CIL-102 binds to tubulin at colchicine binding site and triggers apoptosis in MCF-7 cells by inducing monopolar and multinucleated cells

A plant dictamine analog, 1-[4-(furo[2,3-b]quinolin-4-ylamino)phenyl]ethanone (CIL-102) has been shown to exert potent anti-tumor activity. In this study, we examined the mode of interaction of CIL-102 with tubulin and unraveled the cellular mechanism responsible for its anti-tumor activity. CIL-102 bound to tubulin at a single site with a dissociation constant similar to 0.4 mu M. Isothermal titration calorimetry revealed that CIL-102-tubulin interaction is highly enthalpy driven and that the binding affords a large negative heat capacity change (Delta C-p = 790 cal mol(-1) K-1) with an enthalpy-entropy compensation. An analysis of the modified Dixon plot suggested that CIL-102 competitively inhibited the binding of podophyllotoxin, a colchicine-binding site agent, to tubulin. Computational modeling indicated that CIL-102 binds exclusively at the beta-subunit of tubulin and that CIL-102 and colchicine partially share their binding sites on tubulin. It bound to tubulin reversibly and the binding was estimated to be similar to 1000 times faster than that of colchicine. CIL-102 potently inhibited the proliferation of MCF-7 cells, induced monopolar spindle formation and multi-nucleation. At half-maximal inhibitory concentration, the spindle microtubules were visibly depolymerized and disorganized. CIL-102 reduced the inter-polar distances of bipolar mitotic cells indicating that it impaired microtubule-kinetochore attachments. CIL-102-treatment induced apoptosis in MCF-7 cells in association with increased nuclear accumulation of p53 and p21 suggesting that apoptosis is triggered through a p53-p21 dependent pathway. The results indicated that CIL-102 exerted anti-proliferative activity by disrupting microtubule functions through tubulin binding and provided important insights into the differential mode of tubulin binding by CIL-102 and colchicine. (c) 2012 Elsevier Inc. All rights reserved.