Abstract 52: Dynamic rewiring of apoptotic signaling networks by combined EGFR/FRGR inhibition enhances killing of head and neck squamous tumor by DNA damage

Abstract

We have previously shown that a subset of triple-negative breast cancers can be dramatically sensitized to killing by DNA-damaging chemotherapy by time-staggered inhibition of EGFR. This sensitization effect results from dynamic re-wiring of apoptotic signaling pathways to engage a caspase-8-dependent cell death mechanism (Figure 1). Here we explored whether combined EGFR and/or FGFR inhibition could enhance the killing of head and neck squamous cell cancers by DNA damaging treatments through a similar re-wiring mechanism. The epidermal growth factor receptor (EGFR) and FGFR pathways are two of the most dysregulated molecular pathways in human head-and-neck squamous cell carcinoma (HNSCC). Despite overexpression in approximately 90% of HNSCC tumors, EGFR inhibitors alone have not exerted a major therapeutic impact on tumor response or patient survival. A recent study provides evidence that the insensitivity of the majority of HNSCC to EGFR inhibitors is mediated by dominant activity of alternative receptor tyrosine kinase (RTK) systems such as FGFR signaling (Clinical Cancer Research 2011). We have found that time-staggered administration of either EGFR inhibitors, or FGFR inhibitors, can dramatically enhance the apoptotic response of HNSCCs to DNA damage from doxorubicin. Importantly, combined inhibition of both the EGFR and FGFR pathways was more effective than inhibition of either pathway alone, at inducing sensitization to cytotoxic chemotherapy through dynamic network re-rewiring. Enhanced cell death by dual EGFR/FGFR inhibition and subsequent genotoxic injury results from greater activation of Caspase-8 than that seen by either EGFR or FGFR inhibitors alone. This enhanced Caspase-8 acitivty, together with Caspase-9 activation, accounts for the majority of apoptotic death. Our data further suggest that Src family kinases are a critical downstream node of EGFR/FGFR activity since treatment of HNSCC cell lines with Src kinase inhibitors resulted in similar sensitization to doxorubicin treatment. In summary, our data extend the utility of therapeutic dynamic rewiring for the targeting of tumors with redundant receptor signaling pathways as well as their critical downstream nodes. Citation Format: Yogesh Dayma, Michael B. Yaffe. Dynamic rewiring of apoptotic signaling networks by combined EGFR/FRGR inhibition enhances killing of head and neck squamous tumor by DNA damage [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 52.