Induction of tumor cell-based ADCC resistance to create new tumor cell survival and therapy resistance mechanisms.

Abstract

130 Background: EGFR overexpression & amplification is seen in many types of cancer. Cetuximab is an EGFR targeting monoclonal antibody that acts by signal perturbation, complement activation & inducing antibody dependent cellular cytotoxicity(ADCC) by recruiting effector cells. Cetuximab resistance has been extensively investigated, but it has proven difficult to study the molecular mechanisms underlying ADCC resistance because such models are not readily available. Methods: We established an EGFR-targeted ADCC resistance model system using NK92-CD16V effector cells, Cetuximab, and the A431 EGFR-expressing squamous cell carcinoma cell line. Continuous ADCC challenge of A431 (26+ passages) yielded an ADCC-resistant phenotype (ADCCr) that exhibits a stable phenotype in the absence of continued ADCC selection. To further understand the evolution of resistance to ADCC, we explored the ADCCr cell surface signature, gene expression profile & ability to activate NK cells. Results: We find that ADCCr cells(when compared to its ADCC-sensitive(ADCCs) counterpart) have a modest reduction of EGFR expression, a distinctive transcriptional profile highlighted by overexpression of histone & interferon related genes, altered cell surface expression of important cell adhesion molecules, reduced in vitro proliferation and in vivo growth & resistance that is specific to the formation and function of immune synapses. ADCCr can be partially reversed by the exposure to an inhibitor of the histone acetyl transferase p300 subunit. Interestingly, the ADCCr cell line has reduced sensitivity (compared with ADCCs) to antimetabolite, DNA-intercalating and ABC transporter-regulated cytotoxic agents.The PD-L1 immune checkpoint does not modulate ADCC in this model system. Conclusions: These findings suggest that the induction of resistance to EGFR-targeted immune attack in this model system creates broadly useful survival and potential therapy resistance mechanisms.