Research Article The Dynamin Inhibitors MiTMAB and OcTMAB Induce Cytokinesis Failure and Inhibit Cell Proliferation in Human Cancer Cells Sanket Joshi 1 , Swetha Perera 1 , Jayne Gilbert 2 , Charlotte M. Smith 1 , Anna Mariana 1 , Christopher P. Gordon 3 , Jennette A. Sakoff 2 , Adam McCluskey 3 , Phillip J. Robinson 1 , Antony W. Braithwaite 1,4 , and Megan Chircop (nee Fabbro) 1 Abstract The endocytic protein dynamin II (dynII) participates in cell cycle progression and has roles in centrosome cohesion and cytokinesis. We have described a series of small-molecule inhibitors of dynamin [myristyl tri- methyl ammonium bromides (MiTMAB)] that competitively interfere with the ability of dynamin to bind phospholipids and prevent receptor-mediated endocytosis. We now report that dynII functions specifically during the abscission phase of cytokinesis and that MiTMABs exclusively block this step in the cell cycle. Cells treated with MiTMABs (MiTMAB and octadecyltrimethyl ammonium bromide) and dyn-depleted cells remain connected via an intracellular bridge for a prolonged period with an intact midbody ring before mem- brane regression and binucleate formation. MiTMABs are the first compounds reported to exclusively block cytokinesis without affecting progression through any other stage of the cell cycle. Thus, MiTMABs represent a new class of antimitotic compounds. We show that MiTMABs are potent inhibitors of cancer cell growth and have minimal effect on nontumorigenic fibroblast cells. Thus, MiTMABs have toxicity and antiprolifera- tive properties that preferentially target cancer cells. This suggests that dynII may be a novel target for phar- macologic intervention for the treatment of cancer. Mol Cancer Ther; 9(7); 1995–2006. ©2010 AACR. Introduction Dynamin II (dynII) is a member of the dynamin super- family, composed of three classic dynamins and four dy- namin-related proteins conserved throughout eukaryotes (1). Among the three human dynamin genes, dynI is neu- ron specific, dynII is ubiquitously expressed, and dynIII is found in testis and brain (2). DynII is the ancestral form most closely related to the dynamin-related proteins. Dy- nII is a 100-kDa GTPase enzyme best known for its role in membrane trafficking processes, specifically clathrin- mediated endocytosis (1, 3, 4). It also participates in caveola-mediated and clathrin- and caveola-independent endocytosis (5–8), macropinocytosis (9), phagocytosis (10, 11), and trafficking from the trans-Golgi network (12–14). Involvement of dynII in nonmembrane traffick- ing processes has been reported, including regulation of actin assembly and reorganization via interactions with actin-binding proteins (15–18). Whether dynII functions in these processes in an endocytic-independent or endo- cytic-dependent manner remains to be determined. DynII also participates in apoptosis. Overexpressed dynII activates caspase-3, triggering apoptosis in a p53-depen- dent manner (19), and this is dependent on its GTPase activity (19). Mutations in the GTPase effector domain that block dynII assembly enhance caspase-3 activation (20). DynII-induced apoptosis therefore seems to be inde- pendent of its endocytic function. DynII also plays a role in cell cycle progression. During interphase, dynII localizes to centrosomes, participating in centrosome cohesion (21, 22). It is unknown if dynII is associated with the mitotic centrosome. DynII is also associated with the final stage of mitosis, cytokinesis (21, 23–26). During cytokinesis, dynamin localizes to the spindle midzone and the intracellular bridge (21, 26). DynII-knockout cells grow at a slower rate than their wild-type counterparts (24). These cells exhibit cytokine- sis defects, whereby an increased percentage of cells is connected via an intracellular bridge with detectable midbodies (24). These findings suggest a role for dyna- min in the abscission phase of division. Several small-molecule inhibitors of dynamin have been reported that are proving to be valuable tools for Authors' Affiliations: 1 Children's Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia; 2 Department of Medical Oncology, Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia; 3 Chemistry, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia; and 4 Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand Note: Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/). Corresponding Author: Megan Chircop, Children's Medical Research Institute, The University of Sydney, Locked Bag 23, Wentworthville, New South Wales 2145, Australia. Phone: 61-2-9687-2800; Fax: 61-2- 9687-2120. E-mail: mchircop@cmri.com.au doi: 10.1158/1535-7163.MCT-10-0161 ©2010 American Association for Cancer Research. Molecular Cancer Therapeutics www.aacrjournals.org 1995 on May 20, 2016. © 2010 American Association for Cancer Research. mct.aacrjournals.org Downloaded from Published OnlineFirst June 22, 2010; DOI: 10.1158/1535-7163.MCT-10-0161