A Gilbert's syndrome UGT1A1 variant confers susceptibility to tranilast-induced hyperbilirubinemia

Cabozantinib Induces Isolated Hyperbilirubinemia in Renal Cell Carcinoma Patients carrying the UGT1A1*28 Polymorphism

BACKGROUND

Genetic variants of UGT1A1, involved in glucuronidation and clearance of bilirubin, are associated with reduced bilirubin metabolization and drug-induced isolated hyperbilirubinemia. We studied the impact of the UGT1A1*28 polymorphism on drug-induced isolated hyperbilirubinemia in metastatic renal cell carcinoma patients treated with pazopanib, cabozantinib, and axitinib.

METHODS

We genotyped the UGT1A1*28 TA6/TA6-TA6/TA7-TA7/TA7 polymorphism and correlated with median baseline, on-treatment and peak bilirubin levels during therapy, incidence of grade-1- or -2 (G1/2)-hyperbilirubinemia and time-to-G1-hyperbilirubinemia.

RESULTS

Of the 66 patients treated with pazopanib, 29 received axitinib and 28 cabozantinib upon progression. Median baseline bilirubin was higher in TA7/TA7-carriers versus TA6/TA6+TA6/TA7-carriers at start of pazopanib (P < .0001), cabozantinib (P < .0001), and axitinib (P = .007). During pazopanib therapy, median bilirubin increased 1.4-fold in TA7/TA7+TA6/TA7-carriers but not in TA6/TA6-carriers. On cabozantinib, bilirubin increased 1.5-fold in TA7/TA7-carriers but not in TA6/TA6+TA6/TA7-carriers. Axitinib did not increase bilirubin in any genotype. Peak bilirubin in TA7/TA7- versus TA6/TA6+TA6/TA7-carriers was higher on pazopanib (P < .0001) or cabozantinib (P < .0001). With pazopanib, G1-hyperbilirubinemia occurred in 57% of TA7/TA7- and 12% of TA6/TA6+TA6/TA7-carriers (P = .0009) and G2-hyperbilirubinemia in 36% and 6% of the patients, respectively (P = .004). On cabozantinib, G1-hyperbilirubinemia occurred in 100% of TA7/TA7- and 5% of TA6/TA6+TA6/TA7-carriers (P < .0001) and G2-hyperbilirubinemia in 33% and 0% of the patients, respectively (P = .04). On axitinib, no correlation between the genotypes and G1/2-hyperbilirubinemia was observed.

CONCLUSION

We validate the previously described impact of the UGT1A1*28 polymorphism on isolated bilirubin increase on pazopanib. We report for the first time that cabozantinib also interferes with UGT1A1 and causes isolated bilirubin increase.

Preoperative serum bilirubin is an independent prognostic factor for curatively resected esophageal squamous cell carcinoma

PURPOSE

This study examines prognostic value of preoperative serum bilirubin, including unconjugated bilirubin (UCB), conjugated bilirubin (CB), and total bilirubin (TB), in esophageal squamous cell carcinoma (ESCC) patients who underwent curative resection.

METHODS

Between May 2010 and December 2012, a total of 351 ESCC patients were retrospectively reviewed. All the patients underwent curative resection as their primary treatment. Clinicopathological features and overall survival (OS) rate were investigated. Kaplan-Meier curves were used to calculate the OS rate, and the prognostic factors were identified by Cox regression model. Besides, the potential inhibition effect of UCB on ESCC was investigated with both in vitro and in vivo models.

RESULTS

The higher-level groups of UCB, CB, and TB demonstrated longer OS than their low counterparts, with hazard ratio (HR) values of 0.567 (95% CI: 0.424-0.759), 0.698 (95% CI: 0.522-0.933), and 0.602 (95% CI: 0.449-0.807), respectively. All three forms of bilirubin were identified as independent prognostic factors for patients with ESCC, and they were found to effectively stratify the survival risk of patients at TNM stage III. In vivo and in vitro models further confirmed the inhibitory effect of unconjugated bilirubin (UCB) on the proliferation of ESCC.

CONCLUSION

The findings of our study have shed new light on the prognostic value and biological functions of bilirubin in relation to ESCC. These results may contribute to a better understanding of the underlying mechanisms involved in ESCC tumorigenesis and provide potential therapeutic pathways for treating ESCC.

Genetic Biomarkers of Metabolic Detoxification for Personalized Lifestyle Medicine

Metabolic detoxification (detox)—or biotransformation—is a physiological function that removes toxic substances from our body. Genetic variability and dietary factors may affect the function of detox enzymes, thus impacting the body’s sensitivity to toxic substances of endogenous and exogenous origin. From a genetic perspective, most of the current knowledge relies on observational studies in humans or experimental models in vivo and in vitro, with very limited proof of causality and clinical value. This review provides health practitioners with a list of single nucleotide polymorphisms (SNPs) located within genes involved in Phase I and Phase II detoxification reactions, for which evidence of clinical utility does exist. We have selected these SNPs based on their association with interindividual variability of detox metabolism in response to certain nutrients in the context of human clinical trials. In order to facilitate clinical interpretation and usage of these SNPs, we provide, for each of them, a strength of evidence score based on recent guidelines for genotype-based dietary advice. We also present the association of these SNPs with functional biomarkers of detox metabolism in a pragmatic clinical trial, the LIFEHOUSE study.

UGT1A1 regulatory variant with potential effect on efficacy of HIV and cancer drugs commonly prescribed in South Africa

Aim: Despite the high disease burden of human immunodeficiency virus (HIV) infection and colorectal cancer (CRC) in South Africa (SA), treatment-relevant pharmacogenetic variants are understudied. Materials & methods: Using publicly available genotype and gene expression data, a bioinformatic pipeline was developed to identify liver expression quantitative trait loci (eQTLs). Results: A novel cis-eQTL, rs28967009, was identified for UGT1A1, which is predicted to upregulate UGT1A1 expression thereby potentially affecting the metabolism of dolutegravir and irinotecan, which are extensively prescribed in SA for HIV and colorectal cancer treatment, respectively. Conclusion: As increased UGT1A1 expression could affect the clinical outcome of dolutegravir and irinotecan treatment by increasing drug clearance, patients with the rs28967009A variant may require increased drug doses to reach therapeutic levels or should be prescribed alternative drugs.

Evaluation of the effect of UGT1A1 polymorphisms on the pharmacokinetics of oral and long-acting injectable cabotegravir

Background

Cabotegravir is an HIV integrase inhibitor in clinical development with both oral and long-acting (LA) injectable formulations. Cabotegravir is primarily metabolized by uridine 5′-diphospho-glucuronosyltransferase (UGT) 1A1, a known polymorphic enzyme with functional variants that can affect drug metabolism and exposure.

Objectives

To investigate the pharmacogenetic effects of the reduced-function alleles UGT1A1*6, UGT1A1*28 and/or UGT1A1*37 on steady-state pharmacokinetics (PK) and safety of oral cabotegravir (30 mg/day) and intramuscular cabotegravir LA (400 mg every 4 weeks or 600 mg every 8 weeks).

Methods

Plasma cabotegravir PK was assessed in 346 UGT-genotyped participants with and without UGT1A1 functional variants across six studies (four Phase I and two Phase II) of oral cabotegravir, including 215 HIV-infected participants who received oral cabotegravir followed by cabotegravir LA. Changes from baseline in total bilirubin and ALT were assessed in one study (LATTE; NCT01641809).

Results

Statistically significant (P < 0.05) associations were observed between UGT1A1 genotype and plasma cabotegravir PK parameters, with 28%–50% increases following oral cabotegravir [plasma cabotegravir concentration at the end of the dosing interval (C_tau), 1.50-fold; AUC_tau, 1.41-fold; and C_max, 1.28-fold] and 16%–24% increases following cabotegravir LA administration (48 week C_tau, 1.24-fold; AUC_tau, 1.16-fold; and C_max, 1.18-fold) among those with low-versus-normal genetically predicted UGT1A1 activity. A statistically significant (P < 10⁻⁵) association between predicted UGT1A1 activity and maximum change in total bilirubin was also observed (2.45-fold asymptomatic increase for low versus normal) without a corresponding change in ALT.

Conclusions

This modest increase in oral and parenteral cabotegravir exposure associated with a reduced function of UGT1A1 is not considered clinically relevant based on accumulated safety data; no dose adjustment is required.

UGT1A1 Guided Cancer Therapy: Review of the Evidence and Considerations for Clinical Implementation

Simple Summary

The use of multi-gene testing platforms to individualize treatment is rapidly expanding into routine oncology practice. UGT1A1, which encodes for the uridine diphosphate glucuronosyltransferase (UGT) 1A1 enzyme, is commonly included on multi-gene molecular testing assays. UGT1A1 polymorphisms may influence drug-induced toxicities of numerous medications used in oncology. However, guidance for incorporating UGT1A1 results into therapeutic decision-making is sparse and can differ depending on the referenced resource. We summarize the literature describing associations between UGT1A1 polymorphisms and toxicity risk with irinotecan, belinostat, pazopanib, and nilotinib. Resources that provide recommendations for UGT1A1-guided drug prescribing are reviewed, and considerations for implementation into patient care are provided.

Abstract

Multi-gene assays often include UGT1A1 and, in certain instances, may report associated toxicity risks for irinotecan, belinostat, pazopanib, and nilotinib. However, guidance for incorporating UGT1A1 results into therapeutic decision-making is mostly lacking for these anticancer drugs. We summarized meta-analyses, genome-wide association studies, clinical trials, drug labels, and guidelines relating to the impact of UGT1A1 polymorphisms on irinotecan, belinostat, pazopanib, or nilotinib toxicities. For irinotecan, UGT1A1*28 was significantly associated with neutropenia and diarrhea, particularly with doses ≥ 180 mg/m², supporting the use of UGT1A1 to guide irinotecan prescribing. The drug label for belinostat recommends a reduced starting dose of 750 mg/m² for UGT1A1*28 homozygotes, though published studies supporting this recommendation are sparse. There was a correlation between UGT1A1 polymorphisms and pazopanib-induced hepatotoxicity, though further studies are needed to elucidate the role of UGT1A1-guided pazopanib dose adjustments. Limited studies have investigated the association between UGT1A1 polymorphisms and nilotinib-induced hepatotoxicity, with data currently insufficient for UGT1A1-guided nilotinib dose adjustments.

The Association between Serum Bilirubin Levels and Colorectal Cancer Risk: Results from the Prospective Cooperative Health Research in the Region of Augsburg (KORA) Study in Germany

Emerging studies have suggested that bilirubin, particularly unconjugated bilirubin (UCB), has substantial anti-inflammatory and antioxidant properties that protect against oxidative stress-associated diseases such as cancer. Few observational studies have investigated the etiological role of bilirubin in colorectal cancer (CRC) development. In this case-control study, nested in the population-based prospective cohort of the Cooperative Health Research in the Region of Augsburg (KORA) study in south Germany, pre-diagnostic circulating UCB concentrations were measured by high-performance liquid chromatography in 77 CRC cases and their individually matched controls. Multivariable unconditional logistic regression was used to estimate the odds ratios (OR) and 95% confidence intervals (CI) for associations between log-transformed UCB levels (log-UCB), standardized per one-standard-deviation (one-SD) increment, and CRC risk. The models were a priori stratified by sex based on previous evidence. In the fully adjusted models, each one-SD increment in log-UCB was indicative of a positive association with CRC risk (OR, 1.20; 95% CI, 0.52-2.79) among men, and of an inverse association (OR, 0.76; 95% CI, 0.34-1.84) among women (Pheterogeneity = 0.4 for differences between men and women). We found little evidence for sex-specific associations of circulating bilirubin with CRC risk, and further studies are needed to confirm or refute the potential associations.

Preventive Effect of Synthetic Tryptophan Metabolite on Silicone Breast Implant-Induced Capsule Formation

BACKGROUND

In the field of plastic surgery, capsular contracture after silicone breast implant surgery is a major clinical problem. This experimental study confirms that the synthetic tryptophan metabolite N-(3',4'-dimethoxycinnamonyl) anthranilic acid (Tranilast) reduces capsule formation and prevents capsular contracture.

METHODS

Eighteen New Zealand white rabbits were divided into 2 groups. In the experimental group, implants were inserted into each rabbit, and oral synthetic tryptophan metabolite was administered daily at a dose of 5 mg/kg in 10 mL of saline. In the control group, rabbits received implants and the same amount of saline without the metabolite. After 2 months, peri-implant tissues were harvested and analyzed.

RESULTS

The thickness of the capsules and the inflammatory cell counts were decreased in the experimental group (P < 0.001). The collagen fibers in the experimental group were thinner, less dense, and more organized than in control group. The results of reverse transcription quantitative polymerase chain reaction analysis showed that the genes for transforming growth factor β1 (P = 0.002), alpha smooth muscle actin (P < 0.001), and collagen types I (P = 0.002) and III (P = 0.004) were underexpressed in the experimental groups. Furthermore, the counts of T-cell immunity-related cytokine presenting cells were decreased in the experimental groups (CD3, 4, 25, 45RA, 45RO, 69, interleukin-2, 4 [P < 0.001], and interferon γ [P = 0.028]).

CONCLUSIONS

This study confirms that a synthetic derivative of a tryptophan metabolite decreases capsule formation and prevents capsular contracture by inhibiting the differentiation of fibroblasts to myofibroblasts, selectively inhibiting collagen synthesis, and decreasing specific T-cell immune responses by changing anti-inflammatory cytokine expression.

Regioselectivity significantly impacts microsomal glucuronidation efficiency of R/S-6, 7-, and 8-hydroxywarfarin

Coumadin (R/S-warfarin) metabolism plays a critical role in patient response to anticoagulant therapy. Several cytochrome P450s oxidize warfarin into R/S-6-, 7-, 8-, 10, and 4'-hydroxywarfarin that can undergo subsequent glucuronidation by UDP-glucuronosyltransferases (UGTs); however, current studies on recombinant UGTs cannot be adequately extrapolated to microsomal glucuronidation capacities for the liver. Herein, we estimated the capacity of the average human liver to glucuronidate hydroxywarfarin and identified UGTs responsible for those metabolic reactions through inhibitor phenotyping. There was no observable activity toward R/S-warfarin, R/S-10-hydroxywarfarin or R/S-4'-hydroxywarfarin. The observed metabolic efficiencies (V_max/K_m) toward R/S-6-, 7-, and especially 8-hydroxywarfarin indicated a high glucuronidation capacity to metabolize these compounds. UGTs demonstrated strong regioselectivity toward the hydroxywarfarins. UGT1A6 and UGT1A1 played a major role in R/S-6- and 7-hydroxywarfarin glucuronidation, respectively, whereas UGT1A9 accounted for almost all of the generation of the R/S-8-hydroxywarfarin glucuronide. In summary, these studies expanded insights to glucuronidation of hydroxywarfarins by pooled human liver microsomes, novel roles for UGT1A6 and 1A9, and the overall degree of regioselectivity for the UGT reactions.

Genetic polymorphisms associated with adverse reactions of molecular-targeted therapies in renal cell carcinoma

The prognosis of patients with metastatic renal cell carcinoma has drastically improved due to the development of molecular-targeted drugs and their use in clinical practice. However, these drugs cause some diverse adverse reactions in patients and sometimes affect clinical outcomes of cancer therapy. Therefore, predictive markers are necessary to avoid severe adverse reactions, to establish novel and effective prevention methods, and to improve treatment outcomes. Some genetic factors involved in these adverse reactions have been reported; however, perspectives on each adverse response have not been integrated yet. In this review, genetic polymorphisms relating to molecular-targeted therapy-induced adverse reactions in patients with renal cell carcinoma are summarized in the points of pharmacokinetic and pharmacodynamic mechanisms. We also discuss about the relationship between systemic drug exposure and adverse drug reactions.

Characteristics of the heme catabolic pathway in mild unconjugated hyperbilirubinemia and their associations with inflammation and disease prevention

Heme catabolism exerts physiological functions that impact health through depressing inflammation. Upon reactive pathway progression, as in Gilbert’s Syndrome (GS; UGT1A1*28 polymorphism), aggravated health effects have been determined. Based on lower inflammation and improved metabolic health reported for GS, inter-group differences in heme catabolism were explored. Therefore, a case-control study including 120 fasted, healthy, age- and gender matched subjects with/without GS, was conducted. Genetic expressions of HMOX-1 and BLVRA were measured. Additionally participants were genotyped for those polymorphisms that are known (UGT1A1*28) or likely (HMOX-1 microsatellites) to impact bilirubinemia. Intracellular interleukins (IL-6, IL-1β, TNFα), circulatory C-reactive protein (CRP), serum amyloid A (SAA) and haptoglobin (Hpt) were analysed as inflammatory markers. To assess intracellular heme oxygenase 1 (HO-1) isolated PBMCs were used. In GS vs. C, inflammation markers were significantly decreased. This was supported by an altered heme catabolism, indirectly reflecting in elevated unconjugated bilirubin (UCB; main phenotypic feature of GS) and iron, decreased hemopexin (Hpx) and Hpt and in up-regulated biliverdin reductase (BLVRA) gene expressions. Moreover, HMOX (GT)_n short alleles were non-significantly more prominent in female GS individuals. Herewith, we propose a concept to elucidate why GS individuals encounter lower inflammation, and are thus less prone to oxidative-stress mediated diseases.

Features of an altered AMPK metabolic pathway in Gilbert's Syndrome, and its role in metabolic health

Energy metabolism, involving the ATP-dependent AMPK-PgC-Ppar pathway impacts metabolic health immensely, in that its impairment can lead to obesity, giving rise to disease. Based on observations that individuals with Gilbert's syndrome (GS; UGT1A1(*)28 promoter mutation) are generally lighter, leaner and healthier than controls, specific inter-group differences in the AMPK pathway regulation were explored. Therefore, a case-control study involving 120 fasted, healthy, age- and gender matched subjects with/without GS, was conducted. By utilising intra-cellular flow cytometry (next to assessing AMPKα1 gene expression), levels of functioning proteins (phospho-AMPK α1/α2, PgC 1 α, Ppar α and γ) were measured in PBMCs (peripheral blood mononucleated cells). In GS individuals, rates of phospho-AMPK α1/α2, -Ppar α/γ and of PgC 1α were significantly higher, attesting to a boosted fasting response in this condition. In line with this finding, AMPKα1 gene expression was equal between the groups, possibly stressing the post-translational importance of boosted fasting effects in GS. In reflection of an apparently improved health status, GS individuals had significantly lower BMI, glucose, insulin, C-peptide and triglyceride levels. Herewith, we propose a new theory to explain why individuals having GS are leaner and healthier, and are therefore less likely to contract metabolic diseases or die prematurely thereof.

UGT genotyping in belinostat dosing

Certain genetic polymorphisms of UDP glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) can reduce gene expression (*28, *60, *93) or activity (*6), thereby altering the pharmacokinetics, pharmacodynamics, and the risk of toxicities of UGT1A1 substrates, of which irinotecan is a widely-described example. This review presents an overview of the clinical effects of UGT1A1 polymorphisms on the pharmacology of UGT1A1 substrates, with a special focus on the novel histone deacetylase inhibitor belinostat. Belinostat, approved for the treatment of peripheral T-cell lymphoma, is primarily glucuronidated by UGT1A1. Recent preclinical and clinical data showed that UGT1A1*28 was associated with reduced glucuronidation in human liver microsomes, while in a retrospective analysis of a Phase I trial with patients receiving belinostat UGT1A1*60 was predominantly associated with increased belinostat plasma concentrations. Furthermore, both UGT1A1*28 and *60 variants were associated with increased incidence of thrombocytopenia and neutropenia. Using population pharmacokinetic analysis a 33% dose reduction has been proposed for patients carrying UGT1A1 variant alleles. Clinical effects of this genotype-based dosing recommendation is currently prospectively being investigated. Overall, the data suggest that UGT1A1 genotyping is useful for improving belinostat therapy.

Tranilast: a review of its therapeutic applications

Tranilast (N-[3',4'-dimethoxycinnamoyl]-anthranilic acid) is an analog of a tryptophan metabolite. Initially, tranilast was identified as an anti-allergic agent, and used in the treatment of inflammatory diseases, such as bronchial asthma, atypical dermatitis, allergic conjunctivitis, keloids and hypertrophic scars. Subsequently, the results showed that it could be also effective in the management of a wide range of conditions. The beneficial effects of tranilast have also been seen in a variety of disease states, such as fibrosis, proliferative disorders, cancer, cardiovascular problems, autoimmune disorders, ocular diseases, diabetes and renal diseases. Moreover, several trials have shown that it has very low adverse effects and it is generally well tolerated by patients. In this review, we have attempted to accurately summarize previously published studies relating to the use of tranilast for a range of disorders and discuss the drug's possible mode of action. The major mode of the drug's efficacy appears to be the suppression of the expression and/or action of the TGF-β pathway, but the drug affects other factors as well. The findings presented in this review demonstrate the potential of tranilast for the control of a vast array of pathological situations, furthermore, it is a prescribed drug without severe side effects.

Population genetics for target identification

In this review, we address how to best use data from the Human Genome Project to discover new drug targets for common disease. We focus on population genetic approaches to identify variants associated with disease and how these can illuminate new targets and pathways for intervention. We discuss new insights into patterns of human genetic variation, evolving strategies for genome-wide case-control design, and developments in bioinformatic technologies. Hypothesis versus non-hypothesis-driven approaches to target identification are considered.:

Importance of UDP-glucuronosyltransferase 1A1 expression in skin and its induction by UVB in neonatal hyperbilirubinemia

UDP-glucuronosyltransferase (UGT) 1A1 is the sole enzyme that can metabolize bilirubin. Human infants physiologically develop hyperbilirubinemia as the result of inadequate expression of UGT1A1 in the liver. Although phototherapy using blue light is effective in preventing jaundice, sunlight has also been suggested, but without conclusive evidence, to reduce serum bilirubin levels. We investigated the mRNA expression pattern of human UGT1A1 in human skin, human skin keratinocyte (HaCaT) cells, and skin of humanized UGT1 mice. The effects of UVB irradiation on the expression of UGT1A1 in the HaCaT cells were also examined. Multiple UGT1A isoforms, including UGT1A1, were expressed in human skin and HaCaT cells. When HaCaT cells were treated with UVB-exposed tryptophan, UGT1A1 mRNA and activity were significantly induced. Treatment of the HaCaT cells with 6-formylindolo[3,2-b]carbazole, which is one of the tryptophan derivatives formed by UVB, resulted in an induction of UGT1A1 mRNA and activity. In neonates, the expression of UGT1A1 was greater in the skin; in adults, UGT1A1 was expressed mainly in the liver. Treatment of humanized UGT1 mice with UVB resulted in a reduction of serum bilirubin levels, along with increased UGT1A1 expression and activity in the skin. Our data revealed a protective role of UGT1A1 expressed in the skin against neonatal hyperbilirubinemia. Sunlight, a natural and free source of light, makes it possible to treat neonatal jaundice while allowing mothers to breast-feed neonates.

Genetic characterization to improve interpretation and clinical management of hepatotoxicity caused by tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) represent important therapeutic alternatives to, or combinations with, traditional cytotoxic chemotherapy. Despite their selective molecular targeting and demonstrated clinical benefit, TKIs produce a range of serious adverse events, including drug-induced liver injury, that require careful patient management to maintain treatment benefit without harm. Genetic characterization of serious adverse events can identify mechanisms of injury and improve safety risk management. This review presents pharmacogenetic comparisons of two approved TKIs, lapatinib and pazopanib, which reveal different mechanisms of injury and inform the characteristics and risk of serious liver injury in treated patients. The data presented demonstrate the utility of genetic studies to investigate drug-induced liver injury and potentially support its management in patients.

The impact of pharmacogenomics research on drug development

Over the last two decades, identification of polymorphisms that influence human diseases has begun to have an impact on the provision of medical care. The promise of genetics lies in its ability to provide insight into an individual's susceptibility to disease, the likely nature of the disease and the most appropriate therapy. For much of its history, pharmacogenomics (PGx) has been limited to relatively simple phenotypes such as plasma drug levels. Progress in genetic technologies has broadened the scope of exploratory PGx and its implementation into safety and efficacy studies, impacting a broad spectrum of drug discovery and development activities. Recent PGx data show the ability of this approach to generate information that can be applied to target selection, dose selection, efficacy determination and safety issues. This in turn will lead to significant opportunities to influence the approaches to drug discovery, clinical development and the probability of success. In particular, adverse drug reactions are critical issues for pharmaceutical companies and for the patients who will benefit from these new medicines. In this review, we outline current progress in PGx, using examples to highlight the influence of polymorphisms, and discuss contemporary challenges for both researchers and clinicians.

Direct-to-Consumer Genetic Testing

Genetics has fascinated societies since ancient times, and references to traits or behaviors that appear to be shared or different among related individuals have permeated legends, literature, and popular culture. Biomedical advances from the past century, and particularly the discovery of the DNA double helix, the increasing numbers of links that were established between mutations and medical conditions or phenotypes, and technological advances that facilitated the sequencing of the human genome, catalyzed the development of genetic testing. Genetic tests were initially performed in health care facilities, interpreted by health care providers, and included the availability of counseling. Recent years have seen an increased availability of genetic tests that are offered by companies directly to consumers, a phenomenon that became known as direct-to-consumer genetic testing. Tests offered in this setting range from the ones that are also provided in health care establishments to tests known as ‘recreational genomics,’ and consumers directly receive the test results. In addition, testing in this context often does not involve the availability of counseling and, when this is provided, it frequently occurs on-line or over the phone. As a field situated at the interface between biotechnology, biomedical research, and social sciences, direct-to-consumer genetic testing opens multiple challenges that can be appropriately addressed only by developing a complex, inter-disciplinary framework.

Prevalence of clinically relevant UGT1A alleles and haplotypes in African populations

Variation of a short (TA)(n) repeat sequence (rs8175347) covering the TATA box of UGT1A1 (UDP-glucuronosyltransferase1A1) is associated with hyperbilirubinaemia (Gilbert's syndrome) and adverse drug reactions, and is used for dosage advice for irinotecan. Several reports indicate that the low-activity (risk) alleles ((TA)(7) and (TA)(8) )) are very frequent in Africans but the patterns of association with other variants in the UGT1A gene complex that may modulate these responses are not well known. rs8175347 and two other clinically relevant UGT1A variants (rs11692021 and rs10929302) were assayed in 2616 people from Europe and Africa. Low-activity (TA)(n) alleles frequencies were highest in equatorial Africa, (TA)(7,) being the most common in Cameroon, Ghana, southern Sudan, and in Ethiopian Anuak. Haplotypic diversity was also greatest in equatorial Africa, but in Ethiopia was very variable across ethnic groups. Resequencing of the promoter of a sample subset revealed no novel variations, but rs34547608 and rs887829 were typed and shown to be tightly associated with (TA)(n) . Our results illustrate the need for investigation of the effect of UGT1A variants other than (TA)(n) on the risk of irinotecan toxicity, as well as hyperbilirubinaemia due to hemolytic anaemia or human immunodeficiency virus protease inhibitors, so that appropriate pharmacogenetic advice can be given.

Associations of various gene polymorphisms with toxicity in colorectal cancer patients receiving oral uracil and tegafur plus leucovorin: a prospective study

BACKGROUND

To assess the predictive value of polymorphism in nine genes, primarily thymidylate synthase (TS) and orotate phosphoribosyltransferase (OPRT), which relates to 5-fluorouracil (5-FU) metabolism, for toxicity in patients treated with oral uracil/tegafur (UFT) plus leucovorin (LV).

PATIENTS AND METHODS

We treated 99 patients with stage II or III colorectal carcinoma with oral UFT + LV. Germline DNA from patients was genotyped for 5-FU and folate metabolism-relating genes. CYP2A6, tegafur-activating enzyme, and uridine diphosphate-glucuronosyltransferase 1A1 genetic variation were also assessed. Toxicity was graded by the National Cancer Institute Common Toxicity Criteria, version 2.0.

RESULTS

The multivariate logistic regression revealed that OPRT 638G>C polymorphism was associated with grade 3 diarrhea [odds ratio (OR) 19.84 for patients with the C/C homozygous type compared with patients with wild type, P = 0.014] and polymorphisms of UGT1A1 were associated with hyperbilirubinemia (OR 38.76 for homozygotes and double heterozygotes of *6 or *28 compared with wild type, P = 0.0008). No relationships were observed between TS polymorphisms and any toxicity.

CONCLUSIONS

OPRT polymorphism predicts toxicity, especially grade 3 or greater diarrhea to oral UFT + LV adjuvant chemotherapy, whereas TS does not, in our study cohort. UGT1A1 polymorphism seems to be a risk factor for hyperbilirubinemia due to UFT+LV.

Pazopanib-induced hyperbilirubinemia is associated with Gilbert's syndrome UGT1A1 polymorphism

BACKGROUND

Pazopanib has shown clinical activity against multiple tumour types and is generally well tolerated. However, isolated elevations in transaminases and bilirubin have been observed. This study examined polymorphisms in molecules involved in pharmacokinetic and pharmacodynamic pathways of pazopanib and their association with hepatic dysfunction.

METHODS

Twenty-eight polymorphisms in 11 genes were evaluated in pazopanib-treated renal cell carcinoma patients. An exploratory analysis was conducted in 116 patients from a phase II study; a replication study was conducted in 130 patients from a phase III study.

RESULTS

No polymorphisms were associated with alanine aminotransferase elevation. The Gilbert's uridine-diphosphoglucuronate glucuronosyltransferase 1A1 (UGT1A1) TA-repeat polymorphism was significantly associated with pazopanib-induced hyperbilirubinemia in the phase II study. This association was replicated in the phase III study (P<0.01). Patients with TA6/TA6, TA6/TA7, and TA7/TA7 genotypes experienced median bilirubin increases of 0.31, 0.37, and 0.71 x upper limit of the normal range (ULN), respectively. Of the 38 patients with hyperbilirubinemia (> or = 1.5 x ULN), 32 (84%) were either TA7 homozygotes (n=18) or TA7 heterozygotes (n=14). For TA7 homozygotes, the odds ratio (95% CI) for developing hyperbilirubinemia was 13.1 (5.3-32.2) compared with other genotypes.

CONCLUSIONS

The UGT1A1 polymorphism is frequently associated with pazopanib-induced hyperbilirubinemia. These data suggest that some instances of isolated hyperbilirubinemia in pazopanib-treated patients are benign manifestations of Gilbert's syndrome, thus supporting continuation of pazopanib monotherapy in this setting.

Evaluation and optimization of antifibrotic activity of cinnamoyl anthranilates

Tranilast is an anti-inflammatory drug in use for asthma and atopic dermatitis. In studies over the last decade it has been revealed that tranilast can reduce fibrosis occurring in the kidney during diabetes, thereby delaying and/or preventing kidney dysfunction. We report a structure-activity study aimed at optimizing the antifibrotic activity of tranilast. A series of cinnamoyl anthranilates were prepared and assessed for their ability to prevent TGF-beta-stimulated production of collagen in cultured renal mesangial cells. We reveal derivatives with improved potency and reduced cellular toxicity relative to tranilast. 3-Methoxy-4-propargyloxycinnamoyl anthranilate reduces albuminuria in a rat model of progressive diabetes, and thus has potential as an innovative treatment for diabetic nephropathy.

Prediction of deleterious non-synonymous single-nucleotide polymorphisms of human uridine diphosphate glucuronosyltransferase genes

UDP glucuronosyltransferases (UGTs) are an important class of Phase II enzymes involved in the metabolism and detoxification of numerous xenobiotics including therapeutic drugs and endogenous compounds (e.g. bilirubin). To date, there are 21 human UGT genes identified, and most of them contain single-nucleotide polymorphisms (SNPs). Non-synonymous SNPs (nsSNPs) of the human UGT genes may cause absent or reduced enzyme activity and polymorphisms of UGT have been found to be closely related to altered drug clearance and/or drug response, hyperbilirubinemia, Gilbert's syndrome, and Crigler-Najjar syndrome. However, it is unlikely to study the functional impact of all identified nsSNPs in humans using laboratory approach due to its giant number. We have investigated the potential for bioinformatics approach for the prediction of phenotype based on known nsSNPs. We have identified a total of 248 nsSNPs from human UGT genes. The two algorithms tools, sorting intolerant from tolerant (SIFT) and polymorphism phenotyping (PolyPhen), were used to predict the impact of these nsSNPs on protein function. SIFT classified 35.5% of the UGT nsSNPs as "deleterious"; while PolyPhen identified 46.0% of the UGT nsSNPs as "potentially damaging" and "damaging". The results from the two algorithms were highly associated. Among 63 functionally characterized nsSNPs in the UGTs, 24 showed altered enzyme expression/activities and 45 were associated with disease susceptibility. SIFT and Polyphen had a correct prediction rate of 57.1% and 66.7%, respectively. These findings demonstrate the potential use of bioinformatics techniques to predict genotype-phenotype relationships which may constitute the basis for future functional studies.

Can UGT1A1 genotyping reduce morbidity and mortality in patients with metastatic colorectal cancer treated with irinotecan? An evidence-based review

This evidence-based review addresses the question of whether testing for UGT1A1 mutations in patients with metastatic colorectal cancer treated with irinotecan leads to improvement in outcomes (e.g., irinotecan toxicity, response to treatment, morbidity, and mortality), when compared with no testing. No studies were identified that addressed this question directly. The quality of evidence on the analytic validity of current UGT1A1 genetic testing methods is adequate (scale: convincing, adequate, inadequate), with available data indicating that both analytic sensitivity and specificity for the common genotypes are high. For clinical validity, the quality of evidence is adequate for studies reporting concentration of the active form of irinotecan (SN-38), presence of severe diarrhea, and presence of severe neutropenia stratified by UGT1A1 common genotypes. The strongest association for a clinical endpoint is for severe neutropenia. Patients homozygous for the *28 allele are 3.5 times more likely to develop severe neutropenia compared with individuals with the wild genotype (risk ratio 3.51; 95% confidence interval 2.03-6.07). The proposed clinical utility of UGT1A1 genotyping would be derived from a reduction in drug-related adverse reactions (benefits) while at the same time avoiding declines in tumor response rate and increases in morbidity/mortality (harms). At least three treatment options for reducing this increased risk have been suggested: modification of the irinotecan regime (e.g., reduce initial dose), use of other drugs, and/or pretreatment with colony-stimulating factors. However, we found no prospective studies that examined these options, particularly whether a reduced dose of irinotecan results in a reduced rate of adverse drug events. This is a major gap in knowledge. Although the quality of evidence on clinical utility is inadequate, two of three reviewed studies (and one published since our initial selection of studies for review) found that individuals homozygous for the *28 allele had improved survival. Three reviewed studies found statistically significant higher tumor response rates among individuals homozygous for the *28 allele. We found little or no direct evidence to assess the benefits and harms of modifying irinotecan regimens for patients with colorectal cancer based on their UGT1A1 genotype; however, results of our preliminary modeling of prevalence, acceptance, and effectiveness indicate that reducing the dose would need to be highly effective to have benefits outweigh harms. An alternative is to increase irinotecan dose among wild-type individuals to improve tumor response with minimal increases in adverse drug events. Given the large number of colorectal cancer cases diagnosed each year, a randomized controlled trial of the effects of irinotecan dose modifications in patients with colorectal cancer based on their UGT1A1 genotype is feasible and could clarify the tradeoffs between possible reductions in severe neutropenia and improved tumor response and/or survival in patients with various UGT1A1 genotypes.

Pharmacokinetics of raltegravir in individuals with UGT1A1 polymorphisms

Raltegravir is a human immunodeficiency virus-1 (HIV-1) integrase strand transfer inhibitor metabolized by glucuronidation via UDP-glucuronosyltransferase 1A1 (UGT1A1). In this study, 30 subjects with a UGT1A1*28/*28 genotype (associated with decreased activity of UGT1A1) and 27 UGT1A1*1/*1 control subjects (matched by race, age, gender, and body mass index) received a single 400-mg dose of raltegravir after fasting. No serious adverse experiences were reported, and there were no discontinuations due to adverse experiences. The geometric mean ratio (GMR) (UGT1A1*28/*28 to UGT1A1*1/*1) and 90% confidence interval (CI) were 1.41 (0.96, 2.09) for raltegravir area under the concentration-time curve (AUC(0-infinity)), 1.40 (0.86, 2.28) for maximum plasma concentration (C(max)), and 1.91 (1.43, 2.55) for concentration at the 12-h time point (C(12 h)). No clinically important differences in time to maximum concentration (T(max)) or half-life were observed. Plasma concentrations of raltegravir are modestly higher in individuals with the UGT1A1*28/*28 genotype than in those with the UGT1A1*1/*1 genotype. This increase is not clinically significant, and therefore no dose adjustment of raltegravir is required for individuals with the UGT1A1*28/*28 genotype.

Data-driven methods to discover molecular determinants of serious adverse drug events

The dangers of serious adverse drug reactions (SADRs) are well known to clinicians, pharmacologists, and the lay public. Efforts to elucidate the molecular mechanisms behind SADRs have made significant progress through genetics and gene expression measurements. However, as the field of pharmacology adopts the same novel higher-density measurement modalities that have proven successful in other areas of biology, one wonders whether there can be more ways to benefit from the explosion of data created by these tools. The development of analytic tools and algorithms to interpret these biological data to create tools for medicine is central to the field of translational bioinformatics. In this review we introduce some of the types of SADR predictors that are required, and we discuss several databases that are publicly available for the study of SADRs, ranging from clinical to molecular measurements. We also describe recent examples of how bioinformatics methods coupled with data repositories can advance the science of SADRs.

PhRMA white paper on ADME pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross-industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003-2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug-metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss three specific SADRs with an emphasis on genetic risk factors. These SADRs, selected based on wide-sweeping clinical interest, are drug-induced liver injury, statin-induced myotoxicity and drug-induced long QT and torsades de pointes. Key challenges for the discovery of predictive risk alleles for these SADRs are also considered.

UGT1A1 promoter polymorphism increases risk of nilotinib-induced hyperbilirubinemia

Nilotinib is a novel BCR-ABL inhibitor with significantly improved potency and selectivity over imatinib. In Phase I and Phase II clinical studies of nilotinib in patients with a variety of leukemias, infrequent instances of reversible, benign elevation of bilirubin were observed. Uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) glucuronidates bilirubin in humans, and a polymorphism in the promoter of the gene that encodes it has been associated with hyperbilirubinemia during treatment with a number of drugs. Pharmacogenetic analysis of that TA-repeat polymorphism found an association between the (TA)7/(TA)7 genotype and risk of hyperbilirubinemia in Phase I patients with imatinib-resistant/intolerant chronic myeloid leukemia (CML) or relapsed/refractory Ph+ acute lymphoblastic leukemia (ALL); this result was replicated in two separate analyses of the chronic phase (CP) and accelerated phase (AP) CML arms of a Phase II study. As nilotinib is not known to be glucuronidated by UGT1A1, the combined impact of inhibition of UGT1A1 activity by nilotinib and genetic polymorphism is the most likely cause of the increased rate of hyperbilirubinemia.

Glucuronidation of antiallergic drug, Tranilast: identification of human UDP-glucuronosyltransferase isoforms and effect of its phase I metabolite

Tranilast is an oral antiallergic agent widely used in Japan. Recently, in Western populations, hyperbilirubinemia induced by tranilast was suspected during clinical trials. Tranilast has been reported to be mainly metabolized to a glucuronide and a phase I metabolite, 4-demethyltranilast (N-3). In the present study, we investigated the in vitro metabolism of tranilast in human liver and jejunum microsomes and recombinant UDP-glucuronosyltransferases (UGTs). The glucuronidation of tranilast was clarified to be mainly catalyzed by UGT1A1 in human liver and intestine. The K(m) values of tranilast glucuronosyltransferase activity were 51.5, 50.6, and 38.0 microM in human liver microsomes, human jejunum microsomes, and recombinant UGT1A1, respectively. The V(max) values were 10.4, 42.9, and 19.7 pmol/min/mg protein in human liver microsomes, human jejunum microsomes, and recombinant UGT1A1, respectively. When the intrinsic clearance was calculated using the in vitro kinetic parameters, microsomal protein content, and weight of tissues, tranilast glucuronosyltransferase activity was 2.5-fold higher in liver than in intestine. Tranilast glucuronosyltransferase activity was strongly inhibited by bilirubin, a typical UGT1A1 substrate, and N-3, indicating that the phase I metabolite could affect the tranilast glucuronosyltransferase activity. In the case of N-3 formation, the K(m) and V(max) values were 37.1 microM and 27.6 pmol/min/mg protein in human liver microsomes. The bilirubin glucuronosyltransferase activity was strongly inhibited by both tranilast and N-3, suggesting that tranilast-induced hyperbilirubinemia would be responsible for the inhibition by tranilast and N-3 of the bilirubin glucuronosyltransferase activity, as would the UGT1A1 genotype.

Pharmacogenomics and the future of drug therapy

With the completion of the human genome project, many investigators are striving to translate the resulting wealth of new information into new and improved clinical practices. Pharmacogenomics represents one of the most promising of these applications for adult- and pediatric-based therapies. This article provides a historical perspective, but most importantly, uses this background to illustrate important principles of the field. The application of pharmacogenomics to asthma therapy is presented as an example of the current status of pharmacogenomics as it is being applied to an important pediatric health problem. Finally, a discussion of future promises and challenges to the application of pharmacogenomics is presented, including economic and ethical issues.

Stepwise haplotype analysis: are LD patterns repeatable?

A variety of techniques exist to describe and depict patterns of pairwise linkage disequilibrium (LD). In the current paper, a new log-linear framework is proposed for the summarisation of local interactions among single nucleotide polymorphisms (SNPs). Our approach provides a straightforward means of capturing the diversity of higher-order LD relationships for small numbers of loci by investigating inter-marker interactions. Our method was applied to a dataset of 76 SNP markers spanning a genomic interval of length 2.8 megabases. The analysis of three short sub-regions is described in detail here. Model and graphical representations of contiguous markers in medium to high LD are presented. In the regions studied, evidence for sub-structure was detected, supporting the view that the genomic reality is complex. Interestingly, a critical evaluation of the method by bootstrapping showed that while some LD relationships were captured in a highly repeatable fashion, the majority were not. Large numbers of small interactions, both direct and indirect, mean that many models can adequately summarise the data at hand. Our results suggest that repeatability should be further investigated in the application of LD-based approaches.

The role of Gilbert's syndrome and frequent NAT2 slow acetylation polymorphisms in the pharmacokinetics of retigabine

Retigabine (RGB) is an investigational antiepileptic drug, which undergoes extensive UGT1A1, 1A9 and 1A4-mediated N-glucuronidation and N-acetylation. The mono-acetylated metabolite of RGB has some pharmacological activity and is denoted AWD21-360. We investigated whether the pharmacokinetics (PK) of RGB and AWD21-360 are altered in subjects with Gilbert's syndrome (GS) and/or with frequent N-acetyltransferase 2 (NAT2) slow acetylator (SA) polymorphisms. Based on consistent genotyping and phenotyping screening results, 37 Caucasian subjects (21-46 years; 31 men, six women) were assigned to one of the following groups: (1) absence of GS (non-GS)/rapid acetylator (RA) (N=11); (2) GS/RA (N=8); (3) non-GS/SA (N=11); (4) GS/SA (N=7). Subjects received single and multiple (b.i.d.) 200-mg oral RGB doses over 5 days. Blood samples were collected up to 60 h after dosing for plasma PK of RGB and AWD21-360. Group comparisons were performed by ANOVA. Single-dose PK of RGB and AWD21-360 and multiple-dose PK of RGB did not differ significantly between groups. After multiple dose treatment, RA subjects showed a significantly higher total exposure to AWD21-360 of about 32% (95% CI 101.9-172.5) relative to SA subjects (P=0.0362). The UGT1A1 metabolic capacity (i.e. presence or absence of GS), however, did not significantly affect the overall exposure to AWD21-360. The results indicate that the PK of RGB is unaltered in individuals with GS, in subjects with NAT2 SA status, and in carriers of both variants, whereas the total exposure to AWD21-360 is significantly related to the RA or SA status of subjects. Results further suggest that metabolic switching to the mono-acetylated metabolite AWD21-360 may partially compensate for the impaired glucuronidation capacity in GS subjects. RGB treatment showed no significant differences in tolerability and safety between groups.

Pharmacogenetics in drug development

Over the last two decades, identification of polymorphisms that influence human diseases has begun to have an impact on the provision of medical care. The promise of genetics lies in its ability to provide insights into an individual's susceptibility to disease, the likely nature of the disease and the most appropriate therapy. For much of its history, pharmacogenetics (PGx-the use of genetic information to impact drug choice) has been limited to comparatively simple phenotypes such as plasma drug levels. Progress in genetics technologies has broadened the scope of PGx efficacy and safety studies that can be implemented, impacting on a broad spectrum of drug discovery and development activities. Recent PGx data show the ability of this approach to generate information that can be applied to dose selection, efficacy determination and safety issues. This in turn will lead to significant opportunities to affect both the approach to clinical development and the probability of success--the latter being an important aspect for pharmaceutical companies and for the patients who will benefit from these new medicines.

Comparative genomics analysis of human sequence variation in the UGT1A gene cluster

Common polymorphisms within the human UGT1A gene locus are associated with irinotecan and tranilast toxicity. To uncover additional functional variation across this gene cluster, cross-species sequence comparisons were performed. Evolutionarily conserved segments (a total of 47.1 kb) were re-sequenced in 24 African-American, 24 European-American, and 24 Asian individuals, and 381 segregating sites (including 123 singletons) were identified. Highly conserved coding sites were less likely to be polymorphic than diverged sites (P<0.0001) but this pattern was not observed at non-coding sites (P=0.1025). Among coding variants, the distribution of those computationally predicted to affect function was skewed toward low frequencies. Some alleles occurred at similar frequencies in each population; others had wide disparities. Although strong linkage disequilibrium was detected among the hepatically expressed genes, the degree of linkage disequilibrium varied among populations. These results suggest that rare functional gene variants and inter-population variability must be considered in the interpretation of association studies between UGT1A and drug metabolism/toxicity phenotypes.

Theragenomic knowledge management for individualised safety of drugs, chemicals, pollutants and dietary ingredients

Severe adverse drug reactions (ADRs) are a major problem in drug development and clinical practice and the most common cause of market withdrawals of drugs. Individualised drug safety aims at the prospective identification of single patients who carry genetic predispositions for the development of serious or fatal ADRs under drug treatment. For a comprehensive individualised drug safety evaluation a clearly structured organisation, linkage and representation of diverse and heterogeneous, yet related, knowledge is imperative. To efficiently support experts in this process a platform, coined OKAPI, was specified that combines multiple concepts in knowledge management to perform ontological knowledge acquisition, processing and integration. SafeBase (TheraSTrat) is an ontology driven implementation of the OKAPI specification and an innovative, user-friendly and interactive platform for storage, management and visualisation of knowledge across multiple scientific disciplines pertinent to current and future theragenomics-based drug discovery and development and to strategies of individualised drug safety.

Pharmacogenetics in drug regulation: promise, potential and pitfalls

Pharmacogenetic factors operate at pharmacokinetic as well as pharmacodynamic levels-the two components of the dose-response curve of a drug. Polymorphisms in drug metabolizing enzymes, transporters and/or pharmacological targets of drugs may profoundly influence the dose-response relationship between individuals. For some drugs, although retrospective data from case studies suggests that these polymorphisms are frequently associated with adverse drug reactions or failure of efficacy, the clinical utility of such data remains unproven. There is, therefore, an urgent need for prospective data to determine whether pre-treatment genotyping can improve therapy. Various regulatory guidelines already recommend exploration of the role of genetic factors when investigating a drug for its pharmacokinetics, pharmacodynamics, dose-response relationship and drug interaction potential. Arising from the global heterogeneity in the frequency of variant alleles, regulatory guidelines also require the sponsors to provide additional information, usually pharmacogenetic bridging data, to determine whether data from one ethnic population can be extrapolated to another. At present, sponsors explore pharmacogenetic influences in early clinical pharmacokinetic studies but rarely do they carry the findings forward when designing dose-response studies or pivotal studies. When appropriate, regulatory authorities include genotype-specific recommendations in the prescribing information. Sometimes, this may include the need to adjust a dose in some genotypes under specific circumstances. Detailed references to pharmacogenetics in prescribing information and pharmacogenetically based prescribing in routine therapeutics will require robust prospective data from well-designed studies. With greater integration of pharmacogenetics in drug development, regulatory authorities expect to receive more detailed genetic data. This is likely to complicate the drug evaluation process as well as result in complex prescribing information. Genotype-specific dosing regimens will have to be more precise and marketing strategies more prudent. However, not all variations in drug responses are related to pharmacogenetic polymorphisms. Drug response can be modulated by a number of non-genetic factors, especially co-medications and presence of concurrent diseases. Inappropriate prescribing frequently compounds the complexity introduced by these two important non-genetic factors. Unless prescribers adhere to the prescribing information, much of the benefits of pharmacogenetics will be squandered. Discovering highly predictive genotype-phenotype associations during drug development and demonstrating their clinical validity and utility in well-designed prospective clinical trials will no doubt better define the role of pharmacogenetics in future clinical practice. In the meantime, prescribing should comply with the information provided while pharmacogenetic research is deservedly supported by all concerned but without unrealistic expectations.

Emerging strategies and applications of pharmacogenomics

The rapid pace of genomic science advancements, including the completion of the human genome sequence, the extensive cataloguing of genetic variation and the acceleration of technologies to assess such variation, combined with clinical programmes with rich phenotypic data, serve as the foundation for the design and execution of pharmacogenomic studies which have an impact on the pharmaceutical pipeline from early discovery through to the marketplace. The authors discuss the required infrastructure to support pharmacogenomic studies and provide insight into the strategies and practical application to influence decision making in the pharmaceutical setting. Further, the influence of pharmacogenomics is currently affecting patient care in the oncology area and is highlighted as evident impact in the marketplace.

Elucidating mechanisms of drug-induced toxicity

The early and high-throughput application of assays for non-genetic toxicity is of great interest to the pharmaceutical industry, although few systems have been validated as being of good predictive value. New technologies could enable toxicity to be studied in the context of systems biology. An important factor to be considered is the metabolism of drugs to reactive intermediates. Chemical reactions of these with cell and tissue nucleophiles are relatively well understood, but predicting how biological modifications will affect signalling and regulatory networks remains a challenge. Some of these pathways could be useful as sentinels for toxicity. This article will cover some examples of drug toxicity and the prospects for future technology development.

Mechanistic basis of adverse drugreactions: the perils of inappropriate dose schedules

Adverse drug reactions (ADRs) have long been recognised as a significant cause of morbidity and mortality. They account for a substantial number of clinical consultations, hospital admissions and extended duration of in-patient stay as well as mortality. By far the most common ADRs are the concentration-dependent pharmacological reactions, the majority of which ought to be preventable. As a result of high concentrations of the parent drug and/or its metabolite(s), there is an augmentation of primary pharmacological activity and/or appearance of new and undesirable secondary pharmacological activity. Typically, these high concentrations result from administration of high doses in an attempt to maximise efficacy and/or modulation of the pharmacokinetics of a drug by either genetic or non-genetic factors. High plasma concentrations of parent drug may result from inherited impairment or drug-induced inhibition of its pharmacokinetic disposition. Conversely, inherited overcapacity or drug-induced induction of the metabolism of a drug may result in low concentrations of parent drug and frequently, rapid accumulation of its metabolites. Environmental, dietary and phytochemical factors may also influence the activity of drug metabolising enzymes. As with inherited polymorphisms of acetylation and cytochrome P450-based drug metabolising enzymes, polymorphisms of other conjugation reactions, such as glucuronidation, increasingly appear to be associated with drug toxicity. Diseases of organs involved in elimination of a drug also alter its pharmacokinetics, plasma concentration and, therefore, the profile of its concentration-dependent ADRs. Inherited mutations, concurrently administered drugs or presence of certain diseases may also alter the sensitivity of some pharmacological targets, accounting for a substantial number of ADRs and interactions. When there is enhanced pharmacodynamic sensitivity, plasma drug concentrations that are apparently within the normal 'non-toxic' range give rise to ADRs. Recent advances have also provided important insights into the wider scope of drug-drug interactions. Interactions that occur at P-glycoproteins, drug transporters and efflux pumps, at various transmembrane interfaces such as the gastrointestinal wall, renal tubules, hepatobiliary border and blood-brain barrier, are beginning to explain many non-metabolic interactions. These alter the systemic exposure to drugs and have so far, begun to explain unexpected neurotoxicity and hepatotoxicity. The function of these transporters is also genetically modulated. These advances, together with continued increased awareness and education of prescribers and pharmacists, offer great opportunities for substantially minimising concentration-related ADRs.

Substrate Specificity of Human Hepatic Udp‐Glucuronosyltransferases

Five human hepatic UDP-glucuronosyltransferases (UGTs) catalyze the facilitated excretion of more than 90% of drugs eliminated by glucuronidation. The substrate specificity of these UGTs has been examined using cloned expressed enzymes and liquid chromatography-mass spectrometry assays to determine the intrinsic clearance of drug glucuronidation in vitro. Specific substrates for the five individual UGTs have been identified. These five probe substrates could be used to predict the drug clearance catalyzed by individual UGTs in vivo.

Will tomorrow's medicines work for everyone?

Throughout much of the world, 'race' and 'ethnicity' are key determinants of health. For example, African Americans have, by some estimates, a twofold higher incidence of fatal heart attacks and a 10% higher incidence of cancer than European Americans, and South Asian- or Caribbean-born British are approximately 3.5 times as likely to die as a direct result of diabetes than are British of European ancestry. The health care that people receive also depends on 'race' and 'ethnicity'. African Americans are less likely to receive cancer-screening services and more likely to have late-stage cancer when diagnosed than European Americans. Health disparities such as these are one of the greatest social injustices in the developed world and one of the most important scientific and political challenges.

Pharmacogenetics and drug development: the path to safer and more effective drugs

Pharmacogenetics provides opportunities for informed decision-making along the pharmaceutical pipeline. There is a growing literature of retrospective studies of marketed medicines that describe efficacy or safety on the basis of patient genotypes. These studies emphasize the potential prospective use of genome information to enhance success in finding new medicines. An example of a prospective efficacy pharmacogenetic Phase-IIA proof-of-concept study is described. Inserting a rapidly performed efficacy pharmacogenetic step after initial clinical data are obtained can provide confidence for a commitment to full drug development. The rapid identification of adverse events during and after drug development using genomic mapping tools is also reviewed.