Restoring the Regulation of a Central Signaling Pathway to Prevent Metastases and Reinstate Tumor Immunity

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Our long-term goals are to understand the mechanisms by which IL-1 receptor associated kinase-M (IRAK- M) expression in melanoma regulates metastasis and to develop clinically-relevant approaches to induce and sustain anti-tumor T cell immunity by restoring IRAK-M expression. Cancer metastasis is the main cause of cancer mortality and morbidity, accounting for 90% of cancer-related deaths. Immunotherapy has revolutionized the treatment of advanced (metastatic) melanoma and is now the standard of care for most patients. Despite these successes however, clinical benefits are restricted to small percentage of patients. An underlying and universal hindrance to immunotherapies is a variety of immunosuppressive mechanisms that in large part originate from the chronic expression of inflammatory signals. Understanding the fundamental mechanisms that regulate these factors and targeting these pathways is critical for developing effective strategies to prevent or reduce metastases and to restore antitumor T cell activity. We previously reported that the IL-1 receptor associated kinase-4 (IRAK-4) is overexpressed and activated in melanoma. IRAK-4 is a central kinase in the inflammatory process that also regulates the expression of metastases-promoting and immunosuppressive molecules (including ATP, VEGF PDGF, IL-1). This signaling pathway is activated by IL- 1 receptor and toll-like receptors. We previously reported that inhibiting IRAK-4 activity in melanoma drastically reduces the expression of many of these inflammatory factors and reduces cancer progression in mice. By examining the levels of endogenous proteins that normally inhibit IRAK-4 signaling we found IRAK-M to be deficient in melanomas (patients and cell lines). IRAK-M is unique among the IRAK family members in that it is a negative regulator of inflammatory IRAK-4 signaling. We found that restoring IRAK-M expression in melanoma cells drastically reduced their ability to invade (in vitro) and to metastasize (in preclinical models). This was associated with changes in the expression levels of key molecules associated with cell mobility, cytoskeletal dynamics, and formation of lamellipodium in non-cancerous cells but their role in melanoma or metastasis is unknown. These molecules include Distal-Less Homeobox 5 (DLX5; a factor with transcription activating and repressing activity), the integrin ITGA11, and cytoplasmic FMR1 Interacting Protein 2 (Cyfip2). Furthermore, we observed that IRAK-4 signaling in melanoma accelerated T cell dysfunction while inhibiting IRAK-4 enhanced antitumor T cell activity. IRAK-4’s ability to alter T cell activity was associated with its ability to regulate extracellular ATP levels; ATP’s metabolite, adenosine, strongly suppresses T cell activity. Through these studies, we will test the hypothesis that restoring IRAK-M expression in melanoma impairs their metastatic potential by regulating the expression of DLX5 which in turn regulates cell invasion. We further postulate that IRAK-M expression in cancer cells restores antitumor T cell activity by reducing the expression levels of and signals originating from extracellular ATP. In Aim 1, we will determine the mechanism by which IRAK-M regulates cancer cell invasion. This aim builds on compelling preliminary data indicating that IRAK-M induction in cancer cells impairs their ability to invade through matrix or endothelial cells (in vitro) and to metastasize (in vivo). We conjecture that DLX5 upregulates ITGA11 but downregulates Cyfip2 expression thereby controlling cell migration, cell morphogenesis and invasion. Through Aim 2, we propose to restore tumor immunity by reinstating IRAK-M signaling in tumor cells. We will use genetic approaches and a predefined panel of drugs, that selectively induce IRAK-M in melanoma, to investigate the cellular and molecular mechanisms by which IRAK-M enhances anti-tumor T cell activity. These studies have the potential to provide mechanistic insights as to how IRAK-M regulate cancer cell metastasis and opportunities to develop clinically relevant, novel strategies to restore tumor immunity.