hellebrigenin and hellebrin

The in vitro growth inhibitory effects of 27 bufadienolides and eight degradation products, with two cardenolides (ouabain and digoxin) chosen as reference compounds, were analyzed by means of an MTT colorimetric assay in six human and two mouse cancer cell lines. A structure-activity analysis was then performed to highlight the most important substituents relating to the in vitro growth inhibitory activity of bufadienolides in cancer cells. Thus, the current study revealed that various bufadienolides, including gamabufotalin rhamnoside (1a), bufotalin (2a), and hellebrin (3a), displayed higher growth inhibitory activities for various human cancer cell lines when compared to ouabain and digoxin. Gamabufotalin rhamnoside (1a) was the only compound that displayed growth inhibitory effects of <1 μM in mouse cancer cells that expressed mutated forms of the Na(+),K(+)-ATPase α-1 subunit. In addition, all genins and degradation products displayed weaker (if any) in vitro growth inhibitory effects on cancer cells when compared to their respective glycosylated homologue, with the exception of hellebrigenin (3b), which was as active as hellebrin (3a).

Topics: Animals; Bufanolides; Drug Screening Assays, Antitumor; Humans; Mice; Molecular Structure; Sodium-Potassium-Exchanging ATPase; Structure-Activity Relationship

Surface-expressed Na+/K+-ATPase (NaK) has been suggested to function as a non-canonical cardiotonic steroid-binding receptor that activates multiple signaling cascades, especially in cancer cells. By contrast, the current study establishes a clear correlation between the IC50in vitro growth inhibitory concentration in human cancer cells and the Ki for the inhibition of activity of purified human α1β1 NaK.. The in vitro growth inhibitory effects of seven cardiac glycosides including five cardenolides (ouabain, digoxin, digitoxin, gitoxin, uzarigenin-rhamnoside, and their respective aglycone forms) and two bufadienolides (gamabufotalin-rhamnoside and hellebrin, and their respective aglycone forms) were determined by means of the MTT colorimetric assay and hellebrigenin-induced cytotoxic effects were visualized by means of quantitative videomicroscopy. The binding affinity of ten of the 14 compounds under study was determined with respect to human α1β1, α2β1 and α3β1 NaK complexes. Lactate releases and oxygen consumption rates were also determined in cancer cells treated with these various cardiac glycosides.. Although cardiotonic steroid aglycones usually display weaker binding affinity and in vitro anticancer activity than the corresponding glycoside, the current study demonstrates that the hellebrin / hellebrigenin pair is at odds with respect to this rule. In addition, while some cardiac steroid glycosides (e.g., digoxin), but not the aglycones, display a higher binding affinity for the α2β1 and α3β1 than for the α1β1 complex, both hellebrin and its aglycone hellebrigenin display ~2-fold higher binding affinity for α1β1 than for the α2β1 and α3β1 complexes. Finally, the current study highlights a common feature for all cardiotonic steroids analyzed here, namely a dramatic reduction in the oxygen consumption rate in cardenolide- and bufadienolide-treated cells, reflecting a direct impact on mitochondrial oxidative phosphorylation.. Altogether, these data show that the binding affinity of the bufadienolides and cardenolides under study is usually higher for the α2β1 and α3β1 than for the α1β1 NaK complex, excepted for hellebrin and its aglycone form, hellebrigenin, with hellebrigenin being as potent as hellebrin in inhibiting in vitro cancer cell growth.

Topics: Apoptosis; Bufanolides; Cardiac Glycosides; Cell Line, Tumor; Cell Proliferation; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Glycosylation; HT29 Cells; Humans; Inhibitory Concentration 50; Isoenzymes; Lactic Acid; Metabolome; Neoplasms; Oxidation-Reduction; Oxygen Consumption; Protein Binding; Sodium-Potassium-Exchanging ATPase

The concentration of acrihellin rapidly declines in oxygenated Tyrode-solution, because the compound escapes from the organ-bath being enriched in droplets sprayed from the surface of the bubbled solution. As checked by radiochromatography, acrihellin remains chemically unaltered during this process. Hellebrin and hellebrigenin persist in gassed Tyrode-solution, suggesting that the 3 beta-substituent dimethylacrylic acid endows acrihellin with amphiphilic properties, thus promoting its enrichment at gas-water interphases. Measurements of the inotropic effects in guinea pig left atria performed at concentrations of acrihellin kept constant yielded a dose-response curve, which closely resembles that of the conventional cardioactive steroid ouabain.

Topics: Animals; Bufanolides; Cardiotonic Agents; Female; Guinea Pigs; Heart; In Vitro Techniques; Injections; Male; Myocardial Contraction; Myocardium; Ouabain; Radioligand Assay