Measuring swainsonine in serum of cancer patients: phase I clinical trial

Swainsonine, an indolizidine alkaloid and competitive inhibitor of Golgi alpha-mannosidase II (EC 3.2.1.114), reduces tumor growth and stimulates immune function in mice. On the basis of these observations, a phase I clinical trial was initiated to determine whether swainsonine could be administered safely to cancer patients. We describe a method for extraction, acetylation, and quantification of swainsonine in human serum samples. Methyl alpha-D-mannopyranoside and methyl beta-D-galactopyranoside were added to serum samples as internal standards and, after sequential extraction of lipids and proteins with chloroform and acetonitrile, respectively, samples were acetylated with acetic anhydride and 4-dimethylaminopyridine and separated by gas-liquid chromatography. The identity of swainsonine and the internal standards after their extraction from serum and acetylation was confirmed by gas chromatography/mass spectrometry. Swainsonine was recovered at an efficiency of 90%, relative to internal standards, and calibration graphs were rectilinear from 3 to 18 mg/L with a detection limit of approximately 0.1 mg/L. The CV for multiple samples was < or = 6.7%. In patients receiving swainsonine (50-550 micrograms/kg per day) continuously for 5 days by intravenous infusion, serum concentrations of the drug reached 3-11.8 mg/L, 100 to 400 times greater than the 50% inhibitory concentration for Golgi alpha-mannosidase II and lysosomal alpha-mannosidases. Accurate measurements of swainsonine in biological fluids with this method should facilitate further clinical studies with the drug.