Identification of Combinations of Approved Drugs With Synergistic Activity Against Ebola Virus in Cell Cultures

Abstract

Background: A need to develop therapeutics to treat Ebola virus disease patients in remote and resource-challenged settings remains in the wake of the 2013-2016 epidemic in West Africa. Toward this goal, we screened drugs under consideration as treatment options and other drugs of interest, most being small molecules approved by the Food and Drug Administration. Drugs demonstrating in vitro antiviral activity were advanced for evaluation in combinations because of advantages often provided by drug cocktails.

Methods: Drugs were screened for blockade of Ebola virus infection in cultured cells. Twelve drugs were tested in all (78 pair-wise) combinations, and 3 were tested in a subset of combinations.

Results: Multiple synergistic drug pairs emerged, with the majority comprising 2 entry inhibitors. For the pairs of entry inhibitors studied, synergy was demonstrated at the level of virus entry into host cells. Highly synergistic pairs included aripiprazole/piperacetazine, sertraline/toremifene, sertraline/bepridil, and amodiaquine/clomiphene.

Conclusions: Our study shows the feasibility of identifying pairs of approved drugs that synergistically block Ebola virus infection in cell cultures. We discuss our findings in terms of the theoretic ability of these or alternate combinations to reach therapeutic levels. Future research will assess selected combinations in small-animal models of Ebola virus disease.

Figure 1.

Four drug combinations with synergistic activity against Ebola virus. Huh7 cells were pretreated with drug combinations (shipped frozen) for 1 hour, inoculated at a multiplicity of infection of 0.5 for 48 hours, and assessed by fluorescence assay. Shown are findings of dose matrix (6 × 6) evaluation of 4 drug combinations from Matrix 1: clomiphene citrate/sertraline HCl (A), clomiphene citrate/apilimod (B), sertraline HCl/toremifene citrate (C), and toremifene citrate/apilimod (D). A, The heat map of the percentage response shows the antiviral activity of each combination (100% corresponds to no activity), and the Δ Bliss plot indicates how much a combination effect differs from the additive effect as determined by the Bliss model. The experiment was run once or twice with triplicate wells per dose. A Δ Bliss of 0 indicates an additive effect, a Δ Bliss of <0 indicates a synergistic effect, and a Δ Bliss of >0 indicates an antagonistic effect.

Figure 2.

Additional drug combinations with synergistic activity against Ebola virus. Shown are findings of a dose matrix (6 × 6) evaluation of piperacetazine/aripiprazole (A), sertraline HCl/toremifene citrate (B), bepridil HCl/sertraline HCl (C), and amodiaquine/clomiphene citrate (D). Huh7 cells were pretreated with drug combinations (freshly prepared) for 1 hour, inoculated at a multiplicity of infection (MOI) of 0.21 (A and D) or a MOI of 0.5 (B and C) for 48 hours, and assessed by chemiluminescence assay. Data are displayed as in Figure 1. The experiment was run twice with triplicate wells per dose. Heat maps from 1 of 2 experiments are shown. A Δ Bliss of 0 indicates an additive effect, a Δ Bliss of <0 indicates a synergistic effect, and a Δ Bliss of >0 indicates an antagonistic effect.