A rifampicin-induced hepatic microsomal enzyme system for the generation of cyclosporine metabolites

Production of human metabolites of cyclosporin A, AM1, AM4N and AM9, by microbial conversion

In humans, cyclosporin A (CyA) is primarily metabolized to two hydroxylated (AM1 and AM 9) and one N-demethylated (AM 4 N) derivative. To produce these derivatives, 1237 actinomycetes were screened for their ability to convert CyA. Among them, 89 strains (7.2%) produced these derivatives from CyA. Finally, Dactylosporangium variesporum IFO 14104, Actinoplanes sp. ATCC 53771 and Streptosporangium sp. AF 935 were selected for the production of AM1, AM 4 N, and AM 9, respectively. Composition of the production medium and the incubation period with CyA were important for obtaining a high yield of CyA derivatives. Large-scale microbial conversion of CyA (1.5 g) using a 30-l jar fermentor yielded 288 mg of AM1 (19.2%), 147 mg of AM 4 N (9.8%) and 115 mg of AM 9 (7.7%).

Monitoring Cyclosporine of Pre-dose and Post-dose Samples Using Nonextraction Homogeneous Immunoassay

A nonextraction homogeneous immunoassay (CEDIA Cyclosporine Plus Assay) has been developed for the measurement of cyclosporine in predose (trough) and post-dose (C2 to C8) whole-blood samples. The method includes a low-range assay that measures cyclosporine from 25 to 450 ng/mL in pre-dose samples and a high-range assay that detects cyclosporine from 450 to 2000 ng/mL in post-dose samples. The high-range assay allows a direct measurement of post-dose samples without a dilution step. Alternatively, post-dose samples can be correctly measured by the low-range assay following a twofold dilution. Using an NCCLS precision protocol, the assay exhibited less than 10% CV or error less than the functional sensitivity. Functional sensitivity of the low-range assay was demonstrated at 20 ng/mL cyclosporine. Cross-reactivity was measured in the presence of cyclosporine and was found to be 4.4%, 19.8%, 16.4%, 0.9%, 1.0%, and 1.6% for metabolites AM1, AM9, AM4n, AM19, AM4n9, and AM1c, respectively. When 53 samples were evaluated using an HPLC method, the three most significant cross-reactive metabolites, AM1, AM4n, and AM9, exhibited an average concentration profile of 123%, 19%, and 0.06% of the parent cyclosporine, respectively. The average total contribution to cyclosporine quantification from these metabolites was estimated at 7.2% based on the percentage cross-reactivity of each metabolite in the CEDIA assay and the concentration of each metabolite as determined by HPLC. The method comparison study revealed a linear regression correlation of CEDIA = 1.095 x HPLC + 6.6, r = 0.972, for the low-range assay, and CEDIA = 1.018 x HPLC - 36.4, r = 0.968, for the high-range assay. In conclusion, the CEDIA Cyclosporine Plus Assay is a precise and accurate method for quantification of cyclosporine in pre-dose and post-dose samples.

Structural characterization of two novel oxidative derivatives of cyclosporine generated by a chemical method

OBJECTIVES

To study the generation of cyclosporine derivatives (CMs) by chemical oxidation of the parent compound using hydrogen peroxide.

METHODS AND RESULTS

Hydrogen peroxide was added to cyclosporine (CsA), which was dissolved in ether. After liquid-liquid extraction, CMs were purified by high performance liquid chromatography (HPLC). Detailed structures of CMs were determined by fast atomic bombardment mass spectrometry (FABMS) and nuclear magnetic resonance spectroscopy (NMR). Our results indicated that the parent compound was modified at amino acid number 1 by hydroxylation of the carbon and the formation of a tetrahydrofuran five member ring structure. In addition, these two oxidative products of CsA were determined to be isomeric to each other, differing only in the configuration at one or more carbon atoms. This modification is in contrast to that observed for the formation of the cyclic metabolite of CsA, namely AM1c, by cytochrome P-450 isoenzymes, where the addition of the hydroxyl group occurs on the carbon of amino acid 1.

CONCLUSION

3 to 4 mg of 2 oxidative derivatives could be produced from 5 mg of CsA by chemical modification of the parent compound. In comparison, biotransformation using the drug-induced hepatic microsomal enzyme system could only produce 0.5 to 1 mg of metabolites/derivatives from 5 mg of CsA.