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 αβ-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).

BaR domains are found in proteins that bind and remodel membranes and participate in cytoskeletal and nuclear processes. Here, we report the crystal structure of the BAR domain from the human Bin1 protein at 2.0 Å resolution. Both the quaternary and tertiary architectures of the homodimeric Bin1 BAR domain are built upon "knobs-into-holes" packing of side chains, like those found in conventional left-handed coiled-coils, and this packing governs the curvature of a putative membrane-engaging concave face. Our calculations indicate that the Bin1 BAR domain contains two potential sites for protein-protein interactions on the convex face of the dimer. Comparative analysis of structural features reveals that at least three architectural subtypes of the BAR domain are encoded in the human genome, represented by the Arfaptin, Bin1/ Amphiphysin, and IRSp53 BAR domains. We discuss how these principal groups may differ in their potential to form regulatory heterotypic interactions.

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.

The structural changes taking place in the enzyme thymidine phosphorylase (TPase, also known as PD-ECGF) that are required to achieve catalytic competence upon binding thymidine and phosphate have been simulated by means of targeted molecular dynamics (tMD). The hinge regions were characterized by structural homology comparisons with pyrimidine nucleoside phosphorylase, whose X-ray structure has been solved both in a closed and in an open form. The rearrangement of residues around the substrate that was observed during the tMD trajectory suggested that His-85 could be playing an important role in the catalytic mechanism. A quantum mechanical study of the reaction in the presence of the most relevant active site residues was then performed at the semiempirical level. The results revealed that His-85 could be involved in the protonation of the pyrimidine base at the O2 position to yield the enol tautomer of the base. To establish the role of this oxygen atom in the reaction, ground states, transition states, and final products were studied using higher level ab initio methods starting from both thymidine and 2-thiothymidine as alternative substrates. Comparison of both transition states showed that replacing the oxygen at position 2 of the pyrimidine base by sulfur should accelerate the reaction rate. Consistent with this result, 2-thiothymidine was shown to be a better substrate for TPase than the natural substrate, thymidine. For simulating the final step of the reaction, tMD simulations were used to study domain opening upon product formation considering both the enol and keto tautomers of thymine. Product release from the enzyme was easiest in the simulation that incorporated the keto tautomer of thymine, suggesting that the enol intermediate spontaneously tautomerizes back to the more energetically stable keto form. These results highlight a previously unreported role for His-85 in the catalytic mechanism of TPase and can have important implications for the design of novel TPase inhibitors.