Antivascular and antitumor properties of the tubulin-binding chalcone TUB091.

We investigated the microtubule-destabilizing, vascular-targeting, anti-tumor and anti-metastatic activities of a new series of chalcones, whose prototype compound is (E)-3-(3''-amino-4''-methoxyphenyl)-1-(5'-methoxy-3',4'-methylendioxyphenyl)-2-methylprop-2-en-1-one (TUB091). X-ray crystallography showed that these chalcones bind to the colchicine site of tubulin and therefore prevent the curved-to-straight structural transition of tubulin, which is required for microtubule formation. Accordingly, TUB091 inhibited cancer and endothelial cell growth, induced G2/M phase arrest and apoptosis at 1-10 nM. In addition, TUB091 displayed vascular disrupting effects in vitro and in the chicken chorioallantoic membrane (CAM) assay at low nanomolar concentrations. A water-soluble L-Lys-L-Pro derivative of TUB091 (i.e. TUB099) showed potent antitumor activity in melanoma and breast cancer xenograft models by causing rapid intratumoral vascular shutdown and massive tumor necrosis. TUB099 also displayed anti-metastatic activity similar to that of combretastatin A4-phosphate. Our data indicate that this novel class of chalcones represents interesting lead molecules for the design of vascular disrupting agents (VDAs). Moreover, we provide evidence that our prodrug approach may be valuable for the development of anti-cancer drugs.

Blocking Blood Flow to Solid Tumors by Destabilizing Tubulin: An Approach to Targeting Tumor Growth.

The unique characteristics of the tumor vasculature offer the possibility to selectively target tumor growth and vascularization using tubulin-destabilizing agents. Evidence accumulated with combretastatin A-4 (CA-4) and its prodrug CA-4P support the therapeutic value of compounds sharing this mechanism of action. However, the chemical instability and poor solubility of CA-4 demand alternative compounds that are able to surmount these limitations. This Perspective illustrates the different classes of compounds that behave similar to CA-4, analyzes their binding mode to αß-tubulin according to recently available structural complexes, and includes described approaches to improve their delivery. In addition, dissecting the mechanism of action of CA-4 and analogues allows a closer insight into the advantages and drawbacks associated with these tubulin-destabilizing agents that behave as vascular disrupting agents (VDAs).

Synthesis and antiproliferative activity of 6-phenylaminopurines.

A series of novel 6-phenylaminopurines have been efficiently synthesized in 3 steps exploring different groups at positions 2, 8 and 9 of the purine ring and at the exocyclic nitrogen atom at position 6. Among the newly described purines, five compounds showed antiproliferative activity with IC50 values below 10 µM, the tetrahydroquinoline derivative at position 6 of phenylaminopurine being the most active of the series in the six cell lines tested. Moreover, the compounds induced G2/M phase arrest in human cervical carcinoma HeLa cells as reported for tubulin depolymerizing agents.

Identification of [1,2,3]triazolo[4,5-d]pyrimidin-7(6H)-ones as novel inhibitors of Chikungunya virus replication.

Chikungunya virus (CHIKV) is a re-emerging Alphavirus that is transmitted to humans by Aedes mosquitoes. Currently, there are still no drugs or vaccines available for the treatment or prevention of this disease. Although traditionally restricted to Africa and Asia, the adaptation of the virus to Aedes albopictus, a mosquito species with an almost worldwide distribution, has contributed to the geographical spread of this virus in the past decade. Here, we report on a new family of compounds named [1,2,3]triazolo[4,5-d]pyrimidin-7(6H)-ones that inhibit CHIKV replication in the low micromolar range with no toxicity to the host (Vero) cells. The most potent compound in this series has an EC50 value below 1 µM with no cytotoxicity detected up to 668 µM, therefore affording a selectivity index greater than 600. Interestingly, the compounds have little or no antiviral activity on the replication of other members of the Togaviridae family. The exploration and study of this class of selective inhibitors of CHIKV replication will contribute to deeper insights into the CHIKV life cycle and may be a first step toward the development of a clinical drug candidate.

Novel colchicine-site binders with a cyclohexanedione scaffold identified through a ligand-based virtual screening approach.

Vascular disrupting agents (VDAs) constitute an innovative anticancer therapy that targets the tumor endothelium, leading to tumor necrosis. Our approach for the identification of new VDAs has relied on a ligand 3-D shape similarity virtual screening (VS) approach using the ROCS program as the VS tool and as query colchicine and TN-16, which both bind the α,ß-tubulin dimer. One of the hits identified, using TN-16 as query, has been explored by the synthesis of its structural analogues, leading to 2-(1-((2-methoxyphenyl)amino)ethylidene)-5-phenylcyclohexane-1,3-dione (compound 16c) with an IC50 = 0.09 ± 0.01 µM in HMEC-1 and BAEC, being 100-fold more potent than the initial hit. Compound 16c caused cell cycle arrest in the G2/M phase and interacted with the colchicine-binding site in tubulin, as confirmed by a competition assay with N,N'-ethylenebis(iodoacetamide) and by fluorescence spectroscopy. Moreover, 16c destroyed an established endothelial tubular network at 1 µM and inhibited the migration and invasion of human breast carcinoma cells at 0.4 µM. In conclusion, our approach has led to a new chemotype of promising antiproliferative compounds with antimitotic and potential VDA properties.

Binding of glutathione to enterovirus capsids is essential for virion morphogenesis.

Enteroviruses (family of the Picornaviridae) cover a large group of medically important human pathogens for which no antiviral treatment is approved. Although these viruses have been extensively studied, some aspects of the viral life cycle, in particular morphogenesis, are yet poorly understood. We report the discovery of TP219 as a novel inhibitor of the replication of several enteroviruses, including coxsackievirus and poliovirus. We show that TP219 binds directly glutathione (GSH), thereby rapidly depleting intracellular GSH levels and that this interferes with virus morphogenesis without affecting viral RNA replication. The inhibitory effect on assembly was shown not to depend on an altered reducing environment. Using TP219, we show that GSH is an essential stabilizing cofactor during the transition of protomeric particles into pentameric particles. Sequential passaging of coxsackievirus B3 in the presence of low GSH-levels selected for GSH-independent mutants that harbored a surface-exposed methionine in VP1 at the interface between two protomers. In line with this observation, enteroviruses that already contained this surface-exposed methionine, such as EV71, did not rely on GSH for virus morphogenesis. Biochemical and microscopical analysis provided strong evidence for a direct interaction between GSH and wildtype VP1 and a role for this interaction in localizing assembly intermediates to replication sites. Consistently, the interaction between GSH and mutant VP1 was abolished resulting in a relocalization of the assembly intermediates to replication sites independent from GSH. This study thus reveals GSH as a novel stabilizing host factor essential for the production of infectious enterovirus progeny and provides new insights into the poorly understood process of morphogenesis.

Efficient synthesis and anti-enteroviral activity of 9-arylpurines.

To further explore the anti-enteroviral activity of 9-aryl-6-chloropurines, three different series of compounds with a dialkylamino, (alkyl)amido, or oxazolidinone substituent at the aryl ring have been synthesized, in most cases with the aid of microwave-assisted synthesis. The resulting compounds efficiently inhibit Coxsackie virus type B3 (CVB3) replication with EC(50) values varying from 3 to 15 µM, and with no significant toxicity in Vero cells. The most potent compounds also selectively inhibit the replication of other enteroviruses including Coxsackie virus B4 and Echo virus 11. The cross-resistance studies performed with different 9-aryl-6-chloropurines indicate that they all belong to the same pharmacological family and differ from other CVB3 drugs such as enviroxime.