Abstract A26: A self-sustained gradient of CCL8 drives breast cancer metastasis

The establishment of chemoattractive gradients between the neoplastic epithelium, the stroma and the peripheral tissues represents an attractive, yet elusive, mechanism that may contribute to metastasis. Here we provide evidence for the maintenance of a gradient of increasing CCL8 concentration between the epithelium, the stroma and the periphery that is instrumental for breast cancer cells dissemination promoting the directional movement of cancer cells from the site of primary tumor towards the periphery. Experiments in breast cancer cells cultured in vitro and in vivo studies in tumor-bearing mice showed that CCL8 production is enhanced in stromal fibroblasts at the tumor margins and in tissues at which breast cancer cells tend to metastasize such as the lungs and the brain. This stimulation of CCL8 expression in the stroma was driven by signals elicited by the neoplastic epithelium and could be recapitulated by administration of breast cancer cells conditioned media in tumor free mice. Experiments involving transwell-based migration assays established that CCL8-mediated chemoattraction was produced in breast cancer cells while genetic and antibody-based manipulation of CCL8 activity in mice influenced the histology of the tumors and promoted all major steps of the metastatic process such as invasion to adjacent stroma, intravasation and ultimately extravasation and seeding. Specifically, tumors growing in CCL8 deficient animals had well defined borders and high cellularity as opposed to the ill-defined margins of the tumors of wild type animals. In tumor-bearing mice acute i.v. administration of CCL8 increased the number of circulating tumor cells while antibody-mediated inhibition of CCL8 activity reduced the number of cancer cells invading towards adjacent fibroblasts that had been enclosed in matrigel and implanted proximally to the tumors. Only fibroblasts inoculated in the vicinity of breast tumors exhibited elevated CCL8 expression but not the fibroblasts growing in tumor-free mice, which is consistent with the active role of the epithelium in triggering CCL8 expression in the stroma. The stromal origin of CCL8 is also consistent with the strong correlation observed between circulating levels of CCL8 and tumor size, in EO771 mouse breast cancers at which CCL8 expression is minimal and in human MDA-MB-231 breast cancers at which species specific immunoassays permit the distinction between CCL8 originating from the neoplastic epithelium or the host. Analysis of publicly available data suggested that CCL8 is overexpressed in breast tumors as compared to normal breast tissue while high CCL8 expression in clinical breast cancers is associated with poor prognosis. These findings exemplify how self-sustained CCL8-like gradients of chemoattractive factors, between the epithelium, the stroma and the periphery can be induced by breast cancer cells to drive the metastatic process and suggest that interference with their operation may provide means for breast cancer management. Citation Format: Elena Farmaki, Ioulia Chatzistamou, Vimala Kaza, Hippokratis Kiaris. A self-sustained gradient of CCL8 drives breast cancer metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A26.