Small interfering RNA-mediated silencing of cytochrome P450 3A4 gene

A novel mathematical model describing adaptive cellular drug metabolism and toxicity in the chemoimmune system

Cells cope with the threat of xenobiotic stress by activating a complex molecular network that recognizes and eliminates chemically diverse toxic compounds. This "chemoimmune system" consists of cellular Phase I and Phase II metabolic enzymes, Phase 0 and Phase III ATP Binding Cassette (ABC) membrane transporters, and nuclear receptors regulating these components. In order to provide a systems biology characterization of the chemoimmune network, we designed a reaction kinetic model based on differential equations describing Phase 0-III participants and regulatory elements, and characterized cellular fitness to evaluate toxicity. In spite of the simplifications, the model recapitulates changes associated with acquired drug resistance and allows toxicity predictions under variable protein expression and xenobiotic exposure conditions. Our simulations suggest that multidrug ABC transporters at Phase 0 significantly facilitate the defense function of successive network members by lowering intracellular drug concentrations. The model was extended with a novel toxicity framework which opened the possibility of performing in silico cytotoxicity assays. The alterations of the in silico cytotoxicity curves show good agreement with in vitro cell killing experiments. The behavior of the simplified kinetic model suggests that it can serve as a basis for more complex models to efficiently predict xenobiotic and drug metabolism for human medical applications.

Three new shRNA expression vectors targeting the CYP3A4 coding sequence to inhibit its expression

RNA interference (RNAi) is useful for selective gene silencing. Cytochrome P450 3A4 (CYP3A4), which metabolizes approximately 50% of drugs in clinical use, plays an important role in drug metabolism. In this study, we aimed to develop a short hairpin RNA (shRNA) to modulate CYP3A4 expression. Three new shRNAs (S1, S2 and S3) were designed to target the coding sequence (CDS) of CYP3A4, cloned into a shRNA expression vector, and tested in different cells. The mixture of three shRNAs produced optimal reduction (55%) in CYP3A4 CDS-luciferase activity in both CHL and HEK293 cells. Endogenous CYP3A4 expression in HepG2 cells was decreased about 50% at both mRNA and protein level after transfection of the mixture of three shRNAs. In contrast, CYP3A5 gene expression was not altered by the shRNAs, supporting the selectivity of CYP3A4 shRNAs. In addition, HepG2 cells transfected with CYP3A4 shRNAs were less sensitive to Ginkgolic acids, whose toxic metabolites are produced by CYP3A4. These results demonstrate that vector-based shRNAs could modulate CYP3A4 expression in cells through their actions on CYP3A4 CDS, and CYP3A4 shRNAs may be utilized to define the role of CYP3A4 in drug metabolism and toxicity.

RNA Interference Protects Against 5-Lipoxygenase-Induced Cocarcinogen, Benzidine, Oxidation and Cytotoxicity in Human Tracheobronchial Epithelial Cells

Lipoxygenase (LOX)-catalyzed cooxidation of the human carcinogen benzidine (BZD) has been shown in in vitro enzyme systems. This study aimed to determine whether BZD could be activated by arachidonate 5-lipoxygenase (ALOX5) in the human tracheobronchial epithelial cells (HBECs) using RNA interference strategy and a 5-LOX-specific inhibitor, AA861. We show that the soybean LOX catalyzed the cooxidation of BZD, generating BZD diimine. Benzidine induced expression of ALOX5 messenger RNA and 5-LOX protein in HBECs, and significantly decreased cell proliferation, but enhanced DNA damage and apoptosis in HBECs which were significantly inhibited by lentiviral-mediated small hairpin RNA-knockdown of ALOX5 and by AA861. Thus, BZD could upregulate the expression of ALOX5 in HBECs, while inhibition of the protein or gene expression or enzyme activity could prevent BZD-induced cytotoxicity and DNA damage in HBECs, which might be caused by the 5-LOX-catalyzed oxidative activation of BZD.

The role of molecular biology in the biomonitoring of human exposure to chemicals

Exposure to different substances in an occupational environment is of utmost concern to global agencies such as the World Health Organization and the International Labour Organization. Interest in improving work health conditions, particularly of those employees exposed to noxious chemicals, has increased considerably and has stimulated the search for new, more specific and selective tests. Recently, the field of molecular biology has been indicated as an alternative technique for monitoring personnel while evaluating work-related pathologies. Originally, occupational exposure to environmental toxicants was assessed using biochemical techniques to determine the presence of higher concentrations of toxic compounds in blood, urine, or other fluids or tissues; results were used to evaluate potential health risk. However, this approach only estimates the presence of a noxious chemical and its effects, but does not prevent or diminish the risk. Molecular biology methods have become very useful in occupational medicine to provide more accurate and opportune diagnostics. In this review, we discuss the role of the following common techniques: (1) Use of cell cultures; (2) evaluation of gene expression; (3) the “omic” sciences (genomics, transcriptomics, proteomics and metabolomics) and (4) bioinformatics. We suggest that molecular biology has many applications in occupational health where the data can be applied to general environmental conditions.

MicroRNAs regulate CYP3A4 expression via direct and indirect targeting

CYP3A4 metabolizes many drugs on the market. Although transcriptional regulation of CYP3A4 is known to be tightly controlled by some nuclear receptors (NR) including vitamin D receptor (VDR/NR1I1), posttranscriptional regulation of CYP3A4 remains elusive. In this study, we show that noncoding microRNAs (miRNAs) may control posttranscriptional and transcriptional regulation of CYP3A4 by directly targeting the 3'-untranslated region (3'UTR) of CYP3A4 and indirectly targeting the 3'UTR of VDR, respectively. Luciferase reporter assays showed that CYP3A4 3'UTR-luciferase activity was significantly decreased in human embryonic kidney 293 cells transfected with plasmid that expressed microRNA-27b (miR-27b) or mouse microRNA-298 (mmu-miR-298), whereas the activity was unchanged in cells transfected with plasmid that expressed microRNA-122a or microRNA-328. Disruption of the corresponding miRNA response element (MRE) within CYP3A4 3'UTR led to a 2- to 3-fold increase in luciferase activity. Immunoblot analyses indicated that CYP3A4 protein was down-regulated over 30% by miR-27b and mmu-miR-298 in LS-180 and PANC1 cells. The decrease in CYP3A4 protein expression was associated with significantly decreased CYP3A4 mRNA levels, as determined by quantitative real-time PCR (qPCR) analyses. Likewise, interactions of miR-27b or mmu-miR-298 with VDR 3'UTR were supported by luciferase reporter assays. The mmu-miR-298 MRE site is well conserved within the 3'UTR of mouse, rat, and human VDR. Down-regulation of VDR by the two miRNAs was supported by immunoblot and qPCR analyses. Furthermore, overexpression of miR-27b or mmu-miR-298 in PANC1 cells led to a lower sensitivity to cyclophosphamide. Together, these findings suggest that CYP3A4 gene expression may be regulated by miRNAs at both the transcriptional and posttranscriptional level.

Cytochrome P450 reaction-phenotyping: an industrial perspective

It is now widely accepted that the fraction of the dose metabolized by a given drug-metabolizing enzyme is one of the major factors governing the magnitude of a drug interaction and the impact of a polymorphism on (total) drug clearance. Therefore, most pharmaceutical companies determine the enzymes involved in the metabolism of a new chemical entity (NCE) in vitro, in conjunction with human data on absorption, distribution, metabolism and excretion. This so called reaction-phenotyping, or isozyme-mapping, usually involves the use of multiple reagents (e.g., recombinant proteins, liver subcellular fractions, enzyme-selective chemical inhibitors and antibodies). For the human CYPs, reagents are readily available and in vitro reaction-phenotyping data are now routinely included in most regulatory documents. Ideally, the various metabolites have been definitively identified, incubation conditions have afforded robust kinetic analyses, and well characterized (high quality) reagents and human tissues have been employed. It is also important that the various in vitro data are consistent (e.g., scaled turnover with recombinant CYP proteins, CYP inhibition and correlation data with human liver microsomes) and enable an integrated in vitro CYP reaction-phenotype. Results of the in vitro CYP reaction-phenotyping are integrated with clinical data (e.g., human radiolabel and drug interaction studies) and a complete package is then submitted for regulatory review. If the NCE receives market approval, information on key routes of clearance and their associated potential for drug-drug interactions are included in the product label. The present review focuses on in vitro CYP reaction-phenotyping and the integration of data. Relatively simple strategies enabling the design and prioritization of follow up clinical studies are also discussed.

Novel tissue engineered tubular heart tissue for in vitro pharmaceutical toxicity testing

A growing problem in cardiac drug toxicity has been blamed on the lack of adequate testing prior to authorization for prescription use. This study offers an effective alternative to the current method of in vivo pharmaceutical testing, which is time and cost prohibitive. We have accomplished this by developing the novel three-dimensional heart tube model. At the "heart" of our model lies our patented collagen scaffold that enables the cardiac myocytes to display an in vivo-like architecture. The cardiac myocytes were cocultured with the collagen tube for a period of 5 weeks, resulting in the heart tubes. Our heart tubes were treated with specific drugs (nifedipine, isoproterenol, and lidocaine) at varying concentrations. The percent of apoptotic cells was calculated based on observing the number of cells that labeled positive for caspase-3 via confocal microscopy. All three drugs exhibited negative effects at high concentrations in that the number of living cells decreased. Lidocaine showed an increase in apoptosis at concentrations of 75 microM and above. This may indicate that certain drugs have a minimum concentration level that must be reached before the cells experience apoptosis from the toxic levels.