Cancer stem cell as therapeutic target for melanoma treatment

Effect of melanoma stem cells on melanoma metastasis

Cancer stem cells (CSCs) are involved in the metastatic process, the resistance of many types of cancer to therapeutic treatments and consequently the onset of recurrences. The CSC concept therefore significantly extends our understanding of melanoma biology. More recently, melanoma stem cells (MSCs) have been described in melanoma as expressing specific biomarkers. These primitive melanoma cells are not only capable of self-renewal and differentiation plasticity, but may also confer virulence via immune evasion and multidrug resistance, and potentially, via vasculogenic mimicry and transition to migratory and metastasizing derivatives. This review will present the specific biomarkers of MSCs, including CD133, ATP binding cassette subfamily B member 5, CD271, CD20 and aldehyde dehydrogenase, which can regulate the transduction of tumor-related signals. These signal molecules can reversely act on tumor cells and regulate tumor angiogenesis, leading to the occurrence of melanoma metastasis. Targeting these specific biomarkers could inhibit the progression of melanoma and may help the development of novel therapeutic strategies for melanoma.

Correlation between the Expression of Angiogenic Factors and Stem Cell Markers in Human Uveal Melanoma

Uveal melanoma (UM) is the most common malignant tumor of the eye with extremely high metastatic potential. UM tumor cells can disseminate only hematogenously, thus, angiogenic signals have a particular role in the prognosis of the disease. Although the presence of cancer stem cells (CSCs) in densely vascularized UMs has been reported previously, their role in the process of hematogenous spread of UM has not been studied. In this study, we investigated the regulation of angiogenesis in UM in correlation with the presence of CSCs. Seventy UM samples were collected to analyze the expression of CSC markers and angiogenic factors. The expression of CSC markers was studied by RT-PCR, Western blotting techniques and IHC-TMA technique. RT-PCR showed high expression of CSC markers, particularly nestin, FZD6 and SOX10 and somewhat lower expression of NGFR. The protein expression of FZD6, HIF-1α and VEGFA was further evaluated in 52 UM samples by the IHC-TMA technique. We report here for the first time a significant correlation between FZD6 and VEGFA expression in UM samples. The observed correlation between FZD6 and VEGFA suggests the presence of CSCs in UM that are associated with the vascularization process.

Targeting melanoma stem cells with the Vitamin E derivative δ-tocotrienol

The prognosis of metastatic melanoma is very poor, due to the development of drug resistance. Cancer stem cells (CSCs) may play a crucial role in this mechanism, contributing to disease relapse. We first characterized CSCs in melanoma cell lines. We observed that A375 (but not BLM) cells are able to form melanospheres and show CSCs traits: expression of the pluripotency markers SOX2 and KLF4, higher invasiveness and tumor formation capability in vivo with respect to parental adherent cells. We also showed that a subpopulation of autofluorescent cells expressing the ABCG2 stem cell marker is present in the A375 spheroid culture. Based on these data, we investigated whether δ-TT might target melanoma CSCs. We demonstrated that melanoma cells escaping the antitumor activity of δ-TT are completely devoid of the ability to form melanospheres. In contrast, cells that escaped vemurafenib treatment show a higher ability to form melanospheres than control cells. δ-TT also induced disaggregation of A375 melanospheres and reduced the spheroidogenic ability of sphere-derived cells, reducing the expression of the ABCG2 marker. These data demonstrate that δ-TT exerts its antitumor activity by targeting the CSC subpopulation of A375 melanoma cells and might represent a novel chemopreventive/therapeutic strategy against melanoma.

Intercellular crosstalk in human malignant melanoma

Incidence of malignant melanoma is increasing globally. While the initial stages of tumors can be easily treated by a simple surgery, the therapy of advanced stages is rather limited. Melanoma cells spread rapidly through the body of a patient to form multiple metastases. Consequently, the survival rate is poor. Therefore, emphasis in melanoma research is given on early diagnosis and development of novel and more potent therapeutic options. The malignant melanoma is arising from melanocytes, cells protecting mitotically active keratinocytes against damage caused by UV light irradiation. The melanocytes originate in the neural crest and consequently migrate to the epidermis. The relationship between the melanoma cells, the melanocytes, and neural crest stem cells manifests when the melanoma cells are implanted to an early embryo: they use similar migratory routes as the normal neural crest cells. Moreover, malignant potential of these melanoma cells is overdriven in this experimental model, probably due to microenvironmental reprogramming. This observation demonstrates the crucial role of the microenvironment in melanoma biology. Indeed, malignant tumors in general represent complex ecosystems, where multiple cell types influence the growth of genetically mutated cancer cells. This concept is directly applicable to the malignant melanoma. Our review article focuses on possible strategies to modify the intercellular crosstalk in melanoma that can be employed for therapeutic purposes.

p75 Neurotrophin Receptor in the Skin: Beyond Its Neurotrophic Function

p75 neurotrophin receptor (p75^NTR), also known as CD271, is the low-affinity receptor that, together with the tyrosine kinase receptor tropomyosin-receptor kinase (Trk), mediate neurotrophin (NT) functions. Beside their classic role in skin innervation, NT and their receptors constitute a complex cutaneous network associated with a number of autocrine and paracrine activities. In this context, the role of p75^NTR is becoming more and more important. This review will focus on the intriguing functions of p75^NTR in healthy and diseased skin. First, p75^NTR counterbalances the proliferative and survival activities of its cognate receptor Trk by inducing keratinocyte apoptosis. In addition, p75^NTR identifies an early transit-amplifying (TA) keratinocyte population and plays a critical role in keratinocyte stem cell transition to its progeny as well as in epidermal differentiation. p75^NTR is absent in psoriatic TA cells, thus rendering these cells resistant to apoptosis. On the other hand, p75^NTR infection restores NT-induced apoptosis in psoriatic keratinocytes. Taken together, these results provide evidence for a critical role of p75^NTR in epidermal homeostasis, while its lack may account for the TA defect in psoriasis. While the issue of p75^NTR as a marker of melanoma initiating cells is still to be solved, there is strong evidence that downregulation of this receptor is a precondition to melanoma invasion and metastasis in vitro and in vivo. All in all, this review points to p75^NTR as a major actor in both physiologic and pathologic conditions at the skin level.

Expression of PIWIL3 in primary and metastatic melanoma

PURPOSE

The PIWI-interacting RNA machinery in malignant melanoma (MM) has not been sufficiently studied. We aimed to investigate the PIWIL3 expression profiles in primary melanomas and metastases of MM including a correlation with clinical data.

METHODS

We studied 161 primary melanomas, 45 lymph node metastases, and 16 distant metastases of 183 patients with MM. We used immunohistochemistry to assess PIWIL3 protein expression in situ. The relationship between the immunoreactivity of PIWIL3 and clinical data was statistically evaluated.

RESULTS

We observed a significantly (P = 0.000059) higher median immunoreactivity score in primary melanomas (4.9; range, 0.1-6), lymph node metastases (5.1; range, 3.3-6), and distant metastases (5.6; range, 4.5-6). PIWIL3 was expressed significantly higher (P = 0.0002) in primary nodular melanomas and acral melanomas (5.2; range, 3.4-6) when compared to other melanoma subtypes (4.7; range, 0.1-6). On univariate analysis, a significant positive correlation was observed between primary melanoma PIWIL3 expression and tumor thickness (r = 0.2; P = 0.014). On univariate and multivariate analysis, PIWIL3 did not prove to be an independent predictor for melanoma relapse or death.

CONCLUSIONS

Our data indicate that PIWIL3 protein expression is elevated in more aggressive primary MM and metastatic disease. As also observed in other malignancies, PIWIL3 seems to play a role in MM progression.

B-cell-specific Moloney murine leukemia virus integration site 1: potential stratification factor and therapeutic target for epithelial ovarian cancer

Epithelial ovarian cancer, a vexing challenge for clinical management, still lacks biomarkers for early diagnosis, precise stratification, and prognostic evaluation of patients. B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1), a member of the polycomb group of proteins, engages in diverse cellular processes, including proliferation, differentiation, senescence, and stem cell renewal. In addition, BMI1, as a cancer stem-cell marker, participates in tumorigenesis through various pathways. Rewardingly, recent studies have also revealed a relationship between BMI1 expression and the clinical grade/stage, therapy response, and survival outcome in a majority of human malignancies, including epithelial ovarian cancer. Therefore, BMI1 might serve as a potential stratification factor and treatment target for epithelial ovarian cancer, pending evidence from further investigations.