Grape Polyphenols Inhibit Akt/Mammalian Target of Rapamycin Signaling and Potentiate the Effects of Gefitinib in Breast Cancer

Abstract

We recently reported that a combination of dietary grape polyphenols resveratrol, quercetin, and catechin (RQC), at low concentrations, was effective at inhibiting metastatic cancer progression. Herein, we investigate the molecular mechanisms of RQC in breast cancer and explore the potential of RQC as a potentiation agent for the epidermal growth factor receptor (EGFR) therapeutic gefitinib. Our in vitro experiments showed RQC induced apoptosis in gefitinib-resistant breast cancer cells via regulation of a myriad of proapoptotic proteins. Because the Akt/mammalian target of rapamycin (mTOR) signaling pathway is often elevated during development of anti-EGFR therapy resistance, the effect of RQC on the mTOR upstream effector Akt and the negative regulator AMP kinase (AMPK) was investigated. RQC was found to reduce Akt activity, induce the activation of AMPK, and inhibit mTOR signaling in breast cancer cells. Combined RQC and gefitinib decreased gefitinib resistant breast cancer cell viability to a greater extent than RQC or gefitinib alone. Moreover, RQC inhibited Akt and mTOR and activated AMPK even in the presence of gefitinib. Our in vivo experiments showed combined RQC and gefitinib was more effective than the individual treatments at inhibiting mammary tumor growth and metastasis in nude mice. Therefore, RQC treatment inhibits breast cancer progression and may potentiate anti-EGFR therapy by inhibition of Akt/mTOR signaling.

ACKNOWLEDGEMENTS

This study is sponsored by the Department of Defense/Breast Cancer Research Program awards W81XWH-07-1-0330 to Suranganie F. Dharmawardhane and W81XWH-08-01-0258 to Linette Castillo-Pichardo, NIH/NIGMS SC3GM084824 to Suranganie F. Dharmawardhane, NIH/NCRR grants 2G12RR003035 to Universidad Central del Caribe and G12-RR03051 to University of Puerto Rico, Medical Sciences Campus. We thank Dr. Aldo Pérez for his excellent technical assistance with animal protocols and Vanita Flanagan for assistance with imaging organs. We also acknowledge the services of the Animal Resources Center, Universidad Central del Caribe, Bayamón, Puerto Rico.