Antibody dependent cellular cytotoxicity (ADCC) is one mechanism by which monoclonal antibodies (mAb) work. In addition to ADCC, mAbs act on their target by causing signal perturbation and complement activation. Cetuximab is an EGFR targeting mAb used to target EGFR overexpression and amplification seen in many types of cancer. While mechanisms of resistance to EGFR targeted therapy have been extensively studied, resistance to ADCC has not, mainly due to the lack of ADCC-resistance models for study. To address this limitation we established a model system for anti-EGFR ADCC using NK92-CD16V effector cells, cetuximab, and the high EGFR-expressing squamous cell carcinoma cell line A431. Continuous A431 exposure to ADCC yielded an ADCC resistant phenotype (ADCCr) that exhibits a stable phenotype in the absence of continued ADCC selection. We have explored: ADCCr cell gene expression profile, NK cell activation, metabolic signature and subsequent RPPA analysis to further understand the causes and properties associated with this resistance. This ADCCr cell line has a distinctive transcriptional profile highlighted by overexpression of histone- and interferon-related genes, reduced sensitivity to antimetabolites, DNA-intercalating and ABC transporter-regulated cytotoxic agents. Intense ADCC selection causes epigenetic modification and stress response characterized by the transcriptional overexpression of PCAF (KAT2B), which initiates histone hyper-acetylation and epigenetic changes, inducing DNA replication arrest, DNA damage and stress responses that activate checkpoint signaling in the cell cycle. The pharmacologic inhibition of KAT2B reverses the ADCCr phenotype. Immune checkpoints such as PD-L1 do not modulate ADCC in this model system. These results shed light on new mechanisms of ADCC resistance and inform future combinatorial treatments for mAb therapy. We are exploring the possibility that stress response mechanisms are responsible for resistance for diverse selection pressures imposed by immune synapse-mediated cytotoxic attack.

Citation Format: Dalal S. Aldeghaither, Joseph C. Murray, Sarah M. Roth, Elana J. Fertig, Shaojun Tang, Sandra A. Jablonski, Louis M. Weiner. Induction of ADCC resistance profoundly alters tumor cell phenotype and stress response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 633. doi:10.1158/1538-7445.AM2017-633