Expression of the c-kit receptor in choroidal melanomas

KIT Expression Is Regulated by DNA Methylation in Uveal Melanoma Tumors

Uveal melanoma (UM) is an ocular tumor with a dismal prognosis. Despite the availability of precise molecular and cytogenetic techniques, clinicopathologic features with limited accuracy are widely used to predict metastatic potential. In 51 UM tissues, we assessed a correlation between the expression of nine proteins evaluated by immunohistochemistry (IHC) (Melan-A, S100, HMB45, Cyclin D1, Ki-67, p53, KIT, BCL2, and AIFM1) and the presence of UM-specific chromosomal rearrangements measured by multiplex ligation-dependent probe amplification (MLPA), to find IHC markers with increased prognostic information. Furthermore, mRNA expression and DNA methylation values were extracted from the whole-genome data, achieved by analyzing 22 fresh frozen UM tissues. KIT positivity was associated with monosomy 3, increasing the risk of poor prognosis more than 17-fold (95% CI 1.53–198.69, p = 0.021). A strong negative correlation was identified between mRNA expression and DNA methylation values for 12 of 20 analyzed positions, five located in regulatory regions of the KIT gene (r = −0.658, p = 0.001; r = −0.662, p = 0.001; r = −0.816; p < 0.001; r = −0.689, p = 0.001; r = −0.809, p < 0.001, respectively). DNA methylation β values were also inversely associated with KIT protein expression (p = 0.001; p = 0.001; p = 0.015; p = 0.025; p = 0.002). Our findings, showing epigenetic deregulation of KIT expression, may contribute to understanding the past failure to therapeutically target KIT in UM.

Uveal melanoma

Uveal melanoma (UM) is the most common primary intraocular malignancy in adults. UMs are usually initiated by a mutation in GNAQ or GNA11, unlike cutaneous melanomas, which usually harbour a BRAF or NRAS mutation. The annual incidence in Europe and the USA is ~6 per million population per year. Risk factors include fair skin, light-coloured eyes, congenital ocular melanocytosis, ocular melanocytoma and the BAP1-tumour predisposition syndrome. Ocular treatment aims at preserving the eye and useful vision and, if possible, preventing metastases. Enucleation has largely been superseded by various forms of radiotherapy, phototherapy and local tumour resection, often administered in combination. Ocular outcomes are best with small tumours not extending close to the optic disc and/or fovea. Almost 50% of patients develop metastatic disease, which usually involves the liver, and is usually fatal within 1 year. Although UM metastases are less responsive than cutaneous melanoma to chemotherapy or immune checkpoint inhibitors, encouraging results have been reported with partial hepatectomy for solitary metastases, with percutaneous hepatic perfusion with melphalan or with tebentafusp. Better insight into tumour immunology and metabolism may lead to new treatments.

Protein expression of KIT, BRAF, GNA11, GNAQ and RASSF1 in feline diffuse iris melanomas

Feline iris melanoma, the most common feline intraocular tumour, has a reported metastatic rate of 19-63%. However, there is a lack of knowledge about its molecular biology. Previous studies have reported that feline iris melanomas do not harbour mutations comparable to common mutations found in their human counterpart. Nevertheless, there are differences in the gene expression patterns. The aim of this study was to investigate the protein expression of B-RAF oncogene serine/threonine kinase (BRAF), G protein subunit alpha q (GNAQ) and 11 (GNA11), KIT proto-oncogene receptor tyrosine kinase (KIT), and Ras association family member 1 (RASSF1) in feline iris melanomas. Fifty-seven formalin-fixed paraffin embedded (FFPE) iris melanomas and 25 FFPE eyes without ocular abnormalities were stained with antibodies against the respective proteins using immunofluorescence. Averaged pixel intensities/μm² and percentage of stained area from total tissue area were measured and the results were compared. Compared to the control group, iris melanomas showed overexpression of BRAF, GNAQ, GNA11 and KIT. The higher expression of BRAF, GNAQ, GNA11 and KIT in feline iris melanomas suggest that these proteins may play a key role in the development of feline iris melanomas and KIT may present a possible target for future therapies in cats with feline iris melanomas.

Expression and prognostic value of putative cancer stem cell markers CD117 and CD15 in choroidal and ciliary body melanoma

AIMS

The aim of the present study was to immunohistochemically investigate the expression and prognostic significance of putative cancer stem cell markers CD117 (c-kit), CD34, CD20 and CD15 in a cohort of patients with primary choroidal and ciliary body melanoma.

METHODS

The immunohistochemical expression of these markers was evaluated using 3,3'-diaminobenzidine tetrahydrochloride (DAB) and 3-amino-9-ethylcarbazole (AEC) chromogens on paraffin-embedded tissue samples from 40 patients who underwent enucleation in the period from 1985 through 2000. Thirty-one patients had adequate tissue specimens for the analysis.

RESULTS

CD117 overexpression was observed in 12 of the 31 samples (39%) when AEC chromogen was used and in 14 of 26 (54%) samples when DAB was used. CD15 positivity was seen in three out of 30 (10%) samples with AEC and in six out of 26 (23%) samples with DAB. CD20 and CD34 exhibited no positivity in the tested samples. During the average follow-up time of 8.7 years (range 0.5-22 years), 17 patients (55%) died due to metastatic disease. The Kaplan-Meier plots showed a significantly shorter overall and disease-free survival in CD117-positive patients when the AEC chromogen was used. CD15 expression was not associated with patients' survival. In multivariate analysis, patients expressing the CD117 AEC had 4.13 times higher risk of lethal outcome in comparison with CD117 AEC negative patients.

CONCLUSIONS

Our retrospective cohort study has for the first time demonstrated a small proportion of CD15-positive uveal melanomas. CD117 AEC overexpression was associated with a worse outcome in patients with choroidal and ciliary body melanoma. Further studies should confirm the validity of these observations and their potential for targeted treatment modalities.

Mechanisms of resistance to imatinib mesylate in KIT-positive metastatic uveal melanoma

Imatinib mesylate is used in targeted therapy of cancer to inhibit type III tyrosine kinase receptors, such as KIT and platelet-derived growth factor receptors (PDGFRs). Expression of KIT in uveal melanoma (UM) suggests that this receptor may be the target of imatinib mesylate therapy. However, phase II multicenter clinical studies have shown no effect of imatinib mesylate in patients with unresectable liver metastases of UM. We therefore investigated which molecular mechanisms promote imatinib mesylate-resistance in metastatic UM. Expression of KIT, stem cell factor (SCF), PDGFRα and PDGFRβ, was analyzed by RT-PCR, immunostaining, and Western blot in twenty-four samples of UM liver metastases, as well as UM primary tumor and metastatic cell lines. Soluble SCF was quantified in UM cell lines using enzyme-linked immunosorbent assay. Cell viability of UM cell lines treated with imatinib mesylate and grown in SCF-supplemented medium or in microvascular endothelial cells-conditioned medium was studied by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assays. UM liver metastases and cell lines expressed KIT and SCF, but not the PDGFRs. Ninety-five percent of liver metastases expressed KIT at the protein level, but PDGFRs were not detected in these samples. Imatinib mesylate reduced the viability of UM metastatic cell lines in a concentration-dependent manner, but an increased resistance to this drug was observed when cells were incubated in SCF-supplemented or microvascular endothelial cells-conditioned medium. This study provides evidence that tumor microenvironment cytokines such as SCF may promote resistance to imatinib mesylate in metastatic UM.

Expression analysis of genes and pathways associated with liver metastases of the uveal melanoma

Background

Uveal melanoma is an aggressive cancer which has a high percentage metastasizing to the liver, with a worse prognosis. Identification of patients at high risk of metastases may provide information for early detection of metastases and treatment.

Methods

Expression profiling of ocular tumor tissues from 46 liver metastatic uveal melanoma samples and 45 non-metastatic uveal melanoma samples were got from GEO database. Bioinformatic analyses such as the Gene Oncology and Kyoto Encyclopedia of Genes and Genomes were used to identify genes and pathways specifically associated with liver metastases of the uveal melanoma.

Results

A total of 1138 probes were differentially expressed in two group samples. All differential gene interactions in the Signal-Net were analyzed. Of them, 768 probes were up-regulated and 370 down-regulated. They mainly participated in 125 GO terms and 16 pathways. Of the genes differentially expressed between two group cancers, HTR2B, CHL1, the ZNF family, YWHAZ and FYN were the most significantly altered.

Conclusions

Bioinformatics may help excavate and analyze large amounts of data in microarrays by means of rigorous experimental planning, scientific statistical analysis and collection of complete data about liver metastases of uveal melanoma patients. In the present study, a novel differential gene expression pattern was constructed and advanced study will provide new targets for diagnosis and mechanism of uveal melanoma liver metastases.

A pilot study of sunitinib malate in patients with metastatic uveal melanoma

The prognosis of patients with metastatic uveal melanoma is poor and there are limited therapeutic options. C-kit is expressed in the majority of patients with metastatic uveal melanoma. In this pilot trial, we examined the toxicity and efficacy of sunitinib malate, a multitarget tyrosine kinase inhibitor, in patients with metastatic uveal melanoma. Twenty patients with metastatic uveal melanoma expressing c-kit, 17 of whom failed previous treatments, were included in this study. Patients received sunitinib malate 37.5 mg daily continuously in 4-week cycles. The evaluation of response was carried out every 8 weeks. The overall survival (OS) and progression-free survival (PFS) were evaluated using Kaplan-Meier survival curves and differences in survivals were tested using the log-rank test. There was one partial response and 12 stable disease (SD) after sunitinib treatment. The median OS and PFS were 8.2 and 4.2 months, respectively. Three patients had SD for more than 12 months with sunitinib after failing previous treatments. The most common adverse events were fatigue (90%), diarrhea (60%), hemorrhage (55%), anorexia (45%), hand-foot syndrome (25%), hypothyroidism (25%), and rash (25%). Eleven patients required a dose reduction to 25 mg daily secondary to grade 3 adverse events. The degree of c-kit expression in melanoma cells was not associated with longer PFS or OS. Patients who developed systemic metastases after more than 5 years of their initial diagnosis had better PFS (median PFS: 5.8 vs. 2.6 months, P=0.005). Sunitinib was safely administered and showed potential clinical benefit in patients with metastatic uveal melanoma. The lack of a correlation between c-kit expression and clinical outcomes requires further investigation on the mechanism of sunitinib in metastatic uveal melanoma.

Uveal melanoma dormancy: an acceptable clinical endpoint?

Uveal melanoma is a rare but life-threatening malignancy. Over the past decades, the morbidity of uveal melanoma has been markedly reduced as a result of advances in the diagnostic ability to detect smaller tumors at an earlier stage. This has allowed for the use of more conservative treatments, avoiding enucleation. Mortality, however, has remained unchanged. This indicates that life expectancy is independent of local tumor control. Metastatic disease, the leading cause of death, is usually diagnosed many years later, despite successful treatment of the primary tumor, and at a late stage, when no effective therapy is available. These observations suggest that the disease was already disseminated at the time of tumor diagnosis. The detection of circulating malignant cells in the bloodstream of patients at different time points in the course of the disease supports this observation. Tumor dormancy has been considered as the leading theory for this intriguing delayed appearance of metastasis. Recent knowledge gained about the biological behavior of uveal melanoma as well as novel potential therapeutic targets are presented in this review.

Driver mutations in melanoma: lessons learned from bench-to-bedside studies

The identification of somatic driver mutations in human samples has allowed for the development of a molecular classification for melanoma. Recent breakthroughs in the treatment of metastatic melanoma have arisen as a result of these significant new insights into the molecular biology of the disease, particularly the development of inhibitors of activating BRAF(V600E) mutations. In this article the roles of several mutations known to be involved in the malignant transformation of melanocytes are reviewed including BRAF, PTEN, NRAS, ckit, and p16 as well as some of the emerging mutations in cutaneous and uveal melanoma. The bench to bedside collaborations that resulted in these discoveries are summarized, and potential therapeutic strategies to target driver mutations in specific patient subsets are discussed.

Insights into melanoma: targeting the mTOR pathway for therapeutics

INTRODUCTION

Cutaneous melanoma represents < 5% of all skin cancers, but is responsible for the majority of skin cancer-related deaths. Ocular melanoma is the most common primary eye tumor in adults, and accounts for approximately 5% of all melanomas. Despite new diagnostic and therapeutic tools, the overall survival of patients treated for melanoma has not improved and most patients die of metastatic disease. Therefore, clarification of the molecular mechanisms underlying the etiopathogenesis of cutaneous and ocular melanomas may help determining the prognosis and tailoring therapy of patients harboring melanomas.

AREAS COVERED

In this review the authors aim to survey relevant research in the molecular mechanisms underlying melanomagenesis, and therapies under evaluation with emphasis in the mTOR pathway.

EXPERT OPINION

Despite an increasingly understanding of the genetics and biochemistry of melanoma, the mechanisms underlying their complex interactions are still poorly understood. Their clarification will lead to more successful therapeutic strategies and evidence-based management of patients with melanoma. More active drug combinations together with appropriate melanoma patient stratification based on molecular biomarkers will be essential for new advances in melanoma therapy.

Mda-9/syntenin is expressed in uveal melanoma and correlates with metastatic progression

Uveal melanoma is an aggressive cancer that metastasizes to the liver in about half of the patients, with a high lethality rate. Identification of patients at high risk of metastases may provide indication for a frequent follow-up for early detection of metastases and treatment. The analysis of the gene expression profiles of primary human uveal melanomas showed high expression of SDCBP gene (encoding for syndecan-binding protein-1 or mda-9/syntenin), which appeared higher in patients with recurrence, whereas expression of syndecans was lower and unrelated to progression. Moreover, we found that high expression of SDCBP gene was related to metastatic progression in two additional independent datasets of uveal melanoma patients. More importantly, immunohistochemistry showed that high expression of mda-9/syntenin protein in primary tumors was significantly related to metastatic recurrence in our cohort of patients. Mda-9/syntenin expression was confirmed by RT-PCR, immunofluorescence and immunohistochemistry in cultured uveal melanoma cells or primary tumors. Interestingly, mda-9/syntenin showed both cytoplasmic and nuclear localization in cell lines and in a fraction of patients, suggesting its possible involvement in nuclear functions. A pseudo-metastatic model of uveal melanoma to the liver was developed in NOD/SCID/IL2Rγ null mice and the study of mda-9/syntenin expression in primary and metastatic lesions revealed higher mda-9/syntenin in metastases. The inhibition of SDCBP expression by siRNA impaired the ability of uveal melanoma cells to migrate in a wound-healing assay. Moreover, silencing of SDCBP in mda-9/syntenin-high uveal melanoma cells inhibited the hepatocyte growth factor (HGF)-triggered invasion of matrigel membranes and inhibited the activation of FAK, AKT and Src. Conversely syntenin overexpression in mda-9/syntenin-low uveal melanoma cells mediated opposite effects. These results suggest that mda-9/syntenin is involved in uveal melanoma progression and that it warrants further investigation as a candidate molecular marker of metastases and a potential therapeutic target.

Therapeutic opportunities in noncutaneous melanoma

Recent evidence suggests that the biology of noncutaneous melanoma differs significantly from cutaneous melanoma and may provide therapeutic opportunity. The most frequent sites of origin of noncutaneous melanoma are the eye and mucosal surfaces. Although noncutaneous melanomas are an uncommon group of cancers (representing less than 10% of all melanomas) a greater understanding of their genetic and molecular abnormalites is being translated into novel treatment strategies. These developments are important because there is currently no effective systemic therapy for noncutaneous melanoma. Significant attention has been focused on the role of c-kit (KIT, CD117), a transmembrane receptor with tyrosine kinase activity. In vitro and ex vivo evidence suggests that c-kit is frequently expressed/over expressed/mutated in noncutaneous melanoma. Anti-tumour effects with c-kit inhibitors are seen in pre-clinical models. A variety of multitargeted kinase inhibitors which have activity against c-kit are currently in early phase clinical trials in metastatic ocular, mucosal and acral melanoma. The few case reports of significant clinical activity with targeted therapies provides hope that greater understanding of the biology of noncutaneous melanoma can be translated into effective treatment.

KIT mutations in ocular melanoma: frequency and anatomic distribution

KIT mutations are known to occur in ~15% of chronic sun damaged cutaneous, mucosal, and acral melanomas. Melanomas with demonstrated activating mutations in KIT or platelet-derived growth factor receptor A (PDGFRA) may benefit from treatment with tyrosine kinase inhibitors. Currently, the limited data regarding KIT mutational status in ocular melanoma suggest that activating mutations are extremely rare. PDGFRA mutational status in ocular melanoma has not been determined. Seventy-five ocular melanomas (53 choroidal, 6 iris, 11 ciliary body, and 5 conjuctival) were selected from the files of the Department of Ophthalmology. High-resolution melting curve analysis and sequencing were performed to detect mutations in KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18. Results of mutational analysis were correlated with anatomical site and KIT (CD117) immunohistochemistry. Eight of 75 (11%) ocular melanomas contained mutations in either the KIT or PDGFRA gene. Five of 53 (9%) choroidal melanomas were associated with mutations (KIT exon 11=3; KIT exon 17=1; PDGFRA intron 18=1). Two of six (33%) iris melanomas and a single (9%) ciliary body melanoma harbored KIT exon 11 mutations. No mutations were identified in conjunctival melanomas. The distribution of KIT and PDGFRA mutations by ocular melanoma anatomical site did not reach statistical significance (P=0.393) CD117 positivity was not predictive of KIT mutational status as only 6 of 58 (10%) CD177-positive tumors harbored KIT mutations. In addition, a KIT exon 17 mutation was identified in one CD117-negative tumor. KIT and PDGFRA mutations do occur in ocular melanomas at a frequency (11%) that is similar to acral and mucosal melanomas. Limited correlation of CD117 positivity with mutational status suggests that all ocular melanomas should undergo mutational analysis to determine if imatinib therapy is appropriate.

Differential effects of imatinib mesylate against uveal melanoma in vitro and in vivo

Uveal melanoma is refractory to chemotherapy. The receptor tyrosine kinase inhibitor, imatinib mesylate, has demonstrated antiproliferative effects against uveal melanoma cells in vitro. The effects of imatinib mesylate, alone and combined with the alklyating agent, temozolomide, were examined in vivo as well as in vitro. Proliferation and angiogenic factor production of human uveal melanoma cell lines in response to imatinib mesylate and temozolomide were examined in vitro. Tumor growth, angiogenic factor production, tumor interstitial fluid pressure, and stroma constituents in response to imatinib mesylate and temozolomide were examined in vivo in mice bearing human uveal melanoma xenografts. Imatinib mesylate in vitro antagonized the antiproliferative effects of temozolomide and increased the production of angiogenic factors. In contrast, pretreatment with imatinib mesylate in vivo could improve the antitumor activity of temozolomide. Imatinib mesylate in vivo decreased the production of angiogenic factors in the tumor stroma and tumor interstitial fluid pressure. These effects were transient. Increases in angiogenic factors, interstitial fluid pressure, and tumor infiltrating macrophages were observed with continued imatinib mesylate treatment in vivo. The antitumor effects of imatinib mesylate can vary in vivo when compared with in vitro. Imatinib mesylate can both positively and negatively modify host-tumor interactions in uveal melanoma.

Overexpression of the KIT/SCF in uveal melanoma does not translate into clinical efficacy of imatinib mesylate

PURPOSE

Recently, gene amplification and overexpression of KIT as well as activating mutations in the KIT gene have been described to occur in certain subsets of melanoma. These findings suggest KIT as a potential target for therapy with imatinib mesylate in these melanomas. To date, data on the KIT status in uveal melanoma (UM) is limited.

EXPERIMENTAL DESIGN

We analyzed the expression of the KIT protein (CD117, c-kit) and its ligand, stem cell factor (SCF), in primary and metastatic UM.

RESULTS

By immunohistochemistry, SCF-positive tumor cells (>90%) were detectable in 43% of primary UM and in 58% of UM metastases. Strong expression of KIT (>90%) in tumor cells was present in 55% of primary UM and in 76% of UM metastases. This overexpression of both KIT and SCF suggests the clinical application of imatinib mesylate in metastatic UM. This notion was tested in a clinical study using Simon's two-stage design. Patients received imatinib (600 mg p.o. daily) until progress or unacceptable toxicities. The trial did not enter stage II as no objective response was observed in the first group. This observation prompted further molecular analysis, which revealed no mutations in the genomic sequence of KIT in exons 11, 13, 17, and 18. Moreover, the mitogen-activated protein kinase pathway was not activated in any of the tumors as measured by ERK phosphorylation.

CONCLUSIONS

These results show the lack of clinical effectiveness of imatinib in UM, which was originally anticipated based on the high levels of KIT and SCF expression.

The reproductive activity in the testis of Podarcis s. sicula involves D-aspartic acid: a study on c-kit receptor protein, tyrosine kinase activity and PCNA protein during annual sexual cycle

The current study provides substantial evidence that the pattern of synthesis of D-aspartic acid (D-Asp) in the testes of lizard Podarcis s. sicula throughout the reproductive cycle is in parallel with seasonal variations of testosterone, c-kit receptor protein, tyrosine kinase activity, and proliferating cell nuclear antigen (PCNA) protein. Although the trend is the same in all phases of the sexual cycle, the peaks of these three molecules are detectable only during the reproductive period. Using Western blot technique, we demonstrated that both polyclonal c-kit and PCNA antibodies specifically recognized bands with molecular mass of approximately 150 and approximately 36 kDa, respectively. By immunocytochemical methods, D-Asp immunopositivity appeared spread in the germinal epithelium as well as in the interstitial compartment of the testes. We also found specific c-kit labeling in I and II spermatogonia (SPG), in I and II spermatocytes (SPC), in the elongated spermatides, in spermatozoa, in Sertoli and Leydig cells. Like c-kit, PCNA positivity was located in the germinal epithelium pattern. Furthermore, we investigated the relationship between testosterone, c-kit receptor, tyrosine kinases activity and PCNA following treatment with D-Asp. In vivo experiments, entailing a single injection of D-Asp (2.0 micromol/g body weight), demonstrated that this amino acid significantly accumulated in the testes. After 3 h, its uptake was accompanied by an increase in testosterone levels and in the expression and intensity of immunostaining of c-kit receptor protein. Furthermore, at 6 h, exogenous D-Asp affected the phosphorylation of tyrosine kinases, whose activation was positively correlated with the temporal uptake of both D-Asp and testosterone detected in the testes. Thereafter, between 6 and 15 h, the expression of PCNA was induced and an increase in its immunolabeling intensity was observed. Taken all together, these results provide new insights into the testicular activity during the reproductive cycle of Podarcis s. sicula, suggesting that a sequential cascade of a functional relationship between testosterone levels, c-kit receptor protein, tyrosine kinase activity and PCNA could be partly mediated by D-aspartic acid.

The biology and management of uveal melanoma

Uveal melanoma is the most common primary intraocular malignancy in adults. Overall mortality rate remains high because of the frequent development of metastatic disease, especially hepatic metastasis. While traditional systemic chemotherapies provide only marginal benefit to patients, local treatments for hepatic metastases, such as immunoembolization, have improved patient prognoses. Progress has also been made in identifying potential targets in the pathways involved in apoptosis, proliferation, invasion, metastasis, and angiogenesis of uveal melanoma. Among these pathways, the c-Kit, c-Met, and IGF-1R signal pathways and the PTEN-related PI3K-Akt pathway are the most important targets. Clinical trials using blockades of these pathways in conjunction with strategies to facilitate apoptosis is a direction for future clinical trials. Application of these approaches in the adjuvant setting after primary therapy for high-risk uveal melanoma patients is also a future consideration to improve the clinical outcome of this disease.

O-Mel-Inib: a Cancéro-pôle Nord-Ouest multicenter phase II trial of high-dose imatinib mesylate in metastatic uveal melanoma

BACKGROUND

Nowadays, there is no consensual and effective treatment in metastatic uveal melanoma (MUM). Numerous preclinical data (for example, 75% of MUM express c-kit) suggest that imatinib mesylate (IM) may be a potential treatment of UMM.

METHODS

The primary objective of this phase II trial was to determine the non-progression rate at 3 months for patients receiving IM at dose of 400 mg twice per day orally. The study was based on a Simon's optimal design, which allows entry a total of 29 patients, if at least two non-progressions among ten first patients were observed.

RESULT

Thirteen patients including ten assessable patients were enrolled in 12 months. No objective response and only one stable disease with duration of 5 months were noted. Five and one out of 13 enrolled patients experienced grade 3 and grade 4 toxicities, respectively. The most common severe adverse events were abdominal pain. The overall survival was 10.8 months.

CONCLUSIONS

Despite promising preclinical data, IM is an inactive single agent in MUM. This phase II clinical trial has been stopped at the first step.

Targeted therapy for uveal melanoma

Uveal melanoma is the most common primary intra-ocular malignancy in adults. Overall mortality rate remains high because of the development of metastatic disease, which is highly resistant to systemic therapy. Improved understanding of the molecular pathogenesis of cancers has led to a new generation of therapeutic agents that interfere with a specific pathway critical in tumor development or progression. Although no specific genes have been linked to the pathogenesis of uveal melanoma, which differs from that of cutaneous melanoma, progress has been made in identifying potential targets involved in uveal melanoma apoptosis, proliferation, invasion, metastasis, and angiogenesis. This review focuses on the prospects for improving the systemic therapy of uveal melanoma using molecularly targeted agents that are currently in clinical use as well as agents being tested in clinical trials. Preclinical studies suggest potential benefit of inhibitors of Bcl-2, ubiquitin-proteasome, histone deactylase, mitogen-activated protein kinase and phosphatidylinositol-3-kinase-AKT pathways, and receptor tyrosine kinases. Modifiers of adhesion molecules, matrix metalloproteinase, and angiogenic factors also have demonstrated potential benefit. Clinical trials of some of these approaches have been initiated in patients with metastatic uveal melanoma as well as in the adjuvant setting after primary therapy.

KIT (CD117): a review on expression in normal and neoplastic tissues, and mutations and their clinicopathologic correlation

CD117 (KIT) is a type III receptor tyrosine kinase operating in cell signal transduction in several cell types. Normally KIT is activated (phosphorylated) by binding of its ligand, the stem cell factor. This leads to a phosphorylation cascade ultimately activating various transcription factors in different cell types. Such activation regulates apoptosis, cell differentiation, proliferation, chemotaxis, and cell adhesion. KIT-dependent cell types include mast cells, some hematopoietic stem cells, germ cells, melanocytes, and Cajal cells of the gastrointestinal tract, and neoplasms of these cells are examples of KIT-positive tumors. Other KIT-positive normal cells include epithelial cells in skin adnexa, breast, and subsets of cerebellar neurons. KIT positivity has been variably reported in sarcomas such as angiosarcoma, Ewing sarcoma, synovial sarcoma, leiomyosarcoma, and MFH; results of the last three are controversial. The variations in published data may result from incomplete specificity of some polyclonal antibodies, possibly contributed by too high dilutions. Also, KIT is expressed in pulmonary and other small cell carcinomas, adenoid cystic carcinoma, renal chromophobe carcinoma, thymic, and some ovarian and few breast carcinomas. A good KIT antibody reacts with known KIT positive cells, and smooth muscle cells and fibroblasts are negative. KIT deficiency due to hereditary nonsense/missense mutations leads to disruption of KIT-dependent functions such as erythropoiesis, skin pigmentation, fertility, and gastrointestinal motility. Conversely, pathologic activation of KIT through gain-of-function mutations leads to neoplasia of KIT-dependent and KIT-positive cell types at least in three different systems: mast cells/myeloid cells--mastocytosis/acute myeloid leukemia, germ cells--seminoma, and Cajal cells--gastrointestinal stromal tumors (GISTs). KIT tyrosine kinase inhibitors such as imatinib mesylate are the generally accepted treatment of metastatic GISTs, and their availability has prompted an active search for other treatment targets among KIT-positive tumors such as myeloid leukemias and small cell carcinoma of the lung, with variable and often nonconvincing results.

The role of c-kit and imatinib mesylate in uveal melanoma

Background

Uveal melanoma (UM) is the most common primary intraocular tumor in adults, leading to metastasis in 40% of the cases and ultimately to death in 10 years, despite local and/or systemic treatment. The c-kit protein (CD117) is a membrane-bound tyrosine kinase receptor and its overexpression has been observed in several neoplasms. Imatinib mesylate is a FDA approved compound that inhibits tyrosine quinase receptors, as well as c-kit. Imatinib mesylate controls tumor growth in up to 85% of advanced gastrointestinal stromal tumors, a neoplasia resistant to conventional therapy.

Methods

Fifty-five specimens of primary UM selected from the archives of the Ocular Pathology Laboratory, McGill University, Montreal, Canada, were immunostained for c-kit. All cells displaying distinct immunoreactivity were considered positive. Four human UM cell lines and 1 human uveal transformed melanocyte cell line were tested for in vitro proliferation Assays (TOX-6) and invasion assay with imatinib mesylate (concentration of 10 μM).

Results

The c-kit expression was positive in 78.2% of the UM. There was a statistical significant decrease in the proliferation and invasion rates of all 5 cell lines.

Conclusion

The majority of UM expressed c-kit, and imatinib mesylate does decrease the proliferation and invasion rates of human UM cell lines. These results justify the need for a clinical trial to investigate in vivo the response of UM to imatinib mesylate.

Les mélanocytes choroïdiens normaux et malins : de la cellule à la clinique

The molecular and cellular basis of human choroidal malignant melanoma progression has remained largely unknown. However, choroidal melanoma is the most important primary intraocular tumor in adults. Developmentally, choroidal melanocytes are of neural crest origin similar to cutaneous melanocytes. However, there are some significant differences between cutaneous and uveal melanocytes that have yet to be fully assessed. The purpose of this study is to describe choroidal melanocytes. We will describe the significant differences between cutaneous and uveal melanocytes as well as the congenital and acquired diseases of uveal melanocytes. We will then describe the cellular and molecular mechanisms involved in melanoma progression.

Normal and Oncogenic Forms of the Receptor Tyrosine Kinase Kit

Kit is a receptor tyrosine kinase (RTK) that binds stem cell factor. This receptor ligand combination is important for normal hematopoiesis, as well as pigmentation, gut function, and reproduction. Structurally, Kit has both an extracellular and intracellular region. Theintra-cellular region is comprised of a juxtamembrane domain (JMD), a kinase domain, a kinase insert, and a carboxyl tail. Inappropriate expression or activation of Kit is associated with a variety of diseases in humans. Activating mutations in Kit have been identified primarily in the JMD and the second part of the kinase domain and have been associated with gastrointestinal stromal cell tumors and mastocytosis, respectively. There are also reports of activating mutations in some forms of germ cell tumors and core binding factor leukemias. Since the cloning of the Kit ligand in the early 1990s, there has been an explosion of information relating to the mechanism of action of normal forms of Kit as well as activated mutants. This is important because understanding this RTK at the biochemical level could assist in the development of therapeutics to treat primary and secondary defects in the tissues that require Kit. Furthermore, understanding the mechanisms mediating transformation of cells by activated Kit mutants will help in the design of interventions for human disease associated with these mutations. The objective of this review is to summarize what is known about normal and oncogenic forms of Kit. We will place particular emphasis on recent developments in understanding the mechanisms of action of normal and activated forms of this RTK and its association with human disease, particularly in hematopoietic cells.

Roles of stem cell factor/c-Kit and effects of Glivec/STI571 in human uveal melanoma cell tumorigenesis

The B-Raf(V599E)-mediated constitutive activation of ERK1/2 is involved in establishing the transformed phenotype of some uveal melanoma cells (Calipel, A., Lefevre, G., Pouponnot, C., Mouriaux, F., Eychene, A., and Mascarelli, F. (2003) J. Biol. Chem. 278, 42409-42418). We have shown that stem cell factor (SCF) is involved in the proliferation of normal uveal melanocytes and that c-Kit is expressed in 75% of primary uveal melanomas. This suggests that the acquisition of autonomous growth during melanoma progression may involve the SCF/c-Kit axis. We used six human uveal melanoma tumor-derived cell lines and normal uveal melanocytes to characterize the SCF/c-Kit system and to assess its specific role in transformation. We investigated the possible roles of activating mutations in c-KIT, the overexpression of this gene, and ligand-dependent c-Kit overactivation in uveal melanoma cell tumorigenesis. Four cell lines (92.1, SP6.5, Mel270, and TP31) expressed both SCF and c-Kit, and none harbored the c-KIT mutations in exons 9, 11, 13, and 17 that have been shown to induce SCF-independent c-Kit activation. Melanoma cell proliferation was strongly inhibited by small interfering RNA-mediated depletion of c-Kit in these cells, despite the presence of (V599E)B-Raf in SP6.5 and TP31 cells. We characterized the signaling pathways involved in SCF/c-Kit-mediated cell growth and survival in normal and tumoral melanocytes and found that constitutive ERK1/2 activation played a key role in both the SCF/c-Kit autocrine loop and the gain of function of (V599E)B-Raf for melanoma cell proliferation and transformation. We also provide the first evidence that Glivec/STI571, a c-Kit tyrosine kinase inhibitor, could be used to treat uveal melanomas.