PRIMARY TARGETS FOR PHOTOINACTIVATION OF VESICULAR STOMATITIS-VIRUS BY ALPCS(4) OR PC4 AND RED-LIGHT

Phthalocyanines are useful sensitizers for the photodynamic sterilizat ion of red blood cell concentrates. The mechanism of photoinactivation of lipid-enveloped viruses is not completely understood, Vesicular st omatitis virus (VSV) was used as a model virus to study the primary ta rgets of photoinactivation by aluminum phthalocyanine tetrasulfonate ( AlPcS(4)) or silicon phthalocyanine HOSiPcOSi(CH3)(2)(CH2)(3)N(CH3)(2) (Pc4) and red light. Inactivation conditions for VSV in buffer were d etermined using an end point dilution assay, and viral RNA synthesis i n host cells was measured to determine the loss of infectivity in a di rect way. The very rapid decrease in the viral RNA synthesis after pho todynamic treatment was correlated with respect to different potential primary targets that are involved in different steps of the viral rep lication cycle. Damage to the viral proteins, induced by treatment wit h AlPcS(4) or Pc4 and analyzed by gel electrophoresis, could not accou nt for the observed loss of infectivity. Binding of VSV to host cells was only slightly impaired after photodynamic treatment with both sens itizers and could therefore not be responsible for the rapid decrease in viral RNA synthesis in cells. A very strong inhibition of viral RNA polymerase activity after treatment with AlPcS(4) and red light was d etectable using an in vitro assay. This decrease correlated well with the loss of infectivity, indicating that either the RNA or the viral R NA polymerase is the primary target for photoinactivation of VSV with AlPcS(4). Treatment with Pc4 did not cause inhibition of viral RNA pol ymerase activity to an extent that could account for the observed very rapid loss of infectivity. It was therefore concluded that neither th e viral proteins nor the binding to the host cells nor the RNA or RNA polymerase are the primary targets for photoinactivation of VSV by Pc4 .