The legacy of pharmacogenetics and potential applications

Flattening and Unpacking Human Genetic Variation in Mexico, Postwar to Present

Argument This paper analyzes the research strategies of three different cases in the study of human genetics in Mexico - the work of Rubén Lisker in the 1960s, INMEGEN's mapping of Mexican genomic diversity between 2004 and 2009, and the analysis of Native American variation by Andrés Moreno and his colleagues in contemporary research. We make a distinction between an approach that incorporates multiple disciplinary resources into sampling design and interpretation (unpacking), from one that privileges pragmatic considerations over more robust multidisciplinary analysis (flattening). These choices have consequences for social, demographic, and biomedical practices, and also for accounts of genetic variation in human populations. While the former strategy unpacks fine-grained genetic variation - favoring precision and realism, the latter tends to flatten individual differences and historical depth in lieu of generalization.

Sequencing and its consequences: path dependence and the relationships between genetics and medicalization

Both advocacy for and critiques of the Human Genome Project assume a self-sustaining relationship between genetics and medicalization. However, this assumption ignores the ways in which the meanings of genetic research are conditional on its position in sequences of events. Based on analyses of three conditions for which at least one putative gene or genetic marker has been identified, this article argues that critical junctures in the institutional stabilization of phenotypes and the mechanisms that sustain such classifications over time configure the practices and meanings of genetic research. Path dependence is critical to understanding the lack of consistent fit between genetics and medicalization.

Drug metabolism and pharmacogenetics: the British contribution to fields of international significance

The branch of pharmacology we now call 'drug metabolism', the consideration of the enzymes and procesess determining the disposition of drugs in the body, emerged in the 1840s on the continent of Europe, but British science made little or no contribution until the 1920s. From this point on, the development of the field through the 20th century was shaped to a very significant extent by a series of influential British workers, whose contributions were of global significance and who can now be seen as fathers of the subject. Since the 1950s, and gaining pace inexorably from the 1970s, the significance of drug metabolism to human therapeutics has been greatly added to by the emergence of pharmacogenetics, clinically important hereditary variation in response to drugs, which underpins the current emphasis on personalised medicine. This review examines the British contributions to both these fields through the lives of seven key contributors and attempts to place their work both in the context of its time and its lasting influence.

Combinatorial pharmacogenetics

Combinatorial pharmacogenetics seeks to characterize genetic variations that affect reactions to potentially toxic agents within the complex metabolic networks of the human body. Polymorphic drug-metabolizing enzymes are likely to represent some of the most common inheritable risk factors associated with common 'disease' phenotypes, such as adverse drug reactions. The relatively high concordance between polymorphisms in drug-metabolizing enzymes and clinical phenotypes indicates that research into this class of polymorphisms could benefit patients in the near future. Characterization of other genes affecting drug disposition (absorption, distribution, metabolism and elimination) will further enhance this process. As with most questions concerning biological systems, the complexity arises out of the combinatorial magnitude of all the possible interactions and pathways. The high-dimensionality of the resulting analysis problem will often overwhelm traditional analysis methods. Novel analysis techniques, such as multifactor dimensionality reduction, offer viable options for evaluating such data.

‘At the point at which you can do something about it, then it becomes more relevant’: Informed consent in the pharmacogenetic clinic

Sociological investigation of informed consent has generated rich and complex descriptions of the clinical encounter, often challenging the straightforward picture painted by medical ethicists. This paper builds on this work, drawing on ideas from the Sociology of Science and Technology, to explore informed consent issues surrounding the use of the drug Herceptin, widely cited as an example of a novel approach to drug development called pharmacogenetics. Drawing on qualitative semi-structured interviews with 25 UK-based breast cancer specialists, this paper explores Herceptin's disputed epistemological status, as an example of pharmacogenetics or as something out of the ordinary in terms of clinical practice. It considers how, in turn, this impacts on the way in which informed consent is sought and influenced by clinicians' desire to protect patients from possibly distressing test results. It highlights the flexible, contingent and context dependent nature of informed consent in the clinical setting.

Drug-gene interactions between genetic polymorphisms and antihypertensive therapy

Genetic factors may influence the response to antihypertensive medication. A number of studies have investigated genetic polymorphisms as determinants of cardiovascular response to antihypertensive drug therapy. In most candidate gene studies, no such drug-gene interactions were found. However, there is observational evidence that hypertensive patients with the 460 W allele of the alpha-adducin gene have a lower risk of myocardial infarction and stroke when treated with diuretics compared with other antihypertensive therapies. With regard to blood pressure response, interactions were found between genetic polymorphisms for endothelial nitric oxide synthase and diuretics, the alpha-adducin gene and diuretics, the alpha-subunit of G protein and beta-adrenoceptor antagonists, and the ACE gene and angiotensin II type 1 (AT(1)) receptor antagonists. Other studies found an interaction between ACE inhibitors and the ACE insertion/deletion (I/D) polymorphism, which resulted in differences in AT(1) receptor mRNA expression, left ventricular hypertrophy and arterial stiffness between different genetic variants. Also, drug-gene interactions between calcium channel antagonists and ACE I/D polymorphism regarding arterial stiffness have been reported. Unfortunately, the quality of these studies is quite variable. Given the methodological problems, the results from the candidate gene studies are still inconclusive and further research is necessary.

Evaluating direct-to-consumer marketing of race-based pharmacogenomics: a focus group study of public understandings of applied genomic medication

Some medical providers have advocated applied genomics, including the use of genetically linked racial phenotypes in medical practice, raising fear that race-based medication will become justified. As with other emerging medical genetic technologies, pharmaceutical companies may advertise these treatments. Researchers fear that consumers will uncritically accept pharmaceutical messages and demand the product. In this exploratory study, we examined public reactions to advertisements for applied genomic medications. A focus group methodology was employed. Participants tended to resist the message and generated warrants for doing so, indicating critical reception of the messages. Message accepters also provided warrants. Warrants for resistance and acceptance differ between self-identified racial groups. Consumers, health care providers, and pharmaceutical corporations will benefit from a better understanding of direct-to-consumer advertisements as medical communication. Our study concludes that both advocates and opponents of direct-to-consumer advertisements should recognize that potential consumers of pharmacogenomics act as critical consumers of health advertising discourse.

Ethical, social and legal implications of pharmacogenomics: a critical review

OBJECTIVE

My aim was to examine the ethical, social and legal implications of pharmacogenomics.

METHODS

I performed a critical review of the literature. The primary focal point is the bioethical principle discussed. The second outcome measure is the perspective of the discussion.

RESULTS

This review documents that the pharmacogenomics issues of concern are comparable to issues concerning other genetic developments in general. However, two main issues are particular to the case of pharmacogenomics. Firstly, this review reveals that society, industry, groups and individuals appreciate the prospect of pharmacogenomics very differently. Secondly, there is a lack of research into the post-marketing implications of pharmacogenomics.

CONCLUSION

An extensive focus on the ethical, social and legal implications of pharmacogenomics, in terms of both pre- as well as post-marketing issues, is essential. Also, a multidisciplinary approach which includes individual and group opinions in an upfront manner in the research and development process is essential. Otherwise, there is a substantial risk that the positive prospects of pharmacogenomics will not survive due to fear and a lack of acceptance and understanding on the part of the general public.

The drugs don't work: expectations and the shaping of pharmacogenetics

This article examines one particular set of technologies arising from developments in human genetics, those aimed at improving the targeting, design and use of conventional small molecule drugs-pharmacogenetics. Much of the debate about the applications and consequences of pharmacogenetics has been highly speculative, since little or no working technology is yet on the market. This article provides a novel analysis of the development of pharmacogenetics, and the social and ethical issues it raises, based on the sociology of technological expectations. In particular, it outlines how two alternative visions for the development of the technology are being articulated and embedded in a range of heterogeneous discourses, artefacts, actor strategies and practices, including: competing scientific research agendas, experimental technologies, emerging industrial structures and new ethical discourses. Expectations of how pharmacogenetics might emerge in each of these arenas are actively shaping the trajectory of this nascent technology and its potential socio-economic consequences.

Pharmacogenetics and personalised medicine

The traditional concern of pharmacogenetics was Mendelian (monogenic) variation, which visibly affected some drug responses. Pharmacogenetics was broadened by the observation that multifactorial genetic influences, in conjunction with environmental factors, usually determine drug responses. Variability of gene expression, a new theme of the science of genetics, also affects pharmacogenetics; for example, enhanced enzyme activity does not necessarily indicate a mutation, but may be the consequence of a drug-induced enhancement of gene expression. Methodological advances permit the conversion of pharmacogenetics into the broad practice of pharmacogenomics; this improves the possibility of identifying genetic causes of common diseases, which means establishing new drug targets, thereby stimulating the search for new drugs. While the main medical effect of pharmacogenetics was an improvement of drug safety, pharmacogenomics is hoped to improve drug efficacy. On the way to personalized medicine, we may stepwise improve the chances of choosing the right drug for a patient by categorizing patients into genetically definable classes that have similar drug effects (as, for example, human races, or any population group carrying a particular set of genes). It is wise to expect that, even after we have reached the goal to establish personalized medicine, we will not have eliminated all uncertainties.

Polymorphisms in a human kidney xenobiotic transporter, OCT2, exhibit altered function

The completion of the Human Genome Project and the development of high-throughput polymorphism identification methods have allowed researchers to carry out full genetic analyses of many clinically relevant genes. However, few studies have combined genetic analysis with in vitro phenotyping to better understand the relationship between genetic variation and protein function. Many transporters in the kidney are thought to play key roles in defense against a variety of foreign substances. The goal of this study was to understand the relationship between variation in a gene encoding a major renal xenobiotic transporter, OCT2, and transporter function. We report a comprehensive genetic analysis and functional characterization of variants of OCT2. Twenty-eight variable sites in the OCT2 gene were identified in a collection of 247 ethnically diverse DNA samples. Eight caused non-synonymous amino acid changes, of which four were present at >/= 1% in an ethnic population. All four of these altered transporter function assayed in Xenopus laevis oocytes. Analysis of nucleotide diversity (pi) revealed a higher prevalence of synonymous (pi = 22.4 x 10-4) versus non-synonymous (pi = 2.1 x 10-4) changes in OCT2 than in other genes. In addition, the non-synonymous sites had a significant tendency to exhibit more skewed allele frequencies (more negative Tajima's D-values) compared to synonymous sites. The population-genetic analysis, together with the functional characterization, suggests that selection has acted against amino acid changes in OCT2. This selection may be due to a necessary role of OCT2 in the renal elimination of endogenous amines or xenobiotics, including environmental toxins, neurotoxic amines and therapeutic drugs.

In vitro characterization of hepatic flavopiridol metabolism using human liver microsomes and recombinant UGT enzymes

PURPOSE

To assess the contribution of drug metabolism to the variability on flavopiridol glucuronidation observed in cancer patients, and to determine the ability of all known human UDP-glucuronosyltransferase (UGT) isoforms to glucuronidate flavopiridol.

METHODS

Inter-individual variation in flavopiridol glucuronidation was determined by HPLC using hepatic microsomes from 62 normal liver donors. Identification of enzymes capable of glucuronidating flavopiridol was determined by LC/MS using human embryonic kidney 293 (HEK293) cells stably expressing all sixteen known human UGTs.

RESULTS

The major product of the flavopiridol glucuronidation reaction in human liver microsomes was FLAVO-7-G. High variability (coefficient of variation = 49%) was observed in the glucuronidation of flavopiridol by human liver microsomes. In vitro formation of FLAVO-7-G and FLAVO-5-G was mainly catalyzed by UGT1A9 and UGT1A4, respectively. Similar catalytic efficiencies (Vmax/Km) were observed for human liver microsomes (1.6 microl/min/mg) and UGT1A9 (1.5 microl/min/mg).

CONCLUSIONS

UGT1A9 is the major UGT involved in the hepatic glucuronidation of flavopiridol in humans. The data suggests that hepatic glucuronidation may be a major determinant of the variable systemic glucuronidation of flavopiridol in cancer patients. The large variability in flavopiridol glucuronidation may be due to differences in liver metabolism among individuals, as a result of genetic differences in UGT1A9.

Pharmacogenetic tactics and strategies: implications for paediatrics

Genetic diversity exerts profound effects on variation in human drug response in adults, but comparatively little research that specifically relates to genetically abnormal responses in infancy and childhood has been reported. Specific genetic changes in human enzymes, receptors and other proteins that are implicated in drug response and their associated phenotypic correlates provide needed data for construction of profiles individualised to predict susceptibility to adverse drug reactions. If therapy adheres to such guidelines, failure to respond to drug therapy and drug toxicity among genetically susceptible persons can be greatly minimised or averted.