Induction of differentiation of human leukemia cells by combinations of COX inhibitors and 1,25-dihydroxyvitamin D3 involves Raf1 but not Erk 1/2 signaling

Novel Quinoline Compounds Active in Cancer Cells through Coupled DNA Methyltransferase Inhibition and Degradation

DNA methyltransferases (DNMTs) play a relevant role in epigenetic control of cancer cell survival and proliferation. Since only two DNMT inhibitors (azacitidine and decitabine) have been approved to date for the treatment of hematological malignancies, the development of novel potent and specific inhibitors is urgent. Here we describe the design, synthesis, and biological evaluation of a new series of compounds acting at the same time as DNMTs (mainly DNMT3A) inhibitors and degraders. Tested against leukemic and solid cancer cell lines, 2a-c and 4a-c (the last only for leukemias) displayed up to submicromolar antiproliferative activities. In HCT116 cells, such compounds induced EGFP gene expression in a promoter demethylation assay, confirming their demethylating activity in cells. In the same cell line, 2b and 4c chosen as representative samples induced DNMT1 and -3A protein degradation, suggesting for these compounds a double mechanism of DNMT3A inhibition and DNMT protein degradation.

Long-term vitamin D treatment decreases human uterine leiomyoma size in a xenograft animal model

OBJECTIVE

To study the effects of short- and long-term vitamin D treatment on uterine leiomyomas in vivo through cell proliferation, extracellular matrix (ECM) degradation, and apoptosis.

DESIGN

Preclinical study of human leiomyoma treatment with vitamin D in an nonhuman animal model.

SETTING

Hospital and university laboratories.

PATIENT(S)/ANIMAL(S)

Human leiomyomas were collected from patients and implanted in ovariectomized NOD-SCID mice.

INTERVENTION(S)

Mice were treated with vitamin D (0.5 μg/kg/d or 1 μg/kg/d) or vehicle for 21 or 60 days.

MAIN OUTCOME MEASURE(S)

Vitamin D effect in xenograft tissue was assessed by monitoring tumor size (¹⁸F-FDG positron-emission tomography/computerized tomography and macroscopic examination), cell proliferation (immunohistochemistry and quantitative real-time polymerase chain reaction [qRT-PCR]), ECM (Western blot), transforming growth factor (TGF) β3 (qRT-PCR), and apoptosis (Westrn blot and TUNEL).

RESULT(S)

Short-term treatment with vitamin D did not appear to alter leiomyoma size, based on in vivo monitoring and macroscopic examination. However, long-term high-dose treatment induced a significant reduction in leiomyoma size. Cell proliferation was not decreased in the short term, whereas 1 μg/kg/d vitamin D in the long term significantly reduced proliferation compared with control. Although collagen-I and plasminogen activator inhibitor 1 were not modified by short-term treatment, they were both significantly reduced by long-term high-dose vitamin D. Similarly, long-term high-dose vitamin D significantly reduced TGF-β3 expression. Finally, apoptosis significantly increased with both short- and long-term high-dose vitamin D treatment.

CONCLUSION(S)

Long-term vitamin D acts as an antiproliferative, antifibrotic, and proapoptotic therapy that provides a safe, nonsurgical therapeutic option for reducing uterine leiomyoma size without side-effects.

Inhibition of tumor cell proliferation in human uterine leiomyomas by vitamin D via Wnt/β-catenin pathway

OBJECTIVE

To assess the effect of vitamin D (VitD) on human uterine leiomyomas through Wnt/β-catenin pathway inhibition, apoptosis induction, and cell growth arrest.

DESIGN

A prospective study comparing leiomyoma vs. myometrium tissues. Paired design study comparing human uterine leiomyoma primary (HULP) cells treated with or without VitD.

SETTING

University hospital.

PATIENT(S)

Human uterine leiomyoma and myometrium were collected from women (aged 35-52 years) without hormonal treatment.

INTERVENTION(S)

Samples were collected from women undergoing surgery due to symptomatic uterine leiomyoma pathology.

MAIN OUTCOME MEASURE(S)

Uterine leiomyoma and myometrium tissues were analyzed by western blot (WB) to determine proliferation, Wnt/β-catenin, and apoptosis pathways. HULP cells were used to study VitD effect in cell proliferation (WB), cell cycle (flow cytometry), Wnt/β-catenin and apoptosis genes (polymerase chain reaction arrays), Wnt-related proteins (protein array), and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling [TUNEL] assay).

RESULTS

Human leiomyoma tissues compared with matched myometrium showed higher proliferation (fold change = 8.16; P=.0006) and altered Wnt/β-catenin pathway (fold change = 5.5; P<.0001), whereas no differences in apoptosis were observed. VitD induced cell growth arrest and decreased proliferation in HULP cells (fold change = 0.74; P=.007). Moreover, VitD decreased Wnt-pathway expression in HULP cells at gene (activity score = -0.775; P<.001) and protein levels. However, VitD did not induce apoptosis expression.

CONCLUSION

Increased proliferation and Wnt/β-catenin pathway deregulation play a role in the development and growth of leiomyomas, whereas apoptosis appears not to contribute. VitD exerts an antiproliferative action on HULP cells through cell growth arrest and Wnt/β-catenin pathway inhibition, but not through apoptosis regulation, suggesting VitD as an effective therapy to stabilize leiomyoma size and prevent its growth.

Indomethacin Disrupts Autophagic Flux by Inducing Lysosomal Dysfunction in Gastric Cancer Cells and Increases Their Sensitivity to Cytotoxic Drugs

NSAIDs inhibit tumorigenesis in gastrointestinal tissues and have been proposed as coadjuvant agents to chemotherapy. The ability of cancer epithelial cells to adapt to the tumour environment and to resist cytotoxic agents seems to depend on rescue mechanisms such as autophagy. In the present study we aimed to determine whether an NSAID with sensitizing properties such as indomethacin modulates autophagy in gastric cancer epithelial cells. We observed that indomethacin causes lysosomal dysfunction in AGS cells and promotes the accumulation of autophagy substrates without altering mTOR activity. Indomethacin enhanced the inhibitory effects of the lysosomotropic agent chloroquine on lysosome activity and autophagy, but lacked any effect when both functions were maximally reduced with another lysosome inhibitor (bafilomycin B1). Indomethacin, alone and in combination with chloroquine, also hindered the autophagic flux stimulated by the antineoplastic drug oxaliplatin and enhanced its toxic effect, increasing the rate of apoptosis/necrosis and undermining cell viability. In summary, our results indicate that indomethacin disrupts autophagic flux by disturbing the normal functioning of lysosomes and, by doing so, increases the sensitivity of gastric cancer cells to cytotoxic agents, an effect that could be used to overcome cancer cell resistance to antineoplastic regimes.

Novel analogs of 1,25-dihydroxyvitamin D2 combined with a plant polyphenol as highly efficient inducers of differentiation in human acute myeloid leukemia cells

1α,25-Dihydroxyvitamin D₃ [1,25(OH)₂D₃] is known to act as a powerful differentiation inducer in various types of cancer cells, including acute myeloid leukemia (AML) cells. However, supraphysiological concentrations of 1,25(OH)₂D₃ required to induce terminal maturation of AML cells can cause lethal hypercalcemia in vivo. Here we characterized the differentiation-inducing effects of novel double-point modified analogs of 1,25-dihydroxyvitamin D₂ [1,25(OH)₂D₂], PRI-5201 and PRI-5202 [Pietraszek et al. (2013) Steroids, 78:1003-1014], on HL60, U937 and MOLM-13 human AML cells in comparison with their direct precursors (PRI-1906 and PRI-1907, respectively) and 1,25(OH)₂D₃. The results demonstrated the following order of potency for the tested compounds: PRI-5202>PRI-1907>PRI-5201>PRI-1906≥1,25(OH)₂D₃, as determined by measuring the expression of cell surface markers of myeloid differentiation. Particularly, the sensitivity of different AML cell lines to PRI-5201 and PRI-5202 was 3-15-fold and 13-50 fold higher, respectively, compared to that of 1,25(OH)₂D₃. Importantly, all the analogs tested at 0.25-1nM concentrations retained the ability of 1,25(OH)₂D₃ to cooperate with the rosemary polyphenol carnosic acid, which strongly potentiated their prodifferentiation activity in a cell type-dependent manner. These synergistic effects were associated with increased induction of the vitamin D receptor (VDR) protein expression. However, surprisingly, carnosic acid was able to significantly enhance only 1,25(OH)₂D₃-induced transactivation of the direct repeat 3 (DR3)-type vitamin D response element (VDRE), whereas no such cooperation was seen with 1,25(OH)₂D₂ analogs. Furthermore, dose-response analysis revealed that 1,25(OH)₂D₃ was more efficacious than the analogs in inducing VDRE activation. This suggests that the superior prodifferentiation activity of the analogs, as compared to 1,25(OH)₂D₃, may be due to their potential for enhanced activation of the differentiation-related VDRE(s) that differ from the DR3-type element tested in this study. Collectively, the results demonstrate that the new double-point modified 1,25(OH)₂D₂ analogs are much stronger inducers of myeloid differentiation than 1,25(OH)₂D₃ and that their efficacy can be further enhanced by combination with plant polyphenols. These combinations warrant their further mechanistic and translational exploration in AML and other types of cancer.

Vitamin D Control of Hematopoietic Cell Differentiation and Leukemia

It is now well known that in the mammalian body vitamin D is converted by successive hydroxylations to 1,25-dihydroxyvitamin D (1,25D), a steroid-like hormone with pleiotropic properties. These include important contributions to the control of cell proliferation, survival and differentiation, as well as the regulation of immune responses in disease. Here, we present recent advances in current understanding of the role of 1,25D in myelopoiesis and lymphopoiesis, and the potential of 1,25D and analogs (vitamin D derivatives; VDDs) for the control of hematopoietic malignancies. The reasons for the unimpressive results of most clinical studies of the therapeutic effects of VDDs in leukemia and related diseases may include the lack of a precise rationale for the conduct of these studies. Further, clinical trials to date have generally used extremely heterogeneous patient populations and, in many cases, small numbers of patients, generally without controls. Although low calcemic VDDs have been used and combined with agents that can increase the leukemia cell killing or differentiation effects in acute leukemias, the sequencing of agents used for combination therapy should to be more clearly delineated. Most importantly, it is recommended that in future clinical trials the rationale for the basis of the enhancing action of drug combinations should be clearly articulated and the effects on anticancer immunity should also be evaluated.

Role of vitamin D in cytotoxic T lymphocyte immunity to pathogens and cancer

The discovery of vitamin D receptor (VDR) expression in immune cells has opened up a new area of research into immunoregulation by vitamin D, a niche that is distinct from its classical role in skeletal health. Today, about three decades since this discovery, numerous cellular and molecular targets of vitamin D in the immune system have been delineated. Moreover, strong clinical associations between vitamin D status and the incidence/severity of many immune-regulated disorders (e.g. infectious diseases, cancers and autoimmunity) have prompted the idea of using vitamin D supplementation to manipulate disease outcome. While much is known about the effects of vitamin D on innate immune responses and helper T (T(H)) cell immunity, there has been relatively limited progress on the frontier of cytotoxic T lymphocyte (CTL) immunity--an arm of host cellular adaptive immunity that is crucial for the control of such intracellular pathogens as human immunodeficiency virus (HIV), tuberculosis (TB), malaria, and hepatitis C virus (HCV). In this review, we discuss the strong historical and clinical link between vitamin D and infectious diseases that involves cytotoxic T lymphocyte (CTL) immunity, present our current understanding as well as critical knowledge gaps in the realm of vitamin D regulation of host CTL responses, and highlight potential regulatory connections between vitamin D and effector and memory CD8 T cell differentiation events during infections.

Ascorbic acid inhibits TPA-induced HL-60 cell differentiation by decreasing cellular H₂O₂ and ERK phosphorylation

Retinoic acid (RA), vitamin D and 12-O‑tetradecanoyl phorbol-13-acetate (TPA) can induce HL-60 cells to differentiate into granulocytes, monocytes and macrophages, respectively. Similar to RA and vitamin D, ascorbic acid also belongs to the vitamin family. High‑dose ascorbic acid (>100 µM) induces HL‑60 cell apoptosis and induces a small fraction of HL‑60 cells to express the granulocyte marker, CD66b. In addition, ascorbic acid exerts an anti‑oxidative stress function. Oxidative stress is required for HL‑60 cell differentiation following treatment with TPA, however, the effect of ascorbic acid on HL‑60 cell differentiation in combination with TPA treatment remains to be fully elucidated. The aim of the present study was to investigate the cellular effects of ascorbic acid treatment on TPA-differentiated HL-60 cells. TPA-differentiated HL-60 cells were used for this investigation, this study and the levels of cellular hydrogen peroxide (H2O2), caspase activity and ERK phosphorylation were determined following combined treatment with TPA and ascorbic acid. The results demonstrated that low‑dose ascorbic acid (5 µM) reduced the cellular levels of H2O2 and inhibited the differentiation of HL‑60 cells into macrophages following treatment with TPA. In addition, the results of the present study further demonstrated that low‑dose ascorbic acid inactivates the ERK phosphorylation pathway, which inhibited HL‑60 cell differentiation following treatment with TPA.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

Vitamin D in inflammatory diseases

Changes in vitamin D serum levels have been associated with inflammatory diseases, such as inflammatory bowel disease (IBD), rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis (MS), atherosclerosis, or asthma. Genome- and transcriptome-wide studies indicate that vitamin D signaling modulates many inflammatory responses on several levels. This includes (i) the regulation of the expression of genes which generate pro-inflammatory mediators, such as cyclooxygenases or 5-lipoxygenase, (ii) the interference with transcription factors, such as NF-κB, which regulate the expression of inflammatory genes and (iii) the activation of signaling cascades, such as MAP kinases which mediate inflammatory responses. Vitamin D targets various tissues and cell types, a number of which belong to the immune system, such as monocytes/macrophages, dendritic cells (DCs) as well as B- and T cells, leading to individual responses of each cell type. One hallmark of these specific vitamin D effects is the cell-type specific regulation of genes involved in the regulation of inflammatory processes and the interplay between vitamin D signaling and other signaling cascades involved in inflammation. An important task in the near future will be the elucidation of the regulatory mechanisms that are involved in the regulation of inflammatory responses by vitamin D on the molecular level by the use of techniques such as chromatin immunoprecipitation (ChIP), ChIP-seq, and FAIRE-seq.

Role of cell cycle regulatory molecules in retinoic acid- and vitamin D3-induced differentiation of acute myeloid leukaemia cells

The important role of cell cycle regulatory molecules in all trans-retinoic acid (ATRA)- and vitamin D3-induced growth inhibition and differentiation induction has been intensively studied in both acute myeloid leukaemia primary cells and a variety of leukaemia cell lines. Cyclin-dependent kinases (CDK)-activating kinase has been demonstrated to interact with retinoic acid receptor (RAR)α in acute promyelocytic leukaemia cells, and inhibition of CDK-activating kinase by ATRA causes hypophosphorylation of PML-RARα, leading to myeloid differentiation. In many cases, downregulation of CDK activity by ATRA and vitamin D3 is a result of elevated p21- and p27-bound CDKs. Activation of p21 is regulated at the transcriptional level, whereas elevated p27 results from both (indirectly) transcriptional activation and post-translational modifications. CDK inhibitors (CKIs) of the INK family, such as p15, p16 and p18, are mainly involved in inhibition of cell proliferation, whereas CIP/KIP members, such as p21, regulate both growth arrest and induction of differentiation. ATRA and vitamin D3 can also downregulate expression of G1 CDKs, especially CDK2 and CDK6. Inhibition of cyclin E expression has only been observed in ATRA- but not in vitamin D3-treated leukaemic cells. In vitro, not only dephosphorylation of pRb but also elevation of total pRb is required for ATRA and vitamin D3 to suppress growth and trigger their differentiation. Finally, sharp reduction in c-Myc has been observed in several leukaemia cell lines treated with ATRA, which may regulate expression of CDKs and CKIs.

The influence of Cox-2 and bioactive lipids on hematological cancers

Inflammation is implicated in the progression of multiple types of cancers including lung, colorectal, breast and hematological malignancies. Cyclooxygenases (Cox) -1 and -2 are important enzymes involved in the regulation of inflammation. Elevated Cox-2 expression is associated with a poor cancer prognosis. Hematological malignancies, which are among the top 10 most predominant cancers in the USA, express high levels of Cox-2. Current therapeutic approaches against hematological malignances are insufficient as many patients develop resistance or relapse. Therefore, targeting Cox-2 holds promise as a therapeutic approach to treat hematological malignancies. NSAIDs and Cox-2 selective inhibitors are anti-inflammatory drugs that decrease prostaglandin and thromboxane production while promoting the synthesis of specialized proresolving mediators. Here, we review the evidence regarding the applicability of NSAIDs, such as aspirin, as well as Cox-2 specific inhibitors, to treat hematological malignancies. Furthermore, we discuss how FDA-approved Cox inhibitors can be used as anti-cancer drugs alone or in combination with existing chemotherapeutic treatments.

Salicylic acid derivatives: synthesis, features and usage as therapeutic tools

INTRODUCTION

In the field of medicinal chemistry, there is a growing interest in the use of small molecules. Although acetyl salicylic acid is well known for medical applications, little is known about other salicylic acid derivatives, and there is serious lack of data and information on the effects and biological evaluation that connect them.

AREAS COVERED

This review covers the synthesis and drug potencies of salicylic acid derivatives. After a brief overview of the information on salicylic acid and its features, a detailed review of salicylic acids as drugs and prodrugs, usage as cyclooxygenase inhibitors, properties in plants, synthesis and recent patents, is developed.

EXPERT OPINION

Salicylic acid research is still an important area and innovations continue to arise, which offer hope for new therapeutics in related fields. It is anticipated that this review will guide the direction of long-term drug/nutraceutical safety trials and stimulate ideas for future research.

Differentiation therapy of acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a predominant acute leukemia among adults, characterized by accumulation of malignantly transformed immature myeloid precursors. A very attractive way to treat myeloid leukemia, which is now called 'differentiation therapy', was proposed as in vitro studies have shown that a variety of agents stimulate differentiation of the cell lines isolated from leukemic patients. One of the differentiation-inducing agents, all-trans retinoic acid (ATRA), which can induce granulocytic differentiation in myeloid leukemic cell lines, has been introduced into clinics to treat patients with acute promyelocytic leukemia (APL) in which a PML-RARA fusion protein is generated by a t(15;17)(q22;q12) chromosomal translocation. Because differentiation therapy using ATRA has significantly improved prognosis for patients with APL, many efforts have been made to find alternative differentiating agents. Since 1,25-dihydroxyvitamin D3 (1,25D) is capable of inducing in vitro monocyte/macrophage differentiation of myeloid leukemic cells, clinical trials have been performed to estimate its potential to treat patients with AML or myelodysplastic syndrome (MDS). Unfortunately therapeutic concentrations of 1,25D can induce potentially fatal systemic hypercalcemia, thus limiting clinical utility of that compound. Attempts to overcome this problem have focused on the synthesis of 1,25D analogs (VDAs) which retain differentiation inducing potential, but lack its hypercalcemic effects. This review aims to discuss current problems and potential solutions in differentiation therapy of AML.

Oncoprotein Cot1 represses kinase suppressors of Ras1/2 and 1,25-dihydroxyvitamin D3-induced differentiation of human acute myeloid leukemia cells

Metabolites and derivatives of vitamin D are well-known inducers of monocytic differentiation, but the mechanistic basis for their action is not fully elucidated. Here we show that the product of protooncogene Cot1 represses the monocytic phenotype in human acute myeloid leukemia (AML) cells induced to differentiate by 1,25-dihydroxyvitamin D(3) (1,25D), even though the expression of cellular Cot1 increases early in the process of 1,25D-induced differentiation. Interestingly, the expression of the two members of the Kinase Suppressor of Ras (KSR) family of molecular scaffolds, known to be positive regulators of Ras signaling and of 1,25D-induced differentiation, increases in parallel with Cot1 in 1,25D-treated cells. However, KSR1/2 are negatively regulated by Cot1, as determined by transfection of siCot1, and confirmed by a reverse effect of ectopic expression of Cot1. The effect of Cot1 in AML cells appears to be cell-type specific, as previous reports in other cell types found KSR-2 to be a negative regulator of Cot1, a reverse relationship. Also in contrast to findings in other cells, in AML cells Cot1 exerts negative control on the MAP kinase pathways, since siCot1 increases the levels of activated Raf1, p90RSK, JNK1, c-jun, and p38, though not of MEK/ERK. These findings have implications for therapy of AML, since in AML cells active MAPKs hasten cell differentiation, and specific pharmacological inhibitors of Cot1 kinase activity have recently became available, thus making Cot1 a "druggable" target.

Vitamin D in combination cancer treatment

As a steroid hormone that regulates mineral homeostasis and bone metabolism, 1α, 25-dihydroxycholecalciferol (calcitriol) also has broad spectrum anti-tumor activities as supported by numerous epidemiological and experimental studies. Calcitriol potentiates the anti-tumor activities of multiple chemotherapeutics agents including DNA-damaging agents cisplatin, carboplatin and doxorubicin; antimetabolites 5-fluorouracil, cytarabine, hydroxyurea, cytarabine and gemcitabine; and microtubule-disturbing agents paclitaxel and docetaxel. Calcitriol elicits anti-tumor effects mainly through the induction of cancer cell apoptosis, cell cycle arrest, differentiation, angiogenesis and the inhibition of cell invasiveness by a number of mechanisms. Calcitriol enhances the cytotoxic effects of gamma irradiation and certain antioxidants and naturally derived compounds. Inhibition of calcitriol metabolism by 24-hydroxylase promotes growth inhibition effect of calcitriol. Calcitriol has been used in a number of clinical trials and it is important to note that sufficient dose and exposure to calcitriol is critical to achieve anti-tumor effect. Several trials have demonstrated that safe and feasible to administer high doses of calcitriol through intermittent regimen. Further well designed clinical trials should be conducted to better understand the role of calcitriol in cancer therapy.

Vitamin D3-driven signals for myeloid cell differentiation--implications for differentiation therapy

Primitive myeloid leukemic cell lines can be driven to differentiate to monocyte-like cells by 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and, therefore, 1,25(OH)(2)D(3) may be useful in differentiation therapy of myeloid leukemia and myelodysplastic syndromes (MDS). Recent studies have provided important insights into the mechanism of 1,25(OH)(2)D(3)-stimulated differentiation. For myeloid progenitors to complete monocytic differentiation a complex network of intracellular signals has to be activated and/or inactivated in a precise temporal and spatial pattern. 1,25(OH)(2)D(3) achieves this change to the 'signaling landscape' by (i) direct genomic modulation of the level of expression of key regulators of cell signaling and differentiation pathways, and (ii) activation of intracellular signaling pathways. An improved understanding of the mode of action of 1,25(OH)(2)D(3) is facilitating the development of new therapeutic regimens.

Vitamin D and differentiation in cancer

This paper reviews the current understanding of the vitamin D-induced differentiation of neoplastic cells, which results in the generation of cells that acquire near-normal, mature phenotype. Examples of the criteria by which differentiation is recognized in each cell type are provided, and only those effects of 1alpha,25-dihydroxyvitamin D(3) (1,25D) on cell proliferation and survival that are associated with the differentiation process are emphasized. The existing knowledge, often fragmentary, of the signaling pathways that lead to vitamin D-induced differentiation of colon, breast, prostate, squamous cell carcinoma, osteosarcoma, and myeloid leukemia cancer cells is outlined. The important distinctions between the different mechanisms of 1,25D-induced differentiation that are cell-type and cell-context specific are pointed out where known. There is a considerable body of evidence that the principal human cancer cells can be suitable candidates for chemoprevention or differentiation therapy with vitamin D. However, further studies are needed to fully understand the underlying mechanisms in order to improve the therapeutic approaches.

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.