Volume 29, Issue 4

CYP2C9 metabolizes approximately 20% of clinically used drugs, including the narrow therapeutic window drugs warfarin and phenytoin. More than 16,000 variants have been reported in the National Center for Biotechnology Information CYP2C9 database, as well as 58 alleles in the official P450 Nomenclature Committee website. Two single nucleotide polymorphisms represented by the CYP2C9*2 and CYP2C9*3 alleles have been studied extensively. However, in addition to these two alleles, other genetic factors and an individual’s biological characteristics contribute to the overall drug phenotype. A major bottleneck for CYP2C9 pharmacogenomics in clinical field applications is the lack of knowledge regarding the numerous genetic polymorphisms and their molecular functionalities. An unmet gap exists between the ever-growing number of genetic variants and their molecular mechanisms. In the present review, functional changes of all known CYP2C9 protein coding alleles were predicted using in silico analyses and compared with the in vitro and in vivo data. We also summarize functional information from recently reported CYP2C9 variants. Regarding the previously known CYP2C9 variants, we provide an update on the functional information obtained from in vitro and in vitro data.

Spanning over 2000 years, the Jewish population has a long history of migration, population bottlenecks, expansions, and geographical isolation, which has resulted in a unique genetic architecture among the Jewish people. As such, many Mendelian disease genes and founder mutations for autosomal recessive diseases have been discovered in several Jewish groups, which have prompted recent genomic studies in the Jewish population on common disease susceptibility and other complex traits. Although few studies on the genetic determinants of drug response variability have been reported in the Jewish population, a number of unique pharmacogenetic variants have been discovered that are more common in Jewish populations than in other major racial groups. Notable examples identified in the Ashkenazi Jewish (AJ) population include the vitamin K epoxide reductase complex subunit 1 ( VKORC1 ) c.106G>T (p.D36Y) variant associated with high warfarin dosing requirements and the recently reported cytochrome P450 2C19 ( CYP2C19 ) allele, CYP2C19*4B , that harbors both loss-of-function [ *4 (c.1A>G)] and increased-function [ *17 (c.-806C>T)] variants on the same haplotype. These data are encouraging in that like other ethnicities and subpopulations, the Jewish population likely harbors numerous pharmacogenetic variants that are uncommon or absent in other larger racial groups and ethnicities. In addition to unique variants, common multi-ethnic variants in key drug metabolism genes (e.g., ABCB1 , CYP2C8 , CYP2C9 , CYP2C19 , CYP2D6 , NAT2 ) have also been detected in the AJ and other Jewish groups. This review aims to summarize the currently available pharmacogenetics literature and discuss future directions for related research with this unique population.

The cytochrome P450 (CYP450) enzyme family is involved in the oxidative metabolism of many therapeutic drugs and various endogenous substrates. These enzymes are highly polymorphic. Prevalence of CYP450 enzyme gene polymorphisms vary among different populations and substantial inter- and intra-ethnic variability in frequency of CYP450 enzyme gene polymorphisms has been reported. This paper provides an overview and investigation of CYP450 genotypic and phenotypic reports published in the Greek population.

Background: The potential of tyrosine kinase inhibitors (TKIs) interacting with other therapeutics through hepatic uptake transporter inhibition has not been fully delineated in drug-drug interactions (DDIs). This study was designed to estimate the half-maximal inhibitory concentration (IC 50 ) values of five small-molecule TKIs (pazopanib, nilotinib, vandetanib, canertinib and erlotinib) interacting with organic anion-transporting polypeptides (OATPs): OATP-1B1 and -1B3. Methods: The IC 50 values of TKIs and rifampicin (positive control) were determined by concentration-dependent inhibition of TKIs on cellular accumulation of radiolabeled probe substrates [ 3 H]estrone sulfate and [ 3 H]cholecystokinin octapeptide. Chinese hamster ovary cells transfected with humanized OATP-1B1 and OATP-1B3 transporter proteins, respectively, were utilized to carry out these studies. Results: Pazopanib and nilotinib show inhibitory activity on OATP-1B1 transporter protein. IC 50 values for rifampicin, pazopanib and nilotinib were 10.46±1.15, 3.89±1.21 and 2.78±1.13 μM, respectively, for OATP-1B1 transporter. Vandetanib, canertinib and erlotinib did not exhibit any inhibitory potency toward OATP-1B1 transporter protein. Only vandetanib expressed inhibitory potential toward OATP-1B3 transporter protein out of the five selected TKIs. IC 50 values for rifampicin and vandetanib for OATP-1B3 transporter inhibition were 3.67±1.20 and 18.13±1.21 μM, respectively. No significant inhibition in the presence of increasing concentrations of pazopanib, nilotinib, canertinib and erlotinib were observed for OATP-1B3 transporter. Conclusions: Because selected TKIs are inhibitors of OATP-1B1 and -1B3 expressed in hepatic tissue, these compounds can be regarded as molecular targets for transporter-mediated DDIs. These findings provide the basis for further preclinical and clinical studies investigating the transporter-based DDI potential of TKIs.

Background: The aim of this study was to investigate the effect of silymarin pretreatment on domperidone oral bioavailability in humans. Methods: The rats were pretreated with silymarin for 7 days. The transport of domperidone across the rat intestine (duodenum, jejunum, ileum, and colon) was studied by using in vitro everted and non-everted sac methods. Samples were collected at preset time points and replaced with buffer. The drug content in the samples was estimated. The first part of the study included oral administration of 10 mg domperidone tablet alone, and blood was sampled from the antecubital vein. The second part of the study was conducted after a washout period of 2 weeks. Five hundred milligrams of silymarin was administered twice daily for 6 days. On day 7, one tablet each of 10 mg domperidone and 500 mg silymarin were administered concomitantly. Results: In the everted sac and non-everted sac study with silymarin pretreatment, domperidone transport increased from the duodenum, jejunum, ileum, and colon. The silymarin pretreatment increased the bioavailability of domperidone. There was a statistically significant difference in the pharmacokinetic parameters C max , T12${T_{{\textstyle{1 \over 2}}}}$, AUC 0–∞ , and AUC 0 – 24 . Conclusions: The significant difference in absorption of domperidone on pretreatment with silymarin is due to the inhibition of P-glycoprotein and CYP3A. Silymarin, which inhibits CYP3A4, should be contraindicated for domperidone.

Background: As the use of herbal supplements continues to rise throughout the world, the potential for drug-herbal interactions also increases. For chemotherapeutic prodrugs, this interaction could prevent the metabolic conversion of the prodrug to its active metabolite(s), thereby potentially resulting in subtherapeutic systemic exposure of the drug and reduced efficacy of the therapy. Methods: In this study, in vitro metabolism with human liver microsomes is used to measure the impact of ten commonly used herbal supplements on the biotransformation of the chemotherapeutic prodrugs tamoxifen (TAM) and irinotecan (IR). Results: Four of the herbals tested, echinacea, ginseng, lemon balm, and skullcap, were found to be strong inhibitors of the CYP450 enzymatic bioactivation pathways of TAM with IC50 values as percent of a single dose ranging from 0.019% to 0.34%. Two of the herbals, skullcap and lemon balm, were found to inhibit the carboxyesterase pathway of IR with values of 0.21 and 0.25, respectively. Conclusions: Our data suggests that based on the measured IC50 values that skullcap and lemon balm could have potential negative clinical impact on the bioactivation of TAM but not likely with IR.