Influence of diimine bidentate ligand in the nitrosyl and nitro terpyridine ruthenium complex on the HSA/DNA interaction and antiviral activity.

Nitric oxide (NO) acts in different physiological processes, such as blood pressure control, antiparasitic activities, neurotransmission, and antitumor action. Among the exogenous NO donors, ruthenium nitrosyl/nitro complexes are potential candidates for prodrugs, due to their physicochemical properties, such as thermal and physiological pH stability. In this work, we proposed the synthesis and physical characterization of the new nitro terpyridine ruthenium (II) complexes of the type [RuII(L)(NO2)(tpy)]PF6 where tpy = 2,2':6',2″-terpyridine; L = 3,4-diaminobenzoic acid (bdq) or o-phenylenediamine (bd) and evaluation of influence of diimine bidentate ligand NH.NHq-R (R = H or COOH) in the HSA/DNA interaction as well as antiviral activity. The interactions between HSA and new nitro complexes [RuII(L)(NO2)(tpy)]+ were evaluated. The Ka values for the HSA-[RuII(bdq)(NO2)(tpy)]+ is 10 times bigger than HSA-[RuII(bd)(NO2)(tpy)]+. The sites of interaction between HSA and the complexes via synchronous fluorescence suppression indicate that the [RuII(bdq)(NO2)(tpy)]+ is found close to the Trp-241 residue, while the [RuII(bd)(NO2)(tpy)]+ complex is close to Tyr residues. The interaction with fish sperm fs-DNA using direct spectrophotometric titration (Kb) and ethidium bromide replacement (KSV and Kapp) showed weak interaction in the system fs-DNA-[RuII(bdq)(NO)(tpy)]+. Furthermore, fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+ system showed higher intercalation constant. Circular dichroism spectra for fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+, suggest semi-intercalative accompanied by major groove binding interaction modes. The [RuII(bd)(NO2)(tpy)]+ and [RuII(bd)(NO)(tpy)]3+ inhibit replication of Zika and Chikungunya viruses based in the nitric oxide release under S-nitrosylation reaction with cysteine viral.

Discovery of an imidazonaphthyridine and a riminophenazine as potent anti-Zika virus agents through a replicon-based high-throughput screening.

The 2015/16 Zika virus (ZIKV) epidemic led to almost 1 million confirmed cases in 84 countries and was associated to the development of congenital microcephaly and Guillain-Barré syndrome. More recently, a ZIKV African lineage was identified in Brazil raising concerns about a future outbreak. The long-term consequences of viral infection emphasizes the need for the development of effective anti-ZIKV drugs. In this study, we developed and characterized a ZIKV replicon cell line for the screening of viral replication inhibitors. The replicon system was developed by engineering the IRES-Neo cassette into the 3' UTR terminus of the ZIKV Rluc DNA construct. After in vitro transcription, replicon RNA was used to transfect BHK-21 cells, that were selected with G418, thus generating the BHK-21-RepZIKV_IRES-Neo cell line. Through this replicon-based cell system, we identified two molecules with potent anti-ZIKV activities, an imidazonaphthyridine and a riminophenazine, both from the MMV/DNDi Pandemic Response Box library of 400 drug-like compounds. The imidazonaphthyridine, known as RO8191, showed remarkable selectivity against ZIKV, while the riminophenazine, the antibiotic Clofazimine, could act as a non-nucleoside analog inhibitor of viral RNA-dependent RNA polymerase (RdRp), as evidenced both in vitro and in silico. The data showed herein supports the use of replicon-based assays in high-throughput screening format as a biosafe and reliable tool for antiviral drug discovery.