P66.03 The Functional Role of TGF-β Signaling in SCLC Heterogeneity and Metastasis

Abstract

Small cell lung cancer (SCLC) is the most aggressive lung cancer and highly heterogeneous phenotypes have been observed in human and mouse SCLC cells. Tumor heterogeneity has been proven to contribute to SCLC malignant progression and/or metastasis in RP-based models. And the unique therapeutic vulnerabilities across different SCLC subtypes have been linked with their specific gene expression profile, indicating the need of personal therapeutic strategy in clinic. The TGF-β signaling consists of secreted TGF-β family members, receptors and SMAD proteins, and is implicated in multiple cell biological processes, such as cell proliferation and survival, epithelial to mesenchymal transition (EMT), cell fate control, immune response, and tumorigenesis. Dysregulation of the TGF-β signaling pathway has been reported in different cancer types and dual role of this pathway in cancer development and progression has been documented. Activation of this pathway results in cell cycle arrest and apoptosis at the early-stage of cancer development, indicating a tumor suppressive function. On the other hand, TGF-β could promote EMT as well as tumor malignant progression at the late-stage disease. Up to date, the contribution of the TGF-β pathway in SCLC development and progression remains elusive. Using the Rb1L/L/Trp53 L/L (RP) mouse model, we find that mouse SCLC cells with adherent growth pattern are composed of mesenchymal-like (Mes) and epithelial-like (Epi) subpopulations. Take advantage of in vitro functional assay and in vivo allograft assay, we find that the Mes cells harbor higher malignant transformation and metastatic capabilities than Epi cells. Through the analysis of microarray data, we find that the TGF-β signaling is enriched in Mes cells. And the inhibition of TGF-β signaling in Mes cells significantly abrogates its metastatic ability in allograft assay. Moreover, genetic deletion of the key components of the TGF-β signaling pathway, dramatically attenuated SCLC metastasis in the RP mouse model. In this study, we find that mouse SCLC cells derived from RP autochthonous mouse model with adherent growth pattern are composed of Mes and Epi subpopulations. The Mes cells have increased ability to form colonies in soft agar and harbored stronger metastatic capability in vivo when compared to the Epi cells. Gene Set Enrichment Analysis (GSEA) reveals that the TGF-β signaling is enriched in the Mes cells. Inhibition of the TGF-β signaling through either ectopic expression of dominant negative Tgfbr2 (Tgfbr2-DN) or treatment with Tgfbr1 inhibitor SD-208 consistently greatly abrogates the tumor metastasis in allograft assays. Moreover, genetic deletion of Tgfbr2 or Smad4, key components of the TGF-β signaling pathway, dramatically attenuates SCLC metastasis in the RP autochthonous mouse model of SCLC. Our results suggest the critical role of TGF-β signaling in SCLC heterogeneity and metastasis. Importantly, inhibition of TGF-β signaling significantly abrogates SCLC metastasis, providing a potential therapeutic avenue for SCLC management in clinic.