Dormancy of growth-stunted malignant melanoma: sustainable and smoldering patterns

Emerging Role of Deubiquitinating Enzymes (DUBs) in Melanoma Pathogenesis

Metastatic melanoma is the leading cause of death from skin cancer. Therapies targeting the BRAF oncogenic pathway and immunotherapies show remarkable clinical efficacy. However, these treatments are limited to subgroups of patients and relapse is common. Overall, the majority of patients require additional treatments, justifying the development of new therapeutic strategies. Non-genetic and genetic alterations are considered to be important drivers of cellular adaptation mechanisms to current therapies and disease relapse. Importantly, modification of the overall proteome in response to non-genetic and genetic events supports major cellular changes that are required for the survival, proliferation, and migration of melanoma cells. However, the mechanisms underlying these adaptive responses remain to be investigated. The major contributor to proteome remodeling involves the ubiquitin pathway, ubiquitinating enzymes, and ubiquitin-specific proteases also known as DeUBiquitinases (DUBs). In this review, we summarize the current knowledge regarding the nature and roles of the DUBs recently identified in melanoma progression and therapeutic resistance and discuss their potential as novel sources of vulnerability for melanoma therapy.

Mechanisms of Immunotherapy Resistance in Cutaneous Melanoma: Recognizing a Shapeshifter

Melanoma is one of the seven most common cancers in the United States, and its incidence is still increasing. Since 2011, developments in targeted therapies and immunotherapies have been essential for significantly improving overall survival rates. Prior to the advent of targeted and immunotherapies, metastatic melanoma was considered a death sentence, with less than 5% of patients surviving more than 5 years. With the implementation of immunotherapies, approximately half of patients with metastatic melanoma now survive more than 5 years. Unfortunately, this also means that half of the patients with melanoma do not respond to current therapies and live less than 5 years after diagnosis. One major factor that contributes to lower response in this population is acquired or primary resistance to immunotherapies via tumor immune evasion. To improve the overall survival of melanoma patients new treatment strategies must be designed to minimize the risk of acquired resistance and overcome existing primary resistance. In recent years, many advances have been made in identifying and understanding the pathways that contribute to tumor immune evasion throughout the course of immunotherapy treatment. In addition, results from clinical trials focusing on treating patients with immunotherapy-resistant melanoma have reported some initial findings. In this review, we summarize important mechanisms that drive resistance to immunotherapies in patients with cutaneous melanoma. We have focused on tumor intrinsic characteristics of resistance, altered immune function, and systemic factors that contribute to immunotherapy resistance in melanoma. Exploring these pathways will hopefully yield novel strategies to prevent acquired resistance and overcome existing resistance to immunotherapy treatment in patients with cutaneous melanoma.

The Genetic Basis of Dormancy and Awakening in Cutaneous Metastatic Melanoma

Immune dysregulation, in combination with genetic and epigenetic alterations, induces an excessive proliferation of uncontrolled melanoma cells followed by dissemination of the tumor cells to distant sites, invading organs and creating metastasis. Although immunotherapy, checkpoint inhibitors and molecular targeted therapies have been developed as treatment options for advanced melanoma, there are specific mechanisms by which cancer cells can escape treatment. One of the main factors associated with reduced response to therapy is the ability of residual tumor cells to persist in a dormant state, without proliferation. This comprehensive review aimed at understanding the genetic basis of dormancy/awakening phenomenon in metastatic melanoma will help identify the possible therapeutical strategies that might eliminate melanoma circulating tumor cells (CTCs) or keep them in the dormant state forever, thereby repressing tumor relapse and metastatic spread.

Histologic Features Associated With an Invasive Component in Lentigo Maligna Lesions

Importance

Lentigo maligna (LM) presents an invasive component in up to 20% of biopsied cases, but to date the histologic features useful in detecting this invasive component have not been described. Some histologic characteristics are hypothesized to contribute to the progression of LM invasion.

Objective

To identify the histologic characteristics associated with lentigo maligna melanoma (LMM) in patients with LM diagnosed by a partial diagnostic biopsy.

Design, Setting, and Participants

A retrospective cross-sectional study of patients treated between January 1, 2000, and December 31, 2017, was conducted in a referral oncology center in València, Spain. Data and specimens of patients (n = 96) with a diagnosis of primary cutaneous melanoma in the form of either LM or LMM who had undergone surgical treatment, a complete histologic examination of the whole tumor, and an initial diagnostic partial biopsy of LM were included in the study. Histologic assessment was blinded to the presence of an invasive component.

Interventions

All biopsy specimens were evaluated for the presence of certain histologic characteristics.

Main Outcomes and Measures

Comparisons between invasive samples and samples without an invasive component were performed. The differences in the distribution of variables between the groups were assessed using the χ2 and Fisher exact tests, and the degree of association of the relevant variables was quantified by logistic regression models. A classification and regression tree analysis was performed to rank the variables by importance.

Results

In total, 96 patients had sufficient histologic material that could be evaluated. The patients were predominantly male (56 [58.3%]) and had a mean (SD) age at diagnosis of 72 (12) years. Of these patients, 63 (65.6%) had an LM diagnosis and 33 (34.4%) had an LMM diagnosis (an invasive component). The histologic variables associated with the presence of an invasive component were melanocytes forming rows (odds ratio [OR], 11.5; 95% CI, 1.4-94.1; P = .02), subepidermal clefts (OR, 2.8; 95% CI, 1.0-7.9; P = .049), nests (OR, 3.0; 95% CI, 1.1-8.6; P = .04), and a lesser degree of solar elastosis (OR, 0.4; 95% CI, 0.1-1.1; P = .07). A classification and regression tree analysis of the relevant histologic features was able to accurately identify lentigo maligna with an invasive component (LMM) in more than 60% of patients.

Conclusions and Relevance

These findings may be useful in classifying early LM specimens at higher risk of invasion, which may eventually be relevant in identifying the most appropriate management for LM.

Islet-1 promotes the proliferation and invasion, and inhibits the apoptosis of A375 human melanoma cells

The aim of this study was to examine the effects of the insulin gene enhancer-binding protein, islet-1 (ISL1), on the proliferation, invasion and apoptosis of the human melanoma cell line, A375. An ISL1 overexpression lentiviral vector was constructed and transfected into the A375 cells. The proliferation of the A375 cells transfected with the ISL1 vector (termed A375/ISL1 cells) was examined by MTT assay, flow cytometry and TUNEL assay, and cell invasion was examined by Transwell assay. The expression levels of matrix metalloproteinase (MMP)-2 and MMP-9 were measured by qPCR and western blot analysis; the expression levels of Akt and p-Akt were measured in the cells treated with vascular endothelial growth factor (VEGF) and the PI3K/Akt inhibitor, LY294002, by western blot analysis. The optical density value of the A375/ISL1 cells was increased after 12 h of culture (P<0.001), as shown by MTT assay. The ratio of apoptotic A375/ISL1 cells was significantly decreased (P<0.001), as shown by flow cytometry and TUNEL assay. In addition, the average penetration rate of the A375/ISL1 cells significantly increased (P<0.001), as shown by Transwell assay. The expression levels of MMP-2 and MMP-9 were significantly increased in the A375/ISL1 cells, as shown by qPCR and western blot analysis (P<0.001). Moreover, treatment of the A375/ISL1 cells with VEGF for 48 h increased the expression of Akt and p-Akt compared with the control cells transfected with A375/green fluorescent protein (GFP) (P<0.05; P<0.001, respectively). In addition, in the A375/ISL1 cells treated with the LY294002 inhibitor for 24 and 48 h, the level of Akt was also found to increase compared to the control A375/GFP cells (P<0.05). On the whole, the findings of this study indicate that the overexpression of ISL1 promotes the proliferation and invasion, and inhibits the apoptosis of A375 melanoma cells. ISL1 thus plays an important role in A375 cell survival, and these effects are possibly mediate via the PI3K/Akt signaling pathway.

A slow-cycling subpopulation of melanoma cells with highly invasive properties

Melanoma is a heterogeneous tumor with different subpopulations showing different proliferation rates. Slow-cycling cells were previously identified in melanoma, but not fully biologically characterized. Using the label-retention method, we identified a subpopulation of slow-cycling cells, defined as label-retaining cells (LRC), with strong invasive properties. We demonstrate through live imaging that LRC are leaving the primary tumor mass at a very early stage and disseminate to peripheral organs. Through global proteome analyses, we identified the secreted protein SerpinE2/protease nexin-1 as causative for the highly invasive potential of LRC in melanomas.

Luciferase Expression Allows Bioluminescence Imaging But Imposes Limitations on the Orthotopic Mouse (4T1) Model of Breast Cancer

Implantation of reporter-labeled tumor cells in an immunocompetent host involves a risk of their immune elimination. We have studied this effect in a mouse model of breast cancer after the orthotopic implantation of mammary gland adenocarcinoma 4T1 cells genetically labelled with luciferase (Luc). Mice were implanted with 4T1 cells and two derivative Luc-expressing clones 4T1luc2 and 4T1luc2D6 exhibiting equal in vitro growth rates. In vivo, the daughter 4T1luc2 clone exhibited nearly the same, and 4T1luc2D6, a lower growth rate than the parental cells. The metastatic potential of 4T1 variants was assessed by magnetic resonance, bioluminescent imaging, micro-computed tomography, and densitometry which detected 100-μm metastases in multiple organs and bones at the early stage of their development. After 3-4 weeks, 4T1 generated 11.4 ± 2.1, 4T1luc2D6, 4.5 ± 0.6; and 4T1luc2, <1 metastases per mouse, locations restricted to lungs and regional lymph nodes. Mice bearing Luc-expressing tumors developed IFN-γ response to the dominant CTL epitope of Luc. Induced by intradermal DNA-immunization, such response protected mice from the establishment of 4T1luc2-tumors. Our data show that natural or induced cellular response against the reporter restricts growth and metastatic activity of the reporter-labelled tumor cells. Such cells represent a powerful instrument for improving immunization technique for cancer vaccine applications.

Therapeutic implications of cellular and molecular biology of cancer stem cells in melanoma

Melanoma is a form of cancer that initiates in melanocytes. Melanoma has multiple phenotypically distinct subpopulation of cells, some of them have embryonic like plasticity which are involved in self-renewal, tumor initiation, metastasis and progression and provide reservoir of therapeutically resistant cells. Cancer stem cells (CSCs) can be identified and characterized based on various unique cell surface and intracellular markers. CSCs exhibit different molecular pattern with respect to non-CSCs. They maintain their stemness and chemoresistant features through specific signaling cascades. CSCs are weak in immunogenicity and act as immunosupressor in the host system. Melanoma treatment becomes difficult and survival is greatly reduced when the patient develop metastasis. Standard conventional oncology treatments such as chemotherapy, radiotherapy and surgical resection are only responsible for shrinking the bulk of the tumor mass and tumor tends to relapse. Thus, targeting CSCs and their microenvironment niche addresses the alternative of traditional cancer therapy. Combined use of CSCs targeted and traditional therapies may kill the bulk tumor and CSCs and offer a promising therapeutic strategy for the management of melanoma.

Simulants of Malignant Melanoma

During the recent period, dermoscopy has yielded improvement in the early disclosure of various atypical melanocytic neoplasms (AMN) of the skin. Beyond this clinical procedure, AMN histopathology remains mandatory for establishing their precise diagnosis. Of note, panels of experts in AMN merely report moderate agreement in various puzzling cases. Divergences in opinion and misdiagnosis are likely increased when histopathological criteria are not fine-tuned and when facing a diversity of AMN types. Furthermore, some AMN have been differently named in the literature including atypical Spitz tumor, metastasizing Spitz tumor, borderline and intermediate melanocytic tumor, malignant Spitz nevus, pigmented epithelioid melanocytoma or animal-type melanoma. Some acronyms have been further suggested such as MELTUMP (after melanocytic tumor of uncertain malignant potential) and STUMP (after Spitzoid melanocytic tumor of uncertain malignant potential). In this review, such AMN at the exclusion of cutaneous malignant melanoma (MM) variants, are grouped under the tentative broad heading skin melanocytoma. Such set of AMN frequently follows an indolent course, although they exhibit atypical and sometimes worrisome patterns or cytological atypia. Rare cases of skin melanocytomas progress to loco regional clusters of lesions (agminate melanocytomas), and even to regional lymph nodes. At times, the distinction between a skin melanocytoma and MM remains puzzling. However, multipronged immunohistochemistry and emerging molecular biology help profiling any malignancy risk if present.