Antiretroviral activities of hypericin and rose bengal: photodynamic effects on Friend leukemia virus infection of mice.

The ability of hypericin to protect mice from splenomegaly resulting from infection with Friend leukemia virus (FLV) was re-examined in light of recent evidence showing that light is absolutely required for this drug's antiviral activity. FLV-induced splenomegaly was not prevented or ameliorated in mice injected with 100 micrograms hypericin, either mixed with the FLV inoculum or administered 1 day p.i., either under normal laboratory light or in the dark. These results contradict previous findings. Both hypericin and rose bengal, however, inactivated the FLV inoculum at low doses (< 11 micrograms), provided that the mixture was illuminated for 1 h under a normal fluorescent desk lamp. This procedure protected mice completely from FLV-induced splenomegaly, and provided a possible explanation for the discrepancy between our results and those reported previously. We conclude that for FLV, as for other enveloped viruses studied previously, illumination of hypericin with the virus is absolutely required for hypericin's antiviral (virucidal) effects, thus limiting its potential usefulness as an antiretroviral agent.