Preclinical Evaluation of Mesothelin-Specific Ligands for SPECT Imaging of Triple-Negative Breast Cancer.
Mesothelin is a cell-surface glycoprotein restricted to mesothelial cells overexpressed in several types of cancer, including triple-negative breast cancer not responding to trastuzumab or hormone-based therapies. Mesothelin-targeting therapies are currently being developed. However, the identification of patients potentially eligible for such a therapeutic strategy remains challenging. The objective of this study was to perform the radiolabeling and preclinical evaluation of Tc-A1 and Tc-C6, two antimesothelin single-domain antibody (sdAb)-derived imaging agents. A1 and C6 were radiolabeled with Tc and evaluated in vitro on recombinant protein and cells, as well as in vivo in xenograft mouse models of the triple-negative breast cancer cell lines HCC70 (mesothelin-positive) and MDA-MB-231 (mesothelin-negative). Both Tc-A1 and Tc-C6 bound mesothelin with high affinity in vitro, with Tc-A1 affinity being 2.4-fold higher than that of Tc-C6 (dissociation constant, 43.9 ± 4.0 vs. 107 ± 16 nM, 80% at 2 h) and ex vivo in human blood (>90% at 6 h). In vivo Tc-A1 uptake (percentage injected dose) in HCC70 tumors was 5-fold higher than in MDA-MB-231 tumors and 1.5-fold higher than that of Tc-C6 (2.34% ± 0.36% vs. 0.48% ± 0.18% and 1.56% ± 0.43%, respectively, < 0.01) and resulted in elevated tumor-to-background ratios. In vivo competition experiments demonstrated the specificity of Tc-A1 uptake in HCC70 tumors. Mesothelin-positive tumors were successfully identified by SPECT using Tc-A1 and Tc-C6. Considering its superior characteristics, Tc-A1 was selected as the most suitable tool for further clinical translation.Read the article