MPS1 kinase is a key regulator of the spindle assembly checkpoint (SAC), a mitotic mechanism specifically required for proper chromosomal alignment and segregation. It has been found aberrantly overexpressed in a wide range of human tumors and is necessary for tumoral cell proliferation. Here we report the identification and characterization of NMS-P715, a selective and orally bioavailable MPS1 small-molecule inhibitor, which selectively reduces cancer cell proliferation, leaving normal cells almost unaffected. NMS-P715 accelerates mitosis and affects kinetochore components localization causing massive aneuploidy and cell death in a variety of tumoral cell lines and inhibits tumor growth in preclinical cancer models. Inhibiting the SAC could represent a promising new approach to selectively target cancer cells.

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The mechanism of action of many antitumor agents involves DNA damage, either by direct binding of the drug to DNA or to DNA-binding proteins. However, most of the DNA-interacting agents have only a limited degree of sequence specificity, which implies that they may hit all the cellular genes. DNA minor groove binders, among which the derivatives of distamycin A play an important role, could provide significant improvement in cancer management, increasing gene specificity, due to high selectivity of interaction with thymine-adenine (TA) rich sequences. We now report and discuss the synthesis, the in vitro and in vivo activities, and some mechanistic features of alpha-halogenoacrylamido derivatives of distamycin A. The final result of this work was the selection of brostallicin 17 (PNU-166196). Brostallicin, presently in phase II clinical trials, shows a broad spectrum of antitumor activity and an apoptotic effect higher than distamycin derivative tallimustine. An important in vitro toxicological feature of brostallicin is the very good ratio between myelotoxicity on human haematopoietic progenitor cells and cytotoxicity on tumor cells, in comparison with clinically tested DNA minor groove binders. A peculiarity of brostallicin is its in vitro reactivity in the DNA alkylation assays only in the presence of glutathione. Moreover brostallicin's antitumor activity, both in in vitro and in vivo tumor models, is higher in the presence of increased levels of glutathione/glutathione-S-tranferases. These findings contribute to the definition of brostallicin as a novel anticancer agent that differs from other minor groove binders and alkylating agents for both the profile of activity and the mechanism of action and to classify the alpha-bromoacrylamido derivatives of distamycin as a new class of cytotoxics. Moreover, due to its interaction with glutathione, brostallicin may have a role for the tailored treatment of tumors characterized by constitutive or therapy-induced overexpression of glutathione/glutathione-S-tranferase levels.

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