Brominated Derivatives of Noscapine Are Potent Microtubule-interfering Agents That Perturb Mitosis and Inhibit Cell Proliferation

Abstract

Noscapine, a microtubule-interfering agent, has been shown to arrest mitosis, to induce apoptosis, and to have potent antitumor activity. We report herein that two brominated derivatives of noscapine, 5-bromonoscapine (5-Br-nosc) and reduced 5-bromonoscapine (Rd 5-Br-nosc), have higher tubulin binding activity than noscapine and affect tubulin polymerization differently from noscapine. In addition, they are able to arrest cell cycle progression at mitosis at concentrations much lower than noscapine. Interestingly, whereas noscapine-arrested cells have nearly normal bipolar spindles, cells arrested by 5-Br-nosc and Rd 5-Br-nosc form multipolar spindles. Nevertheless, noscapine and the two derivatives all affect the attachment of chromosomes to spindle microtubules and they impair the tension across paired kinetochores to similar degrees. 5-Br-nosc and Rd 5-Br-nosc are also more active than noscapine in inhibiting the proliferation of various human cancer cells, including those that are resistant to paclitaxel and epothilone. Our results thus indicate a great potential for the use of 5-Br-nosc and Rd 5-Br-nosc both as biological tools for studying microtubule-mediated processes and as chemotherapeutic agents for the treatment of human cancers.

Synthesis of microtubule-interfering halogenated noscapine analogs that perturb mitosis in cancer cells followed by cell death

“…The precise mechanism of action of these compounds involved a selective arrest of cell cycle progression at the G 2 /M phase in rapidly dividing cancer cells. Interestingly, whereas noscapine-arrested cells have nearly normal bipolar spindles [12], cells arrested by all halogenated analogs of noscapine formed pronounced multipolar spindles as revealed by immunofluorescence microscopy.…”

“…The cell proliferation assay was performed in 96-well plates as described previously [12,28]. Adherent cells (MCF-7 and MDA-MB-231) were seeded in 96-well plates at a density of 5 Â 10 3 cells per well.…”

“…The flow cytometric evaluation of the cell cycle status was performed as described previously [12]. Briefly, 2 Â 10 6 cells were centrifuged, washed twice with ice-cold PBS, and fixed in 70% ethanol.…”

“…Among the various antimitotic agents that perturb microtubule dynamics, noscapinoids constitute an emerging class of compounds receiving considerable attention [9][10][11][12][13][14][15][16]. A key structure for the cytotoxic activity of this class of compounds is the presence of two chiral centers forcing the two aromatic rings to be non-coplanar and in half-chair conformation [17].…”

“…The water solubility and feasibility for oral administration also represent valuable advantages of noscapine over many other antimicrotubule drugs [25][26][27]. Recently, several noscapine analogs have been reported by us and others that have much better therapeutic indices and improved pharmacological profiles [9][10][11][12][13][14][15][16].…”