Preclinical Evaluation of Mesothelin-Specific Ligands for SPECT Imaging of Triple-Negative Breast Cancer

Abstract

Mesothelin is a cell-surface glycoprotein restricted to mesothelial cells overexpressed in several types of cancer, including triplenegative breast cancer not responding to trastuzumab or hormonebased 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 99m Tc-A1 and 99m Tc-C6, two antimesothelin single-domain antibody (sdAb)-derived imaging agents. Methods: A1 and C6 were radiolabeled with 99m Tc and evaluated in vitro on recombinant protein and cells, as well as in vivo in xenograft mouse models of the triplenegative breast cancer cell lines HCC70 (mesothelin-positive) and MDA-MB-231 (mesothelin-negative). Results: Both 99m Tc-A1 and 99m Tc-C6 bound mesothelin with high affinity in vitro, with 99m Tc-A1 affinity being 2.4-fold higher than that of 99m Tc-C6 (dissociation constant, 43.9 ± 4.0 vs. 107 ± 16 nM, P , 0.05). 99m Tc-A1 and 99m Tc-C6 remained stable in vivo in murine blood (.80% at 2 h) and ex vivo in human blood (.90% at 6 h). In vivo 99m 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 99m Tc-C6 (2.34% ± 0.36% vs. 0.48% ± 0.18% and 1.56% ± 0.43%, respectively, P , 0.01) and resulted in elevated tumor-to-background ratios. In vivo competition experiments demonstrated the specificity of 99m Tc-A1 uptake in HCC70 tumors. Conclusion: Mesothelin-positive tumors were successfully identified by SPECT using 99m Tc-A1 and 99m Tc-C6. Considering its superior characteristics, 99m Tc-A1 was selected as the most suitable tool for further clinical translation.

99mTc-A1 as a Novel Imaging Agent Targeting Mesothelin-Expressing Pancreatic Ductal Adenocarcinoma

“…Our in vivo experiments showed that 99m Tc-A1 enabled the noninvasive visualization of AsPC-1-derived tumors by SPECT imaging at early time points. These results reinforce our study on triple-negative breast cancer, despite the lower 99m Tc-A1 uptake of PDAC mesothelin-positive tumors [9]. In addition to triple-negative breast cancer and PDAC, 99m Tc-A1 imaging represents a relevant option to visualize other aggressive cancers overexpressing mesothelin such as ovarian and lung cancers, for which the imaging modalities are mainly based on the use of conventional antibodies.…”

“…Nuclear imaging represents a highly sensitive and noninvasive imaging modality that could address this challenge. Indeed, we previously validated 99m Tc-A1, which is a single-domain antibody-derived imaging agent, as an efficient probe in accurately targeting mesothelin-expressing triple-negative breast cancer [9]. Herein, we evaluated the potential of 99m Tc-A1 as an imaging probe of mesothelin-expressing PDAC.…”

“…We recently validated 99m Tc-A1 as a single-domain-based imaging agent used for the phenotypic imaging of membrane mesothelin-expressing breast cancer [9]. In this study, we tested the ability of 99m Tc-A1 in imaging mesothelin-expressing PDAC tumors.…”

Targeted Nanobody-Based Molecular Tracers for Nuclear Imaging and Image-Guided Surgery

“…A major application field for nanobody-based radiotracers is cancer imaging. Radiolabeled nanobodies targeting tumor biomarkers such as the epidermal growth factor receptor (EGFR), carcinoembryonic antigen (CEA), mesothelin, prostate-specific membrane antigen (PSMA), CD20, or HER2 showed high specific tumor uptake (ranging typically between 2 and 10% IA/g, depending on the expression level of the target) in preclinical tumor models as soon as 1 h after administration, with tumor-to-blood ratios of up to 10–30 (Figure 1B,C) [23,35,38,41,42,45,48,49,53,54,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71]. Of particular interest is the anti-HER2 nanobody 2Rs15d that has been selected as a lead compound for clinical translation.…”

Metastatic Heterogeneity of Breast Cancer: Companion and Theranostic Approach in Nuclear Medicine

“…Hence, several molecules are currently in clinical phases to evaluate the therapeutic performance of its targeting in tumors expressing mesothelin [96]. Among companion markers, some monoclonal antibodies and nanobodies have been evaluated in clinical and in preclinical models of breast cancers [89][90][91]. Once available in clinical practice, such agents will allow selecting patients eligible to all these therapies.…”