The catalytic DNA topoisomerase II inhibitor dexrazoxane (ICRF-187) induces endopolyploidy in Chinese hamster ovary cells

The bisdioxopiperazines, including dexrazoxane (ICRF-187), are catalytic or noncleavable complex-forming inhibitors of DNA topoisomerase II that do no t produce DNA strand breaks. In this study we show that dexrazoxane inhibit s the division of Chinese hamster ovary (CHO) cells resulting in marked inc reases in cell size (up to 80 mum in diameter), volume (up to 150-fold grea ter), and ploidy (as high as 32N). This last result indicates that the dexr azoxane-induced DNA reduplication was restricted to once per cell cycle. Ki netic analysis of the flow cytometry data indicated that the conversion bet ween successively higher ploidy levels was progressively slowed at longer t imes of exposure to dexrazoxane. Both the protein and DNA content of dexraz oxane-treated CHO cells increased linearly over time in the same proportion . Light and electron microscopic studies of dexrazoxane-treated cells showe d ring-like multilobulated nuclei. Immunohistochemical staining of dexrazox ane-treated cells showed that F-actin and acetylated alpha -tubulin were pr esent in large, highly organized networks. Immunohistochemical staining of the dexrazoxane-treated CHO cells also showed that the topoisomerase II a c olocalized with the DNA of the multilobulated nuclei. Staining of gamma -tu bulin revealed that the dexrazoxane-treated cells contained multiple centro somes, indicating that dexrazoxane prevents cytokinesis but not centrosome reduplication. It is concluded that dexrazoxane inhibits CHO cytokinesis in cells by virtue of its ability to inhibit topoisomerase II.