Solubilized triterpenes from mistletoe show anti-tumor effects on skin-derived cell lines

Abstract

The European mistletoe (Viscum album L.) contains anti-tumorigenic triterpene acids such as oleanolic acid (OA) [1] and betulinic acid (BA) [2] in relatively high amounts [3]. Due to their low water solubility <0.02µg/ml [3] most in vitro experiments with OA and BA are performed by using the toxic solvent DMSO. We could now avoid for the first time the use of DMSO by aqueous solubilization. Water solubility of the triterpene acids was achieved by complexation with cyclodextrins as carrier molecules. We tested the effects of different aqueous triterpene-cyclodextrin solutions on cell viability (Via Light Assay; Lonza), proliferation (Cell Proliferation ELISA, BrdU; Roche) and DNA fragmentation (Cell Death Detection ELISA; Roche) of human (HaCaT and Cal-39) and murine (B16. F10) skin-derived cell lines and compared them to triterpene acids dissolved in DMSO. We show here that mistletoe derived triterpene acids dose dependently decrease cell viability and proliferation of skin-derived cell lines. We have also shown that solubilized triterpene acids induce caspase dependent DNA fragmentation. The cyclodextrins used as carrier molecules did not contribute to the anti-tumor effects and did not cause toxic effects. The comparison with triterpene acids dissolved in DMSO shows that inhibitory effects were mediated by the main component OA whereas efficient concentrations of the minor component BA were not reached. In summary, we have demonstrated that solubilization of triterpene acids is superior to the use of DMSO and that these new formulations efficiently induce anti-tumor effects in vitro.