[Modern Nanomedicine in Treatment of Lung Carcinomas]

BACKGROUNDS

Despite the fast development of new effective cytostatics and targeted therapy, the treatment efficiency of lung cancer is still insufficient. The systemic administration of drugs results in a decrease in drug concentrations in tumor site, particularly due to specific extracellular environment in lungs. Nanotransporters could serve as a platform, protecting a drug against these undesired effects, which may enhance its therapeutic index and reduce side effects of a drug. Moreover, nanotechnologies possess the potential to improve the diagnostics of lung cancer, and thus increase a survival rate of oncologic patients.

AIM

The presented study is aimed to demonstrate the possibilities provided by nanotechnologies in the field of treatment and diagnostic of lung cancers and discuss the obstacles, which complicate a translation into clinical practice.

Photo-initiated crosslinking extends mapping of the protein-protein interface to membrane-embedded portions of cytochromes P450 2B4 and b₅

Protein-protein interactions play a central role in the regulation of many biochemical processes (e.g. the system participating in enzyme catalysis). Therefore, a deeper understanding of protein-protein interactions may contribute to the elucidation of many biologically important mechanisms. For this purpose, it is necessary to establish the composition and stoichiometry of supramolecular complexes and to identify the crucial portions of the interacting molecules. This study is devoted to structure-functional relationships in the microsomal Mixed Function Oxidase (MFO) complex, which is responsible for biotransformation of many hydrophobic endogenous compounds and xenobiotics. In particular, the cytochrome b5 interaction with MFO terminal oxygenase cytochrome P-450 (P450) was studied. To create photolabile probes suitable for this purpose, we prepared cytochrome b5 which had a photolabile diazirine analog of methionine (pMet) incorporated into the protein sequence, employing recombinant expression in Escherichia coli. In addition to wild-type cytochrome b5, where three methionines (Met) are located at positions 96, 126, and 131, six mutants containing only one Met in the sequence were designed and expressed (see Table 1). In these mutants, a single Met was engineered into the catalytic domain (at positions 23, 41, or 46), into the linker between the protein domains (at position 96), or into the membrane region (at positions 126 or 131). These mutants should confirm or exclude these portions of cytochrome b5 which are involved in the interaction with P450. After UV irradiation, the pMet group(s) in the photolabile cytochrome b5 probe was(were) activated, producing covalent crosslinks with the interacting parts of P450 2B4 in the close vicinity. The covalent complexes were analyzed by the "bottom up" approach with high-accuracy mass spectrometry. The analysis provided an identification of the contacts in the supramolecular complex with low structural resolution. We found that all the above-mentioned cytochrome b5 Met residues can form intermolecular crosslinks and thus participate in the interaction. In addition, our results indicate the existence of at least two P450:cytochrome b5 complexes which differ in the orientation of individual proteins. The results demonstrate the advantages of the photo-initiated crosslinking technique which is able to map the protein-protein interfaces not only in the solvent exposed regions, but also in the membrane-embedded segments (compared to a typical crosslinking approach which generally only identifies crosslinks in solvent exposed regions).

Fluorescent cellular assay for screening agents inhibiting Pseudomonas aeruginosa adherence

Antibodies against Pseudomonas aeruginosa (PA) lectin, PAIIL, which is a virulence factor mediating the bacteria binding to epithelium cells, were prepared in chickens and purified from egg yolks. To examine these antibodies as a prophylactic agent preventing the adhesion of PA we developed a well plate assay based on fluorescently labeled bacteria and immortalized epithelium cell lines derived from normal and cystic fibrosis (CF) human lungs. The antibodies significantly inhibited bacteria adhesion (up to 50%) in both cell lines. In agreement with in vivo data, our plate assay showed higher susceptibility of CF cells towards the PA adhesion as compared to normal epithelium. This finding proved the reliability of the developed experimental system.

The Hepatic Reductase Null (HRN™) and Reductase Conditional Null (RCN) mouse models as suitable tools to study metabolism, toxicity and carcinogenicity of environmental pollutants

This review describes the applicability of the Hepatic Reductase Null (HRN) and Reductase Conditional Null (RCN) mouse models to study carcinogen metabolism.

The anticancer drug ellipticine activated with cytochrome P450 mediates DNA damage determining its pharmacological efficiencies: studies with rats, Hepatic Cytochrome P450 Reductase Null (HRN™) mice and pure enzymes

Ellipticine is a DNA-damaging agent acting as a prodrug whose pharmacological efficiencies and genotoxic side effects are dictated by activation with cytochrome P450 (CYP). Over the last decade we have gained extensive experience in using pure enzymes and various animal models that helped to identify CYPs metabolizing ellipticine. In this review we focus on comparison between the in vitro and in vivo studies and show a necessity of both approaches to obtain valid information on CYP enzymes contributing to ellipticine metabolism. Discrepancies were found between the CYP enzymes activating ellipticine to 13-hydroxy- and 12-hydroxyellipticine generating covalent DNA adducts and those detoxifying this drug to 9-hydroxy- and 7-hydroellipticine in vitro and in vivo. In vivo, formation of ellipticine-DNA adducts is dependent not only on expression levels of CYP3A, catalyzing ellipticine activation in vitro, but also on those of CYP1A that oxidize ellipticine in vitro mainly to the detoxification products. The finding showing that cytochrome b5 alters the ratio of ellipticine metabolites generated by CYP1A1/2 and 3A4 explained this paradox. Whereas the detoxification of ellipticine by CYP1A and 3A is either decreased or not changed by cytochrome b5, activation leading to ellipticine-DNA adducts increased considerably. We show that (I) the pharmacological effects of ellipticine mediated by covalent ellipticine-derived DNA adducts are dictated by expression levels of CYP1A, 3A and cytochrome b5, and its own potency to induce these enzymes in tumor tissues, (II) animal models, where levels of CYPs are either knocked out or induced are appropriate to identify CYPs metabolizing ellipticine in vivo, and (III) extrapolation from in vitro data to the situation in vivo is not always possible, confirming the need for these animal models.

Role of rat cytochromes P450 in the oxidation of 17α-ethinylestradiol

17α-Ethinylestradiol (EE2) is an endocrine disruptor (ED) used as an ingredient of oral contraceptives. Rat hepatic microsomes metabolize EE2 to three products; two of them are hydroxylated EE2 derivatives. Of the hydroxylation reactions, 2-hydroxylation, is the major reaction. Cytochrome P450 (CYP) plays a major role in EE2 hydroxylation. To resolve which rat CYPs are responsible for EE2 oxidation, three approaches were used: induction of specific CYPs, selective inhibition of CYPs, and recombinant rat CYPs. The results demonstrate that EE2 is hydroxylated by several rat CYPs, among them CYP2C6 and 2C11 are most efficient in 2-hydroxy-EE2 formation, while CYP2A and 3A catalyze EE2 hydroxylation to the second product. EE2 is also an inhibitor of CYP2C- and CYP3A-catalyzed hydroxylation of endogenous EDs progesterone and testosterone. EE2 acts as a reversible inhibitor of CYP3A-mediated progesterone 6β-hydroxylation and inactivates CYP3A- and CYP2C-catalyzed testosterone 6β-hydroxylation and progesterone 21- or 16α-hydroxylation, respectively, in a mechanism-based manner.

Flexible docking-based molecular dynamics/steered molecular dynamics calculations of protein-protein contacts in a complex of cytochrome P450 1A2 with cytochrome b5

Formation of transient complexes of cytochrome P450 (P450) with another protein of the endoplasmic reticulum membrane, cytochrome b5 (cyt b5), dictates the catalytic activities of several P450s. Therefore, we examined formation and binding modes of the complex of human P450 1A2 with cyt b5. Docking of soluble domains of these proteins was performed using an information-driven flexible docking approach implemented in HADDOCK. Stabilities of the five unique binding modes of the P450 1A2-cyt b5 complex yielded by HADDOCK were evaluated using explicit 10 ns molecular dynamics (MD) simulations in aqueous solution. Further, steered MD was used to compare the stability of the individual P450 1A2-cyt b5 binding modes. The best binding mode was characterized by a T-shaped mutual orientation of the porphyrin rings and a 10.7 Å distance between the two redox centers, thus satisfying the condition for a fast electron transfer. Mutagenesis studies and chemical cross-linking, which, in the absence of crystal structures, were previously used to deduce specific P450-cyt b5 interactions, indicated that the negatively charged convex surface of cyt b5 binds to the positively charged concave surface of P450. Our simulations further elaborate structural details of this interface, including nine ion pairs between R95, R100, R138, R362, K442, K455, and K465 side chains of P450 1A2 and E42, E43, E49, D65, D71, and heme propionates of cyt b5. The universal heme-centric system of internal coordinates was proposed to facilitate consistent classification of the orientation of the two porphyrins in any protein complex.

The influence of ochratoxin A on DNA adduct formation by the carcinogen aristolochic acid in rats

Exposure to the plant nephrotoxin and carcinogen aristolochic acid (AA) leads to the development of AA nephropathy, Balkan endemic nephropathy (BEN) and upper urothelial carcinoma (UUC) in humans. Beside AA, exposure to ochratoxin A (OTA) was linked to BEN. Although OTA was rejected as a factor for BEN/UUC, there is still no information whether the development of AA-induced BEN/UUC is influenced by OTA exposure. Therefore, we studied the influence of OTA on the genotoxicity of AA (AA-DNA adduct formation) in vivo. AA-DNA adducts were formed in liver and kidney of rats treated with AA or AA combined with OTA, but no OTA-related DNA adducts were detectable in rats treated with OTA alone or OTA combined with AA. Compared to rats treated with AA alone, AA-DNA adduct levels were 5.4- and 1.6-fold higher in liver and kidney, respectively, of rats treated with AA combined with OTA. Although AA and OTA induced

NAD(P)H

quinone oxidoreductase (NQO1) activating AA to DNA adducts, their combined treatment did not lead to either higher NQO1 enzyme activity or higher AA-DNA adduct levels in ex vivo incubations. Oxidation of AA I (8-methoxy-6-nitrophenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid) to its detoxification metabolite, 8-hydroxyaristolochic acid, was lower in microsomes from rats treated with AA and OTA, and this was paralleled by lower activities of cytochromes P450 1A1/2 and/or 2C11 in these microsomes. Our results indicate that a decrease in AA detoxification after combined exposure to AA and OTA leads to an increase in AA-DNA adduct formation in liver and kidney of rats.

Ellipticines as DNA-targeted chemotherapeutics

The anti-tumor therapeutic ellipticine and its derivatives act as potent anticancer agents via a combined mechanism involving cell cycle arrest and induction of apoptosis. Cell death induced by ellipticine has been shown to engage a p53-dependent pathway, cell cycle arrest, interaction with several kinases and induction of the mitochondrial pathway of apoptotic cell death. Cell cycle arrest was shown to result from DNA damage caused by a variety of tumor chemotherapeutic agents; this is also the case for ellipticines. The prevalent DNA-mediated mechanisms of anti-tumor, mutagenic and cytotoxic activities of ellipticine are (i) intercalation into DNA, (ii) inhibition of DNA topoisomerase II activity, and (iii) covalent binding to DNA in vitro and in vivo after enzymatic activation by cytochrome P450 and/or peroxidase enzymes The mechanism leading to apoptosis by ellipticine is thought to also be associated with DNA damage, by inhibition of topoisomerase II and the covalent modification of DNA. In addition, the formation of ellipticine-DNA adducts ultimately can mutate cancer cells or initiate cell death. The aim of this review is to summarize our knowledge on the molecular mechanisms with the aim to explain the effectiveness of ellipticines as DNA-targeted chemotherapeutics in cancer cells.

The effect of aristolochic acid I on expression of NAD(P)H:quinone oxidoreductase in mice and rats--a comparative study

Aristolochic acid is the cause of aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN) and their associated urothelial malignancies. Using Western blotting, we investigated the expression of

NAD(P)H

quinone oxidoreductase (NQO1), the most efficient cytosolic enzyme that reductively activates aristolochic acid I (AAI) in mice and rats. In addition, the effect of AAI on the expression of the NQO1 protein and its enzymatic activity in these experimental animal models was examined. We found that NQO1 protein levels in cytosolic fractions isolated from liver, kidney and lung of mice differed from those expressed in these organs of rats. In mice, the highest levels of NQO1 protein and NQO1 activity were found in the kidney, followed by lung and liver. In contrast, the NQO1 protein levels and enzyme activity were lowest in rat-kidney cytosol, whereas the highest amounts of NQO1 protein and activity were found in lung cytosols, followed by those of liver. NQO1 protein and enzyme activity were induced in liver and kidney of AAI-pretreated mice compared with those of untreated mice. NQO1 protein and enzyme activity were also induced in rat kidney by AAI. Furthermore, the increase in hepatic and renal NQO1 enzyme activity was associated with AAI bio-activation and elevated AAI-DNA adduct levels were found in ex vivo incubations of cytosolic fractions with DNA and AAI. In conclusion, our results indicate that AAI can increase its own metabolic activation by inducing NQO1, thereby enhancing its own genotoxic potential.

Introduction of water into the heme distal side by Leu65 mutations of an oxygen sensor, YddV, generates verdoheme and carbon monoxide, exerting the heme oxygenase reaction

The globin-coupled oxygen sensor, YddV, is a heme-based oxygen sensor diguanylate cyclase. Oxygen binding to the heme Fe(II) complex in the N-terminal sensor domain of this enzyme substantially enhances its diguanylate cyclase activity which is conducted in the C-terminal functional domain. Leu65 is located on the heme distal side and is important for keeping the stability of the heme Fe(II)-O2 complex by preventing the entry of the water molecule to the heme complex. In the present study, it was found that (i) Escherichia coli-overexpressed and purified L65N mutant of the isolated heme-bound domain of YddV (YddV-heme) contained the verdoheme iron complex and other modified heme complexes as determined by optical absorption spectroscopy and mass spectrometry; (ii) CO was generated in the reconstituted system composed of heme-bound L65N and NADPH:cytochrome P450 reductase as confirmed by gas chromatography; (iii) CO generation of heme-bound L65N in the reconstituted system was inhibited by superoxide dismutase and catalase. In a concordance with the result, the reactive oxygen species increased the CO generation; (iv) the E. coli cells overexpressing the L65N protein of YddV-heme also formed significant amounts of CO compared to the cells overexpressing the wild type protein; (v) generation of verdoheme and CO was also observed for other mutants at Leu65 as well, but to a lesser extent. Since Leu65 mutations are assumed to introduce the water molecule into the heme distal side of YddV-heme, it is suggested that the water molecule would significantly contribute to facilitating heme oxygenase reactions for the Leu65 mutants.

Mechanisms of enzyme-catalyzed reduction of two carcinogenic nitro-aromatics, 3-nitrobenzanthrone and aristolochic acid I: Experimental and theoretical approaches

This review summarizes the results found in studies investigating the enzymatic activation of two genotoxic nitro-aromatics, an environmental pollutant and carcinogen 3-nitrobenzanthrone (3-NBA) and a natural plant nephrotoxin and carcinogen aristolochic acid I (AAI), to reactive species forming covalent DNA adducts. Experimental and theoretical approaches determined the reasons why human

NAD(P)H

quinone oxidoreductase (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 have the potential to reductively activate both nitro-aromatics. The results also contributed to the elucidation of the molecular mechanisms of these reactions. The contribution of conjugation enzymes such as N,O-acetyltransferases (NATs) and sulfotransferases (SULTs) to the activation of 3-NBA and AAI was also examined. The results indicated differences in the abilities of 3-NBA and AAI metabolites to be further activated by these conjugation enzymes. The formation of DNA adducts generated by both carcinogens during their reductive activation by the NOQ1 and CYP1A1/2 enzymes was investigated with pure enzymes, enzymes present in subcellular cytosolic and microsomal fractions, selective inhibitors, and animal models (including knock-out and humanized animals). For the theoretical approaches, flexible in silico docking methods as well as ab initio calculations were employed. The results summarized in this review demonstrate that a combination of experimental and theoretical approaches is a useful tool to study the enzyme-mediated reaction mechanisms of 3-NBA and AAI reduction.

The influence of dicoumarol on the bioactivation of the carcinogen aristolochic acid I in rats

Aristolochic acid I (AAI) is the major toxic component of the plant extract AA, which leads to the development of nephropathy and urothelial cancer in human. Individual susceptibility to AAI-induced disease might reflect variability in enzymes that metabolise AAI. In vitro

NAD(P)H

quinone oxidoreductase (NQO1) is the most potent enzyme that activates AAI by catalyzing formation of AAI-DNA adducts, which are found in kidneys of patients exposed to AAI. Inhibition of renal NQO1 activity by dicoumarol has been shown in mice. Here, we studied the influence of dicoumarol on metabolic activation of AAI in Wistar rats in vivo. In contrast to previous in vitro findings, dicoumarol did not inhibit AAI-DNA adduct formation in rats. Compared with rats treated with AAI alone, 11- and 5.4-fold higher AAI-DNA adduct levels were detected in liver and kidney, respectively, of rats pretreated with dicoumarol prior to exposure to AAI. Cytosols and microsomes isolated from liver and kidney of these rats were analysed for activity and protein levels of enzymes known to be involved in AAI metabolism. The combination of dicoumarol with AAI induced NQO1 protein level and activity in both organs. This was paralleled by an increase in AAI-DNA adduct levels found in ex vivo incubations with cytosols from rats pretreated with dicoumarol compared to cytosols from untreated rats. Microsomal ex vivo incubations showed a lower AAI detoxication to its oxidative metabolite, 8-hydroxyaristolochic acid (AAIa), although cytochrome P450 (CYP) 1A was practically unchanged. Because of these unexpected results, we examined CYP2C activity in microsomes and found that treatment of rats with dicoumarol alone and in combination with AAI inhibited CYP2C6/11 in liver. Therefore, these results indicate that CYP2C enzymes might contribute to AAI detoxication.

Cytochrome b5 and epoxide hydrolase contribute to benzo[a]pyrene-DNA adduct formation catalyzed by cytochrome P450 1A1 under low NADPH:P450 oxidoreductase conditions

In previous studies we had administered benzo[a]pyrene (BaP) to genetically engineered mice (HRN) which do not express NADPH:cytochrome P450 oxidoreductase (POR) in hepatocytes and observed higher DNA adduct levels in livers of these mice than in wild-type mice. To elucidate the reason for this unexpected finding we have used two different settings for in vitro incubations; hepatic microsomes from control and BaP-pretreated HRN mice and reconstituted systems with cytochrome P450 1A1 (CYP1A1), POR, cytochrome b5, and epoxide hydrolase (mEH) in different ratios. In microsomes from BaP-pretreated mice, in which Cyp1a1 was induced, higher levels of BaP metabolites were formed, mainly of BaP-7,8-dihydrodiol. At a low POR:CYP1A1 ratio of 0.05:1 in the reconstituted system, the amounts of BaP diones and BaP-9-ol formed were essentially the same as at an equimolar ratio, but formation of BaP-3-ol was ∼ 1.6-fold higher. Only after addition of mEH were BaP dihydrodiols found. Two BaP-DNA adducts were formed in the presence of mEH, but only one when CYP1A1 and POR were present alone. At a ratio of POR:CYP1A1 of 0.05:1, addition of cytochrome b5 increased CYP1A1-mediated BaP oxidation to most of its metabolites indicating that cytochrome b5 participates in the electron transfer from NADPH to CYP1A1 required for enzyme activity of this CYP. BaP-9-ol was formed even by CYP1A1 reconstituted with cytochrome b5 without POR. Our results suggest that in livers of HRN mice Cyp1a1, cytochrome b5 and mEH can effectively activate BaP to DNA binding species, even in the presence of very low amounts of POR.

Hypoxia-mediated histone acetylation and expression of N-myc transcription factor dictate aggressiveness of neuroblastoma cells

Cells of solid malignancies generally adapt to entire lack of oxygen. Hypoxia induces the expression of several genes, which allows the cells to survive. For DNA transcription, it is necessary that DNA structure is loosened. In addition to structural characteristics of DNA, its epigenetic alterations influence a proper DNA transcription. Since histones play a key role in epigenetics, changes in expression levels of acetylated histones H3 and H4 as well as of hypoxia-inducible factor-1α (HIF-1α) in human neuroblastoma cell lines cultivated under standard or hypoxic conditions (1% O2) were investigated. Moreover, the effect of hypoxia on the expression of two transcription factors, c-Myc and N-myc, was studied. Hypoxic stress increased levels of acetylated histones H3 and H4 in UKF-NB-3 and UKF-NB-4 neuroblastoma cells with N-myc amplification, whereas almost no changes in acetylation of these histones were found in an SK-N-AS neuroblastoma cell line, the line with diploid N-myc status. An increase in histone H4 acetylation caused by hypoxia in UKF-NB-3 and UKF-NB-4 corresponds to increased levels of N-myc transcription factor in these cells.

Quantification of interactions between cytochrome P450 2B4 and cytochrome b5 in a functional membrane complex

OBJECTIVES

The mammalian mixed function oxidase (MFO) system participates in hydroxylation of many hydrophobic endogenous compounds as well as xenobiotics such as drugs and carcinogens. This biotransformation system, located in a membrane of endoplasmic reticulum, consists of cytochrome P-450 (P450), NADPH:P450 oxidoreductase and a facultative component, cytochrome b5. The knowledge of the interactions among the individual components of the MFO system is essential to understand the relationships between the structure and function of this system that finally dictate a qualitative and quantitative pattern of produced metabolites (e.g. detoxified xenobiotics and/or activated carcinogens). To elucidate the quantitative aspects of the interactions within the MFO system we acquired the photo-initiated cross-linking approach.

METHODS

The photo-initiated cross-linking employing cytochrome b5 as a protein nanoprobe [an amino acid analogue of methionine (pMet) was incorporated into cytochrome b5 sequence during recombinant expression] was used to quantify its interaction with P450 2B4 in a functional membrane complex. The cross-linking was initiated by UV-irradiation that formed from a pMet photolabile diazirine group highly reactive carbene biradical. This biradical is able to covalently bind amino acids in the close proximity and to form cross-link. The Met 96 of cytochrome b5 is situated in a linker region between its catalytic and membrane domains, while Met 126 and 131 are located in its membrane domain. The combination of several methods (electrophoresis in polyacrylamide gel, isoelectric focusing, Edman N-terminal degradation and amino acid analysis) was employed to characterize the molar ratio of P450 2B4 to cytochrome b5 in formed covalent cross-links to quantify their transient interactions.

RESULTS

The successfully produced cytochrome b5 nanoprobe (with confirmed pMet incorporation by mass spectrometry) stimulates the catalytical activity of P450 2B4 when reconstituted with NADPH:P450 oxidoreductase in vitro in dilauroylphosphatidylcholine (DLPC) vesicles. The cross-linking was carried out in similar reconstituted system without NADPH:P450 oxidoreductase, and at least three products were separated on 1D SDS-PAGE. The molar ratio of P450 to cytochrome b5 in each complex was estimated using the above-mentioned combination of methods as 1:1, 1:2 and 2:1.

CONCLUSIONS

The results demonstrate the utility of cytochrome b5 nanoprobe to study the interactions in MFO system. Using this nanoprobe, heterodimer with P450 2B4 and in addition also heterooligomers were identified, suggesting rather complex interactions of both proteins in this system that suppose the formation of such multimeric structures in the membrane of endoplasmic reticulum.

Knockout and humanized mice as suitable tools to identify enzymes metabolizing the human carcinogen aristolochic acid

1. Aristolochic acid I (AAI) is the predominant component in plant extract of Aristolochia genus that is involved in development of aristolochic acid nephropathy, Balkan endemic nephropathy and urothelial cancer. The diseases do not develop in all individuals exposed to AAI and patients exhibit different clinical outcomes. Differences in the activities of enzymes catalyzing the metabolism of AAI might be one of the reasons for this individual susceptibility. 2. Understanding which human enzymes are involved in reductive activation of AAI generating AAI-DNA adducts, and/or its detoxication to the O-demethylated metabolite, aristolochic acid Ia (AAIa), is necessary in the assessment of the susceptibility to this compound. 3. This review summarizes the results of the latest studies utilizing genetically engineered mouse models to identify which human and rodent enzymes catalyze the reductive activation of AAI to AAI-DNA adducts and its oxidative detoxication to AAIa in vivo. 4. The use of hepatic cytochrome P450 (Cyp) reductase null (HRN) mice, in which NADPH:Cyp oxidoreductase (Por) is deleted in hepatocytes, Cyp1a1((-/-)), Cyp1a2((-/-)) single-knockout, Cyp1a1/1a2((-/-)) double-knockout and CYP1A-humanized mice revealed that mouse and human CYP1A1 and 1A2, besides mouse

NAD(P)H

quinone oxidoreductase, were involved in the activation of AAI but CYP1A1 and 1A2 also oxidatively detoxified AAI.

The relationship between DNA adduct formation by benzo[a]pyrene and expression of its activation enzyme cytochrome P450 1A1 in rat

Benzo[a]pyrene (BaP) is a human carcinogen requiring metabolic activation prior to reaction with DNA. Cytochrome P450 (CYP) 1A1 is the most important hepatic and intestinal enzyme in both BaP activation and detoxification. CYP1A2 is also capable of oxidizing BaP, but to a lesser extent. The induction of CYP1A1/2 by BaP and/or β-naphthoflavone in liver and small intestine of rats was investigated. Both BaP and β-naphthoflavone induced CYP1A expression and increased enzyme activities in both organs. Moreover, the induction of CYP1A enzyme activities resulted in an increase in formation of BaP-DNA adducts detected by (32)P-postlabeling in rat liver and in the distal part of small intestine in vivo. The increases in CYP1A enzyme activity were also associated with bioactivation of BaP and elevated BaP-DNA adduct levels in ex vivo incubations of microsomes of both organs with DNA and BaP. These findings indicate a stimulating effect of both compounds on BaP-induced carcinogenesis.

[Modern imaging techniques for anthracycline cytostatics - review of the literature]

Anthracycline cytostatics can be observed at the level of organelles, cells and whole organisms due to their fluorescent properties. Imaging techniques based on detection of fluorescence can be used not only for observation of drug interaction with tumor cells, but also for targeting therapy of tumors with nanoparticles containing anthracycline cytostatics. Doxorubicin and daunorubicin, enclosed in liposomes, as representatives of nanoparticles suitable for targeted therapy, are used in clinical practice. The main advantage of liposomal drugs is to reduce the side effects due to differences in pharmacokinetics and distribution of the drug in the body. Due to the fact that all biological mechanisms of action of anthracycline drugs are not still fully understood, modern imaging techniques offer tool for in vivo studies of these mechanisms.

Enzymes metabolizing aristolochic acid and their contribution to the development of aristolochic acid nephropathy and urothelial cancer

Aristolochic acid (AA), a plant nephrotoxin and carcinogen, causes aristolochic acid nephropathy (AAN) and its associated urothelial malignancy, and is hypothesized to be responsible for Balkan endemic nephropathy (BEN). The major component of AA, aristolochic acid I (AAI), is the predominant compound responsible for these diseases. The reductive activation of AAI leads to the formation of covalent DNA adducts. The most abundant DNA adduct, 7-(deoxyadenosin-N6-yl)aristolactam I, causes characteristic AT→TA transversions found in the TP53 tumor suppressor gene in tumors from AAN and BEN patients. Understanding which human enzymes are involved in AAI activation to species forming DNA adducts and/or detoxication to the AAI O-demethylated metabolite, aristolochic acid Ia (AAIa), is important in the assessment of the susceptibility to this carcinogen. This review summarizes the latest data on identifying human and rodent enzymes participating in AAI metabolism. NAD(P)H:quinone oxidoreductase (NQO1) is the most efficient cytosolic nitroreductase activating AAI in vitro and in vivo. In human hepatic microsomes, AAI is activated by cytochrome P450 1A2 (CYP1A2) and, to a lesser extent, by CYP1A1; NADPH:CYP oxidoreductase also plays a minor role. Human and rodent CYP1A1 and 1A2 are also the principal enzymes involved in oxidative detoxication of AAI to AAIa in vitro and in vivo. The orientation of AAI in the active sites of human CYP1A1/2 and NQO1 was predicted from molecular modeling and is consistent with the efficient reduction of AAI by them observed experimentally. Molecular modeling also shows why CYP1A2 plays an important role in the oxidation of AAI to AAIa.

The epidemiology, diagnosis, and management of aristolochic acid nephropathy: a narrative review

It has been 20 years since the first description of a rapidly progressive renal disease that is associated with the consumption of Chinese herbs containing aristolochic acid (AA) and is now termed aristolochic acid nephropathy (AAN). Recent data have shown that AA is also the primary causative agent in Balkan endemic nephropathy and associated urothelial cancer. Aristolochic acid nephropathy is associated with a high long-term risk for renal failure and urothelial cancer, and the potential worldwide population exposure is enormous. This evidence-based review of the diagnostic approach to and management of AAN draws on the authors' experience with the largest and longest-studied combined cohort of patients with this condition. It is hoped that a better understanding of the importance of this underrecognized and severe condition will improve epidemiologic, preventive, and therapeutic strategies to reduce the global burden of this disease.