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The drug development process

The drug development process. From discovery of drug candidate to approval to market Overall procedure for drug development 1. Discovery of drug candidate based on underlying mechanisms of diseases 2. Initial characterization in terms of pharmacodynamics , especially

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The drug development process

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  1. The drug development process From discovery of drug candidate to approval to market Overall procedure for drug development 1. Discovery of drug candidate based on underlying mechanisms of diseases 2. Initial characterization in terms of pharmacodynamics, especially effectiveness for a targeted disease 3. Preclinical trials (in animals) : to prove efficacy and to get approval from a regulatory authority to commence clinical trials in humans (~ 3 years) 4. Submission of preclinical data to the regulatory authority Approval for clinical trials in humans by regulatory authority

  2. 5. Clinical trials (phase I, II, III) (more than 5 years) 6. Submission of clinical trials data and manufacturing process to the regulatory authority : Manufacturing process should be also approved for the production 7. Regulatory authority review the data and information, and grant manufacturing and marketing licenses : cGMP (currently good manufacturing practice) 8. New drug goes to the market 9. Post-marketing surveillance : to investigate any drug-induced side effects and to inspect the manufacturing facility

  3. Drug Discovery Process • Advances in biological/medical sciences : understanding the underlying molecular mechanisms of diseases  provide a potential strategy to cure/control the target diseases • Knowledge-based discovery of drug candidate Ex) : insulin, human growth hormone, EPO, Cerezyme for Gaucher’s disease : essentially caused by deficiency or defect of a single regulatory molecule • Multi-factorial and more complex : cancer, inflammation, autoimmune disease cf) Cytokines like interferons and interleukins stimulate the immune response and/or regulate inflammation, and also cause diseases

  4. Why clinical trials are required ? • Understanding of the actions of various regulatory proteins, or the progression of a specific disease does not automatically translate into pinpointing an effective treatment strategy • Physiological responses induced by the potential biopharmaceutical in vitro (or in animal models)  may not accurately predicts the physiological responses when administered in humans Ex) Many of the most promising therapeutic agents (e.g. virtually all the cytokines) display multiple activities on different cell populations  Difficult to predict the overall effect of the administered drug on the whole body  Require clinical trials to test efficacy and side effect

  5. Medical use of a biopharmaceutical is banned by relatively toxic side effects  Need clinical trials in humans • TNF-α (Tumor Necrosis Factor-α , 185 aa) - Cytokines produced by macrophages, and by a broad variety of other cell types including lymphoid cells, mast cells, endothelial cells, - First noted because of its cytotoxic effects on some cancer cell types in vitro - Clinical trials to asses the therapeutic application : Disappointing due to toxic side effects and moderate efficacy

  6. Discovery of a new aspect of TNF-α-related signaling • Currently known to causes apoptotic cell death, cellular proliferation, differentiation, inflammation, and viral replication promoting various aspects of immunity and inflammation • High level of TNF-α induces the inflammatory response, which in turn causes many of the clinical problems associated with autoimmune disorders such as rheumatoid arthritis Reduction in the level of TNF-α  new therapeutics to treat autoimmune disease like rheumatoid arthritis  Development of a newtherapeutic protein

  7. Neutralizing the biological effects of TNF-α in situations where over-expression of TNF-α causes negative clinical effects • Soluble forms of TNF receptor : trapping TNF-α in blood  reduce the severity of many diseases caused by high level of TNF-α • Enbrel : TNF-α blocker approved for medical use - Developed by Immunex and approved by FDA in 1998 - Amgen acquired Immunex in 2002 - Engineered hybrid protein consisting of the extracellular domain of the TNF-α-R75 fused directly to the Fc region of human IgG - Dimeric soluble protein Fc TNF-Receptor

  8. Most widely used for treatment of disorders caused by excess TNF-α - Rheumatoid arthritis, psoriasis, ankylosing spondylitis, psoriatic arthritis, and juvenile rheumatoid arthritis. - Administered as a twice weekly via subcutaneous injection (25 mg in WFI) - Annual sale : $ 4.5 billion in 2010 • Competitors : Humira, Remicade(Monoclonal Ab) • Development of new version with greater potency • Protein engineering : structure-based rational design - increased affinity /specificity - stability in blood

  9. Impact of genomics and proteomics on Biology and drug discovery • Genomics : Systemic study of the entire genome of an organism • To sequence the entire genome and to physically map the genome arrangement (assign exact position of the genes /non-coding regions in genome) • Before 1990s, the sequencing and study at a single gene level: laborious and time-consuming task • Development of high throughput sequencing technologies and highly automated hardware system  Faster (in excess of 1 kb/h), cheaper, and more accurate sequencing  Sequencing a human whole genome: ~ $ 10,000

  10. Genome sequences of more than 2,000 organisms • Genomes of various animals and plants :, mouse, rat, sheep, pig, monkey, dog, chicken, wheat, barley, Arabidopsis • Human genome project - Started in 1990 - Completed in 2003 : ~ 3.2 giga bases(Gb), 1,000 times larger than a typical bacterial genome - Less than 1/3 of the genome is transcribed into RNA - Only 5 % of the RNA encodes polypeptides  Number of polypeptide-encoding genes :~ 30,000

  11. Significance of genome data in drug discovery • and development • Provide full sequence information of every protein: - Identification of undiscovered proteins - Discovery of new drug targets  Current drugs on the market target one of at most 500 proteins: Major targets are proteins • Sequence data of many human pathogens (e.g., Helicobacter pylori, Mycobacterium tuberculosis, Vibrio cholerae)  Provide drug targets against pathogens (e.g., gene products essential for pathogen viability or infectivity)  Offer some clues in underlying mechanism of diseases New methods/tools inBiology and Medical sciences

  12. The ability to interrogate the human genome has altered our approach to studying complex diseases and development of therapies. • The emergence of genome-wide analysis tools has opened the door to genomic biomarker discovery, validation, and pharmacogenomics. • Leading clinical researchers: • Actively studying genomic approaches to understanding disease, and learn how these can be translated into medical and clinical settings.  Translational research

  13. Functional genomics • Issues • Biological function of between one-third and half of sequenced gene products remains unknown • Assessment of biological functions of the sequenced genes  Crucial to understanding the relationship between genotype and phenotype as well as direct identification of drug targets • Shift in the focus of genome research • Elucidation of biological function of genes

  14. In the narrow sense : Biological function/activity of the isolated gene product • In broader meaning : - Where in the cell the product acts, and what other cellular elements it interacts with  Interactome - How such interactions contributes to the overall physiology of the organism  Systems Biology • General definition of functional genomics : • Determining the function of proteins deduced from genome sequence is a central goal in the post genome era • Elucidating the biological function of gene products

  15. Assignment of function of gene products (Proteins) • Biochemical (molecular) function • Assignment based on sequence homology • Based on structure • Based on ligand-binding specificity • Based on cellular process • Based on biological process • Based on proteomics or high-throughput functional genomics

  16. Conventional approaches • Clone and express a gene to produce the protein encoded by the gene • Try to purify the protein to homogeneity - Size, charge, hydro-phobicity • Develop an assay for its function • Identify the activity/function - Grow crystals, solve structure • Time-consuming and laborious for huge numbers of genes

  17. Assignment of function to the sequenced gene products • Sequence/structure data comparison in a high through manner • Sequence homology study • Computer-based sequence comparison between a gene of unknown function and genes whose functions (or gene product function) have been assigned • High homology : high similarity in function • Assigning a putative function to 40 - 60 % of all new gene sequences

  18. Phylogenetic profiling • Study of evolutionary relationships among various biological species or other entities based on similarities and differences in their physical and/or genetic characteristics • Closely related species should be expected to have very similar sets of genes • Proteins that function in the same cellular context frequently have similar phylogenetic profiles :During evolution, all such functionally linked proteins tend to be either preserved or eliminated in a new species: Proteins with similar profiles are likely to belong to a common group of functionally linked proteins.

  19. Establishing a pattern of presence or absence of a particular gene coding for a protein of unknown function across a range of different organisms whose genomes have been sequences: • Discovery of previously unknown enzymes in metabolic pathways, transcription factors that bind to conserved regulatory sites, and explanations for roles of certain mutations in human disease, plant specific gene functions

  20. Rosetta Stone Approach • Hypothesis: Some pairs of interacting proteins are encoded by two genes in some genome or by fused genes in other genomes • Two separate polypeptides (X and Y) found in one organism may occur in a different organism as a single fused protein(XY) • Function of the unknown gene in one organism can be deduced from the function of “fused genes” in different organism

  21. Gyrase: Relieves strain while double-stranded DNA is being unwound by helicase • Type II topoisomerase (heterodimer) : catalyzes the introduction of negative supercoils in DNA in the presence of ATP. • Gyraseholoenzyme (bactrial topoisomerase II) : heterotetramer made up of 2 gyrA (97 kDa) subunits and 2 gyrB (90 kDa) subunits.

  22. Knock-out animal study • Generation and study of mice in which a specific gene has been deleted • Phenotype observation • Structural genomics approach - Resolution of 3-D structure of proteins

  23. Pathway maps • Linked set of biochemical reactions • Questions: • Is the extrapolation between species valid? • Have orthologs been identified accurately? • Orthologs: Genes in different species that evolved from a common ancestral gene by speciation, retaining the same function in the course of evolution. Identification of orthologs is critical for reliable prediction of gene function in newly sequenced genomes. • Homologs : A gene related to a second gene by descent from a common ancestral DNA sequence.

  24. DNA microarray technology : DNA chip • Sequence data provide a mapand possibility of assigning the putative functions of the genes in genome based on sequence comparisons • Information regarding which genes are expressed and functionally active at any given circumstance and time • Provide clues as to the biological function of the corresponding genes • Offer an approach to search for disease biomarkers and drug targets ex) If a particular mRNA is only produced by a cancer cell compared to a normal cell, the mRNA (or its polypeptide product) may be a good target for a new anti-cancer drug,biomarker for diagnosis or a target for basic research.

  25. Microarrays: tool for gene expression profiling • DNA microarray (gene chip) : • Comparison of mRNA expression levels between sample (cancer cell) and reference (normal cell) in high throughput way : mRNA expression profiling - cDNA chip : mRNA expression profiling - Oligo chip ( ~ 50 mers) : mRNA expression profiling - SNPs (Single Nucleotide Polymorphisms) - Complementary probes are designed from gene sequence

  26. Solid support (such as a membrane or glass microscope • slide) on which DNA of known sequence is deposited in • a grid-like array • - 250,000 different short oligonucleotide probes in cm2 • - 10,000 full-length cDNA in cm2 • General procedure for mRNA expression profiling • mRNA is isolated from matched samples of interest. • mRNA is typically converted to cDNA, labeled with • fluorescence dyes(Cy3, Cy5) or radioactivity • Hybridization with the complementary probes • Analysis and comparison of expression levels of mRNAs • between sample and reference •  mRNA expression profiling Page 173

  27. Microarrays: array surface Southern et al. (1999) Nature Genetics, microarray supplement

  28. Questions addressed using microarrays • Wild-type versus mutant cells • Cultured cells +/- drug • Physiological states (hibernation, cell polarity formation) • Normal versus disease tissues (cancer, autism)

  29. Organisms represented on microarrays • Metazoans: human, mouse, rat, worm, insect • Fungi: yeast • Plants: Arabidopsis • Other organisms: e.g. bacteria, viruses

  30. DNA Microarray Methodology - Flash Animation www.bio.davidson.edu/Courses/genomics/chip/chip.html

  31. mRNA expression profiling using cDNAmicroarray cDNA clones sample reference exitation Laser2 Laser1 mRNA Reverse transcriptase emission PCR amplification Purification cy3 cy5 Robotic printing Computer analysis Hybridize targets to microarray Green : up-regulated in sample Red : up-regulated inn reference Yellow : equally expressed Cy3 : ex 550 nm / em 570 Cy5 : ex 649 nm / em 670

  32. Commercially available DNA chip

  33. Overall procedure experimental design Sample acquisition purify RNA, label Data acquisition hybridize, wash, image Data analysis data storage Data confirmation Biological insight

  34. Stage 1: Experimental design - Biological samples: technical and biological replicates - RNA extraction, conversion, labeling, hybridization - Arrangement of array elements on a surface

  35. PCR (Polymerase Chain Reaction) Developed in 1983 by Kary Mullis Nobel prize in Chemistry in 1993 Melting at 95 oC Annealing at 55 oC Elongation at 72 oC Thermostable DNA polymerase from thermophilic bacterium

  36. Stage 2: RNA and probe preparation • Confirm purity by running agarose gel • Measure the absorbance at 260 and 280 nm and • calculate the ratio to confirm purity and quantity • Synthesis of cDNA and labeling using reverse • transcriptase

  37. Stage 3: Hybridization to DNA arrays • Mixing of equal amounts of cDNA from a reference • and a sample • Load the solution to DNA microarray • Incubation for hybridization followed by washing and • drying

  38. Stage 4: Image analysis • Gene expression levels are quantified • Fluorescence intensities are measured with a scanner, • or radioactivity with a phosphorimage analyzer

  39. Example of an approximately 37,500 probe spotted oligo microarray with enlarged inset to show detail

  40. Fig. 6.20 Page 181

  41. Stage 5: Microarray data analysis • How can arrays be compared? • Which genes are regulated? • Are differences authentic? • What are the criteria for statistical significance? • Are there meaningful patterns in the data • (such as groups)?

  42. Stage 6: Biological confirmation • Microarray experiments can be thought of as • “hypothesis-generating” experiments : Clues • Differential up- or down-regulation of specific • genes can be measured using independent assays : • - Northern blots • - polymerase chain reaction (RT-PCR) • - in situ hybridization

  43. Use of DNA microarray Comparison of gene expression levels • Different tissues • Different environmental conditions • (drug treated) • Normal and cancer cells

  44. Outcome of data analysis • Search for biopharmaceuticals/drug targets • Search for a specific gene(s) responsible for biological phenomenon • Identification of potential biomarkers for diagnosis • SNP detection But need validation

  45. Search for a gene responsible for a disease Rett syndrome is a childhood neuro-developmental disorder characterized by normal early development followed by loss of purposeful use of the hands, distinctive hand movements, slowed brain and head growth, gait abnormalities, seizures, and mental retardation. It affects females almost exclusively. Control A-B Crystallin is over-expressed in Rett Syndrome Rett

  46. mRNA Expression Profiling in lung cancer patient and normal person using DNA Microarray Choi et al., J ThoracOncol(2006), 1, 622-628

  47. Expression profiles under different nutritional conditions cDNAmicroarray chip containing 2,500 genes from yeast Expression profiling of genes from Yeast grown at 2% galactose and glucose Green: up-regulation in yeast grown at galactose Red : up-regulation in yeast grown at glucose Yellow: equally expressed Lashkariet al., PNAS (1997)

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