Two thiosemicarbazones derived from 1-indanone as potent non-nucleoside inhibitors of bovine viral diarrhea virus of different genotypes and biotypes

Bovine viral diarrhea virus (BVDV) is a widespread pathogen of cattle and other mammals that causes major economic losses in the livestock industry. N4-TSC and 6NO₂-TSC are two thiosemicarbazones derived from 1-indanone that exhibit anti-BVDV activity in vitro. These compounds selectively inhibit BVDV and are effective against both cytopathic and non-cytopathic BVDV-1 and BVDV-2 strains. We confirmed that N4-TSC acts at the onset of viral RNA synthesis, as previously reported for 6NO₂-TSC. Moreover, resistance selection and characterization showed that N4-TSC^R mutants were highly resistant to N4-TSC but remained susceptible to 6NO₂-TSC. In contrast, 6NO₂-TSC^R mutants were resistant to both compounds. Additionally, mutations N264D and A392E were found in the viral RNA-dependent RNA polymerase (RdRp) of N4-TSC^R mutants, whereas I261 M was found in 6NO₂-TSC^R mutants. These mutations lay in a hydrophobic pocket within the fingertips region of BVDV RdRp that has been described as a “hot spot” for BVDV non-nucleoside inhibitors.