Therapeutics , Targets , and Chemical Biology GF-15 , a Novel Inhibitor of Centrosomal Clustering , Suppresses Tumor Cell Growth In Vitro and In Vivo

In contrast to normal cells, malignant cells are frequently aneuploid and contain multiple centrosomes. To allow for bipolar mitotic division, supernumerary centrosomes are clustered into two functional spindle poles in many cancer cells. Recently, we have shown that griseofulvin forces tumor cells with supernumerary centrosomes to undergo multipolar mitoses resulting in apoptotic cell death. Here, we describe the characterization of the novel smallmolecule GF-15, a derivative of griseofulvin, as a potent inhibitor of centrosomal clustering inmalignant cells. At concentrations where GF-15 had no significant impact on tubulin polymerization, spindle tension wasmarkedly reduced inmitotic cells uponexposure toGF-15.Moreover, isogenic cellswith conditional centrosomeamplification were more sensitive to GF-15 than parental controls. In a wide array of tumor cell lines, mean inhibitory concentrations (IC50) for proliferation and survival were in the range of 1 to 5 mmol/L and were associated with apoptotic cell death. Importantly, treatment of mouse xenograft models of human colon cancer and multiple myeloma resulted in tumor growth inhibition and significantly prolonged survival. These results show the in vitro and in vivoantitumor efficacyof aprototype smallmolecule inhibitorof centrosomal clustering and strongly support the further evaluation of this new class of molecules. Cancer Res; 72(20); 5374–85. 2012 AACR. Introduction Centrosomes are small cytoplasmic organelles, which consist of a pair of centrioles embedded in pericentriolar material and act as microtubule-organizing centers. During mitosis, centrosomes function as spindle poles, directing the formation of bipolar spindles, a process essential for accurate chromosomal segregation (1, 2). Centrosomes duplicate precisely once per cell cycle to assure spindle bipolarity, with each daughter cell receiving one centrosome upon cytokinesis. Centrosome amplification is frequent in both solid tumors and hematologic malignancies, and is linked to tumorigenesis and aneuploidy (3–10). The extent of centrosomal aberrations correlates with the degree of chromosomal instability andmalignant behavior in tumor cell lines, mouse tumor models, and human tumors (6, 9–12). In mitosis, supernumerary centrosomes can lead to the formation of multipolar spindles, which is a hallmark of many tumor types (8). Multipolar cell division, however, is antagonistic to cell viability (13, 14). Most progeny derived from a multipolar mitosis will undergo apoptosis. To circumvent this problem, many cancer cells seem to have mechanisms that suppress multipolar division, the best studied being clustering of supernumerary centrosomes into 2 spindle poles enabling bipolar division (8, 13–20). Bipolar spindle formation via centrosomal clustering is associated with an increased frequency of lagging chromosomes during anaphase, thereby explaining the link between supernumerary centrosomes and chromosomal instability (14, 15). The mechanisms of centrosomal clustering in tumor cells are incompletely understood. Recent genome-wide RNAi screens in cells containing supernumerary centrosomes suggest the involvement of the spindle assembly checkpoint and spindle tension as controlled by the cortical actin cytoskeleton, cell adhesionmolecules aswell as centrosome and kinetochore components in this process (19, 20). Supernumerary centrosomes are almost exclusively found in a wide variety of neoplastic disorders but rarely in Authors' Affiliations: Department of Internal Medicine V, Clinical Cooperation Unit Molecular Hematology/Oncology, German Cancer Research Center and Department of Internal Medicine V; National Center for Tumor Diseases, University of Heidelberg; Max-Eder Group Experimental Therapies for Hematologic Malignancies, German Cancer Research Center (DKFZ); Department of Nuclear Medicine, University Hospital Heidelberg, Heidelberg, Germany; Department of Medical Oncology, Dana-Farber Cancer Institute; Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts; Center for Nanomedicine and Theranostics & Department of Chemistry; and Center for Microbial Biotechnology, Department of Systems Biology, Technical University of Denmark, Kgs. Lyngby, Denmark Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). M.S. Raab and I. Breitkreutz contributed equally to this work. Corresponding Author: Alwin Kr€ amer, Clinical Cooperation Unit Molecular Hematology/Oncology, German Cancer Research Center and Department of Internal Medicine V, University of Heidelberg, ImNeuenheimer Feld 581, 69120 Heidelberg, Germany. Phone: 49-6221-42-1440; Fax: 496221-42-1444; E-mail: a.kraemer@dkfz.de doi: 10.1158/0008-5472.CAN-12-2026 2012 American Association for Cancer Research. Cancer Research Cancer Res; 72(20) October 15, 2012 5374 on April 14, 2017. © 2012 American Association for Cancer Research. cancerres.aacrjournals. org Downloaded from Published OnlineFirst August 31, 2012; DOI: 10.1158/0008-5472.CAN-12-2026