BY : PHARMACOGENETICS V L Srividya, II Pharm.D(PB), N.E.T. PC,Raichur

PHARMACOGENETICS The study of genetically controlled variations in drug response. Pharmacogenetics is the special area of biochemical genetics that deals with variation in drug response and the contribution of genetics to such variation. It is a subset of Pharmacogenomics and is the study of variations in DNA sequence as related to drug response.

Key Concepts and Terms Monogenic: due to allelic variation at a single gene Polygenic: due to variations at two or more genes Polymorphic: frequently occurring monogenic variants occurring at a frequency >1%

Normal Distribution Frequency Activity

Polymorphic Distribution

GENETIC POLYMORPHISMS Pharmacokinetic Pharmacodynamic Transporters Plasma protein binding Metabolism Receptors Ion channels Enzymes Immune molecules

Genetic polymorphisms in drug metabolizing enzymes From: Evans WE, Relling MV. Pharmacogenomics: Translating functional genomics into rational therapeutics. Science 286:487-491, 1999.

Atypical Plasma Cholinesterase succinylmonocholine choline Hydrolysis by pseudocholinesterase a rapid acting, rapid recovery muscle relaxant - 1951 usual paralysis lasted 2 to 6 min in patients occasional pt exhibited paralysis lasting hrs cause identified as an “atypical” plasma cholinesterase

Soon after the introduction of muscle relaxant in 1951, an occasional atypical patient was encountered, suffering prolonged muscle paralysis and consequently apnea.These atypical patients showed low activity of plasma cholinesterase. MALIGNANT HYPERTHERMIA It is an uncommon complication of general anesthesia. Many inhalants and muscle relaxing agents have been incriminated as precipitating the event. The clinical features of malignant hyperthermia are muscular rigidity, tachycardia, cyanosis and respiratory acidosis.

The disorder is usually inherited as mendelian autosomal dominant, but about 20% of cases are sporadic and in a few instances recessive inheritance. It is possible that the gene locus is on chromosome 19. But, only a minority of malignant hyperthemia alleles are localized on chromosome 19. Another malignant hyperthermia locus has been proposed on chromosome 17 → malignant hyperthermia is a heterogeneous condition.

Glucose-6-phosphate dehydrogenase activity Effects >100 million worldwide CYP MPO PGH Synthase R-NH2 R-NOH ERYTHROCYTE O2 NADP+ or GSSG(?) NAD+ HgbFe+2 HMP Shunt G-6-PD Dependent R-NOH MetHgb Reductase NADPH or GSH(?) R-NO HgbFe+3 NADH GSH Reactive Oxygen Splenic Sequestration Semi-mercaptal SOD Catalase GSH Peroxidase sulfinamide Detoxification Hemolytic Anemia R-NH2

Drugs and Chemicals Unequivocally Demonstrated to Precipitate Hemolytic Anemia in Subjects with G6PD Deficiency Acetanilide Nitrofurantoin Primaquine Methylene Blue Sulfacetamide Nalidixic Acid Naphthalene Sulfanilamide Sulfapyridine Sulfamethoxazole

ATP – binding (ABC) superfamily Termed as (MFS)- Major Facilitator Superfamily Belongs to membrane associated transporter and include diverse group of proteins present in wide variety of organism & Cell types Currently about 250 ABC transporters (Traffic ATPases) have been identified 50 are identified in humans Further genome map will reveal more .

3 genetic mechanism influence pharmacotherapy Pharmacogenetic Trait Clinically Relevant : 3 genetic mechanism influence pharmacotherapy 1 - Genetic Polymorphism of genes  which results in Altered metabolism of drugs (metabolism of tricyclic antidepressants) Increased or decreased metabolism of a drug may change its concentration Of active, inactive or toxic metabolites

Hemolysis in glucose -6 –phosphate dehydrogenase deficiency 2 – Genetic variants  may produce unexpected drug effect (toxicity or it may be lethal to patient) Hemolysis in glucose -6 –phosphate dehydrogenase deficiency 3 – Genetic variation in drug targets May alter the clinical response & frequency of side effects Variants of β –adrenergic receptor alter response to β – agonists in asthma patients

CYP2D6 ACTIVITY

Discovery and Incidence of the PM Phenotype: Mahgoup et al and Tucker et al. (1977) explained Hydroxylation of antihypertensive drug debrisoquine is polymorphic in nature Eichlbaum et al showed the oxidation of sparteine is polymorhpic Metabolic Ratio (MR) of the two drug were closely correlated &metabolized by the enzyme CYP2D6 The existence of two or more forms of individuals within the same animal species (independent of sex differences). M EM – Extensive Metabolizers PM – Poor Metabolizersers

DRUGS WHOSE METABOLISM CO-SEGREGATES WITH DEBRISOQUINE alprenolol amitriptyline bufuralol clomipramine codeine desipramine encainide ethylmorphine flecainide fluoxetine guanoxan imipramine metoprolol nortriptyline paroxetine phenformin propafenone propranolol

THIOPURINE METHYLTRANSFERASE (TPMT)

TPMT POLYMORPHISM

Future Role of SNPs and Pharmacogenetics SNP - Single Nucleotide Polymorphisms ……. G G T A A C T G …… ……. G G C A A C T G …... AS of February 2001, 1.42 million SNPs had been identified in the human genome.

Identification of large no. of SNPs is needed “Genetic fingerprint” – acts as  probable individual Drug response Coding region of a gene Coding SNP’s (cSNP’s)  ~30,000 -1,00,000/genome Cause amino acid changes & changes in protein function or can be neutral SNP’s inside genes or in regulatory regions (perigenic or pSNP’s) Cause differences in protein expression Used “drug response profile’

Genetic Polymorphisms of Clinical Relevance Drug Metabolism Pharmacogenetics of Cancer Chemotherapy Fatal bone marrow cancer (TPMT) – Thiopurine methyltransferase  mercaptopurine, thioguanine & Azathioprine (to treat  Acute lymphoblastic leukemia (ALL) Drug Transport Drug Targets

THANK YOU THANK YOU TEXT BOOKS-REFERENCES: ·      1. Werner Kalow, Rachel F Tyndale, Urs A Meyer, Pharmacogenomics, Marcel Dekker Inc., 2001 ·      2. J. Licinio, Ma-LiWong, Pharmacogenomics: The Search for Individualized Therapies, Wiley-VCH, 2002 3.Adam Hedgecoe-The politics of personalized medicine – Pharmacogenetics in the Clinic,Cambridge University Press,2004. 4. Mark A. Rothstein Pharmacogenomics- Social,ethical and Clinical dimensions –Wily Liss 2003 5 https://www.pharmacogenomics.org THANK YOU