20-O-IngenolEZ, a catalytic topoisomerase II inhibitor, specifically inhibits cell proliferation and induces double-strand DNA breaks in BLM-/-cells

Abstract

Bis-dioxopiperazines have been termed catalytic inhibitors to distinguish them from topoisomerase poisons that induce DNA double-strand breaks (DSBs). However, it has been reported that ICRF-193 acts as a poison in cells containing mutated genes related to checkpoint mechanisms. We also showed previously that 20-O-ingenolEZ acts as a catalytic inhibitor to inhibit the ATPase activity of topoisomerase IIα, inducing the G2 arrest of mouse mammary tumor (MMT) cells. In this study, we observed the effects of 20-O-ingenolEZ on cells containing a mutation in the RecQ helicase gene. 20-O-IngenolEZ completely inhibited the proliferation of BLM^-/-cells in BLM^-/- and WRN^-/-DT40 cells and wild-type DT40 cells. This inhibition induced the phosphorylation of H2AX in response to agents that introduce topoisomerase II-mediated DSBs. Following DNA damage, the induction of apoptosis in the BLM^-/-cells by 20-O-ingenolEZ showed the characteristics of a topoisomerase II poison.