Small animal PET imaging of recombinant single chain fragment variable of anti-TAG-72 humanized antibody in colon cancer xenograft model

Objectives The 3E8 was anti-tumor associated glycoprotein(TAG)-72 humanized antibody. The TAG-72 is expressed in the majority of various human adenocarcinomas, which makes it a potential target for diagnosis and therapy. In this study, we report production and small animal PET imaging of recombinant 3E8 single chain fragment variable (ScFv) using E. coli system.

Methods Recombinant 3E8 ScFv gene was expressed in E. coli under T7 promoter by IPTG induction using pET23a. 3E8 ScFv was purified by 6xHis and T7 column. Purity of 3E8 ScFv was checked by SDS-PAGE. ScFv 3E8 was labeled with ¹²⁴I and ¹³¹I using Iodobead. Radiolabeling yield was determined by ITLC. Gamma camera image and dynamic PET image were obtained in LS-174T xenograft mice.

Results Recombinant 3E8 ScFv was produced from E. coli with 1.47 mg/L yield. The molecular weight of 3E8 ScFv was 28 kDa by SDS-PAGE. Radiolabeling yields of ¹²⁴I- and ¹³¹I-ScFv were above 97% and 95%, respectively. ¹²⁴I-3E8 ScFv was specifically localized in TAG-72 expressing tumor by PET images. Maximum tumor uptake showed at 60 min and retained until 120 min in PET image. Gamma camera image of ¹³¹I-3E8 ScFv also showed similar pattern to PET image.

Conclusions Recombinant 3E8 ScFv showed efficient tumor targeting to TAG-72 expressing tumor. Recombinant 3E8 ScFv produced by genetic engineering could be labeled with quantum dot and MR nanoparticle as well as radioisotope, so we suggest that it could be used as a multimodal imaging agent for diagnosis in TAG-72 expressing tumor.