Everolimus Inhibits the Progression of Ductal Carcinoma <i>In Situ</i> to Invasive Breast Cancer Via Downregulation of MMP9 Expression.

Abstract

We evaluated the role of everolimus in the prevention of ductal carcinoma <i>in situ</i> (DCIS) to invasive ductal carcinoma (IDC) progression. The effects of everolimus on breast cancer cell invasion, DCIS formation, and DCIS progression to IDC were investigated in a 3D cell culturing model, intraductal DCIS xenograft model, and spontaneous MMTV-Her2/neu mouse model. The effect of everolimus on matrix metalloproteinase 9 (MMP9) expression was determined with Western blotting and IHC in these models and in patients with DCIS before and after a window trial with rapamycin. Whether MMP9 mediates the inhibition of DCIS progression to IDC by everolimus was investigated with knockdown or overexpression of MMP9 in breast cancer cells. Everolimus significantly inhibited the invasion of human breast cancer cells <i>in vitro</i>. Daily intragastric treatment with everolimus for 7 days significantly reduced the number of invasive lesions from intraductal DCIS foci and inhibited DCIS progression to IDC in the MMTV-Her2/neu mouse mammary tumor model. Mechanistically, everolimus treatment decreased the expression of MMP9 in the <i>in vitro</i> and <i>in vivo</i> models, and in breast tissues from patients with DCIS treated with rapamycin for 1 week. Moreover, overexpression of MMP9 stimulated the invasion, whereas knockdown of MMP9 inhibited the invasion of breast cancer cell-formed spheroids <i>in vitro</i> and DCIS <i>in vivo</i>. Knockdown of MMP9 also nullified the invasion inhibition by everolimus <i>in vitro</i> and <i>in vivo</i>. Targeting mTORC1 can inhibit DCIS progression to IDC via MMP9 and may be a potential strategy for DCIS or early-stage IDC therapy.