Lecture 8

• Targets for drug action

  • Receptors
  • Enzymes
  • Ion channels
  • Transporters
• Receptors


  • Usually don't see complete absence — affect either function of receptor/level of expression
  • GPCRs - Polymorphism affect receptor or G protein coupling process
  • Most receptors relevant to pharmacogenetics have this structure — more minor role for nuclear receptors in drug response
• Study of polymorphism


  1. Not usually possible — discovered by scanning of genes by sequencing/other methods

  2. Coding seq — express variant + compare function

  3. Upstream polymorphism — reporter gene studies (luciferase as reporter enzyme) → clone section of promoter region into luciferase reporter vector → transfect into cell line

  4. Can use alkaline phosphatase reporter instead of luciferase — released into growth cells, no need to lyse cells, less sensitive
• β2-adrenergic receptor


  Product of intronless gene — 1239bp
• β2-adrenergic receptor variations


  • 9 known polymorphisms resulting in 4 known aa substitutions
  • Arg16Gly
  • Gln27Glu
  • Val34Met
  • Thr164Ile
  • Single polymorphism in leader peptide - Arg19Cys
  • Haplotypes - Combination of alleles on particular chromosome
  • Three common haplotypes in Europeans (2,4,6)
  • In African-Americans — 1 commmon, 2 rare
• Functional effect of β2 adrenergic receptor polymorphisms

  • Haplotype 4 = arginine
  • Reduced FEV seen in 4/4
• β1-adrenergic receptor


  • Main type in the heart
  • β-blocker target eg atenolol
• Gly389Arg


  • Gly variant less frequent
  • Arg form shows enhanced Gs protein interaction + incr adenylyl cyclase activation
• Clinical relevance of Gly389Arg


  • Arg form = enhanced Gs interaction ⇒ incr adenylyl cyclase activation
  • See better response to metoprolol in patients homozygous for Arg form
• Vitamin K epoxide reductase


  • Target for anticoagulants — warfarin
  • Gene — VKORC1
• VKORC1 polymorphisms


  • G1639A — upstream region, A at -1639 = low expression, G at -1639 = high expression
  • C1173T — in first intron, Affects patients warfarin dose requirement
• Warfarin resistance


  • Normal dose ⇒ 5 mg/day, each patient should be titrated
  • Warfarin resistant patients — more than 10mg/day ⇒ aa subs in gene, coding region subs rare
  • Non-compliance most usual cause
  • Affect warfarin binding NOT Vit K epoxide reduction
  • Mutations - D36Y + V66M in CL domain — warfarin resistance, D36Y common in Middle East (4-10%)
  • Screening not considered — rarity
• Combined CYP2C9/VKORC1 genotype


  • Combination of genetic + environmental factors → 55% of warfarin dose variability
  • Developed equation = quantifies effect of each factor + allows dose prediction
  • Warfarin prescribed less commonly due to DOACs — less variation in dose requirements
• Cystic fibrosis


  Defect in CFTR ⇒ Cl- transport channel
• ΔF508del


  • Protein not inserted into cell membrane
  • Orkambi - Ivacaftor + lumacaftor — helps movement to the plasma membrane
  • Symkevi - Ivacaftor + tezacaftor + elexacaftor → More efficient than Orkambi
• G551D


  • Involved in 5% cases
  • Channel reaches cell surface — doesn't transport Cl-
  • Gating defect — channel no longer responds to ligand
  • Class 3 + 4 drugs - Ivacaftor — reverses defect in Cl- channel
  • Effects for 48 weeks - Sweat chloride reduced, FEV1.0 improved by 11%, 55% decrease in pulmonary exacerbations