Targeting mTOR and Its Associated Signaling to Induce Cell Death in Breast Cancer Stem Cells

Breast cancer (BC) is a frequently diagnosed neoplasm in women and the second major cause of cancer-related deaths. Many BC patients develop metastasis and advanced tumors, increasing morbidity and mortality. There is substantial evidence that tumor relapses in BC patients are driven by a unique population of cells called cancer stem cells (CSCs). Breast CSCs confer stemness to BC and survive through the maintenance of several mechanisms, among which is the involvement of the mTOR signaling pathway. mTOR and its associated AKT signaling play a crucial role in regulating CSCsin various human cancers, including breast cancer. This study investigated the role of targeting mTOR/AKT signaling in the modulation of cell death in 2D and 3D breast cancer models. Torin-2, a dual mTOR inhibitor, effectively suppressed cell proliferation by inducing mitochondrial apoptosis. The inhibition of mTOR led to a decrease in AKT activity and downregulation of key translational machinery components, including 4EBP1, eIF4E, and p70S6K. Torin-2 treatment activated autophagy signaling in both 2D and 3D cell models. The induction of autophagy was evidenced by an increase in the autophagy protein LC3II/I in response to Torin-2 treatment. In addition, Torin-2 treatment of spheroids derived from breast cancer cells suppressed the expression of stem cell marker ALDH. Altogether, the dual inhibition of mTORC1 and mTORC2 by Torin-2 resulted in a more profound antitumor activity. This broader and more potent inhibition of the mTOR pathway contributes to effectiveness in suppressing 2D and 3D breast cancer cell growth and survival.