MK-5204: An orally active β-1,3-glucan synthesis inhibitor

Our previously reported efforts to produce an orally active β-1,3-glucan synthesis inhibitor through the semi-synthetic modification of enfumafungin focused on replacing the C2 acetoxy moiety with an aminotetrazole and the C3 glycoside with a N,N-dimethylaminoether moiety. This work details further optimization of the C2 heterocyclic substituent, which identified 3-carboxamide-1,2,4-triazole as a replacement for the aminotetrazole with comparable antifungal activity. Alkylation of either the carboxamidetriazole at C2 or the aminoether at C3 failed to significantly improve oral efficacy. However, replacement of the isopropyl alpha amino substituent with a t-butyl, improved oral exposure while maintaining antifungal activity. These two structural modifications produced MK-5204, which demonstrated broad spectrum activity against Candida species and robust oral efficacy in a murine model of disseminated Candidiasis without the N-dealkylation liability observed for the previous lead.     

The role of MAPK signalling pathways in the response to endoplasmic reticulum stress

Perturbations in endoplasmic reticulum (ER) homeostasis, including depletion of Ca^2 + or altered redox status, induce ER stress due to protein accumulation, misfolding and oxidation. This activates the unfolded protein response (UPR) to re-establish the balance between ER protein folding capacity and protein load, resulting in cell survival or, following chronic ER stress, promotes cell death. The mechanisms for the transition between adaptation to ER stress and ER stress-induced cell death are still being understood. However, the identification of numerous points of cross-talk between the UPR and mitogen-activated protein kinase (MAPK) signalling pathways may contribute to our understanding of the consequences of ER stress. Indeed, the MAPK signalling network is known to regulate cell cycle progression and cell survival or death responses following a variety of stresses. In this article, we review UPR signalling and the activation of MAPK signalling pathways in response to ER stress. In addition, we highlight components of the UPR that are modulated in response to MAPK signalling and the consequences of this cross-talk. We also describe several diseases, including cancer, type II diabetes and retinal degeneration, where activation of the UPR and MAPK signalling contribute to disease progression and highlight potential avenues for therapeutic intervention. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.     

Cooperative Modulation of [3H]MK-801 Binding to the N-Methyl-d-Aspartate Receptor-Ion Channel Complex by l-Glutamate, Glycine, and Polyamines

In extensively washed rat cortical membranes [3H](+)-5-methyl-10,11-dihydro-5 H-dibenzo [a,d]cyclohepten-5,10-imine ([3H]MK-801) labeled a homogeneous set of sites (Bmax = 1.86 pmol/mg protein) with relatively low affinity (KD = 45 nM). L-Glutamate, glycine, and spermidine produced concentration-dependent increases in specific [3H]MK-801 binding due to a reduction in the KD of the radioligand. In the presence of high concentrations of L-glutamate, glycine, or spermidine, the KD values for [3H]MK-801 were reduced to 11 nM, 18 nM, and 15 nM, respectively. Maximally effective concentrations of combinations of the three compounds further increased [3H]MK-801 binding affinity as follows: L-glutamate + glycine, KD = 6.2 nM; L-glutamate + spermidine, KD = 2.2 nM; glycine + spermidine, KD = 8.3 nM. High concentrations of spermidine did not inhibit either [3H]glycine orf [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding to the N-methyl-D-aspartate (NMDA) receptor complex. The concentration of L-glutamate required to produce half-maximal enhancement (EC50) of [3H]MK-801 binding was reduced from 218 nM to 52 nM in the presence of 30 microM glycine and to 41 nM in the presence of 50 microM spermidine. The EC50 value for glycine enhancement of [3H]MK-801 binding was 184 nM. This was lowered to 47 nM in the presence of L-glutamate and to 59 nM in the presence of spermidine. Spermidine enhanced [3H]MK-801 binding with an EC50 value of 19.4 microM which was significantly reduced by high concentrations of L-glutamate (EC50 = 3.9 microM) or glycine (EC50 = 6.2 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of thyrotropin-releasing hormone (TRH) and MK-771 on behavior of squirrel monkeys controlled by noxious stimuli

The effects of TRH (0.1-30 mg/kg) and an enzyme-resistant analogue, MK-771 (0.1-10 mg/kg), were characterized in squirrel monkeys on responding maintained in the presence of different visual stimuli by a multiple 3-min fixed-interval (FI), 30-response fixed-ratio (FR) schedule of stimulus-shock termination or by a multiple 5-min FI schedule of food or shock presentation. Under the termination schedule, the first response at the end of 3 min in the FI component or the completion of the 30-response requirement in the FR component terminated the visual stimulus in the presence of which shocks occurred (escape schedule). Under the schedule of food or shock presentation, the first response at the end of the 5-min FI produced food in the presence of red stimulus lights or shock in the presence of white lights. TRH and MK-771 produced large, dose-related increases in responding maintained under the FR stimulus-shock termination schedule whereas these peptides produced smaller increases or did not affect responding under the FI schedule. TRH and MK-771 also produced marked increases in responding maintained by shock presentation at doses that did not alter or decreased food-maintained responding in the same subject. Thus, performances maintained by noxious stimuli are uniquely sensitive to the rate-increasing effects of TRH and MK-771. These findings suggest that the behavioral effects of the neuropeptides, TRH and MK-771, can depend on the specific consequences of behavior and, as such, the effects of these substances are determined by many of the same variables that determine the effects of other behaviorally-active drugs.     

Allosteric Regulation of the N-Methyl-d-Aspartate Receptor-Linked Ion Channel Complex and Effects of Ethanol in Ethanol-Withdrawal Seizure-Prone and -Resistant Mice

Abstract: The effects of ethanol, glycine, and spermidine on the specific binding of [³H]MK-801 were characterized in Triton-treated membranes prepared from the hippocampus and cortex of ethanol-withdrawal seizure-prone (WSP) and -resistant (WSR) mice. Glycine, an allosteric agonist at the NMDA receptor-linked ion channel complex, caused an increase in specific [³H]MK-801 binding to hippocampal membrane preparations. There were no significant differences in EC₅₀ values between the selected lines for the effect of glycine (WSP, 391.7 ± 48.4 nM; WSR, 313.4 ± 77 nM) in the presence of 10 µM NMDA or in the maximal response to the agonist (WSP, 1.75 ± 0.26 pmol/mg of protein; WSR, 1.67 ± 0.22 pmol/mg of protein). The EC₅₀ values for the spermidine-induced increase in [³H]MK-801 binding in membranes from hippocampus in the absence (WSP, 11.7 ± 0.83 µM; WSR, 9.98 ± 1.29 µM) or in the presence of 10 µM glycine and 10 µM NMDA (WSP, 2.1 ± 0.35 µM; WSR, 2.37 ± 0.42 µM) also did not differ. Similar results were obtained in cortical membranes. Saturation isotherms indicated that there was no difference in the density of [³H]MK-801 binding sites, or in their affinity for the radioligand, between the mouse lines. In addition, administration of ethanol by inhalation (24 h) to WSP and WSR mice did not cause an increase in the density of [³H]MK-801 binding sites, and there was no difference in the density or affinity of binding sites between the mouse lines. Withdrawal from ethanol (6 h), which causes an increase in the severity of handling-induced convulsions in WSP mice, also did not alter the binding site density or affinity for radioligand. The results suggest that the characteristics of the NMDA receptor-linked ion channel complex in the tissue preparations described here do not differ in WSP and WSR mice. Thus, genetic differences in seizure susceptibility during ethanol withdrawal can be dissociated from the total density of hippocampal or cortex NMDA receptors under activating conditions.     

Quantitative determination of a novel dual PPAR alpha/gamma agonist using on-line turbulent flow extraction with liquid chromatography-tandem mass spectrometry

Turbulent flow chromatograph (TFC) is a technique for the direct and efficient analysis of drugs and metabolites in biological matrices. We report here TFC on-line with an HPLC-MS/MS assay for the determination of 5-[2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl)phenyl]methyl]benzamide (I, MK-0767, KRP297, Fig. 1) in plasma. Samples were transferred using an automated system followed by the addition of internal standard (II), prepared in 0.1 M ammonium acetate (pH 4.0). The plasma samples were directly injected onto a C18 turbulent flow column on-line with an HPLC-MS/MS system, and the analytical column used was a ThermoHypersil Keystone C18. Detection was achieved by MS/MS, using positive ionization on a TurboIonSpray probe, operated in multiple reaction monitoring (MRM) mode. The linear range was 4-2000 ng/mL for I when using 50 microL of plasma. The method exhibited good linearity and reproducibility. The method also showed good selectivity and ruggedness when applied to clinical samples, and was successfully cross-validated with a conventional off-line SPE, LC-MS/MS method.     

Effects of estrogen and progesterone treatment on rat hippocampal NMDA receptors: relationship to Morris water maze performance

Estrogen modulates NMDA receptors function in the brain. It increases both dendritic spine density and synapse number in the hippocampus, an effect that can be blocked by NMDA antagonist. In this study, we investigated the effect of 17beta-estradiol and progesterone treatment on NMDA receptors in ovariectomized rats. Two different doses were used for 10 weeks. Receptor autoradiography was done on brain sections using [(3)H] MK-801 as a ligand. Our results showed a significant increase in [(3)H] MK-801 binding in the dentate gyrus, CA3 and CA4 areas of the hippocampus of ovariectomized compared to sham operated rats. In addition, we observed similar changes in CA1. 17beta-estradiol treatment in both doses reduced the binding back to the normal level while progesterone treatment did not show any effect. Spatial reference memory was tested on Morris water maze task. Ovariectomy severely impaired spatial reference memory. Estradiol but not progesterone treatment significantly improved the memory performance of the ovariectomized rats. Low dose treatment showed better learning than high dose estrogen treatment. The decrease in the antagonist sites by estradiol treatment could result in an increase in the sensitivity of the hippocampus to the excitatory stimulation by glutamate system and hence the effect of estradiol on learning and memory. The changes of NMDA receptors in the hippocampus support the concept that estrogen-enhancing effect on spatial reference memory could be through the enhancing of NMDA function.     

Enhanced antitumor activity of a combination treatment with a mouse/human chimeric anti-MK-1 antibody and lymphokine-activated killer cells in vitro and in a severe combined immunodeficient mouse xenograft model

Mouse monoclonal antibody FU-MK-1, raised against a human gastric adenocarcinoma, recognizes a glycoprotein antigen (termed MK-1 antigen) present on most carcinomas and seems to be valuable in immunodiagnosis and immunotherapy of various cancers. In a recent study, we constructed a mouse/human chimeric antibody, designated Ch FU-MK-1, by fusing the FU-MK-1 V_H and Vκ genes to the human Cγ1 and Cκ genes, respectively. In the present study, we tested combination immunotherapy of Ch FU-MK-1 with human lymphokine-activated killer (LAK) cells in vitro and in mice with severe combined immunodeficiency (SCID) bearing human MK-1-expressing tumors. In in vitro experiments, Ch FU-MK-1 effectively mediated antibody-dependent cell-mediated cytotoxicity (ADCC) against MK-1-expressing MKN-74 cells, which was completely blocked by an anti-FcR antibody. Since the apoptotic pathway as well as the necrotic pathway have been shown to be utilized in various cytotoxic effector mechanisms, we investigated the role of apoptosis in ADCC mediated by LAK cells and Ch FU-MK-1 against MKN-74 cells. The implication of the apoptosis during ADCC was demonstrated by means of both a terminal-deoxynucleotidyltransferase-mediated dUTP-biotin nick-end-labeling assay and a propidium iodide staining method. In vivo antitumor activity of combination treatment with LAK cells and Ch FU-MK-1 was estimated using SCID mice inoculated s.c. with MKN-74 cells. The i.v. administration of LAK cells and i.p. administration of Ch FU-MK-1 and interleukin-2 (IL-2) produced a marked growth inhibition of MKN-74 tumors in SCID mice. When the actual tumor weights were measured 16 days after initiation of treatment, more than 70% reduction was observed in the group receiving LAK cells plus Ch FU-MK-1 plus IL-2 as compared to the control untreated group. Together these results suggest that Ch FU-MK-1 may serve as a potentially useful immunotherapeutic reagent for human MK-1-expressing tumors. Received: 27 November 1998 / Accepted: 23 February 1999     

Characterization of the direct physical interaction of nc886, a cellular non-coding RNA, and PKR

We have recently shown that nc886 (pre-miR-886 or vtRNA2-1) is not a genuine microRNA precursor nor a vault RNA, but a novel type of non-coding RNA that represses PKR, a double-stranded RNA (dsRNA) dependent kinase. Here we have characterized their direct physical association. PKR’s two RNA binding domains form a specific and stable complex with nc886’s central portion, without any preference to its 5′-end structure. By binding to PKR with a comparable affinity, nc886 competes with dsRNA and attenuates PKR activation by dsRNA. Our data suggest that nc886 sets a threshold for PKR activation so that it occurs only during genuine viral infection but not by a minute level of fortuitous cellular dsRNA.     

Measurement of menadione in urine by HPLC

Menadione is a metabolite of vitamin K that is excreted in urine. A high performance liquid chromatography (HPLC) method using a C₃₀ column, post-column zinc reduction and fluorescence detection was developed to measure urinary menadione. The mobile phase was composed of 95% methanol with 0.55% aqueous solution and 5% DI H₂O. Menaquinone-2 (MK-2) was used as an internal standard. The standard calibration curve was linear with a correlation coefficient (R²) of 0.999 for both menadione and MK-2. The lower limit of quantification (LLOQ) was 0.3 pmole menadione/mL urine. Sample preparation involved hydrolysis of menadiol conjugates and oxidizing the released menadiol to menadione. Using this method, urinary menadione was shown to increase in response to 3 years of phylloquinone supplementation. This HPLC method is a sensitive and reproducible way to detect menadione in urine.