Therapeutic Efficacy of Natural Compounds From Viscum Album l. In Acute Lymphoblastic Leukemia

Abstract 3261

Viscum album L. (mistletoe) is one of the most widely used complementary cancer therapies. Due to their low solubility, aqueous extracts contain hardly any triterpenes which are known to possess anti-tumoral properties. Using cyclodextrins it was possible to solubilisate mistletoe triterpenes (mainly oleanolic acid (OA)) and achieve a plant extract with high levels of OA and mistletoe lectins (ML).

In the present study, we determined for the first time the effect of clearly defined mistletoe extracts against human acute lymphoblastic leukemia (ALL) in vitro and in vivo. These mistletoe extracts contain either lectins (aqueous extract, viscum) or cyclodextrin solubilised triterpenes (STE) such as oleanolic - and betulinic acid and combinations thereof (viscumTT). We used the C.B-17/SCID mouse model and tested efficacy and mechanisms of the treatment with these preparations in vitro and in vivo. The human leukemia cell line NALM-6 was incubated with increasing concentrations of mistletoe preparations (10-60 μg/ml OA; 0.8–8 ng/ml ML) and tested for their cytotoxicity in vitro. Apoptosis was determined using mitochondrial potential, DNA fragmentation and Annexin/PI assays. In vivo efficacy was determined in the C.B-17/SCID mouse model. For this purpose, 1×10⁶ NALM-6 cells were injected IV into groups of C.B-17/SCID mice (n=8) and STE extracts were administered three times per week for 14 days by intraperitoneal (IP) injection.

Viscum album L. extracts inhibited cell proliferation and show cytotoxic properties in vitro. The highest level of apoptosis with a decrease of the mitochondrial potential was observed with STE preparation at a concentration of 50 μg/ml OA and for lectin-treated cells for 4.7 ng/ml (IC₅₀). To exclude an unwanted cell death via necrosis, LDH release was measured after 4h of incubation with different doses and extracts of Viscum album L without significant LDH release.

Based on these data, we investigated the effect of Viscum album L. extracts in vivo. For this purpose 40 mg/kg/day oleanolic acid (STE), 3 μg/kg/day lectin (viscum) or a combination thereof (viscumTT) were administered IP. In line with the in vitro results, mice treated with viscumTT showed a significant longer survival. Mice receiving PBS had a mean survival time of 38 days whereas mice treated with viscumTT had a mean survival of 50,5 days (p=0,005). In summary, we demonstrate for the first time that either solubilised triterpenes or lectins and combinations thereof induce dose- and time-dependent apoptosis in the ALL cell line NALM-6. Based on the in vivo data we believe that triterpene containing Viscum album L. extracts may possess an impressive therapeutic potential. Thus, our investigations provide an important base line for the design of further experimental studies and clinical trials to investigate the effects of individual components and potential synergisms in ALL.