Epithelial-to-mesenchymal transition confers mechanical resistance to hemodynamic stress during hematogenous dissemination

Metastatic dissemination requires circulating tumor cells (CTCs) to survive hemodynamic forces, yet the biological traits that enable survival under fluid shear stress (FSS) remain poorly defined. While current paradigms suggest that fluid shear stress (FSS) broadly induces an epithelial-to-mesenchymal transition (EMT), we investigated an alternative mechanism: FSS acts as a mechanical bottleneck that selectively enriches for pre-existing mesenchymal cancer cells by destroying more epithelial-like phenotypes prior to detectable changes in EMT marker expression. Using epithelial and mesenchymal subpopulations isolated from the same cell lines, we exposed single cells in suspension to pulsatile FSS to demonstrate that mesenchymal cells exhibit significantly higher survival rates and lower membrane rupture following pulsatile FSS. Immediate post-shear single-cell analysis revealed stable vimentin-to-cytokeratin (VIM/KRT) ratios in mesenchymal populations, whereas epithelial-like populations showed a selective loss of low-VIM/KRT cells, consistent with immediate mechanical depletion prior to biological induction of EMT. Direct manipulation of EMT states confirmed this causal relationship: TGFβ-induced EMT rescued survival in epithelial cells, while E-cadherin overexpression sensitized mesenchymal cells to mechanical rupture. To validate these findings clinically, we analyzed single-cell RNA-seq data from three patient-derived CTC datasets and found that higher VIM/KRT ratios significantly correlate with increased CTC abundance in the bloodstream. Together, these results demonstrate that hemodynamic forces impose a deterministic mechanical selection pressure on CTCs, identifying epithelial-associated biophysical traits as a primary therapeutic vulnerability in the metastatic cascade.