INHIBITION OF TRIPLE NEGATIVE AND HER-2 RESISTANT BREAST CANCER PROGRESSION BY ANNEXIN A2 ANTIBODIES

Purpose: Herceptin, an immunotherapy directed against the Her-2 receptor, inhibits cancer growth and progression in Her-2 positive breast cancer by blocking the downstream survival pathways. In these cells however, the expression of another major tyrosine kinase receptor EGFR is significantly low. Interestingly, EGFR expression is significantly increased in Her-2 negative breast cancer thereby contributing to cancer growth and progression. Present studies were designed to investigate whether or not Annexin A2 (AnxA2), a calcium dependent phospholipid binding protein, regulated EGFR downstream signaling pathway and if the functions of EGFR can be inhibited by the AnxA2 antibody in TNBC and Herceptin resistant cancer cell lines. Methods: Triple negative breast cancer cell line MDA-MB-231 and Her-2 resistant breast cancer cell line JIMT-1 were grown in complete DMEM and DMEM/F12 medium respectively, in a humidified incubator at 37C with 5% CO2. The AnxA2 function at cell surface was blocked incubating with AnxA2 antibody (2µg/ml) after 12 h of serum starvation. The cells were treated with/without EGF (50ng/ml) for 20 min after 2 h of antibody treatment. The cell lysate was analyzed for pEGFR and EGFR mediated downstream signaling by Western blotting. Results: The results of the present study indicate that AnxA2 interacts with EGFR at the cell surface and plays an important role in the regulation of EGFR mediated downstream signaling. Treatment of MDA-MB-231 and JIMT-1 cells with AnxA2 antibody causes significant decrease in EGF-mediated phosphorylation of EGFR at Y845 and Y1068 sites. In addition, treatment of cells with AnxA2 antibody decreases the ligand induced EGFR dimerization and internalization. Our results also demonstrate that blocking cell surface AnxA2 functions causes the downregulation of proteins such as pAKT, and pERK1/2 which are regulated by EGFR resulting in lower cell survival, proliferation, and migration. Conclusions: These studies indicate that association of AnxA2 with EGFR in the membrane domain might play a positive regulatory role in keeping EGFR signaling events in an activated state in triple negative and Her-2 resistant breast cancer thus making AnxA2 an important therapeutic target.