Indirubin-3‘-Monoxime, an Inhibitor of Cyclin Dependent Kinases, Induces Growth Inhibition and Apoptosis in Renal Cell Cancer in Vitro

The compound indirubin is the active constituent of a traditional Chinese phytomedicine (Danggui Longhui Wan). This preparation has been used for years in the treatment of chronic myelocytic leukemia. A derivate of the original indirubin compound is indirubin-3′-monoxime which is a selective and potent inhibitor of cyclin-dependent kinases. In this study we investigated if indirubin-3′-monoxime can induce apoptosis and tumor cell death in 3 human (A498, CAKI-1, CAKI-2) and 1 murine (RENCA) renal cell cancer cell lines. The growth inhibitory and apoptosis induction properties were evaluated by EZ4U, a cytotoxic assay and by flow cytometry of annexin-V/PI staining during treatment with doses ranging from 5.0 to 15.0 μm indirubin-3′-monoxime over 72 h. To further evaluate the underlying molecular actions of indirubin-3′-monoxime, survivin, a major antiaptotic protein, was additionally determined by intracellular flow cytometry. Our results show that indirubin-3′-monoxime induces growth arrest and apoptosis in all RCC cell lines. All RCC lines expressed survivin. However, no clear correlation between apoptosis induction and expression of survivin was found. As treatment of metastatic RCC remains a challenge, the need for continuing assessment of novel agents in the treatment of this disease is mandatory. Indirubin-3’-monoxime seems a candidate for further evaluation.