Abstract 4169: Inhibition of EphB4-ephrin-B2 signaling results in enhanced sensitivity to cetuximab-radiation therapy in head and neck cancers
Authors: Bhatia Shilpa , Sharma Jaspreet , Bukkapatnam Sanjana , Oweida Ayman , Lennon Shelby , Gill Parkash , Jimeno Antonio , Raben David , Heasley Lynn , Karam Sana D. 
Published: August 2018

Abstract
Introduction: The management of locally-advanced head and neck cancer patients relies on the combination treatment involving 7 weeks of radiation therapy (RT) with Cetuximab, an EGFR-inhibitor. Only a fraction of HNSCC patients, however, show response to cetuximab-radiation with an estimated 5-year overall survival of 46% compared to 36% with radiotherapy alone. This suggests potential involvement of redundant or compensatory tumor survival pathway that comes into action and blunts the therapeutic response. Based on our previous findings and published reports, elevated expression of EphB4, a member of Eph family of receptor tyrosine kinases and its membrane-bound ligand, ephrin-B2 might play a role in mediating this effect. In the current study, we hypothesized that EphB4-ephrin-B2 favors pro-tumorigenic survival signaling by altering the sensitivity to EGFR inhibitor and radiation. Therefore, combined inhibition of EphB4-ephrin-B2 signaling is critical to enhance sensitization of HNSCC towards anti-EGFR and radiation therapy.
Materials and methods: To test the underlying hypothesis, we used a blocking protein targeting EphB4-ephrin-B2 axis in the absence and presence of EGFR inhibitor with radiation in HNSCC cell lines and patient-derived xenograft (PDX) model. Alteration in the protein levels in control and treatment groups was detected by Western blotting and immunohistochemistry. Circulating levels of cytokines was analyzed in vivo by Mesoscale U-plex assay. Tumor tissues were subjected to human PhosphoRTK array to assess changes in the activation status of downstream targets of EphB4-ephrin-B2 signaling mediating response in the triple combination groups.
Results: Our data from locally advanced HNSCC patients treated with standard of care definitive Cetuximab-RT show high levels of both EphB4 and ephrin-B2 after failure of Cetuximab-RT. We observed significant tumor growth delay and increased response towards Cetuximab and radiation therapy following EphB4-ephrin-B2 inhibition resulting in better overall survival in PDX tumors and HNSCC cells. The tumor growth inhibition effects observed in vivo was accompanied by decrease in the levels of proliferation marker, angiogenic regulators, and increased apoptosis. Changes in levels of phopsho-receptor kinases and in circulating immune profile was also evident in tumors subjected to triple combination strategy.
Conclusions: Overall, our data suggest that EphB4-ephrin-B2 and EGFR pathway cross-talk with each other to circumvent the therapeutic response resulting in uncontrolled tumor growth, apoptotic evasion, and immune escape. Therefore, development of combinatorial approaches targeting Eph-ephrin family of proteins might show promising outcome to enhance sensitivity towards anti-EGFR therapeutics and radiation in head and neck cancers.
Citation Format: Shilpa Bhatia, Jaspreet Sharma, Sanjana Bukkapatnam, Ayman Oweida, Shelby Lennon, Parkash Gill, Antonio Jimeno, David Raben, Lynn Heasley, Sana D. Karam. Inhibition of EphB4-ephrin-B2 signaling results in enhanced sensitivity to cetuximab-radiation therapy in head and neck cancers [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 4169.