The molecular etiology of human progenitor reprogramming into self-renewing leukemia stem cells (LSC) has remained elusive. Although DNA sequencing has uncovered spliceosome gene mutations that ...promote alternative splicing and portend leukemic transformation, isoform diversity also may be generated by RNA editing mediated by adenosine deaminase acting on RNA (ADAR) enzymes that regulate stem cell maintenance. In this study, whole-transcriptome sequencing of normal, chronic phase, and serially transplantable blast crisis chronic myeloid leukemia (CML) progenitors revealed increased IFN-γ pathway gene expression in concert with BCR-ABL amplification, enhanced expression of the IFN-responsive ADAR1 p150 isoform, and a propensity for increased adenosine-to-inosine RNA editing during CML progression. Lentiviral overexpression experiments demonstrate that ADAR1 p150 promotes expression of the myeloid transcription factor PU.1 and induces malignant reprogramming of myeloid progenitors. Moreover, enforced ADAR1 p150 expression was associated with production of a misspliced form of GSK3β implicated in LSC self-renewal. Finally, functional serial transplantation and shRNA studies demonstrate that ADAR1 knockdown impaired in vivo self-renewal capacity of blast crisis CML progenitors. Together these data provide a compelling rationale for developing ADAR1-based LSC detection and eradication strategies.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Abstract Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is an oncoembryonic antigen. Because of its expression on the cell surface of leukemia cells from patients with chronic lymphocytic ...leukemia (CLL), but not on normal B-cells or other postpartum tissues, ROR1 is an attractive candidate for targeted therapies. UC-961 is a first-in-class humanized monoclonal antibody that binds the extracellular domain of ROR1. In this article we outline some of the preclinical studies leading to an investigational new drug designation, enabling clinical studies in patients with CLL.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Formative research suggests that a human embryonic stem cell-specific alternative splicing gene regulatory network, which is repressed by Muscleblind-like (MBNL) RNA binding proteins, is involved in ...cell reprogramming. In this study, RNA sequencing, splice isoform-specific quantitative RT-PCR, lentiviral transduction, and in vivo humanized mouse model studies demonstrated that malignant reprogramming of progenitors into self-renewing blast crisis chronic myeloid leukemia stem cells (BC LSCs) was partially driven by decreased MBNL3. Lentiviral knockdown of MBNL3 resulted in reversion to an embryonic alternative splice isoform program typified by overexpression of CD44 transcript variant 3, containing variant exons 8–10, and BC LSC proliferation. Although isoform-specific lentiviral CD44v3 overexpression enhanced chronic phase chronic myeloid leukemia (CML) progenitor replating capacity, lentiviral shRNA knockdown abrogated these effects. Combined treatment with a humanized pan-CD44 monoclonal antibody and a breakpoint cluster region - ABL proto-oncogene 1, nonreceptor tyrosine kinase (BCR-ABL1) antagonist inhibited LSC maintenance in a niche-dependent manner. In summary, MBNL3 down-regulation–related reversion to an embryonic alternative splicing program, typified by CD44v3 overexpression, represents a previously unidentified mechanism governing malignant progenitor reprogramming in malignant microenvironments and provides a pivotal opportunity for selective BC LSC detection and therapeutic elimination.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Dormant leukemia stem cells (LSC) promote therapeutic resistance and leukemic progression as a result of unbridled activation of stem cell gene expression programs. Thus, we hypothesized that 1) ...deregulation of the hedgehog (Hh) stem cell self-renewal and cell cycle regulatory pathway would promote dormant human LSC generation and 2) that PF-04449913, a clinical antagonist of the GLI2 transcriptional activator, smoothened (SMO), would enhance dormant human LSC eradication.
To test these postulates, whole transcriptome RNA sequencing (RNA-seq), microarray, qRT-PCR, stromal co-culture, confocal fluorescence microscopic, nanoproteomic, serial transplantation and cell cycle analyses were performed on FACS purified normal, chronic phase (CP) chronic myeloid leukemia (CML), blast crisis (BC) phase CML progenitors with or without PF-04449913 treatment.
Notably, RNA-seq analyses revealed that Hh pathway and cell cycle regulatory gene overexpression correlated with leukemic progression. While lentivirally enforced GLI2 expression enhanced leukemic progenitor dormancy in stromal co-cultures, this was not observed with a mutant GLI2 lacking a transactivation domain, suggesting that GLI2 expression prevented cell cycle transit. Selective SMO inhibition with PF-04449913 in humanized stromal co-cultures and LSC xenografts reduced downstream GLI2 protein and cell cycle regulatory gene expression. Moreover, SMO inhibition enhanced cell cycle transit and sensitized BC LSC to tyrosine kinase inhibition in vivo at doses that spare normal HSC.
In summary, while GLI2, forms part of a core HH pathway transcriptional regulatory network that promotes human myeloid leukemic progression and dormant LSC generation, selective inhibition with PF-04449913 reduces the dormant LSC burden thereby providing a strong rationale for clinical trials predicated on SMO inhibition in combination with TKIs or chemotherapeutic agents with the ultimate aim of obviating leukemic therapeutic resistance, persistence and progression.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Leukemia initiating cells (LIC) contribute to therapeutic resistance through acquisition of mutations in signaling pathways, such as NOTCH1, that promote self-renewal and survival within supportive ...niches. Activating mutations in NOTCH1 occur commonly in T cell acute lymphoblastic leukemia (T-ALL) and have been implicated in therapeutic resistance. However, the cell type and context specific consequences of NOTCH1 activation, its role in human LIC regeneration, and sensitivity to NOTCH1 inhibition in hematopoietic microenvironments had not been elucidated.
We established humanized bioluminescent T-ALL LIC mouse models transplanted with pediatric T-ALL samples that were sequenced for NOTCH1 and other common T-ALL mutations. In this study, CD34(+) cells from NOTCH1(Mutated) T-ALL samples had higher leukemic engraftment and serial transplantation capacity than NOTCH1(Wild-type) CD34(+) cells in hematopoietic niches, suggesting that self-renewing LIC were enriched within the NOTCH1(Mutated) CD34(+) fraction. Humanized NOTCH1 monoclonal antibody treatment reduced LIC survival and self-renewal in NOTCH1(Mutated) T-ALL LIC-engrafted mice and resulted in depletion of CD34(+)CD2(+)CD7(+) cells that harbor serial transplantation capacity.
These results reveal a functional hierarchy within the LIC population based on NOTCH1 activation, which renders LIC susceptible to targeted NOTCH1 inhibition and highlights the utility of NOTCH1 antibody targeting as a key component of malignant stem cell eradication strategies.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Progesterone in hormonal preparations increases the incidence of breast cancer. Tissue factor (TF), the initiator of the extrinsic coagulation pathway, is associated with metastasis in a wide variety ...of cancers. We demonstrate herein that TF mRNA and protein are up-regulated by progesterone in the breast cancer cell line ZR-75. Epidermal growth factor, also associated with increased breast cancer risk, did not regulate TF. The increase in TF is both rapid and transient; increasing after 6 h, reaching a maximum at 24 h, before decreasing to basal levels at 72 h. Sucrose gradient experiments demonstrated that TF is located in the heavy fraction of the plasma membrane, although caveolin-1 is not expressed in ZR-75. To understand the physiological implications of an increase in TF, we performed coagulation and invasion assays. An increase in TF corresponded to an increase in procoagulant activity. Furthermore, progesterone increased the invasion of ZR-75 cells through a matrigel, an effect that was blocked by an antibody against TF. Because TF expression is associated with an enhanced risk of metastasis, we postulate that the progesterone-dependent up-regulation of TF provides a survival advantage to burgeoning breast cancer cells and may contribute to the increased risk of cancer associated with combined hormone replacement therapy.
Post-transcriptional adenosine-to-inosine RNA editing mediated by adenosine deaminase acting on RNA1 (ADAR1) promotes cancer progression and therapeutic resistance. However, ADAR1 editase-dependent ...mechanisms governing leukemia stem cell (LSC) generation have not been elucidated. In blast crisis chronic myeloid leukemia (BC CML), we show that increased JAK2 signaling and BCR-ABL1 amplification activate ADAR1. In a humanized BC CML mouse model, combined JAK2 and BCR-ABL1 inhibition prevents LSC self-renewal commensurate with ADAR1 downregulation. Lentiviral ADAR1 wild-type, but not an editing-defective ADAR1E912A mutant, induces self-renewal gene expression and impairs biogenesis of stem cell regulatory let-7 microRNAs. Combined RNA sequencing, qRT-PCR, CLIP-ADAR1, and pri-let-7 mutagenesis data suggest that ADAR1 promotes LSC generation via let-7 pri-microRNA editing and LIN28B upregulation. A small-molecule tool compound antagonizes ADAR1’s effect on LSC self-renewal in stromal co-cultures and restores let-7 biogenesis. Thus, ADAR1 activation represents a unique therapeutic vulnerability in LSCs with active JAK2 signaling.
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•JAK2 signaling activates ADAR1-mediated A-to-I RNA editing•JAK2 and BCR-ABL1 signaling converge on ADAR1 activation through STAT5a•ADAR1-mediated microRNA editing impairs let-7 biogenesis and enhances LSC self-renewal•JAK2 and BCR-ABL1 inhibition reduces ADAR1 expression and prevents LSC self-renewal
Zipeto, Court, and colleagues show a pivotal role for let-7 microRNA editing in leukemia stem cell self-renewal. Impairment of let-7 is dependent on JAK2 and BCR-ABL-mediated activation of ADAR1 editing. This provides a novel mechanism of malignant reprogramming that can be targeted through combined JAK2 and BCR-ABL or ADAR1 inhibition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cancers of the reproductive tract account for 12% of all malignancies in women. As previous studies have shown that oestrogen metabolites can cause apoptosis, we characterised the effect of oestrogen ...and oestrogen metabolites on non-cancerous and cancerous human endometrial cells. Herein, we demonstrate that 2-methoxyoestradiol (2ME), but not 17β-oestradiol, induces apoptosis in cancer cell lines and primary cultured tumours of endometrial origin. In contrast, 2ME had no effect on cell viability of corresponding normal tissue. This ability of 2ME to induce apoptosis does not require oestrogen receptor activation, but is associated with increased entry into the G2/M phases of the cell cycle and the activation of both the intrinsic and the extrinsic apoptotic pathways. The selective behaviour of 2ME on cancerous as opposed to normal tissue may be due to a reduction in 17β-hydroxysteroid dehydrogenase type II levels in cancer cells and to a differential down-regulation of superoxide dismutase. Furthermore, we demonstrate that pre-treatment with 2ME enhances the sensitivity of reproductive tract cancer cells to the apoptotic drug tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), without the loss in cell viability to normal cells incurred by currently chemotherapeutic drugs. In conclusion, 2ME, alone or in combination with TRAIL, may be an effective treatment for cancers of uterine origin with minimal toxicity to corresponding healthy female reproductive tissue.
Age-related human hematopoietic stem cell (HSC) exhaustion and myeloid-lineage skewing promote oncogenic transformation of hematopoietic progenitor cells into therapy-resistant leukemia stem cells ...(LSCs) in secondary acute myeloid leukemia (AML). While acquisition of clonal DNA mutations has been linked to increased rates of secondary AML for individuals older than 60 years, the contribution of RNA processing alterations to human hematopoietic stem and progenitor aging and LSC generation remains unclear. Comprehensive RNA sequencing and splice-isoform-specific PCR uncovered characteristic RNA splice isoform expression patterns that distinguished normal young and aged human stem and progenitor cells (HSPCs) from malignant myelodysplastic syndrome (MDS) and AML progenitors. In splicing reporter assays and pre-clinical patient-derived AML models, treatment with a pharmacologic splicing modulator, 17S-FD-895, reversed pro-survival splice isoform switching and significantly impaired LSC maintenance. Therapeutic splicing modulation, together with monitoring splice isoform biomarkers of healthy HSPC aging versus LSC generation, may be employed safely and effectively to prevent relapse, the leading cause of leukemia-related mortality.
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•Splice isoform signatures distinguish normal and malignant progenitor cell aging•Pro-survival splice isoform switching is a feature of secondary AML LSC•Splice isoform biomarkers provide diagnostic and therapeutic targets for AML•Spliceosome modulators impair AML LSC maintenance in humanized pre-clinical models
Crews et al. show that unique splice isoform signatures distinguish normal human HSC and progenitor cell aging from AML and MDS progenitors. Widespread deregulation of splicing factor gene expression typified AML progenitors and sensitized them to small-molecule splicing-targeted agents, supporting the utility of spliceosome modulation in leukemia stem cell eradication and anti-aging strategies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Aberrant activation of the Hedgehog (Hh) signaling pathway is involved in a variety of cancers, and required for maintenance of the leukemic stem cell (LSC) populations in several ...experimental systems. Cumulative evidence suggests that dormant self-renewing LSC contribute to acute myeloid leukemia (AML) propagation and relapse by evading conventional chemotherapies that target cycling cells. PF-04449913 (PF-913) is a novel oral small molecule inhibitor that selectively binds and targets Smoothened (SMO), a membrane protein regulating the Hh pathway. Treatment with PF-913 has shown promising results regarding safety, tolerability, and early signs of efficacy in patients with hematologic malignancies including AML. However, the detailed mechanisms and biomarkers remain to be elucidated in AML therapy. Using the co-culturing system with HS-5 stromal cells, the colony assay system, and the immunodeficient NOD/SCID/IL2rγnull (NOG) mouse model serially xenotransplanted with primary AML cells, we examined the effects of PF-913 on LSC population and AML propagation. In primary AML cells, the Hh signaling pathway was activated more in CD34-positive cells than CD34-negative cells. Ex vivo-treatment with PF-913 inhibited proliferation and induced minimal cell death in leukemia cell lines and primary AML cells. However, in vivo-treatment with PF-913 attenuated leukemia-initiation potential in AML cells through the serial transplantation system (0% human-CD45+ cells in bone marrow cells derived from the 2nd recipient mice), while limiting reduction of tumor burden in the primary leukemia system. Also in the colony-assay system using primary AML cells, treatment with PF-913 reduced serially colony formation. In leukemia cell lines and primary AML cells, treatment with PF-913 decreased the quiescent (Hoechst-33342low/Pyronin-Ylow) cell population as well as down-regulated mRNA encoding downstream effector GLIs and GLI-targeting molecules in the canonical Hh pathway. In the in vivo-NOG mouse system, comprehensive Gene Set Enrichment Analysis (GSEA) revealed that PF-913 treatment modulated cell cycle regulation and self-renewal signaling in primary AML cells. Moreover, combined treatment with PF-913 abrogated resistance to Ara-C in AML cell lines co-cultured with HS-5 stromal cells and sensitized AML cells to Ara-C in the cutaneous tumor system. Our findings imply that selective Hh inhibitor, PF-913 treatment can attenuate the leukemia-initiation potential in AML cells by modulation of cell cycle regulation and self-renewal signaling, and can also improve AML therapy through sensitizing dormant LSC to chemotherapy and overcoming the resistance in the bone marrow microenvironment.
Citation Format: Yosuke Minami, Nobuaki Fukushima, Anil Sadarangani, Hironobu Minami, Catriona Jamieson, Tomoki Naoe. Treatment with Hedgehog inhibitor PF-913 attenuates leukemia-initiation potential in acute myeloid leukemia cells. abstract. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1884. doi:10.1158/1538-7445.AM2014-1884
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