Development and validation of a chiral high-performance liquid chromatography assay for rogletimide and rogletimide-N-oxide isomers in plasma.

The purpose of the present study was to develop and validate a stereo-specific high-performance liquid chromatography (HPLC) assay for rogletimide (Rog) and rogletimide-N-oxide (Nox) isomers in plasma. The assay was performed with a chiral cellulose-[4-methylbenzoate]ester column (Chiracel OJ). Optimal separation was achieved isocratically with a mobile phase consisting of n-hexane/anhydrous ethanol (65/35, v/v) at a flow rate of 0.9 ml/min, with the column being thermostated at +35°C (UV detection at 257 nm). Under these conditions, retention times were approximately 17, 28, 31 and 76 min for R-Rog, S-Rog, R-Nox and S-Nox, respectively. S-aminoglutethimide (S-Ag) served as the internal standard (retention time 70 min). An extraction procedure from plasma samples was developed on Bond Elut RP8 500-mg cartridges; conditioning was performed with 5 ml methanol and 5 ml water, after which 1 ml plasma that had previously been spiked with 5 μM S-Ag was applied. Washing was done with 6 ml water and elution, with 4 ml methanol. After evaporation to dryness, residues were dissolved in 400 μl anhydrous ethanol and 12–48 μl was injected onto the HPLC system. Blank plasma from healthy donors showed the random presence of a small interference eluting at the retention time of R-Rog, precluding the accurate quantification of R-Rog concentrations below 2.5 μM. Reproducibility assays demonstrated the need to use an internal standard. Taking into account the internal standard, at 2.5 μM the intra- and inter-assay coefficients of variation were 10.5% and 21.0% for R-Rog, 5.5% and 8.7% for S-Rog, 7.6% and 20.8% for R-Nox and 11.7% and 6.4% for S-Nox, respectively. The detection limit was 2.5 μM for R-Rog, 0.5 μM for S-Rog, 0.25 μM for R-Nox and 0.5 μM for S-Nox. Linearity was satisfactory at concentrations ranging from 2.5 to 10 μM for R-Rog, from 0.5 to 10 μM for S-Rog, from 0.25 to 2.5 μM for R-Nox and from 0.50 to 2.5 μM for S-Nox. This assay was applied to plasma obtained from rogletimide-treated breast cancer patients receiving conventional oral doses and demonstrated its feasibility with regard to sensitivity. The preliminary pharmacokinetic results reported herein suggest for the first time that both the R-Rog and S-Rog isomers are metabolized into rogletimide-N-oxide.