Targeting EGFRs and Src signaling with a modified ectodomain of human EGFR (EBIP) and dasatinib in breast cancer.

Abstract

Abstract Abstract #3069 It is becoming increasingly evident that many solid tumors including breast cancer show increased activation of several growth factor receptors, specifically EGFR and its family members (EGFRs) as well as c-Src, a non-receptor tyrosine kinase that promote proliferation, inhibit apoptosis and induce metastasis. The EGF-receptor (EGFR) consists of an extracellular ligand-binding domain, a hydrophobic transmembrane region, and an intracellular tyrosine kinase domain. The extracellular or ectodomain of EGFR is essential for ligand-binding and subsequent homo/heterodimerization of the receptor. This raises the possibility that the ectodomain of EGFR could be utilized to inhibit EGFR functions and in turn cellular growth. Recently, we generated an ectodomain of human EGFR (hEGFR), composed of 1-448 amino acids fragment of hEGFR and the 30 amino acid epitope (known as “U” region) of rat EGFR-Related Protein (ERRP) fused at the carboxy-terminal end. The new protein, referred to as EBIP (ErbB Inhibitory Protein), as has been observed for ERRP (Xu et al. Mol. Cancer Ther. 2005 (4): 435-42), inhibits growth of colon and breast cancer cells that express varying levels of EGFR and/or its family members. We hypothesize that inhibition of c-Src and EGFRs will be an effective therapeutic strategy for breast cancer. To test our hypothesis we used Dasatinib (BMS-354825; Bristol-Myers Squibb), a newly developed highly potent, ATP-competitive Src and Abl kinase inhibitor and ErbB Inhibitory Protein (EBIP). Four different breast cancer cell lines (MDA-MB-468, SKBr-3, MDA-MB-453 and MDA-MB-231) expressing different levels of EGFR and/or its family members were used. Both EBIP and dasatinib caused a dose dependent inhibition of growth in all breast cancer cells, but dasatinib was less effective compared to EBIP. However, the combination of Dasatinib and EBIP synergistically inhibited cell growth. In EGFR overexpressing MDA-MB-468 cells, the combination therapy also inhibited invasion through extracellular matrix and decreased colony formation. Induction of apoptosis could be attributed to activation of caspases -9 and -8 and by modulating phosphorylation of anti- and pro-apoptotic proteins, Bcl-2 and Bad, respectively. The combination of Dasatinib and EBIP produced a greater inhibition of EGFR and Src activation and their downstream signaling pathways involving Akt and p44/42 MAPK. Additionally, we observed that EGFR promoter activities as well as transactivation of NFκB in MDA-MB-468 cells were greatly reduced. In conclusion, our data suggest that combination treatment of Dasatinib and EBIP that target EGFRs and Src could be a highly effective therapy for breast cancer than mono therapy, as they are likely to impact several aspects of tumor progression. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3069.