Cathepsin B inhibitory activities of phthalates isolated from a marine Pseudomonas strain

Two cathepsin B inhibitors were isolated from the culture supernatant of a marine Pseudomonas sp. PB01 (GenBank Accession No. EU126129). Their structures were elucidated by spectroscopic analyses as dibutyl phthalate and di-(2-ethylhexyl) phthalate. Both dibutyl phthalate and di-(2-ethylhexyl) phthalate showed dose-dependent cathepsin B inhibitions with IC50 of 0.42 and 0.38 mM, respectively. It is also observed from kinetic analyses that dibutyl phthalate and di-(2-ethylhexyl) phthalate acted as noncompetitive inhibitors with Ki values of 0.64 and 0.42 mM, respectively. Furthermore, both of them caused inactivation of the pericellular cathepsin B of murine melanoma cell with no acute cytotoxicity. The IC50 values were found to be 0.23 mM for dibutyl phthalate and 0.14 mM for di-(2-ethylhexyl) phthalate, respectively, and were 50% compared to that of purified cathepsin B.