Preactivation--a novel antitumour and antiviral approach.

Merocyanine 540 was activated by exposure to 514 nm laser light. This preactivated merocyanine 540 was then mixed (in the dark) with tumour cells, normal cells and envelope viruses to assess its antiproliferative activity. This treatment resulted in 70-90% killing of tumour cells from different cell lines while 85% of normal human peripheral blood mononuclear cells survived the treatment. However, not all types of tumour cells were affected. Preactivated merocyanine 540 was also effective in virtually completely inactivating cell-free herpes simplex and human immunodeficiency viruses. Preactivated photoactive compounds can exert their toxic effects in the dark without further dependence on light and may have potential systemic use.