Remarkable photodynamic activity of tetra-cationic porphyrins against Vaccinia virus and Monkeypox virus.

In this context, we evaluated the photodynamic effects of four cationic tetra-(pyridyl)porphyrins against Vaccinia virus Western Reserve (VACV WR) and Monkeypox virus (MPXV). The porphyrins were initially analyzed for cytotoxicity to Vero cells by MTT assay and the maximal non-cytotoxic concentrations were used in virucidal assays. For virucidal assays, VACV-WR (107.5 TCID50/mL) and MPXV suspensions (106.97 TCID50/mL) were incubated with porphyrins, exposed (or not) to white light conditions at 45 min. Aliquots of virus suspensions were collected and quantitated, comparing the titers with those of virus suspensions not exposed to porphyrins and/or to light. Porphyrins 4-PtTPyP, 3-HTMeP and 4-HTMeP exhibited light-dependent activity and completely inactivated VACV-WR and MPXV after 5, 30 and 45 min of light exposure, respectively. In contrast, derivative 3-PtTPyP inactivated the viruses even in the absence of white light exposure, a light-independent virucidal activity. Virucidal assays were performed in the presence/absence of ROS scavengers. Ascorbic acid (AA) was the only capable of completely inhibiting photodynamic inactivation by the three porphyrins. This indicates a type II photodynamic mechanism by singlet oxygen (O). These results demonstrated photodynamic inactivation of poxviruses by tetra-cationic porphyrins, supporting their potential use - especially 4-PtTPyP - for virus inactivation in many applications. These results also pave the way for testing porphyrin in PDT of poxvirus-induced cutaneous lesions. In addition, our data validated the use of VACV as a in vitro model for targeted MPXV virucidal testing.