Intracellular Nucleotide Concentrations Research Articles

Exploring the Role of Surface and Mitochondrial ATP-Sensitive Potassium Channels in Cancer: From Cellular Functions to Therapeutic Potentials.

ATP-sensitive potassium (KATP) channels are found in plasma membranes and mitochondria. These channels are a type of ion channel that is regulated by the intracellular concentration of adenosine triphosphate (ATP) and other nucleotides. In cell membranes, they play a crucial role in linking metabolic activity to electrical activity, especially in tissues like the heart and pancreas. In mitochondria, KATP channels are involved in protecting cells against ischemic damage and regulating mitochondrial function. This review delves into the role of KATP channels in cancer biology, underscoring their critical function. Notably responsive to changes in cellular metabolism, KATP channels link metabolic states to electrical activity, a feature that becomes particularly significant in cancer cells. These cells, characterized by uncontrolled growth, necessitate unique metabolic and signaling pathways, differing fundamentally from normal cells. Our review explores the intricate roles of KATP channels in influencing the metabolic and ionic balance within cancerous cells, detailing their structural and operational mechanisms. We highlight the channels' impact on cancer cell survival, proliferation, and the potential of KATP channels as therapeutic targets in oncology. This includes the challenges in targeting these channels due to their widespread presence in various tissues and the need for personalized treatment strategies. By integrating molecular biology, physiology, and pharmacology perspectives, the review aims to enhance the understanding of cancer as a complex metabolic disease and to open new research and treatment avenues by focusing on KATP channels. This comprehensive approach provides valuable insights into the potential of KATP channels in developing innovative cancer treatments.

DHODH: A Promising New Therapeutic Target in Pediatric T-ALL

Acute T-cell lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy in children and young adults. When compared to B-ALL, T-ALL has a higher rate of induction failure as well as relapse, with very poor overall survival in both scenarios. T-ALL has not benefitted from the same immune-mediated therapies (e.g., anti-CD19 CAR-T cells) and poses an ongoing treatment challenge as well as an unmet therapeutic need. Here, we demonstrate that inhibition of dihydroorotate dehydrogenase (DHODH), an enzyme that converts dihydroorotate to orotate as part of the de novo synthesis of uridine, has a robust anti-leukemia effect in both in vitro and in vivo models of T-ALL. DHODH is ubiquitously-expressed, and inhibition of DHODH (DHODHi) leads to rapid depletion of pyrimidine ribo- and deoxyribonucleotides. A cell's ability to tolerate periods of pyrimidine starvation is dependent on a variety of alternative salvage pathways and is not well-understood. Clinical grade DHODH inhibitors are currently under investigation in trials assessing their effect in myeloid malignancies, where they are also known to have a pre-clinical anti-leukemic effect. We sought to understand the mechanism underlying the sensitivity of T-lymphoblasts to DHODHi, and to develop new DHODHi therapeutic combinations for patients with T-ALL. It is known that the intracellular concentration of nucleotides is high in activated T-lymphocytes, underlying the fact that two low-potency DHODHi's are approved for the treatment of autoimmune T-cell diseases (e.g., teriflunomide for multiple sclerosis and leflunomide for rheumatoid arthritis). We hypothesized that T-cells may have a particular addiction to de novo nucleotide synthesis and that this can be exploited as a vulnerability by the small molecule inhibition of DHODH. We demonstrated that T-ALL is highly sensitive to both chemical and genetic DHODHi using a variety of in vitro models (Figure A). Furthermore, we show that T-lymphoblasts respond to DHODHi by undergoing rapid cell cycle arrest and apoptosis. Additionally, we quantified the changes in intracellular nucleotides using PCA extraction and high-performance liquid chromatography (HPLC). The abundance of UTP, CTP, ATP, and GTP were determined across a panel of T-ALL cell lines at baseline and following treatment with a small molecular inhibitor of DHODH. The depletion of intracellular pyrimidines is rapid, falling to ~30% of baseline at 6 hours and confirming that the extracellular salvage is not able to meet the nucleotide demands of these cells even in the presence of complete media. Of note, the concentration of ATP and GTP are unaffected, confirming the specificity of DHODH on de novo pyrimidine synthesis as well as the viability of the cells over the 24-hour treatment. In several in vivo T-ALL models, we demonstrated that DHODH inhibition (specifically using the small molecule inhibitor brequinar) led to rapid, robust disease response (Figure B). These single agent treatment studies (brequinar, 50 mg/kg given every 3-days) were initiated between day 7 - 14 when the leukemias had engrafted and were established with detectable disease in the bone marrow. Three model systems were used: (1) a genetically engineered mouse model (GEMM) of immature T-ALL in which an activated intracellular NOTCH is expressed by retroviral transduction, (2) a transgenic mouse model of mature T-cell leukemia/lymphoma driven by the HTLV1 protein Tax, and (3) a human PDX from a young man with relapsed/refractory T-ALL. DHODH inhibitor therapy was effective in all three models, though clearly and most dramatically prolonged the survival in the GEMM model, driven by dysregulated NOTCH. We are now focused on elucidating the mechanisms by which T-lymphoblasts are so incredibly sensitive to inhibition of DHODH. New data suggests that changes in mitochondrial membrane potential and mitochondrial mass following exposure to DHODHi may offer additional insights into this sensitivity. We are also studying DHODHi in combination with other approved and experimental agents toward the goal of a new therapeutic combination that is safe, well-tolerated, and efficacious for this patient population. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Cardiac Mitochondria Dysfunction in Dyslipidemic Mice.

Dyslipidemia triggers many severe pathologies, including atherosclerosis and chronic inflammation. Several lines of evidence, including our studies, have suggested direct effects of dyslipidemia on cardiac energy metabolism, but details of these effects are not clear. This study aimed to investigate how mild dyslipidemia affects cardiac mitochondria function and vascular nucleotide metabolism. The analyses were performed in 3- and 6-month-old knock-out mice for low-density lipoprotein receptor (Ldlr−/−) and compared to wild-type C57Bl/6J mice (WT). Cardiac isolated mitochondria function was analyzed using Seahorse metabolic flux analyzer. The mechanical function of the heart was measured using echocardiography. The levels of fusion, fission, and mitochondrial biogenesis proteins were determined by ELISA kits, while the cardiac intracellular nucleotide concentration and vascular pattern of nucleotide metabolism ecto-enzymes were analyzed using reverse-phase high-performance liquid chromatography. We revealed the downregulation of mitochondrial complex I, together with a decreased activity of citrate synthase (CS), reduced levels of nuclear respiratory factor 1 and mitochondrial fission 1 protein, as well as lower intracellular adenosine and guanosine triphosphates’ pool in the hearts of 6-month Ldlr−/− mice vs. age-matched WT. The analysis of vascular ecto-enzyme pattern revealed decreased rate of extracellular adenosine monophosphate hydrolysis and increased ecto-adenosine deaminase activity (eADA) in 6-month Ldlr−/− vs. WT mice. No changes were observed in echocardiography parameters in both age groups of Ldlr−/− mice. Younger hyperlipidemic mice revealed no differences in cardiac mitochondria function, CS activity, intracellular nucleotides, mitochondrial biogenesis, and dynamics but exhibited minor changes in vascular eADA activity vs. WT. This study revealed that dysfunction of cardiac mitochondria develops during prolonged mild hyperlipidemia at the time point corresponding to the formation of early vascular alterations.

CoCl2-Mimicked Endothelial Cell Hypoxia Induces Nucleotide Depletion and Functional Impairment That Is Reversed by Nucleotide Precursors.

Chronic hypoxia drives vascular dysfunction by various mechanisms, including changes in mitochondrial respiration. Although endothelial cells (ECs) rely predominantly on glycolysis, hypoxia is known to alter oxidative phosphorylation, promote oxidative stress and induce dysfunction in ECs. Our work aimed to analyze the effects of prolonged treatment with hypoxia-mimetic agent CoCl2 on intracellular nucleotide concentration, extracellular nucleotide breakdown, mitochondrial function, and nitric oxide (NO) production in microvascular ECs. Moreover, we investigated how nucleotide precursor supplementation and adenosine deaminase inhibition protected against CoCl2-mediated disturbances. Mouse (H5V) and human (HMEC-1) microvascular ECs were exposed to CoCl2-mimicked hypoxia for 24 h in the presence of nucleotide precursors: adenine and ribose, and adenosine deaminase inhibitor, 2′deoxycoformycin. CoCl2 treatment decreased NO production by ECs, depleted intracellular ATP concentration, and increased extracellular nucleotide and adenosine catabolism in both H5V and HMEC-1 cell lines. Diminished intracellular ATP level was the effect of disturbed mitochondrial phosphorylation, while nucleotide precursors effectively restored the ATP pool via the salvage pathway and improved endothelial function under CoCl2 treatment. Endothelial protective effects of adenine and ribose were further enhanced by adenosine deaminase inhibition, that increased adenosine concentration. This work points to a novel strategy for protection of hypoxic ECs by replenishing the adenine nucleotide pool and promoting adenosine signaling.

Direct Measurement of the Intracellular Concentration of 8-Oxo-2'-Deoxyguanosine-5'-Triphosphate by LC-MS/MS

Exposure to reactive oxygen species can result in formation of oxidized nucleotides which increase the frequency of mutations, DNA damage, and cell death. MutT Homolog 1 (MTH1) is an enzyme that catalyzes removal of pyrophosphate from the highly mutagenic oxidized nucleoside triphosphate 8-oxo-2'-deoxyguanosine-5'-triphosphate (8-oxo-dGTP). Interest in MTH1 as a potential new target for cancer therapy surged due to reports of MTH1 inhibitors causing DNA damage and inducing cell death in cancer cells. However, questions have been raised about MTH1 target validation. One critical piece of information that is currently lacking is a quantitative understanding of the levels of 8-oxo-dGTP in cancer cells and the effect of MTH1 inhibition on them. In this study, we developed a sensitive and selective method to simultaneously measure the intracellular concentrations of 8-oxo guanosine nucleotides and their unmodified counterparts using liquid chromatography coupled to tandem mass spectrometry (LC-MS/ MS). An ion-pairing reversed phase liquid chromatography method using dimethylhexylamine was employed to quantify the highly polar analytes. The method was validated fit for purpose using a combination of authentic standards and cell samples. The intracellular oxo-nucleotide concentrations in human bone osteosarcoma cell line U2OS were determined using the method. We observed very low levels of 8-oxo nucleotides in untreated and hydrogen peroxide treated cells and MTH1 knockdown in these cells had minimal if any effect on 8-oxo nucleotide levels. This method will allow for a more comprehensive understanding of oxidized nucleotide detoxification pathways and MTH1 as a target for cancer therapy.

New insights into KATP channel gene mutations and neonatal diabetes mellitus

To read the full abstract: Nat Rev Endocrinol 2020 May 6. doi: 10.1038/s41574-020-0351-y. [Epub ahead of print]. PMID:32376986

Intracellular Pharmacokinetics of Pyrimidine Analogues used in Oncology and the Correlation with Drug Action.

Pyrimidine analogues can be considered as prodrugs, like their natural counterparts, they have to be activated within the cell. The intracellular activation involves several metabolic steps including sequential phosphorylation to its monophosphate, diphosphate and triphosphate. The intracellularly formed nucleotides are responsible for the pharmacological effects. This review provides a comprehensive overview of the clinical studies that measured the intracellular nucleotide concentrations of pyrimidine analogues in patients with cancer. The objective was to gain more insight into the parallels between the different pyrimidine analogues considering their intracellular pharmacokinetics. For cytarabine and gemcitabine, the intracellular pharmacokinetics have been extensively studied over the years. However, for 5-fluorouracil, capecitabine, azacitidine and decitabine, the intracellular pharmacokinetics was only very minimally investigated. This is probably owing to the fact that there were no suitable bioanalytical assays for a long time. Since the advent of suitable assays, the first exploratory studies indicate that the intracellular 5-fluorouracil, azacitidine and decitabine nucleotide concentrations are very low compared with the intracellular nucleotide concentrations obtained during treatment with cytarabine or gemcitabine. Based on their pharmacology, the intracellular accumulation of nucleotides appears critical to the cytotoxicity of pyrimidine analogues. However, not many clinical studies have actually investigated the relationship between the intracellular nucleotide concentrations in patients with cancer and the anti-tumour effect. Only for cytarabine, a relationship was demonstrated between the intracellular triphosphate concentrations in leukaemic cells and the response rate in patients with AML. Future clinical studies should show, for the other pyrimidine analogues, whether there is a relationship between the intracellular nucleotide concentrations and the clinical outcome of patients. Research that examined the intracellular pharmacokinetics of cytarabine and gemcitabine focused primarily on the saturation aspect of the intracellular triphosphate formation. Attempts to improve the dosing regimen of gemcitabine were aimed at maximising the intracellular gemcitabine triphosphate concentrations. However, this strategy does not make sense, as efficient administration also means that less gemcitabine can be administered before dose-limiting toxicities are achieved. For all pyrimidine analogues, a linear relationship was found between the dose and the plasma concentration. However, no correlation was found between the plasma concentration and the intracellular nucleotide concentration. The concentration–time curves for the intracellular nucleotides showed considerable inter-individual variation. Therefore, the question arises whether pyrimidine analogue therapy should be more individualised. Future research should show which intracellular nucleotide concentrations are worth pursuing and whether dose individualisation is useful to achieve these concentrations.

Enhanced migration of breast and lung cancer cells deficient for cN-II and CD73 via COX-2/PGE2/AKT axis regulation.

Purine metabolism involves various intracellular and extracellular enzymes, including cN-II and CD73 that dephosphorylate intracellular and extracellular nucleoside monophosphates into their corresponding nucleosides. We conducted a study to better understand the biological roles of these enzymes in breast and lung cancer cells. We modified cN-II and/or CD73 expression in human breast cancer cells (MDA-MB-231), human lung cancer cells (NCI-H292) and murine breast cancer cells (4T1) using the CRISPR/Cas9 technique, and evaluated their impact on various cellular parameters such as proliferation, migration, invasion, intracellular nucleotide pools and nucleotide metabolism-related gene expression under extracellular nucleotide stress conditions. Intracellular nucleotide contents were found to be altered in the modified cancer cell models both at their basal levels and after exposure to adenosine or AMP. Altered cN-II and CD73 levels were also found to be associated with cell migration and invasion alterations, involving TIMP-2, MMP-2 and MMP-9 expression, as well as alterations in the COX-2/PGE2/AKT pathway. Our results highlight new cell-specific roles of cN-II and CD73 in cancer cell biology and provide insight into their interactions with different intracellular pathways.

New insights into KATP channel gene mutations and neonatal diabetes mellitus.

The ATP-sensitive potassium channel (KATP channel) couples blood levels of glucose to insulin secretion from pancreatic β-cells. KATP channel closure triggers a cascade of events that results in insulin release. Metabolically generated changes in the intracellular concentrations of adenosine nucleotides are integral to this regulation, with ATP and ADP closing the channel and MgATP and MgADP increasing channel activity. Activating mutations in the genes encoding either of the two types of KATP channel subunit (Kir6.2 and SUR1) result in neonatal diabetes mellitus, whereas loss-of-function mutations cause hyperinsulinaemic hypoglycaemia of infancy. Sulfonylurea and glinide drugs, which bind to SUR1, close the channel through a pathway independent of ATP and are now the primary therapy for neonatal diabetes mellitus caused by mutations in the genes encoding KATP channel subunits. Insight into the molecular details of drug and nucleotide regulation of channel activity has been illuminated by cryo-electron microscopy structures that reveal the atomic-level organization of the KATP channel complex. Here we review how these structures aid our understanding of how the various mutations in the genes encoding Kir6.2 (KCNJ11) and SUR1 (ABCC8) lead to a reduction in ATP inhibition and thereby neonatal diabetes mellitus. We also provide an update on known mutations and sulfonylurea therapy in neonatal diabetes mellitus.

Metabolic Pathway Profiling in Intracellular and Extracellular Environments of Streptococcus thermophilus During pH-Controlled Batch Fermentations.

Elucidating the metabolite profiles during the growth of Streptococcus thermophilus is beneficial for understanding its growth characteristics. The changes in the intracellular and extracellular concentrations of carbohydrates, nucleotides, amino sugars, nucleoside sugars, fatty acids, and amino acids, as well as their metabolites over time, were investigated by metabolomics technology. Most metabolites of nucleotides were highly accumulated in the intracellular environment after the mid-exponential phase. Increases in the intracellular unsaturated fatty acids and N-acetyl-glucosamine and N-acetyl-muramoate recycling provided potential evidence that cell envelope remodeling occurred after the mid-exponential phase. At the later fermentation stages, potentially functional metabolite produced by glycine was highly accumulated in the intracellular environment. Additionally, potential toxic metabolites produced by phenylalanine and tyrosine could not be excreted into the extracellular environment in a timely basis. The accumulation of large amounts of these metabolites might be the primary cause of the overconsumption of amino acids and influence the growth of S. thermophilus.

Vaccine & Immunotherapy Summit October 14-15, 2020 | Brussels, Belgium

Exposure to reactive oxygen species can result in formation of oxidized nucleotides which increase the frequency of mutations, DNA damage, and cell death. MutT Homolog 1 (MTH1) is an enzyme that catalyzes removal of pyrophosphate from the highly mutagenic oxidized nucleoside triphosphate 8-oxo-2'-deoxyguanosine-5'-triphosphate (8-oxo-dGTP). Interest in MTH1 as a potential new target for cancer therapy surged due to reports of MTH1 inhibitors causing DNA damage and inducing cell death in cancer cells. However, questions have been raised about MTH1 target validation. One critical piece of information that is currently lacking is a quantitative understanding of the levels of 8-oxo-dGTP in cancer cells and the effect of MTH1 inhibition on them. In this study, we developed a sensitive and selective method to simultaneously measure the intracellular concentrations of 8-oxo guanosine nucleotides and their unmodified counterparts using liquid chromatography coupled to tandem mass spectrometry (LC-MS/ MS). An ion-pairing reversed phase liquid chromatography method using dimethylhexylamine was employed to quantify the highly polar analytes. The method was validated fit for purpose using a combination of authentic standards and cell samples. The intracellular oxo-nucleotide concentrations in human bone osteosarcoma cell line U2OS were determined using the method. We observed very low levels of 8-oxo nucleotides in untreated and hydrogen peroxide treated cells and MTH1 knockdown in these cells had minimal if any effect on 8-oxo nucleotide levels. This method will allow for a more comprehensive understanding of oxidized nucleotide detoxification pathways and MTH1 as a target for cancer therapy.

Inosine pranobex enhances human NK cell cytotoxicity by inducing metabolic activation and NKG2D ligand expression.

Inosine pranobex (IP) is a synthetic immunomodulating compound, indicated for use in the treatment of human papillomavirus‐associated warts and subacute sclerosing panencephalitis. Previous studies demonstrate that the immunomodulatory activity of IP is characterized by enhanced lymphocyte proliferation, cytokine production, and NK cell cytotoxicity. The activation of NKG2D signaling on NK cells, CD8+ T cells, and γδ T cells also produces these outcomes. We hypothesized that IP alters cellular immunity through the induction of NKG2D ligand expression on target cells, thereby enhancing immune cell activation through the NKG2D receptor. We tested this hypothesis and show that exposure of target cells to IP leads to increased expression of multiple NKG2D ligands. Using both targeted metabolic interventions and unbiased metabolomic studies, we found that IP causes an increase in intracellular concentration of purine nucleotides and tricarboxylic acid (TCA) cycle intermediates and NKG2D ligand induction. The degree of NKG2D ligand induction was functionally significant, leading to increased NKG2D‐dependent target cell immunogenicity. These findings demonstrate that the immunomodulatory properties of IP are due to metabolic activation with NKG2D ligand induction.

Development, validation, and clinical application of a high-performance liquid chromatography-tandem mass spectrometry assay for the quantification of total intracellular β-decitabine nucleotides and genomic DNA incorporated β-decitabine and 5-methyl-2′-deoxycytidine

DNA hypermethylation is an epigenetic event that is commonly found in malignant cells and is used as a therapeutic target for β-decitabine (β-DEC) containing hypomethylating agents (eg Dacogen® and guadecitabine). β-DEC requires cellular uptake and intracellular metabolic activation to β-DEC triphosphate before it can get incorporated into the DNA. Once incorporated in the DNA, β-DEC can exert its hypomethylating effect by trapping DNA methyltransferases (DNMTs), resulting in reduced 5-methyl-2′-deoxycytidine (5mdC) DNA content. β-DEC DNA incorporation and its effect on DNA methylation, however, have not yet been investigated in patients treated with β-DEC containing therapies. For this reason, we developed and validated a sensitive and selective LC–MS/MS method to determine total intracellular β-DEC nucleotide (β-DEC-XP) concentrations, as well as to quantify β-DEC and 5mdC DNA incorporation relative to 2′-deoxycytidine (2dC) DNA content. The assay was successfully validated according to FDA and EMA guidelines in a linear range from 0.5 to 100 ng/mL (β-DEC), 50 to 10,000 ng/mL (2dC), and 5 to 1,000 ng/mL (5mdC) in peripheral blood mononuclear cell (PBMC) lysate. An additional calibrator at a concentration of 0.1 ng/mL was added for β-DEC to serve as a limit of detection (LOD). Clinical applicability of the method was demonstrated in patients treated with guadecitabine. Our data support the use of the validated LC–MS/MS method to further explore the intracellular pharmacokinetics in patients treated with β-DEC containing hypomethylating agents.

Fluorous-assisted metal chelate affinity extraction for nucleotides followed by HILIC-MS/MS analysis

We herein developed a selective method for the determination of nucleotides by fluorous-assisted metal chelate affinity extraction followed by hydrophilic interaction liquid chromatography (HILIC) combined with tandem mass spectrometric (MS/MS) analysis. In this study, the nucleotides were selectively chelated by Fe(III)-immobilized perfluoroalkyliminodiacetic acid, and the resulting chelates were subsequently extracted into a fluorous solvent. The nucleotides present in the fluorous solvent were then back-extracted into a non-fluorous solution, such as a solution of ammonia in aqueous acetonitrile. The resulting non-fluorous solution containing the nucleotides was then directly injected into an amide-type HILIC column using a mixture of acetonitrile and aqueous ammonium bicarbonate as the mobile phase for gradient elution, and the nucleotides were detected using the negative electrospray ionization MS/MS mode. In this method, the extraction recoveries of the nucleotides ranged from 43.2 to 94.7% within a relative standard deviation of 17%. This method enabled the determination of intracellular concentrations of nucleotides.

Degradation of brown adipocyte purine nucleotides regulates uncoupling protein 1 activity

ObjectiveNon-shivering thermogenesis in mammalian brown adipose tissue depends on thermogenic uncoupling protein 1. Its activity is triggered by free fatty acids while purine nucleotides mediate inhibition. During activation, it is thought that free fatty acids overcome purine-mediated inhibition. We measured the cellular concentration and the release of purine nucleotide metabolites to uncover a possible role of purine nucleotide degradation in uncoupling protein 1 activation. MethodsWith mass spectrometry, purine nucleotide metabolites were quantified in cellular homogenates and supernatants of cultured primary brown adipocytes. We also determined oxygen consumption in response to a β-adrenergic agonist. ResultsUpon adrenergic activation, brown adipocytes decreased the intracellular concentration of inhibitory nucleotides (ATP, ADP, GTP and GDP) and released the respective degradation products. At the same time, an increase in cellular calcium occurred. None of these phenomena occurred in white adipocytes or myotubes. The brown adipocyte expression of enzymes implicated in purine metabolic remodeling is altered upon cold exposure. Pharmacological and genetic interference of purine metabolism altered uncoupling protein 1 mediated uncoupled respiration. ConclusionAdrenergic stimulation of brown adipocytes lowers the intracellular concentration of purine nucleotides, thereby contributing to uncoupling protein 1 activation.

Expanding metabolic pathway for de novo biosynthesis of the chiral pharmaceutical intermediate l-pipecolic acid in Escherichia coli

BackgroundThe six-carbon circular non-proteinogenic compound l-pipecolic acid is an important chiral drug intermediate with many applications in the pharmaceutical industry. In the present study, we developed a metabolically engineered strain of Escherichia coli for the overproduction of l-pipecolic acid from glucose.ResultsThe metabolic pathway from l-lysine to l-pipecolic acid was constructed initially by introducing lysine cyclodeaminase (LCD). Next, l-lysine metabolic flux from glucose was amplified by the plasmid-based overexpression of dapA, lysC, and lysA under the control of the strong trc promoter to increase the biosynthetic pool of the precursor l-lysine. Additionally, since the catalytic efficiency of the key enzyme LCD is limited by the cofactor NAD+, the intracellular pyridine nucleotide concentration was rebalanced by expressing the pntAB gene encoding the transhydrogenase, which elevated the proportion of LCD with bound NAD+ and enhanced l-pipecolic acid production significantly. Further, optimization of Fe2+ and surfactant in the fermentation process resulted in 5.33 g/L l-pipecolic acid, with a yield of 0.13 g/g of glucose via fed-batch cultivation.ConclusionsWe expanded the metabolic pathway for the synthesis of the chiral pharmaceutical intermediate l-pipecolic acid in E. coli. Using the engineered E. coli, a fast and efficient fermentative production of l-pipecolic acid was achieved. This strategy could be applied to the biosynthesis of other commercially and industrially important chiral compounds containing piperidine rings.

A unique choanoflagellate enzyme rhodopsin exhibits light-dependent cyclic nucleotide phosphodiesterase activity

Photoactivated adenylyl cyclase (PAC) and guanylyl cyclase rhodopsin increase the concentrations of intracellular cyclic nucleotides upon illumination, serving as promising second-generation tools in optogenetics. To broaden the arsenal of such tools, it is desirable to have light-activatable enzymes that can decrease cyclic nucleotide concentrations in cells. Here, we report on an unusual microbial rhodopsin that may be able to meet the demand. It is found in the choanoflagellate Salpingoeca rosetta and contains a C-terminal cyclic nucleotide phosphodiesterase (PDE) domain. We examined the enzymatic activity of the protein (named Rh-PDE) both in HEK293 membranes and whole cells. Although Rh-PDE was constitutively active in the dark, illumination increased its hydrolytic activity 1.4-fold toward cGMP and 1.6-fold toward cAMP, as measured in isolated crude membranes. Purified full-length Rh-PDE displayed maximal light absorption at 492 nm and formed the M intermediate with the deprotonated Schiff base upon illumination. The M state decayed to the parent spectral state in 7 s, producing long-lasting activation of the enzyme domain with increased activity. We discuss a possible mechanism of the Rh-PDE activation by light. Furthermore, Rh-PDE decreased cAMP concentration in HEK293 cells in a light-dependent manner and could do so repeatedly without losing activity. Thus, Rh-PDE may hold promise as a potential optogenetic tool for light control of intracellular cyclic nucleotides (e.g. to study cyclic nucleotide-associated signal transduction cascades).

Structure of a Pancreatic ATP-Sensitive Potassium Channel

ATP-sensitive potassium channels (KATP) couple intracellular ATP levels with membrane excitability. These channels play crucial roles in many essential physiological processes and have been implicated extensively in a spectrum of metabolic diseases and disorders. To gain insight into the mechanism of KATP, we elucidated the structure of a hetero-octameric pancreatic KATP channel in complex with a non-competitive inhibitor glibenclamide by single-particle cryoelectron microscopy to 5.6-Å resolution. The structure shows that four SUR1 regulatory subunits locate peripherally and dock onto the central Kir6.2 channel tetramer through the SUR1 TMD0-L0 fragment. Glibenclamide-bound SUR1 uses TMD0-L0 fragment to stabilize Kir6.2 channel in a closedconformation. In another structural population, aputative co-purified phosphatidylinositol 4,5-bisphosphate (PIP2) molecule uncouples Kir6.2 from glibenclamide-bound SUR1. These structural observations suggest a molecular mechanism for KATP regulation by anti-diabetic sulfonylurea drugs, intracellular adenosine nucleotide concentrations, and PIP2 lipid.

Anti-Leukemia Effect of FF-10501-01, a Novel Inosine 5'-Monophosphate Dehydrogenase Inhibitor, in Acute Myeloid Leukemia

IntroductionInosine 5'- monophosphate dehydrogenase (IMPDH) plays a critical role in nucleotide synthesis by serving as a rate-limiting step for the de novo production of guanine from its precursors. Overexpression of IMPDH has been observed in both solid and hematologic malignancies. FF-10501-01 is a potent new competitive IMPDH inhibitor. In this study, we systematically investigated the anti-leukemia effect of FF-10501-01 in acute myeloid leukemia (AML) cell lines, including hypomethylating agent (HMA)-resistant derivative cells.MethodsThirteen leukemia cell lines were studied, including 5 parental AML cell lines and their HMA-resistant derivatives (MOLM13, SKM1, HL60, TF1, and U937) as well as three other AML cell lines (KG1, HEL, and OCI-AML3). Cell proliferation was determined using trypan blue analysis. Flow cytometry was performed to detect drug-induced apoptosis and cell cycle status. High-performance liquid chromatography (HPLC) was performed to detect the intracellular concentration of guanine nucleotides, with mycophenolic acid (MPA) treated cells used as positive control. We also studied the effect of guanosine supplementation on FF-10501-01-treated cells.ResultsTo understand whether FF-10501-01 was able to effectively limit AML cell proliferation, we subjected a variety of cell lines to 72 hours of FF-10501-01 treatment at various concentrations. We also included a large number of HMA-resistant cell lines in an effort to understand whether or not FF-10501-01 could be a useful secondary or complimentary treatment to HMA therapy. FF-10501-01 inhibited the proliferation of all 13 AML cell lines studied with 72 hours of treatment. The IC-50 of FF-10501-01 ranged between 4.3 and 144.5 µM. The IC50 values for HMA-resistant cells were all higher than those values in their HMA-sensitive counterparts, except SKM1, in which the HMA-sensitive line had a higher IC50 than the HMA-resistant SKM1 line. To further understand the mechanism by which FF-10501-01 effectively reduced cell numbers in these cell lines, we assessed the level of apoptosis in each line after FF-10501-01 exposure. FF-10501-01-induced apoptosis was observed in all of the studied cell lines in a dose-dependent manner except for the HMA-resistant TF-1 cell line. We then assessed whether FF-10501-01 affected cell cycle progression. This effect was highly variable. Increased numbers of cells in G1 phase and decreased numbers of cells in S phase were observed in MOLM13, SKM1, and TF-1 cell lines treated with less than 100 µM FF-10501-01. To understand the mechanistic effects of FF-10501-01, we performed rescue experiments with both HMA-resistant and HMA-sensitive MOLM13 and HL60 cells. Concurrent treatment with FF-10501-01 and guanosine in these cells partially rescued the antiproliferation effect of FF-10501-01. To further characterize the effect of FF-10501-01 on guanosine metabolism, we then performed HPLC experiments to analyze the levels of phosphoguanosine in treated MOLM13 and SKM1 cells. FF-10501-01 treatment effectively reduced the intracellular phosphoguanosine levels in both cell lines. This effect was seen for GMP, GDP, and GTP. We then sought to assess whether the combination of FF-10501-01 and HMAs could be effective in limiting MOLM13 and HL-60 cell proliferation, especially in their HMA resistant derivatives. The combination of HMA and FF-10501-01 showed little synergy beyond the effects of FF-10501-01 alone, regardless of HMA sensitivity, except in HMA-resistant HL-60 cells, in which FF-10501-01 showed moderate synergy with HMA. We further assessed the antiproliferative effect of FF-10501-01 in bone marrow blast samples taken from 3 AML patients. There was a minor dose-dependent antiproliferation effect seen in these samples, but this was not statistically significant. Notably, one patient showed a sharp increase in cell counts at the lowest concentration of FF-10501-01, but that sample’s cell numbers decreased more rapidly as FF-10501-01 concentration increased. This implies that FF-10501-01 treatment response may be related to cell proliferation.ConclusionsThe IMPDH inhibitor FF-10501-01 can produce potent anti-proliferative and apoptotic induction effects on AML cell lines, including HMA-resistant cell lines, through inhibition of de novo guanine nucleotide synthesis. These results indicate that FF-10501-01 might be a promising new therapeutic agent for AML. DisclosuresParadiso:Strategia Therapeutics, Inc.: Employment. Iwamura:FUJIFILM Corporation: Employment.

Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels.

KATP channels act as key regulators of electrical excitability by coupling metabolic cues—mainly intracellular adenine nucleotide concentrations—to cellular potassium ion efflux. However, their study has been hindered by their rapid loss of activity in excised membrane patches (rundown), and by a second phenomenon, the decline of activation by Mg-nucleotides (DAMN). Degradation of PI(4,5)P2 and other phosphoinositides is the strongest candidate for the molecular cause of rundown. Broad evidence indicates that most other determinants of rundown (e.g. phosphorylation, intracellular calcium, channel mutations that affect rundown) also act by influencing KATP channel regulation by phosphoinositides. Unfortunately, experimental conditions that reproducibly prevent rundown have remained elusive, necessitating post hoc data compensation. Rundown is clearly distinct from DAMN. While the former is associated with pore-forming Kir6.2 subunits, DAMN is generally a slower process involving the regulatory sulfonylurea receptor (SUR) subunits. We speculate that it arises when SUR subunits enter non-physiological conformational states associated with the loss of SUR nucleotide-binding domain dimerization following prolonged exposure to nucleotide-free conditions. This review presents new information on both rundown and DAMN, summarizes our current understanding of these processes and considers their physiological roles.This article is part of the themed issue ‘Evolution brings Ca2+ and ATP together to control life and death’.