Carbonyl reduction of the potential cytostatic drugs benfluron and 3,9-dimethoxybenfluron in human in vitro

Stereochemical considerations in pharmacokinetic processes of representative antineoplastic agents

The vast majority of chemical drugs or drug candidates contain stereocenter(s) in their molecular structures. In these molecules, stereochemical properties are vital properties that influence or even determine their drug actions. Therefore, studying the stereochemical issues of drugs (or drug candidates) is necessary for rational drug use. These stereochemical issues are usually involved with the stereoselectivity in pharmacokinetic processes, especially in the metabolism process. Thus, the investigation of the stereochemical issues in drug metabolism process deserves great attention, especially in those chiral/prochiral antineoplastic agents exhibiting pharmacodynamics and toxicologic differences between stereoisomers. Published reviews concerning this certain issue are inspiring, however they were covering all drug types and only limited antineoplastic drugs were discussed. Here in this review, the research on stereochemical issues in pharmacokinetic processes of some representative antineoplastic agents were described, especially focusing on some newly developed compounds. We highlight the chemical transformations in pharmacokinetic processes of these chiral/prochiral compounds and discuss their different behaviors with metabolic enzymes or transporter proteins, to explicate the observed stereoselectivity intrinsically.

An Efficient Approach towards the Synthesis, Crystal Structures, DFT and Cytotoxic Activity of Highly Congested 11-Aryl-10,12-Dihydrodiindino[1,2-b‘,2′,1′-e]Pyridine

An efficient and novel method for the synthesis of a series of 11-aryl-10,12-dihydrodiindino[1,2- b‘,2′,1′- e]pyridine via one-pot multi-component reactions of aldehydes, indan-1-one and ammonium acetate has been delineated. All prepared compounds were structurally elucidated by IR, UV-Vis, 1H and 13C NMR and X-ray diffraction techniques. The molecules adopted monoclinic crystal system with P21/ c space group and almost similar unit cell dimensions. The X-ray molecular geometries of the studied compounds were in excellent agreement with those computed by B3LYP/6-311++G(d,p) level of theory. The energies of the frontier orbitals calculated by B3LYP/6-311++G(d,p) level of theory enabled monitoring the reactivity and stability of the title molecules. The non-linear optical properties (NLO) and pNA were also computed and discussed. Compounds have shown broad spectrum cytotoxic activity against some human tumour cell lines; two of them rendering the most profound effect.

Identification of phase I and phase II metabolites of benfluron and dimefluron in rat urine using high-performance liquid chromatography/tandem mass spectrometry

Biotransformation products of two potential antineoplastic agents, benfluron and dimefluron, are characterized using our integrated approach based on the combination of high-performance liquid chromatography (HPLC) separation of phase I and phase II metabolites followed by photodiode-array UV detection and electrospray ionization tandem mass spectrometry (MS/MS). High mass accuracy measurement allows confirmation of an elemental composition and metabolic reactions according to exact mass defects. The combination of different HPLC/MS/MS scans, such as reconstructed ion current chromatograms, constant neutral loss chromatograms or exact mass filtration, helps the unambiguous detection of low abundance metabolites. The arene oxidation, N-oxidation, N-demethylation, O-demethylation, carbonyl reduction, glucuronidation and sulfation are typical mechanisms of the metabolite formation. The interpretation of their tandem mass spectra enables the distinction of demethylation position (N- vs. O-) as well as to differentiate N-oxidation from arene oxidation for both phase I and phase II metabolites. Two metabolic pathways are rather unusual for rat samples, i.e., glucosylation and double glucuronidation. The formation of metabolites that lead to a significant change in the chromophoric system of studied compounds, such as the reduction of carbonyl group in 7H-benzo[c]fluorene-7-one chromophore, is reflected in their UV spectra, which provides valuable complementary information to MS/MS data.

Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily

Carbonyl reduction of aldehydes, ketones, and quinones to their corresponding hydroxy derivatives plays an important role in the phase I metabolism of many endogenous (biogenic aldehydes, steroids, prostaglandins, reactive lipid peroxidation products) and xenobiotic (pharmacologic drugs, carcinogens, toxicants) compounds. Carbonyl-reducing enzymes are grouped into two large protein superfamilies: the aldo-keto reductases (AKR) and the short-chain dehydrogenases/reductases (SDR). Whereas aldehyde reductase and aldose reductase are AKRs, several forms of carbonyl reductase belong to the SDRs. In addition, there exist a variety of pluripotent hydroxysteroid dehydrogenases (HSDs) of both superfamilies that specifically catalyze the oxidoreduction at different positions of the steroid nucleus and also catalyze, rather nonspecifically, the reductive metabolism of a great number of nonsteroidal carbonyl compounds. The present review summarizes recent findings on carbonyl reductases and pluripotent HSDs of the SDR protein superfamily.

Use of chiral liquid chromatography for the evaluation of stereospecificity in the carbonyl reduction of potential benzo[c]fluorene antineoplastics benfluron and dimefluron in various species

Benfluron (B) [5-(2-dimethylaminoethoxy)-7H-benzo[c]fluorene-7-one hydrochloride] is a potential antineoplastic agent. In the organism, B undergoes a rapid phase I biotransformation through oxidative and reductive metabolic pathways. The carbonyl reduction of B leads to reduced benfluron, red-B, this is one of the principal pathways for the deactivation of this compound. The structure of B was modified to suppress its rapid deactivation via the carbonyl reduction on C7. Dimefluron, D (3,9-dimethoxy-benfluron) is one of the derivatives of B, in which an alternative metabolic pathway (O-desmethylation) prevails over the carbonyl reduction. The goal of this study was to develop HPLC methods enabling chiral separations of the red-B and -D enantiomers. The separation of red-B enantiomers was successful done on a Chiralcel OD-R column (250 mm x 4.6 mm ID, 5 microm) using a mobile phase acetonitrile-1 M NaClO4 (40:60, v/v). Another mobile phase, methanol-1 M NaClO4 (75:25, v/v), had to be employed for the sufficient resolution of red-D enantiomers. Flow rate was 0.5 ml min(-1) in both cases. Red-B was detected at 340 nm, red-D at 370 nm. The above chiral HPLC methods were used for the study of the biotransformation of B and D in the microsomal fractions of liver homogenates prepared from various species (rat, rabbit, pig, guinea pig, goat and human). The enantiospecificity of the respective carbonyl reductases was evaluated and discussed for both prochiral compounds, B and D.

Disposition study of a new potential antineoplastic agent dimefluron in rats using high-performance liquid chromatography with ultraviolet and mass spectrometric detection

The disposition of a new potential antineoplastic drug dimefluron after an oral administration to rats was investigated. Dimefluron, 3,9-dimethoxy-5-(2-dimethylaminoethoxy)-7H-benzo[c]fluoren-7-one hydrochloride, was administered in a single oral dose (250 mg kg(-1) of body weight) in the form of an aqueous solution via a gastric probe. Dimefluron metabolites were being searched for in rat faeces. Synthetic standards of the expected phase I metabolites (the products of O- and N-desmethylation, N-oxidation and carbonyl reduction of dimefluron) were prepared and used together with dimefluron and internal standard in the development of two HPLC bioanalytical methods based on different separation principles. The first separation of dimefluron and the phase I metabolites was tested on a 250 mm x 4 mm chromatographic column with LiChrospher 60 RP-selectB 5 microm (Merck) using an isocratic mobile phase containing 0.01 M nonylamine buffer (pH 7.4) and acetonitrile in the 1:2 ratio (v/v). The second separation was performed on a 250 mm x 4 mm chromatographic column Discovery HS F5, 5 microm (Supelco) using a linear gradient mode with the mobile phase containing acetonitrile and phosphate buffer (0.05 M KH2PO4, pH 3). The flow rate was 1 ml min(-1) in both cases. UV detection was performed in the dual wavelength mode, with 317 nm having been used for dimefluron and all 7H-benzo[c]fluoren-7-one metabolites, 367 nm for 7H-benzo[c]fluoren-7-ol metabolites. A higher homologue of dimefluron served as an internal standard. The identity of the dimefluron metabolites in biological samples was confirmed using HPLC-MS experiments. The elimination study showed that the concentration maximum for dimefluron and its metabolites in rat faeces was reached 48 h after the administration of the parent drug. O-Desmethylated derivatives of dimefluron prevailed among the phase I metabolites.

Measurement of xenobiotic carbonyl reduction in human liver fractions

Carbonyl reducing enzymes are involved in the metabolism of endogenous as well as xenobiotic molecules. Enzymes that catalyze the reversible oxidoreduction of aldehyde and ketone moieties include alcohol dehydrogenases, aldo-keto reductases, quinone reductases, and short-chain dehydrogenases/reductases. These enzymes differ with respect to subcellular location, cofactor dependence, and susceptibility to chemical inhibitors. Thus, it is possible to assess the relative contributions of these enzyme systems in the hepatic metabolism of a particular xenobiotic through simple in vitro experiments with commercially available reagents. The approaches described in this unit assume the availability of analytical procedures for measuring the parent compound and metabolites, such as HPLC with radiochemical, UV, or MS detection. Thus, the purpose of this unit is to outline methods for the study of the enzymatic carbonyl reduction of a drug development candidate or other xenobiotic molecule of interest.

Human Carbonyl Reduction Pathways and a Strategy for Their Study In Vitro

Carbonyl reduction plays a significant role in physiological processes throughout the body. Although much is known about endogenous carbonyl metabolism, much less is known about the roles of carbonyl-reducing enzymes in xenobiotic metabolism. Multiple pathways exist in humans for metabolizing carbonyl moieties of xenobiotics to their corresponding alcohols, readying these molecules for subsequent conjugation and/or excretion. When exploring carbonyl reduction clearance pathways for a drug development candidate, it is possible to assess the relative contributions of these enzymes due to their differences in subcellular locations, cofactor dependence, and inhibitor profiles. In addition, the contributions of these enzymes may be explored by varying incubation conditions, such as pH. Presently, individual isoforms of carbonyl-reducing enzymes are not widely available, either in recombinant or purified form. However, it is possible to study carbonyl reduction clearance pathways from simple experiments with commercially available reagents. This article provides an overview of carbonyl-reducing enzymes, including some kinetic data for substrates and inhibitors. In addition, an experimental strategy for the study of these enzymes in vitro is presented.

The novel anticancer drug oracin: different stereospecificity and cooperativity for carbonyl reduction by purified human liver 11β-hydroxysteroid dehydrogenase type 1

Inherent or acquired resistance of tumor cells to anti-cancer drugs is a problem of major importance in chemotherapy. In addition to detailed research into the mechanisms of drug inactivation, attention has also been paid to the synthesis of new structures. Oracin is a promising cytostatic drug, which is presently in phase II of clinical trials. This investigation was designed to characterize the metabolic inactivation of oracin by carbonyl reduction to 11-dihydrooracin (DHO). We identified 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) as the principal enzyme being responsible for oracin carbonyl reduction in human liver microsomes. The purified 11beta-HSD 1 catalyses this reaction in a stereospecific manner. Formation of (-)-DHO surpasses that of (+)-DHO by a factor of around four. Moreover, 11beta-HSD 1 exhibits enzyme cooperativity for the formation of both enantiomers (Hill coefficients of 2.26 +/- 0.20 and 1.84 +/- 0.29 for (-)-DHO and (+)-DHO, respectively). Comparing the differences in the stereospecificity and Hill coefficients between the microsomes and purified 11beta-HSD 1 could anticipate contribution of another microsomal enzyme. In case of oracin, this enzyme cooperativity may become important with respect to maximal plasma concentrations, and, by inhibition of 11beta-HSD 1, to enhance the chemotherapeutic efficacy of this anti-cancer drug.