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Vadivel Parthsarathy PhD February 2013 How are drugs discovered and developed? Slide 2 What is a drug? Any chemical agent that affects the processes of living A medicinal substance that interacts with a biological system - and changes it In Pharmacology terms a drug is a substance used in the diagnosis, treatment or prevention of disease or as a component of medicine or used to enhance physical or mental wellbeing Drugs may be medicinal, performance enhancing/ relaxing. Duration of treatment relies on disease duration e.g. Seasonal flu few days; T1D/Hypothyroidism life long. Slide 3 Why is drug discovery essential? Unmet medical need : new diseases (vCJD; AIDS, Alzheimers; obesity); low efficacy (dementia, cancer); side effects (antidepressants, antipsychotics) downstream health costs; (Alzheimers; spinal injury) cost of therapy; (Interleukins) costs to individual/country; (depression) sustain industrial activity; pharmaceutical industry employs thousands and makes a massive contribution to overseas earnings); patent expiry Slide 4 Changed context of drug discovery and development The 1800s: natural sources; limited possibilities; prepared by individuals; small scale; not purified, standardized or tested; limited administration; no controls; no idea of mechanisms. The 1990s : synthetic source; unlimited possibilities; prepared by companies; massive scale; highly purified, standardized and tested; world-wide administration; tight legislative control; mechanisms partly understood. Slide 5 Selection Criteria A. Medical Need Life threatening or self limiting disease B. Availability of current therapy- any advantage compared to existing drug (e.g. less dosing; oral vs inj.) C. Competitor activity- higher selectivity or novel approach D. Commercial potential- potential market; duration of therapy; acute or chronic disease Slide 6 Drug Discovery Process Disease Lead compound Target Preclinical testing Phase I IV trials Slide 7 Drug Discovery Process Disease Lead compound Target Preclinical testing Phase I IV trials Slide 8 Lead Compounds A compound from a series of similar compounds that have some desirable biological activity. This molecule could be characterized and modified to produce other molecules with better profile of wanted properties compared to unwanted side effects. A lead compound is first foothold in the drug discovery ladder. Much more effort is required to make a lead compound a drug candidate as they are n ot good enough to be the drug itself. Slide 9 Finding a lead compound METHODS 1) Traditional/folklore remedies 2) Natural resources 3) By chance 4) Enhancing side effects of existing compounds 5) Structural similarity to natural ligand 6) Computer assisted drug design Slide 10 Traditional/Folklore remedies Slide 11 Isolation of active ingredients from traditional remedies. e.g. Slide 12 Ethnobotanical approach Systematic screening of: - Published literature on traditional medicinal plant use (e.g. documented traditional healers experience) Historical texts- (ancient botanico-medicinal manuscripts) Advantages:- Preselection of potentially active resources - Promising safety profile (age-long experience) - Cost-efficient and comparatively fast Slide 13 Traditional (Salicin) Native American Cherokees have used willow bark for the treatment of fever for centuries also mentioned in ancient Egyptian text. Rev Edward Stone in 1763 observed medicinal properties and published the findings. Willow bark contains salicin. Salicin is metabolized in-vivo active agent salicilic acid Aspirin (acetyl salicilic acid) is a synthetic altered version of salicin. Slide 14 Quechua people, native of Peru used powdered dried bark of cinchona tree to treat shivering due to low temperature. Observed by Jesuit Priest living in Lima and sent to Rome to treat malaria. Quinine (meaning Holy bark) was isolated and named in 1820 by French researchers Joseph Pelletier and Joseph Caventou. Traditional (Quinine) Slide 15 Natural resources Slide 16 Natural Resources Isolation of many bioactive agents from natural resources have led to systematic screening of plant and animal extracts for activity 52% of the drugs approved in the U.S. from 1981-2002 were natural products or derived from them 26 plant based drugs were approved during 2000-2006, including novel-molecular based drugs. Slide 17 Natural Resources Disadvantages: 1) Isolation and determination of structure is difficult. 2) Mixture is always complex and contains macromolecule, which may hide the biological activity. 3) Lead compounds present in natural resources are often in low concentration and their isolation usually corresponds with waste. 4) Structures are complex and synthetic synthesis is often difficult. Life form SpeciesLead/Drug MouldCephalosporin acremoniumCephalosporin (antibacterial) PlantYew Tree Taxol (anti neoplastic) MarineDeep water spongeDiscodermolide (anti tumour) ReptileGlia monsterExenatide (anti diabetic) Slide 18 By chance Slide 19 Lead compound may be identified by chance. e.g. 1) Penicillin Discovered by Alexander Fleming (and others) 2) Librium (anxiolytic): Discovered by Sternbach An active compounds structure was misassigned and the project was shelved. The compound was unearthed years later in lab tidy up and tested for a new project. Found to be active as a treatment for anxiety. First in the class of Benzodiazepines. By Chance Slide 20 Enhancing side effects of existing compounds Slide 21 Some drugs have side effects. Drug structure could be modified to optimize the side effects. e.g. 1) Enhancing side effects of existing compounds Slide 22 2) Chlorpromazine (antipsychotic-tranquilizers) Phenothiazines were being developed as antihistamines but French navy surgeon Laborit observed that this drug has relaxing effects on patients who are about to have surgeries Enhancing side effects of existing compounds Slide 23 Structural similarity to natural ligand Slide 24 5 Hydroxytryptamine Sumatryptan (Imitrix) Serotonine (a natural neurotransmitter used to treat migraine headaches produced from neurons in CNS) Known to be 5-HT1 agonist Structural similarity to natural ligand Slide 25 Computer assisted drug design Slide 26 If one knows the precise molecular structure of the target (enzyme or receptor), then one can use a computer to design a perfectly-fitting ligand. Examples: Zanamivir antiviral drug, COX2 inhibitors - NSAIDs Disadvantages: Most commercially available programs do not allow conformational movement in the target (as the ligand is being designed and/or docked into the active site). Thus, most programs are inaccurate representations of reality. Computer Assisted Drug Design Slide 27 Once a lead has been discovered, it is important to understand precisely which structural features are responsible for its biological activity (i.e. to identify the pharmacophore) Finding the Lead compound Slide 28 This may enable one to prepare a more active molecule This may allow the elimination of excessive functionality, thus reducing the toxicity and cost of production of the active material This can be done through synthetic modifications Example: a amino acid which docks in the receptor; a hydrogen bond, aromatic ring etc. Lead compound - Pharmacophore Diazepam binding site on GABA receptor: Red (H1, H2/A3) are hydrogen bond donating and accepting site. White (L1, L2, L3) are lipohilic binding sites Slide 29 Drug Discovery Process Disease Lead compound Target Preclinical testing Phase I IV trials Slide 30 Drug Target = specific macromolecule, or biological system, which the drug will interact with. Most often proteins but nucleic acids may also be attractive drug targets. Identifying the drug target Slide 31 Examples of drug targets TargetMechanismExamples EnzymeInhibitor reversible or irreversible antiretroviral drugs - HIV ReceptorAgonist or AntagonistGPCRs (Liraglutide Diabetes) Nucleic acidIntercalator (binder), modifier (alkylating agent) Doxorubicin (cancer), Mechlorethamine (prostate cancer) Ion channels Blockers or openersDiazepam, Verapamil TransportersUptake inhibitorsProcaine, amphetamines Slide 32 The identification of new, clinically relevant, molecular targets is of utmost importance to the discovery of innovative drugs. There are around 5000-10000 potential drug targets. Current therapy is based upon less than 500 molecular targets- 48% are G-protein coupled receptor 28% are enzymes 11% hormone and factors 5% ion channels Therefore, many more drug targets exist Why so important? Slide 33 Besides classical methods of cellular and molecular biology, new techniques of target identification are becoming increasingly important. These include: A) Genomics B) Bioinformatics C) Proteomics Methods Slide 34 Mapping of Human Genome (complete set of genetic information stored in DNA sequences ) Identification of new targets has benefited from genomics approach. Sequencing of human genome will give us blueprint of all proteins and will help in selective target of the disease. e.g. Breast cancer type 2 susceptibility protein (BRCA2); Cystic fibrosis (CFTR), APP gene (Familial Alzheimers) Genomics Slide 35 Study of information processes in biological system. It is the in silico (computer simulation) identification of novel drug targets by systematically searching for paralogs (related proteins within an organism) of known drug targets (e.g. may be able to modify an existing drug to bind to the paralog). It can compare the entire genome of pathogenic and non pathogenic strains of a microbe and identify genes/proteins associated with pathogenesis. Bioinformatics Slide 36 It is the systematic high-throughput separation and characterization of proteins within biological systems. Target identification with proteomics is performed by comparing the protein expression levels in normal and diseased issues. These high-throughput studies are carried out using state of the art chromatographs (HPLC, GC) and mass spectrometer (MALDI-TOF) Proteomics Slide 37 Drug Discovery Process Disease Lead compound Target Preclinical testing Phase I IV trials Slide 38 Preclinical information required before a selected Drug Candidate can be administered to humans Pharmacological activity Pharmacokinetics and drug metabolism Toxicology Pharmaceutics Preclinical testing - Biological activity Slide 39 Pharmacodynamic studies: What does the drug do to the body? Investigate: - Physiological effects (blood glucose, electrolytes, kidney and liver function etc) - Mechanism of Drug action (molecular and cellular responses to drugs) - Relationship between drug concentration and effect (optimal dose) Pharmacokinetic studies: What does the body do to the drug? Investigate:- Absorption (bioavailability) - Distribution (circulation and tissue) - Metabolism (breakdown) - Excretion (kidney and liver) Biological activity Slide 40 Preclinical testing In vitro Slide 41 In vitro profiling: - Biochemical assays (e.g. enzyme activity assays) - Cell culture assays (e.g. cancer cell lines) E.g. BRIN BD11 cells for insulin secretion In vitro toxicology: - Investigate potential toxic effects in bacteria- or cell cultures Cell death assays MTT/LDH assay, Comet assay, apoptosis assays Preclinical testing in vitro Slide 42 Advantages: Quick and requires relatively small amounts of compound Speed may be increased to the point where it is possible to analyze several hundred compounds in a single day (high throughput screening) Disadvantage: Results may not translate to living animals Slide 43 Preclinical testing In vivo Slide 44 In vivo testing: Determine toxicity in animal models (death, behavioral changes, morphological changes, blood parameters) Efficacy (disease management) General observational studies in animals (locomotion, feeding/ drinking behaviour, body weight). CNS evaluation (Anxiety, depression). Psychomotor testing (Behaviour parameters) Study on drug dependence (addiction) Preclinical testing in vivo Slide 45 Advantages: Similar physiology to humans Side effects such as birth defects and cancer on other tissues is easy to monitor Disadvantages: More expensive Results may be clouded by interference with other biological systems Animal Scientific Procedures Act (1986) regulates the use of animals for scientific research and hence experimental studies are tightly controlled to ensure minimal suffering to animals Slide 46 Preclinical Data before Phase I trial Safety pharmacology CVS, CNS, RS PKs preliminary studies on ADME Acute toxicity 2 species by 2 routes of administration Repeat dose toxicity rodent and non-rodent; two 14 day studies before human trial Reproductive toxicology embryo/foetal development studies 2 species Mutagenicity/chromosomal abnormality Slide 47 Provide pharmacist with information for optimal formulation Concentrations and volumes of injections Strength of capsules or tablets Choose unit doses providing greatest flexibility PHARMACEUTICS Slide 48 Drug Discovery Process Disease Lead compound Target Preclinical testing Phase I IV trials Slide 49 Clinical Trials are designed to: - determine safety and tolerance in humans - pharmokinetics (what the body does with the drug) - bioavailibility for a range of doses - determine the pharmacological profile. The main phases of pre-clinical and clinical trials are: Preclinical Animal studies. Submission of Investigational New Drug application to government bodies. e.g. US FDA. Phase I Normal healthy human volunteers. Phase II To evaluate safety and efficacy of drug in patients. Phase III Large patient number to establish efficacy vs placebo or comparator compound. Phase IV Long term surveillance/monitoring of adverse reaction. Clinical trials Slide 50 Initial studies to evaluate Pk, Pd, tolerability. 30- 50 volunteers usually healthy. Starting dose. Single Ascending Dose (SAD). Multiple Ascending Dose (MAD). 80% of drugs fail at phase I trials Clinical trials: Phase I Slide 51 Define success/fail criteria of the drug before starting the study Study objectives based on a combination of: -Tolerability/ safety - Kinetics - +/- Dynamics - +/- Quantitative dose-response, concentration-response relationships Clinical trials: Phase I Slide 52 Factors to be considered in deciding the starting dose: Maximum no effect dose/exposure in toxicity studies using most sensitive species Nature & severity of toxicity seen in animals. Nature of PD activity in animals and slope of dose- response curve. Clinical trials: Phase I Slide 53 Stopping drug development: Half-life (t ) too short or too long. Poor bioavailability. Inconsistent bioavailability with low therapeutic index. Saturable clearance mechanisms. Multiple metabolites not covered by toxicity studies. Clinical trials: Phase I Slide 54 Project Termination: Poor tolerability at therapeutic concentrations Unsatisfactory kinetics/metabolism Low potency Absence of efficacy Clinical trials: Phase I Slide 55 Small scale studies in patient population. 250-500 human exposures. Pharmacokinetics. Pharmacodynamics / surrogate endpoints Tolerability. Decisions before full Phase III. Clinical trials: Phase II Slide 56 Large scale efficacy trials (1000s patients). Placebo effect (sham) Several hundred to several thousand. Power curves (statistics). Ongoing PK studies special populations. Ongoing formulation studies (stable and acceptable to patients). Ongoing toxicity / oncogenicity studies. Usually 2 successful phase 3 trials required for FDA approval Clinical trials: Phase III Slide 57 Drug is placed on the market and patients are monitored for side effects Post licensing safety evaluation Pharmacovigilance (PV) Safety Assessment of Marketed Medicines Clinical trials: Phase IV Slide 58 Pharmacovigilance is the science of collecting, monitoring, researching, assessing and evaluating information from healthcare providers and patients on the adverse effects of medicines, biological products, herbals and traditional medicines with a view to: Identifying information about potential new hazards Preventing harm to patients. Pharmacovigilance Slide 59 Human Medicines Regulation (2012) The MHRA Pharmacovigilance Inspectorate is part of the Inspections and Standards Division of the MHRA. It assesses pharmaceutical companies compliance with UK and EU legislation relating to the monitoring of the safety of medicines given to patients Legislation Slide 60 Thalidomide: German pharmaceutical company Grnenthal. Sold from 1957 to 1961 (40 different brands) in almost 50 countries. To pregnant women, as an antiemetic to combat morning sickness and as an aid to help them sleep. Inadequate tests were performed to assess the drug's safety, with catastrophic results for the children of women who had taken thalidomide during their pregnancies. Antiemetic = a medication that helps prevent and control nausea and vomiting Why so strict? Slide 61 Approximately 10,000 children (1956-1962) were born with severe malformities, including Phocomelia (presents at birth very short or absent long bones and flipper-like appearance of hands and sometimes feet). In 1962, in reaction to the tragedy, the United States Congress enacted laws requiring tests for safety during pregnancy before a drug can receive approval for sale in the U.S. Why so strict? Thalidomide Slide 62 Production and quality control Manufacture- Manufacturing of the product - Controls to the established batch release GMP and GLP environments Marketing authorisation process Approval - Drug is approved for marketing by the Authorities Post Registration Slide 63 THE COST OF DRUG DEVELOPMENT Costs of drug development 500 million for one drug Takes 15-16 year to develop a drug 75% of this cost is attributable to failure 90% of all drugs developed dont make it to the market Slide 64 FUNDING Slide 65 Allocation of Time (in years) Slide 66 I. PROJECT CONCEPTION II. LEAD IDENTIFICATION III. TARGET IDENTIFICATION IV. PRECLINICAL DEVELOPMENT V. CLINICAL DEVELOPMENT V. POST REGISTRATION Summary Slide 67 Bartlett J Blake; Dredge Keith; Dalgleish Angus G The evolution of thalidomide and its IMiD derivatives as anticancer agents. Nature reviews. Cancer (2004), 4(4), 314-22. Cragg, G. M.; Newman, D. J. Nature: a vital source of leads for anticancer drug development. Phytochemistry Reviews (2009), 8(2), 313-331. Betz, U. A. K. et al. Genomics: success or failure to deliver drug targets? Current Opinion in Chemical Biology (2005), 9: 387-391 Sams-Dodd, F. Target-based drug discovery: is something wrong? Drug Discovery Today (2005) 10: 139-147. Franks Michael E; Macpherson Gordon R; Figg William D Thalidomide. Lancet (2004), 363(9423), 1802-11. Abou-Gharbia, Magid. Discovery of innovative small molecule therapeutics. Journal of Medicinal Chemistry (2009), 52(1), 2-9. Jorgensen, W. L. The many roles of computation in drug discovery. Science (2004) 303: 1813-1818. References Slide 68 Slide 69 Metabolism of Drugs The body regards drugs as foreign substances, not produced naturally. Sometimes such substances are referred to as xenobiotics Body has goal of removing such xenobiotics from system by excretion in the urine The kidney is set up to allow polar substances to escape in the urine, so the body tries to chemically transform the drugs into more polar structures. Slide 70 Phase 1 Metabolism involves the conversion of nonpolar bonds (eg C-H bonds) to more polar bonds (eg C-OH bonds). A key enzyme is the cytochrome P450 system, which catalyzes this reaction Metabolism of Drugs Slide 71 Phase I metabolism may either detoxify or toxify: Phase I reactions produce a more polar molecule that is easier to eliminate. Phase I reactions can sometimes result in a substance more toxic than the originally ingested substance. An example is the Phase I metabolism of acetonitrile Metabolism of Drugs Slide 72 Phase II metabolism links the drug to still more polar molecules to render them even more easy to excrete Metabolism of Drugs Slide 73 Phase II reactions most commonly detoxify Phase II reactions usually occur at polar sites, like COOH, OH, etc. Metabolism of Drugs