EMBO J 30 10, 1990-2007 (2011); published online 5 April 2011Since the beginning of micro-RNA (miR) research, several attempts have been made to identify the 'melano-miRs', which are involved in ...melanoma progression. Indeed, a small number of miRs have been identified to regulate some genes involved in melanogenesis. However, the miRs that control the pathway to the malignant phenotype are yet undescribed. In this issue of the EMBO Journal, Penna et al (2011) demonstrate that miR-214 is overexpressed in metastatic melanoma cell lines and tumour specimens. miR-214 regulates the expression of two transcription factors AP-2γ (directly) and AP-2α (indirectly). These transcription factors, particularly AP-2α, have been previously shown to play major roles in melanoma metastasis via regulation of genes involved in extravasation, invasion and angiogenesis. As such, this study has identified miR-214 as a driver of melanoma metastasis.
VEGF-targeted therapies have modest efficacy in cancer patients, but acquired resistance is common. The mechanisms underlying such resistance are poorly understood.
To evaluate the potential role of ...immune cells in the development of resistance to VEGF blockade, we first established a preclinical model of adaptive resistance to anti-VEGF therapy. Additional
and
studies were carried out to characterize the role of macrophages in such resistance.
Using murine cancer models of adaptive resistance to anti-VEGF antibody (AVA), we found a previously unrecognized role of macrophages in such resistance. Macrophages were actively recruited to the tumor microenvironment and were responsible for the emergence of AVA resistance. Depletion of macrophages following emergence of resistance halted tumor growth and prolonged survival of tumor-bearing mice. In a macrophage-deficient mouse model, resistance to AVA failed to develop, but could be induced by injection of macrophages. Downregulation of macrophage VEGFR-1 and VEGFR-3 expression accompanied upregulation of alternative angiogenic pathways, facilitating escape from anti-VEGF therapy.
These findings provide a new understanding of the mechanisms underlying the modest efficacy of current antiangiogenesis therapies and identify new opportunities for combination approaches for ovarian and other cancers.
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Why is melanoma so metastatic? Braeuer, Russell R.; Watson, Ian R.; Wu, Chang-Jiun ...
Pigment cell and melanoma research,
January 2014, Letnik:
27, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Summary
Malignant melanoma is one of the most aggressive cancers and can disseminate from a relatively small primary tumor and metastasize to multiple sites, including the lung, liver, brain, bone, ...and lymph nodes. Elucidating the molecular and genetic changes that take place during the metastatic process has led to a better understanding of why melanoma is so metastatic. Herein, we describe the unique features that distinguish melanoma from other solid tumors and contribute to the malignant phenotype of melanoma cells. For example, although melanoma cells are highly antigenic, they are extremely efficient at evading host immune response. Melanoma cells share numerous cell surface molecules with vascular cells, are highly angiogenic, are mesenchymal in nature, and possess a higher degree of ‘stemness’ than do other solid tumors. Finally, analysis of melanoma mutations has revealed that the gene expression profile of malignant melanoma is different from that of other cancers. Elucidating these molecular and genetic processes in highly metastatic melanoma can lead to the development of improved treatment and individualized therapy options.
Cancer-related deregulation of miRNA biogenesis has been suggested, but the underlying mechanisms remain elusive. Here we report a previously unrecognized effect of hypoxia in the downregulation of ...Drosha and Dicer in cancer cells that leads to dysregulation of miRNA biogenesis and increased tumour progression. We show that hypoxia-mediated downregulation of Drosha is dependent on ETS1/ELK1 transcription factors. Moreover, mature miRNA array and deep sequencing studies reveal altered miRNA maturation in cells under hypoxic conditions. At a functional level, this phenomenon results in increased cancer progression in vitro and in vivo, and data from patient samples are suggestive of miRNA biogenesis downregulation in hypoxic tumours. Rescue of Drosha by siRNAs targeting ETS1/ELK1 in vivo results in significant tumour regression. These findings provide a new link in the mechanistic understanding of global miRNA downregulation in the tumour microenvironment.
Brain metastases occur frequently in melanoma patients with advanced disease whereby the prognosis is dismal. The underlying mechanisms of melanoma brain metastasis development are not well ...understood. Identification of molecular determinants regulating melanoma brain metastasis would advance the development of prevention and therapy strategies for this disease. Gene expression profiles of cutaneous and brain‐metastasizing melanoma variants from three xenograft tumor models established in our laboratory revealed that expression of tight junction component CLDN1 was lower in the brain‐metastasizing variants than in cutaneous variants from the same melanoma. The objective of our study was to determine the significance of CLDN1 downregulation/loss in metastatic melanoma and its role in melanoma brain metastasis. An immunohistochemical analysis of human cells of the melanocyte lineage indicated a significant CLDN1 downregulation in metastatic melanomas. Transduction of melanoma brain metastatic cells expressing low levels of CLDN1 with a CLDN1 retrovirus suppressed their metastatic phenotype. CLDN1‐overexpressing melanoma cells expressed a lower ability to migrate and adhere to extracellular matrix, reduced tumor aggressiveness in nude mice and, most importantly, eliminated the formation of micrometastases in the brain. In sharp contrast, the ability of the CLDN1‐overexpressing cells to form lung micrometastases was not impaired. CLDN1‐mediated interactions between these cells and brain endothelial cells constitute the mechanism underlying these results. Taken together, we demonstrated that downregulation or loss of CLDN1 supports the formation of melanoma brain metastasis, and that CLDN1 expression could be a useful prognostic predictor for melanoma patients with a high risk of brain metastasis.
What's new?
Melanoma often metastasizes to the brain, but if researchers could find out how it does so, perhaps they could prevent it. Cells poised to metastasize often reveal themselves by molecular clues, and indeed, melanoma cells likely to infiltrate the brain express less of the tight‐junction protein CLDN1 than other melanoma cells. In this study, the authors showed that when melanoma cells express extra CLDN1, they could not form micro‐metastases in the brain – though their ability to metastasize to the lungs was not impaired. Thus, CLDN1 expression could help predict the likelihood of brain metastasis, and targeting cells expressing low levels of the protein could help prevent or treat this deadly complication.
Summary
Metastatic melanoma is extremely refractory to existing chemotherapeutic drugs and bioimmune adjuvant therapies, and the life span of patients with metastatic melanoma is often measured in ...months. Understanding the mechanisms responsible for the development of tumor metastasis is critical for finding successful curative measures. An expending amount of data reveal the importance of inflammatory microenvironment and stroma in cancer initiation and progression, which brings new directions and approaches to cancer treatment. This review will summarize current data on the role of the tumor microenvironment in shaping the metastatic phenotype of melanoma.
Background Interleukin-8 (IL-8) is a proangiogenic cytokine that is overexpressed in many human cancers. We investigated the clinical and biologic significance of IL-8 in ovarian carcinoma using ...human samples and orthotopic mouse models. Methods Tumor expression of IL-8 was assessed by immunohistochemistry among ovarian cancer patients (n = 102) with available clinical and survival data. We examined the effect of IL-8 gene silencing with small interfering RNAs incorporated into neutral liposomes (siRNA-DOPCs), alone and in combination with docetaxel, on in vivo tumor growth, angiogenesis (microvessel density), and tumor cell proliferation in mice (n = 10 per treatment group) bearing orthotopic taxane-sensitive (HeyA8 and SKOV3ip1) and taxane-resistant (SKOV3ip2.TR) ovarian tumors. All statistical tests were two-sided. Results Of the 102 cancer specimens, 43 (42%) had high IL-8 expression and 59 (58%) had low or no IL-8 expression; high IL-8 expression was associated with advanced tumor stage (P = .019), high tumor grade (P = .031), and worse survival (median survival for patients with high vs low IL-8 expression: 1.62 vs 3.79 years; P < .001). Compared with empty liposomes, IL-8 siRNA-DOPC reduced the mean tumor weight by 32% (95% confidence interval CI = 14% to 50%; P = .03) and 52% (95% CI = 27% to 78%; P = .03) in the HeyA8 and SKOV3ip1 mouse models, respectively. In all three mouse models, treatment with IL-8 siRNA-DOPC plus the taxane docetaxel reduced tumor growth the most compared with empty liposomes (77% to 98% reduction in tumor growth; P < .01 for all). In the HeyA8 and SKOV3ip1 models, tumors from mice treated with IL-8 siRNA-DOPC alone had lower microvessel density than tumors from mice treated with empty liposomes (HeyA8: 34% lower, 95% CI = 32% to 36% lower P = .002; SKOV3ip1: 39% lower, 95% CI = 34% to 44% lower P = .007). Compared with empty liposomes, IL-8 siRNA-DOPC plus docetaxel reduced tumor cell proliferation by 35% (95% CI = 25% to 44%; P < .001) and 38% (95% CI = 28% to 48%; P < .001) in the HeyA8 and SKOV3ip1 models, respectively. Conclusions Increased IL-8 expression is associated with poor clinical outcome in human ovarian carcinoma, and IL-8 gene silencing decreases tumor growth through antiangiogenic mechanisms.
Summary
Melanoma is the leading cause of skin cancer‐related deaths, which is due in large part to its aggressive behavior, resistance to therapy, and ability to metastasize to multiple organs such ...as the lymph nodes, lung, and brain. Melanoma progresses in a stepwise manner from the benign nevus, to radial spreading through the dermis, to a vertical invasive phase, and finally to metastasis. The carbohydrate‐binding family of galectins has a strong influence on each phase of melanoma progression through their effects on immune surveillance, angiogenesis, cell migration, tumor cell adhesion, and the cellular response to chemotherapy. Galectins share significant homology in their carbohydrate recognition domain (CRD), which mediates binding to an array of N‐glycosylated proteins located on the surface of tumor cells, endothelial cells, T‐cells, and to similarly glycosylated extracellular matrix proteins. Galectins are also present within tumor cells where they perform anti‐apoptotic functions and enhance intracellular signaling that results in deregulated expression of genes involved in tumor progression. The most extensively studied galectins, galectin‐1 and galectin‐3, have been shown to have profound effects on melanoma growth and metastasis by influencing many of these biological processes.
The epithelial-to-mesenchymal transition (EMT) is a cell development-regulated process in which noncoding RNAs act as crucial modulators. Recent studies have implied that EMT may contribute to ...resistance to epidermal growth factor receptor (EGFR)-directed therapy. The aims of this study were to determine the potential role of microRNAs (miRNA) in controlling EMT and the role of EMT in inducing the sensitivity of human bladder cancer cells to the inhibitory effects of the anti-EGFR therapy.
miRNA array screening and real-time reverse transcription-PCR were used to identify and validate the differential expression of miRNAs involved in EMT in nine bladder cancer cell lines. A list of potential miR-200 direct targets was identified through the TargetScan database. The precursor of miR-200b and miR-200c was expressed in UMUC3 and T24 cells using a retrovirus or a lentivirus construct, respectively. Protein expression and signaling pathway modulation, as well as intracellular distribution of EGFR and ERRFI-1, were validated through Western blot analysis and confocal microscopy, whereas ERRFI-1 direct target of miR-200 members was validated by using the wild-type and mutant 3'-untranslated region/ERRFI-1/luciferse reporters.
We identified a tight association between the expression of miRNAs of the miR-200 family, epithelial phenotype, and sensitivity to EGFR inhibitors-induced growth inhibition in bladder carcinoma cell lines. Stable expression of miR-200 in mesenchymal UMUC3 cells increased E-cadherin levels, decreased expression of ZEB1, ZEB2, ERRFI-1, and cell migration, and increased sensitivity to EGFR-blocking agents. The changes in EGFR sensitivity by silencing or forced expression of ERRFI-1 or by miR-200 expression have also been validated in additional cell lines, UMUC5 and T24. Finally, luciferase assays using 3'-untranslated region/ERRFI-1/luciferase and miR-200 cotransfections showed that the direct down-regulation of ERRFI-1 was miR-200-dependent because mutations in the two putative miR-200-binding sites have rescued the inhibitory effect.
Members of the miR-200 family appear to control the EMT process and sensitivity to EGFR therapy in bladder cancer cells and the expression of miR-200 is sufficient to restore EGFR dependency at least in some of the mesenchymal bladder cancer cells. The targets of miR-200 include ERRFI-1, which is a novel regulator of EGFR-independent growth.
We performed parallel investigations in cabozantinib-treated patients in a phase II trial and simultaneously in patient-derived xenograft (PDX) models to better understand the roles of MET and VEGFR2 ...as targets for prostate cancer therapy.
In the clinical trial, radiographic imaging and serum markers were examined, as well as molecular markers in tumors from bone biopsies. In mice harboring PDX intrafemurally or subcutaneously, cabozantinib effects on tumor growth, MET, PDX in which MET was silenced, VEGFR2, bone turnover, angiogenesis, and resistance were examined.
In responsive patients and PDX, islets of viable pMET-positive tumor cells persisted, which rapidly regrew after drug withdrawal. Knockdown of MET in PDX did not affect tumor growth in mice nor did it affect cabozantinib-induced growth inhibition but did lead to induction of FGFR1. Inhibition of VEGFR2 and MET in endothelial cells reduced the vasculature, leading to necrosis. However, each islet of viable cells surrounded a VEGFR2-negative vessel. Reduction of bone turnover was observed in both cohorts.
Our studies demonstrate that MET in tumor cells is not a persistent therapeutic target for metastatic castrate-resistant prostate cancer (CRPC), but inhibition of VEGFR2 and MET in endothelial cells and direct effects on osteoblasts are responsible for cabozantinib-induced tumor inhibition. However, vascular heterogeneity represents one source of primary therapy resistance, whereas induction of FGFR1 in tumor cells suggests a potential mechanism of acquired resistance. Thus, integrated cross-species investigations demonstrate the power of combining preclinical models with clinical trials to understand mechanisms of activity and resistance of investigational agents.
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