Validation of epidermal AMBRA1 and loricrin (AMBLor) as a prognostic biomarker for nonulcerated American Joint Committee on Cancer stage I/II cutaneous melanoma.

BACKGROUND: Combined expression of the autophagy-regulatory protein AMBRA1 (activating molecule in Beclin1-regulated autophagy) and the terminal differentiation marker loricrin in the peritumoral epidermis of stage I melanomas can identify tumour subsets at low risk of -metastasis. OBJECTIVES: To validate the combined expression of peritumoral AMBRA1 and loricrin (AMBLor) as a prognostic biomarker able to identify both stage I and II melanomas at low risk of tumour recurrence. METHODS: Automated immunohistochemistry was used to analyse peritumoral AMBRA1 and loricrin expression in geographically distinct discovery (n = 540) and validation (n = 300) cohorts of nonulcerated American Joint Committee on Cancer (AJCC) stage I and II melanomas. AMBLor status was correlated with clinical outcomes in the discovery and validation cohorts separately and combined. RESULTS: Analysis of AMBLor in the discovery cohort revealed a recurrence-free survival (RFS) rate of 95.5% in the AMBLor low-risk group vs. 81.7% in the AMBLor at-risk group (multivariate log-rank, P < 0.001) and a negative predictive value (NPV) of 96.0%. In the validation cohort, AMBLor analysis revealed a RFS rate of 97.6% in the AMBLor low-risk group vs. 78.3% in the at-risk group (multivariate log-rank, P < 0.001) and a NPV of 97.6%. In a multivariate model considering AMBLor, Breslow thickness, age and sex, analysis of the combined discovery and validation cohorts showed that the estimated effect of AMBLor was statistically significant, with a hazard ratio of 3.469 (95% confidence interval 1.403-8.580, P = 0.007) and an overall NPV of 96.5%. CONCLUSIONS: These data provide further evidence validating AMBLor as a prognostic biomarker to identify nonulcerated AJCC stage I and II melanoma tumours at low risk of disease recurrence.

Oncogenic BRAF signalling increases Mcl-1 expression in cutaneous metastatic melanoma.

The Bcl-2 family member Mcl-1 is essential for melanoma survival; however, the influence of oncogenic BRAF signalling remains elusive. In this study, Mcl-1 splice variant expression was determined in a panel of melanoma cell lines in relation to BRAF mutational status. Mcl-1L mRNA expression was increased in melanoma cells compared with primary melanocytes with significantly increased mRNA and protein expression observed in BRAF(V600E) mutant melanoma cells. Although no change in Mcl-1S mRNA was observed, Mcl-1S protein expression also increased in BRAF mutant melanoma cells. Additionally, while over-expression of mutant BRAF(V600E) increased both Mcl-1L and Mcl-1S expression, inhibition of hyperactive BRAF signalling resulted in decreased Mcl-1L expression. These studies suggest that the regulation of Mcl-1 expression by BRAF signalling is increased by oncogenic activation of BRAF, revealing a mechanism of apoptotic resistance which may be overcome by the use of more specifically targeted Mcl-1 inhibitors.

Novel retinoic acid 4-hydroxylase (CYP26) inhibitors based on a 3-(1H-imidazol- and triazol-1-yl)-2,2-dimethyl-3-(4-(phenylamino)phenyl)propyl scaffold.

Retinoic acid (RA), the biologically active metabolite of vitamin A, is used medicinally for the treatment of hyperproliferative diseases including dermatological conditions and cancer. The antiproliferative effects of RA have been well documented as well as the limitations owing to toxicity and the development of resistance to RA therapy. RA metabolism inhibitors (RAMBAs or CYP26 inhibitors) are attracting increasing interest as an alternative method for enhancing endogenous levels of retinoic acid in the treatment of hyperproliferative disease. Here the synthesis and inhibitory activity of novel 3-(1H-imidazol- and triazol-1-yl)-2,2-dimethyl-3-(4-(phenylamino)phenyl)propyl derivatives in a MCF-7 CYP26A1 microsomal assay are described. The most promising inhibitor methyl 2,2-dimethyl-3-(4-(phenylamino)phenyl)-3-(1H-1,2,4-triazol-1-yl)propanoate (6) exhibited an IC(50) of 13 nM (compared with standards Liarozole IC(50) 540 nM and R116010 IC(50) 10 nM) and was further evaluated for CYP selectivity using a panel of CYP with >100-fold selectivity for CYP26 compared with CYP1A2, 2C9 and 2D6 observed and 15-fold selectivity compared with CYP3A4. The results demonstrate the potential for further development of these potent inhibitors.

Synthesis and CYP26A1 inhibitory activity of novel methyl 3-[4-(arylamino)phenyl]-3-(azole)-2,2-dimethylpropanoates.

The role of all-trans-retinoic acid (ATRA) in the development and maintenance of many epithelial and neural tissues has raised great interest in the potential of ATRA and related compounds (retinoids) as pharmacological agents, particularly for the treatment of cancer, skin, neurodegenerative and autoimmune diseases. The use of ATRA or prodrugs as pharmacological agents is limited by a short half-life in vivo resulting from the activity of specific ATRA hydroxylases, CYP26 enzymes, induced by ATRA in liver and target tissues. For this reason retinoic acid metabolism blocking agents (RAMBAs) have been developed for treating cancer and a wide range of other diseases. The synthesis, CYP26A1 inhibitory activity and molecular modeling studies of novel methyl 3-[4-(arylamino)phenyl]-3-(azole)-2,2-dimethylpropanoates are presented. From this series of compounds clear SAR can be derived for 4-substitution of the phenyl ring with electron-donating groups more favourable for inhibitory activity. Both the methylenedioxyphenyl imidazole (17, IC(50) = 8 nM) and triazole (18, IC(50) = 6.7 nM) derivatives were potent inhibitors with additional binding interactions between the methylenedioxy moiety and the CYP26 active site likely to be the main factor. The 6-bromo-3-pyridine imidazole 15 (IC(50) = 5.7 nM) was the most active from this series compared with the standards liarozole (IC(50) = 540 nM) and R116010 (IC(50) = 10 nM).

Regulation of endoplasmic reticulum stress-induced cell death by ATF4 in neuroectodermal tumor cells.

The neuroectodermal tumors neuroblastoma and melanoma represent biologically aggressive and chemoresistant cancers. The chemotherapeutic agents fenretinide and bortezomib induce apoptosis through endoplasmic reticulum (ER) stress in these tumor types. The aim of this study was to test the hypothesis that the early events of ER stress signaling and response pathways induced by fenretinide and bortezomib are mediated by the eukaryotic initiation factor 2alpha (eIF2alpha)-ATF4 signaling pathway. Treatment of neuroblastoma and melanoma cell lines with fenretinide, bortezomib, or thapsigargin resulted in induction of eIF2alpha signaling, characterized by increased expression of phosphorylated eIF2alpha, ATF4, ATF3, and GADD34. These events correlated with induction of the pro-apoptotic protein Noxa. The cytotoxic response, characterized by up-regulation of Noxa and cell death, was dependent on ATF4, but not the ER-related pro-death signaling pathways involving GADD153 or IRE1. Although PERK-dependent phosphorylation of eIF2alpha enhanced ATF4 protein levels during ER stress, cell death in response to fenretinide, bortezomib, or thapsigargin was not abrogated by inhibition of eIF2alpha phosphorylation through PERK knockdown or overexpression of wild-type eIF2alpha. Furthermore, ATF4 induction in response to ER stress was dependent primarily on transcriptional activation, which occurred in a PERK- and phosphorylated eIF2alpha-independent manner. These results demonstrate that ATF4 mediates ER stress-induced cell death of neuroectodermal tumor cells in response to fenretinide or bortezomib. Understanding the complex regulation of cell death pathways in response to ER stress-inducing drugs has the potential to reveal novel therapeutic targets, thus allowing the development of improved treatment strategies to overcome chemoresistance.

Combining the endoplasmic reticulum stress-inducing agents bortezomib and fenretinide as a novel therapeutic strategy for metastatic melanoma.

PURPOSE: Single-agent chemotherapy is largely the treatment of choice for systemic therapy of metastatic melanoma, but survival rates are low, and novel adjuvant and systemic therapies are urgently required. Endoplasmic reticulum (ER) stress is a potential therapeutic target, and two relatively new drugs, fenretinide and bortezomib (Velcade), each acting via different cellular mechanisms, induce ER stress leading to apoptosis in melanoma cells. The aim of this study was to test the hypothesis that apoptosis of melanoma cells may be increased by combining clinically achievable concentrations of fenretinide and bortezomib. EXPERIMENTAL DESIGN: Three human melanoma cell lines were used to assess changes in viability and the induction of apoptosis in response to fenretinide, bortezomib, or both drugs together. A s.c. xenograft model was used to test responses in vivo. RESULTS: Fenretinide and bortezomib synergistically decreased viability and increased apoptosis in all three melanoma lines at clinically achievable concentrations. This was also reflected by increased expression of GADD153, a marker of ER stress-induced apoptosis. In vivo, fenretinide in combination with bortezomib gave a marked reduction in xenograft tumor volume and an increase in apoptosis compared with fenretinide or bortezomib alone. The cell cycle stage of tumor cells in vivo were similar to that predicted from the effects of each drug or the combination in vitro. CONCLUSIONS: These results suggest that fenretinide and bortezomib, both of which are available in clinical formulation, warrant clinical evaluation as a combination therapy for metastatic melanoma.

Novel azolyl-(phenylmethyl)]aryl/heteroarylamines: potent CYP26 inhibitors and enhancers of all-trans retinoic acid activity in neuroblastoma cells.

The synthesis and potent inhibitory activity of novel 4-[(imidazol-1-yl and triazol-1-yl)(phenyl)methyl]aryl-and heteroaryl amines versus a MCF-7 CYP26A1 cell assay is described. Biaryl imidazole ([4-(imidazol-1-yl-phenyl-methyl)-phenyl]-naphthalen-2-yl-amine (8), IC(50)=0.5 microM; [4-(imidazol-1-yl-phenyl-methyl)-phenyl]-indan-5-yl-amine (9), IC(50)=1.0 microM) and heteroaryl imidazole derivatives ((1H-benzoimidazol-2-yl)-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (15), IC(50)=2.5 microM; benzooxazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (16), IC(50)=0.9 microM; benzothiazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (17), IC(50)=1.5 microM) were the most potent CYP26 inhibitors. Using a CYP26A1 homology model differences in activity were investigated. Incubation of SH-SY5Y human neuroblastoma cells with the imidazole aryl derivative 8, and the imidazole heteroaryl derivatives 16 and 17 potentiated the atRA-induced expression of CYP26B1. These data suggest that further structure-function studies leading to clinical development are warranted.

13-cis retinoic acid and isomerisation in paediatric oncology--is changing shape the key to success?

Retinoic acid isomers have been used with some success as chemotherapeutic agents, most recently with 13-cis retinoic acid showing impressive clinical efficacy in the paediatric malignancy neuroblastoma. The aim of this commentary is to review the evidence that 13-cis retinoic acid is a pro-drug, and consider the implications of retinoid metabolism and isomerisation for the further development of retinoic acid for cancer therapy. The low binding affinity of 13-cis retinoic acid for retinoic acid receptors, low activity in gene expression assays and the accumulation of the all-trans isomer in cells treated with 13-cis retinoic acid, coupled with the more-favourable pharmacokinetic profile of 13-cis retinoic acid compared to other isomers, suggest that intracellular isomerisation to all-trans retinoic acid is the key process underlying the biological activity of 13-cis retinoic acid. Intracellular metabolism of all-trans retinoic acid by a positive auto-regulatory loop may result in clinical resistance to retinoic acid. Agents that block or reduce the metabolism of all-trans retinoic acid are therefore attractive targets for drug development. Devising strategies to deliver 13-cis retinoic acid to tumour cells and facilitate the intracellular isomerisation of 13-cis retinoic acid, while limiting metabolism of all-trans retinoic acid, may have a major impact on the efficacy of 13-cis retinoic acid in paediatric oncology.

A Novel Fully Humanized 3D Skin Equivalent to Model Early Melanoma Invasion.

Metastatic melanoma remains incurable, emphasizing the acute need for improved research models to investigate the underlying biologic mechanisms mediating tumor invasion and metastasis, and to develop more effective targeted therapies to improve clinical outcome. Available animal models of melanoma do not accurately reflect human disease and current in vitro human skin equivalent models incorporating melanoma cells are not fully representative of the human skin microenvironment. We have developed a robust and reproducible, fully humanized three-dimensional (3D) skin equivalent comprising a stratified, terminally differentiated epidermis and a dermal compartment consisting of fibroblast-generated extracellular matrix. Melanoma cells incorporated into the epidermis were able to invade through the basement membrane and into the dermis, mirroring early tumor invasion in vivo. Comparison of our novel 3D melanoma skin equivalent with melanoma in situ and metastatic melanoma indicates that this model accurately recreates features of disease pathology, making it a physiologically representative model of early radial and vertical growth-phase melanoma invasion.

Exploiting cannabinoid-induced cytotoxic autophagy to drive melanoma cell death.

Although the global incidence of cutaneous melanoma is increasing, survival rates for patients with metastatic disease remain <10%. Novel treatment strategies are therefore urgently required, particularly for patients bearing BRAF/NRAS wild-type tumors. Targeting autophagy is a means to promote cancer cell death in chemotherapy-resistant tumors, and the aim of this study was to test the hypothesis that cannabinoids promote autophagy-dependent apoptosis in melanoma. Treatment with Δ(9)-Tetrahydrocannabinol (THC) resulted in the activation of autophagy, loss of cell viability, and activation of apoptosis, whereas cotreatment with chloroquine or knockdown of Atg7, but not Beclin-1 or Ambra1, prevented THC-induced autophagy and cell death in vitro. Administration of Sativex-like (a laboratory preparation comprising equal amounts of THC and cannabidiol (CBD)) to mice bearing BRAF wild-type melanoma xenografts substantially inhibited melanoma viability, proliferation, and tumor growth paralleled by an increase in autophagy and apoptosis compared with standard single-agent temozolomide. Collectively, our findings suggest that THC activates noncanonical autophagy-mediated apoptosis of melanoma cells, suggesting that cytotoxic autophagy induction with Sativex warrants clinical evaluation for metastatic disease.

The impact of retinoic acid treatment on the sensitivity of neuroblastoma cells to fenretinide.

Despite the successful introduction of 13-cis retinoic acid (13cisRA) therapy for the treatment of neuroblastoma, approximately 50% patients do not respond or experience relapse. A retinoid analogue, fenretinide [N-(4-hydroxyphenyl) retinamide; 4-HPR] can induce apoptosis in neuroblastoma cell lines and could have clinical use after therapy with 13cisRA. However, there are important questions concerning potential retinoid drug interactions which need to be addressed. The aim of this study was to investigate the influence of retinoic acid pre-treatment on fenretinide-induced apoptosis and fenretinide metabolism in neuroblastoma cell lines. Apoptosis was measured by flow cytometry of propidium iodide-stained neuroblastoma cells and a live-cell imaging assay. Intracellular fenretinide metabolism was determined by HPLC analysis. Pre-treatment of neuroblastoma cell lines with retinoic acid (RA) resulted in a significant decrease in the apoptotic response to fenretinide in three of the four lines tested. Comparison between responsive and non-responsive cell lines suggested that RA sensitivity was required to promote fenretinide resistance, and that this was mediated by up-regulation of Bcl-2 and the inhibition of pro-apoptotic fenretinide signalling pathways. Induction of the oxidative metabolism of fenretinide after RA pre-treatment did not significantly impact on intracellular parent drug levels and is unlikely to explain the decreased apoptotic response observed. The interaction between RA and fenretinide could have important implications for the scheduling of fenretinide in therapeutic protocols for neuroblastoma.

Synthesis and biological evaluation of 3-(1H-imidazol- and triazol-1-yl)-2,2-dimethyl-3-[4-(naphthalen-2-ylamino)phenyl]propyl derivatives as small molecule inhibitors of retinoic acid 4-hydroxylase (CYP26).

The synthesis and potent inhibitory activity of novel 3-(1H-imidazol- and triazol-1-yl)-2,2-dimethyl-3-(4-(naphthalen-2-ylamino)phenyl)propyl derivatives vs a MCF-7 CYP26A1 microsomal assay is described. This study focused on the effect of modifying the heme binding azole group and the flexible C3 chain on inhibitory activity and selectivity. The most promising inhibitor 2,2-dimethyl-3-[4-(naphthalen-2-ylamino)-phenyl]-3-[1,2,4]triazol-1-yl-propionic acid methyl ester (17) (IC(50) = 0.35 nM as compared with liarozole IC(50) = 540 nM and R116010 IC(50) = 10 nM) was evaluated for CYP selectivity and hepatic stability. Compounds with CYP26 inhibitory IC(50) values ≤50 nM enhanced the biological activity of exogenous ATRA, as evidenced by a 3.7-5.8-fold increase in CYP26A1 mRNA in SH-SY5Y neuroblastoma cells as compared with ATRA alone. All compounds demonstrated an activity comparable with or better than R116010, and the induction correlated well with CYP26 inhibition data. These studies highlight the promising activity profile of this novel CYP26 inhibitor and suggest it as an appropriate candidate for future development.

Small molecule inhibitors of retinoic acid 4-hydroxylase (CYP26): synthesis and biological evaluation of imidazole methyl 3-(4-(aryl-2-ylamino)phenyl)propanoates.

The synthesis and potent inhibitory activity of novel imidazole methyl 3-(4-(aryl-2-ylamino)phenyl)propanoates in a MCF-7 CYP26A1 microsomal assay is described. The induction of CYP26A1 mRNA was used to evaluate the ability of the compounds to enhance the biological effects of all-trans retinoic acid (ATRA) in a retinoid-responsive neuroblastoma cell line. The most promising inhibitor, 3-imidazol-1-yl-2-methyl-3-[4-(naphthalen-2-ylamino)-phenyl]-propionic acid methyl ester (20), with an IC(50) of 3 nM (compared with liarozole IC(50) of 540 nM and R116010 IC(50) of 10 nM) was further evaluated for CYP selectivity using a panel of CYP enzymes, mutagenicity (Ames screen), and hepatic stability.

Oncogenic B-RAF signaling in melanoma impairs the therapeutic advantage of autophagy inhibition.

PURPOSE: Metastatic melanoma is characterized by extremely poor survival rates and hence novel therapies are urgently required. The ability of many anticancer drugs to activate autophagy, a lysosomal-mediated catabolic process which usually promotes cell survival, suggests targeting the autophagy pathway may be a novel means to augment therapy. EXPERIMENTAL DESIGN: Autophagy and apoptosis were assessed in vitro in human melanoma cell lines in response to clinically achievable concentrations of the endoplasmic reticulum (ER) stress-inducing drugs fenretinide or bortezomib, and in vivo using a s.c. xenograft model. RESULTS: Autophagy was activated in response to fenretinide or bortezomib in B-RAF wild-type cells, shown by increased conversion of LC3 to the autophagic vesicle-associated form (LC3-II) and redistribution to autophagosomes and autolysosomes, increased acidic vesicular organelle formation and autophagic vacuolization. In contrast, autophagy was significantly reduced in B-RAF-mutated melanoma cells, an effect attributed partly to oncogenic B-RAF. Rapamycin treatment was unable to stimulate LC3-II accumulation or redistribution in the presence of mutated B-RAF, indicative of de-regulated mTORC1-dependent autophagy. Knockdown of Beclin-1 or ATG7 sensitized B-RAF wild-type cells to fenretinide- or bortezomib-induced cell death, demonstrating a pro-survival function of autophagy. In addition, autophagy was partially reactivated in B-RAF-mutated cells treated with the BH3 mimetic ABT737 in combination with fenretinide or bortezomib, suggesting autophagy resistance is partly mediated by abrogated Beclin-1 function. CONCLUSIONS: Our findings suggest inhibition of autophagy in combination with ER stress-inducing agents may represent a means by which to harness autophagy for the therapeutic benefit of B-RAF wild-type melanoma.

Targeting X-linked inhibitor of apoptosis protein to increase the efficacy of endoplasmic reticulum stress-induced apoptosis for melanoma therapy.

Melanoma remains notoriously resistant to current chemotherapeutics, leaving an acute need for novel therapeutic approaches. The aim of this study was to determine the prognostic and therapeutic significance of X-linked inhibitor of apoptosis protein (XIAP) in melanoma through correlation of XIAP expression with disease stage, RAS/RAF mutational status, clinical outcome, and susceptibility to endoplasmic reticulum (ER) stress-induced cell death. XIAP expression and N-RAS/B-RAF mutational status were retrospectively determined in a cohort of 55 primary cutaneous melanocytic lesions selected and grouped according to the American Joint Committee on Cancer staging system. Short hairpin RNA interference of XIAP was used to analyze the effect of XIAP expression on ER stress-induced apoptosis in response to fenretinide or bortezomib in vitro. The results showed that XIAP positivity increased with progressive disease stage, although there was no significant correlation between XIAP positivity and combined N-RAS/B-RAF mutational status or clinical outcome. However, XIAP knockdown significantly increased ER stress-induced apoptosis of melanoma cells in a caspase-dependant manner. The correlation of XIAP expression with disease stage, as well as data showing that XIAP knockdown significantly increases fenretinide and bortezomib-induced apoptosis of metastatic melanoma cells, suggests that XIAP may prove to be an effective therapeutic target for melanoma therapy.

Increasing melanoma cell death using inhibitors of protein disulfide isomerases to abrogate survival responses to endoplasmic reticulum stress.

Exploiting vulnerabilities in the intracellular signaling pathways of tumor cells is a key strategy for the development of new drugs. The activation of cellular stress responses mediated by the endoplasmic reticulum (ER) allows cancer cells to survive outside their normal environment. Many proteins that protect cells against ER stress are active as protein disulfide isomerases (PDI) and the aim of this study was to test the hypothesis that apoptosis in response to ER stress can be increased by inhibiting PDI activity. We show that the novel chemotherapeutic drugs fenretinide and velcade induce ER stress-mediated apoptosis in melanoma cells. Both stress response and apoptosis were enhanced by the PDI inhibitor bacitracin. Overexpression of the main cellular PDI, procollagen-proline, 2-oxoglutarate-4-dioxygenase beta subunit (P4HB), resulted in increased PDI activity and abrogated the apoptosis-enhancing effect of bacitracin. In contrast, overexpression of a mutant P4HB lacking PDI activity did not increase cellular PDI activity or block the effects of bacitracin. These results show that inhibition of PDI activity increases apoptosis in response to agents which induce ER stress and suggest that the development of potent, small-molecule PDI inhibitors has significant potential as a powerful tool for enhancing the efficacy of chemotherapy in melanoma.

Role of Noxa in p53-independent fenretinide-induced apoptosis of neuroectodermal tumours.

Fenretinide-induced apoptosis of neuroectodermal tumour cells is mediated through generation of reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, mitochondrial cytochrome c release and caspase activation. The present study describes the requirement of the BH3-domain only protein Noxa for this process and its regulation by p53. Noxa expression was induced by fenretinide in neuroblastoma and melanoma cells, including those with mutated p53, and this induction was abolished by antioxidants. Knockdown of p53 by RNA interference (RNAi) demonstrated upregulation of Noxa protein levels in response to fenretinide was p53-independent, although evidence suggested that Noxa may be transcriptionally regulated by p53. The ER stress-inducing agent thapsigargin also induced p53-independent Noxa expression. Conversely, Noxa transcription in response to the chemotherapeutic agents cisplatin or temozolomide was inhibited by p53 knockdown. Apoptosis in response to cisplatin or temozolomide was also inhibited by abrogation of p53 expression yet apoptosis in response to fenretinide or thapsigargin was unaffected. RNAi-mediated down-regulation of Noxa inhibited apoptosis in response to fenretinide or thapsigargin, whereas apoptosis induced by cisplatin or temozolomide was unaffected. These data demonstrate the importance of Noxa induction in determining the apoptotic response to fenretinide and emphasise the role of Noxa in p53-independent apoptosis.