Cytochrome P450s in the development of target-based anticancer drugs

Genetic variants, haplotype determination, and function of novel alleles of CYP2B6 in a Han Chinese population

Amino acid variants in protein may result in deleterious effects on enzymatic activity. In this study we investigate the DNA variants on activity of CYP2B6 gene in a Chinese Han population for potential use in precision medicine. All exons in CYP2B6 gene from 1483 Chinese Han adults (Zhejiang province) were sequenced using Sanger sequencing. The effects of nonsynonymous variants on recombinant protein catalytic activity were investigated in vitro with Sf12 system. The haplotype of novel nonsynonymous variants with other single nucleotide variants in the same allele was determined using Nanopore sequencing. Of 38 alleles listed on the Pharmacogene Variation Consortium, we detected 7 previously reported alleles and 18 novel variants, of which 11 nonsynonymous variants showed lower catalytic activity (0.00-0.60) on bupropion compared to CYP2B6*1. Further, these 11 novel star-alleles (CYP2B6*39-49) were assigned by the Pharmacogene Variation Consortium, which may be valuable for pharmacogenetic research and personalized medicine.

Differentiation of umbilical cord mesenchymal stem cells into hepatocytes with CYP450 metabolic enzyme activity induced by a liver injury microenvironment

The aim of this study was to observe the effect of a simulated liver tissue injury microenvironment on the directed differentiation of umbilical cord mesenchymal stem cells into hepatocytes with CYP450 metabolic activity in vitro, and to explore the mechanisms underlying this directed differentiation. Normal and damaged liver tissue homogenate supernatants (LHS and CCl₄-LHS, respectively) were used as induction fluids. After induction for different durations, Western blot and RT-PCR were used to measure the protein and gene expression of the hepatocellular proteins AFP, CK18, ALB, and the CYP450 family. Simultaneously, the metabolic activity of CYP450 in hepatocytes was determined. Compared with the LHS and CCl₄-LHS controls, the LHS and CCl₄-LHS induction groups showed a significantly elevated protein and gene expression of AFP, CK18, ALB, CYP1A1/2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 (P < 0.05). The metabolic activity of CYP450 in hepatocytes was increased (P < 0.05). In addition, compared with the LHS group, the CCl₄-LHS group induced cell differentiation more rapidly and with a higher efficiency. The results suggested that a liver injury microenvironment is conducive for the directed differentiation of umbilical cord mesenchymal stem cells into hepatocytes with metabolic enzyme activity.

An Evaluation of the Novel Biological Properties of Diterpenes Isolated from Plectranthus ornatus Codd. In Vitro and In Silico

Plectranthus ornatus Codd, the genus Plectranthus of the Lamiaceae family, has been used as traditional medicine in Africa, India and Australia. Pharmacological studies show the use of this plant to treat digestive problems. In turn, leaves were used for their antibiotic properties in some regions of Brazil to treat skin infections. The present study examines the anti-inflammatory, antioxidant and cytotoxic effects of the halimane and labdane diterpenes (11R*,13E)-11-acetoxyhalima-5,13-dien-15-oic acid (HAL) and 1α,6β-diacetoxy-8α,13R*-epoxy-14-labden-11-one (PLEC) and the forskolin-like 1:1 mixture of 1,6-di-O-acetylforskolin and 1,6-di-O-acetyl-9-deoxyforskolin (MRC) isolated from P. ornatus on lung (A549) and leukemia (CCRF-CEM) cancer cell lines, and on normal human retinal pigment epithelial (ARPE-19) cell line in vitro. Additionally, molecular docking and computational approaches were used. ADMET properties were analysed through SwissADME and proTox-II—Prediction. The results indicate that all tested compounds significantly reduced the viability of the cancer cells and demonstrated no cytotoxic effects against the non-neoplastic cell line. The apoptosis indicators showed increased ROS levels for both the tested A549 and CCRF-CEM cancer cell lines after treatment. Furthermore, computational studies found HAL to exhibit moderate antioxidant activity. In addition, selected compounds changed mitochondrial membrane potential (MMP), and increased DNA damage and mitochondrial copy number for the CCRF-CEM cancer cell line; they also demonstrated anti-inflammatory effects on the ARPE-19 normal cell line upon lipopolysaccharide (LPS) treatment, which was associated with the modulation of IL-6, IL-8, TNF-α and GM-CSF genes expression. Docking studies gave indication about the lowest binding energy for 1,6-di-O-acetylforskolin docked into IL-6, TNF-α and GM-CSF, and 1,6-di-O-acetyl-9-deoxyforskolin docked into IL-8. The ADMET studies showed drug-likeness properties for the studied compounds. Thus, halimane and labdane diterpenes isolated from P. ornatus appear to offer biological potential; however, further research is necessary to understand their interactions and beneficial properties.

Distribution of alleles, genotypes and haplotypes of the CYP2B6 (rs3745274; rs2279343) and CYP3A4 (rs2740574) genes in the Malian population: Implication for pharmacogenetics

Cytochrome P450 enzymes play a central role in the phase I biotransformation process of a wide range of compounds, including xenobiotics, drugs, hormones and vitamins. It is noteworthy that these enzymes are highly polymorphic and, depending on the genetic makeup, an individual may have impaired enzymatic activity. Therefore, the identification of genetic variants in these genes could facilitate the implementation of pharmacogenetic studies and genetic predisposition to multifactorial diseases. We have established the frequencies of CYP2B6 (rs3745274; rs2279343) and CYP3A4 (rs2740574) alleles and genotypes in 209 healthy Malian subjects using TaqMan drug metabolism genotyping assays for allelic discrimination. Allele frequencies were 37% for CYP2B6 rs3745274; 38% for CYP2B6 rs2279343; and 75% for CYP3A4 rs2740574 respectively. Overall, the frequencies observed in Mali are statistically comparable to those reported across Africa except North Africa. The major haplotypes in CYP2B6 rs3745274 and CYP2B6 rs2279343 were represented by GA (60.24%) followed by TG (35.36%). We noted a strong linkage disequilibrium between CYP2B6 rs3745274 and CYP2B6 rs2279343 with D' = 0.91 and r2 = 0.9. The frequencies of the genotypic combinations were 43.5% (GT/AG), 37.3% (GG/AA) and 11.5% (TT/GG) in the combination of CYP2B6-rs3745274 and CYP2B6-rs2279343; 26.8% (GT/CC), 25.4%, (GT/CT), 17.2% and GG/CT in the combination CYP2B6-rs3745274-CYP3A4-rs2740574; 26.8% (AG/CC), 23.9% (AA/CC), 19.1% (AG/CT), and 11% (AA/CT) in the combination CYP2B6-rs2279343-CYP3A4-rs2740574, respectively. The most common triple genotype was GT/AG/CC with 24.9%, followed by GG/AA/CC with 23.9%, GT/AG/CT with 16.7%, and GG/AA/CT with 10%. Our results provide new insights into the distribution of these pharmacogenetically relevant genes in the Malian population. Moreover, these data will be useful for studies of individual genetic variability to drugs and genetic predisposition to diseases.

Drug-Metabolizing Cytochrome P450 Enzymes Have Multifarious Influences on Treatment Outcomes

Drug metabolism is a critical process for the removal of unwanted substances from the body. In humans, approximately 80% of oxidative metabolism and almost 50% of the overall elimination of commonly used drugs can be attributed to one or more of various cytochrome P450 (CYP) enzymes from CYP families 1-3. In addition to the basic metabolic effects for elimination, CYP enzymes in vivo are capable of affecting the treatment outcomes in many cases. Drug-metabolizing CYP enzymes are mainly expressed in the liver and intestine, the two principal drug oxidation and elimination organs, where they can significantly influence the drug action, safety, and bioavailability by mediating phase I metabolism and first-pass metabolism. Furthermore, CYP-mediated local drug metabolism in the sites of action may also have the potential to impact drug response, according to the literature in recent years. This article underlines the ability of CYP enzymes to influence treatment outcomes by discussing CYP-mediated diversified drug metabolism in primary metabolic sites (liver and intestine) and typical action sites (brain and tumors) according to their expression levels and metabolic activity. Moreover, intrinsic and extrinsic factors of personal differential CYP phenotypes that contribute to interindividual variation of treatment outcomes are also reviewed to introduce the multifarious pivotal role of CYP-mediated metabolism and clearance in drug therapy.

Riboflavin Is Directly Involved in N-Dealkylation Catalyzed by Bacterial Cytochrome P450 Monooxygenases

Like a vast number of enzymes in nature, bacterial cytochrome P450 monooxygenases require an activated form of flavin as a cofactor for catalytic activity. Riboflavin is the precursor of FAD and FMN that serves as indispensable cofactor for flavoenzymes. In contrast to previous notions, herein we describe the identification of an electron-transfer process that is directly mediated by riboflavin for N-dealkylation by bacterial P450 monooxygenases. The electron relay from NADPH to riboflavin and then via activated oxygen to heme was proposed based on a combination of X-ray crystallography, molecular modeling and molecular dynamics simulation, site-directed mutagenesis and biochemical analysis of representative bacterial P450 monooxygenases. This study provides new insights into the electron transfer mechanism in bacterial P450 enzyme catalysis and likely in yeasts, fungi, plants and mammals.

A dual functional probe for assessing human CYP450 3A5 and 3A enzymes bioactivities

Aim: CYP3A5 plays a vital role in the drug metabolism, it displays varied expression levels among individuals and is easily influenced by genetic polymorphisms and some diseases. Methodology & results: A dual function probe isobutyryl-11-keto-β-boswellic acid (IKBA) was developed; it possessed a high selectivity toward CYP3A5 and CYP3A enzymes for its two individual metabolites, respectively. The probe has the high accuracy and wide applicability in measuring the real activity of CYP3A5. Finally, IKBA was successfully used for the evaluation of the activity of CYP3A5 and CYP3A enzymes in various bio samples. Conclusion: IKBA could serve as a useful tool for exploring the physiology and pathology functions of CYP3A5 and give some useful guidance for the rational use of clinical drugs.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Ligand characterization of CYP4B1 isoforms modified for high-level expression in Escherichia coli and HepG2 cells

Human CYP4B1, a cytochrome P450 monooxygenase predominantly expressed in the lung, inefficiently metabolizes classical CYP4B1 substrates, such as the naturally occurring furan pro-toxin 4-ipomeanol (4-IPO). Highly active animal forms of the enzyme convert 4-IPO to reactive alkylating metabolite(s) that bind(s) to cellular macromolecules. By substitution of 13 amino acids, we restored the enzymatic activity of human CYP4B1 toward 4-IPO and this modified cDNA is potentially valuable as a suicide gene for adoptive T-cell therapies. In order to find novel pro-toxins, we tested numerous furan analogs in in vitro cell culture cytotoxicity assays by expressing the wild-type rabbit and variants of human CYP4B1 in human liver-derived HepG2 cells. To evaluate the CYP4B1 substrate specificities and furan analog catalysis, we optimized the N-terminal sequence of the CYP4B1 variants by modification/truncation and established their heterologous expression in Escherichia coli (yielding 70 and 800 nmol·l-1 of recombinant human and rabbit enzyme, respectively). Finally, spectral binding affinities and oxidative metabolism of the furan analogs by the purified recombinant CYP4B1 variants were analyzed: the naturally occurring perilla ketone was found to be the tightest binder to CYP4B1, but also the analog that was most extensively metabolized by oxidative processes to numerous non-reactive reaction products.

Overexpression of cytochrome P450 2A6 in adrenocortical carcinoma

BACKGROUND

Cytochrome P450-mediated metabolism of chemotherapeutic agents contributes to chemotherapy resistance in multiple malignancies. Adrenocortical carcinoma is known to have a poor response to adjuvant therapies; however, the mechanism remains unknown. Recent comprehensive genetic analyses of adrenocortical carcinomas demonstrated recurrent copy number gains in multiple cytochrome P450 genes prompting investigation into whether cytochrome P450 overexpression potentiates adrenocortical carcinoma chemoresistance.

METHODS

We determined the expression patterns of 6 cytochrome P450 genes (CYP2A6, CYP2A7, CYP2A13, CYP2B6, CYP2S1, and CYP4F2) predicted to be amplified in adrenocortical carcinoma (n = 29) relative to normal adrenal cortex (n = 10). Gene copy numbers were determined with the TaqMan copy number assay. Gene silencing was performed via small interfering RNA (siRNA) in the adrenocortical carcinoma cell line NCI-H295R and treated with mitotane and cisplatin.

RESULTS

Of the 6 cytochrome P450 genes tested, CYP2A6 was overexpressed with a 55-fold mean increase compared to normal adrenal samples (P < .05). Immunohistochemical analysis confirmed protein overexpression. Copy gains of CYP2A6 were found in 26% (7/27) of adrenocortical carcinoma specimens. Silencing of CYP2A6 in NCI-H295R cells resulted in decreased cell viability and increased chemosensitivity (P < .05).

CONCLUSION

Frequent upregulation in adrenocortical carcinomas and the reversal of chemoresistance in adrenocortical carcinoma cells via enforced silencing suggest a role for CYP2A6 in adrenocortical malignancy.

Association of CYP2B6 gene polymorphisms and anti-tuberculosis drug-induced hepatotoxicity in a Chinese population

OBJECTIVES

Antituberculosis drug-induced hepatotoxicity (ATDH) remains a common and severe challenge in tuberculosis (TB) chemotherapy. A growing number of studies have revealed that genetic polymorphisms affect an individual's susceptibility to ATDH. The aim of this study was to explore the role of cytochrome P450 family 2 subfamily B member 6 (CYP2B6) gene polymorphisms in the development of ATDH in Chinese TB patients.

METHODS

CYP2B6*6 genotypes were determined in TB patients with and without ATDH. Association between polymorphisms and risk of ATDH was estimated by multiple logistic regression analysis.

RESULTS

A total of 343 eligible TB patients (166 with ATDH; 177 without ATDH) were included in this study. Analysis of all subjects revealed no statistical differences in genotype distribution between the two groups. However, the CYP2B6 *6/*6 genotype was significantly associated with decreased risk of ATDH in the male subgroup (P=0.039, OR=0.097, 95% CI: 0.011-0.885). Furthermore, in male patients, the presence of the CYP2B6*6 allele was significantly higher in the non-ATDH group compared with the ATDH group (26.2% vs. 15.5%, P=0.020, OR=0.522, 95% CI: 0.301-0.903).

CONCLUSIONS

This study is the first to demonstrate an association between CYP2B6 polymorphisms and the risk of ATDH in the Chinese population. We have shown that males who have the CYP2B6 *6/*6 genotype may be less susceptible to the development of ATDH. Further studies are required to confirm this genetic association result.

Cheminformatics studies to analyze the therapeutic potential of phytochemicals from Rhazya stricta

Rhazya stricta is a unique medicinal plant source for many indole alkaloids, non-alkaloids, flavonoids, triterpenes and other unknown molecules with tremendous potential for therapeutic applications against many diseases. In the present article, we generated computational data on predictive properties and activity across two key therapeutic areas of cancer and obesity, and corresponding cheminformatics studies were carried out to examine druggable properties of these alkaloids. Computed physiochemical properties of the 78 indole alkaloids from R. stricta plant using industry-standard scientific molecular modeling software and their predictive anti-cancer activities from reliable web-source technologies indicate their plausible therapeutic applications. Their predictive ADME properties are further indicative of their drug-like-ness. We believe that the top-ranked molecules with anti-cancer activity are clearly amenable to chemical modifications for creating potent, safe and efficacious compounds with the feasibility of generating new chemical entities after pre-clinical and clinical studies.

Insights into CYP2B6-mediated drug-drug interactions

Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.

Co-expression of active human cytochrome P450 1A2 and cytochrome P450 reductase on the cell surface of Escherichia coli

Background

Human cytochrome P450 (CYP) enzymes mediate the first step in the breakdown of most drugs and are strongly involved in drug–drug interactions, drug clearance and activation of prodrugs. Their biocatalytic behavior is a key parameter during drug development which requires preparative synthesis of CYP related drug metabolites. However, recombinant expression of CYP enzymes is a challenging bottleneck for drug metabolite biosynthesis. Therefore, we developed a novel approach by displaying human cytochrome P450 1A2 (CYP1A2) and cytochrome P450 reductase (CPR) on the surface of Escherichia coli.

Results

To present human CYP1A2 and CPR on the surface, we employed autodisplay. Both enzymes were displayed on the surface which was demonstrated by protease and antibody accessibility tests. CPR activity was first confirmed with the protein substrate cytochrome c. Cells co-expressing CYP1A2 and CPR were capable of catalyzing the conversion of the known CYP1A2 substrates 7-ethoxyresorufin, phenacetin and the artificial substrate luciferin-MultiCYP, which would not have been possible without interaction of both enzymes. Biocatalytic activity was strongly influenced by the composition of the growth medium. Addition of 5-aminolevulinic acid was necessary to obtain a fully active whole cell biocatalyst and was superior to the addition of heme.

Conclusion

We demonstrated that CYP1A2 and CPR can be co-expressed catalytically active on the cell surface of E. coli. It is a promising step towards pharmaceutical applications such as the synthesis of drug metabolites.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0427-5) contains supplementary material, which is available to authorized users.

Cytochrome P450 3 A expression in pigs livers after 24-hour preservation in Biolasol solution depending on the type of transgenesis

BACKGROUND

An insufficient number of organs for transplantation shows the need for the development of new technologies. Xenotransplantation might be the answer.

OBJECTIVE

To determine if the type of transgenesis influences the level of CYP3A4, which takes an active part in xenobiotics metabolism in livers after 24-hour storage, depending on the kind of solution used for preservation.

MATERIALS AND METHODS

The experiment was carried out on 30 livers of Polish White Landrace divided into 5 groups depending on transgene type. The following human genes were transferred: α1,2-fucosyltransferase (groups I and II), α-galactosidase (III), combined α1,2-fucosyltransferase/α-galactosidase transgene (IV), and livers without modification (V). The livers were perfused and subsequently stored for 24 hours in Ringer's solution (group I) or Biolasol solution (II-V). Reperfusion/reflush was performed. CYP3A29 isomer concentration was analyzed in liver specimens collected twice: 30 minutes after perfusion and 30 minutes after reperfusion/reflush. Expression of mRNA CYP3A29 was marked using RT-PCR analysis and of protein CYP3A29 using Western blotting technique.

RESULTS

The most significant decrease in protein CYP3A29 expression after 24-hour preservation was observed in group I (55.88% decrease), while the least significant was observed in group IV (10.44% decrease). mRNA expression evaluation was similar: the most significant decrease was observed in group I (87.8% decrease) and the least significant in group III (4.6% decrease).

CONCLUSION

α1,2-Fcosyltransferase transgene seems to influence mRNA and protein CYP3A expression in case of liver grafting and preservation for transplantation. CYP3A expression was also influenced by the kind of preservation solution used.

Metabolism-related pharmacokinetic drug-drug interactions with tyrosine kinase inhibitors: current understanding, challenges and recommendations

Drug-drug interactions (DDIs) occur when a patient's response to the drug is modified by administration or co-exposure to another drug. The main cytochrome P450 (CYP) enzyme, CYP3A4, is implicated in the metabolism of almost all of the tyrosine kinase inhibitors (TKIs). Therefore, there is a substantial potential for interaction between TKIs and other drugs that modulate the activity of this metabolic pathway. Cancer patients are susceptible to DDIs as they receive many medications, either for supportive care or for treatment of toxicity. Differences in DDI outcomes are generally negligible because of the wide therapeutic window of common drugs. However for anticancer agents, serious clinical consequences may occur from small changes in drug metabolism and pharmacokinetics. Therefore, the objective of this review is to highlight the current understanding of DDIs among TKIs, with a focus on metabolism, as well as to identify challenges in the prediction of DDIs and provide recommendations.

Monooxygenase, peroxidase and peroxygenase properties and reaction mechanisms of cytochrome P450 enzymes

This review examines the monooxygenase, peroxidase and peroxygenase properties and reaction mechanisms of cytochrome P450 (CYP) enzymes in bacterial, archaeal and mammalian systems. CYP enzymes catalyze monooxygenation reactions by inserting one oxygen atom from O2 into an enormous number and variety of substrates. The catalytic versatility of CYP stems from its ability to functionalize unactivated carbon-hydrogen (C-H) bonds of substrates through monooxygenation. The oxidative prowess of CYP in catalyzing monooxygenation reactions is attributed primarily to a porphyrin π radical ferryl intermediate known as Compound I (CpdI) (Por•+FeIV=O), or its ferryl radical resonance form (FeIV-O•). CYP-mediated hydroxylations occur via a consensus H atom abstraction/oxygen rebound mechanism involving an initial abstraction by CpdI of a H atom from the substrate, generating a highly-reactive protonated Compound II (CpdII) intermediate (FeIV-OH) and a carbon-centered alkyl radical that rebounds onto the ferryl hydroxyl moiety to yield the hydroxylated substrate. CYP enzymes utilize hydroperoxides, peracids, perborate, percarbonate, periodate, chlorite, iodosobenzene and N-oxides as surrogate oxygen atom donors to oxygenate substrates via the shunt pathway in the absence of NAD(P)H/O2 and reduction-oxidation (redox) auxiliary proteins. It has been difficult to isolate the historically elusive CpdI intermediate in the native NAD(P)H/O2-supported monooxygenase pathway and to determine its precise electronic structure and kinetic and physicochemical properties because of its high reactivity, unstable nature (t½~2 ms) and short life cycle, prompting suggestions for participation in monooxygenation reactions of alternative CYP iron-oxygen intermediates such as the ferric-peroxo anion species (FeIII-OO-), ferric-hydroperoxo species (FeIII-OOH) and FeIII-(H2O2) complex.

Inhibiton of cytochrome P450 isoenzymes and P-gp activity by multiple extracts of Huang-Lian-Jie-Du decoction

ETHNOPHARMACOLOGICAL RELEVANCE

Huang-Lian-Jie-Du-Decotion (HLJDD), an important traditional Chinese medicine formula, has been used for various diseases in clinical practice, and thus has high potential to induce cytochrome P450 (CYP) isoenzymes/P-glycoprotein (P-gp) mediated herb-drug interactions (HDIs) with other co-administered drugs. The purpose of this study was to investigate the in vitro effects of multiple extracts including aqueous extracts, total flavonoids, iridoids, alkaloids from HLJDD on the activities of CYPs in rats (CYP1A2, CYP2C6, CYP2D2, CYP2E1 and CYP3A1) and P-gp, and then to predict potential interactions with co-administered drugs.

MATERIALS AND METHODS

The effects of the four extracts from HLJDD on the CYPs activity were evaluated in rat liver microsomes incubation system, and then determined by LC-MS/MS-based CYPs probe substrate assay. Caco-2 cell monolayer was used to investigate the effect of the four extracts on the efflux of Rhodamine 123 to evaluate their influences on P-gp activity.

RESULTS

The results show that total flavonoids and alkaloids exibited strong inhibition on rat CYP isoenzymes activities. Total flavonoids exhibited different inhibitory effects on CYPs activities with an order of CYP3A1>CYP2C6>CYP2E1>CYP1A2>CYP2D2, and the values of IC₅₀ were 4.24, 8.16, 17.56, 19.03, 29.51 μg/mL, respectively. Total alkaloids possessed similar inhibition on CYPs and could strongly inhibit the activity of CYP2D2 (IC₅₀=2.38 μg/mL), CYP3A1 (IC₅₀=2.61 μg/mL), CYP2E1 (IC₅₀=22.35 μg/mL), CYP1A2 (IC₅₀=23.2 μg/mL) and CYP2C6 (IC₅₀=43.09 μg/mL). Moderate degree of inhibition on CYPs activities was observed in aqueous and total iridoids extracts. Results from transport assay revealed that total flavonoids and alkaloids exhibited significant inhibitory effect on P-gp activity as evidenced by strong inhibition on the efflux of Rhodamine-123 with IC₅₀ of 104.6 and 82.6 μg/mL. But aqueous extract showed weak and iridoids had negligible effect on P-gp activity.

CONCLUSIONS

This study clearly demonstrated that total flavonoids and alkaloids from HLJDD can significantly inhibit the activities of CYPs and P-gp, which should be taken into consideration to predict any potential HDIs when HLJDD and its bioactive components are co-administered with other therapeutic drugs metabolized by CYPs or transported by P-gp.

Necrosis, and then stress induced necrosis-like cell death, but not apoptosis, should be the preferred cell death mode for chemotherapy: clearance of a few misconceptions

Cell death overarches carcinogenesis and is a center of cancer researches, especially therapy studies. There have been many nomenclatures on cell death, but only three cell death modes are genuine, i.e. apoptosis, necrosis and stress-induced cell death (SICD). Like apoptosis, SICD is programmed. Like necrosis, SICD is a pathological event and may trigger regeneration and scar formation. Therefore, SICD has subtypes of stress-induced apoptosis-like cell death (SIaLCD) and stress-induced necrosis-like cell death (SInLCD). Whereas apoptosis removes redundant but healthy cells, SICD removes useful but ill or damaged cells. Many studies on cell death involve cancer tissues that resemble parasites in the host patients, which is a complicated system as it involves immune clearance of the alien cancer cells by the host. Cancer resembles an evolutionarily lower-level organism having a weaker apoptosis potential and poorer DNA repair mechanisms. Hence, targeting apoptosis for cancer therapy, i.e. killing via SIaLCD, will be less efficacious and more toxic. On the other hand, necrosis of cancer cells releases cellular debris and components to stimulate immune function, thus counteracting therapy-caused immune suppression and making necrosis better than SIaLCD for chemo drug development.

Enzyme kinetic and molecular docking studies for the inhibitions of miltirone on major human cytochrome P450 isozymes

Previous studies have shown that major tanshinones isolated from Danshen (Salvia miltiorrhiza) inhibited human and rat CYP450 enzymes-mediated metabolism of model probe substrates, with potential in causing herb-drug interactions. Miltirone, another abietane type-diterpene quinone isolated from Danshen, has been reported for its anti-oxidative, anxiolytic and anti-cancer effects. The aim of this study was to study the effect of miltirone on the metabolism of model probe substrates of CYP1A2, 2C9, 2D6 and 3A4 in pooled human liver microsomes. Miltirone showed moderate inhibition on CYP1A2 (IC(50)=1.73 μM) and CYP2C9 (IC(50)=8.61 μM), and weak inhibition on CYP2D6 (IC(50)=30.20 μM) and CYP3A4 (IC(50)=33.88 μM). Enzyme kinetic studies showed that miltirone competitively inhibited CYP2C9 (K(i)=1.48 μM), and displayed mixed type inhibitions on CYP1A2, CYP2D6 and CYP3A4 with K(i) values of 3.17 μM, 24.25 μM and 35.09 μM, respectively. Molecular docking study further confirmed the ligand-binding conformations of miltirone in the active sites of these human CYP450 isoforms, and provided some information on structure-activity relationships for the CYPs inhibition by tanshinones. Taken together, CYPs inhibitions of miltirone were weaker than dihydrotanshinone, but stronger than cryptotanshinone, tanshinone I and tanshinone IIA.

Saccharomyces cerevisiae as a model system to study the response to anticancer agents

The development of new strategies for cancer therapeutics is indispensable for the improvement of standard protocols and the creation of other possibilities in cancer treatment. Yeast models have been employed to study numerous molecular aspects directly related to cancer development, as well as to determine the genetic contexts associated with anticancer drug sensitivity or resistance. The budding yeast Saccharomyces cerevisiae presents conserved cellular processes with high homology to humans, and it is a rapid, inexpensive and efficient compound screening tool. However, yeast models are still underused in cancer research and for screening of antineoplastic agents. Here, the employment of S. cerevisiae as a model system to anticancer research is discussed and exemplified. Focusing on the important determinants in genomic maintenance and cancer development, including DNA repair, cell cycle control and epigenetics, this review proposes the use of mutant yeast panels to mimic cancer phenotypes, screen and study tumor features and synthetic lethal interactions. Finally, the benefits and limitations of the yeast model are highlighted, as well as the strategies to overcome S. cerevisiae model limitations.

Towards personalized medicine with a three-dimensional micro-scale perfusion-based two-chamber tissue model system

A three-dimensional micro-scale perfusion-based two-chamber (3D-μPTC) tissue model system was developed to test the cytotoxicity of anticancer drugs in conjunction with liver metabolism. Liver cells with different cytochrome P450 (CYP) subtypes and glioblastoma multiforme (GBM) brain cancer cells were cultured in two separate chambers connected in tandem. Both chambers contained a 3D tissue engineering scaffold fabricated with biodegradable poly(lactic acid) (PLA) using a solvent-free approach. We used this model system to test the cytotoxicity of anticancer drugs, including temozolomide (TMZ) and ifosfamide (IFO). With the liver cells, TMZ showed a much lower toxicity to GBM cells under both 2D and 3D cell culture conditions. Comparing 2D, GBM cells cultured in 3D had much high viability under TMZ treatment. IFO was used to test the CYP-related metabolic effects. Cells with different expression levels of CYP3A4 differed dramatically in their ability to activate IFO, which led to strong metabolism-dependent cytotoxicity to GBM cells. These results demonstrate that our 3D-μPTC system could provide a more physiologically realistic in vitro environment than the current 2D monolayers for testing metabolism-dependent toxicity of anticancer drugs. It could therefore be used as an important platform for better prediction of drug dosing and schedule towards personalized medicine.

Synthesis and structure elucidation of novel fused 1,2,4-triazine derivatives as potent inhibitors targeting CYP1A1 activity

Synthesis and structure elucidation of new series of novel fused 1,2,4-triazine derivatives 3a-3f, 4a-4i and 6a-6b and their inhibitory activities are presented. Molecular structures of the synthesized compounds were confirmed by (1)H NMR, (13)C NMR, MS spectra and elemental analyses. X-ray crystallographic analysis was performed on 2-acetyl-8-(N,N-diacetylamino)-6-(4-methoxybenzyl)-3-(4-methoxy-phenyl)-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 3d and 2-acetyl-8-(N-acetylamino)-6-benzyl-3-(4-chlorophenyl)-3-methyl-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 4e to secure their structures. The inhibitory effect of these compounds toward the CPY1A1 activity was screened to determine their potential as promising anticancer drugs. Our data showed that compounds 4e, 5a, 5b and 6b possess the highest inhibitory effects among all tested compounds. Furthermore, analysis of triazolotriazine derivatives docking showed that these compounds bind only at the interface of substrate recognition site 2 (SRS2) and (SRS6) at the outer surface of the protein. Amino-acids ASN214, SER216 and ILE462 participate in the binding of these compounds through H-bonds.

The phosphate makes a difference: cellular functions of NADP

Recent research has unraveled a number of unexpected functions of the pyridine nucleotides. In this review, we will highlight the variety of known physiological roles of NADP. In its reduced form (NADPH), this molecule represents a universal electron donor, not only to drive biosynthetic pathways. Perhaps even more importantly, NADPH is the unique provider of reducing equivalents to maintain or regenerate the cellular detoxifying and antioxidative defense systems. The roles of NADPH in redox sensing and as substrate for NADPH oxidases to generate reactive oxygen species further extend its scope of functions. NADP(+), on the other hand, has acquired signaling functions. Its conversion to second messengers in calcium signaling may have critical impact on important cellular processes. The generation of NADP by NAD kinases is a key determinant of the cellular NADP concentration. The regulation of these enzymes may, therefore, be critical to feed the diversity of NADP-dependent processes adequately. The increasing recognition of the multiple roles of NADP has thus led to exciting new insights in this expanding field.

Engineering cytochrome P450 biocatalysts for biotechnology, medicine and bioremediation

IMPORTANCE OF THE FIELD

Cytochrome P450 enzymes comprise a superfamily of heme monooxygenases that are of considerable interest for the: i) synthesis of novel drugs and drug metabolites; ii) targeted cancer gene therapy; iii) biosensor design; and iv) bioremediation. However, their applications are limited because cytochrome P450, especially mammalian P450 enzymes, show a low turnover rate and stability, and require a complex source of electrons through cytochrome P450 reductase and NADPH.

AREAS COVERED IN THIS REVIEW

In this review, we discuss the recent progress towards the use of P450 enzymes in a variety of the above-mentioned applications. We also present alternate and cost-effective ways to perform P450-mediated reaction, especially using peroxides. Furthermore, we expand upon the current progress in P450 engineering approaches describing several recent examples that are utilized to enhance heterologous expression, stability, catalytic efficiency and utilization of alternate oxidants.

WHAT THE READER WILL GAIN

The review provides a comprehensive knowledge in the design of P450 biocatalysts for potentially practical purposes. Finally, we provide a prospective on the future aspects of P450 engineering and its applications in biotechnology, medicine and bioremediation.

TAKE HOME MESSAGE

Because of its wide applications, academic and pharmaceutical researchers, environmental scientists and healthcare providers are expected to gain current knowledge and future prospects of the practical use of P450 biocatalysts.

Automated brain tumor biopsy prediction using single-labeling cDNA microarrays-based gene expression profiling

AIMS

Gene signatures obtained from microarray experiments may be of use to improve the prediction of brain tumor diagnosis. Nevertheless, automated and objective prediction with accuracy comparable to or better than the gold standard should be convincingly demonstrated for possible clinician uptake of the new methodology. Herewith, we demonstrate that primary brain tumor types can be discriminated using microarray data in an automated and objective way.

METHODS

Postsurgical biopsies from 35 patients [17 glioblastoma multiforme (Gbm) and 18 meningothelial meningioma (Mm)] were stored in liquid nitrogen, total RNA was extracted, and cDNA was labeled with Cy3 fluorochrome and hybridized onto a cDNA-based microarray containing 11,500 cDNA clones representing 9300 loci. Scanned data were preprocessed, normalized, and used for predictor development. The predictive functions were fitted to a subset of samples and their performance evaluated with an independent subset. Expression results were validated by means of real time-polymerase chain reaction.

RESULTS

Some gene expression-based predictors achieved 100% accuracy both in training resampling validation and independent testing. One of them, composed of GFAP, PTPRZ1, GPM6B and PRELP, produced a 100% prediction accuracy for both training and independent test datasets. Furthermore, the gene signatures obtained, increased cell detoxification, motility and intracellular transport in Gbm, and increased cell adhesion and cytochrome-family genes in Mm, agree well with the expected biologic and pathologic characteristics of the studied tumors.

CONCLUSIONS

The ability of gene signatures to automate prediction of brain tumors through a fully objective approach has been demonstrated. A comparison of gene expression profiles between Gbm and Mm may provide additional clues about patterns associated with each tumor type.

Mechanisms of multidrug resistance in cancer

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Resistance exists against every effective anticancer drug and can develop by numerous mechanisms including decreased drug uptake, increased drug efflux, activation of detoxifying systems, activation of DNA repair mechanisms, evasion of drug-induced apoptosis, etc. In the first part of this chapter, we briefly summarize the current knowledge on individual cellular mechanisms responsible for MDR, with a special emphasis on ATP-binding cassette transporters, perhaps the main theme of this textbook. Although extensive work has been done to characterize MDR mechanisms in vitro, the translation of this knowledge to the clinic has not been crowned with success. Therefore, identifying genes and mechanisms critical to the development of MDR in vivo and establishing a reliable method for analyzing clinical samples could help to predict the development of resistance and lead to treatments designed to circumvent it. Our thoughts about translational research needed to achieve significant progress in the understanding of this complex phenomenon are therefore discussed in a third section. The pleotropic response of cancer cells to chemotherapy is summarized in a concluding diagram.

CYP2B6: new insights into a historically overlooked cytochrome P450 isozyme

Human CYP2B6 has been thought to account for a minor portion (<1%) of total hepatic cytochrome P450 (CYP) content and to have a minor function in human drug metabolism. Recent studies, however, indicate that the average relative contribution of CYP2B6 to total hepatic CYP content ranges from 2% to 10%. An increased interest in CYP2B6 research has been stimulated by the identification of an ever-increasing substrate list for this enzyme, polymorphic and ethnic variations in expression levels, and evidence for cross-regulation with CYP3A4, UGT1A1 and several hepatic drug transporters by the nuclear receptors pregnane X receptor and constitutive androstane receptor. Moreover, 20- to 250-fold interindividual variation in CYP2B6 expression has been demonstrated, presumably due to transcriptional regulation and polymorphisms. These individual differences may result in variable systemic exposure to drugs metabolized by CYP2B6, including the antineoplastics cyclophosphamide and ifosfamide, the antiretrovirals nevirapine and efavirenz, the anesthetics propofol and ketamine, the synthetic opioid methadone, and the anti-Parkinsonian selegiline. The potential clinical significance of CYP2B6 further enforces the need for a comprehensive review of this xenobiotic metabolizing enzyme. This communication summarizes recent advances in our understanding of this traditionally neglected enzyme and provides an overall picture of CYP2B6 with respect to expression, localization, substrate-specificity, inhibition, regulation, polymorphisms and clinical significance. Emphasis is given to nuclear receptor mediated transcriptional regulation, genetic polymorphisms, and their clinical significance.

Impact of smoking cessation on global gene expression in the bronchial epithelium of chronic smokers

Cigarette smoke is the major cause of lung cancer and can interact in complex ways with drugs for lung cancer prevention or therapy. Molecular genetic research promises to elucidate the biological mechanisms underlying divergent drug effects in smokers versus nonsmokers and to help in developing new approaches for controlling lung cancer. The present study compared global gene expression profiles (determined via Affymetrix microarray measurements in bronchial epithelial cells) between chronic smokers, former smokers, and never smokers. Smoking effects on global gene expression were determined from a combined analysis of three independent data sets. Differential expression between current and never smokers occurred in 591 of 13,902 measured genes (P < 0.01 and >2-fold change; pooled data)--a profound effect. In contrast, differential expression between current and former smokers occurred in only 145 of the measured genes (P < 0.01 and >2-fold change; pooled data). Nine of these 145 genes showed consistent and significant changes in each of the three data sets (P < 0.01 and >2-fold change), with eight being down-regulated in former smokers. Seven of the eight down-regulated genes, including CYP1B1 and three AKR genes, influence the metabolism of carcinogens and/or therapeutic/chemopreventive agents. Our data comparing former and current smokers allowed us to pinpoint the genes involved in smoking-drug interactions in lung cancer prevention and therapy. These findings have important implications for developing new targeted and dosing approaches for prevention and therapy in the lung and other sites, highlighting the importance of monitoring smoking status in patients receiving oncologic drug interventions.