Inhibition of various steps in the replication cycle of vesicular stomatitis virus contributes to its photoinactivation by AlPcS4 or Pc4 and red light

Vesicular stomatitis virus (VSV) was used as a model virus to study the pro cesses involved in photoinactivation by aluminum phthalocyanine tetrasulfon ate (AIPcS(4),) or silicon phthalocyanine HOSiPcOSi(CH3)(2)(CH2)(3)N(CH3)(2 ) (Pc4) and red light. Previously a very rapid decrease in the intracellula r viral RNA synthesis after photodynamic treatment was observed. This decre ase was correlated to different steps in the replication cycle. Binding of VSV to host cells and internalization were only slightly impaired and could be visualized by electron microscopy. The capability of the virus to fuse with membranes in an acidic endosomal environment was studied using both py rene-labeled liposomes and a hemolysis assay as a model. These tests indica te a rapid decrease of fusion capacity after AIPcS(4), treatment, which cor related with the decrease in RNA synthesis, For Pc4 treatment no such corre lation was found. The fusion process is the first step in the replication c ycle, affected by AIPcS(4) treatment, but also in vitro RNA polymerase acti vity was previously shown to be inhibited. Inactivation of VSV by Pc4 treat ment is apparently caused by damage to a variety of viral components. Photo dynamic treatment of virus suspensions with both sensitizers causes formati on of 8-oxo-7,8-dihydroguanosine in viral RNA as measured by HPLC with elec trochemical detection. This damage might be partly responsible for inhibiti on of the in vitro viral RNA polymerase activity by photodynamic treatment.