Characterization of the anticancer properties of monoglycosidic cardenolides isolated from Nerium oleander and Streptocaulon tomentosum.

AIM OF THE STUDY: For identification of the active constituents we investigated the anticancer activity of cardenolides from Streptocaulon tomentosum Wight & Arn. (Asclepiadaceae) and from Nerium oleander L. (Apocynaceae) which are both used against cancer in the traditional medicine in their region of origin. MATERIAL, METHODS AND
RESULTS: The antiproliferative activity of cardenolides isolated from roots of Streptocaulon tomentosum (IC(50)<1-15.3 μM after 2 days in MCF7) and of cardenolide containing fractions from the cold aqueous extract of Nerium oleander leaves ("Breastin", mean IC(50) 0.85 μg/ml in a panel of 36 human tumor cell lines), their influence on the cellular viability and on the cell cycle (block at the G2/M-phase or at the S-phase in tumor cells, respectively) were determined using different cell lines. The murine cell line L929 and normal non-tumor cells were not affected. Bioactivity guided fractionation of Breastin resulted in the isolation of the monoglycosidic cardenolides oleandrine, oleandrigeninsarmentoside, neritaloside, odoroside H, and odoroside A (IC(50)-values between 0.010 and 0.071 μg/ml).
CONCLUSIONS: The observed anticancer activities of extracts and isolated cardenolides are in agreement with the ethnomedicinal use of Streptocaulon tomentosum and Nerium oleander. The most active anticancer compounds from both species are monoglycosidic cardenolides possessing the 3β,14β-dihydroxy-5β-card-20(22)-enolide structure with or without an acetoxy group at C-16. The results indicate that the cytotoxic effects are induced by the inhibition of the plasma membrane bound Na(+)/K(+)-ATPase.