Expression Enhancement in Trastuzumab Therapeutic Monoclonal Antibody Production using Genomic Amplification with Methotrexate

BACKGROUND: Trastuzumab (Herceptin) is a humanized monoclonal antibody (mAb) which is used for specific treatment of metastatic breast cancer in patients with overexpression of HER2/neu receptor. In this study, we have attempted to develop a biosimilar version of trastuzumab mAb. METHODS: According to in silico studies, the heavy and light chains of trastuzumab mAb were designed and constructed. The recombinant constructs were co-transfected in CHO DG44 cell line. Stable transformants were selected on a semi solid medium. Genomic amplification with methotrexate was achieved for heavy chain gene amplification. Biological activity of produced antibody in comparison with Herceptin was tested by flow cytometry method. RESULTS: Three folds of amplification were obtained after seven rounds of methotrexate treatments. The results indicated the equal expression level of heavy and light chains. The yield of purified mAb was between 50 to 60 mg/l /day. According to the results, the produced mAb had similar affinity to HER2(+) tumor cells to that of Herceptin. CONCLUSION: High-level recombinant protein expression can be achieved by amplification of the recombinant gene with a selectable marker, such as Dihydrofolate Reductase (DHFR). It is usually accepted that DHFR gene can be amplified in DHFR(－) CHO cells, which consequently leads to amplification of the co-linked target gene, and finally amplification of recombinant protein. In this research, with the aim of producing a biosimilar version of herceptin, the effect of genomic amplification was investigated on the increasing the gene copy number using quantitative real-time PCR.