Administration of low-dose cytarabine results in immediate S-phase arrest and subsequent activation of cell cycling in murine stem cells

Protective Effects of L-Theanine on IPEC-J2 Cells Growth Inhibition Induced by Dextran Sulfate Sodium via p53 Signaling Pathway

L-theanine is a nonprotein amino acid found in tea leaves and has been widely used as a safe food additive in beverages or foods because of its varied bioactivities. The aim of this study was to reveal the in vitro gastrointestinal protective effects of L-theanine in DSS-induced intestinal porcine enterocyte (IPEC-J2) cell models using molecular and metabolic methods. Results showed that 2.5% dextran sulfate sodium (DSS) treatment inhibited the cell proliferation of IPEC-J2 and blocked the normal operation of the cell cycle, while L-theanine pretreatment significantly preserved these trends to exert protective effects. L-theanine pre-treatment also up-regulated the EGF, CDC2, FGF2, Rb genes and down-regulated p53, p21 proliferation-related mRNA expression in DSS-treated cells, in accompany with p53 signaling pathway inhibition. Meanwhile, metabolomics analysis revealed that L-theanine and DSS treated IPEC-J2 cells have different metabolomic profiles, with significant changes in the key metabolites involved in pyrimidine metabolism and amino acid metabolism, which play an important role in nucleotide metabolism. In summary, L-theanine has a beneficial protection in DSS-induced IPEC-J2 cells via promoting proliferation and regulating metabolism disorders.

DFF40 deficiency in cancerous T cells is implicated in chemotherapy drug sensitivity and resistance through the regulation of the apoptotic pathway

The regulation of the apoptotic pathway is one of the most studied mechanisms regarding cancer cell resistance. Many mutations have been linked to drug resistance. The DNA fragmentation factor 40 (DFF40) has been gaining interest regarding cancer cell response to chemotherapy and patient outcomes. Glioblastomas and uterine leiomyosarcomas have been shown to have a downregulation of DFF40 expression, conferring a poor patient prognosis. In concordance with these observations, in this study, we showed that DFF40 gene is also downregulated in breast, endocervical, ovarian, lung, pancreas and glioblastomas. DFF40 is the endonuclease responsible of DNA fragmentation during apoptosis. In this study, we sought to determine if a DFF40 deficiency in Jurkat T cells could impact the sensitivity to conventional chemotherapy drugs. CRISPR-cas9 generated DFF40 knockout (DFF40 KO) stable Jurkat cells and wild-type (DFF40 WT) cells were treated with different antimetabolites and topoisomerase II (TOP2) inhibitors, and cell viability was subsequently assessed. DFF40 deficient cells show chemoresistance to antimetabolites (e.g. methotrexate, 6-mercaptopurine and cytarabine) and surprisingly, they are more sensitive to TOP2 inhibitors (e.g. etoposide and teniposide). DFF40 deficient cells exposed to cytarabine present lower phosphatidylserine translocation levels to the outer cell membrane layer. Etoposide exposure in DFF40 deficient cells induces higher mortality levels and downregulation of Bcl-xL cells compared to DFF40 expressing T cells. The abolition of DFF40 expression in Jurkat cells significantly impairs histone H2AX phosphorylation following etoposide and cytarabine treatments. Our findings suggest that DFF40 is a novel key target in cancer cell resistance that potentially regulates genomic stability.

The expression and activity of thymidine kinase 1 and deoxycytidine kinase are modulated by hydrogen peroxide and nucleoside analogs

Thymidine kinase 1 (TK1) and deoxycytidine kinase (dCK) are required for the activation of thymidine and deoxycytidine analogs used in antiviral and anticancer therapies. Many anticancer drugs cause oxidative stress, and the rise of GSSG and other reactive oxygen species may lead to alteration in gene expression, protein, nucleic acids and lipid modifications. Here, we investigated the effects of oxidative stress and nucleoside analog on the expression and activity of TK1 and dCK. Treatment with GSSG resulted in glutathionylation of dCK and dGK but not TK1 and Dm-dNK, and glutathionylation led to increased dCK activity but decreased dGK activity. Treatment with hydrogen peroxide resulted in induction of TK1, however, the TK1 activity did not correlate with TK1 protein levels, indicating that TK1 protein was inactive. The cellular expression of dCK, however, was reduced but dCK activity was not affected at concentration ≤ 4 mM. Treatment with TFT or 5FdU resulted in downregulation of both TK1 and dCK. However, araC and dFdC treatment led to increased dCK protein but decreased dCK activity. In contrast, both TK1 protein and activity were upregulated after araC and dFdC treatment. Doxorubicin treatment led to upregulation of the TK1 but downregulation of dCK. In conclusion TK1 and dCK expression and activity are apparently affected by oxidative stress and treatment by nucleoside analogs. These results demonstrate the pharmacokinetic importance of characterizing the expression and activity of TK1 and dCK during chemotherapy with thymidine and deoxycytidine analogs in order to optimize their efficacy.

Upregulation of miR-99a is associated with poor prognosis of acute myeloid leukemia and promotes myeloid leukemia cell expansion

Leukemia stem cells (LSCs) can resist available treatments that results in disease progression and/or relapse. To dissect the microRNA (miRNA) expression signature of relapse in acute myeloid leukemia (AML), miRNA array analysis was performed using enriched LSCs from paired bone marrow samples of an AML patient at different disease stages. We identified that miR-99a was significantly upregulated in the LSCs obtained at relapse compared to the LSCs collected at the time of initial diagnosis. We also found that miR-99a was upregulated in LSCs compared to non-LSCs in a larger cohort of AML patients, and higher expression levels of miR-99a were significantly correlated with worse overall survival and event-free survival in these AML patients. Ectopic expression of miR-99a led to increased colony forming ability and expansion in myeloid leukemia cells after exposure to chemotherapeutic drugs in vitro and in vivo, partially due to overcoming of chemotherapeutic agent-mediated cell cycle arrest. Gene profiling and bioinformatic analyses indicated that ectopic expression of miR-99a significantly upregulated genes that are critical for LSC maintenance, cell cycle, and downstream targets of E2F and MYC. This study suggests that miR-99a has a novel role and potential use as a biomarker in myeloid leukemia progression.

Adiponectin Enhances Quiescence Exit of Murine Hematopoietic Stem Cells and Hematopoietic Recovery Through mTORC1 Potentiation

Myelotoxic injury, such as chemotherapeutic agents and ionizing radiation, unlocks the vigorous power of hematopoietic stem cells (HSCs) to replenish the hematopoietic system, making quiescent HSCs enter the cell cycle. Considering that both HSC-intrinsic and -extrinsic mechanisms enforce quiescence of HSCs, the drastic change in bone marrow (BM) environment after injury, represented by massive expansion of BM adipocytes, might trigger HSC activation. BM adipocytes, the major cellular component in the ablated marrow, however, reportedly suppress proliferation of hematopoietic cells, which may indicate the BM adipocytogenesis is an irrational response of injured organism. Given that adipose tissue is an endocrine organ with pleiotropic functions, we hypothesized that adipocyte-derived factors, especially adiponectin, an anti-inflammatory adipokine involved in regulation of granulopoiesis, are implicated in HSC activation. Myeloablative intervention increased BM adiponectin by multiple mechanisms, including adipocyte expansion and increased diffusion from the blood. Adiponectin-null (Adipoq ^-/- ) mice showed delayed hematopoietic recovery after BM injury, with Adipoq^-/- HSCs more quiescent and defective in mammalian target of rapamycin complex 1 (mTORC1) activation. Recombinant adiponectin promoted not only HSC activation in vivo but cytokine-induced activation in vitro, and shortened the time for exit from quiescence in an mTORC1-dependent manner. These data illustrate a scarcely-reported example of a cell-extrinsic factor, adiponectin, enhancing quiescence exit of HSCs, and subsequent hematopoietic recovery. Our findings also highlight adipocytes as a source of adiponectin to ensure the proliferative burst of hematopoietic cells in ablated marrow. Stem Cells 2017;35:1835-1848.

HDAC8, A Potential Therapeutic Target for the Treatment of Malignant Peripheral Nerve Sheath Tumors (MPNST)

Introduction

HDAC isoform-specific inhibitors may improve the therapeutic window while limiting toxicities. Developing inhibitors against class I isoforms poses difficulties as they share high homology among their catalytic sites; however, HDAC8 is structurally unique compared to other class I isoforms. HDAC8 inhibitors are novel compounds and have affinity for class I HDAC isoforms demonstrating anti-cancer effects; little is known about their activity in malignant peripheral nerve sheath tumors (MPNST). Recently, we demonstrated anti-MPNST efficacy of HDAC8i in human and murine-derived MPNST pre-clinical models; we now seek to consider the potential therapeutic inhibition of HDAC8 in MPNST.

Methods

Four Human MPNST cell lines, a murine-derived MPNST cell line, and two HDAC8 inhibitors (PCI-34051, PCI-48012; Pharmacyclics, Inc. Sunnyvale, CA) were studied. Proliferation was determined using MTS and clonogenic assays. Effects on cell cycle were determined via PI FACS analysis; effects on apoptosis were determined using Annexin V-PI FACS analysis and cleaved caspase 3 expression. In vivo growth effects of HDAC8i were evaluated using MPNST xenograft models. 2D gel electrophoresis and mass spectrometry were used to identify potential HDAC8 deacetylation substrates.

Results

HDAC8i induced cell growth inhibition and marked S-phase cell cycle arrest in human and murine-derived MPNST cells. Relative to control, HDAC8i induced apoptosis in both human and murine-derived MPNST cells. HDAC8i exhibited significant effects on MPNST xenograft growth (p=0.001) and tumor weight (p=0.02). Four potential HDAC8 substrate targets were identified using a proteomic approach: PARK7, HMGB1, PGAM1, PRDX6.

Conclusions

MPNST is an aggressive sarcoma that is notoriously therapy-resistant, hence the urgent need for improved anti-MPNST therapies. HDAC8 inhibition may be useful for MPNST by improving efficacy while limiting toxicities as compared to pan-HDACis.

Efficient in vivo regulation of cytidine deaminase expression in the haematopoietic system using a doxycycline-inducible lentiviral vector system

Regulated transgene expression may reduce transgene-specific and genotoxic risks associated with gene therapy. To prove this concept, we have investigated the suitability of doxycycline (Dox)-inducible human cytidine deaminase (hCDD) overexpression from lentiviral vectors to mediate effective myeloprotection while circumventing the lymphotoxicity observed with constitutive CDD activity. Rapid Dox-mediated transgene induction associated with a 6-17-fold increase in drug resistance was observed in 32D and primary murine bone marrow (BM) cells. Moreover, robust Dox-regulated transgene expression in the entire haematopoietic system was demonstrated for primary and secondary recipients of hCDD-transduced R26-M2rtTA transgenic BM cells. Furthermore, mice were significantly protected from myelosuppressive chemotherapy as evidenced by accelerated recovery of granulocytes (1.9±0.6 vs 1.3±0.3, P=0.034) and platelets (883±194 vs 584±160 10(3) per μl, P=0.011). Minimal transgene expression in the non-induced state and no overt cellular toxicities including lymphotoxicity were detected. Thus, using a relevant murine transplant model our data provide conclusive evidence that drug-resistance transgenes can be expressed in a regulated fashion in the lymphohaematopoietic system, and that Dox-inducible systems may be used to reduce myelotoxic side effect of anticancer chemotherapy or to avoid side effects of high constitutive transgene expression.

Telomerase reverse transcriptase protects ATM-deficient hematopoietic stem cells from ROS-induced apoptosis through a telomere-independent mechanism

Telomerase reverse transcriptase (TERT) contributes to the prevention of aging by a largely unknown mechanism that is unrelated to telomere lengthening. The current study used ataxia-telangiectasia mutated (ATM) and TERT doubly deficient mice to evaluate the contributions of 2 aging-regulating molecules, TERT and ATM, to the aging process. ATM and TERT doubly deficient mice demonstrated increased progression of aging and had shorter lifespans than ATM-null mice, while TERT alone was insufficient to affect lifespan. ATM-TERT doubly null mice show in vivo senescence, especially in hematopoietic tissues, that was dependent on p16(INK4a) and p19(ARF), but not on p21. As their HSCs show decreased stem cell activities, accelerated aging seen in these mice has been attributed to impaired stem cell function. TERT-deficient HSCs are characterized by reactive oxygen species (ROS) fragility, which has been suggested to cause stem cell impairment during aging, and apoptotic HSCs are markedly increased in these mice. p38MAPK activation was indicated to be partially involved in ROS-induced apoptosis in TERT-null HSCs, and BCL-2 is suggested to provide a part of the protective mechanisms of HSCs by TERT. The current study demonstrates that TERT mitigates aging by protecting HSCs under stressful conditions through telomere length-independent mechanisms.

Osteoclasts are involved in the maintenance of dormant leukemic cells

Osteoclasts (OCs) are specialized cells for the resorption of bone matrix that have also been recently reported to be involved in the mobilization of hematopoietic progenitor cells. When Ba/F3 cells expressing wild-type bcr-abl were co-cultured with osteoblasts (OBs), OCs, and bone slices, their proliferation was significantly suppressed, and the Ki-67 negative population, which is believed to be in G(0) phase, was increased. The results of our in vitro experiments suggest that OCs could be involved in the maintenance of dormant leukemic cells in the bone marrow (BM) microenvironment through the release of soluble factors, one of which could be TGF-beta.

Dexamethasone increases angiopoietin-1 and quiescent hematopoietic stem cells: a novel mechanism of dexamethasone-induced hematoprotection

Angiopoietin-1 (Ang-1) is known to have hematoprotective effects by increasing the quiescence of hematopoietic stem cells. However, it remains to be determined if the upregulation of Ang-1 and the subsequent increase in the quiescence of hematopoietic stem cells are also involved in the dexamethasone (Dex)-mediated bone marrow protection. Here Western blotting and flow cytometric analyses demonstrate that Dex increases the levels of Ang-1 in mouse bone marrow and the quiescence of hematopoietic stem cells. Our data for the first time suggest that the increased quiescence of hematopoietic stem cells provides a novel mechanism of Dex-induced hematoprotection.

The use of experimental murine models to assess novel agents of hematopoietic stem and progenitor cell mobilization

The recent explosion in the understanding of the cellular and molecular mechanisms underlying hematopoietic stem and progenitor cell (HSPC) mobilization has facilitated development of novel therapeutic agents, targeted at improving mobilization kinetics as well as HSPC yield. With the development of new agents comes the challenge of choosing efficient and relevant preclinical studies for the testing of the HSPC mobilization efficacy of these agents. This article reviews the use of the mouse as a convenient small animal model of HSPC mobilization and transplantation, and outlines the range of murine assays that can be applied to assess novel HSPC mobilizing agents. Techniques to demonstrate murine HSPC mobilization are discussed, as well as the role of murine assays to confirm human HSPC mobilization, and techniques to investigate the biologic phenotype of HSPC mobilized by these novel agents. Technical aspects regarding mobilization regimens and control arms, and choice of experimental animals are also discussed.

Leukemia stem cells in a genetically defined murine model of blast-crisis CML

Myeloid leukemia arises from leukemia stem cells (LSCs), which are resistant to standard chemotherapy agents and likely to be a major cause of drug-resistant disease and relapse. To investigate the in vivo properties of LSCs, we developed a mouse model in which the biologic features of human LSCs are closely mimicked. Primitive normal hematopoietic cells were modified to express the BCR/ABL and Nup98/HoxA9 translocation products, and a distinct LSC population, with the aberrant immunophenotype of lineage(-), Kit(+/-), Flt3(+), Sca(+), CD34(+), and CD150(-), was identified. In vivo studies were then performed to assess the response of LSCs to therapeutic insult. Treatment of animals with the ABL kinase inhibitor imatinib mesylate induced specific modulation of blasts and progenitor cells but not stem- cell populations, thereby recapitulating events inferred to occur in human chronic myelogenous leukemia (CML) patients. In addition, challenge of leukemic mice with total body irradiation was selectively toxic to normal hematopoietic stem cells (HSCs), suggesting that LSCs are resistant to apoptosis and/or senescence in vivo. Taken together, the system provides a powerful means by which the in vivo behavior of LSCs versus HSCs can be characterized and candidate treatment regimens can be optimized for maximal specificity toward primitive leukemia cells.