TY - JOUR T1 - Biological Characterization of an Improved Pyrrole-Based Colchicine Site Agent Identified Through Structure-based Design JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.115.101592 SP - mol.115.101592 AU - Cristina C Rohena AU - Nakul Telang AU - Chenxiao Da AU - April Risinger AU - James A Sikorski AU - Glen E Kellogg AU - John T Gupton AU - Susan L Mooberry Y1 - 2015/01/01 UR - http://molpharm.aspetjournals.org/content/early/2015/12/11/mol.115.101592.abstract N2 - A refined model of the colchicine site on tubulin was used to design an improved analog of the pyrrole parent compound JG-03-14. The optimized compound, NT-7-16, was evaluated in biological assays that confirm that it has potent activities as a new colchicine site microtubule depolymerizer. NT-7-16 exhibits antiproliferative and cytotoxic activities against multiple cancer cell lines with IC50 values of 10-16 nM and it is able to overcome drug resistance mediated by the expression of P-glycoprotein and the βIII isotype of tubulin. NT-7-16 initiated the concentration-dependent loss of cellular microtubules and caused the formation of abnormal mitotic spindles leading to mitotic accumulation. The direct interaction of NT-7-16 with purified tubulin was confirmed and it was more potent than combretastatin A-4 in these assays. Binding studies verified that NT-7-16 binds to tubulin within the colchicine site. The antitumor effects of NT-7-16 were evaluated in an MDA-MB-435 xenograft model and it had excellent activity at concentrations that were not toxic. A second compound, NT-9-21, that contains dichloro moieties in place of the 3,5-dibromo substituents of NT-7-16, had a poorer fit within the colchicine site as predicted by modeling and the HINT score. Biological evaluations showed that NT-9-21 has 10-fold lower potency than NT-7-16, confirming the modeling predictions. These studies highlight the value of the refined colchicine site model and identify a new pyrrole-based colchicine site agent with potent in vitro activities and promising in vivo antitumor actions. ER -