A presentation outlining the various processes a chemical compound undergoes (thorough & rigorous screening procedures) before it is finally introduced into the drug market

1. Drug Discovery & Development
DR. KARUN KUMAR
JUNIOR RESIDENT – II
DEPT. OF PHARMACOLOGY

2. INTRODUCTION
Creation 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

4. Drug discovery process
Process by which pharmaceutical, biotechnology,
academic & Govt. laboratories identify or screen
compounds to find potentially active therap. agents

5. Multidisciplinary nature of drug
discovery

6. Drug discovery process

7. Stages of
drug
discovery

8. Target identification
• Target  Molecular recognition site to which drug
binds
• Target may be
• Protein molecule
• A receptor
• Enzyme
• Transport molecule
• Ion channel
• Tubulin
• Immunophilin

9. Therapeutic drug targets

10. 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

11. 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

12. Disease modifying genes
• Most important category
• Approaches used :-
1. Gene expression profiling
2. Gene knockout studies

13. Gene expression profiling
Principle  Development of any disease phenotype
involves changes in gene expression in cells & tissues
involved
Method  DNA microarray (‘gene chips’)

14. DNA microarray

15. Cluster
analysis of
gene
expression
experiment
(Dendrogram)

16. 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

17. 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

18. 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

19. 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

20. RNA interference
Short lengths of dsRNA (siRNAs)
↓
Activate RISC (RNA induced silencing complex)
↓
Destroys corresponding fmRNA in the cell
↓
Gene silenced

21. Transgenic animals

22. 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

23. • 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

24. Screening
1. 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

25. 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

26. 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

27. • 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)

28. 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)

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. Drug development

37. • 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

38. Stages of drug development
Stage 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 of
chemical/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

39. Phases of Precl. & Clinical Development
Phase Primary goal Dose Patient monitor
Number of
participants
Preclinic
al
Testing of drug in non-
human subjects
Unrestricted
A graduate level
researcher-Ph.D.
In vitro & in vivo
animal models
Phase 0
Oral bioavailability & half-
life of drug
Subtherapeutic
Clinical
researcher
10 people
Phase I
Testing of drug on healthy
volunteers (safety)
Subtherapeutic
with asc. Doses
Clinical
researcher
20-100 people
Phase II
Testing of drug on patients
(efficacy & tolerability)
Therapeutic dose
Clinical
researcher
100-300 people
Phase III
Testing of drug on pts.
(confirm efficacy)
Therapeutic dose
Clinical research.
& Physician
1000-2000
people
Phase IV
Post-marketing
surveillance (A/E, D-D I)
Therapeutic dose Physician
Anyone 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 Edition
Goodman and Gilman's The Pharmacological Basis of Therapeutics, (2011) 12th Edition

40. 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)

41. 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

42. 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

43. • 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

44. 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

45. • 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

46. 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)

47. 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

48. 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. MRT  Mean residence time (Avg. time a drug
molecule rem. In body after rapid i.m. injection)

49. Dosing & blood sampling schedule
for phase I studies

50. 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])

51. 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)

52. 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.)

53. 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

54. Double blind Cross Over Design
Pt. grp.
(randomi
zed)
Week 1 Week 2 Week 3
I Standard
drug
Placebo New drug
II Placebo New drug Standard
drug
III New drug Standard
drug
Placebo

55. 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

56. 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 Giannoudis
Academic 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.

57. 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

58. Timing of safety assessment

59. 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)

60. 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

61. 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

62. THANK YOU