Characterization of novel inhibitors of CDC25 phosphatases: biochemical and biological analysis

The dual phosphatases cell division cycle 25 (CDC25) are crucial regulators of cell cycle progression, also involved in cell response to DNA damage. Their overexpression was detected in many tumors, including melanoma [1]. The characterization of molecules with an inhibitory potency on CDC25 activity, such as compound 19 (NSC 28620) [2], contributes to the research of novel anti-cancer drugs. The structure of this lead compound was engineered to produce more potent inhibitors. The most active compounds synthesized had Ki values in the 0.79 – 10.0 μM interval. Kinetic studies identified two different mechanisms of inhibition, related to specific functional groups possessed by the inhibitors. Information on positioning/interaction of the inhibitors was also obtained by intrinsic fluorescence measurements of CDC25B. The possible cytotoxicity of the most active compounds on melanoma cell lines was analysed. Data from MTT assay indicated that at a low concentration, i.e. 10 μM, essentially one compound (cpd 21) significantly reduced the cell growth of melanoma cells in a time dependent manner. The effect of cpd 21 on cell viability was further confirmed by the colony-forming assay, that showed a similar trend in the ability to inhibit the clonogenicity of melanoma cells. Moreover, cpd 21 provoked an early increase of pCdk1 protein level and an arrest of melanoma cells in G2/M of cell cycle, followed by the activation of a caspase-mediated apoptotic program. Conversely, cpd 21 didn’t show cytotoxic effect on BJ-5ta, a nonmalignant fibroblast cell line. Finally, a reduction of pAkt and an increase of p53 protein level could mediate the cytotoxic effect of cpd 21 on melanoma cells. References 1) Boutros et al. Nat Rev Cancer (2007),7,495-507. 2) Lavecchia et al. J. Med. Chem. (2012), 55, 4142-4158.