Abstract 3603: Molecular targeting of cetuximab resistant head and neck cancer

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Despite promising preclinical data, the EGFR targeted monoclonal antibody, cetuximab, has limited use as single agent therapy in the treatment of head and neck cancer due to the development of therapeutic resistance. Improved approaches to treat these cancers will need to address the evolving molecular landscape of head and neck cancer. Recent reports describing mutations or copy number alterations in PI3K and PTEN as potential causes of cetuximab resistance have sparked interest in therapeutics that target these pathways as alternatives to or in combination with EGFR targeting drugs. Using both in vitro and in vivo models of head and neck squamous cell carcinoma (HNSCC) we have recapitulated the diversity of responses to cetuximab observed in the patient population and are testing alternative therapies. Examining an array of HNSCC cell lines, including both human papillomavirus (HPV) positive and negative lines, we observed a wide range of sensitivities to this drug, with little to no growth inhibition in some lines even at micromolar concentrations. For lines that were sensitive to drug, effective growth inhibition, demonstrated in both proliferation and colony formation assays, was linked with suppressed phosphorylation of both Akt and ERK/MAPK signaling downstream of EGFR. Additionally, in the sensitive HPV+ HNSCC lines, cetuximab treatment induced apoptosis marked by caspase activity. Both sensitive and resistant HNSCC lines were then tested for response to both AZD8055, a dual mTORC1/2 inhibitor and BEZ235, a PI3K/mTORC1 inhibitor, resulting in both growth inhibition and successful suppression of phosphorylation of their Akt and S6 targets, suggesting that these drugs may be useful alternatives or adjuvants for cetuximab treatment. In vivo models of HNSCC were also utilized to test the efficacy of cetuximab treatment and begin to evaluate alternative or combination therapies. Using immunocompromised mouse models, both cell line xenografts and novel patient derived xenografts presented a range of sensitivities to cetuximab. In an effort to identify potential biomarkers that would predict response to cetuximab, IHC staining of pre-treatment tumor samples was carried out and demonstrated that low phospho-Akt and phospho-ERK levels correlated with cetuximab sensitivity. Initial in vivo studies using the PI3K/mTORC inhibitors AZD8055 and BEZ235 to treat both cetuximab sensitive and resistant xenografts, have shown that these compounds may be effective at suppressing growth in both categories of tumors. These studies provide initial pre-clinical data to support the use of PI3K inhibition for the treatment of head and neck cancer. Citation Format: Adam D. Swick, Dana Gunderson, Molly Smith, Grace Blitzer, Andrew Stein, Kwangok P. Nickel, Randall J. Kimple. Molecular targeting of cetuximab resistant head and neck cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3603. doi:10.1158/1538-7445.AM2015-3603