Pharmacological activation of NF-κB as a strategy to sensitize HPV-associated head and neck cancer to radiation therapy

Summary: Human papillomavirus-associated (HPV+) head and neck squamous cell carcinoma (HNSCC) surpassed uterine cervical cancer as the most frequently diagnosed HPV+ cancer in 2012, and its incidence continues to increase. We recently identified two intrinsic subtypes of HPV+ HNSCCs from several independent patient cohorts, which relied exclusively on NF-κB activity and have marked molecular and biological differences. The high NF-κB activity subtype is associated with improved patient survival whereas tumors with low NF-κB had approximately 4-fold increased risk of treatment failure. Cancer recurrence in these molecularly high-risk patients is in the range of 35-50%, based on other clinical factors such as smoking history. Therefore, a subset of HPV+ HNSCC patients would greatly benefit from more efficacious therapies as compared to the current standard of care. Our data strongly indicates that constitutive activation of NF-κB in HPV+ HNSCC, typically driven by somatic mutations (e.g. TRAF3/CYLD inactivation), directly enhances these cancer cells and tumors response to radiation. Therefore, we hypothesize that pharmacological activation of NF-κB in HPV+ HNSCCs that have low baseline NF-κB activity will significantly sensitize this subtype of cancer with poor prognosis to radiation therapy. To begin exploring our hypothesis, we utilized a Toll-like receptor 5 (TLR5) agonist entolimod as an NF-κB activator. Preliminary experiments revealed that entolimod activated NF-κB in HPV+ head and neck cancer cells and improved HPV+ xenografted tumors response to fractionated radiation with extension of maximal mouse survival by almost 3-fold (33 days in control group vs 93 days in combination group). To further support our hypothesis that activation of NF-κB is a useful tool to sensitize HPV+ HNSCC to radiation, we performed a preliminary testing of chemical NF-κB activators with a completely different mechanism of action. Mitochondria-derived activator of caspases (SMAC) mimetics are potent inhibitors of IAPs (inhibitors of apoptosis proteins), including XIAP (X-linked IAP) and c-IAP1/2 (cellular IAP 1 and 2) that are potent natural regulators of NF-κB activity. We confirmed NF-κB activation and decreased levels of c-IAP1/2 proteins in HPV+ HNSCC cells after treatment with SMAC mimetics. Importantly, SMAC mimetics significantly sensitized low NF-κB HPV+ head and neck cancer cells to radiation. Although historically, NF-κB activity is associated with worse prognosis in many solid cancers, we show that genetic activation of NF-κB in HPV+ HNSCC is associated with significantly improved patient survival and sensitizes HPV+ HNSCC to radiation. Likewise, drugs that are approved for clinical use and that activate NF-κB show promise to increase the efficacy of radiotherapy in a high-risk subtype of HPV+ HNSCC. Aditi Kothari (she/her/hers), PhD (Presenting Author) - University of North Carolina at Chapel Hill; Travis Schrank (he/him/his), MD, PhD (Co-Author) - University of North Carolina at Chapel Hill; wendell yarbrough, MD (Co-Author) - University of North Carolina at Chapel Hill; natalia isaeva (she/her/hers), PhD (Co-Author) - University of North Carolina at Chapel Hill