The anticancer activity of the fungal metabolite terrecyclic acid A is associated with modulation of multiple cellular stress response pathways

Thomas J. Turbyville, E. M.Kithsiri Wijeratne, Luke Whitesell, A. A.Leslie Gunatilaka

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

Tumors are dependent on cellular stress responses, in particular the heat shock response, for survival in their hypoxic, acidotic, and nutrient-deprived microenvironments. Using cell-based reporter assays, we have identified terrecyclic acid A (TCA) from Aspergillus terreus, a fungus inhabiting the rhizosphere of Opuntia versicolor of the Sonoran desert, as a small-molecule inducer of the heat shock response that shows anticancer activity. Further characterization suggested that TCA also affects oxidative and inflammatory cellular stress response pathways. The presence of an α-methylene ketone moiety suggested that TCA may form adducts with sulfhydryl groups of proteins. Reaction with labile intracellular cysteines was supported by our finding that the glutathione precursor N-acetyl-cysteine protected tumor cells from the cytotoxic effects of TCA whereas the glutathione-depleting agent buthionine sulfoximine enhanced its activity. Related sesquiterpenes have been shown to increase levels of reactive oxygen species (ROS) and to inhibit nuclear factor κB (NF-κB) transcriptional activity. To assess whether TCA could have similar activities, we used a ROS-sensitive dye and flow cytometry to show that TCA does indeed increase ROS levels in 3LL cells. When tested in cells carrying NF-κB reporter constructs, TCA also exhibited concentration-dependent inhibition of cytokine-induced NF-κB transcriptional activity. These findings suggest that TCA modulates multiple stress pathways - the oxidative, heat shock, and inflammatory responses - in tumor cells that promote their survival. Small-molecule natural products such as TCA may serve as useful probes for understanding the relationships between these pathways, potentially providing leads for the design of novel and effective anti-cancer drugs.

Original languageEnglish (US)
Pages (from-to)1569-1576
Number of pages8
JournalMolecular Cancer Therapeutics
Volume4
Issue number10
DOIs
StatePublished - Oct 1 2005

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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