Drug discovery and development
-
Upload
karun-kumar -
Category
Education
-
view
412 -
download
3
description
Transcript of Drug discovery and development
Drug Discovery & Development
DR. KARUN KUMAR
JUNIOR RESIDENT – II
DEPT. OF PHARMACOLOGY
INTRODUCTIONCreation of a new drug involves :-
1. Drug discovery (Research) :- Identification of a
potential therapeutic target Selection of a single
molecule for testing in humans.
2. Drug development (Development) :- Preclinical
studies that support initial clinical trials through
approval of the drug by regulatory authorities.
3. Commercialization (Marketing) :- Product
Therapeutic application Sales
Drug discovery process
Process by which pharmaceutical, biotechnology,
academic & Govt. laboratories identify or screen
compounds to find potentially active therap. agents
Multidisciplinary nature of drug discovery
Drug discovery process
Stages of drug discovery
Target identification
• TargetMolecular recognition site to which drug binds
• Target may be• Protein molecule
• A receptor
• Enzyme
• Transport molecule
• Ion channel
• Tubulin
• Immunophilin
Therapeutic drug targets
Strategies to find new drug targets
1. Conventional strategies
a) Analysis of pathophysiology
b) Analysis of MOA of existing drugs
2. New strategies
a) Disease genes
b) Disease-modifying genes
Disease genes
• Abl-kinase Molecular target for Imatinib
• Secretase inhibitors Anti-Alzheimer drugs
• Most promising field Cancer therapies
• Identifying d/s gene Valuable pointers to drug
targets
Disease modifying genes
• Most important category
• Approaches used :-
1. Gene expression profiling
2. Gene knockout studies
Gene expression profiling
Principle Development of any disease phenotype
involves changes in gene expression in cells & tissues
involved
Method DNA microarray (‘gene chips’)
DNA microarray
Cluster analysis of gene expression experiment (Dendrogram)
Gene knockout screening
• Generation of transgenic ‘gene knockout’ strains of mice
• Examples
1. Inactiv. Of gene for ACE/ATR ↓ B.P.
2. Elim. Of gene encoding GABAA Irrit. In mice
3. Cathepsin K Osteoporosis
4. Melanocortin receptors Obesity
• Flatworm & zebrafish Speed up the process
Target validation• Experimental approach by which a “potential” drug
target can be tested & given further credibility
• Main approach• Pharmacological mGluR for pain
• Genetic • Antisense oligonuceotides
• RNA interference
• Transgenic animals
Phase D0 ‘Target identification’ (Research with intent of identifying a therapeutic target)
Phase D1 + D2 ‘Lead identification’ (Initial screening to discover chemical template for lead optimization).Tests include HTS,LTS(in vitro & in vivo)
Phase D3 ‘Lead optimization’ (Optimiz. & biol. Testing of compound).Outcome Best in potency & selectivity, as well as ADME properties
Phase D4 Completion of studies to allow 1st
application in man
Antisense Oligonucleotides
Stretches of RNA complementary to gene of interest
↓
Bind to cellular mRNA (Prevent its translation)
↓
Inhibits expression of specific genes
↓
Role of ‘specific genes’ in disease phenotype can be determined
RNA interference
Short lengths of dsRNA (siRNAs)
↓
Activate RISC (RNA induced silencing complex)
↓
Destroys corresponding fmRNA in the cell
↓
Gene silenced
Transgenic animals
Important definitions• Screening Testing many compounds in assays
relevant to the disease in question
• Hit A compound that passes such a ‘screen’
• Primary hit Compound giving positive result in a
screening assay
• Confirmed hit Compound is confirmed as
positive when assay is repeated
• Validated hit Confirmed hit that shows selective
activity
• Lead compound A new chemical entity that could be
developed in a new drug by optimizing beneficial
effects & minimizing S/E
Should comply with Lipinski’s rule of 5 :-
• Mol. Wt. < 500 Da cLogP < 5
• No. of H bond donors <5 Sum of no. of Ns & Os <10
• Drug candidate End result of lead optimization (A
compound judged suitable for precl. & cl. Develop.)
• Development compound Drug candidate that has
been accepted for further development
Screening1. Selectivity screening In vitro tests (If compound
is selective to merit further investigation)
2. Pharmacological profiling
• In vitro profiling Study on isolated tissues has been
the mainstay
• In vivo profiling Imaging technologies used
• MRI
• USG
• PET
• X-ray densitometry tomography
Animal models of disease
1. Acute physiological & pharmacological models
• Seizures induced by electrical stimulation of the
brain Epilepsy
• Histamine induced bronchoconstriction Asthma
• Eddy’s hot plate test Pain
• Injection of LPS & cytokines Septic shock
• Elevated plus maze test Anxiolysis
2. Chronic physiological or pharmacological models
• Use of Alloxan / Streptozotocin Type I DM
• Inducing brain ischemia Stroke
• Inducing coronary ischemia IHD
• “Kindling” Epilepsy
• Self-admin. of opiates/nicotine Drug dependence
• Cholesterol fed rabbits Hypercholesterolemia &
atherosclerosis
• Immunization with myelin basic protein MS
• Admin. Of MPTP Parkinson’s disease
• Transplant. Of malignant cells into immunodef.
Animals Progressive tumors (Cancer)
3. Genetic models
1. SHR
2. Seizure-prone dogs
3. Rats insensitive to ADH
4. Obese mice
1. CF
2. DMD
3. Leptin gene (mutated in ob/ob mice)
5. Alzheimer’s disease (APP)
Validity criteria (Willner 1984)
1. Face validity Accuracy with which model
reproduces the phenomena char. human d/s
2. Construct validity Extent to which etiology of
human disease is reflected in model
3. Predictive validity Extent to which
manipulation (drug t/t) is predictive of effects in
the human disorder
Identification of hits
1. Compound centered approach Traditional
Compound is identified
↓
Biological profile is explored
↓
If compd. displays desirable pharmacologic activity
↓
Compound is refined & developed further
2. Target centered approach
Putative drug target (receptor/enzyme) is identified
↓
Researchers search for compounds which interact with target (agonist/antagonist/modulator)
Search maybe:
1. Systematic Uses info. About structure of target as a starting point
2. Shotgun approach All compounds in a large library of substances are tested in a high-speed automated assay
High-throughput screening
• Simplest target centered approach
• Uses a target based assay & robotic automation to
test thousands of compounds in a few days time
• 2 critical aspects :-
1. A large library of compounds must be available
for screening
2. Assay (Simple/sophisticated) that leads to rapid
identification of true hits must be developed
Lead identification
Library is “run through” the assay (96/384-well plate)
↓
‘Primary hits’ are examined more closely
↓
Further screening is done (To eliminate false positives & false negatives)
↓
Leads are advanced in ‘lead optimization’ process
Lead optimization
Physical, chemical, biological & pharmacological
properties of promising lead molecules (that
appear to interact with the target in a desirable
way) are
Characterized & refined with the ultimate goal
Of selecting a single molecule to enter into
Clinical testing & formal drug development
Factors causing termination 1. Failure to demonstrate efficacy in a rigorous animal
model of human disease
2. Low bioavailability
3. Extensive/complex metabolism Potentially
dangerous reactive metabolites
4. Toxic effects in preliminary animal toxicology studies
5. In vitro evidence that molecule may damage DNA
6. Extremely difficult chemical synthesis
Drug development
• All activities involved in transforming a compound from
drug candidate Product approved for marketing by
appropriate regulatory authorities
• Falls in 3 main parts :-
1. Technical development Ensuring quality of end-
product
2. Investigative studies Safety & efficacy
3. Managerial functions Co-ordination,
documentation & liaison with regulatory authorities
Stages of drug developmentStage No. of yrs.
Synthesis/isolation of compound 1-2
Preclinical studies (Scr.,eval.,pk. & short term toxicity test. in animals)
2-4
Scrutiny & grant of permission for clinical trials 0.25-0.5
Pharmaceutical formulation, standardization ofchemical/biological/immuno-assay of the compound
0.5-1
Clinical studies: Phase I,II,III trials; Long term animal toxicity testing
3-10
Review & grant of marketing permission 0.5-2
Post-marketing surveillance No fixed duration
Phases of Precl. & Clinical Development
Phase Primary goal Dose Patient monitorNumber of
participants
Preclinical
Testing of drug in non-human subjects
UnrestrictedA graduate level researcher-Ph.D.
In vitro & in vivo animal models
Phase 0Oral bioavailability & half-life of drug
SubtherapeuticClinical researcher
10 people
Phase ITesting of drug on healthy volunteers (safety)
Subtherapeuticwith asc. Doses
Clinical researcher
20-100 people
Phase IITesting of drug on patients (efficacy & tolerability)
Therapeutic doseClinical researcher
100-300 people
Phase IIITesting of drug on pts.(confirm efficacy)
Therapeutic doseClinical research.& Physician
1000-2000 people
Phase IVPost-marketing surveillance (A/E, D-D I)
Therapeutic dose PhysicianAnyone seeking treatment
Phase V Translational research No dosing None All reported use
DeMets D., Friedman L. and Furberg C.(2010).Fundamentals of Clinical Trials. Springer 4th EditionGoodman and Gilman's The Pharmacological Basis of Therapeutics, (2011) 12th Edition
Preclinical development
Aim Meet all requirements before a new compound is
deemed ready to be tested for the 1st time in humans
Work falls into :-
1. Safety pharmacology Testing to check that drug
does not produce hazardous acute effects
2. Preliminary toxicological testing Eliminate
genotoxicity & determine maximum non-toxic dose of
drug (given daily for 28 days & tested in 2 species)
1. Pharmacokinetic testing (ADME studies) in laboratory animals
2. Chemical & pharmaceutical dev
3. Pharmacokinetic testing (ADME studies) in
laboratory animals
4. Chemical & pharmaceutical development
Assess feasibility of large scale synthesis &
purification
5. Assess stability of compound under various
conditions
6. Develop a formulation suitable for clinical studies
• Work done in accordance with GLP
IND
• New drug ready to be studied in humans a
Notice of Claimed Investigational Exemption for a
New Drug (IND) must be filed with the FDA
• It includes :-
1. Info. on the composition and source of the drug
2. Chemical and manufacturing information
• Includes :-
1. Info. on the composition and source of the drug
2. Chemical and manufacturing information
3. All data from animal studies
4. Proposed plans for clinical trials
5. Names and credentials of physicians who will
conduct the clinical trials
6. A compilation of the key data relevant to study of
the drug in humans that has been made available
to investigators and their institutional review
boards
Phase 0 (Microdosing study)
• Developed by FDA & EMA as “cost-cutting” tools
Very low doses (1/100th of estimated human dose or
max. of 100 µg total dose of candidate drug) are
administered to healthy volunteers
↓
Pharmacok worked out using AMS with radiolabelled
drug/LC-MS to measure ultra low drug levels
• Subpharm. dose No toxic / therapeutic eff. But
yields human pharmacokinetic information
• Elaborate animal studies & costly phase I human
trials could be avoided for candidate drugs
• Useful in more precise selection of doses for phase
I study
• They are promising & most regulatory authorities
are willing to allow & consider them
Phase I• Studies carried out Phase I clinics (All vital func. Are
measured & emergency/resuscitative facilities avail.)
• Clinical investigators Clinical pharmacologists
• Trial subjects Healthy volunteers (25-100)
• Objectives :-
1. Check for safety (Drug affects CV, hepatic or renal
functions adversely)
2. Check for tolerability (Drug produces unpleasant
symptoms like headache, nausea & vomiting)
1. 3.
2. 3.
3. Determine whether humans & animals show
significant pharmacokinetic differences
4. Determine a safe clinical dosage range in humans
(Common rule Begin with 1/5th or 1/10th of
MTD in animals & calc. it for 70 kg body wt.)
5. Determine the pharmacokinetics of the drug in
humans (Whether deficiency in drug effect is due
to lack of absorption / faster elimination)
6. Detect any predictable toxicity
Pharmacokinetic parameters
1. Cmax Peak drug &/or metabolite concentration
2. Tmax Time to peak drug &/or metabolite conc.
3. AUC0-∞ Area under conc.-time curve e.p. to inf.
4. AUC0-T AUC calc. to a specific time point T
5. T1/2 Time taken for level of drug to dec. by 1/2
6. VD Volume of distr.
7. CL Clearance
8. MRTMean residence time (Avg. time a drug molecule rem. In body after rapid i.m. injection)
Dosing & blood sampling schedule for phase I studies
Phase II
• Drug studied for 1st time in pts. with target disease
• Main purpose Gather evidence that drug has
effects suggested by preclinical trials
• End points :-
1. Definitive end point (Measures drug effect
directly Pain relief [analgesic])
2. Surrogate end point (Predictive of the definitive
end point Reduction in tumor size[anticancer])
Phase IIa
• “Proof of concept”/ “Proof of claims”
• Preliminary evidence of efficacy & safety
• Up to 200 pts. are studied Potential therapeutic
benefits & side effects are observed
• Establishment of dose range for more definitive
therapeutic trials in phase IIb
• Study design Single blind (Subject unaware if he
is taking placebo/positive control/new drug)
Phase IIb
• Dose-finding studies
• To confirm efficacy with statistical significance
• Determine the optimal dose & dosing regimen
• Large no. of patients used (200-400)
• Study design Double blind (3rd party holds the
code identifying each medication & this code is not
deciphered until all clinical data has been coll.)
Phase III• Large scale, multicentered randomized double blind
trials to further establish safety & efficacy
• Made using “Double-blind cross over” designs to
minimize errors
• NDA After completion of phase III trials,
sponsors file a “New Drug Application” with the
drug control authorities of that country
• NDS If documentation is acceptable & in
compliance, drug enters market with NDS
Double blind Cross Over DesignPt. grp. (randomized)
Week 1 Week 2 Week 3
I Standard drug
Placebo New drug
II Placebo New drug Standard drug
III New drug Standard drug
Placebo
Phase IV
• Surveillance phase during the post marketing
clinical use of the drug
• Used to discover
• Relatively rare side effects
• Previously unknown drug interaction
• Previously unknown therapeutic use detected by a
chance discovery
Phase V
• Aims to bridge the gap between basic and clinical research1
• Encompasses laboratory studies, clinical demands, public health and health management, policies and economics1
• Crucial in the evolution of contemporary biomedical science1
• It is used to signify the integration of a new clinical treatment into widespread public health practice2
1-Translational research: from benchside to bedside.N C Keramaris, N K Kanakaris, C Tzioupis, G Kontakis, P V GiannoudisAcademic Department of Trauma and Orthopaedics, Leeds Teaching Hospitals, University of Leeds, Great George Street, Leeds LS1 3EX, UK.Injury (Impact Factor: 1.93). 07/2008; 39(6):643-50. DOI: 10.1016/j.injury.2008.01.051 Source: PubMed
2-Margaret A. Rogers (June 2009). "What are the phases of intervention research?". American Speech-Language-Hearing Association. Retrieved Jan 8, 2013.
Preclinical safety assessment
1. Exploratory toxicology
• Rough estimate of toxicity (2 weeks)
• Provides an indication of main organs & physiological
systems involved
2. Regulatory toxicology (GLP)
• Reqd. by regulatory authorities/EC before compound
can be given for 1st time to humans
• Studies reqd. to support an application for marketing
approval
Timing of safety assessment
Genotoxicity
• Mutagenicity Chemical alteration of DNA
sufficient to cause abnormal gene expression in the
affected cell & its offspring
• Chromosomal damage
• End results Carcinogenesis & Teratogenicity
(detected by long-term animal studies)
Toxicokinetics
“Generation of pharmacokinetic data, either as an
integral component in the conduct of non-clinical
toxicity studies, or in specially designed supportive
studies, in order to assess systemic exposure” (ICH
Guideline S3A)
• Pharmacokinetics applied to toxicological studies
Toxicity measures
1. NTEL Largest dose in most sensitive species
2. LD50 Estimated dose reqd. to kill 50% expt. An.
3. NOAEL Largest dose causing neither tissue
toxicity nor undesirable physiological effects
4. MTD Largest dose tested causing no obvious
signs of ill-health
5. NOEL Threshold for producing any observed
pharmacological or toxic effect
THANK YOU