Abstract 3058: Syndecan-1 mediates breast cancer metastasis to the brain through IL-8 and PECAM-1 signaling

Abstract

Abstract Brain metastasis is a devastating, late-stage event affecting approximately 10-30% of breast cancer patients. However, it is not well understood how breast cancer cells migrate across the blood-brain barrier (BBB) and invade into the brain. Syndecans (Sdcs) are cell surface heparan sulfate proteoglycans (HSPGs) that have previously been linked to breast cancer progression and metastasis. Preliminary findings from our lab indicate that Sdc1 may be involved in breast cancer metastasis to the brain. In clinical samples from breast cancer patients with brain metastases, 67% of the brain metastasis samples stained positive for Sdc1 expression. In an experimental mouse model of metastasis, we found that silencing expression of Sdc1 in MDA-231 breast cancer cells greatly reduced metastasis specifically to the brain, with no difference in lung or bone metastases. Additionally, silencing expression of Sdc1 in MDA-231 cells resulted in a reduction in cancer cell migration across an in vitro BBB transwell model system. These findings prompted us to investigate the mechanism through which Sdc1 facilitates breast cancer cell migration across the BBB. Since BBB endothelial cell junctions have been reported to be disrupted in metastasis to the brain, immunofluorescence was performed to examine localization of junction proteins in our BBB model following addition of conditioned medium (CM) from MDA-231 non-silenced (NS1) control and Sdc1KD cells. We observed disruption in PECAM-1 localization at BBB endothelial cell junctions upon addition of CM from MDA-231 NS1 cells with markedly less disruption occurring upon treatment with CM from Sdc1KD cells. These results suggest that paracrine factors secreted from MDA-231 cells may facilitate breast cancer cell migration across the BBB by affecting PECAM-1 localization on BBB endothelial cells. By performing a cytokine array using CM from MDA-231 cells, we determined that Sdc1KD CM contained lower levels of IL-8 than MDA-231 NS1 cell CM. These findings were confirmed by ELISA, qRT-PCR, and multiplex analysis. We then went on to treat endothelial cells in the xCELLigence in vitro BBB model system with IL-8 and observed a sufficient decrease in cell index readings, suggesting that IL-8 affects BBB barrier permeability. Taken together, our results suggest that Sdc1 supports breast cancer cell migration across the BBB through a signaling mechanism involving IL-8 and PECAM-1. Elucidating this mechanism will allow for the development of therapeutic strategies to combat breast cancer cell metastasis to the brain. [S.M.W. and M.S. contributed equally to this work.] Citation Format: Sierra Mosticone Wangensteen, Megan Sayyad, Madhavi Puchalapalli, Megan Sullivan, Jamie Singh, Briana Ratchford, Jayda Abrams, Majid Jahromi, Bin Hu, Michael Idowu, Jennifer Koblinski. Syndecan-1 mediates breast cancer metastasis to the brain through IL-8 and PECAM-1 signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3058. doi:10.1158/1538-7445.AM2017-3058