bioltest active compounds

7/29/2019 Bioltest Active Compounds

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PRE-CLINICALBIOLOGICAL TESTING OFACTIVE COMPOUNDS

Dr Charles FOKUNANG

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Strategy for HTS Screens Run HTS Decided which compounds are active

and which are inactive Cluster the actives to put them into

series Visualize clusters of actives (showing

2D structures) and pick series of

interest Identify scaffold for each series Use similarity or substructure search on inactives

to find inactives related to these series Use SAR techniques to discover differences

between actives and inactives in a series


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n orma on genera e a eren po n s n eDrug Design process

Gene chip experiments

Project selection decisionsAssay protocols

HTS resultsSeries selection decisions

SAR studies

Protein structures

Combinatorial Expts.

PharmacophoresADME studies

Toxicology studiesScaleup reactions

Lead cmpd decisions

Clinical Trials data

Doctor/patient studies

Marketing, surveys, etc
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Information storagebreakdowns Large amounts of information generated:

Some is not kept at all

Some is kept but loses its meaning

Often datais kept, but not semanticsor decisions

e.g. keep the HVX2 assay result for this compound was3.2, but not what the assay protocol was, whether thecompound was considered active, nor whether it wasfollowed up on.

Bigger picture or derivative information is usually not

stored E.g. all the compounds with a tri-methyl group seemed to

have much lower activity for this project


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Information access breakdowns

Some information is only available in one physical

location Some information is only available within one part

of the discovery process

Often information is not contextualized for use

outside a particular domain When someone is clear about a piece of

information they need; that piece of informationexists, but they dont know how to access it.

E.g. What system to use, what Oracle table itsin, or even the knowledge of whether that pieceof information does exist!


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Missed opportunities Not a specific breakdown, but if the right piece of

information had been available at the right time, betterdecisions could have been made

E.g.

A group of compounds is being followed up as potentialdrugs, but a rival company just applied for a patent onthe compounds

A large amount of money is being spent developing anHTS assay for a target, but marketing research showsany drug is unlikely to be a success

A group of compounds is selected from an HTS as goodcandidates for follow up, but 20 years ago they werefollowed up for a similar project and had severe solubilityproblems


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Information use breakdowns

The meaning of data is incorrectlyinterpreted

A single piece of information is used, whilst

using a wider range of information wouldlead to different conclusions

Lessons learned from one project areincorrectly applied to another

Fuzzy information is taken as concreteinformation


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Genomics & Proteomics Information Handling

Understanding the link between diseases,genetic makeup and expression of proteins


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Genomics Genomics is fast-forwarding our understanding of how DNA, genes,

proteins and protein function are related, in both normal and diseaseconditions

Human genome project has mapped the genes in human DNA

Hope is that this understanding will provide many more potential protein

targets Allows potential personalization of therapies

ATACGGAT

TATGCCTAfunctions


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Gene Chips Gene chips allow us to

look for changes inprotein expression fordifferent people with avariety of conditions, andto see if the presence of

drugs changes thatexpression

Makes possible the designof drugs to targetdifferent phenotypes

compounds administered

people / conditions

e.g. obese, cancer,caucasian

expression profile

(screen for 35,000

genes)


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DRUG DISCOVERY:FINDING A LEAD


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Drug discovery: Finding a lead

When a pharmaceutical company oruniversity research group initiates a new

medicinal chemistry project through to the

identification of a lead compound, they willconsider the following steps in order:

1-Choosing the disease


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2-Choosing a drug target Drug targets

Discovering drug targets

Target specificity and selectivity betweenspecies

Target specificity and selectivity within

the body Targeting drugs to specific organs andtissues

Pitfalls


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3-Identifying a bioassay Choice of bioassay In vitro test

In vivo tests Test validity High-through screening Screening by NMR Affinity screening Surface Plasmon resonance Scintillation proximity assay


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Drug discovery: Finding a lead 4-Finding a lead compound

Screening of natural products (the plantkingdom, the microbial world, the marineworld, animal sources, venoms andtoxins)

Medical folklore

Screening synthetic compound libraries

Existing drugs

Starting from natural ligand or modulator(natural ligands for receptors, naturalsubstrates for enzymes, enzymeproducts as lead compounds, natural

modulators as lead compounds)


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4-Finding a lead compound

Combinatorial synthesis

Computer aided design

Serendipity and prepared mind

Computerized searching ofstructural databases

Designing lead compounds by NMR


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5-Isolation and purification

6-Structural determination

7-Herbal medicine


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I- Choosing the disease

Pharmaceutical companies tend to concentrate ondeveloping 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 whendesigning a new drug.

A huge investment has to be made towards the

research and development of a new drug.


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I- Choosing the disease

Therefore, companies must ensure that they get a goodfinancial return for their investment.

As a result, research projects tend to focus on diseasesthat are important in the developed world, because it is thebest market for new drugs.

Thus, research is carried out on ailments such as migraine,depression, ulcers, obesity, flu, cancer and cardiovasculardisease.

Less is carried out on the tropical diseases of the developedworld. Only when such diseases start to make an impact inricher countries, the pharmaceutical companies sit up andtake notice.

Example: research in antimalarial drugs has increased due toincrease in tourism to more exotic countries and the spread

of malaria into southern states of US.


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II- Choosing a drug target

Choosing which disease to tackle is usually amatter for companys market strategists. The

science becomes important at the next stage.

A molecular target is chosen which is believedto influence a particular disease when

affected by a drug.

The greater the selectivity that can beachieved, the less chance of side effects.


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II- Choosing a drug target1- Drug targets

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 biomacromolecules 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.

For example, tricyclic antidepressants such asDesipramineare 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 ofFluoxetine, the best selling

antidepressant.


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II- Choosing a drug target2- 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. 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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II- Choosing a drug target3-Target specificity and selectivity betweenspecies

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 thatit 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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II- Choosing a drug target4-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 - receptor) or even

a particular receptor subtype 2- receptor.

Ideally, enzyme inhibitors should show selectivity between the various

isozymes of an enzyme.


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II- Choosing a drug target5-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. For example, adrenergic receptors in the heart

are predominantly1 while those in the lungs are 2. If a drug acts on

either, less side effects would be observed.


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II- Choosing a drug target6-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


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II- Choosing a drug target6-Pitfalls

For example, there is no one simple cause forhypertension, there are variety of receptors and

enzymes which can be targeted in its treatment. These

include 1-adrenoceptors, calcium ion channels,

angiotessin-converting enzyme (ACE), and potassium ion

channels.

Sometimes, more than one target may need to be

addressed for a particular ailment. For example, most ofthe current therapies for asthma involve a combination

of bronchodilator (2 agonist) and an anti-inflammatory

agent such as a corticosteroid


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III-Identifying a bioassay1-Choice of bioassay

Choosing the right bioassay or test system is crucial tothe success of a drug research program.

The test should be simple, quick and relevant as there

are usually a large number of compounds to be analyzed. Human testing is not possible at such early stage, so

the test has to be done in vitro first. Because in vitrotests are cheaper, easier to carry out, less

controversial and can be automated than in vivo one. In vivo tests needed to check the drugs interaction

with specific target and to monitor theirpharmacokinetics properties.


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III-Identifying a bioassay2-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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III-Identifying a bioassay3-In vivo tests

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 drugalleviates 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.


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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 mouses

gene may be altered to be susceptible for some disease

such as breast cancer.


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There are several problems associated with in vivo

testing. It is slow and it also causes animal suffering.

There are also 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.


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III-Identifying a bioassay4-Test validity

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 anaesthetics 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.


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III-Identifying a bioassay5-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 cellgrowth, 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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III-Identifying a bioassay6-Screening by NMR

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 relaxationtimes of ligands bound to a macromolecule are shorter than when

they are unbound (cant 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.


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There are, several advantages in using NMR as adetection system:

1-It is possible to screen 1000 small molecular weightcompounds a day with one machine.

2-The method can detect weak binding which would bemissed by conventional screening methods.

3-It can identify the binding of small molecules todifferent regions of binding site.

4-It is complementary to HTS. The later may give false-positive results, but these can be checked by NMR toensure that the compounds concerned are binding in thecorrect binding site.


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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.


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III-Identifying a bioassay7-Surface Plasmon resonance (SPR) &

scintillation proximity assay (SPA)

SPR (change in refractive index)& SPR (reduction of

emission of light) are two visual methods of detecting

whether ligands bind to macromolecular targets .

IV Fi di l d d


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IV-Finding a lead compound

Once a target and a testing system have been chosen, the next

stage is to find a lead compound. A lead compound is a compound

which shows the desired pharmaceutical activity.

The level of the activity may not be very great and there may

be undesirable side effects.

The lead compound provides a start for the drug design and

development process.

There are various ways in which a lead compound might be

discovered. However, the following are the ways of discovering

the lead compound:

1-Screening of natural products (the plant kingdom, themicrobial world, the marine world, animal sources, venoms

and toxins)


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2-Medical folklore 3-Screening synthetic compound libraries

4-Existing drugs (Me too drugs & Enhancing the sideeffects)

5-Starting from natural ligand or modulator (naturalligands for receptors, natural substrates for enzymes,enzyme products as lead compounds, natural modulatorsas lead compounds)

6-Combinatorial synthesis 7-Computer aided design

8-Serendipity and prepared mind

9-Computerized searching of structural databases

10-Designing lead compounds by NMR


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IV-Finding a lead compound1-Screening of natural products

Natural products are a rich source of biologically activecompounds.

Many of todays medicines are either obtained directlyfrom a natural source or were developed from a leadcompound originally obtained from a natural source.

The compound responsible for that activity is known asthe active principle.

Most biologically active natural products are secondarymetabolites with quite complex structures. This hasadvantage in that they are extremely novel compounds.


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But the disadvantage of their complexity makes their synthesisdifficult and the compound needs to be extracted from itsnatural source (i.e. costly & inefficient process).

As a result, there is a need to design simpler analogues of the

lead compounds . Natural products can be obtained from different sources such

as:

1-The plant kingdom: It is rich source of lead compounds(e.g. morphine, cocaine, digitalis, quinine, tubocurarine, nicotineand muscarine, paclitaxel (Taxol, recent anticancer), either usefuldrugs as morphine or basis for synthetic ).Plants continue toremain a promising source of new drugs.

l


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2-The microbial world: microorganisms such as bacteria and fungiare rich for lead compounds (e.g. Antgimicrobial Drugs: pencillins,

cephalosporines, tetracyclines, aminoglycosides, chloramphenicol,

rifamycins).

3-The marine world: coral, sponges, fish and marine

microorganisms have biological potent chemicals, with interesting,

anti-inflammatory, antiviral, and anticancer activity. E.g Curacin A

(anti-tumour, from marine cyanobacterium) 4-Animal sources: antibiotic peptides were extracted from the

skin of African clawed frog.

Epibatidine (potent Analgasic) was also obtained from Ecuadorian

fro .

F d l d d


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5-Venoms and toxins: from animals, plants,snakes, spiders, scorpions, insects andmicroorganisms. They are potent because theyhave specific interaction with a macromoleculartarget in the body. Thus, they provide importanttools in studying receptors, ion channels, and

enzymes. e.g. Teprotide (from venom of viper) was the lead

compound for the development of

antihypertensive agents Cilazapril & Captopril


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IV-Finding a lead compound2- Medical folklore

Berries, leaves and roots used by local healer or shaman

as medicines. Many are useless or dangerous and if they

work this may be due to Palcebo Effect.

Some of these extracts indeed have a real effect. (e.g.

quinine (cinchona), reserpine (Rauwolfia), atropine

(atropa beladona), morphine (opium poppy), digitalis

(foxglove), emetine (ipeca), cocaine (coca).


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IV-Finding a lead compound3-Screening synthetic compounds

(libraries) Thousands of compounds have been synthesized . The

majority of these compounds are not used or not been in

the market. They have been stored in compound

libraries, and are still available for testing.

Pharmaceutical companies screen their library to study

a new target and find a lead compound


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4-Existing drugs A) Me too drugs: Many companies use established drugs

from their competitors as a lead compound in order to

design a drug. By modifying the structure in such way that

avoids the patent restrictions, retain the activity, andimproved the therapeutic properties.

For example i) Captopril (Anti-hypertension) used as lead

compound by different companies to produce their ownanti-hypertension drugs.

ii) Modern penicillins are more selective, more potent and

more stable than original penicillins


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4-Existing drugs B) Enhancing a side effect: An existing drug may have a

minor or undesirable side effect, which might be used in

another area of medicine. And such compound could be a

lead compound on the basis of its side effects.

The aim is to enhance the desired side effect and to

eliminate the major biological activity.

e.g. Sulfonamides are Antibacterial agents but some

sulfonamides has convulsive side effect due tohypoglycaemia effect. This, undesirable side effect was

useful in the development sulfonamides drugs for

treatment of diabetes (e.g.antidiabetic sulfonyl urea,

Tolbutamine).


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IV-Finding a lead compound5- Starting from the natural ligands or

modulator A) Natural ligands for receptors:

Natural ligands of a target has been sometimeused as the lead compound.

E.g. Adrenaline and noradrenaline (naturalneurotransmitters) were used fordevelopement adrenergic -agonists such as

Salbutamol, dobutamine, xamoterol, H2antagonists as cimetidine, and morphine(led toopiate receptors, and endogenous

opiates:endorphins and enkephalins.


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IV-Finding a lead compound5- Starting from the natural ligands or modulator

B) Natural substrates forenzymes: The natural substrate for an enzyme

can be used as the lead compound inthe design of enzyme inhibitors.

e.g. enkephalines used as a lead

compound to design an inhibitor ofenkephalinases.


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IV-Finding a lead compound5- Starting from the natural ligands or

modulator C) Enzyme products as lead compounds: enzymes catalyze a

reaction in both directions ,so enzyme products can be used as a lead

compound for an enzyme inhibitor e.g. L-benzyl succinic acid inhibit

enzyme catalyzed carboxy peptidase hydrolysis of peptides.

D) Natural modulators as lead compounds:the natural or

endogenous chemicals that exert allosteric control of receptor or

enzymes called Modulators and can be also as lead compounds.

e.g. Benzodiazepines: were discovered to modulate the receptor -

aminobutyric acid (GABA) by binding to allosteric binding site then

endogenous endozepines were discovered.


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6-Combinatorial synthesis Combinatorial synthesis is automated solid-phase

procedure aimed at produce as many as different

structures as possible in short time as possible.

The reactions are carried out on very small scale, often

in a way that will produce mixtures of compounds.

Combinatorial synthesis aims to mimic what plants do, i.e.

produce a pool of chemicals.

One of these compounds may be prove to be a useful lead

compound.


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IV-Finding a lead compound7-Computer aided design

Knowledge of target binding site aids in design of novel

compounds intended to bind with that target.

The enzyme and receptors can be crystallized and it is

possible to determine their structure (structure of

protein & binding site) by X-ray crystallography.

Molecular modelling software programs can be used to

study the binding site and to design drugs.


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IV-Finding a lead compound7- Serendipity and the prepared mind

Lead compounds are found as a result of serendipity (i.e.chance)

e.g. i) Cisplatin (Anti-cancer) & peniciilins

ii) Development of propanolol (-blocking) haveunexpected give a benefit of discover Practolol.

Propanolol is a -blocker but it is a lipophilic drug and canenter CNS and cause side effect, by introducinghydrophilic amide group inhibit passage the blood-brainbarrier and Practolol produced more selectivecardioselective 1 inhibitor with fewer side effects onCNS.

Sulfonamides and tolbutamide


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IV-Finding a lead compound7- Serendipity and the prepared mind

Workers in TNT factories always complained fromheadache due to dilatation of brain blood vessels.TNT was the basis to prepare nitro derivatives

which were used in angina to dilate coronary bloodvessels and alleviate pain. Mustard gas tanks used in second world war

exploded in italian harbor. They discovered thatpersons who survived and inhaled this gas lost their

defense against microorganisms due to destructionof white blood cells.This led to the discovery of mustard like drugs

which were used in leukemia to inhibit excessiveproliferation of white blood cells.


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IV-Finding a lead compound9-Computerized searching of

structural databases

New lead compounds can be found by carrying out

computerized searches of structural databases.

In order to carry out such search, it is necessary to know

the desired pharmacophore.

Data base searching is known as database mining.


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IV-Finding a lead compound10-Designing lead compounds by NMR

Recently NMR spectroscopy has been used to design a

lead compound rather than to discover one.

The method sets out to find small molecules

(epitopes) which can bind to specific binding site.

Lead discovering by NMR can be applied to proteins

of known structure which are labeled with N15.


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V-Isolation and purification

If a lead compound is present in a mixture of other compounds it

has to be isolated and purified.

The isolation and purification depends upon structure, stability,

and quantity of the compound.

e.g. Fleming recognized penicillin, qualities & non-toxic to human

but could not use it clinically because he was unable to purify it.

He could isolate it in aqueous solution, but when he tried to remove

water the drug was destroyed.

Purification and isolation of penicillins were possible until

development of new experimental procedure such as freeze-drying

and chromatography.

6 St t d t i ti


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6-Structure determination

X-ray crystallography, NMR spectroscopy, mass,

and IR are important in structure

deterimination.

7 H b l di i


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7-Herbal medicines

Herbal medicines contain a large variety of different

compounds.

Several of these may have biological activity, but there

is a significant risk of side effects and toxicity. The

active principle present in small amount, so herbals areexpected to be less active than pure compound.

Herbal medicines may be interacting with prescribed

medicines and there is no regulations or control of thismatter and their uses.

But it is an important lead to discover and design new

drugs.

Summary


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A lead compound is a structure which shows a useful pharmacological

activity and can act as the starting point for drug design. Natural products are a rich source of lead compounds. The agent

responsible for biological activity of a natural extract is known as

the active principle.

Lead compound have been isolated from plants, trees,microorganisms, animals, venoms, and toxin. A study of medical

folklore indicates plants and herbs which may contain novel lead

compounds.

Lead compounds can be found by screening synthetic compounds

obtained from combinatorial syntheses and other sources.

Existing drugs can be used as a lead compounds for design of novel

structures in the same therapeutic area. Alternatively, the side

effects of an existing drug can be enhanced to design novel drugs in

a different therapeutic area.

Summary


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Preclinical StudiesADME/PK

Objective: To study the effects of test materialswith respect to absorption, distribution, metabolism,and excretion

Duration: hours to days

Animals Required: typically 2 species (rodent andnon-rodent)

Safety Pharmacology Objective: To investigate undesirable

pharmacological effects of the test material

Duration: Usually single dose

Animals Required: 2 species (rodent and non-rodent)

Core battery: Cardiovascular, Respiratory, CNS


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Preclinical StudiesAcute Toxicity

Objective: To determine Maximum Tolerated Dose(MTD) and No Observable Effect Level (NOEL)

Duration: Typically 14 days after single dose

Animals Required: 2 species (rodent and non-

rodent)

Parameters:

Mortality Clinical pathology Gross necropsy Weight change Clinical observations

Points to consider:

Dose selection for repeat dose studies

Choice of Species (Fialuridine)


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Preclinical StudiesSub Acute Toxicity

Objective: To determine toxicity after repeatedadministration of the test material

Duration: 14 28 days

Animals Required: 2 species (rodent and non-rodent)

Parameters: Mortality Clinical pathology Urinalysis Histology Weight change Clinical obs

Points to consider: Dosing regimen similar to clinical Recovery period Duration of clinical trials (Phase I, II, III) Toxicokinetics Immunotoxicity


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Preclinical Studies

Subchronic/Chronic Toxicity Objective: In support of products used to

treat chronic conditions

Duration: 30 days to 2 years

Animals Required: 2 species (rodent andnon-rodent)

Parameters: Mortality Clinical pathology

Clinical obs Behavioral Assessment

Histology Weight change

Points to consider: Clinical Trials (EU)


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Preclinical StudiesCarcinogenicity

Objective: To evaluate the tumorigenic potential inanimals and risk to humans

Duration: 12 months +

Species: Mouse or Rat

Parameters: Tumor development Clinical pathology Clinical observations and assessment

Points to consider: Considerations from:

Pharmacology, Pharmacokinetic or Toxicology(mechanistic in vitro and in vivo) data Structure-activity relationships Compound accumulation over long-term use Continuous use in humans for 6 months +

S


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Summary The natural ligand, substrate, product, or modulator for a

particular target can act as a lead compound. The ability to crystallize a molecular target allows the use

of X-ray crystallography and molecular modeling to designlead compounds which will fit the relevant binding site.

Serendipity has played a role in the discovery of new lead

compounds. Knowledge of an existing drugs pharmacophore allows the

computerized searching of structural databases toidentify possible new lead compounds which share thepharmacophore.

NMR spectroscopy can be used to identify whether smallmolecules (epitopes) bind to specific region of a bindingsite. Epitopes can be optimized then linked together togive a lead compound.

S


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Summary If a lead compound is present in a natural extract or a

combinatorial synthetic mixture, it has to be isolated andpurified such that its structure can be determined. X- raycrystallography and NMR spectroscopy are particularimportant in structure determination.

bioltest active compounds

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