Abstract 903: Evaluation of predictive biomarkers and resistance mechanisms of PI3K pathway inhibition in head and neck squamous cell carcinoma
Authors: Mazumdar Tuhina , Byers Lauren A. , Ng Patrick , Mills Gordon B. , Peng Shaohua , Diao Lixia , Fan Youhong , Stemke-Hale Katherine , Heymach John V. , Myers Jeffrey N. , Glisson Bonnie S. , Johnson Faye M. 
Published: May 2015

Abstract
Head and neck Squamous cell carcinoma (HNSCC) is a lethal, disabling and disfiguring cancer with no biomarker-directed therapeutic options. We are in a desperate need for novel targeted therapies. PI3K/AKT/mTOR is one of the most often altered pathways in HNSCC. This pathway is important for cancer cell signaling and several pharmacological inhibitors are already in clinical trials for other cancer types. Our lab previously found that HNSCC cell lines with PIK3CA mutations were more sensitive to pathway inhibitors compared to other PI3K pathway alterations such as PIK3CA amplification or PTEN loss and that activation of ERK is one mechanism responsible for PI3K inhibitor resistance. In this report we extended our study to further investigate the predictive biomarkers, biological effects of PI3K inhibition, the potential pathways of resistance and the use of rational drug combination in a diverse panel of HNSCC cell lines. We tested 64 HNSCC cell lines with the PI3K inhibitor GDC0941 and correlated drug sensitivity with basal PI3K pathway activation, PI3K copy number or PIK3CA mutation. We confirmed that cell lines with PIK3CA mutations were more sensitive to GDC0941 (P= 6.35X 10 -13) and those with amplification were not. We tested another four PI3K pathway inhibitors, including one PI3K inhibitor GSK1059615, one dual PI3K/mTOR inhibitor GDC0980, one AKT inhibitor GDC690693 and one mTOR inhibitor AZD8055 in a panel of 18 cell lines and found that the trend of drug sensitivity was similar (P &lt; 0.05) in two PI3K inhibitors and one dual inhibitor where as AKT and mTOR inhibitors had a distinct trend. We evaluated the basal activation of PI3K/AKT/mTOR pathway using reverse phase protein array (RPPA) with two proteomic scores: PI3K/AKT and TSC/mTOR. Neither score predicted sensitivity to GDC0941. We also analyzed the PI3K/AKT and TSC/mTOR scores in 200 HNSCC tumors from the TCGA . In the same way PIK3CA amplification did not correlate with the scores whereas the PI3K/AKT score was higher in the PIK3CA mutants (P &lt; 0.039) compared to WT PIK3CA. The RPPA did identify several biomarkers, including VEGFR2, pCRAF and PCNA, whose expression correlated with GDC0941 sensitivity. Treatment with GDC0941 caused cell cycle arrest in sensitive cell lines, but not in resistant cell lines. To identify potential resistance pathways following GDC0941 treatment in resistant lines, we tested 39 phosphoproteins using phosphoscan analysis and found that EGFR, IGF-1R, RET, FGFR3, and M-CSFR were activated in resistant cell lines after incubation with GDC0941. Combination therapy with GDC0941 and the EGFR inhibitor erlotinib was synergistic in resistant cell lines. Our data will be useful to conduct biomarker-based clinical trials in HNSCC in the near future.
Citation Format: Tuhina Mazumdar, Lauren A. Byers, Patrick Ng, Gordon B. Mills, Shaohua Peng, Lixia Diao, Youhong Fan, Katherine Stemke-Hale, John V. Heymach, Jeffrey N. Myers, Bonnie S. Glisson, Faye M. Johnson. Evaluation of predictive biomarkers and resistance mechanisms of PI3K pathway inhibition in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 903. doi:10.1158/1538-7445.AM2014-903