Pharmacogenetic Outcomes Research Articles

Functional Characterization of Pharmcogenetic Variants of Human Cytochrome P450 2C9 in Korean Populations.

Human cytochrome P450 2C9 is a highly polymorphic enzyme that is required for drug and xenobiotic metabolism. Here, we studied eleven P450 2C9 genetic variants—including three novel variants F69S, L310V, and Q324X—that were clinically identified in Korean patients. P450 2C9 variant enzymes were expressed in Escherichia coli and their bicistronic membrane fractions were prepared The CO-binding spectra were obtained for nine enzyme variants, indicating P450 holoenzymes, but not for the M02 (L90P) variant. The M11 (Q324X) variant could not be expressed due to an early nonsense mutation. LC-MS/MS analysis was performed to measure the catalytic activities of the P450 2C9 variants, using diclofenac as a substrate. Steady-state kinetic analysis revealed that the catalytic efficiency of all nine P450 2C9 variants was lower than that of the wild type P450 2C9 enzyme. The M05 (R150L) and M06 (P279T) variants showed high kcat values; however, their Km values were also high. As the M01 (F69S), M03 (R124Q), M04 (R125H), M08 (I359L), M09 (I359T), and M10 (A477T) variants exhibited higher Km and lower kcat values than that of the wild type enzyme, their catalytic efficiency decreased by approximately 50-fold compared to the wild type enzyme. Furthermore, the novel variant M07 (L310V) showed lower kcat and Km values than the wild type enzyme, which resulted in its decreased (80%) catalytic efficiency. The X-ray crystal structure of P450 2C9 revealed the presence of mutations in the residues surrounding the substrate-binding cavity. Functional characterization of these genetic variants can help understand the pharmacogenetic outcomes.

Association of HTR1A gene polymorphisms with obsessive–compulsive disorder and its treatment response: the influence of sex and clinical characteristics

Objective: There have been controversial results in the literature on the association between HTR1A polymorphisms (rs10042486, C-1019G, and Gly272Asp) and obsessive–compulsive disorder (OCD). Here, the plausibility for such genetic and pharmacogenetic association was investigated by assessing a sample of Iranian OCD patients.Method: OCD patients had fulfilled the criteria for DSM-IV-TR with Y-BOCS scores higher than 9. A total of 207 controls and 205 patients’ blood samples were genotyped by means of PCR-RFLP.Results: The results showed that there was no association between these three SNPs and the treatment response. The distribution of rs10042486 genotypes was significantly different in the patients compared to the controls. The association analyses of the C-1019G showed significant differences in the genotypic frequency of the patients with or without a positive family history of psychiatric disorders. Similar differences in female patients were also observed. We found that the age of onset also associates with the C-1019G polymorphism but only in the female patients. No association of Gly272Asp polymorphism and OCD was observed in this study.Conclusion: We concluded that among the HTR1A polymorphisms, only the association of rs10042486 CT genotype and OCD was statistically significant. The association of C-1019G with OCD by considering the age of onset and family history was just significant in the female patients. No significant association between the studied HTR1A SNPs with treatment response was observed. Acquiring both positive and negative pharmacogenetic outcomes in each population helps to select the appropriate medication for a particular patient with fewer side effects.

Pharmacogenetic and Germline Prognostic Markers of Lung Cancer

Lung cancer is the leading global cause of cancer-related mortality. Interindividual variability in treatment response and cancer outcomes has focused attention on genetic polymorphisms as prognostic markers. We evaluated the overall contribution of candidate polymorphism association studies to our current understanding of the genetic predictors of lung cancer outcomes. We examined the results of 90 studies that evaluated associations between genetic polymorphisms and lung cancer outcomes published between January 1990 and May 2009. A total of 170 genetic variations in 90 studies were identified. Overall survival was a primary outcome in 81% of the studies and toxicity in 19%. Candidate polymorphisms in the DNA repair/synthesis pathway were the most frequently studied. Strong evidence in large-scale confirmatory studies of any single polymorphism was lacking. Polymorphisms of EGFR, XRCC1, and ERCC1 were associated with pharmacogenetic outcomes, whereas polymorphisms of MDM2, p53, and GSTM1 were associated with prognostic outcomes. All remaining polymorphisms had results lacking or failing replication testing. Heterogeneity in study populations, incomplete reporting of important population or study characteristics, inadequate power, and inconsistencies in methodology were common. Although the quality of existing studies involving the candidate polymorphism approach is highly variable, a small set of candidate polymorphisms was identified as potential biomarkers of clinical or pharmacogenetic outcome and would benefit from further replication testing. Newer approaches including haplotype tagging, pathway, genome-wide association, and combination methods with validative approaches may facilitate a more accurate prediction of lung cancer outcomes by genetic variation.

Pharmacogenetic testing and therapeutic drug monitoring are complementary tools for optimal individualization of drug therapy

Genetic factors contribute to the phenotype of drug response, but the translation of pharmacogenetic outcomes into drug discovery, drug development or clinical practice has proved to be surprisingly disappointing. Despite significant progress in pharmacogenetic research, only a few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed. There are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. First, pharmacogenetic tests could be more clinically applicable if they included a comprehensive survey of variation in the human genome and took into account the multigenic nature of many phenotypes of drug disposition and response. Unfortunately, much of the existing research in this area has been hampered by limitations in study designs and the nonoptimal selection of gene variants. Secondly, although responses to drugs can be influenced by the environment, only fragmentary information is currently available on how the interplay between genetics and environment affects drug response. Third, the use of a pharmacogenetic test as a standard of care for drug therapy has to overcome significant scientific, economic, commercial, political and educational barriers, among others, in order for clinically useful information to be effectively communicated to practitioners and patients. Meanwhile, the lack of efficacy is in this process is quite as costly as drug toxicity, especially for very expensive drugs, and there is a widespread need for clinically and commercially robust pharmacogenetic testing to be applied. In this complex scenario, therapeutic drug monitoring of parent drugs and/or metabolites, alone or combined with available pharmacogenetic tests, may be an alternative or complementary approach when attempts are made to individualize dosing regimen, maximize drug efficacy and enhance drug safety with certain drugs and populations (e.g. antidepressants in older people).

Pharmacogenetic Outcomes of Pediatric Acute Lymphoblastic Leukemia in Korea

Treatment result of pediatric acute lymphoblastic leukemia (ALL) has been markedly improved, but treatment related toxicities and relapse are still remaining problems. Genetic polymorphism is an important factor in the effectiveness and toxicity of anti-leukemic drugs and pharmacogenetics are beginning to emerge as useful research filed to solve those problems. In our experience in the treatment of ALL, many Korean patients could not tolerate full dosages of Western protocols. To make basis for individualized therapy with pharmacogenetics, we analyzed major genes implicated in the treatment of ALL. Fourteen genes of total 103 patients with ALL were analyzed with TotalPlex gene amplification methods (Mol Cell Probes. 2008. 22: 193). Among the drug related genes (percentage of mutant type) including CYP3A4*1B (0%), CYP3A5*3 (0%), GSTP1 (22.3%), GSTM1 (20.4%), GSTT1 (16.5%), MDR1 exon 21 (76.3%), MDR1 exon 26 (61.2%), MTHFR (64.1%), MTHFR 1298 (29.1%), NR3C1 1088 (0%), RFC 80 (79.6%), TPMT combined genotype (7%), VDR intron 8 (10.7%), VDR FokI (67%), incidence of mutant was higher in GSTM1 deletion, lower in MTHFR 1298, TYMS enhancer repeat, and VDR intron 8 comparing with the data of Western whites (Rocha J.C. et al. Blood 2005). As we had modified the dose of anti-leukemic agents depending on the toxicity during the treatment, we analyzed the relationship between the dose percent of actually administered dose and the distribution of each mutant to find out polymorphisms affecting toxicities of chemotherapeutic drugs. The mean dose percent of mercaptopurine was lower in patients with variant TPMT then those with wild type (33.2% vs. 53.5%, P=0.04), but there was no polymorphism that influenced the dose percent of methotrexate, daunorubicin, doxorubicin, and L-asparaginase. There was no significant difference in the incidence of genotypes between risk groups and individual mutant did not affect long term survival and relapse in Korean patients with ALL. In conclusion, we found some difference in the incidence of mutant genotypes related to the pharmacogenetics of ALL between Korean and Western whites, but there was no individual genetic polymorphism that affect on the treatment outcome. We expect more extensive researches about pharmacogenetics of Korean to establish the basis for individualized therapy with the consideration of ethnical difference.

A Rapid Outcomes Ascertainment System Improves the Quality of Prognostic and Pharmacogenetic Outcomes from Observational Studies

Case-control and observational studies are popular choices for evaluating molecular prognostic/pharmacogenetic outcomes, but data quality is rarely tested. Using clinical trial and epidemiologic methods, we assessed the quality of prognostic and outcomes data obtainable from a large case-control study of lung cancer. We developed an explicit algorithm (set of standard operating procedures forming a rapid outcomes ascertainment system) that encompassed multiple tests of quality assurance, and quality of data for a range of prognostic and outcomes variables, in several cancers, across several centers and two countries were assessed. Based on these assessments, the algorithm was revised and physicians' clinical practice changed. We reevaluated the quality of outcomes after these revisions. Development of an algorithm with internal quality controls showed specific patterns of data collection errors, which were fixable. Although the major discrepancy rate in retrospective data collection was low (0.6%) when compared with external validated sources, complete data were found in <50% of patients for treatment response rate, toxicity, and documentation of patient palliative symptoms. Prospective data collection and changes to clinical practice led to significantly improved data quality. Complete data on response rate increased from 45% to 76% (P = 0.01, Fisher's exact test), for toxicity data, from 26% to 56% (P = 0.02), and for palliative symptoms, from 25% to 70% (P < 0.05), in one large lung cancer case-control study. Observational studies can be a useful source for studying molecular prognostic and pharmacogenetic outcomes. A rapid outcomes ascertainment system with strict ongoing quality control measures is an excellent means of monitoring key variables.