Identification of Small-Molecule Inhibitors Targeting Different Signaling Pathways in Cancer-Associated Fibroblast Reprogramming Under Tumor-Stroma Interaction

Cancer-associated fibroblasts (CAFs) interact reciprocally with tumor cells through various signaling pathways in many Cancer types including cutaneous squamous cell carcinoma (cSCC). Among normal fibroblast (NF) subtypes, papillary fibroblasts (PFs) and reticular fibroblasts (RFs) respond distinctly to tumor cell signaling, eventuating the differentiation of RFs, rather than PFs, into CAFs. The regulation of subtype differentiation in fibroblasts remains poorly explored. In this study, we assessed the differences between PFs, RFs, and CAFs, and examined the effects of small-molecule inhibitors targeting the TGFβ, PI3K/Akt/mTOR, and Notch pathways on the tumor-promoting property of CAFs and CAF reprogramming in 2D and 3D cultures. Blocking TGFβ and PI3K strongly deactivated and concurrently induced a PF phenotype in RFs and CAFs. 3D co-culturing a cSCC cell line MET2 with RFs or CAFs led to enhanced tumor invasion, "RF-CAF" transition and cytokine production, which were further repressed by blocking TGFβ and PI3K/mTOR pathways, but not Notch pathway. In conclusion, the study identified biomarkers for PFs, RFs and CAFs, and displayed different effects of blocking key signaling pathways in CAFs and tumor cell-CAF interplay. These findings prompted a "CAF to PF" therapeutic strategy, and provided perspectives of using included inhibitors in CAF-based Cancer therapy.

Cancer-Associated Fibroblast; PI3K; SCC; Skin Model; TGFβ.