Establishment and characterization of a new human colon adenocarcinoma cell line: BCS-TC2

A new cell line designated as BCS-TC2 was established in culture from a primary human colon adenocarcinoma. This cell line has been in continuous culture over a 36-month period. The cells grow as a monolayer sheet, displaying areas with a multilayered pattern as well as single cells and free-floating aggregates. The morphological, immunological, and ultrastructural features of these cells are in agreement with their epithelial origin. The characterization of this cell line indicated a 38 hr doubling time, and a colony forming efficiency of 2% in semisolid media and 22% in liquid culture, at low cell densities. These cells produce low amounts of carcinoembryonic antigen in culture (0.1 ng of CEA/10⁶ cells). Sub-cutaneous injection into athymic mice shows that these cells have a non-tumorigenic capacity. Chromosomal analysis showed a karyotype 46 XX,-15, +der (15), inv (16) (p13::q13). BCS-TC2 cell line, which maintains in culture several characteristics of the original tumor, represents a useful model system for cell biology studies of primary and non-metastatic tumors.     

Characterization of a human colonic adenocarcinoma cell line,LS123

Summary An epithelial cell line, LS123, was established in 1974 from the second in a series of three primary colonic tumors resected from a Caucasian female. The cell line is aneuploid, releases low concentrations of carcinoembryonic antigen (CEA), fails to grow progressively in nude mice, and forms colonies only in enriched semisolid medium developed for tumor stem cells. LS123 cells grow on confluent cell monolayers and in either low serum or serum-free medium. In the chick embryonic skin assay, LS123 cells grew as a well-differentiated abnormal colonic epithelium with little mitotic activity but with some indication of invasion. On floating collagen gels LS123 cells formed a one to three-cell-layer-thick undifferentiated epithelial sheet. The apparent low invasiveness of the cells of this line is supported by the patient's history of three primary colon tumors without systemic metastases during the past 30 yr. Therefore, although LS123 cells possess several properties associated with neoplasia, they have little invasive potential. Thus, LS123 cells may represent an important model for the study of human colon cancer. Presented in part at the 33rd Annual Meeting of the Tissue Culture Association, San Diego, CA, June 6–10, 1982. The work has been partially supported by U.S. Public Health Service Grants CA23871 (L. P. R.), CA24024 and RCDAK04-CA00579 (B. H. T.), and CA27124 and CA22370 (B. D. K.); the latter was awarded through the National Large Bowel Cancer Project.     

Expression of CYP and GST in human normal and colon tumor tissues

We investigated the immunohistochemical staining characteristics of cytochrome P450 1A1 (CYP1A1), CYPB1, CYP2E1, and glutathione S-transferase P1 (GSTP1), GSTT1, GSTO1, GSTK1 in colon tumor and surrounding normal colon tissues. Tissues were obtained from 47 patients with colon adenocarcinoma and the staining intensity of tumor and control tissues was compared. CYP1A1, CYP1B1, CYP2E1, GSTP1, GSTT1, GSTO1 and GSTK1 expressions in colon cancer cells were significantly greater than those in normal colon epithelial cells. No significant relation was found between the isoenzyme expressions and age, gender, smoking status, tumor grade and tumor stage. The higher expressions of CYP1A1, CYP1B1, CYP2E1, GSTP1, GSTO1, GSTT1 and GSTK1 in tumor than in normal colon tissues may be important for colon cancer progression and development.     

Structure-activity relationships of organosulfur compounds as inhibitors of cytochrome P450 1-mediated activation of benzo[a]pyrene in a human cell model

Twelve naturally-occurring organosulfur compounds were investigated as inhibitors of cytochrome P450 1 (CYP450 1)-mediated activation of benzo[a]pyrene (B[a]P) in human hepatoma (HepG2) cells. Inhibition depended on the presence of a diallyl group and the number of S atoms. Diallyl trisulfide (DATS), with a diallyl group and three S atoms, had the highest activity with an IC₅₀ of 0.4 mM, and 1.5-fold higher potency than diallyl disulfide (DADS) containing a diallyl group and two S atoms. Organosulfur compounds containing an alkyl group were less effective, or even ineffective, inhibitors of both CYP450 1 and B[a]P-induced cytotoxicity than DADS and DATS. Alliin and S-allyl cysteine containing the S-cysteinyl group had no inhibition.     

东亚钳蝎毒素对Caco-2人结肠癌细胞的体外药理学研究

研究东亚钳蝎毒素对人结肠癌细胞Caco-2增殖的影响。以不同浓度的东亚钳蝎（Buthus martensii Karsch）毒素（10、20、40滋g/mL）干预体外培养的Caco-2细胞,分别于24 h、48 h后,用四甲基偶氮唑盐（MTT）比色法,观察毒素对Caco-2细胞的增殖抑制作用。运用淋巴细胞转化实验和乳酸脱氢酶（LDH）释放实验检测蝎毒素对Caco-2细胞的作用途径。结果表明：东亚钳蝎毒不仅能抑制Caco-2细胞的增殖而且能促进淋巴细胞转化,毒素对Caco-2细胞增殖的抑制作用与浓度和作用时间密切相关。     

New findings in studies of cytochromes P450

Cytochromes P450 represent a numerous family of heme-containing enzymes belonging to the group of monooxygenases. In prokaryotes, cytochromes P450 usually perform a plastic function, whereas in eukaryotes their functions are very diverse. Mammalian cytochromes P450 are components of membranes and are involved in biosynthesis and metabolism of many physiologically active substances; moreover, these cytochromes are unique in their ability to catalyze biotransformation of xenobiotics, i.e. metabolize substances of foreign origin (drugs, toxins, environmental pollutants). The latter promotes elimination of xenobiotics, but sometimes intermediates of their metabolism are even more toxic and dangerous than the original xenobiotics per se. Some catalytic features of cytochromes P450 still need unambiguous explanation, i.e. broad substrate specificity, diversity of catalytic reactions, and unusual kinetics. Under some conditions, cytochromes P450 can produce reactive oxygen species, and this is another problem attracting increasing attention. In this respect, a recent finding in mitochondria of analogs of microsomal cytochromes P450 seems especially intriguing; it was postulated that P450 can be responsible for mitochondrial dysfunction, cell apoptosis, and pathogenesis of some diseases. In this paper the present state of the art concerning these problems is considered.     

Metabolism of a liver-selective nitric oxide-releasing agent, V-PYRRO/NO, by human microsomal cytochromes P450

Endogenously generated nitric oxide (NO) mediates a host of important physiological functions, playing roles in the vascular, immunological, and neurological systems. As a result, exogenous agents that release NO have become important therapeutic interventions and research tools. O(2)-Vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) is a prodrug designed with the hypothesis that it might release nitric oxide via epoxidation of the vinyl group by cytochrome P450, followed by enzymatic and/or spontaneous epoxide hydration to release the ultimate NO-donating moiety, 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (PYRRO/NO) ion. In this study, we investigated this hypothetical activation mechanism quantitatively for V-PYRRO/NO using cDNA-expressed human cytochrome P450 (CYP)2E1. Incubation with CYP2E1 and an NADPH-regenerating system resulted in a time-dependent decomposition of V-PYRRO/NO, with a turnover rate of 2.0 nmol/min/pmol CYP2E1. Nitrate and nitrite were detected in high yield as metabolites of NO. The predicted organic metabolites pyrrolidine and glycolaldehyde were also detected in near-quantitative yields. The enzymatic decomposition of V-PYRRO/NO was also catalyzed, albeit at lower rates, by CYP2A6 and CYP2B6. We conclude that the initial step in the metabolism of V-PYRRO/NO to NO in the liver is catalyzed efficiently but not exclusively by the alcohol-inducible form of cytochrome P450 (CYP2E1). The results confirm the proposed activation mechanism involving enzymatic oxidation of the vinyl group in V-PYRRO/NO followed by epoxide hydration and hydrolytic decomposition of the resulting PYRRO/NO ion to generate nitric oxide.     

Mechanism of taurine-induced apoptosis in human colon cancer cells

Taurine （Tau） has been shown to possess cancer therapeutic effect through induction of apoptosis, while the underlying molecular mechanism of its anti-cancer effect is not well understood. PUMA （p53-upregulated modulator of apoptosis） plays an important role in the process of apoptosis induction in a variety of human tumor ceils in both p53- dependent and -independent manners. However, whether PUMA is involved in the process of Tau-induced apoptosis in cancer cells has not been well studied. In the present study, we treated human colorectal cancer cells HT-29 （mutant p53） and LoVo （wild-type p53） with different concentrations of Tau, which led to the repression of cell proliferation and induction of apoptosis in both cell fines. Meanwhile, we also observed the increased expression of PUMA and high Bax/Bcl-2 ratios. To determine the role of PUMA in Tau-induced apoptosis, we used small interfering RNA interference to suppress PUMA expression. As a result, apoptosis was decreased in response to Tau treatment. All these results indicated that PUMA plays a critical role in Tauinduced apoptosis pathway in human colorectal cancer ceils. Demonstration of the molecular mechanism involved in the anti-tumor effect of Tau may be useful in the therapeutic target selection for p53-deficient colorectal cancer.     

Preparation of human metabolites of propranolol using laboratory-evolved bacterial cytochromes P450

Testing the toxicities and biological activities of the human metabolites of drugs is important for development of safe and effective pharmaceuticals. Producing these metabolites using human cytochrome P450s is difficult, however, because the human enzymes are costly, poorly stable, and slow. We have used directed evolution to generate variants of P450 BM3 from Bacillus megaterium that function via the "peroxide shunt" pathway, using hydrogen peroxide in place of the reductase domain, oxygen and NADPH. Here, we report further evolution of the P450 BM3 heme domain peroxygenase to enhance production of the authentic human metabolites of propranolol by this biocatalytic route. This system offers a versatile, cost-effective, and scaleable route to the synthesis of drug metabolites.     

Electrochemistry of cytochromes P450: Analysis of current-voltage characteristics of electrodes with immobilized cytochromes P450 for the screening of substrates and inhibitors

In the current study, an approach to elucidating the substrate specificity of cytochromes P450 based on the analysis of current-voltage characteristics of voltammograms and amperograms is proposed. Data on the electrochemical behavior of bioelectrodes with immobilized cytochromes P450 2B4, 1A2, 3A4, 11A1 (P450scc), and 51b1 (Mycobacterium tuberculosis sterol 14α-demethylase or CYP51 MT) in the presence of typical substrates and inhibitors for these hemoprotein forms are reported. Immobilization of the enzymes was accomplished by using graphite screen-printed electrodes modified with gold nanoparticles and with the synthetic membrane-like compound didodecyldimethylammonium bromide. The method of electro-analysis can be applied to the search of potential substrates and inhibitors of cytochromes P450 and to creation of multichannel electrochemical plates (chips, panels) with immobilized cytochromes P450. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 4, pp. 542–549.     

Inhibition of benzo[a]pyrene-induced cytotoxicity and cytochrome P450 1A activity by dietary flavonoids in human liver cell model: structure-activity relationship

Inhibition of benzo[a]pyrene (B[a]P)-induced cytotoxicity and cytochrome p450 1A (CYP 1A) activity by flavonoids (1–100 M) was examined in terms of the structure-activity relationship in the human liver-derived cell model (HepG2). Two hydroxyl groups in the 5- and 7-position of flavonoids were essential to inhibit B[a]P-induced cytotoxicity. Generally, flavones (IC₅₀; 5.0–17.2 M) were more potent than the corresponding flavonols (IC₅₀; 42.7–131.8 M), and flavonoids such as apigenin (IC₅₀; 7.2 M) were more active than the corresponding isoflavonoids, genistein (IC₅₀; 61.7 M). The planar structure of flavone proved to be important in inhibiting B[a]P-induced toxicity and CYP 1A activity. The inhibitory effect of flavonoids on B[a]P-induced CYP 1A activity was correlated well with the inhibition of B[a]P-induced cytotoxicity (r=0.635, p<;0.01).     

Displacement of histamine from liver cells and cell components by ligands for cytochromes P450

Intracellular histamine (HA) and cytochrome P450 monooxygenases (P450) each have been proposed as mediators of cell function, growth, and proliferation. The P450 family of heme enzymes is found in virtually all cells and generates, transforms, or inactivates steroids and other lipids that participate in cell regulation. We previously demonstrated a second messenger role for HA in blood platelets and the formation of a HA-P450 heme complex when exogenous HA was added to microsomes isolated from rat liver cells or to purified human P450 isozymes. Employing a radioimmunoassay, we now demonstrate that rat liver slices, microsomes derived from the livers of adult male rats and mast cell-deficient mice, and hepatoma cells, all contain endogenous HA. HA release from microsomes into the incubation medium, as determined by radioimmunoassay, is enhanced in the presence of carbon monoxide, steroids, and certain drugs, all agents that unite either directly with the iron atom or bind elsewhere within the heme cavity. Rat liver slices preincubated with (3)H-HA release labeled amine into the medium in the presence of those same ligands. These findings provide evidence of an in situ HA-P450 complex and offer further support that the imidazole, HA, is a physiological, intracellular modulator of cytochromes P450 in liver cells, and perhaps of these and other heme proteins in tissues in general.     

Preliminary crystallographic analysis of an enzyme involved in erythromycin biosynthesis: Cytochrome P450eryF

Cytochrome P450eryF was overexpressed in Escherichia coli and purified in high yield. Crystals of the protein in the presence of the substrate, 6-deoxyerythronolide B, have been obtained by the hanging drop vapor diffusion method, using polyethylene glycol 4000 as a precipitant. The crystals belong to the orthorhombic space group P2₁2₁2₁ with unit cell dimensions of a = 54.16 Å, b = 79.67 Å, and c = 99.48 Å and one molecule per asymmetric unit. A complete native data set has been collected to a resolution of 2.1 Å, and anomalous dispersion difference Patterson maps have revealed the location of the single heme iron atom. © 1994 Wiley-Liss, Inc.     

Plant activation of aromatic amines mediated by cytochromes P450 and flavin-containing monooxygenases

To know the mechanisms involved in the activation of promutagenic aromatic amines mediated by plants, we used Persea americana S117 system (S117) for the activation of 2-aminofluorene (2-AF) and m-phenylenediamine (m-PDA) in Ames assays. In these assays, the effect of the diphenylene iodonium (DPI), an inhibitor of flavin-containing monooxygenases (FMOs), of the 1-aminobenzotriazole (1-ABT), an inhibitor of cytochromes P450 (cyt-P450s) and of the methimazole, a high-affinity substrate for FMOs, was studied. The efficacy of both inhibitors and of the methimazole was verified to find that they did partially inhibit the mutagenesis of both aromatic amines, activated with rat liver S9. Similarly, both inhibitors and methimazole did produce a significant decrease in 2-AF and m-PDA mutagenesis, when the activation system was S117, indicating that, similar to what occurs in mammalian systems, plant FMOs and cyt-P450s can metabolize aromatic amines to mutagenic product(s). However, the affinity of both FMOs and cyt-P450s of plant for 2-AF and m-PDA was different. Data obtained indicate that the activities of plant FMOs must be the main enzymatic system of m-PDA activation while, in 2-AF activation, plant cyt-P450s have the most relevant activities. In addition, peroxidases of the S117 system must contribute to 2-AF activation and some isoforms of FMOs and/or cyt-P450s of the S117 system, uninhibited by the inhibitors used, must be the responsible for a partial activation of m-PDA.     

Omega oxygenases: nonheme-iron enzymes and P450 cytochromes

Enzymes that effect with ease one of the most difficult chemical reactions, hydroxylation of an unfunctionalized alkyl group, are of particular interest because highly reactive intermediates must be produced. A typical example, the hydroxylation of fatty acids in the omega position, is now known to occur widely in nature. The catalysts, which can be called "omega-oxygenases," also insert molecular oxygen into a variety of other substrates at positions removed from activating functional groups, as in steroids, eicosanoids, and numerous drugs and other xenobiotics. Progress in the characterization of bacterial nonheme-iron enzymes, and plant, bacterial, and mammalian P450 cytochromes that catalyze fatty acid omega-oxidation, and evidence for multiple functional oxidants are summarized.     

Electrochemical reduction of cytochromes P450 using electrodes containing immobilized substrates

A new approach for the electrochemical reduction of cytochromes P450 (P450, CYPs) with electrodes chemically modified with CYP appropriate substrates (“reverse” electrodes) has been proposed. The method is based on the analysis of cyclic voltammograms, square wave voltammograms, amperograms and determination of such electrochemical characteristics as catalytic current and redox potential. The differences of maximal current and potentials in square wave voltammograms and catalytic current in amperometric measurements are more sensitive and reliable. The planar mode of screen-printed electrodes permits to use 20–60 μl of electrolyte volume. We have investigated P450 2B4-benzphetamine or P450scc-cholesterol enzyme-substrate pairs. Electrochemical parameters of electrodes with nonspecific P450 substrate were differed from the electrodes with appropriate substrates.     

Characterization of WiDr: A human colon carcinoma cell line

Summary We describe the establishment and characterization of WiDr, a cell line derived from a human colon carcinoma. It produces carcinoembryonic antigen in culture, and has a doubling time of 15 hr with plating efficiency of 51%. The HLA antigenic profile and the allozyme genetic signature (composed of eight gene-enzyme systems) of WiDr cells are different from those of HeLa cells. Furthermore, WiDr cells possess three marker chromosomes, again distinct from the HeLa marker chromosomes. Finally, it is highly tumorigenic in four different xenogeneic animal models. Based on these studies, WiDr represents a useful model cell line for tumor cell biology investigations.     

cytochrome p450 superfamily in Arabidopsis thaliana: isolation of cDNAs,Differential Expression,and RFLP mapping of multiple cytochromes P450

We have isolated multiple cDNAs encoding cytochromes P450 (P450s) from Arabidopsis thaliana employing a PCR strategy. Degenerate oligonucleotide primers were designed from amino acid sequences conserved between two plant P450s, CYP71A1 and CYP73A2, including the heme-binding site and the proline-rich motif found in the N-terminal region, and 11 putative P450 fragments were amplified from first-strand cDNA from 7-day-old Arabidopsis as a template. With these PCR fragments as hybridization probes, 13 full-length and 3 partial cDNAs encoding different P450s have been isolated from an Arabidopsis cDNA library. These P450s have been assigned to either one of the established subfamilies: CYP71B, CYP73A, and CYP83A; or novel subfamilies: CYP76C, CYP83B, and CYP91A. The primary protein structures predicted from the cDNA sequences revealed that the regions around both the heme-binding site and the proline-rich motif were highly conserved among all these P450s. The N-terminal structures of the predicted P450 proteins suggested that these Arabidopsis P450s were located at the endoplasmic reticulum membrane. The loci of four P450 genes were determined by RFLP mapping. One of the clones, CYP71B2, was located at a position very close to the ga4 and gai mutations. RNA blot analysis showed expression patterns unique to each of the P450s in terms of tissue specificity and responsiveness to wounding and light/dark cycle, implicating involvement of these P450s in diverse metabolic processes.     

Crystal structure of a phenol-coupling P450 monooxygenase involved in teicoplanin biosynthesis

The lipoglycopeptide antibiotic teicoplanin has proven efficacy against gram‐positive pathogens. Teicoplanin is distinguished from the vancomycin‐type glycopeptide antibiotics, by the presence of an additional cross‐link between the aromatic amino acids 1 and 3 that is catalyzed by the cytochrome P450 monooxygenase Orf6* (CYP165D3). As a goal towards understanding the mechanism of this phenol‐coupling reaction, we have characterized recombinant Orf6* and determined its crystal structure to 2.2‐Å resolution. Although the structure of Orf6* reveals the core fold common to other P450 monooxygenases, there are subtle differences in the disposition of secondary structure elements near the active site cavity necessary to accommodate its complex heptapeptide substrate. Specifically, the orientation of the F and G helices in Orf6* results in a more closed active site than found in the vancomycin oxidative enzymes OxyB and OxyC. In addition, Met226 in the I helix replaces the more typical Gly/Ala residue that is positioned above the heme porphyrin ring, where it forms a hydrogen bond with a heme iron‐bound water molecule. Sequence comparisons with other phenol‐coupling P450 monooxygenases suggest that Met226 plays a role in determining the substrate regiospecificity of Orf6*. These features provide further insights into the mechanism of the cross‐linking mechanisms that occur during glycopeptide antibiotics biosynthesis. Proteins 2011; © 2011 Wiley‐Liss, Inc.     

Development and characterization of a rainbow trout liver cell line expressing cytochrome P450-dependent monooxygenase activity

A cell line RTL-W1, has been developed from the normal liver of an adult rainbow trout by proteolytic dissociation of liver fragments. RTL-W1 can be grown routinely in the basal medium, L-15, supplemented with 5% fetal bovine serum. In this medium, the cells have been passaged approximately 100 times over an 8-year period. The cells do not form colonies or grow in soft agar. The cultures are heteroploid. The cell shape was predominantly polygonal or epithelial-like, but as cultures became confluent, bipolar or fibroblast-like cells appeared. Among the prominent ultrastructural features of RTL-W1 were distended endoplasmic reticulum and desmosomes. Benzo[a]pyrene was cytotoxic to RTL-W1. Activity for the enzyme, 7-ethoxyresorufin O-deethylase (EROD), which is a measure of the cytochrome P4501A1 protein, increased dramatically in RTL-W1 upon their exposure to increasing concentrations of either -naphthoflavone (BNF) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). With these properties, RTL-W1 should be useful for studying the expression of the cytochrome P450 enzymes and as a tool for assessing the toxic potency of environmental contaminants.Abbreviations AHH aryl hydrocarbon hydroxylase - B[a]P benzo[a]pyrene - BNF -naphthoflavone - CHSE-214 Chinook salmon embryo cells - CYP cytochrome P450 - DMSO dimethyl sulfoxide - ECOD 7-ethoxycoumarinO-deethylase - EDTA ethylenediaminetetraacetic acid - EROD 7-ethoxyresorufinO-deethylase - FBS fetal bovine serum - HEPES N-[-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] - H4IIE rathepatoma cells - PCB polychlorinated biphenyls - PHH planar halogenated hydrocarbons - TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin - TEM transmission electron microscopy - TEFs toxic equivalent factors - TS 0.05 mM Tris 0.2M sucrose - RLE rat liver epithelial cells - RTL-W1 rainbow trout liver-Waterloo 1 cells