RT Journal Article SR Electronic T1 Cytotoxic Activity and Absence of Tumor Growth Stimulation of Standardized Mistletoe Extracts in Human Tumor Models In Vitro JF Anticancer Research JO Anticancer Res FD International Institute of Anticancer Research SP 223 OP 233 VO 27 IS 1A A1 GERHARD KELTER A1 JÖRG M. SCHIERHOLZ A1 IMMA U. FISCHER A1 HEINZ-HERBERT FIEBIG YR 2007 UL http://ar.iiarjournals.org/content/27/1A/223.abstract AB Mistletoe extracts are widely used in complementary and alternative cancer therapy in Europe. The extracts possess cytotoxic, as well as immunostimulatory effects. However, some investigators have suggested that low doses of mistletoe extracts could also induce tumor growth. The mistletoe extracts Helixor A, Helixor M and Helixor P were investigated for growth inhibitory and stimulatory effects in a panel of 38 human tumor cell lines in vitro. Mistletoe lectin I (ML-1), adriamycin and interleukin-6 (IL-6) were used as reference compounds. All three mistletoe preparations showed cytotoxic activity [T/C (Test/Control) <30%]: Helixor P was the most potent, followed by Helixor M and Helixor A with IC50 (50% inhibitory concentration) values of 68.4, 114 and 133 μg/ml, respectively. The IC50 values of ML-1 and adriamycin were 0.026 and 0.069 μg/ml. None of the human tumor cell lines in the panel showed growth stimulation (T/C (Test/Control) >125%) by the mistletoe extracts or ML-1, apart from two exceptions in the colon carcinoma cell line HCC-2998, in which Helixor M and ML-1 showed a marginal stimulation (T/C 128% and 131%, respectively) at one concentration only. Further investigations into the latter effect of Helixor M and ML-1 in the HCC-2998 line using five different proliferation assays, modified cell culture conditions and the identical production charge of mistletoe extract, as well as a new one, did not confirm the previous observation. It was concluded that the marginal stimulation found in the earlier experiments was a statistical coincidence. Helixor mistletoe preparations and ML-1 have cytotoxic activity and do not stimulate tumor cell proliferation in vitro which is in accordance with previous scientifically based observations on aqueous mistletoe extracts.