Janus kinase 2: a critical target in chronic myelogenous leukemia

Ponatinib and STAT5 Inhibitor Pimozide Combined Synergistic Treatment Applications Potentially Overcome Drug Resistance via Regulating the Cytokine Expressional Network in Chronic Myeloid Leukemia Cells

Chronic myeloid leukemia (CML) is a clonal myeloproliferative hematological disease characterized by the chimeric breakpoint-cluster region/Abelson kinase1 (BCR::ABL1) oncoprotein; playing a pivotal role in CML molecular pathology, diagnosis, treatment, and possible resistance arising from the success and tolerance of tyrosine kinase inhibitor (TKI)-based therapy. The transcription factor STAT5 constitutive signaling, which is influenced by the cytokine signaling network, triggers BCR::ABL1-based CML pathogenesis and is also relevant to acquired TKI resistance. The unsuccessful therapeutic approaches targeting BCR::ABL1, in particular third-line therapy with ponatinib, still need to be further developed with alternative combination strategies to overcome drug resistance. As treatment with the STAT5 inhibitor pimozide in combination with ponatinib resulted in an efficient and synergistic therapeutic approach in TKI-resistant CML cells, this study focused on identifying the underlying amplification of ponatinib response mechanisms by determining different cytokine expression profiles in parental and ponatinib-resistant CML cells, in vitro. The results showed that expression of interleukin (IL) 1B, IL9, and IL12A-B was increased by 2-fold, while IL18 was downregulated by 2-fold in the ponatinib-resistant cells compared to sensitive ones. Importantly, ponatinib treatment upregulated the expression of 21 of the 23 interferon and IL genes in the ponatinib-resistant cells, while treatment with pimozide or a combination dose resulted in a reduction in the expression of 19 different cytokine genes, such as for example, inflammatory cytokines, IL1A-B and IL6 or cytokine genes associated with supporting tumor progression, leukemia stem cell growth or poor survival, such as IL3, IL8, IL9, IL10, IL12, or IL15. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis results showed that the genes were mainly enriched in the regulation of receptor signaling through the Janus kinase/signal transducer and activator of transcription pathway, cytokine-cytokine receptor interaction, and hematopoietic cell lineage. Protein-protein interaction analysis showed that IL2, IL6, IL15, IFNG, and others appeared in the top lists of pathways, indicating their high centrality and importance in the network. Therefore, pimozide could be a promising agent to support TKI therapies in ponatinib resistance. This research would help to clarify the role of cytokines in ponatinib resistance and advance the development of new therapeutics to utilize the STAT5 inhibitor pimozide in combination with TKIs.

Discovery of furopyridine-based compounds as novel inhibitors of Janus kinase 2: In silico and in vitro studies

Janus kinase 2 (JAK2), one of the JAK isoforms participating in a JAK/STAT signaling cascade, has been considered a potential clinical target owing to its critical role in physiological processes involved in cell growth, survival, development, and differentiation of various cell types, especially immune and hematopoietic cells. Substantial studies have proven that the inhibition of this target could disrupt the JAK/STAT pathway and provide therapeutic outcomes for cancer, immune disorders, inflammation, and COVID-19. Herein, we performed docking-based virtual screening of 63 in-house furopyridine-based compounds and verified the first-round screened compounds by in vitro enzyme- and cell-based assays. By shedding light on the integration of both in silico and in vitro methods, we could elucidate two promising compounds. PD19 showed cytotoxic effects on human erythroblast cell lines (TF-1 and HEL) with IC50 values of 57.27 and 27.28 μM, respectively, while PD12 exhibited a cytotoxic effect on TF-1 with an IC50 value of 83.47 μM by suppressing JAK2/STAT5 autophosphorylation. In addition, all screened compounds were predicted to meet drug-like criteria based on Lipinski's rule of five, and none of the extreme toxicity features were found. Molecular dynamic simulations revealed that PD12 and PD19 could form stable complexes with JAK2 in an aqueous environment, and the van der Waals interactions were the main force driving the complex formation. Besides, all compounds sufficiently interacted with surrounding amino acids in all crucial regions, including glycine, catalytic, and activation loops. Altogether, PD12 and PD19 identified here could potentially be developed as novel therapeutic inhibitors disrupting the JAK/STAT pathway.

Harmonizing the craft of crafting clinically endorsed small-molecule BCR-ABL tyrosine kinase inhibitors for the treatment of hematological malignancies

The advancement and practical use of small-molecule tyrosine kinase inhibitors (TKIs) that specifically target the BCR-ABL fusion protein have introduced a revolutionary era of precision medicine for the treatment of chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL). This review offers a comprehensive exploration of the synthesis, mechanisms of action, and clinical implementation of clinically validated TKIs in the context of BCR-ABL, emphasizing the remarkable strides made in achieving therapeutic precision. We delve into the intricate design and synthesis of these small molecules, highlighting the synthetic strategies and modifications that have led to increased selectivity, enhanced binding affinities, and reduced off-target effects. Additionally, we discuss the structural biology of BCR-ABL inhibition and how it informs drug design. The success of these compounds in inhibiting aberrant kinase activity is a testament to the meticulous refinement of the synthetic process. Furthermore, this review provides a detailed analysis of the clinical applications of these TKIs, covering not only their efficacy in achieving deep molecular responses but also their impact on patient outcomes, safety profiles, and resistance mechanisms. We explore ongoing research efforts to overcome resistance and enhance the therapeutic potential of these agents. In conclusion, the synthesis and utilization of clinically validated small-molecule TKIs targeting BCR-ABL exemplify the transformative power of precision medicine in the treatment of hematological malignancies. This review highlights the evolving landscape of BCR-ABL inhibition and underscores the continuous commitment to refining and expanding the therapeutic repertoire for these devastating diseases.

Pathobiology and Therapeutic Relevance of GSK-3 in Chronic Hematological Malignancies

Glycogen synthase kinase-3 (GSK-3) is an evolutionarily conserved, ubiquitously expressed, multifunctional serine/threonine protein kinase involved in the regulation of a variety of physiological processes. GSK-3 comprises two isoforms (α and β) which were originally discovered in 1980 as enzymes involved in glucose metabolism via inhibitory phosphorylation of glycogen synthase. Differently from other proteins kinases, GSK-3 isoforms are constitutively active in resting cells, and their modulation mainly involves inhibition through upstream regulatory networks. In the early 1990s, GSK-3 isoforms were implicated as key players in cancer cell pathobiology. Active GSK-3 facilitates the destruction of multiple oncogenic proteins which include β-catenin and Master regulator of cell cycle entry and proliferative metabolism (c-Myc). Therefore, GSK-3 was initially considered to be a tumor suppressor. Consistently, GSK-3 is often inactivated in cancer cells through dysregulated upstream signaling pathways. However, over the past 10–15 years, a growing number of studies highlighted that in some cancer settings GSK-3 isoforms inhibit tumor suppressing pathways and therefore act as tumor promoters. In this article, we will discuss the multiple and often enigmatic roles played by GSK-3 isoforms in some chronic hematological malignancies (chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, and B-cell non-Hodgkin’s lymphomas) which are among the most common blood cancer cell types. We will also summarize possible novel strategies targeting GSK-3 for innovative therapies of these disorders.

Overcoming Resistance to Kinase Inhibitors: The Paradigm of Chronic Myeloid Leukemia

Protein kinases (PKs) play crucial roles in cellular proliferation and survival, hence their deregulation is a common event in the pathogenesis of solid and hematologic malignancies. Targeting PKs has been a promising strategy in cancer treatment, and there are now a variety of approved anticancer drugs targeting PKs. However, the phenomenon of resistance remains an obstacle to be addressed and overcoming resistance is a goal to be achieved. Chronic myeloid leukemia (CML) is the first as well as one of the best examples of a cancer that can be targeted by molecular therapy; hence, it can be used as a model disease for other cancers. This review aims to summarize up-to-date knowledge on the main mechanisms implicated in resistance to PK inhibitory therapies and to outline the main strategies that are being explored to overcome resistance. The importance of molecular diagnostics and disease monitoring in counteracting resistance will also be discussed.

Metabolic convergence on lipogenesis in RAS, BCR-ABL, and MYC-driven lymphoid malignancies

BACKGROUND

Metabolic reprogramming is a central feature in many cancer subtypes and a hallmark of cancer. Many therapeutic strategies attempt to exploit this feature, often having unintended side effects on normal metabolic programs and limited efficacy due to integrative nature of metabolic substrate sourcing. Although the initiating oncogenic lesion may vary, tumor cells in lymphoid malignancies often share similar environments and potentially similar metabolic profiles. We examined cells from mouse models of MYC-, RAS-, and BCR-ABL-driven lymphoid malignancies and find a convergence on de novo lipogenesis. We explore the potential role of MYC in mediating lipogenesis by 13C glucose tracing and untargeted metabolic profiling. Inhibition of lipogenesis leads to cell death both in vitro and in vivo and does not induce cell death of normal splenocytes.

METHODS

We analyzed RNA-seq data sets for common metabolic convergence in lymphoma and leukemia. Using in vitro cell lines derived in from conditional MYC, RAS, and BCR-ABL transgenic murine models and oncogene-driven human cell lines, we determined gene regulation, metabolic profiles, and sensitivity to inhibition of lipogenesis in lymphoid malignancies. We utilize preclinical murine models and transgenic primary model of T-ALL to determine the effect of lipogenesis blockade across BCR-ABL-, RAS-, and c-MYC-driven lymphoid malignancies. Statistical significance was calculated using unpaired t-tests and one-way ANOVA.

RESULTS

This study illustrates that de novo lipid biogenesis is a shared feature of several lymphoma subtypes. Using cell lines derived from conditional MYC, RAS, and BCR-ABL transgenic murine models, we demonstrate shared responses to inhibition of lipogenesis by the acetyl-coA carboxylase inhibitor 5-(tetradecloxy)-2-furic acid (TOFA), and other lipogenesis inhibitors. We performed metabolic tracing studies to confirm the influence of c-MYC and TOFA on lipogenesis. We identify specific cell death responses to TOFA in vitro and in vivo and demonstrate delayed engraftment and progression in vivo in transplanted lymphoma cell lines. We also observe delayed progression of T-ALL in a primary transgenic mouse model upon TOFA administration. In a panel of human cell lines, we demonstrate sensitivity to TOFA treatment as a metabolic liability due to the general convergence on de novo lipogenesis in lymphoid malignancies driven by MYC, RAS, or BCR-ABL. Importantly, cell death was not significantly observed in non-malignant cells in vivo.

CONCLUSIONS

These studies suggest that de novo lipogenesis may be a common survival strategy for many lymphoid malignancies and may be a clinically exploitable metabolic liability.

TRIAL REGISTRATION

This study does not include any clinical interventions on human subjects.

Combination Therapies in Chronic Myeloid Leukemia for Potential Treatment-Free Remission: Focus on Leukemia Stem Cells and Immune Modulation

Although tyrosine Kinase Inhibitors (TKI) has revolutionized the treatment of chronic myeloid leukemia (CML), patients are not cured with the current therapy modalities. Also, the more recent goal of CML treatment is to induce successful treatment-free remission (TFR) among patients achieving durable deep molecular response (DMR). Together, it is necessary to develop novel, curative treatment strategies. With advancements in understanding the biology of CML, such as dormant Leukemic Stem Cells (LSCs) and impaired immune modulation, a number of agents are now under investigation. This review updates such agents that target LSCs, and together with TKIs, have the potential to eradicate CML. Moreover, we describe the developing immunotherapy for controlling CML.

Current Views on the Interplay between Tyrosine Kinases and Phosphatases in Chronic Myeloid Leukemia

Simple Summary

The chromosomal alteration t(9;22) generating the BCR-ABL1 fusion protein represents the principal feature that distinguishes some types of leukemia. An increasing number of articles have focused the attention on the relevance of protein phosphatases and their potential role in the control of BCR-ABL1-dependent or -independent signaling in different areas related to the biology of chronic myeloid leukemia. Herein, we discuss how tyrosine and serine/threonine protein phosphatases may interact with protein kinases, in order to regulate proliferative signal cascades, quiescence and self-renewals on leukemic stem cells, and drug-resistance, indicating how BCR-ABL1 can (directly or indirectly) affect these critical cells behaviors. We provide an updated review of the literature on the function of protein phosphatases and their regulation mechanism in chronic myeloid leukemia.

Abstract

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by BCR-ABL1 oncogene expression. This dysregulated protein-tyrosine kinase (PTK) is known as the principal driver of the disease and is targeted by tyrosine kinase inhibitors (TKIs). Extensive documentation has elucidated how the transformation of malignant cells is characterized by multiple genetic/epigenetic changes leading to the loss of tumor-suppressor genes function or proto-oncogenes expression. The impairment of adequate levels of substrates phosphorylation, thus affecting the balance PTKs and protein phosphatases (PPs), represents a well-established cellular mechanism to escape from self-limiting signals. In this review, we focus our attention on the characterization of and interactions between PTKs and PPs, emphasizing their biological roles in disease expansion, the regulation of LSCs and TKI resistance. We decided to separate those PPs that have been validated in primary cell models or leukemia mouse models from those whose studies have been performed only in cell lines (and, thus, require validation), as there may be differences in the manner that the associated pathways are modified under these two conditions. This review summarizes the roles of diverse PPs, with hope that better knowledge of the interplay among phosphatases and kinases will eventually result in a better understanding of this disease and contribute to its eradication.

Design, synthesis, biological activity evaluation of 3-(4-phenyl-1H-imidazol-2-yl)-1H-pyrazole derivatives as potent JAK 2/3 and aurora A/B kinases multi-targeted inhibitors

In this study, a series of 3-(4-phenyl-1H-imidazol-2-yl)-1H-pyrazole derivatives were designed, synthesized, and evaluated for their biological activities. Upon performing kinase assays, most of the compounds exhibited potent inhibition against JAK2/3 and Aurora A/B with the IC₅₀ values ranging from 0.008 to 2.52 μM. Among these derivatives, compound 10e expressed the most moderate inhibiting activities against all the four kinases with the IC₅₀ values of 0.166 μM (JAK2), 0.057 μM (JAK3), 0.939 μM (Aurora A), and 0.583 μM (Aurora B), respectively. Moreover, most of the derived compounds exhibited potent cytotoxicity against human chronic myeloid leukemia cells K562 and human colon cancer cells HCT116, while compound 10e expressed antiproliferative activities against K562 (IC₅₀₌6.726  μM). According to western blot analysis, compound 10e down-regulated the phosphorylation of STAT3, STAT5, Aurora A, and Aurora B in a dose-dependent manner in K562 and HCT116 cells. Cell cycle analysis revealed that compound 10e inhibited the proliferation of cells by inducing cell cycle arrest in the G2 phase. The molecular modeling suggested that compound 10e could maintain a binding mode similar to the binding mode of AT9832, a common JAK 2/3 and Aurora A/B kinases multi-target kinase inhibitor. Therefore, compound 10e might be a potential agent for cancer therapy deserving further research.

The JAK2/STAT3 pathway inhibitor, AG490, suppresses the abnormal behavior of keloid fibroblasts in vitro

AG490 is a selective inhibitor of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. The present study examined its effects on the abnormal behavior of human keloid fibroblasts (HKFs) and evaluated its potential use in the treatment of keloids. Human normal fibroblasts (HNFs) and HKFs were treated with increasing concentrations of AG490. The proliferation of HNFs and HKFs was inhibited by AG490 in both a time‑ and concentration‑dependent manner by increasing apoptosis and inducing G1 cell cycle arrest. The downregulation of cyclin D1 and connective tissue growth factor (CTGF) expression was associated with a decrease in STAT3 expression in response to AG490. The effects of AG490 on TGF‑β‑stimulated fibroblasts, including HNFs, HKFs and hypertrophic scar fibroblasts (HSFs) were also evaluated. The TGF‑β1‑stimulated excessive proliferation and CTGF production were markedly inhibited by the application of AG490 in the HNFs, HSFs and HKFs. In addition, the STAT3‑specific decoy oligodeoxynucleotides (SODNs) were transfected into HKFs. The invasive ability of the SODN‑transfected HKFs was determined and the expression of extracellular matrix components was quantified. Similarly, SODNs blocked the constitutive activation of STAT3. SODNs inhibited the invasion and progression of HKFs, possibly via the upregulation of the expression of tissue inhibitor of metalloproteinase‑2 (TIMP‑2), and the downregulation of the expression of matrix metalloproteinase‑2 (MMP‑2) and vascular endothelial growth factor (VEGF). On the whole, the findings of the present study demonstrate that STAT3‑specific elimination, such as the application of AG490 and decoy ODNs, may serve as promising therapeutic strategies for the treatment of keloids.

Response and Resistance to BCR-ABL1-Targeted Therapies

Chronic myeloid leukemia (CML), caused by constitutively active BCR-ABL1 fusion tyrosine kinase, has served as a paradigm for successful application of molecularly targeted cancer therapy. The development of the tyrosine kinase inhibitor (TKI) imatinib allows patients with CML to experience near-normal life expectancy. Specific point mutations that decrease drug binding affinity can produce TKI resistance, and second- and third-generation TKIs largely mitigate this problem. Some patients develop TKI resistance without known resistance mutations, with significant heterogeneity in the underlying mechanism, but this is relatively uncommon, with the majority of patients with chronic phase CML achieving long-term disease control. In contrast, responses to TKI treatment are short lived in advanced phases of the disease or in BCR-ABL1-positive acute lymphoblastic leukemia, with relapse driven by both BCR-ABL1 kinase-dependent and -independent mechanisms. Additionally, the frontline CML treatment with second-generation TKIs produces deeper molecular responses, driving disease burden below the detection limit for a greater number of patients. For patients with deep molecular responses, up to half have been able to discontinue therapy. Current efforts are focused on identifying therapeutic strategies to drive deeper molecular responses, enabling more patients to attempt TKI discontinuation.

Unraveling survivin expression in chronic myeloid leukemia: Molecular interactions and clinical implications

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the BCR-ABL oncoprotein, known to drive leukemogenesis by orchestrating multiple signaling pathways ultimately involved in cell survival. Despite successful response rates of CML patients to tyrosine kinase inhibitors (TKIs), resistance eventually arises due to BCR-ABL-dependent and independent mechanisms. Survivin is an inhibitor of apoptosis protein acting in the interface between apoptosis deregulation and cell cycle progression. In CML, high levels of survivin have been associated with late stages of disease and therapy resistance. In this review, we provide an overview of important aspects concerning survivin subcellular localization and expression pattern in CML patients and cell lines. Moreover, we highlight the relevance of molecular networks involving survivin for disease progression and treatment resistance. Finally, we discuss the mechanisms accounting for survivin overexpression, as well as novel therapeutic interventions that have been designed to counteract survivin-associated malignancy in CML.

Icaritin: A Novel Natural Candidate for Hematological Malignancies Therapy

Hematological malignancies including leukemia and lymphoma can severely impact human health. With the current therapies combined with chemotherapy, stem cell transplantation, radiotherapy, and immunotherapy, the prognosis of hematologic malignancies improved significantly. However, most hematological malignancies are still incurable. Therefore, research for novel treatment options was continuing with the natural product as one source. Icaritin is a compound extracted from a traditional Chinese herb, Epimedium Genus, and demonstrated an antitumor effect in various neoplasms including hematological malignancies such as leukemia, lymphoma, and multiple myeloma. In hematological malignancies, icaritin showed multiple cytotoxic effects to induce apoptosis, arrest the cell cycle, inhibit proliferation, promote differentiation, restrict metastasis and infiltration, and suppress the oncogenic virus. The proved underlying mechanisms of the cytotoxic effects of icaritin are different in various cell types of hematological malignancies but associated with the critical cell signal pathway, including PI3K/Akt, JAK/STAT3, and MAPK/ERK/JNK. Although the primary target of icaritin is still unspecified, the existing evidence indicates that icaritin is a potential novel therapeutic agent for neoplasms as with hematological malignancies. Here, in the field of hematology, we reviewed the reported activity of icaritin in hematologic malignancies and the underlying mechanisms and recognized icaritin as a candidate for therapy of hematological malignancies.

RIPK1-dependent cell death: a novel target of the Aurora kinase inhibitor Tozasertib (VX-680)

The Aurora kinase family (Aurora A, B and C) are crucial regulators of several mitotic events, including cytokinesis. Increased expression of these kinases is associated with tumorigenesis and several compounds targeting Aurora kinase are under evaluation in clinical trials (a.o. AT9283, AZD1152, Danusertib, MLN8054). Here, we demonstrate that the pan-Aurora kinase inhibitor Tozasertib (VX-680 and MK-0457) not only causes cytokinesis defects through Aurora kinase inhibition, but is also a potent inhibitor of necroptosis, a cell death process regulated and executed by the RIPK1, RIPK3 and MLKL signalling axis. Tozasertib’s potency to inhibit RIPK1-dependent necroptosis and to block cytokinesis in cells is in the same concentration range, with an IC50 of 1.06 µM and 0.554 µM, respectively. A structure activity relationship (SAR) analysis of 67 Tozasertib analogues, modified at 4 different positions, allowed the identification of analogues that showed increased specificity for either cytokinesis inhibition or for necroptosis inhibition, reflecting more specific inhibition of Aurora kinase or RIPK1, respectively. These results also suggested that RIPK1 and Aurora kinases are functionally non-interacting targets of Tozasertib and its analogues. Indeed, more specific Aurora kinase inhibitors did not show any effect in necroptosis and Necrostatin-1s treatment did not result in cytokinesis defects, demonstrating that both cellular processes are not interrelated. Finally, Tozasertib inhibited recombinant human RIPK1, human Aurora A and human Aurora B kinase activity, but not RIPK3. The potency ranking of the newly derived Tozasertib analogues and their specificity profile, as observed in cellular assays, coincide with ADP-Glo recombinant kinase activity assays. Overall, we show that Tozasertib not only targets Aurora kinases but also RIPK1 independently, and that we could generate analogues with increased selectivity to RIPK1 or Aurora kinases, respectively.

Role of ZNF224 in c-Myc repression and imatinib responsiveness in chronic myeloid leukemia

The transcription factor ZNF224 plays a key proapoptotic role in chronic myelogenous leukemia (CML), by modulating Wilms Tumor protein 1 (WT1) dependent apoptotic genes transcription. Recently, we demonstrated that Bcr-Abl signaling represses ZNF224 expression in Bcr-Abl positive CML cell lines and in CML patients. Interestingly, Imatinib and second-generation tyrosine kinase inhibitors specifically increase ZNF224 expression.

On the other hand, Bcr-Abl positively modulates, via JAK2 activation, the expression of the c-Myc oncogene, which is required for Bcr-Abl oncogenic transformation in CML. Consequently, JAK2 inhibitors represent promising molecular therapeutic tools in CML.

In this work, we demonstrate that ZNF224 is a novel transcriptional repressor of c-Myc in CML. We also show that ZNF224 induction by Imatinib and AG490, a specific JAK2 inhibitor, is responsible for the transcriptional repression of c-MYC, thus highlighting the crucial role of the ZNF224/c-Myc axis in Imatinib responsiveness.

Interestingly, we also report that ZNF224 is induced by AG490 in Imatinib-resistant CML cells, leading to c-Myc repression and apoptosis induction. These findings suggest that the development of molecular tools able to induce ZNF224 expression could provide promising means to bypass Imatinib resistance in CML.

Cellular and Molecular Networks in Chronic Myeloid Leukemia: The Leukemic Stem, Progenitor and Stromal Cell Interplay

The use of imatinib, second and third generation ABL tyrosine kinase inhibitors (TKI) (i.e. dasatinib, nilotinib, bosutinib and ponatinib) made CML a clinically manageable and, in a small percentage of cases, a cured disease. TKI therapy also turned CML blastic transformation into a rare event; however, disease progression still occurs in those patients who are refractory, not compliant with TKI therapy or develop resistance to multiple TKIs. In the past few years, it became clear that the BCRABL1 oncogene does not operate alone to drive disease emergence, maintenance and progression. Indeed, it seems that bone marrow (BM) microenvironment-generated signals and cell autonomous BCRABL1 kinase-independent genetic and epigenetic alterations all contribute to: i. persistence of a quiescent leukemic stem cell (LSC) reservoir, ii. innate or acquired resistance to TKIs, and iii. progression into the fatal blast crisis stage. Herein, we review the intricate leukemic network in which aberrant, but finely tuned, survival, mitogenic and self-renewal signals are generated by leukemic progenitors, stromal cells, immune cells and metabolic microenvironmental conditions (e.g. hypoxia) to promote LSC maintenance and blastic transformation.

FZD7 regulates BMSCs-mediated protection of CML cells

Inspite of effective treatment with imatinib (IM), chronic myeloid leukemia (CML) is still an incurable disease. Some patients became refractory because of IM resistance. Bone marrow mesenchymal stem cells (BMSCs) have been implicated a role in promoting CML cells' resistance against IM treatment. The detailed molecular mechanisms, however, remain largely unknown. In this study, we found that BMSCs increased the expression of FZD7 and activated Wnt/β-catenin signaling pathway in CML cells. BMSCs from CML patients showed increased efficiency to accelerate CML cell proliferation, enhance the drug resistance of K562 cells and up-regulate the expression of FZD7. Antagonism of FZD7 expression by shRNA significantly suppressed proliferation and increased IM sensitivity of CML cells co-cultured with BMSCs cells. Our findings suggest that FZD7, involved in canonical Wnt signaling pathway, plays a critical role in mediating BMSCs-dependent protection of CML cells, and potentially provide a novel therapeutic target for CML.

Codelivery of Ponatinib and SAR302503 by Active Bone-Targeted Polymeric Micelles for the Treatment of Therapy-Resistant Chronic Myeloid Leukemia

Point mutations in the BCR-ABL1 domain and primitive chronic myelogenous leukemia (CML) cells existing in the bone marrow environment insensitive to tyrosine kinase inhibitors (TKIs) have become two major challenges in the CML therapy. In this study, combined TKI ponatinib and JAK2 inhibitor SAR302503 short-term treatment effectively suppressed growth and promoted apoptosis of BaF3/T315I cells in cytokine-containing medium in vitro. SAR302503 prevented cytokine-dependent resistance to ponatinib via inhibition of JAK2/STAT5 phosphorylation. Codelivery of ponatinib and SAR302503 by active bone-targeted polymeric micellar formulation greatly increased the drug accumulation in medullary cavity. The therapeutic efficacy of bone-targeted formulation was demonstrated in BaF3/T315I cells inoculated murine model with no dose-limited toxicity detectable in health mice. Thus, the intravenous injectable bone-homing ponatinib and SAR302503 micellar formulation represents a promising strategy for the treatment of therapy-resistant CML.

Natural-Based Indirubins Display Potent Cytotoxicity toward Wild-Type and T315I-Resistant Leukemia Cell Lines

Drug resistance in chronic myelogenous leukemia (CML) requires the development of new CML chemotherapeutic drugs. Indirubin, a well-known mutikinase inhibitor, is the major active component of "Danggui Longhui Wan", a Chinese traditional medicine used for the treatment of CML symptoms. An in-house collection of indirubin derivatives was screened at 1 μM on wild-type and imatinib-resistant T315I mutant CML cells. Herein are reported that only 15 analogues of the natural 6-bromoindirubin displayed potent cytotoxicity in the submicromolar range. Kinase assays in vitro show that eight out of the 15 active molecules strongly inhibited both c-Src and Abl oncogenic kinases in the nanomolar range. Most importantly, these eight molecules blocked the activity of T315I mutant Abl kinase at the submicromolar level and with analogue 22 exhibiting inhibitory activity at the low nanomolar range. Docking calculations suggested that active indirubins might inhibit T315I Abl kinase through an unprecedented binding to both active and Src-like inactive conformations. Analogue 22 is the first derivative of a natural product identified as an inhibitor of wild-type and imatinib-resistant T315I mutant Abl kinases.

Combination of JAK2 and HSP90 inhibitors: an effective therapeutic option in drug-resistant chronic myelogenous leukemia

Recent studies suggest that JAK2 serves as a novel therapeutic target in Bcr-Abl+ chronic myelogenous leukemia (CML). We have reported the existence of an HSP90- associated high molecular weight network complex (HMWNC) that is composed of HSP90 client proteins BCR-ABL, JAK2, and STAT3 in wild type Bcr-Abl+ leukemic cells. Here we showed that the HSP90-HMWNC is present in leukemia cells from CML patients in blast stage, and in Imatinib (IM)-resistant 32Dp210 (T315I) leukemia cells. We found that the HSP90-HMWNC could be disassembled by depleting JAK2 with either Jak2-specific shRNA or treatment with JAK2 inhibitors (TG101209 or Ruxolitinib) and HSP90 inhibitor (AUY922). Combinational treatment with JAK2 and HSP90 inhibitors diminished the activation of BCR-ABL, JAK2 and its downstream targets. As a result, the IM-resistant 32Dp210 T315I cells underwent apoptosis. When administered in mice bearing 32Dp210 T315I leukemia, combinational therapy using Ruxolitinib and AUY922 prolonged the survival significantly. Thus, a combination of JAK2 and HSP90 inhibitors could be a powerful strategy for the treatment of CML, especially in IM-resistant patients.

Effective Concentration of a Multikinase Inhibitor within Bone Marrow Correlates with In Vitro Cell Killing in Therapy-Resistant Chronic Myeloid Leukemia

Leukemia cells escape BCR-ABL-targeted therapy by developing mutations, such as T315I, in the p210(BCR-ABL) fusion protein in Philadelphia chromosome-positive chronic myeloid leukemia (CML). Although most effort has been focused on development of new tyrosine kinase inhibitors, enrichment of these small-molecule inhibitors in the tumor tissue can also have a profound impact on treatment outcomes. Here, we report that a 2-hour exposure of the T315I-mutant CML cells to 10 μmol/L of the multikinase inhibitor TG101209 suppressed BCR-ABL-independent signaling and caused cell-cycle arrest at G2-M. Further increase in drug concentration to 17.5 μmol/L blocked phosphorylation of the mutant BCR-ABL kinase and its downstream JAK2 and STAT5. The effective dosage to overcome therapy resistance identified in an in vitro setting serves as a guidance to develop the proper drug formulation for in vivo efficacy. A targeted formulation was developed to achieve sustained bone marrow TG101209 concentration at or above 17.5 μmol/L for effective killing of CML cells in vivo Potent inhibition of leukemia cell growth and extended survival were observed in two murine models of CML treated with 40 mg/kg intravenously administered targeted TG101209, but not with the untargeted drug at the same dosage. Our finding provides a unique approach to develop treatments for therapy-resistant CML. Mol Cancer Ther; 15(5); 899-910. ©2016 AACR.

Indirubin derivatives: a patent review (2010 - present)

INTRODUCTION

Indirubins are bisindole alkaloids naturally occurring in indigo-bearing plants or in mollusks from the Muricidae family. They belong to the rather small family of indigoids, which has nevertheless found an extreme importance in the fields of dyes and medicinal chemistry. Indirubin has been found to be the active ingredient of a traditional Chinese Medicine used to treat the symptoms of leukemia. Further biological explorations revealed the ability of indirubin to bind cyclin-dependent kinases and 6-bromoindirubin, extracted from mollusks, to bind glycogen synthase kinase-3. The high affinity displayed by the two natural products has opened a vast field of research and triggered the development of hundred of derivatives with biological activities.

AREAS COVERED

The traditional use of indirubin for the treatment of leukemia has prompted different research groups to study the cytotoxic effect of indirubin derivatives on both solid tumors and leukemia. Moreover, the affinity of indirubins for kinases also allowed the exploration of their activity towards stem cells.

EXPERT OPINION

The derivatives presented are in accordance with first discoveries and establish the close relation between activity and kinase inhibition. New derivatives have been patented and new interferences in signaling pathways are described. However, few in vivo studies have been performed and more efficient solutions are needed to unravel the major issue of solubility.

Chabamide induces cell cycle arrest and apoptosis by the Akt/MAPK pathway and inhibition of P-glycoprotein in K562/ADR cells

One of the major mechanisms of multidrug resistance in cancer therapy is the overexpression of P-glycoprotein (P-gp). Chabamide, a dimeric alkaloid isolated from Piper chaba Hunter, shows antimalarial, antituberculosis, and cytotoxic activities. However, its mechanism of action has not been elucidated. In this study, the molecular mechanism underlying the cytotoxicity and downregulation of P-gp expression by chabamide in adriamycin-resistant human leukemia cells (K562/ADR) was clarified. Results show that chabamide inhibited the growth of K562/ADR cells in a dose-dependent and time-dependent manner, and significantly inhibited cell proliferation by cell cycle arrest in the G0/G1 phase, which was associated with an obvious increase in p21 and decrease in cyclin D1 and CDK2/4/6 protein expression. Moreover, chabamide could regulate the changes in the mitochondrial membrane potential, increase the expression of apoptosis-related proteins, such as Bax and cytochrome c, and decrease the protein expression levels of Bcl-2, caspase-9, caspase-3, PARP-1, and p-Akt. In addition, we found that JNK, ERK1/2, and p38 were regulated by chabamide in K562/ADR cells. Further studies indicated that the decrease in the reactive oxygen species level inhibited intrinsic P-gp expression. Therefore, chabamide-induced apoptosis in K562/ADR cells was associated with Akt/MAPK and the inhibition of P-gp. These results provide a biochemical basis for possible clinical applications of chabamide in the treatment of leukemia.

Inhibition of Ras-mediated signaling pathways in CML stem cells

BACKGROUND

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by the presence of the BCR-ABL1 oncoprotein in cells with a hematopoietic stem cell (HSC) origin. BCR-ABL1 tyrosine kinase activity leads to constitutive activation of Ras, which in turn acts as a branch point to initiate multiple downstream signaling pathways governing proliferation, self-renewal, differentiation and apoptosis. As aberrant regulation of these cellular processes causes transformation and disease progression particularly in advanced stages of CML, investigation of these signaling pathways may uncover new therapeutic targets for the selective eradication of CML stem cells. Transcription factors play a crucial role in unbalancing the Ras signaling network and have recently been investigated as potential modulators in this regard. In this review, we first briefly summarize the Ras-associated molecular pathways that are involved in the regulation of CML stem cell properties. Next we discuss the relevance of Ras-associated transcription factors as nuclear targets in combination treatment strategies for CML.

CONCLUSIONS

A closer investigation of the influence of Ras-mediated signaling pathways on CML progression to blast crisis is warranted to uncover new directions for targeted therapies, particularly in cases that are resistant to current tyrosine kinase inhibitors.

Cytokine Regulation of Microenvironmental Cells in Myeloproliferative Neoplasms

The term myeloproliferative neoplasms (MPN) refers to a heterogeneous group of diseases including not only polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), but also chronic myeloid leukemia (CML), and systemic mastocytosis (SM). Despite the clinical and biological differences between these diseases, common pathophysiological mechanisms have been identified in MPN. First, aberrant tyrosine kinase signaling due to somatic mutations in certain driver genes is common to these MPN. Second, alterations of the bone marrow microenvironment are found in all MPN types and have been implicated in the pathogenesis of the diseases. Finally, elevated levels of proinflammatory and microenvironment-regulating cytokines are commonly found in all MPN-variants. In this paper, we review the effects of MPN-related oncogenes on cytokine expression and release and describe common as well as distinct pathogenetic mechanisms underlying microenvironmental changes in various MPN. Furthermore, targeting of the microenvironment in MPN is discussed. Such novel therapies may enhance the efficacy and may overcome resistance to established tyrosine kinase inhibitor treatment in these patients. Nevertheless, additional basic studies on the complex interplay of neoplastic and stromal cells are required in order to optimize targeting strategies and to translate these concepts into clinical application.

Aurora Kinase Inhibitors in Oncology Clinical Trials: Current State of the Progress

The Aurora kinase family of kinases (Aurora A, B, and C) are involved in multiple mitotic events, and aberrant expression of these kinases is associated with tumorigenesis. Aurora A and Aurora B are validated anticancer targets, and the development of Aurora kinase inhibitors has progressed from preclinical to clinical studies. A variety of Aurora A, B and pan-Aurora kinase inhibitors have entered the clinic. The main side effects include febrile neutropenia, stomatitis, gastrointestinal toxicity, hypertension, and fatigue. Responses including complete remissions have been described in diverse, advanced malignancies, most notably ovarian cancer and acute myelogenous leukemia. This review highlights the biologic rationale for Aurora kinase as a target, and clinical trials involving Aurora kinase inhibitors, with particular emphasis on published early phase studies, and the observed anti-tumor activity of these agents.

Characterization and targeting of neoplastic stem cells in Ph+ chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of an oncogenic fusion gene, BCR–ABL1. This fusion gene produces a cytoplasmic protein with tyrosine kinase activity that acts as a main driver of oncogenesis and abnormal proliferation of myeloid cells in CML. Targeted therapy with BCR–ABL1 tyrosine kinase inhibitors (TKIs) such as imatinib is followed by long-term responses in most patients. However, despite continuous treatment, relapses occur, suggesting the presence of TKI-resistant neoplastic stem cells in these patients. Here, we discuss potential mechanisms and signaling molecules involved in the prosurvival and self-renewal capacity of CML neoplastic stem cells as well as antigens expressed by these cells. Several of these signaling molecules and cell surface antigens may serve as potential targets of therapy and their use may overcome TKI resistance in CML in the future.

Selective JAK2/ABL dual inhibition therapy effectively eliminates TKI-insensitive CML stem/progenitor cells

Imatinib Mesylate (IM) and other tyrosine kinase inhibitor (TKI) therapies have had a major impact on the treatment of chronic myeloid leukemia (CML). However, TKI monotherapy is not curative, with relapse and persistence of leukemic stem cells (LSCs) remaining a challenge. We have recently identified an AHI-1-BCR-ABL-JAK2 protein complex that contributes to the transforming activity of BCR-ABL and IM-resistance in CML stem/progenitor cells. JAK2 thus emerges as an attractive target for improved therapies, but off-target effects of newly developed JAK2 inhibitors on normal hematopoietic cells remain a concern. We have examined the biological effects of a highly selective, orally bioavailable JAK2 inhibitor, BMS-911543, in combination with TKIs on CD34⁺ treatment-naïve IM-nonresponder cells. Combination therapy reduces JAK2/STAT5 and CRKL activities, induces apoptosis, inhibits proliferation and colony growth, and eliminates CML LSCs in vitro. Importantly, BMS-911543 selectively targets CML stem/progenitor cells while sparing healthy stem/progenitor cells. Oral BMS-911543 combined with the potent TKI dasatinib more effectively eliminates infiltrated leukemic cells in hematopoietic tissues than TKI monotherapy and enhances survival of leukemic mice. Dual targeting BCR-ABL and JAK2 activities in CML stem/progenitor cells may consequently lead to more effective disease eradication, especially in patients at high risk of TKI resistance and disease progression.

HSP90 inhibitor AUY922 induces cell death by disruption of the Bcr-Abl, Jak2 and HSP90 signaling network complex in leukemia cells

The Bcr-Abl protein is an important client protein of heat shock protein 90 (HSP90). We evaluated the inhibitory effects of the HSP90 ATPase inhibitor AUY922 on 32D mouse hematopoietic cells expressing wild-type Bcr-Abl (b3a2, 32Dp210) and mutant Bcr-Abl imatinib (IM)-resistant cell lines. Western blotting results of fractions from gel filtration column chromatography of 32Dp210 cells showed that HSP90 together with Bcr-Abl, Jak2 Stat3 and several other proteins co-eluted in peak column fractions of a high molecular weight network complex (HMWNC). Co-IP results showed that HSP90 directly bound to Bcr-Abl, Jak2, Stat 3 and Akt. The associations between HSP90 and Bcr-Abl or Bcr-Abl kinase domain mutants (T315I and E255K) were interrupted by AUY922 treatment. Tyrosine phosphorylation of Bcr-Abl showed a dose-dependent decrease in 32Dp210T315I following AUY922 treatment for 16h. AUY922 also markedly inhibited cell proliferation of both IM-sensitive 32Dp210 (IC50 =6 nM) and IM-resistant 32Dp210T315I cells (IC50 ≈6 nM) and human KBM-5R/KBM-7R cell lines (IC50 =50 nM). AUY922 caused significant G1 arrest in 32Dp210 cells but not in T315I or E255K cells. AUY922 efficiently induced apoptosis in 32Dp210 (IC50 =10 nM) and T315I or E255K lines with IC50 around 20 to 50 nM. Our results showed that Bcr-Abl and Jak2 form HMWNC with HSP90 in CML cells. Inhibition of HSP90 by AUY922 disrupted the structure of HMWNC, leading to Bcr-Abl degradation, nhibiting cell proliferation and inducing apoptosis. Thus, inhibition of HSP90 is a powerful way to inhibit not only IM-sensitive CML cells but also IM-resistant CML cells.

Influence of Bone Marrow Microenvironment on Leukemic Stem Cells: Breaking Up an Intimate Relationship

The bone marrow microenvironment (BMM) plays a critical role in hematopoietic stem cells (HSCs) maintenance and regulation. There is increasing interest in the role of the BMM in promoting leukemia stem cell (LSC) maintenance, resistance to conventional chemotherapy and targeted therapies, and ultimately disease relapse. Recent studies have enhanced our understanding of how the BMM regulates quiescence, self-renewal, and differentiation of LSC. In this comprehensive review, we discuss recent advances in our understanding of the crosstalk between the BMM and LSC, and the critical signaling pathways underlying these interactions. We also discuss potential approaches to exploit these observations to create novel strategies for targeting therapy-resistant LSC to achieve relapse-free survival in leukemic patients.

Mechanisms of resistance to BCR-ABL TKIs and the therapeutic strategies: A review

BCR-ABL caused by the translocation of t(9,22) with elevated tyrosine-kinase activity could induce leukemia in mice, which established BCR-ABL as the molecular pathogenic event in CML (Chronic myeloid leukemia). In recent years, a variety of tyrosine kinase inhibitors (TKIs) targeting at BCR-ABL specifically and effectively have been developed, which has fundamentally promoted the treatment of CML. However, the efficacy of TKIs was limited by its resistance induced by the development of kinase domain mutations and other mechanisms illustrated. In this review, we summarized BCR-ABL inhibitors approved by Food and Drug Administration (FAD), with the same concerns focus on the resistant mechanisms of BCR-ABL inhibitors and therapeutic resistant strategies.

Critical role of STAT3 in melanoma metastasis through anoikis resistance

Anoikis is an anchorage-independent cell death. Resistance to anoikis is one of the key features of metastatic cells. Here, we analyzed the role of STAT3 in anoikis resistance in melanoma cells leading to metastasis. When grown under anchorage-independent conditions, significant proportion of cells resisted anoikis and these resistant cells had higher rate of migration and invasion as compared to the cells grown under anchorage-dependent conditions. The anoikis resistant cells also had significantly higher expression and phosphorylation of STAT3 at Y705 than the cells that were attached to the basement membrane. STAT3 inhibitors, AG 490 and piplartine (PL) induced anoikis in a concentration-dependent manner in anoikis resistant cells. Over-expression of STAT3 or treatment with IL-6 not only increased anoikis resistance, but also protected the cancer cells from PL-induced anoikis. On the other hand, silencing STAT3 decreased the potential of cancer cells to resist anoikis and to migrate. STAT3 knock-down cells and PL treated cells did not form tumors as well as failed to metastasize in SCID-NSG mice as compared to untreated anchorage-independent cells, which formed big tumors and extensively metastasized. In summary, our results for the first time establish STAT3 as a critical player that renders anoikis resistance to melanoma cells and enhance their metastatic potential.

JAK2/STAT5 inhibition by nilotinib with ruxolitinib contributes to the elimination of CML CD34+ cells in vitro and in vivo

Chronic myeloid leukemia (CML) stem cell survival is not dependent on BCR-ABL protein kinase and treatment with ABL tyrosine kinase inhibitors cures only a minority of CML patients, thus highlighting the need for novel therapeutic targets. The Janus kinase (JAK)2/signal transducer and activator of transcription (STAT)5 pathway has recently been explored for providing putative survival signals to CML stem/progenitor cells (SPCs) with contradictory results. We investigated the role of this pathway using the JAK2 inhibitor, ruxolitinib (RUX). We demonstrated that the combination of RUX, at clinically achievable concentrations, with the specific and potent tyrosine kinase inhibitor nilotinib, reduced the activity of the JAK2/STAT5 pathway in vitro relative to either single agent alone. These effects correlated with increased apoptosis of CML SPCs in vitro and a reduction in primitive quiescent CML stem cells, including NOD.Cg-Prkdc(scid) IL2rg(tm1Wjl) /SzJ mice repopulating cells, induced by combination treatment. A degree of toxicity toward normal SPCs was observed with the combination treatment, although this related to mature B-cell engraftment in NOD.Cg-Prkdc(scid) IL2rg(tm1Wjl) /SzJ mice with minimal effects on primitive CD34(+) cells. These results support the JAK2/STAT5 pathway as a relevant therapeutic target in CML SPCs and endorse the current use of nilotinib in combination with RUX in clinical trials to eradicate persistent disease in CML patients.

c-Abl activates janus kinase 2 in normal hematopoietic cells

Jak2 is involved in cytokine growth factor-stimulated signal transduction, but the mechanism of its activation is largely unknown. Here, we investigated Jak2 activation in a normal hematopoietic cell line, 32D mouse myeloid cells. The bimolecular fluorescence complementation studies showed that c-Abl formed a stable complex with Jak2 in live cells. Co-immunoprecipitation results showed that c-Abl bound to the βc chain of IL-3/IL-5/GM-CSF receptors. The kinase activities of both c-Abl and Jak2 were stimulated by IL-3 in 32D cells. Decreasing c-Abl protein expression in 32D cells by inducible shRNA decreased Jak2 activity and resulted in the failure of Jak2 activation in response to IL-3. Treatment of IL-3 and serum-starved 32D cells with 1 μM imatinib mysylate inhibited IL-3 stimulated kinase activities of both c-Abl and Jak2. In addition, the kinase-deficient Bcr-Abl mutant (p210K1172R) was defective for activation of Jak2 in 32D cells and impaired IL-3 independent growth, which was rescued by overexpression of c-Abl (+Abl). IL-3 efficiently inhibited apoptosis of 32Dp210K/R+Abl cells induced by imatinib mysylate but not Jak2 kinase inhibitor TG101209. In summary, our findings provide evidence that the kinase function of c-Abl and its C-terminal CT4 region is crucial for its interaction with Jak2 and its activation. c-Abl kinase activity induced by IL-3 is required for IL-3-stimulated Jak2 and Jak1 activation. Our findings reveal a novel regulatory role of c-Abl in Jak2 activation induced by IL-3 cytokine growth factor in 32D hematopoietic cells.

BCR-ABL affects STAT5A and STAT5B differentially

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors linking extracellular signals to target gene transcription. Hematopoietic cells express two highly conserved STAT5-isoforms (STAT5A/STAT5B), and STAT5 is directly activated by JAK2 downstream of several cytokine receptors and the oncogenic BCR-ABL tyrosine kinase. Using an IL-3-dependent cell line with inducible BCR-ABL-expression we compared STAT5-activation by IL-3 and BCR-ABL in a STAT5-isoform specific manner. RNAi targeting of STAT5B strongly inhibits BCR-ABL-dependent cell proliferation, and STAT5B but not STAT5A is essential for BCL-X_L-expression in the presence of BCR-ABL. Although BCR-ABL induces STAT5-tyrosine phosphorylation independent of JAK2-kinase activity, BCR-ABL is less efficient in inducing active STAT5A:STAT5B-heterodimerization than IL-3, leaving constitutive STAT5A and STAT5B-homodimerization unaffected. In comparison to IL-3, nuclear accumulation of a STAT5A-eGFP fusion protein is reduced by BCR-ABL, and BCR-ABL tyrosine kinase activity induces STAT5A-eGFP translocation to the cell membrane and co-localization with the IL-3 receptor. Furthermore, BCR-ABL-dependent phosphorylation of Y682 in STAT5A was detected by mass-spectrometry. Finally, RNAi targeting STAT5B but not STAT5A sensitizes human BCR-ABL-positive cell lines to imatinib-treatment. These data demonstrate differences between IL-3 and BCR-ABL-mediated STAT5-activation and isoform-specific effects, indicating therapeutic options for isoform-specific STAT5-inhibition in BCR-ABL-positive leukemia.

Myc and cell cycle control

Soon after the discovery of the Myc gene (c-Myc), it became clear that Myc expression levels tightly correlate to cell proliferation. The entry in cell cycle of quiescent cells upon Myc enforced expression has been described in many models. Also, the downregulation or inactivation of Myc results in the impairment of cell cycle progression. Given the frequent deregulation of Myc oncogene in human cancer it is important to dissect out the mechanisms underlying the role of Myc on cell cycle control. Several parallel mechanisms account for Myc-mediated stimulation of the cell cycle. First, most of the critical positive cell cycle regulators are encoded by genes induced by Myc. These Myc target genes include Cdks, cyclins and E2F transcription factors. Apart from its direct effects on the transcription, Myc is able to hyperactivate cyclin/Cdk complexes through the induction of Cdk activating kinase (CAK) and Cdc25 phosphatases. Moreover, Myc antagonizes the activity of cell cycle inhibitors as p21 and p27 through different mechanisms. Thus, Myc is able to block p21 transcription or to induce Skp2, a protein involved in p27 degradation. Finally, Myc induces DNA replication by binding to replication origins and by upregulating genes encoding proteins required for replication initiation. Myc also regulates genes involved in the mitotic control. A promising approach to treat tumors with deregulated Myc is the synthetic lethality based on the inhibition of Cdks. Thus, the knowledge of the Myc-dependent cell cycle regulatory mechanisms will help to discover new therapeutic approaches directed against malignancies with deregulated Myc. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Methylation and decreased expression of SHP-1 are related to disease progression in chronic myelogenous leukemia

Despite the unprecedented success of tyrosine kinase inhibitors (TKIs) in treating chronic myelogenous leukemia (CML), some patients nevertheless progress to advanced stages of the disease. Thus far, the biological basis leading to CML progression remains poorly understood. SH2-containing tyrosine phosphatase 1 (SHP-1) is reported to bind to p210BCR‑ABL1 and to function as a tumor suppressor. Furthermore, its substrates have been found to be essential for p210BCR-ABL1 leukemogenesis or CML progression. In the present study, we found that SHP-1 mRNA and protein levels were markedly decreased in patients in the accelerated and blastic phases of CML (AP-CML and BP-CML) compared to those in the chronic phase (CP-CML). In vitro, we demonstrated that overexpression of SHP-1 reduced p210BCR-ABL1 protein expression and activity in the K562 CML cell line and negatively regulated the AKT, MAPK, MYC and JAK2/STAT5 signaling pathways. Moreover, using a methylation-specific polymerase chain reaction (MSP) assay, abnormal methylation of the SHP-1 gene promoter region was found both in K562 cells and bone marrow (BM) or peripheral blood (PB) cells from AP-CML and BP-CML patients. In conclusion, our findings suggest that decreased expression levels of SHP-1 caused by aberrant promoter hypermethylation may play a key role in the progression of CML by dysregulating BCR-ABL1, AKT, MAPK, MYC and JAK2/STAT5 signaling.

Kinase-independent mechanisms of resistance of leukemia stem cells to tyrosine kinase inhibitors

Tyrosine kinase inhibitors such as imatinib mesylate have changed the clinical course of chronic myeloid leukemia; however, the observation that these inhibitors do not target the leukemia stem cell implies that patients need to maintain lifelong therapy. The mechanism of this phenomenon is unclear: the question of whether tyrosine kinase inhibitors are inactive inside leukemia stem cells or whether leukemia stem cells do not require breakpoint cluster region (Bcr)-Abl signaling is currently under debate. Herein, I propose an alternative model: perhaps the leukemia stem cell requires Bcr-Abl, but is dependent on its kinase-independent functions. Kinases such as epidermal growth factor receptor and Janus kinase 2 possess kinase-independent roles in regulation of gene expression; it is worth investigating whether Bcr-Abl has similar functions. Mechanistically, Bcr-Abl is able to activate the Ras, phosphatidylinositol 3-kinase/Akt, and/or the Src-kinase Hck/Stat5 pathways in a scaffolding-dependent manner. Whereas the scaffolding activity of Bcr-Abl with Grb2 is dependent on autophosphorylation, kinases such as Hck can use Bcr-Abl as substrate, inducing phosphorylation of Y177 to enable scaffolding ability in the absence of Bcr-Abl catalytic activity. It is worth investigating whether leukemia stem cells exclusively express kinases that are able to use Bcr-Abl as substrate. A kinase-independent role for Bcr-Abl in leukemia stem cells would imply that drugs that target Bcr-Abl's scaffolding ability or its DNA-binding ability should be used in conjunction with current therapeutic regimens to increase their efficacy and eradicate the stem cells of chronic myeloid leukemia.

Effects of Jak2 type 1 inhibitors NVP-BSK805 and NVP-BVB808 on Jak2 mutation-positive and Bcr-Abl-positive cell lines

Janus kinases are critical components of signaling pathways that regulate hematopoiesis. Mutations of the non-receptor tyrosine kinase JAK2 are found in many BCR-ABL-negative myeloproliferative neoplasms. Preclinical results support that JAK2 inhibitors could show efficacy in treating chronic myeloproliferative neoplasms. JAK2 has also been postulated to play a role in BCR-ABL signal transduction. Therefore, inhibitors of JAK2 kinases are turning into therapeutic strategies for treatment of chronic myelogenous leukemia (CML). In this study, the effects of two novel JAK2 inhibitors, NVP-BSK805 and NVP-BVB808, have been investigated in cell lines expressing either BCR-ABL or mutant JAK2. Possible synergies between NVP-BSK805/NVP-BVB808 and the kinase inhibitors imatinib and nilotinib were assessed. Proliferation and apoptosis tests with both substances showed response in the following cell lines: CHRF-288-11, SET-2 and UKE-1. All BCR-ABL-positive cell lines showed some reduction in proliferation, but with half-maximal growth-inhibitory values >1 µM. Combination of the JAK2 inhibitors with imatinib and nilotinib showed no significant additive or synergistic effects, although all BCR-ABL-positive cell lines responded well to both CML therapeutic agents. Interestingly, it seemed that the combination of imatinib with NVP-BSK805 had a protective effect on the cells. Combination treatment with nilotinib did not show this effect.

Targeting survival pathways in chronic myeloid leukaemia stem cells

Chronic myeloid leukaemia (CML) is a clonal myeloproliferative disorder characterized by the presence of a fusion oncogene BCR-ABL, which encodes a protein with constitutive TK activity. The implementation of tyrosine kinase inhibitors (TKIs) marked a major advance in CML therapy; however, there are problems with current treatment. For example, relapse occurs when these drugs are discontinued in the majority of patients who have achieved a complete molecular response on TKI and these agents are less effective in patients with mutations in the BCR-ABL kinase domain. Importantly, TKI can effectively target proliferating mature cells, but do not eradicate quiescent leukaemic stem cells (LSCs), therefore allowing disease persistence despite treatment. It is essential that alternative strategies are used to target the LSC population. BCR-ABL activation is responsible for the modulation of different signalling pathways, which allows the LSC fraction to evade cell death. Several pathways have been shown to be modulated by BCR-ABL, including PI3K/AKT/mTOR, JAK-STAT and autophagy signalling pathways. Targeting components of these survival pathways, alone or in combination with TKI, therefore represents an attractive potential therapeutic approach for targeting the LSC. However, many pathways are also active in normal stem cells. Therefore, potential targets must be validated to effectively eradicate CML stem cells while sparing normal counterparts. This review summarizes the main pathways modulated in CML stem cells, the recent developments and the use of novel drugs to target components in these pathways which may be used to target the LSC population.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Effects of AG490 and S3I-201 on regulation of the JAK/STAT3 signaling pathway in relation to angiogenesis in TRAIL-resistant prostate cancer cells in vitro

The aim of the present study was to analyze the molecular mechanisms involved in blocking the signaling pathway and the effects of this on the progression of prostate cancer (CaP) cells in vitro. LNCaP human CaP cell line was stimulated with interleukin-6 (IL-6) in the presence/absence of Janus kinase (JAK) 2 (AG490), signal transducer and activator of transcription 3 [(STAT3) S3I-201] inhibitors and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Cytotoxic activity, the activation of phosphorylated (p)-STAT3 protein, caspase (CASP) 3 activity at protein level, vascular endothelial growth factor (VEGF) A, VEGFC, vascular endothelial growth factor receptor 2, STAT3, matrix metalloproteinase-2, myeloid cell leukemia sequence 1 (MCL-1), CASP8 and CASP9 messenger RNA (mRNA) levels were determined. Morphology and apoptosis were confirmed by DAPI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. IL-6 rapidly induced the phosphorylation of STAT3 in a dose- and time-dependent manner with a peak expression at 3 h at a concentration of 25 ng/ml. In addition, AG490 (50 μM) and S3I-201 (300 μM) inhibited STAT3 activation. Western blotting results revealed that p-STAT3 protein expression decreased significantly with AG490 and S3I-201 treatment in LNCaP cells. AG490 and S3I-201 induced the downregulation of VEGFA, MCL-1 and STAT3 and the upregulation of CASP8 and CASP9 mRNA transcription levels. In addition, the inhibitors increased the level of CASP3 protein. Combinations of AG490- and S3I-201-TRAIL did not result in an increase in this effect. Parallel results were found by DAPI staining and TUNEL assay. To the best of our knowledge, this is the first study to investigate the possible clinical use of AG490 or S3I-201, together with the reduced use of chemotherapeutic agents with high cytotoxicity, for their ability to exert an apoptotic effect, targeting the JAK/STAT3 pathway.