Sustained Aurora Kinase B Expression Confers Resistance to PI3K Inhibition in Head and Neck Squamous Cell Carcinoma.

Tumor suppressor mutations in head and neck squamous cell carcinoma (HNSCC) dominate the genomic landscape, hindering the development of effective targeted therapies. Truncating and missense mutations in NOTCH1 are frequent in HNSCC, and inhibition of PI3K can selectively target NOTCH1 mutant (NOTCH1MUT) HNSCC cells. In this study, we identify several proteins that are differentially regulated in HNSCC cells after PI3K inhibition based on NOTCH1MUT status. Expression of Aurora kinase B (Aurora B), AKT, and PDK1 following PI3K inhibition was significantly lower in NOTCH1MUT cell lines than in wild-type NOTCH1 (NOTCH1WT) cells or NOTCH1MUT cells with acquired resistance to PI3K inhibition. Combined inhibition of PI3K and Aurora B was synergistic, enhancing apoptosis in vitro and leading to durable tumor regression in vivo. Overexpression of Aurora B in NOTCH1MUT HNSCC cells led to resistance to PI3K inhibition, while Aurora B knockdown increased sensitivity of NOTCH1WT cells. In addition, overexpression of Aurora B in NOTCH1MUT HNSCC cells increased total protein levels of AKT and PDK1. AKT depletion in NOTCH1WT cells and overexpression in NOTCH1MUT cells similarly altered sensitivity to PI3K inhibition, and manipulation of AKT levels affected PDK1 but not Aurora B levels. These data define a novel pathway in which Aurora B upregulates AKT that subsequently increases PDK1 selectively in NOTCH1MUT cells to mediate HNSCC survival in response to PI3K inhibition. These findings may lead to an effective therapeutic approach for HNSCC with NOTCH1MUT while sparing normal cells. SIGNIFICANCE: Aurora B signaling facilitates resistance to PI3K inhibition in head and neck squamous cell carcinoma, suggesting that combined inhibition of PI3K and Aurora kinase is a rational therapeutic strategy to overcome resistance.