Construction of synthetic lethal networks for p53 tumor suppressor pathways identifies candidate therapeutic targets for metastatic, chemotherapy resistant HNSCC

p53 deficient cells are resistant to apoptosis, which contributes to malignant progression and therapy resistance of p53 mutant tumors. For this reason, identifying and targeting p53 independent cell death pathways is an important therapeutic goal. We previously reported that the DNA damage kinases Atm and DNA-PK exhibit p53 independent synthetic lethal interactions (Current Biology 11:191-194, 2001) and that DNA-PK regulates a DNA damage induced apoptotic response that is p53 independent (EMBO Reports, 10:87-93, 2009). To identify additional synthetic lethal interactions with the p53 pathway, we used high throughput siRNA screens to interrogate the kinomes of both human and mouse tumor cell cultures stratified for p53 status and metastatic potential. Mouse cells included low passage squamous cell carcinoma (SCC) cells isolated from tumors from five genotypes of mice: wild type, Atm-/-, DNA-PKcs-/-, p19/Arf -/- and p53+/-. Human cells were derived from both primary and metastatic head and neck squamous cell carcinomas (HNSCC). siRNA kinome screens were run in the presence of three concentrations of the chemotherapy agent doxorubicin to identify genotype specific sensitizers. We identified numerous additional synthetic partners with each p53 pathway mutation: Atm, DNA-PKcs, p19/Arf, and p53. These synthetic lethal interactions varied with doxorubicin exposure, thus defining gene targets that sensitize tumor cells of defined genotype to genotoxic therapy. Cross species comparison and independent validation was used to prioritize 20 survival kinases specific to p53 mutant metastatic HNSCC. These kinases are involved in phosphatidylinositol, Src, focal adhesion and integrin signaling pathways, and G2/M cell cycle transition. We selected the G2/M regulatory kinase, WEE1, for preclinical testing as a small molecule inhibitor is available with potential for clinical application. Relative to p53 wild type SCC cells, p53 deficient cells were more sensitive to the WEE1 inhibitor MK-1775, as well as the CHK1 inhibitor AZD7762 providing chemical confirmation of our siRNA screen results. Examination of 42 additional SCC cell lines revealed that p53 mutation conferred increased sensitivity to a dual WEE1/CHK1 inhibitor. Treatment of mice bearing xenografts of p53 mutant HNSCC cells with MK-1775, either alone or in conjunction with cisplatin, impaired tumor growth and in some cases led to tumor regression. These results demonstrate the utility of high throughput siRNA screens applied to genetically defined early passage tumor cells combined with cross species comparisons to efficiently pinpoint novel drug targets for p53 mutant cancers. This abstract is also presented as Poster A04. Citation Format: Russell Moser, Chang Xu, Michael Kao, In Sock Jang, Kay Gurley, Adam Margolin, Carla Grandori, Eddie Mendez, Chris Kemp. Construction of synthetic lethal networks for p53 tumor suppressor pathways identifies candidate therapeutic targets for metastatic, chemotherapy resistant HNSCC. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr PR05.