Nucleotides (molecules containing sugar, nitrogen containing purine and pyrimidine bases, and a phosphate group) are the building blocks of DNA

Codon (units of three adjacent nucleotides)Each codon specifies one amino acid

Arrangement of codons in the DNA (organ specific)

Transcription into messenger RNA (mRNA)

Determination of the sequence of amino acid that forms a particular protein

The number of possible biosynthetic permutations is very high if one considers that a typical protein can be made of 500 amino acids and that one of these may be occupied by any one of 20 different amino acids

Proteins:• Make up the cell cytoskeleton• Directed movement of molecules throughout the cell• Pump nutrients and ions across the membranes• Serve as receptor sites for hormones that finitely adjust the functions of the cell according to

changing bodily needs• A group of proteins regulates gene activities by binding to DNA and activating or repressing

gene transcription

• Some serve as carrier molecules like hemoglobin, the body’s oxygen carrier.

• Some small proteins (peptides) are secreted by cells as neurotransmittersor hormones like insulin. These hormones and other peptide molecules hold enormous power. Because they can act on numerous specific cell surface receptors, they can influence virtually all bodily functions from the nervous system to immune system

Their selectivity, potency, and often-desired evanescent effects on selective target cells make them enormously attractive as magic bullets (Paul Ehrlich)

The concept that genetic information flows from DNA to RNA to proteins has become a fundamental milestone of modern biology

Pharmacogenomics

Pharmacogenomics is the study of how an individual's genetic inheritance affects the body's response to drugs. The term comes from the words pharmacology and genomics and is thus the intersection of pharmaceuticals and genetics.

Effect on drug absorption

MDR1 gene encodes P-glycoprotein (P-gp) a large transmembrane protein that is an integral part of the blood-brain barrier and mucosal barriers

P-gp functions as a drug-efflux pump effluxing a variety of drugs

P-gp is also involved in imparting resistance to multiple structurally unrelated chemotherapeutic agents

MDR1 has been mapped to chromosome 7Chan et al. (1991) demonstrated that the measurement of

P-gp immunohistochemically in tumor samples in children with neuroblastoma is helpful in predicting the success or failure of therapy

Hoffmeyer et al. (2000) found a significant correlation between a polymorphism in exon 26 of MDR1, 3435C-T, with expression levels of MDR1

People who are homozygous for the 3435T allele of MDR1 have on average substantially lower intestinal P-gp expression than those homozygous for the C allele

83% of west africans (Ghanaians) studied and 61% of African Americans were homozygous for the C allele, whereas only 26% Caucasians and 34% Janpanese showed this genotype (P<0.0001)

Influence on drug elimination

The cytochrome P450 (CYP) family of liver enzymes is responsible for breaking down more than 30 different classes of drugs. DNA variations in genes that code for these enzymes can influence their ability to metabolize certain drugs. Less active or inactive forms of CYP enzymes that are unable to break down and efficiently eliminate drugs from the body can cause drug overdose in patients. Today, clinical trials researchers use genetic tests for variations in cytochrome P450 genes to screen and monitor patients. In addition, many pharmaceutical companies screen their chemical compounds to see how well they are broken down by variant forms of CYP enzymes

Another enzyme called TPMT (thiopurine methyltransferase) plays an important role in the chemotherapy treatment of a common childhood leukemia by breaking down a class of therapeutic compounds called thiopurines. A small percentage of Caucasians have genetic variants that prevent them from producing an active form of this protein. As a result, thiopurines elevate to toxic levels in the patient because the inactive form of TMPT is unable to break down the drug. Today, doctors can use a genetic test to screen patients for this deficiency, and the TMPT activity is monitored to determine appropriate thiopurine dosage levels.

Clin Pharmacol Ther. 2004;75(1):13-33 9

P Glycoprotein is Widely Distributed

Efflux activity reduces intestinal absorption while enhancing elimination through liver and kidney

At barrier sites (blood-brain, testes, or placenta), P-gp limits tissue exposure to potentially toxic compounds

Portal Vein

P glycoprotein transports

substrates back into the gut lumen

J Clin Invest. 1999; 104(2): 147–153 11

P-Glycoprotein is Inducible

Mean (n = 8) plasma concentration (mean ± SD) time curves of orally administered digoxin (1 mg) before (open circles) and during (filled circles) coadministration of rifampin (600 mg)

J Clin Invest. 1999; 104(2): 147–153 12

Before Rifampin…

Duodenal biopsy (villus tip, ×40) immunostained for P-glycoprotein before administration of rifampin

J Clin Invest. 1999; 104(2): 147–153 13

9 Days Later…

Duodenal biopsy (villus tip, ×40) immunostained for P-glycoprotein after administration of 600 mg of rifampin for 9 days

P-glycoprotein polymorphism

Significant correlation between a polymorphism in exon 26 of MDR1, 3435C-T, with expression levels of MDR1 (Hoffmeyer et al., 2000)

People who are homozygous for the 3435T allele have on average substantially lower intestinal P-gp expression than those homozygous for the C allele

83% of west africans (Ghanaians) studied and 61% of African Americans were homozygous for the C allele, whereas only 26% Caucasians and 34% Janpanese showed this genotype (P<0.0001)

No Clinically relevant polymorphisms were reported for CYP3A4

MDR1 Haplotypes

CEPH population

Yoruba population

MDR1 gene LD blocks

CEPH population

Yoruba population

CYP3A4 Haplotypes

CEPH population

Yoruba population

CYP3A4 gene LD blocks

CEPH population

Yoruba population

MDR1 gene tag SNP ratios in CEPH populationrs6946119 867735163'UTR CT=20 CC=4 TT=36 TC=0 NN=0rs7802783 867750483'UTR CT=10 CC=45 TT=1 TC=0 NN=4rs1055302 867775673'UTR AG=10 AA=1 GG=49 GA=0 NN=0rs6979885 86782112Int27 AG=24 AA=2 GG=32 GA=0 NN=2rs4437575 86783967Int26 AG=36 AA=12 GG=9 GA=0 NN=3rs1002204 86786148Int26 GT=29 GG=11 TT=13 TG=0 NN=7rs6949448 86786465Int26 CT=33 CC=19 TT=8 TC=0 NN=0rs4148743rs2373589rs7787082 86801702Int22 AG=20 AA=1 GG=39 GA=0 NN=0rs10234411 86809543Int21 AT=31 AA=20 TT=7 TA=0 NN=2rs4148737 86815803Int18 AG=30 AA=19 GG=11 GA=0 NN=0rs10276603 86816178Int18 CT=16 CC=1 TT=42 TC=0 NN=1rs2091766 86819155Int16 CT=30 CC=21 TT=9 TC=0 NN=0rs1128503 86824252Ex13 CT=31 CC=21 TT=8 TC=0 NN=0rs1922241 86830545Int9 AG=30 AA=3 GG=27 GA=0 NN=0rs11772987 86830669Int9 CG=18 CC=41 GG=1 GC=0 NN=0rs10244266 86833118Int9 GT=15 GG=2 TT=41 TG=0 NN=2rs868755 86834581Int9 AC=33 AA=6 CC=21 CA=0 NN=0rs13237132 86836320Int8 CG=28 CC=28 GG=4 GC=0 NN=0rs1202170 86839757Int8 AG=32 AA=13 GG=15 GA=0 NN=0rs2235015 86844215Int5 GT=22 GG=32 TT=0 TG=0 NN=6rs6950978 86845118Int5 AT=29 AA=27 TT=3 TA=0 NN=1rs2520464 86845737Int5 AG=31 AA=7 GG=22 GA=0 NN=0rs12334183 86846031Int5 CT=26 CC=2 TT=32 TC=0 NN=0rs10260862 86846133Int5 CG=24 CC=2 GG=33 GC=0 NN=1rs10264990 86847266Int5 CT=32 CC=6 TT=22 TC=0 NN=0rs13226726 86851266Int5 CT=12 CC=44 TT=0 TC=0 NN=4rs1202172 86855625Int5 GT=28 GG=13 TT=19 TG=0 NN=0rs1202171 86855696Int5 AT=26 AA=13 TT=20 TA=0 NN=1rs4148733 86857883Int5 CT=12 CC=0 TT=48 TC=0 NN=0rs1211152 86859765Int4 GT=14 GG=46 TT=0 TG=0 NN=0rs17327624 86861468Int4 GT=14 GG=45 TT=1 TG=0 NN=0rs11763872 86861866Int4 CT=35 CC=8 TT=8 TC=0 NN=9rs7802773 86862998Int4 AG=42 AA=12 GG=6 GA=0 NN=0rs13229143 86864132Int4 CG=38 CC=9 GG=13 GC=0 NN=0rs12535512 86864985Int4 CT=36 CC=4 TT=20 TC=0 NN=0rs2188526 86865213Int4 AG=40 AA=5 GG=15 GA=0 NN=0rs3789243 86865537Int4 CT=40 CC=6 TT=14 TC=0 NN=0rs2214102 86874152Ex3 AG=16 AA=0 GG=44 GA=0 NN=0rs13233308 86889611Int1 CT=36 CC=16 TT=8 TC=0 NN=0rs10246878 86920292Int1 AG=29 AA=3 GG=28 GA=0 NN=0rs2157930