Study of the time-dependent uptake of mistletoe lectin by cultured tumor cells

In cancer therapy phytopreparations of Viscum album L. (Santalaceae) are used as an alternative treatment [1]. The main ingredients of the aqueous extracts are the mistletoe lectins which belong to the ribosome-inactivating proteins type II [2]. In this work, the intracellular uptake of these lectins by cultured tumor cells was analysed in order to determine its time-dependency. Furthermore, we analysed the uptake in relation to the mistletoe triterpenes, mainly oleanolic acid.

The uptake of mistletoe lectin by THP 1-, HL 60-, HOS 143B- and Ewing TC 71-cells were determined after 30, 60 and 120 minutes by an enzyme linked immunosorbent assay (Sandwich-ELISA) which quantifies the a-chain of the hololectin. The isolated lectin and the aqueous extract, with or without added mistletoe triterpenes, were analysed. After 120 minutes, an intracellular uptake of 20% was reached in all cell lines by aqueous extract with added triterpenes. Furthermore, the HOS 143B-cells – unlike the other models – pick up mistletoe lectin only with concomitant mistletoe triterpenes. The uptake in THP 1-, HL 60- and Ewing TC 71-cells was time-dependent. The addition of triterpenes did not influence the process. Interestingly, the uptake of mistletoe lectin by HOS 143B-cells could only be measured after addition of triterpenes. The reason of this special behavior is still not known and needs further investigations.

Acknowledgements: We thank the BIRKEN AG for mistletoe extract preparation and Prof. U. Pfüller for mistletoe lectin I isolation.

References:

[1] Grothey A et al. Dtsch Med Wochenschr 1998; 123: 923 – 929

[2] Olsnes S et al. J Biol Chem 1982; 257: 13263 – 13270