Novel therapies in melanoma

The pleiotropic role of galectin-3 in melanoma progression: Unraveling the enigma

Melanoma is a highly aggressive skin cancer with poor outcomes associated with distant metastasis. Intrinsic properties of melanoma cells alongside the crosstalk between melanoma cells and surrounding microenvironment determine the tumor behavior. Galectin-3 (Gal-3), a ß-galactoside-binding lectin, has emerged as a major effector in cancer progression, including melanoma behavior. Data from melanoma models and patient studies reveal that Gal-3 expression is dysregulated, both intracellularly and extracellularly, throughout the stages of melanoma progression. This review summarizes the most recent data and hypotheses on Gal-3 and its tumor-modulating functions, highlighting its role in driving melanoma growth, invasion, and metastatic colonization. It also provides insight into potential Gal-3-targeted strategies for melanoma diagnosis and treatment.

The glycomic effect of N-acetylglucosaminyltransferase III overexpression in metastatic melanoma cells. GnT-III modifies highly branched N-glycans

N-acetylglucosaminyltransferase III (GnT-III) is known to catalyze N-glycan "bisection" and thereby modulate the formation of highly branched complex structures within the Golgi apparatus. While active, it inhibits the action of other GlcNAc transferases such as GnT-IV and GnT-V. Moreover, GnT-III is considered as an inhibitor of the metastatic potential of cancer cells both in vitro and in vivo. However, the effects of GnT-III may be more diverse and depend on the cellular context. We describe the detailed glycomic analysis of the effect of GnT-III overexpression in WM266-4-GnT-III metastatic melanoma cells. We used MALDI-TOF and ESI-ion-trap-MS/MS together with HILIC-HPLC of 2-AA labeled N-glycans to study the N-glycome of membrane-attached and secreted proteins. We found that the overexpression of GnT-III in melanoma leads to the modification of a broad range of N-glycan types by the introduction of the "bisecting" GlcNAc residue with highly branched complex structures among them. The presence of these unusual complex N-glycans resulted in stronger interactions of cellular glycoproteins with the PHA-L. Based on the data presented here we conclude that elevated activity of GnT-III in cancer cells does not necessarily lead to a total abrogation of the formation of highly branched glycans. In addition, the modification of pre-existing N-glycans by the introduction of "bisecting" GlcNAc can modulate their capacity to interact with carbohydrate-binding proteins such as plant lectins. Our results suggest further studies on the biological function of "bisected" oligosaccharides in cancer cell biology and their interactions with carbohydrate-binding proteins.

AC-1001 H3 CDR peptide induces apoptosis and signs of autophagy in vitro and exhibits antimetastatic activity in a syngeneic melanoma model

Antibody‐derived peptides modulate functions of the immune system and are a source of anti‐infective and antitumor substances. Recent studies have shown that they comprise amino acid sequences of immunoglobulin complementarity‐determining regions, but also fragments of constant regions. V_H CDR3 of murine mAb AC‐1001 displays antimetastatic activities using B16F10‐Nex2 murine melanoma cells in a syngeneic model. The peptide was cytotoxic in vitro in murine and human melanoma cells inducing reactive oxygen species (ROS) and apoptosis by the intrinsic pathway. Signs of autophagy were also suggested by the increased expression of LC3/LC3II and Beclin 1 and by ultrastructural evidence. AC‐1001 H3 bound to both G‐ and F‐actin and inhibited tumor cell migration. These results are important evidence of the antitumor activity of Ig CDR‐derived peptides.

Is oestrogen an important player in melanoma progression?

The oestrogen-dependent regulation of cell behaviour is realised by stimulation of specific oestrogen receptors. The classical oestrogen receptors ERα and ERβ are transcription factors, and they modulate expression of hormonally regulated genes, while the third one, GPER, is thought to be responsible for the observed rapid, non-genomic cellular response. Oestrogen dependency is attributed to a number of cancers, including breast, ovarian and endometrial cancer; however, there is still growing evidence that melanoma should also be cited as a hormonally dependent tumour. This comes from the observations of gender-related differences in melanoma progression and reports concerning the history of the malignant course of melanomas during pregnancy. Although, the observations of oestrogen regulation of melanoma progression are controversial, the effect of oestrogen should not be neglected, as the skin possesses its own hormonal microenvironment. This aspect of melanoma progression should be taken under careful consideration as it may offer new therapeutic possibilities.

Heat shock factor 1 is required for migration and invasion of human melanoma in vitro and in vivo

Heat shock factor 1 (HSF1) is a major transactivator of the heat shock response. Recent studies have demonstrated that HSF1 is involved in tumor initiation, maintenance, and progression by regulating the expression of heat shock proteins (HSPs) and other molecular targets. Furthermore, HSF1 was identified as a potent proinvasion oncogene in human melanomas. However, the biological functions of HSF1 in human melanoma remain poorly understood. To determine the functional role of HSF1 in melanoma, we used short hairpin RNA (shRNA) to silence HSF1 in human melanoma cell lines and investigated its effect on cell migration and invasive ability in vitro. We found that HSF1 knockdown led to a marked reduction in migration and invasive ability, and these functions were restored by overexpression of wild-type HSF1. To confirm the in vitro results, we performed subcutaneous xenograft experiments in athymic nude mice. We found that HSF1 was required for melanoma invasion and metastasis, as well as tumorigenic potential in vivo. Overall, these results show that HSF1 is indispensable for melanoma progression and metastasis, and suggests that HSF1 could be a promising therapeutic target for melanoma.

The role of melanocortin 1 receptor in cutaneous malignant melanoma: along the mitogen-activated protein kinase pathway

Cutaneous malignant melanoma (CMM) is an epidemic cancer in the United States. Survival rates for invasive CMM have not increased in past decades despite numerous clinical trials and the effective use of various combinations of chemotherapy agents to treat other cancers. Recent research has investigated the role of melanocortin 1 receptor (MC1R), a gene associated with red-hair phenotype in White individuals and with increased risk for developing CMM, in the mitogen-activated protein kinase (MAPK) pathway. This limited narrative review discusses the incidence, history, and risk factors for CMM. It explores familial CMM and provides a brief review of melanocyte development and melanogenesis. Histology of CMM and cytogenetic techniques used to identify CMM mutations is also discussed. The structure and function of MC1R is described, with particular attention to MC1R's role in the MAPK pathway. Finally, the review touches on individualized therapy for CMM using genetic biomarkers and explores the promise of genomic research for finding effective treatments.

Heterogeneous distribution of BRAF/NRAS mutations among Italian patients with advanced melanoma

BACKGROUND

Prevalence and distribution of pathogenetic mutations in BRAF and NRAS genes were evaluated in multiple melanoma lesions from patients with different geographical origin within the same Italian population.

METHODS

Genomic DNA from a total of 749 tumor samples (451 primary tumors and 298 metastases) in 513 consecutively-collected patients with advanced melanoma (AJCC stages III and IV) was screened for mutations in exon 15 of BRAF gene and, at lower extension (354/513; 69%), in the entire coding DNA of NRAS gene by automated direct sequencing. Among tissues, 236 paired samples of primary melanomas and synchronous or asynchronous metastases were included into the screening.

RESULTS

Overall, mutations were detected in 49% primary melanomas and 51% metastases, for BRAF gene, and 15% primary tumors and 16% secondaries, for NRAS gene. A heterogeneous distribution of mutations in both genes was observed among the 451 primary melanomas according to patients' geographical origin: 61% vs. 42% (p = 0.0372) BRAF-mutated patients and 2% vs. 21% (p < 0.0001) NRAS-mutated cases were observed in Sardinian and non-Sardinian populations, respectively. Consistency in BRAF/NRAS mutations among paired samples was high for lymph node (91%) and visceral metastases (92.5%), but significantly lower for brain (79%; p = 0.0227) and skin (71%; p = 0.0009) metastases.

CONCLUSIONS

Our findings about the two main alterations occurring in the different tumor tissues from patients with advanced melanoma may be helpful in improving the management of such a disease.

The effect of ionizing radiation on the homeostasis and functional integrity of murine splenic regulatory T cells

OBJECTIVE

Radiotherapy affects antitumor immune responses; therefore, it is important to study radiation effects on various compartments of the immune system. Here we report radiation effects on the homeostasis and function of regulatory T (Treg) cells, which are important in down-regulating antitumor immune responses.

METHODS

C57Bl/6 mice were irradiated with 2 Gy and alterations in splenic lymphocyte fractions analyzed at different intervals.

RESULTS

Total CD4+ numbers showed stronger decrease after irradiation than CD4+Foxp3+ Tregs. Tregs were less prone to radiation-induced apoptosis than CD4+Foxp3- T cells. The ratio of CD4+Foxp3- and CD4+Foxp3+ fractions within the proliferating CD4+ pool progressively changed from 74:26 in control animals to 59:41 eleven days after irradiation, demonstrating a more dynamic increase in the proliferation and regeneration of the Treg pool. The CD4+Foxp3+ fraction expressing cell-surface CTLA4, an antigen associated with Treg cell activation increased from 5.3 % in unirradiated mice to 10.5 % three days after irradiation. The expression of IL-10 mRNA was moderately upregulated, while TGF-β expression was not affected. On the other hand, irradiation reduced Treg capacity to suppress effector T cell proliferation by 2.5-fold.

CONCLUSION

Tregs are more radioresistant, less prone to radiation-induced apoptosis, and have faster repopulation kinetics than CD4+Foxp3- cells, but irradiated Tregs are functionally compromised, having a reduced suppressive capacity.

MODULATING CO-STIMULATION DURING ANTIGEN PRESENTATION TO ENHANCE CANCER IMMUNOTHERAPY

One of the key roles of the immune system is the identification of potentially dangerous pathogens or tumour cells, and raising a wide range of mechanisms to eliminate them from the organism. One of these mechanisms is activation and expansion of antigen-specific cytotoxic T cells, after recognition of antigenic peptides on the surface of antigen presenting cells such as dendritic cells (DCs). However, DCs also process and present autoantigens. Therefore, antigen presentation has to occur in the appropriate context to either trigger immune responses or establishing immunological tolerance. This is achieved by co-stimulation of T cells during antigen presentation. Co-stimulation consists on the simultaneous binding of ligand-receptor molecules at the immunological synapse which will determine the type and extent of T cell responses. In addition, the type of cytokines/chemokines present during antigen presentation will influence the polarisation of T cell responses, whether they lead to tolerance, antibody responses or cytotoxicity. In this review, we will focus on approaches manipulating co-stimulation during antigen presentation, and the role of cytokine stimulation on effective T cell responses. More specifically, we will address the experimental strategies to interfere with negative co-stimulation such as that mediated by PD-L1 (Programmed cell death 1 ligand 1)/PD-1 (Programmed death 1) to enhance anti-tumour immunity.

RSK regulates activated BRAF signalling to mTORC1 and promotes melanoma growth

The Ras/mitogen-activated protein kinase (MAPK) signalling cascade regulates various biological functions, including cell growth, proliferation and survival. As such, this pathway is often deregulated in cancer, including melanomas, which frequently harbour activating mutations in the NRAS and BRAF oncogenes. Hyperactive MAPK signalling is known to promote protein synthesis, but the mechanisms by which this occurs remain poorly understood. Here, we show that expression of oncogenic forms of Ras and Raf promotes the constitutive activation of the mammalian target of rapamycin (mTOR). Using pharmacological inhibitors and RNA interference, we find that the MAPK-activated protein kinase RSK (p90 ribosomal S6 kinase) is partly required for these effects. Using melanoma cell lines carrying activating BRAF mutations, we show that ERK/RSK signalling regulates assembly of the translation initiation complex and polysome formation, as well as the translation of growth-related messenger RNAs containing a 5'-terminal oligopyrimidine (TOP) motif. Accordingly, we find that RSK inhibition abrogates tumour growth in mice. Our findings indicate that RSK may be a valuable therapeutic target for the treatment of tumours characterized by deregulated MAPK signalling, such as melanoma.

Surgical treatment of malignant melanoma: practical guidelines

Melanoma is currently the fifth and sixth most common solid malignancy diagnosed in men and women, respectively. Although accounting for only 4% of cases of all cutaneous malignancies, melanoma accounts for more than 75% of all deaths from skin cancer. This article discusses epidemiology and risk factors, proper biopsy technique, advanced histologic evaluation of biopsy material, assessment of tumor thickness and staging, preoperative metastatic evaluation, excision margin, treatment of regional lymph nodes, treatment of recurrence, and some special clinical situations.