A phase I/II study of imatinib plus reinduction therapy for c-kit-positive relapsed/refractory acute myeloid leukemia: inhibition of Akt activation correlates with complete response

Mutated KIT Tyrosine Kinase as a Novel Molecular Target in Acute Myeloid Leukemia

KIT is a type-III receptor tyrosine kinase that contributes to cell signaling in various cells. Since KIT is activated by overexpression or mutation and plays an important role in the development of some cancers, such as gastrointestinal stromal tumors and mast cell disease, molecular therapies targeting KIT mutations are being developed. In acute myeloid leukemia (AML), genome profiling via next-generation sequencing has shown that several genes that are mutated in patients with AML impact patients’ prognosis. Moreover, it was suggested that precision-medicine-based treatment using genomic data will improve treatment outcomes for AML patients. This paper presents (1) previous studies regarding the role of KIT mutations in AML, (2) the data in AML with KIT mutations from the HM-SCREEN-Japan-01 study, a genome profiling study for patients newly diagnosed with AML who are unsuitable for the standard first-line treatment (unfit) or have relapsed/refractory AML, and (3) new therapies targeting KIT mutations, such as tyrosine kinase inhibitors and heat shock protein 90 inhibitors. In this era when genome profiling via next-generation sequencing is becoming more common, KIT mutations are attractive novel molecular targets in AML.

Current status of drug repositioning in hematology

INTRODUCTION

Drug repositioning (DR) is defined as determining new therapeutic applications for existing drugs. This approach is advantageous over de novo drug discovery in accelerating clinical development, in terms of lower costs, a shortened development period, a well-known action mechanism, a feasible dosage, and an acceptable safety profile.

AREAS COVERED

This work was aimed at reviewing agents with successful DR in hematology.

EXPERT OPINION

Thalidomide and plerixafor have been successfully repositioned for treating multiple myeloma and harvesting peripheral blood stem cells, respectively. The former was originally developed as a sedative and the latter as an anti-HIV drug. Currently, the feasibility of repositioning various agents is being explored (e.g. an anti-influenza virus drug oseltamivir for primary immune thrombocytopenia, an anti-HIV drug abacavir for adult T-cell leukemia, and a macrolide antibiotic clarithromycin for multiple myeloma). Furthermore, bosutinib for chronic myeloid leukemia or the antiplatelet drug cilostazol have been suggested to have clinical benefits for the management of amyotrophic lateral sclerosis and ischemic stroke, respectively. To promote DR, effective application of artificial intelligence or stem cell models, comprehensive database construction shared between academia and pharmaceutical companies, suitable handling of drug patents, and wide cooperation in the area of specialty are warranted.

The important roles of protein SUMOylation in the occurrence and development of leukemia and clinical implications

Leukemia is a severe malignancy of the hematopoietic system, which is characterized by uncontrolled proliferation and dedifferentiation of immature hematopoietic precursor cells in the lymphatic system and bone marrow. Leukemia is caused by alterations of the genetic and epigenetic regulation of processes underlying hematologic malignancies, including SUMO modification (SUMOylation). Small ubiquitin-like modifier (SUMO) proteins covalently or noncovalently conjugate and modify a large number of target proteins via lysine residues. SUMOylation is a small ubiquitin-like modification that is catalyzed by the SUMO-specific activating enzyme E1, the binding enzyme E2, and the ligating enzyme E3. SUMO is covalently linked to substrate proteins to regulate the cellular localization of target proteins and the interaction of target proteins with other biological macromolecules. SUMOylation has emerged as a critical regulatory mechanism for subcellular localization, protein stability, protein-protein interactions, and biological function and thus regulates normal life activities. If the SUMOylation process of proteins is affected, it will cause a cellular reaction and ultimately lead to various diseases, including leukemia. There is growing evidence showing that a large number of proteins are SUMOylated and that SUMOylated proteins play an important role in the occurrence and development of various types of leukemia. Targeting the SUMOylation of proteins alone or in combination with current treatments might provide powerful targeted therapeutic strategies for the clinical treatment of leukemia.

Chlorpromazine eliminates acute myeloid leukemia cells by perturbing subcellular localization of FLT3-ITD and KIT-D816V

Mutated receptor tyrosine kinases (MT-RTKs) such as internal tandem duplication of FMS-like tyrosine kinase 3 (FLT3 ITD) and a point mutation KIT D816V are driver mutations for acute myeloid leukemia (AML). Clathrin assembly lymphoid myeloid leukemia protein (CALM) regulates intracellular transport of RTKs, however, the precise role for MT-RTKs remains elusive. We here show that CALM knock down leads to severely impaired FLT3 ITD- or KIT D814V-dependent cell growth compared to marginal influence on wild-type FLT3- or KIT-mediated cell growth. An antipsychotic drug chlorpromazine (CPZ) suppresses the growth of primary AML samples, and human CD34+CD38- AML cells including AML initiating cells with MT-RTKs in vitro and in vivo. Mechanistically, CPZ reduces CALM protein at post transcriptional level and perturbs the intracellular localization of MT-RTKs, thereby blocking their signaling. Our study presents a therapeutic strategy for AML with MT-RTKs by altering the intracellular localization of MT-RTKs using CPZ.

Targeting the RAS/MAPK pathway with miR-181a in acute myeloid leukemia

Deregulation of microRNAs' expression frequently occurs in acute myeloid leukemia (AML). Lower miR-181a expression is associated with worse outcomes, but the exact mechanisms by which miR-181a mediates this effect remain elusive. Aberrant activation of the RAS pathway contributes to myeloid leukemogenesis. Here, we report that miR-181a directly binds to 3′-untranslated regions (UTRs); downregulates KRAS, NRAS and MAPK1; and decreases AML growth. The delivery of miR-181a mimics to target AML cells using transferrin-targeting lipopolyplex nanoparticles (NP) increased mature miR-181a; downregulated KRAS, NRAS and MAPK1; and resulted in decreased phosphorylation of the downstream RAS effectors. NP-mediated upregulation of miR-181a led to reduced proliferation, impaired colony formation and increased sensitivity to chemotherapy. Ectopic expression of KRAS, NRAS and MAPK1 attenuated the anti-leukemic activity of miR-181a mimics, thereby validating the relevance of the deregulated miR-181a-RAS network in AML. Finally, treatment with miR-181a-NP in a murine AML model resulted in longer survival compared to mice treated with scramble-NP control. These data support that targeting the RAS-MAPK-pathway by miR-181a mimics represents a novel promising therapeutic approach for AML and possibly for other RAS-driven cancers.

Targeting HDAC3, a new partner protein of AKT in the reversal of chemoresistance in acute myeloid leukemia via DNA damage response

Resistance to cytotoxic chemotherapy drugs remains as the major cause of treatment failure in acute myeloid leukemia. Histone deacetylases (HDAC) are important regulators to maintain chromatin structure and control DNA damage; nevertheless, how each HDAC regulates genome stability remains unclear, especially under genome stress conditions. Here, we identified a mechanism by which HDAC3 regulates DNA damage repair and mediates resistance to chemotherapy drugs. In addition to inducing DNA damage, chemotherapy drugs trigger upregulation of HDAC3 expression in leukemia cells. Using genetic and pharmacological approaches, we show that HDAC3 contributes to chemotherapy resistance by regulating the activation of AKT, a well-documented factor in drug resistance development. HDAC3 binds to AKT and deacetylates it at the site Lys20, thereby promoting the phosphorylation of AKT. Chemotherapy drug exposure enhances the interaction between HDAC3 and AKT, resulting in decrease in AKT acetylation and increase in AKT phosphorylation. Whereas HDAC3 depletion or inhibition abrogates these responses and meanwhile sensitizes leukemia cells to chemotoxicity-induced apoptosis. Importantly, in vivo HDAC3 suppression reduces leukemia progression and sensitizes MLL-AF9⁺ leukemia to chemotherapy. Our findings suggest that combination therapy with HDAC3 inhibitor and genotoxic agents may constitute a successful strategy for overcoming chemotherapy resistance.

Radotinib induces high cytotoxicity in c-KIT positive acute myeloid leukemia cells

Previously, we reported that radotinib, a BCR-ABL1 tyrosine kinase inhibitor, induced cytotoxicity in acute myeloid leukemia (AML) cells. However, the effects of radotinib in the subpopulation of c-KIT-positive AML cells were unclear. We observed that low-concentration radotinib had more potent cytotoxicity in c-KIT-positive cells than c-KIT-negative cells from AML patients. To address this issue, cell lines with high c-KIT expression, HEL92.1.7, and moderate c-KIT expression, H209, were selected. HEL92.1.7 cells were grouped into intermediate and high c-KIT expression populations. The cytotoxicity of radotinib against the HEL92.1.7 cell population with intermediate c-KIT expression was not different from that of the population with high c-KIT expression. When H209 cells were grouped into c-KIT expression-negative and c-KIT expression-positive populations, radotinib induced cytotoxicity in the c-KIT-positive population, but not the c-KIT-negative population. Thus, radotinib induces cytotoxicity in c-KIT-positive cells, regardless of the c-KIT expression intensity. Therefore, radotinib induces significant cytotoxicity in c-KIT-positive AML cells, suggesting that radotinib is a potential target agent for the treatment of c-KIT-positive malignancies including AML.

Integration of Technical, Bioinformatic, and Variant Assessment Approaches in the Validation of a Targeted Next-Generation Sequencing Panel for Myeloid Malignancies

CONTEXT

- Detection of variants in hematologic malignancies is increasingly important because of a growing number of variants impacting diagnosis, prognosis, and treatment response, and as potential therapeutic targets. The use of next-generation sequencing technologies to detect variants in hematologic malignancies in a clinical diagnostic laboratory setting allows for efficient identification of routinely tested markers in multiple genes simultaneously, as well as the identification of novel and rare variants in other clinically relevant genes.

OBJECTIVE

- To apply a systematic approach to evaluate and validate a commercially available next-generation sequencing panel (TruSight Myeloid Sequencing Panel, Illumina, San Diego, California) targeting 54 genes. In this manuscript, we focused on the parameters that were used to evaluate assay performance characteristics.

DATA SOURCES

- Analytical validation was performed using samples containing known variants that had been identified previously. Cases were selected from different disease types, with variants in a range of genes. Panel performance characteristics were assessed and genomic regions requiring additional analysis or wet-bench approaches identified.

CONCLUSIONS

- We validated the performance characteristics of a myeloid next-generation sequencing panel for detection of variants. The TruSight Myeloid Sequencing Panel covers more than 95% of target regions with depth greater than 500×. However, because of unique variant types such as large insertions or deletions or genomic regions of high GC content, variants in CEBPA, FLT3, and CALR required supplementation with non-next-generation sequencing assays or with informatics approaches to address deficiencies in performance. The use of multiple bioinformatics approaches (2 variant callers and informatics scripts) allows for maximizing calling of true positives, while identifying limitations in using either method alone.

Antibody-siRNA conjugates: drugging the undruggable for anti-leukemic therapy

INTRODUCTION

Generating effective RNAi-based therapies with the potential to achieve leukemia remission remains critical unmet need. Despite a growing number of leukemia clinical trials, tissue specific delivery of therapeutic siRNA is a major roadblock in translating its clinical potential. The most recent reports in the antibody-siRNA-conjugates (ARCs) field add new dimensions to leukemic therapy, where a covalently ligated therapeutic antisense-RNA with the potential to repress the oncogenic transcript is selectively delivered into the cancer cells. Despite ARC localization to leukemic cells due to high affinity antigen-antibody interactions, multiple challenges exist to unlock the therapeutic potential of siRNA targeting. Areas covered: This review focuses on antibody and siRNA-based therapies for leukemia as well as potential antibody engineering-based strategies to generate an optimal ARC platform. Expert opinion: In vitro and clinical results have revealed that non-targeted delivery and inefficient cellular internalization of therapeutic siRNA are major contributing factors for the lack of efficacy in leukemia patients. Rational antibody design and selective protein engineering with the potential to neutralize siRNA charge, stabilize ARC complex, restrict off-targeted delivery, optimize endosomal escape, and extend serum half-life will generate clinically relevant leukemic therapies that are safe, selective, and effective.

Molecular therapy for acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease that is, in general, associated with a very poor prognosis. Multiple cytogenetic and molecular abnormalities that characterize different forms of AML have been used to better prognosticate patients and inform treatment decisions. Indeed, risk status in patients with this disease has classically been based on cytogenetic findings; however, additional molecular characteristics have been shown to inform risk assessment, including FLT3, NPM1, KIT, and CEBPA mutation status. Advances in sequencing technology have led to the discovery of novel somatic mutations in tissue samples from patients with AML, providing deeper insight into the mutational landscape of the disease. The majority of patients with AML (>97%) are found to have a clonal somatic abnormality on mutational profiling. Nevertheless, our understanding of the utility of mutation profiling in clinical practice remains incomplete and is continually evolving, and evidence-based approaches to application of these data are needed. In this Review, we discuss the evidence-base for integrating mutational data into treatment decisions for patients with AML, and propose novel therapeutic algorithms in the era of molecular medicine.

Pathology Consultation on Gene Mutations in Acute Myeloid Leukemia

OBJECTIVES

Acute myeloid leukemia (AML) is a rapidly fatal disease without the use of aggressive chemotherapy regimens. Cytogenetic and molecular studies are commonly used to classify types of AML based on prognosis, as well as to determine therapeutic regimens.

METHODS

Although there are several AML classifications determined by particular translocations, cytogenetically normal AML represents a molecularly, as well as clinically, heterogeneous group of diseases. Laboratory evaluation of AML will become increasingly important as new mutations with both prognostic and therapeutic implications are being recognized. Moreover, because many patients with AML are being treated more effectively, these mutations may become increasingly useful as markers of minimal residual disease, which can be interpreted in an individualized approach.

RESULTS

Current laboratory studies of gene mutations in AML include analysis of NPM1, FLT3, CEBPA, and KIT. In addition to these genes, many other genes are emerging as potentially useful in determining patients' prognosis, therapy, and disease course.

CONCLUSIONS

This article briefly reviews the current most clinically relevant gene mutations and their clinical and immunophenotypic features, prognostic information, and methods used for detection.

The use of molecular genetics to refine prognosis in acute myeloid leukemia

The discovery and application of advanced molecular techniques, such as gene and microRNA expression profiling, whole genome and exome sequencing, proteomic analysis and methylation assays, have allowed for the identification of recurrent molecular abnormalities in acute myeloid leukemia (AML) that have revolutionized our understanding of the genetic landscape of the disease. These modalities have emerged as valuable tools that permit a more comprehensive and detailed molecular characterization of AML. Many of these molecular abnormalities have been shown to predict prognosis, particularly within the context of cytogenetically normal AML. This review will discuss the major techniques and platforms that have been used to identify novel recurrent gene mutations in AML and briefly describe how these discoveries have impacted on outcome prediction.

Mass cytometry: a highly multiplexed single-cell technology for advancing drug development

Advanced single-cell analysis technologies (e.g., mass cytometry) that help in multiplexing cellular measurements in limited-volume primary samples are critical in bridging discovery efforts to successful drug approval. Mass cytometry is the state-of-the-art technology in multiparametric single-cell analysis. Mass cytometers (also known as cytometry by time-of-flight or CyTOF) combine the cellular analysis principles of traditional fluorescence-based flow cytometry with the selectivity and quantitative power of inductively coupled plasma-mass spectrometry. Standard flow cytometry is limited in the number of parameters that can be measured owing to the overlap in signal when detecting fluorescently labeled antibodies. Mass cytometry uses antibodies tagged to stable isotopes of rare earth metals, which requires minimal signal compensation between the different metal tags. This unique feature enables researchers to seamlessly multiplex up to 40 independent measurements on single cells. In this overview we first present an overview of mass cytometry and compare it with traditional flow cytometry. We then discuss the emerging and potential applications of CyTOF technology in the pharmaceutical industry, including quantitative and qualitative deep profiling of immune cells and their applications in assessing drug immunogenicity, extensive mapping of signaling networks in single cells, cell surface receptor quantification and multiplexed internalization kinetics, multiplexing sample analysis by barcoding, and establishing cell ontologies on the basis of phenotype and/or function. We end with a discussion of the anticipated impact of this technology on drug development lifecycle with special emphasis on the utility of mass cytometry in deciphering a drug's pharmacokinetics and pharmacodynamics relationship.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

Rational combination of dual PI3K/mTOR blockade and Bcl-2/-xL inhibition in AML

Acute myeloid leukemia (AML) continues to represent an area of critical unmet need with respect to new and effective targeted therapies. The Bcl-2 family of pro- and antiapoptotic proteins stands at the crossroads of cellular survival and death, and the expression of and interactions between these proteins determine tumor cell fate. Malignant cells, which are often primed for apoptosis, are particularly vulnerable to the simultaneous disruption of cooperative survival signaling pathways. Indeed, the single agent activity of agents such as mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase kinase (MEK) inhibitors in AML has been modest. Much work in recent years has focused on strategies to enhance the therapeutic potential of the bona fide BH3-mimetic, ABT-737, which inhibits B-cell lymphoma 2 (Bcl-2) and Bcl-xL. Most of these strategies target Mcl-1, an antiapoptotic protein not inhibited by ABT-737. The phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR and Ras/Raf/MEK/ERK signaling pathways are central to the growth, proliferation, and survival of AML cells, and there is much interest currently in pharmacologically interrupting these pathways. Dual inhibitors of PI3K and mTOR overcome some intrinsic disadvantages of rapamycin and its derivatives, which selectively inhibit mTOR. In this review, we discuss why combining dual PI3K/mTOR blockade with inhibition of Bcl-2 and Bcl-xL, by virtue of allowing coordinate inhibition of three mutually synergistic pathways in AML cells, may be a particularly attractive therapeutic strategy in AML, the success of which may be predicted for by basal Akt activation.

The role of the dysfunctional akt-related pathway in cancer: establishment and maintenance of a malignant cell phenotype, resistance to therapy, and future strategies for drug development

Akt serine/threonine kinases, or PKB, are key players in the regulation of a wide variety of cellular activities, such as growth, proliferation, protection from apoptotic injuries, control of DNA damage responses and genome stability, metabolism, migration, and angiogenesis. The Akt-related pathway responds to the stimulation mediated by growth factors, cytokines, hormones, and several nutrients. Akt is present in three isoforms: Akt1, Akt2, and Akt3, which may be alternatively named PKB α , PKB β , and PKB γ , respectively. The Akt isoforms are encoded on three diverse chromosomes and their biological functions are predominantly distinct. Deregulations in the Akt-related pathway were observed in many human maladies, including cancer, cardiopathies, neurological diseases, and type-2 diabetes. This review discusses the significance of the abnormal activities of the Akt axis in promoting and sustaining malignancies, along with the development of tumor cell populations that exhibit enhanced resistance to chemo- and/or radiotherapy. This occurrence may be responsible for the relapse of the disease, which is unfortunately very often related to fatal consequences in patients.

Phase I clinical, pharmacokinetic, and pharmacodynamic study of the Akt-inhibitor triciribine phosphate monohydrate in patients with advanced hematologic malignancies

Akt, a serine/threonine protein kinase, is constitutively phosphorylated and hyperactivated in multiple cancers, including acute myeloid leukemia. High levels are linked to poor survival and inferior responses to chemotherapy, making Akt inhibition an attractive therapeutic target. In this phase I/II study of TCN-PM, a small-molecule Akt inhibitor, TCN-PM therapy was well tolerated in patients with advanced hematological malignancies, and reduced levels of phosphorylation of Akt and its substrate Bad were shown, consistent with inhibition of this survival pathway and induction of cell death. Further investigation of TCN-PM alone or in combination in patients with high Akt levels is warranted.

Immunohistochemical evaluation of AKT protein activation in canine mast cell tumours

The pathogenesis of canine mast cell tumour (MCT) remains unknown. Moreover, therapeutic options are limited and resistance to targeted drugs and recurrences are common, necessitating the identification of additional cellular targets for therapy. In this study we investigated the expression of phosphorylated AKT protein in 25 archival canine MCT samples by immunohistochemistry and examined the correlation between the immunohistochemical scores and histopathological tumour grades. AKT protein was detected in all of the samples and 24 of the 25 samples expressed the phosphorylated form of the protein, albeit with variable intensity. However, when the immunohistochemical scores of weak, intermediate and strong labelling were compared with the histopathological grades I to III, there was no strong correlation. This study suggests that canine MCT cells have activated AKT and indicates the need for further research on the role of the AKT protein and the possibility of targeting the AKT signalling pathway in MCTs.

New agents for acute myeloid leukemia: is it time for targeted therapies?

INTRODUCTION

The prognosis of acute myeloid leukemia (AML) is improved in the last two decades, even though induction and consolidation chemotherapy has not involved new drugs. The more effective use of well-known agents as well as refinement of supportive care during the inevitable phase of severe pancytopenia following intensive chemotherapy accounts for the reduction of treatment-related death rate. In addition, mortality due to allogeneic and autologous stem cell transplantation has also been reduced, due to adoption of more effective therapies for graft versus host disease and other transplant-related complications.

AREAS COVERED

The multitude of chromosomal and molecular abnormalities makes the treatment of AML a challenging prospect. In addition, genetic aberrations are not mutually exclusive and coexist in the leukemic cells. As a consequence, the clinical development of new biologic agents proceeds slowly. Data for this review were identified from PubMed and references from relevant articles published in English from 2000 to 2011.

EXPERT OPINION

In Phase II studies, different new agents have been found to be active in AML and are currently under investigation in Phase III trials also in combination with conventional chemotherapy. In the near future, we would have more information about the possibility of introducing new drugs into daily practice.

Traumatic stress in acute leukemia

OBJECTIVE

Acute leukemia is a condition with an acute onset that is associated with considerable morbidity and mortality. However, the psychological impact of this life-threatening condition and its intensive treatment has not been systematically examined. In the present study, we investigate the prevalence and correlates of post-traumatic stress symptoms in this population.

METHODS

Patients with acute myeloid, lymphocytic, and promyelocytic leukemia who were newly diagnosed, recently relapsed, or treatment failures were recruited at a comprehensive cancer center in Toronto, Canada. Participants completed the Stanford Acute Stress Reaction Questionnaire, Memorial Symptom Assessment Scale, CARES Medical Interaction Subscale, and other psychosocial measures. A multivariate regression analysis was used to assess independent predictors of post-traumatic stress symptoms.

RESULTS

Of the 205 participants, 58% were male, mean age was 50.1 ± 15.4 years, 86% were recently diagnosed, and 94% were receiving active treatment. The mean Stanford Acute Stress Reaction Questionnaire score was 30.2 ± 22.5, with 27 of 200 (14%) patients meeting criteria for acute stress disorder and 36 (18%) for subsyndromal acute stress disorder. Post-traumatic stress symptoms were associated with more physical symptoms, physical symptom distress, attachment anxiety, and perceived difficulty communicating with health-care providers, and poorer spiritual well-being (all p < 0.05).

CONCLUSIONS

The present study demonstrates that clinically significant symptoms of traumatic stress are common in acute leukemia and are linked to the degree of physical suffering, to satisfaction with relationships with health-care providers, and with individual psychological characteristics. Longitudinal study is needed to determine the natural history, but these findings suggest that intervention may be indicated to alleviate or prevent traumatic stress in this population.