THE TOPOISOMERASE-II INHIBITOR TENIPOSIDE (VM-26) INDUCES APOPTOSIS IN UNSTIMULATED MATURE MURINE LYMPHOCYTES

This study shows that not only concanavalin A-stimulated proliferating lymphocytes but also unstimulated mouse splenic lymphocytes are sensitive to the topoisomerase II (topo II) inhibitor teniposide (VM-26). When unstimulated lymphocytes are pretreated with VM-26 for a 2-h period and are then incubated in drugfree medium, cell viability, as determined by trypan blue exclusion, decreases to 40% of the control by 6 h. The drugtreated cultures show two to three times the level of detergent soluble DNA than the control cultures and agarose gel electrophoresis of the soluble DNA shows the presence of oligonucleosomal-sized fragments, a feature considered to be a hallmark of apoptosis. Phase contrast microscopy, Hoechst staining for DNA, and immunofluorescence microscopy of various nuclear and cytoplasmic antigens (nucleolar fibrillarin, snRNP, ubiquitin, vimentin, tubulin) in the VM-26-treated cells characterize the morphological changes during apoptosis of these cells. The role of topo II as the mediator of the VM-26 effects is supported by pulsed field gel electrophoresis, which shows the typical topo II-induced cleavage of supercoiled DNA into loop-sized 300- and 50-kbp fragments. We conclude that the cancer chemotherapeutic agent VM-26 interacts with topo II and induces apoptosis in unstimulated lymphocytes. © 1992.