Let-7d increases ovarian cancer cell sensitivity to a genistein analog by targeting c-Myc

c-Myc is a key oncogenic transcription factor that participates in tumor pathogenesis. In this study, we found that levels of c-Myc mRNA and protein were higher in early ovarian cancer tissues than normal ovary samples. Increased c-Myc levels correlated positively with clinical stage I (Ia+b/Ic) in ovarian cancer patients. Patients with higher nuclear c-Myc expression had shorter overall survival times than patients with low c-Myc expression. Knocking down c-Myc sensitized ovarian cancer cells to 7-difluoromethoxyl-5,4'-di-n-octylgenistein (DFOG), a novel synthetic genistein analogue that suppressed PI3K/AKT signaling in vitro and in vivo. Finally, c-Myc was confirmed to be a direct target of let-7d, and let-7d-induced suppression of c-Myc increased the DFOG-sensitivity of ovarian cancer cells. These results indicate that nuclear c-Myc expression is an unfavorable factor in early ovarian cancer, and that let-7d increases ovarian cancer cell sensitivity to DFOG by suppressing c-Myc and PI3K/AKT signaling.