drug discovery case Flashcards
what was the Black Death and what treatments were used?
started around 1348-1350
killed 1.5 million people.
treatments that was used were • Bezoar stones, from animal stomachs
• Goa stones made from clay, silt, shells, resin and musk
– Scrapings were drunk as a remedy for ailments – Also used to counteract suspected poisoning
– Highly valued and expensive
what are opium alkaloids?
Obtained from the latex of Papaver somniferum L.
• Known since antiquity for its analgesic and sedating properties
• Opium is the dried latex of the opium poppy, containing all the alkaloids
what is morphine?
first isolated in 1804. it is an analgesic antitussive reduced gastric motility respiratory depressant
what are some of the traditional drugs and medicines?
Herbal medicines
• Poisons e.g. from plants, minerals
• Toxins e.g., snake, spider and scorpion venoms
• Either as a purified substance or a mixture of substances
what were some key observations when making a drug?
• Possible to isolate active substances
• Frequently >1 chemically similar active
– Structurally related (but different) molecules from natural sources frequently have similar (but subtly different) biological activities
• E.g. different cardiac glycosides have similar activity but different durations of action
what is the traditional approach to drug discovery?
Isolation and purification of active substance
• Structural modifications to active substance
• Some screening of groups of molecules
– Dyes
– Plant extracts
• Test molecule is synthesised on mg to g scale
• Sent for bioassay testing
• Data returned and analysed
• Structural changes made and new molecule synthesized, tested etc
what considerations is needed in the drug discovery process
The drug target • A lead activity molecule • Drug candidates (new chemical entities, NCE) having appropriate properties – Pharmacodynamic – Pharmacokinetic – Toxicological – Chemical
how do you go about searching for new drug targets?
Knowledge of physiology / pathology
– Elucidation of biochemical pathways and regulatory systems
• Knowledge of mechanisms of actions of drugs, poisons, toxins and venoms
• Structural similarities in biomolecules suggesting new targets, e.g. G-protein coupled receptors have conserved sections in their structure
• Genomics
– Search for new receptors, enzymes, ion channels on the basis of amino acid sequence homology with similar known targets
what are the drug targets?
Humans are our primary area of concern • Animals also need medicines • Principles are broadly similar – Mammals – Birds – Reptiles – Other animals
Infectious diseases • Viruses
• Bacteria
• Fungi
• Parasites • Prions
how do you exploit a drug target?
Need information on
– Structural nature of the target
– Possible mechanism of interaction between the target and potential drugs • Need to develop an assay that accurately measures the activity of the target
– Dose dependent response
– Capable of comparison with other ligands
Once scientisits discovered this cycle, they were able to inhibit or stimulate different pathways
• Renin, ACE, AII, Aldosterone
how do you go about finding targets?
Physiology and biochemistry
• Pharmacology – drug effects
• Toxins and venoms from the natural world • Human genome
what are the steps in drug discovery?
- Target identification/validation
- Hit (pre-lead) identification – what the drug does • Lead optimization
- Pre-clinical development
- Clinical candidate
- Clinical trials
what are the two types of target identification strategies?
Target Deconvolution
– Start with an efficacious drug and identify the target retrospectively
• Target discovery (obviously more logical)
– Identify a target and develop a drug to affect it
what is meant by a target?
Any system that can potentially be modulated by a molecule to produce a beneficial effect • Biological macromolecule or molecular complex that is critical for the disease
o E.g. an enzyme critical in the life cycle of a virus
list the types of targets
Enzymes - inhibitors (competitive or non-competitive, reversible or irreversible) or activators
• Receptors - agonist or antagonist
• Ion channels - blockers or activators
• Transporters - inhibit or stimulate
• Viral surface proteins - blocking the entry to cell
• DNA-intercalating agents, minor groove binders, anti-sense drugs
• Cells-vaccines
what is meant by target validation
Form of risk assessment, the better the validation the lower the risk in advancing the project
• Mitigates selection of wrong target and wrong patient population
what is meant by target identification
Is the target critically involved in disease?
• Is the target critically involved in normal biology? – if so, you don’t really want to do anything to it (is it going to harm the patient if we temper with it?)
• Location of the target
– Ideally one that is not evenly distributed throughout the body (to minimize side effects) • Does manipulation lead to desired effect?
• Can the target be effectively studied?
• Is the target amenable to High Throughput Screening?
• The proposed target has a favorable intellectual property status?
what is high throughput screening?
is a drug discovery process that allows automated testing of large numbers of chemical and/or biological compounds for a specific biological target
what are the major components of target identification
tissue expression
- targets protein is expressed or active in the desired organ
- target mRNA expression is altered in the desired disease tissue
- target protein expression is altered in diseased tissue
Genetics
– Genetic association of a variant with a disease
– Genetic polymorphisms linked to a disease state
• Clinical experience
– Known ligand affecting target pathway or protein has shown efficacy in the disease
what are the different methods in identifying targets?
Many different technologies can identify novel targets including: • DNA microarrays • Proteomics – Post-translational modifications – Protein isoforms – Antibodies interacting with the traget • RNA knockdown – Gene knockouts – Antisense technology
what are DNA microarrays used for?
the DNA microarray is a tool used to determine whether the DNA from a particular individual contains a mutation in genes
what is meant by proteomics?
it is a large scale study of proteomes which is a set of proteins produced in an organism, system or biological context.
it is used to investigate when and where portions are expressed, rate of protein production, degradation and steady state abundance
what is meant by knockdown in biology?
deletion or inactivation of genes is known as knockdown or knockout. in most organisms, the genes are encoded in DNA. DNA is transcribed into RNA and RNA is translated into protein which become the building blocks and catalysts for the whole organism.
what are validated targets?
- Literature survey and competitor information
- Identification of a pathophysiologically relevant molecule target e.g. an enzyme, receptor, etc
- Analysis of molecular signaling pathways
- Molecular pharmacology of variants
- Determination of the DNA and protein structure
- Elucidation of the function and mechanism of the protein
- Proof of therapeutic concept in animals
what is target validation in pharmacology?
Pharmacological tool moderates disease associated pathway in vitro
• Ligand with intended mode of action modulates disease associated pathways ex vivo or in native tissue
• Ligands with intended mode of action modulate disease associated pathway in vivo with target engagement-activity relationship established
what is antisense technology
it is a tool for controlling gene expression in a cell. using synthetic antisense oligonucleotides, it targets the gene at the level of mRNA rather than DNA and prevents them from producing proteins
- siRNA blocks synthesis of the targeted protein
- Example-blockage of the P2X3 receptor was able to lower pain sensitivity
- Advantage is that this is reversible model so can be sure that it is the target that is responsible for the effect
what is meant by transgenic animals
means that 1 or more DNA sequence from another species have been introduced by artificial means. animals are usually made transgenic by having a small sequence of foreign DNA injected into a fertilised eggs or developing embryo
Specific protein expression inhibited in every cell
• Identification of role of the protein not just in disease but also in normal biology • Tissue-restricted and/or inducible knockouts are now more desirable with the advancements of drug delivery
what is ligand pharmacology
Determine whether a specific ligand against the identified target have a pharmacological effect in the disease state
what is meant by animal models of disease
- Animal models are essential to bridge the translational gap between preclinical and clinical research
- Is there a suitable animal model of the disease you want to treat?
- How close is it to the human condition?
give an example of animal model of disease
Colitis
– DSS model
– IL-10 KO mouse • Arthritis
– Subdermal collagen injection • Hemorrhagic shock
– Blood removal and replacement • Septic shock
– LPS injection i.p.
• Adult respiratory distress syndrome
– Intratracheal LPS application • Myocardial infarction
– Tie off left ventricular artery
what is diabetes animal model
Type 1 – Auto-immune disease – Genetic component • Type 2 – Obesity – Insulin resistance
give an example of is type 1 diabetes model
Multiple-low-dose-streptozotocin model (MLDS)
– Chemically induced
– Fast see data after 21 days – Not a very good model
• Non-Obese diabetic (NOD) mouse
– Genetic
– Incidence increases after 5 weeks
– 80% of female mice develop diabetes only 20% of male mice (not gender generalizable) – Experiments run to 30 weeks (very long)
– Also not a very good model • Virally-induced
– Role of viruses in development of diabetes
give an example of type 2 diabetes model
enetically obese models
– ZDF rats or OB/OB mice
– Treatments to improve insulin resistance or improve beta cell function • Induced obesity
– High fat feeding mice or rats • Non-obese models
– GK rat
why can animal models fail to identify effective treatments
Disease model does not truly reflect the disease
– Key cellular elements in animal models are not the major players in human disease
– The model is quantitatively wrong with species differences in capacity, sensitivity or rate constants governing the relationship between elements are not captured
• Incorrect translation of the intervention to the patient so target is relevant but not appropriately engaged pharmacologically
– Incorrect dosing regimen because of species differences in pharmacokinetics
– Physiology of the primary target is different between species, or altered in human disease
• Clinical endpoints differ in animal models
– Quality of life is an important endpoint in clinical trials and is measured usually by questionnaire which cannot be done with animals
– Animals models use an easy to measure and objective endpoint for disease but these may not be the same endpoints for clinical trials e.g. tumor size in animal models of a cancer drug while overall survival is the endpoint in clinical trials
why do drugs fail even though the animal models is correct
Clinical trial design not appropriate to test the intervention under investigation. Negative clinical trials risks abandoning a correct hypothesis
– Wrong dosing regimen
– Study too short
– Wrong patient population
what is the standard drug development approach
Identify target (e.g., enzyme, receptor, ion channel, transporter) • Develop assay for high-throughput molecular screen • Mass screening and/or directed synthesis program • Select one or more lead structures
