STING Signaling and Skin Cancers

Tumor associated macrophages as key contributors and targets in current and future therapies for melanoma

INTRODUCTION

Despite the success of immunotherapies for melanoma in recent years, there remains a significant proportion of patients who do not yet derive benefit from available treatments. Immunotherapies currently licensed for clinical use target the adaptive immune system, focussing on Tcell interactions and functions. However, the most prevalent immune cells within the tumor microenvironment (TME) of melanoma are macrophages, a diverse immune cell subset displaying high plasticity, to which no current therapies are yet directly targeted. Macrophages have been shown not only to activate the adaptive immune response, and enhance cancer cell killing, but, when influenced by factors within the TME of melanoma, these cells also promote melanoma tumorigenesis and metastasis.

AREAS COVERED

We present a review of the most up-to-date literatureavailable on PubMed, focussing on studies from within the last 10 years. We also include data from ongoing and recent clinical trials targeting macrophages in melanoma listed on clinicaltrials.gov.

EXPERT OPINION

Understanding the multifaceted role of macrophages in melanoma, including their interactions with immune and cancer cells, the influence of current therapies on macrophage phenotype and functions and how macrophages could be targeted with novel treatment approaches, are all critical for improving outcomes for patients with melanoma.

Toxic Epidermal Necrolysis Caused by Eribulin

Eribulin, a chemotherapy drug classified as a microtubule inhibitor, is known to target cell microtubule structures, impeding cancer cell growth and spread. This paper discusses a rare case of toxic epidermal necrolysis (TEN) induced by eribulin in a patient with angiosarcoma, marking it as an uncommon adverse reaction. This patient developed severe mucosal and skin lesions after the third dose of eribulin. Laboratory tests and a skin biopsy confirmed the diagnosis of TEN. The patient responded well to steroid therapy, although skin eruptions reoccurred with further eribulin treatment. This case highlights the need for further study on the immunological effects of eribulin, especially concerning severe drug eruptions potentially related to its impact on microtubule dynamics and immune cell functions.

Modulation of Skin Cancer by the Stimulator of Interferon Genes

Morbidity and mortality from skin cancer continue to rise domestically and globally, and melanoma and non-melanoma skin cancers are a topic of interest in the dermatology and oncology communities. In this review, we summarize the stimulator of interferon genes (STING) pathway, its specific role in the pathogenesis of DNA damage and skin cancer, and STING-specific therapies that may fight both melanoma and non-melanoma skin (NMSC) cancers. Furthermore, we discuss specific portions of the STING pathway that may be used in addition to previously used therapies to provide a synergistic effect in future oncology treatments and discuss the limitations of current STING-based therapies.

Co-occurrence of Malignant Melanoma and Squamous Cell Carcinoma on Burn Scars: A Case Report

Tumors arising from burn scars are not rare but sometimes cause the rare co-existence of different tumors. However, detailed information on this topic remains largely unknown. We present a case of the co-occurrence of malignant melanoma and squamous cell carcinoma in a patient with a history of burn scars. A 73-year-old man presented with an erythematous plaque on his left lower leg that gradually turned into a tumor with ulceration. He also presented with scaly tumors at other sites within the same burn scar lesion. He had a history of burns on the left leg at the age of 20 years. After surgical resection of the tumors, histological analysis revealed that the posterior aspect of the largest tumor was malignant melanoma, and the remaining two tumors were squamous cell carcinomas, indicating the co-existence of different types of malignant skin cancers. Based on a literature review of previously published case reports, this is the first report to highlight the importance of complete skin grafts in reducing this risk.

The Crucial Roles and Research Advances of cGAS-STING Pathway in Cutaneous Disorders

The cGAS-STING signaling pathway senses the presence of cytosolic DNA, induces strong type I interferon responses, and enhances inflammatory cytokine production, placing it as an important axis in infection, autoimmunity, and tumor immunity. Recent studies have shown that the abnormalities and/or dysfunctions of cGAS-STING signaling are closely related to the pathogenesis of skin diseases and/or cancers. Additionally, a variety of new therapeutics targeting the cGAS-STING signaling are in development for the treatment of skin disorders. However, the precise molecular mechanisms of cGAS-STING-mediated cutaneous disorders have not been fully elucidated. In this review, we will summarize the regulatory roles and mechanisms of cGAS-STING signaling in skin disorders and recent progresses of cGAS-STING-related drugs as well as their potential clinical applications.

How the Innate Immune DNA Sensing cGAS-STING Pathway Is Involved in Apoptosis

The cGAS-STING signaling axis can be activated by cytosolic DNA, including both non-self DNA and self DNA. This axis is used by the innate immune system to monitor invading pathogens and/or damage. Increasing evidence has suggested that the cGAS-STING pathway not only facilitates inflammatory responses and the production of type I interferons (IFN), but also activates other cellular processes, such as apoptosis. Recently, many studies have focused on analyzing the mechanisms of apoptosis induced by the cGAS-STING pathway and their consequences. This review gives a detailed account of the interplay between the cGAS-STING pathway and apoptosis. The cGAS-STING pathway can induce apoptosis through ER stress, NLRP3, NF-κB, IRF3, and IFN signals. Conversely, apoptosis can feed back to regulate the cGAS-STING pathway, suppressing it via the activation of caspases or promoting it via mitochondrial DNA (mtDNA) release. Apoptosis mediated by the cGAS-STING pathway plays crucial roles in balancing innate immune responses, resisting infections, and limiting tumor growth.

Non-coding RNAs in skin cancers:Biological roles and molecular mechanisms

Cutaneous malignancies, including basal cell carcinoma, cutaneous squamous cell carcinoma, and cutaneous melanoma, are common human tumors. The incidence of cutaneous malignancies is increasing worldwide, and the leading cause of death is malignant invasion and metastasis. The molecular biology of oncogenes has drawn researchers’ attention because of the potential for targeted therapies. Noncoding RNAs, including microRNAs, long noncoding RNAs, and circular RNAs, have been studied extensively in recent years. This review summarizes the aspects of noncoding RNAs related to the metastasis mechanism of skin malignancies. Continuous research may facilitate the identification of new therapeutic targets and help elucidate the mechanism of tumor metastasis, thus providing new opportunities to improve the survival rate of patients with skin malignancies.

STING expression is an independent prognostic factor in patients with mycosis fungoides

Mycosis fungoides is recognized as an indolent cutaneous malignant T-cell lymphoma. In contrast, there are few therapeutic options for advanced forms of mycosis fungoides. Since immunotherapy is desirable as an alternative therapeutic option, identifying candidate molecules is an important goal for clinicians. Although tumor-derived negative immunomodulatory molecules, such as PD-1/PD-L1, have been identified in various malignancies, the useful positive immunological drivers of mycosis fungoides are largely unknown. We found that the stimulator of interferon (IFN) genes (STING) was highly upregulated in early-stage mycosis fungoides. Immunohistochemical examination revealed different STING staining patterns in patients with mycosis fungoides. Although there were no significant differences in clinical factors’ characteristics, STING expression was associated with the survival of patients with mycosis fungoides. The survival rate was significantly poor in patients with low STING-expressing mycosis fungoides. Univariate and multivariate analyses revealed that low STING expression was associated with an increased hazard ratio. Our results indicate that STING expression independently influences the prognosis of mycosis fungoides.

Epigenetic Modification of PD-1/PD-L1-Mediated Cancer Immunotherapy against Melanoma

Malignant melanoma is one of the representative skin cancers with unfavorable clinical behavior. Immunotherapy is currently used for the treatment, and it dramatically improves clinical outcomes in patients with advanced malignant melanoma. On the other hand, not all these patients can obtain therapeutic efficacy. To overcome this limitation of current immunotherapy, epigenetic modification is a highlighted issue for clinicians. Epigenetic modification is involved in various physiological and pathological conditions in the skin. Recent studies identified that skin cancer, especially malignant melanoma, has advantages in tumor development, indicating that epigenetic manipulation for regulation of gene expression in the tumor can be expected to result in additional therapeutic efficacy during immunotherapy. In this review, we focus on the detailed molecular mechanism of epigenetic modification in immunotherapy, especially anti-PD-1/PD-L1 antibody treatment for malignant melanoma.

The Influences of Omega-3 Polyunsaturated Fatty Acids on the Development of Skin Cancers

Dietary nutrition intake is essential for human beings and influences various physiological and pathological actions in the human body. Among various nutritional factors, dietary intake of omega-3 polyunsaturated fatty acids (PUFAs) has been shown to have various beneficial effects against inflammatory diseases. In addition to their therapeutic potency against inflammation, omega-3 PUFAs have also been shown to have anti-tumor effects via various mechanisms, such as cell arrest and apoptosis. To date, limited information is available on these effects in cutaneous malignancies. In this review, we focused on the effect of omega-3 PUFAs on skin cancers, especially malignant melanoma, basal cell carcinoma, lymphoma, and squamous cell carcinoma and discussed the detailed molecular mechanism of the omega-3 PUFA-mediated anti-tumor response. We also explored the molecular mechanisms mediated by epigenetic modifications, cell adhesion molecules, and anti-tumor immune responses.