Head and neck squamous cell carcinomas (HNSCCs) coincide with poor survival rates. The lack of driver oncogenes complicates the development of targeted treatments for HNSCC. Here, we follow-up on two previous genome-wide RNA and microRNA interference screens in HNSCC to cross-examine tumor-specific lethality by targeting ATM , ATR , CHEK1 , or CHEK2 . Our results uncover CHEK1 as the most promising target for HNSCC. CHEK1 expression is essential across a panel of HNSCC cell lines but redundant for growth and survival of untransformed oral keratinocytes and fibroblasts. LY2603618 (Rabusertib), which specifically targets Chk1 kinase, kills HNSCC cells effectively and specifically. Our findings show that HNSCC cells depend on Chk1-mediated signaling to progress through S-phase successfully. Chk1 inhibition coincides with stalled DNA replication, replication fork collapses, and accumulation of DNA damage. We further show that Chk1 inhibition leads to bimodal HNSCC cell killing. In the most sensitive cell lines, apoptosis is induced in S-phase, whereas more resistant cell lines manage to bypass replication-associated apoptosis, but accumulate chromosomal breaks that become lethal in subsequent mitosis. Interestingly, CDK1 expression correlates with treatment outcome. Moreover, sensitivity to Chk1 inhibition requires functional CDK1 and CDK4/6 to drive cell cycle progression, arguing against combining Chk1 inhibitors with CDK inhibitors. In contrast, Wee1 inhibitor Adavosertib progresses the cell cycle and thereby increases lethality to Chk1 inhibition in HNSCC cell lines. We conclude that Chk1 has become a key molecule in HNSCC cell cycle regulation and a very promising therapeutic target. Chk1 inhibition leads to S-phase apoptosis or death in mitosis. We provide a potential efficacy biomarker and combination therapy to follow-up in clinical setting.

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HPV-negative head and neck squamous cell carcinomas (HNSCCs) develop in precancerous changes in the mucosal lining of the upper-aerodigestive tract. these precancerous cells contain cancerassociated genomic changes and cause primary tumors and local relapses. therapeutic strategies to eradicate these precancerous cells are very limited. Using functional genomic screens, we identified the therapeutic vulnerabilities of premalignant mucosal cells, which are shared with fully malignant HNSCC cells. We screened 319 previously identified tumor-lethal siRNAs on a panel of cancer and precancerous cell lines as well as primary fibroblasts. In total we identified 147 tumor-essential genes including 34 druggable candidates. Of these 34, 13 were also essential in premalignant cells. We investigated the variable molecular basis of the vulnerabilities in tumor and premalignant cell lines and found indications of collateral lethality. Wee1-like kinase (WEE1) was amongst the most promising targets for both tumor and precancerous cells. All four precancerous cell lines were highly sensitive to Wee1 inhibition by Adavosertib (AZD1775), while primary keratinocytes tolerated this inhibitor. Wee1 inhibition caused induction of DNA damage during S-phase followed by mitotic failure in (pre)cancer cells. In conclusion, we uncovered Wee1 inhibition as a promising chemopreventive strategy for precancerous cells, with comparable responses as fully transformed HnScc cells. Head and neck squamous cell carcinomas (HNSCCs) arise in the mucosal lining of the upper-aerodigestive tract and account for around 5% of the total cancer incidence 1,2. The main risk factors for head and neck cancer are smoking and excessive alcohol consumption, infection with a high-risk type of the human papillomavirus (HPV), or genetic predisposition such as Fanconi anemia (FA) 2. FA is characterized by congenital abnormalities, progressing anemia, and cancer predisposition, particularly of oral cancers. These tumors are difficult to manage as FA-patients are sensitive to cross-linking agents such as cisplatin, hampering clinical management of tumors, and for these patients surveillance and prevention is key. Tumors in the head and neck region develop in premalignant mucosal changes, large epithelial areas characterized by cancer-associated genetic changes, also referred to as "fields". These precancerous fields can be centimeters in size, and are often macroscopically invisible. A minority manifests as visible mucosal lesions known as leukoplakia or erythroplakia, which occur with a prevalence of around 0.1-0.2% for leukoplakia 3 , and 0.02-0.2% for erythroplakia 4. Every year, 1-2% of the leukoplakia lesions progress into cancer, and erythroplakia lesions inevitably progress. Despite the occurrence and prevalence of these visible lesions, the large majority of head and neck cancers develop de novo. In resected tumor specimen, however, preceding premalignant changes can be often identified in the surgical margins by either microscopic detection of dysplasia or by ge...