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EBI is an Outstation of the European Molecular Biology Laboratory.
Small Molecules in Bioinformatics
EBI Bioinformatics Roadshow16th March 2011
Dusseldorf
Small molecule resources at the EBI21.04.232
Agenda
• Introduction
• Small molecule resources • ChEMBL• ChEBI
• Searching and browsing
• Hands-on Exercises
Annotation of bioinformatics data
• Essential for capturing and understanding and knowledge associated with core data
• Often captured in free text, which is easier to read and better for conveying understanding to a human audience, but…
• Difficult for computers to parse• Quality varies from database to database• Terminology used varies from annotator to annotator
• Towards annotation using standard vocabularies: ontologies within bioinformatics
Small molecule resources at the EBI21.04.233
Small molecules participate in all processes of life
What are Small Molecules?
• A small molecule is defined as a low molecular weight organic compound.
• Most drugs are small molecules to allow passage over cell membranes and oral bioavailability.
• They are also able to bind to proteins and enzymes, thereby altering function, which can lead to a therapeutic effect.
• Small molecules are used in everyday life.
Some common
small molecules:
Amino Acids
Signalingγ-aminobutyric acid
GABA: chief inhibitory neurotransmitter in the mammalian central nervous system.
In humans, also regulates muscle tone.
• synthesized by neurons
• found mostly as a zwitterion, that is, with the carboxyl group deprotonated and the amino group protonated
• conformational flexibility of GABA is important for its biological function, as it has been found to bind to different receptors with different conformations
• GABA deficiency linked to
• anxiety disorder, depression, alcoholism
• multiple sclerosis, action tremors, tardive dyskinesia
Small molecule resources at the EBI21.04.237
Metabolism
Adenosine 5’-triphosphate (ATP): the
"molecular unit of currency" of intracellular
energy transfer.
• generated in the cell by energy-consuming processes, broken down by energy-releasing processes
• proteins that bind ATP do so in a characteristic protein fold known as the Rossmann fold, which is a general nucleotide-binding structural domain that can also bind the cofactor NAD
Adenosine 5'-triphosphate
Small molecule resources at the EBI21.04.238
Enzymes
• Enzyme inhibitors are molecules that bind to enzymes and decrease their activity.
• Many drugs are enzyme inhibitors. They are also used as herbicides and pesticides.
• Enzyme activators bind to enzymes and increase their enzymatic activity.
• Enzyme activators are often involved in the allosteric regulation of enzymes in the control of metabolism.
clavulanic acid acts as a suicide inhibitor of bacterial β-lactamase
enzymes
Small molecule resources at the EBI21.04.239
Pathways
http://www.genome.jp/kegg-bin/highlight_pathway?scale=1.0&map=map00231&keyword=tryptophan
Small molecule resources at the EBI21.04.2310
Systems biology
BioModels: quantitative models of biochemical and cellular systems
tryptophan
D-enantiomer: sweet L-enantiomer: bitter
Small molecule resources at the EBI21.04.2311
Drug types 2003 - 2009
'Small molecules' in various shades of blue (http://chembl.blogspot.com/)
Small molecule resources at the EBI21.04.2312
Small Molecule Databases
• Small Molecule Databases can be used to:
• Investigate historical compounds and associated bioactivity data.• To give fresh insight into previously rejected drugs.
• Create Structure-Activity Relationships (SARs)
• Look at how changing a functional group can change the biological activity of a compound – before you start your own synthesis.
21.04.2313 Small molecule resources at the EBI
• Direct synthesis• Could reduce number of compounds made – if any similar
compounds have significant toxicity or unfavourable binding data, you can save time by not making analogues.
• Direct end product testing• Suggest what testing could be carried out – the database can
give you an idea of what testing has given ‘good’ (i.e. clear) results.
• Reduce number of compounds put through High Throughput Screening (HTS).
21.04.2314 Small molecule resources at the EBI
ChEBI and ChEMBL
Small molecule resources at the EBI
What is ChEBI?
• Chemical Entities of Biological Interest• Freely available• Focused on ‘small’ chemical entities (no proteins or
nucleic acids)• Illustrated dictionary of chemical nomenclature• High quality, manually annotated• Provides chemical ontology
Access ChEBI at http://www.ebi.ac.uk/chebi/
Small molecule resources at the EBI21.04.2316
ChEBI home page
Small molecule resources at the EBI21.04.2317
ChEBI data overview
Visualisation
caffeine1,3,7-trimethylxanthine methyltheobromine
Nomenclature
Formula: C8H10N4O2Charge: 0 Mass: 194.19
Chemical data
metaboliteCNS stimulanttrimethylxanthines
Ontology
MSDchem: CFFKEGG DRUG: D00528
Database Xrefs
Chemical Informatics
InChI=1/C8H10N4O2/c1-10-4-9-6-5(10)7(13)12(3)8(14)11(6)2/h4H,1-3H3
SMILES: CN1C(=O)N(C)c2ncn(C)c2C1=O
ChEBI – Chemical Entities of Biological Interest21.04.2319
ChEBI entry view
Chemical Structures
• Chemical structure may be interactively exploredusing MarvinView applet
• Available in formats• Image• Molfile• InChI and InChIKey• SMILES
Small molecule resources at the EBI21.04.2320
ChEBI – Chemical Entities of Biological Interest21.04.2321
Automatic Cross-references
What is ChEMBL?
• Database of bioactive, drug-like small molecules.• Contains 2D structures, calculated properties (logP, mol
weight, Lipinski etc)• Contains abstracted bioactivity data, e.g. binding data
and IC50, from multiple primary scientific journals• Covers about 30 years of compound synthesis and
testing• Annotated FDA-approved drugs
Access ChEMBL at https://www.ebi.ac.uk/chembldb/
Small molecule resources at the EBI21.04.2322
ChEMBL Main Search Page
Small molecule resources at the EBI
Master headline21.04.2324
Calc. properties
Drug Information
Clickable structure
Small molecule resources at the EBI
21.04.2325
Structural Representations
Small molecule resources at the EBI
21.04.2326 Small molecule resources at the EBI
21.04.2327
Parent and Salt Forms
Database links
Small molecule resources at the EBI
ChEBI Link:
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This will take you back to ChEMBL
ChemSpider Links:
21.04.2330
The link works both ways. They
link TO ChemSpider and
FROM ChemSpider.
They link on Standard_Inchi
Small molecule resources at the EBI
Wikipedia Links:
21.04.2331
We also have links with Wikipedia. These also use the Standard_Inchi as the common identifier. These
links will link to the Compound Report Card in
ChEMBL.
The links are added by a ChemoBot and can be
updated with each release, if required.
Small molecule resources at the EBI
STRUCTURAL REPRESENTATION
21.04.2332 Small molecule resources at the EBI
Stereoisomers
• Compounds that have same molecular formula and configuration, but differ in the 3-dimensional orientations.
• The central tetrahedral carbon has 4 different molecular groups/atoms attached. This is known as the chiral centre.
21.04.2333 Small molecule resources at the EBI
Stereoisomerism Example - Thalidomide
• Caused thousands of deformities in babies across 46 countries between 1957 and 1961.
• The R isomer is to control morning sickness but the S isomer was teratogenic.
• Sparked more tightly controlled laboratory practices across the world.
21.04.2334 Small molecule resources at the EBI
Stereoisomers
• Where known, the stereochemistry of the compound is noted in the structure and in the name.
• If a stereoisomer of an existing compound is submitted, it is given a separate id number.
• If a mixture of two stereoisomers had data submitted, we will also give this a separate id number if the activity of the compounds can not be isolated.
• If you draw a planar compound into the structure search, you will receive data on all stereoisomers.
21.04.2335 Small molecule resources at the EBI
Ofloxacin, Levofloxacin and Dextrofloxacin
• Fluoroquinolone antibiotics• Ofloxacin is a racemic (equal) mixture of Levo and Dextro
isomers.• Levofloxacin is the more active stereoisomer• Dextrofloxacin is the less active stereoisomer
• ChEMBL has data on each with separate bioactivities.
21.04.2336 Small molecule resources at the EBI
Tautomers (keto-enol form)
• Two forms readily interconvert via the migration of a hydrogen to the adjacent oxygen and the swapping of a single to a double bond, and vice versa.
• ChEMBL does not differentiate between different tautomers.• The preferred tautomeric structure is retained.
• ChEBI does differentiate and will store the separate tautomers.
21.04.2337 Small molecule resources at the EBI
Salts• About 50% of marketed drugs are combined with salts to
aid in their activity.• Some salts prevent the drug from being absorbed in the mouth.• Some salts help the drug be activated in the intestines, rather than
the stomach.
• There are approx 40,200 ChEMBL compounds with salts.
• Bioactivity data is recorded against the parent drug and against the salt.
• Therefore, it’s important to give these compounds different ChEMBL ids.
21.04.2338 Small molecule resources at the EBI
Salt Example: Morphine• Morphine can be adminstered with many different salts:
• Hydrochloride (HCl)• Sulphate (SO4)• Tartrate• Acetate• Citrate• Methobromide (MeBr)• Hyrobromide (HBr)• Hydroiodide (HI)• Lactate• Chloride (Cl)• Bitartrate
21.04.2339 Small molecule resources at the EBI
Dealing with Salts in ChEMBL
• Each compound, if in a salt form, is analysed and matched to a ‘parent’ – i.e. the base form of the compound. (Not inorganic compounds)
• For example, morphine hydrochloride (CHEMBL556578), morphine sulfate (CHEMBL422878) and morphine sulfate hydrate (CHEMBL1200603) are matched to their parent morphine (CHEMBL70)
• This relationship is shown on the interface of the compound page.
• Additionally, when you run a search for a compound, you will only be brought back the parent form in the results grid.
21.04.2340 Small molecule resources at the EBI
Parents and Salts on the Compound Page
21.04.2341
PARENT (compound report
page)
SALTS (with hyperlinks beneath)
Small molecule resources at the EBI
• Clicking on the Bioactivity Summary pie chart will give you the bioactivity data for ALL forms of the compound
• To get salt specific bioactivity data, click on the hyperlink beneath the salt form of interest to be taken to its compound page.
21.04.2342
Morphine - All Data Morphine HCl specific data
Small molecule resources at the EBI
Naming and Classification
Small molecule resources at the EBI
Chemical names
Common or trivial names are those that are highly used.
Advantages of common names include simplicity, pronounceability and universally recognised
The main disadvantage is ambiguity – the same common name may refer to more than one type of chemical.
Small molecule resources at the EBI
Systematic names
A systematic name is one which corresponds to the chemical structure such that the structure can be determined from the name, e.g. 1,2-dimethyl-naphthalene
Software packages exist which can generate structures from the systematic names (e.g. ACD/Name, ChemOffice, MarvinSketch).
More than one correct systematic name can be assigned to the same molecular structure, depending on the manner in which naming rules are applied.
Small molecule resources at the EBI
Examples of common and systematic names
Common names Systematic names
caffeine
guaranine
theine
1,3,7-trimethyl-3,7-dihydro-1H-purine-2,6-
dione
7-methyltheophylline
1,3,7-trimethyl-2,6-dioxopurine
Small molecule resources at the EBI
SEARCHING IN CHEBI
Why?
• Ontological data• Structure classification
• Chemical entity, e.g. hydrocarbon• Role, e.g. ligand• Subatomic particle, e.g. electron
• Links to other databases• Kegg• DrugBank• PDBEChem
• Citations
How?Text-based
Drawing
The ChEBI ontology
Organised into three sub-ontologies, namely• Molecular structure ontology
• Subatomic particle ontology
• Role ontology
(R)-adrenaline
Small molecule resources at the EBI21.04.2350
Molecular structure ontology
Small molecule resources at the EBI21.04.2351
Role ontology
Small molecule resources at the EBI21.04.2352
ChEBI – Chemical Entities of Biological Interest21.04.2353
ChEBI ontology relationships
• Generic ontology relationships
• Chemistry-specific relationships
ChEBI – Chemical Entities of Biological Interest21.04.2354
Viewing ChEBI ontology
Simple and advanced text search
Narrow by category
Narrow by categoryAND, OR
and BUT NOT
AND, OR and BUT
NOT
Small molecule resources at the EBI21.04.2355
Structure searchSearch optionsSearch options
Structure drawing tools
Structure drawing tools
Small molecule resources at the EBI21.04.2356
Search Results
Click to go to compound page
Click to go to compound page
Hover-over for search menu
Hover-over for search menu
Small molecule resources at the EBI21.04.2357
Types of structure search
• Identity – based on InChI
• Substructure – uses fingerprints to narrow search range, then performs full substructure search algorithm
• Similarity – based on Tanimoto coefficient calculated between the fingerprints
InChI=1/H2O/h1H2
10101101110010110010
1010110111
0010110010Tanimoto(a,b)
= c / (a+b-c)
= 4 / (4+7-4) = 0.57
a
b
Small molecule resources at the EBI21.04.2358
21.04.2359
Browse via Periodic Table
Molecular entities / Elements
Molecular entities / Elements
Small molecule resources at the EBI
21.04.2360
Navigate via links in ontology
Click to follow linksClick to follow links
Small molecule resources at the EBI
CHEBI SEARCH EXAMPLE
ChEBI example
• Search for ‘Glycine’• What is the ChEBI ID for this?• Is it available as a Kegg compound?• What are the IUPAC names?• What is ‘glycine zwitterion’?• • 15428• Yes• Glycine, aminoacetic acid• It is a tautomer of glycine
SEARCHING IN CHEMBL
21.04.2363 Small molecule resources at the EBI
How to search in ChEMBL:
• Keywords• Compound name – dopamine, haloperidol• Assay name – cytotoxicity, liver hepatotoxicity• Target – RAF-1, IRAK-4
• Structure
• BLAST search – FASTA sequence from UniProt
• Protein or taxonomy hierarchy
21.04.2364 Small molecule resources at the EBI
Where to search:
21.04.2365 Small molecule resources at the EBI
Using the search field (found on main page):
• Best for single words• E.g. ‘dopamine’, ‘Muscarinic’
• Looks for matching text in compound name, key or synonym• 3-o-methyl-alpha-methyldopamine• Muscarinic receptor 4
• Needs an exact match• Can’t use wildcards, e.g. ‘%’, ‘?’…
21.04.2366 Small molecule resources at the EBI
Using the Protein Sequence Search
21.04.2367
• Useful for searching for a specific protein or a protein from the same family
• The results brought back will show a percentage similarity to the inputted sequence. • An exact match will give 100%.• Same targets but different organisms will give ~90%
Small molecule resources at the EBI
Compound Drawing
• Can draw the full structure of interest or a partial structure
• Using the Substructure Search you can find compounds containing your partial structure
• Using the Similarity Search, you can find similar compounds – based on a percentage score (70-100%)
21.04.2368 Small molecule resources at the EBI
DOWNLOAD AND ANALYSIS OF CHEMBL RESULTS
21.04.2369 Small molecule resources at the EBI
• The compounds can be downloaded as an *.SDFile.
21.04.2371 Small molecule resources at the EBI
• The bioactivity data can be downloaded as *.XLS
21.04.2372 Small molecule resources at the EBI
21.04.2373 Small molecule resources at the EBI
CHEMBL WORKED EXAMPLE
STRUCTURE ACTIVITY RELATIONSHIPS
Small molecule resources at the EBI
Drug design
• Ligand-based: relies on knowledge of other molecules that bind to the biological target of interest.
• Structure-based: relies on knowledge of the 3D structure of the biological target.
• A lead has• evidence that modulation of the target will have therapeutic value: e.g. disease
linkage studies showing associations between mutations in the biological target and certain disease states.
• evidence that the target is druggable, i.e. capable of binding to a small molecule and that its activity can be modulated by the small molecule.
• Target is cloned and expressed, then libraries of potential drug compounds are screened using screening assays
Small molecule resources at the EBI21.04.2376
Drug Discovery Process
> 2,900,000 bioactivities
> 600,000 compounds
~30,000 distinct lead series
~12,000 candidates ~2000
drugs
Target Discovery
Lead Discovery
Lead Optimisatio
n
Preclinical Development
Phase 1
Phase 2
Phase 3
Launch
•Target identification•Microarray
profiling•Target
validation•Assay
development•Biochemistry
•Clinical/Animaldisease models
•High-throughputScreening (HTS)•Fragment-based
screening•Focused libraries
•Screening collection
•Medicinal Chemistry
•Structure-baseddrug design•Selectivity
screens•ADMET screens•Cellular/Animaldisease models•Pharmacokineti
cs
•Toxicology•In vivo safety pharmacology•Formulation
•Dose prediction
PK
tolerability
Efficacy
Safety
&
Efficacy
Indication
Discovery & expansion
Med. Chem. SAR Clinical Candidates
Drugs
Discovery Development Use
Clinical Trials
ChEMBL database
Small molecule resources at the EBI
SAR DataSAR Data
CompoundCompoundA
ssay
Ass
ay
Ki=4.5 nM
>Thrombin MAHVRGLQLPGCLALAALCSLVHSQHVFLAPQQARSLLQRVRRANTFLEEVRKGNLERECVEETCSYEEAFEALESSTATDVFWAKYTACETARTPRDKLAACLEGNCAEGLGTNYRGHVNITRSGIECQLWRSRYPHKPEINSTTHPGADLQENFCRNPDSSTTGPWCYTTDPTVRRQECSIPVCGQDQVTVAMTPRSEGSSVNLSPPLEQCVPDRGQQYQGRLAVTTHGLPCLAWASAQAKALSKHQDFNSAVQLVENFCRNPDGDEEGVWCYVAGKPGDFGYCDLNYCEEAVEEETGDGLDEDSDRAIEGRTATSEYQTFFNPRTFGSGEADCGLRPLFEKKSLEDKTERELLESYIDGRIVEGSDAEIGMSPWQVMLFRKSPQELLCGASLISDRWVLTAAHCLLYPPWDKNFTENDLLVRIGKHSRTRYERNIEKISMLEKIYIHPRYNWRENLDRDIALMKLKKPVAFSDYIHPVCLPDRETAASLLQAGYKGRVTGWGNLKETWTANVGKGQPSVLQVVNLPIVERPVCKDSTRIRITDNMFCAGYKPDEGKRGDACEGDSGGPFVMKSPFNNRWYQMGIVSWGEGCDRDGKYGFYTHVFRLKKWIQKVIDQFGE
APTT 11 min
Target
Compound
Bioactivity
Small molecule resources at the EBI
Current Data Content (ChEMBL_09)
• Abstracted from 39,094 papers from 16 journals• Ongoing curation and clean-up of all data
• 759,220 compound records• 623,012 distinct compound structures
• 8,091 targets• 4,912 protein molecular targets
• 3,030,317 experimental bioactivities • binding measurements, functional assays and ADMET
Small molecule resources at the EBI
ChEMBL Assay Data
• ChEMBL contains >3 million data points relating compounds to targets or effects.
• These activities come from ~490K assays reported in medicinal chemistry literature.
• Assays can be classified as:• binding measurements
e.g., IC50
• functional assay endpointse.g., Vasodilation
• ADME/toxicity datae.g., LD50
Small molecule resources at the EBI
Compound Properties and Selectivity
• Stores a wide range of calculated compound properties (e.g., mol wt, logP, RO5 violations) • Can be used to identify compounds most likely to have good in vivo
properties (Absorption, Distribution, Metabolism, Excretion)
• Contains activity information against liability targets (e.g., cytochrome P450s, HERG K+ channel)• If compounds have been tested in these assays, can avoid those
with potential toxicity issues
• Contains data on a wide range of targets• If compounds have been tested against multiple targets, can get an
idea of their selectivity (important for validation studies)
Small molecule resources at the EBI21.04.2381
Identifying Chemical Tools
• Search ChEMBL for protein of interest• Simple text search against protein names/synonyms• Browse protein family tree• Sequence search using BLAST (can find related proteins)
• Identify compounds active against this protein• Sort/filter by relevant activity types and potency• E.g., retrieve compounds with IC50/Ki < 100nM
• Retrieve other data for these compounds• Structures, chemical properties, other activities
Small molecule resources at the EBI21.04.2382
Example SAR
1. Run a search on RAF-1
2. Filter on all IC50 values less than 100nM
3. Run the structures through an external source, such as Pipeline Pilot, to show the most common substructures.
• This will give you an idea of what type of compounds have a good IC50 for the target RAF-1.
• You can then design a similar compound(s) based on these substructures.
Assessing selectivity
• So far we have only identified compounds that may be active against a target of interest
• Often the aim is to find compounds that are selective for that target (i.e., not active against other targets)
• Need to consider all of the available activity data for each compound to see if it is known to be active against any other targets
Small molecule resources at the EBI
• Extract the list of SMILES from the XLS spreadsheet
• Run this through ChEMBL SMILES list search tool
• Filter the bioactivity for IC50 > 100nM
• Download the filtered bioactivity as another XLS spreadsheet
• Run a filter on the spreadsheet• Not RAF-1• Collect the subset of compounds that showed the specificity for
RAF-1
• Selective for RAF-1
• Selective for RAF-1 and inactive for other targets
• You can use external programs like Pipeline Pilot™ and Spotfire Decision Site™ to analyse the results.
21.04.2387 Small molecule resources at the EBI
Pipeline pilot protocol to extract all data with an IC50 of 0-100nM
21.04.2388 Small molecule resources at the EBI
IC50 vs Molecular Weight - Spotfire™
21.04.2389 Small molecule resources at the EBI
Downloads and programmatic access
Downloading ChEBI flavours
21.04.2391
• All downloads come in two flavours• 3 star only entries (manually annotated ChEBI
entries)• 2 and 3 star entries (manually annotated ChEBI,
ChEMBL and user submissions)
Small molecule resources at the EBI
21.04.2392
Downloading ChEBI
• OBO file• Use on OBO-edit
• SDF File• Chemistry software compliant such as Bioclipse
• Flat file, tab delimited• Import all the data into Excel• Parse it into your own database structure
• Oracle binary dumps• Import into an oracle database
• Generic SQL insert statements• Import into MySQL or postgresql database
Small molecule resources at the EBI
21.04.2393
The ChEBI web service
• Programmatic access to a ChEBI entry
• SOAP based Java implementation• Clients currently available in Java and perl
• Methods• getLiteEntity• getCompleteEntity and getCompleteEntityByList• getOntologyParents• getOntologyChildren and getAllOntologyChildrenInPath• getStructureSearch
• Documented at http://www.ebi.ac.uk/chebi/webServices.do.
Small molecule resources at the EBI
Downloading ChEMBL
• Frequent releases (approx monthly)• SDFile • Text• MySQL• Oracle
Small molecule resources at the EBI
Downloading ChEMBL
Small molecule resources at the EBI
Help and Feedback
• Email addresses for support queries and feedback
• General questions and feedback on ChEMBL interface:
[email protected]• Reporting of data errors:
• General questions, support and feedback on ChEBI
Small molecule resources at the EBI21.04.2396
Thank you