Theranostics 2024; 14(3):1195-1211. doi:10.7150/thno.90376 This issue Cite
Research Paper
1. Institute for Molecular Imaging and Theranostics, Department of Nuclear Medicine, Chonnam National University Medical School and Hwasun Hospital, Jeollanam-do, Republic of Korea.
2. Research Division for Radiation Science, Korea Atomic Energy Research Institute, Jeollabuk-do, Republic of Korea.
3. Department of Microbiology, Chonnam National University Medical School, Jeollanam-do, Republic of Korea.
4. Department of Laboratory Medicine, Chonnam National University Medical School and Chonnam National University Hospital, Gwangju, Republic of Korea.
5. CNCure Biotech, Inc., Jeollanam-do, Republic of Korea.
6. Brain Tumor Research Laboratory, Biomedical Research Institute, Chonnam National University Hwasun Hospital, Jeollanam-do, Republic of Korea.
7. New Uzbekistan University, Tashkent, Uzbekistan.
8. Republican Oncology Research Center Tashkent Region Branch, Tashkent, Uzbekistan.
9. Current affiliation: State Key Laboratory of Drug Research, Molecular Imaging Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, 201203, China.
Radiotherapy (RT) triggers immunogenic cell death (ICD). L-ASNase, which catalyzes the conversion of asparagine (Asn), thereby depleting it, is used in the treatment of blood cancers. In previous work, we showed that CRT3LP and CRT4LP, PASylated L-ASNases conjugated to the calreticulin (CRT)-specific monobodies CRT3 and CRT4, increase the efficacy of ICD-inducing chemotherapy. Here, we assessed their efficacy in tumor-bearing mice treated with RT.
Methods: Monobody binding was evaluated by in silico molecular docking analysis. The expression and cellular localization of ecto-CRT were assessed by confocal imaging and flow cytometry. The antitumor effect and the roles of CRT3LP and CRT4LP in irradiation (IR)-induced ICD in tumors were analyzed by ELISA, immunohistochemistry, and immune analysis methods.
Results: Molecular docking analysis showed that CRT3 and CRT4 monobodies were stably bound to CRT. Exposure to 10 Gy IR decreased the viability of CT-26 and MC-38 tumor cells in a time-dependent manner until 72 h, and increased the expression of the ICD marker ecto-CRT (CRT exposed on the cell surface) and the immune checkpoint marker PD-L1 until 48 h. IR enhanced the cytotoxicity of CRT3LP and CRT4LP in CT-26 and MC-38 tumor cells, and increased reactive oxygen species (ROS) levels. In mice bearing CT-26 and MC-38 subcutaneous tumors treated with 6 Gy IR, Rluc8-conjugated CRT-specific monobodies (CRT3-Rluc8 and CRT4-Rluc8) specifically targeted tumor tissues, and CRT3LP and CRT4LP increased total ROS levels in tumor tissues, thereby enhancing the antitumor efficacy of RT. Tumor tissues from these mice showed increased mature dendritic, CD4+ T, and CD8+ T cells and pro-inflammatory cytokines (IFNγ and TNFα) and decreased regulatory T cells, and the expression of tumor cell proliferation markers (Ki67 and CD31) was downregulated. These data indicate that the combination of IR and CRT-targeting L-ASNases activated and reprogramed the immune system of the tumor microenvironment. Consistent with these data, an immune checkpoint inhibitor (anti-PD-L1 antibody) markedly increased the therapeutic efficacy of combined IR and CRT-targeting L-ASNases.
Conclusion: CRT-specific L-ASNases are useful as additive drug candidates in tumors treated with RT, and combination treatment with anti-PD-L1 antibody increases their therapeutic efficacy.
Keywords: Cancer radiotherapy, immunogenic cell death, calreticulin, L-ASNase, reactive oxygen species, immune checkpoint inhibitor