High Throughput Drug Screening of Leukemia Stem Cells Reveals Resistance to Standard Therapies and Sensitivity to Other Agents in Acute Myeloid Leukemia

Abstract Background: Leukemia stem cells (LSCs) play a critical role in AML propagation and relapse. Other investigators have also highlighted unique gene expression profiles for the leukemia stem cell population. Here we compared the results of in vitro drug sensitivity testing against a custom panel of drugs and drug combinations for blast populations vs. leukemia stem cell populations derived from the same patients, as well as mutation analysis for a panel of 194 recurrently mutated genes in AML. Patients and Methods: Patient AML samples were obtained with IRB approval. LSCs were isolated by fluorescence-activated cell sorting (FACS) and the blast population enriched to >90% using immunomagnetic beads from blood samples from 5 patients with AML. A sixth AML patient sample was used for NOD/SCID IL2R γc−/− engraftment, in order to compare characteristics of pre- and post-engraftment subclones. Our CLIA approved custom assay includes 153 drugs and targeted agents, both FDA approved and investigational, with additional drug combinations. High throughput screens (HTS) were conducted with enriched cells adherent to matrix protein in 384 well plates with 8 concentrations of each drug spanning 4 logs. Viability was assessed with CellTiter-Glo (Promega). HTS were performed on LSCs, blasts and pre- as well as post-engraftment AML subclones from the xenograft. Dose-response curves were generated to calibrate drug resistance patterns. Mutation analysis by NGS for a panel of 194 recurrently mutated genes in AML (MyAML®) including 37 translocations was also conducted for the LSC and blast populations. Results: AML blasts and LSCs exhibited divergent drug susceptibility patterns (see volcano plot in Figure). Of 11 drugs commonly used in AML, 8 were typical chemotherapy drugs. Five of these compounds were effective against blasts, but none were effective against LSCs (p-value: 0.0256), suggesting a possible mechanism for post-treatment relapse or primary refractoriness. LSCs were also resistant to mitomycin-C, an agent that induces DNA interstrand crosslinks and DNA breaks, in contrast to blasts that were variably sensitive. Of note, we identified 12 drugs from 8 classes defined by mechanism of action that may target LSCs, in some cases preferentially, when compared with blasts. Drugs effective in preferentially targeting LSCs included tyrosine kinase inhibitors, histone deacetylase inhibitors, 1 cyclin-dependent kinase inhibitor, 1 proteasome inhibitor and 1 microtubule assembly inhibitor. Several of the drugs that efficiently killed LSCs have been studied clinically in AML, while others have theoretical or established efficacy against LSCs by drug class. Only one commonly used drug in AML, sorafenib, a multikinase inhibitor used in FLT3+ disease that may improve survival in younger patients, was effective against LSCs. Blast specific drugs include romidepsin, dinaciclib, alvocidib, ganetespib, selinexor, dorsomorphin, vinblastine, cladribine, dabrafenib, selumetinib, etoposide, torkinib and those in Figure. Blast and LSC drug susceptibility patterns were distinct for each patient. Further, the engrafted xenograft subclone grew very rapidly, was resistant to standard chemotherapy, and possessed three new deleterious mutations in KMT2C (2), SF3B1 and 1 possibly damaging mutation in NUP214, suggesting possible genetic contributions to chemotherapy resistance. We also compared mutation profiles for LSCs vs. blasts in 5 patients, and identified LSC specific mutations in WNK3, WNK4 and BUB1, each in 2 of the 5, and there were also other mutations that were LSC or blast specific. Of note, Bub1 is a mitotic checkpoint serine/threonine kinase that controls mitosis in cancer stem cells (Venere et al Cancer Discov. 2013). WNK3 and WNK4 also both encode serine/threonine protein kinases. Conclusions: The distinct drug susceptibility patterns of patient-specific LSC and blast populations highlight the potential of an individualized approach to treat AML. LSCs are resistant to S-phase agents used in standard-of-care chemotherapy. Genetically distinct minority resistant LSC subclones present at diagnosis may grow rapidly under some conditions, and contribute to drug resistance and relapse. Incorporating the results of functional drug screening focused on LSC subclones may allow more individualized treatment of AML patients and identify patient-specific therapies that lead to improved outcomes. Figure Figure. Disclosures Carson: Invivoscribe Inc.: Employment. Patay:Invivoscribe Inc.: Consultancy, Equity Ownership, Patents & Royalties. Becker:Novartis: Research Funding; Trovagene: Research Funding; CVS Caremark: Consultancy; JW Pharmaceuticals: Research Funding; Rocket Pharmaceuticals: Research Funding; Pfizer: Consultancy; Amgen: Research Funding; BMS: Research Funding; Abbvie: Research Funding; GlycoMimetics: Research Funding.

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Modeling CML Development and Drug Resistance Using iPSC Technology,

Blood ◽

10.1182/blood.v118.21.3767.3767 ◽

2011 ◽

Vol 118 (21) ◽

pp. 3767-3767

Author(s):

Kran Suknuntha ◽

Yuki Ishii ◽

Kejin Hu ◽

Jean YJ Wang ◽

Igor Slukvin

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Drug Resistance ◽

Stem Cell ◽

Blood Cells ◽

Kinase Activity ◽

Hematopoietic Cells ◽

Patient Specific ◽

Hematopoietic Progenitors ◽

Abl Kinase

Abstract Abstract 3767 Reprogramming of neoplastic cells to pluripotency provides a unique tool to personalize the exploration of tumor pathogenic mechanisms and drug resistance using iPSCs with patient-specific chromosomal abnormalities. We have developed a technology to generate transgene-free iPSCs from bone marrow and cord blood cells employing episomal vectors. Using this approach we created transgene-free iPSCs from a patient with CML in the chronic phase. CMLiPSCs showed a unique complex chromosomal translocation identified in the patinet's marrow sample while displaying typical embryonic stem cell phenotype and pluripotent differentiation potential. Importantly, these CMLiPSCs are devoid of genomic integration and expression of reprogramming factors, which are incompatible for modeling tumor development and drug response (Hu et al. Blood 117:e109). We have also shown that these CMLiPSCs contain the BCR-ABL oncogene without any detectable mutations in its kinase domain. By coculture with OP9, we generated APLNR+ mesodermal cells, MSCs, and lin-CD34+CD45+ hematopoietic progenitors from CMLiPSCs, and control BMiPSCs from a normal subject and analyzed the levels of BCR-ABL protein and tyrosine-phosphorylated (pTyr) cellular proteins in the different cell populations. The highest level of BCR-ABL protein expression was found in the in undifferentiated iPSCs, however, the overall cellular pTyr levels was lower than the control BMiPSCs, suggesting that BCR-ABL kinase activity was suppressed in the CMLiPScs. Consistent with these findings, imatinib does not inhibit the growth and survival of these CMLiPSCs. The levels of BCR-ABL protein decreased upon differentiation with a major reduction observed when cells became mesoderm. Following differentiation of CMLiPSC-derived mesoderm into the MSCs and lin-CD34+CD45+ hematopoietic progenitors, the levels of BCR-ABL protein did not change significantly, indicating that the major epigenetic regulation of BCR-ABL expression occurs during the transition to mesoderm. In spite of the decrease in BCR-ABL expression, the total pTyr levels significantly increased following transition of CMLiPSCs to mesoderm and blood cells, suggesting recovery of BCR-ABL kinase activity during differentiation. Interestingly, we found that imatinib had no effect on CFC potential of the most primitive lin-CD34+CD45+ hematopoietic progenitors derived from CMLiPSCs, while significant inhibition in hematopoietic CFC potential was observed when we used the patient's bone marrow cells. Following expansion of lin-CD34+CD45+ progenitors in serum-free medium with cytokines, we found that more differentiated hematopoietic cells became imatinib sensitive. The differential response of progenitors versus more differentiated cells to imatinib recapitulate the clinical observation that CML stem cells display innate resistance to imatinib but their differentiated progenies become sensitive to this BCR-ABL kinase inhibitor. The iPSC-based models provide several advantages for the study of CML pathogenesis. iPSCs can provide an unlimited supply of hematopoietic cells carrying patient-specific genetic abnormalities. Using well-defined temporal windows and surface markers, distinct cell subsets with tumor-initiating/tumor-propagating potential after transplantation in immunodeficient mice could be identified and used for drug screening. iPSC models make it possible to address CML stem-cell potential at various stages of differentiation for which it may be difficult to obtain samples from the patient, for example, at the hemangioblast stage. They also provide a unique opportunity to explore the interplays between epigenetics and oncogene function, as we have demonstrated using the CMLiPSCs. The major unsolved question is why CML stem cells are naturally resistant to imatinib, and this question can be addressed using the iPS system. Disclosures: Slukvin: CDI: Consultancy, Equity Ownership.

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Niche-Based Screening Reveals Leukemia Stem Cell Specific Therapeutics

Blood ◽

10.1182/blood.v118.21.760.760 ◽

2011 ◽

Vol 118 (21) ◽

pp. 760-760

Author(s):

Kimberly A. Hartwell ◽

Peter G. Miller ◽

Alison L. Stewart ◽

Alissa R. Kahn ◽

David J. Logan ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Drug Discovery ◽

Small Molecules ◽

Small Molecule ◽

High Throughput ◽

Hematopoietic Cells ◽

Leukemia Stem Cells

Abstract Abstract 760 Recent insights into the molecular and cellular processes that drive leukemia have called attention to the limitations intrinsic to traditional drug discovery approaches. To date, the majority of cell-based functional screens have relied on probing cell lines in vitro in isolation to identify compounds that decrease cellular viability. The development of novel therapeutics with greater efficacy and decreased toxicity will require the identification of small molecules that selectively target leukemia stem cells (LSCs) within the context of their microenvironment, while sparing normal cells. We hypothesized that it would be possible to systematically identify LSC susceptibilities by modeling key elements of bone marrow niche interactions in high throughput format. We tested this hypothesis by creating and optimizing an assay in which primary murine stem cell-enriched leukemia cells are plated on bone marrow stromal cells in 384-well format, and examined by a high content image-based readout of cobblestoning, an in vitro morphological surrogate of cell health and self-renewal. AML cells cultured in this way maintained their ability to reinitiate disease in mice with as few as 100 cells. 14,720 small molecule probes across diverse chemical space were screened at 5uM in our assay. Retest screening was performed in the presence of two different bone marrow stromal types in parallel, OP9s and primary mesenchymal stem cells (MSCs). Greater than 60% of primary screen hits positively retested (dose response with IC50 at or below 5 μM) on both types of stroma. Compounds that inhibited leukemic cobblestoning merely by killing the stroma were identified by CellTiter-Glo viability analysis and excluded. Compounds that killed normal primary hematopoietic stem and progenitor cell inputs, as assessed by a related co-culture screen, were also excluded. Selectivity for leukemia over normal hematopoietic cells was additionally examined in vitro by comingling these cells on stroma within the same wells. Primary human CD34+ AML leukemia and normal CD34+ cord blood cells were also tested, by way of the 5 week cobblestone area forming cell (CAFC) assay. Additionally, preliminary studies of human AML cells pulse-treated with small molecules ex vivo, followed by in vivo transplantation, provided further evidence of potent leukemia kill across genotypes. A biologically complex functional approach to drug discovery, such as the novel method described here, has previously been thought impossible, due to presumed incompatibility with high throughput scale. We show that it is possible, and that it bears fruit in a first pilot screen. By these means, we discover small molecule perturbants that act selectively in the context of the microenvironment to kill LSCs while sparing stroma and normal hematopoietic cells. Some hits act cell autonomously, and some do not, as evidenced by observed leukemia kill when only the stromal support cells are treated prior to the plating of leukemia. Some hits are known, such as parthenolide and celastrol, and some are previously underappreciated, such as HMG-CoA reductase inhibition. Others are entirely new, and would not have been revealed by conventional approaches to therapeutic discovery. We therefore present a powerful new approach, and identify drug candidates with the potential to selectively target leukemia stem cells in clinical patients. Disclosures: No relevant conflicts of interest to declare.

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Functional Genomics and Computational Approaches Identify Novel Small Molecules Targeting Quiescent Leukemia Stem Cells

Blood ◽

10.1182/blood.v126.23.1391.1391 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1391-1391

Author(s):

Costakis Frangou ◽

Jason Den Haese ◽

Jordan Warunek ◽

Scott Portwood ◽

Norma J Nowak ◽

...

Keyword(s):

Stem Cells ◽

Drug Resistance ◽

Signaling Pathways ◽

Research Funding ◽

Cell Tracking ◽

Leukemia Stem Cells ◽

Self Renewal ◽

Hematopoietic Stem ◽

Nsg Mice

Abstract Chemotherapy or targeted cancer therapies have greatly improved the treatment outcome of patients with leukemia; however, many will ultimately die because of disease relapse and development of drug resistance. Leukemias are cancers of the blood cells that result from alteration of the normal physiological constraints that regulate hematopoietic stem cells (HSCs). General characteristics of leukemia stem cells (LSCs) such as self-renewal, self-protection and proliferative quiescence represent inherent mechanisms that at least partially explain drug resistance and recurrence in post-therapy leukemia patients. Acute myeloid leukemia (AML) is a heterogeneous disease, both biologically and clinically, in which a number of distinct genetic abnormalities have been described. Several recent studies suggest that this heterogeneity extends to LSCs and can vary between patient subgroups, and even within individual patients. Moreover, the complexity of AML is further complicated by the existence of functionally diverse leukemic and preleukemic clones. Accordingly, the hierarchical organization of AML suggests that this may be relevant to current therapies that primarily target proliferating progenitors/blast cells, which lack self-renewal capacity, and not LSCs. In the current study, we rationalized that understanding how LSCs differ from normal HSCs at the molecular level, is an essential first step towards developing novel targeted therapies and achieving permanent disease remission. Despite the identification of novel LSC-specific markers, there is considerable heterogeneity in expression of these markers amongst AML patients. However, in addition to marker-enrichment strategies, LSCs can be identified by virtue of their quiescent and slow-cycling properties. For example, label-retaining cells can be isolated and used in functional assays but significant technical limitations impede broad utility of this approach. To this end, we describe the development and use of novel multi-fluorescent protein markers and DNA bar codes integrated into the cellular genomes by lentivirus, as single-cell tracking devices for monitoring LSCs in vivo. We demonstrate how LSCs can transition between a "proliferation phase" and a "quiescence phase" in vivo. Furthermore, using high-throughput quantitative transcriptome sequencing (Q-RNA-Seq) and RNAi genetic perturbation's focusing on well-defined self-renewal signaling pathways, we develop a differential network-based model to identify LSC-specific genes and subsequently prioritize/rank candidates as potential drug targets. In the current study, we identify several molecular targets deregulated in quiescent versus proliferating LSCs and a mutual set of signaling pathways that facilitate leukemic transformation downstream of diverse initiating mutations/lesions. Remarkably, both quiescent and dividing LSCs but not HSCs, were 'addicted' to SSRP1 - an essential component of the ubiquitous FACT chromatin remodeling complex. Two orally available quinacrine-related DNA-intercalating compounds inhibiting function of FACT (CBL0100 and CBL0175, respectively) suppressed LSC proliferation in vitro and in vivo, as demonstrated by production of leukemic clonogenic cells (CFU) and long-term engraftment of immunodeficient NSG mice, by simultaneous inhibition of NF-kB (stimulated and basal forms) and activation of p53. Furthermore, in a secondary transplantation experiment, leukemic cells obtained from CBL0175 treated mice (primary) failed to engraft into secondary NSG mice in a serial transplantation model by selectively targeting the LSC compartment. Collectively, we present a novel network-based polypharmacology approach that provides unique opportunities to preferentially ablate LSCs (quiescent and dividing types), with potentially profound clinical implications. Disclosures Frangou: Cellecta: Employment. Portwood:ImmunoGen: Research Funding. Wang:ImmunoGen: Research Funding.

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How to Overcome Myeloma Stem Cell Resistance to Therapy - Targeting the Stem Cell Niche

Blood ◽

10.1182/blood.v116.21.sci-6.sci-6 ◽

2010 ◽

Vol 116 (21) ◽

pp. SCI-6-SCI-6

Author(s):

Constantine S. Mitsiades

Keyword(s):

Stem Cells ◽

Drug Resistance ◽

Stem Cell ◽

Cancer Stem Cells ◽

Cancer Stem Cell ◽

Tumor Cells ◽

Cell Lines ◽

Cell Population ◽

Research Funding ◽

Accessory Cells

Abstract Abstract SCI-6 The concept of cancer stem cells has attracted again intense research interest, as the drug resistance attributed to this infrequent subpopulation of tumor cells could explain how patients can relapse even after prolonged complete clinical, biochemical, radiologic or even molecular remissions. In multiple myeloma (MM), several aspects of the cancer stem cell concept remain to be elucidated, including the potential heterogeneity of this cell subpopulation or whether CD138+ expression is incompatible or not with a MM stem cell. As these questions are being resolved, emerging data highlight that the drug resistance of MM cells with clonogenic/stem cell-like features is heavily influenced by interactions with non-malignant accessory cells of the local microenvironment, including bone marrow stromal cells (BMSCs). Indeed, transcriptional signatures of “stemness”, as identified in normal stem cells or cancer stem cells from other neoplasias, are detected in the bulk population of MM cell lines and are upregulated after MM cell interaction with BMSCs. MM cell lines and primary tumor cells contain subpopulations with clonogenic potential, such as the side population (SP) cells. SP cells, detected by low intracellular accumulation of Hoechst 33342 dye (in contrast to the tumor's “main population” (MP), are considered an enriched source of tumor-initiating cells in diverse neoplasias and were detected among CD138− CD20+ CD27+ clonogenic cells in primary MM samples. Interaction with BMSCs increases the viability of SP cells and their percentage within the MM cell population. While interaction with BMSCs or other accessory cells of the microenvironmental niche suppresses the anti-MM activity of glucocorticoids, conventional chemotherapeutics and certain investigational agents, other agents (e.g. immunomodulatory thalidomide derivatives (IMIDs), such as lenalidomide) have increased activity against MM SP cells in the context of this tumor-microenvironment interaction. These observations suggest that MM cells with stem cell-like features exhibit functional plasticity depending on which specific microenvironmental niche they interact with. The Hedgehog, Wnt and Notch pathways, as well as regulators of chromatin remodeling, e.g. histone demethylases, have emerged as putative links between drug resistance, “cancer stemness” and how these functional outcomes are modulated by the local microenvironment in MM. These pathways, as well as embryonic stem cell-associated antigens (e.g. SOX2), represent intriguing targets for investigational therapies. However, clinical translation of such treatments has notable challenges, as conventional criteria for response assessment may not accurately reflect the treatment's impact on clonogenic tumor cells. Progression-free survival is considered a more appropriate endpoint for cancer stem-cell targeting agents, its assessment, however, may be confounded without concomitant treatment that suppresses the bulk of the tumor. Consequently, candidate cancer stem cell-targeting agents may have to be evaluated in combination with regimens (including lenalidomide-bortezomib-Dex (RVD) or other combinations built around the therapeutic “backbone” of proteasome inhibition and IMIDs) which potently target the bulk MM cell population and induce high rates of complete/near complete responses. Further improvements of this dual targeting of clonogenic and bulk tumor cells may be facilitated by recently developed high-throughput platforms (e.g. compartment-specific bioluminescence imaging, CS-BLI) which screen, in the presence vs. absence of stroma or other accessory cells, large numbers of anti-tumor agents and combinations thereof against the bulk tumor cell population or its clonogenic compartments. These new platforms will inform the rational design of regimens that will hopefully improve the long-term outcome of MM patients by suppressing a clonogenic/stem cell-like tumor compartment and circumventing microenvironment-dependent drug resistance. Disclosures: Mitsiades: Millennium: Consultancy, Honoraria; Novartis Pharmaceuticals: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Merck &Co.: Consultancy, Honoraria; Kosan Pharmaceuticals: Consultancy, Honoraria; Pharmion: Consultancy, Honoraria; Centrocor: Consultancy, Honoraria; PharmaMar: Patents & Royalties; OSI Pharmaceuticals: Research Funding; Amgen Pharmaceuticals: Research Funding; AVEO Pharma: Research Funding; EMD Serono: Research Funding; Sunesis: Research Funding; Gloucester Pharmaceuticals: Research Funding.

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CXCL12 Knock-out Enhances Leukemia Stem Cell Response to Combination Chemotherapy Plus Tyrosine Kinase Inhibition in Flt3-ITD Acute Myeloid Leukemia

Blood ◽

10.1182/blood-2020-142579 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 7-8

Author(s):

Nick R Anderson ◽

Hui Li ◽

Mason W Harris ◽

Shaowei Qiu ◽

Amanda K Mullen ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Drug Resistance ◽

Mesenchymal Stem Cells ◽

Stem Cell ◽

Conflicts Of Interest ◽

Single Agent ◽

Fold Increase ◽

Long Term Effects ◽

Leukemia Stem Cell

One of the most common mutations in adult AML is a constitutively activating internal tandem duplication in the juxtamembrane domain of the Flt3 receptor (Flt3-ITD), which portends poor prognosis due to high recurrence rates and defines a distinct subtype of disease with unique features and biology. Although several FLT3 TKIs have been developed for clinical use, responses to these drugs, especially as single agents, are limited and are not sustained. The objective of our study was to determine the contribution of bone marrow stromal populations to LSC resistance to Flt3-targeted TKI in Flt3-ITD AML. We utilized a newly generated Flt3-ITD TET2flox/flox Mx1-cre mouse model of AML, as well as primary Flt3-ITD TET2 mutant AML patient samples, to identify phenotypic populations with leukemia initiating capacity (LIC) in Flt3-ITD AML. In the animal model, administration of pIpC leads to deletion of TET2 and development of AML characterized by leukocytosis, accumulation of blasts, splenomegaly, anemia, thrombocytopenia, and lethality. Limiting dilution transplantation of FACS-sorted ST-HSC, MPP and GMP populations revealed that LIC were absent from GMPs and almost exclusively limited to the phenotypic ST-HSC population (calculated stem cell frequencies: <1:180,000, 1:63,635, and 1:2,730 for GMP, MPP, and ST-HSC, respectively). We similarly found that in samples from human Flt3-ITD TET2 mutant AML patients LIC capacity was restricted to primitive HSPC populations (Lin-CD34+CD38-), and was not seen in committed GMP (Lin-CD34+CD38+CD123+CD45RA+). We characterized bone marrow stromal cells in Flt3-ITD AML mice by flow cytometry on collagenase digested bone fragments. We also transplanted murine AML cells into CXCL12-GFP mice to assess alterations in CXCL12-expressing stromal populations in AML bone marrow. We found expansion of several stromal populations in AML vs. WT mice, including a 3.5-fold increase in mesenchymal stem cells (CD45-Ter119-CD31-VECadherin-Sca1+CD51+) and a 1.5-fold increase in osteoprogenitors (CD45-Ter119-CD31-VECadherin-Sca1-CD51+). CXCL12 expression, however, was greater than 2-fold higher in osteoprogenitors and 2-fold lower in mesenchymal stem cells in AML vs. WT mice. We also showed that Flt3-ITD AML HSPCs have nearly 2-fold higher CXCR4 expression than WT HSPCs. These data taken together supported further exploration of the role of a CXCL12-expressing niche in supporting Flt3-ITD AML LSC. To assess the effect of CXCL12 deletion from the marrow microenvironment on AML TKI response, we transplanted murine AML cells into CXCL12flox/flox UBC-cre mice and control Cre-ve mice. We found that AML developing in Cre-ve control mice was resistant to single agent Flt3 TKI (AC220, Quizartinib) treatment, but that CXCL12 deletion modestly improved response to TKI. We next tested a combination of standard-of-care "7+3" chemotherapy (cytarabine + doxorubicin) and AC220, and found that this approach resulted in more effective and selective, but only partial, reduction of leukemia cells in this model. We found that control AML mice showed an initial response to combination chemo + TKI, but developed disease recurrence by 3 weeks of treatment. In contrast, CXCL12-deleted AML mice maintained peripheral blood response for up to 3 weeks, and showed enhanced suppression of LIC-containing populations compared to control mice. We are now performing secondary transplants using BM cells harvested from these treated mice to assess long-term effects on leukemia stem cell capacity. We are also testing the effect of the combination of chemotherapy and TKI following osteoblast-specific deletion of CXCL12, using CXCL12flox/flox BGLAP-cre mice, to assess whether osteoblastic cells are the source of CXCL12 responsible for this effect. In conclusion, our results suggest that LSC in Flt3-ITD AML are found within a primitive phenotypic ST-HSC population as opposed to GMP populations as seen in some other types of AML. Furthermore, CXCL12-expressing bone marrow microenvironmental cells contribute to drug resistance in AML LSC and global knockout of CXCL12 enhances drug response in these populations. Our studies support a potential role for a CXCL12-expressing osteoprogenitor niche in supporting Flt3-ITD AML LSC growth and drug resistance, targeting of which could improve responses and outcomes in Flt3-ITD AML. Disclosures No relevant conflicts of interest to declare.

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Wnt-Pathway Directed Compound Targets Blast Crisis and Chronic Phase CML Leukemia Stem Progenitors.

Blood ◽

10.1182/blood.v114.22.2168.2168 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2168-2168 ◽

Cited By ~ 6

Author(s):

Luke F Peterson ◽

Anjanette J Turbiak ◽

Diane M Giannola ◽

Nicholas Donato ◽

Hollis H.D. Showalter ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Wnt Pathway ◽

Blast Crisis ◽

Chronic Phase ◽

Leukemia Stem Cells ◽

Apoptotic Response ◽

Leukemia Stem Cell ◽

Cd34 Cells ◽

Wnt Inhibitor

Abstract Abstract 2168 Poster Board II-145 The deregulated tyrosine kinase associated with t(9;22) fusion protein BCR-ABL is efficiently targeted by tyrosine kinase inhibitors (Imatinib, Nilotinib and Dasatinib). It is generally believed that most patients have residual disease. The inability to eliminate the refractory leukemia stem cell in chronic myeloid leukemia (CML) is not well understood. The refractory stem cell is present despite effective inhibition of the BCR-ABL kinase in these cells, and dissociation between kinase inhibition and cell death implies lack of dependency on BCR-ABL aberrant kinase activity, unlike the one seen in more mature CML cells. Thus the oncogene addictive dependency of these leukemia stem cells may be overcome by intrinsic and/or extrinsic factors/pathways. One such pathway involved in hematopoeitic stem cell maintenance is the Wnt/β-catenin signaling pathway. BCR-ABL signaling is known to directly activate the Wnt/β-catenin pathway. The loss of function of a negative regulator of the Wnt/β-catenin pathway, known as GSK3β is associated with CML progression from chronic phase to the blast phase. Lastly, the loss of β-catenin in murine models impairs the self renewal capacity of both the normal and the BCR-ABL+ leukemia stem cell. Thus this pathway is important during various stages of the disease. We explored the effect of Wnt inhibition using a novel Wnt pathway inhibitor (AG-214, University of Michigan). AG-214 is structurally related to a previously reported Wnt-inhibitor. AG-214 is able to antagonize β-catenin/TCF in luciferase reporter assays, and expression of Wnt targets in colon cancer cell lines. We utilized a serum free culture system with 5 added cytokines and treated both CML blast crisis CD34+ as well as chronic phase CD34+ cells with AG-214. Our in vitro experiments show that primary blast crisis CD34+ cells are induced to undergo apoptosis at an IC-50 of approximately 2 μM. Furthermore, combination of 1.25 μM of AG-214 with 2 μM Imatinib achieved greater than 50% apoptosis. Analysis of chronic phase CML CD34+ cells showed that targeting of Wnt/β-catenin pathway requires higher concentration of the Wnt-inhibitor (>2.5 μM), and that the addition of Imatinib can cooperate to enhance the apoptotic response. Furthermore, chronic phase progenitors (Lin-CD38+/CD34+) are more sensitive to lower concentrations of AG-214 whereas 5 μM is required to induce significant apoptosis of ∼70% in the primitive leukemia stem cell (Lin-/CD38-/CD34+) population, and addition of 2 μM Imatinib increased their apoptotic response to ∼84%. Normal CD34+ cells do not undergo significant apoptosis with 5 μM of AG-214 (∼10%) even when combined with 2 μM Imatinib (∼20%). Targeting of the Wnt/β-catenin pathway enhances apoptosis in both blast crisis and chronic phase CML progenitors and leukemia stem cells. Disclosures: No relevant conflicts of interest to declare.

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Deciphering the Mechanisms of Osteoblast-Induced Resistance of Leukemic Stem Cell (LSC) in Ph+ CML: Role of PI3-Kinase, BRD4 and MYC and Development of Strategies to Overcome Osteoblast-Induced Resistance

Blood ◽

10.1182/blood-2021-152415 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 1481-1481

Author(s):

Yueksel Filik ◽

Karin Bauer ◽

Barbara Peter ◽

Emir Hadzijusufovic ◽

Georg Greiner ◽

...

Keyword(s):

Stem Cells ◽

Flow Cytometry ◽

Drug Resistance ◽

Endothelial Cells ◽

Stem Cell ◽

Cell Line ◽

Induced Resistance ◽

Research Funding ◽

Mtor Inhibitor ◽

Pi3 Kinase

Abstract Chronic myeloid leukemia (CML) is a stem cell neoplasms characterized by the chromosome translocation t(9;22) and the related BCR-ABL1 fusion gene. Therapy with BCR-ABL1 kinase inhibitors is highly effective in the treatment of CML and deep molecular responses are achieved in most patients. However, not all patients respond to these drugs due to resistance of leukemic stem cells (LSC). Recent data suggest that the disease-related microenvironment, known as the stem cell niche contributes to drug resistance and relapse in CML. So far, little is known about the resistance mechanisms protecting niche cells in the bone marrow of patients with CML. We have recently shown that osteoblasts are a major site of LSC-mediated resistance against BCR-ABL1-targeting drugs in CML. In the current study, we screened for drugs that are able to suppress growth and viability of osteoblasts and/or other niche-related cells and can thereby overcome drug resistance of CML LSC. Proliferation was analyzed by determining 3H-thymidine uptake in niche-related cells and apoptosis was measured by Annexin-V/DAPI-staining and flow cytometry. We found that the dual PI3 kinase (PI3K) and mTOR inhibitor BEZ235 and the selective pan-PI3K inhibitor copanlisib suppress proliferation of primary osteoblasts (BEZ235 IC 50: 0.05 µM; copanlisib IC 50: 0.05 µM), the osteoblastic cell line CAL-72 (BEZ235 IC 50: 0.5 µM; copanlisib IC 50: 1 µM), primary human umbilical vein endothelial cells (BEZ235 IC 50: 0.5 µM; copanlisib IC 50: 0.5 µM) and the endothelial cell line HMEC-1 (BEZ235 IC 50: 1 µM; copanlisib IC 50: 1 µM), whereas no comparable effects were seen with the mTOR inhibitor rapamycin. As determined by flow cytometry, BEZ235 and copanlisib suppressed the expression of phosphorylated (p) pAKT and pS6 in endothelial cells and osteoblasts whereas rapamycin downregulated pS6 expression but did not decrease expression of pAKT. Moreover, we found that BEZ235 and copanlisib cooperate with nilotinib and ponatinib in suppressing growth and viability of osteoblasts and endothelial cells. Furthermore, BEZ235 and copanlisib were found to overcome osteoblast-induced resistance of K562, KU812 cells, and primary CD34 +/CD38 − CML LSC against nilotinib and ponatinib. This effect was also seen when CAL-72 cells were first exposed to BEZ235 or copanlisib and washed before co-cultures with CML cells and BCR-ABL1 inhibitors were prepared, suggesting that osteoblast inhibition was a crucial event capable of disrupting LSC resistance in these co-cultures. Of all other drugs tested, only the BRD4-targeting drug JQ1 was found to suppress CAL72-induced resistance in the CML cell lines KU812 and K562, suggesting that osteoblast-induced resistance of CML cells is also mediated by a BRD4-MYC pathway. In a next step, we examined the expression of resistance-mediating immune checkpoint molecules on CML cells (KU812, K562, LSC) and on osteoblasts by flow cytometry. We found that CML cells and CAL72 cells constitutively express PD-L1 and that interferon-gamma (IFN-G) promotes the expression of PD-L1 in all cell types tested. Moreover, we found that the BRD4 blocker JQ1 and the BRD4-degrader dBET6 suppress the IFN-G-induced upregulation of PD-L1 in CML LSC and osteoblasts. In conclusion, our data show that osteoblast-induced resistance of CML stem cells is mediated by a PI3K-dependent pathway and BRD4/MYC, and that BRD4-inhibition or BRD4-degradation counteracts osteoblast-induced resistance of CML (stem) cells against BCR-ABL1 inhibitors and PD-L1 expression on CML LSC and osteoblasts. We hypothesize that checkpoint inhibition may assist in drug-induced eradication of CML LSC and thus in the development of curative drug therapies in Ph + CML. Disclosures Hoermann: Novartis: Honoraria. Gleixner: Pfizer: Honoraria; Abbvie: Honoraria; BMS: Honoraria; Incyte: Honoraria; Novartis: Honoraria. Sperr: AbbVie, BMS-Celgene, Daiichi Sankyo, Deciphera, Incyte, Jazz, Novartis, Pfizer, StemLine, Thermo Fisher: Honoraria, Research Funding. Valent: Novartis: Honoraria; Pfizer: Honoraria, Research Funding; Celgene/BMS: Honoraria, Research Funding; Incyte: Honoraria, Research Funding; OAP Orphan Pharmaceuticals: Honoraria.

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Modeling the functional heterogeneity of leukemia stem cells: role of STAT5 in leukemia stem cell self-renewal

Blood ◽

10.1182/blood-2009-06-227603 ◽

2009 ◽

Vol 114 (19) ◽

pp. 3983-3993 ◽

Cited By ~ 52

Author(s):

Michael Heuser ◽

Laura M. Sly ◽

Bob Argiropoulos ◽

Florian Kuchenbauer ◽

Courteney Lai ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Constitutive Expression ◽

Leukemia Stem Cells ◽

Functional Heterogeneity ◽

Self Renewal ◽

Leukemia Stem Cell ◽

Gm Csf ◽

Stat Signaling

Abstract Although the cancer stem cell (CSC) concept implies that CSCs are rare, recent reports suggest that CSCs may be frequent in some cancers. We hypothesized that the proportion of leukemia stem cells would vary as a function of the number of dysregulated pathways. Constitutive expression of MN1 served as a 1-oncogene model, and coexpression of MN1 and a HOX gene served as a 2-oncogene model. Leukemia-initiating cell (LIC) number and in vitro expansion potential of LICs were functionally assessed by limiting dilution analyses. LIC expansion potential was 132-fold increased in the 2- compared with the 1-oncogene model, although phenotypically, both leukemias were similar. The 2-oncogene model was characterized by granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity and activated STAT/ERK signaling. GM-CSF hypersensitivity of the 2-oncogene model (MN1/HOXA9) was lost in Stat5b−/− cells, and the LIC expansion potential was reduced by 86- and 28-fold in Stat5b−/− and Stat1−/− cells, respectively. Interestingly, in 201 acute myeloid leukemia (AML) patients, coexpression of MN1 and HOXA9 was restricted to patients with the poorest prognosis and was associated with highly active STAT signaling. Our data demonstrate the functional heterogeneity of LICs and show that STAT signaling is critical for leukemia stem cell self-renewal in MN1- and HOXA9-expressing leukemias.

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Regulation of Self-Renewal through Modulation of Let-7 Stem Cell Regulatory Family of microRNAs in Chronic Myeloid Leukemia Stem Cells

Blood ◽

10.1182/blood.v124.21.4527.4527 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4527-4527

Author(s):

Maria Anna Zipeto ◽

Qingfei Jiang ◽

Leslie A Crews ◽

Angela Court Recart ◽

Catriona HM Jamieson

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Chronic Myeloid Leukemia ◽

Myeloid Leukemia ◽

Research Funding ◽

Blast Crisis ◽

Family Members ◽

Leukemia Stem Cells ◽

Self Renewal ◽

Qrt Pcr

Abstract Introduction Chronic myeloid leukemia (CML) was one of the first malignancies shown to be initiated in hematopoietic stem cells by the BCR-ABL1 oncogene and sustained in blast crisis (BC) by progenitor cells that co-opt stem cell properties and behave like leukemia stem cells (BC LSCs). The BCR-ABL fusion oncogene encodes a constitutively active tyrosine kinase BCR-ABL. Although tyrosine kinase inhibitor (TKI) therapy targeting BCR-ABL suppresses CML during the chronic phase (CP), progenitors undergo expansion as a consequence of subsequent genetic and epigenetic alterations that fuel blast crisis transformation, BC LSC generation and TKI resistance. Self-renewing human BC LSCs harbor increased expression of Inflammation responsive adenosine deaminase acting on RNA (ADAR1), which can alter transcript as well as microRNA (miRNA) maturation, splicing and translation by Adenosine (A)-to-Inosine (I) editing of double stranded RNA. miRNAs are a family of small non-coding RNA molecules that regulate gene expression at a post-transcriptional level by inhibiting protein translation and/or reducing mRNA stability. Eukaryotic cells employ miRNAs in diverse biological processes including cell proliferation, differentiation, pluripotency and self-renewal. The stem cell pluripotency RNA binding protein LIN28B plays critical roles in BC transformation of CML. In this study we sought to characterize CML related-oncogenes, such as BCR-ABL, JAK2 and ADAR1, alone or in stromal co-culture in terms of their ability to regulate LSC self-renewal through modulation of let-7 /LIN28B stem cell transcriptional regulatory axis. Methods MiRNAs were extracted from purified CD34+ cells derived from CP and BC CML patient samples as well as cord blood by RNeasy microKit (QIAGEN) and let-7 expression was evaluated by qRT-PCR using miScript Primer assay (QIAGEN). CD34+ cord blood (n=3) were transduced with lentiviral human BCR-ABL, JAK2, let-7a, wild type ADAR1 and ADAR1 mutant, which lacks a functional deaminase domain. Then, 72 hours after transduction, lentivirally transduced cells were plated on irradiated SL/M2 cells. After 5 days of culture, cells were collected for RNA and microRNA extraction. Transduction efficiency and LIN28B levels were evaluated by qRT-PCR and let-7 expression was quantified by qRT-PCR using miScript primer assay. Hematopoietic Progenitor and Replating assaywere performed on lenti-let-7a-overexpressing CB cells to assess differentiation, survival and self-renewal capacity. Results Lentiviral overexpression of human BCR-ABL in CD34+ CB did not induce any significant change in let-7 family members and LIN28B expression in absence of stromal co-culture. However, stromal co-culture of BCR-ABL overexpressing CB led to the significant downregulation of members of the let-7 family as well as to upregulation of their target gene LIN28B, thus suggesting that extrinsic microenvironmental cues are necessary for modulating let-7 family levels in presence of BCR-ABL. Notably, qRT-PCR of CB transduced with JAK2 showed significant upregulation of ADAR1 in the absence of stroma, thus suggesting that JAK2 might be a mediator of inflammatory cytokine-driven ADAR1 activation. Lentiviral overexpression of both human JAK2 and ADAR1 significantly reduced the expression of let-7 family members and induced up-regulation of LIN28B. Interestingly, lentiviral overexpression of ADAR1 mutant did not induce any significant change in most let-7 family members. Finally, lentiviral overexpression of let-7a induced significant reduction in survival and self-renewal. Conclusion These finding suggest that BCR-ABL requires extrinsic signals from the niche to modulate self-renewal of BC LSCs. Conversely, lentiviral JAK2 overexpression induces activation of aberrant RNA editing and subsequent reduction of let-7 family members in the absence of the niche. Interestingly, experiments with ADAR1 mutant, suggest that ADAR1 downregulates most of the let-7 family members in a RNA–editing dependent way manner. In summary these findings suggest a novel mechanism for BC LSC generation that may have utility in prognostication and selective LSCs targeting. Disclosures Jamieson: J&J: Research Funding; Sanofi: Research Funding, Travel Support, Travel Support Other; Roche: Research Funding.

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Stem cell therapies and benefaction of somatic cell nuclear transfer cloning in COVID-19 era

Stem Cell Research & Therapy ◽

10.1186/s13287-021-02334-5 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Birbal Singh ◽

Gorakh Mal ◽

Vinod Verma ◽

Ruchi Tiwari ◽

Muhammad Imran Khan ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Regenerative Medicine ◽

Somatic Cell ◽

Somatic Cell Nuclear Transfer ◽

Nuclear Transfer ◽

Drug Testing ◽

Human Interaction ◽

Patient Specific ◽

Wide Range

Abstract Background The global health emergency of COVID-19 has necessitated the development of multiple therapeutic modalities including vaccinations, antivirals, anti-inflammatory, and cytoimmunotherapies, etc. COVID-19 patients suffer from damage to various organs and vascular structures, so they present multiple health crises. Mesenchymal stem cells (MSCs) are of interest to treat acute respiratory distress syndrome (ARDS) caused by SARS-CoV-2 infection. Main body Stem cell-based therapies have been verified for prospective benefits in copious preclinical and clinical studies. MSCs confer potential benefits to develop various cell types and organoids for studying virus-human interaction, drug testing, regenerative medicine, and immunomodulatory effects in COVID-19 patients. Apart from paving the ways to augment stem cell research and therapies, somatic cell nuclear transfer (SCNT) holds unique ability for a wide range of health applications such as patient-specific or isogenic cells for regenerative medicine and breeding transgenic animals for biomedical applications. Being a potent cell genome-reprogramming tool, the SCNT has increased prominence of recombinant therapeutics and cellular medicine in the current era of COVID-19. As SCNT is used to generate patient-specific stem cells, it avoids dependence on embryos to obtain stem cells. Conclusions The nuclear transfer cloning, being an ideal tool to generate cloned embryos, and the embryonic stem cells will boost drug testing and cellular medicine in COVID-19.

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