Abstract SY21-03: Fibroblast recruitment and activation in breast cancer progression
Authors: Avgustinova Alexandra , Iravani Marjan , Calvo Fernando , Sahai Erik , Klingbeil Pamela , Isacke Clare 
Published: May 2015

The tumor microenvironment is characterized by the infiltration and activation of stromal cells and the establishment of reinforcing tumor-stroma crosstalk pathways. There is now strong evidence that these interactions not only promote tumor progression and metastasis, but also influence tumor cell responses to chemotherapy, endocrine therapy and targeted agents. As a consequence, there is an urgent need to identify strategies to efficiently target these crosstalk pathways for the prevention or suppression of metastatic disease and to overcome treatment-resistant tumor progression in advanced breast cancer.

Experimentally, the majority of studies characterizing fibroblast activation in tumors have compared CAFs to normal breast fibroblasts. Consequently, despite the recognition that individual breast cancers display a striking variation in fibroblast infiltration and composition, and that non-activated CAFs and activated CAFs can have distinct functional roles, the mechanisms underlying the tumor-fibroblast crosstalk that drive inter-tumor stromal heterogeneity remain poorly understood.

We have employed cell lines of the orthotopic 4T1 mammary carcinoma series, all of which form primary tumors but differ in their aggressiveness and metastatic potential. By immunohistochemical staining of the primary tumors and gene expression profiling of freshly isolated tumor fibroblasts we have demonstrated that fibroblast infiltration and activation correlate with tumor aggressiveness in this model. Conversely by profiling freshly isolated tumor cells, we identified Wnt7a as a key factor secreted exclusively by aggressive tumor cells that in both in vitro and in vivo models drives the recruitment and activation of stromal fibroblasts. Importantly, using two separate breast cancer patient cohorts, tumor cell Wnt7a expression significantly correlates with the presence of an activated stromal and is an independent prognostic marker of poor patient outcome. Functionally, Wnt7a promotes the fibroblasts' ability to remodel the extracellular matrix as a permissive environment for tumor cell invasion. Surprisingly, Wnt7a-dependent fibroblast activation is not mediated by canonical Wnt signaling, rather, Wnt7a acts to modulate TGFβ signaling. Crosstalk between TGFβ and Wnt signaling in both development and disease has been documented previously, however, the majority of reports have focused on the convergence of Wnt and TGFβ at the level of their respective downstream pathways. In contrast, our data support a model in which Wnt7a potentiates TGFβ receptor signaling and we suggest that a consequence of this is to drive increased autocrine TGFβ expression thus creating an autocrine loop to maintain an activated CAF phenotype.

In conclusion, this study demonstrates a key interaction between two of the major signaling pathways involved in both development and disease. Further, these data highlight a novel level of signaling interplay in tumor fibroblasts that could be exploited in stromally targeted therapies to complement the tumor-targeting regimes used to treat invasive cancers.

Current author addresses: Alexandra Avgustinova (Institute for Research in Biomedicine Barcelona, Spain), Pamela Klingbeil (Evotec AG, Hamburg, Germany).

Citation Format: Alexandra Avgustinova, Marjan Iravani, Fernando Calvo, Erik Sahai, Pamela Klingbeil, Clare Isacke. Fibroblast recruitment and activation in breast cancer progression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr SY21-03. doi:10.1158/1538-7445.AM2014-SY21-03