title: Chrysin blocks topotecan-induced apoptosis in Caco-2 cells in spite of inhibition of ABC-transporters.
abstract: ATP-driven efflux pumps such as phosphoglycoprotein-170 (P-gp), multidrug-resistance-associated protein-2 (MRP-2), or breast cancer resistance protein (BCRP) play a crucial role in limiting the efficacy of tumor pharmacotherapy. Selected flavonoids have been suggested to inhibit individual efflux-transporters and to act therefore as multidrug-resistance reversing agents. In the present study it is shown that the flavonoid chrysin acts as a potent inhibitor of P-gp, MRP-2, and BCRP in Caco-2 colon carcinoma cells. As a consequence, cells accumulated higher rates of the apoptosis-inducing chemotherapeutic topotecan in the presence of chrysin, even though under these conditions the expression of the transporters was markedly increased. Interestingly, in spite of the enhanced cellular drug accumulation the topotecan-induced apoptosis, assessed according to DNA-fragmentation, chromatin condensation, and by determination of sub-G1 peaks using fluorescence-assisted-cell sorting (FACS), was potently inhibited by chrysin. Suggested transport-independent apoptosis inhibiting activities of ATP-binding cassette (ABC)-transporters, such as the inhibition of caspases, were shown to be necessary for the inhibition of topotecan-induced apoptosis and were found to be associated with stabilization of beta-catenin especially in the cytosol. Inhibition of topotecan-induced intracellular acidification, however, was proven not to prevent caspase-activation and apoptosis. 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.
authors.affiliation: Interdisciplinary Research Center, Justus-Liebig-University of Giessen, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Schumacher
authors.forename: Anja
authors.initials: A
authors.lastname: Hautzinger
authors.forename: Annette
authors.initials: A
authors.lastname: Rossmann
authors.forename: Susanne
authors.initials: S
authors.lastname: Holzhauser
authors.forename: Daniela
authors.initials: D
authors.lastname: Popovic
authors.forename: Anke
authors.initials: A
authors.lastname: Hertrampf
authors.forename: Sabine
authors.initials: S
authors.lastname: Kuntz
authors.forename: Michael
authors.initials: M
authors.lastname: Boll
authors.forename: Uwe
authors.initials: U
authors.lastname: Wenzel
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D001692:Biological Transport; D018938:Caco-2 Cells; D002478:Cells, Cultured; D004336:Drug Antagonism; D019008:Drug Resistance, Neoplasm; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D020014:K562 Cells; D000089762:Multidrug Resistance-Associated Protein 2; D019772:Topotecan / Q000494:pharmacology*
chemical_list: C000715087:ABCC2 protein, human; D018528:ATP-Binding Cassette Transporters; D005419:Flavonoids; D000089762:Multidrug Resistance-Associated Protein 2; C043561:chrysin; D019772:Topotecan