Immunogenicity of an AS01-adjuvanted respiratory syncytial virus prefusion F (RSVPreF3) vaccine in animal models.

Respiratory syncytial virus (RSV) causes a high disease burden in older adults. An effective vaccine for this RSV-primed population may need to boost/elicit robust RSV-neutralizing antibody responses and recall/induce RSV-specific T cell responses. To inform the selection of the vaccine formulation for older adults, RSVPreF3 (RSV fusion glycoprotein engineered to maintain the prefusion conformation) with/without AS01 adjuvant was evaluated in mice and bovine RSV infection-primed cattle. In mice, RSVPreF3/AS01 elicited robust RSV-A/B-specific neutralization titers and RSV F-specific polyfunctional CD4+ T cell responses exceeding those induced by non-adjuvanted RSVPreF3. In primed bovines, RSVPreF3/AS01 tended to induce higher pre-/post-vaccination fold-increases in RSV-A/B-specific neutralization titers relative to non-adjuvanted and Alum-adjuvanted RSVPreF3 formulations, and elicited higher RSV F-specific CD4+ T cell frequencies relative to the non-adjuvanted vaccine. Though AS01 adjuvanticity varied by animal species and priming status, RSVPreF3/AS01 elicited/boosted RSV-A/B-specific neutralization titers and RSV F-specific CD4+ T cell responses in both animal models, which supported its further clinical evaluation as prophylactic candidate vaccine for older adults.

The RSVPreF3-AS01 vaccine elicits broad neutralization of contemporary and antigenically distant respiratory syncytial virus strains.

The RSVPreF3-AS01 vaccine, containing the respiratory syncytial virus (RSV) prefusion F protein and the AS01 adjuvant, was previously shown to boost neutralization responses against historical RSV strains and to be efficacious in preventing RSV-associated lower respiratory tract diseases in older adults. Although RSV F is highly conserved, variation does exist between strains. Here, we characterized variations in the major viral antigenic sites among contemporary RSV sequences when compared with RSVPreF3 and showed that, in older adults, RSVPreF3-AS01 broadly boosts neutralization responses against currently dominant and antigenically distant RSV strains. RSV-neutralizing responses are thought to play a central role in preventing RSV infection. Therefore, the breadth of RSVPreF3-AS01-elicited neutralization responses may contribute to vaccine efficacy against contemporary RSV strains and those that may emerge in the future.

Human sirtuins: Structures and flexibility.

In recent years, sirtuins (SIRTs), members of histone deacetylases (HDACs) class III, have been found to modulate cellular processes related to the development of human aging-related pathologies (i.e. cancer, neurodegeneration, metabolic disorders). Several crystallographic structures and computational studies have shed light into their catalytic mechanism of action, identifying also the structural elements for the design of selective drug candidates. In this review, we first aim at summarizing the structural features characterizing human SIRTs. We then describe the observed mass and one-off movements related to conformational changes upon SIRT-mediated recognition events. Such information will be useful not only for rationalizing the design of new SIRT modulators, but also for improving the comprehension of SIRT-related biological roles.

5-Benzylidene-hydantoin is a new scaffold for SIRT inhibition: From virtual screening to activity assays.

Sirtuins (SIRTs) are a family of enzymes able to catalyze the deacetylation of the N-acetyl lysines of both histone and non-histone substrates. Inhibition of SIRTs catalytic activity was recently reported in the literature as being beneficial in human diseases, with very promising applications in cancer therapy and enzymatic neurodegeneration. By combining a structure-based virtual screening of the Specs database with cell-based assays, we identified the 5-benzylidene-hydantoin as new scaffold for the inhibition of SIRT2 catalytic activity. Compound 97 (Specs ID AH-487/41657829), active in the low µM range against SIRT2, showed the optimal physicochemical properties for passive absorption as well as relatively low cytotoxicity in vitro. Further studies revealed non-competitive and mixed-type kinetics toward acetyl-lysine substrates and NAD(+), respectively, and a non-selective profile for SIRT inhibition. A binding mode consistent with the experimental evidence was proposed by molecular modeling. Additionally, the levels of acetyl-p53 were shown to be increased in HeLa cells treated with 97. Taken together, these results encourage further investigation of 5-benzylidene-hydantoin derivatives for their SIRT-related therapeutic effects.

Alkaloids from psychotria target sirtuins: in silico and in vitro interaction studies.

Epigenetic enzymes such as histone deacetylases play a crucial role in the development of ageing-related diseases. Among the 18 histone deacetylase isoforms found in humans, class III histone deacetylases, also known as sirtuins, seem to be promising targets for treating neurodegenerative conditions. Recently, Psychotria alkaloids, mainly monoterpene indoles, have been reported for their inhibitory properties against central nervous system cholinesterase and monoamine oxidase proteins. Given the multifunctional profile of these alkaloids in the central nervous system, and the fact that the indole scaffold has been previously associated with sirtuin inhibition, we hypothesized that these indole derivatives could also interact with sirtuins. In the present study, alkaloids previously isolated from Psychotria spp. were evaluated for their potential interaction with human sirtuin 1 and sirtuin 2 by molecular docking and molecular dynamics simulation approaches. The in silico results allowed for the selection of five potentially active compounds, namely, prunifoleine, 14-oxoprunifoleine, E-vallesiachotamine, Z-vallesiachotamine, and vallesiachotamine lactone. The sirtuin inhibition of these compounds was confirmed in vitro in a dose-response manner, with preliminary information on their pharmacokinetics properties.

Non-specific SIRT inhibition as a mechanism for the cytotoxicity of ginkgolic acids and urushiols.

Ginkgolic acids and urushiols are natural alkylphenols known for their mutagenic, carcinogenic and genotoxic potential. However, the mechanism of toxicity of these compounds has not been thoroughly elucidated so far. Considering that the SIRT inhibitory potential of anacardic acids has been hypothesized by in silico techniques, we herein demonstrated through both in vitro and computational methods that structurally related compounds such as ginkgolic acids and urushiols are able to modulate SIRT activity. Moreover, their SIRT inhibitory profile and cytotoxicity were comparable to sirtinol, a non-specific SIRT inhibitor (SIRT1 and SIRT2), and different from EX-527, a SIRT1 specific inhibitor. This is the first report on the SIRT inhibition of ginkgolic acids and urushiols. The results reported here are in line with previously observed effects on the induction of apoptosis by this class of compounds, and the non-specific SIRT inhibition is suggested as a new mechanism for their in vitro cytotoxicity.

Computational studies on sirtuins from Trypanosoma cruzi: structures, conformations and interactions with phytochemicals.

BACKGROUND: The silent-information regulator 2 proteins, otherwise called sirtuins, are currently considered as emerging anti-parasitic targets. Nicotinamide, a pan-sirtuin inhibitor, is known to cause kinetoplast alterations and the arrested growth of T. cruzi, the protozoan responsible for Chagas disease. These observations suggested that sirtuins from this parasite (TcSir2rp1 and TcSir2rp3) could play an important role in the regulation of the parasitic cell cycle. Thus, their inhibition could be exploited for the development of novel anti-trypanosomal compounds. METHODS: Homology modeling was used to determine the three-dimensional features of the sirtuin TcSir2rp1 from T. cruzi. The apo-form of human SIRT2 and the same structure solved in complex with its co-substrate NAD(+) allowed the modeling of TcSir2rp1 in the open and closed conformational states. Molecular docking studies were then carried out. A library composed of fifty natural and diverse compounds that are known to be active against this parasite, was established based on the literature and virtually screened against TcSir2rp1 and TcSir2rp3, which was previously modeled by our group. RESULTS: In this study, two conformational states of TcSir2rp1 were described for the first time. The molecular docking results of compounds capable of binding sirtuins proved to be meaningful when the closed conformation of the protein was taken into account for calculations. This specific conformation was then used for the virtual screening of antritrypanosomal phytochemicals against TcSir2rp1 and TcSir2rp3. The calculations identified a limited number of scaffolds extracted from Vismia orientalis, Cussonia zimmermannii, Amomum aculeatum and Anacardium occidentale that potentially interact with both proteins. CONCLUSIONS: The study provided reliable models for future structure-based drug design projects concerning sirtuins from T. cruzi. Molecular docking studies highlighted not only the advantages of performing in silico interaction studies on their closed conformations but they also suggested the potential mechanism of action of four phytochemicals known for their anti-trypanosomal activity in vitro.

Structural insights of SIR2rp3 proteins as promising biotargets to fight against Chagas disease and leishmaniasis.

Trypanosoma cruzi and Leishmania spp. are protozoan pathogens responsible for Chagas disease and leishmaniasis, respectively. Current therapies rely only on a very small number of drugs, most of them are inadequate because of their severe host toxicity or drug-resistance phenomena. In order to find therapeutic alternatives, the identification of new biotargets is highly desired. In this study, homology modelling, docking and molecular dynamics simulations have been used to generate robust 3D models of NAD(+)-dependent deacetylases from Trypanosoma and Leishmania spp., known as SIR2rp3, whose structures have never been described before. Molecular docking of known inhibitors revealed strong analogies with the mitochondrial human SIRT5 in terms of binding mode and interaction strength. On the other hand, by extending the analysis to the channel rims, regions of difference between host and parasitic targets, useful for future selective drug design projects, were pointed out.