Cdc25 inhibitors in melanoma cells

Cell division cycle 25 (Cdc25) proteins are dual specificity phosphatases involved in the progression of the cell cycle. In particular, mammalian cells express three isoforms of Cdc25, called Cdc25A, -B and -C: Cdc25A mainly controls G1/S progression, whereas Cdc25B and Cdc25C predominantly activate G2/M transition. Moreover, over-expression of Cdc25A and B activities has been frequently observed in a wide variety of human tumors with poor prognosis. Thus, the design and study of small molecules endowed with an inhibitory activity towards Cdc25 proteins represent a promising strategy for the development of new anti-cancer therapies. A previous work from this group described the properties of a set of small molecules, which were able to inhibit Cdc25 functions (Lavecchia et al. J Med Chem 55, 2012, 4142–4158). Among them, compound 11, possessing a quinonic structure, acted as an irreversible inhibitor of Cdc25B and showed a strong antiproliferative action on some cancer cell lines. To expand the structure-activity relationship study and to explore potential new structure analogues of 11, we performed a multiple ligand-based chemoinformatics approach against full ZINC database (~35 million purchasable compounds) and NCI Open database (~260 000 compounds). 25 structures identified from these searches (hereafter called AL1–AL25) were analyzed, and selected compounds were tested in vitro to assess the Cdc25B inhibition activity. In particular, compounds AL11, -12, -13, -14, -15, -16, -23, -24 and -25 maintained a percentage of Cdc25B inhibition comparable to that exerted by compound 11, and some of them were even more powerful. The effect of these active analogues was also evaluated on melanoma cell lines (A2058 and SAN), because of the limited information on the effect of Cdc25 inhibitors in this cellular system. In both melanoma cells, after 48-h treatment with 100 mM of each inhibitor, a significant reduction of cell growth was observed only with AL11, whereas the other active analogues, as well as compound 11, were ineffective. Furthermore, cytofluorimetric analysis and measurements of the activity of caspase-9 and -3 indicated that AL11 exerted a pro-apoptotic effect on melanoma cells. In addition, the cellular treatment with AL11 produced an alteration of the cellular redox state and a reduction of the mitochondrial membrane potential. Studies are in progress to clarify the mechanisms involved in the cytotoxic potential of AL11 and other related molecules in melanoma cell lines, with the aim at the refinement of the inhibitory action of the studied compounds.