Pharmacogenomics is the study of how an individual's genetic inheritance affects their response to drugs. It aims to develop personalized medicine by determining the "right dose of the right drug to the right person". Genetic variations can influence drug pharmacokinetics, pharmacodynamics, and disease mechanisms. Examples include CYP2C19 polymorphisms affecting clopidogrel metabolism and VKORC1/CYP2C9 variants influencing warfarin dosing. While pharmacogenomics holds promise for optimizing drug therapy, barriers include complexity in identifying clinically-relevant genetic factors and challenges in educating healthcare providers and patients.

2. “The right dose of the
right drug to the right
person” is one of the
goals of
pharmacogenomics
and personalized
medicine.

4. WHAT IS PHARMACOGENOMICS?
 Pharmacogenomics is the study of how an individual's genetic
inheritance affects the body's response to drugs.
 The term ‘Pharmacogenomics’ comes from the words
‘pharmacology’ (the science of drugs) and ‘genomics’ (the
study of genes and their functions) and is thus the intersection
of pharmaceuticals and genetics.
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5. PRINCIPLES OF PHARMACOGENETICS
A prerequisite for pharmacogenetics is heterogeneity in
drug response. The definitions of drug response are varied
and can include surrogate measurements measured in the
laboratory (e.g., international normalized ratio [INR] for
warfarin) or clinical endpoints (e.g., stent thrombosis for
clopidogrel).
A genetic basis for drug response is suggested when
responses are similar within family members (and therefore
are heritable) or significantly different in across ethnic
backgrounds.

6. THREE BROAD CLASSES OF GENETIC VARIANTS INFLUENCE
DRUG RESPONSE: 1) PHARMACOKINETIC; 2)
PHARMACODYNAMIC; AND 3) THOSE ASSOCIATED WITH THE
UNDERLYING DISEASE MECHANISM

8. Genetic polymorphisms in drug-metabolizing enzymes,
transporters, receptors, and other drug targets have been
linked to inter individual differences in the efficacy and
toxicity of many medications.
Pharmacogenomic studies are rapidly elucidating the
inherited nature of these differences in drug disposition
and effects, thereby enhancing drug discovery and
providing a stronger scientific basis for optimizing drug
therapy on the basis of each patient’s genetic
constitution.
Pharmacogenomic Studies

9. Pharmacogenomic Studies
Pharmacogenomics uses genome-wide approaches to elucidate
the inherited basis of differences between persons in the
response to drugs.
More than 1.4 million single-nucleotide polymorphisms were
identified in the initial sequencing of the human genome,
with over 60,000 of them in the coding region of genes.

10. A QUICK LOOK ON GENETICS
Central dogma theory of molecular biology
1. DNA is transcribed into RNA which is translated into a protein
2. Three nucleotides form a codon
3. A series of codons constitutes a gene
(a) Genes encode proteins which may affect drug response:
(i) Metabolizing enzyme
(ii) Transporter
(iii) Receptor
Human DNA sequence
1. 99.9% identical from person to person
2. 3 billion total nucleotides (0.1% difference is larger than it seems)
(a) Differences can predict pharmacokinetic and pharmacodynamic
response to drugs

11. Examples of gene mutations (source of genetic differences):
1. Single nucleotide polymorphism – one nucleotide base pair
replaces another
2. Insertion/deletions – nucleotide or nucleotide sequence is added or
deleted
3. Tandem repeats – nucleotide sequence repeats in tandem (e.g.
AGAGAGAG)
4. Frameshift mutation – an insertion/deletion mutation in which the
change in number of nucleotides is not a multiple of three
5. Defective splicing – internal polypeptide segment is abnormally
removed and remaining ends are joined
6. Premature stop codon – premature termination of the polypeptide
chain
7. Copy number variations – an abnormal number of copies of a gene

12. Polymorphisms – variation (mutation) in at least 1% of
population
Eg. Eye color , Hair color , Blood type and Drug metabolizing
enzymes

13. SINGLE-NUCLEOTIDE POLYMORPHISMS (SNPS)
 Single Nucleotide Polymorphism (SNP):
GAATTTAAG
GAATTCAAG
 SNPs are defined as Single base-pair
positions in genomic DNA that vary
among individuals in one or several
populations.
 SNPs are believed to underlie
susceptibility to such common
diseases as cancer, diabetes, and heart
disease and to contribute to the traits
that make individuals unique.
 SNPs are used as genomic biomarkers.
 Hence SNP analysis can be used to
enhance drug discovery and
development.
DNA molecule 1 differs
from DNA molecule 2 at
a single base-pair
location (a C/T

14. PHARMACOGENETICS AND CYP ENZYMES
a) Over 50 cytochrome P450 isoenzymes
 Three families – CYP1, CYP2, CYP3
 Fifteen known to metabolize drugs
 At least seven with documented polymorphisms –
CYP2A6, 2C9, 2C19, 2D6, 3A4/5, 1A2
b) Two copies of each gene encode for a CYP enzyme
Each copy is referred to as an allele
c) Example of a polymorphic CYP enzyme

15. NORMAL GENE SNP VARIANT GENE
TODAY’S DRUG
PHARMACOGENOMIC DRUG
Principle of Pharmacogenomics:

16. PHARMACOGENOMICS IN CARDIOLOGY

17. THIENOPYRIDINES
CLOPIDOGREL

18. CLOPIDOGREL
Activation and mechanism
.
Clopidogrel is a pro-drug that requires hepatic bioactivation
 85% of the dose is hydrolyzed by ubiquitous esterases, which
leaves only 15% to be converted to the active form.
 The activation of clopidogrel is a two step process:
(a) Clopidogrel is converted to 2-oxoclopidogrel via CYP2C19,
CYP1A2, and CYP2B6 with each enzyme contributing 45%,
36%, and 19%, respectively.
(b) 2-oxoclopidogrel is converted to the thiol active metabolite
via CYP3A4/5, CYP2B6, CYP2C19, and CYP2C9 with a
contribution reported to be 40%, 33%, 21%, and 7%,
respectively.

19.  The thiol active metabolite irreversibly forms a disulfide
bridge with a cysteine residue within the P2Y12 receptor
 This action prevents activation of the GPIIb/IIIa receptor
complex, thereby inhibiting aggregation for the platelet’s
lifespan (about 10 days)

21. RESPONSE VARIABILITY
There is high
Interindividual variability in
platelet response to
clopidogrel after stenting.
Clopidogrel “resistance” is
defined as an absolute
change in platelet
aggregation <10% before
and after clopidogrel
administration in response
to 5μmol/L ADP.

22. PROPOSED CAUSES OF RESPONSE VARIABILITY

24. CLOPIDOGREL PHARMACOGENETICS AND CYP2C19

25. Clinical response to clopidogrel :
In parallel with the platelet function data, the
CYP2C19*2 allele is associated with a graded risk of
death, MI, or stroke. Carriers of 1 allele (intermediate
metabolizers) have a 1.5-fold increased risk, and
carriers of 2 alleles (poor metabolizers) experience a
1.8-fold increase. This pattern also extends to stent
thrombosis as well with a 2.6- and 4-fold increased risk
in those with 1 and 2 *2 alleles, respectively .
Therefore, the CYP2C19 genetic associations with
platelet function are mirrored in the clinical response to
clopidogrel in the setting of PCI. These observations
formed the foundation for updating the clopidogrel label
by the Food and Drug Administration to include
pharmacogenetic information.

26. BLACK BOX WARNING

27. .
Similarly, the gain of function variant, CYP2C19*17, is
associated with increased risk of bleeding , and protection
from ischemic events CYP2C19*2 carriers treated with
prasugrel or ticagrelor do not show a heightened risk of
cardiovascular death, MI, stroke, or stent thrombosis

28. Genetic testing
Available tests to analyze CYP2C19 genotype
i. TaqMan® assay
ii. AmpliChip® CYP450
iii. INFINITITM Analyzer assay

29. CLINICAL PHARMACOGENETICS IMPLEMENTATION
CONSORTIUM GUIDELINES

30. Alternative strategies
a. Increased clopidogrel dose
A loading dose of 900 mg or a maintenance dose of 225 mg
have been shown to overcome resistance in carriers of one
CYP2C19 reduced-function allele but not two reduced-function
alleles
b. Prasugrel
Rapidly hydrolyzed to active metabolite. CYP variants not
shown to affect PK/PD or clinical outcomes
c. Ticlopidine
Not shown to be dependent on CYP2C19 status
d. Ticagrelor
Directly binds to platelets without need of activation. Not
shown to be affected by CYP2C19 status
e. Cilostazol + clopidogrel
Reduces platelet reactivity in CYP2C19 reduced-function
allele carriers but not noncarriers

31. Consensus statements currently do not recommend routine
testing. However, there is sufficient evidence to support
physicians who may choose to pursue CYP2C19*2 testing
in selected patients:
1)for diagnosis in patients with complications of clopidogrel
therapy such as stent thrombosis in compliant clopidogrel
users; or
2) for the choice of dual antiplatelet therapy in the ACS/PCI
setting where the physician believes that additional
information regarding the risk/benefit profile for clopidogrel
will influence the choice of drug therapy .
Outside of these scenarios, there is minimal rationale to
support CYP2C19 testing

32. STATINS
Genetic variations effect 4 types (at least) of “responses”
elicited by statins:
 low-density lipoprotein cholesterol (LDLc) lowering
 protection from cardiovascular events
 musculoskeletal side effects; and
 statin adherence.

34. WARFARIN
METABOLISM AND SITE OF ACTION

35. CYP2C9 SNPs alter warfarin metabolism:
CYP2C9*1 (WT) – normal activity
CYP2C9*2 (Arg144Cys) - low/intermediate activity
CYP2C9*3 (Ile359Leu) - low activity
Two relatively common variants, CYP2C9*2 and CYP2C9*3,
encode an enzyme with reduced activity, requiring lower
maintenance doses of warfarin.
Approximately 25% of whites have at least one variant
allele of CYP2C9*2 or CYP2C9*3, whereas these variant
alleles are less common in blacks and Asians.
Warfarin dose reduction requires as follows :
Heterozygosity for CYP2C9*2 or CYP2C9*3 allele : 20%-
30%
Homozygosity for the CYP2C9*2 or CYP2C9*3 allele :
50%-70%
Effect of CYP2C9 Genotype on Anticoagulation

36. EFFECT OF VKORC1 GENOTYPE ON ANTICOAGULATION
Three polymorphic variants of VKORC1
 Non-A,Non-A : wild type – Requiring more warfarin
dose
 Non-A/A : Heterozygous – Requiring 25% dose
reduction
 A/A : Homozygous - Requiring 50% dose reduction
Asians have the highest prevalence of VKORC1 variants,
followed by whites and blacks.
Polymorphisms in VKORC1 likely explain 30% of the
variability in warfarin dose requirements.
VKORC1 variants are more prevalent than variants of
CYP2C9.
Genotype Freq in Asians (%) Dose reduction
Non-A,Non-A : wild type 7 --
Non-A/A : Heterozygous 30 26
A/A : Homozygous 63 50

38. BETA BLOCKERS
Beta-adrenergic receptor antagonists (or beta-blockers) are
a diverse class of agents that primarily antagonize the beta-1
adrenergic receptor, encoded by ADBR1.
Variation in CYP2D6 (pharmacokinetic) and ADRB1, ADRB2,
and GRK5 (all pharmacodynamic) have received the most
attention.
Two variants in ADBR1, the Ser49Gly and Arg389Gly , lead
to
impaired down-regulation and higher signal
transduction,respectively Therefore, carriers of either variant
have enhanced, beta-1-receptor activity and more
betablocker sensitivity. Healthy volunteers and patients with
hypertension who carry 2 Arg389 variants have a greater HR
or BP reduction mainly with beta-blockers.

40. Clinical implications. In general, carriers of the Arg389
variant have: 1) enhanced reduction in HR and BP; 2) larger
improvements in LVEF; and 3) longer survival when treated
with chronic beta-blocker therapy compared to persons with
the Gly389 variant. Although it is unlikely that beta-blocker
therapy will ever be withheld for carriers of the Gly389
variant, a potential application of these findings would be to
consider advanced heart failure therapies (e.g., left
ventricular assist devices, biventricular pacing, or
transplantation) at an earlier stage in patients with the
Gly389 variant.
Because certain beta-blockers such as atenolol and carvedilol
are minimally handled by CYP2D6 (131), these may be
reasonable alternates for carriers of CYP2D6*4 with
metoprolol-induced bradycardia.

41. RENIN ANGIOTENSIN ALDOSTERONE SYSTEM
ACE GENE 287 bp insertion
(I) or deletion (D)
in intron 16
DD genotype with
increased ACE
activity and worse
clinical outcome
Use of b blockers
and ACEI
attenuate adverse
outcome of DD
genotype with no
effect on II and
ID.
ANGIOTENSINOG
EN
Methionine to
Threonine switch at
AA 235
Increased
angiotensinogen
levels with HTN
Modest risk of HTN
in whites
Aldosterone
synthase
C to T transition at
position 344
344 C allele ass
with higher
aldosterone levels
TT genotype has
greater impact of
ISDN+ HYDZ
combination

43. POTENTIAL OF PHARMACOGENOMICS

44. BARRIERS
Complexity of finding gene variations that affect drug
response
 Millions of SNPs must be identified and analyzed to
determine their involvement (if any) in drug response.
 Many genes are likely to influence responses
 Limited knowledge of which genes are involved with each
drug response

45. Disincentives for drug companies to make multiple
pharmacogenomic products
 Most pharmaceutical companies have been successful with
their "one size fits all" approach to drug development
 For small market- Pharmaceutical companies has to spend
hundreds of millions of dollars on pharmacogenomics based
drug development!----- “US Orphan Drug law”

46. EDUCATING HEALTHCARE PROVIDERS &
PATIENTS
 Introducing multiple pharmacogenomic products to treat the
same condition for different population subsets complicates
the process of prescribing and dispensing drugs
 Physicians must execute an extra diagnostic step to
determine which drug is best suited to each patient
 Need for a better understanding of genetics by all
physicians