e-content of drug discovery for M.pharm student

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Presenting by:
Mr. Purushotham K N
Asst. Professor
Dept. of Pharm. Chemistry
2021-2022
DRUG DISCOVERY

2. DRUG DISCOVERY
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3. CONTENTS
1.Introduction to drug discovery.
2.Stages of drug discovery.
3.Lead discovery.
(1).Random screening.
(2).Nonrandom (or Targeted or Focused)Screening.
(3).Drug metabolism studies.
(4).Clinical Observations.
(5). Rational approaches to lead discovery.
4.Discovery of drug without a lead.
(1).Penicillin.
(2).Librium.
5.Validation and Diversity of Drug target
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4. INTRODUCTION FOR DRUG
DISCOVERY
Drug discovery is the process by which new candidate medications are discovered.
Drug development is the process of bringing a new pharmaceutical drug to the market once
a lead compound has been identified through the process of drug discovery.
It involves a wide range of scientific disciplines including biology chemistry
pharmacology.
Drug discovery is a very expensive and time consuming process.
Estimates the average time required to bring a drug to the market range from 12-15
years at an average cost of $ 600-800 million.
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5. In recent years the methods used for drug development have undergone various
transformations.
In olden days drugs were discovered by trial and error method but now they are
developed by screening synthetic chemicals or extracts in a sequential manner.
Later radiology and binding assays were developed which gave information about the
interaction of compounds with receptors and helped in selecting the best suited
compound.
In the past most drugs have been discovered either by identifying the active ingredient
from traditional remedies or by serendipitous discovery.
But now we know diseases are controlled at molecular and physiological level. Also
shape of an molecule at atomic level is well understood.
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6. Drug development and discovery phases:
Stages:
• Conceptual
• Development
• Steps :
• Synthesis/ Isolation of compounds(1-2years)
• Pre-clinical studies (2 to 4 years)
oScreening
o Evaluation
o Pharmacokinetic
o Short term toxicity studies.
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•Grant of permission for clinical trials. (3-6 months).
•Pharmaceutical formulation- Standardization of chemical, biological,
Immunological compounds (1year).
•Clinical studies
•Review and grant of marketing (0.5 to 2 years)
•Post marketing surveillance.

8. Steps and techniques involved in
Discovery of a new drug
1) Identification and elucidation of a specific target on which the
new chemical entities or the drug may act.
2) Discovery of new chemical entity by,
a)Modification of known chemical moiety.
b) Random screening of biological activity.
c) Rational approach for drug designing based on biochemical
aspects, receptor mechanism and by chemical structure.
d) Using recombinant DNA technology to produce large peptides
and proteins.
e) Combining known drugs to produce a new molecule having
additive or synergistic effects.
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9. 3) Testing of the lead compound on animal to understand the
pharmacokinetic parameters, safety levels, dose range etc of the
new lead entity.
4) Testing of the new compound in humans to assess the safety,
efficacy, side effects, drug interactions in healthy volunteers and
in patients.
5) Studies about the additional drug interaction, side effects etc.
After the release of the new entity into the market as new drug.
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11. LEAD DISCOVERY
Penicillin V and Librium are, indeed two important drugs that
were discovered without a lead . However, once they were
identified, they then became lead compounds for second-
generation analogs.
A myriad of penicillin-derived antibacterial have been
synthesized as a result of the structure elucidation of the earliest
penicillin's.
Diazepam was synthesized at Roche even before Librium was
introduced on to the market, this drug was derived from the lead
compound Librium and is almost 10 times more potent than the
lead.
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12. Identification of the lead
compound/lead discovery
In general drugs are not discovered but discovery of lead
compound is done first. The lead is a prototype compound that
has a number of attractive characteristics, such that desired
biological/ pharmacological activities on the other hand they
may have undesirable activity like toxicity , pharmacodynamic
and pharmacokinetic problems.
Then the structure of lead compound is modified in such a way
so that to reduce the undesired activity of the compound and to
improve the biological activity.
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13. At this stage of the compound is known as drug candidate.
Now this drug candidate is ready for the study of several
biological and pharmacological parameters.
If results are satisfactory then it becomes a clinical drug which
is ready for the clinical trials.

14. The initial difficulty arises in the discovery of the lead
compound.
Several approaches can be taken to identify a lead.
The first requirement for all of the approaches is to have a
means to assay compounds for a particular biological activity,
so that researchers can tell when a compound is active.
 A bioassay (or screen ) is a mean a of determining in a
biological system, relative to a control compound. If a
compound as desired activity & it so what the relative potency
of the compound.
 Activity is the particular biological or pharmacological effect.
Potency is the strength of that effect.
Some Screenings are in vitro tests, for example the inhibition
of an enzyme or antagonism of receptor.
 In vivo tests, for example- the ability of the compound to
prevent and induced seizure in a mouse.
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15. • The invitro tests are quicker less expensive.
• Currently, High-through output screens (HTS) very rapid & sensitive in vitro
screens initially developed about 1989-1991, that now can be carried out
robotically in 1536 or 3456 well titer plates on small (sub microgram) amounts of
compound (dissolved in sub microliter volumes)or becoming universally used.
• With this Ultra-high-throughput screening. approaches, it is possible to screen
1,00,000 compounds in a day.
• As well as combinatorial chemistry can supply huge numbers of compounds in a
short period of time.
• Currently, HTS appear to have resulted in increase in the number of hts, but this
may be because more lipophilic compounds, which may have more drug-like
properties, can be tested by dissolving them in dimethylsulfoxide (DMSO) rather
than in water.
• An exiting approach for screening compounds that might interact with the
enzyme in a metabolic pathway was demonstrated by Wong, pompliano &
coworkers for the discovery of lead compounds that blocks bacterial cell wall
synthesis.
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16. Several approaches made to discover a lead compound:
a)Random screening
b)Non- Random(Targeted/focussed) screening
c)Drug metabolism studies
d)Clinical observation
e)Rational approach to lead discovery.
1)Random screening :
In case the drug is not known and the compound with desired
activity is not known the random screening is done.
All compounds are tested in the bioassay without regard to
their structures.
This is the choice of technique when nothing is known about
receptor target.
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17. The best example: War on cancer (Streptomycin and Tetracycline
has to be found out).These 2 antibiotics were found when
random screening of several soil sample were being done to get
antibiotics. However this method is little costly and time taking.
2) Non-random/Targeted/ focussed screening:
 It is a narrow approach in this technique the compound
containing functional groups than lead may be tested
selectively. Now used for the cancerous drugs.
 It is a modified form of random screening which was
developed because of budgetary and man power restrictions.
 In this method, only such compounds having similar structural
skeletons to that of lead are tested.
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18. 3)Drug metabolism studies:
During drug metabolism studies, metabolites that are isolated
are screened to determine if the activity observed is derived
from the drug candidate or from a metabolite.
Eg: The anti-inflammatory drug Sulindac is not the active agent.
The metabolic reduction product is responsible for the activity.
Sulindac
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19. 4)Clinical observations:
Many times the drug possesses more than one pharmacological activities the
main activity is called as therapeutic effect while rest of the actions is known
as side effects of the drug.
This compound ,then can be used as a lead for secondary activity.
Ex: In 1947 an antihistamine, dimenhydrinate (Dramamine) was tested at the
allergic clinic at John Hopkins university and was found also to be effective
in reliving patient who suffered from car sickness and air sickness.
Then it is most widely used in the treatment of all forms of motion sickness.
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20. 5) Rational Approaches to Lead Discovery:
 The lead is just found by screening techniques, as a by-product
of drug metabolism studies, or from clinical investigations.
Rational approaches to drug design now have become the
major routes to lead discovery.
 The first step is to identify the cause for the disease state.
Many diseases, or at least the symptoms of diseases, arise from
an imbalance (either excess or deficiency) of particular
chemicals in the body, from the invasion of a foreign organism,
or from aberrant cell growth.
 The effects of the imbalance can be corrected by antagonism
or agonism of a receptor or by inhibition of a particular
enzyme, foreign organism enzyme inhibition or interference
with DNA biosynthesis or function are important approaches to
treat diseases arising from microorganisms and aberrant cell
growth.
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21.  Once the relevant biochemical system is identified, initial lead compounds
then become the natural receptor ligands or enzyme substrates.
 For example, lead compounds for the contraceptives (+)-norgestrel and 17α-
ethynylestradiol (Activella) were the steroidal hormones.
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Norgestrel
17α- ethynylestradiol (Activella)

22.  The rational approaches are directed at lead discovery.
It is not possible, with much accuracy, to foretell toxicity and
side effects, anticipate transport characteristics, or predict the
metabolic fate of a drug.
Once a lead is identified, its structure can be modified until an
effective drug is obtained.
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23. Drug discovery without a lead
(1).Penicillins:
In 1928 Alexander Fleming noticed a green mold growing in a
culture of Staphylococcusaureus, and where the two had
converged, the bacteria were lysed. This led to the discovery of
penicillin, which was produced by the mold.
 Joseph Lister had treated a wounded patient with Penicillium,
the organism later found to be the producer of penicillin.
 The phenomenon initially observed by Fleming.
The culture dish inoculated by Fleming must have become
accidentally and simultaneously contaminated with the mold
spore.
 Instead of placing the dish in the refrigerator or incubator when
he went on vacation as is normally done, Fleming inadvertently
left it on his lab bench. When he returned, he noticed the lysed
bacteria. 23

24. Fleming suggested that penicillin could be useful as a topical
antiseptic, he was not successful in producing penicillin in a form
suitable to treat infections.
Nothing more was done until SIR HOWARD FLOREY at
Oxford University reinvestigated the possibility of producing
penicillin in a useful form.
In 1940 he succeeded in producing penicillin that could be
administered topically and systemically, but the full extent of the
value of penicillin was not revealed until the late 1940.
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25. The original mold was Penicillium notatum , a strain that gave a
relatively low yield of Penicillin.
 It was replaced by Penicillium chysogenum , which had been
cultured from a mold growing on a grapefruit in a market in
Peoria, Illinois.
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Penicillin G

26. 2).Librium
The first benzodiazepine tranquilizer drug, chlordiazepoxide HCI
[7-chloro-2-(methylamino-5-phenyl-3 H-1,4-benzodiazepine 4-
oxide] (Librium) was discovered by Dr. Leo Sternbach at Roche
was involved in a program to synthesize a new class of
tranquilizer drugs. He originally set out to prepare a series of
benzheptoxdiazines.
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Chlordiazepoxide HCl

27. DRUG TARGET
These are the specific sites where drug gets bind alter or enhance those specific
target site and shows its required therapeutic action.
Drug Target Types/ Diversity of Drug Targets
➤ These are cellular or molecular structures which are responsible for pathological
activity.
➤ These are pretentious in nature
These are following types-
1) Receptor 45%
2) Enzymes 28%
3) Nucleic Acid 2%
4) Ion Channel 5%
5) Hormones 1% 27

28. Target Identification:
Identification of the possible therapeutic target and its role in the disease. One of the most
important step in developing anew drug. It is the foremost step for improving efficacy of a new
medical candidate.
Target Identification Strategies
These are of two types:
a) Target De convolution
b) Target Discovery
1.Target De-convolution-:
➤ It is a phenotypic approach to drug discovery falls in the target de-convolution.
It can be achieved by some mentioned methods-
a) By affinity chromatography
b) Expression cloning protein microarray
c) Reverse transfected cell microarray
d) Biochemical suppression
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29. Target discovery
The target based drug discovery, biological target are already established before the
lead discovery started.
The most common approach to drug discovery was initial identification of an
appropriate biological targets.
Techniques for target identification:
1.Cellular and genetic targets
2.Genomics
3.Proteomics
4.bioinformatics
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30. Cellular and genetic targets:
• Involves identification of the function of a potential therapeutic drug target & its role
in the disease process.
• For small molecular drug this step in the process involves identification of the target
receptors or enzymes whereas for some biological approaches the focus is at the gene
or transcription level.
• Drugs usually act on either cellular or genetic chemicals in the body known as target
which are believed to be associated with disease.
Genomics:
• Drug estimate that the number of genes impacted diseases both those due to defects in
single genes and dose arising from combinations of genes is about 1000.
• Based on 5/10 linked proteins per gene be proposes that the number of potential
drug targets may be lie between 5000 &1000.
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31. Proteomics:
• It is the study of the proteome the complete set of proteins
produced by a species using the technologies of large-scale
protein separation & identification.
• It is becoming increasing evident that the complexity of
biological systems.
• It is also act the protein level that diseases process become
manifest and at which most drug acts.
• It is the systematic high through output separation and
characterization of protein with in biological system.
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32. Bioinformatics :
• It is a branch of molecular biology that involves extensive analysis
of biological data using computers for the purpose of enhancing
biological research.
• It plays a role in various stages of the drug discovery process
including-
• Target identification
• Computer screening of chemical compounds
• Pharmacogenomics
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33. TARGET VALIDATION
• It is the process of demonstrating the functional role of
identification target in diseases.
• Ex: protein of a small molecule is verified.
• Target validation can include knockdown or over
expression of the presumed target.
• Tools for target validation
• Si RNA
• Antisense Oligonucleotides
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34. SI RNA-A :
• Small (or short) interfering RNA (siRNA) is the commonly used for
RNA interference (RNAi) tool for inducing short-term silencing of
protein coding genes.
• It is a double stranded RNA molecule which interferes with the
expression of specific genes by degrading mRNA after transcription
& preventing translation. Si is double stranded RNA .
• It consist of 2 RNA stands, an antisense strand and a sense strand ,
which form a duplex.
• 20-24 bp length.
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35. ANTISENSE OLIGONUCLEOTIDE:
• Antisense technology prevent the synthesis of specific protein. AS-
ONS;15-20 nucleotides which are complementary to their target mRNA.
• When these AS-ON combined with target mRNA, a DNA/RNA hybrid
form which degraded by the enzyme RNase H.
• RNase H is a non specific endonuclease which catalyze cleavage of
RNA.
• RNase H has ribonuclease activity cleaves the 3'-O-P bond of RNA in a
DNA/RNA duplex.
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36. ROLE OF TRANSGENIC ANIMALS:
• Transgenic animals are animals that have a foreign gene deliberately
inserted into their genome.
Methods to insert transgene :
• Microinjection
• Embryonic stem cell
• Retroviral vector method
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37. Working example:-
Target identification
 Suppose we identify disease ie. Alzheimer
 Translated this disease model into animals
 Animal model of AD(Streptozocin used to induce beta amyloid protein in
hippocampus)
 Target identification by proteomics and genomics
 Overexpression of APP(Amyloid precursor protein) protein is responsible for
disease.
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38. Target Validation :-
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39. REFERENCE:
1. TEXTBOOK OF ORGANIC CHEMISTRY OF THE DRUG DESIGN
AND DRUG ACTION BY RICHARD.B.SILVERMAN 2ND
EDITION (8-16).
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