Alberto Massarotti

The tubulin colchicine domain: A molecular modeling perspective

Computational approaches have been increasingly applied to drug design over the past three decades and have already provided some useful results in the discovery of anticancer drugs. Given the increased availability of crystal structures in recent years, a growing number of molecular modeling studies on tubulin have been reported. Herein we present a brief overview of the role played by computational methods in anti‐tubulin research, specifically in the context of colchicine binding agent research. An overview of current structures is reported, along with a brief discussion on the issues associated with the various tubulin isotypes. Finally, a summary of the most recent and relevant results is presented, highlighting the challenges and opportunities faced by researchers in this field.

Medicinal Chemistry of Nicotinamide Phosphoribosyltransferase (NAMPT) Inhibitors

Nicotinamide phoshophoribosyltransferase (NAMPT) plays a key role in the replenishment of the NAD pool in cells. This in turn makes this enzyme an important player in bioenergetics and in the regulation of NAD-using enzymes, such as PARPs and sirtuins. Furthermore, there is now ample evidence that NAMPT is secreted and has a role as a cytokine. An important role of either the intracellular or extracellular form of NAMPT has been shown in cancer, inflammation, and metabolic diseases. The first NAMPT inhibitors (FK866 and CHS828) have already entered clinical trials, and a surge in interest in the synthesis of novel molecules has occurred. The present review summarizes the recent progress in this field.

Regioselective Suzuki Coupling of Dihaloheteroaromatic Compounds as a Rapid Strategy To Synthesize Potent Rigid Combretastatin Analogues

Combretastatin A-4 (CA-4) is a potent tubulin depolymerizing agent able to inhibit tumor growth and with antivascular effects. Although it is in clinical trials, the search for novel analogues that may display better/different features is still ongoing. In this manuscript we describe the synthesis of novel constrained analogues of CA-4 obtained in only two synthetic steps exploiting a regioselective Suzuki coupling of dihalogenated heteroaromatic and alicyclic compounds. All the compounds synthesized have been evaluated for cytotoxicity and for their ability to inhibit tubulin assembly. One of them, 38, displayed low nanomolar cytotoxicity and proved to have a pharmacodynamic profile similar to that of CA-4 and a better pharmacokinetic profile, but most important of all, this synthetic strategy may pave the way for the easy and rapid generation of novel rigid analogues of combretastatins.

Are 1,4- and 1,5-disubstituted 1,2,3-triazoles good pharmacophoric groups?

Over the last decade, 1,2,3‐triazoles have received increasing attention in medicinal chemistry thanks to the discovery of the highly useful and widely applicable 1,3‐dipolar cycloaddition reaction between azides and alkynes (click chemistry) catalyzed by copper salts and ruthenium complexes. After a decade of medicinal chemistry research on 1,2,3‐triazoles, we feel that the time is ripe to demonstrate the real ability of this heterocycle to participate in important and pivotal binding interactions with biological targets while maintaining a good pharmacokinetic profile. In this study, we retrieved and analyzed X‐ray crystal structures of complexes between 1,2,3‐triazoles and either proteins or DNA to understand the pharmacophoric role of the triazole. Furthermore, the metabolic stability, the capacity to inhibit cytochromes, and the contribution of 1,2,3‐triazoles to the overall aqueous solubility of compounds containing them have been analyzed. This information should furnish fresh insight for medicinal chemists in the design of novel bioactive molecules that contain the triazole nucleus.

Computer-aided identification, design and synthesis of a novel series of compounds with selective antiviral activity against chikungunya virus.

Chikungunya virus (CHIKV) is an Arbovirus that is transmitted to humans primarily by the mosquito species Aedes aegypti. Infection with this pathogen is often associated with fever, rash and arthralgia. Neither a vaccine nor an antiviral drug is available for the prevention or treatment of this disease. Albeit considered a tropical pathogen, adaptation of the virus to the mosquito species Aedes albopictus, which is also very common in temperate zones, has resulted in recent outbreaks in Europe and the US. In the present study, we report on the discovery of a novel series of compounds that inhibit CHIKV replication in the low μM range. In particular, we initially performed a virtual screening simulation of ∼5 million compounds on the CHIKV nsP2, the viral protease, after which we investigated and explored the Structure-Activity Relationships of the hit identified in silico. Overall, a series of 26 compounds, including the original hit, was evaluated in a virus-cell-based CPE reduction assay. The study of such selective inhibitors will contribute to a better understanding of the CHIKV replication cycle and may represents a first step towards the development of a clinical candidate drug for the treatment of this disease.

Replacement of the double bond of antitubulin chalcones with triazoles and tetrazoles: Synthesis and biological evaluation.

In the chalcone scaffold, it is thought that the double bond is an important structural linker but it is likely not essential for the interaction with tubulin. Yet, it may be a potential site of metabolic degradation and interaction with biological nucleophiles. In this letter, we have replaced this olefinic portion of chalcones with two metabolically stable and chemically inert heterocyclic rings, namely triazole or tetrazole. Yet, our biologic data suggest that, unlike in other antitubulinic structures, the olephinic ring might not be merely a structural linker.

Solution-Phase Parallel Synthesis and Biological Evaluation of Combretatriazoles

Combretastatin A-4 is an antitumoral and antitubulin agent that is active only in its cis configuration. In the present manuscript, we have synthesized cis-locked combretastatins containing a triazole ring (combretatriazoles). To achieve this, we have developed a column chromatography-free parallel solution-phase synthesis that exploits the reaction between azides and alpha-keto phosphorus ylids, which is known to regioselectively generate the 1,5-disubstituted triazoles. The prepared compounds were screened as antitubulinic agents, allowing us to identify three new compounds with high potency, two of which show a new mechanism of action that induces cells to appear multinucleated and display a high number of mitotic spindles.

Molecular field analysis and 3D-quantitative structure-activity relationship study (MFA 3D-QSAR) unveil novel features of bile acid recognition at TGR5

Bile acids regulate nongenomic actions through the activation of TGR5, a membrane receptor that is G protein-coupled to the induction of adenylate cyclase. In this work, a training set of 43 bile acid derivatives is used to develop a molecular interaction field analysis (MFA) and a 3D-quantitative structure-activity relationship study (3D-QSAR) of TGR5 agonists. The predictive ability of the resulting model is evaluated using an external set of compounds with known TGR5 activity, and six bile acid derivatives whose unknown TGR5 activity is herein assessed with in vitro luciferase assay of cAMP formation. The results show a good predictive model and indicate a statistically relevant degree of correlation between the TGR5 activity and the molecular interaction fields produced by discrete positions of the bile acid scaffold. This information is instrumental to extend on a quantitative basis the current structure-activity relationships of bile acids as TGR5 modulators and will be fruitful to design new potent and selective agonists of the receptor.

Estrogenic Analogues Synthesized by Click Chemistry

The estrogen receptors, responsible for the effects of this hormone, are known to be able to recognize nonsteroidogenic molecules, and this has led to the development of molecules with therapeutic potential. The phenomenon of nonsteroidal ligands of the estrogen receptors is also thought to play a major role in food and environmental sciences, with the winepolyphenol resveratrol and the insecticide DDT thought to act as estrogenic substances. It is therefore evident that it is of great interest to develop specific nonsteroidal substances that interfere with the estrogen receptors in a receptor-specific and/or tissue-specific manner and that display agonistic, antagonistic, or partial agonistic properties. Indeed, a number of strategies have been or could be employed to generate new structures, namely the screening of existing chemical libraries, the screening of natural compound libraries, novel modifications of known compounds with estrogenic potential, or the de novo generation of chemical libraries using rapid synthetic methods. Click chemistry is an increasingly common method for rapid synthesis of novel biologically active compounds. This term, coined by Barry K. Sharpless, now refers to reactions yielding the product in high yield without the need for further purification, without generating offensive byproducts, and operating in a benign solvent, usually water. In this way, it is possible to generate a plethora of new compounds reliably and thereby accelerate the process of drug discovery. Briefly, the paradigmatic “click” reaction is the [3+2] cycloaddition between an azide and an alkyne in the presence of copper (I) salts which generate the 1,4 disubstituted 1H-1,2,3-triazole ring in excellent yield. Three distinct observations have drawn our attention to the possibility of applying click chemistry to the synthesis of ER ligands: 1) reports that a pyrazole core can be used to build compounds that are ER ligands, 2) the successful bioisosteric replacement of pyrazole with a triazole in fibronil, an insecticide acting as a GABA receptor antagonist, and 3) our report that several resveratrol analogues synthesized by click chemistry retain estrogen-like activity. We have therefore used the archetypical [3+2] azide-alkyne cycloaddition to link two phenol rings, bearing the hydroxyl moieties in different positions, with a distance comparable to estradiol or diethylstilbestrol. Azides (1–3, Figure 1) were obtained by reacting commercially available amine phenols, via diazonium salt, with sodium azide. The desired ethynyl phenols (4–6, Figure 1) were ob-

Design, Synthesis, and Biological Evaluation of Combretabenzodiazepines: A Novel Class of Anti-Tubulin Agents

In the present manuscript, starting from the 1,4-benzodiazepin-2-one nucleus, a privileged structure in medicinal chemistry, we have synthesized a novel class of cis-locked combretastatins named combreatabenzodiazepines. They show similar cytotoxic and antitubulin activity compared to combretastatin A-4 in neuroblastoma cells, showing a better pharmacokinetic profile. This class of compounds has therefore the potential for further development as antitubulin agents.