Abstract 876: Effective reduction of PD-L1 expression by simultaneous blockade of EGFR and HER3 (ErbB3) in head and neck cancer
Authors: Chen Zhuo Georgia , Wang Dongsheng , Griffith Christopher C. , Nannapaneni Sreenivas , Steuer Conor , Patel Mihir R. , El-Deiry Mark W. , Wang Xu , Zhang Yuzi , Chen Zhengjia , Alvarado Diego , Shin Dong M. , Saba Nabil F. 
Published: August 2018

Abstract
Background: We previously reported that simultaneous blockade of EGFR and HER3 by antibodies cetuximab and MM-121, respectively, could more potently reduce tumor growth in both squamous cell carcinoma of head and neck (SCCHN) cell lines and patient derived xenograft (PDX) models (Jiang et al, MCT, 13:1826-36, 2014; Wang et al., CCR, 23:677-86, 2016). Recently, we tested a new anti-HER3 antibody CDX-3379 (provided by Celldex Therapeutics, Inc) in combination with cetuximab for treatment of SCCHN. The effects of this combination on expression of the immune check point regulator PD-L1 and regulatory pathways underlying these effects were examined. In fact, a Phase II clinical trial combining CDX-3379 with cetuximab in checkpoint and cetuximab refractory patients has already been initiated. Method: Antitumor effects of cetuximab and CDX-3379 combination were investigated in SCCHN PDX animal models. Both HPV positive and negative SCCHN cell lines, UM-SCC47 (HPV+), 93Vu147T (HPV+), FaDu (HPV-), and JHU-022 (HPV-), were used for western blot analysis to examine EGFR and HER3 downstream pathways and PD-L1 expression in the presence and absence of interferon γ (IFNγ) after treatment with cetuximab, CDX-3379, or both agents in combination. Results: The PDX study indicated that, similar to MM-121, combining CDX-3379 with cetuximab inhibited tumor growth more potently than cetuximab alone or the untreated control (control vs. combination: p &lt; 0.0001; cetuximab vs. combination: p &lt; 0.0001). Mechanistic in vitro studies demonstrated that in addition to co-blocking ERK and AKT pathways, and regardless of HPV status, the cetuximab and CDX-3379 combination reduced PD-L1 expression more effectively than any of the single agents in the presence or absence of IFNγ, which has been previously reported to be secreted by natural killer (NK) cells through cetuximab-mediated antibody-dependent cell mediated cytotoxicity, leading to induction of PD-L1 expression in vivo. Using an AKT inhibitor, we confirmed that the AKT pathway was one of the major regulatory pathways involved in regulation of PD-L1. Considering that HER3 exerts its inhibitory effect mainly through regulation of the AKT pathway, reducing AKT activity by addition of CDX-3379 to cetuximab contributed significantly to the reduction of PD-L1 expression. Conclusion: In addition to its anti-tumor effect, the combination of cetuximab and CDX-3379 significantly reduced PD-L1 expression. The role of this combination in the regulation of tumor immunology and the tumor microenvironment in SCCHN deserves further investigation.
Citation Format: Zhuo Georgia Chen, Dongsheng Wang, Christopher C. Griffith, Sreenivas Nannapaneni, Conor Steuer, Mihir R. Patel, Mark W. El-Deiry, Xu Wang, Yuzi Zhang, Zhengjia Chen, Diego Alvarado, Dong M. Shin, Nabil F. Saba. Effective reduction of PD-L1 expression by simultaneous blockade of EGFR and HER3 (ErbB3) in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 876.