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

Current Understanding of the Role of Autophagy in the Treatment of Myeloid Leukemia

The most important issues in acute myeloid leukemia are preventing relapse and treating relapse. Although the remission rate has improved to approximately 80%, the 5-year survival rate is only around 30%. The main reasons for this are the high relapse rate and the limited treatment options. In chronic myeloid leukemia patients, when a deep molecular response is achieved for a certain period of time through tyrosine kinase inhibitor treatment, about half of them will reach treatment-free remission, but relapse is still a problem. Therefore, potential therapeutic targets for myeloid leukemias are eagerly awaited. Autophagy suppresses the development of cancer by maintaining cellular homeostasis; however, it also promotes cancer progression by helping cancer cells survive under various metabolic stresses. In addition, autophagy is promoted or suppressed in cancer cells by various genetic mutations. Therefore, the development of therapies that target autophagy is also being actively researched in the field of leukemia. In this review, studies of the role of autophagy in hematopoiesis, leukemogenesis, and myeloid leukemias are presented, and the impact of autophagy regulation on leukemia treatment and the clinical trials of autophagy-related drugs to date is discussed.

Vitamin D-Binding Protein and Acute Myeloid Leukemia: A Genetic Association Analysis in Combination with Vitamin D Levels

Genetic variations in the vitamin D-binding protein (VDBP) may be associated with the plasma level of serum 25-hydroxyvitamin D. Furthermore, vitamin D deficiency increases the risk of acute myeloid leukemia (AML). This study aimed to examine the potential association of VDBP genetic variants (rs7041 and rs4588) with AML susceptibility. The polymorphisms in the VDBP gene and serum 25-hydroxyvitamin D levels were analyzed in 227 AML patients and 240 healthy controls enrolled in this study. Our data revealed that rs4588 CA and AA genotypes were significantly associated with AML susceptibility (OR = 1.483, p = 0.046; OR = 2.154, p = 0.013, respectively) and also with 61.59% vitamin D deficiency in the total group of AML patients. Under the TG co-dominant and dominant models, however, the rs7041 genotypes were significantly associated with AML protection (OR < 0.6; p < 0.05). In addition, vitamin D deficiency was prevalent in vitamin-D-deficient vs. sufficient AML patients who carried rs7041 and rs4588 mutant alleles (OR ≥ 2.2). Indeed, vitamin D deficiency and its interaction with the genetic variants of VDBP could change the risk of AML. Thus, vitamin D deficiency could be considered an important molecular factor in AML risk assessment.

Targeting the Tumor Microenvironment in Acute Myeloid Leukemia: The Future of Immunotherapy and Natural Products

The tumor microenvironment (TME) plays an essential role in the development, proliferation, and survival of leukemic blasts in acute myeloid leukemia (AML). Within the bone marrow and peripheral blood, various phenotypically and functionally altered cells in the TME provide critical signals to suppress the anti-tumor immune response, allowing tumor cells to evade elimination. Thus, unraveling the complex interplay between AML and its microenvironment may have important clinical implications and are essential to directing the development of novel targeted therapies. This review summarizes recent advancements in our understanding of the AML TME and its ramifications on current immunotherapeutic strategies. We further review the role of natural products in modulating the TME to enhance response to immunotherapy.

Novel Insights into the Cardioprotective Effects of Calcitriol in Myocardial Infarction

BACKGROUND

Increasing evidence indicates that vitamin D deficiency negatively affects the cardiovascular system. Here we studied the therapeutic effects of calcitriol in myocardial infarction (MI) and investigated its underlying mechanisms.

METHODS

A MI model of Kun-ming mice induced by left anterior descending coronary artery ligation was utilized to study the potential therapeutic effects of calcitriol on MI. AC16 human cardiomyocyte-like cells treated with TNF-α were used for exploring the mechanisms that underlie the cardioprotective effects of calcitriol.

RESULTS

We observed that calcitriol reversed adverse cardiovascular function and cardiac remodeling in post-MI mice. Mechanistically, calcitriol suppressed MI-induced cardiac inflammation, ameliorated cardiomyocyte death, and promoted cardiomyocyte proliferation. Specifically, calcitriol exerted these cellular effects by upregulating Vitamin D receptor (VDR). Increased VDR directly interacted with p65 and retained p65 in cytoplasm, thereby dampening NF-κB signaling and suppressing inflammation. Moreover, up-regulated VDR was translocated into nuclei where it directly bound to IL-10 gene promoters to activate IL-10 gene transcription, further inhibiting inflammation.

CONCLUSION

We provide new insights into the cellular and molecular mechanisms underlying the cardioprotective effects of calcitriol, and we present comprehensive evidence to support the preventive and therapeutic effects of calcitriol on MI.

The dual role of autophagy in acute myeloid leukemia

Acute myeloid leukemia (AML) is a severe hematologic malignancy prevalent in older patients, and the identification of potential therapeutic targets for AML is problematic. Autophagy is a lysosome-dependent catabolic pathway involved in the tumorigenesis and/or treatment of various cancers. Mounting evidence has suggested that autophagy plays a critical role in the initiation and progression of AML and anticancer responses. In this review, we describe recent updates on the multifaceted functions of autophagy linking to genetic alterations of AML. We also summarize the latest evidence for autophagy-related genes as potential prognostic predictors and drivers of AML tumorigenesis. We then discuss the crosstalk between autophagy and tumor cell metabolism into the impact on both AML progression and anti-leukemic treatment. Moreover, a series of autophagy regulators, i.e., the inhibitors and activators, are described as potential therapeutics for AML. Finally, we describe the translation of autophagy-modulating therapeutics into clinical practice. Autophagy in AML is a double-edged sword, necessitating a deeper understanding of how autophagy influences dual functions in AML tumorigenesis and anti-leukemic responses.

Vitamin D promotes autophagy in AML cells by inhibiting miR-17-5p-induced Beclin-1 overexpression

MicroRNA (miR)-17-5p has been investigated in many diseases as a regulator of disease progression and is highly expressed in acute myeloid leukemia (AML). However, potential mechanisms underlying the function of miR-17-5p in AML need more elucidation. MiR-17-5p expression was augmented, while 25(OH)D3 and Beclin-1 levels were decreased in AML patients with the highest risk for disease progression. MiR-17-5p, 25(OH)D3 and Beclin-1 were determined to be clinically important in AML based on ROC curve analysis. Higher miR-17-5p expression as well as lower 25(OH)D3 and Beclin-1 expression were relevant with poor prognosis in AML. In addition, miR-17-5p was negatively correlated with and bound to BECN1. Vitamin D was found to diminish cell proliferation and enhance autophagy. Finally, through rescue assays, miR-17-5p facilitated the ability of cell proliferation, inhibited autophagy and apoptosis by modulating Beclin-1 in HL-60 cells following the treatment of 4 μM vitamin D. Vitamin D promoted autophagy in AML cells by modulating miR-17-5p and Beclin-1.

Current Understandings of Myeloid Differentiation Inducers in Leukemia Therapy

Differentiation therapy using all-trans retinoic acid for acute promyelocytic leukemia (APL) is well established. Several attempts have been made to treat non-APL, AML patients by employing differentiation inducers, such as hypomethylating agents (HMAs), and low-dose cytarabine (Ara-C) (LDAC), with encouraging results. Other than HMAs and LDAC, various inducers of myeloid cell differentiation have been identified. This review describes and categorizes these inducers, which include glycosylation modifiers, epigenetic modifiers, vitamin derivatives, cytokines, and chemotherapeutic agents. Some of these inducers are currently being used in clinical trials. I highlight the potential applications of glycosylation modifiers and epigenetic modifiers, which are attracting increasing attention in their use as differentiation therapy against AML. Among the agents described in this review, epigenomic modifiers seem particularly promising, and particular attention should also be paid to glycosylation modifiers. These drugs may signal a new era for AML differentiation therapy.

The role of VDR and BIM in potentiation of cytarabine-induced cell death in human AML blasts

Acute Myeloid Leukemia (AML) has grave prognosis due to aggressive nature of the disease, the toxicity of standard treatment, and overall low cure rates. We recently showed that AML cells in established culture treated with cytarabine (AraC) and a differentiation agent combination show enhancement of AraC cytotoxicity. Here we elucidate molecular changes which underlie this observation with focus on AML blasts in primary culture. The cells were treated with AraC at concentrations achievable in clinical settings, and followed by the addition of Doxercalciferol, a vitamin D2 derivative (D2), together with Carnosic acid (CA), a plant-derived antioxidant. Importantly, although AraC is also toxic to normal bone marrow cell population, the enhanced cell kill by D2/CA was limited to malignant blasts. This enhancement of cell death was associated with activation of the monocytic differentiation program as shown by molecular markers, and the increased expression of vitamin D receptor (VDR). Apoptosis elicited by this treatment is caspase-dependent, and the optimal blast killing required the increased expression of the apoptosis regulator Bim. These data suggest that testing of this regimen in the clinic is warranted.

Vitamin D-deficiency induces eosinophil spontaneous activation

Eosinophils (Eo) play a critical role in immunity and immune inflammation. The maintenance of Eo homeostasis is not fully understood yet. Vitamin D (VitD) is involved in the regulation of a large number of biochemical reactions. This study tests a hypothesis that VitD receptor (VDR) contributes to the homeostasis of Eos. In this study, EoL-1 cells (an Eo cell line) were cultured in the presence or absence of calcitriol. The Eo-mediators, including major basic protein (MBP), Eo peroxidase (EPX), Eo cationic protein (ECP) and Eo-derived neurotoxin (EDN), were assessed in the culture supernatant and in EoL-1 cells. We observed that, in a VitD deficient environment, EoL-1 cells produced high levels of the Eo-mediators, including MBP, EPX, ECP and EDN, which could be suppressed by the addition of calcitriol to the culture. EoL-1 cells expressed VitD receptor (VDR), which was up regulated by exposure to calcitriol. VDR formed complexes with the transcription factors of the Eo-mediators, which prevented the transcription factors to bind to the promoters of the Eo-mediators, and therefore prevented the Eo-mediated gene transcription. The Eo spontaneous activation was also found in the intestinal mucosa of VDR-deficient mice, in which the intestinal epithelial barrier dysfunction was observed. In conclusion, VDR contributes to the maintenance of the homeostasis of Eos by regulating the gene transcription of the Eo mediators. The VDR-deficiency is one of the causative factors inducing Eo spontaneous activation. This phenomenon may be taken into account in the management of the Eo-related diseases.

MicroRNA-155 Deficiency in Kupffer Cells Ameliorates Liver Ischemia-Reperfusion Injury in Mice

BACKGROUND

MicroRNA-155 (miR-155) is known to be involved in autoimmune diseases, inflammation, and transplantation. However, its role in a warm hepatic ischemia-reperfusion (IR) model has not been fully elucidated.

METHODS

Partial hepatic IR was performed in wild-type and miR-155-deficient mice treated with or without GdCl3, and then the serum transaminase concentration and histology were analyzed. Kupffer cells (KCs) were isolated from the liver after IR, and immunohistochemistry was used to evaluate activation and polarization. In addition, the mRNA concentrations of various inflammatory cytokines were measured. Macrophages were obtained from the abdominal cavity and challenged with or without lipopolysaccharide to determine the influence of miR-155 deficiency on macrophage polarization in vitro. Furthermore, we used in vitro coculture assays to determine the effect of miR-155 deficiency on hepatocyte apoptosis induced directly by KCs.

RESULTS

miR-155 deficiency ameliorated liver IR injury, and inhibition of KCs by GdCl3 abolished this protective effect. miR-155 deficiency decreased CD80, CD86, and major histocompatibility complex class II expression in KCs after IR and tipped the M1/M2 balance toward an anti-inflammatory profile, where proinflammatory cytokine secretion was suppressed and IL-10 was enhanced. In addition, hepatocyte apoptosis was reduced in coculture with miR-155-deficient KCs in vitro.

CONCLUSIONS

miR-155 deficiency plays an effective role in attenuating liver IR injury likely by regulating the activation and inflammatory response, as well as modifying the polarization of KCs.

Vitamin D decreases STAT phosphorylation and inflammatory cytokine output in T-LGL leukemia

Large granular lymphocyte leukemia (LGLL) is a rare incurable chronic disease typically characterized by clonal expansion of CD3+ cytotoxic T-cells. Two signal transducer and activator of transcription factors, STAT1 and STAT3, are constitutively active in T-LGLL. Disruption of this activation induces apoptosis in T-LGLL cells. Therefore, considerable efforts are focused on developing treatments that inhibit STAT activation. Calcitriol, the active form of vitamin D, has been shown to decrease STAT1 and STAT3 phosphorylation in cancer cell lines and autoimmune disease mouse models. Thus, we investigated whether calcitriol could be a valid therapeutic for T-LGLL. Calcitriol treatment of the TL-1 cell line (model of T-LGLL) led to decreased phospho-Y701 STAT1 and phospho-Y705 STAT3 and increased vitamin D receptor (VDR) levels. Doses of 10 and 100 nM calcitriol also significantly decreased the inflammatory cytokine IFN-γ in the TL-1 cell line. The overall cell viability did not change when the TL-1 cell line was treated with 0.1 to 1000 nM calcitriol. Studies with primary T-LGLL patient peripheral blood mononuclear cells showed that the majority of T-LGLL patients have detectable VDR and activated STATs in contrast to normal donor controls. Treatment of primary T-LGLL patient cells with calcitriol recapitulated findings from the TL-1 cell line. Overall, our results suggest that calcitriol may reprogram T-cells to decrease essential STAT activation and pro-inflammatory cytokine output. These data support further investigation into calcitriol as an experimental therapeutic for T-LGLL.

DNA Repair in Despair-Vitamin D Is Not Fair

The role of vitamin D as a treatment option for neoplastic diseases, once considered to have a bright future, remains controversial. The preclinical studies discussed herein show compelling evidence that Vitamin D Derivatives (VDDs) can convert some cancer and leukemia cells to a benign phenotype, by differentiation/maturation, cell cycle arrest, or induction of apoptosis. Furthermore, there is considerable, though still evolving, knowledge of the molecular mechanisms underlying these changes. However, the attempts to clearly document that the treatment outcomes of human neoplastic diseases can be positively influenced by VDDs have been, so far, disappointing. The clinical trials to date of VDDs, alone or combined with other agents, have not shown consistent results. It is our contention, shared by others, that there were limitations in the design or execution of these trials which have not yet been fully addressed. Based on the connection between upregulation of JNK by VDDs and DNA repair, we propose a new avenue of attack on cancer cells by increasing the toxicity of the current, only partially effective, cancer chemotherapeutic drugs by combining them with VDDs. This can impair DNA repair and thus kill the malignant cells, warranting a comprehensive study of this novel concept. J. Cell. Biochem. 117: 1733-1744, 2016. © 2016 Wiley Periodicals, Inc.

Deciphering the cross-talking of human competitive endogenous RNAs in K562 chronic myelogenous leukemia cell line

Chronic myelogenous leukemia (CML) is a myeloproliferative disorder characterized by increased proliferation or abnormal accumulation of the granulocytic cell line without the depletion of their capacity to differentiate.