Planta Med 2020; 86(15): 1073-1079
DOI: 10.1055/a-1097-8722
Biological and Pharmacological Activity
Original Papers

Destabilization of FoxM1 and Inhibition of Topoisomerase I Contribute to Cytotoxicity of Prenylated Xanthones Isolated from Metaxya rostrata [ # ]

Eva Mittermair
1   Institute of Cancer Research, Department of Medicine I, Medical University Vienna, Vienna, Austria
2   Department of Pharmacognosy, University of Vienna, Vienna, Austria
,
Hemma Schueffl
1   Institute of Cancer Research, Department of Medicine I, Medical University Vienna, Vienna, Austria
,
Petra Heffeter
1   Institute of Cancer Research, Department of Medicine I, Medical University Vienna, Vienna, Austria
,
Liselotte Krenn
2   Department of Pharmacognosy, University of Vienna, Vienna, Austria
,
Brigitte Marian
1   Institute of Cancer Research, Department of Medicine I, Medical University Vienna, Vienna, Austria
› Author Affiliations
Supported by: Hochschuljubiläumsstiftung der Stadt Wien H-211753/2018

Abstract

We recently isolated the prenylated xanthones 2-deprenyl-rheediaxanthone B (XB) and 2-deprenyl-7-hydroxy-rheediaxanthone B (OH-XB) from the South American tree fern Metaxya rostrata. This study explores the mechanisms underlying the FoxM1 downregulation induced by both xanthones. Analysis of cell viability and cell-death induction in SW480, HCT116, Caco-2, DLD1 and HT29 exposed to xanthones found cell-loss and activation of caspase in all cell lines except HT29 that do not have high FoxM1 protein levels. To determine the cellular mechanism of xanthone-induced FoxM1 loss, protein stability was analyzed by cycloheximide-chase experiments and showed reduction of FoxM1 stability by XB but not OH-XB. Destabilization was prevented by inhibiting proteasome activity using MG-132 and moderately by the lysosomal inhibitor bafilomycin A1 (baf A1). OH-XB had a stronger impact than XB on FoxM1 mRNA expression by qRT-PCR, and MG-132 positively affected FoxM1 protein level in OH-XB exposed cells even though no decrease in protein abundance had been induced by the xanthone. Additionally, the compound inhibited topoisomerase I causing DNA DSB and early cell cycle arrest. This may reduce FoxM1 gene expression, which may in turn compromise DNA repair and enhance xanthone-induced cell death. With regard to xanthone-induced cell death, MG-132 protected cultures from cell loss induced by both compounds, and baf A1 was active against these XB-induced effects. In summary, both destabilization of FoxM1 protein and topoisomerase I inhibition contribute to both XB and OH-XB cytotoxic activity albeit at different ratios.

# Dedicated to Prof. Wolfgang Kubelka on the occasion of his 85th birthday.


Supporting Information



Publication History

Received: 08 November 2019

Accepted: 13 January 2020

Article published online:
05 February 2020

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