Metal coordinating inhibitors of Rift Valley fever virus replication

Abstract

Rift Valley fever virus (RVFV) is a veterinary and human pathogen and is an agent of bioterrorism concern. Currently, RVFV treatment is limited to supportive care, so new drugs to control RVFV infection are urgently needed. RVFV is a member of the order Bunyavirales, whose replication depends on the enzymatic activity of the viral L protein. Screening for RVFV inhibitors among compounds with divalent cation-coordinating motifs similar to known viral nuclease inhibitors identified 47 novel RVFV inhibitors with selective indexes from 1.1-103 and 50% effective concentrations of 1.2-56 μM in Vero cells, primarily α-Hydroxytropolones and N-Hydroxypyridinediones. Inhibitor activity and selective index was validated in the human cell line A549. To evaluate specificity, select compounds were tested against a second Bunyavirus, La Crosse Virus (LACV), and the flavivirus Zika (ZIKV). These data indicate that the α-Hydroxytropolone and N-Hydroxypyridinedione chemotypes should be investigated in the future to determine their mechanism(s) of action allowing further development as therapeutics for RVFV and LACV, and these chemotypes should be evaluated for activity against related pathogens, including Hantaan virus, severe fever with thrombocytopenia syndrome virus, Crimean-Congo hemorrhagic fever virus.

Fig 1. Development and validation of RVFV antiviral screen.

A. Identification of optimal mAb for the detection of RVFV by mAb staining of a serial dilution of RVFV strain MP-12 in an FFA. B. Impact of cell number on the sensitivity of antiviral compound screen. C. Evaluation of the sensitivity of the antiviral compound screen based upon the evaluation of ribavirin and β-D-N4-Hydroxycytidine N4-Hydroxycytidine (NHC/EIDD-1931), a known antiviral for RVFV. Data is presented as focus forming units. These data are the cumulation of three independent experiments with technical duplicates.

Fig 2. In vitro dose-response and cytotoxicity of compounds against RVFV (MP12).

A549 cells were infected with RVFV MP12 then treated with decreasing concentrations of compound. The reduction in virus concentration was measured by FFA at twenty-four hours post infection. Data is representative of three individual experiments with two biological replicates. Error bars represent standard deviation.

Fig 3. Antiviral effect of compounds on bunyavirus replication.

Vero cells were infected with either RVFV ZH501 (A) or LACV (B) then treated with decreasing concentrations of antiviral compound. Viral growth was measured by FFA. Data represents three independent experiments completed with biological replicates. Error bars represent standard deviation.

Fig 4. Representative structures of RFVF inhibitors.

(A) Inactive and active troponoid natural products, illustrating preference for oxygen triad, along with common nuclease inhibition mode for αHTs. (B) Synthetic αHTs with activity under 10 μM against RVFV, demonstrating broad substitution tolerance. (C) Representative examples of alternative scaffolds with activity against RFVF.