GENOMICS AND PROTEOMICS

BY

RAJASHEKAR MANTHRI

M.PHARMACY II SEMESTER

DEPARTMENT OF PHARMACEUTICS

VAAGDEVI COLLEGE OF PHARMACY

CONTENTSINTRODUCTION

Genomics and Proteomics

Bioinformatics

PHARMACOGENOMICS

SNPs

Personalized medicine

Benefits of pharmacogenomics

HUMAN GENOME PROJECT

Birth and activity of HGP

Mapping of HG

Approaches for genome sequence

GENETIC POLYMORPHISMS INFLUENCING DRUG DISPOSITION

Metabolizing enzymes

Transporters

GENETIC POLYMORPHISMS IN DRUG TARGETS

β2 – receptors

Apolipoproteins

GENE: An inherited factor that determines a biological

characteristics of an organism is called gene.

GENOME: The total genetic information contained in an organism

or cell is regarded as the genome.

•Genes carry the information for making the proteins required for the

body growth and maintenance.

GENOMICS: The study of the structure and function of the

genome is genomics.

Structural genomics: refers to the structural motifs and complete

protein structure.

Functional genomics: It focuses on genome wide patterns of gene

expression, the mechanism by which gene expression is coordianted

and the interrelation ships of gene expression when a cellular

environmental change occurs.

PROTEOME:

•Proteome defines a complete protein entity encoded by a specific

gene of an organism or cell.

•Proteome plays a key role in intracellular signalling pathways of the

immune system and intercellular metabolism as being the interface

between the cell and the environment.

•Proteins are important targets of drug discovery. In several disease

states, the protein expression is altered. This is one of the reasons for

the evolution of proteomic techniques.

PROTEOMICS:

Proteomics is the study of protein characteristics and functions to

obtain a global integrated view of:

• normal and abnormal cellular processes

• protein-protein interactions

Mining: Identification of all proteins in a sample.

Protein Expression Profiling: Identification of protein in a sample as

a function of a state of the organism or cell under certain condition.

Protein Network Mapping: Approach to determine how proteins

interact with each other in living systems.

Mapping of protein modifications: Identification how and where

proteins are modified.

BIOINFORMATICS

Bioinformatics is the combination of biology and information

technology.

It broadly involves the computational tools and methods used to

manage, analyze and manipulate volumes and volumes of biological

data.

It requires advanced knowledge of computer science, mathematics

and statistical methods for the understanding of biological

phenomena at the molecular level.

Components of Bioinformatics:It comprises three components

1.Creation of databases:

This involves the organizing, storage and management the biological

data sets.

Database: The collection of the biological data on a computer which

can be manipulated to appear in varying arrangements and subsets is

regarded as a database.

The biological information can be stored in different databases.

Some of the examples of databases are

Protein sequence database:

• SWISS – PROT (www.expasy.ch/sport): it provides the

description of the structure of a protein.

• PIR (Protein Information Resource) is a database provided by

the National Biomedical Research Foundation (NBRF) in USA

• PROSITE: provides information on protein families and

domains.

Nucleotide sequence database:

•Gene bank: provides nucleotide sequence maintained by the

National Center for Biotechnology Information (NCBI), USA

•EMBL: European Molecular Biology Laboratory maintained by

European Bioinformatics Institute (EBI)

2. Development of Algorithms and statistics:

It involves the development of tools and resources to determine the

relation ship among the members of large data sets.

E.g. comparison of protein sequence data with the already existing

protein sequences.

3. Analysis of data and interpretation:

Above said two components used to analyze the data and interpret the

results.

Applications of Bioinformatics:

Identification of nucleotide sequence of functional genes.

Finding of sites that can be cut by restriction enzymes.

Prediction of functional gene products.

Prediction of 3 – dimensional structure of proteins.

Designing of drugs for medical treatment.

Molecular modeling of biomolecules.

PHARAMACOGENOMICS

•Pharmacogenomics is the study of how an individuals genetic

differences effects the body’s response to drugs.

•Pharmacogenomic studies explain the inherited nature of these

differences in drug disposition and effects.

•It is the branch of pharmacology which deals with studying the

influence of genetic variation on drug response in patients.

•Study of pharmacogenomics helps to study how different drugs

interact with multiple genes and biological molecules they encode.

•Pharmacogenomic analysis promises to identify disease susceptibility

genes thus discovering new drug targets.

Promises of Pharmacogenomics:

Pharmacogenomics hold the promise that drug might one day be

tailor made for individuals that is to say as the tailor stitches the dress

of an individual by taking the size in the same way the dose of drug

will be decided by the individual genetic make up.

The promise of pharmacogneomics is that both the choice of the drug

and its dose will be determined by the individual genetic make up

leading to the personalized, more efficacious and less harmful drug

therapy.

The emerging discipline of pharmacogenomics attempts to

apply the innovative technologies of genome sequencing in order to

better understand drug response to produce more effective drugs with

fewer side effects on the basis of individual patients genetic makeup

and making personalized medicine an economically viable

possibility.

Human genetic variation in DNA:

•Single nucleotide polymorphisms (SNPs)

•Insertions

•Deletions

•Short Tandem Repeats (STRs)

•Translocations

Polymorphism

Deletions

Insertions

Translocations

Common Sequence

Variations

A Single Nucleotide Polymorphism, or SNP (pronounced

"snip") is a small genetic change, or variation, that can occur within a

person's DNA sequence.

• One-letter variations in the DNA sequence.

• SNPs contribute to differences among individuals.

What are SNPs and How are They Found?

• The majority have no effect, others cause differences in

characteristics, including risk for certain diseases and influence

their response to a drug.

• Most SNPs are found outside of "coding sequences."

SNPs found within a coding sequence are alter the

biological function of a protein.

• SNPs represent as much as 90% of all human genetic

variation. More than 1.4 million single nucleotide

polymorphisms were identified in the initial sequencing of

the human genome.

Role of SNPs in Pharmacogenomics:

For pharmacogenomics to be effective, it is essential to identify the

markers that can correlate drug response and genetic make up.

SNPs are believed to underlie susceptibility to such common

diseases as cancer, diabetes, cardio vascular and inflammatory

diseases and to contribute to the traits that make individuals unique.

Mapping of these SNPs in an individual helps in understanding

which genetic factors will influence drug action in an individual.

SNPs also helps to explain why different people respond

differently to same drug.

SNPs are most common and most technically accessible class of

genetic variants. These are much more frequent than other variations

and spread through out the genome, so SNPs are turning into useful

markers of drug response.

Pharmacogenomics has become a key to develop personalized drugs.

Genetic markers such as single-nucleotide polymorphisms may lead

to personalized medicines for a wide variety of diseases

PERSONALISED MEDICINE

What is it?Developing drugs on the basis of individual genetic differences

How does it work?Tailoring therapies to genetically similar subpopulations results in improved efficacy and less toxicity

What is it based upon?Pharmacogenomics = Pharmacology + Genomics

Personalized medicine is the use of detailed information about

a patient’s genotype or level of gene expression and a patient’s clinical

data in order to select a medication, therapy or preventive measure that

is particularly suited to that patient at the time of administration.

Certain drugs work differently in different individuals. In some

individuals they produce therapeutic effects and in some other

individuals, they produce severe toxic effects at the same dose.

Inter individual variability can be seen in drug absorption, distribution,

elimination and excretion.

This inter individual variation in drug efficacy and toxicity is

related to inherited differences in the genes that encode drug

metabolizing enzymes drug transporters or drug receptors.

Inter individual variability in drug response and ADRs are major public health

problems.

The ADRs are the major cause on non - compliance and failure of

treatment, particularly for chronic pathologies.

Many of these deaths can be avoided, if the physician has prior knowledge of

patient’s genetic profile of drug metabolizing enzymes and receptors, which determine

drug responses.

In the near future, the present prescription model of “one dose for all” (based on

age, sex, gender, weight, drug interactions) will be replaced by ―individualized

prescription‖ (i.e. individualized / personalized therapy) – that is the right drug in

right dose for right person.

The whole purpose of the study of genetic variations in drug responses is to identify

patients who may benefit from a particular medicine and avoid dangerous prescription

to others.

ANTICIPATED BENEFITS OF PHARMACOGENOMICS

Facilitated drug discovery:

Based on genetic makeup, most appropriate drugs can be designed

which are more targeted to specific diseases. Thus maximum

therapeutic effects can be obtained.

Screening for disease:

Genetic profile helps in prevention of diseases at early stages. It can

also help to determine individual’s susceptibility to a particular disease.

Better vaccines:

Vaccines made of genetic material, either DNA or RNA activate the

immune system but will be unable to cause infections. They will be

inexpensive, stable, easy to store and capable of being engineered to

carry several strains of a pathogen at once.

Facilitate drug approvals:

Pharmaceutical companies can discover new drugs by targeting

genomes. Risk of adverse effects in clinical trials can be minimized

by targeting only those who will respond to drug.

Accuracy in dosing:

By knowing a person’s genetic makeup, it becomes easier to

determine, how the body processes the medicine.

Thus instead of using conventional method of calculating

dosage based on age and weight, dosage can be calculated based on

person’s genetic profile. This reduces chances of overdose and under

dose thereby optimizing drug therapy

The Human Genome Project

Until the early 1970’s, DNA was the most difficult cellular molecule

for biochemists to analyze.

DNA is now the easiest molecule to analyze – we can now isolate a

specific region of the genome, produce a virtually unlimited number

of copies of it, and determine its nucleotide sequence overnight.

Aims of the project:

– To identify the approximate 100,000 genes in the human DNA.

– Determine the sequences of the 3 billion bases that make up human DNA.

– Store this information in databases.

– Develop tools for data analysis.

– Address the ethical, legal, and social issues that arise from genome research.

THE BIRTH AND ACTIVITY OF HUMAN GENOME PROJECT

•The human genome project (HGP) was conceived in 1984 and

officially begun in earnest in October 1990.

•The primary objective of HGP was to determine the nucleotide

sequence of the entire human nuclear genome.

•First director of HGP was James Watson (who elucidated DNA

structure).

•In 1997, united states established the national human genome

research institute (NHGRI).

•The HGP was an international venture involving research groups

from six countries USA,UK,FRANCE,GERMANY,JAPAN, CHINA

and several individual laboratories and a large number of scientists and

technicians from various disciplines.

•This collaborative venture was named as international human

genome sequencing consortium (IHGSC), and was headed by

Francis Collins.

•Total expenditure of $ 3 billion and a time period of 10 to 15 years

for the completion of HGP was expected and it was completed in

June 2000.

•A second human genome project was setup by a private company —Celera genomics of Maryland USA in 1998. This team was led by

Craig Venter.

ANNOUNCEMENT OF THE DRAFT SEQUENCE OF HUMAN

GENOME:

Working drafts of human genome sequence was announced in the

year of 2000 on June 26th by the leaders of the two HGPs, Francis

Collins and Venter.

Mapping of the Human Genome:-

The most important objective of human genome project was to

construct a series of maps for each chromosomes.

Cytogenetic map: This is a map of the chromosome in which the

active genes respond to a chemical dye and display themselves as

bands on the chromosomes.

Gene linkage map: A chromosome map in which the active genes

are identified by locating closely associated marker genes. The most

commonly used DNA markers are restriction fragment length

polymorphism (RFLP), variable tandem repeats(VNTRs) and short

tandem repeats (STRs). VNTRs are also called as minisatellites while

STRs are microsatellites.

Restriction fragment map: This consists of the random DNA

fragments that have been sequenced.

Physical map: This is the ultimate map of the chromosome with

highest resolution base sequence.

Cytogenetic map

Gene linkage map

Restriction fragment map

Physical map

Gene Gene

Restriction fragments

Base sequence

Approaches for genome sequencing:

For elucidating human genome, different approaches were used by

the two HGP groups.

This approach involves fragmentation of the genome into small

fragments, inserting them into vectors (mostly bacterial artificial

chromosomes) and cloning. The cloned fragments can be

sequenced.

•Nested shotgun approach: used by IHGSC

•Whole genome shotgun approach: used by Celera genomics

It involves blasting of whole genome into small fragments. Each

fragment is sequenced and assembled in order.

They also used high powerful computer programmes that helped for

the early completion of human genome sequence.

Major highlights of human genome

•Genes present in the human genome: 30,000 – 40,000

•Human genome is composed of 3.2 billion base pairs.

•Approximately 1.1 to 1.5% of the genome codes for proteins.

•Genes and DNA sequences associated with many diseases such as breast

cancer, muscle diseases, deafness and blindness have been identified.

•Between the humans the DNA differs only by 0.2% or one in 500 bases.

•More than 1.4 million single nucleotide polymorphisms(SNPs) have

been identified.

Some interesting analogs about human genome

•The base sequence in human genome would fill about 200 telephone

books of 1000 pages each.

•If a typist types at the rate of 60 words per minute for 8 hours a day,

he would take around 50 years to type human genome.

•If the DNA in the entire human body is put end to end it would reach

to the sun and back over 600 times.

Benefits of HGP:-

Medical benefits:

•Improved diagnosis of disease

•Earlier detection of predisposition to disease

•Gene therapy and control systems for drugs

•Development of pharmacogenomics.

DNA Forensics:

•Identify potential suspects at crime scenes

•Exonerate wrongly accused persons

•Identify crime victims

•Establish paternity and other family relations

Risk assessment:

• reduce the likelihood of heritable mutations.

Genetic polymorphism influencing drug

disposition( e.g. metabolizing enzymes and

transporters):

Polymorphism: refers to the occurrence of two or more genetically

determined alternative sequences or alleles in a population.

A polymorphic marker or site is the locus at which divergence occurs.

•A polymorphism may comprise one or more base changes, an

insertion, a repeat or a deletion.

•Single nucleotide polymorphism (SNPs)

• Polymorphisms can occur in:

– Drug targets (including cell surface receptors and target

proteins)

– Hormonal-regulated enzymes

– Genes involved in drug pharmacokinetics that impact drug

absorption, distribution, metabolism, and excretion

• Genetic polymorphisms can lead to:

– Severe toxicity when drugs not metabolized normally

– Diminished or increased therapeutic affect

So identification of the genetic polymorphism that contribute to

susceptibility for common diseases facilitates the development of

diagnostics and therapeutics.

Genetic polymorphism translates into either exaggerated or

diminished drug effects depending on whether the enzyme inactivates

or activates the drug.

POLYMORPHIC ENZYMES:

There are more than 30 families of drug metabolizing enzymes in

humans and essentially all have genetic variants, many of which

translate into changes in the proteins they encode.

Phase I enzymes:

•Cytochrome P450 enzymes

CYP2D6

CYP2C19

CYP2C9

•Dihydro pyrimidine dehydrogenase

•Aldehyde dehydrogenase

•Alcohol dehydrogenase

Phase II enzymes:

•Thopurine S - methyl transferases

•N – acetyl transferases (NAT 1 and

NAT 2)

Polymorphic Enzymes Drug Substrates

Cytochrome P – 450 CYP2D6 Most antidepressants,

neuroleptics and

antiarrrhythmics

Cytochrome P – 450 CYP2C9 S – warfarin, losartan, phenytion,

tolbutamide and NSAIDs

Cytochrome P – 450 CYP2C19 diazepam, proguanil, omeprazole

Dihydro pyrimidine dehydrogenase 5 – FU

Aldehyde dehydrogenase cyclophosphamide

Thopurine S - methyl transferases 6 – mercaptopurine, azathioprine

N – acetyl transferases( NAT 2) isoniazide, procainamide

Cytochrome P450 enzymes:

•The cytochrome P-450 enzymes, a superfamily of microsomal drug-

metabolizing enzymes, are the most important of the enzymes that

catalyze phase I drug metabolism.

•Most drugs are lipophilic compounds that are mainly eliminated by

oxidation catalyzed by the cytochrome P450(CYP) enzyme system in

the liver. The total number CYP genes in all species is 270 but the

human CYP super family consists of 57 CYP genes.

Cytochrome P – 450 2D6:

The CYP2D6 oxidizes drugs including -

•All Tricyclic anti depressants,

•Antipsychotics,

•Selective serotonin reuptake inhibitors,

•Anti hypertensive agents e.g. debrisoquine,

•Opiates e.g. codeine

Cytochrome P-450 2D6 (CYP2D6) represents one of the most

intensively studied and best understood examples of Pharmacogenetic

variation in drug metabolism.

Approximately 5 to 10 percent of white subjects were found to have a

relative deficiency in their ability to oxidize the antihypertensive drug

debrisoquin. They also had an impaired ability to metabolize the anti

arrhythmic drug sparteine.

These subjects are referred to as PMs. Poor metabolism is due to less

or no expression of CYP 2D6 enzyme due to mutations in the CYP

2D6 gene.

The gene encoding the CYP 2D6 enzyme localized on chromosome 22.

The three major mutant alleles are CYP 2D6 *3

CYP 2D6 *4

CYP 2D6 *5

•Subjects with poor metabolism of these two drugs had lower urinary

concentrations of metabolites and higher plasma concentrations of the

parent drug than did subjects with extensive metabolism.

•Furthermore, the drugs had an exaggerated effect in these subjects,

and family studies demonstrated that poor oxidation of debrisoquin

and sparteine was inherited as an autosomal recessive trait.

That is, subjects with poor metabolism had inherited

two copies of a gene or genes that encoded either an enzyme with

decreased CYP2D6 activity or one with no activity.

•Rapid CYP2D6 mediated metabolism is due to multiple copies of the

CYP2D6 gene. Such subjects can have an inadequate therapeutic

response to standard doses of the drugs metabolized by CYP2D6.

•Although the occurrence of multiple copies of the CYP2D6 gene is

relatively infrequent among northern Europeans, in East African

populations, the allele frequency can be as high as 29 percent.

A plot of the ratio of urinary debrisoquin to 4-hydroxydebrisoquin — a

so-called metabolic ratio — is shown in following figure.

The higher the metabolic ratio, the less metabolite was excreted.

Therefore, subjects with poor metabolism are shown at the far right of

the graph and subjects with ultra rapid metabolism are shown at the far

left of the graph.

Among 1011 Swedish Caucasians, 6.3% PMs of debrisoquine were

found. This incidence is very similar to other European and American

Caucasian populations.

Among 695 Chinese, only 1.0% PMs of debrisoquine were found, a

similar low incidence of PM has been shown in Japanese and Koreans.

Metabolism of CYP2D6 Drug Substrates in Relation to Genotypes

Nortriptyline was one of the first clinically important drug metabolized

by CYP2D6.

Nortriptyline was given as a single oral dose to 21 healthy subjects

with different genotypes. The plasma concentrations of the parent drug

were extremely low in one subject with 13 CYP2D6 genes.

The plasma concentrations of the formed metabolite 10-

hydroxynortriptyline show the opposite pattern, i.e., highest

concentrations in the subject with 13 genes and lowest in the PMs. This

study clearly shows the impact of the CYP2D6*4 allele as well as the

duplication/amplification of the CYP2D6*2 gene on the metabolism of

nortriptyline.

CYP4502C sub family

• In humans the CYP2C subfamily of CYP450 catalyzes roughly 20% of the CYP mediated metabolism of drugs .

• The first polymorphisms discovered in the CYP2C subfamily was a well described deficiency in the ability to metabolize the anticonvulsant drug mephenytoin. The inherited variability in the metabolism of mephenytoin was due to genetic variations in the gene coding for CYP2C19.

• CYP2C9 is the major CYP2C subfamily member in the liver and is primarily responsible for the oxidative metabolism of drugs including warfarin, phenytoin, glipizide, and losartan.

• Variants of CYP2C9 are CYP2C9*1, *2, *3, *4, *5 and *6.

• Patients with CYP2C9 genetic variants *2 and *3 have higher risk of acute bleeding complications than patients with a *1 variant upon administration of warfarin.

Thiopurine methyl transferases:

Thiopurine methyl transferase (TPMT) catalyzes the S- methylation

of the thiopurines like azathiopurine, mercaptopurine and

thioguanine.

These agents commonly used in the treatment of leukemia,

rheumatic diseases, inflammatory bowel diseases etc.

TPMT activity is highly variable and polymorphic, such that

approximately 90% of individuals have high enzyme activity, 10%

have intermediate activity and 0.3% have low or no detectable

activity.

At least 8 TPMT variant alleles have been identified, among 8, three

alleles (TPMT*2, TPMT*3A, TPMT*3C) accounting for about 95%

of patients with intermediate or low enzyme activity.

The mutant allele TPMT*2 is due to single nucleotide transversion

(G238C) in the coding sequence, leading to an amino acid substitution

at codon 18 (ala>pro).

TPMT*3A contains two nucleotide transition mutations (G460A

&A719G), leading to amino acid substitutions at codon 154 (Ala>Thr)

and codon 240(Tyr>Cys).

TPMT*3C contains only the A719G transition mutation.

Phenotypic deficiency in TPMT activity is rare but the mutant alleles

differs among various ethnic populations.

phenotype common mutant allele

Caucasians TPMT*3A

Africans TPMT*3c

Asians TPMT*3C

•Azathioprine is an imidazole derivative of, and metabolized non-enzymatically to,

6-mercaptopurine.

• 6-Mercaptopurine is metabolized by several pathways one of which is catalyzed by

TPMT and leads to inactive methyl-thiopurine metabolites. Other pathways

catalyzed by several other enzymes leads to the active thioguanine nucleotides (6-

TGN).

•The resulting 6-TGNs act as purine antagonists through their incorporation into the

DNA molecule and subsequent prevention of DNA replication. The reduction in

DNA replication suppresses various immunological functions in lymphocytes, T

cells, and plasma cells.

•TPMT-deficient patients are at very high risk of developing severe hematopoietic

toxicity. At high concentrations, 6-TGNs may cause toxicity and bone marrow

suppression (result of low TPMT activity due to TPMT polymorphism).

• On the other hand low concentrations (result of high TPMT activity) may give an

increased risk of therapeutic failure and due to other metabolite accumulation, such

as 6-methylmercaptopurine nucleotides, also to liver toxicity.

GENE SUBSTRATE DRUG ACTION DUE TO VARIANCE IN THE GENE

CYP2C9 warfarin Reduced anticoagulant effect

CYP2C19 omeprazole Enhanced cure rates of H.Pylori

CYP2D6 debrisoquine Excessive hypotension

N- acetyl transferases isoniazide Increased risk of hepatotoxicity(slow metabolizers)

TPMT 6- mercapto purine Bone marrow aplasia in poor metabolizers

DRUG TRANSPORTERS

Transport proteins have an important role in regulating the absorption,

distribution, and excretion of many drugs.

The most widely studied class of membrane transporters belong to the

ABC (ATP – binding cassette) family involved in the drug disposition

are

P – Glycoprotein

MRP – 6(multidrug resistant proteins)

OCT (organic cation transporter)

OAT (organic anion transporter)

P-gp is encoded by the human ABCB1 gene (also called MDR1).

MDR1 gene is located on chromosome 7 and consists of 28 exons.

•The principal function of Pgp is the energy dependant cellular efflux

of substrates including bilurubin, several anti cancer drugs, cardiac

glycosides, immuno suppressive agents, glucocorticoids, HIV type -1

protease inhibitors and many other medications.

•Pgp also plays a role in the excretion of xenobiotics into urine, bile

and the intestinal lumen.

•At blood brain barrier, Pgp in the choroid plexus limits the

accumulation of many drugs in the brain, including digoxin,

vinblastin, dexamethasone, cyclosporine, domperidone and

loperamide.

•Pgp expression is highly variable among individuals, the variability

in Pgp expression and function may be inherited differences in the

ABCB1 gene.

Genetic variability of ABCB1:

The first naturally-occurring polymorphisms in the human ABCB1

gene reported was the amino acid substitution Gly185Val, and more

recently Ala893Ser and Met986Val.

Now at least, 105 variants have been discovered in the ABCB1

gene.

The majority of these SNPs were in the non-coding region, thus not

changing Pgp amino acid composition, and of the 28 variants in the

coding region, lead to an exchange of amino acids.

ABCB1 polymorphisms and Pgp function:

•Synonymous polymorphism ( i.e. a SNPs that does not change the

amino acid encoded) in exon 26 (3435C>T) has been identified, and

despite the fact that the polymorphism does not result in an amino acid

substitution, the variant has been associated with decreased duodenal

Pgp expression.

•Non synonymous polymorphism (i.e. is SNP causing an amino acid

change) was identified in exon 21(2677G>T) of ABCB1.The 2677T

variant allele, resulting in a alanine to serine amino acid

substitution, has been associated with increased Pgp function.

Individuals with the CC genotype had an approximately two fold

higher P-gp expression in small intestine in comparison to subjects

with the TT genotype. Heterozygous subjects had an intermediate P-

gp expression

E.g. :

•Digoxin is the most

extensively studied P-

glycoprotein substrate. Single

dose and steady-state plasma

levels of digoxin were

significantly higher in

individuals with the 3435TT

genotype relative to the 3435CC

individuals.

•Individuals with 2677GG and

3435CC genotypes had higher

fexofenadine AUC values than

individuals with the variant

alleles (2677TT and 2677GT).

Data on the influence of MDR1 single nucleotide polymorphisms (SNPs) on P-gp

expression or function in various normal tissues

Data on the influence of MDR1 single nucleotide polymorphisms (SNPs) on disposition of

P-gp substrates

GENETIC POLYMORPHISMS IN DRUG TARGETS

•A drug target is defined as either the direct protein target of a drug

(e.g., a receptor or enzyme) proteins involved in a pharmacologic

response or proteins associated with disease risk that is somehow

altered by the drug.

•The major objective of drug target pharmacogenomics research is to

identify the inherited basis for interindividual variability in drug

response and toxicity, particularly when the variability is not

explained by differences in pharmacokinetics.

•Genetic variation in drug targets (e.g. receptors) can have a

profound effect on drug efficacy.

Gene or gene product Medication Drug effect associated

with polymorphism

ACE ACE inhibitors(eg

enalapril)

Renoprotective effects,

blood pressure reduction,

Arachidonate 5 –

lipoxygenase

Leukotriene inhibitors Improvement in Forced

Expiratory Volume.

β2 adrenegic receptor β2 agonists (eg albuterol) Bronchodilation,

susceptibility to agonist

induced desensitization,

CVS effects

Dopamine receptor (D1,

D2, D4)

Antipsychotics(eg.

Haloperidol, clozapine)

Antipsychotic response,

antipsychotic induced

tardive dyskinesia(D3),

antipsychotic induced

acute akathisia(D3)

Estrogen receptor Conjugated estrogens Bone mineral density

increases.

Genetic polymorphisms in drug target genes that can influence drug response

β2 – ADRENERGIC RECEPTOR :

•β2 – adrenergic receptor is a G – protein coupled receptor that

interacts with endogenous catecholamines and various medications.

•These receptors are widely distributed and play an important role in

regulating cardiac, vascular, pulmonary and metabolic functions.

•In heart activation of β2 receptors results in an increased rate and

force of cardiac muscle, whereas stimulation in the lungs acts to relax

air way smooth muscle.

•The β2 adrenoreceptor is coded by the gene called ADRB2.

•Genetic polymorphism of the β2 adrenoreceptor can alter the process

of signal transduction by these receptors.

SNPs are

Arg to Gly amino acid change at codon 16

Gln to Glu amino acid change at codon 27

Patients who were homozygous for Arg at ADRB2 codon 16 had

nearly complete desensitization after continuous infusion of

isoproterenol.

Patients homozygous for Gly at codon 16 had no significant change

in venodilatation.

Forced expiratory volume in one second (FEV1) after a single oral

dose of albuterol was higher in patients with the Arg/Arg genotype at

codon 16 of ADRB2 than in those with the Gly/Gly genotype.

Two single nucleotide polymorphisms in ADRB2 have been associated

with altered expression in response to β2 agonists.

APOLIPOPROTEIN E:

Human apolipoprotein E (apoE) plays an important role in lipid

metabolism and neurobilolgy through its interactions with the low

density lipoprotein (LDL) receptors.

Major genetic variants of ApoE are, apoE2, apoE3 and apoE4, each

differing by a cysteine or arginine at amino acids 112 and 158.

• ApoE3 the most common variant, contains cysteine at 112 and

arginine at 158

• ApoE2 contains two cysteines

• ApoE4 contains two arginines

These differences have profound effects on both the physical stability

and biological function of ApoE.

For example, while both apoE3 and apoE4 bind to the LDL receptor

with high affinity, apoE2 exhibits defective LDL receptor binding.

In addition the presence of the apoE4 allele is associated with

elevated plasma cholesterol levels and an increased risk for both

coronary artery and Alzheimer’s disease.

Tacrine (acetyl cholinesterase inhibitor) used in the treatment

of Alzheimer’s disease. Individuals without the apoE4 genotype

showed improvement in total response compared to patients with the

apoE4 genotype.

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