Abstract 2879: Pre-clinical characterization of Dacomitinib, an irreversible pan-HER inhibitor, combined with radiation therapy in head and neck cancer models
Authors: Williams Justin P. , Kim Inki , Yue Shijun , Shi Wei , Ito Emma , Siu Lillian L. , Waldron John , Liu Fei-Fei 
Published: August 2012

Introduction: Head and neck cancer is the 5th most common cancer worldwide; the majority of cases (&gt;90%) are squamous cell carcinomas (SCCHNs). Despite advances in treatment, the 5-year overall survival rate for SCCHN patients still remains at ∼40-50%, underscoring the need to develop novel therapeutic strategies. EGFR is over-expressed in ∼90% of SCCHN cases, and is associated with tumor progression and poor prognosis. Dacomitinib (D), an irreversible pan-HER inhibitor, has demonstrated clinical potential in patients with non-small cell lung cancer, leading us to explore its therapeutic efficacy in SCCHN pre-clinical models, in combination with radiation therapy (RT), a curative modality for HNC management. Methods: The basal expression of EGFR family members was assessed via qRT-PCR in three SCCHN models (FaDu (human hypopharyngeal), UTSCC-8 & -42a (both laryngeal) squamous cancer, and NOE (normal oral epithelial) cell lines. MTS-based cell viability and clonogenic assays were performed with various concentrations of D, both alone and in combination with irradiation (IR). Inhibition of EGFR signalling by D was confirmed via immunoblotting. Cell cycle analysis was performed to assess mode of cytotoxicity. In vivo therapeutic studies were performed using FaDu xenografts in SCID mice; tumors were extracted post-treatment and examined for TUNEL, CD31, Ki67, and pEGFR via IHC. Results: EGFR was over-expressed in all three SCCHN, compared to the NOE cells. PF (50 nM) reduced FaDu cell viability by ∼25%, with an additive interaction being observed when D was combined with 2 Gy IR (∼36%). Similar trends were observed in the other two cell lines and also in the clonogenic assays. Immunoblotting confirmed a dose-dependent inhibition of EGFR signalling in D-treated SCCHN cells, along with downstream reduction of p-Erk, p-Akt, and p-mTOR expression. Cell cycle analyses showed ∼20% increase in the G0/G1 cell population in D-treated FaDu cells, and ∼10% increase in the sub-G cell population when D and IR were combined. Mice treated with the combination of D + IR exhibited a maximum tumor growth delay of ∼21 days, as compared to the IR only group, determined by time to tumor-plus-leg diameter of 14mm. Preliminary histological analysis of the extracted tumor tissue show ∼40% reduction in Ki67 staining in the PF + IR treated mice. The addition of D to IR appeared to be well-tolerated, with no change in body weight, or extent of alopecia. Conclusion: Dacomitinib effectively inhibited EGFR signalling in SCCHN models, leading to a reduction in cell viability and clonogenic survival in vitro, along with tumor growth delay in vivo. When D was combined with IR, there was an additive interaction, both in vitro and in vivo. Thus, D combined with RT may have a therapeutic benefit for patients with SCCHN.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2879. doi:1538-7445.AM2012-2879