BACKGROUND Epidemiologic studies suggest that metformin has antitumor effects. Laboratory studies indicate metformin impacts cancer stem-like cells (CSCs). As part of a phase II trial, we evaluated the impact of metformin on CSC number and on carcinoma-associated mesenchymal stem cells (CA-MSCs) and clinical outcomes in nondiabetic patients with advanced-stage epithelial ovarian cancer (EOC).METHODS Thirty-eight patients with stage IIC (n = 1)/III (n = 25)/IV (n = 12) EOC were treated with either (a) neoadjuvant metformin, debulking surgery, and adjuvant chemotherapy plus metformin or (b) neoadjuvant chemotherapy and metformin, interval debulking surgery, and adjuvant chemotherapy plus metformin. Metformin-treated tumors, compared with historical controls, were evaluated for CSC number and chemotherapy response. Primary endpoints were (a) a 2-fold or greater reduction in aldehyde dehydrogenase–positive (ALDH+) CD133+ CSCs and (b) a relapse-free survival at 18 months of more than 50%.RESULTS Metformin was well tolerated. Median progression-free survival was 18.0 months (95% CI 14.0–21.6) with relapse-free survival at 18 months of 59.3% (95% CI 38.6–70.5). Median overall survival was 57.9 months (95% CI 28.0–not estimable). Tumors treated with metformin had a 2.4-fold decrease in ALDH+CD133+ CSCs and increased sensitivity to cisplatin ex vivo. Furthermore, metformin altered the methylation signature in CA-MSCs, which prevented CA-MSC–driven chemoresistance in vitro.CONCLUSION Translational studies confirm an impact of metformin on EOC CSCs and suggest epigenetic change in the tumor stroma may drive the platinum sensitivity ex vivo. Consistent with this, metformin therapy was associated with better-than-expected overall survival, supporting the use of metformin in phase III studies.TRIAL REGISTRATION ClinicalTrials.gov NCT01579812.
Jason R. Brown, Daniel K. Chan, Jessica J. Shank, Kent A. Griffith, Huihui Fan, Robert Szulawski, Kun Yang, R. Kevin Reynolds, Carolyn Johnston, Karen McLean, Shitanshu Uppal, J. Rebecca Liu, Lourdes Cabrera, Sarah E. Taylor, Brian C. Orr, Francesmary Modugno, Pooja Mehta, Michael Bregenzer, Geeta Mehta, Hui Shen, Lan G. Coffman, Ronald J. Buckanovich