Characterization of growth, apoptosis, and differentiation of CHO and human erythroleukemic K562 cells exposed to dexrazoxane, and the selection of a dexrazoxane-resistant K562 cell line

Abstract

The bisdioxopiperazines including dexrazoxane are strong catalytic inhibitors of DNA topoisomerase II. The aim of the following study was to examine the ' in vitro' effects of dexrazoxane on the growth, cytotoxicity, morphology, cell cycle progression, and where applicable induction of apoptosis and differentiation of Chinese hamster ovary (CHO), and human erythroleukemic K562 cell lines. Finally, a dexrazoxane-resistant strain of K562 cells was selected and characterized for cross-resistance towards other bisdioxopiperazines and antineoplastic agents. Daily exposure to dexrazoxane inhibited growth of both CHO and K562 cell lines, while permitting a significant increase in cell size. Cell cycle analysis revealed that these cells were highly polyploid (up to 32 N DNA content). Confocal, electron, and fluorescence microscopy revealed mulitlobed nuclei, and together with the presence of multiple centrosomes suggested continued cell cycling in the absence of cytokinesis. Mean protein and DNA content increased 3.8- and 5.4-fold respectively in CHO cells after 120 hr, and only marginally in K562 cells. Delayed apoptosis was observed only in K562 cells as seen by an increase of sub-diploid apoptotic bodies, condensed and/or fragmented fluorescent stained chromatin, and agarose gel electrophoretic DNA laddering. Dexrazoxane induced erythroid-like differentiation in K562 cells, as measured by increased hemoglobin content and glycophorin A staining. Dexrazoxane-resistant K562/DZ1 cells (~126-fold), were highly cross-resistant towards ICRF-154 and ICRF-193, as well as against doxorubicin (2.4-fold) and etoposide (4-fold). Thus, the prevention of cytokinesis does not necessarily preclude continued cell cycling. The ability of the bisdioxopiperazines to induce differentiation and apoptosis suggests that these compounds may be useful in treating some types of leukemia.