Cutaneous in vivo metabolism of topical lidocaine formulation in human skin.

Little is known about the metabolising capacity of the human skin in relation to topically applied drugs and formulations. We chose lidocaine as a model compound since the metabolic pathways are well known from studies concerning hepatic metabolism following systemic drug administration. However, the enzymes involved are also expressed in the skin. Hence, the aim of the current study was to investigate the extent of the cutaneous in vivo metabolism of topically applied lidocaine in human volunteers. A dose of 5 mg/cm(2) of Xylocaine(R) (5% lidocaine) ointment was applied onto the buttock skin of the volunteers. After 2 h, residual formulation was removed, and two 4-mm punch biopsies were taken from each volunteer. The quantity of lidocaine extracted from the skin samples (epidermis + dermis) was 109 +/- 43 ng/mm(2) skin. One metabolite (monoethylglycine xylidide, MEGX) was detected in skin from 7 of the 9 volunteers. The quantity of MEGX formed, relative to the quantity of lidocaine in the skin, was not consistent and ranged from <0.8 to 12.8%. No other metabolites were detected.

Molecular evaluation of vitamin D3 receptor agonists designed for topical treatment of skin diseases.

MC903 (calcipotriol) is a synthetic, low calcemic analog of the nuclear hormone 1alpha,25-dihydroxyvitamin D3 and used in the treatment of psoriasis. The beneficial effects of MC903 on psoriasis are based on gene regulatory events. The genomic actions of 1alpha,25-dihydroxyvitamin D3 and its analogs are primarily mediated by a complex of the vitamin D3 receptor and the retinoid X receptor bound to a 1alpha,25-dihydroxyvitamin D3 response element that can be considered as the molecular switch of 1alpha,25-dihydroxyvitamin D3 signaling. In this study, the interaction of MC903 and two new analogs, GS1500 and EB1213, with this molecular switch was compared with that of 1alpha,25-dihydroxyvitamin D3. In DNA-dependent limited protease digestion assays, ligand-dependent gel shift assays and mammalian-one-hybrid assays, all four ligands appeared to be equally sensitive VDR agonists that activated vitamin D3 receptor-retinoid X receptor-1alpha,25-dihydroxyvitamin D3 response element complexes at a concentration of approximately 0.2 nM. The analyzed VDR agonists, however, also showed individual molecular properties, such as a reduced sensitivity in HaCaT cells (MC903), a selectivity for DNA-bound vitamin D3 receptor-retinoid X receptor heterodimers (GS1500) and a long-lasting stabilization of vitamin D3 receptor-retinoid X receptor-1alpha,25-dihydroxyvitamin D3 response element complexes (EB1213). This molecular evaluation demonstrated that the sensitivity in activating the vitamin D3 receptor is already optimal for MC903, but the analog may not be ideal in keeping the receptor active and in selectively triggering 1alpha,25-dihydroxyvitamin D3 signaling pathways.

The vitamin D analog, KH1060, is rapidly degraded both in vivo and in vitro via several pathways: principal metabolites generated retain significant biological activity.

Vitamin D analogs are valuable drugs with established and potential uses in hyperproliferative disorders. Lexacalcitol (KH1060) is over 100 times more active than 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3], as judged by in vitro antiproliferative and cell differentiating assays. The underlying biochemical reasons for the increased biological activity of KH1060 are unknown, but are thought to include 1) metabolic considerations in addition to explanations based upon 2) enhanced stability of KH1060-liganded transcriptional complexes. In this study we explored the in vivo and in vitro metabolism of KH1060. We established by physicochemical techniques the existence of multiple side-chain hydroxylated metabolites of KH1060, including 24-, 24a-, 26-, and 26a-hydroxylated derivatives as well as side-chain truncated forms. KH1060 metabolism could be blocked by the cytochrome P450 inhibitor, ketoconazole. KH1060 was not an effective competitor of C24 oxidation of 1alpha,25-(OH)2D3. Certain hydroxylated metabolites of KH1060 retained significant biological activity in vitamin D-dependent reporter gene systems (chloramphenicol acetyltransferase). Likewise, those metabolites accumulating in the target cell culture models in metabolism studies, particularly 24a-hydroxy-KH1060 and 26-hydroxy-KH1060, retained biological activities superior to those of 1alpha,25-(OH)2D3 in native gene expression systems in vitamin D target cells (osteopontin and P450cc24). We conclude that KH1060 is rapidly metabolized by a variety of cytochrome P450-mediated enzyme systems to products, many of which retain significant biological activity in vitamin D-dependent assay systems. These results provide an explanation for the considerable biological activity advantage displayed by KH1060 compared with 1alpha,25-(OH)2D3 in various in vitro assay systems.

Metabolism of the vitamin D3 analogue EB1089 alters receptor complex formation and reduces promoter selectivity.

1. 1alpha,25-dihydroxyvitamin3 (VD) is a nuclear hormone that has important cell regulatory functions but also a strong calcemic effect. EB1089 is a potent antiproliferative VD analogue, which has a modified side chain resulting in increased metabolic stability and a selective functional profile. Since EB1089 is considered for potential systemic application, it will be investigated to what extent its recently identified metabolites (hydroxylated at positions C26 and C26a) contribute to biological profile of the VD analogue. 2. Limited protease digestion analysis demonstrated that EB1089 is able to stabilize the high affinity ligand binding conformation of the VDR, starting at concentrations of 0.1 nM and affecting up to 80% of all receptor molecules. The metabolites EB1445 and EB1470 showed to be 100 fold less potent than EB1089, whereas the remaining three metabolites (EB1435, EB1436 and EB1446) showed a clearly reduced ability to stabilize the high affinity ligand binding conformation. Interestingly, at pharmacological concentrations all EB1089 metabolites stabilized a second, apparently lower affinity conformation to a much higher extent than EB1089. 3. In reporter gene assays all metabolites showed lower potency than EB1089. Moreover, the preference of EB1089 for activation of VDR binding to sites formed by inverted palindromic arrangements spaced by nine nucleotide (IP9-type VD response elements) appeared to be reduced (with EB1445 and EB1470) or completely lost (with EB1435, EB1436 and EB1446). The ranking of EB1089 and its metabolites that was obtained by limited protease digestion and reporter gene assays was confirmed by an analysis of their antiproliferative effect in breast cancer cells. . The potency and selectivity of the EB1089 metabolites in mediating gene regulatory effects was found to be drastically reduced in comparison to the parent compound suggesting that the contribution of the metabolites to the biological effect of EB1089 is minor. However, the compounds showed to be interesting tools for understanding the selective biological profile of EB1089.

Calcipotriol (MC 903): pharmacokinetics in rats and biological activities of metabolites. A comparative study with 1,25(OH)2D3.

Calcipotriol (MC 903) is a novel analogue of the physiologically active metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3]. MC 903 and 1,25(OH)2D3 have similar effects on cell proliferation and cell differentiation in vitro using the human histiocytic lymphoma cell line U 937, but in vivo MC903 has 100-200 times less effect on calcium metabolism. To elucidate this difference, the pharmacokinetic profiles after a single intravenous dose (50 micrograms/kg) of the two compounds to rats were compared. The area under the serum level/time curve (AUC) was more than 100 times higher for 1,25(OH)2D3 than for MC903 and the rate of clearance was more than 100 times higher for MC903 than for 1,25(OH)D3. Serum from MC903 or 1,25(OH)2D3 dosed rats (i.v. 10 micrograms/kg) was investigated for biological activities by incubation of U 937 cells with serum collected 0-24 hr after drug administration. Serum from MC903 dosed rats had an effect only when collected shortly after dosing, whereas serum from 1,25(OH)2D3 dosed rats had an effect when collected up to 4 hr after dosing. The biological effects on the U937 cells of the two major metabolites of MC903 (MC 1046 and MC 1080) were investigated. The metabolites had effects that were more than 100 times weaker than those of the parent compound. The effect of MC903 on proliferative disorders, its fast elimination and the formation of inactive metabolites makes MC903 suitable for topical treatment of psoriasis.

Metabolism of the vitamin D analog EB 1089: identification of in vivo and in vitro liver metabolites and their biological activities.

1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1'(E),3'(E)-dien -1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (EB 1089) is a novel analog of the vitamin D hormone, calcitriol that has been modified in the side-chain resulting in an increased metabolic stability relative to other side-chain modified analogs (e.g. calcipotriol and 22-oxacalcitriol). To further investigate the metabolism of EB 1089, we set out to study this metabolism both in the rat in vivo as well as in the postmitochondrial liver fractions from rat, man, and minipig in vitro. The same pattern of metabolism was observed in all biological systems employed, both in vivo and in vitro, namely 26- and 26a-hydroxylation of EB 1089. The same metabolites were produced using cultured cell systems (Shankar et al., see this issue). All the possible isomers of 26- and 26a-hydroxy EB 1089 were synthesised and these were compared to biologically generated material using HPLC, NMR, and GC-MS techniques. The predominant natural isomer observed in vitro and in vivo in rats as well as in vitro in humans was identified to be (25S),26R-hydroxy EB 1089. The biological activities of the EB 1089 metabolites on cell growth regulation were 10- to 100-fold lower than that of EB 1089. The effects of the metabolites on calcium metabolism in vivo were comparable to the effect of EB 1089; however, these effects were reduced for the major metabolite in rat and man and for the isomers of 26a-hydroxy EB 1089. We conclude that EB 1089 is metabolised by a different route of side-chain metabolism than calcitriol and that this may explain its relative metabolic stability in pharmacokinetic experiments in vivo compared to that of other vitamin D analogs.

Metabolism of the vitamin D analog EB1089 by cultured human cells: redirection of hydroxylation site to distal carbons of the side-chain.

1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1'(E),3' (E)-dien-1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (EB1089) is a novel synthetic analog of 1 alpha,25-dihydroxyvitamin D [1,25-(OH)2D3] with potential for use in the treatment of hyperproliferative disorders. It has an altered side-chain structure compared to 1,25-(OH)2D3, featuring 26,27 dimethyl groups, insertion of an extra carbon atom (24a) at C-24, and two double bonds at C-22,23 and C-24,24a. In vitro metabolism of EB1089 was studied in a human keratinocyte cell model, HPK1A-ras, previously shown to metabolize 1,25-(OH)2D3. Four metabolites were formed, all of which possessed the same UV chromophore as EB1089, indicating the retention of the side-chain conjugated double bond system. Two metabolites were present in sufficient quantities to identify them as 26-hydroxy EB1089 (major product) and 26a-hydroxy EB1089 (minor product), based on mass spectral analysis and cochromatography with synthetic standards. Similar metabolites were generated in vivo and using a liver postmitochondrial fraction in vitro (Kissmeyer et al., companion paper). Studies with the human hepatoma Hep G2 gave rise to 2 isomers of 26-hydroxy EB1089. Studies using ketoconazole, a general cytochrome P450 inhibitor, implicated cytochrome P450s in the formation of the EB1089 metabolites. COS-1 transfection cell experiments using vectors containing CYP27 and CYP24 suggest that these cytochrome P450s are probably not involved in 26- or 26a-hydroxylation of EB1089. Other experiments that examined the HPK1A-ras metabolism of related analogs containing only a single side-chain double bond: 1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1' (E)-en-1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (MC1473; double bond at C-22,23) and 1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-3'(E)-en-1'-yl)-9, 10-secopregna-5(Z),7(E),10(19)-triene (MC1611; double bond at C-24,24a) revealed that the former compound was subject to 24-hydroxylation and the latter compound was mainly 23-hydroxylated. Metabolism experiments involving EB1089, MC1473, and MC1611 in competition with [1 beta-3H]1,25-(OH)2D3 in HPK1A-ras confirmed that CYP24 is probably not involved in the metabolism of EB1089 whereas, in the case of MC1473 and MC1611, it does appear to carry out side-chain hydroxylation. Our interpretation is that the conjugated double bond system in the side-chain of EB1089 is responsible for directing the target cell hydroxylation to the distal positions, C-26 and C-26a. We conclude that EB1089 is slowly metabolized via unique in vitro metabolic pathways, and that these features may explain the relative stability of EB1089 compared to other analogs in vivo.

Enhanced biological activity of 1alpha,25-dihydroxy-20-epi-vitamin D3, the C-20 epimer of 1alpha,25-dihydroxyvitamin D3, is in part due to its metabolism into stable intermediary metabolites with significant biological activity.

1alpha,25-dihydroxy-20-epi-vitamin D3 (1alpha,25(OH)2-20-epi-D3), the C-20 epimer of the natural hormone 1alpha,25(OH)2D3, is several fold more potent than the natural hormone in inhibiting cell growth and inducing cell differentiation. At present, the various mechanisms responsible for the enhanced biological activities of this unique vitamin D3 analog are not fully understood. In our present study we compared the target tissue metabolism of 1alpha,25(OH)2D3 with that of 1alpha,25(OH)2-20-epi-D3 using the technique of isolated perfused rat kidney. The results indicated that the C-24 oxidation pathway plays a major role in the metabolism of both compounds in the rat kidney. However, it was noted that the concentrations of two of the intermediary metabolites of 1alpha,25(OH)2-20-epi-D3, namely, 1alpha,24(R),25(OH)3-20-epi-D3 and 1alpha,25(OH)2-24-oxo-20-epi-D3 in the kidney perfusate, exceeded the concentrations of the corresponding intermediary metabolites of 1alpha,25(OH)2D3. Furthermore, 1alpha,25(OH)2-24-oxo-20-epi-D3 induces the conformation of the vitamin D receptor similar to that induced by its parent analog and is nearly as potent as its parent in inducing transactivation of a gene construct containing the human osteocalcin vitamin D-responsive element. We conclude that 1alpha,25(OH)2-20-epi-D3 by itself is not metabolically stable when compared to 1alpha,25(OH)2D3, but it acquires its metabolic stability because of the reduced rate of catabolism of its intermediary metabolites. Furthermore, 1alpha,25(OH)2-24-oxo-20-epi-D3, the stable bioactive intermediary metabolite plays a significant role in generating the enhanced biological activities ascribed to 1alpha,25(OH)2-20-epi-D3.

Effect of the leukotriene LTD4/LTE4 antagonist, SR 2640, in ulcerative colitis: an open clinical study.

This investigation was performed in order to examine the role of sulfidopeptide-leukotrienes in a chronic inflammatory bowel disease, ulcerative colitis, by use of the recently developed LTD4/LTE4 antagonist, SR 2640 (2-[3-(2-quinolylmethoxy)phenylamino]benzoic acid). Eight ulcerative colitis patients with a mild to moderate disease activity were included in this open and uncontrolled study and SR 2640, 250 mg t.i.d., was administered for 6 weeks. Treatment of the patients with SR 2640 reduced the inhibitory effect of LTD4 on LTB4-directed chemotaxis of neutrophils purified from their blood. This indicates that the dose administered was sufficiently high to obtain systemic LTD4 receptor antagonism. Three of the 8 patients were in clinical remission at the end of the study, and the lack of clinical symptoms persisted for at least 2 months after discontinuing the drug. The condition of 3 patients was unchanged, and that of 2 patients deteriorated after 5 weeks, requiring treatment with sulphasalazine and steroids. SR 2640 was well tolerated by all patients. In a previously published study dealing with 4 weeks sulphasalazine treatment in the same category of patients, remission rates of 5% and 25% were found in the placebo and sulphasalazine groups, respectively, and the remission rate of SR 2640 thus seems to be of the same magnitude as that of sulphasalazine. The serum and faecal concentrations of SR 2640, and its metabolite, the beta-glucuronide, were found to be lower in ulcerative colitis patients as compared to healthy volunteers, and it is therefore possible that altered pharmacokinetics of SR 2640 is present in patients with chronic inflammatory bowel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitive analysis of 1alpha,25-dihydroxyvitamin D3 in biological fluids by liquid chromatography-tandem mass spectrometry.

A liquid chromatographic-tandem mass spectrometric assay using 5% bovine serum albumin as the calibration matrix has been developed for the quantitative analysis of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] in biological fluids. The analyte was extracted from the matrix after protein precipitation using an automated solid-phase extraction procedure involving both a reversed-phase and normal-phase procedure on a single C18 cartridge. The analytical chromatography was performed using a Symmetry C8 50 x 2.1 mm, 3.5 microm column. The mobile phase was a linear gradient from 75 to 99% methanol with a constant concentration of 2 mM ammonium acetate. 1alpha,25(OH)2D3 and the internal standard [2H6]1alpha,25(OH)2D3 were detected by using MS-MS. The ion source was operated in the positive electrospray ionisation mode. The assay is specific, sensitive, and has a capacity of more than 100 samples per day, with a limit of quantitation of 20 pg ml(-1) for a 1.0-ml sample aliquot. The assay has been used for the analysis of 1alpha,25(OH)2D3 in serum from rats and pigs simultaneously with the analysis of the vitamin D analog seocalcitol.

[Study of the elimination of residues and local tissue injury following intramuscular injection of a solution of the combination trimethoprim/sulfatroxazole in pigs]. / Onderzoek naar de eliminatie van residuen en lokale weefselbeschadiging na intramusculaire injectie van een oplossing van de combinatie van trimethoprim/sulfatroxazol bij varkens.

Two different studies are described. The first study deals with the elimination of residues of trimethoprim (TMP), sulfatroxazole (STX) and its main metabolite N4-acetyl-sulfatroxazole (N4-acetyl-STX) in pigs. Thirty -six pigs were treated with trimethoprim/sulfatroxazole IM in the nec k at a dosage of 16 mg/kg body weight for five days. Groups of four pig s were slaughtered at different time intervals. The study showed that concentration of STX, N4-acetyl-STX and TMP in edible tissues and at the injection sites were below 0.1 ppm on day nine after the last injection. S TX was eliminated the slowest, and STX can therefore be selected as a marker for residues of the trimethoprim/sulfatroxazole formulation in the tissues. The second study deals with irritation aspects of this trimethoprim /sulfatroxazole formulation. Four pigs of 32-35 kg were treated IM w with trimethoprim/sulfatroxazole and benzylpenicillin sodium. Each pig received the same injection volume, namely four trimethoprim/sulfatroxazole injections (16 mg/kg body weight per injection site), two in the back and two in the neck muscle, and two benzylpenicillin sodium injections (20,000 I.U./kg body weight per injection site), in the back muscle. All pigs were slaughtered 14 days after treatment and the extent of the irritation was compared. There were no differences between trimethoprim/sulfatroxazole and benzylpenicillin sodium with regard to irritation at the injection site in the back muscle. The irritation in the neck site was statistically less prominent than that in the back muscle and was considered not to affect the quality of the meat.

Pharmacokinetics and metabolism of a vitamin D analogue (Seocalcitol) in rat and minipig.

1. Seocalcitol (EB 1089), a vitamin D analogue with strong antiproliferative effects in vitro and in vivo, is presently under clinical evaluation for the systemic treatment of various solid tumours. 2. The aim was to investigate the pharmacokinetics of Seocalcitol after single and multiple oral administration to rat and minipig. Furthermore, the hepatic metabolism of Seocalcitol was studied both in vitro and in vivo. In vitro metabolism was also investigated in human. 3. In rat, the pharmacokinetic profile of Seocalcitol (Cmax, AUC, Tmax, T(1/2)) was the same after single and oral administration. Pharmacokinetics were also demonstrated as dose-independent. The same was more difficult to evaluate in the minipig due to a great variation among individual animals. 4. In the male rat, the serum T(1/2) was 3 h, but in the female rat and minipig (both genders) T(1/2) = 8 h. 5. At Tmax the concentration of Seocalcitol in the liver (both species) was 10-fold higher than the concentration in serum. The major metabolites in the liver were various isomers of 26-hydroxy Seocalcitol, although the concentration of the individual isomers in rat and minipig were not the same. 6. The same metabolites were formed in vitro following incubations with rat, minipig and human S9 fractions.

Determination of the vitamin D analog EB 1089 (seocalcitol) in human and pig serum using liquid chromatography-tandem mass spectrometry.

A liquid chromatographic-tandem mass spectrometric assay in human and pig serum has been developed for quantitative analysis of EB 1089 (seocalcitol). EB 1089 is a novel vitamin D analog under development for the treatment of cancer. The analyte was extracted from serum after protein precipitation using an automated solid-phase extraction procedure involving both a reversed-phase and normal-phase procedure on a single C18 cartridge. The analytical chromatography was performed using a Symmetri C8 50x2.1 mm, 3.5 microm column. The mobile phase was a linear gradient from 75% to 99% methanol with a constant concentration of 2 mM ammonium acetate. EB 1089 and the internal standard [d6]-EB 1089 were detected by using MS-MS. The ion source was operated in the positive electrospray ionisation (ESI) mode. The assay is specific, sensitive, and has a capacity of more than 100 samples per day, with a limit of quantitation of 10 pg ml(-1) for a 1.0-ml sample aliquot. It is now used for routine analysis in connection with pharmacokinetic studies in humans and toxicokinetic studies in pigs.

Pharmacokinetics and metabolism of a leukotriene D4/E4-antagonist (2-[3'-(2"-quinolylmethoxy)phenylamino]benzoic acid) in rat, dog,guinea pig and man.

1. The absorption, distribution, metabolism and excretion of 2-[3'-(2"-quinolyl-methoxy)phenylamino]benzoic acid (QMPB), a novel leukotriene D4/E4 antagonist, were investigated in rat, dog, guinea pig and man. 2. The oral absorption of the potassium salt of QMPB was rapid and almost complete (90%) in rats, and about 50% in dogs. In man, high oral bioavailability was indicated. Absorption in dogs of the zwitterion form was only 7%. 3. The distribution of 3H-QMPB was examined in rats and guinea pigs. Whole-body autoradiography in rats showed that radioactivity was concentrated predominantly in the liver, bile and intestinal lumen, after both oral and i.v. administration. 4. A major metabolite was identified as the O-ester beta-glucuronide of QMPB. 5. Renal excretion in rat, dog and man was very low. In rat, almost complete biliary excretion of QMPB as the glucuronide conjugate was demonstrated. 6. Pronounced enterohepatic circulation of QMPB was demonstrated in rats, and the plasma concentration curves and the negligible renal excretion in dog and man also indicate enterohepatic circulation in these species.