(P<0.05),48 h的IC50值分别为(187.6±48.4)、(185.5±48.1)nmol/L。100 nmol/L wortmannin作用于K562细胞、50nmol/L wortmannin作用于HL-60细胞12和24 h后,细胞凋亡率均较对照细胞显著升高[(12.4±0.7)%、(17.6±2.3)%vs(5.0±0.6)%,P<0.05;(11.0±0.2)%、(17.9±1.6)%vs(6.8±0.4)%,P<0.05]。Wortmannin分别作用于K562、HL-60细胞12、24、36 h后,p-Akt、PHLPP的蛋白表达水平明显降低;rapamycin同样可使K562、HL-60细胞中PHLPP蛋白的表达水平降低。结论:PI3K/Akt/mTOR信号通路抑制剂抑制白血病细胞株增殖的同时降低其PHLPP蛋白的表达。     

急性髓系白血病靶向治疗的研究进展

近年来,治疗急性髓系白血病（acute myeloid leukemia,AML）的新药层出不穷,目前已经有几种新的靶向药物获得FDA批准。本文综述了包括针对FLT3信号通路的靶向药物、针对CD33抗原的靶向药物、针对BCL-2基因的靶向药物、针对IDH基因的靶向药物、针对免疫检查点的靶向药物以及CPX-351等药物的作用机制及临床研究进展,为AML未来治疗选择的扩大化、精准化和个性化提供了思路。     

Hedgehog pathway inhibition as a therapeutic target in acute myeloid leukemia

Introduction: The Hedgehog (HH) pathway constitutes a collection of signaling molecules which critically influence embryogenesis. In adults, however, the HH pathway remains integral to the proliferation, maintenance, and apoptosis of adult stem cells including hematopoietic stem cells.

Areas covered: We discuss the current understanding of the HH pathway as it relates to normal hematopoiesis, the pathology of acute myeloid leukemia (AML), the rationale for and data from combination therapies including HH pathway inhibitors, and ultimately the prospects that might offer promise in targeting this pathway in AML.

Expert opinion: Efforts to target the HH pathway have been focused on impeding this disposition and restoring chemosensitivity to conventional myeloid neoplasm therapies. The year 2018 saw the first approval of a HH pathway inhibitor (glasdegib) for AML, though for an older population and in combination with an uncommonly-used therapy. Several other clinical trials with agents targeting modulators of HH signaling in AML and MDS are underway. Further study and understanding of the interplay between the numerous aspects of HH signaling and how it relates to the augmented survival of AML will provide a more reliable substrate for therapeutic strategies in patients with this poor-risk disease.     

Gemtuzumab ozogamicin in the treatment of acute myeloid leukemia

Gemtuzumab ozogamicin (GO) is a chemotherapeutic agent that consists of a humanized anti-CD33 antibody (hP67.6) linked to N-acetyl-calicheamicin 1,2-dimethyl hydrazine dichloride, a potent enediyne antitumor antibiotic. GO was approved conditionally by the Federal Drug Administration in May 2000 as single-agent therapy for first recurrence of acute myeloid leukemia (AML) in patients over the age of 60 years who are unfit for conventional cytotoxic therapy. In this setting, it produces a complete response (CR) rate of 13%, with another 13% achieving CR with inadequate platelet recovery (CRp). The most common adverse effects associated with GO are infusion-related reactions and myelosuppression. GO monotherapy at the dose of 9 mg/m(2) is complicated with hepatic veno-occlusive disease in approximately 5% of cases, particularly prior to or following stem cell transplantation. Attenuated doses of GO or fractionated doses appear to be equally effective and better tolerated. GO has shown remarkable activity in acute promyelocytic leukemia, particularly for the elimination of minimal residual disease. Combinations of GO with chemotherapy as induction or post-remission therapy are promising, and phase III trials are ongoing.     

Targeting of hyperactivated mTOR signaling in high-risk acute lymphoblastic leukemia in a pre-clinical model

Despite increasingly successful treatment of pediatric ALL, up to 20% of patients encounter relapse. By current biomarkers, the majority of relapse patients is initially not identified indicating the need for prognostic and therapeutic targets reflecting leukemia biology. We previously described that rapid engraftment of patient ALL cells transplanted onto NOD/SCID mice (short time to leukemia, TTL^short) is indicative of early patient relapse. Gene expression profiling identified genes coding for molecules involved in mTOR signaling to be associated with TTL^short/early relapse leukemia.Here, we now functionally address mTOR signaling activity in primograft ALL samples and evaluate mTOR pathway inhibition as novel treatment strategy for high-risk ALL ex vivo and in vivo. By analysis of S6-phosphorylation downstream of mTOR, increased mTOR activation was found in TTL^short/high-risk ALL, which was effectively abrogated by mTOR inhibitors resulting in decreased leukemia proliferation and growth. In a preclinical setting treating individual patient-derived ALL in vivo, mTOR inhibition alone, and even more pronounced together with conventional remission induction therapy, significantly delayed post-treatment leukemia reoccurrence in TTL^short/high-risk ALL.Thus, the TTL^short phenotype is functionally characterized by hyperactivated mTOR signaling and can effectively be targeted ex vivo and in vivo providing a novel therapeutic strategy for high-risk ALL.     

Targeted therapy of acute myeloid leukemia

Advances in the understanding of the genetic underpinnings of acute myeloid leukemia are rapidly being translated into novel treatment strategies. Genomic profiling has highlighted the importance of the epigenetic machinery for leukemogenesis by identifying recurrent somatic mutations involving chromatin-modifier proteins. These genetic alterations function as dynamic regulators of gene expression and involve DNA-methyltransferase 3A, methyltransferase DOT1L, enhancer of zeste homologue 2, isocitrate dehydrogenases 1 and 2 and bromodomain-containing proteins. New therapeutic targets are also emerging from further delineation of cell signaling networks in acute myeloid leukemia blasts mediated by PIM kinases, polo-like kinase 1, cell surface protein CD98 and nucleocytoplasmic shuttling receptors, among others. Early results of targeted therapies directed at these molecular mechanisms are discussed in this review and their potential to improve the outcomes of patients by allowing the use of more effective and less toxic treatments.     

Activity of the novel mTOR inhibitor Torin-2 in B-precursor acute lymphoblastic leukemia and its therapeutic potential to prevent Akt reactivation

The PI3K/Akt/mTOR signaling cascade is a key regulatory pathway controlling cell growth and survival, and its dysregulation is a reported feature of B-precursor acute lymphoblastic leukemia (B-pre ALL).Torin-2 is a novel, second-generation ATP-competitive inhibitor that is potent and selective for mTOR with a superior pharmacokinetic profile to previous inhibitors. It has been shown that Torin-2 displayed dramatic antiproliferative activity across a panel of cancer cell lines.To investigate if Torin-2 could represent a new option for the treatment of B-pre ALL, we tested its activity on a panel of B-pre ALL cell lines. In all of them Torin-2 showed a powerful cytotoxic activity, inhibiting the growth of each cell line in a dose-dependent manner, with an IC₅₀ in the nanomolar range. Torin-2 caused both apoptosis and autophagy, induced cell cycle arrest in G₀/G₁ phase and affected both mTORC1 and mTORC2 activities as assessed by their specific substrate dephosphorylation.Torin-2 alone suppressed feedback activation of PI3K/Akt, whereas the mTORC1 inhibitor RAD001 required the addition of the Akt inhibitor MK-2206 to achieve the same effect. These pharmacological strategies targeting PI3K/Akt/mTOR at different points of the signaling pathway cascade might represent a new promising therapeutic strategy for treatment of B-pre ALL patients.     

Emerging treatment strategies for acute myeloid leukemia (AML) in the elderly

Acute myeloid leukemia (AML) is more prevalent in older adults, with an incidence in the United States of 17.6 per 100,000 for those 65 years of age, compared with an incidence of 1.8 per 100,000 for those <65 years of age. While there have been improvements in survival during the last decade for younger patients, prognosis in elderly patients is still poor; approximately 50% achieve complete responses, but many of them relapse. With increasing age, more patients are suboptimal candidates for standard induction chemotherapy due to poor performance status, pre-existing myelodysplasia, unfavorable cytogenetics, treatment-related AML, multidrug resistance protein expression, and CD34 positivity, which are often characteristic of this patient population. In addition, the presence of comorbid conditions make many treatment options less tolerable for elderly patients. Several investigators have described subgroups showing no benefit after intensive treatment approaches in recent years. However, several novel agents have been developed to treat elderly AML patients. These include new chemotherapeutic agents, such as nucleoside analogs, as well as targeted therapies like farnesyltransferase inhibitors, tyrosine kinase inhibitors, epigenetic drugs, and antibodies. On the other hand new insights into the biology of the disease lead to a better understanding of its heterogeneity. Thus, with a variety of novel substances at hand it is increasingly important to introduce a risk-adapted approach for the optimal management of patients. This review will identify subgroups not likely to benefit from intensive chemotherapy and highlight the efficacy and tolerability of new agents in the treatment of AML.     

Cell cycle control in acute myeloid leukemia

Acute myeloid leukemia (AML) is the result of a multistep transforming process of hematopoietic precursor cells (HPCs) which enables them to proceed through limitless numbers of cell cycles and to become resistant to cell death. Increased proliferation renders these cells vulnerable to acquiring mutations and may favor leukemic transformation. Here, we review how deregulated cell cycle control contributes to increased proliferation in AML and favors genomic instability, a prerequisite to confer selective advantages to particular clones in order to adapt and independently proliferate in the presence of a changing microenvironment. We discuss the connection between differentiation and proliferation with regard to leukemogenesis and outline the impact of specific alterations on response to therapy. Finally, we present examples, how a better understanding of cell cycle regulation and deregulation has already led to new promising therapeutic strategies.     

老年急性髓系白血病治疗进展

 由于老年患者本身的特点及疾病的生物学特征,老年急性髓系白血病（AML）患者的疗效及预后均较差。近年老年AML患者的治疗取得许多进展诸如标准化疗方案的改良、新化疗药物的应用、免疫治疗、表观遗传学治疗药物及靶向治疗药物的研发等,临床试验结果提示部分患者疗效改善。     

Targeting the PI3K/Akt/mTOR pathway--beyond rapalogs

It is well established that the PI3K pathway plays a central role in various cellular processes that can contribute to the malignant phenotype. Accordingly, pharmacological inhibition of key nodes in this signaling cascade has been a focus in developmental therapeutics. To date, agents targeting upstream receptor tyrosine kinases are best studied and have achieved greatest clinical success. Further downstream, despite efficacy in certain tumor types, the rapalogs have been somewhat disappointing in the clinic. Novel inhibitors of PI3K, Akt, and mTORC1 and 2 are now passing through early phase clinical trials. It is hoped that these agents will circumvent some of the shortcomings of the rapalogs and lead to meaningful benefits for cancer patients.     

PI3K/AKT/mTOR信号通路抑制剂在淋巴瘤中的研究进展*

磷脂酰肌醇-3 激酶（phosphatidylinositol 3-kinase,PI 3K）- 蛋白激酶B（protein kinaseB ,PKB ,又称AKT ）- 雷帕霉素靶蛋白（mammalian target of  rapamycin,mTOR）信号通路与细胞的生长、增殖、分化、凋亡、代谢等密切相关,在多种实体肿瘤中已发现该信号通路的异常。近年来,以抑制该通路特定位点的靶向治疗已成为抗肿瘤的研究热点。许多该位点新型抑制剂也已进入淋巴瘤的临床试验中,本文就该通路在淋巴瘤中的活化状态及各个分子靶点抑制剂的研究进展做一综述。