Targeting flavivirus RNA dependent RNA polymerase through a pyridobenzothiazole inhibitor

AbstractRNA dependent RNA polymerases (RdRp) are essential enzymes for flavivirus replication. Starting from an in silico docking analysis we identified a pyridobenzothiazole compound, HeE1-2Tyr, able to inhibit West Nile and Dengue RdRps activity in vitro, which proved effective against different flaviviruses in cell culture. Crystallographic data show that HeE1-2Tyr binds between the fingers domain and the priming loop of Dengue virus RdRp (Site 1). Conversely, enzyme kinetics, binding studies and mutational analyses suggest that, during the catalytic cycle and assembly of the RdRp-RNA complex, HeE1-2Tyr might be hosted in a distinct binding site (Site 2). RdRp mutational studies, driven by in silico docking analysis, allowed us to locate the inhibition Site 2 in the thumb domain. Taken together, our results provide innovative concepts for optimization of a new class of anti-flavivirus compounds

1,2,4-Triazolo[1,5-a]pyrimidines as a Novel Class of Inhibitors of the HIV-1 Reverse Transcriptase-Associated Ribonuclease H Activity

Despite great efforts have been made in the prevention and therapy of human immunodeficiency virus (HIV-1) infection, however the difficulty to eradicate latent viral reservoirs together with the emergence of multi-drug-resistant strains require the search for innovative agents, possibly exploiting novel mechanisms of action. In this context, the HIV-1 reverse transcriptase (RT)-associated ribonuclease H (RNase H), which is one of the few HIV-1 encoded enzymatic function still not targeted by any current drug, can be considered as an appealing target. In this work, we repurposed in-house anti-influenza derivatives based on the 1,2,4-triazolo[1,5-a]-pyrimidine (TZP) scaffold for their ability to inhibit HIV-1 RNase H function. Based on the results, a successive multi-step structural exploration around the TZP core was performed leading to identify catechol derivatives that inhibited RNase H in the low micromolar range without showing RT-associated polymerase inhibitory activity. The antiviral evaluation of the compounds in the MT4 cells showed any activity against HIV-1 (IIIB strain). Molecular modelling and mutagenesis analysis suggested key interactions with an unexplored allosteric site providing insights for the future optimization of this class of RNase H inhibitors

Deciphering the Molecular Recognition Mechanism of Multidrug Resistance Staphylococcus aureus NorA Efflux Pump Using a Supervised Molecular Dynamics Approach

The use and misuse of antibiotics has resulted in critical conditions for drug-resistant bacteria emergency, accelerating the development of antimicrobial resistance (AMR). In this context, the co-administration of an antibiotic with a compound able to restore sufficient antibacterial activity may be a successful strategy. In particular, the identification of efflux pump inhibitors (EPIs) holds promise for new antibiotic resistance breakers (ARBs). Indeed, bacterial efflux pumps have a key role in AMR development; for instance, NorA efflux pump contributes to Staphylococcus aureus (S. aureus) resistance against fluoroquinolone antibiotics (e.g., ciprofloxacin) by promoting their active extrusion from the cells. Even though NorA efflux pump is known to be a potential target for EPIs development, the absence of structural information about this protein and the little knowledge available on its mechanism of action have strongly hampered rational drug discovery efforts in this area. In the present work, we investigated at the molecular level the substrate recognition pathway of NorA through a Supervised Molecular Dynamics (SuMD) approach, using a NorA homology model. Specific amino acids were identified as playing a key role in the efflux pump-mediated extrusion of its substrate, paving the way for a deeper understanding of both the mechanisms of action and the inhibition of such efflux pumps

Structural Modifications of the Quinolin-4-yloxy Core to Obtain New Staphylococcus aureus NorA Inhibitors

: Tackling antimicrobial resistance (AMR) represents a social responsibility aimed at renewing the antimicrobial armamentarium and identifying novel therapeutical approaches. Among the possible strategies, efflux pumps inhibition offers the advantage to contrast the resistance against all drugs which can be extruded. Efflux pump inhibitors (EPIs) are molecules devoid of any antimicrobial activity, but synergizing with pumps-substrate antibiotics. Herein, we performed an in silico scaffold hopping approach starting from quinolin-4-yloxy-based Staphylococcus aureus NorA EPIs by using previously built pharmacophore models for NorA inhibition activity. Four scaffolds were identified, synthesized, and modified with appropriate substituents to obtain new compounds, that were evaluated for their ability to inhibit NorA and synergize with the fluoroquinolone ciprofloxacin against resistant S. aureus strains. The two quinoline-4-carboxamide derivatives 3a and 3b showed the best results being synergic (4-fold MIC reduction) with ciprofloxacin at concentrations as low as 3.13 and 1.56 µg/mL, respectively, which were nontoxic for human THP-1 and A549 cells. The NorA inhibition was confirmed by SA-1199B ethidium bromide efflux and checkerboard assays against the isogenic pair SA-K2378 (norA++)/SA-K1902 (norA-). These in vitro results indicate the two compounds as valuable structures for designing novel S. aureus NorA inhibitors to be used in association with fluoroquinolones

Switching the three-component Biginelli-like reaction conditions for the regioselective synthesis of new 2-amino[1,2,4]triazolo[1,5-a]pyrimidines

: Among the eight different triazolopyrimidine isomers existing in nature, 1,2,4-triazolo[1,5-a]pyrimidine (TZP) is one of the most studied and used isomers in medicinal chemistry. For some years, our group has been involved in developing regioselective one-pot procedures for the synthesis of 2-amino-7-aryl-5-methyl- and 2-amino-5-aryl-7-methyl-TZPs of interest in the preparation of antiviral agents. In this work, taking advantage of a Biginelli-like multicomponent reaction (MCR), we report the identification of finely tunable conditions to regioselectively synthesize C-6 ester-substituted amino-TZP analogues, both in dihydro and oxidized forms. Indeed, the use of mild acidic conditions is strongly directed toward the regioselective synthesis of 5-aryl-7-methyl C-6-substituted TZP analogues, while the use of neutral ionic liquids shifted the regioselectivity towards 7-aryl-5-methyl derivatives. In addition, the novel synthesized scaffolds were functionalized at the C-2 position and evaluated for their antiviral activity against RNA viruses (influenza virus, flaviviruses, and SARS-CoV-2). Compounds 25 and 26 emerged as promising anti-flavivirus agents, showing activity in the low micromolar range

A Journey around the Medicinal Chemistry of Hepatitis C Virus Inhibitors Targeting NS4B: From Target to Preclinical Drug Candidates

Hepatitis C virus (HCV) infection is a global health burden with an estimated 130-170 million chronically infected individuals and is the cause of serious liver diseases such as cirrhosis and hepatocellular carcinoma. HCV NS4B protein represents a validated target for the identification of new drugs to be added to the combination regimen recently approved. During the last years, NS4B has thus been the object of impressive medicinal chemistry efforts, which led to the identification of promising preclinical candidates. In this context, the present review aims to discuss research published on NS4B functional inhibitors focusing the attention on hit identification, hit-to-lead optimization, ADME profile evaluation, and the structure-activity relationship data raised for each compound family taken into account. The information delivered in this review will be a useful and valuable tool for those medicinal chemists dealing with research programs focused on NS4B and aimed at the identification of innovative anti-HCV compounds

Pharmacological Agents Targeting the Cellular Prion Protein

Prion diseases are associated with the conversion of the cellular prion protein (PrPC), a glycoprotein expressed at the surface of a wide variety of cell types, into a misfolded conformer (the scrapie form of PrP, or PrPSc) that accumulates in brain tissues of affected individuals. PrPSc is a self-catalytic protein assembly capable of recruiting native conformers of PrPC, and causing their rearrangement into new PrPSc molecules. Several previous attempts to identify therapeutic agents against prion diseases have targeted PrPSc, and a number of compounds have shown potent anti-prion effects in experimental models. Unfortunately, so far, none of these molecules has successfully been translated into effective therapies for prion diseases. Moreover, mounting evidence suggests that PrPSc might be a difficult pharmacological target because of its poorly defined structure, heterogeneous composition, and ability to generate different structural conformers (known as prion strains) that can elude pharmacological intervention. In the last decade, a less intuitive strategy to overcome all these problems has emerged: targeting PrPC, the common substrate of any prion strain replication. This alternative approach possesses several technical and theoretical advantages, including the possibility of providing therapeutic effects also for other neurodegenerative disorders, based on recent observations indicating a role for PrPC in delivering neurotoxic signals of different misfolded proteins. Here, we provide an overview of compounds claimed to exert anti-prion effects by directly binding to PrPC, discussing pharmacological properties and therapeutic potentials of each chemical class