Current Topics in Medicinal Chemistry - Volume 14, Issue 20, 2014

As enabling technology, the development and application of multicomponent reactions (MCRs) are now an integral part of the work of any major medical research unit. Targeted MCR approaches focused on specific antimitotic pathways afford new solutions for the medicinal chemistry of the XXI century. In this review, the contribution of these procedures to the discovery of antimitotic drugs that are currently in clinical trials or already in the market is discussed.

Colchicine site ligands have proved to be potent inhibitors of tubulin polymerization, which leads them not only to display cytotoxic effects but also vascular disrupting effects on tumour neovasculature. In recent years, many compounds have been designed, synthesized and evaluated in order to improve the potency, stability and physicochemical properties of these agents with the aim of developing an agent that could reach the clinical assay level. Here we analyze the eleven X-ray structures of tubulin in complex with ligands at the colchicine site by dividing it into four different zones of interaction, we review the new compounds that have appeared in the literature since 2008 and that were designed based on any of these X-ray structures and, finally, we describe our latest results in the design of new potent antimitotic indole derivatives that have confirmed the flexibility of one of the zones described for the colchicine site.

Microtubules are high dynamic protein filaments fundamental for cells growth and proliferation. Hence, tubulin inhibitors are useful anticancer compounds. Three major binding site have been identified in tubulin, on the basis of known ligands: the vinca domain, the colchicine domain and the taxane domain. Several compounds able to bind the colchicine and the taxane domains have been to date synthesized and evaluated. In this review we give a description of the developed QSAR and 3D-QSAR models, giving particular attention to those studies that give structural insight in the binding modes of compounds with the target.

Currently approved antimitotic therapies used in chemotherapy are microtubule-targeting agents (MTAs). Despite they achieved some level of success, they have limited efficacy as single agents, with issues of slippages and resistance, and cause significant side effects. The advances in the identification of other mitosis-related targets led to the development of new mitotic regulators aimed to perturb mitosis without interfering with microtubule dynamics in non-dividing cells trying to reduce side effects in patients. Some of these compounds like those targeted to entry and mitotic kinases, mitotic kinesins/motor proteins, and multiprotein complexes have been evaluated in vitro and in animal models, and some of them have reached clinical trials. Despite promising preclinical results, in many cases, the efficacy demonstrated by these new antimitotics was not better than current microtubule inhibitors. In this paper we review present and future strategies on the search for new antimitotic compounds based on identification of new protein targets and development of multifunctional inhibitors of mitosis in cancer cells.

Natural products still play an important role in the medicinal chemistry, especially in some therapeutic areas. As example more than 60% of currently-used anticancer agents are derives from natural sources including plants, marine organisms or micro-organism. Thus natural products (NP) are an high-impact source of new “lead compounds” or new potential therapeutic agents despite the large development of biotechnology and combinatorial chemistry in the drug discovery and development. Many examples of anticancer drugs as paclitaxel, combretastatin, bryostatin and discodermolide have shown the importance of NP in the anticancer chemotherapy through many years. Many organisms have been studied as sources of drugs namely plants, micro-organisms and marine organisms and the obtained NP can be considered a group of “privileged chemical structures” evolved in nature to interact with other organisms. For this reason NP are a good starting points for pharmaceutical research and also for library design. Tubulin and microtubules are one of the most studied targets for the search of anticancer compounds. Microtubule targeting agents (MTA) also named antimitotic agents are compounds that are able to perturb mitosis but are also able to arrest cell growing during interphase. The anticancer drugs, taxanes and vinca alkaloids have established tubulin as important target in cancer therapy. More recently the vascular disrupting agents (VDA) combretastatin analogues were studied for their antimitotics properties. This review will consider the anti mitotic NP and their potential impact in the development of new therapeutic agents.

There is a strong need for new antimitotic drugs that overcome the limitations of the currently used antitubulin compounds, mainly neurotoxicity and the development of resistance. One of the most promising new targets is kinesin spindle protein (KSP, also known as Eg5), which contributes to the formation of mitotic spindle during cell division and has not been reported to play any other cellular role so far. This review covers KSP inhibitors binding at the allosteric, induced-fit L5 site reported between 2008 and December 2013. Among them, main groups include dihydropyrimidines, STLC derivatives, quinazoline-based compounds and pyrrole/ pyrazole and related agents. Structure-activity relationships are described, as well as the synthesis of representative compounds. They are remarkably selective for KSP and produce G2/M mitotic arrest accompanied by a characteristic monoastral cellular phenotype. Some of them have entered clinical trials, the most advanced being in Phase II. Therefore, KSP inhibitors show great potential as future clinical antimitotic agents, especially due to their activity in taxane-resistant tumors.

Epothilones are natural compounds isolated from a myxobacterium at the beginning of the 1990s, and showed a remarkable anti-neoplastic activity. They act through the same mechanism of action of paclitaxel, by stabilizing microtubules and inducing apoptosis. Although, their chemical structure, simpler than taxanes, makes them more suitable for derivatization. Their interesting pharmacokinetic and bioavailabilty profiles, and the activity against paclitaxel-resistant cell lines make them interesting therapeutic agents. Here a brief historical perspective of epothilones is presented, since their isolation, the identification of their mechanism of action and activity, to the recent clinical trials.

Agents that interfere with tubulin function have a broad anti-tumour spectrum and they represent one of the most significant classes of anti-cancer agents. In the past few years, several small synthetic molecules that have an azaflavone nucleus as a core structure have been identified as tubulin inhibitors. Among these, several arylquinolinones, arylnaphthyridinones, arylquinazolinones and arylpyrroloquinolinones have shown to exert their anticancer activity through inhibition of tubulin polymerisation via the colchicine binding site. They arrest the cell growth at G2/M phase providing cell death via both mitotic and apoptotic pathway. Recently, some of them proved to be multi-inhibitor simultaneously targeting both PI3K-Akt-mTOR pathway and the microtubule cytoskeleton. Furthermore, some were demonstrated to possess effective anti-angiogenic properties similar to that of natural compounds combretastatine-A4 and vincristine. This article reviews the synthesis, biological activities and SARs of the main classes of azaflavones. Brief mention of the subtype 2- styrylquinazolinones has also been made.

ADP-ribosylation or PARsylation is one of the most abundant modifications of proteins and DNA. Although the usual context for PARsylation involves the detection and repair of DNA damage in the cell, poly(ADP-ribose) polymerases are known to regulate a number of biological processes besides maintaining genome integrity. One of these processes is the assembly and maintenance of the mitotic spindle where the presence of PARP-1 and tankyrase 1 (TNKS1), two of the best-characterized members of the PARP superfamily, is of critical importance. Here, we recapitulate the biological implications of the absence of poly(ADP-ribose) polymerases and depletion of PARsylation occurrence in mitosis in order to better understand the antimitotic effects of PARP inhibitors. In this regard, we also present an overview of the existing and more relevant molecules, with a special attention to the historical development of their pharmacological properties and structures, as well as a brief summary of clinical trials involving PARP inhibitors.