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The basement membrane (BM) is a special type of extracellular matrix and presents the major barrier cancer cells have to overcome multiple times to form metastases. Here we show that BM stiffness is a major determinant of metastases formation in several tissues and identify netrin-4 (Net4) as a key regulator of BM stiffness. Mechanistically, our biophysical and functional analyses in combination with mathematical simulations show that Net4 softens the mechanical properties of native BMs by opening laminin node complexes, decreasing cancer cell potential to transmigrate this barrier despite creating bigger pores. Our results therefore reveal that BM stiffness is dominant over pore size, and that the mechanical properties of 'normal' BMs determine metastases formation and patient survival independent of cancer-mediated alterations. Thus, identifying individual Net4 protein levels within native BMs in major metastatic organs may have the potential to define patient survival even before tumour formation. The ratio of Net4 to laminin molecules determines BM stiffness, such that the more Net4, the softer the BM, thereby decreasing cancer cell invasion activity. The manuscript has been formally accepted for publication by Nature Materials. The manuscript needs shortening of the body, wherefore, final acceptance will be given upon re-submission of the shortened manuscript body. ispartof: Nature Materials vol:20 issue:6 ispartof: location:England status: Published online

Cancer-associated fibroblasts (CAFs) comprise a heterogeneous population of stromal cells within the tumour microenvironment. CAFs exhibit both tumour-promoting and tumour-suppressing functions, making them exciting targets for improving cancer treatments. A careful identification and characterisation of the CAF heterogeneity is thus necessary before implementing CAF-targeted strategies in cancer. With that in mind, we developed a flow cytometry strategy based on exclusion of non-CAF cells and successfully employed it to explore the temporal heterogeneity of CAFs in two models of triple-negative breast cancer (4T1 and 4T07). Analysing 128 murine tumours we identified 5-6 main CAF subpopulations and numerous minor ones based on the analysis of alpha smooth muscle actin, fibroblast activation protein alpha, platelet derived growth factor receptor alpha and beta, CD26/DPP4 and podoplanin. All markers showed temporal changes, and CD26+ CAFs emerged as a large novel subpopulation. These results form the foundation needed for the future elucidation of tumour-promoting CAF subpopulations.

Metastatic cancer spread is responsible for most cancer-related deaths. To colonize a new organ, invading cells adapt to, and remodel, the local extracellular matrix (ECM), a network of proteins and proteoglycans underpinning all tissues, and a critical regulator of homeostasis and disease. However, there is a major lack in tools to study cancer cell behavior within native 3D ECM. Here, an in-house designed bioreactor, where mouse organ ECM scaffolds are perfused and populated with cells that are challenged to colonize it, is presented. Using a specialized bioreactor chamber, it is possible to monitor cell behavior microscopically (e.g., proliferation, migration) within the organ scaffold. Cancer cells in this system recapitulate cell signaling observed in vivo and remodel complex native ECM. Moreover, the bioreactors are compatible with co-culturing cell types of different genetic origin comprising the normal and tumor microenvironment. This degree of experimental flexibility in an organ-specific and 3D context, opens new possibilities to study cell–cell and cell–ECM interplay and to model diseases in a controllable organ-specific system ex vivo.

Quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) is a sensitive technique for quantifying gene expression. Stably expressed reference genes are necessary for normalization of RT-qPCR data. Only a few articles have been published on reference genes in canine tumours. The objective of this study was to demonstrate how to identify suitable reference genes for normalization of genes of interest in canine soft tissue sarcomas using RT-qPCR. Primer pairs for 17 potential reference genes were designed and tested in archival tumour biopsies from six dogs. The geNorm algorithm was used to analyse the most suitable reference genes. Eight potential reference genes were excluded from this final analysis because of their dissociation curves. β-Glucuronidase (GUSB) and proteasome subunit, beta type, 6 (PSMB6) were most stably expressed with an M value of 0.154 and a CV of 0.053 describing their average stability. We suggest that choice of reference genes should be based on specific testing in every new experimental set-up.

Cancer bearing dogs represent a unique clinical cancer model with a direct potential for accelerating translation into human patients. A research collaboration between the veterinary and human medical facilities at Copenhagen University and Rigshospitalet has taken offset in this. Canine cancer patients are implemented for development of new strategies in molecular imaging and radiotherapy. The obtained results will be used to guide human clinical trials.