Preparation and SPECT/CT Imaging of (177)Lu-Labeled Peptide Nucleic Acid (PNA) Targeting CITED1: Therapeutic Evaluation in Tumor-Bearing Nude Mice

PURPOSE: The expression of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 1 (CITED1) is upregulated in papillary thyroid carcinoma (PTC) and mediates cell proliferation and migration. To facilitate early diagnosis and monitoring of recurrent or metastatic PTC, we designed (177)Lu-labeled antisense peptide nucleic acid (PNA) targeting CITED1 mRNA to evaluate the therapeutic potential, while analyzing its distribution in nude mice and the characteristics withsingle-photon emission-computed tomography/computed tomography (SPECT/CT) imaging. MATERIALS AND METHODS: (177)Lu-DOTA-anti-CITED1-PNA ((177)Lu-asPNA) was obtained by indirect labeling. High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were used to determine the labeling rate and radiochemical purity. The stability of (177)Lu-asPNA was evaluated by TLC, and the radioactivity count was measured by a γ counter to calculate its uptake capacity in K1 cells. To analyze the distribution of (177)Lu-asPNA in body tissues and organs of nude mice, static single-photon emission-computed tomography (SPECT) imaging and SPECT/CT image fusion were performed. Then, the therapeutic effects of probes were explored by tumor growth curves and survival analysis. RESULTS: Our probe showed a radiochemical purity of 96.5±0.15% at 1 hr and specific activity of 8.7±0.53 MBq/μg. The uptake rate in the (177)Lu-asPNA group was much higher than that in the (177)Lu-DOTA-nonsense-PNA ((177)Lu-nonsense-PNA) and (177)Lu-DOTA groups (P<0.05). The biological distribution showed that the tumor/muscle ratio was at its highest at 24 h (4.98±0.34) post-inoculation, with SPECT/CT imaging showing clear tumor development. By measuring tumor volume of tumor-bearing nude mice, the (177)Lu-asPNA group showed a significant difference in tumor size 9 days after injection (P < 0.05). Kaplan-Meier survival curves showed that the overall survival rate in the (177)Lu-asPNA group was significantly different from those in the DOTA-anti-CITED1-PNA (asPNA) and saline groups (P = 0.002, log-rank test). CONCLUSION: (177)Lu-asPNA was developed successfully, showing a high labeling rate and good stability. SPECT/CT imaging demonstrated tumor growth in nude mice, which was effectively inhibited by our probe, thus prolonging survival.