ADAMs contribute to triple negative breast cancer via mTORC1 pathway: targeting ADAM-mTOR axis improves efficacy

Breast cancer is the most frequently diagnosed cancer globally and the second leading cause of cancer-related deaths in American women. Triple-negative breast cancer (TNBC) lacks estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Thus, fewer targeting therapies are available for this most aggressive subtype. The A Disintegrin and Metalloproteinase (ADAM) family plays a vital role in cancer pathophysiology. Previous studies focused on single ADAM members. However, none of these have entered into the clinical arena as diagnostics or therapeutics for breast cancer. In this study, we demonstrate the upregulation of a panel of ADAM members in TNBC, and overexpression of all the individual ADAMs tested are correlated with poor patient survival, making it unlikely that targeting a single ADAM member would be effective. Reverse-phase protein array and multiplexed immunofluorescence revealed that ADAM10/15/17 expression was associated with activated mTOR signaling. Individual knockdown of ADAM10, ADAM15, or ADAM17 modestly reduced mTOR signaling, cellular proliferation and survival. However, the concurrent knockdown of the three ADAMs drastically decreased mTOR signaling and cellular aggressiveness. Consistently, combined targeting of ADAMs and mTOR increased inhibitory efficacy compared to monotherapy in ADAM-mTOR-activated tumor growth and invasion in vitro and in immunodeficient and immunocompetent mice. These results establish a functional link between ADAMs and activation of mTOR signaling, suggesting the ADAM-mTOR axis as a therapeutic target and biomarker for ADAM-enriched TNBC and, potentially, other tumor lineages with high ADAM activity.