Advances in Pharmacogenomics Reduce Side Effects and Save Lives

Jun 01, 2005

New tests approved by the FDA can allow clinicians to genetically test for patients who may be low- or high-responders to certain drugs. How effective are these tests and what might the ethical implications be?

Psychiatric Times

June 2005

Vol. XXII

Issue 7

When a 9-year-old diagnosed with attention-deficit/hyperactivity disorder, obsessive-compulsive disorder and Tourette's disorder died, the medical examiner attributed the cause of death to fluoxetine (Prozac) toxicity (Sallee et al., 2000). Genetic testing of autopsy tissue confirmed the presence of a gene defect at the cytochrome P450 (CYP) 2D6 locus, which resulted in poor fluoxetine metabolism. In another case, a woman spent 10 years trying different treatments for her depression, but with each new antidepressant, she experienced excruciating headaches or other intolerable adverse effects until she was switched to a drug that did not need the CYP 2D6 enzyme to function (Lerner, 2004).

Psychiatrists and other physicians have long known that patients vary considerably in their responses to psychotropic medications, with some requiring much higher or lower doses than average and others failing to respond at all. Many factors, including diet, drug-drug interactions, gender, age, overall health, hepatic disease and genetic variations, can affect the availability of a drug in the body. Now, technology, clinical research and government policy are converging to create what has been called "personalized medicine." Advances in DNA testing combined with clinical studies are helping clinicians identify the best drug or dosing strategy for a particular patient.

Recently, the U.S. Food and Drug Administration cleared for marketing the first laboratory test system that allows physicians to consider unique genetic information from patients in selecting medications and doses for psychiatric disorders, among other medical conditions. The new test, the AmpliChip Cytochrome P450 Genotyping Test made by Roche Molecular Systems, Inc., was cleared for use with the Affymetrix GeneChip Microarray Instrumentation System, manufactured by Affymetrix, Inc. A microarray is similar to a computer microchip, but instead of tiny circuits, the chip contains millions of tiny DNA molecules. The test is performed using DNA extracted from a patient's blood. A person's DNA sequence is determined based on the sequence of the probe molecule to which the DNA is most similar.

Last December, the FDA cleared the AmpliChip CYP450 Test for CYP 2D6 and two weeks later cleared the test for CYP 2C19. The complete test kit and instrument system, a company spokesperson told Psychiatric Times, are being made available to reference laboratories and high complexity labs. The AmpliChip CYP450 Test was launched in Europe in fall 2004.

The test checks for the 31 polymorphisms (naturally occurring variations in DNA sequence) and mutations, including gene deletions and duplications, on a single chip (29 polymorphisms and mutations for the 2D6 gene and two polymorphisms for the 2C19 gene). The CYP 2D6 and CYP 2C19 enzymes play a role in the metabolism of about 25% of all prescription drugs. The polymorphisms influence how an individual metabolizes antidepressants, antipsychotics and other psychotropic medications. For example, by recognizing common DNA polymorphisms in the CYP 2D6 or CYP 2C19 genes, DNA chips can determine if an individual is a poor metabolizer who would be at increased risk for experiencing adverse drug reactions or toxicities or an ultrarapid metabolizer who would be at increase risk of being a nonresponder (Table).

Genotyping for CYP 450 drug-metabolizing enzyme DNA sequence variants can be accomplished using a variety of test formats. Several companies are offering testing services either for research studies or for patient management (Technology Evaluation Center, Blue Cross and Blue Shield Association, 2004). Some new pharmacogenetic technologies include GE Healthcare's CodeLink Human P450 SNP Bioarray that genotypes 110 single nucleotide polymorphisms (SNPs) with nine P450 genes, including 2C9, 2C19, 2D6 and 3A4; Jurilab Ltd.'s Drug Met Genotyping Test, a microarray that profiles patients for the presence of SNPs in eight different enzymes, chosen according to their importance in drug metabolism; and Tm Bioscience Corp.'s Tag-It Mutation Detection Kits for the CYP 2D6, CYP 2C9 and CYP 2C19 genes to identify the presence or absence of 26 mutations that can be associated with adverse drug reactions. Some companies providing clinical diagnostics include Seryx-Signature Genetics, Genelex, Esoterix and Quest Diagnostics.

Clinical Studies

In tandem with the advancing technology have come studies looking at the clinical utility of pharmacogenomic genotyping. De Leon and colleagues (2005) found that the CYP 2D6 poor-metabolizer phenotype may be associated with adverse drug reactions to risperidone (Risperdal) and discontinuation, while the CYP 3A5 and P-glycoprotein exon 21 and 26 genotypes were not significantly associated with risperidone response.

Adult inpatients and outpatients from psychiatric facilities in central Kentucky were recruited from July 2000 to March 2003. There were 325 patients who were stabilized on risperidone therapy (73 of whom were having moderate-to-marked adverse drug reactions [ADRs] such as resting tremor, stiffness, hypersalivation and sedation), and there were 212 patients who had discontinued risperidone (81 because of adverse drug reactions and 131 for other reasons). Genetic tests were performed by allele-specific polymerase chain reaction (PCR) and by the AmpliChip CYP450 microarray system for up to 34 separate CYP 2D6 alleles. Polymorphism within CYP 3A5 and the drug transporter P-glycoprotein, thought to be capable of influencing risperidone pharmacokinetics, were also evaluated. The study investigators wanted to determine whether the CYP 2D6 phenotype would prove useful in predicting which patients discontinue risperidone therapy in a real clinical setting. They noted:

If genetic testing is to be introduced as a standard clinical tool, it is important to determine if it can provide meaningful information for clinicians in the uncontrolled, 'noisy' clinical environment where psychiatrists use different doses, prescribe co-medications and often make experience-based decisions that vary from patient to patient.

The authors found that among those still taking the drug, the CYP 2D6 poor-metabolizer phenotype increased the odds of having moderate adverse drug reactions by 3:1. Additionally, the univariate analysis suggested that the CYP 2D6 poor-metabolizer phenotype increased the odds of having risperidone discontinued due to ADRs by 3:0.

"Clinical confounders did not explain the CYP2D6 poor metabolizer phenotype association with moderate-to-marked ADRs or with risperidone discontinuation due to ADRs," the authors wrote. "In fact, the OR [odds ratio] increased from 3.0 to 6.0 for the CYP2D6 poor metabolizer phenotype when confounders were considered among patients who discontinued risperidone due to ADRs."

Not every participant who had CYP 2D6 poor metabolizer phenotype had problems while taking risperidone, the authors added. Low doses of risperidone appear to offer CYP 2D6 poor metabolizers some protection from developing ADRs.

The lead author, Jose de Leon, M.D., is associate professor of psychiatry at the University of Kentucky and medical director of the Mental Health Research Center at Eastern State Hospital. His pharmacogenetic laboratory and research activities are possible due to the support from the Bluegrass Regional Mental Health and Mental Retardation board, which manages Eastern State Hospital. He told PT that he and his colleagues are now engaged in a study funded by Roche Molecular Systems looking at the association of CYP 2D6 genotype with psychiatric treatment outcomes. Part of the study will explore the cost-effectiveness of such testing.

"From the point of view of the patient, these tests are beneficial. If I am a poor metabolizer or my son is a poor metabolizer of CYP 2D6, I want to know. In general, when we do these tests on the patients, the families are very grateful, because for the first time we can provide them with an explanation as to why patients have had problems for so many years. But when you go to a hospital or medical center and tell the administrator that you want the hospital to buy a machine to do this testing, the first question he or she is going to ask is, 'Is it cost-effective?'" de Leon said.

The purpose of the new study is to do testing on 3,000 to 4,000 patients and determine if the DNA tests can be used in clinical practice and whether appropriately matching patients to the drug and dosage can save money over the long term.

"Patients who don't have CYP 2D6, or who have too much, usually don't do well on typical doses of medications. Their doctors have to try several times until they find the right dosage or the right medication," he added.

De Leon already has DNA samples from some 2,500 patients. The study will be much broader than the risperidone study and will look at other antipsychotics and antidepressants metabolized by CYP 2D6. He is also conducting a study funded by the National Alliance for Research on Schizophrenia and Depression to explore the association between genetic variants and selective serotonin reuptake inhibitors toxicity.

"We are going to be looking at genetic variations in the serotonin system (serotonin receptors and serotonin transporters) in brain," he said. "What we are going to be doing is seeing if any variations also have anything to do with the side effects of SSRIs."

The University of California at Los Angeles' (UCLA) Pharmacogenetics and Pharmacogenomics group is carrying out a prospective, phenotype-to-genotype study, known as the Pharmacogenetics of Antidepressant Treatment Response in Mexican-Americans (PATRIMA), involving fluoxetine and desipramine (Norpramine). Another study on the effects of genetic factors on citalopram (Celexa) treatment response in African-Americans and whites is being conducted at Cedars-Sinai Medical Center, Harbor-UCLA Medical Center and UCLA-King/Drew Hospital.

Possibly one of the largest studies in Europe is a multicenter, integrated project focusing on functional genomics of depression and pharmacogenomics of antidepressant treatment (GENDEP). The 7.5 million euro project, funded by the European Union under its Sixth Research and Development Framework Programme, seeks to find a way to use information about patients' genes to help physicians decide which antidepressant treatment will work best with the least side effects. Peter McGuffin, Ph.D., and Katherine Aitchison, Ph.D., both of the Social, Genetic and Developmental Psychiatry Centre at King's College Institute of Psychiatry in London, are leading a team of scientists and clinicians from 10 countries.

In the patient-based part of the project, 1,000 patients with depression will be randomly assigned to one of two antidepressant treatments (the SSRI escitalopram [Lexapro] or the tricyclic antidepressant nortriptyline [Pamelor, Aventyl]). Recruitment for the three-year project began in September of 2004. The clinical progress of the participants and any development of any side effects will be monitored during a six-month follow-up period. The team will then compare how the patients responded to their assigned treatment with information about their genetic makeup being determined by a single blood sample.

The project also provides long-term access to well-characterized samples from specialist groups across Europe and to the platform to identify new targets for drug discovery and for early diagnosis of disease. The team will carry out basic research using cells grown in the laboratory and rodent models to learn more about how antidepressants work at the cellular level and how they affect the nervous system.

Additionally, project funders stipulated that there be a corollary study of the ethical, legal and social implications of pharmacogenetics, examining such issues as informed consent, confidentiality, data handling, findings dissemination, intellectual property, commercialization and attitudes toward tailoring drugs to a person's DNA.

"One third of individuals treated with antidepressants will fail to show an adequate clinical response or will suffer intolerable adverse events," explained McGuffin in the GENDEP proposal. "The resultant delay in effective treatment may contribute to chronicity of illness, and consequent morbidity with resultant burden of disease to society, while the experience of adverse effects may lead to poor compliance with future treatments. There is, therefore, an urgent need to improve our understanding of the aetiology of depression and the efficacy and tolerability of antidepressants."

A spokesperson for Roche Molecular Systems said that their company is providing its DNA testing materials for the GENDEP study and also to Aitchison, who is studying the impact of CYP 2D6 genotyping on reduction of side effects in patients taking TCAs. In the United States, the Roche spokesperson said the company is fully funding a study on the CYP 2D6 genotyping and atomoxetine (Straterra), a selective norepinephrine reuptake inhibitor. The labeling for atomoxetine, which is a CYP 2D6-metabolized drug, includes a discussion of poor metabolizers.

In several countries in Europe, psychiatrists are using CYP 2D6 testing in their clinical practice, de Leon said. In the United States, he knows of two places: the Pharmacogenetics Diagnostic Laboratory at the University of Louisville School of Medicine and the Mayo Medical Laboratories.

"We have been using clinical genotyping of the 2D6 cytochrome gene since February 2003. The test for the 2C19 gene became available in 2004," said David Mrazek, M.D., chairperson of Mayo Clinic's department of psychiatry and psychology and director of Mayo Clinic's Genomic Expression and Neuropsychiatric Evaluation Unit. He explained to PT that psychiatrists from all over the country having been sending in samples for testing over the past year to the Mayo Medical Laboratories. The testing is particularly helpful if the patient has a history of problematic reactions to medications. The purposes of the test, Mrazek added, are to identify poor metabolizers who are at high risk for side effects, ultrarapid metabolizers who do not respond to normal doses of some medications because these medications are metabolized too quickly, and intermediate metabolizers who will usually require a lower dose of the relevant medications.

The University of Louisville lab also works with physicians, clinics and hospitals. Costs of pharmacogenetic testing are about $200 to $500 for each test. The CYP 2D6 (single enzyme) test, for example, is approximately $250.

Federal Initiatives

On the federal level, several initiatives are underway to support the development of pharmacogenetics. The Pharmacogenetics Research Network (PGRN) is a nationwide collaboration of scientists established in 2000 and funded by the National Institutes of Health to study the effect of genes on people's responses to a variety of medications, including antidepressants and drugs for heart disease and asthma. One aspect of the PGRN is PharmGKB, a publicly available Internet research tool developed by Stanford University. The PharmGKB database is a central repository for genetic and clinical information about people who have participated in research studies at various medical centers in the network, as well as genomic, molecular and cellular phenotype data submitted by the scientific community.

Last November, the U.S. Department of Health and Human Services (HHS) launched a Family History Initiative to encourage all Americans to learn about their families' health histories. As an assist, HHS released a free computer program that organizes important health data into a printout that can be taken to a physician to help determine whether a patient is at higher risk for disease. The printout can also be placed in a patient's medical record. Called "My Family Health Portrait," the tool can be downloaded at .

"Family history can be a window into a person's genome," said Francis S. Collins, M.D., Ph.D., director of the National Human Genome Research Institute. He told the press, "In the future, tests resulting from the Human Genome Project will make it possible to identify the glitches we all carry in our genes, glitches that increase our susceptibility to common illnesses. Until then, tracking illnesses from one generation of a family to the next can help doctors infer the illnesses for which we are at risk, and thus enable them to create personalized disease-prevention plans."

Last February, the U.S. Senate approved S. 306, a bill introduced by Sen. Olympia Snow (R-Maine) to prohibit discrimination on the basis of genetic information with respect to health insurance and employment, by a vote of 98-0. The bill amends current employment and medical legislation to prevent genetic information from being used to discriminate against individuals. It prohibits the use of genetic information (including results of genetic tests and family history of disease) by employers in employment decisions and by health insurers and health plans in making enrollment determinations and setting insurance premiums. President George W. Bush and Collins have indicated their support for the bill.

In March, Rep. Judy Biggert (R-Ill.) introduced H.R. 1227 in the House, a bill identical to S. 306. The bill has been sent to three different committees: the House Committee on Ways and Means, House Committee on Energy and Commerce, and House Committee on Education and the Workforce, each of which has jurisdiction over separate sections of the bill. Each committee is likely to hold hearings on it and mark up relevant sections, according to Melissa Guido, Biggert's press secretary.

"We have high hopes for the bill's passage, because of the high number of cosponsors [76], administration support and its early introduction into the 109th Congress so it is on the radar of the House leadership," Guido said.

While efforts are being made to ease the way in gathering genetic information on psychiatric disorders, psychiatrists prominent in the field talk of new responsibilities and the need for education.

Paul Appelbaum, M.D. (2004), warned that as knowledge grows regarding the genetic bases of psychiatric disorders, a variety of ethical issues will need to be confronted. Among these issues are pressures for screening of children and adults, particularly potential adoptees, and family members at risk for major psychiatric disorders, as well as the impact of knowing one's genetic makeup on one's sense of self.

"Many of our training programs fail to educate residents in even the basics of psychiatric genetics, and few practicing psychiatrists stay current with this rapidly developing area," Appelbaum wrote. "The development of residency-based curricula and continuing education programs would be a first step toward the literacy that will be essential in developing policy in the future."

References

Appelbaum PS (2004), Ethical issues in psychiatric genetics. J Psychiatr Pract 10(6):343-351.

de Leon J, Susce MT, Pan RM et al. (2005), The CYP2D6 poor metabolizer phenotype may be associated with risperidone adverse drug reactions and discontinuation. J Clin Psychiatry 66(1):15-27.

Lerner M (2004), The right drug? Ask your DNA. Star Tribune. Nov. 28.

Sallee FR, DeVane CL, Ferrell RE (2000), Fluoxetine-related death in a child with cytochrome P-450 2D6 genetic deficiency. J Child Adolesc Psychopharmacol 10(1):27-34.

Technology Evaluation Center, Blue Cross and Blue Shield Association (2004), Special report: genotyping for cytochrome P450 polymorphism to determine drug-metabolizer status. Chicago: Blue Cross and Blue Shield Association. Available at: www.bcbs.com tec/vol19/19_09.html. Accessed April 20, 2005.

x