Cell line-dependent activation and antiviral activity of T-1105, the non-fluorinated analogue of T-705 (favipiravir)

The antiviral drug T-705 (favipiravir) and its non-fluorinated analogue T-1105 inhibit the polymerases of RNA viruses after being converted to their ribonucleoside triphosphate (RTP) metabolite. We here compared the activation efficiency of T-705 and T-1105 in four cell lines that are commonly used for their antiviral evaluation. In MDCK cells, the levels of T-705-RTP were markedly lower than those of T-1105-RTP, while the opposite was seen in A549, Vero and HEK293T cells. In the latter three cell lines, T-1105 activation was hindered by inefficient conversion of the ribonucleoside monophosphate to the ribonucleoside diphosphate en route to forming the active triphosphate. Accordingly, T-1105 had better anti-RNA virus activity in MDCK cells, while T-705 was more potent in the other three cell lines. Additionally, we identified a fourth metabolite, the NAD analogue of T-705/T-1105, and showed that it can be formed by nicotinamide mononucleotide adenylyltransferase.