Matrix stiffening and EGFR cooperate to promote the collective invasion of cancer cells.

In squamous cell carcinoma (SCC), tissue invasion by collectively invading cells requires physical forces applied by tumor cells on their surrounding extracellular matrix (ECM). Cancer-related ECM is composed of thick collagen bundles organized by carcinoma-associated fibroblasts (CAF) within the tumor stroma. Here we show that SCC cell collective invasion is driven by the matrix-dependent mechano-sensitization of EGF signaling in cancer cells. Calcium (Ca2+) was a potent intracellular second messenger that drove acto-myosin contractility. Tumor-derived matrix stiffness and EGFR signaling triggered increased intracellular Ca2+ through CaV1.1 expression in SCC cells. Blocking L-type calcium channel expression or activity using Ca2+ channel blockers verapamil and diltiazem reduced SCC cell collective invasion both in vitro and in vivo. These results identify verapamil and diltiazem, two drugs long used in medical care, as novel therapeutic strategies to block the tumor-promoting activity of the tumor niche.

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