A simple method for predicting modes of actions of antitumor agents

Modes of actions of antitumor agents can be predicted by comparison of antitumor activities against L1210 cells in the presence and absence of some nucleosides. 1) Deoxyribonucleic acid (DNA) inhibitors were mainly antagonized by thymidine. 2) Both DNA and ribonucleic acid (RNA) inhibitors were mainly antagonized by adenosine and uridine. 3) Uridine antagonized the activities of an RNA inhibitor. 4) None of these nucleosides tested antagonized the antitumor activities of an inhibitor of protein synthesis. 5) A mitotic inhibitor was weakly antagonized by thymidine, adenosine and uridine. This method is useful for approximating the modes of actions of antitumor agents without using radioactive precursors.