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Acute myeloid leukaemia (AML) is a clonal haematological malignancy affecting the myeloid lineage, with generally poor patient outcomes owing to the lack of targeted therapies. The histone lysine demethylase 4A (KDM4A) has been established as a novel therapeutic target in AML, due to its selective oncogenic role within leukaemic cells. We identify that the transcription factor nuclear factor of activated T cells 2 (NFATC2) is a novel binding and transcriptional target of KDM4A in the human AML THP-1 cell line. Furthermore, cytogenetically diverse AML cell lines, including THP-1, were dependent on NFATC2 for colony formation in vitro, highlighting a putative novel mechanism of AML oncogenesis. Our study demonstrates that NFATC2 maintenance of cell cycle progression in human AML cells was driven primarily by CCND1. Through RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq), NFATc2 was shown to bind to the promoter region of genes involved in oxidative phosphorylation and subsequently regulate their gene expression in THP-1 cells. Furthermore, our data show that NFATC2 shares transcriptional targets with the transcription factor c-MYC, with MYC knockdown phenocopying NFATC2 knockdown. These data suggest a newly identified co-ordinated role for NFATC2 and MYC in the maintenance of THP-1 cell function, indicative of a potential means of therapeutic targeting in human AML., (© 2024 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

Whilst it is recognised that targeting self-renewal is an effective way to functionally impair the quiescent leukaemic stem cells (LSC) that persist as residual disease in chronic myeloid leukaemia (CML), developing therapeutic strategies to achieve this have proved challenging. We demonstrate that the regulatory programmes of quiescent LSC in chronic phase CML are similar to that of embryonic stem cells, pointing to a role for wild type p53 in LSC self-renewal. In support of this, increasing p53 activity in primitive CML cells using an MDM2 inhibitor in combination with a tyrosine kinase inhibitor resulted in reduced CFC outputs and engraftment potential, followed by loss of multilineage priming potential and LSC exhaustion when combination treatment was discontinued. Our work provides evidence that targeting LSC self-renewal is exploitable in the clinic to irreversibly impair quiescent LSC function in CML residual disease - with the potential to enable more CML patients to discontinue therapy and remain in therapy-free remission., (© 2024. The Author(s).)

Acute myeloid leukemia is a heterogeneous hematopoietic malignancy, characterized by uncontrolled clonal proliferation of abnormal myeloid progenitor cells, with poor outcomes. The internal tandem duplication (ITD) mutation of the Fms-like receptor tyrosine kinase 3 (FLT3) (FLT3-ITD) represents the most common genetic alteration in AML, detected in approximately 30% of AML patients, and is associated with high leukemic burden and poor prognosis. Therefore, this kinase has been regarded as an attractive druggable target for the treatment of FLT3-ITD AML, and selective small molecule inhibitors, such as quizartinib, have been identified and trialled. However, clinical outcomes have been disappointing so far due to poor remission rates, also because of acquired resistance. A strategy to overcome resistance is to combine FLT3 inhibitors with other targeted therapies. In this study, we investigated the preclinical efficacy of the combination of quizartinib with the pan PI3K inhibitor BAY-806946 in FLT3-ITD cell lines and primary cells from AML patients. We show here that BAY-806946 enhanced quizartinib cytotoxicity and, most importantly, that this combination increases the ability of quizartinib to kill CD34 + CD38 - leukemia stem cells, whilst sparing normal hematopoietic stem cells. Because constitutively active FLT3 receptor tyrosine kinase is known to boost aberrant PI3K signaling, the increased sensitivity of primary cells to the above combination can be the mechanistic results of the disruption of signaling by vertical inhibition., Competing Interests: Declaration of competing interest None, (Copyright © 2023 Università degli Studi di Modena e Reggio Emilia. Published by Elsevier Ltd.. All rights reserved.)

Tyrosine kinase inhibitors (TKI) have revolutionised the treatment of CML. However, TKI do not eliminate the leukaemia stem cells (LSC), which can re-initiate the disease. Thus, finding new therapeutic targets in CML LSC is key to finding a curative treatment. Using microarray datasets, we defined a list of 227 genes that were differentially expressed in CML LSC compared to the healthy controls but were not affected by TKI in vitro. Two of them, CD33 and PPIF , are targeted by gemtuzumab-ozogamicin and cyclosporin A, respectively. We treated CML and the control CD34 + cells with either drug with or without imatinib to investigate the therapeutic potential of the TKI-independent gene expression programme. Cyclosporine A, in combination with imatinib, reduced the number of CML CFC compared with non-CML controls, but only at supra-therapeutic concentrations. Gemtuzumab-ozogamicin showed an EC 50 of 146 ng/mL, below the plasma peak concentration of 630 ng/mL observed in the AML patients and below the EC 50 of 3247 ng/mL observed in the non-CML cells. Interestingly, gemtuzumab-ozogamicin seems to promote cell cycle progression in CML CD34 + cells and demonstrated activation of the RUNX1 pathway in an RNAseq experiment. This suggests that targeting the TKI-independent genes in CML LSC could be exploited for the development of new therapies in CML.

Acute myeloid leukemia (AML) is an aggressive hematopoietic malignancy, characterized by a heterogeneous genetic landscape and complex clonal evolution, with poor outcomes. Mutation at the internal tandem duplication of FLT3 (FLT3-ITD) is one of the most common somatic alterations in AML, associated with high relapse rates and poor survival due to the constitutive activation of the FLT3 receptor tyrosine kinase and its downstream effectors, such as PI3K signaling. Thus, aberrantly activated FLT3-kinase is regarded as an attractive target for therapy for this AML subtype, and a number of small molecule inhibitors of this kinase have been identified, some of which are approved for clinical practice. Nevertheless, acquired resistance to these molecules is often observed, leading to severe clinical outcomes. Therapeutic strategies to tackle resistance include combining FLT3 inhibitors with other antileukemic agents. Here, we report on the preclinical activity of the combination of the FLT3 inhibitor quizartinib with the dual PI3K/mTOR inhibitor PF-04691502 in FLT3-ITD cells. Briefly, we show that the association of these two molecules displays synergistic cytotoxicity in vitro in FLT3-ITD AML cells, triggering 90% cell death at nanomolar concentrations after 48 h., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Epigenomic dysregulation is a common pathological feature in human hematological malignancies. H3K9me3 emerges as an important epigenomic marker in acute myeloid leukemia (AML). Its associated methyltransferases, such as SETDB1, suppress AML leukemogenesis, whilst H3K9me3 demethylases KDM4C is required for mixed-lineage leukemia rearranged AML. However, the specific role and molecular mechanism of action of another member of the KDM4 family, KDM4A has not previously been clearly defined. In this study, we delineated and functionally validated the epigenomic network regulated by KDM4A. We show that selective loss of KDM4A is sufficient to induce apoptosis in a broad spectrum of human AML cells. This detrimental phenotype results from a global accumulation of H3K9me3 and H3K27me3 at KDM4A targeted genomic loci thereby causing downregulation of a KDM4A-PAF1 controlled transcriptional program essential for leukemogenesis, distinct from that of KDM4C. From this regulatory network, we further extracted a KDM4A-9 gene signature enriched with leukemia stem cell activity; the KDM4A-9 score alone or in combination with the known LSC17 score, effectively stratifies high-risk AML patients. Together, these results establish the essential and unique role of KDM4A for AML self-renewal and survival, supporting further investigation of KDM4A and its targets as a potential therapeutic vulnerability in AML.

Acute myeloid leukemia (AML) is a highly heterogeneous hematopoietic malignancy characterized by excessive proliferation and accumulation of immature myeloid blasts in the bone marrow. AML has a very poor 5-year survival rate of just 16% in the UK; hence, more efficacious, tolerable, and targeted therapy is required. Persistent leukemia stem cell (LSC) populations underlie patient relapse and development of resistance to therapy. Identification of critical oncogenic signaling pathways in AML LSC may provide new avenues for novel therapeutic strategies. The phosphatidylinositol-3-kinase (PI3K)/Akt and the mammalian target of rapamycin (mTOR) signaling pathway, is often hyperactivated in AML, required to sustain the oncogenic potential of LSCs. Growing evidence suggests that targeting key components of this pathway may represent an effective treatment to kill AML LSCs. Despite this, accruing significant body of scientific knowledge, PI3K/Akt/mTOR inhibitors have not translated into clinical practice. In this article, we review the laboratory-based evidence of the critical role of PI3K/Akt/mTOR pathway in AML, and outcomes from current clinical studies using PI3K/Akt/mTOR inhibitors. Based on these results, we discuss the putative mechanisms of resistance to PI3K/Akt/mTOR inhibition, offering rationale for potential candidate combination therapies incorporating PI3K/Akt/mTOR inhibitors for precision medicine in AML.

Tyrosine kinase inhibitor (TKI) therapy is the standard treatment for chronic phase (CP)-chronic myeloid leukemia (CML), yet patients in blast crisis (BC) phase of CML are unlikely to respond to TKI therapy. The transcription factor E2F1 is a down-stream target of the tyrosine kinase BCR-ABL1 and is up-regulated in TKI-resistant leukemia stem cells (LSC). Pyrrole imidazole polyamides (PA) are minor groove binders which can be programmed to target DNA sequences in a gene-selective manner. This manuscript describes such an approach with a PA designed to down-regulate E2F1 controlled gene expression by targeting a DNA sequence within 100 base pairs (bp) upstream of the E2F1 consensus sequence. Human BC-CML KCL22 cells were assessed after treatment with PA, TKI or their combination. Our PA inhibited BC-CML cell expansion based on cell density analysis compared to an untreated control after a 48-hour time-course of PA treatment. However, no evidence of cell cycle arrest was observed among BC-CML cells treated with PA, with respect to their no drug control counterparts. Thus, this work demonstrates that PAs are effective in inhibiting E2F1 TF activity which results in a temporal reduction in BC-CML cell number. We envisage that PAs could be used in the future to map genes under E2F1 control in CML LSCs., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Growing evidence has demonstrated that epigenetic dysregulation is a common pathological feature in human cancer cells. Global alterations in the epigenetic landscape are prevalent in malignant cells across different solid tumors including, prostate cancer, non-small-cell lung cancer, renal cell carcinoma, and in haemopoietic malignancy. In particular, DNA hypomethylation and histone hypoacetylation have been observed in acute myeloid leukemia (AML) patient blasts, with histone methylation being an emerging area of study. Histone 3 lysine 9 trimethylation (H3K9me3) is a post-translational modification known to be involved in the regulation of a broad range of biological processes, including the formation of transcriptionally silent heterochromatin. Following the observation of its aberrant methylation status in hematological malignancy and several other cancer phenotypes, recent studies have associated H3K9me3 levels with patient outcome and highlighted key molecular mechanisms linking H3K9me3 profile with AML etiology in a number of large-scale meta-analysis. Consequently, the development and application of small molecule inhibitors which target the histone methyltransferases or demethylase enzymes known to participate in the oncogenic regulation of H3K9me3 in AML represents an advancing area of ongoing study. Here, we provide a comprehensive review on how this particular epigenetic mark is regulated within cells and its emerging role as a potential therapeutic target in AML, along with an update on the current research into advancing the generation of more potent and selective inhibitors against known H3K9 methyltransferases and demethylases.

Background and Purpose: Approaches to prevent selective and progressive loss of insulin-producing beta cells in Type 1 diabetes mellitus (T1DM) will help to manage this prevalent and devastating disease. Curcumin (CUR), a natural anti-inflammatory substance, suppresses diabetes-associated inflammation and cell death. However, very high doses need to be used because of poor oral bioavailability, making it difficult to translate the anti-inflammatory actions to clinical situations., Experimental Approach: We have prepared biodegradable nanosystems encapsulating curcumin (nCUR), resulting in at least nine-fold improvement in oral bioavailability. Here, we tested the ability of nCUR to prevent streptozotocin (STZ)-induced inflammation and apoptosis in pancreatic islets and beta cells, in rats., Key Results: Non-fasted rats pretreated with 10 or 50 mg·kg -1 nCUR 6 h prior to STZ challenge had up to 37% reduction in the glucose levels, while plain CUR (50 mg·kg -1 ) results in 12% reduction. This treatment with nCUR was accompanied by decreased islet or beta cell death, as shown by TUNEL assay and H&E staining. Both CUR and nCUR significantly decreased levels of inflammatory cytokines in pancreatic tissue homogenates that correlated well with minimal histiocytic infiltration. Pre-treatment with nCUR, but not CUR, decreased 8-oxo-2'-deoxyguanosine, a sensitive biomarker of ROS-induced DNA damage, in pancreas. In normal rodents, daily dosing for 28 days, with nCUR (25-100 mg·kg -1 ) did not cause any deleterious health issues by the carrier., Conclusions and Implications: Together, these data indicate a potentially translatable dose of nCUR that is safe and efficacious in improving beta cell function, which could prevent T1DM., (© 2017 The British Pharmacological Society.)

Targeting the fusion oncoprotein BCR-ABL with tyrosine kinase inhibitors has significantly affected chronic myeloid leukemia (CML) treatment, transforming the life expectancy of patients; however the risk for relapse remains, due to persistence of leukemic stem cells (LSCs). Therefore it is imperative to explore the mechanisms that result in LSC survival and develop new therapeutic approaches. We now show that major histocompatibility complex (MHC)-II and its master regulator class II transactivator (CIITA) are downregulated in CML compared with non-CML stem/progenitor cells in a BCR-ABL kinase-independent manner. Interferon γ (IFN-γ) stimulation resulted in an upregulation of CIITA and MHC-II in CML stem/progenitor cells; however, the extent of IFN-γ-induced MHC-II upregulation was significantly lower than when compared with non-CML CD34 + cells. Interestingly, the expression levels of CIITA and MHC-II significantly increased when CML stem/progenitor cells were treated with the JAK1/2 inhibitor ruxolitinib (RUX). Moreover, mixed lymphocyte reactions revealed that exposure of CD34 + CML cells to IFN-γ or RUX significantly enhanced proliferation of the responder CD4 + CD69 + T cells. Taken together, these data suggest that cytokine-driven JAK-mediated signals, provided by CML cells and/or the microenvironment, antagonize MHC-II expression, highlighting the potential for developing novel immunomodulatory-based therapies to enable host-mediated immunity to assist in the detection and eradication of CML stem/progenitor cells., (© 2017 by The American Society of Hematology.)

Treatment of chronic myelogenous leukemia (CML) with BCR-ABL tyrosine kinase inhibitors (TKI) fails to eliminate leukemia stem cells (LSC). Patients remain at risk for relapse, and additional approaches to deplete CML LSC are needed to enhance the possibility of discontinuing TKI treatment. We have previously reported that expression of the pivotal proinflammatory cytokine interleukin-1 (IL-1) is increased in CML bone marrow. We show here that CML LSC demonstrated increased expression of the IL-1 receptors, IL-1 receptor accessory protein and IL-1 receptor type 1 (IL-1R1), and enhanced sensitivity to IL-1-induced NF-κB signaling compared with normal stem cells. Treatment with recombinant IL-1 receptor antagonist (IL-1RA) inhibited IL-1 signaling in CML LSC and inhibited growth of CML LSC. Importantly, the combination of IL-1RA with TKI resulted in significantly greater inhibition of CML LSC compared with TKI alone. Our studies also suggest that IL-1 signaling contributes to overexpression of inflammatory mediators in CML LSC, suggesting that blocking IL-1 signaling could modulate the inflammatory milieu. We conclude that IL-1 signaling contributes to maintenance of CML LSC following TKI treatment and that IL-1 blockade with IL-1RA enhances elimination of TKI-treated CML LSC. These results provide a strong rationale for further exploration of anti-IL-1 strategies to enhance LSC elimination in CML., (© 2016 by The American Society of Hematology.)

The use of tyrosine kinase inhibitors (TKI), including nilotinib, has revolutionized the treatment of chronic myeloid leukemia (CML). However current unmet clinical needs include combating activation of additional survival signaling pathways in persistent leukemia stem cells after long-term TKI therapy. A ubiquitous signaling alteration in cancer, including CML, is activation of reactive oxygen species (ROS) signaling, which may potentiate stem cell activity and mediate resistance to both conventional chemotherapy and targeted inhibitors. We have developed a novel nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, imipramine blue (IB) that targets ROS generation. ROS levels are known to be elevated in CML with respect to normal hematopoietic stem/progenitor cells and not corrected by TKI. We demonstrate that IB has additive benefit with nilotinib in inhibiting proliferation, viability, and clonogenic function of TKI-insensitive quiescent CD34+ CML chronic phase (CP) cells while normal CD34+ cells retained their clonogenic capacity in response to this combination therapy in vitro. Mechanistically, the pro-apoptotic activity of IB likely resides in part through its dual ability to block NF-κB and re-activate the tumor suppressor protein phosphatase 2A (PP2A). Combining BCR-ABL1 kinase inhibition with NADPH oxidase blockade may be beneficial in eradication of CML and worthy of further investigation., Competing Interests: J.L.A. is the inventor of imipramine blue (US Patent 8435979) which is owned by Emory University. Imipramine blue has been licensed by Emory to ABBY Therapeutics of which JLA is a cofounder.

Biodegradable nanoparticles are being considered more often as drug carriers to address pharmacokinetic/pharmacodynamic issues, yet nano-product safety has not been systematically proven. In this study, haematological, biochemical and histological parameters were examined on 28 day daily dosing of rats with nano- or micro-particle encapsulated cyclosporine (CsA) to confirm if any changes observed were drug or carrier dependent. CsA encapsulated poly(lactide-co-glycolide) [PLGA] nano- (nCsA) and micro-particles (mCsA) were prepared by emulsion techniques. CsA (15, 30, 45 mg/kg) were administered by oral gavage to Sprague Dawley (SD) rats over 28 days. Haematological and biochemical metrics were followed with tissue histology performed on sacrifice. Whether presented as nCsA or mCsA, 45 mg/kg dose caused significant loss of body weight and lowered food consumption compared to untreated control. Across the doses, both nCsA and mCsA produce significant decreases in lymphocyte numbers compared to controls, commensurate with the proprietary product, Neoral(®) 15. Dosing with nCsA showed higher serum drug levels than mCsA presumably owing to the smaller particle size facilitating absorption. The treatment had no noticeable effects on inflammatory/oxidative stress markers or antioxidant enzyme levels, except an increase in ceruloplasmin (CP) levels for high dose nCsA/mCsA group. Further, only subtle, sub-lethal changes were observed in histology of nCsA/mCsA treated rat organs. Blank (drug-free) particles did not induce changes in the parameters studied. Therefore, it is extremely important that the encapsulated drug in the nano-products is considered when safety of the overall product is assessed rather than relying on just the particle size. This study has addressed some concerns surrounding particulate drug delivery, demonstrating safe delivery of CsA whilst achieving augmented serum concentrations., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

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., (© 2014 by The American Society of Hematology.)

Chronic myeloid leukemia (CML) stem cells are not dependent on BCR-ABL kinase for their survival, suggesting that kinase-independent mechanisms must contribute to their persistence. We observed that CML stem/progenitor cells (SPCs) produce tumor necrosis factor-α (TNF-α) in a kinase-independent fashion and at higher levels relative to their normal counterparts. We therefore investigated the role of TNF-α and found that it supports survival of CML SPCs by promoting nuclear factor κB/p65 pathway activity and expression of the interleukin 3 and granulocyte/macrophage-colony stimulating factor common β-chain receptor. Furthermore, we demonstrate that in CML SPCs, inhibition of autocrine TNF-α signaling via a small-molecule TNF-α inhibitor induces apoptosis. Moreover TNF-α inhibition combined with nilotinib induces significantly more apoptosis relative to either treatment alone and a reduction in the absolute number of primitive quiescent CML stem cells. These results highlight a novel survival mechanism of CML SPCs and suggest a new putative therapeutic target for their eradication.

MECOM oncogene expression correlates with chronic myeloid leukaemia (CML) progression. Here we show that the knockdown of MECOM (E) and MECOM (ME) isoforms reduces cell division at low cell density, inhibits colony-forming cells by 34% and moderately reduces BCR-ABL1 mRNA and protein expression but not tyrosine kinase catalytic activity in K562 cells. We also show that both E and ME are expressed in CD34(+) selected cells of both CML chronic phase (CML-CP), and non-CML (normal) origin. Furthermore, MECOM mRNA and protein expression were repressed by imatinib mesylate treatment of CML-CP CD34(+) cells, K562 and KY01 cell lines whereas imatinib had no effect in non-CML BCR-ABL1 -ve CD34(+) cells. Together these results suggest that BCR-ABL1 tyrosine kinase catalytic activity regulates MECOM gene expression in CML-CP progenitor cells and that the BCR-ABL1 oncoprotein partially mediates its biological activity through MECOM. MECOM gene expression in CML-CP progenitor cells would provide an in vivo selective advantage, contributing to CML pathogenesis., (© 2012 Blackwell Publishing Ltd.)

Omacetaxine is a natural product extract originating from Chinese medicine and finding therapeutic use as a potent myelosuppressive agent in leukemia. When planning in vitro cell biology experiments to assess omacetaxine activity against primary leukemic stem cells, it became apparent that the literature rarely describes the in vitro stability of the molecule, although accessible chromatographic methods have been published. Clearly whole organisms vs their component cells will differ in the way in which they handle xenobiotics, with the latter more dependent on physiochemical parameters such as pH and temperature in the absence of active metabolism or excretion. This could impact on the cells' experience of drug in culture. We therefore report here on examination of a modified, high-performance liquid chromatography (HPLC) method with assessment of degradant production from a 72 h solution stability study, clearly demonstrating that omacetaxine is highly stable in representative cell culture conditions (37 °C, neutral pH) and persists for many days in marked contrast to its short-half life in vivo., (Copyright © 2011 John Wiley & Sons, Ltd.)

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.

Chronic Myeloid Leukemia (CML) stem/progenitor cells, which over-express Bcr-Abl, respond to imatinib by a reversible block in proliferation without significant apoptosis. As a result, patients are unlikely to be cured owing to the persistence of leukemic quiescent stem cells (QSC) capable of initiating relapse. Previously, we have reported that intracellular levels of imatinib in primary primitive CML cells (CD34+38(lo/⁻)), are significantly lower than in CML progenitor cells (total CD34+) and leukemic cell lines. The aim of this study was to determine if potentially sub-therapeutic intracellular drug concentrations in persistent leukemic QSC may be overcome by targeted drug delivery using synthetic Low Density Lipoprotein (sLDL) particles. As a first step towards this goal, however, the extent of uptake of sLDL by leukemic cell lines and CML patient stem/progenitor cells was investigated. Results with non-drug loaded particles have shown an increased and preferential uptake of sLDL by Bcr-Abl positive cell lines in comparison to Bcr-Abl negative. Furthermore, CML CD34+ and primitive CD34+38(lo/⁻) cells accumulated significantly higher levels of sLDL when compared with non-CML CD34+ cells. Thus, drug-loading the sLDL nanoparticles could potentially enhance intracellular drug concentrations in primitive CML cells and thus aid their eradication., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Imatinib mesylate and nilotinib are highly effective at eradicating the majority of chronic myeloid leukemia (CML) cells; however, neither agent induces apoptosis of primitive CML CD34(+) cells. One possible explanation is that CD34(+) cells do not accumulate sufficient intracellular drug levels because of either inadequate active uptake or increased efflux. To determine the interaction of nilotinib with major clinically implicated drug transporters, we analyzed their interactions with MDR1 (ABCB1), MRP1 (ABCC1), ABCG2 (BCRP) and human organic cation transporter (hOCT)1 in CML cell lines and primitive (CD34(+)) primary CML cells. Nilotinib is neither dependent on active import by hOCT1, nor effluxed through the ATP-binding cassette transporters analyzed. Indeed, we found nilotinib to be an inhibitor of hOCT1, MDR1 and ABCG2. The efflux transporters MDR1, MRP1 and ABCG2 are expressed on CML CD34(+) cells at 13.5, 108 and 291% of control, respectively, although hOCT1 expression was absent; however, inhibition of efflux transporter activity did not potentiate the effect of nilotinib on apoptosis, Bcr-Abl inhibition or CML CD34(+) cell proliferation. Therefore, we have found no evidence for either active uptake of nilotinib through hOCT1 or efflux through MDR1, MRP1 or ABCG2, and it is therefore unlikely that these transporters will have any effect on the clinical response to this drug.

Objective: To investigate the interaction of imatinib mesylate (IM) with the clinically relevant adenosine triphosphate-binding cassette efflux transporter MDR1 (ABCB1) in cells from patients with chronic myeloid leukemia (CML) and to explore whether inhibition of this transporter would improve IM's efficacy in the elimination of CML CD34(+) cells by increasing cell-associated drug accumulation., Materials and Methods: Cells from newly diagnosed chronic-phase CML patients were harvested by leukapheresis and enriched to >95% CD34(+). Expression of the transporter gene MDR1 was performed by quantitative reverse transcription polymerase chain reaction. Interaction of IM with MDR1 was analyzed by substrate (rhodamine 123) displacement assay. Cell-associated levels of IM in CML CD34(+) cells were measured by high-pressure liquid chromatography. Intracellular phospho-CrkL levels, apoptosis in total CML CD34(+) cells and high-resolution tracking of cell division were assayed by flow cytometry., Results: Measurements of cell-associated IM uptake showed significantly lower drug levels in CD34(+) cells, particularly the CD38(-) subpopulation, as compared to IM-sensitive K562 cells. MDR1 was expressed at low level and dye efflux studies demonstrated very little MDR1 activity in CML CD34(+) cells. Furthermore, combination treatment of primitive CML cells with IM and the MDR1 inhibitor PSC833 did not result in elevated cell-associated IM levels. Although we observed slightly enhanced cytostasis with IM when combined with PSC833, this was independent of BCR-ABL inhibition because no associated decrease in phospho-CrkL was observed., Conclusions: Our findings demonstrate that inhibition of MDR1 neither enhances the effect of IM against BCR-ABL activity, nor significantly potentiates IM's efficiency in eliminating primitive CML cells.

Objective: This study investigated two approaches, short hairpin RNA (shRNA) and the potent ABL inhibitor, dasatinib, alone and together, to achieve complete inhibition of BCR-ABL activity in Philadelphia-positive (Ph(+)) cells., Materials and Methods: shRNA specific for BCR-ABL b3a2 were delivered, by lentiviral transduction or electroporation, to K562 cells, with or without dasatinib. mRNA and protein knockdown were measured by quantitative reverse transcriptase polymerase chain reaction, flow cytometry, and Western blotting. BCR-ABL activity was assessed by intracellular flow cytometry for pCrkL. Cell death and apoptosis were assayed using trypan blue exclusion, Annexin-V, and active caspase-3 staining., Results: Forty-eight hours after transduction or electroporation of shRNA, BCR-ABL mRNA, and protein were reduced by 75% and >90%, respectively, and sustained for 5 days. Lentiviral delivery and electroporation were equally effective. pCrkL was inhibited in association with cell death. By 5 days after transduction or electroporation, viable cells represented 50% of input, with a 12-fold reduction vs control, which expanded 6-fold. When shRNA, titrated by green fluorescent protein into low and high, was combined with dasatinib (concentration range, 0-10 nM), low shRNA was additive with low dasatinib (0.6 and 1 nM), leading to inhibition of pCrkL, induction of activated caspase-3, expression of Annexin-V, and marked reduction in viable cells., Conclusion: These results confirm that by lowering BCR-ABL levels with shRNA, complete inhibition of oncoprotein activity can be achieved with a lower concentration of dasatinib, thus providing a rationale for combining these approaches in the setting of high target expression, such as found in advanced phase disease and in the stem cell compartment.

CML (chronic myeloid leukaemia) is a myeloproliferative disease that originates in an HSC (haemopoietic stem cell) as a result of the t(9;22) translocation, giving rise to the Ph (Philadelphia chromosome) and bcr-abl oncoprotein. The disease starts in CP (chronic phase), but as a result of genomic instability, it progresses over time to accelerated phase and then to BC (blast crisis), becoming increasingly resistant to therapy. bcr-abl is a constitutively active tyrosine kinase that has been targeted by TKIs (tyrosine kinase inhibitors), including IM (imatinib mesylate), nilotinib and dasatinib. We have developed various flow cytometry techniques to enable us to isolate candidate CML stem cells from CP patients at diagnosis that efflux Hoechst dye, express CD34, lack CD38 and are cytokine-non-responsive in culture over periods of up to 12 days in growth factors. These stem cells have been shown to regenerate bcr-abl-positive haemopoiesis in immunocompromised mice upon transplantation. We previously demonstrated that IM was antiproliferative for CML stem cells but did not induce apoptosis. Clinical experience now confirms that IM may not target CML stem cells in vivo with few patients achieving complete molecular remission and relapse occurring rapidly upon drug withdrawal. Our recent efforts have focused on understanding why CML stem cells are resistant to IM and on trying to find novel ways to induce apoptosis of this population. We have shown that CML stem cells express very high levels of functional wild-type bcr-abl; no kinase domain mutations have been detected in the stem cell population. Dasatinib, a more potent multitargeted TKI than IM, inhibits bcr-abl activity more efficiently than IM but still does not induce apoptosis of the stem cell population. Most recently, we have tested a number of novel drug combinations and found that FTIs (farnesyl transferase inhibitors) have activity against CML. BMS-214662 is the most effective of these and induces apoptosis of phenotypically and functionally defined CML stem cells in vitro, as a single agent and in combination with IM or dasatinib. The effect against CML stem cells is selective with little effect on normal stem cells. The drug is also effective against BC CML stem cells and equally effective against wild-type and mutant bcr-abl, including the most resistant mutant T315I. In association with apoptosis, there is activation of caspase 8 and caspase 3, inhibition of the MAPK pathway, IAP-1 (inhibitor of apoptosis protein-1), NF-kappaB (nuclear factor kappaB) and iNOS (inducible nitric oxide synthase). Furthermore, BMS-214662 synergizes with MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1/2] inhibitors, suggesting a second mechanism other that RAS inhibition for induction of apoptosis. Our intentions are now to explore the activity of BMS-214662 in other cancer stem cell disorders and to move this preclinical work to a clinical trial combining dasatinib with BMS-214662 in CML.

Chronic myeloid leukemia (CML) stem and progenitor cells overexpress BcrAbl and are insensitive to imatinib mesylate (IM). We therefore investigated whether these cells were efficiently targeted by nilotinib. In K562, the inhibitory concentration (IC50) of nilotinib was 30 nM versus 600 nM for IM, consistent with its reported 20-fold-higher potency. However, in primary CD34(+) CML cells, nilotinib and IM were equipotent for inhibition of BcrAbl activity, producing equivalent but incomplete reduction in CrkL phosphorylation at 5 microM. CML CD34(+) cells were still able to expand over 72 hours with 5 microM of either drug, although there was a concentration-dependent restriction of amplification. As for IM, the most primitive cells (CFSE(max)) persisted and accumulated over 72 hours with nilotinib and remained caspase-3 negative. Furthermore, nilotinib with IM led to further accumulation of this population, suggesting at least additive antiproliferative effects. These results confirmed that, like IM, the predominant effect of nilotinib is antiproliferative rather than proapoptotic.

Purpose: Primitive quiescent chronic myeloid leukemia (CML) cells are biologically resistant to imatinib mesylate, an inhibitor of the p210(BCR-ABL) kinase. The present study was designed to investigate whether either continuous or intermittent exposure of these cells to granulocyte-colony stimulating factor (G-CSF) in vitro can overcome this limitation to the effectiveness of imatinib mesylate therapy., Experimental Design: CD34(+) leukemic cells were isolated from six newly diagnosed chronic phase CML patients and cultured for 12 days in serum-free medium with or without G-CSF and/or imatinib mesylate present either continuously or intermittently (three cycles of G-CSF for 0, 1, or 4 days +/- imatinib mesylate for 0, 3, or 4 days). Every 4 days, the number of residual undivided viable cells and the total number of viable cells present were measured., Results: Intermittent but not continuous exposure to G-CSF significantly accelerated the disappearance in vitro of initially quiescent CD34(+) CML cells. This resulted in 3- and 5-fold fewer of these cells remaining after 8 and 12 days, respectively, relative to continuous imatinib mesylate alone (P < 0.04). Cultures containing imatinib mesylate and intermittently added G-CSF also showed the greatest reduction in the total number of cells present after 12 days (5-fold more than imatinib mesylate alone)., Conclusion: Intermittent exposure to G-CSF can enhance the effect of imatinib mesylate on CML cells by specifically targeting the primitive quiescent leukemic elements. A protocol for treating chronic-phase CML patients with imatinib mesylate that incorporates intermittent G-CSF exposure may offer a novel strategy for obtaining improved responses in vivo.

Objective: In chronic myeloid leukemia (CML), imatinib mesylate (IM; Gleevec, Glivec) induces a G0/G1 cell-cycle block in total CD34(+) cells without causing significant apoptosis. Bryostatin-1 (bryo), a protein kinase C (PKC) modulator, was investigated for its ability to increase IM-mediated apoptosis either through induction of cycling of G0/G1 Ph(+) cells or antagonism of the IM-induced cell-cycle block., Methods: The Ph(+) K562 cell line and primary CD34(+) CML cells were studied for cell-cycle progression (PI staining), proliferation ((3)H thymidine uptake), and survival (dye exclusion)., Results: Following 48 hours exposure to IM, on average more than 80% of surviving K562 cells were in G0/G1 as compared to approximately 50% for untreated control cultures (p < 0.001). After accounting for IM-induced cell kill, the absolute number of viable G0/G1 cells was significantly increased, confirming its anti-proliferative effect. However, pretreatment for 24 hours with bryo both increased K562 total cell kill and normalized the percentage of cells recovered in G0/G1, thus reducing their absolute number. For primary CML CD34(+) cells, pretreatment with bryo prior to IM significantly enhanced cell death of both total and, critically, G0/G1 populations., Conclusion: These results suggest that carefully scheduled drug combinations that include an agent to antagonize the anti-proliferative effect of IM may prove more efficacious within the Ph(+) stem cell compartment than IM monotherapy.

Chronic myeloid leukaemia (CML) is a clonal disease of stem cell origin that develops when a single pluripotent haemopoietic stem cell acquires the Philadelphia (Ph) chromosome. The unique fusion gene product translated, p210 (Bcr-Abl), is a constitutively active tyrosine kinase that is specific to, and has a central role in the pathogenesis of, CML, making it an atractive target for drug therapy. Imatinib mesylate (IM) is one such therapy that also targets Abl, c-kit and PDGF-R tyrosine kinases. Although IM induces a much higher rate of complete cytogenetic remission (CCR), with improved tolerability and better progression free survival compared to other licensed therapies, resistance is a significant clinical problem. The most common mechanism of IM resistance is mutation of the Bcr-Abl kinase catalytic domain. In addition, molecular persistence in patients in CCR is most likely attributable to persisting Ph(+) stem cells that are insensitive to IM by unknown mechanisms and this is a major focus of current research interest. Current results from pre-clinical in vitro work on novel agents and combination strategies as well as clinical trials including immunotherapy approaches are reviewed. Despite the widespread use of molecularly targeted therapies and the development of new therapeutic drugs and strategies, it is our belief that there is a requirement for further research into and development of stem cell-directed therapies to overcome molecular persistence. It is likely that a combination of molecularly targeted therapies or treatment modalities will finally eliminate the quiescent stem cell population, leading to a "molecular cure" of CML.

Recent studies indicate that a rare population of primitive quiescent BCR-ABL(+) cells are innately insensitive to imatinib mesylate (IM) and persist after IM therapy of patients with chronic myeloid leukemia (CML). New approaches to the eradication of these cells are therefore likely to be crucial to the development of curative therapies for CML. We have now found that Ara-C, LY294002 (a PI-3 (phosphatidylinositol-3' kinase) kinase inhibitor), 17AAG (a heat-shock protein (HSP)-90 antagonist) and lonafarnib (a farnesyltransfease inhibitor) all enhance the toxicity of IM on K562 cells and on the total CD34(+) leukemic cell population from chronic phase CML patients. However, for quiescent CD34(+) leukemic cells, this was achieved only by concomitant exposure of the cells to lonafarnib. Ara-C or LY294002 alone blocked the proliferation of these cells but did not kill them, and Ara-C, LY294002 or 17AAG in combination with IM enhanced the cytostatic effect of IM but did not prevent the subsequent regrowth of the surviving leukemic cells. These studies demonstrate the importance of in vitro testing of novel agents on the subset of primary leukemic cells most likely to determine long-term treatment outcomes in vivo.

Following tendon injury, severe loss of function often occurs either as a result of obliteration of the synovial canal with fibrous scar tissue or from rupture of the repaired tendon. The role of cell engineering in tendon repair is to promote strong and rapid healing of tendon whilst at the same time facilitating rapid reconstitution of the synovial canal. Modification of the immediate inflammatory response around healing tendon has been found to be of value. Experimentally this has been achieved by neutralisation of transforming growth factor-beta over the first 3 days following injury, or by blockade of inflammatory cell binding to the CS-1 locus on fibronectin with an anti-VLA-4 antibody, or with the synthetic VLA-4 inhibitor, CS-1 peptide, in a rat model of tendon transection. It is concluded from this pilot study that the treatments described hold promise in improving outcomes of the common clinical problem of tendon injury in man.

Imatinib mesylate (Gleevec) or Glivec), a small molecule tyrosine kinase inhibitor for the treatment of chronic myeloid leukaemia, has been said to herald the dawn of a new era of rationally designed, molecularly targeted oncotherapy. Lurking on the same new horizon, however, is the age-old spectre of drug resistance. This review sets the intoxicating clinical perspective against the more sobering laboratory evidence of such divergent mechanisms of imatinib resistance as gene amplification and stem cell quiescence. Polychemotherapy has already been considered to combat resistance, but a more innovative, as yet unformulated, approach may be advocated.

The haemopoietic stem cell (HSC) has long been regarded as an archetypal, tissue specific, stem cell, capable of completely regenerating haemopoiesis after myeloablation. It has proved relatively easy to harvest HSC, from bone marrow or peripheral blood. In turn, isolation of these cells has allowed therapeutic stem cell transplantation protocols to be developed, that capitalise on their prodigious self renewal and proliferative capabilities. Ex vivo approaches have been described to isolate, genetically manipulateand expand pluripotent stem cell subsets. These techniques have been crucial to the development of gene therapy, and may allow adults to enjoy the potential advantages of cord blood transplantation. Recently, huge conceptual changes have occurred in stem cell biology. In particular, the dogma that, in adults, stem cells are exclusively tissue restricted has been questioned and there is great excitement surrounding the potential plasticity of these cells, with the profound implications that this has, for developing novel cellular therapies. Mesenchymal stem cells, multipotent adult progenitor cells and embryonic stem cells are potential sources of cells for transplantation purposes. These cells may be directed toproduce HSC, in vitro and in the future may be used for therapeutic, or drug development, purposes.

Despite the efficacy of STI571 (Glivec, Novartis, Basle, Switzerland) in treating chronic myeloid leukemia (CML), drug resistance has already been noted both in vitro and in vivo. As plasma proteins, including alpha-1-acid glycoprotein (AGP), may reduce drug efficacy through binding, AGP was investigated for its ability to interact with STI571. At all stages of CML, AGP plasma level was significantly higher than in normal controls (P <.05). The glycoprotein was purified from normal plasma and individual chronic myeloid leukemia (CML) patients' plasma by low-pressure chromatography. The influence of alpha1-acid glycoprotein (AGP), in the presence of STI571, on the proliferation of Philadelphia chromosome-positive (Ph+) cells was examined. Normal AGP, even at supraphysiological concentrations, did not block the effect of STI571 on K562-cell proliferation in vitro. Moreover, CML-derived AGP failed to block the effect of STI571 on Ph+ cells in vitro. Thus, these in vitro findings suggest that AGP will not abrogate the antileukemic activity of STI571.

In clinical trials, the tyrosine kinase inhibitor STI571 has proven highly effective in reducing leukemic cell burden in chronic myeloid leukemia (CML). The overall sensitivity of CML CD34(+) progenitor cells to STI571 and the degree to which cell death was dependent on cell cycle status were determined. Stem cells (Lin(-)CD34(+)) from the peripheral blood of patients with CML in chronic phase and from granulocyte-colony-stimulating factor-mobilized healthy donors were labeled with carboxy-fluorescein diacetate succinimidyl diester dye to enable high-resolution tracking of cell division. Then they were cultured for 3 days with and without growth factors +/- STI571. After culture, the cells were separated by fluorescence-activated cell sorting into populations of viable quiescent versus cycling cells for genotyping. For healthy controls, in the presence of growth factors, STI571 affected neither cell cycle kinetics nor recovery of viable cells. In the absence of growth factors, normal cells were unable to divide. For CML samples, in the presence or absence of growth factors, the response to STI571 was variable. In the most sensitive cases, STI571 killed almost all dividing cells; however, a significant population of viable CD34(+) cells was recovered in the undivided peak and confirmed to be part of the leukemic clone. STI571 also appeared to exhibit antiproliferative activity on the quiescent population. These studies confirm that CML stem cells remain viable in a quiescent state even in the presence of growth factors and STI571. Despite dramatic short-term responses in vivo, such in vitro insensitivity to STI571, in combination with its demonstrated antiproliferative activity, could translate into disease relapse after prolonged therapy.

Chronic Myeloid Leukemia (CML), a myeloproliferative disease of stem cell origin, is characterized by the presence of the Philadelphia (Ph) chromosome and the bcr-abl oncogene. The BCR-ABL fusion gene product, thought to be causative in CML, has multiple effects on diverse cell functions such as growth, differentiation and turnover as well as adhesion and apoptosis. Persistent Ph-negative progenitors co-exist with leukemic cells, both in the marrow and blood of patients, in the early chronic phase of the disease. Despite accumulating knowledge of hemopoiesis and the disease process, CML remains incurable with conventional chemotherapy. Nonetheless, with the efficacy of the ABL tyrosine kinase inhibitor STI-571 (signal transduction inhibitor 571) as a novel therapy in CML recently being realized in clinical trials, it is therefore timely to review our current understanding of the cell biology of this fascinating disease., (Copyright 2001 John Wiley & Sons, Ltd.)

Alpha-1-acid glycoprotein (AGP) is an extensively glycosylated acute phase protein of imprecisely defined physiological function. Nonetheless it is known that the oligosaccharide component comprising 42% of the 41 kDa molecular weight is critical to the previously described multifarious immunomodulatory functions of AGP in vitro. Complex oligosaccharides were enzymically released from AGP purified from the blood of rheumatoid arthritis sufferers by our oligosaccharide protective method. Oligosaccharide profiling was by means of high pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Monosaccharide composition analysis revealed increased fucosylation of inflammatory AGP oligosaccharide chains, suggesting the potential for expression of the tetrasaccharide antigen and E-Selectin ligand, sialyl Lewis X (sLeX). The hypothesis that AGP may function to inhibit blood cell binding to activated endothelium at E-Selectin was tested in a microtitre cell-protein binding assay. In this system we have shown that the oligosaccharide moiety of AGP, as expressed in inflammatory disease, can inhibit the sLeX/E-Selectin interaction. Thus we have identified a correlation between the abnormal glycosylation of AGP in rheumatoid arthritis and suppression of sLeX dependent cell adhesion through inhibition of E-selectin binding which could be the basis of a novel, site specific, anti-inflammatory agent.