Pieter van der Bijl, Emeritus Professor and Former Head of Pharmacology, Faculty of Health Sciences, Stellenbosch University,

Cape Town, South Africa

GDF: Introduction: 1 The focus of traditional medical practice is on

clinical signs and symptoms in accordance with medical history

Not always the most effective approach given the different genetic profile of each individual

Pharmacogenetic studies over many decades have documented that genetic variability can affect PK and PD

Polymorphisms of drug metabolising enzymes, transporters and receptors contribute to variable drug responses (in addition to environmental , physiological & compliance factors)

GDF: Introduction: 2

Most drugs act on: Enzymes Transporters Membrane ion channels Receptors

and

Are biotransformed by: Drug metabolising enzymes

Drug

GDF: Introduction: 3 Foregoing molecular systems are all proteins

coded for by certain genes Not surprising that genetic factors are major

determinants of variability of drug effects and many pts do not respond adequately to their medication ( confusion in the‘therapeutic jungle’)

Some blockbuster drugs have only limited efficacy in 70% of pts

Many reasons for this, but pharmacogenetics plays an important role

Most information hitherto from genetic diversity obtained wrt drug metabolising enzymes

Drug

AbsorptionDistributionMetabolismExcretion

Blood levels

Drug

ReceptorTranscriptionfactors

CellAdverse drugreactions

Beneficial effects

reactions

Genes

Genes

Genes

Genes

GDF: Effects of genes on drugs : 4

GDF: Variable efficacy of drugs: 5

Drug Class Insufficient response (%)

SSRIsSSRIs 10-2510-25

ACE-inhibitorsACE-inhibitors 10-3010-30

-blockers-blockers 15-2515-25

AntidepressantsAntidepressants 20-5020-50

StatinsStatins 30-7030-70

22-agonists-agonists 40-7040-70

GDF: Pharmacogenetics/-nomics: 6

Recently pharmacogenetics has evolved into ‘pharmacogenomics’

The latter involves a shift from a focus on individual candidate genes to genome-wide association studies

Pharmacogenomics is a precursor of personalised medicine

This constitutes a shift from ‘one-drug-fits-all’ to ‘the right drug for the right patient at the right dose and time’

But, each pt will not be treated differently from every other pt (economically untenable)

GDF: Pharmacogenetics/-nomics: 7 Rather, pts will be divided into groups by genetic and

other markers that predict disease progression and treatment outcome

For drug treatment one needs to avoid lack of response or toxicity

If ADRs can be from 5% to 2% by excluding 10% of the targeted population, the drug gains a better risk/benefit ratio 1st choice Rx and a market share

There is a growing trend to link new drugs with diagnostic biomarkers (often genetic) (FDA, EMA) improved Rx outcome (personalised medicine!)

GDF: Benefits Pharmacogenetics/-nomics: 8

Improvement of drug choices In USA 100 000 pts die annually due to ADRs and

2 000 000 are hospitalised Pharmacogenomics will predict who will have a + or - reaction

Safer dosing options Testing of genomic variation will correct dosing

Improved drug development industry to determine in which populations new drugs will be

effective

Decreased health care costs deaths and hospitalisation due to ADRs purchase of drugs ineffective in certain pts Speed up clinical trials for new drugs

GDF: Benefits Pharmacogenetics/-nomics: 9

GDF: Altered drug responses: 10

P-genetic biomarker Drug DiseaseFDA class.

EMA labels

Aim of genotyping

G6PD deficiencyG6PD deficiency PrimaquinePrimaquine MalariaMalaria ++Elimination of Elimination of

ADRsADRs

NAT variantsNAT variants INHINH TuberculosisTuberculosis ++ **Elimination of Elimination of

ADRsADRs

CCR5 expressionCCR5 expression MaravirocMaraviroc HIVHIV ++++++ **** EfficiencyEfficiency

C-KIT expressionC-KIT expression ImatinibImatinib GI stromal tumourGI stromal tumour ++ **** EfficiencyEfficiency

CYP2C9 & VKORC1 CYP2C9 & VKORC1 variantsvariants WarfarinWarfarin ThromboembolismThromboembolism ++++ Elimination of Elimination of

ADRsADRs

CYP2C19 variantsCYP2C19 variants VoriconazoleVoriconazole Fungal infectionFungal infection ++Elimination of Elimination of

ADRsADRs

EGFR expression and K-EGFR expression and K-RAS mutationRAS mutation CetucimabCetucimab Colorectal CAColorectal CA ++++++ **** EfficiencyEfficiency

HER/neu overexpressionHER/neu overexpression TraztuzumabTraztuzumab Breast CABreast CA ++++++ **** EfficiencyEfficiency

Ph1 chromosomePh1 chromosome ImatinibImatinib ALLALL ++++++ **** EfficiencyEfficiency

TPMT variantsTPMT variants MercaptopurineMercaptopurine ALLALL ++++ ** EfficiencyEfficiency

UGT1A1 variantsUGT1A1 variants IrinotecanIrinotecan Colorectal CAColorectal CA ++++ Elimination of Elimination of ADRsADRs

+++ required; ++ recommended;+ for information only

** included into indication or contraindication label* included in the other label information

GDF: G6PD deficiency: 11

G6PD (glucose-6-phosphate dehydrogenase) an enzyme in hexose monophosphate shunt (a main source of NADPH generation)

NADPH needed to reduce disulphide bonds of glutathione (GS-SGGSH) and other proteins

Many drugs and their metabolites can use up GSH and lead to GSH levels in G6PD deficient pts

GSH deficiency in RBC results in: Membrane fragilityhaemolysishaemolytic anaemia

GDF: G6PD deficiency: 12

GDF: N-acetylation: 13

In late 1940’s discovered that there was a high incidence of peripheral neuropathy in pts Tx with isoniazid (INH) for tuberculosis

INH is cleared from the blood after acetylation in the liver by N-acetyltransferase (NAT2)

Hereafter the N-acetyl INH and some minor metabolites areexcreted in the urine

Hepatic insufficiency may t½

N CO-NH-NH2

Acetyl CoA acts as a donor of the acetylgroup on INH

Isoniazid (INH)

N-Acetyltransferase(NAT2)

Acetyl-Isoniazid (INH)

GDF: N-acetylation: 14

CoA-COCH3+

Acetyl-Coenzyme A

N CO-NH-NH-COCH3 CoA+

Coenzyme A

GDF: Rapid and slow acetylators: 15

Individuals who are rapid acetylators: Have failure rate with INH in Tx of TB Require doses of hydralazine to control HT

Individuals who are slow acetylators have risk of: Drug-induced SLE with hydralazine Haematological ADRs after INH Idiosyncratic ADRs to sulphonamides Bladder CA after exposure to carcinogenic

arylamines Breast CA in postmenopausal females (4x)

GDF: N-acetylation: 16 Work done in the Department of Pharmacology, SU has

shown that there exist three well-defined groups of acetylators of INH [N-acetyltransferase (NAT2)] in the Western Cape Coloured population (mixed-race)

The proportion of patients in these groups (fast, intermediate and slow) depends on racial characteristics

Wide variation in other ethnic populations found (Eskimo’s, Asians, Africans,European & Egyptian)

F20%

I50%

S30%

GDF: Warfarin: 17

The most commonly prescribed anticoagulant (vit K antagonist) (role of dabigatran & rivaroxaban)

Has a narrow therapeutic index that varies widely between individuals (monitoring)

Pts may be: Resistant and need dose to prevent CVAs (strokes) Sensitive and need dose to prevent CNS bleeding

Metabolised by CYP450 (CYP2C9*2 and *3) Vit K is recycled by vit K epoxide reductase

(VKORC1)

GDF: Warfarin: 18

GDF: Genomics/Proteomics: 19

Implications of postgenomic medicine wrt drug development

Apart from improved drug choices and development, safer dosing and decreased health costs genetically modified organisms can be used for drug production, eg insulin, monoclonal antibodies etc

GDF: Genomics/Proteomics: 20

GDF: Genomics/Proteomics: 21

First regulatory review of targeted therapeutic agent with diagnostic test

Approval of trastuzumab and HercepTest for pts with HER-2/neu overexpressing in breast CA (FDA,1999)

Trastuzumab (Herceptin) is a humanised IgG1 against ectodomain of the HER-2 /neu receptor

GDF: Traztuzumab: 22

Y

HER-2/neu

GDF: Genomics/Proteomics: 23

Another example, diagnostic kit for Bcr-Abl translocation in CML and selection for Rx with small molecule drug, imatinib (Gleevec)

Acts by inhibiting tyrosine kinase and activation of target proteins in cellular proliferation

GDF: Imatinib: 24

Tyrosine kinase

O

H3C

N

HN

CH3

N N N

N

HN

GDF: Genomics/Proteomics: 25

Also variety of diagnostic tests for management of major nonmalignant diseases are becoming available Germline-based SNP detection or biomarkers

on serum or synovial fluid for progression of RA and selection of Rx

Measurement of C-reactive protein markers in novel ways for CV disease

Also genotyping and molecular diagnostics for diabetes mellitus

Viral load testing and drug resistance (HIV) measuring is becoming standard

GDF: Genomics/Proteomics: 26Conclusions Trial and error medicine to precise

biomarker-assisted diagnosis and more effective molecularly-guided Rx

For drug companies efficiency, productivity and product lines

Over next 5 years will see large impact of targeted drug approach guided by diagnostic tests in Rx of CA

Exciting future wrt new specificdrug development increased quality of life

GDF: Personalised prescribing- the future: 27

•A drop of blood or smear from buccal pouch •Microchip (gene chip) checks for 31 variations (polymorphisms) in two genes (CYP2D6 & CYP2C19)•Phenotype (eg ultrarapid metabolisers) identified

1. mRNA extracted from sample2. cDNA copies made and dye

(green/red)labelled (eg CA/N)3. Microarray, 1000’s wells (many

identical copies of same gene)4. cDNA pipetted into each well and

hybridizes with complementary strands (wash)

5. Microarray scanner6. Expression pattern obtained

?

большое cпасибо