KDM6 demethylases integrate DNA repair gene regulation and loss of KDM6A sensitizes human acute myeloid leukemia to PARP and BCL2 inhibition

Acute myeloid leukemia (AML) is a heterogeneous, aggressive malignancy with dismal prognosis and with limited availability of targeted therapies. Epigenetic deregulation contributes to AML pathogenesis. KDM6 proteins are histone-3-lysine-27-demethylases that play context-dependent roles in AML. We inform that KDM6-demethylase function critically regulates DNA-damage-repair-(DDR) gene expression in AML. Mechanistically, KDM6 expression is regulated by genotoxic stress, with deficiency of KDM6A-(UTX) and KDM6B-(JMJD3) impairing DDR transcriptional activation and compromising repair potential. Acquired KDM6A loss-of-function mutations are implicated in chemoresistance, although a significant percentage of relapsed-AML has upregulated KDM6A. Olaparib treatment reduced engraftment of KDM6A-mutant-AML-patient-derived xenografts, highlighting synthetic lethality using Poly-(ADP-ribose)-polymerase-(PARP)-inhibition. Crucially, a higher KDM6A expression is correlated with venetoclax tolerance. Loss of KDM6A increased mitochondrial activity, BCL2 expression, and sensitized AML cells to venetoclax. Additionally, BCL2A1 associates with venetoclax resistance, and KDM6A loss was accompanied with a downregulated BCL2A1. Corroborating these results, dual targeting of PARP and BCL2 was superior to PARP or BCL2 inhibitor monotherapy in inducing AML apoptosis, and primary AML cells carrying KDM6A-domain mutations were even more sensitive to the combination. Together, our study illustrates a mechanistic rationale in support of a novel combination therapy for AML based on subtype-heterogeneity, and establishes KDM6A as a molecular regulator for determining therapeutic efficacy.

Identification of the global miR-130a targetome reveals a role for TBL1XR1 in hematopoietic stem cell self-renewal and t(8;21) AML

Gene expression profiling and proteome analysis of normal and malignant hematopoietic stem cells (HSCs) point to shared core stemness properties. However, discordance between mRNA and protein signatures highlights an important role for post-transcriptional regulation by microRNAs (miRNAs) in governing this critical nexus. Here, we identify miR-130a as a regulator of HSC self-renewal and differentiation. Enforced expression of miR-130a impairs B lymphoid differentiation and expands long-term HSCs. Integration of protein mass spectrometry and chimeric AGO2 crosslinking and immunoprecipitation (CLIP) identifies TBL1XR1 as a primary miR-130a target, whose loss of function phenocopies miR-130a overexpression. Moreover, we report that miR-130a is highly expressed in t(8;21) acute myeloid leukemia (AML), where it is critical for maintaining the oncogenic molecular program mediated by the AML1-ETO complex. Our study establishes that identification of the comprehensive miRNA targetome within primary cells enables discovery of genes and molecular networks underpinning stemness properties of normal and leukemic cells.

Nicotinamide phosphoribosyltransferase inhibitors selectively induce apoptosis of AML stem cells by disrupting lipid homeostasis

Current treatments for acute myeloid leukemia (AML) are often ineffective in eliminating leukemic stem cells (LSCs), which perpetuate the disease. Here, we performed a metabolic drug screen to identify LSC-specific vulnerabilities and found that nicotinamide phosphoribosyltransferase (NAMPT) inhibitors selectively killed LSCs, while sparing normal hematopoietic stem and progenitor cells. Treatment with KPT-9274, a NAMPT inhibitor, suppressed the conversion of saturated fatty acids to monounsaturated fatty acids, a reaction catalyzed by the stearoyl-CoA desaturase (SCD) enzyme, resulting in apoptosis of AML cells. Transcriptomic analysis of LSCs treated with KPT-9274 revealed an upregulation of sterol regulatory-element binding protein (SREBP)-regulated genes, including SCD, which conferred partial protection against NAMPT inhibitors. Inhibition of SREBP signaling with dipyridamole enhanced the cytotoxicity of KPT-9274 on LSCs in vivo. Our work demonstrates that altered lipid homeostasis plays a key role in NAMPT inhibitor-induced apoptosis and identifies NAMPT inhibition as a therapeutic strategy for targeting LSCs in AML.

Mapping the cellular origin and early evolution of leukemia in Down syndrome

Children with Down syndrome have a 150-fold increased risk of developing myeloid leukemia, but the mechanism of predisposition is unclear. Because Down syndrome leukemogenesis initiates during fetal development, we characterized the cellular and developmental context of preleukemic initiation and leukemic progression using gene editing in human disomic and trisomic fetal hematopoietic cells and xenotransplantation. GATA binding protein 1 (GATA1) mutations caused transient preleukemia when introduced into trisomy 21 long-term hematopoietic stem cells, where a subset of chromosome 21 microRNAs affected predisposition to preleukemia. By contrast, progression to leukemia was independent of trisomy 21 and originated in various stem and progenitor cells through additional mutations in cohesin genes. CD117+/KIT proto-oncogene (KIT) cells mediated the propagation of preleukemia and leukemia, and KIT inhibition targeted preleukemic stem cells.

An ERG Enhancer-Based Reporter Identifies Leukemia Cells with Elevated Leukemogenic Potential Driven by ERG-USP9X Feed-Forward Regulation

Acute leukemia is a rapidly progressing blood cancer with low survival rates. Unfavorable prognosis is attributed to insufficiently characterized subpopulations of leukemia stem cells (LSC) that drive chemoresistance and leukemia relapse. Here we utilized a genetic reporter that assesses stemness to enrich and functionally characterize LSCs. We observed heterogeneous activity of the ERG+85 enhancer-based fluorescent reporter in human leukemias. Cells with high reporter activity (tagBFP^High) exhibited elevated expression of stemness and chemoresistance genes and demonstrated increased clonogenicity and resistance to chemo- and radiotherapy as compared with their tagBFP^Neg counterparts. The tagBFP^High fraction was capable of regenerating the original cellular heterogeneity and demonstrated increased invasive ability. Moreover, the tagBFP^High fraction was enriched for leukemia-initiating cells in a xenograft assay. We identified the ubiquitin hydrolase USP9X as a novel ERG transcriptional target that sustains ERG+85-positive cells by controlling ERG ubiquitination. Therapeutic targeting of USP9X led to preferential inhibition of the ERG-dependent leukemias. Collectively, these results characterize human leukemia cell functional heterogeneity and suggest that targeting ERG via USP9X inhibition may be a potential treatment strategy in patients with leukemia. SIGNIFICANCE: This study couples a novel experimental tool with state-of-the-art approaches to delineate molecular mechanisms underlying stem cell-related characteristics in leukemia cells.

A novel method for detecting the cellular stemness state in normal and leukemic human hematopoietic cells can predict disease outcome and drug sensitivity

Acute leukemia is an aggressive blood malignancy with low survival rates. A high expression of stem-like programs in leukemias predicts poor prognosis and is assumed to act in an aberrant fashion in the phenotypically heterogeneous leukemia stem cell (LSC) population. A lack of suitable genome engineering tools that can isolate LSCs based on their stemness precludes their comprehensive examination and full characterization. We hypothesized that tagging endogenous stemness-regulatory regions could generate a genome reporter for the putative leukemia stemness-state. Our analysis revealed that the ERG  + 85 enhancer region can serve as a marker for stemness-state and a fluorescent lentiviral reporter was developed that can accurately recapitulate the endogenous activity. Using our novel reporter, we revealed cellular heterogeneity in several leukemia cell lines and patient-derived samples. Alterations in reporter activity were associated with transcriptomic and functional changes that were closely related to the hematopoietic stem cell (HSC) identity. Notably, the differentiation potential was skewed towards the erythro-megakaryocytic lineage. Moreover, an ERG  + 85^High fraction of AML cells could regenerate the original cellular heterogeneity and was enriched for LSCs. RNA-seq analysis coupled with in silico drug-screen analysis identified 4HPR as an effective inhibitor of ERG  + 85^High leukemia growth. We propose that further utilization of our novel molecular tool will identify crucial determinants of LSCs, thus providing a rationale for their therapeutic targeting.

Abstract PR07: MicroRNA-130a regulates hematopoietic stem cell self-renewal and erythroid differentiation

Hematopoietic homeostasis is tightly regulated by controlling the balance between quiescence, self-renewal, and lineage-commitment of hematopoietic stem cells (HSCs). Deregulation of these processes and aberrant acquisition of stem cell-like properties is believed to be central to the pathogenesis of hematologic malignancies, such as myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). However, little is known about the molecular networks maintaining the stem cell state and the epigenetic and post-transcriptional regulation of determinants that control these programs. MicroRNAs (miRNAs) represent a large class of post-transcriptional regulators that mediate repression of multiple target mRNAs. We have previously shown that miR-126 and miR-125a are differentially expressed across the human hematopoietic hierarchy and function to control self-renewal and cell fate decisions by reinforcing gene expression programs in a developmental stage-specific manner (Lechman et al. Cell Stem Cell, 2012; Wojtowitz et al. Cell Stem Cell, 2016).

To identify additional miRNA(s) that play a functional role in hematopoiesis, we performed an in vivo competitive repopulation screen in which candidate miRNAs were overexpressed (OE) in human CD34+CD38- umbilical cord blood (CB) cells and subsequently transplanted into immune-deficient mice for 24 weeks. miR-130a was shown to enhance long-term hematopoietic reconstitution and chosen for further investigation. At 12 and 24 weeks after transplantation, enforced miR-130a expression (including an mOrange-mO+ indicator) conferred a competitive advantage over untransduced CB cells demonstrated by increased CD45+ human chimerism in the injected femur (IF), bone marrow (BM), and spleen of recipient mice. miR-130 enforced expression (miR-130a OE) increased the proportion of mO+/hCD45+ cells by approximately 2- and 5-fold after 12 and 24 weeks of repopulation, respectively. miR-130a OE xenografts showed multilineage engraftment with increased myeloid lineage output and significantly enhanced erythroid development at the expense of B-lymphoid lineage output in BM and spleen of recipient mice. Detailed flow cytometry analysis of xenografts revealed accumulation of immature GlyA+/CD71+/CD36+ erythroid progenitors, suggesting a differentiation block at the polychromic erythroblast stage. Notably, miR-130a OE induced the expansion of CD34+CD38- Lin- compartment and increased proportion of CD34+CD38-CD90+CD45RA- immuno-phenotypic HSC. Secondary transplantation involving limiting dilution analysis revealed approximately a 10-fold increase in HSC frequency, consistent with a role of miR-130a in HSC self-renewal. The lineage potential of miR-130OE primitive cells was assessed in vitro using single-cell stromal-based myelo-erythroid differentiation assay. Enforced expression of miR-130a in human HSC and multipotent progenitors (MPP) resulted in the decreased frequency of unipotent myeloid output (M colonies) and increased multipotent output (M/E/Meg, E/Meg colonies), supporting a role of miR-130a in erythroid-megakaryocytic fate specification. Label-free semiquantitative proteomics and subsequent gene set enrichment pathway analysis (GSEA) were performed on miR-130a OE and control transduced CD34+ CB cells to elucidate molecular mechanism(s) of miR-130a function. We identified that miR-130a modulated pathways centered on translational regulation and chromatin modification. Together, our data suggest that miR-130a plays a role in the regulation of the HSC self-renewal and erythroid differentiation. Given that several studies showed aberrant expression of miR-130a in MDS and some AML subtypes, it is important to delineate the role of miR-130a in normal hematopoiesis to comprehend its potential contribution to the development of hematologic malignancies.

This abstract is also being presented as Poster 40.

Citation Format: Gabriela Krivdova, Eric R. Lechman, Erwin M. Schoof, Veronique Voisin, Olga I. Gan, Aaron Trotman-Grant, Karin G. Hermans, Gary D. Bader, John E. Dick. MicroRNA-130a regulates hematopoietic stem cell self-renewal and erythroid differentiation [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr PR07.

Global proteomics dataset of miR-126 overexpression in acute myeloid leukemia

A deep proteomics analysis was conducted on a primary acute myeloid leukemia culture system to identify potential protein targets regulated by miR-126. Leukemia cells were transduced either with an empty control lentivirus or one containing the sequence for miR-126, and resulting cells were analyzed using ultra-high performance liquid chromatography (UHPLC) coupled with high resolution mass spectrometry. The mass spectrometry data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PRIDE: PXD001994. The proteomics data and statistical analysis described in this article is associated with a research article, “miR-126 regulates distinct self-renewal outcomes in normal and malignant hematopoietic stem cells” (Lechman et al., 2016) [1], and serves as a resource for researchers working in the field of microRNAs and their regulation of protein levels.

Ectopic miR-125a Expression Induces Long-Term Repopulating Stem Cell Capacity in Mouse and Human Hematopoietic Progenitors

Umbilical cord blood (CB) is a convenient and broadly used source of hematopoietic stem cells (HSCs) for allogeneic stem cell transplantation. However, limiting numbers of HSCs remain a major constraint for its clinical application. Although one feasible option would be to expand HSCs to improve therapeutic outcome, available protocols and the molecular mechanisms governing the self-renewal of HSCs are unclear. Here, we show that ectopic expression of a single microRNA (miRNA), miR-125a, in purified murine and human multipotent progenitors (MPPs) resulted in increased self-renewal and robust long-term multi-lineage repopulation in transplanted recipient mice. Using quantitative proteomics and western blot analysis, we identified a restricted set of miR-125a targets involved in conferring long-term repopulating capacity to MPPs in humans and mice. Our findings offer the innovative potential to use MPPs with enhanced self-renewal activity to augment limited sources of HSCs to improve clinical protocols.

miRNA-126 Orchestrates an Oncogenic Program in B Cell Precursor Acute Lymphoblastic Leukemia

MicroRNA (miRNA)-126 is a known regulator of hematopoietic stem cell quiescence. We engineered murine hematopoiesis to express miRNA-126 across all differentiation stages. Thirty percent of mice developed monoclonal B cell leukemia, which was prevented or regressed when a tetracycline-repressible miRNA-126 cassette was switched off. Regression was accompanied by upregulation of cell-cycle regulators and B cell differentiation genes, and downregulation of oncogenic signaling pathways. Expression of dominant-negative p53 delayed blast clearance upon miRNA-126 switch-off, highlighting the relevance of p53 inhibition in miRNA-126 addiction. Forced miRNA-126 expression in mouse and human progenitors reduced p53 transcriptional activity through regulation of multiple p53-related targets. miRNA-126 is highly expressed in a subset of human B-ALL, and antagonizing miRNA-126 in ALL xenograft models triggered apoptosis and reduced disease burden.

miR-126 Regulates Distinct Self-Renewal Outcomes in Normal and Malignant Hematopoietic Stem Cells

To investigate miRNA function in human acute myeloid leukemia (AML) stem cells (LSC), we generated a prognostic LSC-associated miRNA signature derived from functionally validated subpopulations of AML samples. For one signature miRNA, miR-126, high bioactivity aggregated all in vivo patient sample LSC activity into a single sorted population, tightly coupling miR-126 expression to LSC function. Through functional studies, miR-126 was found to restrain cell cycle progression, prevent differentiation, and increase self-renewal of primary LSC in vivo. Compared with prior results showing miR-126 regulation of normal hematopoietic stem cell (HSC) cycling, these functional stem effects are opposite between LSC and HSC. Combined transcriptome and proteome analysis demonstrates that miR-126 targets the PI3K/AKT/MTOR signaling pathway, preserving LSC quiescence and promoting chemotherapy resistance.

Reduced lymphoid lineage priming promotes human hematopoietic stem cell expansion

The hematopoietic system sustains regeneration throughout life by balancing self-renewal and differentiation. To stay poised for mature blood production, hematopoietic stem cells (HSCs) maintain low-level expression of lineage-associated genes, a process termed lineage priming. Here, we modulated expression levels of Inhibitor of DNA binding (ID) proteins to ask whether lineage priming affects self-renewal of human HSCs. We found that lentiviral overexpression of ID proteins in cord blood HSCs biases myeloerythroid commitment at the expense of lymphoid differentiation. Conversely, reducing ID2 expression levels increases lymphoid potential. Mechanistically, ID2 inhibits the transcription factor E47 to attenuate B-lymphoid priming in HSCs and progenitors. Strikingly, ID2 overexpression also results in a 10-fold expansion of HSCs in serial limiting dilution assays, indicating that early lymphoid transcription factors antagonize human HSC self-renewal. The relationship between lineage priming and self-renewal can be exploited to increase expansion of transplantable human HSCs and points to broader implications for other stem cell populations.

Abstract 2292: Enforced expression of miR-125b promotes the in vivo expansion of human Lin- CB multi-lymphoid progenitors (MLP) and AML leukemia stem cells

We recently demonstrated stem cell gene signatures predict clinical outcome in acute myeloid leukemia (AML) (Eppert et. al., Nature Medicine, 2011). Concomitant to this work, miRNA signatures for hematopoietic stem cells (HSC) and leukemia stem cells (LSC) were also generated. miRNA are small non-coding RNAs that regulate the translation and mRNA stability of protein coding genes with significant roles in the maintenance of human HSC (Lechman et. al., Cell Stem Cell, in press). To understand the functional role of miRNA in normal human blood development, we undertook an in vivo over-expression screen of 10 miRNA candidates over-represented in HSC and LSC. Lineage depleted human umbilical cord blood cells (Lin- CB) were transduced with lentivirus expressing either a candidate miRNA or control vector and xeno-transplanted into NSG mice. Three miRNA displayed a competitive growth advantage while 4 miRNA induced a growth disadvantage along with skewing of lineage output. A top LSC array candidate, miR-125b, showed the most pronounced phenotype with overt expansion of marked cells, enlarged spleens and increased lymphoid and erythroid output. Detailed analysis of miR-125b grafts revealed a greatly expanded MLP population, in comparison to HSC and MPP. Furthermore, upon enforced in vivo expression of miR-125b in 3 AML patient samples, we observed large increases in the CD34+CD117+ populations for all three AML samples, suggesting increased LSC numbers. Secondary LDA experiments revealed up to a 34 fold increase in LSC activity in comparison to control vector transduced AML cells. These data suggest that miR-125b normally functions in the limited self-renewal of lymphoid committed early progenitors and this function may be usurped during leukemogenesis to enhance LSC self-renewal.

Citation Format: Eric R. Lechman, Karin G. Hermans, Stephanie Dobson, Kolja Eppert, Mark Minden, John E. Dick. Enforced expression of miR-125b promotes the in vivo expansion of human Lin- CB multi-lymphoid progenitors (MLP) and AML leukemia stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2292. doi:10.1158/1538-7445.AM2013-2292

Attenuation of miR-126 activity expands HSC in vivo without exhaustion

Lifelong blood cell production is governed through the poorly understood integration of cell-intrinsic and -extrinsic control of hematopoietic stem cell (HSC) quiescence and activation. MicroRNAs (miRNAs) coordinately regulate multiple targets within signaling networks, making them attractive candidate HSC regulators. We report that miR-126, a miRNA expressed in HSC and early progenitors, plays a pivotal role in restraining cell-cycle progression of HSC in vitro and in vivo. miR-126 knockdown by using lentiviral sponges increased HSC proliferation without inducing exhaustion, resulting in expansion of mouse and human long-term repopulating HSC. Conversely, enforced miR-126 expression impaired cell-cycle entry, leading to progressively reduced hematopoietic contribution. In HSC/early progenitors, miR-126 regulates multiple targets within the PI3K/AKT/GSK3β pathway, attenuating signal transduction in response to extrinsic signals. These data establish that miR-126 sets a threshold for HSC activation and thus governs HSC pool size, demonstrating the importance of miRNA in the control of HSC function.

Abstract 1013: Enriched miR-126 bioactivity marks the primitive compartment in human AML and regulates leukemia stem cell numbers

Previous work has shown miRNAs are dysregulated in acute myeloid leukemia (AML), however, there is little known regarding miRNA expression and function in human leukemia stem cells (LSC). In order to elucidate the role of miRNA in LSC, we performed miRNA profiling on fractionated subpopulations of primary AML patient samples. Supervised analysis guided by the in vivo SCID leukemia initiating cell (SL-IC) capacity of each sub-population generated a unique miRNA signature associated with LSC enriched fractions. The biological activity of our top candidate, miR-126, was confirmed at single cell resolution by using a novel bidirectional lentivirus miRNA reporter system in vitro and within primary AML patient samples xenografted into immune-deficient NSG mice. These data suggest that primitive AML cells may express high levels of bioactive miR-126 relative to more “differentiated” blast populations. To test this hypothesis, we FACS sorted miR-126 genetic reporter vector transduced primary AML patient samples and transplanted these populations into immune-compromised secondary mouse recipients. The results of these proof-of-concept experiments demonstrates our ability to prospectively isolate LSC enriched fractions in all 4 AML patient samples tested using only a single biomarker, miR-126. Finally, to understand the functional relevance of miR-126 expression within primitive human AML cells, stable enforced expression and knockdown of miR-126 was achieved using lentiviral vectors. Enforced expression in four primary AML xenografts resulted in a several fold increase of CD34+CD117+ lentivirus marked leukemia cells after 12 weeks. In addition, the miR-126/OE cells showed reduced differentiation marker expression (CD14, CD15) with no significant differences in AML graft size. To determine if the expanded population had SL-IC activity or was a downstream leukemic progenitor, limiting dilution assays were performed by transplantation of FACS sorted lentivirus marked cells into secondary recipient mice for 12 weeks. A 3-20 fold increase in LSC activity was observed with miR-126 forced expression compared to control cells. These data suggest that high levels of miR-126 bioactivity support self-renewal/maintenance of primitive AML cells at the cost of aberrant differentiation. We performed microarray analysis of a primitive human AML cells after miR-126/OE and miR-126/KD. The principal signalling pathway(s) under direct control of miR-126 in primitive AML cells were revealed by subjecting our array data to Gene Set Enrichment Analysis (GSEA) in combination with several published miRNA target prediction algorithms. In summary, this work demonstrates that miR-126 is more abundant and biologically active within the leukemia stem/progenitor cell compartment of the AML functional hierarchy and serves to regulate AML stem cell numbers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1013. doi:1538-7445.AM2012-1013

Abstract 3330: Functional characterization of microRNAs identified in human acute myeloid leukemia stem cells

Human acute myeloid leukemia (AML) is organized as a functional cellular hierarchy and is sustained by a rare population of leukemia stem cells (LSC). AML is a heterogeneous disease with a relapse rate of up to 80% depending on age of the patient and AML subtype. Recent work suggests that leukemia stem cell properties influence therapy response, overall survival, and relapse of the disease. In order develop more effective novel therapies that target this rare cell population; it is imperative that we better understand LSCs at the molecular level. Although it is generally accepted that oncogenic mutations underlie cancer initiation and progression, most studies have focused on protein coding genes. However, there is increasing recognition that non-coding RNAs can also play a role in leukemogenesis. MicroRNAs (miRNAs) are a family of small non-coding RNAs that function as important regulators of the translation of protein-coding genes. In order to identify LSC specific miRNAs, we fractionated 16 primary human AML samples into four sub-populations, each of which were xenotransplanted into immune-deficient mice to evaluate in vivo leukemia initiating capacity. Global miRNA expression profiling was performed on each population and a LSC specific miRNA signature generated by supervised analysis guided by the ability to initiate leukemia in vivo. Similarly, a human cord blood derived hematopoietic stem cell (HSC) enriched miRNA signature was also established. From these lists, we selected ten promising candidate miRNAs to assess for biological function. We have initiated a functional screen to determine the role of the candidate miRNAs using both in vivo and in vitro assays. Preliminary results show that enforced expression of two miRNA candidates strongly reduced engraftment capability of HSCs over untransduced HSCs in immune-deficient recipients. Moreover, enforced expression of three additional miRNA candidates show a competitive growth advantage of transduced HSCs over untransduced HSCs and compared to controls. Also, enforced expression of one of these three miRNAs in the surrogate LSCs of a unique leukemia cell line induces a strong proliferative advantage over untransduced LSCs in an in vitro culture setting. In conclusion, thus far we have identified five miRNAs that affect hematopoietic stem cell properties. Further in vivo and in vitro analysis will determine whether these miRNAs are suitable targets for therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3330. doi:1538-7445.AM2012-3330

Human, viral or mutant human IL-10 expressed after local adenovirus-mediated gene transfer are equally effective in ameliorating disease pathology in a rabbit knee model of antigen-induced arthritis

IL-10 is a Th2 cytokine important for inhibiting cell-mediated immunity while promoting humoral responses. Human IL-10 (hIL-10) has anti-inflammatory, immunosuppressive as well as immunostimulatory characteristics, whereas viral IL-10 (vIL-10), a homologue of hIL-10 encoded by Epstein Barr virus (EBV), lacks several immunostimulatory functions. The immunostimulatory characteristic of hIL-10 has been attributed to a single amino acid, isoleucine at position 87, which in vIL-10 is alanine. A mutant hIL-10 in which isoleucine has been substituted (mut.hIL-10) is biologically active with only immunosuppressive, but not immunostimulatory, functions, making it a potentially superior therapeutic for inflammatory diseases. To compare the efficacy of mut.hIL-10 with hIL-10 and vIL-10 in blocking the progression of rheumatoid arthritis, we used replication defective adenoviral vectors to deliver intra-articularly the gene encoding hIL-10, vIL-10 or mut.hIL-10 to antigen-induced arthritic (AIA) knee joints in rabbits. Intra-articular expression of hIL-10, vIL-10, and mut.hIL-10 resulted in significant improvement of the pathology in the treated joints to similar levels. These observed changes included a significant reduction in intra-articular leukocytosis and the degree of synovitis, as well as normalization of cartilage matrix metabolism. Our results suggest that hIL-10, vIL-10, and mut.hIL-10 are all equally therapeutic in the rabbit AIA model for treating disease pathology.

Hyperactive Himar1 transposase mediates transposition in cell culture and enhances gene expression in vivo

The use of nonviral delivery systems results in transient gene expression, in part because of the low efficiency of DNA integration. Previously, vectors based on transposon systems such as Sleeping Beauty have been shown to be able to increase stable transfection efficiencies in cell culture and in animal models. Himar1, a reconstructed active transposon belonging to the Tc1/mariner superfamily, also has been used as a vector for stable gene delivery, but the rate of transposition after transfection is low. In this paper, we evaluate the potential of the hyperactive Himar1 transposase C9, in combination with the Himar1 inverted repeat transposon, as a gene delivery vector. The C9 transposase is a hyperactive mutant of Himar1 with two amino acid substitutions, Q131R and E137K, that result in an increase in activity relative to wild type. Here we demonstrate that cotransfection of the C9 transposase with a Himar1-based vector increases the frequency of stable gene expression in human cells in a transposase concentration-dependent manner. In addition, we establish that C9 transposase mediates integration of the transgene in mammalian cells at a frequency similar to that of Sleeping Beauty under some of the conditions tested. Last, we show significantly higher levels of reporter gene expression in vivo in mouse liver and in synovium of rabbit knee joints after injection of the transposon plasmid expressing the transgene and the C9 transposase. These data suggest that vectors based on the Himar1 transposable element, in conjunction with the hyperactive mutant transposase C9, may be suitable vectors for gene therapy applications.

Exosomes Derived from Genetically Modified DC Expressing FasL Are Anti-inflammatory and Immunosuppressive

We previously have demonstrated the ability of primary murine bone marrow-derived DC (BM-DC), genetically modified by adenoviral infection to express FasL, to inhibit progression of established collagen-induced arthritis (CIA) following systemic delivery. Here we demonstrate that exosomes derived from genetically modified BM-DC expressing FasL are able to inhibit inflammation in a murine footpad model of delayed-type hypersensitivity (DTH). Local administration of exosomes derived from DC expressing FasL (Exo/FasL) as well as the parental DC/FasL resulted in a significant reduction in swelling in both the treated and the untreated distal paw. However, both the DC/FasL and the Exo/FasL were unable to suppress the DTH response in lpr (Fas-deficient) mice. Gene transfer of FasL to BM-DC from gld (FasL-deficient) mice resulted in restoration of the ability of DC as well as DC-derived exosomes to suppress DTH. The ability of DC-derived exosomes and DC to suppress DTH responses was antigen specific and MHC class II dependent, but class I independent. The injected exosomes were found to be internalized into CD11c(+) cells at the site of injection and in the draining popliteal lymph node. Systemic injection of exosome/FasL into mice with established CIA resulted in significant disease amelioration. These results demonstrate that both systemic and local administration of exosomes derived from FasL-expressing DC are able to suppress antigen-specific immune responses through an MHC class II-dependent pathway, resulting in effective and sustained treatment of established collagen-induced arthritis and suppression of the DTH inflammatory response. These results suggest that DC/FasL-derived exosomes could be used clinically for the treatment of inflammatory and autoimmune diseases.

Exosomes Derived from IL-10-Treated Dendritic Cells Can Suppress Inflammation and Collagen-Induced Arthritis

We have demonstrated previously that local, adenoviral-mediated gene transfer of viral IL-10 to a single joint of rabbits and mice with experimental arthritis can suppress disease in both the treated and untreated contralateral joints. This contralateral effect is mediated in part by APCs able to traffic from the treated joint to lymph nodes as well as to untreated joints. Moreover, injection of dendritic cells (DC) genetically modified to express IL-4 or Fas ligand was able to reverse established murine arthritis. To examine the ability of exosomes derived from immunosuppressive DCs to reduce inflammation and autoimmunity, murine models of delayed-type hypersensitivity and collagen-induced arthritis were used. In this study, we demonstrate that periarticular administration of exosomes purified from either bone marrow-derived DCs transduced ex vivo with an adenovirus expressing viral IL-10 or bone marrow-derived DCs treated with recombinant murine IL-10 were able to suppress delayed-type hypersensitivity responses within injected and untreated contralateral joints. In addition, the systemic injection of IL-10-treated DC-derived exosomes was able suppress the onset of murine collagen-induced arthritis as well as reduce severity of established arthritis. Taken together, these data suggest that immature DCs are able to secrete exosomes that are involved in the suppression of inflammatory and autoimmune responses. Thus DC-derived exosomes may represent a novel, cell-free therapy for the treatment of autoimmune diseases.

The contralateral effect conferred by intra-articular adenovirus-mediated gene transfer of viral IL-10 is specific to the immunizing antigen

We have demonstrated previously that local, adenoviral-mediated gene transfer of vIL-10 to a single joint of rabbits and mice with experimental arthritis can suppress disease in both the treated and untreated contralateral joints. These therapeutic effects observed in distant untreated joints following local intra-articular gene delivery have been termed the 'contralateral effect'. To begin to understand the underlying immunologic mechanism that confers this effect, a dual-antigen model of antigen-induced arthritis (AIA) in rabbit knee joints was utilized. Rabbits were immunized against two antigens, ovalbumin and keyhole limpet hemocyanin, and AIA generated by intra-articular injection of each antigen into contralateral knees. Intra-articular adenovirus-mediated gene transfer of vIL-10 significantly reduced intra-articular leukocytosis and cartilage matrix degradation, while preserving near normal levels of cartilage matrix synthesis within treated joints. However, no antiarthritic effect was conferred in the contralateral control joints that received only a marker gene, in contrast to the results seen in a single-antigen AIA model. These results suggest that the distant antiarthritic effects associated with local gene delivery to joints are antigen-specific, and not due to vIL-10-induced generalized immunosuppression of the animal.

Identification of a synovial fibroblast-specific protein transduction domain for delivery of apoptotic agents to hyperplastic synovium

Synovial hyperplasia, resulting in erosion of cartilage and bone, represents one of the major pathologies associated with rheumatoid arthritis. To develop an approach for efficient delivery of proteins or agents to synovium to induce targeted apoptosis of hyperplastic synovial tissue, we have screened an M13 peptide phage display library for synovial-specific transduction peptides. We identified a novel synovial-targeted transduction peptide, HAP-1, which is able to facilitate specific internalization of protein complexes into human and rabbit synovial cells in culture and rabbit synovial lining in vivo. HAP-1 and a non-tissue-specific cationic protein transduction domain, PTD-5, were fused to an antimicrobial peptide, (KLAK)(2), to generate two proapoptotic peptides termed DP2 and DP1, respectively. Administration of these peptides was able to induce apoptosis of rabbit and human synovial cells in culture, with DP2 inducing synovial cell-specific apoptosis. Intra-articular injection of DP1 and DP2 into arthritic rabbit joints with synovial hyperplasia induced extensive apoptosis of the hyperplastic synovium, while reducing the leukocytic infiltration and synovitis. These results suggest that proapoptotic peptides and, in particular, DP2 can be clinically useful for treatment of synovial hyperplasia, as well as inflammation. Moreover, the results demonstrate the feasibility of identifying tissue-specific transduction peptides capable of mediating efficient transduction in vivo.

Ex vivo gene delivery of IL-1Ra and soluble TNF receptor confers a distal synergistic therapeutic effect in antigen-induced arthritis

Intra-articular expression of antagonists of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) in arthritic rabbit knee and mouse ankle joints by direct adenoviral-mediated intraarticular delivery results in amelioration of disease pathology in both the treated and contralateral untreated joints. Previous experiments suggest that direct adenoviral infection of resident antigen-presenting cells (APCs) and subsequent traveling of these cells to other sites of inflammation and lymph nodes might be responsible for this "contralateral effect." To determine whether genetic modification of APCs is required for the contralateral effect, we have used an ex vivo approach utilizing genetically modified fibroblasts to express IL-1 receptor antagonist protein (IL-1Ra) and soluble TNF-alpha receptor (sTNFR) locally in arthritic joints. Retroviral vectors carrying IL-1Ra, sTNFR-Ig, or both genes together were used to stably infect autologous rabbit fibroblasts that were then injected intra-articularly into arthritic rabbit knee joints. The intra-articular delivery of either IL-1Ra- or sTNFR-Ig-expressing fibroblasts was antiinflammatory and chondro-protective in both the injected and noninjected contralateral joints. In addition, we demonstrate that the co-delivery of both antagonists in combination results in a synergistic effect in disease amelioration in both the treated and nontreated joints. These ex vivo results suggest that trafficking of vector-modified inflammatory cells is not the main mechanism responsible for the observed distal spread of the therapeutic effect. Moreover, the results demonstrate that local, ex vivo gene therapy for arthritis could be effective in blocking pathologies within untreated, distant arthritic joints.

Adenovirus-mediated gene transfer of insulin-like growth factor 1 stimulates proteoglycan synthesis in rabbit joints

OBJECTIVE

To examine the effect of insulin-like growth factor 1 (IGF-1) on the regulation of cartilage synthesis and other articular events in vivo.

METHODS

A first-generation adenoviral vector expressing human IGF-1 (AdIGF-1) from the cytomegalovirus promoter was constructed. Particles of AdIGF-1 (5 x 10(9)) were injected through the patellar tendon into normal rabbit knee joints and rabbit knee joints with antigen-induced arthritis (AIA), with the same dose of a control adenoviral vector injected into the contralateral knees. Lavage fluids were obtained from rabbit knee joints on days 3 and 7 postinjection and used for analysis of IGF-1 expression, white blood cell infiltration, and cartilage breakdown. Cartilage chips from rabbit joints were used for assay of new proteoglycan synthesis, and tissues also were harvested from the dissected knees for histologic study.

RESULTS

Intraarticular injection of AdIGF-1 resulted in a mean of 180.6 ng/ml of IGF-1 expression in the lavage fluid from rabbit joints. IGF-1 expression stimulated new proteoglycan synthesis in both naive and AIA rabbit knees, but had no significant chondroprotective or antiinflammatory effects. Histologic analysis showed that elevated levels of IGF-1 expression in both normal and arthritic knees had no adverse pathologic effects on synovium or adjacent muscles.

CONCLUSION

Gene transfer of IGF-1 into rabbit knee joints promotes proteoglycan synthesis without significantly affecting inflammation or cartilage breakdown. In addition, no adverse effects following intraarticular IGF-1 gene delivery were observed. Thus, local gene transfer of IGF-1 to joints could serve as a therapeutic strategy to stimulate new matrix synthesis in both rheumatoid arthritis and osteoarthritis.

Direct Adenoviral Gene Transfer of Viral IL-10 to Rabbit Knees with Experimental Arthritis Ameliorates Disease in Both Injected and Contralateral Control Knees

IL-10, a cytokine produced primarily by macrophages, B lymphocytes, and Th2 cells, has both immunostimulatory and immunosuppressive properties. A homologue of IL-10 encoded by EBV, known as viral IL-10 (vIL-10), is also able to suppress the immune response, but may lack some of the immunostimulatory properties of IL-10. To evaluate the potential of vIL-10 to block the progression of rheumatoid arthritis, we have utilized a replication-defective adenovirus vector to deliver the gene encoding vIL-10 to the knee joints of rabbits with Ag-induced arthritis. Intraarticular expression of vIL-10 significantly reduced leukocytosis, cartilage matrix degradation, and levels of endogenous rabbit TNF-α, as well as the degree of synovitis, while maintaining high levels of cartilage matrix synthesis. Interestingly, an antiarthritic effect was also observed in opposing contralateral control knee joints that received only a marker gene. An adenoviral vector carrying the enhanced green fluorescent protein marker gene was used to demonstrate that a morphologically similar subset of cells infected in the injected knee joint are able to traffic to the uninjected contralateral knee joint. Our results suggest that direct, local intraarticular delivery of the vIL-10 gene may have polyarticular therapeutic effects.

Direct adenoviral gene transfer of viral IL-10 to rabbit knees with experimental arthritis ameliorates disease in both injected and contralateral control knees

IL-10, a cytokine produced primarily by macrophages, B lymphocytes, and Th2 cells, has both immunostimulatory and immunosuppressive properties. A homologue of IL-10 encoded by EBV, known as viral IL-10 (vIL-10), is also able to suppress the immune response, but may lack some of the immunostimulatory properties of IL-10. To evaluate the potential of vIL-10 to block the progression of rheumatoid arthritis, we have utilized a replication-defective adenovirus vector to deliver the gene encoding vIL-10 to the knee joints of rabbits with Ag-induced arthritis. Intraarticular expression of vIL-10 significantly reduced leukocytosis, cartilage matrix degradation, and levels of endogenous rabbit TNF-alpha, as well as the degree of synovitis, while maintaining high levels of cartilage matrix synthesis. Interestingly, an antiarthritic effect was also observed in opposing contralateral control knee joints that received only a marker gene. An adenoviral vector carrying the enhanced green fluorescent protein marker gene was used to demonstrate that a morphologically similar subset of cells infected in the injected knee joint are able to traffic to the uninjected contralateral knee joint. Our results suggest that direct, local intraarticular delivery of the vIL-10 gene may have polyarticular therapeutic effects.

Lessons learned from gene transfer approaches

Recent technological advances allow the transfer of genes to the synovial lining of joints. As well as opening novel opportunities for therapy, these techniques provide valuable new tools for the study of synovitis and other aspects of the biology of joints in health and disease. This article reviews briefly the results of experiments in which selected genes have been transferred to the knee joints of healthy rabbits and rabbits with antigen-induced arthritis.

Direct adenovirus-mediated gene transfer of interleukin 1 and tumor necrosis factor alpha soluble receptors to rabbit knees with experimental arthritis has local and distal anti-arthritic effects

Adenoviral vectors were used to deliver genes encoding a soluble interleukin 1 (IL-1)-type I receptor-IgG fusion protein and/or a soluble type I tumor necrosis factor alpha (TNFalpha) receptor-IgG fusion protein directly to the knees of rabbits with antigen-induced arthritis. When tested individually, knees receiving the soluble IL-1 receptor had significantly reduced cartilage matrix degradation and white blood cell infiltration into the joint space. Delivery of the soluble TNFalpha receptor was less effective, having only a moderate effect on white blood cell infiltration and no effect on cartilage breakdown. When both soluble receptors were used together, there was a greater inhibition of white blood cell infiltration and cartilage breakdown with a considerable reduction of synovitis. Interestingly, anti-arthritic effects were also seen in contralateral control knees receiving only a marker gene, suggesting that sustained local inhibition of disease activity in one joint may confer an anti-arthritic effect on other joints. These results suggest that local intra-articular gene transfer could be used to treat systemic polyarticular arthritides.

Constitutive intra-articular expression of human IL-1 beta following gene transfer to rabbit synovium produces all major pathologies of human rheumatoid arthritis

To investigate the pathophysiologic effects of chronically elevated intra-articular levels of IL-1 beta, we used an ex vivo gene transfer method to deliver and express human IL-1 beta (hIL-1 beta) in the knee joints of rabbits. Expression of hIL-1 beta resulted in a severe, highly aggressive form of arthritis analogous to chronic rheumatoid arthritis in humans. Intra-articular manifestations included intense inflammation, leukocytosis, synovial hypertrophy and hyperplasia, and highly aggressive pannus formation with erosion of the articular cartilage and periarticular bone. Systemic effects were also observed, including diarrhea, fever, weight loss, and an increased erythrocyte sedimentation rate. In addition, the hIL-1 beta was found to induce elevated levels of both rabbit IL-1 beta and TNF-alpha in synovial fluid. Following the loss of hIL-1 beta transgene expression between 14 and 28 days post-transplantation, many of these changes began to normalize. These results suggest that chronically elevated intra-articular levels of IL-1 beta alone are sufficient to produce virtually all the pathologies found in rheumatoid arthritis, and furthermore, demonstrate that gene transfer can be used to investigate the roles of specific gene products in the pathogenesis of arthritis.

Constitutive intra-articular expression of human IL-1 beta following gene transfer to rabbit synovium produces all major pathologies of human rheumatoid arthritis

To investigate the pathophysiologic effects of chronically elevated intra-articular levels of IL-1 beta, we used an ex vivo gene transfer method to deliver and express human IL-1 beta (hIL-1 beta) in the knee joints of rabbits. Expression of hIL-1 beta resulted in a severe, highly aggressive form of arthritis analogous to chronic rheumatoid arthritis in humans. Intra-articular manifestations included intense inflammation, leukocytosis, synovial hypertrophy and hyperplasia, and highly aggressive pannus formation with erosion of the articular cartilage and periarticular bone. Systemic effects were also observed, including diarrhea, fever, weight loss, and an increased erythrocyte sedimentation rate. In addition, the hIL-1 beta was found to induce elevated levels of both rabbit IL-1 beta and TNF-alpha in synovial fluid. Following the loss of hIL-1 beta transgene expression between 14 and 28 days post-transplantation, many of these changes began to normalize. These results suggest that chronically elevated intra-articular levels of IL-1 beta alone are sufficient to produce virtually all the pathologies found in rheumatoid arthritis, and furthermore, demonstrate that gene transfer can be used to investigate the roles of specific gene products in the pathogenesis of arthritis.

Direct retrovirus-mediated gene transfer to the synovium of the rabbit knee: implications for arthritis gene therapy

We have investigated the feasibility of using high-titer murine leukemia virus-based retroviral vectors to deliver exogenous genes to naive and chronically inflamed knee joints of rabbits in vivo. Intraarticular injection of retrovirus encoding beta-galactosidase (beta-gal or lacZ) was found to transduce synoviocytes in both naive and inflamed joints, but a significantly higher number of lacZ+ cells were found in inflamed knees. Using a retrovirus encoding a secretable marker, human growth hormone (hGH), quantitative comparison of ex vivo and in vivo gene delivery methods demonstrated that transgene expression following in vivo gene transfer was at least equivalent to that of the ex vivo method in inflamed knees. In addition, hGH transgene expression was maintained for at least 4 weeks. These experiments suggest that high-titer retroviral vector could be used for efficient in vivo gene transfer to inflamed joints in patients with rheumatoid arthritis (RA).

Fine specificity of equine infectious anaemia virus gp90-specific antibodies associated with protective and enhancing immune responses in experimentally infected and immunized ponies

Equine infectious anaemia virus (EIAV) provides a model for examining the natural immunological control of a persistent lentivirus infection and for evaluating the efficacy of various vaccine strategies. As an initial characterization of antibody responses associated with protective or enhancing immune responses elicited by experimental infections or vaccinations, we have utilized synthetic peptide ELISA to characterize the fine specificity of antibodies to linear determinants of the EIAV surface glycoprotein, gp90. The data indicated that serum antibodies associated with protective or enhancing immune responses differed quantitatively and qualitatively in their pattern of reactivity to gp90 peptides. Protective and enhancing EIAV vaccines could also be distinguished by their ability to evoke anamnestic antibody responses to gp90 peptides. These studies demonstrate for the first time definitive differences in the specificity of protective and enhancing antibody responses to EIAV and emphasize the importance of using native viral glycoprotein immunogens in lentivirus vaccines.

Lentivirus cross-reactive determinants present in the capsid protein of equine infectious anaemia virus

In this study we used immune sera from equine infectious anaemia virus (EIAV)-infected horses which uniquely display broad reactivity with different lentivirus capsid proteins (CA) to characterize the cross-reactive determinants of lentivirus CA proteins. In particular, the role of the major homology region (MHR) of lentivirus CA proteins in this serological cross-reactivity was evaluated using both equine immune serum and murine monoclonal antibodies (MAbs) directed against the MHR segment of different lentiviruses. The results of our studies indicate that about 80% of sera from long-term experimentally infected ponies or naturally infected horses react with human immunodeficiency virus type 1 CA in Western immunoblot assays. In addition, the cross-reactive determinants on the EIAV CA were localized within the immunodominant carboxyl terminus of the protein (residues 277 to 367). However, the cross-reactive determinants recognized by the equine sera do not appear to correlate with linear peptides from the carboxyl terminus of the EIAV CA, including the MHR. These results suggest cross-reactivity between more distant lentiviruses is associated with non-linear determinants. In contrast, MHR-specific MAbs did react with linear peptides by ELISA and distinguished the primate lentiviruses from EIAV and feline immunodeficiency virus. These data support the concept of a highly conserved structural and antigenic organization among the CA proteins of lentiviruses from different species.