ABSTRACT
Targeted therapies for gastrointestinal stromal tumor (GIST) are modestly effective, but GIST cannot be cured with single agent tyrosine kinase inhibitors. In this study, we sought to identify new therapeutic targets in GIST by investigating the tumor microenvironment. Here, we identified a paracrine signaling network by which cancer-associated fibroblasts (CAFs) drive GIST growth and metastasis. Specifically, CAFs isolated from human tumors were found to produce high levels of platelet-derived growth factor C (PDGFC), which activated PDGFC-PDGFRA signal transduction in GIST cells that regulated the expression of SLUG, an epithelial-mesenchymal transition (EMT) transcription factor and downstream target of PDGFRA signaling. Together, this paracrine induce signal transduction cascade promoted tumor growth and metastasis in vivo. Moreover, in metastatic GIST patients, SLUG expression positively correlated with tumor size and mitotic index. Given that CAF paracrine signaling modulated GIST biology, we directly targeted CAFs with a dual PI3K/mTOR inhibitor, which synergized with imatinib to increase tumor cell killing and in vivo disease response. Taken together, we identified a previously unappreciated cellular target for GIST therapy in order to improve disease control and cure rates.
Subject(s)
Gastrointestinal Stromal Tumors/genetics , Lymphokines/genetics , Platelet-Derived Growth Factor/genetics , Receptor, Platelet-Derived Growth Factor alpha/genetics , Snail Family Transcription Factors/genetics , Cancer-Associated Fibroblasts/drug effects , Cancer-Associated Fibroblasts/pathology , Cell Line, Tumor , Epithelial-Mesenchymal Transition/genetics , Gastrointestinal Stromal Tumors/drug therapy , Gastrointestinal Stromal Tumors/pathology , Humans , Neoplasm Metastasis , Paracrine Communication/drug effects , Phosphatidylinositol 3-Kinases/drug effects , Protein Kinase Inhibitors/pharmacology , Signal Transduction/drug effects , TOR Serine-Threonine Kinases/antagonists & inhibitors , TOR Serine-Threonine Kinases/genetics , Tumor Microenvironment/drug effectsABSTRACT
Cancer-associated fibroblasts (CAFs) are the most abundant cells in the tumor microenvironment. Crosstalk between tumor cells and CAFs contributes to tumor survival in most epithelial cancers. Recently, utilizing gastrointestinal stromal tumor (GIST) as a model for sarcomas, we identified paracrine networks by which CAFs promote tumor progression and metastasis. However, the mechanisms by which CAFs arise in sarcomas remain unclear. Here, RNA sequencing analysis revealed that transforming growth factor-ß1 (TGF-ß1) is highly expressed in both tumor cells and CAFs. To determine the functional role of TGF-ß1, we treated normal gastric fibroblasts (GFs) with recombinant TGF-ß1, which caused the GFs to adopt a more stellate morphology, as well as increased the mRNA expression of CAF-mediated genes (CCL2, RAB3B, and TNC) and genes encoding fibroblast growth factors (FGFs). Moreover, while either GIST or CAF conditioned media enhanced the transition from GFs to CAFs, a TGF-ß1-blocking antibody attenuated this effect. Transwell migration assays revealed that the TGF-ß1-mediated transition from GFs to CAFs enhanced tumor cell migration. This migratory effect was abrogated by an anti-TGF-ß1 antibody, suggesting that TGF-ß1 secreted from GIST cells or CAFs is associated with GIST migration via GF-to-CAF transition. In addition, the murine spleen-to-liver metastasis model showed that GF pre-treated with TGF-ß1 promoted GIST metastasis. Collectively, these findings reveal unappreciated crosstalk among tumor cells, CAFs, and normal resident fibroblasts in the stroma of sarcomas, which enhances a GF-to-CAF transition associated with tumor migration and metastasis.
