Modulation of inflammasome-mediated cytokine activation by EGCG in human melanoma.

Melanoma incidence has increased in the last 30 years and over 800,000 people have a previous diagnosis of melanoma in the US. Melanoma has a high likelihood to metastasize (spread to other parts of the body) and accounts for 80% of the skin cancer-related deaths. As a result, many melanoma survivors constantly fear when their cancers might come back and spread. Currently, there is no active means to prevent tumor recurrence and metastasis for melanoma survivors. Evidence strongly suggests that inflammation is associated with unfavorable clinical prognosis such as tumor progression and recurrence. We have found that human metastatic melanoma cells show a special form of inflammatory response called "autoinflammation" because of constant activation of a unique inflammatory platform called "inflammasome". This autoinflammation is mediated by IL-1β, a pro-inflammatory cytokine inducing a large portfolio of genes. EGCG is an active ingredient in green tea and has many biological effects including anti-cancer, anti-inflammatory, and anti-pathogen properties. Because many inflammatory mediators reported to be inhibited by EGCG are controlled by active IL-1β (secreted form), we hypothesized that EGCG might inhibit IL-1β activation, thereby controlling other mediators that are important for tumor progression and metastasis. We indeed found that a practical and physiologically achievable dose of EGCG (1 µM) suppresses IL-1β secretion in human metastatic melanoma cells that carry a feature of autoinflammation. We propose to explore the molecular mechanisms of action of a practical dose of EGCG in regulating IL-1β activation in human metastatic melanoma in vitro, and analyze the effects of EGCG on a tumor cell population [putative cancer stem cell (CSC) population] that has a high tendency to initiate tumor formation and recurrence. We also propose to study the biological effects of EGCG on melanoma recurrence using a spontaneous metastasis model in vivo. We will use patient-derived tumor xenograft (PDX) model ("avatar model"), one of the best models in human cancer research that recapitulates complex tumor microenvironment. We will also use cells from a genetically engineered mouse (GEM) model of metastasizing melanoma. PDX and GEM tumor cells will be labeled with a modified labeling method with enhanced brightness, high detection sensitivity, high transduction efficiency and stable labeling. State-of-the-art multimodality imaging will be used to longitudinally monitor tumor recurrence at the initial tumor site, lymph nodes and distant metastatic sites. Tumor cells will be examined to define the effects of EGCG on IL-1β pathway, CSC traits, and epithelial-mesenchymal transition. Because IL-1β plays a critical role in tumor progression, such studies will elucidate the mechanisms of action of EGCG on regulating dysregulated cytokines in cancers and will lead to the development of effective chemopreventive agents with limited to no toxicity that can be taken by cancer survivors to control tumor recurrence and prolong their lives.