PHARMACOGENETICS

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PHARMACOGENETICS

• XENIA GONDA
• Department of Pharmacology and Pharmacotherapy
• Department of Clinical and Theoretical Mental
  Health
• Semmelweis University

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• New field within clinical pharmacology (30-40
  years)
• Patients respond differently to a given
  therapeutic agent even if they have the same
  illness
• The same dose of a given drug in some patients
  causes very different plasma levels and different
  therapeutic response

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Pharmacogenetics

• The study of
• genetically determined
• interindividual differences in
• therapeutic response to drugs and
• susceptibility to adverse effects (Lerer)

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History

• 510 BC Pythagoras some people develop haemolytic
  anaemia after eating fava beans
• 1902 Garrod genetic factors direct chemical
  transformations
• 1932 Snyder phenylthiourea nontasting is
  inherited as an autosomal recessive trait
• 1957 Motulsky first demonstration of the
  relationship between adverse drug reaction and
  genetically determined variation
• 1959 Vogel pharmacogenetics the hereditary
  basis of variability in drug effects
• 1960 Evans speed of INH acetylation is under
  genetic control
• 1962 Kalow abnormal form of serum cholinesterase
  causes adverse reactions to succinylcholine
• 1977 Mahgoub polymorphism of CYP2D6 causes
  adverse effects to debrisoquine
• Lerer

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Aim of pharmacogenetic studies

• Identify and categorize the genetic factors that
  underlie the differences and apply this in
  clinical practice
• Rational, individual therapy
• Screening for those patients who carry the genes
  which place them at risk in case of certain
  therapies
• Discovering which drugs are potentially dangerous
  for carriers of a given polymorphism
• Establishing the frequency of pharmacogenetic
  phenotypes

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• Pharmacogenetics study of genetically determined
  interindividual differences in response to drugs
• Pharmacogenomics use of genome based techniques
  in drug development
• The differences in the response to a given drug
  can be attributed to two major factors that are
  under genetic influence
• Pharmacokinetic genetically based differences in
  the processes influencing bioavailability
• Pharmacodynamic genetically based differences in
  the proteins at which the drug acts

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Polymorphism

• Genetic variation occuring with a frequency of 1
  or more in the population
• 1. SNP (single nucleotide polymorphism)
• most frequent type
• difference in a single base of the genomic
  sequence
• usually 1/1000 base
• most does not influence the structure or function
  of proteins
• SNP can occur
• In exons (may alter the structure of proteins and
  may lead to functional consequences)
• In introns (may influence splicing)
• In the regulatory regions (may influence
  expression of the gene)

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Polymorphism II

• 2. Insertion/deletion polymorphism insertion or
  deletion of a few nucleotides
• 3. Variable number tandem repeats variation in
  the number of times a sequence of several hundred
  base pairs is repeated
• 4. Simple tandem repeats (microsatellites) 2-4
  nucleotides repeated a variable number of times

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Polymorphism III

• Pharmacogenetic traits are mainly
• polygenic (influenced by several genes, the
  effect may be additive or interactive)
• multifactorial (both genetic and environmental
  factors contribute)
• Some pharmacogenetic traits are
• monogenic

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• Genotype gene structure encoding for the given
  characteristics
• Phenotype the manifestation of the genotype,
  which can be observed and can be influenced by
  other factors
• Other gene products
• Environment
• Acquired characteristics
• Frequency of genetic polymorphisms differs
  greatly among ethnic groups
• The functional relevance of a given polymorphism
  can vary across ethnic groups

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• Determination of genotype PCR
• Determination of phenotype
• determination of metabolic rate (level of
  original drug/metabolit in urine)
• after administration of a given dose of the drug,
  pharmacokinetic parameters are measured
  (halflife, clearance, plasma levels)
• Distribution of phenotypes in the population
• Multimodal (usually bi- or trimodal) distribution
  indicates determination by a single gene having
  polymorphic variants
• Unimodal distribution indicates polygenic
  multifactorial inharitance, or monogeic
  inheritance but no polymorphism

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• The function is usually bi- or trimodal
  indicating two or three phenotypes
• Enhanced/extensive metaboliser
• intensive metabolisation, resulting in low plasma
  concentration of the drug
• usually heteozygote or homozygote dominant
• Intermedier metaboliser
• Poor metaboliser or nonmetaboliser
• Slow or no metabolisation of the drug resulting
  in high plasma concentration for an extended time
• Usually homozygote recessive

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Types of adverse effects of drug therapy
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• The observed differences in therapeutic response
  and and susceptibility to adverse reíctions are
  due to alterations of pharmacokinetic and
  pharmacodynamic processes
• Absorption
• Distribution
• Protein binding
• ACTION
• METABOLISM
• Disposition

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Inheritance of the activity of metabolic enzymes

• Monogenic inheritance
• one gene is responsible for encoding the enzyme
• mutant enzyme variants may cause defects in
  metabolism, leading to different genotypes within
  the population
• usually autosomal recessive in case of the allele
  carrying the reduced enzyme function
• Polygenic inheritance
• several genes are responsible for encoding the
  enzyme

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Pharmacogenetics of drug metabolism

• Drug metabolism is crucial in determining
  therapeutic and adverse effects
• Genetic factors play an important role in
  individual differences of drug metabolism
• Phase I
• Oxidation, reduction, hydroxilation,
  dealkylation, etc.
• Aim introduce a new functional group
• Cytochrome P450 enzymes in hepatocytes attached
  to SER
• Phase II
• Conjugation with glucuronic acide, glutathione,
  acetate, etc
• Aim to increase water solubility
• Ususally in the cytosol

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Polymorphism of phase I metabolism

• Cytochrome P450 enzyme polymorphisms
• Sample reactions
• Debrisoquine ? 4-OH-debrisoquine CYP2D6
• Dextrometorphan ? dextorphan CYP2D6
• Dextrometorphan ? methoxymorphinan CYP3A
• Sparteine ? 2-dehydrosparteine CYP2D6
• Mephenytoin ? 4-hydroxy-mephenytoin CYP2C9

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• Nomenclature of CYP genes
• Arabic number for gene family
• Capital letter for gene subfamily
• Arabic number for individual gene
• CYP enzymes of different gene families have a 40
  or more homology in their amino acid sequences,
  but enzymes within one subfamily may have
  different substrates, regulation, etc.
• Over 70 of total CYP content of the human liver
  is shared by seven subfamilies CYP1A2, CYP2A6,
  CYP2B6, CYP2C, CYP2D6, CYP2E1, CYP3A
• Extent of metabolism is determined by
• Affinity of substrate-enzyme complex
• Relative abundance of a given CYP enzyme relative
  to the total CYP content

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CYP2D6

• Discovered in the 1970s, one of the most widely
  studied polymorphisms in drug metabolism
• 2 of total liver CYP content
• Distribuiton of PM 7 of Caucasians, 1 of
  Asians
• Involved in metabolism of several drugs
• Psychotropic medications tricyclic
  antidepressants, SSRIs, classical and atypical
  antipsychotics
• Cardiovascular drugs
• ?-receptor antagonists metoprolol, propranolol,
  timolol
• Phenacetine
• D-penicillamine
• Codeine
• Abused drugs

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CYP2D6

• More than 50 alleles, encoding enzymes with
  inactive / decreased / increased / normal
  catalytic function, up to a 1000fold variation in
  the population
• Poor metabolisers
• are at risk of drug toxicity even at standard
  doses, resulting in poor compliance
• may also present with treatment resistance to
  prodrugs that require activation (codeine)
• Ultrarapid metabolisers
• delayed therapeutic response or treatment
  resistance (29 of Ethiopians carry multiplicated
  functional CYP2D6 alleles)
• Also present in brain functionally associated
  with dopamine transporter, might have a role in
  dopaminergic transmission, there are differences
  in presonality traits between PMs and Ems

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Distribution of CYP2D6 enzymes in different
populations
Ingelman-Sundberg et al., 1999
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CYP2D6 polymorphism of debrisoquine metabolism

• Debrisoquine is the most frequently used test
  substrate in studies of the polymorphism of drug
  metabolism
• Frequency of phenotypes

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CYP1A2 nonpolymorphic drug metabolism with
polygenic control

• 13 of total liver CYP content
• Varies up to 130fold in individuals and in
  populations
• Important in disposition of several important
  psychotropic medications clozapine, olanzapine

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Polymorphism of phase II metabolism conjugation
I.

• Paracetamol conjugated with glucuronide (55-60)
  and sulphate (35), can be used for testing of
  polymorphism of phase II reactions
• UDPGT uridinglucuronyltransferase
• PST sulphotransferase, both under monogenic
  control, genetic deficiency is important in
  Parkinsons disease, Gilbert syndrome,
  Crigler-Najjar syndrome

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Polymorphism of phase II metabolism conjugation
II.

• Acetylation
• INH (isoniazid) is acetylated by
  N-acetyltransferase (NAT)
• Speed of acetylation is genetically determined
  bimodal distribution, slow and fast acetylators
• Autosomal recessive inheritance
• The rate of slow acetylators increases with age
• Rate of slow acetylators is higher Gilbert
  syndrome, rheumatoid arthritis, ischaemic heart
  disease
• N-substituted arylamines are less carcinogenic
  after acetylations

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Frequency of fast acetylators in different
populations
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Other important pharmacogenetic polymorphisms I.

• Glucose-6-phosphate dehydrogenase
• Most frequent pharmacogenetic enzymopathy
• 130 enzym variants, only some are abnormal
• Antimalaria drugs (primaquine), antibiotics
  (sulfonamides, chloramphenicol, nitrofurantoine),
  other medicines (quinine, quinidine,
  phenylhydrazine, dapson) cause fatal haemolysis
  in some patients
• Favism haemolysis after consumption of legumes,
  gooseberry, blackcurrant

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Other important pharmacogenetic polymorphisms II.

• Alcohol dehydrogenase (ADH)
• Speed of ethanol?? acetaldehyde reaction is
  increased
• Acetaldehyde dehydrogenase activity is
  unaffected, so acetaldehyde is not metabolised at
  a sufficient rate
• Acetaldehyde is accumulated causing flushing and
  tachycardia
• Frequency 5-20 in caucasians, 90 among Chinese

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Other important pharmacogenetic polymorphisms
III.

• Serum cholinesterase
• Activity of serum cholinesterase is reduced in
  some people (1/25000)
• Administration of succinylcholine causes
  paralysis of breathing muscles

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Gene-environment interactions intraindividual
variability I.

• Diet may alter hepatic cytochrome P 450 activity
• Smoked foods (polycyclic aromatic hydrocarbons)
  increase CYP1A activity (Kall Clausen 1995)
• Cruciferous vegetables (brussels sprouts,
  cabbage, broccoli) alter activity of selected
  CYP isoenzymes
• Indole-containing vegetables (cabbage,
  cauliflower) upregulate CYP1A (Pantuck et al.,
  1989)
• Isothyocyanate-containing vegetables (watercress)
  inhibit CYP2E1 (Kim Wilkinson 1996)
• Organosulfur compounds (garlic) inhibit CYP2E1
  and induce CYP1A, CYP3A and phase II enzymes
• Grapefruit juice phytochemicals influence CYP3A
  activity
• Vitamins, spices

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Gene-environment interactions intraindividual
variability II.

• Drug-drug interactions
• Enzyme inductors or inhibitors rifamycins,
  anticonvulsants, macrolide antibiotics, azole
  antifungal drugs, nefazodone, certain SSRIs
• Nutraceutical influences herbs and dietary
  compounds
• St. Johns wort (Hypericum peforatum) CYP3A
  inductor
• Aging lower blood flow and liver volume
  decreases from the third decade, but the effect
  on enzymes is moderate
• Disease
• Acute inflammation and infection affect drug
  metabolism
• Liver disease modifies blood flow and reduces
  enzyme activity

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Cytochrome P450 isoenzymes involved in
polymorphism of drug metabolism
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PSYCHOPHARMACOGENETICS
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CYP enzymes important in psychiatry

• CYP 1A2
• Antidepressants amitryptiline, clomipramine,
  imipramine, mirtazapine
• Antipsychotics olanzapine
• Beta blockers propranolol
• Caffeine, paracetamol, theophylline, warfarine
• CYP2C19
• antidepressants citalopram, clomipramine,
  imipramine
• Barbiturates hexobarbithal, mefobarbithal
• Beta blockers propranolol

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CYP 2D6

• Antipsychotics
• haloperidol, terfenazine, risperidone,
  thioridazine
• SSRIs
• fluoxetine, N-desmetilcitalopram, paroxetine
• TCAs
• amitryptiline, clomipramine, desipramine,
  imipramine, nortryptiline
• Other antidepressants
• venlafaxine, nefazodone, trazodone, mirtazapine
• Narcotics
• codeine, dextrometorfane, etilmorphine
• Antiarrhythmetics
• encainide, flecainide, mexiletine, propafenone
• Beta blockers
• alprenolole, bufarolole, metoprolole,
  propranolol, timolol

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CYP 3A3/4

• Antidepressants amitryptiline, clomipramine,
  imipramine, nefazodone, sertraline,
  o-desmetil-venlafaxine, mirtazapin
• Antipsychotics clozapine
• Benzodiazepines alprazolam, clonazepam,
  diazepam, midazolam
• Pain killers acetaminophen, alfentanyl, codein,
  dextrometorphan
• Antiarrhytmic drugs amiodarone, disopiramid,
  lidocaine, propaphenon, kinidin
• Ca antagonists diltiazem, felodipine,
  nicardipine, nifedipine
• Spasmolytics carbamazepine, ethosuximid
• Antihistamines astemizole, rolatadine,
  terfenadine
• Anti-estrogens docetaxel, paclitaxel, tamoxifen
• Macrolidos clarithromycine, erithromycine,
• Steroidok androstendione, cortisol, estradiol,
  ethynilestradiol, progesterone, testosterone,
  dexamethasone
• Other cisapride, dapson, lovastatine, omeprazol

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PSYCHOPHARMACOGENETICS

• Polymorphisms concerning the therpaeutic effect
  of drugs influencing psychological functions
• Primarily polymorphisms concerning the target
  molecules of drug action (to a lesser extent
  polymorphism of molecules involved in
  pharmacokinetic processes)

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Psychopharmacons

• Drugs influencing the CNS functions and
  psychological processes
• Each neurotransmitter system regulates several
  functions
• A given drug binds to several target molecules
  binding profile
• In case of a given drug moluceule, target
  molecule binding varies in different brain regions

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Effect of psychopharmacons

• Target molecules of drugs (receptors, enzymes,
  transporters)
• Key role in regulating neurotransmitter function
• Directly or indirectly influence the development
  of neural circuits and neuroplasticity
• Quantity and function of gene products is
  influenced by
• Variations in gene structure (rare)
• Variations in gene expression (more frequent)

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• Treatment response to antidepressant, anxiolytic
  and antipsychotic drugs is influenced by genetic
  factors
• The genetic component is highly complex,
  polygenic, epistatic (suppression of the effect
  of a gene by a nonallelic gene)
• Treatment response involves genetic and
  environmental factors
• Contribution of single genes to drug effect is
  modest
• Interaction between genes can result in a
  dramatic modification of drug response additive,
  nonadditive, synergistic

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Serotonergic system

• Mood
• Cognition
• Motor function
• Circadian rhythms
• Neuroendocrine system
• Food intake
• Sleep
• Reproductive activity

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Psychiatric disorders treatable with medications
acting through the serotonergic system

• Depression
• Anxiety
• Impulse control disorders
• Substance abuse
• OCD
• Somatic disorders, sexual disorders. Psychotic
  disorders?

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5-HTTLPR

• SERT gene (SLC6A4) 17q11.1-q12

Lesch KP. (2001) J Affect Disord, 62 57-76.
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The 5-HTTLPR polymorphism of the serotonin
transporter gene

• 17q11.1-q12
• Promoter region
• Insertion-deletion polymorphism
• 2 alleles s és l ? 3 genotypes ss, sl, ll
• Functional polymorphism

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Serotonin transporter and antidepressant response

• Allelic variation in 5HTT function may lead to
• Increased susceptibility to anxious and
  depressive features
• Less favourable antidepressant response in
  patients affected by mood disorders

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• Smeraldi et al. 1998
• Subjects carrying 5HTTLPR ll and ls genotypes
  show better response for fluvoxamine than ss
  subjects
• Zanardi et al. 2000
• Same results with paroxetine
• Pollock et al 2000
• ll patients display a faster response to
  paroxetine
• No difference in case of nortryptiline
  (predominantly noradrenergic)
• Whyte et al., 2001
• Effect of 5HTTLPR on platelet activation in
  geriatric depression

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• Rausch et al., 2002
• Association between ll genotype and improved
  response to fluoxetine
• Significant increase in response to setraline in
  eldery depressed ll patients
• Former results might only apply to Caucasian
  patients Korean and Japanese patients there is
  a better response to fluoxetine, paroxetine and
  fluvoxamine in ss patients

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• Benedetti et al., 1998
• ll bipolar patients show superior mood
  improvement after total sleep deprivation
• Mundo et al., 2001
• 63 of patients with antidepressant induced mania
  carried the s allele as compared to 29 in
  bipolar subjects exposed to antidepressants not
  developing mania
• Michelon et al., 2006
• Association between 5-HTTLPR genotype and
  therapeutic response to lithium

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Other important polymorphisms in
psychopharmacogenetics schizophrenia

• D3 (Ser9Gly), D2 (Taq I és -141-C Ins/Del)
  antipsychotic response, tardive dyskinesia
• Adams et al. 2008 DRD3 and olanzapine response
  in chronic scz
• Sakumoto et al. 2007 DRD2 polymorphism predicts
  response to DA antagonists in scz (bromberidol,
  nemonaprid)
• Kondo et al. 2003 DRD2 receptor polymophisms
  predict treatment resistance in scz
• 5-HT2C (-759-T/C) antipsychotic treatment
  related weight gain
• (CYP2D6 ultrarapid metabolisers)

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Other important polymorphisms in
psychopharmacogenetics depression

• Choi et al. 2006 BDNF (Val66Met) polymorphism
  and citalopram response
• Domschke et al. 2008 MAO-A and antidepressant
  response
• Baune et al. 2008 COMT-A val158met amd
  antidepressant response
• Wilkie et al. 2008 HTR2A and paroxetine
  treatment
• Serretti et al., 2001 TPH1 slower response to
  fluvoxamine
• Schumann etal. 2001 DRD3 genotype and
  antidepressive effect of sleep deprivation

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Association between genetic polymorphisms and
drug effects

• Beginning of effect
• Response rate
• Remission rate
• Relapse
• Side effect
• Selective decrease in symptoms

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Pharmacogenetics

• Rational framework for evaluation of genetic
  variation of
• Drug metabolising enzymes
• Drug transporters
• Receptors
• Ion channels
• Which influences the risk of adverse drug
  reactions or therapeutic failure
• Reduction of trial-and-error choice of medication
  and dose
• Personalized treatment guidelines
• Lerer

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• THANK YOU FOR YOUR ATTENTION