A sequential blockade strategy for the design of combination therapies to overcome oncogene addiction in chronic myelogenous leukemia

Homoharringtonine: updated insights into its efficacy in hematological malignancies, diverse cancers and other biomedical applications

HHT has emerged as a notable compound in the realm of cancer treatment, particularly for hematological malignancies. Its multifaceted pharmacological properties extend beyond traditional applications, warranting an extensive review of its mechanisms and efficacy. This review aims to synthesize comprehensive insights into the efficacy of HHT in treating hematological malignancies, diverse cancers, and other biomedical applications. It focuses on elucidating the molecular mechanisms, therapeutic potential, and broader applications of HHT. A comprehensive search for peer-reviewed papers was conducted across various academic databases, including ScienceDirect, Web of Science, Scopus, American Chemical Society, Google Scholar, PubMed/MedLine, and Wiley. The review highlights HHT's diverse mechanisms of action, ranging from its role in leukemia treatment to its emerging applications in managing other cancers and various biomedical conditions. It underscores HHT's influence on cellular processes, its efficacy in clinical settings, and its potential to alter pathological pathways. HHT demonstrates significant promise in treating various hematological malignancies and cancers, offering a multifaceted approach to disease management. Its ability to impact various physiological pathways opens new avenues for therapeutic applications. This review provides a consolidated foundation for future research and clinical applications of HHT in diverse medical fields.

Synthesis of portimines reveals the basis of their anti-cancer activity

Marine-derived cyclic imine toxins, portimine A and portimine B, have attracted attention because of their chemical structure and notable anti-cancer therapeutic potential1-4. However, access to large quantities of these toxins is currently not feasible, and the molecular mechanism underlying their potent activity remains unknown until now. To address this, a scalable and concise synthesis of portimines is presented, which benefits from the logic used in the two-phase terpenoid synthesis5,6 along with other tactics such as exploiting ring-chain tautomerization and skeletal reorganization to minimize protecting group chemistry through self-protection. Notably, this total synthesis enabled a structural reassignment of portimine B and an in-depth functional evaluation of portimine A, revealing that it induces apoptosis selectively in human cancer cell lines with high potency and is efficacious in vivo in tumour-clearance models. Finally, practical access to the portimines and their analogues simplified the development of photoaffinity analogues, which were used in chemical proteomic experiments to identify a primary target of portimine A as the 60S ribosomal export protein NMD3.

Repurposing cabozantinib with therapeutic potential in KIT-driven t(8;21) acute myeloid leukaemias

Cabozantinib is an orally available, multi-target tyrosine kinase inhibitor approved for the treatment of several solid tumours and known to inhibit KIT tyrosine kinase. In acute myeloid leukaemia (AML), aberrant KIT tyrosine kinase often coexists with t(8;21) to drive leukaemogenesis. Here we evaluated the potential therapeutic effect of cabozantinib on a selected AML subtype characterised by t(8;21) coupled with KIT mutation. Cabozantinib exerted substantial cytotoxicity in Kasumi-1 cells with an IC₅₀ of 88.06 ± 4.32 nM, which was well within clinically achievable plasma levels. The suppression of KIT phosphorylation and its downstream signals, including AKT/mTOR, STAT3, and ERK1/2, was elicited by cabozantinib treatment and associated with subsequent alterations of cell cycle- and apoptosis-related molecules. Cabozantinib also disrupted the synthesis of an AML1-ETO fusion protein in a dose- and time-dependent manner. In a mouse xenograft model, cabozantinib suppressed tumourigenesis at 10 mg/kg and significantly prolonged survival of the mice. Further RNA-sequencing analysis revealed that mTOR-mediated signalling pathways were substantially inactivated by cabozantinib treatment, causing the downregulation of ribosome biogenesis and glycolysis, along with myeloid leukocyte activation. We suggest that cabozantinib may be effective in the treatment of AML with t(8;21) and KIT mutation. Relevant clinical trials are warranted.

Protein synthesis inhibitor omacetaxine is effective against hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common and the fourth most deadly cancer worldwide. The development cost of new therapeutics is a major limitation in patient outcomes. Importantly, there is a paucity of preclinical HCC models in which to test new small molecules. Herein, we implemented potentially novel patient-derived organoid (PDO) and patient-derived xenografts (PDX) strategies for high-throughput drug screening. Omacetaxine, an FDA-approved drug for chronic myelogenous leukemia (CML), was found to be a top effective small molecule in HCC PDOs. Next, omacetaxine was tested against a larger cohort of 40 human HCC PDOs. Serial dilution experiments demonstrated that omacetaxine is effective at low (nanomolar) concentrations. Mechanistic studies established that omacetaxine inhibits global protein synthesis, with a disproportionate effect on short–half-life proteins. High-throughput expression screening identified molecular targets for omacetaxine, including key oncogenes, such as PLK1. In conclusion, by using an innovative strategy, we report — for the first time to our knowledge — the effectiveness of omacetaxine in HCC. In addition, we elucidate key mechanisms of omacetaxine action. Finally, we provide a proof-of-principle basis for future studies applying drug screening PDOs sequenced with candidate validation in PDX models. Clinical trials could be considered to evaluate omacetaxine in patients with HCC.

Translational Regulation of Cancer Metastasis

Deregulation of the mRNA translational process has been observed during tumorigenesis. However, recent findings have shown that deregulation of translation also contributes specifically to cancer cell spread. During metastasis, cancer cells undergo changes in cellular state, permitting the acquisition of features necessary for cell survival, dissemination, and outgrowth. In addition, metastatic cells respond to external cues, allowing for their persistence under significant cellular and microenvironmental stresses. Recent work has revealed the importance of mRNA translation to these dynamic changes, including regulation of cell states through epithelial-to-mesenchymal transition and tumor dormancy and as a response to external stresses such as hypoxia and immune surveillance. In this review, we focus on examples of altered translation underlying these phenotypic changes and responses to external cues and explore how they contribute to metastatic progression. We also highlight the therapeutic opportunities presented by aberrant mRNA translation, suggesting novel ways to target metastatic tumor cells.

Targeting the Human 80S Ribosome in Cancer: From Structure to Function and Drug Design for Innovative Adjuvant Therapeutic Strategies

The human 80S ribosome is the cellular nucleoprotein nanomachine in charge of protein synthesis that is profoundly affected during cancer transformation by oncogenic proteins and provides cancerous proliferating cells with proteins and therefore biomass. Indeed, cancer is associated with an increase in ribosome biogenesis and mutations in several ribosomal proteins genes are found in ribosomopathies, which are congenital diseases that display an elevated risk of cancer. Ribosomes and their biogenesis therefore represent attractive anti-cancer targets and several strategies are being developed to identify efficient and specific drugs. Homoharringtonine (HHT) is the only direct ribosome inhibitor currently used in clinics for cancer treatments, although many classical chemotherapeutic drugs also appear to impact on protein synthesis. Here we review the role of the human ribosome as a medical target in cancer, and how functional and structural analysis combined with chemical synthesis of new inhibitors can synergize. The possible existence of oncoribosomes is also discussed. The emerging idea is that targeting the human ribosome could not only allow the interference with cancer cell addiction towards protein synthesis and possibly induce their death but may also be highly valuable to decrease the levels of oncogenic proteins that display a high turnover rate (MYC, MCL1). Cryo-electron microscopy (cryo-EM) is an advanced method that allows the visualization of human ribosome complexes with factors and bound inhibitors to improve our understanding of their functioning mechanisms mode. Cryo-EM structures could greatly assist the foundation phase of a novel drug-design strategy. One goal would be to identify new specific and active molecules targeting the ribosome in cancer such as derivatives of cycloheximide, a well-known ribosome inhibitor.

Homoharringtonine promotes BCR‑ABL degradation through the p62‑mediated autophagy pathway

Drug resistance to tyrosine kinase inhibitors (TKIs) is currently a clinical problem in patients with chronic myelogenous leukemia (CML). Homoharringtonine (HHT) is an approved treatment for adult patients with chronic- or accelerated-phase CML who are resistant to TKIs and other therapies; however, the underlying mechanisms remain unclear. In the present study, HHT treatment demonstrated induction of apoptosis in imatinib-resistant K562G cells by using MTS assay and western blotting, and BCR-ABL protein was reduced. CHX chase assay revealed that HHT induced degradation of the BCR-ABL protein, which could be reversed by autophagy lysosome inhibitors Baf-A1 and CQ. Next, HHT treatment confirmed the induction of autophagy in K562G cells, and silencing the key autophagic proteins ATG5 and Beclin-1 inhibited the degradation of the BCR-ABL protein and cytotoxicity. In addition, autophagic receptor p62/SQSTM1(p62) participated during the autophagic degradation of BCR-ABL induced by HHT, and this was confirmed by co-immunoprecipitation, in which HHT enhanced the ubiquitination of the BCR-ABL protein and promoted its binding to p62. In conclusion, HHT induced p62-mediated autophagy in imatinib-resistant CML K562G cells, thus promoting autophagic degradation of the BCR-ABL protein and providing a novel strategy for the treatment of TKI-resistant CML.

Therapeutic Opportunities in Eukaryotic Translation

The ability to block biological processes with selective small molecules provides advantages distinct from most other experimental approaches. These include rapid time to onset, swift reversibility, ability to probe activities in manners that cannot be accessed by genetic means, and the potential to be further developed as therapeutic agents. Small molecule inhibitors can also be used to alter expression and activity without affecting the stoichiometry of interacting partners. These tenets have been especially evident in the field of translation. Small molecule inhibitors were instrumental in enabling investigators to capture short-lived complexes and characterize specific steps of protein synthesis. In addition, several drugs that are the mainstay of modern antimicrobial drug therapy are potent inhibitors of prokaryotic translation. Currently, there is much interest in targeting eukaryotic translation as decades of research have revealed that deregulated protein synthesis in cancer cells represents a targetable vulnerability. In addition to being potential therapeutics, small molecules that manipulate translation have also been shown to influence cognitive processes such as memory. In this review, we focus on small molecule modulators that target the eukaryotic translation initiation apparatus and provide an update on their potential application to the treatment of disease.

Homoharringtonine could induce quick protein synthesis of PSMD11 through activating MEK1/ERK1/2 signaling pathway in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most devastating disease with the 5-year survival rate less than 6%. In this study, we investigated if inhibiting protein synthesis directly with homoharringtonine (HHT) could induce acute apoptosis in pancreatic cancer cells through quick depletion of multiple short-lived critical members of the central proteome, example, PSMD11(26S proteasome non-ATPase regulatory subunit 11). It was shown that although HHT could inhibit proliferation and growth of MiaPaCa-2 and PANC-1 cells in a time- and dose-dependent manner, only part of pancreatic cancer cells could be induced to die through acute apoptosis. Mechanistic studies showed that HHT could induce quick protein synthesis of PSMD11 through activating MEK1/ERK1/2 signaling pathway in pancreatic cancer cells. Inhibiting MEK1/ERK1/2 pathway with sorafenib could improve the cytotoxity of HHT in vitro and in a genetically engineered mouse model of pancreatic cancer. These results suggest that quick induction of PSMD11 or other acute apoptosis inhibitors through activation of the MEK1/ERK1/2 signaling pathway may be one of the important surviving mechanism which can help pancreatic cancer cells avoid acute apoptosis, it may have significant implications for the targeted therapy of pancreatic ductal adenocarcinoma.

Targeting of phospho-eIF4E by homoharringtonine eradicates a distinct subset of human acute myeloid leukemia

More than half of the patients with acute myeloid leukemia (AML) fail to achieve long-term disease-free survival with current therapies and novel therapeutic strategies are urgently needed. The effects of homoharringtonine (HHT) on the growth of AML cell lines and primary leukemia cells were examined using MTT, colony formation assay. The effects of HHT on both eukaryotic translation initiation factor 4E (eIF4E) and phospho-eIF4E(p-eIF4E) were examined through western blot and immunofluorescence staining. HHT selectively reduced levels of p-eIF4E and its downstream oncoprotein Mcl-1, and potently inhibited in vitro and in vivo the growth of a distinct subset of AML cells and primary leukemia cells expressing high level of p-eIF4E through apoptosis. Our findings suggest that HHT might be a first-in-class p-eIF4E-targeted drug and offer a novel therapeutic option for AML patients expressing high level of p-eIF4E.

Cephalotaxus Alkaloids

Cephalotaxus alkaloids represent a family of plant secondary metabolites known for 60 years. Significant activity against leukemia in mice was demonstrated for extracts of Cephalotaxus. Cephalotaxine (CET) (1), the major alkaloid of this series was isolated from Cephalotaxus drupacea species by Paudler in 1963. The subsequent discovery of promising antitumor activity among new Cephalotaxus derivatives reported by Chinese, Japanese, and American teams triggered extensive structure elucidation and biological studies in this family. The structural feature of this cephalotaxane family relies mainly on its tetracyclic alkaloid backbone, which comprises an azaspiranic 1-azaspiro[4.4]nonane unit (rings C and D) and a benzazepine ring system (rings A and B), which is linked by its C3 alcohol function to a chiral oxygenated side chain by a carboxylic function alpha to a tetrasubstituted carbon center. The botanical distribution of these alkaloids is limited to the Cephalotaxus genus (Cephalotaxaceae). The scope of biological activities of the Cephalotaxus alkaloids is mainly centered on the antileukemic activity of homoharringtonine (HHT) (2), which in particular demonstrated marked benefits in the treatment of orphan myeloid leukemia and was approved as soon as 2009 by European Medicine Agency and by US Food and Drug Administration in 2012. Its exact mechanism of action was partly elucidated and it was early recognized that HHT (2) inhibited protein synthesis at the level of the ribosome machinery. Interestingly, after a latency period of two decades, the topic of Cephalotaxus alkaloids reemerged as a prolific source of new natural structures. To date, more than 70 compounds have been identified and characterized. Synthetic studies also regained attention during the past two decades, and numerous methodologies were developed to access the first semisynthetic HHT (2) of high purity suitable for clinical studies, and then high grade enantiomerically pure CET (1), HHT (2), and analogs.

Biochemical and chemical characterization of Cynara cardunculus L. extract and its potential use as co-adjuvant therapy of chronic myeloid leukemia

ETHNOPHARMACOLOGICAL RELEVANCE

Ancient mediterranean diet was characterized by consuming the spontaneous forms of Cynara cardunculus L. (CCL), commonly called artichoke. Cultivated and/or spontaneous forms of CC studies have demonstrated that methanol extract of CCL flower and/or cynaropicrin showed remarkable anti-proliferative activity in vitro models of leukocyte cancer cell.

AIM OF THE STUDY

Chronic myeloid leukemia (CML) is associated with a reciprocal translocation of the long arms of chromosomes 9 and 22 generating the BCR/ABL fusion gene, translated in the p210^BCR/ABL oncoprotein kinase. This chimeric protein is the target of a kinase inhibitor, imatinib, but the development of mutations in the ABL kinase domain resulting in drug resistance and several approaches to overcoming resistance have been study. In this concern, we investigated the effect of CCL extract on human K562 CML and K562 imatinib resistant (IMAR) cell proliferation and on p210^BCR/ABL expression.

MATERIALS AND METHODS

Chemical characterization of the CCL extracts was performed by GC/MS analysis and semipreparative RP-HPLC chromatography. Structural characterization of compounds was assessed by ¹H-¹³C NMR and LC/MS analysis. The effects of CCL extracts on the proliferation of K562 CML human cell line and K562 IMAR were screened by MTT assay. The p210^BCR/ABL mRNA and protein expressions were analyzed by qRT-PCR and Western blot techniques respectively.

RESULTS

We demonstrate that CCL extract affect cell viability of both K562 CML human cell line and K562 IMAR. The biocomponents of CCL were chemical characterized and we identify cynaropicrin and its deacyl derivative having the capability to down-regulate the p210^BCR/ABL oncoprotein.

CONCLUSIONS

Our study suggests that the use of those molecules could represent a novel and promising strategy to potentiate the ability of imatinib or of its analogues to induce cancer growth arrest in CML and to delay or overcome the resistance of CML to chemotherapy.

MPT0B002, a novel microtubule inhibitor, downregulates T315I mutant Bcr-Abl and induces apoptosis of imatinib-resistant chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) is a hematopoietic malignancy caused by the constitutive activation of Bcr-Abl tyrosine kinase. The Bcr-Abl inhibitor imatinib and other second-generation tyrosine kinase inhibitors such as dasatinib and nilotinib have remarkable efficacy in CML treatment. However, gene mutation-mediated drug resistance remains a critical problem. Among point mutations, the Bcr-Abl T315I mutation confers resistance to these Bcr-Abl inhibitors. Previously, we have synthesized the compound (1-methyl-1H-indol-5-yl)-(3,4,5-trimethoxy-phenyl)-methanone (MPT0B002) as a novel microtubule inhibitor. In this study, we evaluated its effects on the proliferation, cell cycle, and apoptosis of K562 CML cells and BaF3 cells expressing either wild-type Bcr-Abl (BaF3/p210) or T315I-mutated Bcr-Abl (BaF3/T315I). MPT0B002 inhibited cell viability in a dose-dependent manner in these cells but did not affect the proliferation of human umbilical vein endothelial cells. It disrupted tubulin polymerization and arrested cell cycle at the G2/M phase. Treatment with MPT0B002 induced apoptosis, and this induction was associated with increased levels of cleaved caspase-3 and cleaved PARP. Furthermore, MPT0B002 can downregulate both Bcr-Abl and Bcr-Abl-T315I mRNA expressions and protein levels and the downstream signaling pathways. Taken together, our findings suggest that MPT0B002 may be considered a promising compound to downregulate not only wild type Bcr-Abl but also the T315I mutant to overcome Bcr-Abl-T315I mutation-mediated resistance in CML cells.

Homoharringtonine binds to and increases myosin-9 in myeloid leukaemia

BACKGROUND AND PURPOSE

Homoharringtonine (HHT) is a natural alkaloid isolated from various Cephalotaxus species. HHT has been used to treat acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocyte leukaemia and myelodysplastic syndromes. Although HHT inhibits protein synthesis and promotes apoptosis of leukaemia cells in preclinical studies, its molecular target proteins remain unknown. The aim of this study was to identify target proteins of HHT.

EXPERIMENTAL APPROACH

We have synthesized a biotinylated affinity column and used it to identify targets of HHT and confirmed the results by MS and Western blots. We also examined the effects of HHT on the target protein and determined roles of the target protein in anti-leukaemia activities of HHT through Western blots, flow cytometry and retrovirus transfection.

KEY RESULTS

Myosin-9, a member of the myosin super-family, was identified as a direct interactor of HHT. Furthermore, HHT up-regulated the expression level of myosin-9 in both AML and CML cell lines in a time-dependent manner. Thus, HHT-induced apoptosis of leukaemia cells begins in 6 h and continues to increase for 24 h. There is a positive correlation between up-regulated myosin-9 expression level and increased percentage of apoptotic cells mediated by HHT. Overexpression of myosin-9 could increase the sensitivity of the leukaemia cells to the cytotoxicity of HHT and arrest cells in S and G2/M phases.

CONCLUSIONS AND IMPLICATIONS

Our results indicated that myosin-9 was the target protein of HHT and played an important role in the HHT-induced apoptosis of leukaemia cells.

Incidence and management of myelosuppression in patients with chronic- and accelerated-phase chronic myeloid leukemia treated with omacetaxine mepesuccinate

Omacetaxine mepesuccinate (Synribo^®) is an inhibitor of protein synthesis indicated for the treatment of patients with chronic- or accelerated-phase chronic myeloid leukemia (CML) with resistance and/or intolerance to two or more tyrosine kinase inhibitors. Myelosuppression is the most common and clinically significant toxicity experienced by patients treated with omacetaxine. Here, we further examine the patterns of hematologic toxicity observed in clinical trials and describe the approach to management as well as resolution of events. Omacetaxine-related myelosuppression typically occurs more frequently during induction cycles. In general, the myelosuppression observed with omacetaxine treatment is manageable and reversible, and long-term administration is feasible. Careful monitoring, dose delays and reduction in administration days, and appropriate supportive care are critical for successful management of hematologic toxicity. Concerns regarding myelosuppression, observed with many cancer treatments, should not prevent eligible patients from receiving omacetaxine, particularly CML patients with unsatisfactory responses to multiple lines of prior treatment.

Omacetaxine mepesuccinate in chronic myeloid leukemia

INTRODUCTION

Homoharringtonine (HHT) and other alkaloid esters were originally isolated from the Cephalotaxus evergreen tree and have been used in traditional Chinese medicine since the 1970s to treat a variety of malignancies. Although HHT was investigated for the treatment of chronic myeloid leukemia (CML) in the 1990s with good results, the advent of BCR-ABL1 tyrosine kinase inhibitors (TKIs) at that time rapidly established a new standard of care for CML. Omacetaxine mepesuccinate is a semisynthetic derivative of HHT with known clinical activity in relapsed or refractory CML following TKI therapy.

AREAS COVERED

In this review, we summarize the biologic effects of HHT and its derivative, omacetaxine, in CML. Additionally, we analyze the concepts learned from the early trials using these drugs. Data from clinical trials resulting in drug approval are also reviewed.

EXPERT OPINION

Omacetaxine has a clear role in the CML armamentarium for patients in chronic and accelerated phase who have failed or were intolerant to two or more TKIs.

Homoharringtonine combined with cytarabine to treat chronic myelogenous leukemia in myeloid blast crisis and its impact on bone marrow CD34+CD7+ cells

BACKGROUND

The therapeutic response of chronic myelogenous leukemia in myeloid blast crisis (CML-MBC) is very poor.

AIM

To explore the therapeutic effect of homoharringtonine (HHT) combined with cytarabine (HA regimen) on CML-MBC and its influence on bone marrow CD34+CD7+ cells.

RESULTS

Thirty-four patients with CML-MBC were treated with the HA regimen and bone marrow CD34+CD7+ cells were assayed prior to and after treatment. Among 33 evaluable patients, the overall hematological response (complete/ partial hematological response and hematological improvement) was 60.1%. Seven patients (21.2%) had a cytogenetic response 12 months after treatment. In the untreated CMLMBC patients, the proportion of bone marrow CD34+CD7+ cells was much higher than in the control group (19.4 ± 7.9 vs. 4.4 ± 1.5%, p < 0.05) and decreased to 14.1 ± 7.1% (p < 0.05) after treatment. Before treatment, the proportion of CD34+CD7+ cells was lower in the patients who had a hematological response to the HA regimen than in the patients who did not respond.

CONCLUSION

The HA regimen is an effective treatment for CML-MBC and CD34+CD7+ cells may be one of the valuable clinical parameters to assess treatment effectiveness.

Omacetaxine: a protein translation inhibitor for treatment of chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is driven by the Bcr-Abl fusion protein, which is a result of a (9;22) chromosomal translocation. Imatinib, dasatinib, and nilotinib (tyrosine kinase inhibitors, TKI) have revolutionized how CML is treated. Although the majority of patients respond to these kinase inhibitors, a subset becomes resistant to these therapeutics. Synribo (omacetaxine mepesuccinate) was recently approved by the U.S. Food and Drug Administration for Philadelphia-positive CML either in the chronic or the accelerated phase whose disease failed two prior TKIs. With omacetaxine 1.25 mg/m(2) twice daily for 14 days during induction and for 7 days during maintenance, a major cytogenetic response occurred in 20% of patients in the chronic phase and major hematologic response in 27% of patients in the accelerated phase. Laboratory investigations unraveled the mechanism of action and effectiveness of this agent. Bcr-Abl protein is intrinsically programmed to turn over with a short half-life that makes it susceptible to protein translation inhibitors. Omacetaxine (homoharringtonine) inhibits total protein biosynthesis by binding to A-site cleft of ribosomes. As a corollary to this action, there is a diminution of short-lived proteins, such as Bcr-Abl, followed by cell death. Approval of this first-in-class protein translation inhibitor opens up new avenues for its use in other diseases as well as mechanism-based combinations.

Homoharringtonine and omacetaxine for myeloid hematological malignancies

Homoharringtonine (HHT), a plant alkaloid with antitumor properties originally identified nearly 40 years ago, has a unique mechanism of action by preventing the initial elongation step of protein synthesis. HHT has been used widely in China for the treatment of chronic myeloid leukemia (CML), acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Omacetaxine, a semisynthetic form of HHT, with excellent bioavailability by the subcutaneous route, has recently been approved by FDA of the United States for the treatment of CML refractory to tyrosine kinase inhibitors. This review summarized preclinical and clinical development of HHT and omacetaxine for myeloid hematological malignancies.

Activin A induction of erythroid differentiation sensitizes K562 chronic myeloid leukemia cells to a subtoxic concentration of imatinib

Chronic myeloid leukemia (CML) is a hematopoietic stem/progenitor cell disorder in which Bcr-Abl oncoprotein inhibits cell differentiation. Differentiation induction is considered an alternative strategy for treating CML. Activin A, a member of the transforming growth factor-β superfamily, induces erythroid differentiation of CML cells through the p38 MAPK pathway. In this study, treatment of the K562 CML stem/progenitor cell line with activin A followed by a subtoxic concentration of the Bcr-Abl inhibitor imatinib strongly induced growth inhibition and apoptosis compared with simultaneous treatment with activin A and imatinib. Imatinib-induced growth inhibition and apoptosis following activin A pretreatment were dose- and time-dependent. Imatinib-induced growth inhibition and apoptosis were also dependent on the pretreatment dose of activin A. More than 90% of the activin A-induced increases in glycophorin A-positive cells were sensitive to imatinib. However, only some of original glycophorin A-positive cells in the activin A treatment group were sensitive to imatinib. Sequential treatment with activin A and imatinib decreased Bcr-Abl, procaspase-3, Mcl-1, and Bcl-xL and also induced cleavage of procaspase-3/poly(ADP-ribose)polymerase. The reduction of erythroid differentiation in p38 MAPK dominant-negative mutants or by short hairpin RNA knockdown of p38 MAPK decreased the growth inhibition and apoptosis mediated by sequential treatment with activin A and imatinib. Furthermore, the same inhibition level of multidrug resistance 1 expression was observed in cells treated with activin A alone, treated sequentially with activin A and imatinib, or treated simultaneously with activin A and imatinib. The p38 MAPK inhibitor SB-203580 can restore activin A-inhibited multidrug resistance 1 expression. Taken together, our results suggest that a subtoxic concentration of imatinib could exhibit strong cytotoxicity against erythroid-differentiated K562 CML cells.

Omacetaxine mepesuccinate (synribo) - newly launched in chronic myeloid leukemia

INTRODUCTION

Omacetaxine mepesuccinate (formerly known as homoharringtonine [HHT]) is a natural alkaloid with significant anticancer activity partly through inhibition of protein synthesis and induction of apoptosis. Prior to the development of tyrosine kinase inhibitors (TKIs), HHT was the most active therapy in chronic myeloid leukemia (CML) after interferon failure. Subsequent trials showed that HHT and omacetaxine are active in patients failing several TKIs or carrying the T315I mutation.

AREAS COVERED

This review will discuss the preclinical development of HHT and omacetaxine mepesuccinate in CML and the clinical studies leading to its approval by the Food and Drug Administration (FDA).

EXPERT OPINION

A sizable number of patients with CML will develop TKI resistance, frequently through the acquisition of BCR-ABL1 kinase domain mutations. Omacetaxine is active in patients with CML after failure to multiple TKIs and in those carrying the T315I mutation, which is highly resistant to all FDA-approved TKIs except for ponatinib. Both ponatinib and omacetaxine have been recently approved by the FDA and represent useful treatment options for patients with CML who failed several TKIs and/or acquired the T315I mutation. The development of an oral formulation of omacetaxine would greatly facilitate its use and provide an attractive option for TKI-based combinatorial strategies.

Everolimus enhances the cytotoxicity of bendamustine in multiple myeloma cells through a network of pro-apoptotic and cell-cycle-progression regulatory proteins

Bendamustine is a bifunctional alkylating agent with some efficacy in the treatment of newly diagnosed and relapsed/refractory multiple myeloma (MM). Everolimus, an mammalian target of rapamycin (mTOR) inhibitor, is a additional promising chemotherapeutic agent that has efficacy in a variety of cancers. We investigated the individual and combinational cytotoxic effects of these drugs in MM cell lines (RPMI8226 and MM1.S) and primary MM cells. Our results demonstrated a synergistic effect of these drugs, which was effective for both p53-wild-type and p-53-deleted MM cells, but was minimal in mononuclear cells from a healthy donor. Combination treatment with the two agents inhibited proliferation and promoted cytotoxicity and apoptosis as assessed by Annexin-V/PI staining, caspase-3 degradation, and PARP cleavage. Cell death was associated with the up-regulation of the pro-apoptotic protein Bax and the down-regulation of the anti-apoptotic proteins Mcl-1 and survivin. The combination drug treatment also promoted a decrease in the levels of the downstream target proteins of the mTOR pathway, p70s6k, and 4EBP-1, as well as an increase in the level of phosphorylation of the tumor suppressor protein p53 in MM1.S cells. p21 was also down-regulated upon treatment with the two drugs, suggesting a mechanism of sensitization through the release of cell cycle arrest. Our results demonstrate a network of regulatory factors that may contribute to the synergistic cytotoxicity of everolimus and bendamustine, and provide a rationale for application for the combinatorial treatment of MM with alkylating agents and mTOR inhibitors in future clinical practice.

Phase 2 study of subcutaneous omacetaxine mepesuccinate for chronic-phase chronic myeloid leukemia patients resistant to or intolerant of tyrosine kinase inhibitors

Omacetaxine mepesuccinate (omacetaxine) is a first-in-class cephalotaxine with a unique mode of action, independent of BCR-ABL, that has shown promising activity in patients with chronic myeloid leukemia (CML). This multicenter, noncomparative, open-label phase 2 study evaluated the efficacy and safety of subcutaneous omacetaxine in CML patients with resistance or intolerance to two or more tyrosine kinase inhibitors (TKIs); results in patients in chronic phase are reported here. Patients received subcutaneous omacetaxine 1.25 mg/m² twice daily days 1-14 every 28 days until hematologic response (up to a maximum of six cycles), then days 1-7 every 28 days as maintenance. Primary endpoints were rates of hematologic response lasting >8 weeks and major cytogenetic response (MCyR). Forty-six patients were enrolled: all had received imatinib, 83% had received dasatinib, and 57% nilotinib. A median 4.5 cycles of omacetaxine were administered (range, 1-36). Hematologic response was achieved or maintained in 31 patients (67%); median response duration was 7.0 months. Ten patients (22%) achieved MCyR, including 2 (4%) complete cytogenetic responses. Median progression-free survival was 7.0 months [95% confidence interval (CI), 5.9-8.9 months], and overall survival was 30.1 months (95% CI, 20.3 months-not reached). Grade 3/4 hematologic toxicity included thrombocytopenia (54%), neutropenia (48%), and anemia (33%). Nonhematologic adverse events were predominantly grade 1/2 and included diarrhea (44%), nausea (30%), fatigue (24%), pyrexia (20%), headache (20%), and asthenia (20%). Subcutaneous omacetaxine may offer clinical benefit to patients with chronic-phase CML with resistance or intolerance to multiple TKI therapies.

Aclacinomycin A sensitizes K562 chronic myeloid leukemia cells to imatinib through p38MAPK-mediated erythroid differentiation

Expression of oncogenic Bcr-Abl inhibits cell differentiation of hematopoietic stem/progenitor cells in chronic myeloid leukemia (CML). Differentiation therapy is considered to be a new strategy for treating this type of leukemia. Aclacinomycin A (ACM) is an antitumor antibiotic. Previous studies have shown that ACM induced erythroid differentiation of CML cells. In this study, we investigate the effect of ACM on the sensitivity of human CML cell line K562 to Bcr-Abl specific inhibitor imatinib (STI571, Gleevec). We first determined the optimal concentration of ACM for erythroid differentiation but not growth inhibition and apoptosis in K562 cells. Then, pretreatment with this optimal concentration of ACM followed by a minimally toxic concentration of imatinib strongly induced growth inhibition and apoptosis compared to that with simultaneous co-treatment, indicating that ACM-induced erythroid differentiation sensitizes K562 cells to imatinib. Sequential treatment with ACM and imatinib induced Bcr-Abl down-regulation, cytochrome c release into the cytosol, and caspase-3 activation, as well as decreased Mcl-1 and Bcl-xL expressions, but did not affect Fas ligand/Fas death receptor and procaspase-8 expressions. ACM/imatinib sequential treatment-induced apoptosis was suppressed by a caspase-9 inhibitor and a caspase-3 inhibitor, indicating that the caspase cascade is involved in this apoptosis. Furthermore, we demonstrated that ACM induced erythroid differentiation through the p38 mitogen-activated protein kinase (MAPK) pathway. The inhibition of erythroid differentiation by p38MAPK inhibitor SB202190, p38MAPK dominant negative mutant or p38MAPK shRNA knockdown, reduced the ACM/imatinib sequential treatment-mediated growth inhibition and apoptosis. These results suggest that differentiated K562 cells induced by ACM-mediated p38MAPK pathway become more sensitive to imatinib and result in down-regulations of Bcr-Abl and anti-apoptotic proteins, growth inhibition and apoptosis. These results provided a potential management by which ACM might have a crucial impact on increasing sensitivity of CML cells to imatinib in the differentiation therapeutic approaches.

Gallotannin-rich Caesalpinia spinosa fraction decreases the primary tumor and factors associated with poor prognosis in a murine breast cancer model

BACKGROUND

Several treatment alternatives are available for primary breast cancer, although those for metastatic disease or inflammation associated with tumor progression are ineffective. Therefore, there is a great need for new therapeutic alternatives capable of generating an immune response against residual tumor cells, thus contributing to eradication of micrometastases and cancer stem cells. The use of complex natural products is an excellent therapeutic alternative widely used by Chinese, Hindu, Egyptian, and ancestral Latin-American Indian populations.

METHODS

The present study evaluated cytotoxic, antitumor, and tumor progression activities of a gallotannin-rich fraction derived from Caesalpinia spinosa (P2Et). The parameters evaluated in vitro were mitochondrial membrane depolarization, phosphatidylserine externalization, caspase 3 activation, DNA fragmentation, and clonogenic activity. The parameters evaluated in vivo were tumor growth, leukocyte number, metastatic cell number, and cytokine production by flow cytometry.

RESULTS

The in vitro results showed that the P2Et fraction induced apoptosis with mitochondrial membrane potential loss, phosphatidylserine externalization, caspase 3 activation, DNA fragmentation, and decreased clonogenic capacity of 4T1 cells. In vivo, the P2Et fraction induced primary tumor reduction in terms of diameter and weight in BALB/c mice transplanted with 4T1 cells and decreased numbers of metastatic cells, mainly in the spleen. Furthermore, decreases in the number of peripheral blood leukocytes (leukemoid reaction) and interleukin 6 (IL-6) serum levels were found, which are events associated with a poor prognosis. The P2Et fraction exerts its activity on the primary tumor, reduces cell migration to distant organs, and decreases IL-6 serum levels, implying tumor microenvironment mechanisms.

CONCLUSIONS

Overall, the P2Et fraction lessens risk factors associated with tumor progression and diminishes primary tumor size, showing good potential for use as an adjuvant in breast cancer ER(+) treatment.

Lapatinib-binding protein kinases in the African trypanosome: identification of cellular targets for kinase-directed chemical scaffolds

Human African trypanosomiasis is caused by the eukaryotic microbe Trypanosoma brucei. To discover new drugs against the disease, one may use drugs in the clinic for other indications whose chemical scaffolds can be optimized via a medicinal chemistry campaign to achieve greater potency against the trypanosome. Towards this goal, we tested inhibitors of human EGFR and/or VEGFR as possible anti-trypanosome compounds. The 4-anilinoquinazolines canertinib and lapatinib, and the pyrrolopyrimidine AEE788 killed bloodstream T. brucei in vitro with GI₅₀ in the low micromolar range. Curiously, the genome of T. brucei does not encode EGFR or VEGFR, indicating that the drugs recognize alternate proteins. To discover these novel targets, a trypanosome lysate was adsorbed to an ATP-sepharose matrix and washed with a high salt solution followed by nicotinamide adenine dinucleotide (NAD⁺). Proteins that remained bound to the column were eluted with drugs, and identified by mass spectrometry/bioinformatics. Lapatinib bound to Tb927.4.5180 (termed T. brucei lapatinib-binding protein kinase-1 (TbLBPK1)) while AEE788 bound Tb927.5.800 (TbLBPK2). When the NAD⁺ wash was omitted from the protocol, AEE788, canertinib and lapatinib eluted TbLBPK1, TbLBPK2, and Tb927.3.1570 (TbLBPK3). In addition, both canertinib and lapatinib eluted Tb10.60.3140 (TbLBPK4), whereas only canertinib desorbed Tb10.61.1880 (TbCBPK1). Lapatinib binds to a unique conformation of protein kinases. To gain insight into the structural basis for lapatinib interaction with TbLBPKs, we constructed three-dimensional models of lapatinib•TbLBPK complexes, which confirmed that TbLBPKs can adopt lapatinib-compatible conformations. Further, lapatinib, AEE788, and canertinib were docked to TbLBPKs with favorable scores. Our studies (a) present novel targets of kinase-directed drugs in the trypanosome, and (b) offer the 4-anilinoquinazoline and pyrrolopyrimidines as scaffolds worthy of medicinal chemistry and structural biology campaigns to develop them into anti-trypanosome drugs.

Alternative approaches to eradicating the malignant clone in chronic myeloid leukemia: tyrosine-kinase inhibitor combinations and beyond

In patients with chronic myeloid leukemia (CML) in chronic phase who have achieved complete molecular remission on imatinib therapy, clinical trials from France and Australia have demonstrated that the majority experience prompt molecular relapse of their leukemia upon discontinuation of the drug, showing that long-term monotherapy with tyrosine kinase inhibitors is not curative in the majority of patients with CML. This has focused attention on strategies to eradicate residual disease in CML that is presumed to arise from malignant Ph+ stem cells, which should result in permanent cure and long-term leukemia-free survival. Here, we review the evidence that targeting CML stem cells will be of clinical benefit and discuss pharmacological and immunological approaches to accomplish this goal. Where possible, we link preclinical studies of CML stem cell biology to emerging results from clinical trials of agents that may target these cells.

Multifaceted actions of 8-amino-adenosine kill BCR-ABL positive cells

Survival of chronic myelogenous leukemia (CML) cells is dependent on BCR-ABL kinase, the activity of which is contingent on the level of BCR-ABL protein and the availability of adenosine triphosphate (ATP). We hypothesized that 8-amino-adenosine (8-amino-Ado)-mediated reduction in cellular ATP level and inhibition of mRNA synthesis leading to a decrease in protein level would result in a multifaceted targeting of BCR-ABL. Using K562 cells, we demonstrated that there was a dose- and time-dependent increase in 8-amino-ATP accompanied by a > 95% decline in the endogenous ATP pool. In parallel, 8-amino-Ado inhibited RNA synthesis and resulted in a depletion of BCR-ABL transcript. Consistent with this, BCR-ABL and ABL protein levels were also decreased. These effects were associated with the initiation of cell death as visualized by poly(ADP-ribose) polymerase (PARP) cleavage, decreased clonogenicity and greater than additive interaction with imatinib. In imatinib-sensitive and -resistant KBM5 cells, 8-amino-Ado treatment augmented the imatinib effect on growth inhibition.

A gallotannin-rich fraction from Caesalpinia spinosa (Molina) Kuntze displays cytotoxic activity and raises sensitivity to doxorubicin in a leukemia cell line

BACKGROUND

Enhancement of tumor cell sensitivity may help facilitate a reduction in drug dosage using conventional chemotherapies. Consequently, it is worthwhile to search for adjuvants with the potential of increasing chemotherapeutic drug effectiveness and improving patient quality of life. Natural products are a very good source of such adjuvants.

METHODS

The biological activity of a fraction enriched in hydrolysable polyphenols (P2Et) obtained from Caesalpinia spinosa was evaluated using the hematopoietic cell line K562. This fraction was tested alone or in combination with the conventional chemotherapeutic drugs doxorubicin, vincristine, etoposide, camptothecin and taxol. The parameters evaluated were mitochondrial depolarization, caspase 3 activation, chromatin condensation and clonogenic activity.

RESULTS

We found that the P2Et fraction induced mitochondrial depolarization, activated caspase 3, induced chromatin condensation and decreased the clonogenic capacity of the K562 cell line. When the P2Et fraction was used in combination with chemotherapeutic drugs at sub-lethal concentrations, a fourfold reduction in doxorubicin inhibitory concentration 50 (IC50) was seen in the K562 cell line. This finding suggested that P2Et fraction activity is specific for the molecular target of doxorubicin.

CONCLUSIONS

Our results suggest that a natural fraction extracted from Caesalpinia spinosa in combination with conventional chemotherapy in combination with natural products on leukemia cells may increase therapeutic effectiveness in relation to leukemia.

Cyclin-dependent kinase 7/9 inhibitor SNS-032 abrogates FIP1-like-1 platelet-derived growth factor receptor α and bcr-abl oncogene addiction in malignant hematologic cells

PURPOSE

The "gate-keeper" mutations T674I platelet-derived growth factor receptor α (PDGFRα) in hypereosinophilic syndrome (HES) and T315I Bcr-Abl in chronic myeloid leukemia (CML) are resistant to imatinib and the second-generation small-molecule tyrosine kinase inhibitors (TKI). However, to combat acquired resistance to imatinib, an alternative approach is to decrease the expression of the addicted gene to efficiently kill resistant malignant hematologic cells. The purpose of this study was to evaluate the strategy of shutting down the transcription and expression of FIP1-like-1 (FIP1L1)-PDGFRα and Bcr-Abl with SNS-032, an inhibitor of cyclin-dependent kinase 7 (CDK7) and CDK9 in phase I clinical trials.

EXPERIMENTAL DESIGN

The effects of SNS-032 on PDGFRα and Bcr-Abl signaling pathways, apoptosis, and cell cycling were analyzed in TKI-resistant cells of HES and CML. The in vivo antitumor activity of SNS-032 was assessed with xenografted BaF3-T674I FIP1L1-PDGFRα and KBM5-T315I Bcr-Abl cells in nude mouse models.

RESULTS

SNS-032 inhibited the phosphorylation on Ser5 and Ser2 of RNA polymerase II. SNS-032 decreased both the mRNA and protein levels of FIP1L1-PDGFRα and Bcr-Abl and inhibited the proliferation of malignant cells expressing FIP1L1-PDGFRα or Bcr-Abl. It also decreased the phosphorylation of downstream molecules. It induced apoptosis by triggering both the mitochondrial pathway and the death receptor pathway.

CONCLUSIONS

This CDK7/9 inhibitor potently inhibits FIP1L1-PDGFRα-positive HES cells and Bcr-Abl-positive CML cells regardless of their sensitivity to imatinib. SNS-032 may have potential in treating hematologic malignancy by abrogating oncogene addiction.

Omacetaxine mepesuccinate for the treatment of leukemia

INTRODUCTION

Omacetaxine mepesuccinate, formerly known as homoharringtonine, is a first-in-class cephalotaxine that has experienced phases of increasing and waning interest since its first use in traditional Chinese medicine. With activity being reported in patients with chronic myeloid leukemia (CML) resistant to currently available tyrosine kinase inhibitors, renewed interest has recently been generated.

AREAS COVERED

The development of omacetaxine mepesuccinate, with emphasis on synthesis and mode of administration, is addressed. An overview on current clinical results as a single agent or within combination regimens in patients with acute myeloid leukemia (AML) and CML is given.

EXPERT OPINION

Omacetaxine mepesuccinate has a unique mode of action and appreciable activity in AML and CML with generally mild nonhematologic toxicity. In patients with AML, results indicate a role within combination regimens in selected, possibly elderly patient populations. In CML, patients with resistance to tyrosine kinase inhibitors, especially due to the T315I mutation, are the most intensively studied. Despite successful results in some patients, single-agent therapy with omacetaxine mepesuccinate has resulted in modest results. However, upfront combination with tyrosine kinase inhibitor represents an attractive option due their differing mechanisms of action.

Oncogene addiction in gliomas: implications for molecular targeted therapy

Oncogene addiction is a phenomenon that the survival of cancer cells depends on an activated oncogene or inactivation of tumor suppressor gene, and is regarded as the 'Achilles heel' of the successful molecular targeted therapies in cancer. However, the role of oncogene addiction in gliomas has not been elucidated systematically. In this review, we summarize the current experimental and clinical evidence for the concept of oncogene addiction and describe the mechanisms explaining oncogene addiction in gliomas. And the clinical implications for oncogene addiction in molecular targeted therapy are further emphasized. In addition, we discuss future direction for defining complex "oncogene addiction network" through the integrated analysis of multiple platforms in the flow of genetic information in gliomagenesis.

Omacetaxine may have a role in chronic myeloid leukaemia eradication through downregulation of Mcl-1 and induction of apoptosis in stem/progenitor cells

Chronic myeloid leukaemia (CML) is maintained by a rare population of tyrosine kinase inhibitor (TKI)-insensitive malignant stem cells. Our long-term aim is to find a BcrAbl-independent drug that can be combined with a TKI to improve overall disease response in chronic-phase CML. Omacetaxine mepesuccinate, a first in class cetaxine, has been evaluated by clinical trials in TKI-insensitive/resistant CML. Omacetaxine inhibits synthesis of anti-apoptotic proteins of the Bcl-2 family, including (myeloid cell leukaemia) Mcl-1, leading to cell death. Omacetaxine effectively induced apoptosis in primary CML stem cells (CD34(+)38(lo)) by downregulation of Mcl-1 protein. In contrast to our previous findings with TKIs, omacetaxine did not accumulate undivided cells in vitro. Furthermore, the functionality of surviving stem cells following omacetaxine exposure was significantly reduced in a dose-dependant manner, as determined by colony forming cell and the more stringent long-term culture initiating cell colony assays. This stem cell-directed activity was not limited to CML stem cells as both normal and non-CML CD34(+) cells were sensitive to inhibition. Thus, although omacetaxine is not leukaemia stem cell specific, its ability to induce apoptosis of leukaemic stem cells distinguishes it from TKIs and creates the potential for a curative strategy for persistent disease.

New developments in the treatment of chronic myeloid leukemia and Philadelphia-positive acute lymphoblastic leukemia

Although imatinib revolutionized the management of chronic myeloid leukemia (CML), recent data indicate a transformation in the treatment approach likely in the near future. The superiority of second-generation tyrosine kinase inhibitors (TKIs) over imatinib in newly diagnosed disease has been recognized. Several investigational agents specific for those patients with the T315I mutation remain under evaluation. In Philadelphia-positive (Ph-positive) acute lymphoblastic leukemia (ALL), the addition of imatinib improved response rates. However, short remission durations with single agent therapy limit the benefit on survival. Early molecular remissions achieved with dasatinib will enable more patients to proceed to stem cell transplant (SCT), with increased likelihood of positive outcomes post-SCT.

Fangjiomics: in search of effective and safe combination therapies

Millennia-old Chinese medicine treats disease with many combination therapies involving ingredients used in clinic practice. Fangjiomics is the science of identifying and designing effective mixtures of bioactive agents and elucidating their modes of action beyond those of Chinese patent medicines. Omics profiling and quantitative optimal modeling have been used to associate the various responses with biological pathways related to disease phenotype. Fangjiomics seeks to study myriad compatible combinations that may act through multiple targets, modes of action, and biological pathways balancing on off-target and on-target effects. This approach may lead to the discovery of controllable array-designed therapies to combine less potent elements that are more effective collectively but have fewer adverse side effects than does any element singly.

ABL fusion oncogene transformation and inhibitor sensitivity are mediated by the cellular regulator RIN1

ABL gene translocations create constitutively active tyrosine kinases that are causative in chronic myeloid leukemia, acute lymphocytic leukemia and other hematopoietic malignancies. Consistent retention of ABL SH3/SH2 autoinhibitory domains, however, suggests that these leukemogenic tyrosine kinase fusion proteins remain subject to regulation. We resolve this paradox, demonstrating that BCR-ABL1 kinase activity is regulated by RIN1, an ABL SH3/SH2 binding protein. BCR-ABL1 activity was increased by RIN1 overexpression and decreased by RIN1 silencing. Moreover, Rin1(-/-) bone marrow cells were not transformed by BCR-ABL1, ETV6-ABL1 or BCR-ABL1(T315I), a patient-derived drug-resistant mutant, as judged by growth factor independence. Rescue by ectopic RIN1 verified a cell autonomous mechanism of collaboration with BCR-ABL1 during transformation. Sensitivity to the ABL kinase inhibitor imatinib was increased by RIN1 silencing, consistent with RIN1 stabilization of an activated BCR-ABL1 conformation having reduced drug affinity. The dependence on activation by RIN1 to unleash full catalytic and cell transformation potential reveals a previously unknown vulnerability that could be exploited for treatment of leukemic cases driven by ABL translocations. The findings suggest that RIN1 targeting could be efficacious for imatinib-resistant disease and might complement ABL kinase inhibitors in first-line therapy.

Homoharringtonine reduced Mcl-1 expression and induced apoptosis in chronic lymphocytic leukemia

Homoharringtonine (HHT) is a plant alkaloid that inhibits the elongation phase of translation that is currently in clinical trials. Because the intrinsically short-lived antiapoptotic protein myeloid cell leukemia-1 (Mcl-1) has been reported to support the survival of chronic lymphocytic leukemia (CLL) cells, we hypothesized that inhibition of protein synthesis by HHT would decrease Mcl-1 expression and induce apoptosis in CLL. In primary CLL cells, HHT induced significant apoptosis independent of the prognostic characteristics of the patients. This was associated with inhibition of translation and decreased Mcl-1 levels in CLL cells. Mcl-1 reduction was evident as early as 2 hours and continued to decrease in the next 6-8 hours, whereas cell death started in 2 hours and continued to increase for 24 hours. Reduction of the Mcl-1 level was due to translation inhibition and proteasome degradation rather than to transcription inhibition or caspase cleavage. HHT and the transcription inhibitor SNS-032 induced synergistic cell killing. Although stromal cells induced Mcl-1 expression and protected CLL cells from the toxicity of fludarabine, this induction was reversed by HHT, which overcame stromal cell-mediated protection. Thus, these results provide a rationale for clinical development of HHT in CLL as single agent or in combinations.

Third-generation tyrosine kinase inhibitors and beyond

Imatinib is considered standard frontline therapy for the management of patients with chronic myeloid leukemia (CML). However, it is estimated that approximately one third of patients will fail imatinib therapy. The recommended therapeutic approach for those patients is the use of a second-generation tyrosine kinase inhibitor (TKI) such as nilotinib or dasatinib. With these agents, approximately 50% of patients achieve a complete cytogenetic response (0% Philadelphia chromosome-positive [Ph(+)] bone marrow metaphases), the duration of which has not yet been established. For the remainder, the options are limited to allogeneic stem cell transplantation (SCT) or enrollment on a clinical trial with an investigational agent. Third-generation TKIs and non-adenosine triphosphate (non-ATP) mimetic compounds with activity against ABL1 mutations associated with failure to approved TKIs are under development for patients who either have failed sequential therapy with at least two TKIs or carry the highly resistant T315I mutation. Some of these agents have already shown promising clinical activity.

ABL tyrosine kinases: evolution of function, regulation, and specificity

ABL-family proteins comprise one of the best conserved branches of the tyrosine kinases. Each ABL protein contains an SH3-SH2-TK (Src homology 3-Src homology 2-tyrosine kinase) domain cassette, which confers autoregulated kinase activity and is common among nonreceptor tyrosine kinases. This cassette is coupled to an actin-binding and -bundling domain, which makes ABL proteins capable of connecting phosphoregulation with actin-filament reorganization. Two vertebrate paralogs, ABL1 and ABL2, have evolved to perform specialized functions. ABL1 includes nuclear localization signals and a DNA binding domain through which it mediates DNA damage-repair functions, whereas ABL2 has additional binding capacity for actin and for microtubules to enhance its cytoskeletal remodeling functions. Several types of posttranslational modifications control ABL catalytic activity, subcellular localization, and stability, with consequences for both cytoplasmic and nuclear ABL functions. Binding partners provide additional regulation of ABL catalytic activity, substrate specificity, and downstream signaling. Information on ABL regulatory mechanisms is being mined to provide new therapeutic strategies against hematopoietic malignancies caused by BCR-ABL1 and related leukemogenic proteins.

Stem cell transplantation for patients with chronic myeloid leukemia resistant to tyrosine kinase inhibitors with BCR-ABL kinase domain mutation T315I

BACKGROUND

Resistance to tyrosine kinase inhibitor (TKIs) therapy is associated with the development of kinase domain mutations. Although many imatinib-resistant mutations respond well to second-generation TKIs, the threonine-to-isoleucine mutation at codon 315 of the breakpoint cluster region/v-abl Abelson murine leukemia viral oncogene protein fusion Bcr-Abl (T315I) is insensitive to all currently available TKIs. The outcome in such patients after stem cell transplantation (SCT) is unknown.

METHODS

Eight patients with TKI-resistant CML who had T315I mutations underwent 9 transplantations. At the time of SCT, 2 patients were in chronic phase, 3 patients were in accelerated phase; and 3 patients were in second chronic phase.

RESULTS

The best responses after SCT were a complete molecular response (CMR) in 3 patients, a complete cytogenetic response (CCyR) in 4 patients, and a complete hematologic response (CHR) in 1 patient, and 1 patient had no response. The best outcome was for patients who underwent transplantation in chronic phase, and both of those patients remained alive and in complete molecular remission 14 months and 42 months after SCT. After a median follow-up of 13 months from SCT, 5 patients remained alive, including 3 patients in CMR, 1 patient in CCyR, and 1 patient in CHR.

CONCLUSIONS

The current results indicated that SCT is an effective strategy for patients with CML who have the T315I mutation, particularly in earlier stages.

Longitudinal studies of SRC family kinases in imatinib- and dasatinib-resistant chronic myelogenous leukemia patients

This report aims to more accurately define the frequency of the involvement of SRC Family Kinases (SFKs) in imatinib- and dasatinib-resistant CML patients. Clinical samples were analysed during in vivo treatment. We confirmed the high frequency of SFKs involvement in Tyrosine kinase inhibitor-resistant CML (52% of the cases) and even further in progressive disease and blast crises (60% of the cases). The SFKs deregulation is also observed in patients harboring BCR-ABL mutations. In T315I and F317L mutated patients, CML-resistance appears to be promoted by SFKs kinase protein reactivation once the BCR-ABL mutated clone has decreased on Omacetaxine.

Responses in mantle cell lymphoma cells to SNS-032 depend on the biological context of each cell line

SNS-032 is a potent inhibitor of cyclin-dependent kinases (Cdk) 2, 7, and 9 that regulate the cell cycle and transcription. Our studies in indolent primary chronic lymphocytic leukemia cells showed that SNS-032 inhibited transcription, diminished the antiapoptotic protein Mcl-1, and induced apoptosis. The present study focuses on evaluating this compound in four proliferating mantle cell lymphoma lines (Jeko-1, Granta 519, Mino, and SP-53). Consistent with its action against Cdk9 and Cdk7, SNS-032 inhibited the phosphorylation of RNA pol II in all four lines and blocked RNA synthesis. The transcripts and protein levels of short-lived proteins decreased, including cyclin D1 and Mcl-1. Cell growth was inhibited in a concentration-dependent manner in all lines. Apoptosis was induced in JeKo-1, Mino, and SP-53 cells without disrupting cell cycle distribution. However, apoptosis was limited in Granta cells; rather, there was a significant reduction of clonogenic survival. Small interfering RNA was used to specifically knock down Mcl-1 and cyclin D1 in JeKo-1 and Granta cells. Knocking down Mcl-1 induced significant apoptosis in Jeko-1 cells but not Granta cells. Reducing cyclin D1, rather than Mcl-1, was associated with loss of clonogenic survival in Granta cells. Thus, these results indicated that mantle cell lymphoma cell lines have distinct mechanisms sustaining their survival, and the mechanism of action of SNS-032 is dependent on the biological context of an individual line.

Pristimerin induces apoptosis in imatinib-resistant chronic myelogenous leukemia cells harboring T315I mutation by blocking NF-kappaB signaling and depleting Bcr-Abl

Background

Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. Bcr-Abl-T315I is the notorious point mutation that causes resistance to imatinib and the second generation tyrosine kinase inhibitors, leading to poor prognosis. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML that may also be effective against CML cells with Bcr-Abl-T315I.

Results

In this report, we discovered that pristimerin, a quinonemethide triterpenoid isolated from Celastraceae and Hippocrateaceae, inhibited growth and induced apoptosis in CML cells, including the cells harboring Bcr-Abl-T315I mutation. Additionally, pristimerin inhibited the growth of imatinib-resistant Bcr-Abl-T315I xenografts in nude mice. Pristimerin blocked the TNFα-induced IκBα phosphorylation, translocation of p65, and expression of NF-κB-regulated genes. Pristimerin inhibited two steps in NF-κB signaling: TAK1→IKK and IKK→IκBα. Pristimerin potently inhibited two pairs of CML cell lines (KBM5 versus KBM5-T315I, 32D-Bcr-Abl versus 32D-Bcr-Abl-T315I) and primary cells from a CML patient with acquired resistance to imatinib. The mRNA and protein levels of Bcr-Abl in imatinib-sensitive (KBM5) or imatinib-resistant (KBM5-T315I) CML cells were reduced after pristimerin treatment. Further, inactivation of Bcr-Abl by imatinib pretreatment did not abrogate the TNFα-induced NF-κB activation while silencing p65 by siRNA did not affect the levels of Bcr-Abl, both results together indicating that NF-κB inactivation and Bcr-Abl inhibition may be parallel independent pathways.

Conclusion

To our knowledge, this is the first report to show that pristimerin is effective in vitro and in vivo against CML cells, including those with the T315I mutation. The mechanisms may involve inhibition of NF-κB and Bcr-Abl. We concluded that pristimerin could be a lead compound for further drug development to overcome imatinib resistance in CML patients.