Merocyanine 540-Sensitized Photoinactivation of Enveloped Viruses in Blood Products: Site and Mechanism

The amphipathic dye, merocyanine 540 (MC540). which preferentially photosensitizes enveloped viruses and virusinfected cells, is currently being evaluated in preclinical models as a blood sterilizing agent. In this communication, we report on an initial analysis of the site and nature of MC54O-mediated photodynamic damages to human herpes simplex virus type 1 and human cytomegalovirus. The comigration of dye molecules and virions on a gel filtration column, the red-shift of the fluorescence emission spectrum of virus-containing fractions, and the distribution of MC540treated virions in an aqueous two-phase partition system were indicative of MC540 binding to the enveloped viruses and localizing in a lipophilic environment (most likely the viral envelope). Fluorescence quenching and fluorescence resonance energy transfer experiments suggested that both