INVESTIGATION OF SURAMIN-ALBUMIN BINDING BY ELECTROSPRAY MASS-SPECTROMETRY

Suramin, an organic polyanion with six sulphonic groups, is under clin ical trials as an agent against hormone-refractory prostate cancer, Th e drug binds strongly to serum albumin. The objectives were to use ele ctrospray to measure the molecular masses of the intact complexes of a lbumin and suramin to determine the number of suramin molecules bound under different molar ratios, and to investigate the binding of surami n in human serum. With albumin in excess (2:1 to 25:1 ratio), only 1 a nd 2 bound suramins were found; with suramin excess (2:1 to 1000:1) up to 20 bound suramin molecules/albumin were found. Up to 5 bound suram ins were found in human serum with 4:1 suramin:albumin ratio, which co rresponds to recommended therapeutic doses (200-300 mu g/mL). At 8:1 r atio, which would be toxic, complexes with up to ten bound suramin mol ecules were found, and unreacted albumin diminished. (C) 1998 John Wil ey & Sons, Ltd.