Targeted Treatment of Head and Neck (Pre)Cancer: Preclinical Target Identification and Development of Novel Therapeutic Applications

SIMPLE SUMMARY: Head and neck squamous cell carcinomas (HNSCCs) develop from mucosal cells in the oral cavity, pharynx and larynx after either prolonged exposure to tobacco and alcohol, or a transforming infection with high-risk human papillomavirus (HPV). HPV-negative HNSCCs develop in a zone of premalignant mucosal cells centimeters in diameter and characterized by tumor-associated genetic changes, also referred to as ‘fields’, which can present as white leukoplakia lesions but are mostly invisible. Patients with HPV-negative HNSCC have an overall 5-years survival rate of 50–60%, despite application of intense treatment protocols, and current treatment regimens seem to have reached their plateau. Recently, immunotherapy using immune checkpoint inhibitors has been introduced, but seems effective in only some patients. Targeted treatments have failed to find their way into the clinic while novel therapies are urgently awaited that could target the tumor as well as the precancerous cells. However, recent data suggest that we are at the dawn of a new era. This review focusses on the preclinical identification of druggable targets for therapy for HPV-negative HNSCC and their preceding precancerous changes. ABSTRACT: Head and neck squamous cell carcinomas (HNSCC) develop in the mucosal lining of the upper-aerodigestive tract. In carcinogen-induced HNSCC, tumors emerge from premalignant mucosal changes characterized by tumor-associated genetic alterations, also coined as ‘fields’ that are occasionally visible as leukoplakia or erythroplakia lesions but are mostly invisible. Consequently, HNSCC is generally diagnosed de novo at more advanced stages in about 70% of new diagnosis. Despite intense multimodality treatment protocols, the overall 5-years survival rate is 50–60% for patients with advanced stage of disease and seems to have reached a plateau. Of notable concern is the lack of further improvement in prognosis despite advances in treatment. This can be attributed to the late clinical presentation, failure of advanced HNSCC to respond to treatment, the deficit of effective targeted therapies to eradicate tumors and precancerous changes, and the lack of suitable markers for screening and personalized therapy. The molecular landscape of head and neck cancer has been elucidated in great detail, but the absence of oncogenic mutations hampers the identification of druggable targets for therapy to improve outcome of HNSCC. Currently, functional genomic approaches are being explored to identify potential therapeutic targets. Identification and validation of essential genes for both HNSCC and oral premalignancies, accompanied with biomarkers for therapy response, are being investigated. Attentive diagnosis and targeted therapy of the preceding oral premalignant (preHNSCC) changes may prevent the development of tumors. As classic oncogene addiction through activating mutations is not a realistic concept for treatment of HNSCC, synthetic lethality and collateral lethality need to be exploited, next to immune therapies. In recent studies it was shown that cell cycle regulation and DNA damage response pathways become significantly altered in HNSCC causing replication stress, which is an avenue that deserves further exploitation as an HNSCC vulnerability for treatment. The focus of this review is to summarize the current literature on the preclinical identification of potential druggable targets for therapy of (pre)HNSCC, emerging from the variety of gene knockdown and knockout strategies, and the testing of targeted inhibitors. We will conclude with a future perspective on targeted therapy of HNSCC and premalignant changes.