CATIONIC DRUG ANALYSIS USING MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRY - APPLICATION TO INFLUX KINETICS, MULTIDRUG-RESISTANCE, AND INTRACELLULAR CHEMICAL-CHANGE

Highly sensitive and convenient analysis of intracellular cationic dru gs has been achieved by applying matrix-assisted laser desorption/ioni zation mass spectrometry (MALD-MS). Tetraphenylphosphonium cation was readily identified and quantified (using methyltriphenylphosphonium ca tion as an internal standard) at subpicomole levels in crude lysate fr om < 4 x 10(3) FaDu human hypopharyngeal carcinoma cells. A quantitati ve MALD-MS time course for tetraphenylphosphonium cation accumulation into FaDu cells was comparable to a time course using scintillation co unting with tritiated tetraphenylphosphonium. MALD-MS was also capable of demonstrating the reduced accumulation of the cationic drug rhodam ine-123 by Dox(R) MCF7, a multiply drug-resistant human breast adenoca rcinoma cell line, relative to the nonresistant parent line MCF7. In a ddition, MALD-MS was used to follow a chemical reaction inside intact FaDu cells: the formation of a hydrazone (II-51) from benzaldehyde and an acylhydrazide, 5-[tris(4-dimethylaminophenyl)phosphoniolpentanoyl hydrazide (II-25). These results suggest that MALD-MS may provide a ra pid and practical alternative to existing methods for the analysis of cationic drugs, toxins, and their metabolites in cells and tissues.