Synthesis and biological evaluation of new BSH-conjugated chlorin derivatives as agents for both photodynamic therapy and boron neutron capture therapy of cancer

•Four new BSH-conjugated chlorin derivatives for both PDT and BNCT were synthesized.•The in vivo biodistribution and clearance of the four derivatives were investigated.•Two derivatives showed good tumor-selective accumulation.•Tumor growth was significantly inhibited by PDT using one of the derivatives.•BSH-conjugated chlorin derivatives might be good candidates for both PDT and BNCT. New disodium mercaptoundecahydro-closo-dodecaborate (BSH)-conjugated chlorin derivatives 11, 12, 16 and 20 as agents for both photodynamic therapy (PDT) and boron neutron capture therapy (BNCT) of cancer were synthesized. The in vivo biodistribution and clearance of 11, 12, 16 and 20 were investigated in tumor-bearing mice. Compounds 12 and 16 showed good tumor-selective accumulation among the four derivatives. The time to maximum accumulation of compound 16 in tumor tissue was one-fourth of that of compound 12, and clearance from normal tissues of compound 16 was similar to that of compound 12. The in vivo therapeutic efficacy of PDT using 16, which has twice as many boron atoms as 12, was evaluated by measuring tumor growth rates in tumor-bearing mice with 660nm light-emitting diode irradiation at 6h after injection of 16. Tumor growth was significantly inhibited by PDT using 16. These results suggested that 16 is a good candidate for both PDT and BNCT of cancer.