Cell cycle modulatory and apoptotic effects of plant-derived anticancer drugs in clinical use or development.
A total of 27 selected analogues of VP-16 and VM-26 were compared with VP-16 and VM-26 for their relative abilities to stabilize the enzyme-substrate intermediate normally formed between eukaryote topoisomerase II and DNA. This activity was compared with cytotoxicity results obtained using the human colon HCT116 cell line and antitumor results obtained after intraperitoneal injection of mice with murine leukemia P388. The most potent analogues were those containing OH groups (demethyl) in either the 3′ and 4′ or the 3′, 4′, and 5′ positions, the latter being twice as potent as VP-16. VM-26 was only 40% more potent than VP-16 in this assay. It was generally found that the 4′-esters had little activity in vitro, yet were cytotoxic and had antitumor activities. All other analogues with little in vitro activity were not very cytotoxic and had little if any antitumor activity. A very good correlation exists between stabilization of topoisomerase II-DNA intermediates, cytotoxicity, and antitumor activity.