LC-MS-MS determination of brostallicin in human plasma following automated on-line SPE

LC-MS-MS method using automated on-line solid-phase extraction (SPE) has been developed and validated for the quantitation of brostallicin (I), a new distamycin derivative, in human plasma. I is a DNA minor groove binder currently under phase I-II clinical evaluation as an anticancer drug. Plasma (0.4 ml) was spiked with 0.2 ml stable label IS solution and placed in a 96-well plate maintained at +4 degrees C. Aliquots of 0.1 ml of prepared samples were loaded into the on-line SPE HySphere Resin SH cartridges (10 mm x 2 mm ID) and the analytes back eluted with the mobile phase into LC-MS-MS system. A Platinum Cyano column (100 mm x 4.6 mm, 3.6 microm) was used to perform the chromatographic analysis. The mobile phase was acetonitrile-ammonium formate buffer (pH 3.5; 20 mM) (70:30, v/v) at a flow rate of 1.0 ml/min. LC flow was split so that 300 microl/min was directed toward the mass spectrometer interface. Retention time of I was 2.6 min and the total cycle time was 8 min. MS detection used an Applied Biosystems/MDS SCIEX API 365 with a TurboIonSpray interface and MRM (m/Z: 725/257 for I and m/Z: 729/257 for IS) operated in positive ion mode. The method was validated over the calibration range 0.124-497 ng/ml. A negligible carry-over effect from the system was observed. In spite of the known instability of I in human plasma (about 20% decrease over 12 h), the ratio analyte/IS peak area showed good stability over the analysis time required for 96 samples. The automated on-line SPE method can be considered as a valid alternative to the off-line manual SPE procedure previously developed.