MAP Kinase Pathways: Molecular Roads to Primary Acral Lentiginous Melanoma

Daphnetin inhibits α-MSH-induced melanogenesis via PKA and ERK signaling pathways in B16F10 melanoma cells

Daphnetin is a dehydroxylated derivative of coumarin isolated from Daphne species. However, the effect of daphnetin on melanogenesis has not been elucidated. This study aims to investigate the inhibitory effect of daphnetin on melanogenesis in α-melanocyte stimulating hormone (α-MSH)-treated B16F10 cells and its potential mechanism. Melanin content analysis and cellular tyrosinase activity assay showed that daphnetin inhibited melanin biosynthesis in α-MSH-treated B16F10 cells. Immunoblotting and qRT-PCR also indicated that daphnetin suppressed the expression of microphthalmia-associated transcription factor, a mastering transcription factor of melanogenesis and its downstream melanogenic enzymes including tyrosinase and tyrosinase-related proteins. Moreover, daphnetin downregulated the phosphorylation of PKA, ERK, MSK1, and CREB. Additionally, daphnetin inhibited melanin synthesis in UVB-irradiated HaCaT conditioned medium system suggesting that daphnetin has potential as an antipigmentation activity in a physiological skin condition. Our data propose that daphnetin inhibits melanogenesis via modulating both the PKA/CREB and the ERK/MSK1/CREB pathways.

The tumor genetics of acral melanoma: What should a dermatologist know?

Dermatologists stand at the gateway of individualization of classification, treatment, and outcomes of acral melanoma patients. The acral melanoma genetic landscape differs in vital ways from that of other cutaneous melanomas. These differences have important implications in understanding pathogenesis, treatment, and prognosis. The selection of molecularly targeted therapy must be adapted for acral melanoma. It is also critical to recognize that tumor development is far more complex than an isolated event, reliably treated by a medication acting on a single target. Tumors exhibit intratumor genetic heterogeneity, metastasis may have different genetic or epigenetic features than primary tumors, and tumor resistance may develop because of the activation of alternative genetic pathways. Microenvironmental, immune, and epigenetic events contribute and sustain tumors in complex ways. Treatment strategies with multiple targets are required to effectively disrupt the tumor ecosystem. This review attempts to translate the current molecular understanding of acral melanoma into digestible concepts relevant to the practice of dermatology. The focus is tumor genetics defining potentially treatable cancer pathways, contextualized within the relevant pathologic and molecular features.

Translational pathology, genomics and the development of systemic therapies for acral melanoma

Acral melanomas arise on the non-hair bearing skin of the palms, soles and in the nail beds. These rare tumors comprise 2-3 % of all melanomas, are not linked to UV-exposure, and represent the most frequent subtype of melanomas in patients of Asian, African and Hispanic origin. Although recent work has revealed candidate molecular events that underlie acral melanoma development, this knowledge is not yet been translated into efficacious local, regional, or systemic therapies. In the current review, we describe the clinical characteristics of acral melanoma and outline the genetic basis of acral melanoma development. Further discussion is given to the current status of systemic therapy for acral melanoma with a focus on ongoing developments in both immunotherapy and targeted therapy for the treatment of advanced disease.

Depletion of primary cilium in acral melanoma

BACKGROUND

A eukaryotic cell's primary cilium (PC) is critical for cell signaling, migration and homeostasis. Primary cilium dysfunction has been demonstrated in several malignancies, but whether primary cilia loss occurs in acral melanoma has remained unknown. To address this, we examined the ciliation index (% melanocytes containing a PC) of patient-derived, biopsy-proven acral melanoma and compared these to benign acral nevi.

METHODS

We generated a pilot initiative study that included six acral melanomas and seven acral nevi derived from the foot. Using fluorescent immunohistochemistry, we calculated ciliation indexes of Sox10+ melanocytes.

RESULTS

Average ciliation index for acral nevi was 74.0% (SE of the mean [SEM] 3.3%) vs 9.3% for acral melanoma (SEM 5.7%), finding a statistically significant difference between the groups (P-value <.001, two tailed t test).

CONCLUSION

The data show a significant loss of primary cilia in malignant acral melanoma vs benign acral nevi, suggesting that cilia may play an important role during acral melanoma formation. Our data, which should be validated by a larger study with longer follow-up period, suggest that examining ciliation index may be a useful diagnostic test when distinguishing benign acral nevi from melanoma.

Acral lentiginous melanoma: a skin cancer with unfavourable prognostic features. A study of the German central malignant melanoma registry (CMMR) in 2050 patients

BACKGROUND

Acral lentiginous melanoma (ALM) is one of the four major subtypes in cutaneous melanoma (CM). Although ALM has a poorer prognosis than other CM subtypes, the prognostic factors associated with ALM have only been verified in small-sized cohorts because of the low incidence of ALM worldwide.

OBJECTIVES

To investigate the clinical characteristics of ALM and to evaluate their prognostic values based on a large dataset from the Central Malignant Melanoma Registry (CMMR) of the German Dermatologic Society.

METHODS

The Kaplan-Meier method was used to estimate the potential influence of clinical and histological parameters on ALM disease-specific survival (DSS) curves, which were compared using the log-rank test. A Cox proportional hazards model was used to identify independent prognostic factors for DSS.

RESULTS

In total, 2050 patients with ALM were identified from 58 949 patients with CM recorded by the CMMR with follow-up data. In multivariate analyses, age (P = 0·006), ulceration (P = 0·013), tumour thickness (P < 0·001) and tumour spread (P < 0·001) turned out to be significant prognostic factors for DSS in ALM whereas sex, nevus association and level of invasion were not independent factors.

CONCLUSIONS

ALM has the same prognostic factors as other subtypes of melanoma. Unfavourable prognosis probably derives from the delay in diagnosis in comparison with other melanoma subtypes.