Drug Discovery and Development PHG 311 · Drug Discovery and Development PHG 311. To Learn the...
Transcript of Drug Discovery and Development PHG 311 · Drug Discovery and Development PHG 311. To Learn the...
Prof. Dr. Amani S. Awaad
Professor of PharmacognosyPharmacognosy Department,
College of Pharmacy Salman Bin Abdulaziz
University,
Al-Kharj. KSA.
Email: [email protected]
Drug Discovery and
Development
PHG 311
To Learn the processes involved in
drug discovery and development?
To understand The Drug Discovery
Process ?
To know what is Choosing a Disease
to know proses of Choosing a drug
tounderstand Finding a lead
compound
Overview of:
Drug Discovery Process.
Target identification and
selection
For R&D
The Drug Discovery Process
• Drug discovery is an expensive and time-
consuming.
• Retrospective analyses of the pharmaceutical
industry during the 1990s estimate that each
new drug in the market takes an average 14
years to develop, costing in the region of
$800 million
• In addition one in nine compounds that
enters clinical trials makes it to the
market.
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• For a drug to work, it has to interact with
a disease target (e.g. receptor, enzyme or
nucleic acid) in our body and intervene in
its way ward functions.
• An analogy is the lock and key
comparison, with the lock being the
disease target and the key representing
the drug. The correct key has to be found
to turn the lock and open the door to treat
the disease.
The Drug Discovery Process
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Drug discovery: Finding a leadWhen a pharmaceutical company or university research group initiates a new medicinal
chemistry project through to the identification of a lead compound, they will consider the
following steps in order
1-Choosing a Disease
-Disease Mechanism
III-Identifying a bioassayChoice of bioassay - In vitro test -In vivo testsTest validity -High-through screeningScreening by NMR -Affinity screeningSurface Plasmon resonance -Scintillation proximity assay
II-Choosing a drug target
Drug targets
Discovering drug targets
Target specificity and selectivity between species
Target specificity and selectivity within the body
Targeting drugs to specific organs and tissues
Pitfalls
Drug discovery: Finding a leadIV-Finding a lead compound
– Screening of natural products
– Medical folklore
– Screening synthetic compound “
libraries”
– Existing drugs
– Starting from natural ligand or
modulator
– Combinatorial synthesis
– Computer aided design
– Serendipity and prepared mind
– Computerized searching of structural
databases
– Designing lead compounds by NMR
VI-Structural determinationV-Isolation and purification VII-Herbal medicine
Most research is carried out on diseases whichafflict “first world” countries: (e.g. cancer,cardiovascular diseases, depression, diabetes, flu,migraine, obesity).
1-Choosing a Disease
The Drug Discovery Process cont..
• Pharmaceutical companies tend to concentrate
on developing drugs for diseases which are
prevalent in developed countries, and aim to
produce compounds with better properties than
existing drugs.
• Pharmaceutical companies have to consider
economic factors as well as medical ones when
they decide which disease to target when
designing a new drug.
• A huge investment has to be made towards the
research and development of a new drug.
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Disease Mechanism
1-Defines the possible cause or causes
of a particular disorder
2-Defines the path or phenotype of the
disease.
3-Understanding the disease mechanism
directs research and formulates a
possible treatment to slow or reverse the
disease process.
4-It also predicts a change of the disease
pattern and its implications.
Why The disease mechanism?
The Drug Discovery Process cont..
I- Choosing the disease
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Disease Mechanism Classifications of Disease mechanisms
5-Trauma and acute disease based
on injury or organ failure
1-Defects in distinct genes
—genetic disorders 3-Infection by bacteria,
fungi, or viruses 2-Immune/autoimmune disease
4-Multiple causal disease
The Drug Discovery Process cont..
I- Choosing the disease
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II-Choosing a drug target
Target-identification, selection and mechanism-of-action studies have important roles in
small-molecule probe and drug discovery
Target identification and selection is the earliest phase of R&D in the drug discovery and
development (DD&D) value chain.
Making the right choice of targets at the beginning of the DD&D process is the crucial first step
down the long and expensive road of creating innovative medicines.
The Drug Discovery Process cont..
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The "drugability" of a given target is defined
either by
how well a therapeutic, such as small molecule
drugs or antibodies, can access the target,
or by
the efficacy a therapeutic can actually achieve.
A long list a parameters
influences drugability of
a given target;
these include: cellular
location, development of
resistance, transport
mechanisms such as
export pumps, side
effects, toxicity, and
others
The Drug Discovery Process cont..
II-Choosing a drug target
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The term biological target is frequently used in pharmaceutical research to describe
the native protein in the body whose activity is modified by a drug resulting in a
specific effect, which may be a desirable therapeutic effect or an unwanted adverse
effect. In this context, the biological target is often referred to as a drug target.
The most common drug targets of currently marketed drugs include
•proteins
• G protein-coupled receptors
(target of 50% of drugs)[
• enzymes (especially protein
kinases, proteases, and
phosphatases)
• ion channels
• nuclear hormone receptors
• structural proteins
• membrane transport proteins
•nucleic acids
The Drug Discovery Process cont..
1.Drug target
II-Choosing a drug target
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a. Target Identification
The starting point for a target-oriented drug-
discovery project is to identify a relevant target.
• The first requirement in
conventional drug discovery is
identification of a valid target, a
molecule which has a link with the
disease of interest, such that
pharmacological intervention
would be expected to cure the
disease or ameliorate its symptoms.
II-Choosing a drug target
The Drug Discovery Process cont..
1.Drug target
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b. Techniques of Target Identification
There are a number of techniques used for target identification.
i)Radio ligand binding was a
common technique until recently.
ii) Now DNA microarrays,
expressed sequence tags are used
The Drug Discovery Process cont..II-Choosing a drug target
1.Drug target
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i)Radio ligand binding (RLBA)
1)The classic method to discover drug targets or
receptors is to bind the potential receptors with radio
ligands, so that targets can be picked out from a pool
of other receptors.
2)Bound receptors are then separated from the
radio ligands and sequenced.
3)Potential drug molecules are then studied with
these receptors or their nucleotide sequences to
determine their interactions in terms of
biochemical and functional properties.
II-Choosing a drug targetThe Drug Discovery Process cont..
1.Drug target
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ii) DNA microarrays.
• DNA microarray, also known as DNA or gene
chips, is a technology to investigate how
genes interact with one another and how they
control biological mechanisms in the body.
• The gene expression profile is dynamic and
responds to external stimuli rapidly. By
measuring the expression profile, scientists
can assess the clues for the regulatory
mechanisms, biochemical pathways, and
cellular functions.
• In this way, microarrays enable scientists to
find out the target genes that cause disease.
II-Choosing a drug targetThe Drug Discovery Process cont..
1.Drug target
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ii) DNA microarrays cont..
What is Microarrays?
• To use the microarray, a known
sequence of short DNA is printed on
a solid support of membrane or
glass slide.
• From healthy and diseased cells,
mRNAs are isolated.
• The mRNAs are used to generate
complementary DNAs (cDNAs).
• Fluorescent tags are attached to the
cDNAs, and the cDNAs are then
mixed and incubated with the
microarray supports (slides
II-Choosing a drug target
The Drug Discovery Process cont..
1.Drug target
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c. Drug Target Selection
Once a therapeutic area has been identified,
the next stage is to identify a suitable drug
target (e.g. receptor, enzyme or nucleic acid)
Understanding which bio macromolecules
are involved in a particular disease state is
very important.
This will allow the medicinal chemist
whether agonist or antagonist to be
designed for a particular receptor or
whether inhibitors should be designed
for a particular enzyme.
The Drug Discovery Process cont..
II-Choosing a drug target
1.Drug target
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b. Drug Target Selection cont..
Tricyclic antidepressants such as Desipramine
are known to inhibit the uptake of NA from
nerve synapses. However, these drugs also
inhibit uptake of serotonin, so the possibility
arose that inhibiting serotonin uptake might be
beneficial.
A search for selective serotonin uptake
inhibitors has led to the discovery of
Fluoxetine, the best selling antidepressant.
For example
The Drug Discovery Process cont..
II-Choosing a drug target
1.Drug target
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2- Discovering drug targets
If a drug or a poison produces a biological effect, there must
be a molecular target for that agent in the body.
In the past, the discovery of drug targets depends on finding the
drug first. Then, natural chemical messengers started to be
discovered.
But many targets still stay hidden (orphan receptors i.e, novel
receptors whose endogenous ligand is unknown ) and their
chemical messengers are also unknown.
The challenge is to find a chemical that will interact with these
targets in order to find their function and whether they will be
suitable as drug targets.
The Drug Discovery Process cont..
II-Choosing a drug target
This is one of the main driving forces behind the rapidly
expanding area of Combinatorial synthesis (synthesis of a large
number of compounds in a short period of time using different
reagents and starting material and are tested for activity.)
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3- Target specificity and selectivity between species
The Drug Discovery Process cont..
II-Choosing a drug target
Target specificity and selectivity is a crucial factor in modern medicinal chemistry research.
The more the selective a drug is for its target, the less chance that it will interact with different
targets and have less undesirable side effects.
For example, penicillin target an enzyme
involved in bacterial cell wall biosynthesis.
Mammalian cells does not have a cell wall, so
this enzyme is absent in human cells and
penicillin has few side effects.
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4-Target specificity and selectivity within the body
• Selectivity is also important for drug acting on
targets within the body
• Enzyme inhibitors should only inhibit the target
enzyme and not some other enzyme.
• Receptors agonist/ antagonist should ideally interact
with a specific kind of receptor (adrenergic
receptor) rather than a variety of different receptors,
or even a particular receptor type ( such as β-
receptor) or even a particular receptor subtype β2-
receptor.
• Ideally, enzyme inhibitors should show selectivity
between the various isozymes of an enzyme.
The Drug Discovery Process cont..
II-Choosing a drug target
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5-Targeting drugs to specific organs and tissues
• Targeting drugs against specific receptor subtypes often allows drugs to be targeted
against specific organ or against specific areas of brain.
• This is because the various receptor subtypes are not uniformly distributed around the
body, but are often concentrated in particular tissues.
II-Choosing a drug target
The Drug Discovery Process cont..
For example, adrenergic
receptors in the heart are
predominantly β1 while
those in the lungs are β2. If
a drug acts on either, less
side effects would be
observed.
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6-Pitfalls
The body is a highly complex
system. It is possible to identify
whether a particular enzyme or
receptor plays a role in a particular
aliments.
For any given function, there are
usually several messengers, receptors,
and enzymes involved in the process
Sometimes, more than one target may
need to be addressed for a particular
ailment
The Drug Discovery Process cont..
II-Choosing a drug target
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6-Pitfalls
There is no one simple cause for
hypertension, there are variety of
receptors and enzymes which can be
targeted in its treatment. These
include β1-adrenoceptors, calcium
ion channels, angiotessin-converting
enzyme (ACE), and potassium ion
channels.
Example
II-Choosing a drug target
The Drug Discovery Process cont..
For example, most of the current
therapies for asthma involve a
combination of bronchodilator (β2
agonist) and an anti-inflammatory
agent such as a corticosteroid
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The Drug Discovery Process cont..
1-Choice of bioassay
III-Identifying a bioassay
Choosing the right bioassay or test system is crucial to the success of a drug research .So it needs
the following
The test should be simple, quick and relevant
Human testing is not possible at such
early stage
in vitro first. Because in vitro testsare cheaper, easier to carry out,less controversial and can beautomated than in vivo one.
In vivo tests needed to check the drugs
interaction with specific target and to monitor
their pharmacokinetics properties
The Drug Discovery Process cont..
III-Identifying a bioassay
2-In vitro tests
They do not involve live animals. Instead, specific tissues, cells, or enzymes are isolated and used.
Enzyme inhibitors
can be tested on pure
enzyme in solution
Receptor agonist
and antagonists
can be tested on
isolated tissues or
cells.
Antibacterial drugs
are tested in vitro by measuring
how effectively they inhibit or kill
bacterial cells in culture
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• In vivo tests on animals often involve inducing a clinical
condition in the animal to produce observable symptoms.
• The animal is then treated to see whether the drug
alleviates the problem by eliminating the observable
symptoms. For example, the development of non-steroidal
inflammatory drugs was carried out by inducing
inflammation on test animals.
• The animals used may be transgenic. i.e,some mouse
genes are replaced by human genes so the mouse produces
the human receptor or enzyme. Or the mouse’s gene may
be altered to be susceptible for some disease such as breast
cancer.
The Drug Discovery Process cont..
III-Identifying a bioassay
3-In vivo tests
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There are several problems associated with in vivo
testing.
• It is slow
• causes animal suffering.
• many problems of pharmacokinetics and the result
obtained may be misleading.
For example, penicillin methyl ester is hydrolyzed in
mice into active penicillin, while it is not hydrolyzed in
humans or rabbits. Also, thalidomide is teratogenic in
rabbits and humans while it is not in mice.
The Drug Discovery Process cont..
III-Identifying a bioassay
3-In vivo test
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• Sometimes the validity of testing procedure is easy and
clear.
For example,
the antibacterial drug can be tested by its effect on killing
bacteria.
Local anesthetics are tested by their effect on blocking
action potential in isolated nerve.
• In other cases, the testing procedure is more difficult.
For example,
there is no animal model for antipsychotic drug.
Thus, validity of the test should be carried out.
The Drug Discovery Process cont..
III-Identifying a bioassay
4-Test validity
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The Drug Discovery Process cont..
III-Identifying a bioassay
5-High throughput screening (HTS)
HTS involves the miniaturization and
automation of in vitro tests such that
a large number of tests can be carried
out in a short period of time.
It involves testing of large number of
compounds versus a large number of
targets.
The test should produce easily
measurable effect. This effect may be
cell growth, an enzyme catalyzed
reaction which produces a color
change (may be a dye) or displacement
of radioactive labelled ligand from its
receptors.
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• NMR was used as a tool for determining the
molecular structures of compounds
• Recently, compounds can be tested or screened
for their affinity to a macromolecular target by
NMR spectroscopy. The relaxation times of
ligands bound to a macromolecule are shorter
than when they are unbound (can’t be detected).
• In NMR spectroscopy the compound is radiated
with a short pulse of energy which excites the
nuclei of specific atoms (H,N,C) afterwards, the
excited nuclei slowly relax back to the ground
state giving off energy as they so.
The Drug Discovery Process cont..
III-Identifying a bioassay
6-Screening by NMR
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• There are, several advantages in using NMR
as a detection system:
1-It is possible to screen 1000 small molecular
weight compounds a day with one machine.
2-The method can detect weak binding which would
be missed by conventional screening methods.
3-It can identify the binding of small molecules to
different regions of binding site.
4-It is complementary to HTS. The later may give
false-positive results, but these can be checked by
NMR to ensure that the compounds concerned are
binding in the correct binding site.
The Drug Discovery Process cont..
III-Identifying a bioassay
6-Screening by NMR
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5-The identification of weakly binding molecules
allows the possibility of using them as building
blocks for the construction of larger molecules
that bind more strongly.
6-Screening can be done on a new protein
without needing to know its function.
• NMR screening also has limitations, the main
one being that at least 200 mg of the protein
required.
The Drug Discovery Process cont..
III-Identifying a bioassay
6-Screening by NMR
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SPR (change in
refractive index)&
SPR (reduction of
emission of light) are
two visual methods of
detecting whether
ligands bind to
macromolecular
targets .
The Drug Discovery Process cont..
III-Identifying a bioassay
7-Surface Plasmon resonance (SPR) & scintillation proximity
assay (SPA)
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