Potential for layered double hydroxides-based, innovative drug delivery systems.

Layered Double Hydroxides (LDHs)-based drug delivery systems have, for many years, shown great promises for the delivery of chemical therapeutics and bioactive molecules to mammalian cells in vitro and in vivo. This system offers high efficiency and drug loading density, as well as excellent protection of loaded molecules from undesired degradation. Toxicological studies have also found LDHs to be biocompatible compared with other widely used nanoparticles, such as iron oxide, silica, and single-walled carbon nanotubes. A plethora of bio-molecules have been reported to either attach to the surface of or intercalate into LDH materials through co-precipitation or anion-exchange reaction, including amino acid and peptides, ATPs, vitamins, and even polysaccharides. Recently, LDHs have been used for gene delivery of small molecular nucleic acids, such as antisense, oligonucleotides, PCR fragments, siRNA molecules or sheared genomic DNA. These nano-medicines have been applied to target cells or organs in gene therapeutic approaches. This review summarizes current progress of the development of LDHs nanoparticle drug carriers for nucleotides, anti-inflammatory, anti-cancer drugs and recent LDH application in medical research. Ground breaking studies will be highlighted and an outlook of the possible future progress proposed. It is hoped that the layered inorganic material will open up new frontier of research, leading to new nano-drugs in clinical applications.

Regulation of human pregnane X receptor and its target gene cytochrome P450 3A4 by Chinese herbal compounds and a molecular docking study.

The pregnane X receptor (PXR) plays a critical role in the regulation of human cytochrome P450 3A4 (CYP3A4) gene. In this study, we investigated the effect of an array of compounds isolated from Chinese herbal medicines on the activity of PXR using a luciferase reporter gene assay in transiently transfected HepG2 and Huh7 cells and on the expression of PXR and CYP3A4 in LS174T cells. Furthermore, molecular docking was performed to investigate the binding modes of herbal compounds with PXR. Praeruptorin A and C, salvianolic acid B, sodium danshensu, protocatechuic aldehyde, cryptotanshinone, emodin, morin, and tanshinone IIA significantly transactivated the CYP3A4 reporter gene construct in either HepG2 or Huh7 cells. The PXR mRNA expression in LS174T cells was significantly induced by physcion, protocatechuic aldehyde, salvianolic acid B, and sodium danshensu. However, epifriedelanol, morin, praeruptorin D, mulberroside A, tanshinone I, and tanshinone IIA significantly down-regulated the expression of PXR mRNA in LS174T cells. All the herbal compounds tested can be readily docked into the ligand-binding cavity of PXR mainly through hydrogen bond and aromatic interactions with Ser247, Gln285, His407, and Arg401. These findings suggest that herbal medicines can significantly regulate PXR and CYP3A4 and this has important implication in herb-drug interactions.

Herbal interactions with anticancer drugs: mechanistic and clinical considerations.

A large number of herbal remedies (e.g. garlic, mistletoe, Essiac, Lingzhi, and astragalus) are used by cancer patients for treating the cancer and/or reducing the toxicities of chemotherapeutic drugs. Some herbal medicines have shown potentially beneficial effects on cancer progression and may ameliorate chemotherapy-induced toxicities. However, there is no or weak scientific basis for the clinical use of these herbal medicines in cancer management and almost none of these plant medicines have been tested in rigorous clinical trials. There are increased reports on the interaction of herbal medicines and anticancer drugs that is becoming a safety concern. For example, a clinical study in cancer patients reported that treatment of St John's wort at 900 mg/day orally for 18 days decreased the plasma levels of the active metabolite of irinotecan, SN-38, by 42%. In healthy subjects, 2 weeks of treatment with St John's wort at 900 mg/day significantly decreased the systemic exposure of imatinib by 32%. In women with advanced breast cancer, coadministration of garlic supplement reduced the clearance of docetaxol by 23.1-35.1%, although the difference did not achieve statistical significance. Most anticancer drugs undergo Phase I and/or II metabolism and are substrates of P-glycoprotein, breast cancer resistance protein, multidrug resistance associated proteins, and/or other transporters. Induction and inhibition of these enzymes and transporters is considered an important mechanism for herb-anticancer drug interactions. Further studies are warranted to investigate potentially harmful herbal interactions with anticancer drugs in patients.

[Target-specific cytotoxic activity of recombinant fusion toxin C-CPE-ETA' against CLDN-3,4-overexpressing ovarian cancer cells].

OBJECTIVE: The aim of this study was to explore the possibility of creating a toxin, C-CPE-ETA', by fusing C-terminal high affinity binding domain of CPE (C-CPE) with a truncated form of Pseudomonas aeruginosa exotoxin A (ETA') and to examine whether C-CPE-ETA' could specifically target CLDN-3, 4 molecule and the targeted toxin was cytotoxic against CLDN-3,4-overexpressing ovarian cancer. METHODS: CLDN-3 and CLDN-4 expressions were analyzed at the mRNA level in three ovarian cancer cell lines and epithelial ovarian cancer tissues from 20 patients. After transforming an expression plasmid of C-CPE-ETA' into E. coli BL21 (DE3) plysS strain, the recombinant protein was purified using His-Bind resin chromatography column and analyzed by Western blot and Coomassie blue staining. The specific binding, proapoptotic and cytolytic activities were evaluated by flow cytometry, fluorescence microscopy with the JC-1 probe and MTT assay in CLDN-3,4-overexpressing ovarian cancer cells. RESULTS: Quantitive RT-PCR results showed there existed high levels of CLDN-3 and CLDN-4 in ovarian cancer cells, CAOV3, OVCAR3 and SKOV3. Moreover, high expressions of CLDN-3 and CLDN-4 were observed in 90.0% (18/20) and 60.0% (12/20) of ovarian cancer tissues, with an expression level 10-fold higher than that in the normal ovarian tissue. A 58 000 recombinant protein C-CPE-ETA' was demonstrated by Western blot and Coomassie blue staining. Purified and recombinant C-CPE-ETA' was bound with high affinity to CLDN-3,4-overexpressing ovarian cancer cells, CAOV3, OVCAR3 and SKOV3 cells. C-CPE-ETA' was strongly proapoptotic and cytotoxic towards the CLDN-3,4-overexpressing ovarian cancer cells. The concentration of IC(50) was 7.364 ng/ml for CAOV3 cells, 8.110 ng/ml for OVCAR3 cells and 22.340 ng/ml for SKOV3 cells, respectively. However, control CLDN-3,4-deficient cell line HUVEC was not susceptible to the recombinant C-CPE-ETA' at a concentration up to 10 µg/ml. CONCLUSIONS: The C-CPE-ETA' protein exhibits remarkably specific cytotoxicity for CLDN-3,4-overexpressing ovarian cancer cells. Its therapeutic potential warrants further development for ovarian cancer molecular targeted therapy.

Substrate specificity, regulation, and polymorphism of human cytochrome P450 2B6.

CYP2B6 is mainly expressed in the liver that has been thought historically to play an insignificant role in human drug metabolism. However, increased interest in this enzyme has been stimulated by the discovery of polymorphic and ethnic differences in CYP2B6 expression, identification of additional substrates for CYP2B6, and evidence for co-regulation with CYP3A4. This paper updates our knowledge about the structure, function, regulation and polymorphism of CYP2B6. CYP2B6 can metabolise approximately 8% of clinically used drugs (n > 60), including cyclophosphamide, ifosfamide, tamoxifen, ketamine, artemisinin, nevirapine, efavirenz, bupropion, sibutramine, and propofol. CYP2B6 is one of the CYP enzymes that bioactivate several procarcinogens and toxicants. This enzyme also metabolizes arachidonic acid, lauric acid, 17beta-estradiol, estrone, ethinylestradiol, and testosterone. Typical substrates of CYP2B6 are non-planar molecules, neutral or weakly basic, highly lipophilic with one or two hydrogen-bond acceptors. The crystal structure of CYP2B6 has not been resolved, while several pharmacophore and homology models of human CYP2B6 have been reported. Human CYP2B6 is closely regulated by constitutive androstane receptor (CAR/NR1I3) which can activate CYP2B6 expression upon ligand binding. Pregnane X receptor and glucocorticoid receptor also play a role in the regulation of CYP2B6. Induction of CYP2B6 may partially explain some clinical drug interactions observed. For example, coadministered carbamazepine decreases the systemic exposure of bupropion. There is a wide interindividual variability in the expression and activity of CYP2B6. Such a large variability is probably due to effects of genetic polymorphisms and exposure to drugs that are inducers or inhibitors of CYP2B6. To date, at least 28 allelic variants and some subvariants of CYP2B6 (*1B through *29) have been described and some of them have been shown to have important functional impact on drug clearance and drug response. For example, the efavirenz plasma levels in African-American subjects with the CYP2B6 homozygous 516T/T genotype are approximately 3-fold higher than individuals carrying the homozygous G/G genotype. The CYP2B6 516T/T genotype is associated with 1.7-fold greater plasma levels of nevirapine in HIV-infected patients. Smokers with the 1459C>T (R487C) variant of CYP2B6 may be more vulnerable to abstinence symptoms and relapse following treatment with bupropion as a smoking cessation agent. Further studies in the structure, function, regulation and polymorphism of CYP2B6 are warranted.

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.

New insights into the structural features and functional relevance of human cytochrome P450 2C9. Part II.

Part I of this article published in the previous issue of Current Drug Metabolism discussed the substrate specificity, inhibitor selectivity and structure-activity relationship (SAR) of human CYP2C9. The features of CYP2C9 pharmacophore and SAR models have been elaborated. Part II of this article will address the homology models of CYP2C9, data from site-directed mutagenesis studies, and crystal structural features of CYP2C9. The heteroactivation of CYP2C9 and its interactions with other CYPs will also be discussed. A number of ligand-based and homology models of CYP2C9 have been reported and this has provided insights into the binding of ligands to the active site of CYP2C9. Site-directed mutagenesis studies have revealed that a number of residues (e.g. R97, F110, F114, R132, R144, D293, F476 and A477) play an important role in ligand binding and determination of substrate specificity. The resolved crystal structures of CYP2C9 have confirmed the importance of these residues in substrate recognition and ligand orientation. Currently, there are three X-ray structures of the human CYP2C9 in Protein Database (PDB): one ligand-free protein (1OG2), and two in complex with S-warfarin (1OG5) or flurbiprofen (1R9O). The published structures of 1OG2 and 1OG5 differ in comparison with 1R9O in residues 30-53 of N-termini, residues 97-121 of B/C-loops, and residues 196-233 of helix F and F/G-loops. CYP2C9 is a two-domain protein with typical fold characteristics of the CYPs. The B-C loop forms part of the active site and contributes to substrate specificity. In the structures of CYP2C9 without ligand bound or with bound S-warfarin, residues 101-106 in the B-C loop form helix B'. In addition, residues 212-222 in the F-G loop form helices F' and G', which was not observed in rabbit CYP2C5 and bacterial CYPs. In the 1OG2 and 1OG5 structures, the heme is stabilized by hydrogen bonds between the propionates and the side chains of W120, R124, H368 and R433. In addition, R97 forms hydrogen bonds to the propionates as well as the carbonyl oxygen atoms of V113 and P367. CYP2C9 is activated by dapsone and its analogues and R-lansoprazole in a stereo-specific and substrate-dependent manner, probably through binding to the active site and inducing positive cooperativity. Further studies are needed to investigate the molecular determinants for ligand-CYP2C9 interactions.

New insights into the structural features and functional relevance of human cytochrome P450 2C9. Part I.

CYP2C9 is one of the most abundant CYP enzymes in the human liver ( approximately 20% of hepatic total CYP content). CYP2C9 metabolizes approximately 20% clinical drugs (>120 drugs), including a number of drugs with narrow therapeutic ranges. Some natural compounds are also metabolized, probably leading to the formation of toxic metabolites. CYP2C9 also plays a role in the metabolism of several endogenous compounds such as steroids, melatonin, retinoids and arachidonic acid. Typical substrates of CYP2C9 such as celecoxib, ibuprofen, flurbiprofen, and diclofenac are relatively small, lipophilic and contain acidic groupings with pK(a) values in the range 3.8-8.1 which will be ionized at physiological pH. The carboxylate groups of tienilic acid and diclofenac have been shown to be responsible for substrate preference and orientation in the active site of CYP2C9. Therefore, a typical CYP2C9 substrate should contain an anionic site and a hydrophobic site. However, neutral or positively charged compounds may also be substrates of CYP2C9. CYP2C9 is subject to inhibition by a number of drugs and other compounds and this may provide an explanation for some clinical drug-drug interactions. With regard to prodrugs that need CYP2C9 for activation, inhibition of CYP2C9 may cause a decrease in the amount of the active metabolite, leading to therapeutic failure. Pharmacophore models have revealed that hydrogen bonding, ion-pair interactions, and probably hydrophobic interactions play a major role in determining the substrate specificity and inhibitor selectivity of CYP2C9. A number of structure-activity relationship studies have identified the structural determinants of compounds for their binding affinity to CYP2C9 and inhibitory potency for CYP2C9. Given the critical role of CYP2C9 in drug metabolism and the presence of polymorphisms, it is important to identify drug candidates as potential substrates and/or inhibitors of CYP2C9 in drug development and drugs with minimal interactions with this enzyme should be chosen for further development. Further studies are warranted to explore the molecular determinants for ligand-CYP2C9 binding and the structure-activity relationships.