DNA damaging therapies induce a pro-tumorigenic fibroblast phenotype

There is growing evidence that anticancer therapies not only target tumour cells but also reshape the tumour microenvironment, paradoxically enabling fibroblasts to acquire a pro-tumorigenic phenotype. These fibroblasts are characterised by an altered secretome and extensive extracellular matrix (ECM) remodelling, which promote therapy resistance and tumour progression. In this study, we demonstrate that DNA damage-inducing anticancer drugs drive normal fibroblasts towards a fibrosis- and cancer-associated fibroblast (CAF)-like phenotype. Using 3D cell-derived ECM deposition assays, we show that treatment of both normal fibroblasts and CAFs stimulates the formation of a more anisotropic ECM with enlarged pores. This remodelled ECM enhances cancer cell adhesion and proliferation, while unexpectedly reducing migration across the matrix. In contrast, the soluble secretome does not affect cancer cell proliferation but significantly increases chemotactic migration towards the therapy-exposed fibroblasts. Gene expression profiling by RNA sequencing combined with 2D and 3D in vitro analyses, reveals that prolonged drug exposure induces fibroblast senescence, marked by upregulation of beta-galactosidase, IL6, CDKN1A, and CDKN2A expression. The therapy-induced senescent fibroblasts also display features of a myofibroblast-like CAF (myCAF) phenotype, including enhanced contractility and increased expression of ACTA2, PDGFRA, MMPs, TIMPs, and extracellular matrix components such as collagens, vitronectin, and VCAM. We have previously shown that myCAFs can promote in vivo growth and metastasis, underscoring their critical role in tumour progression. Our findings suggest that therapy-induced senescence in fibroblasts may create a permissive microenvironment for tumour progression.