A recombinant HiBiT-tagged porcine circovirus type 2 (PCV2) reporter system identifies potent antiviral activity of terameprocol.

Porcine Circovirus type 2 (PCV2), the main causative agent of porcine circovirus-associated diseases in both domestic and wild pigs, is an economically challenging immune suppressive pathogen worldwide which exacerbates diseases caused by other swine viruses despite vaccinations. This signifies the need for alternate control strategies including effective antivirals. We have developed a high-throughput reporter based antiviral screen with a HiBiT tagged recombinant PCV2 (rPCV2-HiBiT) engineered to express HiBiT tagged capsid protein thus enabling a luminescence-based quantification of viral replication. The rPCV2-HiBiT platform was validated using known antiviral compounds, Ivermectin and Ribavirin, which showed a dose-dependent antiviral activity (up to 47% at 100 μM) and a moderate efficacy (30% at 100 μM with IC50 of 4.4 μM), respectively. Upon screening 34 compounds with reported activity against DNA viruses from the Medicines for Malaria Venture (MMV) Pathogen Box, we identified six compounds showing more than 50% inhibition of viral replication at the lowest test dose of 1 μM. Amongst them, terameprocol (MMV1581036) exhibited the strongest antiviral activity against PCV2 with a selectivity index of 38.27 μM. The previously known activity of terameprocol in suppressing the Sp1-mediated transcription, suggests a broad-spectrum activity against DNA viruses with a less likelihood of developing drug resistance. Our study establishes the rPCV2-HiBiT platform as an efficient high throughput antiviral discovery tool and identifies terameprocol as a potential antiviral candidate against PCV2.