Growth arrest and apoptosis induced by kinesin Eg5 inhibitor K858 and by its 1,3,4-thiadiazoline analogue in tumor cells Sabrina Giantulli a , Francesca De Iuliis b , Ludovica Taglieri b , Simone Carradori c , Giusi Menichelli a , Stefania Morrone b , Susanna Scarpa b and Ida Silvestri a Tumors are complex and heterogeneous but, despite this, they share the ability to proliferate continuously, irrespective of the presence of growth signals, leading to a higher fraction of actively growing and dividing cells compared with normal tissues. For this reason, the cytotoxic antimitotic treatments remain an important clinical tool for tumors. Among these drugs, antitubulin compounds constitute one of the most effective anticancer chemotherapies; however, they cause dose-limiting side effects. Therefore, it is still necessary to develop compounds with new targets and new mechanisms of action to reduce side effects or chemoresistance. Mitosis-specific kinesin Eg5 can represent an attractive target for discovering such new anticancer agents because its role is fundamental in mitotic progression. Therefore, we analyzed the effects induced by an inhibitor of kinesin Eg5, K858, and by its 1,3,4-thiadiazoline analogue on human melanoma and prostate cancer cell lines. We found that both compounds have an antiproliferative effect, induce apoptosis, and can determine a downmodulation of survivin. Anti-Cancer Drugs 00:000–000 Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved. Anti-Cancer Drugs 2018, 00:000–000 Keywords: antiproliferative activity, apoptosis, Eg5 inhibitors, K858, thiadiazolines Departments of a Molecular Medicine, b Experimental Medicine, Sapienza University of Rome, Rome and c Department of Pharmacy, ‘G. D’ Annunzio’ University of Chieti–Pescara, Chieti, Italy Correspondence to Ida Silvestri, PhD, Department of Molecular Medicine, Sapienza University of Rome, Viale Regina Elena, 00185 Rome, Italy Tel/fax: + 39 064 997 3335; e-mail: ida.silvestri@uniroma1.it Received 6 October 2017 Revised form accepted 12 April 2018 Introduction Tumors are complex and heterogeneous, but they all share the ability to proliferate continuously, irrespective of the presence of growth signals, leading to a higher fraction of actively growing and dividing cells compared with normal tissues [1]. For this reason, numerous studies have been carried out to identify new targets involved in mitosis [2] and cytokinesis [3] to develop some cytotoxic drugs that impair microtubule polymers. Compounds, such as taxanes and epothilones, that hyperstabilize GDP-binding poly- merized tubulin, or vinca alkaloids and colchicine, which destabilize and depolymerize microtubules, have in fact shown a broad spectrum of antitumor activity [4]. These drugs are currently used in the treatment of all those tumors that are prevalent in the human population, but they induce, at the same time, some clinical side effects, including myelosuppression, allergic reactions, and espe- cially peripheral sensory neuropathy, which are dose lim- iting for the drug itself. Furthermore, the clinical efficacy of these compounds is also hampered by the development of drug resistance [5]. Therefore, despite the considerable progress of cancer treatment with these agents, it is still necessary to develop compounds with new targets and different mechanisms of action to reduce the side effects of chemoresistance. Kinesin Eg5 (kindle spindle protein/KSP/KIF11) inhibitors have been considered novel antimitotic drugs that can overcome the limitations of the currently used antitubulin compounds for anticancer treatment [6]. Kinesin Eg5 is a plus-end directed motor protein responsible for centrosome separation, bipolar spindle formation, and chromosome alignment. Moreover, the overexpression of kinesin Eg5 correlates with a worse prognosis in several solid tumors [7,8]. The inhibition of Eg5 leads to a spindle assembly checkpoint-mediated arrest of cell cycle at mitosis, with the formation of monoastral microtubule array, abnormal chromosome segregation, and ultimately resulting in cell death because of apoptosis, necrosis, or autophagy [7,9]. The downmodulation of Eg5 using different approaches has been shown to decrease cell proliferation in cancer cells [7]. Yet, targeting Eg5 with siRNA induces cells death, especially in tetraploid cells, suggesting a selec- tivity for cancer cells over normal cells [10,11]. Monastrol was the first discovered Eg5 inhibitor able to induce monoastral spindle in cells and mitotic arrest [12,13]. Successively, several small molecules, acting as Eg5 inhibitors, have been developed [5,14–19] and their ability to arrest mitosis by either ATP competitive inhi- bition or binding to an allosteric site of Eg5 has been shown [6]. Recently, some of these compounds have been used in clinical trials as monotherapy for several cancer types [20–23], but the clinical reports were relatively dis- appointing. However, as the Eg5 inhibitors are well tolerated and do not cause neurotoxicity [6], studies for Preclinical report 1 0959-4973 Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/CAD.0000000000000641 Copyright r 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.