Abstract 3783: Adipocytes inhibit trastuzumab-mediated ADCC via induction of GDF15
Authors: Duong Minh Ngoc , Cleret Aurore , Matera Eva-Laure , Chettab Kamel , Poloni Doriane , Valsesia-Wittmann Sandrine , Clémenceau Béatrice , Dumontet Charles 
Published: May 2015

Abstract
Background : Trastuzumab is a monoclonal antibody that has been approved in the treatment of HER2-expressing breast cancer. Despite its efficacy, resistance often occurs. Little is known about the role of the tumor microenvironment in resistance to trastuzumab. Recent studies have shown rising role of adipose tissue in promoting cancer progression and inducing resistance to chemotherapy. Given the abundance of adipose tissue in breast and its proximity to cancer cells, we investigated the impact of adipocytes on antibody-dependent cellular cytotoxicity (ADCC), one of the main mechanisms of action of trastuzumab.
Methods: We set up a co-culture system in the presence of undifferentiated or differentiated human multi-potent adipose-derived stem (hMADS) cells, HER2-expressing human breast cancer cell lines (BT474, MDA-453, SKBR3, MDA-MB-361), and human natural killer NK-92 expressing the Fc receptor CD16. Trastuzumab-mediated cytotoxicity was assessed by calcein-release assay. Morphological changes on cancer cells and NK-92-CD16 cells were investigated by microscopy and flow cytometry.
Results: We found that adipocytes, as well as pre-adipocytes, inhibited trastuzumab-mediated ADCC by approximately 30%. Notably, this inhibition was enhanced in hypoxic conditions with 1% O2 (up to 60% inhibition). The inhibition of ADCC by adipose cells was not due to a titration or degradation of the antibody, but via factors that are secreted by adipose cells into the conditioned media. Analysis of cell phenotype did not reveal any modification of NK cell receptors (CD16, NKG2D, NKG2A, NKp30, NKp44) or NK cell activation markers (CD25, CD69, CD107a), nor of HER2 levels in the presence of adipocytes. Pre-incubation of NK cells with the conditioned medium from adipocytes did not alter NK cytotoxicity. Conversely, pre-incubation of cancer cells with adipocyte-conditioned medium reduced sensitivity of cancer cells to ADCC. Using transcriptomic approach, we found GDF15 to be rapidly up-regulated in cancer cells exposed to adipocyte-conditioned medium. Down-regulation of GDF15 by siRNA reversed the adipocyte-induced inhibition of ADCC.
Conclusion: Adipocytes inhibit antitumor activity of trastuzumab in HER2-expressing breast cancer cells via secretion of factors that reduce cancer cell sensitivity to ADCC. Our findings underline the importance of adipose tissue in the resistance to trastuzumab, and suggest that development of approaches targeting GDF15 may sensitize cancer cells to trastuzumab-based therapy.
Citation Format: Minh Ngoc Duong, Aurore Cleret, Eva-Laure Matera, Kamel Chettab, Doriane Poloni, Sandrine Valsesia-Wittmann, Béatrice Clémenceau, Charles Dumontet. Adipocytes inhibit trastuzumab-mediated ADCC via induction of GDF15. [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 3783. doi:10.1158/1538-7445.AM2014-3783