Selective cytotoxic activity of brefeldin A against human tumor cell lines.

One of the difficult problems in the screening of antitumor agents is the difference of sensitivity between murine experimental tumors and human tumors towards antitumor agents. Therefore, a drug which has strong antitumor activity towards murine experimental tumors is not always active against human tumors in the clinic. In fact, almost all the antitumor drugs exhibit stronger cytotoxic activity against murine tumor cells than humantumor cells in vitro. We therefore started to search for drugs from the fermentation broth of microorganisms which show stronger cytotoxic activity towards humancell lines than murine cell lines. Such activity was found in the culture filtrate of Eupenicillium sp. As a result of purification and structure elucidation, the active substance was revealed to be brefeldin AX). The antitumor activity of brefeldin A was already reportedx\ but its selective cytotoxic activity towards humantumor cells was not. Therefore, we studied the cytotoxic spectrum ofbrefeldin A compared with doxorubicinas a reference antitumor drug. In this study, five murine cell lines and nine human tumor cell lines were used. All cells were cultivated with RPMI-1640 medium supplemented with 10% fetal calf serum and 1 0 ^m of2-hydroxyethyldisulfide (growth medium) at 37°C under 5% CO2 in air. Cytotoxic activity was determined as follows; cells were seeded to 96-well flat-bottomed microtiter plate (Falcon, No. 3002) 3,000 cells/well in 140/il of