Summary

Lu¹⁷⁷-labeled peptide trimers targeting αvβ6-integrin were developed using PEG linkers of different lengths, with the PEG7-containing P7 construct identified as the most promising candidate. In vivo distribution and retention of Lu¹⁷⁷-P7 were monitored using μSPECT imaging. Tumor-associated radioactivity remained detectable for up to 6 days, demonstrating sustained tumor retention. μSPECT therefore enabled non-invasive, longitudinal visualization of radioligand retention in the tumor.

Results from nanoScan^® SPECT/CT: 

The in vivo distribution and tumor retention of Lu¹⁷⁷-P7 were investigated using a nanoScan SPECT/CT (Mediso, Budapest, Hungary). μSPECT imaging was performed at 1, 24, 96, and 144 h after intravenous administration, with a 60-minute acquisition at each time point. Gelofusine ISO was administered prior to imaging to reduce renal uptake, while SPECT reconstruction, image analysis, and quantification were performed using Mediso Nucline and InterView Fusion software. The μSPECT images demonstrated low background activity and clear, sustained tumor retention of Lu¹⁷⁷-P7 for up to 6 days, allowing the radioligand to be followed longitudinally in the same animals. Physiological uptake in the stomach and intestines was also visualized, together with prominent renal activity caused by prolonged retention in the renal cortex. (Fig.5.)

Figure 5. μSPECT MIP images acquired at 1, 24, 96, and 144 h after intravenous administration of 26 MBq P7 with Gelofusine. Images are scaled to the tumor (A) and kidneys (B).

Conclusion

Overall, the Mediso nanoScan SPECT/CT enabled both qualitative visualization and quantitative assessment of Lu¹⁷⁷-P7 distribution, providing clear evidence of its tumor targeting and long-term retention in vivo.

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