Promising Fusion Protein Design to Target the U87 MG Glioma Cell Line

Gliomas, with a poor clinical course, account for 30% to 40% of all intracranial tumors. Immunotherapy with monoclonal antibodies has emerged as a promising area of investigation and recently it has been shown that antibodies utilize complementarity-determining regions (CDRs) of their variable domains to bind to antigens with high affinity and specificity. Here, we designed an antibody mimetic fused with diphtheria toxin to target the U87 MG glioma cell line. VHCDR1 and VLCDR3, together with 5 amino acid residues on both side of the CDRs, through a cognate framework region (VHFR2) yielded a mimetic of BT32/A6 (United States Patent number: 5639863). We fused the mimetic with the first 388 amino acid residues of diphtheria toxin and E. coli strain BL21 (ED3) was used to express the soluble immunotoxin DT-MG. The immunotoxin DT-MG alone did not kill Raji up to the maximal concentration tested (10-6M) in vitro. By contrast, concentrations >= 10-9M, of the fused DT-MG killed more than 95% of U-87 MG cells. It is suggested that the mimetic maintained the synergic interactions and high-affinity associated with the parent antibody. This construct holds promise for targeting specific cancer epitopes and may be useful when incorporated into diagnostic and therapeutic regimens.