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

New boron-containing chlorin derivatives 9 and 13 as agents for both photodynamic therapy (PDT) and boron neutron capture therapy (BNCT) of cancer were synthesized from photoprotoporphyrin IX dimethyl ester (2) and L-4-boronophenylalanine-related compounds. The in vivo biodistribution and clearance of 9 and 13 were investigated in tumor-bearing mice. The time to maximum accumulation of compound 13 in tumor tissue was one-fourth of that of compound 9, and compound 13 showed rapid clearance from normal tissues within 24h after injection. The in vivo therapeutic efficacy of PDT using 13 was evaluated by measuring tumor growth rates in tumor-bearing mice with 660 nm light-emitting diode irradiation at 3h after injection of 13. Tumor growth was significantly inhibited by PDT using 13. These results suggested that 13 might be a good candidate for both PDT and BNCT of cancer.