Introduction to the drug discovery process
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This document discusses the drug discovery process from target identification through FDA approval. It describes methods used for target identification such as genomics, bioinformatics, and proteomics. The stages of lead identification through high-throughput screening and structure-based drug design are outlined. Key aspects of lead optimization like characterizing potency, efficacy, pharmacokinetics, and toxicity are summarized. Details are provided on preclinical and clinical trial phases from Phase 0 through Phase IV post-marketing surveillance. Factors contributing to the declining drug approval rate like increased safety demands are noted. The high costs and failure rates associated with drug development are highlighted.
Introduction to the drug discovery process
- 1. Prof. Thanh N. Truong Department of Chemistry, University of Utah Institute for Computational Science and Technology, Vietnam Astonis LLC
- 2. Top 10 Pharmaceutical Company Sale Figures •2004 (billions USD) •2005 (billions USD) •2006 (billions USD) Johnson & Johnson 47.4 Pfizer 44.2 Pfizer 45.1 Pfizer 45.2 GlaxoSmithKline 34.0 GlaxoSmithKline 37.0 GlaxoSmithKline 39.0 Aventis-Sanofi 34.0 Aventis-Sanofi 35.6 Novartis 28.2 AstraZeneca 24.0 Novartis 28.9 Hoffman LaRoche 24.5 Johnson & Johnson 22.3 Hoffman LaRoche 26.6 Merck 22.9 Merck 21.9 AstraZeneca 25.7 AstraZeneca 21.4 Novartis 20.3 Johnson & Johnson 23.3 Aventis-Sanofi 20.4 Abbott Labs 19.7 Merck 22.6 Abbott Labs 19.7 Hoffman LaRoche 16.6 Wyeth 15.7 Bristol-Myers Squibb 15.3 Eli Lilly 14.8 Bristol-Myers Squibb 19.4
- 3. R&D Spending and Return on Investments Research based pharmaceutical companies, on average, spend about 20% of their sales on research and development (R&D). This percentage is significantly higher than in most other industries, including electronics, aerospace, automobiles, and computers. Since 1980 US pharmaceutical companies have practically doubled spending on R&D every 5 yrs. Despite these enormous expenditures, there has been a steady decline in the number of drugs introduced each year into human therapy. 70-100 in the 60s 60-70 in the 70s ~50 in the 80s ~40 in the 90s Innovation Deficit Jurgen Drews, Hoffmann-LaRoche
- 4. Reasons for Innovation Deficit Increased drug safety demands by FDA the average number of clinical trials per new drug application (NDA) increased from 30 in the 70s to 40 in the 80s, to 70 in the 90s Lead to the prolonged duration of the drug development process. o In the 60s, total development time was 8.1 yrs o In the 70s, total development time was 11.8 yrs o In the 80s, total development time was 14.2 yrs o In the 90s, total development time was 14.9 yrs o Currently, total development time is ~16 yrs “low hanging fruit” have been picked.
- 5. 16 years and about 880 Millions USD for a New Drug Time Line
- 6. Return on Investment About 75% of this cost ($660 million) is attributable to failure during the development. 90% of all drug development candidates fail to make it to market. Methods that enhance the drug discovery process and reduce failure rates are highly desirable!
- 7. The Drug Discovery Process Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review
- 8. Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review The identification of new, clinically relevant, molecular targets is of utmost importance to the discovery of innovative drugs. Current therapy is based upon less than 500 molecular targets of about 10000 possible targets 45% of which are G-protein coupled receptors 28% are enzymes 11% are hormones and factors 5% ion channels 2% nuclear receptors Besides classical methods of cellular and molecular biology, new techniques of target identification are becoming increasingly important. These include: genomics (Biotechniques 31: 626-630 2001) bioinformatics (Drug Discovery Today 7:315-323 2002) proteomics (J. Pharmacol. Toxicol. Methods 44:291-300 2000; Biopolymers 60:206-211 2001)
- 9. Genomics Genetic information is contained with DNA (deoxyribonucleic acid) and RNA (ribonucleic acids) Each plant, animal or bacteria carries its entire genetic code inside almost every one of its cells Genomics is the discipline that aims to decipher and understand the entire genetic information content of an organism Bio-informatics
- 11. Genomics Facts Around 99% of our genes have counterparts in mice Our genetic overlap with chimpanzees is about 97.5% The genetic difference between one person and another is less than 0.1 % But because only a few regions of DNA actively encode life functions, the real difference between one person and another is only 0.0003 % It is becoming increasingly evident that the complexity of biological systems lies at the level of the proteins, and that genomics alone will not suffice to understand these systems.
- 12. Bio-informatics Bioinformatics methods are used to transform the raw sequence into meaningful information (eg. genes and their encoded proteins) and to compare whole genomes (disease vs. not). Sequencing of microbial genomes will enable the identification of novel drug targets, especially when comparing to the human genome. In silico identification of novel drug targets is now feasible by systematically searching for paralogs (related proteins within an organism) of known drug targets (eg. may be able to modify an existing drug to bind to the paralog). Can compare the entire genome of pathogenic and nonpathogenic strains of a microbe and identify genes/proteins associated with pathogenism.
- 13. Proteomics Proteomics 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 tissues. Using gene expression microarrays and gene chip technologies, a single device can be used to evaluate and compare the expression of up to 20000 genes of healthy and diseased individuals at once. --Trends Biotechnology 19:412-415 2001
- 14. Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review Involves demonstrating the relevance of the target protein in a disease process/pathogenicity and ideally requires both gain and loss of function studies. This is accomplished primarily with knock-out or knock-in animal models, small molecule inhibitors/agonists/antagonists, antisense nucleic acid constructs, ribozymes, and neutralizing antibodies. Since strong interactions between a protein and its ligand are characterized by a high degree of complementarities in their shapes and charge distributions, knowledge of the protein three dimensional structure will enable the prediction of “druggability” of the protein.
- 15. Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review Organic compounds are identified which interact with the target protein and modulate its activity by using random (screening) or rational (design) approaches. High-throughput Screening Natural product and synthetic compound libraries with millions of compounds are screened using a test assay. In theory generating the entire ‘chemical space’ for drug molecules and testing them would be an elegant approach to drug discovery. In practice, this isn’t feasible. -- Drug Discovery Today 5:2-4 2000 Structure Based Drug Design Three dimensional structures of compounds from virtual or physically existing libraries are docked into binding sites of target proteins with known or predicted structure. Scoring functions evaluate the steric and electrostatic complementarity between compounds and the target protein. The highest ranked compounds are then suggested for biological testing. -Drug Discovery Today 7:64-70 2002
- 16. Other criteria for leads Pharmacodynamic properties - efficacy, potency, selectivity Physiochemical properties - water solubility, chemical stability, Lipinski’s “rule-of-five”. Pharmacokinetic properties - metabolic stability and toxological aspects. Chemical optimization potential - ease of chemical synthesisand derivatization. Patentability
- 17. Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review Molecules are chemically modified and subsequently characterized in order to obtain compounds with suitable properties to become a drug. Leads are characterized with respect to pharmacodynamic properties such as efficacy and potency in vitro and in vivo, physiochemical properties, pharmacokinetic properties, and toxicological aspects. Once compounds with desirable in vitro profiles have been identified, these are characterized using in vivo models.
- 18. Charaterizing Leads Potency refers to the amount of drug required for its specific effect to occur Efficacy measures the maximum strength of the effect itself, at saturating drug concentrations. Pharmacokinetics - determining the fate of xenobiotics. - “what the body does to the drug.” Pharmacodynamics - determining the biochemical and physiological effects of drugs, the mechanism of drug action, and the relationship between drug concentration and effect. - “what the drug does to the body” Lead optimization requires the simultaneous optimization of multiple parameters and is thus a time consuming and costly step. It is often the tightest bottleneck in drug discovery. Hints on how to modify a lead compound can originate from molecular modeling, quantitative structure-activity relationships, and from structural biology (structure-based drug design)
- 19. Drug Target Identification Target Validation Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review Preclinical studies involve in vitro studies and trials on animal populations. Wide ranging dosages of the compounds are introduced to the cell line or animal in order to obtain preliminary efficacy and pharmacokinetic information.
- 20. Five NIH clinical trial types Treatment trials: test experimental treatments or a new combination of drugs. Prevention trials: look for ways to prevent a disease or prevent it from returning. Diagnostic trials: find better tests or procedures for diagnosing a disease. Screening trials: test methods of detecting diseases. Quality of Life trials: explore ways to improve comfort and quality of life for individuals with a chronic illness.
- 21. Five Phases of Clinical Trials Phase 0 - First-in-human trials -- human micro-dosing studies and are designed to speed up the development of promising drugs by establishing very early on whether the drug behaves in human subjects as was expected from preclinical studies. Phase I - a small group of healthy volunteers (20-80) are selected to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of a therapy. Single Ascending Dose (SAD) studies Multiple Ascending Dose (MAD) studies Food effect- designed to investigate any differences in absorption caused by eating before the dose is given.
- 22. 80% of drugs fail the Phase I clinical trial!
- 23. On the way to FDA review Phase II - performed on larger groups (20-300) and are designed to assess the activity of the therapy, and continue Phase I safety assessments. Phase III - randomized controlled trials on large patient groups (hundreds to thousands) aimed at being the definitive assessment of the efficacy of the new therapy, in comparison with standard therapy. Side effects are also monitored. -it is typically expected that there be at least two successful phase III clinical trials to obtain approval from the FDA. Once a drug has proven acceptable, the trial results are combined into a large document which includes a comprehensive description of manufacturing procedures, formulation details, shelf life, etc. This document is submitted to the FDA for review.
- 24. Post Marketing Surveillance Trial Phase IV - post-launch safety monitoring and ongoing technical support of a drug. may be mandated or initiated by the pharmaceutical company. designed to detect rare or long term adverse effects over a large patient population and timescale than was possible during clinical trials.
- 25. Vioxx Saga: multi-billion-dollar share of the arthritis and pain-relief market USA Today 10/12/2004: How did Vioxx debacle happen? May 1999: FDA approves Vioxx. March 2000: Merck reveals that a new study found Vioxx patients had double the rate of serious cardiovascular problems than those on naproxen, an older nonsteroidal anti-inflammatory drug, or NSAID. November 2000: The New England Journal of Medicine publishes the study, called VIGOR. February 2001: An advisory panel recommends the FDA require a label warning of the possible link to cardiovascular problems. September 2001: The FDA warns Merck to stop misleading doctors about Vioxx's effect on the cardiovascular system. April 2002: The FDA tells Merck to add information about cardiovascular risk to Vioxx's label. Aug. 25, 2004: An FDA researcher presents results of a database analysis of 1.4 million patients; it concludes that Vioxx users are more likely to suffer a heart attack or sudden cardiac death than those taking Celebrex or an older NSAID. Sept. 23, 2004: Merck says it learned this day that patients taking Vioxx in a study were twice as likely to suffer a heart attack or stroke as those on placebo. Sept. 30, 2004: Merck withdraws Vioxx from the U.S. and the more than 80 other countries in which it was marketed. February 2001: Merck tried to convince an FDA advisory committee that Vioxx be allowed to drop the digestive tract warning. But the committee couldn't ignore the cardiovascular findings. September 2001: The FDA ordered the company to send doctors a letter "to correct false or misleading impressions and information" about Vioxx's effect on the cardiovascular system. April 2002: the FDA followed its advisory panel's recommendation and required that Merck note a possible link to heart attacks and strokes on Vioxx's label. Merck was spending more than $100 million a year in direct-to-consumer advertising — another activity regulated by the FDA and a critical mechanism in building the 'blockbuster' status of a drug." Aug. 2004: the company fired off a press release refuting Graham's study. "Merck stands behind the efficacy, overall safety and cardiovascular safety of Vioxx," Sept. 2004: Merck confronted unfavorable findings that it could not explain away. Merck had sponsored a threeyear, 2,600-patient randomized trial to see whether Vioxx, like Celebrex, could claim that it protects against the recurrence of colon polyps, which can become cancerous.
- 26. Structure-based Computer-Aided Drug Design Drug Target Identification Target Validation Shorten development time to Lead Identification Reduce cost Past Successes 1. 2. 3. HIV protease inhibitor amprenavir (Agenerase) from Vertex & GSK (Kim et al. 1995) HIV: nelfinavir (Viracept) by Pfizer (& Agouron) (Greer et al. 1994) Influenza neuraminidase inhibitor zanamivir (Relenza) by GSK (Schindler 2000) Lead Identification Lead Optimization Pre-clinical & Clinical Development FDA Review
- 27. Science Community Laboratory Integrate science research in society Engage citizen scientists to participate in drug discovery Learn how structure-based drug design work while help fighting neglected diseases Join SciCoLab Now!