Apoptosis-inducing properties of Viscum album L. extracts from different host trees, correlate with their content of toxic mistletoe lectins

Background. Extracts from Viscum album L,. (VAL), which are one of the most widely used alternative cancer therapies in Europe, have been recognised t o induce apoptosis. A clinically relevant direct anti-tumour effect might b e induced only by their intratumoural or intrapleural injection, and thus e ffectiveness is highly dependent on the apoptosis-inducing potencies of the extracts used, Materials and Methods. To characterise these properties, hu man lymphocytes were incubated for 72 hours with VAL extracts from differen t host trees and harvest times. Cell death-associated changes such as an ap optotic sub-Gr peak, binding of Annexin-V; generation of reactive oxygen in termediates (ROI), expression of mitochondrial Apo2.7 molecules, and uptake of the DNA-intercalating dye propidium iodide were measured by flow cytome try. Results and Conclusions: Biologically active VAL compounds, and thus c ytotoxicity, are dependent on the manufacturing process, host tree, and tim e of harvest. Although the mistletoe lectin (ML) content of VAL extracts st rongly correlated with their apoptosis-inducing properties, the presence of these proteins will not guarantee its biological activity, indicating the involvement of other components which may modulate ML cytotoxicity.