Inhibition of fibroblasts decreases metastatic breast cancer

Despite significant improvements in the treatment of breast cancer over the past decades, a fifth of the patients will develop incurable metastatic disease. In recent years it has been shown that stromal cells and the composition and physical properties of the extracellular matrix significantly contribute to tumour progression.

In this study we compared a non- and metastatic mouse mammary carcinoma cell line, D2A1 and D2A1-m2, respectively, with regards to their in vivo and in vitro characteristics, as well as crosstalk with the stroma.
While there is no difference in primary tumour growth, only D2A1-m2 cells are capable to spontaneously metastasis to the lungs of BALB/c mice. In vitro analysis did not support proliferation, migration and invasion, as driving forces of the enhanced metastasis, as all of them are reduced in the D2A1-m2 cells compared to D2A1 in in vitro assays. Instead, D2A1-m2 cells show increased resistance to apoptosis when cultured in non-adherent conditions and increased 3D tumour spheroid growth with and without the addition of cancer-associated fibroblasts. Moreover, the enhanced spontaneous metastatic phenotype of the D2A1-m2 subline is associated with an increased ability to recruit an activated tumour stroma. D2A1-m2 primary tumours had more than twice as many blood vessels and cancer-associated fibroblasts than primary tumours formed of D2A1 cells. In vitro analyses revealed that the secretome of D2A1-2 cells not only attracted more fibroblasts but also activated them stronger, measured by 3D collagen contraction. Inhibition of stromal fibroblasts in 3D in vitro assays but also in in vivo metastasis assays significantly reduced the tumour cell growth, highlighting the permissive role of the tumour:stroma crosstalk in breast cancer progression.