Transforming Growth Factor beta (TGF-ß) acts as a tumor suppressor early in carcinogenesis but turns into tumor promoter in later disease stages. In fact, TGF-ß is a known inducer of integrin expression by tumor cells which contributes to cancer metastatic spread and TGF-ß inhibition has been shown to attenuate metastasis in mouse models. However, carcinoma cells often become refractory to TGF-ß-mediated growth inhibition. Therefore identifying patients that may benefit from anti-TGF-ß therapy requires careful selection.
We performed in vitro analysis of the effects of exposure to TGF-ß in NSCLC cell chemotaxis and adhesion to lymphatic endothelial cells. We also studied in an orthotopic model of NSCLC the incidence of metastases to the lymph nodes after inhibition of TGF-ß signaling, ß3 integrin expression or both.
We offer evidences of increased ß3-integrin dependent NSCLC adhesion to lymphatic endothelium after TGF-ß exposure. In vivo experiments show that targeting of TGF-ß and ß3 integrin significantly reduces the incidence of lymph node metastasis. Even more, blockade of ß3 integrin expression in tumors that did not respond to TGF-ß inhibition severely impaired the ability of the tumor to metastasize towards the lymph nodes.
These findings suggest that lung cancer tumors refractory to TGF-ß monotherapy can be effectively treated using dual therapy that combines the inhibition of tumor cell adhesion to lymphatic vessels with stromal TGF-ß inhibition.