Anti-EphA2 Antibodies Decrease EphA2 Protein Levels in Murine CT26 Colorectal and Human MDA-231 Breast Tumors But Do Not Inhibit Tumor Growth

Abstract

The EphA2 receptor tyrosine kinase has been shown to be over-expressed in cancer and a monoclonal antibody (mAb) that activates and down-modulates EphA2 was reported to inhibit the growth of human breast and lung tumor xenografts in nude mice. Reduction of EphA2 levels by treatment with anti-EphA2 siRNA also inhibited tumor growth, suggesting that the anti-tumor effects of these agents are mediated by decreasing the levels of EphA2. As these studies employed human tumor xenograft models in nude mice with reagents whose cross reactivity with murine EphA2 is unknown, we generated a mAb (Ab20) that preferentially binds, activates, and induces the degradation of murine EphA2. Treatment of established murine CT26 colorectal tumors with Ab20 reduced EphA2 protein levels to approximately 12% of control tumor levels, yet had no effect on tumor growth. CT26 tumor cell colonization of the lung was also not affected by Ab20 administration despite having barely detectable levels of EphA2. We also generated and tested a potent agonistic mAb against human EphA2 (1G9-H7). No inhibition of humanMDA-231 breast tumor xenograft growth was observed despite evidence for >85% reduction of EphA2 protein levels in the tumors. These results suggest that molecular characteristics of the tumors in addition to EphA2 over-expression may be important for predicting responsiveness to EphA2-directed therapies.

The receptor tyrosine kinase EphA2 promotes mammary adenocarcinoma tumorigenesis and metastatic progression in mice by amplifying ErbB2 signaling

“…Therefore, effective therapeutic targeting of EphA2 requires an understanding of how EphA2 cooperates with and functionally influences coexisting oncogenic signaling networks within specific tumor types. For example, while downregulation of EphA2 protein levels showed efficacy against human ovarian tumor xenografts (49), an independent, similarly designed antibody reagent had no effect on CT26 human colon cancer xenografts or human mammary adenocarcinoma xenografts (50). Interestingly, like MMTV-PyV-mT tumor cells, CT26 cells do not overexpress ErbB2/HER2 (51), suggesting that EphA2 overexpression enhances malignant transformation and progression particularly in the context of ErbB2 overexpression and is therefore an appropriate target in such tumors.…”

A Human Antibody–Drug Conjugate Targeting EphA2 Inhibits Tumor GrowthIn vivo

“…Recently, an EphrinA1-Pseudomonas aeruginosa exotoxin A conjugate has been used to target and inhibit the growth of EphA2-expressing glioblastoma multiforme (21). However, other studies have suggested that stimulation of EphA2 results in activation of FAK and has no effect on in vivo tumor growth, suggesting that the response to EphA2 stimulation may be context-dependent (22,23). These discrepancies make the functional significance of EphA2 in tumor progression unclear, such that the development path for traditional therapeutic antibody approaches may be challenging.…”

Loss of EphA2 receptor tyrosine kinase reduces Apcmin/+ tumorigenesis

“…[20][21][22] Based on these observations, targeting of EphA2 via immunotherapy, soluble EphA2 receptor domains and other approaches is under clinical development. [23][24][25][26][27][28][29][30][31][32][33][34][35] …”

“…[20][21][22] Based on these observations, targeting of EphA2 via immunotherapy, soluble EphA2 receptor domains and other approaches is under clinical development. [23][24][25][26][27][28][29][30][31][32][33][34][35] Yet, there is also some evidence that EphA2 may function as a tumor suppressor, as activation of EphA2 receptors following ligand binding has been shown to lead a reduction in cell growth that is associated with inhibition of the RAS/MAPK pathways, and EphA2 2/2 gene trap mice demonstrate increased susceptibility to skin carcinogenesis. [36][37][38][39] Further, EphA2 has been reported to be a transcriptional target of the p53 tumor suppressor, 40 and expression of EphA2 was shown to negatively affect the proliferation and promote apoptosis in lung and breast cancer cells.…”