Tetracycline-mediated photodynamic inactivation of animal viruses

Demethylchlortetracycline (DMCT), doxycycline and, to a lesser extent, chlortetracycline were capable of mediating the in vitro photoinactivation of Venezuelan equine encephalitis (VEE) virus. Other tetracyclines tested were found to be inactive in this respect. However, no correlation between chemical structure and photosensitizing activity could be established. The photoinactivation of VEE virus by DMCT proceeds through a photodynamic mechanism as shown by the absolute requirement of O2 for the inactivation to take place. The photoinactivating effect of DMCT was also exerted upon other animal viruses tested, i.e. vesicular stomatitis virus, herpes simplex virus and poliovirus, even when, in the case of poliovirus, the capsid seems to be impermeable to the tetracycline. The fact that the two most effective photosensitizing tetracyclines for VEE virus are also the drugs more frequently associated with drug-induced phototoxicity in humans, suggests that virus photoinactivation could be used as a screening procedure for potentially phototoxic drugs developed for human application.