Inhibition of protein synthesis reduces the cytotoxicity of 4'-(9-acridinylamino)methanesulfon-m-anisidide without affecting DNA breakage and DNA topoisomerase II in a murine mastocytoma cell line

Stimulation of cleavable complex formation by 4'-(9-acridinylamino)methanesulfon-m-anisidide (mAMSA) and related anticancer drugs is an important initial event in drug action which correlates with cytotoxicity. However, it was recently suggested that factors in addition to cleavable complex formation are needed to express lethality. Therefore we investigated the effects of inhibitors of DNA replication and RNA and protein synthesis on mAMSA-induced cell killing in the K21 subline of the P815 murine mastocytoma cell line. This showed that RNA and protein synthesis, but not DNA replication, was necessary for maximal mAMSA cytotoxicity. Moreover, inhibition of RNA synthesis with cordycepin or protein synthesis with cycloheximide protected cells from the cytotoxic action of mAMSA without reducing DNA breakage or cleavable complex formation and there was no decrease in DNA topoisomerase II activity in nuclear extracts from cells treated with cordycepin or cycloheximide. We conclude that cleavable complex formation is independent of RNA and/or protein synthesis and we propose that the subsequent conversion into a lethal event requires an additional labile protein factor.