Pharmacogenetics

Description on definition of pharmacogenetics, role of pharmacogenetics in drug response, role of polymorphism in drug metabolism, drug transporters and drug targets.

1. PHARMACOGENETICS
Dr. RameshBhandari
Asst. Professor,
KLE College of Pharmacy, Belagavi

2. Dr.
Ramesh
Bhandari
PERSONALISED MEDICINES
Same symptoms
Same findings Same Drug
Same disease Same Dose
Different Patients
Different Effects

3. Dr.
Ramesh
Bhandari
ATARECOMMENDED PRESCRIBED
DOSES:
A Drug is efficacious in most
Not efficacious in others Lack
of Efficacy
And harmful in few Side effects

4. Dr.
Ramesh
Bhandari
One Dose Does Not fit all patients
Therapeutic windowis only
Generalisation

5. Dr.
Ramesh
Bhandari
WHYDOESDRUGRESPONSE
VARY?
One of the important reason is:
GENTIC POLYMORPHISM

6. Dr.
Ramesh
Bhandari
WHAT IS THE SOLUTION?
PHARMACOGENTICS
Identifying a population subgroup
More likely or less likely to
respond
More prone to ADRs
Defining better dose and dosage
regimen

7. Dr.
Ramesh
Bhandari
HUMANGENOME
30,000 genes
Each gene composed of sequence of
100s -1000s of DNA
Nucleotides those builds the DNA are:
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
They pair each other with specific rules:
Awith T
C with G

8. Dr.
Ramesh
Bhandari
HUMANGENOME.....
Order of these nucleotides
arrangements in DNA
Structure of RNA Intermediate
ProteinProduct (Enzymes)

9. Dr.
Ramesh
Bhandari
HUMANGENOME.....
EveryIndividualinheritstwocopiesof
mostgene,onefromeachparent.
Though 99percentofnucleotides,
constitutinghumanDNAareidenticalin
anytwoindividuals,millionsofvariantsin
nucleotidessequencestillexistasthetotal
numberofnucleotidesinaDNAissolarge,
approximatelyabout3billion.
Variantsthatarefoundinmorethanone
percentofthepopulationaredefinedas
“Polymorphisms”.

10. Dr.
Ramesh
Bhandari
COMMONEST TYPESOF
POLYMORPHISMS ARE:
Single Nucleotide Polymorphism (SNP):
Insertion
Deletion
Tandem Repeats

11. Dr.
Ramesh
Bhandari
PHARMACOGENTICS VS
PHARMACOGENOMICS
Pharmacogenetics:Study of
variability in drug response
determined by single genes.
Pharmacogenomics : Study of
variability in drug response
determined by multiple genes within
the genome.

12. Dr.
Ramesh
Bhandari
PHARMACOGENETICS
Pharmacogenetics
Genetic Polymorphism:
SNPs
Potential Target Genes are those that encode:
PK PD
Drug metabolizing enzymes Receptors
Transporters Ion Channels
Drug Targets Enzymes
Immune Molecules
The study of variations
in genes that determine
an individual’s response
to drug therapy
Common variation
in DNA sequence
(>1% of population)

13. GENETIC
POLYMORPHISM ON
METABOLISM

14. Dr.
Ramesh
Bhandari
CYTOCHROME ENZYMES
NOMENCLATURE
ThecytochromeP450(CYP450)enzymes
arechieflyinvolvedinthephaseI
metabolismofalargenumberofdrugs.
Theseenzymesareconstituentsofa
superfamilywith57related(isoenzymes).
ThesuperfamilyofCYP450enzymeis
categorizedintofamiliesandsubfamilies
basedonsimilarityinaminoacid
sequences.

15. Dr.
Ramesh
Bhandari
Thesearenamedbytherootsymbol
CYP(cytochromeP450),followedby
anumberdesignatingthefamily,
e.g.CYP2(>40%similarityin
aminoacidsequence),aletter
denotingthesubfamily,e.g.CYP2C
(>55%similarityinaminoacid
sequence),andafinalnumber
indicatingthespecificisoenzyme,
e.g.CYP2C19.

16. Dr.
Ramesh
Bhandari
CYP2C19*1/*1-Homozygous wild type
CYP2C19*1/*2-Heterozygous mutant type
CYP2C19*2/*2-Homozygous mutant type
CYP2C19*2/*3-Heterozygous mutant type
CYP Genotype Nomenclature:

17. Dr.
Ramesh
Bhandari
CYP450 DISTRIBUTION
MajorityofCYPsisfoundintheliver,butcertain
CYPsarealsopresentinthecellsofthe
intestine.
Themammalian CYPsareboundtothe
endoplasmicreticulum,andaretherefore
membranebound.

18. Dr.
Ramesh
Bhandari
CYP450 METABOLIC
CONTRIBUTION
CYP2D6, 30%
CYP2C9, 10%
CYP1A2, 2%
CYP3A4, 55%
OTHERS, 3%
CYP2D6
CYP2C9
CYP1A2
CYP3A4
OTHERS

19. Dr.
Ramesh
Bhandari
PHASEIENZYMES KNOWN TO
HAVEPOLYMORPHISM
CYP2C9: Phenytoin, Warfarin, NSAIDs etc
CYP2C19: Omeprazole, Diazepam etc
CYP2D6: >60 drugs like antidepressants.
CYP1A2: Theophylline, Clozapine etc.

20. Dr.
Ramesh
Bhandari
PHASEII ENZYMES KNOWN TO
HAVEPOLYMORPHISM
N Acetyltransferase: Isoniazid, hydralazine
ThiopurineS Methyl transferase: Azathioprine
UDP glucuronosyltransferase: Irinotecan

21. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
CYP2C19
Highlypolymorphicdrugmetabolizingenzyme.
30variantallelesofCYP2C19reported.
CYP2C19*2&*3isthephenotypeforpoor
metabolizer.
Mainlyfoundinasians29-35%and5-9%respectively.
Omeprazoleresultsinhigherplasmaconcentrations,
hencegreaterefficacyinloweringgastricpHthan
extensivemetabolizer.
CYP2C19*17typeresultsinultrametabolizing
capacity.
Thisresultsinlackofefficacyofclopidogrel.
(clopidogrelactivatedbyCYP2C19).

22. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
CYP2D6
Itisalargeisozymefamilythataffects
metabolismofmanydrugs.Itishighly
polymorphic.
>70allelicvariantshavebeenreported.
Antidepressants,antiarrhythmicsetcare
metabolizedbyCYP2D6.
0-19%Africanand1%Asianhavepoor
metabolizerphenotypeofCYP2D6
resultingin increased plasma
concentration.

23. Dr.
Ramesh
Bhandari
GeneticpolymorphismofCYP2D6wasfirst
investigatedwithdebrisoquinewhichresultsin
exaggeratedhypotensiveresponse.
Iftricyclicantidepressantsareadministeredin
PMphenotypethenincreaseinplasma
concentrationresultsCNSDepression.
Ifmetabolismisrequiredforadrugtohave
activity,thepatientwithPMphenotypeismore
likelytohavetherapeuticfailure.(Tamoxifen)
UMphenotyping(Amitryptyline)therapeutic
failure.

24. Dr.
Ramesh
Bhandari
Codeineisconvertedtomorphinebya
CYP2D6-O-demethylationreactionto
provideanalgesiceffects.Butif
administeredwithUMphenotypepatient
morphinetoxicitycanoccur.

25. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
CYP2C9
30differentallelicvariants.
CYP2C9*2&*3mostcommon.
Bothofthesevariantresultinreducedactivity.
CYP2C9isamajorcontributorofwarfarin.
Whenthepatienthasoneofthose2polymorphismthe
doseofwarfarinshouldbereduced.
Itthedoseisnotreducedthenthereisanincreaseriskof
bleeding.
NSAIDs,ARBsalsoaffectedbypolymorphismof
CYP2C19butduetohightherapeuticindiceswontshow
anyeffect.(exceptphenytoin)

26. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
CYP1A2
Responsibleformetabolismof5%drugs(Fluvoxamine,
clozapine,olanzapineandtheophylline.
Approx.15%ofJapanese,5%oftheChinese,and5%of
theAustralianpopulationsareclassifiedaspoor
metabolizer.
MostfrequentvariantCYP1A2*1Fallele–resultsinan
increasedexpression.HenceEnhancedlevelofenzyme
levelclearsthedrugfaster.Eg:FailuresforClozapinein
smokers.
CYP1A2*1C–Resultsindecreasedexpressionand
seenin25%oftheAsianPopulations.

27. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
CYP3A4
Mostabundantlyfoundintheliver.
Metabolize50%oftheclinicallyuseddrugs.
20allelicvariantsknown.
Limiteddatatoshowanyclinicalsignificance
forCYP3A4substrate.
CYP3A4*1B–mayinfluencegeneexpression.
CYP3A4*2–decreasedclearanceofCCB
nifedipine.

28. Dr.
Ramesh
Bhandari
GENETICPOLYMORPHISM OF
N-ACETYLTRANSFERASE
NAT1andNAT2genes–codeforNAT
activity.
BothgenesarehighlypolymorphicbutNAT2
geneisrelatedtofastandslowacetylators.
SeveralNAT2alleles*5,*6,*7,*10,*14&*17
areeithernullgenesorencodeofdefective
enzymesresultsinslowacetylatorphenotype.
Slowacetylatorsofisoniazidexhibitan
increasedbloodlevelsofthedrugresulting
increaseincidenceofneurotoxicity.

29. GENETIC
POLYMORPHISM IN
DRUGTRANSPORTER

30. Dr.
Ramesh
Bhandari
DRUGTRANSPORTER
Transportersareproteinsthatcarry
eitherendogenouscompoundsor
xenobioticsacrossbiological
membranes.
Transportercanbeeithereffluxor
influxproteins.
GeneticvariationsuchasSNPsofthe
transporterscancausedifferencesin
theeffluxorinfluxofdrugs.

31. Dr.
Ramesh
Bhandari
There are 2 superfamiliesof transport
proteins that have important effectson
the absorption, distribution and
excretionof drugs:
A.ATP Binding Cassette (ABC)
transporters
B.Solute carrier transporters.

32. Dr.
Ramesh
Bhandari
ABC TRANSPORTERS
Presentin cellular and intracellular membranes
and responsible for either importing or removing
the substancesfrom cells and tissues.
Only the following three gene families are important
for drug transport and multiple drug resistance in
tumorcells:
1.ABCB1 gene, encoding MDR1 (P-
Glycoprotein)
2.ABCC family (ABCC1 through ABCC6) or
multidrug resistance proteins (MRP)
3.ABCG2 (breast cancer resistance protein)

33. Dr.
Ramesh
Bhandari
1.MDR1 (P-GLYCOPROTEIN)
TheMDR1orABCB1genecodefor
theeffluxproteinP-glycoproteinthat
isfrequentlyassociatedwithdrug
resistancetoantineoplasticagents.
Atlease66SNPsinABCB1gene
reported.
Amongthem3moststudiedSNPs
include2synonymousand1non
synonymousvariants.

34. Dr.
Ramesh
Bhandari
The synonymous variants results in
decreased expression of PGP due to
mRNA expression, unstable mRNA or
alteration in protein folding.
Effects of these SNPs have been studied
with digoxinand docetaxelwhich shows
inconsistent with increased blood levels or
no change compared with wild type gene.

35. Dr.
Ramesh
Bhandari
2.ABCC TRANSPORTER
FAMILY
Thesearealsoknownasmultidrugresistance
associatedproteins(MRPs).
Foundinbrain,liver,kidney,andintestine.
MRP1(ABCC1), MRP2(ABCC2), and
MRP3(ABCC3)arecommonlyknowntoeffectthe
drugdisposition.
Thesetransporterscanbeexpressedincancercells
whichconfersresistancetothechemotherapeutic
agenttamoxifen.
Polymorphismisrare.

36. Dr.
Ramesh
Bhandari
3.ABCG2 TRANSPORTER
ABCG2isalsoknownasBreastcancerresistance
protein(BCRP),PlacentaspecificABCtransporter
(ABCP),andmitoxantroneresistanceprotein
(MXR).
Itisimportantinlimitingbioavailabilityof
certaindrugs,concentratingdrugsinbreastmilk
andprotectingfetusfromdrugsinmaternal
circulation.
ItishighlyexpressedintheGIT,liver,placenta
andinfluencestheabsorptionanddistributionofa
widevarietyofdrugsandorganicanions.

37. Dr.
Ramesh
Bhandari
SOLUTECARRIERPROTEINS
Transport ions and organic substances across
biological membranes.
These includes organic cationtransporter (OCT)
organic anion transporter protein (OATP).
Located througoutthe body.
OATP1B1(coded by SLCO1B1 gene) is a hepatic
influx transporterwith at least 40 SNP reported
that result in either altered expression or activity of
OATP1B1.
Among them one SNP (c.521T>C)has been
associated with an increased risk of simvastatin
induced myopathydue to lower plasma clearance.

38. GENETIC
POLYMORPHISM IN
DRUGTARGETS

39. Dr.
Ramesh
Bhandari
DRUGTARGETS
Drugtargetsincludereceptors,
enzymes,ionchannelsand
intracellularsignallingproteins.
Geneticpolymorphismsoccur
commonlyfordrugtargetproteins
includingreceptors,enzymes,ion
channelsandintracellularsignalling
proteins.

40. Dr.
Ramesh
Bhandari
RECEPTOR GENOTYPES: DRUG
RESPONSE
β
1receptor:locatedinheartandkidney.
2commonnonsynonymousSNPsintheβ
1
receptorgenearelocatedatcodons49
(Ser>Gly)and389(Arg>Gly).
Hypertensivepatientswhowerehomozygous
forbothSer49andArg389hadgreater
reductionindiastolicBPwithmetoprolol
monotherapycomparedwithcarriersofthe
Gly49and/orGly389alleles.

41. Dr.
Ramesh
Bhandari
ENZYMEGENES: DRUG
RESPONSE
VitaminKepoxidereductase(VKOR)is
antypicalexampleofgeneticvariationto
drugresponse.
Warfarinexertsitsanticoagulationeffects
byinhibitingVKOR,thuspreventing
carboxylationofclottingfactorsII,VII,IX
andX.
VKORC1geneencodesforVKOR
enzyme.

42. Dr.
Ramesh
Bhandari
PolymorphismintheVKORC1coding
regioncauserarecaseofwarfarin
resistance.
VKORC1*2,*3&*4.
Carriersofthesepolymorphismeither
requirehighdoseofwarfarinorfailto
respondtoanydoseofwarfarin.