Renieramycin M (1), a bistetrahydroisoquinolinequinone
alkaloid isolated from the marine sponge Xestospongia sp., has been reported to possess promising anticancer effects. However, its accidental
necrosis inducing effect has limited further development due to concerns of unwanted toxicity. The presence of two
quinone moieties in its structure was demonstrated to induce accidental
necrosis and increase
reactive oxygen species (ROS) levels. Therefore, one
quinone of 1 was modified to produce the 5-O-acetylated
hydroquinone derivative (2), and 2 dramatically reduced the accidental
necrosis inducing effect while preserving the apoptosis-inducing effect of parent 1 on
lung cancer H23 cells. Addition of the
antioxidant N-acetylcysteine suppressed the accidental
necrosis mediated by 1, suggesting that its accidental
necrosis inducing effect was ROS-dependent. The
fluorescent probe dihydroethidium revealed that the accidental
necrosis mediated by 1 was due to its ability to generate intracellular
superoxide anions. Interestingly, the remaining
quinone in 2 was required for its cytotoxicity, as the 5,8,15,18-O-tetraacetylated bishydroquinone derivative (3) exhibited weak cytotoxicity compared to 1 and 2. The present study demonstrates a simple way to eliminate the undesired accidental
necrosis inducing effect of substances that may be developed as improved anticancer
drug candidates.