Anti-mitotic properties of indirubin-3'-monoxime, a CDK/GSK-3 inhibitor: induction of endoreplication following prophase arrest

The bis-indole indirubin is the active ingredient of the Traditional Chines e Medicine recipe Danggui Longhui Wan used against chronic myelocytic leuke mia, We have previously shown that indirubins are potent inhibitors of cycl in-dependent kinases and glycogen synthase kinase-3, We here investigated t he anti-mitotic properties of this class of compounds using the cell permea ble indirubin-3 ' -monoxime and the HBL-100 cell line. Indirubin-3 ' -monox ime reversibly arrests asynchronous HBL-100 cells in G2, This arrest is not accompanied by any significant change in expression of the major cell cycl e regulators, However indirubin-3 ' -monoxime inhibits the phosphorylation of consensus CDK phosphorylation sites as well as of nucleolin at a specifi c CDK1/cyclin B phosphorylation site, suggesting a direct action on the mit otic CDK1/cyclin B, When indirubin-3 ' -monoxime is added to HBL-100 cells synchronized in M phase by nocodazole, cells undergo an endoreplication lea ding to an 8n DNA content. As soon as indirubin-3 ' -monoxime is washed awa y, these polyploid cells become aneuploid and later die from necrosis, This mechanism of endoreplication followed by cell death may contribute to the antitumour properties of indirubins.