Roles of exosomes in liver metastases: Novel diagnosis and treatment choices

Feature-guided deep learning reduces signal loss and increases lesion CNR in diffusion-weighted imaging of the liver

PURPOSE

This research aims to develop a feature-guided deep learning approach and compare it with an optimized conventional post-processing algorithm in order to enhance the image quality of diffusion-weighted liver images and, in particular, to reduce the pulsation-induced signal loss occurring predominantly in the left liver lobe.

METHODS

Data from 40 patients with liver lesions were used. For the conventional approach, the best-suited out of five examined algorithms was chosen. For the deep learning approach, a U-Net was trained. Instead of learning "gold-standard" target images, the network was trained to optimize four image features (lesion CNR, vessel darkness, data consistency, and pulsation artifact reduction), which could be assessed quantitatively using manually drawn ROIs. A quality score was calculated from these four features. As an additional quality assessment, three radiologists rated different features of the resulting images.

RESULTS

The conventional approach could substantially increase the lesion CNR and reduce the pulsation-induced signal loss. However, the vessel darkness was reduced. The deep learning approach increased the lesion CNR and reduced the signal loss to a slightly lower extent, but it could additionally increase the vessel darkness. According to the image quality score, the quality of the deep-learning images was higher than that of the images obtained using the conventional approach. The radiologist ratings were mostly consistent with the quantitative scores, but the overall quality ratings differed among the readers.

CONCLUSION

Unlike the conventional algorithm, the deep-learning algorithm increased the vessel darkness. Therefore, it may be a viable alternative to conventional algorithms.

Exosomes promote pre-metastatic niche formation in colorectal cancer

It is well known that colorectal cancer (CRC) has a high morbidity rate, a poor prognosis when metastasized, and a greatly shortened 5-year survival rate. Therefore, understanding the mechanism of tumor metastasis is still important. Based on the "seed and soil" theory, the concept of " premetastatic niche (PMN)" was introduced by Kaplan et al. The complex interaction between primary tumors and the metastatic organ provides a beneficial microenvironment for tumor cells to colonize at a distance. With further exploration of the PMN, exosomes have gradually attracted interest from researchers. Exosomes are extracellular vesicles secreted from cells that include various biological information and are involved in communication between cells. As a key molecule in the PMN, exosomes are closely related to tumor metastasis. In this article, we obtained information by conducting a comprehensive search across academic databases including PubMed and Web of Science using relevant keywords. Only recent, peer-reviewed articles published in the English language were considered for inclusion. This study aims to explore in depth how exosomes promote the formation of pre-metastatic microenvironment (PMN) in colorectal cancer and its related mechanisms.

Tumour-derived exosomes in liver metastasis: A Pandora's box

The liver is a common secondary metastasis site of many malignant tumours, such as the colorectum, pancreas, stomach, breast, prostate, and lung cancer. The clinical management of liver metastases is challenging because of their strong heterogeneity, rapid progression, and poor prognosis. Now, exosomes, small membrane vesicles that are 40-160 nm in size, are released by tumour cells, namely, tumour-derived exosomes (TDEs), and are being increasingly studied because they can retain the original characteristics of tumour cells. Cell-cell communication via TDEs is pivotal for liver pre-metastatic niche (PMN) formation and liver metastasis; thus, TDEs can provide a theoretical basis to intensively study the potential mechanisms of liver metastasis and new insights into the diagnosis and treatment of liver metastasis. Here, we systematically review current research progress about the roles and possible regulatory mechanisms of TDE cargos in liver metastasis, focusing on the functions of TDEs in liver PMN formation. In addition, we discuss the clinical utility of TDEs in liver metastasis, including TDEs as potential biomarkers, and therapeutic approaches for future research reference in this field.

Liver metastasis from colorectal cancer: pathogenetic development, immune landscape of the tumour microenvironment and therapeutic approaches

Colorectal cancer liver metastasis (CRLM) is one of the leading causes of death among patients with colorectal cancer (CRC). Although immunotherapy has demonstrated encouraging outcomes in CRC, its benefits are minimal in CRLM. The complex immune landscape of the hepatic tumour microenvironment is essential for the development of a premetastatic niche and for the colonisation and metastasis of CRC cells; thus, an in-depth understanding of these mechanisms can provide effective immunotherapeutic targets for CRLM. This review summarises recent studies on the immune landscape of the tumour microenvironment of CRLM and highlights therapeutic prospects for targeting the suppressive immune microenvironment of CRLM.

Non-Coding RNAs Derived from Extracellular Vesicles Promote Pre-Metastatic Niche Formation and Tumor Distant Metastasis

Metastasis is a critical stage of tumor progression, a crucial challenge of clinical therapy, and a major cause of tumor patient death. Numerous studies have confirmed that distant tumor metastasis is dependent on the formation of pre-metastatic niche (PMN). Recent studies have shown that extracellular vesicles (EVs) play an important role in PMN formation. The non-coding RNAs (ncRNAs) derived from EVs mediate PMN formation and tumor-distant metastasis by promoting an inflammatory environment, inhibiting anti-tumor immune response, inducing angiogenesis and permeability, and by microenvironmental reprogramming. Given the stability and high abundance of ncRNAs carried by EVs in body fluids, they have great potential for application in tumor diagnosis as well as targeted interventions. This review focuses on the mechanism of ncRNAs derived from EVs promoting tumor PMN formation and distant metastasis to provide a theoretical reference for strategies to control tumor metastasis.

Hepatic stellate cell-derived exosomes modulate macrophage inflammatory response

BACKGROUND

Hepatic stellate cell (HSC) differentiation/activation is central to liver fibrosis and is innately linked to the immune response to liver injury. Exosomes (EXOs) are important means of communication between cell populations. This study sought to characterize EXO release from HSCs and the effect of HSC-EXOs on macrophage cytokine release/function.

METHODS

Liver from a rat fibrosis model was analyzed for EXO expression and localization. Quiescent and culture-activated rat and mouse HSCs and activated human HSCs were analyzed for microRNA expression. Mouse, rat, and human HSCs were culture-activated and EXOs purified from culture medium prior to addition to macrophages, and interleukin-6 (IL-6) and tumor necrosis factor-α (TNFα) mRNA and protein measured. The effect of activated HSC-EXOs on macrophage migration was assayed.

RESULTS

Activation of rat HSCs led to increased EXO production in vivo, an effect mirrored by in vitro rat HSC culture-activation. Culture activation of mouse and rat HSCs led to altered EXO microRNA profiles, with a similar microRNA profile detected in activated human HSCs. Addition of activated HSC-EXOs to macrophages stimulated IL-6 and TNFα mRNA expression and protein secretion in mouse and human macrophages, but not for rat HSC-EXO-macrophages. Addition of human EXOs to macrophages stimulated migration, effects mirrored by the direct addition of rhIL-6 and rhTNFα.

CONCLUSIONS

HSC-EXOs associate with macrophages and stimulate cytokine synthesis-release and macrophage migration. Constructing a comprehensive understanding of EXO interactions between liver cell populations in the setting of inflammation/fibrosis increases the potential for developing new diagnostic/therapeutic approaches.

Inorganic Nanoparticle-Loaded Exosomes for Biomedical Applications

Exosomes are intrinsic cell-derived membrane vesicles in the size range of 40-100 nm, serving as great biomimetic nanocarriers for biomedical applications. These nanocarriers are known to bypass biological barriers, such as the blood-brain barrier, with great potential in treating brain diseases. Exosomes are also shown to be closely associated with cancer metastasis, making them great candidates for tumor targeting. However, the clinical translation of exosomes are facing certain critical challenges, such as reproducible production and in vivo tracking of their localization, distribution, and ultimate fate. Recently, inorganic nanoparticle-loaded exosomes have been shown great benefits in addressing these issues. In this review article, we will discuss the preparation methods of inorganic nanoparticle-loaded exosomes, and their applications in bioimaging and therapy. In addition, we will briefly discuss their potentials in exosome purification.

An insight into small extracellular vesicles: Their roles in colorectal cancer progression and potential clinical applications

Colorectal cancer (CRC) is one of the most common cancers and a leading cause of mortality worldwide. Small extracellular vesicles (sEVs) are nano-sized extracellular vesicles containing a variety of bioactive molecules, such as nucleic acids, proteins, lipids, and metabolites. Recent evidence from CRC has revealed that sEVs contribute to tumorigenesis, progression, and drug resistance, and serve as a tool for "liquid biopsy" and a drug delivery system for therapy. In this review, we summarize information about the roles of sEVs in the proliferation, invasion, migration, epithelial-mesenchymal transition, formation of the premetastatic niche, and drug resistance to elucidate the mechanisms governing sEVs in CRC and to identify novel targets for therapy and prognostic and diagnostic biomarkers.

Cholangiocyte-Derived Exosomal lncRNA H19 Promotes Macrophage Activation and Hepatic Inflammation under Cholestatic Conditions

Activation of hepatic macrophages represents the critical driving force to promote cholestatic liver injury. Exosomes, as important small extracellular vesicles released by almost all types of cells, contribute to intercellular communication. We previously reported that cholangiocyte-derived exosomal long noncoding RNA (lncRNA) H19 plays a vital role in disrupting bile acid homeostasis in hepatocytes and promoting the activation of hepatic stellate cells (HSCs). Exosomal H19 derived from cholangiocytes was rapidly taken up by Kupffer cells. However, the mechanistic links between exosomal lncRNA H19 and macrophage-driven inflammation in cholestasis remain unclear. Here, we reported that the hepatic H19 level was closely correlated with macrophage activation and hepatic fibrosis in both Mdr2^-/- and bile duct ligation (BDL) cholestatic mouse models, as well as in human primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC) patients. Exosomal H19 significantly induced the expression and secretion of chemokine (C–C motif) ligand 2 (CCL-2) and interleukin 6 (IL-6) in Kupffer cells. H19-enriched exosomes enhanced the activation M1 polarization of Kupffer cells and promoted the recruitment and differentiation of bone marrow-derived macrophages, which were inhibited by a CCL-2 pharmacological inhibitor. In conclusion, Cholangiocyte-derived exosomal H19 played a critical role in macrophage activation, differentiation, and chemotaxis through CCL-2/CCR-2 signaling pathways, which represent a therapeutic target for cholestatic liver diseases.

Endoglin Trafficking/Exosomal Targeting in Liver Cells Depends on N-Glycosylation

Injury of the liver involves a wound healing partial reaction governed by hepatic stellate cells and portal fibroblasts. Individual members of the transforming growth factor-β (TGF-β) superfamily including TGF-β itself and bone morphogenetic proteins (BMP) exert diverse and partially opposing effects on pro-fibrogenic responses. Signaling by these ligands is mediated through binding to membrane integral receptors type I/type II. Binding and the outcome of signaling is critically modulated by Endoglin (Eng), a type III co-receptor. In order to learn more about trafficking of Eng in liver cells, we investigated the membranal subdomain localization of full-length (FL)-Eng. We could show that FL-Eng is enriched in Caveolin-1-containing sucrose gradient fractions. Since lipid rafts contribute to the pool of exosomes, we could consequently demonstrate for the first time that exosomes isolated from cultured primary hepatic stellate cells and its derivatives contain Eng. Moreover, via adenoviral overexpression, we demonstrate that all liver cells have the capacity to direct Eng to exosomes, irrespectively whether they express endogenous Eng or not. Finally, we demonstrate that block of N-glycosylation does not interfere with dimerization of the receptor, but abrogates the secretion of soluble Eng (sol-Eng) and prevents exosomal targeting of FL-Eng.

Ping-Pong-Tumor and Host in Pancreatic Cancer Progression

Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.