The pharmacokinetic modelling of GI198745 (dutasteride), a compound with parallel linear and nonlinear elimination.
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AIMS: To characterize the pharmacokinetics of the dual 5alpha-reductase inhibitor GI198745 (dutasteride) to allow for more accurate predictions of GI198745 concentrations after different dosing schedules. METHODS: In this randomized, single-blind, parallel group study, 32 healthy male volunteers received single oral doses of GI198745 ranging from 0.01 to 40 mg. Data were analysed by nonlinear mixed effects modelling using NONMEM where both linear and nonlinear pharmacokinetic models were examined. RESULTS: The time course of GI198745 serum concentrations indicated concentration dependent elimination, with the apparent half-life increasing with dose. Data were best described by a two-compartment model with first order absorption and parallel linear and nonlinear elimination pathways. Drug absorption was rapid, and was followed by a short distribution phase. A high volume of distribution (511 l) and a low linear clearance (0.58 l h(-1)) combined to give a half-life of up to 5 (1-7) weeks at high concentrations. As concentrations declined towards Km (0.96 ng ml(-1)), the proportion eliminated by the relatively rapid saturable elimination pathway, with a maximum clearance of 6.2 l h(-1), increased and the half-life reduced to about 3 days. The estimated inter individual variability for the linear clearance was high (CV = 70%). CONCLUSIONS: G1198745 pharmacokinetics are well described by a pharmacokinetic model with parallel linear and nonlinear elimination. Simulations using this model show that at daily doses of 0.1 mg the steady state drug concentrations, and the rate at which these are achieved, are mainly influenced by the nonlinear pathway, while at daily doses above 1 mg they are almost entirely influenced by the linear pathway. (+info)
Evaluation and characterization of micronuclei induced by the antitumour agent ASE [3beta-hydroxy-13alpha-amino-13, 17-seco-5alpha-androstan-17-oic-13, 17-lactam-p-bis(2-chloroethyl)amino phenylacetate] in human lymphocyte cultures.
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3beta - Hydroxy - 13alpha - amino - 13, 17 - seco - 5alpha - androstan - 17 -oic-13,17-lactam-p-bis(2-chloroethyl)amino phenylacetate (ASE) is a homo-aza-steroidal ester of p-bis(2-chloroethyl) amino phenyl acetic acid and has been shown to display antineoplastic, mutagenic and genotoxic activity. In the present study an effort has been made to evaluate the ability of ASE to induce micronuclei (MN) in human lymphocytes treated in vitro using the cytokinesis-block assay. Lympocytes were treated with different concentrations of ASE (0.1, 0.25, 0.5, 1, 2.5, 5, 10 and 20 microg/ml) at two different cell culture times, 21 and 41 h after culture initiation. ASE treatment lasted until cell harvest, for 51 and 31 h, respectively. Two types of cultures were used, whole blood and isolated lymphocyte cultures. The content of induced MN was identified by FISH analysis, using an alpha-satellite DNA probe, in binucleate cells. Our results suggest that ASE is capable of increasing MN frequencies in human lymphocytes under both culture conditions. This increase is related to the concentration in a linear dose-dependent manner and is also dependent on the duration of treatment. FISH analysis has shown that the induced MN resulted mainly from breakage events. Additionally, a weak aneugenic effect was found at the higher concentrations in whole blood cultures as well as in isolated lymphocyte cultures. Cytotoxic effects of ASE were observed under both cell culture conditions with a linear dose-dependent relationship according to CBPI evaluation and were more pronounced in isolated lymphocyte cultures. (+info)
Linear relationships between the ligand binding energy and the activation energy of time-dependent inhibition of steroid 5alpha-reductase by delta 1-4-azasteroids.
(3/97)
The inhibition of steroid 5alpha-reductase (5AR) by Delta(1)-4-azasteroids is characterized by a two-step time-dependent kinetic mechanism where inhibitor combines with enzyme in a fast equilibrium, defined by the inhibition constant K(i), to form an initial reversible enzyme-inhibitor complex, which subsequently undergoes a time-dependent chemical rearrangement, defined by the rate constant k(3), leading to the formation of an apparently irreversible, tight-binding enzyme-inhibitor complex (Tian, G., Mook, R. A., Jr., Moss, M. L., and Frye, S. V. (1995) Biochemistry 34, 13453-13459). A detailed kinetic analysis of this process with a series of Delta(1)-4-azasteroids having different C-17 substituents was performed to understand the relationships between the rate of time-dependent inhibition and the affinity of the time-dependent inhibitors for the enzyme. A linear correlation was observed between ln(1/K(i)), which is proportional to the ligand binding energy for the formation of the enzyme-inhibitor complex, and ln(1/(k(3)/K(i))), which is proportional to the activation energy for the inhibition reaction under the second order reaction condition, which leads to the formation of the irreversible, tight-binding enzyme-inhibitor complex. The coefficient of the correlation was -0.88 +/- 0.07 for type 1 5AR and -1.0 +/- 0.2 for type 2 5AR. In comparison, there was no obvious correlation between ln(1/K(i)) and ln(1/k(3)), which is proportional to the activation energy of the second, time-dependent step of the inhibition reaction. These data are consistent with a model where ligand binding energies provided at C-17 of Delta(1)-4-azasteroids is fully expressed to lower the activation energy of k(3)/K(i) with little perturbation of the energy barrier of the second, time-dependent step. (+info)
Mass spectral fragmentation reactions of a therapeutic 4-azasteroid and related compounds.
(4/97)
Mass spectra were acquired for a therapeutic 4-azasteroid (dutasteride), and some related compounds, using various ionization conditions (EI, CI, APCI and ESI) in both positive and negative ion modes. The ionization and fragmentation behavior of the compound dutasteride, its precursors and several analogs is reported. Positive atmospheric pressure chemical ionization (APCI+) and positive electrospray ionization (ESI+) produced distinctive collision-induced dissociation (CID) spectra for the respective [MH]+ ions of dutasteride. The spectral differences are attributed to ion populations having either different structures or different internal energy distributions (as a consequence of the method of ionization). Irrespective of their origin, the protonated molecules undergo interesting fragmentation reactions when collisionally activated. The identity of the major fragmentation products was confirmed by accurate mass measurement. The negative APCI mass spectrum of dutasteride displays extensive dehydrohalogenation, apparently due to the thermal component of the APCI process. Some of the resulting radical anions display remarkable stability toward collisional decomposition. Details of the fragmentation behavior for the negative ion species and their relationship to the positive ion results are discussed. (+info)
Proteomic changes during disturbance of cholesterol metabolism by azacoprostane treatment in Caenorhabditis elegans.
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Although nematodes like Caenorhabditis elegans are incapable of de novo cholesterol biosynthesis, they can utilize nonfunctional sterols by converting them into cholesterol and other sterols for cellular function. The results reported previously and presented here suggest that blocking of sterol conversion to cholesterol in C. elegans by 25-azacoprostane-HCl (azacoprostane) treatment causes a serious defect in germ cell development, growth, cuticle development, and motility behavior. To establish a biochemical basis for these physiological abnormalities, we performed proteomic analysis of mixed stage worms that had been treated with the drug. Our results from a differential display proteomic analysis revealed significant decreases in the levels of proteins involved in collagen and cytoskeleton organization such as protein disulfide isomerase (6.7-fold), beta-tubulin (5.41-fold), and NEX-1 protein (>30-fold). Also reduced were enzymes involved in energy production such as phosphoglycerate kinase (4.8-fold) and phosphoenolpyruvate carboxykinase (8.5-fold), a target for antifilarial drugs such as azacoprostane. In particular, reductions in the expression of lipoprotein families such as vitellogenin-2 (7.7-fold) and vitellogenin-6 (5.4-fold) were prominent in the drug-treated worms, indicating that sterol metabolism disturbance caused by azacoprostane treatment is tightly coupled with suppression of the lipid transfer-related proteins at the protein level. However, competitive quantitative reverse transcriptase polymerase chain reaction showed that the transcriptional levels of vit-2, vit-6, and their receptors (e.g. rme-2 and lrp-1) in drug-treated worms were 3- to 5-fold higher than those in the untreated group, suggesting a presence of a sterol regulatory element-binding protein (SREBP)-like pathway in these genes. In fact, multiple predicted sterol regulatory elements or related regulatory sequences responding to sterols were found to be located at the 5'-flanking regions in vit-2 and lrp-1 genes, and their transcriptional activities fluctuated highly in response to changes in sterol concentration. Thus, many physiological abnormalities caused by azacoprostane-mediated sterol metabolism disturbance appear to be exerted at least in part through SREBP pathway in C. elegans. (+info)
Four-amino acid segment in steroid 5 alpha-reductase 1 confers sensitivity to finasteride, a competitive inhibitor.
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The 4-azasteroid 17 beta-(N-t-butyl)carbamoyl-4-aza-5 alpha-androst-1-en-3-one (finasteride) is 100-fold more potent as a competitive inhibitor of the rat NADPH:delta 4-3-oxosteroid-5-alpha- oxidoreductase (steroid 5 alpha-reductase) type 1 enzyme (Ki = 3-5 nM) than of the human type 1 enzyme (Ki greater than or equal to 300 nM). In this study, we exploit this differential sensitivity to map a major determinant of finasteride sensitivity in steroid 5 alpha-reductase. Chimeric steroid 5 alpha-reductase cDNAs composed of different combinations of rat and human exon sequences were created by genetic engineering, expressed in human embryonic kidney 293 cells, and assayed for their sensitivity to finasteride. Hybrid proteins containing sequences encoded by rat exon 1 were found to be as sensitive to finasteride as the parental enzyme. The exchange of progressively smaller protein segments encoded within exon 1 identified a tetrapeptide sequence (Val-Ser-Ile-Val) in the rat enzyme that conferred sensitivity to finasteride. The analogous sequence in the human enzyme (Ala-Val-Phe-Ala) conferred partial resistance to the drug. Finasteride was a competitive inhibitor of the native and all chimeric enzymes tested, suggesting that the tetrapeptide segments form a portion of the substrate-binding domain of steroid 5 alpha-reductase. (+info)
Laboratory monitoring of androgenic activity in benign prostate hypertrophy treated with a 5 alpha-reductase inhibitor.
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Testosterone and androstenedione are metabolized by 5 alpha- and 5 beta-reductases to androsterone (A) and etiocholanolone (E), respectively. These are excreted in the urine as conjugates, and the A/E ratio in normal men is usually greater than or equal to 1.5 (as opposed to 1 in women) because of the high 5 alpha-reductase activity in the prostate. The A/E ratio can be determined simply by gas chromatography after acid hydrolysis of a urine sample, extraction of steroids, and formation of trimethylsilyl derivatives. A timed collection of urine is unnecessary because the ratio of A/E is used rather than absolute values. In men suffering from benign prostate hypertrophy who are treated with Finasteride (a 5 alpha-reductase inhibitor), the A/E ratio decreases to less than 0.5. The A/E ratio decrease can be detected long before there is clinical improvement. (+info)
The effect of finasteride in men with benign prostatic hyperplasia. The Finasteride Study Group.
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BACKGROUND: Benign prostatic hyperplasia is a progressive, androgen-dependent disease resulting in enlargement of the prostate gland and urinary obstruction. Preventing the conversion of testosterone to its tissue-active form, dihydrotestosterone, by inhibiting the enzyme 5 alpha-reductase could decrease the action of androgens in their target tissues; in the prostate the result might be a decrease in prostatic hyperplasia and therefore in symptoms of urinary obstruction. METHODS: In a double-blind study, we evaluated the effect of two doses of finasteride (1 mg and 5 mg) and placebo, each given once daily for 12 months, in 895 men with prostatic hyperplasia. Urinary symptoms, urinary flow, prostatic volume, and serum concentrations of dihydrotestosterone and prostate-specific antigen were determined periodically during the treatment period. RESULTS: As compared with the men in the placebo group, the men treated with 5 mg of finasteride per day had a significant decrease in total urinary-symptom scores (P less than 0.001), an increase of 1.6 ml per second (22 percent, P less than 0.001) in the maximal urinary-flow rate, and a 19 percent decrease in prostatic volume (P less than 0.001). The men treated with 1 mg of finasteride per day did not have a significant decrease in total urinary-symptom scores, but had an increase of 1.4 ml per second (23 percent) in the maximal urinary-flow rate, and an 18 percent decrease in prostatic volume. The men given placebo had no changes in total urinary-symptom scores, an increase of 0.2 ml per second (8 percent) in the maximal urinary-flow rate, and a 3 percent decrease in prostatic volume. The frequency of adverse effects in the three groups was similar, except for a higher incidence of decreased libido, impotence, and ejaculatory disorders in the finasteride-treated groups. CONCLUSIONS: The treatment of benign prostatic hyperplasia with 5 mg of finasteride per day results in a significant decrease in symptoms of obstruction, an increase in urinary flow, and a decrease in prostatic volume, but at a slightly increased risk of sexual dysfunction. (+info)