Anti-EGFR monoclonal antibody 134-mG(2a) exerts antitumor effects in mouse xenograft models of oral squamous cell carcinoma

The epidermal growth factor receptor (EGFR), a transmembrane receptor and member of the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases, is a critical mediator of cell growth and differentiation. EGFR forms homo- or heterodimers with other HER family members to activate downstream signaling cascades in a number of cancer cells. In a previous study, the authors established an anti-EGFR monoclonal antibody (mAb), EMab-134, by immunizing mice with the ectodomain of human EGFR. EMab-134 binds specifically to endogenous EGFR and can be used to detect receptor on oral cancer cell lines by flow cytometry and western blot analysis; this antibody is also effective for the immunohistochemical evaluation of oral cancer tissues. In the present study, the subclass of EMab-134 was converted from IgG(1) to IgG(2a) (134-mG(2a)) to facilitate antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The dissociation constants (K(D)s) of EMab-134 and 134-mG(2a) against EGFR-expressing CHO-K1 (CHO/EGFR) cells were deter-mined by flow cytometry to be 3.2×10(−9) M and 2.1×10(−9) M, respectively; these results indicate that 134-mG(2a) has a higher binding affinity than EMab-134. The 134-mG(2a) antibody was more sensitive than EMab-134 with respect to antigen detection in oral cancer cells in both western blot analysis and immunohistochemistry applications. Analysis in vitro revealed that 134-mG(2a) contributed to high levels of ADCC and CDC in experiments targeting CHO/EGFR, HSC-2, and SAS cells. Moreover, the in vivo administration of 134-mG(2a) significantly inhibited the development of CHO/EGFR, HSC-2, and SAS mouse xenografts in comparison to the results observed in response to EMab-134. Taken together, the findings of the present study demonstrate that the newly-formulated 134-mG(2a) is useful for detecting EGFR by flow cytometry, western blot analysis and immunohistochemistry. Furthermore, the in vivo results suggested that it may also be useful as part of a therapeutic regimen for patients with EGFR-expressing oral cancer.