The Study Of Anti-Tumor Effect And Working Mechanism Of Anti-ErbB2Antibody ChA21

ErbB2/HER2/P185protein belongs to the human epidermal growth factor receptor (ErbB) family which plays an important role in cell proliferation, differentiation, migration and apoptosis. ErbB2overexpression has been found in many kinds of human cancer, especially in breast and gastric carcinomas. It has been proved that ErbB2overexpression results in dysregulation of cellular signaling transduction which leads on to tumor onset and progression, rendering ErbB2a valid target for cancer therapeutics. Anti-ErbB2monoclonal antibody, such as Trastuzumab and Pertuzumab, has been approved for marketing as first-line cancer treatments. However, a substantial portion of patients have innate or acquired resistance to these antibodies, creating an urgent demand for the development of novel antibody drugs and treatment strategies.In previous studies, our lab has developed an anti-ErbB2human-mouse chimeric antibody chA21and its fully humanized version, E9, with improved affinity. This thesis has focused on the anti-tumor activities and working mechanisms of chA21and E9.In vitro cell proliferation assays have revealed that chA21and E9can significantly inhibit the growth of ErbB2-overexpressing cancer cells. In BT-474breast cancer cell line, chA21and E9showed weaker inhibitory activities than Trastuzumab; while in NCI-N87gastric cancer cell line, better performance were achieved by chA21and E9. Moreover, in both cell lines chA21and E9exhibited superiority over Pertuzumab when administrated alone or in combination with Trastuzumab. In mouse xenograft models of BT-474and MCF-7/HER2, chA21and E9significantly inhibited tumor growth; especially in the MCF-7/HER2xenograft model, they both showed inhibitory activities comparable to Trastuzumab.Further studies have revealed that chA21and Trastuzumab exert different influences on tumor cell migration, aggregation and adhesion. chA21not only inhibited the migration process of SKBR3and BT-474cells, but also induced morphological changes and aggregation of tumor cells, whereas Trastuzumab showed no such effects. On the other hand, chA21showed less impact on the interaction between tumor cell and extracellular matrix compared to Trastuzumab.High-resolution determination of antigen-antibody complex crystal structure reveals that chA21binds to a site on ErbB2extracellular domain between subdomain I C-terminal and subdomain Ⅱ N-terminal, which is a novel epitope different from those of Trastuzumab and Pertuzumab, located in the opposite direction of ErbB2receptor dimerization interface. In addition, chA21induced ErbB2/EGFR/ErbB3receptor downregulation, and synergistic actions were observed when chA21was in combination with Trastuzumab or Pertuzumab. Based on these findings, a new model is proposed to explain the working mechanism of chA21. By simultaneously binding to two ErbB2molecules without conformational hindrance, chA21could crosslink overexpressed ErbB2homodimers and heterodimers on cell surface into large protein complexes, which would undergo further internalization and intracellular degradation to reduce downstream signaling transduction and finally reverse the malignant phenotype of cancer cells. This model provides reasonable explanation for the functional differences in receptor downregulation and tumor inhibition between chA21and other anti-ErbB2antibodies.In conclusion, chA21has exhibited distinctive characteristics in anti-tumor activities, antibody epitope and working mechanisms in comparation with currently available anti-ErbB2antibody drugs. Further research and development will contribute to the promising future of chA21as a novel anti-ErbB2therapeutical antibody for clinical cancer treatment.