LKB 1 pro‐oncogenic activity triggers cell survival in circulating tumor cells

During intravasation, circulating tumor cells ( CTC s) detach from the epithelium of origin and begin the epithelial‐to‐mesenchymal transition ( EMT ) process, where they lose epithelial features and pass through the endothelium to enter circulation. Although detachment from the extracellular matrix is a strong source of metabolic stress, which induces anoikis, CTC s can survive. Recently, the tumor suppressor liver kinase B1 ( LKB 1) has gained attention for its role as a proto‐oncogene in restoring the correct ATP / AMP ratio during metabolic stress. The aim of this study was to assess LKB 1 expression in epithelial‐negative CTC s isolated from patients with metastatic breast cancer and to characterize its possible association with EMT and stemness features. Transcriptome analysis of Ep CAM ‐negative CTC s indicated that over 25% of patients showed enhanced LKB 1 levels, while almost 20% of patients showed enhanced levels of an EMT transcription factor known as ZEB 1. Transcriptome and immunofluorescence analyses showed that patients with enhanced LKB 1 were correspondingly ZEB 1 negative, suggesting complementary activity for the two proteins. Only ZEB 1 was significantly associated with cancer stem cell ( CSC ) markers. Neither LKB 1 nor ZEB 1 upregulation showed a correlation with clinical outcome, while enhanced levels of stemness‐associated CD 44 correlated with a lower progression‐free and overall survival. Ex vivo models showed that MDA ‐ MB ‐231, a mesenchymal tumor cell line, grew in suspension only if LKB 1 was upregulated, but the MCF ‐7 epithelial cell line lost its ability to generate spheroids and colonies when LKB 1 was inhibited, supporting the idea that LKB 1 might be necessary for CTC s to overcome the absence of the extracellular matrix during the early phases of intravasation. If these preliminary results are confirmed, LKB 1 will become a novel therapeutic target for eradicating metastasis‐initiating CTC s from patients with primary breast cancer.