Abstract 3251: Aurora kinase B expression shields HNSCC from PI3K inhibition-induced apoptosis through downstream mediators AKT and PDK1
Authors: Shah Pooja A. , Fernandez Anne M. , Sambandam Vaishnavi , Zhao Hongyun , Mazumdar Tuhina , Shen Li , Wang Jing , Johnson Faye M. 
Published: June 2022

Abstract
Effective targeted therapies are lacking for head and neck squamous cell carcinoma (HNSCC) that is common and fatal. Developing targeted therapies for HNSCC is challenging as the genomic landscape is dominated by mutations in tumor suppressors, including NOTCH1. To address this need, we previously demonstrated that PI3K inhibition led to apoptosis in NOTCH1 mutant HNSCC cell lines. The underlying mechanism of this sensitivity is unknown and important to elucidate as modest responses and development of acquired resistance are the leading causes of failure for targeted therapies. To address this knowledge gap, we measured the levels of 304 proteins using reverse phase protein array in NOTCH1WT and NOTCH1MUT HNSCC cell lines upon PI3K inhibition and identified Aurora kinase B (AURKB) to be differentially regulated. We also identified AURKB levels to be maintained in the NOTCH1MUT cell lines with acquired resistance to PI3K inhibition. To determine if the maintenance of AURKB expression contributes to PI3K inhibitor resistance, we depleted AURKB in resistant NOTCH1WT HNSCC cells and overexpressed AURKB in sensitive NOTCH1MUT HNSCC cells. This manipulation of AURKB levels led to increased sensitivity and resistance to PI3K inhibition respectively. To use a pharmacologic approach, we combined the pan-Aurora kinase inhibitor danusertib (0-2µM) with PI3K/mTOR inhibitor omipalisib (0-200nM) in 56 HNSCC cell lines for 72h and observed a substantial decrease in cell viability in &gt;80% of NOTCH1WT and &gt;90% of NOTCH1MUT HNSCC lines. Additionally, concurrent Aurora kinase and PI3K inhibition in NOTCH1WT, NOTCH1MUT, and NOTCH1MUT acquired resistant HNSCC cells for 24h resulted in elevated cell death compared to single agents, as measured by the induction of cleaved PARP and cleaved Caspase 3; and Annexin V positive cells. Mice bearing NOTCH1MUT xenografts showed complete tumor regression when treated with a combination of pan-PI3K inhibitor Copanlisib and Aurora inhibitor Alisertib as compared to control groups. AURKB depletion in NOTCH1WT and overexpression in NOTCH1MUT HNSCC cells revealed significant changes in the total protein levels of AKT and PDK1. Similarly, AKT depletion and overexpression in NOTCH1WT and NOTCH1MUT HNSCC cells altered sensitivity to PI3K inhibition. However, manipulation of AKT levels affected PDK1 and not AURKB levels, demonstrating AURKB to be upstream to AKT and PDK1. Therefore, maintenance of AURKB levels mediates resistance to PI3K inhibition in HNSCC through AKT and PDK1. We identified AURKB as a central player governing the sensitivity to PI3K inhibitor-induced apoptosis in the context of NOTCH1 mutation status in HNSCC through its effects on AKT and PDK1. These novel findings may lead to the development of more robust therapeutic approach for NOTCH1 mutant squamous carcinoma as well as patients who develop acquired resistance to targeted therapies.
Citation Format: Pooja A. Shah, Anne M. Fernandez, Vaishnavi Sambandam, Hongyun Zhao, Tuhina Mazumdar, Li Shen, Jing Wang, Faye M. Johnson. Aurora kinase B expression shields HNSCC from PI3K inhibition-induced apoptosis through downstream mediators AKT and PDK1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3251.