Inhibition of export of fibroblast growth factor-2 (FGF-2) from the prostate cancer cell lines PC3 and DU145 by anvirzel and its cardiac glycoside component, oleandrin
Anvirzel is an extract of Nerium oleander currently undergoing Phase I clinical evaluation as a potential treatment for cancer. Two of the active components of Anvirzel are the cardiac glycosides oleandrin and oleandrigenin. Previous studies have demonstrated that, in vitro, cardiac glycosides may inhibit fibroblast growth factor-2 (FGF-2) export through membrane interaction with the Na+,K+-ATPase pump. In continuing research on the antitumor activity of this novel plant extract, the relative abilities of oleandrin and oleandrigenin to inhibit FGF-2 export from two human prostate cancer cell lines, DU145 and PC3, were examined. An ELISA assay was utilized to determine the FGF-2 concentration in the cell culture medium before and after exposure to cardiac glycosides or the parent extract material Anvirzel. Both cell lines were exposed to non-cytotoxic concentrations of oleandrin (0.05 and 0.1 ng/mL) for up to 72 hr. Studies also were conducted with Anvirzel and ouabain. Oleandrin (0.1 ng/mL) produced a 45.7% inhibition of FGF-2 release from PC3 cells and a 49.9% inhibition from DU145 cells. Non-cytotoxic concentrations (100 ng/mL) of Anvirzel produced a 51.9 and 30.8% inhibition of FGF-2 release, respectively, in the two cell lines. The decrease in FGF-2 release from cells required continuous incubation for 48–72 hr; shorter incubation times were not effective. These results demonstrate that Anvirzel, like oleandrin, inhibited FGF-2 export in vitro from PC3 and DU145 prostate cancer cells in a concentration- and time-dependent fashion and may, therefore, contribute to the antitumor activity of this novel treatment for cancer.
Biochemical Pharmacology doi:10.1016/S0006-2952(01)00690-6

Enhancement of radiotherapy by oleandrin is a caspase-3 dependent process
Cardiac glycosides such as digitoxin and ouabain have previously been shown to be selectively cytotoxic to tumor as opposed to normal cells. Moreover, this class of agents has also been shown to act as potent radiosensitizers. In the present study we explored the relative radiosensitization potential of oleandrin, a cardiac glycoside contained within the plant extract known as Anvirzel™ that recently underwent a Phase I trial as a novel drug for anticancer therapy. The data show that oleandrin produces an enhancement of sensitivity of PC-3 human prostate cells to radiation; at a cell survival of 0.1, the enhancement factor was 1.32. The magnitude of radiosensitization depended on duration of exposure of cells to drug prior to radiation treatment. While a radiosensitizing effect of oleandrin was evident with only 1 h of cell exposure to drug, the effect greatly increased with 24 h oleandrin pretreatment. Susceptibility of PC-3 cells to oleandrin and radiation-induced apoptosis was dependent on activation of caspase-3. Activation was greatest when cells were exposed simultaneously to oleandrin and radiation. Inhibition of caspase-3 activation with Z-DEVD-FMK abrogated the oleandrin-induced enhancement of radiation response suggesting that both oleandrin and radiation share a caspase-3 dependent mechanism of apoptosis in the PC-3 cell line.
Cancer Letters doi:10.1016/S0304-3835(02)00263-X

Oleandrin-mediated inhibition of human tumor cell proliferation: Importance of Na,K-ATPase α subunits as drug targets
Cardiac glycosides such as oleandrin are known to inhibit the Na,K-ATPase pump, resulting in a consequent increase in calcium influx in heart muscle. Here, we investigated the effect of oleandrin on the growth of human and mouse cancer cells in relation to Na,K-ATPase subunits. Oleandrin treatment resulted in selective inhibition of human cancer cell growth but not rodent cell proliferation, which corresponded to the relative level of Na,K-ATPase α3 subunit protein expression. Human pancreatic cancer cell lines were found to differentially express varying levels of α3 protein, but rodent cancer cells lacked discernable expression of this Na,K-ATPase isoform. A correlation was observed between the ratio of α3 to α1 isoforms and the level of oleandrin uptake during inhibition of cell growth and initiation of cell death; the higher the α3 expression relative to α1 expression, the more sensitive the cell was to treatment with oleandrin. Inhibition of proliferation of Panc-1 cells by oleandrin was significantly reduced when the relative expression of α3 was decreased by knocking down the expression of α3 isoform with α3 siRNA or increasing expression of the α1 isoform through transient transfection of α1 cDNA to the cells. Our data suggest that the relative lack of α3 (relative to α1) in rodent and some human tumor cells may explain their unresponsiveness to cardiac glycosides. In conclusion, the relatively higher expression of α3 with the limited expression of α1 may help predict which human tumors are likely to be responsive to treatment with potent lipid-soluble cardiac glycosides such as oleandrin.
Mol Cancer 2009 doi: 10.1158/1535-7163.MCT-08-1085

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