Synthesis and toxicity of cobaltabisdicarbollide-containing porphyrins of high boron content

Two porphyrins of high boron content (OCP and HCP-PEG) were prepared in high yields from the reaction of the corresponding tri- and tetra-(dihydroxyphenyl)porphyrins with zwitterionic cobaltabisdicarbollide [3,3'-Co(8-C4H8O2-1,2-C2B9H10)(1',2'-C2B9H11)]. Both porphyrins were found to have low cytotoxicity toward human HEp2 cells, and to localize subcellularly mainly in the cell lysosomes. Animal toxicity investigations using male and female BALB/c mice also revealed low toxicity for both compounds. The determined maximum tolerated dose (MTD) for these boronated porphyrins administered intraperitoneally were 160 mg/kg for OCP and 320 mg/kg for HCP-PEG. Our studies warrant further development of these porphyrins of high boron content, and in particular of HCP-PEG, as boron delivery vehicles for BNCT.