Synthesis and cellular studies of a carboranylchlorin for the PDT and BNCT of tumors.

The syntheses of closo- and nido-carboranylchlorins 4 and 5 from a known carboranylporphyrin are described. Water-soluble nido-carboranylporphyrin 5 was found to have very low dark cytotoxicity (IC50 > 500 microM using a MTT-based assay) but to be toxic in the presence of red light (IC50 = 80 microM at 0.55 J/cm2 light dose). Under the same experimental conditions, carboranylchlorin 5 was taken up by human glioma T98G cells to a significantly higher extent than chlorin e6, a chlorophyll degradation product. The preferred sites of subcellular localization of carboranylchlorin 5 were found to be the cell lysosomes. Our results suggest that carboranylchlorin 5 is a promising new dual sensitizer for the PDT and BNCT treatment of tumors.