Clinical, pathologic, and imaging features and biological markers of uveal melanoma

Uveal melanoma pathobiology: Metastasis to the liver

Uveal melanoma (UM) is a type of intraocular tumor with a propensity to disseminate to the liver. Despite the identification of the early driver mutations during the development of the pathology, the process of UM metastasis is still not fully comprehended. A better understanding of the genetic, molecular, and environmental factors participating to its spread and metastatic outgrowth could provide additional approaches for UM treatment. In this review, we will discuss the advances made towards the understanding of the pathogenesis of metastatic UM, summarize the current and prospective treatments, and introduce some of the ongoing research in this field.

Increased Levels of miRNA-146a in Serum and Histologic Samples of Patients with Uveal Melanoma

Purpose: To analyze MiRs expression in serum of UM patients, respect to healthy donors, and to compare this data with MiRs expressed in formalin-fixed, paraffin-embedded UM samples. Methods: Expression profile of 754 miRNAs was performed in serum of patients with uveal melanoma who underwent primary enucleation. The level of miRNAs increased in serum was individually analyzed on FFPE UM samples and compared to choroidal melanocytes from unaffected eyes. Results: Fourteen patients with uveal melanoma were included in the study. We found 8 serum miRNAs differentially expressed compared to normal controls: 2 upregulated miRNAs (miRNA-146a, miR-523); 6 downregulated miRNAs (miR-19a, miR-30d, miR-127, miR-451, miR-518f, miR-1274B). When data on upregulated miRNAs were singularly validated only a significant overexpression of miRNA-146a was found. A statistically significant upregulation of miRNA-146a was also found on FFPE UM samples, compared to choroidal melanocytes from unaffected eyes. Conclusions: miRNA-146a is increased in serum of patients with UM and in FFPE tumor samples. Further studies will show if it could be considered a potential marker of UM in the blood.

Oncogenic role of microRNA‑20a in human uveal melanoma

As a member of the microRNA (miR)-17-92 cluster, miR‑20a has been indicated to be involved in the regulation of the proliferation and invasion of various cancer cells. Previous studies have observed elevated plasma levels of miR‑20a in patients with uveal melanoma (UM), compared with normal controls. In the present study, the potential function of miR‑20a in UM was investigated. Reverse transcription‑quantitative polymerase chain reaction analysis was performed to detect the expression levels of miR‑20a in UM cells and tissues. The functions of miR‑20a on cell proliferation, migration and invasion were determined in vitro using 3‑(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide and Transwell assays, respectively. The expression levels of miR‑20a were significantly increased in the UM cells and tissues (P<0.05). Subsequently, miR‑20a mimics were transfected into UM cells, which led to increases in cell growth, migration and invasion activities. By contrast, miR‑20a inhibition markedly suppressed the viability and motility of UM cells in vitro. These data provided convincing evidence that miR‑20a may function as an oncogenic miRNA, and may be involved in promoting cell growth and motility in the molecular etiology of UM, suggesting its potential as a candidate therapeutic target for the treatment of patients with UM.

Hypoxia-inducible factor 1 upregulation of both VEGF and ANGPTL4 is required to promote the angiogenic phenotype in uveal melanoma

PURPOSE

Expression of the hypoxia-inducible factor (HIF)-1-regulated gene product, vascular endothelial growth factor (VEGF), correlates with tumor vascularity in patients with uveal melanoma (UM). While the relationship between HIF-1 and VEGF in cancer is well-studied, their relative contribution to the angiogenic phenotype in UM has not previously been interrogated. Here we evaluate the contribution of HIF-1, VEGF, and a second HIF-1-regulated gene product, angiopoietin-like 4 (ANGPTL4), to angiogenesis in UM.

EXPERIMENTAL DESIGN

UM cells were examined for expression of HIF-1α, VEGF, and ANGPTL4. Their contribution to the angiogenic potential of UM cells was assessed using the endothelial cell tubule formation and directed in vivo angiogenesis assays. These results were corroborated in tissue from UM animal models and in tissue from patients with UM.

RESULTS

Inhibition of VEGF partially reduced tubule formation promoted by conditioned medium from UM cells. Inhibition of ANGPTL4, which was highly expressed in hypoxic UM cells, a UM orthotopic transplant model, a UM tumor array, and vitreous samples from UM patients, inhibited the angiogenic potential of UM cells in vitro and in vivo; this effect was additive to VEGF inhibition.

CONCLUSIONS

Targeting both ANGPTL4 and VEGF may be required for the effective inhibition of angiogenesis in UM.

MiR-144 Inhibits Uveal Melanoma Cell Proliferation and Invasion by Regulating c-Met Expression

MicroRNAs (miRNAs) are a group endogenous small non-coding RNAs that inhibit protein translation through binding to specific target mRNAs. Recent studies have demonstrated that miRNAs are implicated in the development of cancer. However, the role of miR-144 in uveal melanoma metastasis remains largely unknown. MiR-144 was downregulated in both uveal melanoma cells and tissues. Transfection of miR-144 mimic into uveal melanoma cells led to a decrease in cell growth and invasion. After identification of two putative miR-144 binding sites within the 3' UTR of the human c-Met mRNA, miR-144 was proved to inhibit the luciferase activity inMUM-2B cells with a luciferase reporter construct containing the binding sites. In addition, the expression of c-Met protein was inhibited by miR-144. Furthermore, c-Met-mediated cell proliferation and invasion were inhibited by restoration of miR-144 in uveal melanoma cells. In conclusion, miR-144 acts as a tumor suppressor in uveal melanoma, through inhibiting cell proliferation and migration. miR-144 might serve as a potential therapeutic target in uveal melanoma patients.

miRNA profiling in vitreous humor, vitreal exosomes and serum from uveal melanoma patients: Pathological and diagnostic implications

Uveal melanoma (UM) represents approximately 5-6% of all melanoma diagnoses and up to 50% of patients succumb to their disease. Although several methods are available, accurate diagnosis is not always easily feasible because of potential accidents (e.g., intraocular hemorrhage). Based on the assumption that the profile of circulating miRNAs is often altered in human cancers, we verified whether UM patients showed different vitreous humor (VH) or serum miRNA profiles with respect to healthy controls. By using TaqMan Low Density Arrays, we analyzed 754 miRNAs from VH, vitreal exosomes, and serum of 6 UM patients and 6 healthy donors: our data demonstrated that the UM VH profile was unique and only partially overlapping with that from serum of the same patients. Whereas, 90% of miRNAs were shared between VH and vitreal exosomes, and their alterations in UM were statistically overlapped with those of VH and vitreal exosomes, suggesting that VH alterations could result from exosomal dysregulation. We report 32 miRNAs differentially expressed in UM patients in at least 2 different types of samples analyzed. We validated these data on an independent cohort of 12 UM patients. Most alterations were common to VH and vitreal exosomes (e.g., upregulation of miR-21,-34 a,-146a). Interestingly, miR-146a was upregulated in the serum of UM patients, as well as in serum exosomes. Upregulation of miR-21 and miR-146a was also detected in formalin-fixed, paraffin-embedded UM, suggesting that VH or serum alterations in UM could be the consequence of disregulation arising from tumoral cells. Our findings suggest the possibility to detect in VH and serum of UM patients "diagnostic" miRNAs released by the affected eye: based on this, miR-146a could be considered a potential circulating marker of UM.

MicroRNA dysregulation in uveal melanoma: a new player enters the game

Uveal melanoma is the second most common form of melanoma and a predominant intraocular malignant tumor in adults. The development of uveal melanoma is a multistep process involving genetic and epigenetic alteration of proto-oncogenes and tumor-suppressor genes. Recent discoveries have shed a new light on the involvement of a class of noncoding RNA known as microRNAs (miRNAs) in uveal melanoma. A lot of miRNAs show differential expressions in uveal melanoma tissues and cell lines. Genes coding for these miRNAs have been characterized as novel oncogene and tumor-suppressor genes based on findings that these miRNAs control malignant phenotypes of uveal melanoma cells. Several studies have confirmed that dysregulation of miRNAs promotes cell-cycle progression, confers resistance to apoptosis, and enhances invasiveness and metastasis. Moreover, several miRNAs have also been shown to correlate with uveal melanoma initiation and progression, and thus may be used as biomarkers for early diagnosis and prognosis. Elucidating the biological aspects of miRNA dysregulation may help us better understand the pathogenesis of uveal melanoma and promote the development of miRNA directed-therapeutics against this disease.