American journal of pharmacogenomics : genomics-related research in drug development and clinical practice最新文献

Lithium is considered to be the first choice mood stabilizer in recurrent mood disorders. Its widespread and large-scale use is the result of its proven efficacy. In spite of this fact, patients have been observed to show a variable response to lithium treatment: in some cases it is completely effective in preventing manic or depressive relapses, while in other cases it appears to show no influence on the disease course. The possible definition of a genetic liability profile for adverse effects and efficacy will be of great help, as lithium therapy needs at least 6 months to be effective in stabilizing mood disorders. During the last few years, a number of groups have reported possible liability genes. Lithium long-term prophylactic efficacy has been associated with serotonin transporter protein, tryptophan hydroxylase and inositol polyphosphate 1-phosphatase variants. A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even if some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified. Although the available data may not currently allow a meaningful prediction of lithium response, future research is aimed at the development of individualized treament of mood disorders, including the possibility of 'pharmacological genetic counseling'.

Nociceptin/orphanin FQ (noc/oFQ) is the first novel bioactive substance to have been discovered by the implementation of a functional genomics/reverse pharmacology approach. The neuropeptide was indeed identified in brain extracts as the natural ligand of a previously cloned orphan G protein-coupled receptor, the opioid receptor-like 1 (ORL1) receptor. Since its discovery in 1995, noc/oFQ has been the subject of intensive study to establish its role in normal brain function and its possible involvement in neurophysiopathology. Although the neuropeptide, an inhibitor of neuronal activity, has been found to have a wide spectrum of pharmacological effects in vivo, none has been as intensively investigated as its action on nociception and nociceptive processing. There is now substantial evidence that noc/oFQ has a modulatory role in nociception. However, dependent on the dose and site of injection, and possibly the animal's genetic background and even psychological status, the peptide has been variously reported to cause allodynia, hyperalgesia, analgesia, and even pain, in rodents. Overall, noc/oFQ tends to facilitate pain when administered supraspinally, and to inhibit it when administered spinally. These opposing effects beg the obvious, yet still unanswered, question as to what would be the net effect on nociception of an ORL1 receptor ligand, agonist or antagonist, able to target supraspinal and spinal sites simultaneously. Owing to the research effort of several drug companies, such ligands, i.e. nonpeptidic, brain-penetrating agonists and antagonists, have recently been produced whose systematic screening in animal models of acute and inflammatory pain may help validate the ORL1 receptor as the target for novel, non-opioid analgesics.

There is increasing discussion in public and academic forums about the anticipated benefits of pharmacogenomics, as well as the attendant social and ethical implications of this research. Yet there is often an implicit assumption that the benefits of pharmacogenomics are 'just around the corner' and will significantly outweigh the costs. Furthermore, it is argued that the associated ethical issues are not as profound as those that emerge in other areas of genetics, and that experience gained wrestling with these other issues provides ample ethical and regulatory tools to deal with any problems arising with pharmacogenomics. We contend that this vision of ethical and social issues associated with pharmacogenomics is not so clear-cut. The scientific evidence is more complex and contested than the public, academics, and policy makers, have been led to believe, and while there may be real clinical benefits from this research, they are not likely to arrive in the near future. Pharmacogenomics research is also occurring in a terrain occupied by a multitude of different and powerful actors, with diverse and often competing interests. It is therefore essential to investigate the broader social and political context, unravel the various interests pressuring for early implementation, and deconstruct the hype in order to appreciate a fuller range of ethical and social consequences associated with the current developments of pharmacogenomics.

Since 1965 there have been more than 800 pharmacogenetics/genomics reviews - most suggesting that we are on the verge of offering individualized drug therapy to everyone. However, there are numerous reasons why this approach will be extremely difficult to achieve in the foreseeable future. Drug treatment outcome represents a complex phenotype, encoded by dozens, if not hundreds, of genes, and affected by many environmental factors; therefore, we will almost always see a gradient of response. Phenotyping assays of blood enzyme activities (if feasible) are generally more successful than DNA genotyping for predicting unequivocal outcomes of drug therapy in each and every patient. Phenotyping with probe drugs has generally not succeeded, because of the overlapping substrate specificities not only of drug-metabolizing enzymes but also transporters, receptors, ion channels, transcription factors, and other drug targets; drug-drug interactions, enzyme induction and inhibition, and multiple (enzyme, transporter, second-messenger, signal transduction) pathways also present enormous problems. Genotyping to predict drug disposition, efficacy, toxicity, and clinical outcome has been proposed, but the success of genotyping in individualized drug therapy currently appears unlikely because of the many shortcomings (frequency of DNA variant sites, ethnic differences, admixture) and complexities (plasticity of the genome, multiple mechanisms for determining sizes and locations of haplotype blocks) of this approach. Genomics is an important tool in basic research; yet, it is unrealistic to include genotyping within the realm of tests available to the practicing clinician in the foreseeable future. The same can be said for transcriptomics and proteomics, which also rely on available sources (tumors, biopsies, excreta). The newly emerging fields of metabonomics and phenomics might offer solutions to anticipating and decreasing individual risk for adverse drug reactions in each individual patient; however, tests based on these approaches are not expected to become available to the practicing clinician for at least the next 5-10 years.

The prognosis of patients with colorectal cancer is impacted by various factors at the time of diagnosis, including location of the tumor, gender, age and overall performance status of the patient. Optimal postoperative management of patients who have undergone successful tumor resection involves the utilization of reliable determninants of prognosis to help select patients who would benefit from adjuvant treatment, while sparing others from drug-related adverse effects. Tailoring chemotherapy for patients with disseminated cancer, or for patients who receive adjuvant chemotherapy, is also critical. Interpatient differences in tumor response and drug toxicity are common during chemotherapy. Genomic variability of key metabolic enzyme complexes, drug targets, and drug transport molecules is an important contributing factor. The identification of genetic markers of response and prognosis will aid in the development of more individualized chemotherapuetic strategies for cancer patients. Potential prognostic indicators in colorectal cancer include oncogenes, tumor suppressor genes, genes involved in angiogenic and apoptotic pathways and cell proliferation, and those encoding targets of chemotherapy. Specifically, molecular markers such as deletion of 18q (DCC), p27 and microsatellite instability are promising as indicators of good or poor prognosis. Molecular determinants of efficacy and host toxicity of the most commonly used drugs in colorectal cancer, fluoracil, irinotecan and oxaliplatin, are being investigated. Alterations in gene expression, protein expression and polymorphic variants in genes encoding thymidylate synthase, dihydropyrimidine dehydrogenase, dUTP nucleotidehydrolase and thymidine phosphorylase (for fluoropyrimidine-based chemotherapy), uridine diphosphate glucosyltransferase (UGT) 1A1 and carboxylesterase (for irinotecan therapy), and excision repair cross-complementing genes (ERCC1 and ERCC2) and glutathione-S-transferase P1 (for oxalilplatin-based regimens) may be useful as markers for clinical drug response, survival and host toxicity.

The value of genetics in medicine has been steadily developing with our increasing knowledge of the human genome. Genetic testing to determine disease risk or potential drug effects is set to become more commonplace. With this comes increasing concern about access to genetic information, and the potential for discriminatory usage of such information. At present, the scope and predictability of genetic testing and the conclusions that may be drawn fairly from genetic information are limited. Nonetheless, public concerns about discrimination based on the possession of a genetic trait or condition are well documented. The prospect that such information might be used in decisions regarding employment or insurability has caused anxiety and prompted legislation largely dedicated to the use of information about one's genotype rather than medical information in general. These laws emphasize genetic information as distinct from other medical information and attempt to prioritize interests in genetic information. As the distinction between genetic and medical information becomes untenable, those who would regulate the use of genotypic information will find this approach to policy problematic.In considering the limits of legislation as an effective tool of regulating genetic discrimination, several conclusions can be drawn: firstly, despite the promise of genomic medicine, current knowledge is insufficient to justify the use or application of certain genetic information in nonmedical contexts; secondly, public resistance to genomic medicine that is based on fear of genetic discrimination poses a danger that justifies a policy response; and thirdly, such a response may be purely symbolic and not entirely effective, provided that the policy establishes a consensus regarding the applicability of genetic information in nonmedical contexts.

The glutathione-S-transferase (GST) super family comprises multiple isozymes (Alpha, Mu, Pi, Omega, Theta, and Zeta) with compelling evidence of functional polymorphic variation. Over the last two decades, a significant body of data has accumulated linking aberrant expression of GST isozymes with the development and expression of resistance to cancer drugs. Clinical correlation studies show that genetic differences within the human GST isozymes may play a role in cancer susceptibility and treatment. The initial confusion was presented by the fact that not all drugs used to select for resistance were substrates for thioether bond catalysis by GSTs. However, recent evidence that certain GST isozymes possess the capacity to regulate mitogen activated protein kinases presents an alternative explanation. This dual functionality has contributed to the recent efforts to target GSTs with novel small molecule therapeutics. While the ultimate success of these attempts remains to be shown, at least one drug is in late-stage clinical testing. In addition, the concept of designing new drugs that might interfere with protein:protein interactions between GSTs and regulatory kinases provides a novel approach to identify new targets in the search for cancer therapeutics.

Human biological material is recognized as an important tool in research, and the demand for collections that combine samples and data is increasing. For-profit companies have assumed a leading role in assembling and managing these collections. The emergence of commercial biobanks has raised significant ethical and legal issues. The growing awareness of the importance of human biological material in research has been accompanied by a growing awareness of the deficiencies of existing archives of tissue. Commercial biobanks are attempting to position themselves as a, if not the, solution to problems that include a lack of public trust in researchers and lack of financial resources to support the prospective creation of collections that meet the highest scientific and ethical standards in the non-profit sector. Broad social and policy questions surrounding the operation of commercial biobanks have been raised however. International documents, in particular, suggest discomfort with the idea of gain from the mere transfer or exchange of human genetic material and information. Commercial involvement in the development of useful products from tissue is generally not condemned, so long as there is attention to scientific and social norms. Views on the acceptability of commercial biobanks vary. Specific issues that arise when commercial biobanks are permitted--in the areas of consent, recruitment, confidentiality, and accountability--are also relevant to the operation of public and private, non-profit biobanks. Although many uncertainties remain, consensus seems to be forming on a number of issues. For example, there appears to be agreement that blanket consent to future unspecified research uses, with no conditions, is unacceptable. Indeed, many of the leading commercial biobanks have been attentive to concerns about consent, recruitment, and confidentiality. Unfortunately, the binding nature of assurances in these areas is unclear, especially given the risk of insolvency. Hence, accountability may be the most important area of concern in relation to commercial biobanks. A few countries have enacted general legislation providing for comprehensive regulation of biobanks, for example, through licensure. Efforts to achieve harmonization of standards at the international level, and cautions against an approach that focuses on biobanking for genetic research alone, are to be applauded.

In clinical practice, two potent and selective catechol-O-methyl transferase (COMT) inhibitors are available for the control of motor fluctuation in patients with Parkinson's disease. However, because of the complexity of fluctuating motor symptoms, it is difficult to evaluate the clinical efficacy of COMT inhibitors in each individual. Therefore, an objective factor predicting the clinical efficacy of COMT inhibitors is needed. Individual variation in COMT activity is regulated by a single nucleotide of the COMT gene on the long arm of chromosome 22. Therefore, there could be a correlation between COMT genotype and the clinical efficacy of COMT inhibitors. Three double-blind studies evaluating the efficacy of a single or repeated doses of a COMT inhibitor failed to find significant difference in the improvement in the duration of daily 'on' time and degree of motor abilities between patients with different COMT genotypes. Furthermore, there were no significant differences in the severity and frequency of dopaminergic adverse effects between patients with different COMT genotypes. These data suggest that the COMT genotype is not a major factor in deciding the clinical efficacy of COMT inhibitors.

The pathogenetic mechanism of neuroleptic malignant syndrome (NMS), a potentially lethal adverse effect of antipsychotics, is not well understood. In addition to acquired risk factors, clinical observations suggest a number of genetic factors predisposing patients to NMS. Recent findings in pharmacogenetics indicate that the genetic polymorphisms for drug-metabolizing enzymes, drug transporters, and possibly drug-targeting molecules, are associated with the interindividual differences in drug responses concerning both efficacy and adverse reactions. Genetic association studies have sought to identify polymorphisms influencing susceptibility to NMS, especially with respect to the dopamine D(2) receptor, serotonin receptor, and cytochrome p450 2D6. While a few candidate polymorphisms were associated with NMS, a large controlled study is needed to attain statistical power. On the other hand, NMS might include heterogeneous conditions with common characteristic symptoms but different causative mechanisms. Further analysis of individuals with identified genetic mutations or polymorphisms should advance our understanding of mechanisms underlying NMS.