Role of Apollon in human melanoma resistance to antitumor agents that activate the intrinsic or the extrinsic apoptosis pathways

Overexpression of BIRC6 driven by EGF-JNK-HECTD1 signaling is a potential therapeutic target for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive and highly lethal disease. The lack of targeted therapies and poor patient outcome have fostered efforts to discover new molecular targets to treat patients with TNBC. Here, we showed that baculoviral IAP repeat containing 6 (BIRC6) is overexpressed and positively correlated with epidermal growth factor (EGF) receptor (EGFR) in TNBC cells and tissues and that BIRC6 overexpression is associated with poor patient survival. Mechanistic studies revealed that BIRC6 stability is increased by EGF-JNK signaling, which prevents ubiquitination and degradation of BIRC6 mediated by the E3 ubiquitin ligase HECTD1. BIRC6 in turn decreases SMAC expression by inducing the ubiquitin-proteasome pathway, thereby antagonizing apoptosis and promoting the proliferation, colony formation, tumorsphere formation, and tumor growth capacity of TNBC cells. Therapeutically, the PEGylated cationic lipid nanoparticle (pCLN)-assisted delivery of BIRC6 small interfering RNA (siRNA) efficiently silences BIRC6 expression in TNBC cells, thus suppressing TNBC cell growth in vitro and in vivo, and its antitumor activity is significantly superior to that of the EGFR inhibitor gefitinib. Our findings identify an important regulatory mechanism of BIRC6 overexpression and provide a potential therapeutic option for treating TNBC.

The BIRC Family Genes Expression in Patients with Triple Negative Breast Cancer

The BIRC (baculoviral IAP repeat-containing; BIRC) family genes encode for Inhibitor of Apoptosis (IAP) proteins. The dysregulation of the expression levels of the genes in question in cancer tissue as compared to normal tissue suggests that the apoptosis process in cancer cells was disturbed, which may be associated with the development and chemoresistance of triple negative breast cancer (TNBC). In our study, we determined the expression level of eight genes from the BIRC family using the Real-Time PCR method in patients with TNBC and compared the obtained results with clinical data. Additionally, using bioinformatics tools (Ualcan and The Breast Cancer Gene-Expression Miner v4.5 (bc-GenExMiner v4.5)), we compared our data with the data in the Cancer Genome Atlas (TCGA) database. We observed diverse expression pattern among the studied genes in breast cancer tissue. Comparing the expression level of the studied genes with the clinical data, we found that in patients diagnosed with breast cancer under the age of 50, the expression levels of all studied genes were higher compared to patients diagnosed after the age of 50. We observed that in patients with invasion of neoplastic cells into lymphatic vessels and fat tissue, the expression levels of BIRC family genes were lower compared to patients in whom these features were not noted. Statistically significant differences in gene expression were also noted in patients classified into three groups depending on the basis of the Scarff-Bloom and Richardson (SBR) Grading System.

The Golgi Apparatus May Be a Potential Therapeutic Target for Apoptosis-Related Neurological Diseases

Increasing evidence shows that, in addition to the classical function of protein processing and transport, the Golgi apparatus (GA) is also involved in apoptosis, one of the most common forms of cell death. The structure and the function of the GA is damaged during apoptosis. However, the specific effect of the GA on the apoptosis process is unclear; it may be involved in initiating or promoting apoptosis, or it may inhibit apoptosis. Golgi-related apoptosis is associated with a variety of neurological diseases including glioma, Alzheimer’s disease (AD), Parkinson’s disease (PD), and ischemic stroke. This review summarizes the changes and the possible mechanisms of Golgi structure and function during apoptosis. In addition, we also explore the possible mechanisms by which the GA regulates apoptosis and summarize the potential relationship between the Golgi and certain neurological diseases from the perspective of apoptosis. Elucidation of the interaction between the GA and apoptosis broadens our understanding of the pathological mechanisms of neurological diseases and provides new research directions for the treatment of these diseases. Therefore, we propose that the GA may be a potential therapeutic target for apoptosis-related neurological diseases.

PIM kinases mediate resistance of glioblastoma cells to TRAIL by a p62/SQSTM1-dependent mechanism

Glioblastoma (GBM) is the most common and aggressive brain tumor and is associated with poor prognosis. GBM cells are frequently resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and finding new combinatorial therapies to sensitize glioma cells to TRAIL remains an important challenge. PIM kinases are serine/threonine kinases that promote cell survival and proliferation and are highly expressed in different tumors. In this work, we studied the role of PIM kinases as regulators of TRAIL sensitivity in GBM cells. Remarkably, PIM inhibition or knockdown facilitated activation by TRAIL of a TRAIL-R2/DR5-mediated and mitochondria-operated apoptotic pathway in TRAIL-resistant GBM cells. The sensitizing effect of PIM knockdown on TRAIL-induced apoptosis was mediated by enhanced caspase-8 recruitment to and activation at the death-inducing signaling complex (DISC). Interestingly, TRAIL-induced internalization of TRAIL-R2/DR5 was significantly reduced in PIM knockdown cells. Phospho-proteome profiling revealed a decreased phosphorylation of p62/SQSTM1 after PIM knockdown. Our results also showed an interaction between p62/SQSTM1 and the DISC that was reverted after PIM knockdown. In line with this, p62/SQSTM1 ablation increased TRAIL-R2/DR5 levels and facilitated TRAIL-induced caspase-8 activation, revealing an inhibitory role of p62/SQSTM1 in TRAIL-mediated apoptosis in GBM. Conversely, upregulation of TRAIL-R2/DR5 upon PIM inhibition and apoptosis induced by the combination of PIM inhibitor and TRAIL were abrogated by a constitutively phosphorylated p62/SQSTM1^S332E mutant. Globally, our data represent the first evidence that PIM kinases regulate TRAIL-induced apoptosis in GBM and identify a specific role of p62/SQSTM1^Ser332 phosphorylation in the regulation of the extrinsic apoptosis pathway activated by TRAIL.

Inhibitors of apoptosis: clinical implications in cancer

Inhibitor of apoptosis (IAP) family comprises a group of endogenous proteins that function as main regulators of caspase activity and cell death. They are considered the main culprits in evasion of apoptosis, which is a fundamental hallmark of carcinogenesis. Overexpression of IAP proteins has been documented in various solid and hematological malignancies, rendering them resistant to standard chemotherapeutics and radiation therapy and conferring poor prognosis. This observation has urged their exploitation as therapeutic targets in cancer with promising pre-clinical outcomes. This review describes the structural and functional features of IAP proteins to elucidate the mechanism of their anti-apoptotic activity. We also provide an update on patterns of IAP expression in different tumors, their impact on treatment response and prognosis, as well as the emerging investigational drugs targeting them. This aims at shedding the light on the advances in IAP targeting achieved to date, and encourage further development of clinically applicable therapeutic approaches.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs)

Inhibitors of apoptosis (IAPs) are a family of proteins that play a significant role in the control of programmed cell death (PCD). PCD is essential to maintain healthy cell turnover within tissue but also to fight disease or infection. Uninhibited, IAPs can suppress apoptosis and promote cell cycle progression. Therefore, it is unsurprising that cancer cells demonstrate significantly elevated expression levels of IAPs, resulting in improved cell survival, enhanced tumor growth and subsequent metastasis. Therapies to target IAPs in cancer has garnered substantial scientific interest and as resistance to anti-cancer agents becomes more prevalent, targeting IAPs has become an increasingly attractive strategy to re-sensitize cancer cells to chemotherapies, antibody based-therapies and TRAIL therapy. Antagonism strategies to modulate the actions of XIAP, cIAP1/2 and survivin are the central focus of current research and this review highlights advances within this field with particular emphasis upon the development and specificity of second mitochondria-derived activator of caspase (SMAC) mimetics (synthetic analogs of endogenously expressed inhibitors of IAPs SMAC/DIABLO). While we highlight the potential of SMAC mimetics as effective single agent or combinatory therapies to treat cancer we also discuss the likely clinical implications of resistance to SMAC mimetic therapy, occasionally observed in cancer cell lines.

Primary cross-resistance to BRAFV600E-, MEK1/2- and PI3K/mTOR-specific inhibitors in BRAF-mutant melanoma cells counteracted by dual pathway blockade

Intrinsic cross-resistance to inhibition of different signaling pathways may hamper development of combinatorial treatments in melanoma, but the relative frequency of this phenotype and the strategies to overcome this hurdle remain poorly understood. Among 49 BRAF-mutant melanoma cell lines from patients not previously treated with target therapy, 21 (42.9%) showed strong primary resistance (IC₅₀ > 1 μM) to a BRAFV600E inhibitor. Most of the BRAF-inhibitor-resistant cell lines showed also strong or intermediate cross-resistance to MEK1/2- and to PI3K/mTOR-specific inhibitors. Primary cross-resistance was confirmed in an independent set of 23 BRAF-mutant short-term melanoma cell cultures. MEK1/2 and PI3K/mTOR co-targeting was the most effective approach, compared to BRAF and PI3K/mTOR dual blockade, to counteract primary resistance to BRAF inhibition and the cross-resistant phenotype. This was shown by extensive drug interaction analysis, tumor growth inhibition assays in-vivo, p-ERK and p-AKT inhibition, promotion of melanoma apoptosis, apoptosis-related protein modulation, activation of effector caspases and selective modulation of genes involved in melanoma drug resistance and belonging to the ERK/MAPK and PI3K/AKT canonical pathways. Compared to co-targeting of mutant BRAF and PI3K/mTOR, the association of a MEK1/2 and a PI3K/mTOR inhibitor was more effective in the activation of Bax and of caspase-3 and in the induction of caspase-dependent melanoma apoptosis. Furthermore Bax silencing reduced the latter effects. These results suggest that intrinsic resistance to BRAF inhibition is frequently associated with primary cross-resistance to MEK and PI3K/mTOR blockade in BRAF-mutant melanoma and provide pre-clinical evidence for a combinatorial approach to counteract this phenotype.

BIRC6 Targeting as Potential Therapy for Advanced, Enzalutamide-Resistant Prostate Cancer

Purpose: Enzalutamide resistance has emerged as a major problem in the management of castration-resistant prostate cancer (CRPC). Research on therapy resistance of CRPCs has primarily focused on the androgen receptor pathway. In contrast, there is limited information on antiapoptotic mechanisms that may facilitate the treatment resistance. The inhibitor of apoptosis proteins (IAP) family is well recognized for its role in promoting treatment resistance of cancers by inhibiting drug-induced apoptosis. Here, we examined whether BIRC6, an IAP family member, has a role in enzalutamide resistance of CRPCs and could provide a therapeutic target for enzalutamide-resistant CRPC.Experimental Design: Use of enzalutamide-resistant CRPC models: (i) the transplantable, first high-fidelity LTL-313BR patient-derived enzalutamide-resistant CRPC tissue xenograft line showing primary enzalutamide resistance, (ii) MR42D and MR49F CRPC cells/xenografts showing acquired enzalutamide resistance. Specific BIRC6 downregulation in these models was produced using a BIRC6-targeting antisense oligonucleotide (ASO-6w2). Gene expression was determined by qRT-PCR and gene expression profiling. Molecular pathways associated with growth inhibition were assessed via gene enrichment analysis.Results: Of eight IAPs examined, BIRC6 was the only one showing elevated expression in both enzalutamide-resistant CRPC models. Treatment with ASO-6w2 markedly suppressed growth of LTL-313BR xenografts and increased tumor apoptosis without inducing major host toxicity. Pathway enrichment analysis indicated that GPCR and matrisome signaling were the most significantly altered pathways. Furthermore, ASO-6w2 inhibited expression of prosurvival genes that were upregulated in the LTL-313BR line.Conclusions:BIRC6 targeting inhibited the growth of enzalutamide-resistant CRPC models and may represent a new option for clinical treatment of advanced, enzalutamide-resistant prostate cancer. Clin Cancer Res; 23(6); 1542-51. ©2016 AACR.

Expression and clinical significance of Apollon in esophageal squamous cell carcinoma

Apollon, an unusually large member of the inhibitors of apoptosis protein family, may be important for oncogenesis development. The aim of the present study was to assess the association between esophageal squamous cell carcinoma (ESCC) and Apollon expression levels, and to highlight the association between Apollon and the occurrence, development and prognosis of ESCC. Apollon expression was detected by immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction in ESCC tissues, adjacent non-cancerous tissues and paired normal tissues respectively, in order to analyze the association between Apollon expression and the clinicopathological features of ESCC. Survival analysis was used to assess the prognostic significance of Apollon expression. It was determined that the mRNA and protein expression levels of Apollon were significantly higher in the carcinoma tissues compared with the adjacent non-cancerous tissues and normal control tissues (P<0.001). There was a significant difference in lymph node involvement and the tumor, nodes, and metastases stage in patients categorized according to different Apollon expression levels. The prognostic significance of Apollon was also determined using the log-rank method. The overexpression of Apollon was associated with shorter overall survival and disease-free survival rates. The present study indicates that Apollon expression is associated with the biological characteristics of ESCC, and may be a valuable prognostic factor and a novel chemotherapeutic target for ESCC treatment.

Candidate driver genes involved in genome maintenance and DNA repair in Sézary syndrome

Sézary syndrome (SS) is a leukemic variant of cutaneous T-cell lymphoma (CTCL) and represents an ideal model for study of T-cell transformation. We describe whole-exome and single-nucleotide polymorphism array-based copy number analyses of CD4(+) tumor cells from untreated patients at diagnosis and targeted resequencing of 101 SS cases. A total of 824 somatic nonsynonymous gene variants were identified including indels, stop-gain/loss, splice variants, and recurrent gene variants indicative of considerable molecular heterogeneity. Driver genes identified using MutSigCV include POT1, which has not been previously reported in CTCL; and TP53 and DNMT3A, which were also identified consistent with previous reports. Mutations in PLCG1 were detected in 11% of tumors including novel variants not previously described in SS. This study is also the first to show BRCA2 defects in a significant proportion (14%) of SS tumors. Aberrations in PRKCQ were found to occur in 20% of tumors highlighting selection for activation of T-cell receptor/NF-κB signaling. A complex but consistent pattern of copy number variants (CNVs) was detected and many CNVs involved genes identified as putative drivers. Frequent defects involving the POT1 and ATM genes responsible for telomere maintenance were detected and may contribute to genomic instability in SS. Genomic aberrations identified were enriched for genes implicated in cell survival and fate, specifically PDGFR, ERK, JAK STAT, MAPK, and TCR/NF-κB signaling; epigenetic regulation (DNMT3A, ASLX3, TET1-3); and homologous recombination (RAD51C, BRCA2, POLD1). This study now provides the basis for a detailed functional analysis of malignant transformation of mature T cells and improved patient stratification and treatment.

Sema6A and Mical1 control cell growth and survival of BRAFV600E human melanoma cells

We used whole genome microarray analysis to identify potential candidate genes with differential expression in BRAFV600E vs NRASQ61R melanoma cells. We selected, for comparison, a peculiar model based on melanoma clones, isolated from a single tumor characterized by mutually exclusive expression of BRAFV600E and NRASQ61R in different cells. This effort led us to identify two genes, SEMA6A and MICAL1, highly expressed in BRAF-mutant vs NRAS-mutant clones. Real-time PCR, Western blot and immunohistochemistry confirmed preferential expression of Sema6A and Mical1 in BRAFV600E melanoma. Sema6A is a member of the semaphorin family, and it complexes with the plexins to regulate actin cytoskeleton, motility and cell proliferation. Silencing of Sema6A in BRAF-mutant cells caused cytoskeletal remodeling, and loss of stress fibers, that in turn induced cell death. Furthermore, Sema6A depletion caused loss of anchorage-independent growth, inhibition of chemotaxis and invasion. Forced Sema6A overexpression, in NRASQ61R clones, induced anchorage-independent growth, and a significant increase of invasiveness. Mical1, that links Sema/PlexinA signaling, is also a negative regulator of apoptosis. Indeed, Mical-1 depletion in BRAF mutant cells restored MST-1-dependent NDR phosphorylation and promoted a rapid and massive NDR-dependent apoptosis. Overall, our data suggest that Sema6A and Mical1 may represent new potential therapeutic targets in BRAFV600E melanoma.

The BIRC6 gene as a novel target for therapy of prostate cancer: dual targeting of inhibitors of apoptosis

Treatment resistance, the major challenge in the management of advanced prostate cancer, is in part based on resistance to apoptosis. The Inhibitor of Apoptosis (IAP) family is thought to play key roles in survival and drug resistance of cancer via inhibition of apoptosis. Of the IAP family members, cIAP1, cIAP2, XIAP and survivin are known to be up-regulated in prostate cancer. BIRC6, a much less studied IAP member, was recently shown to be elevated in castration-resistant prostate cancer (CRPC). In the present study, we showed a correlation between elevated BIRC6 expression in clinical prostate cancer specimens and poor patient prognostic factors, as well as co-upregulation of certain IAP members. In view of this, we designed antisense oligonucleotides that simultaneously target BIRC6 and another co-upregulated IAP member (dASOs). Two dASOs, targeting BIRC6+cIAP1 and BIRC6+survivin, showed substantial inhibition of CRPC cells proliferation, exceeding that obtained with single BIRC6 targeting. The growth inhibition was associated with increased apoptosis, cell cycle arrest and suppression of NFkB activation. Moreover, treatment with both dASOs led to significantly lower viable tumor volume in vivo, without major host toxicity. This study shows that BIRC6-based dual IAP-targeting ASOs represent potential novel therapeutic agents against advanced prostate cancer.

Knockdown of the Inhibitor of Apoptosis BRUCE Sensitizes Resistant Breast Cancer Cells to Chemotherapeutic Agents

Background and objectives

Management of patients with breast cancer often fails because of inherent or acquired resistance to chemotherapy. BRUCE (BIR repeat containing ubiquitin-conjugating enzyme) is a member of the inhibitor of apoptosis protein (IAP) family. It has various cellular functions including suppression of apoptosis and promotion of cytokinesis. Furthermore, it pays a critical role in promotion of DNA damage repair and preservation of genome stability, a new function recently reported by our group. Although BRUCE is expressed in breast cancer cell lines, its expression in human primary breast tumors and its contribution to chemoresistance in breast cancers has not been explored. Chemotherapeutic drugs are used in the treatment of breast cancer patients. However, they are not effective to all patients and patients often develop resistance. Consequently we explored if BRUCE protein level, as judged by immunohistochemistry (IHC), is higher in primary breast tumors than normal breast tissue. We also examined if depletion of BRUCE, using a lentiviral shRNA approach, enhances cell sensitivity to multiple chemotherapeutic agents, including cisplatin, an agent that induces DNA damage by generating DNA cross-links, and taxol, a microtubule stabilizer and mitotic inhibitor. The reason for including these two chemotherapeutic agents in this study is that they hit two essential cellular processes of DNA repair and cytokinesis in which BRUCE plays critical roles.

Results and methods

IHC analysis of BRUCE revealed significantly higher levels of BRUCE in primary breast tumors than normal breast tissue. Knockdown of BRUCE protein expression by lentiviral shRNA resulted in increased sensitivity to cisplatin in the resistant breast cancer MDB-MD-231 cell line. Moreover, depletion of BRUCE in this cell line achieved a more profound level of cell killing when coupled to low doses of cisplatin and taxol combined, rather than either drug used alone.

Conclusions

Our data suggest that elevated protein levels of BRUCE in breast tumors may contribute to chemoresistance in breast cancer patients. In support of this suggestion, our data demonstrate that a reduction in BRUCE expression in breast cancer cell lines increases the toxicity of several chemotherapeutic agents. In all likelihood, the contribution of increased BRUCE levels to chemoresistance are likely due to its roles in suppression of apoptosis, promotion of cytokinesis and facilitation of DNA damage repair. These observations suggest that therapeutic suppression of BRUCE could improve chemosensitivity in chemo-resistant breast cancer patients. Therefore, future development of effective inhibitors of BRUCE could benefit patients with high BRUCE expression and chemoresistance.

Key regulators of apoptosis execution as biomarker candidates in melanoma

Resistance to apoptosis is frequently detected in malignant melanoma, a skin cancer with rapidly growing incidence rates. Apoptosis resistance may develop with disease progression and may be associated with the poor responsiveness of metastatic melanoma to apoptosis-inducing treatments, such as genotoxic chemotherapy and radiotherapy. Likewise, the efficacy of novel treatment options (targeted kinase inhibitors and immunotherapeutics) that indirectly lead to cell death may depend on the susceptibility of melanoma to apoptosis. At its core, apoptosis execution is regulated by the interplay between a comparatively small number of pro- and anti-apoptotic proteins, and consequently numerous studies have investigated the potential of these players as biomarker candidates. Here, we provide a comprehensive overview of biomarker discovery studies focusing on key regulators of apoptosis execution, critically review the findings of these studies, and outline strategies that address current limitations and challenges in exploiting regulators of apoptosis execution as prognostic or predictive biomarkers in melanoma.

Synergistic anti-tumor activity and inhibition of angiogenesis by cotargeting of oncogenic and death receptor pathways in human melanoma

Improving treatment of advanced melanoma may require the development of effective strategies to overcome resistance to different anti-tumor agents and to counteract relevant pro-tumoral mechanisms in the microenvironment. Here we provide preclinical evidence that these goals can be achieved in most melanomas, by co-targeting of oncogenic and death receptor pathways, and independently of their BRAF, NRAS, p53 and PTEN status. In 49 melanoma cell lines, we found independent susceptibility profiles for response to the MEK1/2 inhibitor AZD6244, the PI3K/mTOR inhibitor BEZ235 and the death receptor ligand TRAIL, supporting the rationale for their association. Drug interaction analysis indicated that a strong synergistic anti-tumor activity could be achieved by the three agents and the AZD6244–TRAIL association on 20/21 melanomas, including cell lines resistant to the inhibitors or to TRAIL. Mechanistically, synergy was explained by enhanced induction of caspase-dependent apoptosis, mitochondrial depolarization and modulation of key regulators of extrinsic and intrinsic cell death pathways, including c-FLIP, BIM, BAX, clusterin, Mcl-1 and several IAP family members. Moreover, silencing experiments confirmed the central role of Apollon downmodulation in promoting the apoptotic response of melanoma cells to the combinatorial treatments. In SCID mice, the AZD6244–TRAIL association induced significant growth inhibition of a tumor resistant to TRAIL and poorly responsive to AZD6244, with no detectable adverse events on body weight and tissue histology. Reduction in tumor volume was associated not only with promotion of tumor apoptosis but also with suppression of the pro-angiogenic molecules HIF1α, VEGFα, IL-8 and TGFβ1 and with inhibition of tumor angiogenesis. These results suggest that synergistic co-targeting of oncogenic and death receptor pathways can not only overcome melanoma resistance to different anti-tumor agents in vitro but can also promote pro-apoptotic effects and inhibition of tumor angiogenesis in vivo.

BIRC6 promotes hepatocellular carcinogenesis: interaction of BIRC6 with p53 facilitating p53 degradation

The genes that encode inhibitor of apoptosis proteins (IAPs) are frequently overexpressed in human cancers. However, the expression pattern and clinical significance of BIRC6, a member of IAPs, in hepatocellular carcinoma (HCC) remains unclear. Here we investigated the role of BIRC6 in hepatocellular carcinogenesis. We used immunoblot and immunochemical analyses to determine the levels of BIRC6 in 7 hepatoma cell lines and 160 HCC specimens. We evaluated the proognostic value of BIRC6 expression and its association with clinical parameters. A lentivirus-mediated silencing method was used to knockdown BIRC6, and the biological consequences of BIRC6 silencing in three hepatoma cell lines were investigated in vitro and in vivo. We found that BIRC6 overexpression was significantly correlated with serum ALT level and HCC vascular invasion. Patients with positive BIRC6 expression in tumor tissue had a poor survival and a high rate of recurrence. BIRC6 knockdown remarkably suppressed cell proliferation, caused G1/S arrest and sensitized hepatoma cells to sorafenib-induced apoptosis in hepatoma cells, which was partly reversed by RNA interference targeting p53. The mechanistic study revealed that BIRC6 interacted with p53 and facilitated its degradation. The in vivo study showed that BIRC6 knockdown inhibited xenograft tumor growth and increased the sensitivity of tumor cells to sorafenib in nude mice. Taken together, these findings demonstrate that BIRC6 overexpression in HCC specimens is indicative of poor prognosis and that its interaction with p53 facilitates the degradation of p53, leading to carcinogenesis and an anti-apoptotic status.

Molecular subtyping of metastatic melanoma based on cell ganglioside metabolism profiles

BACKGROUND

In addition to alterations concerning the expression of oncogenes and onco-suppressors, melanoma is characterized by the presence of distinctive gangliosides (sialic acid carrying glycosphingolipids). Gangliosides strongly control cell surface dynamics and signaling; therefore, it could be assumed that these alterations are linked to modifications of cell behavior acquired by the tumor. On these bases, this work investigated the correlations between melanoma cell ganglioside metabolism profiles and the biological features of the tumor and the survival of patients.

METHODS

Melanoma cell lines were established from surgical specimens of AJCC stage III and IV melanoma patients. Sphingolipid analysis was carried out on melanoma cell lines and melanocytes through cell metabolic labeling employing [3-3H]sphingosine and by FACS. N-glycolyl GM3 was identified employing the 14 F7 antibody. Gene expression was assayed by Real Time PCR. Cell invasiveness was assayed through a Matrigel invasion assay; cell proliferation was determined through the soft agar assay, MTT, and [3H] thymidine incorporation. Statistical analysis was performed using XLSTAT software for melanoma hierarchical clustering based on ganglioside profile, the Kaplan-Meier method, the log-rank (Mantel-Cox) test, and the Mantel-Haenszel test for survival analysis.

RESULTS

Based on the ganglioside profiles, through a hierarchical clustering, we classified melanoma cells isolated from patients into three clusters: 1) cluster 1, characterized by high content of GM3, mainly in the form of N-glycolyl GM3, and GD3; 2) cluster 2, characterized by the appearance of complex gangliosides and by a low content of GM3; 3) cluster 3, which showed an intermediate phenotype between cluster 1 and cluster 3. Moreover, our data demonstrated that: a) a correlation could be traced between patients' survival and clusters based on ganglioside profiles, with cluster 1 showing the worst survival; b) the expression of several enzymes (sialidase NEU3, GM2 and GM1 synthases) involved in ganglioside metabolism was associated with patients' survival; c) melanoma clusters showed different malignant features such as growth in soft agar, invasiveness, expression of anti-apoptotic proteins.

CONCLUSIONS

Ganglioside profile and metabolism is strictly interconnected with melanoma aggressiveness. Therefore, the profiling of melanoma gangliosides and enzymes involved in their metabolism could represent a useful prognostic and diagnostic tool.

Towards combinatorial targeted therapy in melanoma: from pre-clinical evidence to clinical application (review)

Over the last few years, clinical trials with BRAF and mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitors have shown significant clinical activity in melanoma, but only a fraction of patients respond to these therapies, and development of resistance is frequent. This has prompted a large set of preclinical studies looking at several new combinatorial approaches of pathway- or target-specific inhibitors. At least five main drug association strategies have been verified in vitro and in preclinical models. The most promising include: i) vertical targeting of either MEK or phosphoinositide-3 kinase (PI3K)/mammalian target of rapamycin (mTOR) pathways, or their combined blockade; ii) association of receptor tyrosine kinases (RTKs) inhibitors with other pro-apoptotic strategies; iii) engagement of death receptors in combination with MEK-, mTOR/PI3K-, histone deacetylase (HDAC)-inhibitors, or with anti-apoptotic molecules modulators; iv) strategies aimed at blocking anti-apoptotic proteins belonging to B-cell lymphoma (Bcl-2) or inhibitors of apoptosis (IAP) families associated with MEK/BRAF/p38 inhibition; v) co-inhibition of other molecules important for survival [proteasome, HDAC and Signal transducers and activators of transcription (Stat)3] and the major pathways activated in melanoma; vi) simultaneous targeting of multiple anti-apoptotic molecules. Here we review the anti-melanoma efficacy and mechanism of action of the above-mentioned combinatorial strategies, together with the potential clinical application of the most promising studies that may eventually lead to therapeutic benefit.

Targeting the intrinsic apoptosis pathway as a strategy for melanoma therapy

Melanoma drug resistance is often attributed to abrogation of the intrinsic apoptosis pathway. Targeting regulators of apoptosis is thus considered a promising approach to sensitizing melanomas to treatment. The development of small-molecule inhibitors that mimic natural antagonists of either antiapoptotic members of the BCL-2 family or the inhibitor of apoptosis proteins (IAPs), known as BH3- or SMAC-mimetics, respectively, are helping us to understand the mechanisms behind apoptotic resistance. Studies using BH3-mimetics indicate that the antiapoptotic BCL-2 protein MCL-1 and its antagonist NOXA are particularly important regulators of BCL-2 family signaling, while SMAC-mimetic studies show that both XIAP and the cIAPs must be targeted to effectively induce apoptosis of cancer cells. Although most solid tumors, including melanoma, are insensitive to these mimetic drugs as single agents, combinations with other therapeutics have yielded promising results, and tests combining them with BRAF-inhibitors, which have already revolutionized melanoma treatment, are a clear priority.

Exploration of potential roles of a new LOXL2 splicing variant using network knowledge in esophageal squamous cell carcinoma

LOXL2 (lysyl oxidase-like 2), an enzyme that catalyzes oxidative deamination of lysine residue, is upregulated in esophageal squamous cell carcinoma (ESCC). A LOXL2 splice variant LOXL2-e13 and its wild type were overexpressed in ESCC cells followed by microarray analyses. In this study, we explored the potential role and molecular mechanism of LOXL2-e13 based on known protein-protein interactions (PPIs), following microarray analysis of KYSE150 ESCC cells overexpressing a LOXL2 splice variant, denoted by LOXL2-e13, or its wild-type counterpart. The differentially expressed genes (DEGs) of LOXL2-WT and LOXL2-e13 were applied to generate individual PPI subnetworks in which hundreds of DEGs interacted with thousands of other proteins. These two DEG groups were annotated by Functional Annotation Chart analysis in the DAVID bioinformatics database and compared. These results found many specific annotations indicating the potential specific role or mechanism for LOXL2-e13. The DEGs of LOXL2-e13, comparing to its wild type, were prioritized by the Random Walk with Restart algorithm. Several tumor-related genes such as ERO1L, ITGA3, and MAPK8 were found closest to LOXL2-e13. These results provide helpful information for subsequent experimental identification of the specific biological roles and molecular mechanisms of LOXL2-e13. Our study also provides a work flow to identify potential roles of splice variants with large scale data.

Cross talk between cancer and immune cells: exploring complex dynamics in a microfluidic environment

The reconstitution of a complex microenvironment on microfluidic chips is one of the cornerstones to demonstrate the improved flexibility of these devices with respect to macroscale in vitro approaches. In this work, we realised an on-chip model to investigate the interactions between cancer and immune system. To this end, we exploited mice deficient (Knock Out, KO) for interferon regulatory factor 8 (IRF-8), a transcription factor essential for the induction of competent immune responses, to investigate how IRF-8 gene expression contributes to regulate immune and melanoma cells crosstalk. In vivo, IRF-8 KO mice are highly permissive to B16 melanoma growth due to failure of immune cells to properly exert immunosurveillance. B16 cells and immune cells isolated from the spleen of wild type (WT) and IRF-8 KO mice were co-cultured for one week in a PDMS platform and monitored by fluorescence microscopy and time-lapse recordings. We observed that WT spleen cells migrated through microchannels connecting the culturing chambers towards B16 cells and tightly interacted with tumor cells, forming clusters of activation. In contrast, IRF-8 KO immune cells poorly interacted with melanoma cells. In parallel, B16 cells were more attracted towards microchannels, acquiring a more invasive behaviour in the presence of IRF-8 KO spleen cells, with respect to WT cells. Our results strongly confirm the in vivo observations and highlight the value of on-chip co-culture systems as a useful in vitro tool to elucidate the reciprocal interactions between cancer cells and host immune system, with relevant impact in the development of more effective anti-tumor therapeutic strategies.

Bortezomib/proteasome inhibitor triggers both apoptosis and autophagy-dependent pathways in melanoma cells

Generally, both endoplasmic reticulum (ER) stress and mitochondrial dysregulation are a potential therapeutic target of anticancer agents including bortezomib. The treatment of melanoma cells with bortezomib was found to induce apoptosis together with the upregulation of Noxa, Mcl-1, and HSP70 proteins, and the cleavage of LC3 and autophagic formation. Also, bortezomib induced ER-stress as evidenced by the increase of intracellular Ca(2+) release. In addition, bortezomib enhanced the phosphorylation of inositol-requiring transmembrane kinase and endonuclease 1α (IRE1α), apoptosis signal-regulating kinase 1 (ASK1), c-jun-N-terminal kinase (JNK) and p38, and the activation of the transcription factors AP-1, ATF-2, Ets-1, and HSF1. Bortezomib-induced mitochondrial dysregulation was associated with the accumulation of reactive oxygen species (ROS), the release of both apoptosis inducing factor (AIF) and cytochrome c, the activation of caspase-9 and caspase-3, and cleavage of Poly (ADP-ribose) polymerase (PARP). The pretreatment of melanoma cells with the inhibitor of caspase-3 (Ac-DEVD-CHO) was found to block bortezomib-induced apoptosis that subsequently led to the increase of autophagic formation. In contrast, the inhibition of ASK1 abrogated bortezomib-induced autophagic formation and increased apoptosis induction. Furthermore, the inhibition of JNK, of HSP70 also increased apoptosis induction without influence of bortezomib-induced autophagic formation. Based on the inhibitory experiments, the treatment with bortezomib triggers the activation of both ER-stress-associated pathways, namely IRE1α-ASK1-p38-ATF-2/ets-1-Mcl-1, and IRE1α-ASK1-JNK-AP-1/HSF1-HSP70 as well as mitochondrial dysregulation-associated pathways, namely ROS-ASK1-JNK-AP-1/HSF1-HS70, and AIF-caspase-3-PARP and Cyt.c, and caspase-9-caspase-3-PARP. Taken together, our data demonstrates for the first time the molecular mechanisms, whereby bortezomib triggers both apoptosis and autophagic formation in melanoma cells.