Frontiers in Clinical Drug Research - Hematology: Volume 4 E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Serie: Frontiers in Clinical Drug Research - Hematology
- Sprache: Englisch
Frontiers in Clinical Drug Research – Hematology is a book series that brings updated reviews to readers interested in learning about advances in the development of pharmaceutical agents for the treatment of hematological disorders. The scope of the book series covers a range of topics including the medicinal chemistry, pharmacology, molecular biology and biochemistry of natural and synthetic drugs employed in the treatment of anemias, coagulopathies, vascular diseases and hematological malignancies. Reviews in this series also include research on specific antibody targets, therapeutic methods, genetic hemoglobinopathies and pre-clinical / clinical findings on novel pharmaceutical agents. Frontiers in Clinical Drug Research – Hematology is a valuable resource for pharmaceutical scientists and postgraduate students seeking updated and critically important information for developing clinical trials and devising research plans in the field of hematology, oncology and vascular pharmacology.
The fourth volume of this series features 5 reviews:
-TRP Channels: Potential Therapeutic Targets in Blood Disorders
-Hypercoagulable States: Clinical Symptoms, Laboratory Markers and Management
-Advanced Applications of Gene Therapy in the Treatment of Hematologic Disorders
-Ferroptosis - Importance and Potential Effects in Hematological Malignancies
-Clinical Application of Liquid Biopsy in Solid Tumor HCC: Prognostic, Diagnostic and Therapy Monitoring Tool
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Seitenzahl: 472
Veröffentlichungsjahr: 2020
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PREFACE
This is the fourth volume of the book series: Frontiers in Clinical Drug Research – Hematology. This volume comprises five comprehensive chapters covering various topics including TRP channels as potential therapeutic targets in blood disorders, advanced applications of gene therapy in the treatment of hematologic disorders, hypercoagulable states, importance and potential effects of ferroptosis in hematological malignancies, and clinical applications of liquid biopsy in solid tumor hepatocellular carcinoma (HCC).
In Chapter 1 of the present volume, Mandal presents the importance of TRP (Transient Receptor Potential) channels as potential therapeutic targets in blood disorders. TRP channels are the modulators of the hematopoietic cells and control cellular proliferation, differentiation and apoptosis. Thus, TRP channels appear to be promising targets for hematologic cancer therapy. This chapter briefly discusses the functional roles of some TRP channel proteins that have been emerging as possible drug targets to treat some blood disorders and hematological malignancies.
Hypercoagulable states are a group of disorders that tend to develop venous or arterial thrombi, or both. Understanding this condition can serve to improve outcomes in the clinic for patients Pusparini and Hidayat, in the second chapter of the book, explain the clinical symptoms, laboratory markers and management of hypercoagulable states.
In Chapter 3, Gaurav presents an overview of advanced applications of gene therapy in the treatment of hematologic disorders. In this chapter, the current status of gene therapy is reviewed with a focus on recent technologies such as gene delivery vectors, CRISPR genome editing technology, and CAR T-cell therapy, and their applications in the treatment of various blood disorders, in addition to the demonstration of the outcomes of selected clinical studies. These details are followed by a summary of the current challenges to gene therapy and future outlook, giving the reader a quick and comprehensive update on the subject.
Ferroptosis is a recently identified form of non-apoptotic regulated cell death with distinct properties and several functions involved in physical conditions or diseases. Aranalde focuses on the importance and potential effects of Ferroptosis in hematological malignancies in the next chapter. Ijaz et al., in the last chapter of the book, focus on the clinical application of liquid biopsy in solid tumor management with emphasis on HCC. They also summarize different advanced diagnostic techniques for the isolation and enrichment of circulating tumor cells, circulating tumor DNA and exosome. Moreover, the limitation of the use of liquid biopsy in the healthcare system is also a point of discussion in this chapter.
I hope that the readers will find value in this collection of reviews and draw inspiration for conducting further drug discovery research in the field of hematology.
I am grateful for the timely efforts made by the editorial personnel of Bentham Science Publishers, especially Mr. Mahmood Alam (Director Publications), Mr. Obaid Sadiq (Incharge Books Department) and Ms. Asma Ahmed (Manager Publications).
List of Contributors
TRP Channels: Potential Therapeutic Targets in Blood Disorders
Amritlal Mandal*Abstract
In the recent past, TRP (Transient Receptor Potential) channels have been emerging as promising therapeutic targets to treat different disease conditions. In mammals, 28 TRP channel genes have been reported. TRP channels are nonselective cation channels that respond to different exogenous stimuli, including certain chemicals, osmotic stress, temperature change, etc. Until now, studies on TRP channels in relation to blood disorders are only a handful. Recently, several TRP channels have emerged as potential contributors to different hematological disorders, including blood iron deficiency (TRPML), hereditary hypertension (TRPC3) and blood pressure (BP) regulation (TRPM4). Dysregulated activation of several TRP channel family members has been reported in sickle cell disease (SCD) and in the transgenic mouse model of SCD. In this regard, TRPV1 and TRPA1 channels have been identified as major contributing factors in the rodent SCD pain. Erythropoietin (Epo), a glycated cytokine, secreted by the kidney, plays an important role in red blood cell (RBC) synthesis (erythropoiesis). In murine RBCs, Epo was found to cause TRPC4/TRPC5-mediated calcium entry that certainly appears interesting in order to understand the roles of TRP channels in erythropoiesis. Present evidence indicates functional roles of several TRP channels (TRPC3, TRPC6, TRPV1, TRPV3, TRPV4, TRPA1, TRPM6 and TRPM7) in the progression and/or prevention of fibroproliferative disorders in vital visceral organs including blood vessels and emerges as the main contributor towards several inflammatory processes. TRPV1 channel has gained attention as a required step for T-cell receptor activation by mitogens. Studies involving cell lines derived from hematological and other malignancies indicate TRPV1 could be a potential target for novel cytotoxic therapies. Altered functional roles of several TRP channels have been identified in different classes of hematological malignancies, including leukemias, multiple myelomas (MM) and B-and T-cell lymphomas. TRP channels are the modulators of the hematopoietic cells and control cellular proliferation, differentiation and apoptosis. Thus, TRP channels appear to be promising targets for hematologic cancer therapy and those channels warrant further investigations for novel pharmaceutical and clinical strategies. TRPC1ε has been recently reported as pre-osteoclasts and important functional roles of TRPC1ε in recruiting a subpopulation of circulating mononuclear cells from blood to bone surface have been described in relation to cellular differentiation. Epigenetic changes in TRPA1 promoter methylation
in white blood cells (WBC) have been identified as predictive of human thermal pain sensitivity. An inverse relationship exists between TRPV1 and TRPA1 gene expression in peripheral blood cells with increasing pain symptoms. This chapter reviews different TRP channel expressions in blood cells with a focus on recent advancements of understanding TRP channels as potential therapeutic targets in different blood disorders. This chapter also briefly discusses a few TRP channel modulator drugs that had shown promising results in preclinical studies or in clinical trials. For the sake of simplicity and to stay focused on the present issue of the journal, this chapter briefly discusses the functional roles of some TRP channel proteins that have been emerging as possible drug targets to treat some blood disorders and hematological malignancies.
INTRODUCTION
TRP channels have been emerging as a potential drug target for different pathophysiological conditions in humans, including treating neuropathic pain [1, 2] and hematological disorders [3]. As of 2009, big pharma companies have drawn attention towards finding TRP channel modulator molecules and the interest is ever increasing. Among all those different channel proteins relevant to human health and diseases, the data reported in 2011 show a trend in a research study that depicts a significant increase of TRP channel targeted therapeutic approaches. AstraZeneca put significant effort in the recent past for developing drugs for treating pains, targeting the ligand-gated channels in developing drugs with TRP channels modulators. Hydra Biosciences, another biotech company, that develops drugs for treating pain and psychological disorders including depression and anxiety, has invested multimillion dollars in collaboration with Cubist Pharmaceuticals to develop drugs that interfere with the TRPA1 receptor, which is commonly associated with the perception of pain. A comprehensive list of TRP channel modulator drugs is shown in Table 1.
TRP channel proteins have six transmembrane spanning domains and are widely expressed in wide varieties of mammalian tissues and play a broad spectrum of functional roles. These are cation selective channels and play a crucial role in intracellular sodium, calcium and magnesium ion homeostasis. These channels play a significant role in membrane voltage regulation in excitable and non-excitable cells. TRP channels have been known as important sensors to a variety of cell types and are gated by a wide range of physical and chemical stimuli covering stretch, change in temperature, endogenous ligands (Ca2+, DAG, etc.). Many of them are activated due to intracellular calcium store depletion [4, 5]. TRP channels function is important and has been established in both normal and pathological conditions. Table 2 is a summary of tissue specific expression of different TRP channel proteins and their putative roles in human pathophysiology. TRP channels are polymodal, non-selective cation specific channels and have immense importance in downstream cellular signaling events, which are dependent on cations. Membrane depolarization and Ca2+-dependent cellular mechanisms have been broadly reported in a variety of systems and organs [6]. Faulty or dysregulated TRP channel functions due to abnormal expression, cellular localization or the mutation have been found to be associated with a plethora of disorders and abnormalities in health and disease. TRPV (vanilloid) subfamily was the first reported member of the TRP channel family that has been known to respond to a variety of noxious exogenous signal stimuli. More specifically, TRPV1 has been identified to be responsible as a heat transducer in the peripheral nervous system [7, 8]. TRPV2, TRPV3 and TRPV4 family members are also reported to be activated by a wide range of additional endogenous ligands [9, 10]. So far, TRPV1 has been the most extensively studied TRP family member in normal somatosensation and in diseases like sickle cell disease (SCD) pain. The TRP channelopathy related disease conditions in humans have been linked to cardiovascular disorders, diabetes mellitus, blood disorders, hematological malignancies, and cancer. Some TRP channel modulator drugs that have been thoroughly investigated in clinical trials are listed in Table 3. A point to notice is that though there has been a wide list of different TRP channel modulators, only a handful of them have been investigated under clinical trials and the study of those TRP channel modulators in therapy areas, such as hematological disorders is very much limited.
TRP CHANNELS IN BLOOD DISORDERS
TRP Channels and Abnormalities in RBCs
RBCs are the critical players for cellular calcium (Ca2+) homeostasis and known to participate in numerous processes, including cell volume regulation, cell survival and involved in disease and pathology [11-13]. Abundant expressions of TRPC channels (canonical) have been reported in primary erythroblasts and in erythroid cell lines and in RBCs [14-18]. Cytoplasmic Ca2+ level of RBCs has been found to rise upon erythropoietin (Epo) exposure [15, 16]. Two clinical studies where patients were treated with a therapeutic dose of Epo have revealed low baseline cytoplasmic Ca2+ concentration or lower phosphatidylserine concentration in the outer membrane leaflet that supports the notion of decreased intraerythrocytic loss of Ca2+, which is a secondary event to the cytoplasmic increase of Ca2+ concentration [19, 20].
Prostaglandin E2 (PGE2) was also reported to cause cellular Ca2+ influx in the RBCs [21, 22], which in turn, is mediated through TRPC channels [23]. The significance of PGE2-mediated cellular Ca2+ influx through TRPC channel activation has been described in physiological and pathological conditions in malaria-infected RBCs [24-27]. Though Epo and PGE2 both were found to cause the rise in cytoplasmic Ca2+, the nature of Ca2+ homeostasis by those two modulators have been found to be distinctly different in murine and in human RBCs [28]. Epo does not show any effect on Ca2+ fluxes in human RBCs, but it causes inhibition of PGE2-mediated calcium entry, whereas in murine RBCs, Epo was reported to activate TRPC4 and TRPC5-mediated calcium entry and PGE2 was responsible for TRPC channel-independent Ca2+ influx [28]. Species-specific effects of EPO have been reported in erythropoiesis in murine and human RBCs. In human RBCs, Epo reduces the calcium uptake and protects the RBCs for being prematurely cleared during eryptosis (erythrocyte apoptosis) and hypoxic/anaemic episodes. Mice show the opposite responses to Epo during erythropoiesis. This opposite effect probably could be due to (i) differences in Epo receptor expression, (ii) downstream signaling pathways that control the uptake mechanisms and (iii) Ca2+ uptake pathways. The expression of TRPC channels widely varies depending on cell types and the species. In mouse RBC, Epo receptors are heterogeneously distributed and vary between 2-105 receptors per RBC and the abundance of the receptor expression usually decreased with age [29]. Human reticulocytes are either devoid of Epo-receptors or have very low receptor expression (~6 binding sites/cell) [19]. In mice, increased Epo receptor expression causes increased calcium entry in RBCs during hypoxia and triggers eryptosis (apoptosis of erthocytes). This phenomenon plays an important role in the effective recycling of iron in reticulocytes. An increased Epo level, induced by hypoxia results in increased erythropoiesis and a considerable rise in intracellular Ca2+ triggering eryptosis, which results in immediate recycling of iron and allows effective reticulocytosis. Whereas, in humans, patients receiving high Epo doses could lead to more effective oxygen transportation without significantly increasing the RBC number and ultimately it results in an increased risk of thromboembolytic events [30].
Epo receptors were reported to be devoid in human reticulocytes [31] or to be at least very low in their abundance [19]. An increased Epo level, e.g., induced by hypoxia, not only increases erythropoiesis but considering the increased intracellular Ca2+, also triggers eryptosis. This enables immediate recycling of iron and such an event allows reticulocytosis to happen. A renewal of RBCs may lead to more effective oxygen transportation without a significant increase in RBC number, which eventually would increase the risk of thrombolytic events in patients receiving a high dose of therapeutic Epo [28].
Sickle Cell Disease (SCD)
The pain experienced by the SCD patients widely varies depending on the phases of the disease (e.g., vaso-occlusive crisis pain vs. chronic pain). The detection of noxious stimuli and transmission of the sensory signals is mediated by the unmyelinated C fibers and lightly myelinated Aδ fibers located in the peripheral nervous system. Expression of the TRP channel family of proteins has been detected in the neurons of both classes of nerve fibers. Dysregulated and malfunctioning TRP channels have been reported in both human SCD patients and in a transgenic mouse model of SCD. Detailed research in this specific area have established TRPV1 as a significant contributor to the SCD pain mechanism [32]. During a pain situation, the RBCs’ morphology has been found to change to sickle type cells. Sickled RBCs stick to each other, with endothelial cells, circulating immune cells and the inner lining of the blood vessels and the terminal effect is the overall constrictions of the small blood vessels. The vaso-occlusive events that lead to acute painful episodes in SCD patients are summarized in Fig. (1).
Fig. (1)) Vaso-occlusive events lead to acute painful episodes in SCD patients. Deoxygenation of red blood cells harboring sickle beta globin causes polymerization of hemoglobin and morphological changes in the red blood cell. The cell adheres with greater affinity to endothelial cells lining blood vessel walls, creating a blockage (A). Endothelial cells then become activated, releasing cytokines (B) and allowing for increased extravasation of monocytes (C). The increase of inflammatory cells in the surrounding tissue further contributes to the release of cytokines surrounding nociceptor terminals. This inflammatory soup then activates the nociceptor to allow the release of substance P or CGRP from nociceptor terminals, resulting in a feed-forward mechanism contributing to nociceptor sensitization (D). CGRP: calcitonin gene related peptide; TRPV1: transient receptor potential vanilloid channel 1. Taken from ref [181].Human patients and the mouse model of SCD both experience a chronic state of inflammation and this alone is a major contributor towards chronic hypersensitivity [33]. Neuronal mechanisms are also equally important in the SCD-pain situation. Altered electrophysiological signaling mechanisms have been reported with increased spontaneous firing patterns in the peripheral sensory neurons of the SCD mouse model compared to the control animals [34, 35]. Altered connectivity and activity of CNS circuits have also been reported in both human SCD patients and in the mouse models [36, 37].
To study the acute and chronic SCD pain in detail, two transgenic SCD mouse models have been developed. Berkley (Berk) and Townes mouse models both express the human sickle β SCD. In Berk mice, the murine globin genes are knocked out and normal human α and sickle cell β globin genes are maintained via transgene. In the Townes model, the human α globin and sickle β globin genes are knocked out into the same locus as the murine globin genes. Mice homozygous for sickle cell β globin gene show many phenotypes of human SCD patients, including sickled RBCs, hemolytic anaemia, pulmonary, hepatic and cardiac pathogenesis and chronic hyperalgesia to mechanical, cold and heat stimuli that often frequently increase with age [38-41].
The Berk mice have been reported to be more sensitive to a varied degree of somatosensory stimuli than Townes mice [40]. This indicates underlying hematological issues due to decreased abundance of fetal hemoglobin (HbF). Hbf is the short-lived hemoglobin which is being expressed following birth and has been found to be associated with reduced pain sensation in human SCD patients [38, 39, 42]. TRP channel family members have been discovered as primary sensory detectors because they have been found to be sensitized by a wide variety of physical and chemical stimuli and those channels are abundantly expressed in the SCD patients.
TRPV1 is expressed primarily in unmyelinated c fibers and in less quantity in myelinated Aδ fibers [8, 43] in the peripheral nervous system. TRPV1 is also expressed in the post-synaptic neurons of lamina I and II in the spinal cord [44] and in several regions of the brain [45]. Expression of TRPV1 in the non-neuronal cells has also been widely reported in smooth muscle cells of heart/pulmonary artery [46], mononuclear cells of the circulating blood [47] and keratinocytes within the epidermis [48]. Capsaicin is the known highly potent exogenous activator of TRPV1, but natural activators of TRPV1 are heat, protons and endogenous carbohydrates and lipids [9, 10]. Endogenous compounds, including endocannabinoid anandamide [49], and protons [50], are also known activators of TRPV1.
Proinflammatory signaling molecules like cytokines and eicosanoids also sensitize TRPV1 and do not directly activate the TRPV1 channel. When sensitized, the membrane voltage potential for the channels is significantly decreased, causing the specific TRP channel activators to work at much less concentration to cause a significantly large quantity of cation flow through the channel. Phosphorylation and posttranslational modifications of the TRP channel proteins also play a significant role in its activation [9, 10]. Heat hypersensitivity experienced by SCD patients has been successfully established in the SCD mice model. SCD patients have a lower heat-induced pain tolerance limit compared to the age and race matched controls [51]. In acute pain episodes, further worsening of pain hypersensitivity has not been reported. Controlled and tolerable heat actually found to comfort those patients as analgesics [52].
TRP channels also play important roles in the transition from acute pain to chronic postoperative pain. To understand the implication of TRP channels in such a pain transition mechanism, detailed studies have been carried out in blood cells. TRP channels are now becoming the focus as a new target and biomarker for pain related studies. Blood collected from 13 human patients with chronic pain has been used to perform genome wide mRNA expression for different TRP channels and a detailed study has been performed based on the intensity of pain as experienced by individual patients. Increased expression of TRPV1 mRNA has been found with increased pain symptoms. This data show a strong association of TRPV1 with pain sensation in chronic pain scenarios. Simultaneously, a decrease in TRPA1 has also been found that establishes an inverse relationship of TRPV1 expression with the TRPA1 expression in chronic pain [53].
The adhesive interaction between leukocytes and endothelial cells is mediated by selectins (L, P and E), which has been established as a required event for the inflammatory responses. Elevated expression of soluble E selectin has been reported in the inflammatory diseases which act to promote neutrophil 2-integrin mediated adhesion by extending the phase of cytoplasmic calcium mobilization in the blood neutrophils. This mechanism causes a massive influx of calcium as store-operative calcium entry (SOCE), following activation of platelet-activating factor (PAF) and eventual release of calcium from the InsP3-sensitive stores. TRPC channels have been shown to be activated during such a response and found to be sensitive to specific TRPC channel inhibitors MRS1845 and Gd3+ [54].
TRP Channels in Platelets Related Disorders
Expression and functional roles of different TRPC channels in platelets have been recently reviewed by Dionisio et al. [55]. Human platelets widely express the mammalian homologs of Drosophila TRP channels that are known to be activated by the agonist-induced G protein-coupled receptor, resulting in Na+ and Ca2+ entry into the cell. TRPC channels have been implicated in different calcium handling mechanisms, including the type II InsP3 receptor, the ER calcium sensor Stromal Interaction Molecule-1 (STIM1) or the calcium permeable channel Orai1. Store operated capacitative calcium entry as well as non-capacitative Ca2+ entry, both mechanisms have been implicated in relation to the dynamic interaction of TRPC channels with the above-mentioned proteins. The TRPC channel mediated capacitative calcium entry mechanism is operative in human platelets and is being activated by the decrease of intracellular free calcium in the ER store that activates the complex cascade of Ca2+ entry mechanisms involving the STIM, Orai1, Orai2, TRPC1 and TRPC6. Faulty calcium homeostasis in human platelets has been linked to many platelet-linked disorders including those associated with type II diabetes mellitus (T2DM). Platelet hyperactivity is one such response, which has been found to be dependent on abnormal calcium signaling. Altered expression of several TRP channel proteins, STIM1 and Orai1, as well as their interaction has been found in the platelets isolated from T2DM patients and could be important in pathophysiology in diabetic complications. A separate study [56] involving platelets isolated from T2DM patients has shown evidence that human TRPC1 and TRPC6 channels play a significant role in store-operated calcium entry and modulation of the interactions between several calcium sensors including STIM1 and the channel subunits Orai1. The presence of other non-capacitative calcium entry related mechanisms has also been indicated in this study due to the observed entry of increased calcium when the platelets were stimulated with the SERCA agonist thapsigargin. The possible roles of TRPM7 channels’ kinase domain in activating phospholipase C (PLC) family members to regulate intracellular Ca2+ response-mediated signaling mechanisms in relation to platelets related disorders are summarized in Fig. (2). This model also provides information regarding possible association of other TRPC channels responsible for SOCEs in developing pathological events in platelets disorder.
TRPML and Iron-deficiency Anaemia
TRPML1, the mucolipin subfamily of TRP channel proteins, has been identified as an iron permeable ion channel in the late endosomes and lysosomes. In humans, the mutation in the TRPML1 gene is known to cause mucolipidosis type IV disease (ML4). TRPML1 mutation in the TRPML1 gene has been reported to cause faulty iron influx into the cells and well correlated with the severity of iron deficiency anaemia and indicates a pathological role of TRPML1 in the hematological and degenerative symptoms of ML4 patients [57]. ML4 patients are presented with blood iron-deficiency anaemia along with neuromotor impairment, retinal degeneration and mental retardation. In most mammalian cells, the endosomal/lysosomal release of iron from the transferrin or ferritin-iron complexes is the main source of cellular iron. The divalent metal transporter protein DMT1 (SLC11A2) is the endosomal iron transporting protein, which is widely expressed in the erythroid precursors. In a clinical study, a cohort of human ML4 patients were recruited to analyze the association of the severity of iron-deficiency anaemia, and other related pathological conditions showed a strong correlation of the TRPML1 gene mutation [58].
Fig. (2)) Kinase domain of TRPM7 in the plasma membrane (PM) of platelets interacts with phospholipase C (PLC) family members and regulates cellular calcium homeostasis and platelets function. Agonist-induced protease activated receptor (PAR) activation results in intracellular calcium signaling events and activates phospholipase C (PLCγ2 and PLCβ3) phosphorylation and InsP3 mediated store operated calcium signaling mechanisms in the platelets. STIM1 molecules expressed on ER interact with the Orai1 on PM and controls downstream signal transduction events as a result of store operated Ca2+ entry (SOCE) in association with a coupled mechanism of TRPC channel-mediated calcium influx.TRPM6 in Dysregulated Blood and Serum Mg2+ Homeostasis
The research on TRPM6 has been linked to the mutation-related different channelopathies in humans. Those TRPM6 channels have been implicated in Mg2+ (re)absorption in the intestines and in the kidneys. The mutations in those channels thus cause diseases associated with dysregulated Mg2+ homeostasis in the blood and serum. So far, more than 35 point mutations have been discovered in the TRPM6 gene and have been correlated with autosomal recessive disease hypomagnesemia and associated secondary hypocalcemia (HSH1 or, HOMG1) [59, 60]. Very low serum Mg2+ and Ca2+ levels are the main symptoms of HSH1. The condition is generally diagnosed in the first 6 months of life and is presented with characteristic secondary neurological symptoms. Constitutively lower secretion of parathyroid hormones (PTH) and decreased renal/intestinal Mg2+ reabsorption are the two main functional defects associated with this condition.
TRP Channels and Hematological Malignancies
Leukemia, the cancer of blood-forming cells in the bone marrow, is responsible for about one-third of the global diagnosis of childhood cancer. Different TRP channellopathies have been implicated in leukemia. Lymphoma, the cancer of the immune cells, is characterized by the neoplasia of the lymphoid organs and TRP channel pathophysiology is also identified in lymphoma patients. Differential TRP channel expression and modulation have been identified as hallmarks in different pathological conditions associated with blood diseases, including hematological malignancies.
TRPM Channels
TRPM1
The expression pattern of TRPM1 is positively correlated with terminal melanocytic differentiation. The reduced expression and function of TRPM1 channels are a diagnostic and prognostic biomarker for primary cutaneous melanoma [61]. Interestingly, patients with acute myeloid leukemia (AML) have been found to harbor MLL-AF6 fusion protein, which results from a new three-way translocation. PCR studies have shown evidence for the expression of TRPM1 ion channels in somatic cell hybrids in the cell lines carrying a paternal chromosome 11. This further provides evidence of the silencing of the maternal copy of gene 11 through a mechanism called genome imprinting [62]. A CD41+ megakaryocytic cell line established from mouse had shown the TRPM1 gene expression. Thus, TRPM1 has emerged as an important target for further study in relation to acute megakaryoblastic leukemia.
TRPM2
TRPM2 also allows Ca2+ influx into the cell in a redox-sensitive way. Hydrogen peroxide (H2O2)-induced Ca2+ entry happens to the cell through this channel and is responsible for cell death [63]. The expression of TRPM2 has been reported in glioblastoma [64] and prostate cancer cells [65], along with a rich expression in promyelocytic HL-60 leukemia cells and lymphoblastoid Jurkat T cells [66, 67]. Recent studies have indicated an oxidative stress-induced signaling-dependent induction of Ca2+ entry into the leukemia cells. Full length TRPM2 (TRPM2-L) expressing U937 cells when treated with H2O2 express a short variant of TRPM2 (TRPM2-S) with no calcium permeable pore region. H2O2 or TNFα treatment in U937 cells has been found to cause increased expression of TRPM2-L and induces caspase -3,-7,-8 and -9 dependent apoptosis. Downregulation of full length TRPM2 gene by an SiRNA approach, or increased expression of TRPM2-S significantly reduces the TRPM2 channel-mediated calcium entry and reduces the cellular apoptosis [68].
TRPM4
Molt-4 and Jurkat T leukemia cells, the two T lymphoblast cell lines in human express TRPM4 receptor. The presence of both short form of TRPM4 (TRPM4a) lacking 174 amino acids in the N-terminus [69] and a long form TRPM4b [70] has been reported in those cells. Employing dominant negative mutant of TRPM4 in Jurkat cell lines has been found to convert the short-lasting calcium wave into a long-lasting and sustained elevation of calcium inside the cell that results in IL-2 induction. Increased TRPM4 expression has been reported in prostate cancer [71-73], in human cervical uterine tumor samples and in cervical-uterine cancer-derived cell lines [74]. An aggressive form of large B-cell non-Hodgkin’s lymphoma also expresses TRPM4 [75]. The function of TRPM4 includes regulation of T lymphocyte and mast cell activation and migration of dendritic and mast cells [70, 76-78]. Though the Wnt/β catenin pathway has not been studied extensively in relation to increased TRPM4 expression in cancer, catenin-expression has been found in Jurkat T cells and in several peripheral blood T cells, but is not detected in normal peripheral blood T cells [79-82]. Enhanced TRPM4 gene expression in the CD5+ subgroup of B-cell lymphomas (DLBCL) patients, which is the common form of non-Hodgkin’s Lymphomas has been reported and used as a prognostic clinical marker for the CD5+ signature.
TRPM5
TRPM5 has been proposed to be linked to an abnormal immune response associated with infections during childhood leukemia. Change of cell proliferation following an infection increases the risk of childhood acute lymphocytic leukemia (ALL) [83, 84]. This ultimately suppresses hematopoiesis and/or induces apoptosis [85]. Genetic polymorphisms in the genes responsible for immunological responses have been proposed to play significant roles in developing childhood leukemia. In line with this idea, SNPs analysis in a cohort of childhood Korean leukemia patients shows evidence of rs2301696 SNP of TRPM5 in the CG or GG genotype and this was positively correlated with a decreased risk of childhood leukemia compared to CC genotype [86]. Similar rs2301696 SNP has also been observed in the TRPM5 gene when the genotype analysis has been restricted to childhood ALL. In a separate study, the relationship of NOTCH1 signaling to TRPM5 gene expression has been correlated. Within the NOTCH1 heterodimerization domain, leukemia-associated mutation causes ADAM-type MMPs (S2) and- secretase (S3) cleavage and the resultant peptide plays a role in regulating TRPM5 activity [87]. TRPM5 gene is located close to the locus of the CD81 gene, which is responsible for mediating signals that control the regulation of cell development, activation, growth, and motility [72]. Future studies are required to explore how TRPM5 SNPs make the kids susceptible to childhood leukemia.
TRPM7
Expression of TRPM7 channels has been reported in different tissues, including heart, lung, brain, kidney and hematopoietic tissues, TRPM7 activity is regulated by cytoplasmic concentrations of Mg2+ and Mg2+-ATP. The evidence available in this specific area have linked TRPM7 to cellular Mg2+ homeostasis [60], neuronal death [88], atrial fibrinogenesis [89], cell adhesion [90] and many other events. Expression of TRPM7 has been reported in several hematopoietic cells, including the rat basophilic leukemia cell line (RBL-2H3), human Jurkat T leukemia cells [91], primary murine CD41+ megakaryocytic cell lines [92] and in the K562 erythromyeloblastoid leukemia cell line [93]. SiRNA-mediated selective knockdown of the TRPM7 gene in RBL-2H3 cells caused increased cellular apoptosis [94]. Supporting this finding, TRPM7 deficient cells show a rapid downregulation of their growth and is associated with secondary arrest in cell proliferation [95]. The knockdown of the TRPM7 gene by the siRNA approach has provided evidence for significant inhibition of cell proliferation in normal and PDGF-stimulated osteoblasts. 5-lipoxygenase inhibitor sensitive reduction of a TRPM7 like current has been observed in human erythroleukemia cells. Similar modulation of TRPM7 current has been observed in the leukemic cell line CHRF288-11 under the control of cytoplasmic Mg2+ levels [96]. PIP2 has been implicated in TRPM7 channel activation [97].
Graft-versus-host disease (GVHD) is a serious problem associated with allogeneic stem cell transplantation. Patients receive stem cells from a donor or umbilical cord blood during allogeneic stem cell transplantation. GVHD is observed when the graft (donor’s T cells) comes in contact with the host (recipient‘s) and recognizes as foreign with eventual destruction of the graft by complex immune-response pathways. Depending upon the condition GVHDs are classified as mild, moderate and severe and the final consequence could be life-threatening. Patients with mild GVHD are often treated with local or topical therapies. Recent studies have indicated that TRPM7 plays an important function in harboring cation channel and Ser/Thr kinase, which has been implicated in thymopoiesis and cytokine expression. By using a TRPM7 kinase-dead mutant (Trpm7R/R) mice, Romagnani et al. [98] have shown that the enzymatic activity of the TRPM7 receptor activity is not essential for thymopoiesis, but it is indeed a required step for the transcription of CD103 and gut-homing of intra-epithelial lymphocytes. Their study has indicated a potential role of the functional TRPM7 kinase activity in regulating T cell function, which opens an idea for developing therapeutic approaches of using kinase inhibitors to tackle GVHD.
TRPM8
TRPM8 channels have been described as cold receptors as those channels are activated at low temperature (< 26°C) and mostly expressed in the sensory neurons [99, 100]. Menthol is a common activator for this channel [99]. Expression of those channels has been found in the basophilic leukemia mast cell line, RBL-2H3.
TRPV Channels
TRPV1
Research on TRPV1 and its functional role in hematological malignancies are only a handful. Especially the data is scanty in this specific area supported by both gene (mRNA) and protein expression. The TRPV1 antagonist capsazepine, though it has nonselective actions [101], has been employed in some studies to understand the TRPV1 dependent and independent cytotoxic actions of capsaicin. IC50 of capsaicin (20-500 µM), which far exceeds the known affinity for classical or neuronal TRPV1 channels, indicates a mixed TRPV1-dependent and independent actions. The role of TRPV1 in different hematological malignancies and blood disorders has been reviewed in detail by Omari et al. [102]. The aberrant expression and function of TRPV1 channels proteins have been implicated in adult T-Cell Leukemia (ATL) and in MM. Fig. (3) is a simplified scheme showing the regulatory crosstalk between α1D-adrenergic receptor (α1D-AR) and TRPV1 channels that ultimately lead to downstream cellular signaling cascades causing uncontrolled cell proliferation in different types of cancer initiation and progression.
Fig. (3)) A simplified scheme of regulatory cross-talk between α1D-adrenergic receptor (α1D-AR) and Transient Receptor Potential Vanilloid 1 (TRPV1) that includes multiple parallel and converging downstream signal transduction pathways. DAG: diacylglycerol; IP3: inositol 1,4,5-trisphosphate; IP3R: IP3 receptor; MAPK: mitogen activated protein kinases; NE: norepinephrine; PI3K: phosphatidylinositol-4,5-bisphosphate 3-kinase; PIP2: phosphatidylinositol 4,5-bisphosphate; PKC: protein kinase C; PLC: phospholipase C. Taken from [182].Leukemia Cell Lines
Capsaicin has been reported to inhibit the release of inflammatory cytokines from the cultured human promyelocytic leukemia cells [103]. When cultured HL-60 cells were exposed to various concentrations of capsaicin prior to treating the cells with 12-0-tetradecanoylphorbol-13-acetate (TPA), a typical tumor promoter, capsaicin was able to inhibit the TPA-induced NF-KB activation in a concentration-dependent manner. To understand further regarding the molecular mechanisms of capsaicin-induced NF-KB inactivation, the status of IκBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha), an endogenous inhibitor of NF-KB receptor has been studied. Capsaicin pretreatment was found to protect the TPA-induced IκBα degradation with subsequent inhibition of NF-KB. HL60 cells are found to be differentiated into monocytic or granulocytic lineage when exposed to 1, 25-dihydroxyvitamin D3 [1,25- (OH)2 D3]or all- trans-retinoic acid [104, 105], respectively. Those clearly indicate the functional involvement of retinoic acid signaling pathways in acute promyelocytic leukemia (APL) development. APL has been found to be present in ~10% of the patient population of acute myeloid leukemia (AML) and represents a significantly distinct subtype [subtype M3, according to The French-American-British (FAB) classification of AML] considering clinical, prognostic and morphological features. APL is characterized by the reciprocal translocation of t(15;17)(q22;q21) in ~90% of cases [106]. The consequence of this event results in the fusion of the gene for retinoic acid receptor α (RARA) on 17q21 with the gene for the PML transcription factor on 15q22. The end product is a PML/RARA gene fusion product [107]. The arrest of granulocytic differentiation, reciprocal translocation of t(15;17) followed by the fusion of the PML gene to the RARA gene is the hallmark of APL.
Transcription factors NF-κB and activator protein 1 that plays a significant role in many inflammatory diseases and cellular apoptosis has been reported to be inhibited by capsaicin and resiniferatoxin [103, 108, 109]. The expression of the TRPV1 channel has been found in the monocytic THP-1 leukemia cell line [110]. Activation of the TRPV1 channels and cellular Ca2+ influx has been found to strengthen the adhesion between THP-1 cells and HUVECs, whereas the TRPV1 antagonist SB366791, reduced this adherence [111]. Contrasting data in this regard are also available, that shows capsaicin-induced THP-1 cell death is independent of TRPV1, or cannabinoid CB1/2 receptor activation [112]. Capsaicin-induced inhibition of growth in some leukemia cell lines has been reported due to the induction of G0/G1 phase arrest of the cell cycle, but the normal bone marrow mononuclear cells remain unaffected at the same capsaicin treatment condition [113]. The capsaicin-induced apoptosis in leukemia cell lines has been found to be associated with an increase in reactive oxygen species (ROS) concentration and research in this area has identified capsaicin-induced apoptosis is linked to mitochondrial dysfunction [113, 114]. Capsaicin has been reported to promote the activation of p53 (tumor suppressor) by phosphorylation [115]. Gene knockdown strategy for the p53 caused a significant reduction in the capsaicin-induced cell cycle arrest. Capsaicin-sensitive leukemia cells (NB4 and Kasumi-1) express p53 gene and the activation of p53 by capsaicin causes upregulation of cyclin-dependent kinases (CDK) inhibitor (p21WAF1/CIP1), and the proapoptotic Bcl-2-associated X (Bax) genes [113, 116, 117]. The following signal transduction events are usually associated with the higher synthesis of Bax protein and eventual translocation of the Bax from the cytosol to the outer mitochondrial membrane, causing cytochrome C activation and the activation of caspases with an end result of cellular apoptosis [113, 118, 119]. The involvement of different proteins, such as cyclins, CDKs, and inhibitors, and certain biomolecules that causes cell cycle arrest has been established the capsaicin-induced cell signaling pathways as an important proof of concept for identification of the potential drug targets and developing anti-cancer drugs [120].
Adult T-Cell Leukemia (ATL)
ATL is an aggressive type of human T-cell malignancy and the causative agent for this disease is human T-cell leukemia virus type-1 [121]. NF-κB, an apoptotic inhibitor induction by the viral infection, causes the pathogenic responses and the tumor aggression in ATL [122, 123]. In vitro studies, where ATL cells have been exposed to capsaicin, showed a decreased production of NF-κB which reduced the binding activity of NF-κB to P65 protein, resulting in an improvementof ATL [124].
The effectiveness of capsaicin as a growth inhibitor for the ATL cells takes place due to G1 cell cycle arrest, which is a very common apoptosis mechanism for many anticancer chemotherapeutic drugs [125, 126]. Decreased NF-κB activity due to the capsaicin induction also induces apoptosis by downregulating Bcl-2. On the other hand, Bax, Bcl-2 and B-cell lymphoma-extra-large (Bcl-xL) are the key players that play an essential role as anti-apoptotic elements [127]. Capsaicin has been shown to have the potential to reduce the Bcl-2 expression and to change the Bcl-2/Bax ratio, an important determinant of apoptosis [128] and cause apoptosis in ATL cell lines [124].
Multiple Myeloma (MM)
Signal transducer and activator of transcription (STAT) protein family have been implicated as a regulator for many gene products [129] and STAT3 is the most studied member in this family that has been widely investigated in the context of tumorigenesis. STAT3 is constitutively expressed in the active tumor cells and reported to become activated by interleukin-6 (IL-6), and by the Src Family Kinase (SFK)-mediated mechanisms. STAT3 activation has been reported to cause cell proliferation (e.g., c-myc and cyclin D1) and apoptosis suppression (e.g., Bcl-xL), and facilitates angiogenesis. Recent literature shows that capsaicin is effective in causing cellular apoptosis through an IL-6 induction mechanism due to the induction of STAT3 [130]. Recently, activation of the Jak2/STAT3, NF-κB, and JNK pathways in three MM cell lines (RPMI8226, INA6, and MM.1S) has been reported in cellular acidosis, a hallmark for the MM environment with an upregulation of TRPV1 gene expression [131]. The hypothesis in this specific study was TRPV1-mediated sustained activation of P13K-Akt signaling that makes the survival of the MM cells favorable. When the phosphorylation of the Akt has been inhibited in cultured cells by employing a TRPV1 antagonist SB366791, the reduced proliferation of MM cells have been observed [131].
TRPV2
Expression of TRPV2 channel proteins has been described in the CD34+ hematopoietic stem cells. Calcium plays a significant function in those cells in relation to growth, progression and differentiation [132]. In humans, TRPV2 gene expression has been reported in whole blood cells, lymph nodes, tonsils and CD19+ lymphocytes [133]. Aberrant expression of TRPV2 channel proteins has been reported in several hematological tumors and in cell lines including mantle cell lymphoma, acute myeloid lymphoma, MM, Burkitt lymphoma and in myelodysplastic syndrome [3, 134
