The large scale of the Ebola virus disease (EVD) outbreak in West Africa in 2013-2016 raised the question whether the host cell interactions of the responsible Ebola virus (EBOV) strain differed from those of other ebolaviruses. We previously reported that the glycoprotein (GP) of the virus circulating in West Africa in 2014 (EBOV2014) exhibited reduced ability to mediate entry into two nonhuman primate (NHP)-derived cell lines relative to the GP of EBOV1976. Here, we investigated the molecular determinants underlying the differential entry efficiency. We found that EBOV2014-GP-driven entry into diverse NHP-derived cell lines, as well as human monocyte-derived macrophages and dendritic cells, was reduced compared to EBOV1976-GP, although entry into most human-and all bat-derived cell lines tested was comparable. Moreover, EBOV2014 replication in NHP but not human cells was diminished relative to EBOV1976, suggesting that reduced cell entry translated into reduced viral spread. Mutagenic analysis of EBOV2014-GP and EBOV1976-GP revealed that an amino acid polymorphism in the receptor-binding domain, A82V, modulated entry efficiency in a cell line-independent manner and did not account for the reduced EBOV2014-GP-driven entry into NHP cells. In contrast, polymorphism T544I, located in the internal fusion loop in the GP2 subunit, was found to be responsible for the entry phenotype. These results suggest that position 544 is an important determinant of EBOV infectivity for both NHP and certain human target cells. IMPORTANCEThe Ebola virus disease outbreak in West Africa in 2013 entailed more than 10,000 deaths. The scale of the outbreak and its dramatic impact on human health raised the question whether the responsible virus was particularly adept at infecting human cells. Our study shows that an amino acid exchange, A82V, that was acquired during the epidemic and that was not observed in previously circulating viruses, increases viral entry into diverse target cells. In contrast, the epidemic virus showed a reduced ability to enter cells of nonhuman primates compared to the virus circulating in 1976, and a single amino acid exchange in the internal fusion loop of the viral glycoprotein was found to account for this phenotype.

We have developed compounds with a promising activity against Acinetobacter baumannii and Pseudomonas aeruginosa, which are both on the WHO priority list of antibiotic-resistant bacteria. Starting from DNA gyrase inhibitor 1, we identified compound 27, featuring a 10-fold improved aqueous solubility, a 10-fold improved inhibition of topoisomerase IV from A. baumannii and P. aeruginosa, a 10-fold decreased inhibition of human topoisomerase IIα, and no cross-resistance to novobiocin. Cocrystal structures of 1 in complex with Escherichia coli GyrB24 and (S)-27 in complex with A. baumannii GyrB23 and P. aeruginosa GyrB24 revealed their binding to the ATP-binding pocket of the GyrB subunit. In further optimization steps, solubility, plasma free fraction, and other ADME properties of 27 were improved by fine-tuning of lipophilicity. In particular, analogs of 27 with retained anti-Gram-negative activity and improved plasma free fraction were identified. The series was found to be nongenotoxic, nonmutagenic, devoid of mitochondrial toxicity, and possessed no ion channel liabilities.

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