Tangeretin sensitizes cisplatin-resistant human ovarian cancer cells through downregulation of phosphoinositide 3-kinase/Akt signaling pathway.

Combination of innocuous dietary components with anticancer drugs is an emerging new strategy for cancer chemotherapy to increase antitumor responses. Tangeretin is a citrus flavonoid known to inhibit cancer cell proliferation. Here, we show an enhanced response of A2780/CP70 and 2008/C13 cisplatin-resistant human ovarian cancer cells to various combination treatments of cisplatin and tangeretin. Pretreatment of cells with tangeretin before cisplatin treatment synergistically inhibited cancer cell proliferation. This combination was effective in activating apoptosis via caspase cascade as well as arresting cell cycle at G(2)-M phase. Moreover, phospho-Akt and its downstream substrates, e.g., NF-kappaB, phospho-GSK-3beta, and phospho-BAD, were downregulated upon tangeretin-cisplatin treatment. The tangeretin-cisplatin-induced apoptosis in A2780/CP70 cells was increased by phosphoinositide-3 kinase (PI3K) inhibition and siRNA-mediated Akt silencing, but reduced by overexpression of constitutively activated Akt and GSK-3beta inhibition. The overall results indicated that tangeretin exposure preconditions cisplatin-resistant human ovarian cancer cells for a conventional response to low-dose cisplatin-induced cell death occurring through downregulation of PI3K/Akt signaling pathway. Thus, effectiveness of tangeretin combinations, as a promising modality in the treatment of resistant cancers, warrants systematic clinical studies.