Inhibition of the autocrine IL-6-JAK2-STAT3-calprotectin axis as targeted therapy for HR super(-)/HER2 super(+) breast cancers

HER2-positive (HER2 super(+)) breast adenocarcinomas are a heterogeneous group in which hormone receptor (HR) status influences therapeutic decisions and patient outcome. By combining genome-wide RNAi screens with regulatory network analysis, we identified STAT3 as a critically activated master regulator of HR super(-)/HER2 super(+) tumors, eliciting tumor dependency in these cells. Mechanistically, HR super(-)/HER2 super(+) cells secrete high levels of the interleukin-6 (IL-6) cytokine, inducing the activation of STAT3, which in turn promotes a second autocrine stimulus to increase S100A8/9 complex (calprotectin) production and secretion. Increased calprotectin levels activate signaling pathways involved in proliferation and resistance. Importantly, we demonstrated that inhibition of the IL-6-Janus kinase 2 (JAK2)-STAT3-calprotectin axis with FDA-approved drugs, alone and in combination with HER2 inhibitors, reduced the tumorigenicity of HR super(-)/HER2 super(+) breast cancers, opening novel targeted therapeutic opportunities.