Targeting BCL-2 family-regulated cell death for HNSCC treatment

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Project Summary The goal of this application is to demonstrate the feasibility of new combination treatments in several mouse models of head and neck squamous cell carcinoma (HNSCC). The long-term prognosis of patients with advanced HNSCC has shown little improvement over the last three decades. Induction chemotherapy with platinum-based compounds (e.g. cisplatin) and epidermal growth factor receptor (EGFR)-targeted therapy with cetuximab are the current chemotherapeutic treatments of choice for HNSCC, but the prolonged use of these drugs is limited by their toxicity and by the development of resistance. Tumor cell death induced by both conventional and targeted chemotherapy is often mediated by the BCL-2 family-dependent mitochondrial apoptotic pathway. However, initiators of this apoptotic pathway, such as p53, are frequently mutated or deleted in HNSCC rendering it refractory to treatment. To counter such resistance, direct therapeutic targeting of the BCL-2 family is conceptually appealing. Our long-term goal is to develop novel strategies for HNSCC treatment that directly target this intrinsic apoptotic pathway. We have investigated the cytotoxic effects of cisplatin, which is used as standard therapy for locally advanced HNSCC. As preliminary data, we have demonstrated that (1) The pro-apoptotic BCL-2 family protein Noxa is upregulated by cisplatin and is required for cisplatin-induced apoptosis in a variety of HNSCC cells; (2) Noxa overexpression enhances cell death induced by a pro-survival BCL-2/BCL-XL inhibitor, navitoclax (ABT-263) in HNSCC cells in vitro regardless of p53 status; (3) Noxa can be induced by an endoplasmic reticulum (ER)-stress inducer, fenretinide (N-4- hydroxyphenyl-retinamide). Using fenretinide as an alternative Noxa inducer, combination with fenretinide and navitoclax efficiently induce cell death in HNSCC cells that are resistant to cisplatin. Based on the above results, our central hypothesis is that simultaneous inhibition of MCL-1, BCL-XL, and BCL-2 is crucial for cell death induction during HNSCC treatment. In order to test this hypothesis, we will determine the molecular mechanisms of cisplatin + navitoclax or fenretinide + navitoclax activity in vitro (Aim 1). Furthermore, we will define a new treatment modality by demonstrating the cytotoxic and overall therapeutic effects of cisplatin + navitoclax or fenretinide + navitoclax combination in mouse models of HNSCC (Aim 2). The outcome of this project will lead to development of alternative therapeutic strategies to directly modify the cell death machinery in HNSCC.