Abstract LB-79: Combined treatment with HER3 antibody MM-121/SAR 256212 and EGFR antibody cetuximab in pre-clinical models of head and neck cancer.
Authors: Jiang Ning , Wang Dongsheng , Hu Zhongliang , Rahman Aminur M. , Zhang Hongzheng , Amin Ruhul A. , Wang Xiaojing , Chen Zhengjia , Dong Shin M. , Garcia Gabriela , MacBeath Gavin , Ma Jun , Khuri Fadlo R. , Saba Nabil F. , Chen Georgia Z. 
Published: August 2014

Abstract
Background: The EGFR monoclonal antibody cetuximab is approved for treating head and neck squamous cell cancer (SCCHN) in combination with radiation therapy for locally advanced disease and chemotherapy for recurrent and metastatic disease. Intrinsic or compensatory HER3 signaling and sustained PI3K/Akt activation may play a role in resistance to EGFR-targeted therapy. However, the role of HER3 in resistance to EGFR-targeted therapy in SCCHN has not been elucidated. Therefore, we first tested whether the combination of MM-121/SAR 256212 (M), a HER3 antibody being co-developed by Merrimack Pharmaceuticals and Sanofi, with cetuximab (C) may be more effective than M or C alone in treatment of SCCHN. Methods: We screened for the expression of EGFR, HER3 and their activated forms in 12 SCCHN cell lines. We then evaluated the activity of C, M, and their combination (CM) both in vitro by colony formation assay and in vivo by using SCCHN xenograft models (Tu212 and SCC47). In the in vivo experiment, mice were treated by intraperitoneal injection (i.p.) of C, M or CM twice per week for 4 weeks. The experimental groups include a PBS control, C (6.25ug/dose), M at low dose (300ug/dose, LD), M at high dose (600ug/dose, HD), the combination with LD (CMLD), and the combination with HD (CMHD). In addition, we examined the effect of M and C on HER3 and its downstream pathways in SCCHN cell lines by western blot assay. Results: pHER3 was detected in 9/12 while pEGFR, EGFR and HER3 were expressed in all of 12 SCCHN cell lines. The colony formation assay showed that Tu212 cells were significantly inhibited by CM compared to the control (p &lt;0.001), M (p&lt;0.001) and C (p=0.009) alone. Similar results were also observed using the SCC47 cell line. Western blot analysis confirmed the down-regulation of activated HER3 and its downstream phospho-Akt and phospho-S6 ribosomal protein by CM. Our in vivo study showed significant tumor growth inhibition in both MM-121 LD (p&lt;0.001) and MM-121HD (p&lt;0.001) compared to the control. Moreover, the treatment with both CMLD and CMHD significantly suppressed Tu212 xenograft tumor growth compared to the PBS control (both p&lt;0.0001), C alone (both p&lt;0.0001), and MLD (p=0.0046 and 0.0008, respectively), but only CMHD showed significant inhibition compared to MHD (p = 0.02). There was no significant difference between CMLD and CMHD (p=0.5994). Studies using another SCCHN xenograft model (SCC47) showed a similar inhibitory effect from the treatments by C, M and CM. Conclusion: This study shows that the combination of cetuximab and MM-121 is significantly more active than MM-121 or cetuximab alone in models of head and neck cancer in which both EGFR and HER3 are activated. Further studies will be expanded to understand the underlying mechanisms of this combination. (This study was supported by Merrimack Pharmaceuticals Inc.)
Citation Format: Ning Jiang, Dongsheng Wang, Zhongliang Hu, Aminur M. Rahman, Hongzheng Zhang, Ruhul A. Amin, Xiaojing Wang, Zhengjia Chen, Shin M. Dong, Gabriela Garcia, Gavin MacBeath, Jun Ma, Fadlo R. Khuri, Nabil F. Saba, Georgia Z. Chen. Combined treatment with HER3 antibody MM-121/SAR 256212 and EGFR antibody cetuximab in pre-clinical models of head and neck cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-79. doi:10.1158/1538-7445.AM2013-LB-79