TD: Pharmacogenomics Flashcards
Why is there a need for personalised medicine?
What is medicine like now a days compared to previously?
- Genetic variation between individual therefore different response to drug
- Metabolism of drugs
- Rate of drug absorption
- Medicine in the post-genomic era
- Personalised
- Screening of populations
- Susceptibility to common disease
- Move from reactive ‘diagnose & treat’ to proactive ‘predict & prevent’
Same Drug, same presciption
Answer to the same drug, prescription slide
What is this and what are the aims?
- Pharmacogenomics
- The study of variations in DNA (genetics) and RNA (transcriptomics) characteristics as related to drug response
- Aim:
- More therapeutically effective drugs
- Safer drugs
- More cost effective
How many errors are they in the genetic sequence and how can these be detected?
Mistakes during the initial pairing of template nucleotides and complementary nucleotides occur at a rate of one error per 10,000 base pairs.
The final error rate is only one per billion nucleotides, after DNA polymerase proofreads the newly synthesized DNA.
- >1.4 million SNPs identified in human genome.
- >60,000 SNPs within coding regions.
- Detection methods
- RFLP
- Microarray
Pharmacogenomics and response to medicine largely depends on _______
How may changes in the DNA sequence of drug receptors, drug metabolising enzymes and transporters influence drug response?
- Drug receptor interactions:-
- Changes in gene endocding for receptor may lead to changes in the receptor so that the drug no longer recognises it and interacts
- Drug metabolising enzymes
- Change in genes encoding for these enzymes might lead to a change in specificity of the enzyme so that they no longer metabolise the drug or even do now metabolise the drug
- Drug transporters
- Is drug uptaken by these?
- Efflux proteins? - work to remove toxins from body/prevent absorptoin
- These can affect accumulation of drug in body
- Regulation of the drug target
Describe drug/receptor interactions
The specificty of a receptor is usually dependent on the gene encoding for them. changes or mutations can have significant impacts on the protein produced.
- Is the protein still produced?
- Is the protein folded correctly?
- Does the protein locate to the correct part of the cell (normally the cell membrane/surface)
- Problem with trasnport to that area?
Consequence of SNP is of significance to the design and efficacy
Describe the following graph relating to varriation in drug receptor genotype
Picture 1:
- As drug concentratoion increases the effiacy increases (as receptors present and more interaction). Drug toxicity only crosses over at high drug conc.
Picture 2:
- 1 variated alle leads to decreased amounts of the receptor protein present therefore less receptor for the drug to interact with so less efficacy. At higher concentrations the drug efficacy levels and toxicity levels overlaps
Picture 3:
- 2 mutant alles:- little or no benefit as drug receptor not present for drug to bind to. - only toxicity present
Describe the following graph relating to variation in genotype of drug metabolising enzymes
Picture 2:
- 1 varrient alle/ 1 functioning gene means that only 1/2 the metabolsiing enzyme concentration is produced therefore less metabolism of drug and drug accumulates
Picture 3:
- No enzyme prodcued therefore no metabolism and drug accumulates
Is there was no funtioning metabolsing enzyme for a drug it would not be prescribed
Give an example of a drug which can have polymorphic varients which affect drug response/effacacy/toxicity
CYP 2D6
- Member of cytochrome P450 family of drug metabolising enzymes
- 40+ drugs & environmental chemicals
- As much as 20% of all commonly prescribed drugs
- 77+ alleles identified
- Some are functionally important
- e.g. poor or ultra-rapid metaboliser phenotype
- Significant changes in pharmacokinetics of CYP2D6 substrates
Polyygenic drug response
Main single scientific obstacle to widespread personalised prescribing is that single genotypes are often not reliably predictive of a persons response to a drug
Need to look at multiple e.g. receptor and metaboliszing enzyme genomes
What are P-glycoproteins
What gene encodes for them?
P-glycoprtoeints are drug transporters that cause the effluxation of molecules which have been absorbed out of the body (pump out).
They are encoded for by the multi drug resistance gene - this is known to contain many SNPs or polymorphic varriants.
They are situated on the cell membrane and have intra and extra cellular domains
Give an example of a substrate for the P-glycoproteins
Substrate for P-glycoprotein.
–Belongs to the group of medicines known as cardiac glycosides
–Used to treat arrhythmias and heart failure.
–increased bioavailability of digoxin in TT subjects
–Genotypic variations in digoxin bioavailability
As digoxin is a substrate og P-GP this is taken into account when dosing - higher dose given - as known some will be effluxed out. However if the patient is homozygous for the variant/ mutant allele TT then there is reduced effluxing so this higher dose can actually be toxic and higher concentrations resultant.
Symptoms of condition used to treat and toxicuty are similar therefore can be difficult to detemrine which
Describe the effect of P-GP genotype SNP/varriants on ART therapy
Variations seen between the homozygous and hetrozygous forms of this SNP
Loss of P-glycoproteins can be beneficial for pateints receiving AVT.
Patients with 2 varriant alleles for P-GP express less P-GP therefore less efflux occurs and a greater ocncentration of AVT is acheived in the body to have an effect (TT). Whereas patients with the normal allele have more P-GP, therefore less conc in body to have an effect - duration of treatment longer.
CD4 is a glycoprotein expressed on many immune cells- overall inficator of immune function. HIV uses CD4 to gain entry into host T-cells and achieves this through its viral envelope protein. The binding to CD4 creates a shift in the conformation of this protein allowing HIV to bind to a co-receptor expressed on the host cell. Following a structural change in another viral protein, HIV inserts a fusion peptide into the host cell that allows the outer membrane of the virus to fuse with the cell membrane.
Transcription profiling
- Gene expression profile
- Potential for looking at the expression of genes in response to
–Drug administration
–Disease status
–Disease onset and progression
May involve changes in cells peripheral to affected area
Microarrays
Transcription tells us that genes are being switched on. In response to drug administration or disease progression, this gives valuable information regarding the significance of mutation within the sequences encoding gene products which are heavily involved in response to drugs or disease.
Microarray has huge potential to deliver a significant amount of information about the activity of 1000’s of genes at the same time.
The fact that a large number of transcripts are functionally unclassified tells us there is still much to learn about the role of many genes which are activated under physiological and pathophysiological conditions.
Pharmacogenomics overview
What is the potential for the development of personalised medicines using genomic profiles?
p-gp
What is VKORC1 involved in?
Why is polymorphic varriants in the gene encoding for this protein important?
What is CYP 2C9 involved in?
Examples of drugs it metabolises
Describe the effect of polymorphic varriants on CYP 2C9 on warfarin metabolism
What factors influence dose of warfarin given?
Warfarin dose case study
Distinct grouping of transcripts in synovial tissue
Distinct grouping of transcripts in peripheral blood cells
Describe the relationship between TNF-a and INF inRA
