Abstract 6319: Mechanism of anti-EGFR antibody endostatin fusion protein action on inhibition of vasculogenic mimicry and tumor cell motility in triple negative breast cancer

Abstract Triple Negative Breast Cancer (TNBC) is an aggressive subtype of breast cancer with high metastatic potential and increased morbidity and mortality. Although expression of and signaling by the epidermal growth factor receptor (EGFR) is commonly seen in TNBC, anti-EGFR antibodies such as Cetuximab have had limited therapeutic efficacy, used alone or in combination with chemotherapy. Primary TNBC tumor growth and metastases require supporting vasculature, which develops through a combination of endothelial angiogenesis and vasculogenic mimicry (VM). VM is frequently seen in TNBC and is associated with aggressive metastatic behavior. We previously developed αEGFR-E-P125A, an antibody-endostatin fusion protein, linking an anti-EGFR antibody to a mutated version of the anti-angiogenic protein endostatin (E-P125A). αEGFR-E-P125A delivers a dimeric E-P125A payload which inhibits TNBC angiogenesis and VM in vitro and in vivo, and markedly decreases metastasis in multiple TNBC xenograft models. To study changes in the transcriptome following induction of VM and inhibition of VM with αEGFR-E-P125A, RNA-seq was conducted on MDA-MB-231-4175 TNBC cells grown in a 2D monolayer and compared to TNBC cells undergoing VM when plated in matrigel. A second comparison was made between TNBC cells undergoing VM and TNBC cells in which VM was inhibited by treatment with αEGFR-E-P125A. Differential gene expression analysis and gene set enrichment analysis (GSEA), were used to define pathways which were inversely regulated during the induction of VM on matrigel and inhibition of VM with αEGFR-E-P125A. Gene set enrichment analysis demonstrated that αEGFR-E-P125A treatment significantly downregulated genes in the JAK-STAT and angiogenesis signaling pathways. Phospho-array analysis demonstrated decreased EGFR phosphorylation at Y1069 in addition to decreased phosphorylation of FAK Y397 and STAT3 Y705 sites downstream of α5β1 integrin. Since inhibition of EGFR signaling alone did not inhibit VM, and endostatin is a known ligand of α5β1 integrin, we focused on effects of αEGFR-E-P125A on inhibition of α5β1 integrin/FAK signaling pathway. Independent siRNA knockdowns of α5 integrin and FAK in MDA-MB-231-4175 cells confirmed that downregulation of α5 integrin/FAK signaling inhibited VM in vitro. αEGFR-E-P125A additionally prevented EGF-induced EGFR phosphorylation and fibronectin-induced FAK phosphorylation by α5β1 integrin. Treatment of TNBC cells with αEGFR-E-P125A reduced total α5 integrin protein levels and decreased co-localization of EGFR and α5β1 integrin receptors. These results indicate that αEGFR-E-P125A suppressed both EGFR and α5β1 integrin signaling. Simultaneous inhibition of EGFR and α5β1integrin signaling by αEGFR-E-P125A fusion is a promising approach to inhibition of TNBC growth and metastases. Citation Format: Ankita Sankar, Hava Gil Henn, Hyun Mi Cho, Dania Nassar, Sundaram Ramakrishnan, Yu Zhang, Christian Elledge, Seung Uon Shin, Joseph Rosenblatt. Mechanism of anti-EGFR antibody endostatin fusion protein action on inhibition of vasculogenic mimicry and tumor cell motility in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6319.