Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D

Telomerase Inhibition in the Treatment of Leukemia: A Comprehensive Review

Leukemia, characterized by the uncontrolled proliferation and differentiation blockage of myeloid or lymphoid precursor cells, presents significant therapeutic challenges despite current treatment modalities like chemotherapy and stem cell transplantation. Pursuing novel therapeutic strategies that selectively target leukemic cells is critical for improving patient outcomes. Natural products offer a promising avenue for developing effective chemotherapy and preventive measures against leukemia, providing a rich source of biologically active compounds. Telomerase, a key enzyme involved in chromosome stabilization and mainly active in cancer cells, presents an attractive target for intervention. In this review article, we focus on the anti-leukemic potential of natural substances, emphasizing vitamins (such as A, D, and E) and polyphenols (including curcumin and indole-3-carbinol), which, in combination with telomerase inhibition, demonstrate reduced cytotoxicity compared to conventional chemotherapies. We discuss the role of human telomerase reverse transcriptase (hTERT), particularly its mRNA expression, as a potential therapeutic target, highlighting the promise of natural compounds in leukemia treatment and prevention.

Structural development of silicon-containing retinoids: structure-activity relationship study of the hydrophobic pharmacophore of retinobenzoic acids using silyl functionalities

We designed and synthesized a series of retinobenzoic acids bearing various silyl functionalities in order to explore in detail the structure-activity relationship (SAR) at the hydrophobic moiety of retinoids. Among the synthesized compounds, 24c bearing a t -butyldimethylsilyl (TBS) group at the hydrophobic site exhibited potent retinoid activity comparable to that of the lead compound Am555S ( 4 ). Compound 24c exhibited transcription-promoting activity towards all three subtypes of retinoic acid receptor (RAR), but showed the highest activity towards RARγ, in contrast to the high RARα-selectivity of Am80 ( 3 ) and Am555S ( 4 ). The SARs presented here should be helpful in the development of subtype-selective retinoids, and in particular 24c might be a promising lead compound for new RARγ ligands.

Understanding the Relationship between Glutathione, TGF-β, and Vitamin D in Combating Mycobacterium tuberculosis Infections

Tuberculosis (TB) remains a pervasive global health threat. A significant proportion of the world's population that is affected by latent tuberculosis infection (LTBI) is at risk for reactivation and subsequent transmission to close contacts. Despite sustained efforts in eradication, the rise of multidrug-resistant strains of Mycobacteriumtuberculosis (M. tb) has rendered traditional antibiotic therapy less effective at mitigating the morbidity and mortality of the disease. Management of TB is further complicated by medications with various off-target effects and poor compliance. Immunocompromised patients are the most at-risk in reactivation of a LTBI, due to impairment in effector immune responses. Our laboratory has previously reported that individuals suffering from Type 2 Diabetes Mellitus (T2DM) and HIV exhibited compromised levels of the antioxidant glutathione (GSH). Restoring the levels of GSH resulted in improved control of M. tb infection. The goal of this review is to provide insights on the diverse roles of TGF- β and vitamin D in altering the levels of GSH, granuloma formation, and clearance of M. tb infection. We propose that these pathways represent a potential avenue for future investigation and development of new TB treatment modalities.

Pardaxin Promoted Differentiation and Maturation of Leukemic Cells via Regulating TLR2/MyD88 Signal against Cell Proliferation

Objective

Leukemia is a cancer of the blood cells. Leukemic THP-1 and U937 cells were used in this study as monocytic effectors cells for proliferation responses and macrophage-like cells induction in leukemia. Pardaxin is an antimicrobial peptide isolated from the marine fish species.

Methods

After treatment for 5 days, pardaxin significantly suppressed cell viability and arrested cell cycle at G0/G1 phase in leukemic cells which were evaluated.

Results

Pardaxin also induced cell differentiation and maturation of THP-1 and U937 cells into macrophage-like cells with phagocytotic ability. Moreover, pardaxin elevated the expression of MyD88 but not toll-like receptor (TLR)-2 in both leukemic cells. TLR-2 blocking peptide was used to confirm that pardaxin attenuated phagocytotic ability and superoxide anion production in leukemic cells via activating MyD88 protein.

Conclusions

These findings suggested that pardaxin has a therapeutic potential for leukemia.

Vitamin D and its receptor polymorphisms: New possible prognostic biomarkers in leukemias

Several factors such as chromosomal translocations, gene mutations, and polymorphisms are involved in the pathogenesis of leukemia/lymphoma. Recently, the role of vitamin D (VD) and vitamin D receptor (VDR) polymorphisms in hematologic malignancies has been considered. In this review, we examine the possible role of VD levels, as well as VDR polymorphisms as prognostic biomarkers in leukemia/lymphoma. Relevant English language literature were searched and retrieved from Google Scholar search engine (1985-2017). The following keywords were used: vitamin D, vitamin D receptor, leukemia, lymphoma, and polymorphism. Increased serum levels of VD in patients with leukemia are associated with a better prognosis. However, low VD levels are associated with a poor prognosis, and VDR polymorphisms in various leukemias can have prognostic value. VD biomarker can be regarded as a potential prognostic factor for a number of leukemias, including acute myeloblastic leukemia (AML), chronic lymphoblastic leukemia (CLL), and diffuse large B-cell lymphoma (DLBCL). There is a significant relationship between different polymorphisms of VDR (including Taq I and Fok I) with several leukemia types such as ALL and AML, which may have prognostic value.

Leukemia Cells and the Cytokine Network: Therapeutic Prospects

The network and balance of cytokines is of major importance in maintaining proper homeostasis of hematopoiesis. Abnormalities in this network may result in a variety of blood disorders; however, the role of this network is not clear in leukemia. The use of antineoplastic agents has improved the survival rate of some types of leukemia, and adjunctive therapy with cytokines may be helpful. Chemotherapeutic approaches are no longer the best choice because cytotoxicity may affect normal and leukemic cells, and leukemic cells may develop resistance to the chemotherapeutic agent. Induction of differentiation to a mature phenotype and the control of apoptotic-gene expression have provided other possible alternative therapies. Combined effects of cytokines and vitamin derivatives such as retinoic acid (RA) and 1, 25 dihydroxyvitamin D3 (VD3) were found more beneficial than any of these agents individually. These agents exhibit cooperative effects, potentiate each other's effects, or both. Therefore, understanding the hematopoietic actions of these agents, their interactions with their receptors, and their differentiation signaling pathways may result In the design of new therapies. However, the role of cytokines in apoptosis is controversial because in some cases they were found to increase tumor cell resistance to apoptosis-inducing agents. Recent studies in the molecular biology of gene regulation, transcription factors, and repressors have led to new possible approaches such as differentiation therapy for the treatment of leukemia. In addition, the development of drugs that act on the molecular level such as imatinib is just the beginning of a new era in molecular targeted therapy in which the drug acts specifically on the leukemic cell. There are many possible combinations of cytokines, retinoids, and VD3, and perhaps the best therapeutic combination is yet to be described. This minireview is an update on the role of cytokines and the therapeutic potential of combinations with agents such as RA, VD3, and other chemotherapeutic agents.

Modifications of Cellular Autofluorescence Emission Spectra under Oxidative Stress Induced by 1 α,25dihydroxyvitamin D3 and its Analog EB1089

We attempted to characterize the cellular autofluorescence phenomenon of living HL-60 cells and to appraise its modifications under oxidative stress conditions induced by 1α,25(OH)2D3 (VD3) and its analog EB1089. Autofluorescence emission spectra of human promyelocytic HL-60 leukemic cells were monitored using laser scanning confocal microspectrofluorometry under UV excitation. Evaluation of reactive oxygen species (ROS) release was performed using the 2′,7′-dichlorodihydrofluorescein diacetate (H2-DCFDA) staining and fluorescence emission measurement. VD3 (1, 10, 100 nM) or EB1089 (0.1, 1 and 10 nM) induces a decrease in autofluorescence emission intensity that can be attributed to the oxidation of the coenzyme nicotinamide adenine dinucleotide (phosphate) NAD(P)H into NAD(P)+. A dose-dependent increase (p<0.05) in ROS release is observed in VD3- and EB1089-treated cells. As compared with VD3- or EB1089-treated cells, doxorubicin-VD3 or doxorubicin-EB1089 treatments strongly decrease the autofluorescence intensity and induce a higher release of ROS (p<0.05). The association of antioxidants (N-acetyl cysteine, superoxide dismutase, catalase) with VD3 or EB1089 induce a more limited autofluorescence decrease and a weaker ROS generation, as compared with VD3 and EB1089 treated cells. In conclusion, the free radicals release, generated by VD3 and EB1089, was associated with the decrease in autofluorescence emission and can be modulated by doxorubicin and antioxidants.

All-trans-retinoic acid and CD38 ligation differentially regulate CD1d expression and α-galactosylceramide-induced immune responses

The MHC class-I like molecule CD1d presents glycolipid antigens and thereby activates invariant natural killer-T (NKT) cells. However, little is understood regarding the regulation of its expression. All-trans-retinoic acid (RA) and CD38, which is itself a target of RA, both independently regulate the differentiation of antigen presenting cells. In the current study, we treated human THP-1 cells and murine splenic cells with RA, with and without antibody-mediated ligation of cell-surface CD38. Whereas a physiological concentration (20 nM) of RA alone rapidly and markedly increased CD1d protein in THP-1 cells, there was a marked synergy between RA and ligation of CD38 with antibody to CD38. Moreover, RA and CD38 ligation differentially regulated CD1d protein distribution between the cell surface and intracellular compartments, as, whereas RA mainly increased intracellular CD1d protein, ligation of CD38 increased CD1d protein both at the cell surface and intracellularly. By confocal microscopy, CD1d was located close to the plasma membrane but only partially overlapped with LAMP1, a late endosomes/lysosomal marker. Furthermore, RA and/or CD38 ligation increased splenocyte proliferation and differentiation after treatment with the CD1 ligand α-galactosylceramide (αGalCer), evidenced by an increase in the number of splenic dendritic cells, NKT cells, and germinal center plasmacytes. RA also differentially regulated αGalCer-induced cytokine expression, increasing IL-4 and decreasing IFNγ production by total spleen cells and the NKT cell population. Our results indicate a previously unknown mechanism in which RA and CD38 differentially yet cooperatively regulate CD1d expression and antigen-presenting function, which could be important for the enhancement of immunity.

Decitabine and SAHA-induced apoptosis is accompanied by survivin downregulation and potentiated by ATRA in p53-deficient cells

While p53-dependent apoptosis is triggered by combination of methyltransferase inhibitor decitabine (DAC) and histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) in leukemic cell line CML-T1, reactive oxygen species (ROS) generation as well as survivin and Bcl-2 deregulation participated in DAC + SAHA-induced apoptosis in p53-deficient HL-60 cell line. Moreover, decrease of survivin expression level is accompanied by its delocalization from centromere-related position in mitotic cells suggesting that both antiapoptotic and cell cycle regulation roles of survivin are affected by DAC + SAHA action. Addition of subtoxic concentration of all-trans-retinoic acid (ATRA) increases the efficiency of DAC + SAHA combination on viability, apoptosis induction, and ROS generation in HL-60 cells but has no effect in CML-T1 cell line. Peripheral blood lymphocytes from healthy donors showed no damage induced by DAC + SAHA + ATRA combination. Therefore, combination of ATRA with DAC and SAHA represents promising tool for therapy of leukemic disease with nonfunctional p53 signalization.

Retiferols - synthesis and biological activity of a conceptually novel class of vitamin D analogs

INTRODUCTION

The hypothesis that retiferols are a novel class of vitamin D analogs with therapeutic potential has been recently proved. The CD-ring of vitamin D, originated from a steroid precursor, is not necessary for biological activity. The retiferol, disubstituted at C-13, was bound to the ligand-binding domain (LBD) of vitamin D receptor (VDR) just like the vitamin D hormone [1,25-(OH)2D3]. This finding opens the way for retiferols as a novel class of vitamin D therapeutics.

AREAS COVERED

This review presents the concept of retiferols and their structure evolution. Medicinal chemistry and therapeutic perspective of retiferols are reviewed showing how these vitamin D analogs became a source of potential therapeutics.

EXPERT OPINION

Docking experiments and molecular modeling have shown that positioning of vitamin D analog at the LBD of VDR is not disturbed by deletion of a large portion of the vitamin D, exactly as hypothesized. Twenty years of structural modifications have shown that removal of the CD-ring fragment and regioselective methylation results in an almost complete loss of the undesired calcemic activity of retiferol while gaining the agonistic activity comparable to that of 1,25-(OH)2D3.

γ-Tocopherol inhibits human prostate cancer cell proliferation by up-regulation of transglutaminase 2 and down-regulation of cyclins

To establish a system to study differentiation therapy drugs, we used the androgen-independent human prostate PC-3 tumor cell line as a target and α- and γ-tocopherol as inducers. Effects of α- and γ-tocopherol on the cell cycle, proliferation and differentiation, were examined. A more significant growth inhibition activity for γ- than for α-tocopherol was observed. Flow cytometry analysis of α- and γ-tocopherol-treated prostate carcinoma PC3 cells showed decreased progression into the S-phase. This effect, particularly evident for γ-tocopherol, was associated with an up-regulation and increased activity of transglutaminase 2 (TG2), a reduced DNA synthesis and a remarkable decreased levels of cyclin D1 and cyclin E. Activation of TG2 suggests that γ-tocopherol has an evident differentiative capacity on PC3 cells, leading to an increased expression of TG2, and reduced cyclin D1 and cyclin E levels, affecting cell cycle progression. It is feasible that up-regulation and activation of TG2, associated with a reduced proliferation, are parts of a large-scale reprogramming that can attenuate the malignant phenotype of PC3 cells in vitro. These data suggest further investigation on the potential use of this γ-form of vitamin E as a differentiative agent, in combination with the common cytotoxic treatments for prostate cancer therapy.

LFA-1 on leukemic cells as a target for therapy or drug delivery

Leukemia therapeutics are aiming for improved efficacy by targeting molecular markers differentially expressed on cancerous cells. Lymphocyte function-associated antigen-1 (LFA-1) expression on various types of leukemia has been well studied. Here, the role and expression of LFA-1 on leukemic cells and the possibility of using this integrin as a target for drug delivery is reviewed. To support this rationale, experimental results were also included where cIBR, a cyclic peptide derived from a binding site of LFA-1, was conjugated to the surface of polymeric nanoparticles and used as a targeting ligand. These studies revealed a correlation of LFA-1 expression level on leukemic cell lines and binding and internalization of cIBR-NPs suggesting a differential binding and internalization of cIBR-NPs to leukemic cells overexpressing LFA-1. Nanoparticles conjugated with a cyclic peptide against an accessible molecular marker of disease hold promise as a selective drug delivery system for leukemia treatment.

Ganoderma lucidum Polysaccharides Induce Macrophage-Like Differentiation in Human Leukemia THP-1 Cells via Caspase and p53 Activation

Differentiation therapy by induction of tumor cells is an important method in the treatment of hematological cancers such as leukemia. Tumor cell differentiation ends cancer cells' immortality, thus stopping cell growth and proliferation. In our previous study, we found that fucose-containing polysaccharide fraction F3 extracted from Ganoderma lucidum can bring about cytokine secretion and cell death in human leukemia THP-1 cells. This prompted us to further investigate on how F3 induces the differentiation in human leukemia cells. We integrated time-course microarray analysis and network modeling to study the F3-induced effects on THP-1 cells. In addition, we determined the differentiation effect using Liu's staining, nitroblue tetrazolium (NBT) reduction assay, flow cytometer, western blotting and Q-PCR. We also examined the modulation and regulation by F3 during the differentiation process. Dynamic gene expression profiles showed that cell differentiation was induced in F3-treated THP-1 cells. Furthermore, F3-treated THP-1 cells exhibited enhanced macrophage differentiation, as demonstrated by changes in cell adherence, cell cycle arrest, NBT reduction and expression of differentiation markers including CD11b, CD14, CD68, matrix metalloproteinase-9 and myeloperoxidase. In addition, caspase cleavage and p53 activation were found to be significantly enhanced in F3-treated THP-1 cells. We unraveled the role of caspases and p53 in F3-induced THP-1 cells differentiation into macrophages. Our results provide a molecular explanation for the differentiation effect of F3 on human leukemia THP-1 cells and offer a prospect for a potential leukemia differentiation therapy.

20-Hydroxyvitamin D2 is a noncalcemic analog of vitamin D with potent antiproliferative and prodifferentiation activities in normal and malignant cells

20-hydroxyvitamin D(2) [20(OH)D(2)] inhibits DNA synthesis in epidermal keratinocytes, melanocytes, and melanoma cells in a dose- and time-dependent manner. This inhibition is dependent on cell type, with keratinocytes and melanoma cells being more sensitive than normal melanocytes. The antiproliferative activity of 20(OH)D(2) is similar to that of 1,25(OH)(2)D(3) and of newly synthesized 1,20(OH)(2)D(2) but significantly higher than that of 25(OH)D(3). 20(OH)D(2) also displays tumorostatic effects. In keratinocytes 20(OH)D(2) inhibits expression of cyclins and stimulates involucrin expression. It also stimulates CYP24 expression, however, to a significantly lower degree than that by 1,25(OH)(2)D(3) or 25(OH)D(3). 20(OH)D(2) is a poor substrate for CYP27B1 with overall catalytic efficiency being 24- and 41-fold lower than for 25(OH)D(3) with the mouse and human enzymes, respectively. No conversion of 20(OH)D(2) to 1,20(OH)(2)D(2) was detected in intact HaCaT keratinocytes. 20(OH)D(2) also demonstrates anti-leukemic activity but with lower potency than 1,25(OH)(2)D(3). The phenotypic effects of 20(OH)D(2) are mediated through interaction with the vitamin D receptor (VDR) as documented by attenuation of cell proliferation after silencing of VDR, by enhancement of the inhibitory effect through stable overexpression of VDR and by the demonstration that 20(OH)D(2) induces time-dependent translocation of VDR from the cytoplasm to the nucleus at a comparable rate to that for 1,25(OH)(2)D(3). In vivo tests show that while 1,25(OH)(2)D(3) at doses as low as 0.8 μg/kg induces calcium deposits in the kidney and heart, 20(OH)D(2) is devoid of such activity even at doses as high as 4 μg/kg. Silencing of CY27B1 in human keratinocytes showed that 20(OH)D(2) does not require its transformation to 1,20(OH)(2)D(2) for its biological activity. Thus 20(OH)D(2) shows cell-type dependent antiproliferative and prodifferentiation activities through activation of VDR, while having no detectable toxic calcemic activity, and is a poor substrate for CYP27B1.

Products of vitamin D3 or 7-dehydrocholesterol metabolism by cytochrome P450scc show anti-leukemia effects, having low or absent calcemic activity

Background

Cytochrome P450scc metabolizes vitamin D3 to 20-hydroxyvitamin D3 (20(OH)D3) and 20,23(OH)₂D3, as well as 1-hydroxyvitamin D3 to 1α,20-dihydroxyvitamin D3 (1,20(OH)₂D3). It also cleaves the side chain of 7-dehydrocholesterol producing 7-dehydropregnenolone (7DHP), which can be transformed to 20(OH)7DHP. UVB induces transformation of the steroidal 5,7-dienes to pregnacalciferol (pD) and a lumisterol-like compounds (pL).

Methods and Findings

To define the biological significance of these P450scc-initiated pathways, we tested the effects of their 5,7-diene precursors and secosteroidal products on leukemia cell differentiation and proliferation in comparison to 1α,25-dihydroxyvitamin D3 (1,25(OH)₂D3). These secosteroids inhibited proliferation and induced erythroid differentiation of K562 human chronic myeloid and MEL mouse leukemia cells with 20(OH)D3 and 20,23(OH)₂D3 being either equipotent or slightly less potent than 1,25(OH)₂D3, while 1,20(OH)₂D3, pD and pL compounds were slightly or moderately less potent. The compounds also inhibited proliferation and induced monocytic differentiation of HL-60 promyelocytic and U937 promonocytic human leukemia cells. Among them 1,25(OH)₂D3 was the most potent, 20(OH)D3, 20,23(OH)₂D3 and 1,20(OH)₂D3 were less active, and pD and pL compounds were the least potent. Since it had been previously proven that secosteroids without the side chain (pD) have no effect on systemic calcium levels we performed additional testing in rats and found that 20(OH)D3 had no calcemic activity at concentration as high as 1 µg/kg, whereas, 1,20(OH)₂D3 was slightly to moderately calcemic and 1,25(OH)₂D3 had strong calcemic activity.

Conclusions

We identified novel secosteroids that are excellent candidates for anti-leukemia therapy with 20(OH)D3 deserving special attention because of its relatively high potency and lack of calcemic activity.

The vitamin D-antimicrobial peptide pathway and its role in protection against infection

Vitamin D deficiency has been correlated with increased rates of infection. Since the early 19th century, both environmental (i.e., sunlight) and dietary sources (cod liver) of vitamin D have been identified as treatments for TB. The recent discovery that vitamin D induces antimicrobial peptide gene expression explains, in part, the 'antibiotic' effect of vitamin D and has greatly renewed interest in the ability of vitamin D to improve immune function. Subsequent work indicates that this regulation is biologically important for the response of the innate immune system to wounds and infection and that deficiency may lead to suboptimal responses toward bacterial and viral infections. The regulation of the cathelicidin antimicrobial peptide gene is a human/primate-specific adaptation and is not conserved in other mammals. The capacity of the vitamin D receptor to act as a high-affinity receptor for vitamin D and a low-affinity receptor for secondary bile acids and potentially other novel nutritional compounds suggests that the evolutionary selection to place the cathelicidin gene under control of the vitamin D receptor allows for its regulation under both endocrine and xenobiotic response systems. Future studies in both humans and humanized mouse models will elucidate the importance of this regulation and lead to the development of potential therapeutic applications.

Vitamin D receptor (VDR) localization in human promyelocytic leukemia cells

Although vitamin D analogs are known to induce the differentiation of the HL-60 promyelocytic leukemia cells, the effect of vitamin D analogs on the distribution of vitamin D receptor (VDR) in these cells is not well studied. This report showed, by confocal microscopy, that VDR mainly resided in the cytoplasm in the absence of VDR ligands. When cells were treated with 19-nor-1alpha,25-(OH)(2)D(2) or 1,25(OH)(2)D(3), VDR moved from the cytoplasm into the nucleus in a time-dependent manner. VDR could be observed in the nucleus as early as 6 h after drug treatment and was still observed in the nucleus 3 days after one single addition of 100 nM 19-nor-1alpha,25-(OH)(2)D(2) or 1,25(OH)(2)D(3). The VDR protein level was significantly increased by 19-nor-1alpha,25-(OH)(2)D(2) or 1,25(OH)(2)D(3) in a dose-dependent manner, while the VDR mRNA level was not affected by either compound. These results suggest that binding of vitamin D analogs to VDR induced receptor translocation into the nucleus, which stabilizes the receptor, resulting in an accumulation of the VDR protein.

5-Lipoxygenase inhibitors potentiate 1alpha,25-dihydroxyvitamin D3-induced monocytic differentiation by activating p38 MAPK pathway

The treatment of human promyelocytic leukemia cell lines HL-60, and to some extent NB-4, with 1alpha,25-dihydroxyvitamin D(3) (VD3) induces differentiation toward the monocytic/macrophage lineage, demonstrated by the increased expression of CD11b and CD14, and the production of opsonized zymosan particles (OZP)-stimulated reactive oxygen species (ROS). Moreover, in more sensitive HL-60 cells, increased expression of 5-lipoxygenase (5-LPO), Mcl-1, IkappaB, and c-Jun, accompanied by the activation of p38 MAPK, was detected. These VD3 effects on HL-60 cell differentiation were significantly potentiated by 5-LPO inhibitors MK-886 and AA-861 and were inverted by SB202190 (SB), a p38 MAPK inhibitor. The inhibition of differentiation by SB was demonstrated by a reduction of CD14 expression and by a decrease in OZP-activated ROS production. These results indicated that p38 MAPK pathway is involved in 5-LPO inhibitors-dependent potentiation of VD3-induced monocytic differentiation.

Nargenicin enhances 1,25-dihydroxyvitamin D(3)- and all-trans retinoic acid-induced leukemia cell differentiation via PKCbetaI/MAPK pathways

A major goal in the treatment of acute myeloid leukemia (AML) is to achieve terminal differentiation and prevent drug resistance and side effects. Combined treatment with low doses of ATRA or 1,25-(OH)(2)D(3) that do not induce toxicity with another drug is one useful strategy for the treatment of AML. Actinomycetes are the well known sources of antibiotics and bioactive molecules. Previously, we isolated nargenicin from the culture broth of an actinomycete isolate, Nocardia sp. CS682. In this study, we evaluated the effects of nargenicin on cellular differentiation in a human myeloid leukemia HL-60 cell system. Nargenicin inhibited cell proliferation and induced HL-60 cell differentiation when administered in combination with 1,25-(OH)(2)D(3) or ATRA. In addition, western blot analyses and kinase inhibitor studies demonstrated that nargenicin primarily enhanced leukemia cell differentiation via PKCbeta1/MAPK pathways. The results of this study indicate that nargenicin has the ability to induce differentiation and suggest that it may be useful for the treatment of neoplastic diseases.

A study on the antitumoral and differentiation effects of peganum harmala derivatives in combination with ATRA on leukaemic cells

Plant derived agents may exert a new approach to the treatment of leukaemia. The present study was an evaluation of proliferation, cytotoxicity and differentiation of harmine and harmaline on HL60 cells, alone or in combination with ATRA and G-CSF. Counting of cells, viability, MTT assay, morphology, NBT reduction and flow cytometry analysis were performed using CD11b and CD 14 monoclonal antibodies. The data showed that harmine and harmaline reduced proliferation in dose and time dependent manner. Optimal antiproliferative concentration of these agents was chosen. However, both agents in higher doses were cytotoxic. Combination of ATRA, G-CSF and each agent alone, particularly harmaline in optimal dose, resulted in partially additive decrease in cell proliferation. Cells treated with both harmaline and ATRA demonstrated some morphological changes and NBT positivity, but the extent of changes observed following treatment with harmaline was less than ATRA. Flow cytometric analysis showed that ATRA induced a neutrophilic differentiation, while harmaline led to a predominantly monocytic differentiation. Combination of harmine and harmaline with ATRA and G-CSF did not change the extent of differentiation, and the cells differentiated into the neutrophilic lineage. This shows that the direction of differentiation is dominantly determined by ATRA. These preliminary data implies a new approach in treatment of leukemia.

Dendritic cells and myeloid leukaemias: plasticity and commitment in cell differentiation

Dendritic cells (DCs) are key antigen-presenting cells (APCs), which link innate and adaptive immunity, ultimately activating antigen-specific T cells. This review examines the relationship between the acute and chronic myeloid leukaemias and cells with DC properties. DCs are non-dividing terminally differentiated cells, and ex vivo leukaemic cells or cell lines show little similarity to DCs. However, many leukaemias differentiate further in response to defined stimuli, and retain a degree of lineage plasticity. Therefore, several studies have explored the response of leukaemic cells to the in vitro regimens used to differentiate ex vivo primary DCs. Recent data suggest that the most 'dendritic-like' cells can be derived from more undifferentiated myeloid leukaemias, such as the myelomonocytic Mutz-3 cell line. These findings have important implications for understanding the developmental origins of DCs, for harnessing the APC properties of this class of tumour to stimulate the therapeutic anti-tumour immunity, and for developing useful models for the study of human DC physiology and pathology. There is a strong rationale for further exploration of this class of tumour and its relationship to the normal DC.

Regulation of the CAMP gene by 1,25(OH)2D3 in various tissues

The induction of antimicrobial peptides such as the human cathelicidin, CAMP/hCAP18, by 1,25(OH)(2)D(3) provides a very exciting therapeutic approach in boosting immunity against infectious diseases. To explore the range of cell types and expand the number of cell models for studying the regulation of CAMP gene expression by 1,25(OH)(2)D(3), we treated cell lines from various tissue types and determined CAMP gene expression. Also, we tested additional compounds together with 1,25(OH)(2)D(3) to look for possible cooperative activation of the gene. We identified 1,25(OH)(2)D(3)-mediated induction of the CAMP gene in B-cell lymphomas, prostate and endometrial cancer lines and found cooperative activation with the histone deacetylase inhibitor sodium butyrate. The data suggest that regulation of CAMP by 1,25(OH)(2)D(3) is potentially important in a wide range of tissues.

Identification of a molecular signature predictive of sensitivity to differentiation induction in acute myeloid leukemia

Acute myeloid leukemia (AML) blasts are immature committed myeloid cells unable to spontaneously undergo terminal maturation, and characterized by heterogeneous sensitivity to natural differentiation inducers. Here, we show a molecular signature predicting the resistance or sensitivity of six myeloid cell lines to differentiation induced in vitro with retinoic acid or vitamin D. The identified signature was further validated by TaqMan assay for the prediction of response to an in vitro differentiation assay performed on 28 freshly isolated AML blast populations. The TaqMan assay successfully predicts the in vitro resistance or responsiveness of AML blasts to differentiation inducers. Furthermore, performing a meta-analysis of publicly available microarray data sets, we also show the accuracy of our prediction on known phenotypes and suggest that our signature could become useful for the identification of patients eligible for new therapeutic strategies.

Curcumin abolishes apoptosis resistance of calcitriol-differentiated HL-60 cells

Exposure of HL-60 cells to 1,25-dihydroxyvitamin D(3) (calcitriol) induces their differentiation into monocytes. This terminal differentiation is associated with acquired resistance to many proapoptotic stimuli. Here we show that differentiated HL-60 cells undergo apoptosis upon curcumin treatment although they retain resistance to apoptosis induced by a topoisomerase poison - etoposide. Curcumin induced changes of nuclear morphology, DNA fragmentation, release of cytochrome c as well as caspase activation in both differentiated and undifferentiated cells. Experiments performed in other laboratories suggested that curcumin initiates apoptosis by DNA damage that results from topoisomerase II poisoning. We measured gammaH2AX expression, a marker of DNA double strand breaks, in both undifferentiated and differentiated HL-60 cells treated with curcumin or etoposide. In etoposide-treated undifferentiated cells early gammaH2AX expression correlated with initiation phase of apoptosis. In contrast, in curcumin-treated cells gammaH2AX expression correlated with apoptotic DNA fragmentation, which is characteristic for the execution phase of apoptosis. Our experiments show that curcumin overcomes the resistance of calcitriol-differentiated HL-60 cells to DNA-damage-induced apoptosis by activating other cell signaling pathways leading to cell death of HL-60.

Induction of G1 arrest and differentiation in MDA-MB-231 breast cancer cell by boehmeriasin A, a novel compound from plant

Boehmeriasin A is a new phenanthroquinolizidine alkaloid recently isolated from the Boehmeria siamensis Craib (Urticaceae). In vitro biological activity assay demonstrated that this novel compound has wide-range, strong antitumor activity. This study is aimed to determine the effects of boehmeriasin A on breast cancer cell (MDA-MB-231 cell line). Proliferation assay and fluorescence activated cell sorter (FACS) showed that cell growth inhibition and G1 phase arrest of cell cycle were caused by boehmeriasin A. The concentrations resulting in total and 50% growth inhibition are 0.007 and 0.0035 microg/mL, respectively. Exposed in 0.007 microg/mL boehmeriasin A for 12 h, the G1 phase cell percent increased from 44.8% pre-drug treatment to 66.3%. Consistent with G1 arrest and cell growth inhibition, cyclin E2 and cyclin D1 messenger RNA expression in the cell was down-regulated with drug treatment. Then, few apoptotic cells were detected, and most other cells underwent differentiation, which is characterized by specific changes in cell morphology, lots of lipid droplet accumulation, and increasing expression of adipocyte differentiation-related protein. The result first demonstrates that boehmeriasin A potently inhibits the proliferation of breast cancer cell MDA-MB-231 via the G1 phase cell cycle arrest and differentiation induction, and as such, may be considered as candidate chemotherapeutic and/or chemopreventive agent for breast cancer.

1,25-Dihydroxyvitamin D3 suppresses gene expression of eukaryotic translation initiation factor 2 in human promyelocytic leukemia HL-60 cells

The physiologically active metabolite of vitamin D(3), 1alpha,25-dihydroxyvitamin D(3) (DVD), is a potent inducer of cell differentiation in human myeloid leukemia cells. In the present study, we examined changes in gene expression during DVD-induced cell differentiation of promyelocytic HL-60 cells employing a DNA microarray technique. The results identified 7 up-regulated and 9 down-regulated genes with a change greater than 1.5-fold after the DVD-treatment for both 2 and 6 days. Seven of these genes were further examined by reverse transcription-polymerase chain reaction (RT-PCR). The results showed that findings obtained from the DNA microarray analysis and RT-PCR are generally comparable with each other. Gene expression of the subunits of eukaryotic translation initiation factor 2 was then examined by methods including RT-PCR and real-time PCR. The results indicated the suppression of these genes, suggesting a linkage to differentiation-associated growth inhibition of these cells.

[L-Glutamic acid modulates the cytotoxic effect of tumor necrosis factor in the HL-60 cell line]

L-Glutamic acid was shown to increase the stability of cells of the HL-60 line of human promyelocyte leukemia to the cytotoxic action of tumor necrosis factor alpha (TNF-alpha) due to the inhibition of apoptotic and NF-kappaB-activating cascades induced by this cytokine. At the same time, L-glutamic acid increases the TNF-alpha-mediated differentiating signal and the accompanying enhancement of the phosphatidylinositol-specific phospholipase C activity. Therefore, it is a promising agent for the reduction of total toxicity and inflammatory processes during treatment with TNF-alpha. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 6; see also http://www.maik.ru.

Vitamin D compounds in leukemia

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)(2)D3,] possess in vitro multiple anti-cancer activities including growth arrest, induction of apoptosis and differentiation of a variety of different types of malignant cells. However, its use as a therapeutic agent is hindered by its calcemic effects. Analogs of 1,25(OH)(2)D3 have enhanced anti-tumor activity, with reduced calcemic effects. However, limited clinical studies using vitamin D compounds have not yet achieved major clinical success. Nevertheless, pre-clinical studies suggest that the combination of either 1,25(OH)(2)D3 or its analogs with other agents can have additive or synergistic anti-cancer activities, suggesting future clinical studies.

Noncalcemic actions of vitamin D receptor ligands

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

Requirement for myeloid growth factors in the differentiation of acute promyelocytic leukaemia

It is well known that the differentiation of acute promyelocytic leukaemia (APL) cells by all-trans-retinoic acid (ATRA) may be enhanced by myeloid growth factors, but the requirement for growth factors in this process is unclear. Our previous studies in multiple myeloma and non-APL acute myeloid leukaemia demonstrated that lineage-specific growth factors are required for the maximal activity of many pharmacologic differentiating agents in vitro. Thus, we studied whether the differentiation of APL is similarly dependent on growth factors. We found that the myeloid growth factors granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor markedly increased the differentiation of NB4 cells or APL blasts from clinical samples treated with ATRA, arsenic trioxide (ATO), or bryostatin-1 as evidenced by the enhanced expression of myeloid surface antigens and the inhibition of clonogenic growth. Furthermore, myeloid growth factors were necessary for the differentiation of APL cells since the activity of each pharmacologic agent could be blocked by specific growth factor-neutralizing antibodies. Each differentiating agent was active only at concentrations that inhibited cell cycling, suggesting that this property is also required for differentiation. These data demonstrate that both pharmacologic differentiating agents and myeloid growth factors are required, but neither sufficient, for the differentiation of APL cells. The combined use of pharmacologic differentiating agents and growth factors may improve the clinical efficacy of differentiation therapy in APL.

Identification of B-cell translocation gene 1 as a biomarker for monitoring the remission of acute myeloid leukemia

Acute myeloid leukemia (AML) is a biologically heterogeneous disease of the hematopoietic system characterized by a clonal accumulation of immature blast cells in bone marrow. We used a proteomic approach based on two-dimensional electrophoresis and mass spectrometry to search for biomarkers related to the complete remission (CR) state of AML patients. We detected one AML-related protein, which was identified as the B-cell translocation gene 1 (BTG1) protein that belongs to anti-proliferative protein family. In the CR state of AML-M2 and M3 patients (by French-American-British subtype classification), the BTG1 protein was upregulated in bone marrow mononuclear cells. It was also expressed robustly in normal bone marrow mononuclear cells. In addition, the BTG1 levels in AML-M2 patients in a non-remission state after therapy did not increase as they did before therapy. Overexpression of BTG1 mRNA was also observed in the CR state of all-trans-retinoic acid (ATRA)-treated AML-M3 patients and ATRA-treated HL-60 cells. Taken together, these results suggest that BTG1 may play a role in the differentiation process of myeloid cells and can therefore be used as a potential treatment-related biomarker for monitoring the remission status of AML-M2 and M3 patients.

Differentiation of human prostate cancer PC-3 cells induced by inhibitors of inosine 5'-monophosphate dehydrogenase

To establish a system to study differentiation therapy drugs, we used the androgen-independent human prostate PC-3 tumor cell line as a target and mycophenolic acid (MPA), tiazofurin, or ribavirin, which are inhibitors of IMP dehydrogenase, as inducers. These inhibitors evoked replication arrest, caused an increase in cell size, and triggered vacuolization of the cytoplasm. By Northern and Western blotting and immunostaining, we demonstrated MPA-induced expression of 12 proteins reported to reside in prostasomes, organelles released by secretory luminal prostate cells. Additional MPA-induced proteins were identified by two-dimensional gel electrophoresis. Among these was keratin 17, a prostate cell differentiation marker. By Northern blotting, we also demonstrated the constitutive expression of keratins 8 and 18 and induced expression of keratin 19, three other prostate cell differentiation markers. In addition, we established that cells were committed to differentiate after the 2nd day of MPA treatment using guanosine, which can abrogate the effects of MPA. Based on the expression patterns of prostasomal proteins and keratins and the presence of tentative secretory vacuoles, we hypothesize that IMP dehydrogenase inhibitors induce androgen-independent PC-3 cells to mature into cells with a phenotype that resembles normal prostate luminal cells, but at their intermediate state of differentiation.

MOZ-TIF2 inhibits transcription by nuclear receptors and p53 by impairment of CBP function

Chromosomal rearrangements associated with acute myeloid leukemia (AML) include fusions of the genes encoding the acetyltransferase MOZ or MORF with genes encoding the nuclear receptor coactivator TIF2, p300, or CBP. Here we show that MOZ-TIF2 acts as a dominant inhibitor of the transcriptional activities of CBP-dependent activators such as nuclear receptors and p53. The dominant negative property of MOZ-TIF2 requires the CBP-binding domain (activation domain 1 [AD1]), and coimmunoprecipitation and fluorescent resonance energy transfer experiments show that MOZ-TIF2 interacts with CBP directly in vivo. The CBP-binding domain is also required for the ability of MOZ-TIF2 to extend the proliferative potential of murine bone marrow lineage-negative cells in vitro. We show that MOZ-TIF2 displays an aberrant nuclear distribution and that cells expressing this protein have reduced levels of cellular CBP, leading to depletion of CBP from PML bodies. In summary, our results indicate that disruption of the normal function of CBP and CBP-dependent activators is an important feature of MOZ-TIF2 action in AML.

Retinoid-induced apoptosis in HL-60 cells is associated with nucleolin down-regulation and destabilization of Bcl-2 mRNA

All-trans retinoic acid (ATRA) induces differentiation of promyelocytic leukemia cells, but the mechanisms by which cellular differentiation leads to apoptosis are not well understood. Studies were done to address the question whether ATRA-induced apoptosis is a consequence of destabilization of bcl-2 mRNA and decreased cellular levels of the anti-apoptotic protein, bcl-2. ATRA induced differentiation of HL-60 cells along the granulocytic pathway within 48 h. The half-lives of bcl-2 mRNA in HL-60 cells incubated with ATRA for 48 or 72 h were reduced to 39 and 7% of the corresponding untreated control values, respectively. Cellular differentiation was accompanied by down-regulation of the cytoplasmic levels of nucleolin, a bcl-2 mRNA-stabilizing protein. Binding of a bcl-2 mRNA instability element (AU-rich element-1) to nucleolin in S100 extracts from ATRA-treated cells was decreased to 15% of control within 72 h. The decay of 5' capped, polyadenylated bcl-2 mRNA transcripts containing ARE-1 was more rapid in S100 extracts from ATRA-treated cells compared with untreated cells. However, when recombinant nucleolin was added to extracts of ATRA-treated cells, the rate of bcl-2 mRNA decay was similar to the rate in extracts of untreated cells. These results provide evidence that ATRA-induced apoptosis is a consequence of cellular differentiation, which leads to nucleolin down-regulation and bcl-2 mRNA instability.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

Comparison of the gene expression profiles of monocytic versus granulocytic lineages of HL-60 leukemia cell differentiation by DNA microarray analysis

It is now recognized that precise patterns of differentially expressed genes ultimately direct a particular cell toward a given lineage. In this study, we compared the expression profiles of cancer-related genes by cDNA microarray analysis during the differentiation of human promyelocytic leukemia HL-60 cells into either monocytes or granulocytes. RNA was isolated at times 0, 6, 12, 24, 36, 48, and 72 h following stimulation of differentiation with all-trans retinoic acid (all-trans RA) or 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], and hybridized to the microarray gene chips containing 872 genes related to cell-cycles, oncogenes and leukemias. Several genes were commonly or differentially regulated during cell differentiation into either lineage, as demonstrated by both hierarchical and self-organizing map clustering analysis. At 72 h the expression levels of 45 genes were commonly up- or down-regulated at least a twofold in both lineages. Most importantly, 32 genes including alpha-L-fucosidase gene and adducin gamma subunit gene were up- or down-regulated only in all-trans RA-treated HL-60 cells, while 12 genes including interleukin 1beta and hypoxia-inducible factor 1alpha were up- or down-regulated only in 1,25-(OH)(2)D(3)-treated HL-60 cells. The expression of selected genes was confirmed by Northern blot analysis. As expected, some genes identified have not been examined during HL-60 cell differentiation into either lineage. The identification of genes associated with a specific differentiation lineage may give important insights into functional and phenotypic differences between two lineages of HL-60 cell differentiation.

Proposition of treatment of cancer cells by nuclear protein mixtures from embryonic cells

Several kinds of cancer cells are shown to revert to normal state by action of chemical or biochemical differentiation agents. The analogy between cancer and embryonic cells, with regard to the expression of oncogenes, and the presence, in young embryos, of regulating factors, lead to the proposition of treatment of cancer cells by extracts of nuclei from embryo cells. Preliminary experiments with these extracts, on hepatoma cells in culture, have shown growth and DNA synthesis inhibitions, without cell toxicity, and a prolongation of survival of rats injected with the treated cancer cells.

Retinoic acid inhibits elastase-induced injury in human lung epithelial cell lines

The protective effects of retinoic acid on elastase-induced lung epithelial cell injury were studied using elastase extracted from purulent human sputum, the BEAS-2B human bronchial epithelial cell line, A549 human type II lung cell line, and primary cultures of human tracheal epithelial cells. Elastase decreased viability of BEAS-2B cells, A549 cells, and human tracheal epithelial cells in concentration- and time-dependent fashions. Elastase also induced apoptosis of BEAS-2B cells, A549 cells, and the tracheal epithelial cells detected with cell death detection enzyme-linked immunosorbent assay and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) methods. Retinoic acid alone did not affect the viability of BEAS-2B cells, A549 cells, or the tracheal epithelial cells, and did not induce apoptosis of the cells. However, retinoic acid prevented the decreases in the viability and reduced apoptosis of BEAS-2B cells, A549 cells, and the tracheal epithelial cells induced by elastase. Likewise, retinoic acid inhibited caspase 3 activity in BEAS-2B cells and A549 cells induced by elastase, as well as proteolytic activity of elastase. Furthermore, caspase 3 inhibitor inhibited the elastase-induced apoptosis of the cells. These findings suggest that retinoic acid may inhibit elastase-induced lung epithelial cell injury partly through the inhibition of proteolytic activity of elastase and through the inhibition of caspase 3 activity by elastase. Retinoic acid may, therefore, have protective effects against the elastase-induced lung injury and subsequent development of pulmonary emphysema.

Granulocyte colony-stimulating factor-induced terminal maturation of human myeloid cells is specifically associated with up-regulation of receptor-mediated function and CD10 expression

The acute promyelocytic leukemia cell line NB4 was differentiated by all-trans retinoic acid (ATRA), which enhanced the superoxide-producing capacity stimulated by the chemotactic peptide and phorbol ester in this cell line. Granulocyte colony-stimulating factor (G-CSF) by itself had no effect on NB4 cells but exerted additional enhancing effects on the respiratory burst activity in the presence of ATRA. This finding was not due to the induction of G-CSF receptor by ATRA, because NB4 cells expressed abundant G-CSF receptor with or without ATRA. Unlike ATRA, G-CSF enhanced superoxide release stimulated by the chemotactic peptide but not by phorbol ester. In addition, G-CSF but not ATRA attenuated cell death and enhanced survival during differentiation. Cell surface expression of the chemotactic peptide receptors CD33 and CD10 but not of CD11b and CD11c was up-regulated by ATRA plus G-CSF far more profoundly than by ATRA alone. Fundamentally identical but slightly different phenomena for the cell surface expression of CD33 and CD10 were observed in the normal human bone marrow mononuclear cells; G-CSF induced CD10 even in the absence of ATRA and down-regulated CD33 in normal cells. The present results indicate that G-CSF-induced terminal maturation of human myeloid cells is associated with up-regulation of receptor-mediated function and CD10 expression.

Lipid Droplet Formation in Human Myeloid NB4 Cells Stimulated by All Trans Retinoic Acid and Granulocyte Colony-Stimulating Factor: Possible Involvement of Peroxisome Proliferator-Activated Receptor .GAMMA

All trans retinoic acid (ATRA), a differentiation inducer for human myeloid NB4 cells, induced accumulation of lipid droplet as determined by positivity of Nile Red and Oil Red O in this cell line. Granulocyte colony-stimulating factor (G-CSF), although not having detectable effect by itself, exerted the additive effects on lipid droplet formation in NB4 cells when combined with ATRA. mRNA analysis for peroxisome proliferator-activated receptors (PPARs) revealed the initial transient downregulation followed by upregulation of the transcript for PPARgamma2, a master molecule for adipogenesis, and upregulation of PPARalpha. BADGE, a synthetic antagonist for PPARgamma, potently inhibited lipid droplet formation in NB4 cells stimulated by ATRA and/or G-CSF, but not the functional differentiation of the cells by ATRA and/or G-CSF. These results suggest that ATRA and G-CSF induce lipid droplet formation via certain PPARgamma-mediated specific mechanisms in human myeloid NB4 cells during functional differentiation.

Anti-proliferative and differentiation-inducing activities of the green tea catechin epigallocatechin-3-gallate (EGCG) on the human eosinophilic leukemia EoL-1 cell line

A novel approach for the treatment of leukemia is the differentiation therapy in which immature leukemia cells are induced to attain a mature phenotype when exposed to differentiation inducers, either alone or in combinations with other chemotherapeutic or chemopreventive drugs. Over the past decade, numerous studies indicated that green tea catechins (GTC) could suppress the growth and induce apoptosis on a number of human cancer cell lines. However, the differentiation-inducing activity of GTC on human tumors remains poorly understood. In the present study, the effect of the major GTC epigallocatechin-3-gallate (EGCG) on the proliferation and differentiation of a human eosinophilc leukemic cell line, EoL-1, was examined. Our results showed that EGCG suppressed the proliferation of the EoL-1 cells in a dose-dependent manner, with an estimated IC(50) value of 31.5 microM. On the other hand, EGCG at a concentration of 40 microM could trigger the EoL-1 cells to undergo morphological differentiation into mature eosinophil-like cells. Using RT-PCR and flow cytometry, it was found that EGCG upregulated the gene and protein expression of two eosinophil-specific granule proteins, the major basic protein (MBP) and eosinophil peroxidase (EPO), in EoL-1 cells. Taken together, our findings suggest that EGCG can exhibit anti-leukemic activity on a human eosinophilic cell line EoL-1 by suppressing the proliferation and by inducing the differentiation of the leukemia cells.

Calcium and calpain as key mediators of apoptosis-like death induced by vitamin D compounds in breast cancer cells

The active form of vitamin D(3) (1,25(OH)(2)D(3)) induces an increase in the intracellular free calcium ([Ca(2+)](i)) and caspase-independent cell death in human breast cancer cells. Here we show that the treatment of MCF-7 breast cancer cells with 1,25(OH)(2)D(3) or its chemotherapeutic analog, EB 1089, releases Ca(2+) from the endoplasmic reticulum. The increase in [Ca(2+)](i) was associated with the activation of a calcium-dependent cysteine protease, mu-calpain. Interestingly, ectopic expression of a calcium-binding protein, calbindin-D(28k), in MCF-7 cells not only attenuated the elevation in [Ca(2+)](i) and calpain activation, but also reduced death triggered by vitamin D compounds. Similarly, the inhibition of calpain activity by structurally unrelated chemical inhibitors increased the survival of the cells and reduces the amount of annexin V-positive cells. Despite the complete absence of effector caspase activation, transmission electron microscopy of MCF-7 cells treated with 1,25(OH)(2)D(3) or EB 1089 revealed apoptosis-like morphology characterized by the condensed cytoplasm, nuclei, and chromatin. Overall, these results suggest that calpain may take over the role of the major execution protease in apoptosis-like death induced by vitamin D compounds. Thus, these compounds may prove useful in the treatment of tumors resistant to therapeutic agents dependent on the classical caspase cascade.

Combination of 22-oxa-1,25-dihydroxyvitamin D(3), a vitamin D(3) derivative, with vitamin K(2) (VK2) synergistically enhances cell differentiation but suppresses VK2-inducing apoptosis in HL-60 cells

We originally reported that vitamin K(2) (VK2) effectively induces apoptosis in various types of primary cultured leukemia cells and leukemia cell lines in vitro. In addition, VK2 was shown to induce differentiation of leukemia cells when the cells were resistant against VK2-inducing apoptosis. A novel synthetic vitamin D(3)derivative, 22-oxa-1,25-dihydroxyvitamin D(3) (OCT: oxacarcitriol) shows a more potent differentiation-inducing ability among myeloid leukemia cells in vitro with much lesser extent of the induction of hypercalcemia in vivo as compared to the effects of 1alpha,25(OH)(2)D(3). In the present study, we focused on the effects of a combination of OCT plus VK2 on leukemia cells. Treatment of HL-60 cells with OCT for 72 h induces monocytic differentiation. A combination of OCT plus VK2 dramatically enhances monocytic differentiation as assessed by morphologic features, positivity for non-specific esterase staining, and cell surface antigen expressions. This combined effect far exceeds the maximum differentiation induction ability at the optimal concentrations of either OCT or VK2 alone. In addition, pronounced accumulation of the cells in the G0/G1 phase is observed by combined treatment with OCT plus VK2 as compared with each vitamin alone. In contrast to cell differentiation, caspase-3 activation and apoptosis induction in response to VK2 are significantly suppressed in the presence of OCT in HL-60 cells. These data suggest that monocytic differentiation and apoptosis induction of HL-60 cells are inversely regulated. Furthermore, pronounced induction of differentiation by combined treatment with VK2 plus OCT was also observed in four out of six cases of primary cultured acute myeloid leukemia cells in vitro, suggesting that VK2 plus OCT might be a potent combination for the differentiation-based therapy for acute myeloid leukemias.

Differentiation of promyelocytic leukaemia: alterations in Fas (CD95/Apo-1) and Fas ligand (CD178) expression

The survival of leukaemic blasts contributes to the pathological mechanism of acute promyelocytic leukaemia (APL). While treatment of APL using retinoic acid (RA) is a model of differentiation therapy, little is known about possible effects of this treatment on the Fas/FasL system. Investigation of APL cells from patients undergoing differentiation therapy with RA and of promyelocytic HL-60 and monoblastic U-937 cells cultured with RA revealed a reduction of surface expression of both Fas and its ligand. Accordingly, the sensitivity of the cells to anti-Fas-induced apoptosis decreased proportionally and the reduced expression of FasL resulted in a decreased ability of the leukaemic cells to induce apoptosis in T cells. Our findings demonstrate that there are significant changes in Fas and FasL expression during RA treatment of APL, which probably have consequences for the interaction between host immune and leukaemia cells, and thus may be involved in the beneficial effects of differentiation therapy.