Human cancer cells exhibit in vitro individual receptiveness towards different mistletoe extracts.

In vitro cytotoxic effects of three aqueous mistletoe extracts on cell physiology against different human tumor cell lines and primary cancer cells were investigated in order to compare the receptiveness of different cancer cells against different mistletoe products. Therefore cell proliferation (BrdU-incorporation assay), mitochondrial activity (MTT-testing) and necrotic cell toxicity (LDH assay) were assayed over serial dilutions of the test products. Data obtained with HELA-S3, MOLT-4, MFM-223, COR-L51, KPL-1 and VM-CUB1 tumor cell lines and Iscador M (20 mg/ml), Iscador Q (20 mg/ml) and Abnobaviscum Fraxini -2 (20 mg/ml) indicated significant growth-inhibition of all cell lines, but also different cell susceptibilities against the different extracts. These variations were not only monitored on established cell lines but also on primary mamma carcinoma cells from surgical resectates. Concerning cell proliferation and mitochondrial activity Abnobaviscum Fraxini exhibits stronger inhibitory effects compared to products from the Iscador series. In case the evaluation was standardized on the active contents of VAA-I within the different products, the Iscador extracts possess higher cytotoxic activity. Pure viscotoxins and mistletoe lectins exhibited less effects than the extracts. The simultaneous presence of pure mistletoe lectins and mistletoe polysaccharides diminished the VAA-mediated cytotoxic effects. The presence of fetal calf serum (FCS) in cultivation media during in vitro testing diminished the cytotoxic effects of mistletoe extracts. It was shown that in vivo application of mistletoe preparations led to the formation of antibodies against unknown compounds of the extracts, diminishing the cytotoxic effect.