The test genotypes three polymorphisms in two genes that correlate with warfarin dose and allow individualization of therapy based on genotype. The more active S-enantiomer of warfarin is metabolized to inactive forms by the liver enzyme cytochrome P450 (CYP450) 2C9. Two polymorphisms in the gene for CYP450 2C9 (*2, *3) reduce enzyme activity and are correlated with reduced warfarin dosage and an increased incidence of adverse side effects. The vitamin K epoxide reductase (VKOR) enzyme participates in the pathway of reactions leading to activation of clotting factors and is the target of warfarin action. A warfarin-sensitive haplotype has been identified, and the promoter polymorphism –1639G>A can identify patients with the warfarin-sensitive genotype (–1639AA).

Genotyping of mutations or polymorphisms uses allele-specific signal probes containing ferrocene labels with distinguishable redox potentials. The signal probe matching the wild-type sequence contains a ferrocene label of one electrochemical potential, and a second signal probe matching the mutant sequence contains a second, distinguishable ferrocene label. Both the wild-type and mutant targets bind to the capture probe at a site adjacent to the mutation. Capture probes covalently bound to the electrode hybridize equally to target DNA with both wild-type (WT) and mutant (MUT) sequences. Signal probes complementary to the WT and MUT target sequences are present in the hybridization buffer, and contain ferrocene labels with different redox potentials. The signal probes compete for binding to the region of the target DNA containing the mutation site, and binding of the perfect-match signal probe (i.e., WT signal probe to WT target) predominates. The genotype is determined by measuring the ratio of electrochemical signals from the WT and MUT signal probes

Oxidation of the ferrocene labels and transmission of current through the monolayer depend on proximity of the label to the monolayer surface. As a result, an unbound signal probe is not detected, and washing steps are not required to remove unbound reagents prior to the ACV measurement, even when a large number of signal probes representing multiple target sequences are present. The assay process is simplified, which allows hybridization and detection to be done in a small-footprint instrument without fluid handling or waste containers.

So, for the wildtype, the signal will look like this. For a mutant type, the signal will be offset to indicate that it is not the same signal as a wildtype. For a heterozygote, which carries both a wildtype and mutant form of the gene, the signal will fall under the areas of the wildtype signal and of the mutant signal, with a lower value.

Development of Warfarin Sensitivity Test based on Genetic Variability in P-450 Enzymes: A Pharmacogenomic Approach Suneel A. Chhatre*, Erum F. Naqvi¹ *Chemistry & Cell Biology, Medical University of Americas (MUA), Nevis, WI ¹Centre for Molecular Diagnostics, Princeton Biomedical Laboratories, PA, USA MUA Research Day Spring 2010

2 Overview Clinical Challenges of Warfarin Safety Warfarin Dosing & Inter-Individual Variation Case Study Warfarin Dosing Algorithms Why Test? Princeton Solutions

3 Clinical Challenge: Warfarin Safety • Widely prescribed dangerous drug. – 2 million on warfarin, 30 million Rx a year. – 43,000 ER visits a year, 2nd to Insulin for ER adverse drug reaction (ADR) – 87,000 major bleeding events a year. – 17,000 strokes a year. – 10,000 deaths a year. Source: FDA, AEI-Brookings Joint Center, and The Joint Commission

4 Risks of Warfarin ADR Strongly Depend on INR Value INR below 2 = high risk of stroke INR above 4 = high risk of hemorrhage

5 Warfarin Dosing Inter-individual Variation Narrow therapeutic index & non-linear response. Patients within target INR only 32% to 56% of time. Dose influenced by age, ethnicity, drugs, environmental and genetic factors.

6 Current Methods for Warfarin Dosing Initial dose can be modified by age, gender, body mass, co-morbidities. This will predict only 17-21% of the inter-individual variation. Subsequent dosing based on INR.

7 Genetics & Warfarin Dosing • Single base pair changes in DNA sequence lead to reduced activities in two genes. • These two genes play a key role in the patient’s response to Warfarin. Response – VKORC1 (1386) Metabolism – CYP2C9 *2 & *3

8 Vitamin K Epoxide Reductase 1 (VKORC1) Variations explain up to 25% of patient variability in Warfarin dose response. Approximately 37% of Caucasians, 14% of African-Americans, and 89% of Asians carry at least one variant copy. Patients with certain VKORC1 variations have an increased risk for anticoagulant overdose, and may require lower doses of Warfarin to achieve and maintain therapeutic INR. Warfarin Dose & VKORC1

9 Cytochrome P450 2C9 (CYP2C9) Variations explain approximately 15% of patient variability in Warfarin dose response. Approximately 20% of Caucasians, 5% of African-Americans, and 2% of Asians carry at least one variant copy. Patients with CYP2C9 gene variations require more time to achieve stable INR, are at an increased risk of bleeding, and may require lower doses of Warfarin to achieve and maintain therapeutic INR. Warfarin Dose & CYP2C9

10 Case Study Patient profile: 65 years old White male 260 LBS, 5’9” tall Taking Lipitor® Diagnosis: Deep Vein Thrombosis Therapeutic dose: 5.6 mg/day using available clinical data and existing algorithms.

11 11 Case Study Cont’d Now we genotype this patient: CYP2C9 *3/*3 VKORC1 A/A Resulting optimal warfarin dose: Loading dose: 4.1 mg Therapeutic dose: 1.8 mg/day Without genotype data, this patient would have INR value >4, with potential hemorrhage, and slow return to therapeutic INR

Pharmacogenetics: Warfarin CYP450 2C9 Gene Warfarin Metabolism 2C9 430C>T (*2) Allele 2C9 1075A>C (*3) Allele VKCOR Gene Warfarin Sensitivity VKCORC1 -1639G>A Allele

Warfarin Metabolism 2C9 Genotype/Phenotype

Warfarin Sensitivity VKORC1 Genotype/Phenotype

Hybridization of Target at Working Electrode Surface eSensor® DNA Detection Technology

eSensor® DNA Detection Technology Capture Probe Target Molecule Capture Probe WT Signal Probe Label 1 WT Target Molecule Mut Signal Probe Label 2 Mut

Signal Processing eSensor® DNA Detection Technology

Mutant (MUT) Wild Type (WT) Heterozygous (HET) eSensor® DNA Detection Technology

Assay Workflow

Acknowledgements Molecular Cellular & Development Biology/Chemistry University of Colorado at Boulder, CO NIH, NSF, DOE Chemistry, Eastern New Mexico University Portales, NM NIH NCRR P20-61480