Effects of mistletoe (Viscum album L.) extracts on cultured tumor cells.

Bacterially fermented mistletoe preparations (BFMP) were tested on rat hepatoma tissue culture (HTC) cells and human leukemia Molt 4 cells. A dose-dependent inhibition of the growth rate of the cells was observed. For both cell lines, cytostatic concentrations, expressed in weight of fresh plant, were 0.5 mg/ml culture medium for oak BFMP and 1 mg/ml for apple tree BFMP. However, the action of the two preparations was markedly different on each cell line. Non-viable HTC cells were not stained by trypan blue while non-viable Molt 4 cells were fully colored by this reagent. A lysis of cellular membranes of HTC cells was observed by electron microscopy. Furthermore, oak BFMP inhibited the growth of virus transformed 3T3-SV40 cells more than that of non-transformed 3T3 cells. In contrast to BFMP, non-fermented extracts and a purified mistletoe lectin showed a greater inhibition of the growth of Molt 4 cells than of HTC cells. Samples withdrawn at different times during fermentation gradually lost their inhibitory effect on the growth of Molt 4 cells while their action on HTC cells increased up to the 4th day of fermentation. These results are discussed in relation to the cytotoxic substances of mistletoe already characterized.