Novel indole-based antimitotic agents: design, synthesis and study of the antitumor mechanism of action

Abstract

[EN] Cancer is the second leading cause of death, accountable for about 1 in 6 deaths globally. There is massive investment in the development of novel therapeutic strategies, although brand-new chemotherapy faces several handicaps such as lack of clinical efficacy, pharmacokinetic problems, or the appearance of resistance mechanisms. In this work, we focused on the design of novel compounds aimed to interact with the protein tubulin, which is a validated target in cancer chemotherapy and arguably one of the most successful ones. i) It has proven effective as a therapeutic target since some of the antitumor drugs currently at the forefront in clinical use (e.g. paclitaxel), act by binding to tubulin. ii) It is an essential protein, barely susceptible to relevant mutations that would affect its proper functioning. Microtubules are built up by the lateral association of protofilaments, which in turn, are formed by the head-to-tail polymerization of α,β-tubulin. Microtubules are highly dynamic structures that fulfill a vast range of pivotal functions, such as chromosome segregation during cell division, vesicle transport, or maintenance of cell shape. These roles make them an appealing target in cancer chemotherapy since minor disturbance of their dynamics leads to an antimitotic effect and eventually cell death. Many tubulin binding drugs also exert antivascular activities hampering the growth of solid tumors by shutting down the supply of oxygen and nutrients. Among the several binding pockets described in microtubules to date, we have focused on the colchicine domain. Although some colchicine site ligands are quite advanced in clinical trials, none has yet reached clinical approval. The ligands that bind to this pocket mostly show simple chemical structures, so constructing an extensive library of compounds to explore the impact of structural changes on the antitumor activity is attainable. The colchicine domain has been considered as an ensemble of three consecutive zones (1-2-3) based on the X-ray structures of protein-ligand complexes. Most of the known ligands bind to two zones, and only a few of them interact simultaneously with the three zones of the domain. The primary goal of this work is to obtain compounds with advantageous properties that are able to interact with the colchicine domain, as promising pharmacological agents in cancer therapy. To this end, the design has been approached by parts considering the data provided by PDB structures and structure-activity relationship data of compounds with no X-ray reports, under the presumption of their binding mode. We have designed compounds directed to zones 1-2, 2-3, and 1-2-3, leveraging the common zone 2 in the different approaches by designing common structural elements for this zone that can be later combined with residues in zones 1 and 3. This work has yielded a series of indole-based compounds with two aromatic rings connected by sulfonamide or tetrazole groups that preferentially adopt folded conformations that are required for the interaction with zones 1-2 of the colchicine domain. These compounds bind to the colchicine domain in β-tubulin and preclude the in vitro polymerization of microtubules, inducing disorganization of the tubulin cytoskeleton. Our results expose that these compounds exert antimitotic and antivascular activities. The antimitotic mechanism of action leads to antiproliferative potencies in the submicromolar or nanomolar range against several tumor and non-tumorigenic cell lines. We have studied the mechanism of action and the induction of cell death in the human epithelial cervical carcinoma HeLa cells caused by some representative lead compounds and compared their behavior with other cell lines. This research contributes to further unraveling the molecular processes, both reversible or irreversible, that are involved in the transition from microtubule depolymerization to cell death.