Novel small inhibitors targeting CDC25 dual specificity phosphatases and displaying in vitro efficacy in melanoma cells

CDC25 phosphatases are important regulators of several steps in the cell cycle, including the activation of various cyclin-dependent kinases (CDKs). They also play a role in the cellular response to DNA damage. Mammalian cells express three forms of CDC25: CDC25A, -B and †"C. Overexpression of these phosphatases was reported in the development of several human malignancies, including melanoma. Therefore, CDC25 represent promising targets for anticancer drug discovery. Recently, the compound NSC 119915 was identified as a new quinonoid CDC25 inhibitor with potent antiproliferative activity on cancer cells. In order to improve the inhibitory potency of this compound, 126 structurally related analogs were found by ligand-based chemoinformatic methods. Twenty-five of these structures were synthesized and analyzed by an in vitro assay to evaluate their inhibition properties on CDC25 phosphatases activity. Eight of these (5-9, 21, 24, and 25) posssessed high inhibitory activity towards CDC25A, -B and †"C, and were tested in a cellular context using two human melanoma cell lines, A2058 and SAN. Only the compound 7 (cpd 7) exerted a reduction of proliferative rate of both melanoma cell lines, arrested melanoma cells in G2/M, and caused a reduction of the protein levels of CDC25A and CDC25C. Furthermore, an intrinsic apoptotic pathway was induced, which was mediated by ROS, because it was reverted in the presence of antioxidant N-acetyl-cysteine (NAC). Finally, cpd 7 provoked a significant reduction of the Bcl-2/Bax ratio, decreased the protein levels of phosphorylated Akt and increased those of p53, thus contributing to the regulation of chemosensitivity through the control of downstream Akt pathways in melanoma cells. In conclusion, our data emphasize that CDC25 could be considered as a possible oncotarget in melanoma cells and that cpd 7 is a small CDC25 inhibitor that merits to be further evaluated as a chemotherapeutic agent for melanoma, likely in combination with other therapeutic compounds