Enhancement of hemoglobin and F-cell production by targeting growth inhibition and differentiation of K562 cells with ribonucleotide reductase inhibitors (didox and trimidox) in combination with streptozotocin

Inhibitors of the Cancer Target Ribonucleotide Reductase, Past and Present

Ribonucleotide reductase (RR) is an essential multi-subunit enzyme found in all living organisms; it catalyzes the rate-limiting step in dNTP synthesis, namely, the conversion of ribonucleoside diphosphates to deoxyribonucleoside diphosphates. As expression levels of human RR (hRR) are high during cell replication, hRR has long been considered an attractive drug target for a range of proliferative diseases, including cancer. While there are many excellent reviews regarding the structure, function, and clinical importance of hRR, recent years have seen an increase in novel approaches to inhibiting hRR that merit an updated discussion of the existing inhibitors and strategies to target this enzyme. In this review, we discuss the mechanisms and clinical applications of classic nucleoside analog inhibitors of hRRM1 (large catalytic subunit), including gemcitabine and clofarabine, as well as inhibitors of the hRRM2 (free radical housing small subunit), including triapine and hydroxyurea. Additionally, we discuss novel approaches to targeting RR and the discovery of new classes of hRR inhibitors.

Nitric Oxide Synthase Dependency in Hydroxyurea Inhibition of Erythroid Progenitor Growth

Hydroxyurea (HU) causes nitric oxide (NO) bioactivation, acting as both a NO donor and a stimulator of NO synthase (NOS). To examine whether HU effects are NO mediated by chemical degradation or enzymatic induction, we studied human and mouse erythroid cells during proliferation, apoptosis, and differentiation. The HU and NO donor demonstrated persisted versus temporary inhibition of erythroid cell growth during differentiation, as observed by γ- and β-globin gene expression. HU decreased the percentage of erythroleukemic K562 cells in the G2/M phase that was reversed by N-nitro l-arginine methyl ester hydrochloride (L-NAME). Besides activation of endothelial NOS, HU significantly increased apoptosis of K562 cells, again demonstrating NOS dependence. Administration of HU to mice significantly inhibited colony-forming unit-erythroid (CFU-E), mediated by NOS. Moreover, burst-forming-units-erythroid (BFU-E) and CFU-E ex vivo growth was inhibited by the administration of nitrate or nitrite to mice. Chronic in vivo NOS inhibition with L-NAME protected the bone marrow cellularity despite HU treatment of mice. NO metabolites and HU reduced the frequency of NOS-positive cells from CFU-E and BFU-E colonies that was reverted by NOS inhibition. HU regulation of the G2/M phase, apoptosis, differentiation, cellularity, and NOS immunoreactive cells was NOS dependent. Inhalation of NO therapy as well as strategies to increase endogenous NO production could replace or enhance HU activity.

Epigenetic Reexpression of Hemoglobin F Using Reversible LSD1 Inhibitors: Potential Therapies for Sickle Cell Disease

Sickle cell disease (SCD) is caused by a single nucleotide polymorphism on chromosome 11 in the β-globin gene. The resulting mutant hemoglobin S (HbS) is a poor oxygen transporter and causes a variety of vascular symptoms and organ failures. At birth, the DRED epigenetic complex forms and silences the γ-globin gene, and fetal hemoglobin (HbF, 2 α-, and 2 γ-subunits) is replaced by adult HbA (α2β2) or HbS (α2βs 2) in SCD patients. HbF is a potent inhibitor of HbS polymerization, thus alleviating the symptoms of SCD. The current therapy, hydroxyurea (HU), increases γ-globin and the HbF content in sickle cells but is highly underutilized due to concern for adverse effects and other complications. The DRED complex contains the epigenetic eraser lysine-specific demethylase 1 (LSD1), which appears to serve as a scaffolding protein. Our recently discovered 1,2,4-triazole derivatives and cyclic peptide LSD1 inhibitors promote the upregulation of γ-globin production in vitro without significant toxicity. Herein, we demonstrate that these LSD1 inhibitors can be used to disrupt the DRED complex and increase the cellular HbF content in vitro and in vivo. This approach could lead to an innovative and effective treatment for SCD.

Enumeration of Fetal Red Blood Cells, Hemoglobin-Specific RBC Cells, and F Reticulocytes in Human Blood

Recent advances in analytical cytometry have improved diagnostic tools for the study of erythropoiesis in anemic patients and resolution of differential diagnosis in diseases of the erythron. This article presents three applications of red blood cell (RBC) analysis-quantitation of fetal red cells, F-cell enumeration, and F-reticulocyte analysis-which improve diagnostic precision, sensitivity, and specificity, and provide better laboratory indicators of therapeutic efficacy in a variety of hematologic and obstetric disorders. Such advances also include the measurement and quantitation of RBC hemoglobins and their relative ribonucleic acid levels. These advances not only promise to improve diagnostic accuracy and laboratory precision over techniques such as the traditional manual reticulocyte counting method and the Kleihauer-Betke stain method for evaluating fetomaternal hemorrhage (FMH), but also serve as tools for newer assays of anemia diagnosis and improved clinical outcomes. In addition to the primary methods, supporting techniques for preparing spiked controls, automating data analysis, setting up a fetal hemoglobin acquisition protocol, and assaying reticulocytes using thiazole orange are also presented. © 2019 by John Wiley & Sons, Inc.

Didox (3,4-dihydroxybenzohydroxamic acid) suppresses IL-33-induced cytokine production in primary mouse mast cells

While IgE is considered the primary mediator of mast cell activation, IL-33 contributes substantially in asthma, allergic rhinitis, and atopic dermatitis. To develop effective treatments for allergic disease, it is important to understand the role of therapeutic agents on IL-33 activation. We examined the effect of Didox (3,4-dihydroxybenzohydroxamic acid), an antioxidant and ribonucleotide reductase (RNR) inhibitor, on IL-33-mediated mast cell activation. Didox suppressed IL-6, IL-13, TNF, and MIP-1α (CCL3) production in bone marrow derived mast cells following IL-33 activation. This suppression was observed in different genetic backgrounds and extended to peritoneal mast cells. The antioxidant N-acetylcysteine mimicked the suppression of Didox, albeit at a much higher dose, while the RNR inhibitor hydroxyurea had no effect. Didox substantially suppressed IL-33-mediated NFκB and AP-1 transcriptional activities. These results suggest that Didox attenuates IL-33-induced mast cell activation and should be further studied as a potential therapeutic agent for inflammatory diseases involving IL-33.

Clinical pharmacology and clinical trials of ribonucleotide reductase inhibitors: is it a viable cancer therapy?

PURPOSE

Ribonucleotide reductase (RR) enzymes (RR1 and RR2) play an important role in the reduction of ribonucleotides to deoxyribonucleotides which is involved in DNA replication and repair. Augmented RR activity has been ascribed to uncontrolled cell growth and tumorigenic transformation.

METHODS

This review mainly focuses on several biological and chemical RR inhibitors (e.g., siRNA, GTI-2040, GTI-2501, triapine, gemcitabine, and clofarabine) that have been evaluated in clinical trials with promising anticancer activity from 1960's till 2016. A summary on whether their monotherapy or combination is still effective for further use is discussed.

RESULTS

Among the RR2 inhibitors evaluated, GTI-2040, siRNA, gallium nitrate and didox were more efficacious as a monotherapy, whereas triapine was found to be more efficacious as combination agent. Hydroxyurea is currently used more in combination therapy, even though it is efficacious as a monotherapy. Gallium nitrate showed mixed results in combination therapy, while the combination activity of didox is yet to be evaluated. RR1 inhibitors that have long been used in chemotherapy such as gemcitabine, cladribine, fludarabine and clofarabine are currently used mostly as a combination therapy, but are equally efficacious as a monotherapy, except tezacitabine which did not progress beyond phase I trials.

CONCLUSIONS

Based on the results of clinical trials, we conclude that RR inhibitors are viable treatment options, either as a monotherapy or as a combination in cancer chemotherapy. With the recent advances made in cancer biology, further development of RR inhibitors with improved efficacy and reduced toxicity is possible for treatment of variety of cancers.

Experimental model for ELF-EMF exposure: Concern for human health

Low frequency (LF) electromagnetic fields (EMFs) are abundantly present in modern society and in the last 20 years the interest about the possible effect of extremely low frequency (ELF) EMFs on human health has increased progressively. Epidemiological studies, designed to verify whether EMF exposure may be a potential risk factor for health, have led to controversial results. The possible association between EMFs and an increased incidence of childhood leukemia, brain tumors or neurodegenerative diseases was not fully elucidated. On the other hand, EMFs are widely used, in neurology, psychiatry, rheumatology, orthopedics and dermatology, both in diagnosis and in therapy. In vitro studies may help to evaluate the mechanism by which LF-EMFs affect biological systems. In vitro model of wound healing used keratinocytes (HaCaT), neuroblastoma cell line (SH-SY5Y) as a model for analysis of differentiation, metabolism and functions related to neurodegenerative processes, and monocytic cell line (THP-1) was used as a model for inflammation and cytokines production, while leukemic cell line (K562) was used as a model for hematopoietic differentiation. MCP-1, a chemokine that regulates the migration and infiltration of memory T cells, natural killer (NK), monocytes and epithelial cells, has been demonstrated to be induced and involved in various diseases. Since, varying the parameters of EMFs different effects may be observed, we have studied MCP-1 expression in HaCaT, SH-SY5Y, THP-1 and K562 exposed to a sinusoidal EMF at 50 Hz frequency with a flux density of 1 mT (rms). Our preliminary results showed that EMF-exposure differently modifies the expression of MCP-1 in different cell types. Thus, the MCP-1 expression needs to be better determined, with additional studies, with different parameters and times of exposure to ELF-EMF.

Targeting ribonucleotide reductase for cancer therapy

INTRODUCTION

Ribonucleotide reductase (RR) is a unique enzyme, because it is responsible for reducing ribonucleotides to their corresponding deoxyribonucleotides, which are the building blocks required for DNA replication and repair. Dysregulated RR activity is associated with genomic instability, malignant transformation and cancer development. The use of RR inhibitors, either as a single agent or combined with other therapies, has proven to be a promising approach for treating solid tumors and hematological malignancies.

AREAS COVERED

This review covers recent publications in the area of RR, which include: i) the structure, function and regulation of RR; ii) the roles of RR in cancer development; iii) the classification, mechanisms and clinical application of RR inhibitors for cancer therapy and iv) strategies for developing novel RR inhibitors in the future.

EXPERT OPINION

Exploring the possible nonenzymatic roles of RR subunit proteins in carcinogenesis may lead to new rationales for developing novel anticancer drugs. Updated information about the structure and holoenzyme models of RR will help in identifying potential sites in the protein that could be targets for novel RR inhibitors. Determining RR activity and subunit levels in clinical samples will provide a rational platform for developing personalized cancer therapies that use RR inhibitors.

A cell stress signaling model of fetal hemoglobin induction: what doesn't kill red blood cells may make them stronger

A major goal of hemoglobinopathy research is to develop treatments that correct the underlying molecular defects responsible for sickle cell disease and beta-thalassemia. One approach to achieving this goal is the pharmacologic induction of fetal hemoglobin (HbF). This strategy is capable of inhibiting the polymerization of sickle hemoglobin and correcting the globin chain imbalance of beta-thalassemia. Despite this promise, none of the currently available HbF-inducing agents exhibit the combination of efficacy, safety, and convenience of use that would make them applicable to most patients. The recent success of targeted drug therapies for malignant diseases suggests that this approach could be effective for developing optimal HbF-inducing agents. A first step in applying this approach is the identification of specific molecular targets. However, while >70 HbF-inducing agents have been described, neither molecular mechanisms nor target molecules have been definitively verified for any of these compounds. To help focus investigation in this area, we have reviewed known HbF-inducing agents and their proposed mechanisms of action. We find that in many cases, current models inadequately explain key experimental results. By integrating features of the erythropoietic stress model of HbF induction with data from recent intracellular signaling experiments, we have developed a new model that has the potential to explain several findings that are inconsistent with previous models and to unify most HbF-inducing agents under a common mechanism: cell stress signaling. If correct, this or related models could lead to new opportunities for development of targeted therapies for the beta-hemoglobinopathies.

Reduction of AHSP synthesis in hemin-induced K562 cells and EPO-induced CD34(+) cells leads to alpha-globin precipitation, impairment of normal hemoglobin production, and increased cell death

OBJECTIVE

alpha-Hemoglobin stabilizing protein (AHSP) binds alpha-hemoglobin (Hb), avoiding its precipitation and its pro-oxidant activity. In the presence of betaHb, the alphaHb-AHSP complex is dismembered and betaHb displaces AHSP to generate the quaternary structure of Hb. The relationship between Hb formation and alterations in AHSP expression, which may affect human erythropoiesis, has not yet been described in human cells. Hence, in this study, we examined the effects of AHSP knockdown in hemin-induced K562 and erythropoietin-induced CD34(+) cells with particular reference to cellular aspects and gene expression.

MATERIALS AND METHODS

Short-hairpin RNA expression vectors aimed at the AHSP mRNA target sequence were cloned and transfected into K562 and CD34(+) cells. K562 and CD34(+) cells were stimulated to erythroid differentiation. Cells were examined in terms of gene expression using quantitative real-time polymerase chain reaction; reactive oxygen species (ROS) production, apoptosis, and Hb production through flow cytometry assays; and immunofluorescence assays for globin chains.

RESULTS

RNA interference-mediated knockdown of AHSP expression resulted in considerable alphaHb precipitation, as well as in a significant decrease in HbF formation. AHSP-knockdown cells demonstrated an increased ROS production and increased rate of apoptosis.

CONCLUSION

These findings strengthen the hypothesis that AHSP stabilizes the alphaHb chain, avoiding its precipitation and its ability to generate ROS, which implicate in cell death. Moreover, data indicate that AHSP may be highly significant for human hemoglobin formation and suggest that AHSP is a key chaperone protein during human erythropoiesis.

Potentiation of the activity of cisplatin and cyclophosphamide by trimidox, a novel ribonucleotide reductase inhibitor, in leukemia-bearing mice

We describe the use of the new ribonucleotide reductase inhibitor, trimidox (TDX), in combination chemotherapy under in vitro and in vivo conditions with cisplatin and cyclophosphamide. In vitro, the combination of TDX and cisplatin was tested in L1210 cells. The combination caused concentration dependent antagonistic or additive effects. However, the combination of TDX-cisplatin-cyclophosphamide in vivo is highly synergistic in both, the L1210 and P388D1 leukemia mouse models. Both combinations, TDX with cisplatin or TDX with cyclophosphamide were also synergistic in the L1210 and P388D1 leukemia animal models.

In vitro induction of fetal hemoglobin in human erythroid progenitor cells

OBJECTIVE

Clinical heterogeneity among patients with sickle cell anemia (SCA) is influenced by the amount of fetal hemoglobin (HbF) within circulating erythrocytes. Current pharmacotherapy focuses on increasing HbF in order to reduce hemolysis and help prevent acute vaso-occlusive events. Hydroxyurea, a known S-phase-specific cytotoxic ribonucleotide reductase (RR) inhibitor, is an effective agent for HbF induction in patients with SCA, but the mechanisms by which hydroxyurea induces HbF in vivo have not been elucidated.

MATERIALS AND METHODS

We adapted an in vitro assay for HbF induction, growing burst-forming unit erythroid (BFU-E) colonies in methylcellulose from peripheral blood of children with SCA and extracting the hemoglobin for high-performance liquid chromatography analysis of HbF. Hydroxyurea and other known RR inhibitors, along with cytotoxic agents that are not RR inhibitors, were tested for the ability to induce HbF using this in vitro assay.

RESULTS

Hydroxyurea decreased the number of BFU-E colonies that grew in culture and significantly increased HbF from 13.6%+/-6.2% to 25.4%+/-8.0% at 50 microM HU (p=0.012). Three other known RR inhibitors also significantly induced HbF: 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (p=0.025), guanazole (p=0.008), and gemcitabine (p=0.028). Cytarabine and alkylating agents BCNU and 4-hydroperoxycyclophosphamide, which are cytotoxic agents but not RR inhibitors, reduced BFU-E colony number but did not significantly induce HbF.

CONCLUSION

Hydroxyurea and other RR inhibitors significantly induce HbF in vitro in human erythroid progenitor cells. Inhibition of RR may be a critical mechanism by which hydroxyurea increases HbF in vivo in patients with SCA.

Combined use of nonmyelosuppressive nitrosourea analogues with hydroxyurea in the induction of F-cell production in a human erythroleukemic cell line

OBJECTIVE

Although hydroxyurea (HU) has been used clinically to treat patients with sickle cell disease (SCD), not all patients benefit from HU treatment due to its toxicity. The objective of this study was to investigate the effectiveness of the use of two new Hb F-inducing nitrosourea analogues, 2-[3-(2-methyl, 2-nitroso) ureido]-2-deoxy-D-glucopyranose (MNGU) and 2-[3-(2-chloroethyl) ureido]-2-deoxy-D-glucopyranose (CGU), in combination with HU in K562 cells or erythroid progenitors.

MATERIALS AND METHODS

After K562 cells were cultured with different concentrations of HU with CGU or MNGU, aliquots of the cells were obtained to determine the total (benzidine-positive) hemoglobin level, number of F cells, and Hb F level. Erythroid progenitor cells of SCD patients and healthy donors were cultured with the optimal drug concentrations, and the number of BFU-E and Hb F level were determined.

RESULTS

Our results showed that the combined use of HU with CGU or MNGU increased the number of both benzidine-positive normoblasts and F cells in a synergistic manner. Further, a lower concentration of HU was required to induce a significant level of Hb F synthesis when combined with either of the two compounds in comparison with treatment with HU alone. On day 4, the number of benzidine-positive cells was 4.5- to 6.5-fold and the number of F cells was 5.0- to 8.0-fold higher than the respective numbers in the untreated K562 cells. Similarly, a 3.2- to 14.3-fold induction of Hb F was obtained when human erythroid progenitors from SCD patients were treated with the same drug combinations.

CONCLUSION

Based on these results, the use of CGU or MNGU in combination with HU might offer substantial benefits to patients with SCD and other hemoglobinopathies.

Diagnostic advances in defining erythropoietic abnormalities and red blood cell diseases

The majority of clinical applications of flow cytometry begin with various approaches to remove red blood cells (RBCs) from the clinical sample. However, multiparameter cytometry has and will continue to contribute much to the understanding of the pathophysiology and diagnostic accuracy in the clinical evaluation of human diseases affecting erythroid cells. This review summarizes the diagnostic advances relating to erythroid cells in the areas of immunohematology, laboratory hematology, and infectious disease with particular emphasis on medical evaluation of the anemic patient and fetomaternal hemorrhage. Semin Hematol 38:148-159.