Molecularly targeted therapy for melanoma

Histopathological evaluation of cutaneous malignant melanoma: A retrospective study

Malignant melanoma is a melanocytic neoplasm with a steadily increasing incidence worldwide. In order to define a proper diagnostic protocol and to establish an accurate prognostic method for the disease, specific biomarkers are of notable importance. Their contribution is also significant in the treatment of melanoma for the improvement of newer and more targeted therapeutic approaches. To emphasize the importance of specific immune markers in the diagnosis of melanoma, immunohistochemical analysis was performed on 56 formalin-fixed paraffin-embedded cutaneous melanomas. Besides the traditional prognostic factors, depth of invasion and mitotic rate, the markers tested in the present study were S100 protein family, Melan A, Ki67 and HMB-45. The present results indicated that immunocytochemistry represents a valuable test in the diagnosis and treatment of malignant melanoma and each biomarker had different associations with the progression and prognosis of the disease. Patients with S100 expression were 4.83 times (95% CI=1.2-20.8) more likely to suffer a relapse, whereas patients with a Ki67 expression of >30% had a 5.41-fold higher risk (95% CI=1.3-22.0). The correlation between S100 and the Breslow depth was statistically significant (r-value: 0.43; P=0.027). In addition, the importance of a multidisciplinary team including a plastic surgeon, anatomopathologist and oncologist was highlighted.

Barriers to Effective Drug Treatment for Brain Metastases: A Multifactorial Problem in the Delivery of Precision Medicine

The treatment of metastatic lesions in the brain represents a serious unmet medical need in the field of neuro-oncology. Even though many effective compounds have demonstrated success in treating peripheral (non-CNS) tumors with targeted agents, one aspect of this lack of success in the brain may be related to poor delivery of otherwise effective compounds. Many factors can influence the brain delivery of these agents, but one key barrier is a heterogeneously "leaky" BBB that expresses efflux transporters that limit the BBB permeability for many targeted agents. Future success in therapeutics for brain metastases must take into account the adequate delivery of "active, free drug" to the target, and may include combinations of targeted drugs that are appropriate to address each individual patient's tumor type. This review discusses some issues that are pertinent to precision medicine for brain metastases, using specific examples of tumor types that have a high incidence of brain metastases.

Inhibition of Cell Proliferation in an NRAS Mutant Melanoma Cell Line by Combining Sorafenib and α-Mangostin

α-Mangostin is a natural product commonly used in Asia for cosmetic and medicinal applications including topical treatment of acne and skin cancer. Towards finding new pharmacological strategies that overcome NRAS mutant melanoma, we performed a cell proliferation-based combination screen using a collection of well-characterized small molecule kinase inhibitors and α-Mangostin. We found that α-Mangostin significantly enhances Sorafenib pharmacological efficacy against an NRAS mutant melanoma cell line. The synergistic effects of α-Mangostin and Sorafenib were associated with enhanced inhibition of activated AKT and ERK, induced ER stress, and reduced autophagy, eventually leading to apoptosis. The structure of α-Mangostin resembles several inhibitors of the Retinoid X receptor (RXR). MITF expression, which is regulated by RXR, was modulated by α-Mangostin. Molecular docking revealed that α-Mangostin can be accommodated by the ligand binding pocket of RXR and may thereby compete with RXR-mediated control of MITF expression. In summary, these data demonstrate an unanticipated synergy between α-Mangostin and sorafenib, with mechanistic actions that convert a known safe natural product to a candidate combinatorial therapeutic agent.

Obesity and melanoma: exploring molecular links

Obesity is now a major health problem due to its rapidly increasing incidence worldwide and severe consequences. Among many conditions associated with obesity are some cancers including melanoma. Both genetic defects and environmental risk factors are involved in the carcinogenesis of melanoma. Activation of multiple signal pathways such as the PI3K/Akt and MAPK pathways are necessary for the initiation of melanoma. Activation of the MAPK pathway as a result of activating mutations in BRAF is commonly seen in melanoma though it alone is not sufficient to cause malignant transformation of melanocytes. Obesity can result in the activation of many signal pathways including PI3K/Akt, MAPK, and STAT3. The activation of these pathways may have a synergistic effect with the genetic defects thereby increasing the incidence of melanoma.

The dietary terpene lupeol targets colorectal cancer cells with constitutively active Wnt/β-catenin signaling

SCOPE

Aberrant activation of the Wingless-type mouse mammary tumor virus integration site family (Wnt)/β-catenin signaling pathway is the most common modification, and often considered, a hallmark of colorectal cancer (CRC). Typically in this pathway the β-catenin translocates from the cytoplasm to the nucleus, where it functions as a transcription regulator of several genes that support tumor formation and progression. Thus, any agent that could attenuate the translocation of β-catenin could be extremely valuable against CRC, especially the tumors that exhibit constitutively active Wnt/β-catenin signaling.

METHODS AND RESULTS

Using human CRC cells that exhibit differential expression of Wnt/β-catenin signaling, we demonstrate that treatment of CRC cells with dietary triterpene lupeol results in a dose-dependent (i) decrease in cell viability, (ii) induction of apoptosis, (iii) decrease in colonogenic potential, (iv) decrease in β-catenin transcriptional activity, and (v) decrease in the expression of Wnt target genes. Most importantly lupeol was observed to inhibit the translocation of β-catenin from the cytoplasm to the nucleus. Importantly, all these effects of lupeol were restricted to cells that harbor constitutively active Wnt/β-catenin signaling while negligible effects were observed in cells that lack constitutively active Wnt/β-catenin signaling. Further, we also demonstrate that inhibition of Wnt signaling in cells with constitutive active Wnt/β-catenin results in loss of lupeol efficacy while inducing Wnt signaling sensitizes the cells to inhibitory effects of lupeol.

CONCLUSION

In summary, our data strongly advocate the efficacy of lupeol against CRC cells that exhibit constitutively active Wnt/β-catenin signaling.

A high proliferative index of recurrent melanoma is associated with worse survival

OBJECTIVE

Previous melanoma studies evaluating prognostic factors of survival at recurrence have focused on primary tumor characteristics and clinical variables at first recurrence. We examined the prognostic relevance of recurrent tumor proliferation.

METHODS

114 melanoma patients with available recurrent tissues who were prospectively enrolled at New York University Medical Center were studied. Standard of care prognostic variables (e.g. stage at initial diagnosis and lactate dehydrogenase level) and recurrent tissue expression of proliferative marker Ki-67 were evaluated for their association with overall survival.

RESULTS

High Ki-67 expression was observed in 57 (50%) of the 114 recurrent melanomas. On univariate analysis, the median overall survival of patients whose recurrent tumors overexpressed Ki-67 was significantly shorter than that of patients whose recurrent tumors had low Ki-67 expression (3.6 vs. 9.5 years, p = 0.03). On multivariate analysis, a high proliferative index of the recurrent melanoma remained an independent predictor of worse overall survival, controlling for stage at initial diagnosis, disease-free survival, and stage at first recurrence [HR = 2.09 (95% CI 1.24-3.54), p = 0.006].

CONCLUSIONS

Our results demonstrate the prognostic relevance of tumor proliferation in recurrent melanoma patients. Data also support restratification of risk assessment upon recurrence that considers tumor biology in addition to clinical variables evaluated as part of the standard of care.

Specific targeting of Wnt/β-catenin signaling in human melanoma cells by a dietary triterpene lupeol

Wingless (Wnt) signaling pathway regulates a variety of cellular processes including proliferation, differentiation, survival, apoptosis and cell motility. Aberrant activation of Wnt/β-catenin pathway has been observed in approximately one-third of melanomas and this subset has very poor prognosis suggesting that targeting Wnt signaling could be a promising strategy against this subtype. Mel 928 and Mel 1241 melanoma cells representative of cells with constitutive activation of Wnt/β-catenin signaling pathway and Mel 1011 representative of cells that lack this pathway were treated with a dietary triterpene lupeol and its effects on growth, proliferation, β-catenin transcriptional activity and Wnt target genes were determined both in vitro and in vivo. Lupeol treatment to Mel 928 and Mel 1241 but not Mel 1011 cells resulted in a dose-dependent (i) decrease in cell viability, (ii) induction of apoptosis, (iii) decrease in colonogenic potential, (iv) decrease in β-catenin transcriptional activity and (v) decrease in the expression of Wnt target genes. Most importantly, lupeol restricted the translocation of β-catenin from the cytoplasm to the nucleus. Lupeol also decreased the growth of Mel 928 but not Mel 1011-derived tumors implanted in the athymic nude mice. The decrease in Mel 928-derived tumor growth was associated with a decrease in the expression of Wnt target genes c-myc, cyclin D1, proliferation markers proliferating cell nuclear antigen and Ki-67 and invasion marker osteopontin. We suggest that lupeol alone or as an adjuvant to current therapies could be developed as an agent for the management of human melanomas harboring constitutive Wnt/β-catenin signaling.

MicroRNA-15b represents an independent prognostic parameter and is correlated with tumor cell proliferation and apoptosis in malignant melanoma

MicroRNAs (miRNAs) are small noncoding RNAs ( approximately 22 bp) that posttranscriptionally regulate gene expression. MiRNAs possess oncogenic or tumor suppressor activity in various tumors but little is known about miRNA expression pattern in malignant melanoma. We determined the expression level of 16 potentially relevant miRNAs (miR-15a, miR-15b, miR-16, miR-34a, miR-210, let-7I, miR-23a, miR-23b, miR-24, miR-27a, miR-27b, miR-100, miR-137, miR-222, miR-373-1, miR-373*) by real-time PCR in 6 preparations of normal melanocytes vs. 10 melanoma cell lines and in formalin fixed paraffin embedded tissue of 11 melanocytic nevi versus 16 melanomas. MiR-15b and miR-210 were significantly upregulated, miR-34a was significantly downregulated in melanomas compared with melanocytic nevi. These 3 miRNAs were analyzed in a total of 128 primary melanomas from patients with detailed clinical follow-up information. High expression of miR-15b (but not miR-210 upregulation and miR-34a downregulation) was significantly associated with poor recurrence free survival and overall survival by univariate Kaplan-Meier and multivariate Cox analyses. Downregulation of miR-15b in two melanoma cell lines with high miR-15b expression by transfection with anti-miR-15b siRNA was associated with reduced tumor cell proliferation, whereas apoptosis was increased. In summary, miRNA expression levels show distinct differences comparing benign and malignant melanocytic cell proliferations and can provide independent prognostic informations. MiR-15b appears to represent a particular important miRNA in melanoma that is associated with poor prognosis and tumorigenesis.

Targeted cancer therapies in the twenty-first century: lessons from imatinib

An increased understanding of the molecular etiology of cancer has enabled the development of novel therapies that are collectively referred to as molecular targeted agents. Unlike the drugs used in conventional chemotherapy, these agents are designed to specifically interfere with key molecular events that are responsible for the malignant phenotype. They hold great promise for widening the therapeutic window, which would provide more effective treatment options as compared with cytotoxic therapies. In addition, the targeted approach that is characteristic of these drugs provides unique opportunities for combination therapies with other anticancer agents that have non-overlapping toxicities. Targeted agents are therefore primed to become invaluable therapeutic tools in the multimodal treatment of cancer. The challenges associated with these novel targeted therapies are distinct from those faced in conventional chemotherapy. These unique challenges include the need to select appropriate pharmacodynamic markers to guide dose and schedule and to identify biomarkers that enable selection of patient populations that are most likely to benefit from the treatment. In addition, although the emergence of resistance to targeted therapies is a problem frequently faced in the clinic, the molecular characterization of resistance mechanisms provides the opportunity to design second-generation therapies or combination therapies aimed at preventing resistance or restoring response. The development of the tyrosine kinase inhibitor imatinib has revolutionized the treatment of chronic myeloid leukemia (CML). In this article, we discuss the lessons learned from the application of imatinib and other targeted agents in clinical practice and discuss how these insights may guide the development of novel targeted therapies.

The dual PI3K/mTOR inhibitor PI-103 promotes immunosuppression, in vivo tumor growth and increases survival of sorafenib-treated melanoma cells

Melanoma is the most lethal human skin cancer. If metastatic, it becomes very aggressive and resistant to standard modalities of anticancer treatment. During the last 10 years, several therapeutic strategies have been tested including the use of single and combined small drugs. Experimental results indicate that RAS and PI3K pathways are important for the development and maintenance of melanoma. In this study, we assessed the in vitro and in vivo inhibition potential of PI-103, a PI3K (p110alpha)/mTOR inhibitor and sorafenib, a BRAF inhibitor, as single agents and in combination in primary melanoma cell lines. Although PI-103 and sorafenib inhibited melanoma in vitro cell proliferation and viability, the inhibition of RAS pathway appeared to be more effective. The combination of the two agents in in vitro showed a synergistic effect inhibiting RAS and PI3K pathways in a cell line dependent manner. However, no cooperative effect was observed in blocking in vivo tumor growth in immunocompetent mice. In contrary to the expected, the data indicate that PI-103 induced immunosuppression promoting in vivo tumor growth and inhibiting apoptosis. Furthermore, in vitro studies examining the effects of the PI3K/mTOR inhibitor in tumor derived cell lines indicated that PI-103 induced the anti-apoptotic BH3 family proteins Mcl1, Bcl2 and Bcl(xL) favoring, the in vitro survival of sorafenib treated melanoma cells. These data certainly makes an argument for investigating unexpected effects of rational drug combinations on immunocompetent animal models prior to conducting clinical studies.

Biochemical mechanism of acetylsalicylic acid (Aspirin) selective toxicity toward melanoma cell lines

In the current work, we investigated the biochemical toxicity of acetylsalicylic acid (ASA; Aspirin) in human melanoma cell lines using tyrosinase enzyme as a molecular cancer therapeutic target. At 2 h, ASA was oxidized 88% by tyrosinase. Ascorbic acid and NADH, quinone reducing agents, were significantly depleted during the enzymatic oxidation of ASA by tyrosinase to quinone. The 50% inhibitory concentration (48 h) of ASA and salicylic acid toward SK-MEL-28 cells were 100 micromol/l and 5.2 mmol/l, respectively. ASA at 100 micromol/l was selectively toxic toward human melanocytic SK-MEL-28, MeWo, and SK-MEL-5 and murine melanocytic B16-F0 and B16-F10 melanoma cell lines. However, ASA was not significantly toxic to human amelanotic C32 melanoma cell line, which does not express tyrosinase enzyme, and human nonmelanoma BJ, SW-620, Saos, and PC-3 cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased ASA toxicity toward SK-MEL-28 cells indicating quinone formation and intracellular GSH depletion played important mechanistic roles in ASA-induced melanoma toxicity. Ascorbic acid, a quinone reducing agent, and GSH, an antioxidant and quinone trap substrate, prevented ASA cell toxicity. Trifluoperazine, inhibitor of permeability transition pore in mitochondria, prevented ASA toxicity. ASA led to significant intracellular GSH depletion in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ASA also led to significant reactive oxygen species (ROS) formation in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ROS formation was exacerbated by dicoumarol and 1-bromoheptane in SK-MEL-28. Our investigation suggests that quinone species, intracellular GSH depletion, ROS formation, and mitochondrial toxicity significantly contributed toward ASA selective toxicity in melanocytic SK-MEL-28 melanoma cells.

Development of vitiligo during melanoma treatment with a novel survivin inhibitor: a case report and review of the literature

BACKGROUND

The development of vitiligo has been associated with an improved clinical response in melanoma patients.

METHODS

We report a case of vitiligo associated with a novel antisurvivin drug and review the literature to determine the pathogenesis of vitiligo occurring during melanoma treatment.

RESULTS

A 78-year-old man with stage IV malignant melanoma developed vitiligo after the first therapeutic cycle of a novel antisurvivin drug. Although his vitiligo remained static, his melanoma continued to progress and he died in 8 months. A review of the literature demonstrates a relationship between vitiligo development and improved clinical response in many melanoma cases treated with immunotherapy; however, the relationship may depend on the type of treatment.

CONCLUSIONS

Understanding complex immune responses in vitiliginous skin and melanoma sites is important in order to interpret the development of vitiligo occurring during melanoma treatment.

Epigenetics and dermatological disease

Epigenetics is the study of differences in phenotype, in the absence of variation in the genetic code. Epigenetics is relevant in the pathogenesis of many skin diseases. In the case of the common skin cancers, aberrant methylation of tumor suppressor gene promoters is associated with their transcriptional inactivation. Environmental carcinogens such as ultraviolet radiation and arsenic may act through epigenetic mechanisms. Hypomethylation is associated with activation of systemic autoimmune diseases, such as systemic lupus erythematosus, subacute cutaneous lupus erythematosus and scleroderma. This may be through a mechanism of immunological cross-reactivity with hypomethylated DNA from pathogenic bacteria. Epigenetic factors may also be relevant in the pathogenesis of psoriasis and other inflammatory skin diseases, as well as in the pathogenesis of the disorders of genomic imprinting with cutaneous features.

MAPK-independent impairment of T-cell responses by the multikinase inhibitor sorafenib

Sorafenib, originally developed as CRAF inhibitor but soon recognized as a multikinase inhibitor, is currently widely tested for the treatment of different cancers either alone or in combination therapy. However, the clinical success, particularly in immunogenic tumors such as melanoma, was less than anticipated. Because T-cell activation is tightly regulated by a multitude of kinases, we scrutinized effects of sorafenib on immune responses. To this end, comprehensive in vitro studies revealed that the presence of sorafenib concentrations comparable with observed plasma levels in patients strongly impairs the activation of T cells. Notably, even established tumor-specific immune responses are influenced by sorafenib. Indeed, ELISPOT data of peripheral blood lymphocytes obtained from melanoma patients vaccinated against survivin show markedly diminished survivin-specific immune responses in the presence of sorafenib. Surprisingly, inhibition of T-cell activation was not associated with reduced extracellular signal-regulated kinase phosphorylation. In fact, on T-cell receptor stimulation phospho-extracellular signal-regulated kinase and phospho-mitogen-activated protein kinase kinase levels were found to be elevated in the presence of sorafenib, showing the complexity of signal transduction events following T-cell receptor stimulation. In conclusion, our data show that T-cell function is sensitive toward the multikinase inhibitor sorafenib in a mitogen-activated protein kinase-independent fashion. This observation has important implications for the use of sorafenib as therapy for immunogenic cancers.

Antibody-mediated delivery of interleukin-2 to the stroma of breast cancer strongly enhances the potency of chemotherapy

PURPOSE

There is an interest in the discovery of biopharmaceuticals, which are well tolerated and which potentiate the action of anthracyclines and taxanes in breast cancer therapy.

EXPERIMENTAL DESIGN

We have produced a recombinant fusion protein, composed of the human antibody fragment scFv(F16) fused to human interleukin-2 (F16-IL2), and tested its therapeutic performance in the MDA-MB-231 xenograft model of human breast cancer. The F16 antibody is specific to the alternatively spliced A1 domain of tenascin-C, which is virtually undetectable in normal tissues but is strongly expressed in the neovasculature and stroma of breast cancer.

RESULTS

When used as monotherapy, F16-IL2 displayed a strikingly superior therapeutic benefit compared with unconjugated recombinant IL-2. The administration of doxorubicin either before (8 days, 24 h, or 2 h) or simultaneously with the injection of F16-IL2 did not decrease the accumulation of immunocytokine in the tumor as measured by quantitative biodistribution analysis. Therapy experiments, featuring five once per week coadministrations of 20 mug F16-IL2 and doxorubicin, showed a statistically significant reduction of tumor growth rate and prolongation of survival at a 4 mg/kg doxorubicin dose but not at a 1 mg/kg dose. By contrast, combination of F16-IL2 with paclitaxel (5 and 1 mg/kg) exhibited a significant therapeutic benefit compared with paclitaxel alone at both dose levels. F16-IL2, alone or in combination with doxorubicin, was well tolerated in cynomolgus monkeys at doses equivalent to the ones now used in clinical studies.

CONCLUSIONS

F16-IL2 may represent a new useful biopharmaceutical for the treatment of breast cancer.

Targeting hypoxia-inducible factor-1alpha with Tf-PEI-shRNA complex via transferrin receptor-mediated endocytosis inhibits melanoma growth

Malignant melanoma (MM) is a major public health problem. The development of effective, systemic therapies for MM is highly desired. We showed here that the transferrin receptor (TfR) was a suitable surface marker for targeting of gene therapy in MM and that the hypoxia-inducible factor-1alpha (HIF-1alpha) was an attractive therapeutic molecular target in MM. We observed that inhibition of HIF-1alpha blocked cell proliferation and induced cell apoptosis in vitro. We then showed that a transferrin-polyethylenimine-HIF-1alpha-short-hairpin RNA (Tf-PEI-HIF-1alpha-shRNA) complex could target MM specifically and efficiently both in vivo and in vitro, exploiting the high expression of the TfR in MM. The systemic delivery of sequence-specific small-interfering RNA (siRNA) against HIF-1alpha by the Tf- PEI-HIF-1alpha-shRNA complex dramatically inhibited tumor growth in the A375 MM xenograft model. The underlying concept of transfecting a HIF-1alpha shRNA expression vector complexed with Tf-PEI to block HIF-1alpha holds promise as a clinical approach to gene therapy for MM.

Shedding of distinct cryptic collagen epitope (HU177) in sera of melanoma patients

PURPOSE

Extracellular matrix remodeling during tumor growth plays an important role in angiogenesis. Our preclinical data suggest that a newly identified cryptic epitope (HU177) within collagen type IV regulates endothelial and melanoma cell adhesion in vitro and angiogenesis in vivo. In this study, we investigated the clinical relevance of HUI77 shedding in melanoma patient sera.

EXPERIMENTAL DESIGN

Serum samples from 291 melanoma patients prospectively enrolled at the New York University Medical Center and 106 control subjects were analyzed for HU177 epitope concentration by a newly developed sandwich ELISA assay. HU177 serum levels were then correlated with clinical and pathologic parameters.

RESULTS

Mean HU177 epitope concentration was 5.8 ng/mL (range, 0-139.8 ng/mL). A significant correlation was observed between HU177 concentration and nodular melanoma histologic subtype [nodular, 10.3 +/- 1.6 ng/mL (mean +/- SE); superficial spreading melanoma, 4.5 +/- 1.1 ng/mL; all others, 6.1 +/- 2.1 ng/mL; P = 0.01 by ANOVA test]. Increased HU177 shedding also correlated with tumor thickness (< or =1.00 mm, 3.8 +/- 1.1 ng/mL; 1.01-3.99 mm, 8.7 +/- 1.3 ng/mL; > or =4.00 mm, 10.3 +/- 2.4 ng/mL; P = 0.003 by ANOVA). After multivariate analysis controlling for thickness, the correlation between higher HU177 concentration and nodular subtype remained significant (P = 0.03). The mean HU177 epitope concentration in control subjects was 2.4 ng/mL.

CONCLUSIONS

We report that primary melanoma can induce detectable changes in systemic levels of cryptic epitope shedding. Our data also support that nodular melanoma might be biologically distinct compared with superficial spreading type melanoma. As targeted interventions against cryptic collagen epitopes are currently undergoing phase I clinical trial testing, these findings indicate that patients with nodular melanoma may be more susceptible to such targeted therapies.

A novel transport and delivery mechanism underpins the effectiveness of prolyl-m-sarcolysyl-p-fluorophenylalanine (PSF) in a human melanoma xenograft nude-mouse model

The alkylating peptide PSF shows very promising results in vitro on different cancer cells but its efficacy in animals has not been assessed. Here we evaluate the efficacy of PSF in human melanoma-bearing nude mice and examine the underlying mechanism. In melanoma-bearing nude mice, escalating doses of PSF showed dose-dependent responses and reached tumor regression with an optimal dose of 20 mg/kg for 1 month. A comparison of PSF with its free moiety m-sarcolysin and melphalan showed a highly significant advantage of PSF. Furthermore, dose fractionation yielded an even better control of tumor regrowth. In vitro studies unraveled an original delivery mechanism based on the rapid binding of PSF mainly due to red blood cells to form a pro-drug complex and the subsequent release of active metabolites by tumor-associated proteolytic enzymes. Blood kinetics showed one major metabolite partially released over time, while in the presence of melanoma cells three additional metabolites are generated. Interestingly, tumor-shed proteases also induce the production of these metabolites and varying combinations of enzyme inhibitors indicate the involvement of metallo- and other families of proteases in the delivery process. This particular transport and delivery of such an alkylating agent may have several benefits, mainly lowering the drug-free moiety in plasma and at the same time increasing its concentration in protease rich areas such as tumors.

Targeting lipid rafts inhibits protein kinase B by disrupting calcium homeostasis and attenuates malignant properties of melanoma cells

Failure of current therapeutic modalities to treat melanoma remains a challenge for clinical and experimental oncology. The aggressive growth and apoptotic resistance of this tumor are mediated, in part, by aberrantly activated protein kinase B/Akt (PKB). In many cells, PKB signaling depends on integrity of cholesterol-enriched membrane microdomains (rafts). However, it is still unclear if rafts support deregulated PKB activity in melanoma. In this study, ablation of rafts in murine (B16BL6-8, JB/RH1) and human (GA) melanoma lines by cholesterol-chelating methyl-beta-cyclodextrin (MbetaCD) reduced levels of constitutively active PKB in a dose- and time-dependent manner, while reconstitution of microdomains restored PKB activity. PKB was sensitive to the membrane-permeable Ca2+ chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid tetra (acetocymethyl) ester and to the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide (W7) implying the contribution of Ca2+ signaling to PKB deregulation. Indeed, malignant and apoptosis-resistant clone of B16BL6 melanoma (B16BL6-8) displayed significantly higher [Ca2+](i) and store-operated Ca2+ influx (SOC) relative to non-malignant apoptosis-sensitive B16BL6 clone (Kb30) expressing barely detectable basal levels of active PKB. Raft ablation in B16BL6-8 cells robustly inhibited SOC and decreased [Ca2+](i) to levels comparable with those detected in Kb30 cells. Treating cells by PKB-inhibiting doses of M beta CD dramatically impaired their apoptotic resistance and capacity to generate tumors. Furthermore, weekly intraperitoneal injections of M beta CD to mice grafted with melanoma cells at doses of 300 and 800 mg/kg significantly attenuated tumor development. Our data implicate membrane rafts in enhancing the resistance of melanoma to apoptosis and indicate that targeting raft microdomains is a potentially effective strategy to cure this frequently fatal form of cancer.

[Experimental treatment of malignant melanoma and its rationale]

To treat malignant melanoma successfully currently means to recognize the tumor at an early stage and to remove it immediately. Aside from individual cases, available treatment modalities are not able to increase survival, especially in the palliative situation. Thus innovative experimental approaches are urgently needed to strongly improve the palliative and adjuvant treatment of melanoma. Anti-tumor effects are expected from targeted therapies, which are directed against defined molecules decisive for tumor pathogenesis. Crucial points of attack are signaling pathways, angiogenesis and apoptosis resistance. New diagnostic and therapeutic developments have enhanced the efficacy of chemotherapies. Increasing insights into tumor immunology provide new treatment approaches of vaccination, cell transfer and especially of blocking immune tolerance mechanisms. It will be challenging for the future to identify and characterize more precisely those patients who might most benefit from a certain treatment approach.

Treatment of melanoma and nonmelanoma skin cancer

The incidence of skin cancer is increasing in Caucasian populations worldwide. Treatment approaches for Nonmelanoma skin cancer (NMSC) are predominantly curative and surgery can be regarded as standard of care. Nevertheless, novel and less invasive topical therapy modalities like photodynamic therapy or local immune modifiers are in progress. In contrast to NMSC, the mortality of melanoma has not changed considerably over the last years and decades. Melanoma survival mainly depends on primary tumor thickness underlining the importance of primary and secondary prevention by avoidance or early detection of the disease. The chance to cure melanoma patients is steadily decreasing with tumor stage. As the prognosis in distant metastatic disease is still poor, except for single situations therapy approaches are palliative and accompanied by an optimal supportive care of the patients concerned. Albeit removal of localized metastases is currently the most effective approach in metastatic melanoma, chemo- and chemoimmunotherapy has to be regarded as standard treatment in most of the cases. Novel and promising therapeutic options accrue from growing insights in tumor biology and immunology. Not only in melanoma, development and application of targeted therapies currently attract the most attention in the treatment of advanced tumors. First clinical experiences with those antiproliferative, antiangiogenic and proapoptotic agents reveal only moderate antitumoral activity in melanoma, so that future efforts aim at defining more effective combination strategies using chemo-, targeted and vaccination therapy approaches.

Phospho-ERK staining is a poor indicator of the mutational status of BRAF and NRAS in human melanoma

Mutated BRAF and NRAS are suspected to contribute to melanomagenesis by activation of extracellular signal-regulated kinase (ERK). To test this notion, we analyzed the presence of phosphorylated ERK1/2 in 170 melanomas with established NRAS/BRAF mutational status and well-documented clinical follow-up by immunohistochemistry. Several notable observations were obtained: (i) phospho-ERK staining was very heterogeneous within the tumor; (ii) in most cases, ERK was phosphorylated in only a minority of tumor cells; (iii) the percentage of phospho-ERK-positive cells was not correlated with the mutational status of NRAS and/or BRAF; (iv) the Raf kinase inhibitor protein (RKIP) was expressed homogeneously in virtually all melanoma samples not reflecting the inhomogeneity of phospho-ERK; and, finally, (v) neither the portion of phospho-ERK-positive tumor cells nor the RKIP staining intensity showed any correlation to the clinical course of the patients. Furthermore, the ability of BRAF mutant melanoma cells to downregulate mitogen-activated protein kinase activation was shown in melanoma cell lines cultured at high densities or under nonadherent conditions. Our findings suggest that mitogen-activated protein kinase (MAPK) activity is subject to regulation even in BRAF/NRAS mutant melanoma cells and that high MAPK pathway signaling may be important only in distinct subsets of tumor cells.

Apoptosis pathways and oncolytic adenoviral vectors: promising targets and tools to overcome therapy resistance of malignant melanoma

In the last decades melanoma incidence has been increasing worldwide, while mortality remained on a high level. Until now, there is no suitable therapy for metastasized melanoma, which could lead to a significant increase in overall survival. Apoptosis deficiency is supposed to be a critical factor for therapy resistance, and previous work has characterized the basic mechanisms of apoptosis regulation in melanoma. Genes and strategies suitable for efficient induction of apoptosis in melanoma cells were identified, which are based on proapoptotic Bcl-2 proteins (Bcl-x(S), Bcl-x(AK), Bik/Nbk and Bax) as well as on tumor necrosis factor (TNF)-related death ligands (CD95L/Fas ligand and TNF-related apoptosis-inducing ligand, TRAIL). Proapoptotic genes may be employed in improved gene therapeutic strategies, based on conditional oncolytic adenoviral vectors.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.

[Molecular heterogeneity of malignant melanomas]

Malignant melanomas make up a heterogeneous group of tumors characterized by particular genetic aberrations depending on their anatomic localization and UV exposure. Activation of the mitogen-activated protein kinase (MAPK) signaling pathway is found in the majority of melanomas, with either somatic missense mutations of BRAF or, considerably more rarely, mutations of N-RAS. The loss of both products of the CDKN2A gene, proteins p16(ARF) and p14(INK4a), or amplification of microphthalmia-associated transcriptional factor (MITF) are also predisposing factors in the development of melanoma. BRAF mutations are observed mainly in melanomas on skin liable to intermittent UV exposure. Acral and mucosal melanomas, and also melanomas on skin damaged by chronic exposure to the sun are characterized by distinct patterns of chromosomal aberrations with frequent amplifications and alterations of the KIT gene, while BRAF mutations are rarely found in these sites. Uveal melanomas show recurrent chromosomal losses (1p, 3, 6q) and gains (6p, 8q), but mutations of BRAF are hardly ever found. So far, ancillary molecular studies are not regularly applied in the routine diagnostic procedures performed when malignant melanoma is suspected. In the future, however, the development of targeted molecular therapies will require that molecular pathological techniques are used to identify the melanoma patients who will most probably benefit from a particular therapy.

Toxicogenomics of A375 human malignant melanoma cells

Toxicogenomics applications are increasingly applied to the evaluation of preclinical drug safety, and to explain toxicities associated with compounds at the mechanism level. In this review, we aim to describe the application of toxicogenomics tools for studying the genotoxic effect of active compounds on the gene-expression profile of A375 human malignant melanoma cells, through the other molecular functions of target genes, regulatory pathways and mechanisms of malignant melanomas. It also includes the current systems biology approaches, which are very useful for analyzing the biological system and understanding the entire mechanisms of malignant melanomas. We believe that this review would be very potent and useful for studying the toxicogenomics of A375 melanoma cells, and for further diagnostic and therapeutic applications.

B-RAF and N-RAS mutations are preserved during short time in vitro propagation and differentially impact prognosis

In melanoma, the RAS/RAF/MEK/ERK signalling pathway is an area of great interest, because it regulates tumor cell proliferation and survival. A varying mutation rate has been reported for B-RAF and N-RAS, which has been largely attributed to the differential source of tumor DNA analyzed, e.g., fixed tumor tissues or in vitro propagated melanoma cells. Notably, this variation also interfered with interpreting the impact of these mutations on the clinical course of the disease. Consequently, we investigated the mutational profile of B-RAF and N-RAS in biopsies and corresponding cell lines from metastatic tumor lesions of 109 melanoma patients (AJCC stage III/IV), and its respective impact on survival. 97 tissue biopsies and 105 biopsy-derived cell lines were screened for B-RAF and N-RAS mutations by PCR single strand conformation polymorphism and DNA sequencing. Mutations were correlated with patient survival data obtained within a median follow-up time of 31 months. B-RAF mutations were detected in 55% tissues and 51% cell lines, N-RAS mutations in 23% tissues and 25% cell lines, respectively. There was strong concordance between the mutational status of tissues and corresponding cell lines, showing a differing status for B-RAF in only 5% and N-RAS in only 6%, respectively. Patients with tumors carrying mutated B-RAF showed an impaired median survival (8.0 versus 11.8 months, p = 0.055, tissues; 7.1 versus 9.3 months, p = 0.068, cell lines), whereas patients with N-RAS-mutated tumors presented with a favorable prognosis (median survival 12.5 versus 7.9 months, p = 0.084, tissues; 15.4 versus 6.8 months, p = 0.0008, cell lines), each in comparison with wildtype gene status. Multivariate analysis qualified N-RAS (p = 0.006) but not B-RAF mutation status as an independent prognostic factor of overall survival. Our findings demonstrate that B-RAF and N-RAS mutations are well preserved during short term in vitro propagation and, most importantly, differentially impact the outcome of melanoma patients.