Coupling Gd‑DTPA with a bispecific, recombinant protein anti‑EGFR‑iRGD complex improves tumor targeting in MRI

Recombinant anti‑epidermal growth factor receptor‑internalizing arginine‑glycine‑aspartic acid (anti‑EGFR single‑domain antibody fused with iRGD peptide) protein efficiently targets the EGFR extracellular domain and integrin αvβ/β5, and shows a high penetration into cells. Thus, this protein may improve penetration of conjugated drugs into the deep zone of gastric cancer multicellular 3D spheroids. In the present study, a novel tumor‑targeting contrast agent for magnetic resonance imaging (MRI) was developed, by coupling gadolinium‑diethylene triamine pentaacetate (Gd‑DTPA) with the bispecific recombinant anti‑EGFR‑iRGD protein. The anti‑EGFR‑iRGD protein was extracted from Escherichia coli and Gd was loaded onto the recombinant protein by chelation using DTPA anhydride. Single‑targeting agent anti‑EGFR‑DTPA‑Gd, which served as the control, was also prepared. The results of the present study showed that anti‑EGFR‑iRGD‑DTPA‑Gd exhibited no significant cyto-toxicity to human gastric carcinoma cells (BGC‑823) under the experimental conditions used. Compared with a conventional contrast agent (Magnevist), anti‑EGFR‑iRGD‑DTPA‑Gd showed higher T1 relaxivity (10.157/mM/sec at 3T) and better tumor‑targeting ability. In addition, the signal intensity and the area under curve for the enhanced signal time in tumor, in vivo, were stronger than Gd‑DTPA alone or the anti‑EGFR‑Gd control. Thus, Gd‑labelled anti‑EGFR‑iRGD has potential as a tumor‑targeting contrast agent for improved MRI.