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Abstract Immune checkpoint therapy, where CD8 tumor infiltrating T lymphocytes (TIL) are reactivated, is a promising anti‐cancer treatment approach, yet with low response rates. The extracellular matrix, in particular tenascin‐C, may generate barriers for TIL. To investigate this possibility, we used a MMTV‐NeuNT and syngeneic mammary gland grafting model derived thereof with engineered tenascin‐C levels and observed accumulation of CD8 TIL in tenascin‐C‐rich stroma. Inhibition studies revealed that tenascin‐C induced CXCL12 through TLR4. By binding CXCL12, tenascin‐C retained CD8 TIL in the stroma. Blockade of CXCR4, the receptor of CXCL12, enhanced macrophage and CD8 TIL infiltration and reduced tumor growth and subsequent metastasis. Retention of CD8 TIL by tenascin‐C/CXCL12 was also observed in human breast cancer by tissue staining. Moreover, whereas high CD8 TIL numbers correlated with longer metastasis‐free survival, this was not the case when also tenascin‐C and CXCL12 levels were high. Altogether, these results may be useful for improving tumor immunity as diagnostic tool and to formulate a future “TIL‐matrix‐release‐and‐reactivate” strategy.

The extracellular matrix molecule tenascin-C (TNC) is a major component of the cancer-specific matrix, and high TNC expression is linked to poor prognosis in several cancers. To provide a comprehensive understanding of TNC’s functions in cancer, we established an immune-competent transgenic mouse model of pancreatic β-cell carcinogenesis with varying levels of TNC expression and compared stochastic neuroendocrine tumor formation in abundance or absence of TNC. We show that TNC promotes tumor cell survival, the angiogenic switch, more and leaky vessels, carcinoma progression, and lung micrometastasis. TNC downregulates Dickkopf-1 (DKK1) promoter activity through the blocking of actin stress fiber formation, activates Wnt signaling, and induces Wnt target genes in tumor and endothelial cells. Our results implicate DKK1 downregulation as an important mechanism underlying TNC-enhanced tumor progression through the provision of a proangiogenic tumor microenvironment.

Breast cancer is still a deadly disease despite major achievements in targeted therapies designed to block ligands or ligand-binding subunits of major tyrosine kinase receptors. Relapse is significant and metastases deleterious, which demands novel strategies for fighting this disease. Here, we report a proof-of-concept experiment demonstrating that small peptides interfering with the transmembrane domain of the tyrosine kinase epidermal growth factor receptor ErbB2 exhibit anticancer properties when used at micromolar dosages in a genetically engineered mouse model of breast cancer. Different assays demonstrate the specificity of the ErbB2-targeting peptide, which induces long-term reduction of ErbB2 phosphorylation and Akt signaling consistent with reduced tumor cell proliferation and increased survival. Microcomputed tomography analysis established the antimetastatic activity of the peptide and its impact on primary tumor growth. This reveals the interior of the cell membrane as an unexplored dimension for drug design.