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Extracellular vesicles (EV), structures surrounded by a biological membrane, transport biologically active molecules, and represent a recently identified way of intercellular communication. Colorectal cancer (CRC), one of the most common cancer types in the Western countries, is composed of both tumor and stromal cells and the amount of stromal fibroblasts negatively correlates with patient survival. Here we show that normal colon fibroblasts (NCF) release EVs with a characteristic miRNA cargo profile when stimulated with TGFβ, one of the most important activating factors of fibroblasts, without a significant increase in the amount of secreted EVs. Importantly, fibroblast-derived EVs induce cell proliferation in epidermal growth factor (EGF)-dependent patient-derived organoids, one of the best current systems to model the intra-tumoral heterogeneity of human cancers. In contrast, fibroblast-derived EVs have no effect in 3D models where EGF is dispensible. This EV-induced cell proliferation did not depend on whether NCFs or cancer-associated fibroblasts were studied or on the pre-activation by TGFβ, suggesting that TGFβ-induced sorting of specific miRNAs into EVs does not play a major role in enhancing CRC proliferation. Mechanistically, we provide evidence that amphiregulin, transported by EVs, is a major factor in inducing CRC cell proliferation. We found that neutralization of EV-bound amphiregulin blocked the effects of the fibroblast-derived EVs. Collectively, our data suggest a novel mechanism for fibroblast-induced CRC cell proliferation, coupled to EV-associated amphiregulin.

Small extracellular vesicles (EVs) are membrane enclosed structures that are usually released from cells upon exocytosis of multivesicular bodies (MVBs) as a collection of separate, free EVs. In this study, we analysed paraffin embedded sections of archived human colorectal cancer samples. We studied 3D reconstructions of confocal microscopic images complemented by HyVolution and STED imaging. Unexpectedly, we found evidence that large, MVB-like aggregates of ALIX/CD63 positive EV clusters were released en bloc by migrating tumour cells. These structures were often captured with partial or complete extra-cytoplasmic localization at the interface of the plasma membrane of the tumour cell and the stroma. Their diameter ranged between 0.62 and 1.94 μm (mean±S.D.: 1.17 ± 0.34 μm). High-resolution 3D reconstruction showed that these extracellular MVB-like EV clusters were composed of distinguishable internal particles of small EV size (mean±S.D.: 128.96 ± 16.73 nm). In vitro, HT29 colorectal cancer cells also showed the release of similar structures as confirmed by immunohistochemistry and immune electron microscopy. Our results provide evidence for an en bloc transmission of MVB-like EV clusters through the plasma membrane. Immunofluorescent-based detection of the MVB like small EV clusters in archived pathological samples may represent a novel and unique opportunity which enables analysis of EV release in situ in human tissues.

Abstract Liver is the third most common organ for breast cancer (BC) metastasis. Two main histopathological growth patterns (HGP) exist in liver metastases (LM): desmoplastic and replacement. Although a reduced immunotherapy efficacy is reported in patients with LM, tumor-infiltrating lymphocytes (TIL) have not yet been investigated in BCLM. Here, we evaluate the distribution of the HGP and TIL in BCLM, and their association with clinicopathological variables and survival. We collect samples from surgically resected BCLM (n = 133 patients, 568 H&E sections) and post-mortem derived BCLM (n = 23 patients, 97 H&E sections). HGP is assessed as the proportion of tumor liver interface and categorized as pure-replacement (‘pure r-HGP’) or any-desmoplastic (‘any d-HGP’). We score the TIL according to LM-specific guidelines. Associations with progression-free (PFS) and overall survival (OS) are assessed using Cox regressions. We observe a higher prevalence of ‘any d-HGP’ (56%) in the surgical samples and a higher prevalence of ‘pure r-HGP’ (83%) in the post-mortem samples. In the surgical cohort, no evidence of the association between HGP and clinicopathological characteristics is observed except with the laterality of the primary tumor (p value = 0.049) and the systemic preoperative treatment before liver surgery (p value = .039). TIL is less prevalent in ‘pure r-HGP’ as compared to ‘any d-HGP’ (p value = 0.001). ‘Pure r-HGP’ predicts worse PFS (HR: 2.65; CI: (1.45–4.82); p value = 0.001) and OS (HR: 3.10; CI: (1.29–7.46); p value = 0.011) in the multivariable analyses. To conclude, we demonstrate that BCLM with a ‘pure r-HGP’ is associated with less TIL and with the worse outcome when compared with BCLM with ‘any d-HGP’. These findings suggest that HGP could be considered to refine treatment approaches.