Digitonin

Phytomedicine. 2013 Dec 15;21(1):47-61.

Influence of combinations of digitonin with selected phenolics, terpenoids, and alkaloids on the expression and activity of P-glycoprotein in leukaemia and colon cancer cells.[Pubmed: 23999162]

P-glycoprotein (P-gp or MDR1) is an ATP-binding cassette (ABC) transporter. It is involved in the efflux of several anticancer drugs, which leads to chemotherapy failure and multidrug resistance (MDR) in cancer cells. Representative secondary metabolites (SM) including phenolics (EGCG and thymol), terpenoids (menthol, aromadendrene, β-sitosterol-O-glucoside, and β-carotene), and alkaloids (glaucine, harmine, and sanguinarine) were evaluated as potential P-gp inhibitors (transporter activity and expression level) in P-gp expressing Caco-2 and CEM/ADR5000 cancer cell lines.
METHODS AND RESULTS:
Selected SM increased the accumulation of the rhodamine 123 (Rho123) and calcein-AM (CAM) in a dose dependent manner in Caco-2 cells, indicating that they act as competitive inhibitors of P-gp. Non-toxic concentrations of β-carotene (40μM) and sanguinarine (1μM) significantly inhibited Rho123 and CAM efflux in CEM/ADR5000 cells by 222.42% and 259.25% and by 244.02% and 290.16%, respectively relative to verapamil (100%). Combination of the saponin Digitonin (5μM), which also inhibits P-gp, with SM significantly enhanced the inhibition of P-gp activity. The results were correlated with the data obtained from a quantitative analysis of MDR1 expression. Both compounds significantly decreased mRNA levels of the MDR1 gene to 48% (p<0.01) and 46% (p<0.01) in Caco-2, and to 61% (p<0.05) and 1% (p<0.001) in CEM/ADR5000 cells, respectively as compared to the untreated control (100%). Combinations of Digitonin with SM resulted in a significant down-regulation of MDR1.
CONCLUSIONS:
Our findings provide evidence that the selected SM interfere directly and/or indirectly with P-gp function. Combinations of different P-gp substrates, such as Digitonin alone and together with the set of SM, can mediate MDR reversal in cancer cells.

Methods Cell Biol. 2014;122:331-52.

Analysis of nucleocytoplasmic transport in digitonin-permeabilized cells under different cellular conditions.[Pubmed: 24857737]

The regulation of nucleocytoplasmic transport is crucial not only for basic cellular activities but also for physiological adaptation to specific situation during the cell cycle, development, or stress. Although a wide variety of transport pathways have been identified in eukaryotic cells, the functional significance of their multiplicity remains unclear. The best-characterized nuclear transport receptors (NTRs) are the members of the importin β family (karyopherin, transportin) whose association with specific cargoes is regulated by the GTPase Ran.
METHODS AND RESULTS:
In this chapter, we first provide an overview of the various expression vectors used to purify recombinant NTRs. We then describe two sets of recent examples of using well-established Digitonin-permeabilized cell-free transport systems in mammalian cells to mimic different cellular conditions in living cells: normal/heat-shock conditions and interphase/mitosis. In the former case, physiological regulation impacts different transport pathways in opposite ways. In the latter case, the importin β-Ran system is used at different cell-cycle stages but with the same biochemical principle to specify the nuclear localization and chromatin loading of a specific protein, respectively.
CONCLUSIONS:
This in vitro transport assay, when adapted to specific cellular conditions or particular substrates, should help to uncover specific transport pathways or transport factors function under different cellular conditions.

Phytomedicine. 2012 Nov 15;19(14):1288-97.

Synergism of three-drug combinations of sanguinarine and other plant secondary metabolites with digitonin and doxorubicin in multi-drug resistant cancer cells.[Pubmed: 23146422]

We determined the ability of some phytochemicals, including alkaloids (glaucine, harmine, and sanguinarine), phenolics (EGCG and thymol), and terpenoids (menthol, aromadendrene, β-sitosterol-O-glucoside, and β-carotene), alone or in combination with the saponin Digitonin to reverse the relative multi-drug resistance of Caco-2 and CEM/ADR5000 cells to the chemotherapeutical agent doxorubicin.
METHODS AND RESULTS:
The IC(50) of doxorubicin in Caco-2 and CEM/ADR5000 was 4.22 and 44.08μM, respectively. Combination of non-toxic concentrations of individual secondary metabolite with doxorubicin synergistically sensitized Caco-2 and CEM/ADR5000 cells, and significantly enhanced the cytotoxicity of doxorubicin. Furthermore, three-drug combinations (secondary metabolite+Digitonin+doxorubicin) were even more powerful. The best synergist was the benzophenanthridine alkaloid sanguinarine. It reduced the IC(50) value of doxorubicin 17.58-fold in two-drug combinations (sanguinarine+doxorubicin) and even 35.17-fold in three-drug combinations (sanguinarine+Digitonin+doxorubicin) in Caco-2 cells.
CONCLUSIONS:
Thus synergistic drug combinations offer the possibility to enhance doxorubicin efficacy in chemotherapy.

Physiol Res. 2012 Jul 20;61(3):259-65.

Idebenone-induced recovery of glycerol-3-phosphate and succinate oxidation inhibited by digitonin.[Pubmed: 22480420]

Digitonin solubilizes mitochondrial membrane, breaks the integrity of the respiratory chain and releases two mobile redox-active components: coenzyme Q (CoQ) and cytochrome c (cyt c).
METHODS AND RESULTS:
In the present study we report the inhibition of glycerol-3-phosphate- and succinate-dependent oxygen consumption rates by Digitonin treatment. Our results show that the inhibition of oxygen consumption rates is recovered by the addition of exogenous synthetic analog of CoQ idebenone (hydroxydecyl-ubiquinone; IDB) and cyt c. Glycerol-3-phosphate oxidation rate is recovered to 148 % of control values, whereas succinate-dependent oxidation rate only to 68 %. We find a similar effect on the activities of glycerol-3-phosphate and succinate cytochrome c oxidoreductase. Our results also indicate that succinate-dependent oxidation is less sensitive to Digitonin treatment and less activated by IDB in comparison with glycerol-3-phosphate-dependent oxidation.
CONCLUSIONS:
These findings might indicate the different mechanism of the electron transfer from two flavoprotein-dependent dehydrogenases (glycerol-3-phosphate dehydrogenase and succinate dehydrogenase) localized on the outer and inner face of the inner mitochondrial membrane, respectively.

Phytomedicine. 2012 Nov 15;19(14):1307-14.

Digitonin synergistically enhances the cytotoxicity of plant secondary metabolites in cancer cells.[Pubmed: 23062361]

In phytotherapy, extracts from medicinal plants are employed which contain mixtures of secondary metabolites. Their modes of action are complex because the secondary metabolites can react with single or multiple targets. The components in a mixture can exert additive or even synergistic activities.
METHODS AND RESULTS:
In this study, the cytotoxicity of some phytochemicals, including phenolics (EGCG and thymol), terpenoids (menthol, aromadendrene, β-sitosterol-O-glucoside, and β-carotene) and alkaloids (glaucine, harmine, and sanguinarine) were investigated alone or in combination with the cytotoxic monodesmosidic steroidal saponin Digitonin in Caco-2, MCF-7, CEM/ADR5000, and CCRF-CEM cells. Digitonin was combined in non-toxic concentrations (5μM in each cell line; except in MCF-7 the concentration was 2μM), together with a selection of phenolics, terpenoids, and alkaloids to evaluate potential synergistic or additive effects. An enhanced cytotoxicity was observed in most combinations. Even multi-drug resistant (MDR) cells (such as CEM/ADR5000 cells), with a high expression of P-glycoprotein, were responsive to combinations. Sanguinarine was the most cytotoxic alkaloid against CEM/ADR5000, MCF-7, and CCRF-CEM cells alone and in combination with Digitonin. As compared to sanguinarine alone, the combination was 44.53-, 15.38-, and 6.65-fold more toxic in each cell line, respectively.
CONCLUSIONS:
Most combinations synergistically increased the cytotoxicity, stressing the importance of synergy when using multi-target drugs and mixtures in phytotherapy.