4. LEAD IDENTIFICATION
• Once a target & a testing system has been chosen, the next is
to find a “Lead Compound” which shows the desired
pharmaceutical activity.
•A lead compound is generally defined as a new chemical
entity that could potentially be developed into a new drug by
optimizing its beneficial effects and minimizing its side effects.
What is Lead ?
5. LEAD IDENTIFICATION
• Lead compounds are typically used as starting points in the drug
design to give new drug entities.
•Drug Design strategies can be used to improve the compound’s
pharmacodynamic and pharmacokinetic properties.
• The resulting compounds from drug design go through a series of
preclinical studies and become clinical candidates if the compounds
don’t exhibit adverse effects or toxicity during in vitro and in vivo studies.
• After going through marketing obstacles and clinical trials, compounds
that pass are released in the market as new deug entities.
What is Lead ? Cont’d
6. • New drug entities are generally monitored for safety after their
released on the market.
•Possible Source of Lead Compounds and Novel drugs include-
1. Endogenous Ligands-
i.e.- Substrate for enzyme and transportersor agonist for
receptors
Cont’d
LEAD IDENTIFICATION
What is Lead ?
N
H
NH2
HO
Serotonin
HO
HO
Ac
OH
Norepinephrine
8. Cont’d
LEAD IDENTIFICATION
What is Lead ?
3. Animals
Animal cartilage
Gelatin capsules or gummy vitamins chondroitin
Animal bones
Calcium
Animal blood
Heme iron
11. Properties of Lead
LEAD IDENTIFICATION
Pharmacodynamic Properties –
Efficacy,
Potency,
Selectivity
Physiochemical Properties –
Water solubility,
Chemical stability
Pharmacokinetic Properties –
Metabolic stability
Toxological aspects.
12. LEAD IDENTIFICATION
Chemical Optimization Potential –
Ease of chemical synthesis and
derivatization.
Patentability
Cont’dProperties of Lead
13. LEAD IDENTIFICATION
• During the early stages of drug discovery for a certain
disease, the underlying molecular mechanism behind the
disease are studied.
Organic compounds are identified which interact with
the target protein and modulate its activity by using
random (screening) or rational (design) approaches.
Cont’d
Properties of Lead
15. Cont’d
LEAD IDENTIFICATION
This method was followed before 1970.
All compounds including synthetic chemicals, natural
products of plant, marine and microbial origin from a given
series are tested.
Inspite of budgetary and manpower overuse, this method
may be used to discover drugs or leads that have unexpected
activities.
Antibiotics like, streptomycin and tetracyclines were found
out by this method.
Methods of Lead Identification
Random or Targeted Screening Method
16. LEAD IDENTIFICATION
Cont’d
Methods of Lead Identification
Non-Random Screening Method
After 1970 this method used.
It is a modified form of random screening which
was developed because of budgetary and manpower
restrictions.
In this method, only such compounds having
similar structural skeletons with that of lead, are
tested.
17. LEAD IDENTIFICATION
High-Throughput Screening
Test thousands of compounds against the target to
identify any that might be promising 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 discover
Methods of Lead Identification
Cont’d
18. LEAD IDENTIFICATION
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.
Cont’d
Methods of Lead Identification