Chrysin blocks topotecan-induced apoptosis in Caco-2 cells in spite of inhibition of ABC-transporters

Abstract

In conclusion, our studies show that chrysin in spite of raising the cellular concentrations of topotecan potently inhibits the apoptosis-inducing activities of the anti-tumor drug. Inhibition of caspase-activation was identified as the underlying mechanism and is suggested to be caused by transport-independent functions of ABC-transporters.

Potential Role of P-gp for Flavone-Induced Diminished Apoptosis and Increased Adenoma Size in the Small Intestine of APCmin/+Mice

“…Finally, ß-catenin localization and stability was followed in Caco-2 cells to find out whether those parameters could be linked to P-gp expression and apoptosis. As already shown for chrysin (33), flavone caused translocation of ß-catenin from the plasma membrane to the cytosol. As same translocation was shown for topotecan, it could not be alone responsible for the inhibition of apoptosis.…”

“…As ß-catenin is a substrate of caspase-3 (35), its stabilization is most likely reached by inhibition of the downstream caspase through flavone. Moreover, we have recently shown that inhibition of caspase-3 by a specific inhibitor not only prevented topotecan-induced cleavage of ßcatenin but also apoptosis as caused by the cytotoxic compound (33).…”

“…Although there was a tendency for increased expression in the jejunum and ileum due to the great interindividual variety in these mice, these effects did not achieve much significance. As we have recently shown in Caco-2 human colorectal cancer cells, the flavonoid chrysin potently inhibits apoptosis through increased expression of ATPdependent drug-efflux pumps (33) and thus we looked for more significant effects on apoptosis in this cell line. Similar to chrysin, flavone also increased the expression of P-gp and inhibited potently apoptosis induced by the anti-tumor drug topotecan although it was revealed to be a P-gp transport inhibitor, thus increasing the intracellular concentrations of the cytotoxic drug.…”

“…Serial tissue sections (5-7 µm) were prepared and mounted on slides. For determination of apoptosis by cleaved caspase-3, sections were dewaxed in xylene, endogenous peroxidase was blocked in all sections with 0.5% H 2 O 2 in methanol, and epitope retrieval was performed by microwaving for 33 with a rubber policeman. Cells were pelleted subsequently by centrifugation for 5 min at 300 g. The pelleted cells were dissolved subsequently in lysis buffer (10-mM HEPES, 1-mM EDTA, 1-mM DTT, and 0.2% protease inhibitor cocktail, pH 7.5) and frozen overnight at −80 • C. Thereafter, cells were homogenized by 20 strokes with a Teflon homogenizer.…”

Flavonoids

“…Quite surprisingly, the inhibition of these transporters by fl avonoids (e.g., chrysin) did not lead to drug -mediated apoptosis of cancer cells. The tested fl avonoid was suggested to increase cancer cell survival by enhanced expression of xenobiotic transporters in cancer cells [131] . Moreover, the fl avonoid effect on the signaling pathway associated with the process of apoptosis is also considered.…”