Prediction of tamoxifen outcome by genetic variation of CYP2D6 in post-menopausal women with early breast cancer

The question of whether genetic polymorphisms of CYP2D6 can affect treatment outcome in patients with early post-menopausal oestrogen receptor (ER)-positive breast cancer has been a matter of debate over the past few years. In this article we revisit the hypothesis of CYP2D6 being a potential tamoxifen outcome predictor and provide detailed insight into the ongoing controversy that prevented the CYP2D6 marker from being accepted by the scientific and clinical community. We summarize the available pharmacokinetic, pharmacodynamic and pharmacogenetic evidence and resolve the controversy based on the recognized methodological and statistical issues. The cumulative evidence suggests that genotyping for CYP2D6 is clinically relevant in post-menopausal women. This is important, because the clarification of this issue has the potential to resolve a clinical management question that is relevant to hundreds of thousands of women diagnosed with ER-positive breast cancer each year, who should not be denied effective endocrine therapy.     

北京军区总医院基因导向的个体化给药项目及其临床应用

本文介绍了北京军区总医院药理科应用焦磷酸测序基因分型技术开展的多种个体化给药基因检测项目,包括：β1肾上腺素受体基因和CYP2 D6基因;CYP2C19基因;维生素K环氧化物还原酶复合物1基因和CYP2C9基因;巯嘌呤甲基转移酶基因;表皮生长因子受体基因;IL28B基因;O6-甲基鸟嘌呤-DNA-甲基转移酶基因;SLCO1B1基因;HLA-B＊1502,HLA-B＊5801等位基因等。这些基因检测项目的实施为判断遗传因素对临床疗效及不良反应的影响提供了依据。     

Pharmacogenetics of Naltrexone in Asian Americans: A Randomized Placebo-Controlled Laboratory Study

Recent clinical and laboratory studies have shown that the effects of naltrexone for alcoholism may be moderated by the Asn40Asp single-nucleotide polymorphism (SNP) of the μ-opioid receptor gene (OPRM1). Allele frequencies for this polymorphism, however, have been shown to vary substantially as a function of ethnic background, such that individuals of Asian descent are more likely to carry the minor (Asp40) allele. The objective of this study is to test the naltrexone pharmacogenetic effects of the Asn40Asp SNP in a sample of Asian Americans. This study consists of a double-blinded, randomized, placebo-controlled laboratory trial of naltrexone. Participants (n=35, 10 females; 13 Asn40Asn and 22 Asp40 carriers) were non-treatment-seeking heavy drinkers recruited from the community. After taking naltrexone or placebo, participants completed an intravenous alcohol administration session. The primary outcome measures were subjective intoxication and alcohol craving. Results suggested that Asp40 carriers experienced greater alcohol-induced sedation, subjective intoxication, and lower alcohol craving on naltrexone, as compared to placebo, and to Asn40 homozygotes. There results were maintained when controlling for ALDH2 (rs671) and ADH1B (rs1229984) markers and when examining the three levels of OPRM1 genotype, thereby supporting an OPRM1 gene dose response. These findings provide a much-needed extension of previous studies of naltrexone pharmacogenetics to individuals of Asian descent, an ethnic group more likely to express the minor allele putatively associated with improved biobehavioral and clinical response to this medication. These findings help further delineate the biobehavioral mechanisms of naltrexone and its pharmacogenetics.     

Pharmacokinetics,pharmacodynamics and pharmacogenetics associated with nonsteroidal anti-inflammatory drugs and opioids in pediatric cancer patients

Introduction: Advancing appropriate and adequate analgesic pharmacotherapy in pediatric patients with cancer is an area of clinical need. Few studies have been performed to evaluate the selection of an analgesic and appropriate dosing corresponding to analgesic effect among pediatric cancer patients. This review describes information related to pharmacokinetic, pharmacodynamic, and pharmacogenomic (when applicable) considerations for analgesics that are commonly used to manage pain experienced by pediatric patients with cancer.

Areas covered: Analgesics commonly used to treat pediatric patients with malignancy patterned after the World Health Organization’s ‘analgesic ladder’ for cancer pain management.

Expert opinion: Addressing pain management safely and effectively in pediatric patients with cancer will require advances in both drug development, to increase the armament of analgesics available for children, and our pharmacologic understanding of those analgesics in current use. However, performing the necessary types of studies to develop new analgesics, or gain knowledge of existing therapy, within a population that is relatively small, diverse, and who experience pain originating from a variety of sources, is a tremendous challenge.     

Renal function in HIV/HBV co‐infected and HBV mono‐infected patients on a long‐term treatment with tenofovir in real life setting

The human immunodeficiency virus (HIV)/hepatitis B virus (HBV) co‐infection is likely to be associated with an increased risk of kidney disease, due to the additional factors that may affect renal function in the HIV population. We aimed to evaluate renal toxicity in HIV/HBV and HBV mono‐infected patients on long‐term therapy with tenofovir (TDF) and to explore the association of polymorphisms in ATP‐binding cassette (ABCC)2, ABCC4, ABCC10 with the development of renal dysfunction. From September 2006 to November 2014, 44 HIV/HBV co‐infected and 34 HBV mono‐infected patients were commenced on TDF. Data of renal safety were retrospectively collected and analyzed. ABCC2, ABCC4 and ABCC10 genotypes were identified by real‐time PCR. Over 60 months of observation, there was a significant increase in mean creatinine levels from baseline (P<.01) that was not significantly different between the two study groups. Moreover, a significant decline in estimated glomerular filtration rate (eGFR) was observed from baseline (P<.01), and it was significantly greater in HBV mono‐infected than co‐infected patients (P=.03). The distribution of ABCC2, ABCC4 and ABCC10 genotypes among a subgroup of 34 patients did not show significant association with eGFR decline <90 mL/min per 1.73 m². Although our findings showed a statistically significant decrease in eGFR with long‐term use of TDF, its clinical impact seems to be modest. The role of genetic factors to identify patients at greater risk for developing tenofovir‐induced renal toxicity needs to be further investigated.     

Minor contribution of CYP3A5 to the metabolism of hepatitis C protease inhibitor paritaprevir in vitro

1. Paritaprevir (PTV) is a non-structural protein 3/4A protease inhibitor developed for the treatment of hepatitis C disease as a fixed dose combination of ombitasvir (OBV) and ritonavir (RTV) with or without dasabuvir.

2. The aim of this study was to evaluate the effects of cytochrome P450 (CYP) 3A5 on in vitro PTV metabolism using human recombinant CYP3A4, CYP3A5 (rCYP3A4, rCYP3A5) and human liver microsomes (HLMs) genotyped as either CYP3A5*1/*1, CYP3A5*1/*3 or CYP3A5*3/*3.

3. The intrinsic clearance (CL_int, V_max/K_m) for the production of a metabolite from PTV in rCYP3A4 was 1.5 times higher than that in rCYP3A5. The PTV metabolism in CYP3A5*1/*1 and CYP3A5*1/*3 HLMs expressing CYP3A5 was comparable to that in CYP3A5*3/*3 HLMs, which lack CYP3A5.

4. CYP3A4 expression level was significantly correlated with PTV disappearance rate and metabolite formation. In contrast, there was no such correlation found for CYP3A5 expression level.

5. This study represents that the major CYP isoform involved in PTV metabolism is CYP3A4, with CYP3A5 having a minor role in PTV metabolism. The findings of the present study may provide foundational information on PTV metabolism, and may further support dosing practices in HCV-infected patients prescribed PTV-based therapy.

     

Clinical pharmacokinetics and pharmacogenetics of tamoxifen and endoxifen

Introduction: Tamoxifen dominates the anti-estrogenic therapy in the early and metastatic breast cancer setting. Tamoxifen has a complex metabolism, being mainly metabolized by CYP2D6 into its 30–100 times more potent metabolite, endoxifen. Recently, a phase I study in which endoxifen as an orally z-endoxifen hydrochloride has been successfully evaluated.

Areas covered: the principal pharmacogenetic and non-genetic differences in the pharmacology of tamoxifen and endoxifen are evaluated. To this end, references from PubMed, Embase or Web of Science, among others, were reviewed As non-genetic factors, important differences and similarities such age, or adherence to tamoxifen therapy are comprehensively illustrated. Additionally, since CYP2D6 genotypes are considered the main limitation of tamoxifen, many studies have investigated the association between the worsened clinical outcomes in patients with non-functional CYP2D6 genotypes. In this review, an overview of the research on this field is presented. Also, a summary describing the literature about individualizing tamoxifen therapy with endoxifen concentrations and its limitations is listed.

Expert opinion: z-endoxifen hydrochloride is only investigated in the metastatic setting, still more research is required before its place in therapeutics is known. Similarly, monitoring tamoxifen efficacy based on endoxifen concentrations might not be overall recommended due to the limited evidence available.     

Advanced Pharmacy Practice Experiences in Pharmacogenomics Offered by US Pharmacy Programs

Objective. To characterize advanced pharmacy practice experiences (APPEs) with a primary focus in pharmacogenomics at schools and colleges of pharmacy in the United States.Methods. This was a cross-sectional, multicenter, observational study of pharmacogenomics APPEs at US pharmacy schools. Directors of experiential education at 146 accredited schools of pharmacy were contacted by phone and asked if their school offered a pharmacogenomics APPE. The preceptors of pharmacogenomics APPEs identified by this phone screen were sent an email with a link to an online survey that asked about their APPE offerings.Results. Of the 142 schools of pharmacy that were successfully reached via phone, 40 (28%) offered an APPE with a primary focus in pharmacogenomics. Thirty unique APPEs with pharmacogenomics as a primary focus were identified. The total number of preceptors involved in the pharmacogenomics APPEs was 33: 19 (58%) faculty preceptors and 14 (42%) non-faculty preceptors. Twenty-three of the 30 pharmacogenomics APPEs completed the survey (77% response rate). The APPE sites were diverse and included academic medical centers, community health systems, pharmacogenomic testing laboratories, and schools of pharmacy. Each pharmacogenomics APPE accommodated an average of six students per year. The APPE activities varied across sites.Conclusion. Only a small number of US pharmacy schools offer an APPE with a primary focus in pharmacogenomics. These rotations are diverse in scope and precepted by faculty or non-faculty pharmacists. The Academy should pursue opportunities to increase experiential education in pharmacogenomics.