S36 - Exosomes derived by melanoma cells promote the tumor osteotropism

Abstract

Background: Melanoma-derived exosomes (EXOs) are nanovesicles of 60-100 nm that regulate the intercellular cross-talk of melanoma cells with components of the tumor microenvironment thus driving the cancer cell proliferation, migration and invasiveness. It is noteworthy that EXOs prepare the pre-metastatic niche to house primary tumor cells, thus regulating the metastatic colonization of specific sites. Here, we investigated the in vitro ability of EXOs to regulate the melanoma cell chemotaxis with a particular focus to bone tropism. Material and methods: EXOs were purified by ultracentrifugation from the culture medium of non-metastatic (LCP) and metastatic (WM-266, SK-Mel28) melanoma cell lines as well as from breast cancer cells (MDA-MB231) as control. Basal and EXO-induced migration as well as invasiveness were assessed by Boyden chambers and matrigel-coated membranes. We also assessed the melanoma cell capability to migrate towards human bone fragments and measured this property in non-osteotropic cells (Skmel28) when treated with EXOs isolated from those with higher bone targeting potential (LCP, MDA-MB231). Results: Basal migration and invasiveness of LCP were lower with respect to WM-266 and SK-Mel28 cells, while strongly increased after stimulation by EXOs from both WM-266 (1.38 ± 0.15 and 1.57 ± 0.2 fold increase, respectively) and SK-Mel28 (1.45 ± 0.16 and 1.69 ± 0.22 fold increase) (p < 0.05 in all instances). By contrast, LCP-EXOs poorly influenced their ability to migrate and invade (1.11 ± 0.14 and 1.28 ± 0.21 fold increase; p > 0.2). The migration of LCP and MDA-MB231 cells were highly increased by bone fragments, relatively to unstimulated cells (3.45 ± 0.54 and 2.28 ± 0.23 fold increase, respectively; p < 0.05), whereas SK-Mel28 migration was not influenced (0.98 ± 0.15 fold increase; p 0.87). Finally, the osteotropism of SK-Mel28 cells was enhanced by EXOs from LCP and MDA-MB231 (2.67 ± 0.23 and 2.33 ± 0.21 fold increase, respectively; p < 0.01), while not by homologus EXOs (1.08 ± 0.14 fold increase; p 0.73). Conclusion: Our data suggest that EXOs from metastatic melanoma cells increase the chemotaxis of low migrating and invading cells. Thus, melanoma derived EXOs might play a role in tumor progression by strengthening these functions leading ultimately to promote the melanoma osteotropism.