Modeling malignant melanoma in mice: pathogenesis and maintenance

Cutaneous Melanoma-A Long Road from Experimental Models to Clinical Outcome: A Review

Cutaneous melanoma is a complex disorder characterized by an elevated degree of heterogeneity, features that place it among the most aggressive types of cancer. Although significant progress was recorded in both the understanding of melanoma biology and genetics, and in therapeutic approaches, this malignancy still represents a major problem worldwide due to its high incidence and the lack of a curative treatment for advanced stages. This review offers a survey of the most recent information available regarding the melanoma epidemiology, etiology, and genetic profile. Also discussed was the topic of cutaneous melanoma murine models outlining the role of these models in understanding the molecular pathways involved in melanoma initiation, progression, and metastasis.

Focal adhesion protein expression in human diffuse large B-cell lymphoma

AIMS

Focal adhesions have been associated with poor prognosis in multiple cancer types, but their prognostic value in diffuse large B-cell lymphoma (DLBCL) has not been evaluated. The aim of this study was to investigate the expression patterns and the prognostic value of the focal adhesion proteins FAK, Pyk2, p130Cas and HEF1 in DLBCL.

METHODS AND RESULTS

Focal adhesion protein expression was examined using immunohistochemistry in normal lymphoid tissues and in 60 DLBCL patient samples. Kaplan-Meier survival and Cox regression analysis were performed to evaluate the correlation of focal adhesion protein expression with patient prognosis. FAK, Pyk2, p130Cas and HEF1 expression was mostly found in the germinal centres of normal human lymphoid tissues. When assessed in DLBCL samples, FAK, Pyk2, p130Cas and HEF1 were highly expressed in 45%, 34%, 42% and 45% of the samples, respectively. Multivariate Cox analysis revealed that decreased FAK expression was a significant independent predictor of poorer disease outcome.

CONCLUSIONS

FAK expression is an independent prognostic factor in DLBCL. Our results suggest that the addition of FAK immunostaining to the current immunohistochemical algorithms may facilitate risk stratification of DLBCL patients.

Care and monitoring of a mouse model of melanoma

Melanoma is a devastating form of skin cancer in humans that is rising in incidence. Animal models of melanoma continue to be instrumental for understanding the disease and for developing and testing therapies. A novel line of melanoma-bearing mice developed at the National Institute of Neurological Disorders and Stroke is monitored and cared for by the Animal Health Care Section. Although these mice develop heavy tumor burdens, they show few signs of pain or distress and seem to have high levels of physiologic fitness. The author discusses the monitoring and care of these mice, advocating early flagging and frequent monitoring of melanoma-bearing mice. In the care of melanoma-bearing mice, an emphasis should be placed on evaluating the whole animal and considering new endpoints rather than relying on historically accepted guidelines for maximum tumor size and weight, which may be inappropriate for some mice.

Human relevance of NRAS/BRAF mouse melanoma models

Melanoma is a major problem for many individuals worldwide. Although no effective treatment is available, promising new strategies are being developed. A better understanding of the inner workings of the disease would undoubtedly lead to improved treatments. Mouse melanoma models have been used to elucidate many key regulatory pathways involved in melanoma initiation and progression, and models with mutations in the oncogenes RAF and RAS have been particularly informative. Here, we summarize and evaluate the human relevance of various RAF and RAS mouse melanoma models and their contribution to our understanding of melanoma.

Integrin signalling adaptors: not only figurants in the cancer story

Current evidence highlights the ability of adaptor (or scaffold) proteins to create signalling platforms that drive cellular transformation upon integrin-dependent adhesion and growth factor receptor activation. The understanding of the biological effects that are regulated by these adaptors in tumours might be crucial for the identification of new targets and the development of innovative therapeutic strategies for human cancer. In this Review we discuss the relevance of adaptor proteins in signalling that originates from integrin-mediated cell-extracellular matrix (ECM) adhesion and growth factor stimulation in the context of cell transformation and tumour progression. We specifically underline the contribution of p130 Crk-associated substrate (p130CAS; also known as BCAR1), neural precursor cell expressed, developmentally down-regulated 9 (NEDD9; also known as HEF1), CRK and the integrin-linked kinase (ILK)-pinch-parvin (IPP) complex to cancer, along with the more recently identified p140 Cas-associated protein (p140CAP; also known as SRCIN1).

Gene expression signatures for tumor progression, tumor subtype, and tumor thickness in laser-microdissected melanoma tissues

PURPOSE

To better understand the molecular mechanisms of malignant melanoma progression and metastasis, gene expression profiling was done of primary melanomas and melanoma metastases.

EXPERIMENTAL DESIGN

Tumor cell-specific gene expression in 19 primary melanomas and 22 melanoma metastases was analyzed using oligonucleotide microarrays after laser-capture microdissection of melanoma cells. Statistical analysis was done by random permutation analysis and support vector machines. Microarray data were further validated by immunohistochemistry and immunoblotting.

RESULTS

Overall, 308 genes were identified that showed significant differential expression between primary melanomas and melanoma metastases (false discovery rate<or=0.05). Significantly overrepresented gene ontology categories in the list of 308 genes were cell cycle regulation, mitosis, cell communication, and cell adhesion. Overall, 47 genes showed up-regulation in metastases. These included Cdc6, Cdk1, septin 6, mitosin, kinesin family member 2C, osteopontin, and fibronectin. Down-regulated genes included E-cadherin, fibroblast growth factor binding protein, and desmocollin 1 and desmocollin 3, stratifin/14-3-3sigma, and the chemokine CCL27. Using support vector machine analysis of gene expression data, a performance of >85% correct classifications for primary melanomas and metastases was reached. Further analysis showed that subtypes of primary melanomas displayed characteristic gene expression patterns, as do thin tumors (<or=1.0 mm Breslow thickness) compared with intermediate and thick tumors (>2.0 mm Breslow thickness).

CONCLUSIONS

Taken together, this large-scale gene expression study of malignant melanoma identified molecular signatures related to metastasis, melanoma subtypes, and tumor thickness. These findings not only provide deeper insights into the pathogenesis of melanoma progression but may also guide future research on innovative treatments.

The age of skin cancers

Cancer affects two major cell types in the human skin: epithelial cells and melanocytes. Aging and a previous history of ultraviolet light exposure are major risk factors for skin cancers, including basal and squamous cell carcinomas and melanomas. However, melanomas, which are the most deadly of the skin tumors, display two intriguing characteristics: The incidence is increased and the prognosis is worse in males over 60 years as compared with females of the same age. This Perspective discusses possible reasons for age and gender as melanoma risk factors, as well as the need for studies aimed at unraveling the molecular mechanism of such puzzling events.

Melanocytes in conditional Rb-/- mice are normal in vivo but exhibit proliferation and pigmentation defects in vitro

The function of the retinoblastoma tumour suppressor (Rb1), and the pocket protein family in general, has been implicated as an important focal point for deregulation in many of the molecular pathways mutated in melanoma. We have focused on the role of Rb1 in mouse melanocyte homeostasis using gene targeting and Cre/loxP mediated tissue-specific deletion. We show that constitutive Cre-mediated ablation of Rb1 exon 2 prevents the production of Rb1 and recapitulates the phenotype encountered in other Rb1 knockout mouse models. Mice with conditional melanocyte-specific ablation of Rb1 manifest overtly normal pigmentation and are bereft of melanocytic hyperproliferative defects or apoptosis-induced depigmentation. Histologically, these mice have melanocyte morphology and distribution comparable with control littermates. In contrast, Rb1-null melanocytes removed from their in vivo micro-environment and cultured in vitro display some of the characteristics associated with a transformed phenotype. They proliferate at a heightened rate when compared with control melanocytes and have a decreased requirement for mitogens. With progressive culture the cells depigment at relatively early passage and display a gross morphology which, whilst reminiscent of early passage melanocytes, is generally different to equivalent passage control cells. These results indicate that Rb1 is dispensable for in vivo melanocyte homeostasis when its ablation is targeted from the melanoblast stage onwards, however, when cultured in vitro, Rb1 loss increases melanocyte growth but the cells are not fully transformed.

Melanoma chemoprevention: a role for statins or fibrates?

Although numerous second-generation isoprenylation inhibitors are proposed or under investigation for the treatment and/or prevention of cancer (eg, R115777, SCH 66336, L-778,123, BMS-214662), the chemotherapeutic and chemopreventive potential of commonly prescribed first-generation isoprenylation inhibitors, the statins, and other classes of lipid-lowering medications, the fibrates, has yet to be seriously explored. Two lipid-lowering medications, lovastatin and gemfibrozil, have been associated with a decreased incidence of melanoma in large, prospective, randomized, double-blind, placebo-controlled clinical cardiology trials. This article reviews melanoma biology and the clinical evidence for the use of lipid-lowering medications for melanoma chemoprevention and/or adjuvant chemotherapy.

Animal models of melanoma: an HGF/SF transgenic mouse model may facilitate experimental access to UV initiating events

Cutaneous malignant melanoma, the most lethal of the skin cancers, known for its intractability to current therapies, continues to increase in incidence, providing a significant public health challenge. There is a consensus that skin cancer is initiated by sunlight exposure. For non-melanoma skin cancer there is substantial evidence that chronic exposure to the ultraviolet B radiation (UVB) (280-320 nm) portion of the sunlight spectrum is responsible. Experimentally, UVB is mutagenic and chronic UVB exposure can cause non-melanoma skin cancer in laboratory animals. Non-melanoma tumors in animals and in humans show characteristic UVB signature lesions in the tumor suppressor p53 and/or in the patched (PTCH) gene. An action spectrum or wavelength dependence for squamous cell carcinoma in the mouse shows a major peak of efficacy in the UVB. For malignant melanoma, however, the situation is unclear and the critical direct target(s) of sunlight in initiating melanoma and even the wavelengths responsible are as yet unidentified. This lack of information is in major part a result of a paucity of animal models for melanoma which recapitulate the role of sunlight in initiating this disease. The epidemiology of melanoma differs significantly from non-melanoma skin cancer. Intense sporadic sunlight exposure in childhood, probably exacerbated by additional adult exposure, is associated with elevated melanoma risk. Melanoma is also a disease of gene-environment interactions with underlying genetic factors playing a significant role. These major differences indicate that extrapolation from information for non-melanoma skin cancer to melanoma is unlikely to be useful. We summarize in this review the experimental information available on the role of UV radiation in melanoma and give an overview of animal melanoma models. A new model derived by neonatal UV irradiation of hepatocyte growth factor/scatter factor (HGF/SF) transgenic mice is described which recapitulates the etiology, the histopathology and molecular pathogenesis of human disease. It is anticipated that the HGF/SF transgenic model will provide a means to access the mechanism(s) by which sunlight initiates this lethal disease and provide an appropriate vehicle for derivation of appropriate therapeutic and preventive strategies.