Abstract 5484: Heterogeneity of response to anti-TGF-β antibody therapy in preclinical models.
Authors: Yang Yu-an , Weng Jia , Welsh Michael , Guan Nancy , Webster Josh , Flanders Kathy , Lonning Scott M. , McPherson John , Wakefield Lalage M. 
Published: August 2014

Abstract
TGF-βs are pleiotropic growth factors with complex roles in tumorigenesis. Overexpression of TGF-β1 in many advanced human tumors correlates with metastasis and poor prognosis, and TGF-β antagonists are being developed for cancer therapy. Using a panel of syngeneic mouse transplant models of metastatic breast cancer, we found that an anti-TGF-β neutralizing antibody suppresses metastasis in several models, including the widely-used 4T1 model. However, as expected from the complexity of TGF-β action, responses were heterogeneous and anti-TGF-β antibody treatment had no effect or even stimulated metastasis in other models. This panel of models provides a powerful platform to identify candidate biomarkers for their ability predict therapeutic response to TGF-β antibodies. Previously we have shown that therapeutic outcome does not correlate with the expression of TGF-β ligands, the growth inhibitory response of the tumor model to TGF-β in vitro, the level of Six-1 expression, or the activation of non-canonical TGF-β signaling through formation of mixed Smad complexes. We next performed extensive histopathologic and immunohistochemical characterization of the tumor models to look for features that might correlate with therapeutic response. We found no obvious correlations between therapeutic response and a variety of markers, including estrogen receptor status, cytokeratin expression profile (luminal vs basal differentiation), p63 expression (basal marker), p53 expression or mutation status, smooth muscle actin expression or desmoplasia. There was also no correlation of response with tumor cell proliferation as assessed by quantitation of mitotic figures and Ki67, tumor cell apoptosis, extent of necrosis or histomorphology of the tumor cells (spindled vs polygonal). We then focused on mechanistic analysis of the undesirable stimulatory effect of anti-TGF-β antibodies in the Mvt-1 model in an attempt to generate new leads for biomarker analysis. We showed that the stimulatory effect of anti-TGF-β antibody treatment in the Mvt-1 model is still seen in SCID mice, suggesting that it does not involve T-cell mediated immune responses. Comparison of treated and untreated Mvt-1 tumors showed no effect of anti-TGF-β antibodies on tumor cell apoptosis, or infiltration by F480+ or CD11b+ immune cells. Tumor cell proliferation was actually decreased by the antibody treatment. In vitro assays showed that TGF-β had similar stimulatory effects on migration and invasion in both the 4T1 and Mvt-1 models, suggesting that the stimulatory effect of antibody therapy in the Mvt-1 model could not be explained by an anomalous invasion response to TGF-β. Thus the mechanism by which anti-TGF-β antibodies can stimulate metastasis in this model are unclear. Transcriptomic analyses of treated and untreated tumors are ongoing and results will be presented.
Citation Format: Yu-an Yang, Jia Weng, Michael Welsh, Nancy Guan, Josh Webster, Kathy Flanders, Scott M. Lonning, John McPherson, Lalage M. Wakefield. Heterogeneity of response to anti-TGF-β antibody therapy in preclinical models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5484. doi:10.1158/1538-7445.AM2013-5484