New Disaccharide-Based Ether Lipids as SK3 Ion Channel Inhibitors

Endogenous ether-lipids differentially promote tumour aggressiveness by regulating the SK3 channel

SK3 channels are potassium channels found to promote tumour aggressiveness. We have previously demonstrated that SK3 is regulated by synthetic ether-lipids, but the role of endogenous ether lipids is unknown. Here, we have studied the role of endogenous alkyl- and alkenyl-ether-lipids on SK3 channels and on the biology of cancer cells. Experiments revealed that the suppression of AGPS or PEDS1, which are key enzymes for alkyl- and alkenyl-ether-lipid synthesis, respectively, decreased SK3 expression by increasing miR-499 and miR-208 expression, leading to a decrease in SK3-dependent calcium entry, cell migration, and MMP9-dependent cell adhesion and invasion. We identified several ether-lipids that promoted SK3 expression and found a differential role of alkyl- and alkenyl-ether-lipids on SK3 activity. The expressions of AGPS, SK3, and miR were associated in clinical samples emphasising the clinical consistency of our observations. To our knowledge, this is the first report showing that ether-lipids differentially control tumour aggressiveness by regulating an ion channel. This insight provides new possibilities for therapeutic interventions, offering clinicians an opportunity to manipulate ion channel dysfunction by adjusting the composition of ether-lipids.

Synthesis of ether lipids: natural compounds and analogues

Ether lipids are compounds present in many living organisms including humans that feature an ether bond linkage at the sn-1 position of the glycerol. This class of lipids features singular structural roles and biological functions. Alkyl ether lipids and alkenyl ether lipids (also identified as plasmalogens) correspond to the two sub-classes of naturally occurring ether lipids. In 1979 the discovery of the structure of the platelet-activating factor (PAF) that belongs to the alkyl ether class of lipids increased the interest in these bioactive lipids and further promoted the synthesis of non-natural ether lipids that was initiated in the late 60's with the development of edelfosine (an anticancer drug). More recently, ohmline, a glyco glycero ether lipid that modulates selectively SK3 ion channels and reduces in vivo the occurrence of bone metastases, and other glyco glycero ether also identified as GAEL (glycosylated antitumor ether lipids) that exhibit promising anticancer properties renew the interest in this class of compounds. Indeed, ether lipid represent a new and promising class of compounds featuring the capacity to modulate selectively the activity of some membrane proteins or, for other compounds, feature antiproliferative properties via an original mechanism of action. The increasing interest in studying ether lipids for fundamental and applied researches invited to review the methodologies developed to prepare ether lipids. In this review we focus on the synthetic method used for the preparation of alkyl ether lipids either naturally occurring ether lipids (e.g., PAF) or synthetic derivatives that were developed to study their biological properties. The synthesis of neutral or charged ether lipids are reported with the aim to assemble in this review the most frequently used methodologies to prepare this specific class of compounds.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Thio-ether functionalized glycolipid amphiphilic compounds reveal a potent activator of SK3 channel with vasorelaxation effect

The modulation of SK3 ion channels can be efficiently and selectively achieved by using the amphiphilic compound Ohmline (a glyco-glycero-ether-lipid). We report herein a series of Ohmline analogues featuring the replacement of one ether function by a thioether function located at the same position or shifted close to its initial position. The variation of the lipid chain length and the preparation of two analogues featuring either one sulfoxide or one sulfone moiety complete this series. Patch clamp measurements indicate that the presence of the thioether function (compounds 7 and 17a) produces strong activators of SK3 channels, whereas the introduction of a sulfoxide or a sulfone function at the same place produces amphiphiles devoid of an effect on SK3 channels. Compounds 7 and 17a are the first amphiphilic compounds featuring strong activation of SK3 channels (close to 200% activation). The cytosolic calcium concentration determined from fluorescence at 3 different times for compound 7b (13 min, 1 h, 24 h) revealed that the effect is different suggesting that the compound could be metabolized over time. This compound could be used as a strong SK3 activator for a short time. The capacity of 7b to activate SK3 was then used to induce vasorelaxation via an endothelium-derived hyperpolarization (EDH) pathway. For the first time, we report that an amphiphilic compound can affect the endothelium dependent vasorelaxation.

Development of pyrene-based fluorescent ether lipid as inhibitor of SK3 ion channels

We report the synthesis of three bioactive pyrene-based fluorescent analogues of Ohmline which is the most efficient and selective inhibitor of SK3 ion channel. The interaction of these Ohmline-pyrene (OP1-3) with liposomes of different composition reveals that only OP2 and OP3 are readily integrated into liposomes. Fluorescence measurements indicate that, depending on their concentration, OP2 and OP3 exist either as monomer or as a mixture of monomer and excimers within the liposome bilayer. Among the three Ohmline Pyrene compounds (OP1-3) only OP2 is able to reduce SK3 currents and is the first efficient fluorescent modulator of SK3 channel as revealed by patch clamp measurements (- 71.3 ± 13.3% at 10 μM) and by its inhibition of SK3-dependent cancer cell migration at (-32.5% ± 4.8% at 1 μM). We also report the first fluorescence study on living breast cancer cells (MDA-MB-231) showing that OP2 is rapidly integrated in bio-membranes followed by cell internalization.

"Electrifying dysmorphology": Potassium channelopathies causing dysmorphic syndromes

Potassium channels are a heterogeneous group of membrane-bound proteins, whose functions support a diverse range of biological processes. Genetic disorders arising from mutations in potassium channels are classically recognized by symptoms arising from acute channel dysfunction, such as periodic paralysis, ataxia, seizures, or cardiac conduction abnormalities, often in a patient with otherwise normal examination findings. In this chapter, we review a distinct subgroup of rare potassium channelopathies whose presentations are instead suggestive of a developmental disorder, with features including intellectual disability, craniofacial dysmorphism or other physical anomalies. Known conditions within this subgroup are: Andersen-Tawil syndrome, Birk-Barel syndrome, Cantú syndrome, Keppen-Lubinsky syndrome, Temple-Baraitser syndrome, Zimmerman-Laband syndrome and a very similar disorder called Bauer-Tartaglia or FHEIG syndrome. Ion channelopathies are unlikely to be routinely considered in the differential diagnosis of children presenting with developmental concerns, and so detailed description and photographs of the clinical phenotype are provided to aid recognition. For several of these disorders, functional characterization of the genetic mutations responsible has led to identification of candidate therapies, including drugs already commonly used for other indications, which adds further impetus to their prompt recognition. Together, these cases illustrate the potential for mechanistic insights gained from genetic diagnosis to drive translational work toward targeted, disease-modifying therapies for rare disorders.

Store-independent Orai1-mediated Ca2+ entry and cancer

Ca²⁺ channels play an important role in the development of different types of cancer, and considerable progress has been made to understand the pathophysiological mechanisms underlying the role of Ca²⁺ influx in the development of different cancer hallmarks. Orai1 is among the most ubiquitous and multifunctional Ca²⁺ channels. Orai1 mediates the highly Ca²⁺-selective Ca²⁺ release-activated current (I_CRAC) and participates in the less Ca²⁺-selective store-operated current (I_SOC), along with STIM1 or STIM1 and TRPC1, respectively. Furthermore, Orai1 contributes to a variety of store-independent Ca²⁺ influx mechanisms, including the arachidonate-regulated Ca²⁺ current, together with Orai3 and the plasma membrane resident pool of STIM1, as well as the constitutive Ca²⁺ influx processes activated by the secretory pathway Ca²⁺-ATPase-2 (SPCA2) or supported by physical and functional interaction with the small conductance Ca²⁺-activated K⁺ channel 3 (SK3) or the voltage-dependent K_v10.1 channel. This review summarizes the current knowledge concerning the store-independent mechanisms of Ca²⁺ influx activation through Orai1 channels and their role in the development of different cancer features.

2,6-Bis(2-Benzimidazolyl)Pyridine (BBP) Is a Potent and Selective Inhibitor of Small Conductance Calcium-Activated Potassium (SK) Channels

A variety of polycyclic pyridines have been proposed as inhibitors of the small conductance calcium-activated potassium (SK) channel. To this group belongs 2,6-bis(2-benzimidazolyl)pyridine (BBP), a commercially and readily available small organic compound which has earlier been described in a broad range of chemical and biological uses. Here, we show how BBP can also be used as a potent and specific SK channel blocker in vitro. The potency of BBP was measured using automatic patch clamp on all three SK channel subtypes, resulting in similar IC₅₀ of 0.4 μM. We also assessed the selectivity of BBP on a panel of calcium-activated and voltage-activated potassium channels using two-electrode voltage clamp, automatic and manual patch clamp. BBP did not have any effect on IK, K_ir2.1, K_ir3.1+K_ir3.4, K_v1.5, K_v4.3/K_CHIP2 and K_v7.1/KCNE1 currents and was 4.8-fold and 46-fold more potent on all SK channel subtypes vs. BK and hERG channels, respectively. Moreover, we were able to identify H491 as a critical amino acid for the pharmacological effect of BBP on the SK channel. From a medicinal chemistry perspective, BBP could be used as a starting point for the design of new and improved SK inhibitors.

CRISPR-mediated deletion of prostate cancer risk-associated CTCF loop anchors identifies repressive chromatin loops

BACKGROUND

Recent genome-wide association studies (GWAS) have identified more than 100 loci associated with increased risk of prostate cancer, most of which are in non-coding regions of the genome. Understanding the function of these non-coding risk loci is critical to elucidate the genetic susceptibility to prostate cancer.

RESULTS

We generate genome-wide regulatory element maps and performed genome-wide chromosome confirmation capture assays (in situ Hi-C) in normal and tumorigenic prostate cells. Using this information, we annotate the regulatory potential of 2,181 fine-mapped prostate cancer risk-associated SNPs and predict a set of target genes that are regulated by prostate cancer risk-related H3K27Ac-mediated loops. We next identify prostate cancer risk-associated CTCF sites involved in long-range chromatin loops. We use CRISPR-mediated deletion to remove prostate cancer risk-associated CTCF anchor regions and the CTCF anchor regions looped to the prostate cancer risk-associated CTCF sites, and we observe up to 100-fold increases in expression of genes within the loops when the prostate cancer risk-associated CTCF anchor regions are deleted.

CONCLUSIONS

We identify GWAS risk loci involved in long-range loops that function to repress gene expression within chromatin loops. Our studies provide new insights into the genetic susceptibility to prostate cancer.

Synthesis of Alkyl-Glycerolipids Standards for Gas Chromatography Analysis: Application for Chimera and Shark Liver Oils

Natural O-alkyl-glycerolipids, also known as alkyl-ether-lipids (AEL), feature a long fatty alkyl chain linked to the glycerol unit by an ether bond. AEL are ubiquitously found in different tissues but, are abundant in shark liver oil, breast milk, red blood cells, blood plasma, and bone marrow. Only a few AEL are commercially available, while many others with saturated or mono-unsaturated alkyl chains of variable length are not available. These compounds are, however, necessary as standards for analytical methods. Here, we investigated different reported procedures and we adapted some of them to prepare a series of 1-O-alkyl-glycerols featuring mainly saturated alkyl chains of various lengths (14:0, 16:0, 17:0, 19:0, 20:0, 22:0) and two monounsaturated chains (16:1, 18:1). All of these standards were fully characterized by NMR and GC-MS. Finally, we used these standards to identify the AEL subtypes in shark and chimera liver oils. The distribution of the identified AEL were: 14:0 (20-24%), 16:0 (42-54%) and 18:1 (6-16%) and, to a lesser extent, (0.2-2%) for each of the following: 16:1, 17:0, 18:0, and 20:0. These standards open the possibilities to identify AEL subtypes in tumours and compare their composition to those of non-tumour tissues.

Singular Interaction between an Antimetastatic Agent and the Lipid Bilayer: The Ohmline Case

SK3 channels are abnormaly expressed in metastatic cells, and Ohmline (OHM), an ether lipid, has been shown to reduce the activity of SK3 channels and the migration capacity of cancer cells. OHM incorporation into the plasma membrane is proposed to dissociate the protein complex formed between SK3 and Orai1, a potassium and a calcium channel, respectively, and would lead to a modification in the lipid environment of both the proteins. Here, we report the synthesis of deuterated OHM that affords the determination, through solid-state NMR, of its entire partitioning into membranes mimicking the SK3 environment. Use of deuterated lipids affords the demonstration of an OHM-induced membrane disordering, which is dose-dependent and increases with increasing amounts of cholesterol (CHOL). Molecular dynamics simulations comfort the disordering action and show that OHM interacts with the carbonyl and phosphate groups of stearoylphosphatidylcholine and sphingomyelin and to a minor extent with CHOL. OHM is thus proposed to remove the CHOL OH moieties away from their main binding sites, forcing a new rearrangement with other lipid groups. Such an interaction takes its origin at the lipid-water interface, but it propagates toward the entire lipid molecules and leads to a cooperative destabilization of the lipid acyl chains, that is, membrane disordering. The consequences of this reorganization of the lipid phases are discussed in the context of the OHM-induced inhibition of SK3 channels.

Amphiphilic glycoconjugates as potential anti-cancer chemotherapeutics

Amphiphilicity is one of the desirable features in the process of drug development which improves the biological as well as the pharmacokinetics profile of bioactive molecule. Carbohydrate moieties present in anti-cancer natural products and synthetic molecules influence the amphiphilicity and hence their bioactivity. This review focuses on natural and synthetic amphiphilic anti-cancer glycoconjugates. Different classes of molecules with varying degree of amphiphilicity are covered with discussions on their structure-activity relationship and mechanism of action.

Associations among dietary non-fiber carbohydrate, ruminal microbiota and epithelium G-protein-coupled receptor, and histone deacetylase regulations in goats

BACKGROUND

Diet-derived short-chain fatty acids (SCFAs) in the rumen have broad effects on the health and growth of ruminants. The microbe-G-protein-coupled receptor (GPR) and microbe-histone deacetylase (HDAC) axes might be the major pathway mediating these effects. Here, an integrated approach of transcriptome sequencing and 16S rRNA gene sequencing was applied to investigate the synergetic responses of rumen epithelium and rumen microbiota to the increased intake of dietary non-fiber carbohydrate (NFC) from 15 to 30% in the goat model. In addition to the analysis of the microbial composition and identification of the genes and signaling pathways related to the differentially expressed GPRs and HDACs, the combined data including the expression of HDACs and GPRs, the relative abundance of the bacteria, and the molar proportions of the individual SCFAs were used to identify the significant co-variation of the SCFAs, clades, and transcripts.

RESULTS

The major bacterial clades promoted by the 30% NFC diet were related to lactate metabolism and cellulose degradation in the rumen. The predominant functions of the GPR and HDAC regulation network, under the 30% NFC diet, were related to the maintenance of epithelium integrity and the promotion of animal growth. In addition, the molar proportion of butyrate was inversely correlated with the expression of HDAC1, and the relative abundance of the bacteria belonging to Clostridum_IV was positively correlated with the expression of GPR1.

CONCLUSIONS

This study revealed that the effects of rumen microbiota-derived SCFA on epithelium growth and metabolism were mediated by the GPR and HDAC regulation network. An understanding of these mechanisms and their relationships to dietary components provides better insights into the modulation of ruminal fermentation and metabolism in the promotion of livestock production.

Small conductance Ca2+-activated K+ channels in the plasma membrane, mitochondria and the ER: Pharmacology and implications in neuronal diseases

Ca²⁺-activated K⁺ (K_Ca) channels regulate after-hyperpolarization in many types of neurons in the central and peripheral nervous system. Small conductance Ca²⁺-activated K⁺ (K_Ca2/SK) channels, a subfamily of K_Ca channels, are widely expressed in the nervous system, and in the cardiovascular system. Voltage-independent SK channels are activated by alterations in intracellular Ca²⁺ ([Ca²⁺]_i) which facilitates the opening of these channels through binding of Ca²⁺ to calmodulin that is constitutively bound to the SK2 C-terminus. In neurons, SK channels regulate synaptic plasticity and [Ca²⁺]_i homeostasis, and a number of recent studies elaborated on the emerging neuroprotective potential of SK channel activation in conditions of excitotoxicity and cerebral ischemia, as well as endoplasmic reticulum (ER) stress and oxidative cell death. Recently, SK channels were discovered in the inner mitochondrial membrane and in the membrane of the endoplasmic reticulum which sheds new light on the underlying molecular mechanisms and pathways involved in SK channel-mediated protective effects. In this review, we will discuss the protective properties of pharmacological SK channel modulation with particular emphasis on intracellularly located SK channels as potential therapeutic targets in paradigms of neuronal dysfunction.