INTERACTION OF MERCAPTOUNDECAHYDRODODECABORATE (BSH) WITH PHOSPHATIDYLCHOLINE - RELEVANCE TO BORON NEUTRON-CAPTURE THERAPY

The interaction of mercaptoundecahydrododecaborate (B12H11SH2-, BSH) w ith phosphatidylcholine was investigated in this study in order to ill uminate possible uptake mechanisms of BSH in tumor cells. BSH has been used clinically in Japan as a boron containing agent in patients with malignant brain tumors for boron neutron capture therapy (BNCT). Afte r infusion, BSH accumulates selectively in tumor tissue. Little is kno wn for the mechanism of boron uptake to tumor cells. Fourier transform infrared (FTIR) spectrometry was used to quantify BSH (at wavenumber 2490 cm(-1)) and phosphatidylcholine (at wavenumber 2850-2970 cm(-1)). After extraction into carbon tetrachloride (CCl4), we could find an a bsorbance maximum at 2490 cm(-1) as a B-H band in the mixture of BSH w ith phosphatidylcholine, which is attributed to a BSH-phosphatidylchol ine complex, which could dissolve well in CCl4. The molar ratio of BSH to Phosphatidylcholine in the CCl4 solution was at most one mole of B SH to two moles of phosphatidylcholine independent of the excess BSH. The doubly negatively charged BSH can interact with two phosphatidylch oline molecules through their singly positively charged choline residu es. These ion pairs could be responsible for membrane binding and pene tration, and for cell internalization. (C) 1998 Elsevier Science B.V.