Treatment of acute promyelocytic leukemia by retinoids

Cyanide Poisoning Compromises Gene Pathways Modulating Cardiac Injury in Vivo

Smoke inhalation from a structure fire is a common route of cyanide poisoning in the U.S. Cyanide inhibits cellular respiration, often leading to death. Its rapid distribution throughout the body can result in injuries to multiple organs, and cyanide victims were reported to experience myocardial infarction and other cardiac complications. However, molecular mechanisms of such complications are yet to be elucidated. While FDA-approved CN antidotes such as sodium thiosulfate and hydroxocobalamin are clinically used, they have foreseeable limitations during mass casualty situations because they require intravenous administration. To facilitate the development of better antidotes and therapeutic treatments, a global view of molecular changes induced by cyanide exposure is necessary. As an exploratory pursuit, we performed oligonucleotide microarrays to establish cardiac transcriptomes of an animal model of nose-only inhalation exposure to hydrogen cyanide (HCN), which is relevant to smoke inhalation. We also profiled cardiac transcriptomes after subcutaneous injection of potassium cyanide (KCN). Although the KCN injection model has often been used to evaluate medical countermeasures, this study demonstrated that cardiac transcriptomes are largely different from that of the HCN inhalation model at multiple time points within 24 h after exposure. Pathway analysis identified that HCN-induced transcriptomes were enriched with genes encoding mediators of pathways critical in modulation of cardiac complications and that a large number of such genes were significantly decreased in expression. We utilized the upstream regulatory analysis to propose drugs that can be potentially employed to treat cyanide-induced cardiac complications.

Cardiac retinoic acid levels decline in heart failure

Although low circulating levels of the vitamin A metabolite, all-trans retinoic acid (ATRA), are associated with increased risk of cardiovascular events and all-cause mortality, few studies have addressed whether cardiac retinoid levels are altered in the failing heart. Here, we showed that proteomic analyses of human and guinea pig heart failure (HF) were consistent with a decline in resident cardiac ATRA. Quantitation of the retinoids in ventricular myocardium by mass spectrometry revealed 32% and 39% ATRA decreases in guinea pig HF and in patients with idiopathic dilated cardiomyopathy (IDCM), respectively, despite ample reserves of cardiac vitamin A. ATRA (2 mg/kg/d) was sufficient to mitigate cardiac remodeling and prevent functional decline in guinea pig HF. Although cardiac ATRA declined in guinea pig HF and human IDCM, levels of certain retinoid metabolic enzymes diverged. Specifically, high expression of the ATRA-catabolizing enzyme, CYP26A1, in human IDCM could dampen prospects for an ATRA-based therapy. Pertinently, a pan-CYP26 inhibitor, talarozole, blunted the impact of phenylephrine on ATRA decline and hypertrophy in neonatal rat ventricular myocytes. Taken together, we submit that low cardiac ATRA attenuates the expression of critical ATRA-dependent gene programs in HF and that strategies to normalize ATRA metabolism, like CYP26 inhibition, may have therapeutic potential.

Honokiol induces paraptosis-like cell death of acute promyelocytic leukemia via mTOR & MAPK signaling pathways activation

Acute promyelocytic leukemia (APL) is a blood system disease caused by the accumulation of a large number of immature blood cells in bone marrow. Although the introduction of all-trans retinoic acid (ATRA) and arsenic has reached a high level of complete remission rate and 5-year disease-free survival rate, the occurrence of various adverse reactions still severely affects the quality of life of patients. As a natural product, honokiol (HNK) has the advantages of low toxicity and high efficiency, and it is a potential drug for the treatment of cancer. Since cancer cells can escape apoptotic cell death through multiple adaptive mechanisms, HNK, a drug that induces cancer cell death in a nonapoptotic way, has attracted much interest. We found that HNK reduced the viability of human APL cell line (NB4 cells) by inducing paraptosis-like cell death. The process was accompanied by excessive reactive oxygen species (ROS), mitochondrial damage, endoplasmic reticulum stress, and increased microtubule-associated protein 1 light chain 3 (LC3) processing. The inactivation of proteasome activity was the main cause of misfolded and unfolded protein accumulation in endoplasmic reticulum, such as LC3II/I and p62. This phenomenon could be alleviated by adding cycloheximide (CHX), a protein synthesis inhibitor. We found that mTOR signaling pathway participated in paraptosis-like cell death induced by HNK in an autophagy-independent process. Moreover, the mitogen-activated protein kinase (MAPK) signaling pathway induced paraptosis of NB4 cells by promoting endoplasmic reticulum stress. In summary, these findings indicate that paraptosis may be a new way to treat APL, and provide novel insights into the potential mechanism of paraptosis-like cell death.

Computational Drug Repositioning Identifies Potentially Active Therapies for Chordoma

BACKGROUND

Chordomas are aggressive bone tumors that often recur despite maximal resection and adjuvant radiation. To date there are no Food and Drug Administration (FDA)-approved chemotherapies. Computational drug repositioning is an expanding approach to identify pharmacotherapies for clinical trials.

OBJECTIVE

To identify FDA-approved compounds for repurposing in chordoma.

METHODS

Previously identified highly differentially expressed genes from chordoma tissue samples at our institution were compared with pharmacogenomic interactions in the Comparative Toxicogenomics Database (CTD) using ksRepo, a drug-repositioning platform. Compounds selected by ksRepo were then validated in CH22 and UM-Chor1 human chordoma cells in Vitro.

RESULTS

A total of 13 chemical compounds were identified in silico from the CTD, and 6 were selected for preclinical validation in human chordoma cell lines based on their clinical relevance. Of these, 3 identified drugs are FDA-approved chemotherapies for other malignancies (cisplatin, cytarabine, and lucanthone). Cytarabine, a deoxyribonucleic acid polymerase inhibitor approved for the treatment of various leukemias, exhibited a significant concentration-dependent effect against CH22 and UM-Chor1 cells when compared to positive (THZ1) and negative (venetoclax) controls. Tretinoin exhibited a significant concentration-dependent cytotoxic effect in CH22, sacral chordoma-derived cell lines but to a much lesser extent in UM-Chor1, a cell line derived from skull base chordoma.

CONCLUSION

Cytarabine administration reduces the viability of human chordoma cells. The equally effective reduction in viability seen with tretinoin seems to be cell line dependent. Based on our findings, we recommend the evaluation of cytarabine and tretinoin in an expanded set of human chordoma cell lines and animal models.

Therapeutic Approaches for Acute Promyelocytic Leukaemia: Moving Towards an Orally Chemotherapy-Free Era

The treatment of acute promyelocytic leukaemia (APL) has evolved dramatically over the past several decades, making the disease a highly curable form of acute leukaemia. The discoveries of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) were landmark events, leading to historic revolutions in the treatment of APL. One major change was from chemotherapy-based to chemotherapy-free treatment regimens, and the combination of ATRA plus ATO without chemotherapy has been recommended as the standard therapy for non-high-risk APL. The other major change was from the intravenous administration of medicine in the hospital to a largely home-based oral approach, which is a more cost-effective and convenient treatment model. In this review, we focus on the evolution of therapeutic approaches for APL, as well as the challenges that remain with the current approaches.

Chidamide acts on the histone deacetylase-mediated miR-34a/Bcl-2 axis to regulate NB4 cell line proliferation and apoptosis

Acute promyelocytic leukemia (APL), a biologically and clinically distinct variant of acute myelogenous leukemia, is characterized by the fusion of the N-terminus of promyelocytic leukemia protein to the C terminus of retinoic acid receptor alpha, mostly due to chromosomal translocation t(15;17). Chidamide, a synthetic analogue of MS-275 identified from a group of benzamide-type compounds, has been found to have efficient anticancer activity in basic and clinical research studies. However, the concrete role and underlying mechanism of Chidamide in the treatment of APL has not been well characterized. Our data demonstrate that Chidamide inhibited the expression of histone deacetylase (HDAC) to induce apoptosis and suppress proliferation in NB4 cells. Mechanistically, Chidamide increases the expression of miR-34a by suppressing HDAC. Furthermore, B-cell lymphoma-2 (Bcl-2) is a direct target of miR-34a, the expression of which is regulated by miR-34a. Functionally, Chidamide inhibits cell proliferation and promotes apoptosis through miR-34a/Bcl-2. Chidamide exerts its anticancer effect via the HDAC-mediated miR-34a/Bcl-2 axis, providing potential targets for APL therapy.

Endoplasmic Reticulum Calcium Pumps and Tumor Cell Differentiation

Endoplasmic reticulum (ER) calcium homeostasis plays an essential role in cellular calcium signaling, intra-ER protein chaperoning and maturation, as well as in the interaction of the ER with other organelles. Calcium is accumulated in the ER by sarco/endoplasmic reticulum calcium ATPases (SERCA enzymes) that generate by active, ATP-dependent transport, a several thousand-fold calcium ion concentration gradient between the cytosol (low nanomolar) and the ER lumen (high micromolar). SERCA enzymes are coded by three genes that by alternative splicing give rise to several isoforms, which can display isoform-specific calcium transport characteristics. SERCA expression levels and isoenzyme composition vary according to cell type, and this constitutes a mechanism whereby ER calcium homeostasis is adapted to the signaling and metabolic needs of the cell, depending on its phenotype, its state of activation and differentiation. As reviewed here, in several normal epithelial cell types including bronchial, mammary, gastric, colonic and choroid plexus epithelium, as well as in mature cells of hematopoietic origin such as pumps are simultaneously expressed, whereas in corresponding tumors and leukemias SERCA3 expression is selectively down-regulated. SERCA3 expression is restored during the pharmacologically induced differentiation of various cancer and leukemia cell types. SERCA3 is a useful marker for the study of cell differentiation, and the loss of SERCA3 expression constitutes a previously unrecognized example of the remodeling of calcium homeostasis in tumors.

Acute Promyelocytic Leukemia: Update on the Mechanisms of Leukemogenesis, Resistance and on Innovative Treatment Strategies

This review highlights new findings that have deepened our understanding of the mechanisms of leukemogenesis, therapy and resistance in acute promyelocytic leukemia (APL). Promyelocytic leukemia-retinoic acid receptor α (PML-RARa) sets the cellular landscape of acute promyelocytic leukemia (APL) by repressing the transcription of RARa target genes and disrupting PML-NBs. The RAR receptors control the homeostasis of tissue growth, modeling and regeneration, and PML-NBs are involved in self-renewal of normal and cancer stem cells, DNA damage response, senescence and stress response. The additional somatic mutations in APL mainly involve FLT3, WT1, NRAS, KRAS, ARID1B and ARID1A genes. The treatment outcomes in patients with newly diagnosed APL improved dramatically since the advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). ATRA activates the transcription of blocked genes and degrades PML-RARα, while ATO degrades PML-RARa by promoting apoptosis and has a pro-oxidant effect. The resistance to ATRA and ATO may derive from the mutations in the RARa ligand binding domain (LBD) and in the PML-B2 domain of PML-RARa, but such mutations cannot explain the majority of resistances experienced in the clinic, globally accounting for 5-10% of cases. Several studies are ongoing to unravel clonal evolution and resistance, suggesting the therapeutic potential of new retinoid molecules and combinatorial treatments of ATRA or ATO with different drugs acting through alternative mechanisms of action, which may lead to synergistic effects on growth control or the induction of apoptosis in APL cells.

Transglutaminase 2 programs differentiating acute promyelocytic leukemia cells in all-trans retinoic acid treatment to inflammatory stage through NF-κB activation

Differentiation syndrome (DS) is a life-threatening complication arising during retinoid treatment of acute promyelocytic leukemia (APL). Administration of all-trans retinoic acid leads to significant changes in gene expression, among the most induced of which is transglutaminase 2, which is not normally expressed in neutrophil granulocytes. To evaluate the pathophysiological function of transglutaminase 2 in the context of immunological function and disease outcomes, such as excessive superoxide anion, cytokine, and chemokine production in differentiated NB4 cells, we used an NB4 transglutaminase knock-out cell line and a transglutaminase inhibitor, NC9, which inhibits both transamidase- and guanosine triphosphate-binding activities, to clarify the contribution of transglutaminase to the development of potentially lethal DS during all-trans retinoic acid treatment of APL. We found that such treatment not only enhanced cell-surface expression of CD11b and CD11c but also induced high-affinity states; atypical transglutaminase 2 expression in NB4 cells activated the nuclear factor kappa (κ)-light-chain-enhancer of the activated B-cell pathway, driving pathogenic processes with an inflammatory cascade through the expression of numerous cytokines, including tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and monocyte chemoattractant protein 1. NC9 decreased the amount of transglutaminase 2, p65/RelA, and p50 in differentiated NB4 cells and their nuclei, leading to attenuated inflammatory cytokine synthesis. NC9 significantly inhibits transglutaminase 2 nuclear translocation but accelerates its proteasomal breakdown. This study demonstrates that transglutaminase 2 expression induced by all-trans retinoic acid treatment reprograms inflammatory signaling networks governed by nuclear factor κ-light-chain-enhancer of activated B-cell activation, resulting in overexpression of TNF-α and IL-1β in differentiating APL cells, suggesting that atypically expressed transglutaminase 2 is a promising target for leukemia treatment.

Vernodalol mediates antitumor effects in acute promyelocytic leukemia cells

Acute promyelocytic leukemia (APL) remains a challenge to cure due to the side effects of cytotoxic chemotherapy and drug resistance. The present study demonstrated that vernodalol, an active compound isolated from Centratherum anthelminticum, suppresses APL cell proliferation and induces cell cycle arrest in the G2/M phase through the upregulation of p21 and cell division cycle 25. In addition, vernodalol induced cellular apoptosis via the mitochondrial pathway as observed by the cleavage of caspase-9 as well as the release of cytochrome c and Smac/DIABLO into the cytosol. A mechanistic study revealed that vernodalol may exert its antitumor activity through the suppression of phosphoinositide 3-kinase/protein kinase B/mechanistic target of rapamycin signaling. In conclusion, vernodalol may be developed as a potential therapeutic compound for the treatment of APL.

Catching moving targets: cancer stem cell hierarchies, therapy-resistance & considerations for clinical intervention

It is widely believed that targeting the tumour-initiating cancer stem cell (CSC) component of malignancy has great therapeutic potential, particularly in therapy-resistant disease. However, despite concerted efforts, CSC-targeting strategies have not been efficiently translated to the clinic. This is partly due to our incomplete understanding of the mechanisms underlying CSC therapy-resistance. In particular, the relationship between therapy-resistance and the organisation of CSCs as Stem-Progenitor-Differentiated cell hierarchies has not been widely studied. In this review we argue that modern clinical strategies should appreciate that the CSC hierarchy is a dynamic target that contains sensitive and resistant components and expresses a collection of therapy-resisting mechanisms. We propose that the CSC hierarchy at primary presentation changes in response to clinical intervention, resulting in a recurrent malignancy that should be targeted differently. As such, addressing the hierarchical organisation of CSCs into our bench-side theory should expedite translation of CSC-targeting to bed-side practice. In conclusion, we discuss strategies through which we can catch these moving clinical targets to specifically compromise therapy-resistant disease.

From conventional therapy toward microRNA-based therapy in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a hematopoietic malignancy that is known with its special cytogenetic feature. Several studies have surveyed expression signature of microRNAs (miRNAs) in APL patients, especially patients who are treated with conventional therapy of this disease. Using miRNAs as diagnostic or prognostic biomarkers in various cancers has been widely studied. Currently, most studies are focusing on exploiting miRNAs as therapeutic tools, and promising progress has been achieved in this field. Recently, studies in the field of miRNA-based therapy in APL have been started.

Biodegradable Elastomers with Antioxidant and Retinoid-like Properties

Intimal hyperplasia (IH) is a type of scarring that involves complex pathophysiological responses of the vasculature to injury, including overproliferation and migration of vascular smooth muscle cells (VSMCs), adventitial fibroblasts, and the activation of macrophages. The objective of this research was to develop a biodegradable polymer with intrinsic properties that would combat the cellular processes that contribute to IH. Citric acid, 1,8-octanediol, and all-trans retinoic acid (atRA) were incorporated into a polyester network via a condensation reaction to form the thermoset poly(1,8-octamethylene-citrate-co-retinate) (POCR). POCR was chemically characterized and assessed for the presence of antioxidant and retinoidlike properties. ^HNMR and ATR-FTIR confirmed the incorporation of atRA into the backbone of the polymer network. POCR was able to scavenge radicals and inhibit lipid peroxidation. The proliferation and migration of vascular smooth muscle cells cultured on POCR were inhibited, whereas endothelial cell proliferation and migration were not. These results are consistent with the biological effects of atRA. These results are the first to demonstrate the synthesis of a polymer with intrinsic antirestenotic properties for potential use in the fabrication of vascular devices such as stents and vascular grafts.

Role of Retinoic Acid-Metabolizing Cytochrome P450s, CYP26, in Inflammation and Cancer

Vitamin A (retinol) and its active metabolite, all-trans-retinoic acid (atRA), play critical roles in regulating the differentiation, growth, and migration of immune cells. Similarly, as critical signaling molecules in the regulation of the cell cycle, retinoids are important in cancers. Concentrations of atRA are tightly regulated in tissues, predominantly by the availability of retinol, synthesis of atRA by ALDH1A enzymes and metabolism and clearance of atRA by CYP26 enzymes. The ALDH1A and CYP26 enzymes are expressed in several cell types in the immune system and in cancer cells. In the immune system, the ALDH1A and CYP26 enzymes appear to modulate RA concentrations. Consequently, alterations in the activity of ALDH1A and CYP26 enzymes are expected to change disease outcomes in inflammation. There is increasing evidence from various disease models of intestinal and skin inflammation that treatment with atRA has a positive effect on disease markers. However, whether aberrant atRA concentrations or atRA synthesis and metabolism play a role in inflammatory disease development and progression is not well understood. In cancers, especially in acute promyelocytic leukemia and neuroblastoma, increasing intracellular concentrations of atRA appears to provide clinical benefit. Inhibition of the CYP26 enzymes to increase atRA concentrations and combat therapy resistance has been pursued as a drug target in these cancers. This chapter covers the current knowledge of how atRA and retinol regulate the immune system and inflammation, how retinol and atRA metabolism is altered in inflammation and cancer, and what roles atRA-metabolizing enzymes have in immune responses and cancers.

Periadventitial atRA citrate-based polyester membranes reduce neointimal hyperplasia and restenosis after carotid injury in rats

Oral all-trans retinoic acid (atRA) has been shown to reduce the formation of neointimal hyperplasia; however, the dose required was 30 times the chemotherapeutic dose, which already has reported side effects. As neointimal formation is a localized process, new approaches to localized delivery are required. This study assessed whether atRA within a citrate-based polyester, poly(1,8 octanediolcitrate) (POC), perivascular membrane would prevent neointimal hyperplasia following arterial injury. atRA-POC membranes were prepared and characterized for atRA release via high-performance liquid chromatography with mass spectrometry detection. Rat adventitial fibroblasts (AF) and vascular smooth muscle cells (VSMC) were exposed to various concentrations of atRA; proliferation, apoptosis, and necrosis were assessed in vitro. The rat carotid artery balloon injury model was used to evaluate the impact of the atRA-POC membranes on neointimal formation, cell proliferation, apoptosis, macrophage infiltration, and vascular cell adhesion molecule 1 (VCAM-1) expression in vivo. atRA-POC membranes released 12 μg of atRA over 2 wk, with 92% of the release occurring in the first week. At 24 h, atRA (200 μmol/l) inhibited [(3)H]-thymidine incorporation into AF and VSMC by 78% and 72%, respectively (*P = 0.001), with negligible apoptosis or necrosis. Histomorphometry analysis showed that atRA-POC membranes inhibited neointimal formation after balloon injury, with a 56%, 57%, and 50% decrease in the intimal area, intima-to-media area ratio, and percent stenosis, respectively (P = 0.001). atRA-POC membranes had no appreciable effect on apoptosis or proliferation at 2 wk. Regarding biocompatibility, we found a 76% decrease in macrophage infiltration in the intima layer (P < 0.003) in animals treated with atRA-POC membranes, with a coinciding 53% reduction in VCAM-1 staining (P < 0.001). In conclusion, perivascular delivery of atRA inhibited neointimal formation and restenosis. These data suggest that atRA-POC membranes may be suitable as localized therapy to inhibit neointimal hyperplasia following open cardiovascular procedures.

Histone deacetylase inhibition in the treatment of acute myeloid leukemia: the effects of valproic acid on leukemic cells, and the clinical and experimental evidence for combining valproic acid with other antileukemic agents

Several new therapeutic strategies are now considered for acute myeloid leukemia (AML) patients unfit for intensive chemotherapy, including modulation of protein lysine acetylation through inhibition of histone deacetylases (HDACs). These enzymes alter the acetylation of several proteins, including histones and transcription factors, as well as several other proteins directly involved in the regulation of cell proliferation, differentiation and apoptosis. Valproic acid (VPA) is a HDAC inhibitor that has been investigated in several clinical AML studies, usually in combination with all-trans retinoic acid (ATRA) for treatment of patients unfit for intensive chemotherapy, for example older patients, and many of these patients have relapsed or primary resistant leukemia. The toxicity of VPA in these patients is low and complete hematological remission lasting for several months has been reported for a few patients (<5% of included patients), but increased peripheral blood platelet counts are seen for 30 to 40% of patients and may last for up to 1 to 2 years. We review the biological effects of VPA on human AML cells, the results from clinical studies of VPA in the treatment of AML and the evidence for combining VPA with new targeted therapy. However, it should be emphasized that VPA has not been investigated in randomized clinical studies. Despite this lack of randomized studies, we conclude that disease-stabilizing treatment including VPA should be considered especially in unfit patients, because the possibility of improving normal blood values has been documented in several studies and the risk of clinically relevant toxicity is minimal.

Molecular pathways: current role and future directions of the retinoic acid pathway in cancer prevention and treatment

Retinoids and their naturally metabolized and synthetic products (e.g., all-trans retinoic acid, 13-cis retinoic acid, bexarotene) induce differentiation in various cell types. Retinoids exert their actions mainly through binding to the nuclear retinoic acid receptors (α, β, γ), which are transcriptional and homeostatic regulators with functions that are often compromised early in neoplastic transformation. The retinoids have been investigated extensively for their use in cancer prevention and treatment. Success has been achieved with their use in the treatment of subtypes of leukemia harboring chromosomal translocations. Promising results have been observed in the breast cancer prevention setting, where fenretinide prevention trials have provided a strong rationale for further investigation in young women at high risk for breast cancer. Ongoing phase III randomized trials investigating retinoids in combination with chemotherapy in non-small cell lung cancer aim to definitively characterize the role of retinoids in this tumor type. The limited treatment success observed to date in the prevention and treatment of solid tumors may relate to the frequent epigenetic silencing of RARβ. Robust evaluation of RARβ and downstream genes may permit optimized use of retinoids in the solid tumor arena.

9-Cis-retinoic acid induces growth inhibition in retinoid-sensitive breast cancer and sea urchin embryonic cells via retinoid X receptor α and replication factor C3

There is widespread interest in defining factors and mechanisms that suppress the proliferation of cancer cells. Retinoic acid (RA) is a potent suppressor of mammary cancer and developmental embryonic cell proliferation. However, the molecular mechanisms by which 9-cis-RA signaling induces growth inhibition in RA-sensitive breast cancer and embryonic cells are not apparent. Here, we provide evidence that the inhibitory effect of 9-cis-RA on cell proliferation depends on 9-cis-RA-dependent interaction of retinoid X receptor α (RXRα) with replication factor C3 (RFC3), which is a subunit of the RFC heteropentamer that opens and closes the circular proliferating cell nuclear antigen (PCNA) clamp on DNA. An RFC3 ortholog in a sea urchin cDNA library was isolated by using the ligand-binding domain of RXRα as bait in a yeast two-hybrid screening. The interaction of RFC3 with RXRα depends on 9-cis-RA and bexarotene, but not on all-trans-RA or an RA receptor (RAR)-selective ligand. Truncation and mutagenesis experiments demonstrated that the C-terminal LXXLL motifs in both human and sea urchin RFC3 are critical for the interaction with RXRα. The transient interaction between 9-cis-RA-activated RXRα and RFC3 resulted in reconfiguration of the PCNA-RFC complex. Furthermore, we found that knockdown of RXRα or overexpression of RFC3 impairs the ability of 9-cis-RA to inhibit proliferation of MCF-7 breast cancer cells and sea urchin embryogenesis. Our results indicate that 9-cis-RA-activated RXRα suppresses the growth of RA-sensitive breast cancer and embryonic cells through RFC3.

Bradycardia following retinoic acid differentiation syndrome in a patient with acute promyelocytic leukaemia

The authors describe a 28-year-old woman with newly diagnosed acute promyelocytic leukaemia (APL), who developed junctional bradycardia after receiving the molecular-targeted therapy all-trans retinoic acid (ATRA) and the anthracycline-based chemotherapeutic agent idarubicin following sepsis and the APL differentiation syndrome. The patient was asymptomatic of the bradycardia. Electrolytes and cardiac imaging were unremarkable. No other cases have been reported in this context and the mechanisms of the sinus node dysfunction are unclear. The patient achieved normal sinus rhythm after ATRA was withheld. The patient recovered and went on to achieve complete remission after re-starting ATRA and idarubicin.

Advances in therapies for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL), a distinct subtype of acute myelogenous leukemia (AML), results from the arrest of the maturation of hematopoietic progenitors at the promyelocyte stage. It has been shown that APL is associated with a reciprocal chromosomal translocation, involving chromosomes 15 and 17, which fuses the gene encoding the retinoic acid receptor α (RARα) and the promyelocytic leukemia (PML) gene. The resultant PML-RARα fusion protein plays a critical role in the pathogenesis of APL. Although there are many subtypes of AML, all are typically managed using a standard chemotherapy regimen of an anthracycline plus cytarabine arabinoside (CA). Despite high rates of complete remission following standard chemotherapy, most patients relapse and long-term disease-free survival is only 30-40%. The introduction of drugs such as all-trans retinoic acid (ATRA) that promote progenitor differentiation by directly inhibiting the PML-RARα fusion protein has changed the treatment paradigm for APL and markedly improved patient survival. The purposes of the present review are to provide the latest results and future directions of clinical research into APL and to illustrate how new therapies, such as ATRA plus anthracycline-based induction and consolidation therapy, risk-adapted therapy, salvage therapy containing arsenic trioxide-based regimens, and hematopoietic stem cell transplantation, have improved the treatment outcomes for APL patients.

Inhibition of mitotic kinase Aurora suppresses Akt-1 activation and induces apoptotic cell death in all-trans retinoid acid-resistant acute promyelocytic leukemia cells

BACKGROUND

Aurora kinase ensures accurate chromosome segregation during cell cycle, maintaining genetic integrity in cell division. VX-680, a small-molecule Aurora kinase inhibitor, interferes with mitotic entry and formation of bipolar spindles. Here, we evaluated VX-680 as a potential agent for treatment of all-trans retinoid acid (ATRA)-resistant acute promyelocytic leukemia (APL) in vitro.

METHODS

CD11b expression was utilized to assess cell differentiation by flow cytometry. Immunofluorescence staining was conducted to analyze formation of cell monopolar spindle. Cell proliferation was evaluated by MTT assay. Sub-G1 population and Annexin V/PI staining were used to measure cell apoptosis. Hoechst 33342 staining was applied for identifying morphological changes in nucleus of apoptotic cell. Aurora-A (Aur-A) activation and the signaling pathways involved in apoptosis were detected by Western blot. JC-1 probe was employed to measure mitochondrial depolarization.

RESULTS

VX-680 inhibited Aur-A by reducing autophosphorylation at the activation site, Thr288, accompanied by producing monopolar mitotic spindles in APL cell line NB4-R2 that was resistant to ATRA. In addition, we found that VX-680 inhibited cell proliferation as assessed by MTT assay. Flow cytometry showed that VX-680 led to apoptotic cell death in both dose- and time-dependent manners by either Sub-G1 or Annexin V/PI analysis. Hoechst 33342 staining represented typical apoptotic cells with nuclear fragmentation in VX-680 treated cells. Importantly, VX-680 inhibition of Aurora kinase suppressed Akt-1 activation and induced mitochondrial depolarization, which eventually resulted in apoptosis by activation of caspase pathway, as indicated by increasing proteolytic cleavage of procaspase-3 and poly ADP ribose polymerase (PARP) in NB4-R2 cells.

CONCLUSIONS

Our study suggested potential clinical use of mitotic Aurora kinase inhibitor in targeting ATRA-resistant leukemic cells.

Retinoids, retinoic acid receptors, and cancer

Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells. Nuclear retinoic acid receptors mediate most but not all of the effects of retinoids. Retinoid signaling is often compromised early in carcinogenesis, which suggests that a reduction in retinoid signaling may be required for tumor development. Retinoids interact with other signaling pathways, including estrogen signaling in breast cancer. Retinoids are used to treat cancer, in part because of their ability to induce differentiation and arrest proliferation. Delivery of retinoids to patients is challenging because of the rapid metabolism of some retinoids and because epigenetic changes can render cells retinoid resistant. Successful cancer therapy with retinoids is likely to require combination therapy with drugs that regulate the epigenome, such as DNA methyltransferase and histone deacetylase inhibitors, as well as classical chemotherapeutic agents. Thus, retinoid research benefits both cancer prevention and cancer treatment.

The biological characteristics of adult CD34+ acute promyelocytic leukemia

We aimed to explore the expression of CD34 and its impact on the disease outcome in patients with APL. The study comprised 40 de novo APL patients. Diagnostic tools included peripheral blood and bone marrow morphology and cytochemistry, immunophenotyping, cytogenetic studies, and PML/RARα fusion gene detection using RT-PCR. CD34 was expressed in 13 (32.5%) of cases with higher expression in M3v compared to M3 subtype. All M3v cases were CD34+, while only 7.4% of M3 cases were CD34+. CD34+ cases were associated with significant higher white blood cell count and peripheral blood promyelocytes. No significant association was found between PML/RAR-α isoform and molecular remission. CD34+ expression was significantly associated with decreased incidence of molecular remission and increased incidence of early death. The overall survival of patients with WBC count >11 × 103/μl was inferior to patients with WBC count <11 × 103/μl, but no significant differences were observed in overall survival between CD34- and CD34+ or between bcr1 and bcr3 groups. Immunophenotypic analysis for CD34 could distinguish an APL subset with different biological characteristics and adverse prognostic outcome.

NRF2 as a determinant of cellular resistance in retinoic acid cytotoxicity

Clinical use of retinoic acids (RA) is hindered by toxicity possibly related to oxidative stress. Recently, RA at relatively low concentrations was shown to inhibit NRF2 and the expression of its target antioxidative genes. This raises the possibility that RA toxicity may result from cellular inability to cope with resultant oxidative stress. Using in vitro cell and in vivo mouse models, we report that RA, specifically all-trans-RA (atRA) at concentrations implicated in toxicity, can activate NRF2 and induce NRF2 target genes, particularly the subunits of the rate-limiting enzyme of glutathione biosynthesis, glutamate cysteine ligase (GCLM/GCLC). RNA interference-mediated silencing of NRF2, but not of retinoid X receptor-alpha and -beta, reduced basal and atRA-induced GCLM/GCLC gene expression. Moreover, RA increased nuclear accumulation of NRF2, antioxidant response element (ARE) reporter activity, and NRF2 occupancy at AREs. 4-Hydroxynonenal, a lipid peroxidation product, was increased by RA. Inhibition of MEK1/ERK mitogen-activated protein kinases significantly suppressed atRA-induced NRF2 activation and ARE-regulated gene expression, reducing cell resistance against toxic concentrations of RA. NRF2-silenced cells were vulnerable to atRA-induced mitochondrial toxicity and apoptosis. In conclusion, toxic RA activates NRF2, thereby triggering an adaptive response against the resultant oxidative stress. NRF2 enhancement as a therapeutic target of retinoid toxicity awaits further investigation.

Retinoids, rexinoids and their cognate nuclear receptors: character and their role in chemoprevention of selected malignant diseases

BACKGROUND

Retinoids, rexinoids and their biologically active derivatives are involved in a complex arrangement of physiological and developmental responses in many tissues of higher vertebrates. Both retinoids and rexinoids are either natural or synthetic compounds related to retinoic acids that act through interaction with two basic types of nuclear receptors belonging to the nuclear receptor superfamily: All-trans retinoic acid receptors (RARalpha, RARbeta, and RARgamma) and retinoid X receptors (RXRalpha, RXRbeta and RXRgamma) as retinoid-inducible transcription factors.

AIM

Summarization of selected effects of biologically active natural or synthetic retinoids and rexinoids and their exploitation in chemoprevention of various types of cancer.

RESULTS

Retinoid receptors play a role as ligand-activated, DNA-binding, trans-acting, transcription-modulating proteins involved in a general molecular mechanism responsible for transcriptional responses in target genes. They exert both beneficial and detrimental activity; they have tumour-suppressive activity but on the other hand they are teratogenic. A number of nuclear receptor selective retinoids and rexinoids, have been successfully tested using a variety of cell lines or animal models. Retinoids inhibit carcinogenesis, suppress premalignant epithelial lesions and tumour growth and invasion in a variety of tissues.

CONCLUSIONS

Natural and synthetic retinoids exert important biological effects due to their antiproliferative and apoptosis-inducing effects. They are also known to cause redifferentiation or to prevent further dedifferentiation of various tumour tissues.

NDRG1 contributes to retinoic acid-induced differentiation of leukemic cells

N-Myc downstream-regulated gene 1 (NDRG1) protein has been shown to be up-regulated during leukemic cell differentiation induced by some differentiation-inducing agents such as all-trans retinoic acid (ATRA). However, the potential role of up-regulated NDRG1 in the event is greatly unknown. In this work, we show that inducible NDRG1 expression can drive leukemic U937 cells to undergo differentiation, while the knock-down of NDRG1 expression by specific small interfering RNA significantly antagonizes ATRA-induced differentiation of leukemic cells, proposing the role of NDRG1 in leukemic cell differentiation. Furthermore, our work shows that CCAAT/enhancer-binding protein beta (C/EBPbeta) and PU.1, which are important hematopoiesis-related transcription factors, may act as downstream effectors of NDRG1 in leukemic cell differentiation. Taking together, this study provides direct evidence for the role of NDRG1 protein in myeloid leukemic cell differentiation.

Inhibiting the platelet derived growth factor receptor increases signs of retinoic acid syndrome in myeloid differentiated HL-60 cells

PDGFR inhibitors are successfully used in a number of cancer treatments. The standard treatment for acute promyelocytic leukemia (APL) involves differentiation therapy with retinoic acid (RA). However, the relapse rates are significant. In the present work we evaluated the effects of RA therapy in the presence of PDGFR inhibitor, AG1296. Adding AG1296 with RA increased secretion of TNF-alpha, IL-8, and MMP-9 expression. This treatment induced higher levels of ICAM-1 endothelial cell expression, and increased cellular mobility. Inhibiting PDGFR enhanced RA-induced expression of integrin. Integrin ligand increased differentiation markers CD11b, inducible oxidative metabolism and PDGFR-beta phosphorylation. While the neutrophil-endothelial cell interactions are strengthened by the combined treatment, the endothelium-substratum interactions are weakened, a situation common in RAS.

E3 ligase FLRF (Rnf41) regulates differentiation of hematopoietic progenitors by governing steady-state levels of cytokine and retinoic acid receptors

OBJECTIVE

FLRF (Rnf41) gene was identified through screening of subtracted cDNA libraries form murine hematopoietic stem cells and progenitors. Subsequent work has revealed that FLRF acts as E3 ubiquitin ligase, and that it regulates steady-state levels of neuregulin receptor ErbB3 and participates in degradation of IAP protein BRUCE and parkin. The objective of this study was to start exploring the role of FLRF during hematopoiesis.

MATERIALS AND METHODS

FLRF was overexpressed in a murine multipotent hematopoietic progenitor cell line EML, which can differentiate into almost all blood cell lineages, and in pro-B progenitor cell line BaF3. The impact of FLRF overexpression on EML cell differentiation into myeloerythroid lineages was studied using hematopoietic colony-forming assays. The interaction of FLRF with cytokine receptors and receptor levels in control cells and EML and BaF3 cells overexpressing FLRF were examined with Western and immunoprecipitation.

RESULTS

Remarkably, overexpression of FLRF significantly attenuated erythroid and myeloid differentiation of EML cells in response to cytokines erythropoietin (EPO) and interleukin-3 (IL-3), and retinoic acid (RA), and resulted in significant and constitutive decrease of steady-state levels of IL-3, EPO, and RA receptor-alpha (RARalpha) in EML and BaF3 cells. Immunoprecipitation has revealed that FLRF interacts with IL-3, EPO, and RARalpha receptors in EML and BaF3 cells, and that FLRF-mediated downregulation of these receptors is ligand binding-independent.

CONCLUSIONS

The results of this study have revealed new FLRF-mediated pathway for ligand-independent receptor level regulation, and support the notion that through maintaining basal levels of cytokine receptors, FLRF is involved in the control of hematopoietic progenitor cell differentiation into myeloerythroid lineages.

Regulation of FoxP3 regulatory T cells and Th17 cells by retinoids

Vitamin A has both positive and negative regulatory functions in the immune system. While vitamin A is required for normal formation of immune cells and epithelial cell barriers, vitamin A deficiency can lead to increased inflammatory responses and tissue damage. The mechanism with which vitamin A and its metabolites such as retinoids negatively regulate inflammatory responses has not been clearly defined. Recently, it has been established that retinoids promote the generation of immune-suppressive FoxP3⁺ regulatory T cells while they suppress the T cell differentiation into inflammatory Th17 cells in the periphery such as intestine. These novel functions of retinoids provide a potentially important immune regulatory mechanism. In this review, we discuss the functions of retinoids in the development of the FoxP3⁺ cells and Th17 cells, the phenotype and functions of retinoid-induced FoxP3⁺ T cells, and the impact of retinoid-induced FoxP3⁺ T cells on the immune tolerance.