Metastasis is the most common cause of mortality in breast cancer patients worldwide. To identify improved mouse models for breast cancer growth and spontaneous metastasis, we examined growth and metastasis of both estrogen receptor positive (T47D) and negative (MDA-MB-231, SUM1315, and CN34BrM) human breast cancer cells in nude and NSG mice. Both primary tumor growth and spontaneous metastases were increased in NSG mice compared to nude mice. In addition, a pattern of metastasis similar to that observed in human breast cancer patients (metastases to the lungs, liver, bones, brain, and lymph nodes) was found in NSG mice. Furthermore, there was an increase in the metastatic burden in NSG compared to nude mice that were injected with MDA-MB-231 breast cancer cells in an intracardiac experimental metastasis model. This data demonstrates that NSG mice provide a better model for studying human breast cancer metastasis compared to the current nude mouse model.

Purpose: Although survival rates for patients with localized breast cancer have increased, patients with metastatic breast cancer still have poor prognosis. Understanding key factors involved in promoting breast cancer metastasis is imperative for better treatments. In this study, we investigated the role of syndecan-1 (Sdc1) in breast cancer metastasis. Methods:To assess the role of Sdc1 in breast cancer metastasis, we silenced Sdc1 expression in the triplenegative breast cancer human MDA-MB-231 cell line and overexpressed it in the mouse mammary carcinoma 4T1 cell line. Intracardiac injections were performed in an experimental mouse metastasis model using both cell lines. In vitro transwell blood-brain barrier (BBB) and brain section adhesion assays were utilized to specifically investigate how Sdc1 promotes brain metastasis. A cytokine array was performed to evaluate differences in the breast cancer cell secretome when Sdc1 is silenced.Results: Silencing expression of Sdc1 in breast cancer cells significantly reduced metastasis to the brain. Conversely, overexpression of Sdc1 increased metastasis to the brain. We found that silencing of Sdc1 expression had no effect on attachment of breast cancer cells to brain endothelial cells or astrocytes, but migration across the BBB was reduced as well as adhesion to the perivascular regions of the brain. Loss of Sdc1 also led to changes in breast cancer cell-secreted cytokines/chemokines, which may influence the BBB. Conclusions:Taken together, our study demonstrates a role for Sdc1 in promoting breast cancer metastasis to the brain. These findings suggest that Sdc1 supports breast cancer cell migration across the BBB through regulation of cytokines, which may modulate the BBB. Further elucidating this mechanism will allow for the development of therapeutic strategies to combat brain metastasis.

Purpose: Although survival rates for patients with localized breast cancer have increased, patients with metastatic breast cancer still have poor prognosis. Understanding key factors involved in promoting breast cancer metastasis is imperative for better treatments. In this study, we investigated the role of syndecan-1 (Sdc1) in breast cancer metastasis. Methods:To assess the role of Sdc1 in breast cancer metastasis, we silenced Sdc1 expression in the triplenegative breast cancer human MDA-MB-231 cell line and overexpressed it in the mouse mammary carcinoma 4T1 cell line. Intracardiac injections were performed in an experimental mouse metastasis model using both cell lines. In vitro transwell blood-brain barrier (BBB) and brain section adhesion assays were utilized to specifically investigate how Sdc1 promotes brain metastasis. A cytokine array was performed to evaluate differences in the breast cancer cell secretome when Sdc1 is silenced.Results: Silencing expression of Sdc1 in breast cancer cells significantly reduced metastasis to the brain. Conversely, overexpression of Sdc1 increased metastasis to the brain. We found that silencing of Sdc1 expression had no effect on attachment of breast cancer cells to brain endothelial cells or astrocytes, but migration across the BBB was reduced as well as adhesion to the perivascular regions of the brain. Loss of Sdc1 also led to changes in breast cancer cell-secreted cytokines/chemokines, which may influence the BBB. Conclusions:Taken together, our study demonstrates a role for Sdc1 in promoting breast cancer metastasis to the brain. These findings suggest that Sdc1 supports breast cancer cell migration across the BBB through regulation of cytokines, which may modulate the BBB. Further elucidating this mechanism will allow for the development of therapeutic strategies to combat brain metastasis.

Breast cancer is one of the most common forms of cancer affecting women in the United States, second only to skin cancers. Although treatments have been developed to combat primary breast cancer, metastasis remains a leading cause of death. An early step of metastasis is cancer cell invasion through the basement membrane. However, this process is not yet well understood. AG73, a synthetic laminin-α1 chain peptide, plays an important role in cell adhesion and has previously been linked to migration, invasion, and metastasis. Thus, we aimed to identify the binding partner of AG73 on breast cancer cells that could mediate cancer progression. We performed adhesion assays using MCF10A, T47D, SUM1315, and MDA-231 breast cell lines and found that AG73 binds to syndecans (Sdcs) 1, 2, and 4. This interaction was inhibited when we silenced Sdcs 1 and/or 4 in MDA-231 cells, indicating the importance of these receptors in this relationship. Through actin staining, we found that silencing of Sdc 1, 2, and 4 expression in MDA-231 cells exhibits a decrease in the length and number of filopodia bound to AG73. Expression of mouse Sdcs 1, 2, and 4 in MDA-231 cells provides rescue in filopodia, and overexpression of Sdcs 1 and 2 leads to increased filopodium length and number. Our findings demonstrate an intrinsic interaction between AG73 in the tumor environment and the Sdcs on breast cancer cells in supporting tumor cell adhesion and invasion through filopodia, an important step in cancer metastasis.

Heparan sulfate (HS) are linear polysaccharides conjugated to proteins, heparan sulfate proteoglycans (HSPGs), located on the cell surface and extracellular matrix. The HS chains display varying degrees of sulfation. These sulfate clusters mediate the interaction of polynuclear platinum complexes (PPCs) with HSPG through a “sulfate clamp.” Such PPC-HS interactions can be conceptualized as “polyarginine” mimics. Strong HS-PPC binding protects the oligosaccharide against sulfate loss through metalloshielding. The biological consequences of PPCs metalloshielding HS will in principle affect HS interactions with relevant enzymes and proteins such as heparanase and growth factors, similar in concept to inhibition of DNA-protein binding through modification of DNA structure and conformation. HSPGs, associated growth factors, and heparanase promote tumor progression by facilitating invasion, angiogenesis, and metastasis. High heparanase expression correlates with increased metastatic potential and poor clinical prognosis. PPC-HS interactions inhibit cleavage of a model pentasaccharide by heparanase and further modulated bFGF binding to HS, and bFGF-induced migration and signaling in colon cancer cells. The end-point of functional modulation of HS interactions is inhibition of angiogenesis and metastasis. We report proof-of-principle of strong in vivo anti-metastatic activity of PPCs in triple negative breast cancer (TNBC) models. Further, we examine the anti-metastatic and anti-angiogenic effects of PPC-HS metalloshielding in these in vivo models through multiple growth factor signaling pathways (bFGF, HB-EGF, VEGF), and heparanase activity in breast cancer and endothelial cells. PPCs represent a novel class of intrinsically dual-function agents combining platinum cytotoxicity through DNA targeting with anti-angiogenic effects through glycan targeting. Chicago 14-17 April 2018 Citation Format: Samantha J. Katner, James D. Hampton, Erica J. Peterson, Eriko Katsuta, Megan R. Sayyad, Kazuaki Takabe, Jennifer Koblinski, Nicholas P. Farrell. Heparan sulfate, a new target for platinum in metastatic TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3941.

Brain metastasis is a devastating, late-stage event affecting 10-30% of breast cancer patients, but it is unclear how breast cancer cells can cross the blood-brain barrier (BBB) and colonize the unique brain environment. Exosomes, endosomal-derived extracellular vesicles, have been reported to support premetastatic niche formation through recruitment of tumor growth-supporting cells, creating sites conducive to cancer development. Still, it is not known how exosomes might prime the distinctive brain environment for metastasis despite the ability of circulating exosomes to readily cross the BBB. Glial cells, namely astrocytes and microglia, are important contributors to brain metastasis, and astrocytes in particular secrete exosomes that promote tumor outgrowth in the brain. We therefore investigated the effects of breast cancer exosomes on astrocytes in promoting brain premetastatic niche formation. Using ultracentrifugation, we isolated exosomes from 4T1 metastatic and 67NR nonmetastatic mouse mammary carcinoma and MDA-MB-231 human triple-negative breast cancer cell-conditioned media. Exosomes were characterized using Western immunoblot, dynamic light scatter analysis, and transmission electron microscopy, and labeled with a fluorescent lipid dye. Mouse and human astrocytes were then treated with either 4T1 or MDA-MB-231 exosomes, respectively, and vesicle internalization was assessed using confocal microscopy. Astrocytes were indeed found to internalize cancer exosomes in vitro. Using qPCR analysis, we explored gene expression changes in mouse astrocytes treated with 4T1 exosomes compared to those treated with 67NR exosome nonmetastatic controls. 4T1 exosomes were found to significantly upregulate expression of tenascin C, an astrocyte-derived brain extracellular matrix protein, suggesting the brain matrix could be remodeled prior to cancer cell arrival. Further, astrocytes treated with 4T1 exosomes exhibited significant upregulation of inflammation-associated genes, namely COX-2, IL-6, CCL4 and PDGF-alpha, genes also associated with cancer and metastasis, specifically to the brain. Alternatively, 67NR exosome treated-astrocytes exhibited significant downregulation in these genes of interest, suggesting that there is a unique response profile associated with nonmetastatic versus metastatic breast cancer-derived exosomes. Taken together, these findings suggest that breast cancer exosomes could drive transformation of the brain environment towards a prometastatic site. Citation Format: Megan Sayyad, Madhavi Puchalapalli, Bin Hu, Jennifer Koblinski. Brain metastatic versus non-metastatic breast cancer exosomes influence astrocyte response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 47.

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Brain metastasis affects 10-30% of breast cancer patients, but it is unclear how breast cancer cells can colonize the unique and mostly cellular brain environment. Exosomes, endosomal-derived extracellular vesicles, have been reported to support tumorigenesis, mediate tumor-stromal interactions, and drive pre-metastatic niche formation, ultimately creating sites conducive to cancer development. Still, their role in brain metastasis remains to be fully understood. Glial cells, namely astrocytes, are important contributors to brain metastasis and secrete exosomes that support metastatic outgrowth in the brain. Thus, our study aims to investigate if breast cancer-derived exosomes can transform astrocytes towards a pro-metastatic phenotype. To do this, we isolated exosomes from 4T1 metastatic and 67NR non-metastatic mouse mammary carcinoma cell conditioned media using ultracentrifugation. Exosomes were characterized using Western immunoblot, dynamic light scatter analysis, and transmission electron microscopy. Using confocal microscopy, we found that mouse astrocytes can internalize 4T1 exosomes in vitro. Preliminary studies using qPCR analysis revealed that mouse astrocytes treated with 4T1 exosomes compared to those treated with 67NR exosomes exhibit differential gene expression, suggesting that there is a unique response profile associated with metastatic versus non-metastatic breast cancer-derived exosomes. To further assess this, we are investigating changes in the astrocyte secretome in response to 4T1 and 67NR exosome treatment using protein mass spectrometry. Taking a global approach, we have also been assessing differences between 4T1 and 67NR exosomal miRNA, and protein that could promote a shift in astrocytes towards a pro-metastatic phenotype. For these studies, we have implemented the Nanostring nCounter Analysis System and protein mass spectrometry, respectively. Proteomics assessment revealed distinct differences between the 4T1 metastatic and 67NR non-metastatic exosomes, whereby we identified 259 proteins that were enriched in 4T1 exosomes and 71 proteins that were decreased in 4T1 exosomes compared to 67NR’s. Proteins enriched in 4T1 exosomes were found to be associated with RNA binding and translation machinery, as well as abnormal cell adhesion, and BRCA1 interactions. Proteins identified to be decreased in 4T1 exosomes were found to play a role in IL-6 and IL-12 signaling events, the estrogen signaling pathway, and syndecan-2 signaling. These findings indicate that 4T1 and 67NR exosomes differ in protein cargo and these differences may be important in facilitating brain metastasis. Altogether, these studies will provide a more comprehensive assessment of the differences between metastatic versus non-metastatic cancer exosomes, and ultimately, provide novel insight into understanding breast cancer metastasis to the brain. Citation Format: Megan Sayyad, Madhavi Puchalapalli, Chris Canal, Theresa Swift-Scanlan, Andrew Ottens, Jennifer E. Koblinski. Metastatic v non-metastatic cancer exosomes in brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1988.