BSP :: Drug Metabolism Letters Home Page

Contents

Editorial Pp. 1
[Editorial in PDF]

Effect of Common NAT2 Variant Alleles in the Acetylation of the Major Clonazepam Metabolite, 7-Aminoclonazepam Pp. 3-5
M. Olivera, C. Martínez, G. Gervasini, J.A. Carrillo, S. Ramos, J. Benítez, E. García-Martin and J.A.G. Agúndez
[Abstract] [Full Text Article]

Verapamil, but not Probenecid, Co-Administration Can Convert Desloratadine to a Sedating Antihistamine in Mice Pp. 7-11
A. Katta, M. Dhananjeyan, C. Bykowski, P.E.M. Hacker, D.B. White and K. Bachmann
[Abstract] [Full Text Article]

In Vitro Inhibition of Rat CYP1A1 and CYP1A2 by Piceatannol, a Hydroxylated Metabolite of trans Resveratrol Pp. 13-16
T.K.H. Chang, J. Chen and C.-T. Yu
[Abstract] [Full Text Article]

Comparison of Paraben Stability in Human and Rat Skin Pp. 17-21
H.M. Harville, R. Voorman and J.J. Prusakiewicz
[Abstract] [Full Text Article]

ABCB1, SLCO1B1 and UGT1A1 Gene Polymorphisms are Associated with Toxicity in Metastatic Colorectal Cancer Patients Treated with First-line Irinotecan Pp. 23-30
K.E. Rhodes, W. Zhang, D. Yang, O.A. Press, M. Gordon, D. Vallböhmer, A.M. Schultheis, G. Lurje, R.D. Ladner, W. Fazzone, S. Iqbal and H.-J. Lenz
[Abstract] [Full Text Article]

Prioritization of Clinical Drug Interaction Studies Using In Vitro Cytochrome P450 Data: Proposed Refinement and Expansion of the “Rank Order” Approach Pp. 31-35
A.D. Rodrigues
[Abstract] [Full Text Article]

Drug Confinement and Delivery in Ceramic Implants Pp. 37-40
M. Vallet-Regí, F. Balas, M. Colilla and M. Manzano
[Abstract] [Full Text Article]

Application of Pharmacogenomics in Drug Discovery and Development: Correlations Between Transcriptional Modulation and Preclinical Safety Observations Pp. 41-48
L.G. Yengi, Q. Xiang, L. Shen, A. Chandrasekaran, J. Kao and J. Scatina
[Abstract] [Full Text Article]

A Role for Lysosomal Phospholipase A2 in Drug Induced Phospholipidosis Pp. 49-53
A. Abe, M. Hiraoka and J.A. Shayman
[Abstract] [Full Text Article]

Folate Nutrigenetics: A Convergence of Dietary Folate Metabolism, Folic Acid Supplementation, and Folate Antagonist Pharmacogenetics Pp. 55-60
B. Meshkin and K. Blum
[Abstract] [Full Text Article]

A Unique Example of Drug Metabolism: Tetra- and Penta Oxygenation Reactions of Capravirine in Rats, Dogs and Humans Pp. 61-65
H.-Z. Bu, W.F. Pool, E.Y. Wu and B.V. Shetty
[Abstract] [Full Text Article]

Metabolic Stability Screen for Drug Discovery Using Cassette Analysis and Column Switching Pp. 67-72
J.S. Halladay, S. Wong, S.M. Jaffer, A.K. Sinhababu and S.C. Khojasteh-Bakht
[Abstract] [Full Text Article]

Structures of Various Cytochromes c Evaluated from the Redox Behaviors Using the Optically Active Co(III) Complex-Modified Au Electrode Pp. 73-75
I. Takahashi, C. Nishijima, T. Inomata, Y. Funahashi, T. Ozawa and H. Masuda
[Abstract] [Full Text Article]

Effects of Propofol Analogs on Glucuronidation of Propofol, an Anesthetic Drug, by Human Liver Microsomes Pp. 77-79
M. Shimizu, Y. Matsumoto and H. Yamazaki
[Abstract] [Full Text Article]

Drug Interactions of Tipranavir, a New HIV Protease Inhibitor Pp. 81-84
J. Morello, S. Rodriguez-Novoa, I. Jimenez-Nacher and V. Soriano
[Abstract] [Full Text Article]

Abstracts

[Back to top]
Editorial
[Editorial in PDF]

The development of new and novel techniques and technologies such as combinatorial chemistry, high throughput screening, molecular and cell biology, medical imaging and decoding or sequencing of the human genomes in pharmaceutical research has given discovery scientists the ability to deliver large numbers of new chemical entities (NCE).. However, the success rate of NCEs entering the market place is unacceptably low with estimate of 1 in 5000 compounds. The major reasons for failure of NCEs are poor clinical efficacy, serious undesired side effects, adverse drug reactions and unfavorable drug metabolism and pharmacokinetics (DMPK). Therefore, it has been recognized that in addition of good pharmacological activity (potency and selectivity), safety and pharmacokinetics are crucial determinants of the ultimate clinical success of a drug candidate. The early refinement of these properties has been regarded as essential features of the drug candidate selection process and it has compelled the pharmaceutical industry to integrate more greatly DMPK functions into the early stages of drug discovery. Such DMPK integration should allow the selection of a drug candidate that has good oral absorption and bioavailability, optimum half-life, favorable clearance, and acceptable metabolic and toxicological profiles in patients.

To predict the PK, metabolic profiles and safety of NCEs in humans, drug metabolism scientists have developed novel techniques such as in vitro assays using animals and human liver microsomes, hepatocytes or recombinant enzymes, Cell-based such as the Caco-2 screen and parallel artificial membrane permeability assays, transporter assays, in vivo studies using a range of experimental animal models and in silico models. Recently, the use of microdose strategy to asses the full pharmacokinetics profiles of drug candidates in animals and humans has been reported.

Metabolic drug interactions have received considerable attention in pharmaceutical industries because in recent years several prominent drugs have been withdrawn from the market in the US and Europe due to serious events as a result of significant drug-drug interactions. These drug interactions often result by alteration of the pharmacokinetics of one drug by another co-administered drug. A variety of approaches, in vitro, in silico, and preclinical species are being used to predict these interactions at early stage of drug discovery.

Drug Metabolism Letters (DML) aims to cover all these latest and outstanding scientific advances in all areas of drug metabolism and disposition such as in vitro systems including CYP-450; enzyme induction and inhibition; drug-drug interactions and enzyme kinetics; pharmacokinetics, toxicokinetics, species scaling and extrapolations; P-glycoprotein and transport carriers; target organ toxicity and interindividual variability; drug metabolism and disposition studies; extrahepatic metabolism; phase I and phase II metabolism; identification of drug metabolites, reactive intermediate and glutathione conjugates.

I would like to thank all the authors for taking the time to write informative and interesting articles for this first issue of Drug Metabolism Letters.

As the Editor-in-Chief, I wish Drug Metabolism Letters to become a forum for in-depth discussion of those areas, which we all feel are crucial for the expansion of the field. The journal will be an essential reading to both researchers and clinicians who wish to keep abreast of the latest developments in the field.

Chandra Prakash
Editor-in-Chief, DML
Pfizer Global Research and Development
Groton, CT 06340
USA

[Back to top]
Effect of Common NAT2 Variant Alleles in the Acetylation of the Major Clonazepam Metabolite, 7-Aminoclonazepam
M. Olivera, C. Martínez, G. Gervasini, J.A. Carrillo, S. Ramos, J. Benítez, E. García-Martin and J.A.G. Agúndez

[Full Text Article]

We investigated the role of NAT2 on clonazepam acetylation, using transiently expressed human NAT2 alleles. The NAT25*B and the NAT2*6A variant alleles cause a 20 and 22-fold reduction in the Vmax, respectively. We conclude that NAT2 is responsible for 7-aminoclonazepam acetylation and that NAT2 gene polymorphisms impair such metabolic pathway.

[Back to top]
Verapamil, but not Probenecid, Co-Administration Can Convert Desloratadine to a Sedating Antihistamine in Mice
A. Katta, M. Dhananjeyan, C. Bykowski, P.E.M. Hacker, D.B. White and K. Bachmann

[Full Text Article]

The possibility that non-sedating antihistamines could elicit sedation in mice due to drug-induced inhibition of brain PgP was evaluated by measuring the ability of desloratadine alone or in combination with verapamil to cause ataxia in mice. Also, the concentrations of desloratadine in plasma and in brain homogenates were measured by liquid chromatography-mass spectrometry. Relative to methylcellulose (control) treatment, verapamil plus desloratadine decreased rotarod performance of mice. Plasma concentrations of desloratadine appeared comparable in the mice treated with either desloratadine or verapamil plus desloratadine, however the rate of decline of desloratadine from brain tissue was slower in mice treated with verapamil plus desloratadine compared to mice treated with desloratadine only. These data suggest that inhibition of brain PgP can convert desloratadine to a sedating antihistamine in mice.

[Back to top]
In Vitro Inhibition of Rat CYP1A1 and CYP1A2 by Piceatannol, a Hydroxylated Metabolite of trans Resveratrol Pp. 13-16
T.K.H. Chang, J. Chen and C.-T. Yu

[Full Text Article]

Piceatannol and its parent compound, trans-resveratrol, decreased the in vitro catalytic activity of rat CYP1A1 and CYP1A2 by mixed inhibition. trans-Resveratrol was not a mechanism-based inactivator of rat CYP1A in vitro and the administration of this compound (50 mg/kg) to rats did not affect hepatic microsomal CYP1A-mediated enzyme activity.

[Back to top]
Comparison of Paraben Stability in Human and Rat Skin
H.M. Harville, R. Voorman and J.J. Prusakiewicz

[Full Text Article]

Parabens are widely used preservatives in topical products, and are estrogenic in numerous experimental models. The typical cutaneous metabolism model, rat skin, hydrolyzes parabens much faster than human skin. Chronic application and absorption of parabens, combined with low metabolism rates, may lead to prolonged estrogenic effects in the skin.

[Back to top]
ABCB1, SLCO1B1 and UGT1A1 Gene Polymorphisms are Associated with Toxicity in Metastatic Colorectal Cancer Patients Treated with First-line Irinotecan
K.E. Rhodes, W. Zhang, D. Yang, O.A. Press, M. Gordon, D. Vallböhmer, A.M. Schultheis, G. Lurje, R.D. Ladner, W. Fazzone, S. Iqbal and H.-J. Lenz

[Full Text Article]

We tested specific gene polymorphisms known to be involved in the irinotecan (CPT-11) metabolic pathway. The combination of at least one SLCO1B1 521 T allele, one ABCB1 1236 C allele and one UGT1A1*28 variant 7 repeat demonstrated a statistically significant association with Grade 3/4 toxicities in metastatic colorectal cancer patients.

[Back to top]
Prioritization of Clinical Drug Interaction Studies Using In Vitro Cytochrome P450 Data: Proposed Refinement and Expansion of the “Rank Order” Approach
A.D. Rodrigues

[Full Text Article]

For any new chemical entity (NCE), in vitro inhibition constants (K_i) for the different human cytochrome P450 (CYP) forms can be ranked (lowest to highest). The CYP form with the lowest in vitro K_i is evaluated first clinically, employing a suitable probe drug like midazolam (CYP3A4), theophylline (CYP1A2), (S)-warfarin (CYP2C9) and desipramine (CYP2D6), and the NCE is classified as a “none”, “weak”, “moderate”, or “strong” inhibitor. In turn, the classification governs the next steps. A two stage strategy, in vitro ranking followed by classification, has the potential to enable decision making within an industrial and regulatory setting. With additional refinement and validation, the approach could be applied to mechanism-based inhibitors, inducers and substrates of CYPs also.

[Back to top]
Drug Confinement and Delivery in Ceramic Implants
M. Vallet-Regí, F. Balas, M. Colilla and M. Manzano

[Full Text Article]

Ordered silica-based mesoporous materials could be specially designed and chemically modified for the adsorption of drugs that would be locally released. The drug adsorption and release kinetics are controlled by several factors such as pore size, volume, architecture and chemistry of the silica walls.

[Back to top]
Application of Pharmacogenomics in Drug Discovery and Development: Correlations Between Transcriptional Modulation and Preclinical Safety Observations
L.G. Yengi, Q. Xiang, L. Shen, A. Chandrasekaran, J. Kao and J. Scatina

[Full Text Article]

An integrated systems biology approach of measuring mRNA, protein and enzyme activity, was used to determine the molecular mechanisms responsible for reductions in thyroid hormone levels observed in rats given 1000 mg/kg/day of a nonsteroidal progesterone agonist (NSP). The effect of NSP on drug metabolizing enzyme (DME) expression was determined in livers from treated and vehicle control rats. In treated males, CYP1A1, CYP2B1, CYP2B2, CYP2C12, CYP3A1 and UGT1A mRNAs increased by 2.2, 31.0, 9.4, 13.0, 6.4 and 2.3 fold, while CYP2C11 and CYP3A2 levels decreased by 4.8 and 15.0 fold respectively. CYP1A, CYP2B and UGT1A enzyme activities increased by 2.9, 6.2 and 1.4 fold while CYP2C and CYP3A activities decreased by 2.2 and 1.8 fold respectively. CYP2B and CYP2C proteins increased by 2.1 and 1.3 fold but CYP2C11, the male-specific isozyme, and CYP3A protein decreased by 2.0 and 1.4 fold respectively. In treated females, CYP1A, CYP2B, CYP2C, CYP3A and UGT activities increased by 1.9, 12.0, 23.0, 13.0 and 2.2 fold respectively; with corresponding increases in mRNA ranging from 1.5 to 783 fold. CYP2B, CYP2C and CYP3A proteins increased by 3.6, 2.2 and 6.4 fold respectively, but CYP2C11 remained unchanged. These data suggest that NSP modulates the transcriptional regulation DME in rats and could account for the observed reductions in thyroid hormones, since UGT conjugation is the main pathway of thyroid hormone elimination in rats. These data also show gender and isozyme-specific regulation of some genes, thus demonstrating the value of an integrated approach in determining the contribution of individual genes in drug safety and metabolism observations.

[Back to top]
A Role for Lysosomal Phospholipase A2 in Drug Induced Phospholipidosis
A. Abe, M. Hiraoka and J.A. Shayman

[Full Text Article]

Many therapeutic drugs currently in use are cationic amphiphiles. These cationic amphiphilic drugs (CADs) induce phospholipidosis in humans and experimental animals. The recent study shows that CAD-induced cellular phospholipidosis is linked to the impairment of phospholipid catabolism by inhibition of lysosomal phospholipase A2 activity.

[Back to top]
Folate Nutrigenetics: A Convergence of Dietary Folate Metabolism, Folic Acid Supplementation, and Folate Antagonist Pharmacogenetics Pp. 55-60
B. Meshkin and K. Blum

[Full Text Article]

Folate (Vitamin B9, Folic acid, folinic acid, folacin, pteroyglutamic acid) is essential for life-sustaining processes of DNA synthesis, replication, and repair which are naturally present in common foods such as peas, oranges, broccoli, and whole-wheat products. Folate levels have been associated with birth defects, cardiovascular disease, and many other important healthcare issues, which has resulted in government-mandated food fortification to deliver minimum levels of intake. Despite this one-size-fits-all recommendation by governmental regulatory bodies, studies suggest that a genetic predisposition may exist within as much as 67% (combining both the CT and TT alleles) of the population that causes a metabolic folate deficiency. Thus, genetic factors may play an important role in folate levels and metabolism. A substantial body of scientific evidence supports the importance of folate, genes associated with folate, genes associated with anti-folate therapeutics, and thereby a convergence in nutritional genetics or nutrigenetics. This review will comment on the substantial body of scientific evidence demonstrating the relevance for nutrigenetic measurements to guide dietary folate intake and nutritional supplementation with folic acid.

[Back to top]
A Unique Example of Drug Metabolism: Tetra- and Penta Oxygenation Reactions of Capravirine in Rats, Dogs and Humans
H.-Z. Bu, W.F. Pool, E.Y. Wu and B.V. Shetty

[Full Text Article]

Six tetra- and two penta-oxygenated capravirine metabolites observed in rats, dogs and humans represent the maximum numbers of isomers that can be predicted since oxygenations are restricted at the pyridinyl nitrogen (N-oxidation), sulfur (sulfoxidation), and isopropyl group (hydroxylation), exemplifying a unique case that is very unusual for sequential drug metabolism.

[Back to top]
Metabolic Stability Screen for Drug Discovery Using Cassette Analysis and Column Switching
J.S. Halladay, S. Wong, S.M. Jaffer, A.K. Sinhababu and S.C. Khojasteh-Bakht

[Full Text Article]

In vitro metabolic stability assays are used to screen compounds for stability in the presence of various drug metabolizing enzymes, usually cytochrome P450 in liver preparations (e.g., liver microsomes). High-throughput metabolic stability assays using pooling methods have been developed to keep pace with screening requirements at the lead ADME optimization stage. In our laboratory, we have improved the metabolic stability assay using the cassette analysis method, column switching, and incorporated time saving techniques in method development to yield a robust method which reduces data turnaround time, increases compound throughput, and maximizes mass spectrometer usage. This method can determine metabolic stability using microsomes or hepatocytes from any species. We describe our findings following incubation of 40 different compounds with human liver microsomes and analysis by the cassette and discrete analysis methods. Similar metabolic stability results were obtained using the cassette analysis and discrete analysis method. An overall 70% time savings was achieved by pooling four new compounds into one sample for method development/MS optimization, cassetting four samples into one sample to minimize the number of injections on LC/MS/MS analysis, and using a column switching system to analyze the samples, which results in a two-fold decrease in the LC/MS/MS analysis time.

[Back to top]
Structures of Various Cytochromes c Evaluated from the Redox Behaviors Using the Optically Active Co(III) Complex-Modified Au Electrode
I. Takahashi, C. Nishijima, T. Inomata, Y. Funahashi, T. Ozawa and H. Masuda

[Full Text Article]

Electrochemical studies of three c-type cytochromes (cyt c from horse heart, cyt c₂ from Rhodospirillum rubrum, and cyt c₅₅₃ from Alcaligenes xylosoxidans GIFU 1051) were performed by using the optically active Co^lll complex-modified Au electrode. Three cytochromes gave different redox behaviors reflected from the respective structural information. From relationship between their redox behaviors and their structural characteristics, we evaluated the solution structure around heme center of cyt c₅₅₃.

[Back to top]
Effects of Propofol Analogs on Glucuronidation of Propofol, an Anesthetic Drug, by Human Liver Microsomes
M. Shimizu, Y. Matsumoto and H. Yamazaki

[Full Text Article]

To prevent rapid forming O-glucuronide of propofol (2,6-diisopropylphenol), an intravenous anesthetic, effects of propofol analogs were investigated. Propofol was predominately glucuronidated by human UGT1A9 and intestinal or liver microsomes. 2,5-Diisopropylphenol inhibited the propofol glucuronidation. A possibility of developing orally administrable agents or of reducing propofol dose by coadministration is suggested.

[Back to top]
Drug Interactions of Tipranavir, a New HIV Protease Inhibitor
J. Morello, S. Rodriguez-Novoa, I. Jimenez-Nacher and V. Soriano

[Full Text Article]

Tipranavir is one of the latest approved HIV protease inhibitors. This non-peptidic molecule is an strong inducer of cytochrome P450 and has to be co-administered with low doses ritonavir as pharmacokinetic booster to achieve effective antiviral activity in vivo. As expected, significant drug interactions may occur in patients treated with tipranavir/ritonavir, including diminished exposure to some antiretroviral agents. Although a few interactions can be managed with adequate drug dosing others preclude to use these medications in combination.