Novel Suicide Ligands of Tubulin Arrest Cancer Cells in S-Phase

Abstract

It is presently accepted that the mechanism of action for all anti-tumor tubulin ligands involves the perturbation of microtubule dynamics during the G2/M phase of cell division and subsequent entry into apoptosis [1]. In this report, we challenge the established dogma by describing a unique mechanism of action caused by a novel series of tubulin ligands, halogenated derivatives of acetamido benzoyl ethyl ester. We have developed a suicide ligand for tubulin, which covalently attaches to the target and shows potent cancericidal activity in tissue culture assays and in animal tumor models. These compounds target early S-phase at the G1/S transition rather than the G2/M phase and mitotic arrest. Bcl-2 phosphorylation, a marker of mitotic microtubule inhibition by other tubulin ligands was dramatically altered, phosphorylation was rapid and biphasic rather than a slow linear event. The halogenated ethyl ester series of derivatives thus constitute a unique set of tubulin ligands which induce a novel mechanism of apoptosis.

Protease inhibitor–induced stabilization of p21waf1/cip1 and cell‐cycle arrest in chemical carcinogen–exposed mammary and lung cells†

“…Treatment of such cells with the carcinogen 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine causes early S phase arrest after short exposure times but late S-phase accumulation with longer exposure [29]. Certain tubulin ligands effect early S phase arrest in cancer cells [30].…”

The benzophenanthridine alkaloid sanguinarine perturbs microtubule assembly dynamics through tubulin binding. A possible mechanism for its antiproliferative activity

“…Although mitotic arrest is the common mechanism for microtubule‐targeted drugs, exceptions to this have also been reported. For instance, halogenated derivatives of acetamidobenzoyl ethyl ester were found to depolymerize cellular microtubules and to arrest cells at the G 1 /S transition, indicating that antitubulin agents can inhibit cell proliferation without arresting cells at mitosis [16]. In addition, it was shown that indanocine, a microtubule‐depolymerizing agent, inhibits proliferation of certain types of noncycling tumor cell at G 0 /G 1 phase [17].…”

Artelastin is a cytotoxic prenylated flavone that disturbs microtubules and interferes with DNA replication in MCF-7 human breast cancer cells

“…Reports of G1 and S-phase arrest, by potent inhibitors of microtubule assembly (Davis et al, 1999;Sablina et al, 1999;Weitzel and Vandre, 2000), have been attributed to their interaction with microtubule proteins and/or spindle assembly checkpoints in different cells (Marko et al, 2002). However, by flow cytometry, cell cycle analysis of artelastin treated cells revealed an accumulation in S phase rather than a mitotic arrest.…”