Formation Of Active Metabolite Research Articles

The reversible P2Y antagonist cangrelor influences the ability of the active metabolites of clopidogrel and prasugrel to produce irreversible inhibition of platelet function.

Agents that act as antagonists at P2Y(12) ADP receptors on platelets are in use (clopidogrel), and in development for use (cangrelor and prasugrel), in patients with cardiovascular disease. Cangrelor is a direct-acting reversible antagonist being developed for short-term infusion; clopidogrel and prasugrel are oral prodrugs that provide irreversible inhibition via transient formation of active metabolites. At the cessation of cangrelor infusion, patients are likely to receive clopidogrel or prasugrel as a means of maintaining antiplatelet therapy. To apply an experimental in vitro approach to investigate the possibility that cangrelor influences the ability of the active metabolites of clopidogrel and prasugrel to inhibit ADP-mediated platelet function. The effects of cangrelor and the active metabolites of clopidogrel (C-AM) and prasugrel (P-AM) on platelet function were assessed by ADP-induced platelet P-selectin expression in whole blood. The method involved rapid removal of the antagonists by dilution, and measurement of residual platelet inhibition. Cangrelor, C-AM and P-AM markedly inhibited P-selectin expression. The effect of cangrelor, but not of C-AM and P-AM, was reversible following antagonist removal. Preincubation of blood with cangrelor prior to addition of C-AM or P-AM reduced the ability of metabolites to irreversibly antagonize P2Y(12). Irreversible inhibition was maintained when blood was preincubated with metabolites prior to cangrelor. Cangrelor influences the ability of the active metabolites of clopidogrel or prasugrel to inhibit platelet function irreversibly. Careful consideration should be given to the timing of administration of an oral P2Y(12) antagonist following cangrelor infusion.

The cytostatic activity of pyrimidine nucleosides is strongly modulated by Mycoplasma hyorhinis infection: Implications for cancer therapy

Nucleoside analogues are widely used as chemotherapeutic agents in the treatment of cancer. Several cancers are reported to be associated with mycoplasmas (i.e. Mycoplasma hyorhinis), which contain a number of nucleoside-metabolizing enzymes. Pyrimidine nucleoside analogues, such as 5-fluoro-2′-deoxyuridine (FdUrd), 5-trifluorothymidine (TFT) and 5-halogenated 2′-deoxyuridines can be degraded by thymidine phosphorylase (TP) to their inactive bases. We found in M. hyorhinis-infected MCF-7 breast carcinoma cells (MCF-7/HYOR) a mycoplasma-encoded TP that dramatically (20–150-fold) reduces the cytostatic activity of these compounds. The reduction in cytostatic activity could be fully restored in the presence of TPI (5-chloro-6-[1-(2-iminopyrrolidinyl)methyl]uracil hydrochloride), a known inhibitor of human TP. This observation is in agreement with the markedly decreased formation of active metabolite (i.e. FdUMP for FdUrd) or diminished drug incorporation into nucleic acids (i.e. for TFT and 5-bromo-2′-deoxyuridine) in MCF-7/HYOR cells compared with uninfected MCF-7 cells. Antimetabolite formation is fully restored in the presence of TPI. In contrast, 5-fluoro-5′-deoxyuridine (5′DFUR), an intermediate metabolite of capecitabine, was markedly more cytostatic in MCF-7/HYOR cells than in uninfected cells, due to the activation of this prodrug by the mycoplasma-encoded TP. Thus, our data reveal that M. hyorhinis expresses a TP that activates 5′DFUR but inactivates FdUrd, TFT and 5-halogenated 2′-deoxyuridines, and that is highly sensitive to the inhibitory effect of the TP inhibitor TPI. Given the association of M. hyorhinis with several human cancers, our findings suggest that pyrimidine nucleoside-based but not 5FU-based anti-cancer therapy might be more effective when combined with a mycoplasmal TP inhibitor.

Disposition and Antimuscarinic Effects of the Urinary Bladder Spasmolytics Propiverine: Influence of Dosage Forms and Circadian-Time Rhythms

Propiverine extended release is expected to be better tolerated compared to immediate release tablets because of slower drug release and reduced formation of active metabolites in the colon. CYP3A4 and ABCC2, the major variables in pharmacokinetics of propiverine, are less expressed in the colon. Therefore, disposition and pharmacodynamics of propiverine were measured in a double-blind, double-dummy, crossover study with administration of 15 mg immediate release 3 times daily for 7 days compared to 45 mg extended release once daily for 7 days in 24 healthy subjects. Twelve subjects also received 15 mg propiverine intravenously. Serum and urine propiverine levels were measured repeatedly following oral administration on day 7 for up to 72 hours and correlated to duodenal expression of CYP3A4, ABCB1, and ABCC2. Propiverine immediate release 3 times daily was not different to extended release once daily in areas under the serum concentration-time curve (0-24 hours) and peak-trough fluctuation. The areas under the serum concentration-time curve of propiverine immediate release was circadian-time-dependent, with the lowest values during the night. Disposition of intravenous propiverine and propiverine immediate release administered in the night was influenced by intestinal expression of ABCC2. We concluded that oral absorption of propiverine is site-dependent and influenced by dosage form and circadian-time-dependent elimination processes.

Approaching an age of reason with antiplatelet therapy

The antiplatelet drug prasugrel is one of a new generation of thienopyridines, drugs that inhibit the platelet P2Y12 receptor. With its increased active metabolite formation, prasugrel provides more rapid and consistent platelet inhibition than does clopidogrel.1,2 The recently published TRITON–TIMI 38 trial was the first large-scale study to assess prasugrel in patients with acute coronary syndromes undergoing percutaneous coronary intervention. The trial established that the number of ischaemic events could be reduced by increasing the potency of platelet inhibition.

Screening of synthetic and plant-derived compounds for (anti)estrogenic and (anti)androgenic activities

Recently we constructed yeast cells that either express the human estrogen receptor alpha or the human androgen receptor in combination with a consensus ERE or ARE repeat in the promoter region of a green fluorescent protein (yEGFP) read-out system. These bioassays were proven to be highly specific for their cognate agonistic compounds. In this study the value of these yeast bioassays was assessed for analysis of compounds with antagonistic properties. Several pure antagonists, selective estrogen receptor modulators (SERMs) and plant-derived compounds were tested. The pure antiestrogens ICI 182,780 and RU 58668 were also classified as pure ER antagonists in the yeast estrogen bioassay and the pure antiandrogen flutamide was also a pure AR antagonist in the yeast androgen bioassay. The plant-derived compounds flavone and guggulsterone displayed both antiestrogenic and antiandrogenic activities, while 3,3'-diindolylmethane (DIM) and equol combined an estrogenic mode of action with an antiandrogenic activity. Indol-3-carbinol (I3C) only showed an antiandrogenic activity. Coumestrol, genistein, naringenin and 8-prenylnaringenin were estrogenic and acted additively, while the plant sterols failed to show any effect. Although hormonally inactive, in vitro and in vivo metabolism of the aforementioned plant sterols may still lead to the formation of active metabolites in other test systems.

Increased Active Metabolite Formation Explains the Greater Platelet Inhibition With Prasugrel Compared to High-dose Clopidogrel

Prasugrel pharmacodynamics and pharmacokinetics after a 60-mg loading dose (LD) and daily 10-mg maintenance doses (MD) were compared in a 3-way crossover study to clopidogrel 600-mg/75-mg and 300-mg/75-mg LD/MD in 41 healthy, aspirin-free subjects. Each LD was followed by 7 days of daily MD and a 14-day washout period. Inhibition of platelet aggregation (IPA) was assessed by turbidometric aggregometry (20 and 5 microM ADP). Prasugrel 60-mg achieved higher mean IPA (54%) 30 minutes post-LD than clopidogrel 300-mg (3%) or 600-mg (6%) (P < 0.001) and greater IPA by 1 hour (82%) and 2 hours (91%) than the 6-hour IPA for clopidogrel 300-mg (51%) or 600-mg (69%) (P < 0.01). During MD, IPA for prasugrel 10-mg (78%) exceeded that of clopidogrel (300-mg/75-mg, 56%; 600-mg/75-mg, 52%; P < 0.001). Active metabolite area under the concentration-time curve (AUC0-tlast) after prasugrel 60-mg (594 ng.hr/mL) was 2.2 times that after clopidogrel 600-mg. Prasugrel active metabolite AUC0-tlast was consistent with dose-proportionality from 10-mg to 60-mg, while clopidogrel active metabolite AUC0-tlast exhibited saturable absorption and/or metabolism. In conclusion, greater exposure to prasugrel's active metabolite results in faster onset, higher levels, and less variability of platelet inhibition compared with high-dose clopidogrel in healthy subjects.

What is the true risk of a pharmacokinetic drug–drug interaction?

Reports on pharmacokinetic drug–drug interaction studies account for a major fraction of manuscripts in clinical pharmacology journals; this issue of European Journal of Clinical Pharmacology contains three of them [1–3]. Most of the published reports are positive, i.e. they show some degree of change in the pharmacokinetics of drug A when drug B is co-administered. A standard conclusion of such results is that great care should be applied if the two drugs are given concomitantly. In contrast, many patients take five or more different drugs every day [4], often because there is a clear therapeutic indication for each of them, and nobody really cares about interactions as such, but rather a general clinical monitoring of adverse events and therapeutic effects is done. Indeed, this turns out to be sufficient for patient safety in most cases. However, if in clinical studies a pronounced pharmacokinetic interaction between two partners has been reported, such as the effect of gemfibrozil on cerivastatin [5] or that of mibefradil on CYP3A4 substrates [6], this is also often disregarded by clinicians, and these two cases even required market withdrawal of the drugs. How may we estimate true risk of a drug–drug interaction and identify those interactions that are clinically important in order to generate a signal which clinicians can rely on? Of course, the most reliable data would come from prospective, randomised, double-blind clinical trials using clinical endpoints, but this approach is not feasible for the multitude of potential interactions. We therefore rely on pharmacokinetics and/or on pharmacodynamics of drug A. This is justified because most interactions on the pharmacokinetic level will just change the intensity of the effect and will not qualitatively change therapy, although there may be exceptions in the case of an altered formation of active metabolites and/or a different tissue distribution. How much of a pharmacokinetic change should then be considered as relevant? The definition of bioequivalence, which is considered as the basis for interchangeability of two preparations, has been strictly formalized in respective guidelines [7–10] and usually requires that two preparations differ in mean area under curve (AUC) and Cmax values by not more than 0.8to 1.25-fold. Interchangeability is also the question in the case of pharmacokinetic drug–drug interactions: The clinician needs to know whether the concentrations and related effects of drug A are the same with and without concomitant administration of drug B, or whether some adjustment of the treatment or dosage is needed. Accordingly, it has been proposed to handle drug– drug interactions as an equivalence problem [11]. From a statistical point of view, this is very reasonable because it addresses power limitations and the validity of negative results, and there are also tools to assess interindividual variation in the degree of change (“individual bioavailability” methods) [8, 10]. In contrast to bioequivalence, however, the margins defining that a treatment with co-medication is not interchangeable to the treatment without co-medication are less clear. To be on the safe side, the same strict limits as applied for bioequivalence assessment have been proposed, and fulfilling the standard bioequivalence criteria usually means that a drug–drug interaction is not clinically relevant. However, even in regulatory guidelines, it is acknowledged that depending on the drug, different “no effect boundaries” may be appropriate [12, 13]. The criteria for the assessment of bioequivalence and of drug–drug interactions differ because Eur J Clin Pharmacol (2007) 63:897–899 DOI 10.1007/s00228-007-0357-6

Cytochrome P450 3A Inhibition by Ketoconazole Affects Prasugrel and Clopidogrel Pharmacokinetics and Pharmacodynamics Differently

Prasugrel and clopidogrel inhibit platelet aggregation through active metabolite formation. Prasugrel's active metabolite (R-138727) is formed primarily by cytochrome P450 (CYP) 3A and CYP2B6, with roles for CYP2C9 and CYP2C19. Clopidogrel's activation involves two sequential steps by CYP3A, CYP1A2, CYP2C9, CYP2C19, and/or CYP2B6. In a randomized crossover study, healthy subjects received a loading dose (LD) of prasugrel (60 mg) or clopidogrel (300 mg), followed by five daily maintenance doses (MDs) (15 and 75 mg, respectively) with or without the potent CYP3A inhibitor ketoconazole (400 mg/day). Subjects had a 2-week washout between periods. Ketoconazole decreased R-138727 and clopidogrel active metabolite Cmax (maximum plasma concentration) 34-61% after prasugrel and clopidogrel dosing. Ketoconazole did not affect R-138727 exposure or prasugrel's inhibition of platelet aggregation (IPA). Ketoconazole decreased clopidogrel's active metabolite AUC0-24 (area under the concentration-time curve to 24 h postdose) 22% (LD) to 29% (MD) and reduced IPA 28% (LD) to 33% (MD). We conclude that CYP3A4 and CYP3A5 inhibition by ketoconazole affects formation of clopidogrel's but not prasugrel's active metabolite. The decreased formation of clopidogrel's active metabolite is associated with reduced IPA.

Nabilone Effective in Treating Pain in Upper Motor Neuron Syndromes

The synthetic cannabinoid nabilone has good oral bioavailability and a long duration of action through the formation of active metabolites. In this study, researchers evaluated the potential of nabilone for treating spasticity-related pain in patients with a chronic upper motor neuron syndrome (UMNS), 7 with multiple sclerosis (MS). Of 13 patients enrolled, 11 completed a placebo-controlled, …

A comparison of prasugrel and clopidogrel loading doses on platelet function: magnitude of platelet inhibition is related to active metabolite formation

The aim of this study was to compare rate of onset, magnitude, and consistency of platelet inhibition after administration of prasugrel or clopidogrel and to relate platelet inhibition to systemic exposure to each active metabolite. Thienopyridines are prodrugs, metabolized in vivo to active metabolites that inhibit the platelet P2Y12 adenosine diphosphate (ADP) receptor. This was an open-label, 2-way, crossover study that randomized healthy subjects (n = 68) to an oral loading dose (LD) of prasugrel 60 mg or clopidogrel 300 mg. Platelet aggregation response to 5 and 20 micromol/L of ADP was measured by turbidometric aggregometry. Plasma concentrations of the active metabolites of prasugrel and clopidogrel were quantified by liquid chromatography with tandem mass spectrometry detection methods. Inhibition of platelet aggregation (IPA) after prasugrel was significantly higher (P < .01) than that after clopidogrel from 15 minutes through 24 hours (5 micromol/L ADP) and from 30 minutes through 24 hours (20 micromol/L ADP). For 20 micromol/L ADP, the median time to reach > or = 20% IPA was 30 minutes for prasugrel and 1.5 hours for clopidogrel (P < .001). The maximum IPA was 84.1% +/- 9.5% with prasugrel versus 48.9% +/- 27.0% with clopidogrel for 5 micromol/L ADP and 78.8% +/- 9.2% versus 35.0% +/- 24.5%, respectively, for 20 micromol/L ADP (P < .001). Response to prasugrel was more consistent compared to clopidogrel (P < .01). The lower IPA response to clopidogrel was associated with lower plasma concentrations of its active metabolite (P < .001). Prasugrel 60 mg LD results in more rapid, potent, and consistent inhibition of platelet function than clopidogrel 300 mg LD. Lower IPA responses to clopidogrel were associated with lower concentrations of its active metabolite.

Gemcitabine (G) plamsa and intracellular pharmacokinetics in E6201: Greater metabolite levels using fixed dosing rate (FDR) delivery

2024 Background: Gemcitabine (G) is an antimetabolite which requires activation by the rate-limiting enzyme dCK to its active metabolite, dFdCTP. FDR delivery of G at 10 mg/m2/minute may allow greater formation of active metabolite and improved activity. E6201 randomly assigned first line pancreatic cancer patients to three arms: A (G 1000 mg/m2 over 30 minutes), B FDR G (1500 mg/m2 over 150 minutes), and C GemOx (1000 mg/m2 over 100 minutes with oxaliplatin 100 mg/m2). Methods: Investigators from 18 centers contributed 23 sample sets on the first dose of G. Five time points over 4 hrs were sampled (baseline, mid infusion, end infusion, 1–2 post and 4 hrs). Plasma fractionation along with the PBMC purification and subsequent perchloric acid extraction were conducted locally with THU 1 mg (cytidine deaminase inhibitor). Samples were shipped overnight to the central lab where G and its metabolite dFdU were quantified from deproteinized plasma by reverse phase HPLC. dFdCTP was quantified by ion-exchange HPLC in neutralized PBMC extracts after removal of ribonucleotide triphosphates. Data were fit to nonlinear models (WinNonLin, v4.1) and comparisons amongst dosing groups employed the non-parametric, 2-sided Mann-Whitney test. Results: For Arms A, B and C the plasma AUCs were respectively (median ± SD): 4542 ± 2472 (N=9), 8603 ± 2608 (N=8) and 9130 ± 8788 (N=6) ng/ml x hr. The difference between group A and B (p=0.003) and A and C (p=0.05) were statistically different. Intracellular dFdCTP AUCs for groups A, B, and C were: 1862 ± 794 (N=8); 3725 ± 7763 (N=8) and 5024 ± 2113 (N=5) and significantly different for both A vs. B (p=0.05) and borderline significant for A vs C (p=0.065). The latter comparison is limited by a small number of samples. Conclusions: When studied in a multi-centered, randomized cooperative group setting, FDR delivery of G results in higher plasma AUC, and increased intracellular levels of active metabolite dFdCTP. These data support the concept that fixed dose rate delivery of G results in greater intracellular metabolite production at similar and equitoxic doses. Supported by ECOG NYU620HH04–00, NCI CA16087, CA2115, and from Eli Lilly. No significant financial relationships to disclose.

Blood–brain equilibration kinetics of levo‐α‐acetyl‐methadol using a chronically instrumented sheep preparation

1.--The delayed onset and long duration of action of the opioid agonist levo-alpha-acetyl-methadol (LAAM) has been attributed to the formation of active metabolites. However, at present, little is known about the time course of blood-brain equilibration of LAAM itself. 2.--The cerebral kinetics of LAAM were quantified using physiologically based kinetic models and a conscious chronically instrumented sheep preparation. Seven sheep were administered 4 min intravenous infusions of 30 mg LAAM. Concentrations of LAAM and N-demethylated metabolites (nor-LAAM and di-nor-LAAM) in whole blood (0-75 min) were measured using a validated HPLC assay. 3.--LAAM did not alter cerebral blood flow, mean arterial pressure or cause significant respiratory depression. Cardiac output was similar to baseline at 4 min, but decreased by 30% at 10 min and remained at this level for the duration of the 75 min study period. 4.--Cerebral kinetics were best described by a membrane-limited model, with a relatively slow blood-brain tissue equilibration half-life of 22 min due to intermediate permeability (56 ml min(-1)) and a large cerebral distribution volume (724 ml). 5.--In conclusion, pharmacokinetic-pharmacodynamic modelling of LAAM should account for the large equilibration delay between brain and blood caused by slow equilibration kinetics. This may account for some of the delay in onset of effect previously attributed to the delayed appearance of active metabolites in blood.

Association of genetic variation in tamoxifen-metabolizing enzymes with overall survival and recurrence of disease in breast cancer patients

Tamoxifen has been a mainstay of adjuvant therapy for breast cancer for many years. We sought to determine if genetic variability in the tamoxifen metabolic pathway influenced overall survival in breast cancer patients treated with tamoxifen. We examined functional polymorphisms in CYP2D6, the P450 catalyzing the formation of active tamoxifen metabolites, and UGT2B15, a Phase II enzyme facilitating the elimination of active metabolite in a retrospective study of breast cancer patients. We also examined whether the combination of variant alleles in SULT1A1 and UGT2B15 had more of an impact on overall survival in tamoxifen-treated patients than when the genes were examined separately. We conducted a retrospective study using archived paraffin blocks for DNA extraction and data from pathology reports and hospital tumor registry data for information on clinical characteristics, treatment, and outcomes (162 patients receiving tamoxifen and 175 who did not). Genotypes for CYP2D6 and UGT2B15 were obtained and Cox proportional hazards modeling was performed. After adjusting for age, race, stage of disease at diagnosis, and hormone receptor status, we found no significant association between CYP2D6 genotype and overall survival in either group of breast cancer patients. Tamoxifen-treated patients with UGT2B15 high activity genotypes had increased risk of recurrence and poorer survival. When UGT2B15 and SULT1A1 'at-risk' alleles were combined, women with two variant alleles had significantly greater risk of recurrence and poorer survival than those with common alleles. These studies indicate that genetic variation in Phase II conjugating enzymes can influence the efficacy of tamoxifen therapy for breast cancer.

Determinants of trifluorothymidine sensitivity and metabolism in colon and lung cancer cells

Trifluorothymidine (TFT) is a fluorinated thymidine analog that after conversion to its monophosphate derivative can inhibit thymidylate synthase (TS) and be incorporated into DNA. TFT is a good substrate for thymidine phosphorylase (TP), and the combination of TFT and a TP inhibitor (TPI), called TAS-102, has been developed to enhance the bioavailability of TFT in vivo, and is currently being studied in a phase I study. We aimed to determine the limiting factor(s) in the cytotoxicity of TFT with or without TPI to cancer cells. Colon cancer and lung cancer cell lines with either an overexpression or deficiency of one of the enzymes involved in TFT metabolism were used to study the effect of TPI on TFT sensitivity and the role of TS inhibition. The synthesis of radioactive TFT metabolites was studied using thin-layer chromatography together with the incorporation of TFT into DNA. We found that despite a high rate of TFT phosphorolysis, cells with high TP expression are not more resistant to TFT, while TPI did not increase TFT sensitivity. High TS-expressing cells were shown to be cross-resistant to a 72-h exposure to TFT compared to 5-fluorouracil (5-FU), although this was more pronounced at a 4-h exposure (3.4-fold or more for TFT and 1.4-fold or more for 5-FU). Despite a moderate inhibition of TS activity in cells expressing high TS, these cells were more sensitive to TFT than 5-FU (3.8-fold or more). Only in Colo320TP1 cells expressing high TP, inhibition of TFT phosphorolysis by TPI increased formation of active TFT metabolites 1.8-fold, although this was not related to an increase in TFT incorporation into DNA. These studies show that uptake of TFT and subsequent phosphorylation of TFT by cancer cells is very rapid. Despite a high rate of degradation, the activation pathways are still saturated and sufficient to inhibit TS and enable incorporation into DNA, although the contribution of each effect is exposure time dependent.

Drugs and human memory (part 2). Clinical, theoretical, and methodologic issues.

Drugs and human memory (part 2). Clinical, theoretical, and methodologic issues.

Modulation of native TREK-1 and Kv1.4 K+ channels by polyunsaturated fatty acids and lysophospholipids.

The modulation of TREK-1 leak and Kv1.4 voltage-gated K+ channels by fatty acids and lysophospholipids was studied in bovine adrenal zona fasciculata (AZF) cells. In whole-cell patch-clamp recordings, arachidonic acid (AA) (1-20 microM) dramatically and reversibly increased the activity of bTREK-1, while inhibiting bKv1.4 current by mechanisms that occurred with distinctly different kinetics. bTREK-1 was also activated by the polyunsaturated cis fatty acid linoleic acid but not by the trans polyunsaturated fatty acid linolelaidic acid or saturated fatty acids. Eicosatetraynoic acid (ETYA), which blocks formation of active AA metabolites, failed to inhibit AA activation of bTREK-1, indicating that AA acts directly. Compared to activation of bTREK-1, inhibition of bKv1.4 by AA was rapid and accompanied by a pronounced acceleration of inactivation kinetics. Cis polyunsaturated fatty acids were much more effective than trans or saturated fatty acids at inhibiting bKv1.4. ETYA also effectively inhibited bKv1.4, but less potently than AA. bTREK-1 current was markedly increased by lysophospholipids including lysophosphatidyl choline (LPC) and lysophosphatidyl inositol (LPI). At concentrations from 1-5 microM, LPC produced a rapid, transient increase in bTREK-1 that peaked within one minute and then rapidly desensitized. The transient lysophospholipid-induced increases in bTREK-1 did not require the presence of ATP or GTP in the pipette solution. These results indicate that the activity of native leak and voltage-gated K+ channels are directly modulated in reciprocal fashion by AA and other cis unsaturated fatty acids. They also show that lysophospholipids enhance bTREK-1, but with a strikingly different temporal pattern. The modulation of native K+ channels by these agents differs from their effects on the same channels expressed in heterologous cells, highlighting the critical importance of auxiliary subunits and signaling. Finally, these results reveal that AZF cells express thousands of bTREK-1 K+ channels that lie dormant until activated by metabolites including phospholipase A2 (PLA2)-generated fatty acids and lysophospholipids. These metabolites may alter the electrical and secretory properties of AZF cells by modulating bTREK-1 and bKv1.4 K+ channels.

Behavioral characterization of 2- O-desmethyl and 5- O-desmethyl metabolites of the phenylethylamine hallucinogen DOM

The present investigation was undertaken to test the hypothesis that known metabolites of the phenylethylamine hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) are pharmacologically active. This hypothesis was tested by evaluating the ability of racemic DOM metabolites 2- O-desmethyl DOM (2-DM-DOM) and 5- O-desmethyl DOM (5-DM-DOM) to substitute for the stimulus properties of (+)lysergic acid diethylamide (LSD). The data indicate that both metabolites are active in LSD-trained subjects and are significantly inhibited by the selective 5-HT 2A receptor antagonist M100907. Full generalization of LSD to both 2-DM-DOM and 5-DM-DOM occurred, and 5-DM-DOM was slightly more potent than 2-DM-DOM. Similarly, 5-DM-DOM had a slightly higher affinity than 2-DM-DOM for both 5-HT 2A and 5-HT 2C receptors. Additionally, it was of interest to determine if the formation of active metabolite(s) resulted in a temporal delay associated with maximal stimulus effects of DOM. We postulated that if metabolite formation resulted in the aforementioned delay, direct administration of the metabolites might result in maximally stable stimulus effects at an earlier pretreatment time. This hypothesis was tested by evaluating (1) the time point at which DOM produces the greatest degree of LSD-appropriate responding, (2) the involvement of 5-HT 2A receptor in the stimulus effects of DOM at various pretreatment times by administration of M100907 and (3) the ability of 2-DM-DOM and 5-DM-DOM to substitute for the stimulus properties of LSD using either 15- or 75-min pretreatment time. The data indicate that (a) the DOM stimulus produces the greatest degree of LSD-appropriate responding at the 75-min time point in comparison with earlier pretreatment times and (b) the stimulus effects of DOM are differentially antagonized by M100907 and this effect is a function of DOM pretreatment time prior to testing. Both 2-DM-DOM and 5-DM-DOM were found to be most active, at all doses tested, using a 75-min versus a 15-min pretreatment time. The present data do not permit unequivocal acceptance or rejection of the hypothesis that active metabolites of (−)-DOM provide a full explanation of the observed discrepancy between brain levels of (−)-DOM and maximal stimulus effects.

Anxiety levels and neurosteroid synthesis in the brains of prenatally stressed male rats.

This report presents studies of the effects of immobilization stress applied to pregnant female rats during the last third of pregnancy on anxiety levels and neurosteroid synthesis in brain structures of adult offspring. Neurosteroid synthesis was assessed in terms of changes in the activity of 5alpha-reductase, the enzyme which converts progesterone into active metabolites. Prenatal stress results in a significant decrease in the level of anxiety and an increase in movement activity among adult males. Stressed rats showed increases in progesterone-5alpha-reductase activity in the hypothalamus, hippocampus, and frontal cortex. These results provide evidence that changes in the behavior of adult male rats due to stress in the prenatal period of development may be due to the formation of active progesterone metabolites in the brain.

Use of high-performance liquid chromatographic and microbiological analyses for evaluating the presence or absence of active metabolites of the antifungal posaconazole in human plasma

Posaconazole (SCH 56592) is a novel broad spectrum triazole antifungal agent that is currently in phase III clinical trials for the treatment of systemic fungal infections. This study was initiated to determine if orally administered posaconazole to humans would result in the formation of active metabolite(s). Plasma samples from a multiple-rising dose study in healthy volunteers were analyzed by validated HPLC and microbiological methods. The HPLC analysis involved extraction with a mixture of organic solvent (methylene chloride–hexane) followed by separation on a C 18 column and quantification by UV absorbance at 262 nm. The microbiological assay was performed utilizing an agar diffusion method using Candida pseudotropicalis ATCC 46764 as the test organism. Potency was determined by comparing the growth inhibition zones produced by the test sample to those produced by standard concentrations prepared in plasma. Individual and mean plasma concentration–time profiles were similar for both HPLC and microbiological assays. The area under the plasma concentration–time curves of the microbiological and HPLC results were similar with a mean (RSD) ratio of 105.5% (5.3%), indicating that there was no relevant biologically active metabolite of posaconazole in human plasma.

Role of drug metabolism in drug discovery and development.

Metabolism by the host organism is one of the most important determinants of the pharmacokinetic profile of a drug. High metabolic lability usually leads to poor bioavailability and high clearance. Formation of active or toxic metabolites will have an impact on the pharmacological and toxicological outcomes. There is also potential for drug-drug interactions with coadministered drugs due to inhibition and/or induction of drug metabolism pathways. Hence, optimization of the metabolic liability and drug-drug interaction potential of the new chemical entities are some of the most important steps during the drug discovery process. The rate and site(s) of metabolism of new chemical entities by drug metabolizing enzymes are amenable to modulation by appropriate structural changes. Similarly, the potential for drug-drug interactions can also be minimized by appropriate structural modifications to the drug candidate. However, the optimization of the metabolic stability and drug-drug interaction potential during drug discovery stage has been largely by empirical methods and by trial and error. Recently, a lot of effort has been applied to develop predictive methods to aid the optimization process during drug discovery and development. This article reviews the role of drug metabolism in drug discovery and development.