Preparation and MRI Study of HER2‐Targeted Bimodal Molecular Probe Gd‐Cy5.5‐Pertuzumab for Thyroid Cancer

Abstract

Purpose. A bimodal nanoprobe for thyroid cancer targeting human epidermal growth factor receptor 2 (HER2) was synthesized by coupling the magnetic resonance contrast agent Gd3+ with the fluorescent dyes Cy5.5 and pertuzumab as a preliminary study of Gd‐Cy5.5‐pertuzumab in magnetic resonance and fluorescence imaging. Methods. The bifunctional chelate p‐SCN‐Bn‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic‐acid (DOTA) was dissolved in deionized water, added to pertuzumab solution, and stirred overnight at room temperature to obtain the product DOTA pertuzumab. 1,2‐dichloroethane and N‐hydroxysuccinimide were added to activate the carboxyl group on DOTA. After 0.5 hr of activation, the amino fluorescent dye Cy5.5 was further added to react with it to synthesize the intermediate product Cy5.5‐DOTA‐pertuzumab. Finally, we added GdCl3‐6H2O and placed it in a magnetic stirrer for 6 hr before the unreacted substance was removed by dialysis to obtain Gd‐Cy5.5‐pertuzumab. Following that, the hydrated particle size and zeta potential of the nanoprobe were measured by particle size analyzer, the fluorescence spectrum by a fluorescence detector, the infrared spectrum by the infrared analyzer, the cytotoxicity by CCK‐8 method, the relaxation rate by Niumai small nuclear magnetic field, and the binding ability of HER2 to thyroid cancer 8505C by laser confocal microscope. Nanoprobes were injected into a subcutaneous thyroid cancer nude mouse model through the tail vein, and in vivo MRI and near‐infrared (NIR) fluorescence imaging were performed. Finally, the nude mice were dissected and hematoxylin and eosin (HE) staining of pathological tissues was performed to evaluate the imaging performance of the prepared bimodal probes. Results. The synthesized bimodal probe Gd‐Cy5.5‐pertuzumab had a hydrodynamic size of 131.34 ± 9.43 nm and zeta potential of −31.73 ± 6.24 mV with a significant absorption peak at 685 nm. The relaxation rate of the probe was 46.53 mM−1 s−1, which was determined by Niumai small nuclear magnetism, and the T1 signal intensity increased gradually with the concentration of the probe. Laser confocal microscopy showed that HER2 was mainly expressed in cell membranes. In vitro and in vivo experiments indicated that the probe had low cytotoxicity. MRI and small animal fluorescence imaging of tumor‐bearing nude mice showed that the probe could clearly image tumor tissue. Conclusion. The bimodal probe Gd‐Cy5.5‐pertuzumab was successfully synthesized with good stability, which can specifically bind to target cells in vivo and has good magnetic resonance/fluorescence imaging performance.