Peptide-based PET tracer targeting LAG-3 for evaluating the efficacy of immunotherapy in melanoma

Affiliations

• Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
• Hubei Province Key Laboratory of Molecular Imaging, Wuhan, China.
• Key Laboratory of Biological Targeted Therapy, the Ministry of Education, Wuhan, People's Republic of China.
• Department of Oncology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
• Wuhan-Britain China School, Wuhan, China.
• Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China gykmail@hust.edu.cn xiaoli_lan@hust.edu.cn.

PMID: 39043603 DOI: PMC11284866 DOI: 10.1136/jitc-2024-009010

Abstract

Background:Lymphocyte activation gene 3 (LAG-3) is expressed on activated immune cells and has emerged as a promising target for immune checkpoints blockade. However, conflicting findings have been reported regarding the association between LAG-3 expression in tumors and patient prognosis, indicating the need for further investigation into the significance of LAG-3 expression levels in tumor therapies. In this study,68Ga-NOTA-XH05, a novel peptide-based positron emission tomography (PET) tracer targeting LAG-3, was constructed to non-invasively detect LAG-3 expression in melanoma after CpG oligonucleotide (CpG) treatment and explore the relationship between LAG-3 expression and therapeutic effect.

Methods:The tracer68Ga-NOTA-XH05 was identified by high-performance liquid chromatography after being prepared and purified. Cell uptake and blocking essays were performed to verify the specificity of the tracer in vitro. The expression of LAG-3 in B16-F10 subcutaneous tumors was monitored by flow cytometry, and its correlation with the tracer uptake was analyzed to evaluate the tracer specificity. PET imaging and biodistribution studies were conducted after CpG treatment of unilateral or bilateral B16-F10 subcutaneous tumor models to assess the ability of68Ga-NOTA-XH05 in monitoring immunotherapy efficacy and the abscopal effect of CpG.

Results:Following purification,68Ga-NOTA-XH05 exhibited high radiochemical purity and specificity. Flow cytometry analysis revealed a positive correlation between LAG-3 expression in tumors and the uptake of68Ga-NOTA-XH05. In B16-F10 bearing mice treated with CpG, PET imaging using68Ga-NOTA-XH05 demonstrated a higher tumor to blood ratio (TBR) compared with the control group. Furthermore, TBR values obtained from CpG-treated mice allowed for differentiation between responders and non-responders. In a bilateral subcutaneous tumor model where only right-sided tumors were treated with intratumoral injection of CpG, TBR values of left-sided tumors were significantly higher than those in the control group, indicating that68Ga-NOTA-XH05 could effectively monitor the systemic effect of local CpG injection.

Conclusion:Our findings highlight the detection capability of68Ga-NOTA-XH05 in assessing LAG-3 expression levels within tumors and evaluating response to immunotherapy, thereby suggesting promising clinical translational prospects.

Keywords:PET

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