A Bifunctional Approach of Immunostimulation and uPAR Inhibition Shows Potent Antitumor Activity in Melanoma

Retinoic acid-inducible gene-I like receptor pathway in cancer: modification and treatment

Retinoic acid-inducible gene-I (RIG-I) like receptor (RLR) pathway is one of the most significant pathways supervising aberrant RNA in cells. In predominant conditions, the RLR pathway initiates anti-infection function via activating inflammatory effects, while recently it is discovered to be involved in cancer development as well, acting as a virus-mimicry responder. On one hand, the product IFNs induces tumor elimination. On the other hand, the NF-κB pathway is activated which may lead to tumor progression. Emerging evidence demonstrates that a wide range of modifications are involved in regulating RLR pathways in cancer, which either boost tumor suppression effect or prompt tumor development. This review summarized current epigenetic modulations including DNA methylation, histone modification, and ncRNA interference, as well as post-transcriptional modification like m6A and A-to-I editing of the upstream ligand dsRNA in cancer cells. The post-translational modulations like phosphorylation and ubiquitylation of the pathway's key components were also discussed. Ultimately, we provided an overview of the current therapeutic strategies targeting the RLR pathway in cancers.

Urokinase-type plasminogen activator receptor (uPAR) as a therapeutic target in cancer

Urokinase-type plasminogen activator receptor (uPAR) is an attractive target for the treatment of cancer, because it is expressed at low levels in healthy tissues but at high levels in malignant tumours. uPAR is closely related to the invasion and metastasis of malignant tumours, plays important roles in the degradation of extracellular matrix (ECM), tumour angiogenesis, cell proliferation and apoptosis, and is associated with the multidrug resistance (MDR) of tumour cells, which has important guiding significance for the judgement of tumor malignancy and prognosis. Several uPAR-targeted antitumour therapeutic agents have been developed to suppress tumour growth, metastatic processes and drug resistance. Here, we review the recent advances in the development of uPAR-targeted antitumor therapeutic strategies, including nanoplatforms carrying therapeutic agents, photodynamic therapy (PDT)/photothermal therapy (PTT) platforms, oncolytic virotherapy, gene therapy technologies, monoclonal antibody therapy and tumour immunotherapy, to promote the translation of these therapeutic agents to clinical applications.

Bcl-2-like protein-10 increases aggressive features of melanoma cells

Aim:

B-cell lymphoma-2 (Bcl-2)-like protein-10 (Bcl2L10) is the less studied member of Bcl-2 family proteins, with the controversial role in different cancer histotypes. Very recently, Bcl2L10 expression in melanoma tumor specimens and its role in melanoma response to therapy have been demonstrated. Here, the involvement of Bcl2L10 on the in vitro and in vivo properties associated with melanoma aggressive features has been investigated.

Methods:

Endogenous Bcl2L10 protein expression was detected by western blotting analysis in a panel of patient-derived and commercially available human melanoma cells. In vitro assays to evaluate clonogenicity, cell proliferation, cell migration, cell invasion, and in vitro capillary-like structure formation [vasculogenic mimicry (VM)] have been performed by using human melanoma cells stably overexpressing Bcl2L10 or transiently transfected for loss/gain function of Bcl2L10, grown under two- or three-dimensional (3D) conditions Xenograft melanoma model was employed to evaluate in vivo tumor growth and angiogenesis.

Results:

Results demonstrated that Bcl2L10 acts as an inducer of in vitro cell migration, invasion, and VM, while in vitro cell proliferation, in vivo tumor growth, as well as colony formation properties were not affected. Dissecting different signaling pathways, it was found that Bcl2L10 positively affects the phosphorylation of extracellular-signal-regulated kinase (ERK) and the expression of markers of cell invasion, such as urokinase plasminogen activator receptor (uPAR) and matrix metalloproteinases (MMPs). Of note, Bcl2L10-dependent in vitro migration, invasion, and VM are linked to uPAR. Bcl2L10 also negatively regulates the intracellular calcium level. Finally, reduced invasion capability in 3D spheroid invasion assay of melanoma cells transiently overexpressing Bcl2L10 was observed after treatment with inhibitors of MMPs and uPAR.

Conclusions:

Overall, data reported in this paper provide evidence supporting a positive role of Bcl2L10 in melanoma aggressive features.

HDAC2 Is Involved in the Regulation of BRN3A in Melanocytes and Melanoma

The neural crest transcription factor BRN3A is essential for the proliferation and survival of melanoma cells. It is frequently expressed in melanoma but not in normal melanocytes or benign nevi. The mechanisms underlying the aberrant expression of BRN3A are unknown. Here, we investigated the epigenetic regulation of BRN3A in melanocytes and melanoma cell lines treated with DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC) inhibitors. DNMT and HAT inhibition did not significantly alter BRN3A expression levels, whereas panHDAC inhibition by trichostatin A led to increased expression. Treatment with the isoform-specific HDAC inhibitor mocetinostat, but not with PCI-34051, also increased BRN3A expression levels, suggesting that class I HDACs HDAC1, HDAC2, and HDAC3, and class IV HDAC11, were involved in the regulation of BRN3A expression. Transient silencing of HDACs 1, 2, 3, and 11 by siRNAs revealed that, specifically, HDAC2 inhibition was able to increase BRN3A expression. ChIP-Seq analysis uncovered that HDAC2 inhibition specifically increased H3K27ac levels at a distal enhancer region of the BRN3A gene. Altogether, our data suggest that HDAC2 is a key epigenetic regulator of BRN3A in melanocytes and melanoma cells. These results highlight the importance of epigenetic mechanisms in regulating melanoma oncogenes.

MAGP2 induces tumor progression by enhancing uPAR-mediated cell proliferation

Microfibril-associated glycoprotein 2 (MAGP2) plays an important role in regulating cell signaling and acts as a biomarker to predict the prognostic effect of tumor therapy. However, research on MAGP2 mostly focuses on its extracellular signal transmission features, and its potential intracellular function is rarely reported. Here, we reported that intracellular MAGP2 increased the stability of urokinase-type plasminogen activator receptor (uPAR) in the cell by direct interaction which inhibits the lysosomal-mediated degradation of uPAR. Furthermore, with the detection of protein content changes and proteomics analysis, we found that highly expressed MAGP2 promoted the proliferation of tumor cells through uPAR-mediated p38-NF-ĸB signaling axis activation, enhancement of DNA damage repair and reduction of cell stagnation in the S phase of the cell cycle. In the nude mouse xenograft model of colorectal cancer, the upregulation of MAGP2 in tumor cells significantly promoted tumor progression, while the downregulation of uPAR significantly attenuated tumor progression. These studies elucidate the role of MAGP2 inside the cell and provide a new explanation for why patients with higher MAGP2 expression in tumors are associated with a worse prognosis. In addition, we also determined a mechanism for the stable existence of uPAR in the cell, providing information for the development of tumor drugs targeting uPAR.

Mechanisms of Acquired BRAF Inhibitor Resistance in Melanoma: A Systematic Review

This systematic review investigated the literature on acquired v-raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor resistance in patients with melanoma. We searched MEDLINE for articles on BRAF inhibitor resistance in patients with melanoma published since January 2010 in the following areas: (1) genetic basis of resistance; (2) epigenetic and transcriptomic mechanisms; (3) influence of the immune system on resistance development; and (4) combination therapy to overcome resistance. Common resistance mutations in melanoma are BRAF splice variants, BRAF amplification, neuroblastoma RAS viral oncogene homolog (NRAS) mutations and mitogen-activated protein kinase kinase 1/2 (MEK1/2) mutations. Genetic and epigenetic changes reactivate previously blocked mitogen-activated protein kinase (MAPK) pathways, activate alternative signaling pathways, and cause epithelial-to-mesenchymal transition. Once BRAF inhibitor resistance develops, the tumor microenvironment reverts to a low immunogenic state secondary to the induction of programmed cell death ligand-1. Combining a BRAF inhibitor with a MEK inhibitor delays resistance development and increases duration of response. Multiple other combinations based on known mechanisms of resistance are being investigated. BRAF inhibitor-resistant cells develop a range of 'escape routes', so multiple different treatment targets will probably be required to overcome resistance. In the future, it may be possible to personalize combination therapy towards the specific resistance pathway in individual patients.

Prognostic value of uPAR expression and angiogenesis in primary and metastatic melanoma

Angiogenesis is important for the progression of cutaneous melanoma. Here, we analyzed the prognostic impact of the angiogenic factor urokinase plasminogen activator resecptor (uPAR), vascular proliferation index (VPI) and tumor necrosis as a measure of hypoxia in a patient series of nodular melanomas (n = 255) and matched loco-regional metastases (n = 78). Expression of uPAR was determined by immunohistochemistry and VPI was assessed by dual immunohistochemistry using Factor-VIII/Ki67 staining. Necrosis was recorded based on HE-slides. As novel findings, high uPAR expression and high VPI were associated with each other, and with increased tumor thickness, presence of tumor necrosis, tumor ulceration, increased mitotic count and reduced cancer specific survival in primary melanoma. In matched cases, VPI was decreased in metastases, whereas the frequency of necrosis was increased. Our findings demonstrate for the first time the impact on melanoma specific survival of uPAR expression and VPI in primary tumors, and of increased necrosis as an indicator of tumor hypoxia in loco-regional metastases. These findings support the importance of tumor angiogenesis in melanoma aggressiveness, and suggest uPAR as an indicator of vascular proliferation and a potential biomarker in melanoma.

Targeting the cross-talk between Urokinase receptor and Formyl peptide receptor type 1 to prevent invasion and trans-endothelial migration of melanoma cells

BACKGROUND

Accumulating evidence demonstrates that the Urokinase Receptor (uPAR) regulates tumor cell migration through its assembly in composite regulatory units with transmembrane receptors, and uPAR_88-92 is the minimal sequence required to induce cell motility through the Formyl Peptide Receptor type 1 (FPR1). Both uPAR and FPR1 are involved in melanoma tumor progression, suggesting that they may be targeted for therapeutic purposes. In this study, the role of the uPAR-FPR1 cross-talk to sustain melanoma cell ability to invade extracellular matrix and cross endothelial barriers is investigated. Also, the possibility that inhibition of the uPAR mediated FPR1-dependent signaling may prevent matrix invasion and transendothelial migration of melanoma cells was investigated.

METHODS

Expression levels of uPAR and FPR1 were assessed by immunocytochemistry, Western Blot and qRT-PCR. Cell migration was investigated by Boyden chamber and wound-healing assays. Migration and invasion kinetics, trans-endothelial migration and proliferation of melanoma cells were monitored in real time using the xCELLigence technology. The agonist-triggered FPR1 internalization was visualized by confocal microscope. Cell adhesion to endothelium was determined by fluorometer measurement of cell-associated fluorescence or identified on multiple z-series by laser confocal microscopy. The 3D-organotypic models were set up by seeding melanoma cells onto collagen I matrices embedded dermal fibroblasts. Data were analyzed by one-way ANOVA and post-hoc Dunnett t-test for multiple comparisons.

RESULTS

We found that the co-expression of uPAR and FPR1 confers to A375 and M14 melanoma cells a clear-cut capability to move towards chemotactic gradients, to cross extracellular matrix and endothelial monolayers. FPR1 activity is required, as cell migration and invasion were abrogated by receptor desensitization. Finally, melanoma cell ability to move toward chemotactic gradients, invade matrigel or fibroblast-embedded collagen matrices and cross endothelial monolayers are prevented by anti-uPAR_84-95 antibodies or by the RI-3 peptide which we have previously shown to inhibit the uPAR_84-95/FPR1 interaction.

CONCLUSIONS

Collectively, our findings identify uPAR and FPR1 as relevant effectors of melanoma cell invasiveness and suggest that inhibitors of the uPAR_84-95/FPR1 cross-talk may be useful for the treatment of metastatic melanoma.