Preclinical evaluation of [99mTc]Tc-labeled anti-EpCAM nanobody for EpCAM receptor expression imaging by immuno-SPECT/CT

Abstract

Purpose: Overexpression of epithelial cell adhesion molecule (EpCAM) plays essential roles in tumorigenesis and tumor progression in almost all epithelium-derived cancer. Monitoring EpCAM expression in tumors can be used for the diagnosis, staging, and prognosis of cancer patients, as well as guiding the individualized treatment of EpCAM-targeted drugs. In this study, we described the synthesis and evaluation of a site-specifically [^99mTc]Tc-labeled EpCAM-targeted nanobody for the SPECT/CT imaging of EpCAM expression.

Methods: We first prepared the [^99mTc]Tc-HYNIC-G₄K; then, it was site-specifically connected to EpCAM-targeted nanobody NB4. The in vitro characteristics of [^99mTc]Tc-NB4 were investigated in HT-29 (EpCAM positive) and HL-60 (EpCAM negative) cells, while the in vivo studies were performed using small-animal SPECT/CT in the subcutaneous tumor models and the lymph node metastasis model to verify the specific targeting capacity as well as the potential applications of [^99mTc]Tc-NB4.

Results: [^99mTc]Tc-NB4 displayed a high EpCAM specificity both in vitro and in vivo. SPECT/CT imaging revealed that [^99mTc]Tc-NB4 was cleared rapidly from the blood and normal organs except for the kidneys, and HT-29 tumors were clearly visualized in contrast with HL-60 tumors. The uptake value of [^99mTc]Tc-NB4 in HT-29 tumors was increased continuously from 3.77 ± 0.39%ID/g at 0.5 h to 5.53 ± 0.82%ID/g at 12 h after injection. Moreover, the [^99mTc]Tc-NB4 SPECT/CT could clearly image tumor-draining lymph nodes.

Conclusion: [^99mTc]Tc-NB4 is a broad-spectrum, specific, and sensitive SPECT radiotracer for the noninvasive imaging of EpCAM expression in the epithelium-derived cancer and revealed a great potential for the clinical translation.

Keywords: EpCAM imaging; Immuno-SPECT/CT; Site-specific radiolabeling; [99mTc]Tc-Nanobody.