Привлечение банков к венчурному финансированию в Республике Беларусь

Материалы XIII Междунар. науч.-техн. конф. студентов, магистрантов и молодых ученых, Гомель, 25–26 апр. 2013 г

Autophagic flux blockage by accumulation of weakly basic tenovins leads to elimination of B-Raf mutant tumour cells that survive vemurafenib

This work was supported by five grants to Sonia Laín: Vetenskapsrådet (VR) 521-2014-3341, Cancerfonden (Swedish Cancer Society) 150393, CAN 2014/702, Association for International Cancer Research (AICR) 130086, Barncancerfonden (Swedish Childhood Cancer Foundation) TJ-2014-0038, Barncancerfonden (Swedish Childhood Cancer Foundation) PR-2014-0038; two grants to Ravi Bhatia: Leukemia and Lymphoma Society (LLS) 6137-14 and NIH R01 CA95684; one grant to David P Lane: Vetenskapsrådet (VR) 538-2013-8807; one grant to Marcus J G W Ladds: Karolinska Institute KID Doctoral Student Funding; one grant to Gergana Popova: Karolinska Institutet KID Doctoral Student Funding; two grants to Nicholas J Westwood: Cancer Research UK C21383 and Cancer Research UK A6950; two grants to Gerald McInerney: Vetenskapsrådet (VR) 621-2014-4718 and Cancerfonden (Swedish Cancer Society) 150393, CAN 2015/751; and four grants to Emmet McCormack: Kreftforeningen 182735, Kreftforeningen 732200, Halse Vest 911884, Halse Vest 911789.Tenovin-6 is the most studied member of a family of small molecules with antitumour activity in vivo. Previously, it has been determined that part of the effects of tenovin-6 associate with its ability to inhibit SirT1 and activate p53. However, tenovin-6 has also been shown to modulate autophagic flux. Here we show that blockage of autophagic flux occurs in a variety of cell lines in response to certain tenovins, that autophagy blockage occurs regardless of the effect of tenovins on SirT1 or p53, and that this blockage is dependent on the aliphatic tertiary amine side chain of these molecules. Additionally, we evaluate the contribution of this tertiary amine to the elimination of proliferating melanoma cells in culture. We also demonstrate that the presence of the tertiary amine is sufficient to lead to death of tumour cells arrested in G1 phase following vemurafenib treatment. We conclude that blockage of autophagic flux by tenovins is necessary to eliminate melanoma cells that survive B-Raf inhibition and achieve total tumour cell kill and that autophagy blockage can be achieved at a lower concentration than by chloroquine. This observation is of great relevance as relapse and resistance are frequently observed in cancer patients treated with B-Raf inhibitors.Publisher PDFPeer reviewe

Catalytic mechanisms and evolution of leukotriene A4 hydrolyse

Inflammation is the first response of the body to infection or physical irritation. This response can potentially trigger the whole immune system but in the initial stage mainly involves leukocytes of the innate immune system and a complex cascade of chemical mediators, which by different means control, maintain and resolve the process. One group of such mediators is the leukotrienes, among which LTB4 is found. LTB4 has several immunomodulating properties and mainly acts by recruiting leukocytes to the site of injury or infection. LTB4 is mainly formed by leukocytes of the innate immune system, but recruits cells of both the innate as well as the adaptive immune systems. Thus, it constitutes an important link between the two systems. Moreover, LTB4 is known to be involved in several pathological inflammatory conditions. Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc metalloenzyme that catalyzes the last step in the formation of LTB4. In addition, LTA4H catalyzes hydrolysis of oligo-peptides. Hence the enzyme is bifunctional and the two activities of LTA4H actually share a common active site. While LTB4 has a characterized biological functions in the inflammatory response, the physiological relevance of the peptidase activity of LTA4H is yet unknown. According to sequence homology, LTA4H sorts as a member of the M1 family of aminopeptidases, a vast enzyme family found in most organisms and with a variety of biological functions. Among these peptidases, a subset present in vertebrates has the intrinsic capacity to catalyze LTA4 ¨ LTB4 formation. The present investigations deal with the catalytic mechanism of both activities of LTA4H, as well as the divergent evolution of LTA4H from ancestral aminopeptidases. For the first part of the work, the recently determined crystal structure of LTA4H served as a guideline for the design of experiments. In these, an approach mainly including mutagenesis, enzyme kinetics, molecular modeling and crystallography led to determination of the basic requirements for catalysis by LTA4H as well as an insight into the molecular events underlying its evolution from ancestral aminopeptidases. To refine these findings, a novel assay for enzyme kinetics was developed, which allowed a faster and more adequate analysis of the peptidase activity. Finally, the novel assay in combination with crystal structure determinations of LTA4H in complex with different ligands, allowed a yet deeper understanding of the reaction mechanism for peptide hydrolysis catalyzed by LTA4H. For the peptidase activity it was specifically shown that the peptide substrate is anchored between Arg-563 and Glu-271 with its C- and N-terminal, respectively. Together, these two residues function as an effective filter which selectively favors peptide substrates consisting of three residues, i.e. tri-peptides. The specific preference of the enzyme for arginyl tripeptides is achieved by interaction between basic N-terminal groups of the substrate and Asp-375. During the course of peptide hydrolysis, Tyr-383 together with the zinc ion function as a site for oxyanion stabilization of the reaction intermediate. The general base Glu-296, not only facilitates the nucleophilic attack by the hydrolytic water, but also functions as a proton shuffle, which in the last step of peptide hydrolysis protonates the leaving arnine. Considering sequence homology, these findings to a large extent holds true also for other metallopeptidases of the MA clan and specifically for aminopeptidases of the M1 family. For the epoxide hydrolase activity, it was shown that the carboxylate group of LTA4 binds to Arg-563 to achieve proper positioning, with respect to catalytic residues, of the reacting moieties of the substrate. During LTA4 hydrolysis, Glu-271 and Asp-375 are required for epoxide ring opening and for catalyzing the stereospecific attack by the hydrolytic water at carbon 12 of LTA4. Notably, Arg-563 and Glu-271 are essential for both reaction mechanisms. While Arg-563 serves the same purpose in both reaction mechanisms, i.e. binding of substrate carboxylates, Glu-271 has distinct roles in each reaction. The latter observation, with a single residue serving in two different catalytic mechanisms, is unique to LTA4H. Often, assaying peptidase activity either involves complex assays, when utilizing natural substrates, or relies on chrornogenic model substrates of limited physiological relevance. The novel assay developed circumvents these problems and allows simple and fast screening of natural peptide substrates and determination of kinetic constants for their hydrolysis. For the evolutionary studies, the yeast homologue of human LTA4H, an aminopeptidase with substrate specificities distinct ftom, human LTA4H, was used. This enzyme is activated by LTA4 but also to some extent hydrolyzes it. For peptide hydrolysis, it was shown that the yeast enzyme uses the corresponding residues as, human LTA4H. Additionally, it was shown that the active site pocket of the yeast enzyme allows LTA4 to bind in two conformations: one peptidase-activating and one compatible with LTA4 hydrolysis. A few point mutations of the yeast enzyme, which made it more similar to human LTA4H, sufficed to reengineer the pocket to more resemble the corresponding human one with LTA4-inhibition replacing the LTA4-activating effect. Thus, it appears as LTA4H through evolution has fine-tuned an existing lipid binding site to optimize it for LTA4-binding and turnover

Improved Inhibitor Screening Experiments by Comparative Analysis of Simulated Enzyme Progress Curves

<div><p>A difficulty associated with high throughput screening for enzyme inhibitors is to establish reaction conditions that maximize the sensitivity and resolution of the assay. Deduction of information from end-point assays at single concentrations requires a detailed understanding of the time progress of the enzymatic reaction, an essential but often difficult process to model. A tool to simulate the time progress of enzyme catalyzed reactions and allows adjustment of reactant concentrations and parameters (initial concentrations, <i>K</i>_m, <i>k</i>_cat, <i>K</i>_i values, enzyme half-life, product•enzyme dissociation constant, and the rate constant for the reversed reaction) has been developed. This tool provides comparison of the progress of uninhibited versus inhibited reactions for common inhibitory mechanisms, and guides the tuning of reaction conditions. Possible applications include: analysis of substrate turnover, identification of the point of maximum difference in product concentration (Δ_max[<i>P</i>]) between inhibited and uninhibited reactions, determination of an optimal observation window unbiased for inhibitor mechanisms or potency, and interpretation of observed inhibition in terms of true inhibition. An important observation that can be utilized to improve assay signal strength and resolution is that Δ_max[<i>P</i>] occurs at a high degree of substrate consumption (commonly >75%) and that observation close to this point does not adversely affect observed inhibition or IC₅₀ values.</p></div

Screen dump of a subsection of the simulation tool.

<p>The tool contains three blocks (one for competitive, one for uncompetitive, and one for mixed inhibition; non-competitive inhibition is achieved by setting the two <i>K</i>_i values for mixed inhibition to equal values) in which the reaction parameters and variables can be set. The block for mixed inhibition is shown. Adjustable values are shown in red and are found in the second row of each block. The identities of the adjustable values are shown in the top row. The resulting IC₅₀ value and overall equilibrium constant of the reversible reaction are also shown in the top row. A table presents the time point of Δ_max[<i>P</i>] and the associated key data that result from adjustment of reaction conditions. To deduce the corresponding data at other time points, the desired values can be entered into cells of the top row of the table. In the simulation tool, changes of reaction conditions are also visualized in various graphs.</p

Simulated progress curves and differences between inhibited and uninhibited reactions.

<p>(<b>Left</b>) Simulated progress curves for competitive (blue trace), uninhibited (black trace) reactions, and the difference (Δ[<i>P</i>]) between the two reactions (red trace). Δ_max[<i>P</i>] is indicated by a dashed vertical line. (<b>Right</b>) Δ[<i>P</i>] between inhibited and uninhibited enzyme reactions for competitive (yellow), uncompetitive (green), non-competitive (orange), and mixed (blue) inhibition. In the simulation tool, progress curves for all types of inhibition are shown as in the left panel. Reaction parameters and variables can be entered and the results will be directly displayed in the graphs. Entered reaction conditions were: [<i>S</i>] = <i>K</i>_m = 0.25<i>K</i>_mp = 10[<i>I</i>] = 400[<i>E</i>_o] = 100 µM; [<i>P</i>_o] = 0 µM; <i>k</i>_cat = 0.5 s⁻¹; enzyme <i>t</i>_(1/2) = 24 hours; <i>K</i>_ic = <i>K</i>_iu = <i>K</i>_i-non = 5 µM for competitive, uncompetitive, and non-competitive inhibition; and <i>K</i>_iu = 5<i>K</i>_ic = 15 µM for mixed inhibition.</p

Observation at different time points and with different reaction conditions.

<p>Observation at different time points and with different reaction conditions.</p

Agreement between simulated and experimental data.

<p>A–B) [<i>P</i>] as a function of time for enzyme catalyzed hydrolysis of alanine-4-nitroanilide by LTA4 hydrolase (A), and of Mca-R-P-P-G-F-S-A-F-K(Dnp)-OH by presequence peptidase (B). Reactions were performed with (green traces) and without (gray traces) the inhibitor bestatin for both enzymes. C–D) Δ[<i>P</i>] as a function of time (orange trace, lower x-axis) and as a function of substrate depletion (gray trace, upper x-axis) for LTA4 hydrolase (C) and for presequence peptidase (D). Simulated curves fit well to the experimental data (thin black lines, all panels). The observed (vertical thick dashed lines) and predicted (vertical thin dashed lines) time point of Δ_max[<i>P</i>] are in good agreement. E) Initial reaction rate experiment with presequence peptidase and increasing [<i>S</i>]. The fitted model is shown as a black line, measured data as open circles.</p

Inhibition as a function of substrate conversion.

<p>Observed inhibition (%) as a function of the degree of substrate conversion (%) of the uninhibited reference reaction for competitive (yellow), uncompetitive (green), non-competitive (orange), and mixed (blue) inhibition. In the simulation tool, time points can be entered (see <b><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046764#pone.0046764.s002" target="_blank">Fig. S1</a></b>) to directly study the effects in the graphs, where observed inhibition is also plotted against reaction time. Entered reaction conditions were: [<i>S</i>] = <i>K</i>_m = 0.25<i>K</i>_mp = 10[<i>I</i>] = 400[<i>E</i>_o] = 100 µM; [<i>P</i>_o] = 0 µM; <i>k</i>_cat = 0.5 s⁻¹; enzyme <i>t</i>_(1/2) = 24 hours; <i>K</i>_ic = <i>K</i>_iu = <i>K</i>_i-non = 5 µM for competitive, uncompetitive, and non-competitive inhibition; and <i>K</i>_iu = 5<i>K</i>_ic = 15 µM for mixed inhibition.</p