Determination of Aplidin®, a marine-derived anticancer drug, in human plasma, whole blood and urine by liquid chromatography with electrospray ionisation tandem mass spectrometric detection

A sensitive and highly specific liquid chromatographic method with electrospray ionisation tandem mass spectrometric detection (LC-ESI-MS/MS) is reported for the determination in human plasma, whole blood and urine of Aplidin® (APL), a novel depsipeptide derived from the tunicate Aplidium albicans with a potent cytotoxic activity under investigation in clinical studies. Didemnin B was used as internal standard and, after protein precipitation with acetonitrile and liquid-liquid extraction with chloroform, APL was separated by liquid chromatography using a reversed-phase C ₁₈ column and a linear gradient of acetonitrile in water (both containing 0.5% formic acid). Detection was performed using a turboionspray source operated in positive ion mode and by multiple reaction monitoring (MRM; m/z 1111→295 for APL and m/z 1113→297 for didemnin B). The method was linear (r≥0.9933) over the range 1-250ng/ml, with intra- and inter-batch precision and accuracy below 12.2% (except at LLOQ, ≤15.4%) for both plasma and urine. Recoveries were moderate, ranging from 54 to 70% in plasma and blood, and from 46 to 60% in urine, for both APL and didemnin B. The LOD was 0.25ng/ ml for both matrices. APL resulted stable in the different matrices at least for 6h (both at room temperature and 37°C), after freeze and thaw cycles and long term storage at -20°C. The method allowed demonstrating that APL is in a dynamic equilibrium between plasma and blood cells. Moreover, the method was successfully applied to the pharmacokinetic study of Aplidin® in cancer patients.