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Greg Crowther & Wes Van Voorhis Department of Medicine University of Washington Drug discovery for neglected tropical diseases.

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Presentation on theme: "Greg Crowther & Wes Van Voorhis Department of Medicine University of Washington Drug discovery for neglected tropical diseases."— Presentation transcript:

1 Greg Crowther & Wes Van Voorhis Department of Medicine University of Washington Drug discovery for neglected tropical diseases

2 Protein-based (target-based) projects 1. Prioritization of drug targets TDRtargets.org 2. Structural genomics of pathogen proteins MSGPP.org SSGCID.org 3. “Piggy-back” approach to target-based drug design protein farnesyltransferase glycogen synthase kinase 4. Identifying targets of cell-active compounds thermal melt assays enzyme activity assays PDB: 1tqx Temperature Fluorescence

3 Prioritization of drug targets TDRtargets.org is a database of protein data relevant to drug discovery research. Other team leaders: Fernán Agüero (U. of San Martin), Matt Berriman (Sanger Institute), Stuart Ralph (U. of Melbourne), David Roos (U. of Pennsylvania), Sam Sia (Columbia U.).

4 Prioritization of drug targets TDRtargets.org allows users to “zoom in” on protein targets of particular interest …

5 Prioritization of drug targets … and create genome-wide rankings of targets based on the users’ own criteria.

6 Structural genomics of pathogen proteins Medical Structural Genomics of Pathogenic Protozoa (MSGPP.org) selection of potential drug targets expression, crystallization, 3D structure determination, ligand binding organisms: Plasmodium, T. brucei, T. cruzi, Leishmania, T. gondii, E. histolytica, Giardia, Cryptosporidium collaborators: Fred Buckner, Erkang Fan, Wim Hol, Ethan Merritt, Christophe Verlinde (all UW) Seattle Structural Genomics Center for Infectious Disease (SSGCID.org) like MSGPP, but focused on biodefense-related pathogens and (re-)emerging diseases other team leaders: Peter Myler (SBRI), Lance Stewart (deCODE), Gabriele Varani (UW), Garry Buchko (Battelle)

7 “Piggy-back” approach to target-based drug design Drug development is difficult and expensive when starting from scratch. Look for promising drug targets where a lot of development has already been performed. See if the existing drugs show promise against “our” diseases, then piggy-back onto existing efforts. Image: NASA / Tom Tschida Big Pharma us Collaborators: Fred Buckner, Mike Gelb, K.K. Ojo, Christophe Verlinde (all UW).

8 “Piggy-back” approach to target-based drug design Protein Farnesyltransferase adds farnesyl (C 15 H 25 ) groups to proteins (important for localization, etc.) target for oncology -- in Phase III trials inhibitors cure rodent malaria (PubMed ID: ) current work: optimizing pharmacokinetics Glycogen Synthase Kinase phosphorylates glycogen synthase and signaling-related proteins target for mania, Alzheimer’s, diabetes inhibitors kill T. brucei (PubMed ID: ) current work: testing in animal models

9 Identifying targets of cell-active compounds Thousands of antimalaria compounds have been identified in screens of chemical libraries. Their subcellular targets are unknown, making optimization difficult. How do you improve activity against the parasite without hurting the host? Try to identify targets of some of compounds in order to facilitate optimization. Our (high-throughput) approaches: thermal melts and enzyme activity assays. Collaborators: Roger Wiegand et al. (Broad Institute); Kip Guy (St. Jude); Kelli Kuhen, Richard Glynne, Achim Brinker et al. (Genomics Institute of Novartis Research Foundation). Images: trampledunderfoot.co.uk; tulane.edu/~wiser; clipartof.com

10 Identifying targets of cell-active compounds Temperature Solvent-accessible hydrophobic surface area (measured with fluorescent dye) Adaptation of a figure by Martin C. Stumpe and Helmut Grubmuller (www.mpibpc.mpg.de). Thermal melt: Heat protein, watch it unfold.

11 Melting temperature (T m ) reflects protein stability Fluorescence Temperature less stable (no ligand) more stable (with ligand) TmTm A compound that targets a particular protein should bind to it and stabilize it, shifting the melting curve and T m to the right. Identifying targets of cell-active compounds

12 Preliminary validation of thermal melt approach DHODH inhibitors cause dose-dependent increases in DHODH’s T m Negative controls: HSP90 inhibitors don’t change DHODH’s T m Identifying targets of cell-active compounds

13 Thermal melt assays for target identification Advantages: can be applied to most Plasmodium proteins* a standard buffer (100 mM HEPES, 150 mM KCl, pH 7.5) works well for many proteins* Limitations: false positives ligands bind to protein and raise its T m but don’t inhibit it false negatives not all substrates increase T m ; not all inhibitors do either? *Crowther et al. (2009), J. Biomol. Screen 14: in press. Identifying targets of cell-active compounds

14 Identifying targets of cell-active compounds Advantages: direct readout of target inhibition published info on K m ’s, optimal buffers, etc. is available for many enzymes Limitations: useless for noncatalytic proteins radioactivity, absorbance at UV wavelengths, HPLC, etc. are inappropriate for high-throughput screening substrates may not be available each enzyme is different Enzyme activity assays for target identification

15 Identifying targets of cell-active compounds dUTPase (PF11_0282) Reaction: dUTP => dUMP + PP i Coupling reaction (Pyrophosphatase): PP i => 2P i Detect ↑P i via malachite green kit (absorbance at 620 nm). Glycerol-3-Phosphate Dehydrogenase (PFL0780w) Reaction: glycerol-3-phosphate + NAD + => dihydroxyacetone phosphate + NADH Coupling reaction (Diaphorase): resazurin + NADH => resorufin + NAD + Detect ↑ resorufin via fluorescence (excite at 560 nm, emit at 590 nm). OMP Decarboxylase (PF10_0225) Reaction: OMP => UMP + CO 2 Coupling reaction (CMP Kinase): UMP + ATP => UDP + ADP Detect ↓ATP via Kinase-Glo luminescence, or detect ↑ ADP via fluorescence polarization. S-Adenosylhomocysteine Hydrolase (PFE1050w) Reaction: S-adenosylhomocysteine => homocysteine + adenosine Coupling reaction (Adenosine Deaminase): adenosine => inosine Detect ↑ homocysteine –SH via ThioGlo fluorescence (excite at 379 nm, emit at 513 nm). Examples of high-throughput enzyme activity assays

16 Identifying targets of cell-active compounds Anti-parasitic compounds: inhibit P. falciparum + promising chemical properties Screen for protein- compound associations: thermal melts, enzyme activity assays Test whether the protein is a target of the compound in parasites: a) substrate buildup? b) select resistance = mutations in target? c) overexpress in Plasmodium = increase in ED 50 ? Hit optimization: directed by target High-Throughput Screen: validated proteins that need new scaffolds Thermal melt and enzyme activity assays in the context of drug discovery

17 Summary Target-based drug discovery has not yet led to many new drugs for neglected tropical diseases. Nevertheless there are reasons for optimism. - New genomic/bioinformatic data (e.g., via TDRtargets.org): more possible protein targets better prioritization of targets - New biochemical methods (e.g., thermal melts): more “screenable” proteins - New 3D protein structures (e.g., via MSGPP and SSGCID): more structure-based drug design - New private-sector involvement (e.g., Novartis): better compound libraries more screening horsepower more piggy-backing opportunities

18 Questions? Comments? If we’re out of time, feel free to send to or talk to me tonight at dinner.


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