cellular and molecular biology m pham pharmacology sem I

1. Presented by: Miss Heena.S.Kazi
Dr.D.Y.P.I.P.S.R.PIMPRI, PUNE.
POLYMORPHISM AFFECTING
DRUG METABOLISM

2. CONTENTS
2
• Introduction
• Types
• Causes
• Inducers and Inhibitors
• Drug Metabolism
• Recent Advances

3. WHAT IS GENETIC
POLYMORPHISM
 The existence together of many forms of DNA sequences at a
locus within the population
 A discontinuous genetic variation that results in different
forms or types of individuals among the members of a single
species.
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4. TYPES
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polymorphism
Single nucleotide
polymorphism
(SNPs)
Insertion and
deletion
polymorphosm
Nucleotide
repeat
polymorphism

5. CAUSES
• Balance between variation created by new
mutations and natural selection
• Frequency dependent selection.
• Multiple niche polymorphism
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6. SINGAL NUCLEOTIDE
POLYMORPHISM
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Most common form
Change in a single
base pair (bp)
Affect gene function
eg: Influence the
amount of mRNA
produced.

7. GENETIC POLYMORPHISM AND
DRUG METABOLISM
• Inter-individual variation of drug effects
Polymorphism
Enzyme / / Absent activity
Differ in their ability to perform certain drug biotransformation
reactions.
variation of drug effects

8. Genetic
polymorphisms can
alter individual drug
responses by
interfering with drug
metabolism.

9. Phase I reaction
(Fuctionalization reaction )
Phase II reaction
• Oxidation
• Reduction
• Hydrolysis
( Conjugation reaction )
• Acetylation
• Glucoronoidation
• Sulfation
• Methylation
DRUG METABOLISM

10. POLYMORPHISM
 Genetic differences in drug metabolism are the result of genetically based
variation in alleles for genes that code for enzymes responsible for the
metabolism of drugs.
 In polymorphisms, the genes contain abnormal pairs or multiples or
abnormal alleles leading to altered enzyme function.
 Differences in enzyme activity occur at different rates according to racial
group
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11. Poor
metabolizers
Intermediate
metabolizers
Normal
metabolizers
Extensive
metabolizers
Ultra-rapid
metabolizers

12. Types of metabolizers Types of alleles Names of enzyme
Poor metabolizers 2 Defective CYP2D6* 4/*5
CYP2D6*4/*4
Intermediate metabolizers 1 Wild type 1defective ----------
Normal metabolizers Wild type CYP2D6*1/*3
Extensive metabolizers 1 Wild type & 1 amplified CYP2D6*1/*2 &
CYP2D6*1A/*5
Ultra – rapid metabolizers 2 /more amplified CYP2D6*2/*3
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Eg. Morphine, codeine &TCA - This all drug will differ their metabolism due to the
presence of this type of alleles.

13. INHIBITORS AND INDUCER
Inhibitors
Binds to
enzyme CYP450
Activity
Inducer
Binds to enzyme/
expression of gene
coding
Metabolic activity

14. Inhibitor
Poor metabolizer Extensive metabolizer
• Level of substrate drug remains
high because the metabolism of
the substrate is much less than
normal.
• When an inhibitor is added, the
additional inhibition of
metabolism is not much greater
than is already occurring in the
PM.
• The effect of inhibitor is less in
PM than in normal metabolizers.
• The drug interaction might not
occur.
• Level of substrate drug is
normally low due to rapid
metabolism by the enzyme.
• An inhibitor to the enzyme will
inhibit the extensive metabolism
and cause significant elevations in
the substrate drug.
• Effect of inhibitors is much
greater in an EM level of
substrate

15. Inducer
Poor metaboliser
• Level of substrate drug is
higher than expected in
normal metaboliser because
low metabolism of substrate
• The addition of inducer will
cause significant
metabolism of substrate
low level of substrate than
expected in normal
metabolism
• Drug interaction grater
extent & substrate level
similar to normal metaboliser
Extenssive metaboliser
• Level of substrate drug is lower
due to rapid metabolism
• The addition of inducer does not
cause grater difference in level of
substrate because metabolism is
already greatly
• The drug interaction might not
occur
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16. COMPLEX DRUG INTERACTIONS
Substrate is metabolized through a
polymorphic enzyme
Substrate becomes active metabolite
This active metabolite acts as an
inhibitor or inducer in second system

17. GENETIC POLYMORPHISM IN GENES THAT CAN
INFLUENCE DRUG METABOLISM-CYP450
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18. PHASE I ENZYME
ENZYME SUBSTRATE CLINICAL CONSEQUENCE
CYP1A1 Benzopyrine,phenacetin or cancer risk
CYP1A2 propranolol Theophylline metabolism
CYP1B1 Estrogen metabolite cancer risk
CYP2A6 Coumarin, nicotine,
halothane
nicotine metabolism &
cigarette addiction
CYP2B6 Cyclophosphamide,
mephenytoin
Significance unknown
CYP2C8 Retinoic acid, Significance unknown
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19. ENZYME SUBSTRATE CLINICAL CONSEQUENCE
CYP2C9 Warfarin,NSAIDS Anticoagulant effect on
warfarin
CYP2C19 omeprazole, propranolol Peptic ulcer response to
omeprazole
CYP2D6 Betablockers,antidepressants
antipsychotics
Tardive dyskinesia from
antipsychotics
CYP2E1 Acetaminophen, ethanol Possible effects on alcohol
consumption
Possible cancer risk
CYP3A4/3A5/3A7 Macrolides, cyclosporine,
tacrolimus, calcium channel
blockers
Tacrolimus dose
requirement in pediatric
cancer patients
Dihydrodyrimidine
dehydrogenase
5-fluorouracil 5-fluorouracil toxicity
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20. P450 ENZYMES IN DRUG
METABOLISM
 The polymorphic P450 (CYP) enzyme superfamily is the most important
system involved in the biotransformation of many endogenous and
exogenous substances.
 Genotyping for CYP polymorphisms provides important genetic
information that help to understand the effects of xenobiotics on human
body.
 For drug metabolism, the most important polymorphisms are those of the
genes coding for CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5, which can
result in therapeutic failure or severe adverse reactions.
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21. CYP4502D6
Impaired ability to hydroxylate inactivate debrisoquin
5-10% of white subjects oxidize debrisoquin
Impaired ability to metabolize antiarrhythmic and oxytocic drug
PM -Lower urinary concentration, higher plasma concentrations
Subjects inherited two copies of a gene or genes that encoded an enzyme
with either decreased CYP2D6 activity or no activity at all
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22. CYP4502C SUBFAMILY
 Catalyzes 20% of the CYP mediate metabolism of drugs
 CYP2C19
 Probe drug determined that individuals can be segregated into EMs and
PMs
 PM trait is autosomal recessive –present in 3-5% of Caucasians & 12-
23% of Asian populations
 catalyzes the metabolism of several proton pump inhibitors (i.e.
omeprazole).
 Responsible for inactivation of propranolol and metabolic activation
Of antimalarial drug proquanil
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23.  CYP2C19 & Diazepam
 Demethylated by CYP2C19
 Plasma diazepam half-life :
• Homozygous for the defective CYP2C19*2 allele longer compared to wild type
allele
 Half-life of the desmethyldiazepam metabolite is also longer in CYP2C19 poor
metabolism
 Diazepam induced t0xity-slower metabolism
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24. CYP2C9
 Responsible for the oxidative metabolism of important
compounds –warfarin, phenytoin etc.
 6 different polymorphisms –CYP2C9*1, *2, *3, *4, *5, *6
 CYP2C9*1 –wild type allele, CYP2C9*2-*6 –variants
 CYP2C9*2 and *3 alleles- significant reduction in the
metabolism and clearance of selected CYP2C9 substrates
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25.  CYP2C9 & Warfarin
 For optimal anticoagulation with warfarin Polymorphisms linked to both
toxicity and dosage
 *2 and *3 variants –higher risk of acute bleeding complications than
patients with *1 wild type genotype
 Lower maintenance dose of warfarin -15-30% to achieve target
 Patients with variant CYP2C9 genotype -take a median of 95 days
longer to achieve stable dosing compared to wild-type group
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26.  DIHYDROPYRIMIDINE DEHYDROGENASE
 Metabolism of fluorouracil.
 DPD metabolizes fluorouracil
 Severe fluorouracil toxicity occurs when DPD activity < 100 pmol/min/mg
 3% of population carries heterozygous mutations that inactivate DPD and
1% are homozygous for the inactivating mutations
 Heterozygous individuals do not exhibit no phenotype until challenged
with fluorouracil.
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27. CYP4503A Subfamily
CYP4503A
CYP3A4
CYP3A5CYP3A7
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28. CYP3A4
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Varient –
CYP3A4,CYP3A4*1B
transition in promoter
region
Nifidefine response element
A392G
CYP3A5
Varient
CYP3A5*3
Improper mRNA splicing
translation of
functional protein

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CYP3A7
CYP3A7 expression
CYPA37 promoter
( replacement of 60 nucleotide )
CYP3A4 Promoter
( CYPA37* 1c allele )
Expression of pregnane x receptor
response element

30. PHASE II ENZYMES
ENZYME SUBSTRATE CLINICAL CONSEQUECES
N acetyl transferase
(NAT1)
Aminosalicylicacids
sulfamethoxazole
Possible cancer risk
Hypersensitivity to
sulfonamides,hydralazine-
induced lupus, isoniazid
neurotoxicity and hepatitis
N acetyltransferase(NAT2) Isoniazid, sulfonamides,
Glutathione transferase
(GSTP1)
13-cisretinoic acid, busulfan, Possible cancer risk
Sulphotransferases Tamoxifen,estrogens,
dopamine
Possible or risk; clinical
outcomes in women
receiving tamoxifen for
breast cancer
Catechol-o-methyl
transferases
Estrogens, levodopa Response to amphetamine,
substance abuse, levodopa
response
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31.  N-ACETYLTRANSFERASES
 N-acetylation of isoniazid to acetyl isoniazid
 Individuals are slow or rapid acetylators
 Slow acetylation: Japanese (10%), Chinese (20%), Caucasians (60%)
 NAT2 protein is the specific protein isoform that acetylates isoniazid
• 27 unique NAT2 alleles identified
• NAT2*4 is the wild type allele-
• NAT2 alleles containing the G191A, T341C, A434C, G590A, and/or
G857A missense associated substitutions are associated with slow
acetylator phenotype.
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32. REFERENCES
 CYP2C9, C. C., & CYP2D6, C. A. (2007). The effect of cytochrome P450
metabolism on drug response, interactions, and adverse effects. Am Fam
Physician, 76, 391-6.
 Tu, T. (2005). Pharmacogenomics Frontiers in Medicine and Race. The Journal
of Young Investigators, 13(5).
 http://www.biology-online.org/dictionary/Genetic_polymorphism
 http://en.wikipedia.org/wiki/Drug_metabolism
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