RESUMO
The aim of this study was to synthesize a quinoline-based MRI contrast agent, Gd-DOTA-FAPI04, and assess its capacity for targeting fibroblast activation protein (FAP)-positive tumors in vivo. Gd-DOTA-FAPI04 was synthesized by attaching a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complex of gadolinium(III) to FAP inhibitor FAPI04. The longitudinal relaxation time (T1) of the contrast agent was measured using a Siemens Prisma 3.0T MR system, and the CCK-8 assay was performed to evaluate its potential cytotoxicity. Male nude mice bearing tumors grown from FAP-expressing fibrosarcoma cells were divided into experimental (n = 4) and control (n = 4) groups, and T1-weighted image enhancement was measured at different times (0, 10, 30, 60, 90, and 120 min) postinjection of Gd-DOTA-FAPI04. The control group received an additional preinjection of excess FAPI04. FAP expression in tumor tissue was investigated by using immunohistochemistry with an anti-FAP antibody. The longitudinal relaxivities of gadodiamide and Gd-DOTA-FAPI04 were measured to be 3.734 mM-1 s-1 and 5.323 mM-1 s-1, respectively. The CCK-8 assay demonstrated that Gd-DOTA-FAPI04 has minimal toxicity to cultured human fibrosarcoma cells. In vivo MRI showed that peak accumulation of Gd-DOTA-FAPI04 in FAP-expressing tumors occurred 1 h postinjection and could be blocked by preinjection of excess FAPI04. Immunohistochemical analysis of harvested tumor tissue supported the above findings. Gd-DOTA-FAPI04 is a promising contrast agent for in vivo imaging of FAP.
RESUMO
BACKGROUND: Accumulating studies have demonstrated that elevated TIGIT expression in tumor microenvironment correlates with better therapeutic response to TIGIT-based immunotherapy in pre-clinical studies. Therefore, a non-invasive method to detect tumor TIGIT expression is crucial to predict the therapeutic effect. METHODS: In this study, a peptide-based PET imaging agent, 68Ga-DOTA-DTBP-3, was developed to non-invasively detect TIGIT expression by micro-PET in tumor-bearing BALB/c mice. DTBP-3, a D-peptide comprising of 12 amino acids, was radiolabeled with 68Ga through a DOTA chelator. In vitro studies were performed to evaluate the affinity of 68Ga-DOTA-DTBP-3 to TIGIT and its stability in fetal bovine serum. In vivo studies were assessed by micro-PET, biodistribution, and immunohistochemistry on tumor-bearing BALB/c mice. RESULTS: The in vitro studies showed the equilibrium dissociation constant of 68Ga-DOTA-DTBP-3 for TIGIT was 84.21 nM and its radiochemistry purity was 89.24 ± 1.82% in FBS at 4 h in room temperature. The results of micro-PET, biodistribution and immunohistochemistry studies indicated that 68Ga-DOTA-DTBP-3 could be specifically targeted in 4T1 tumor-bearing mice, with a highest uptake at 0.5 h. CONCLUSION: 68Ga-DOTA-DTBP-3 holds potential for non-invasively detect tumor TIGIT expression and for timely assessment of the therapeutic effect of immune checkpoint blockade.
RESUMO
Accumulating evidence indicates that cancer stem cells (CSCs) are the cause of tumor drug/radio-resistance or distant metastasis; therefore, it is essential to eliminate CSCs to cure cancer completely. The purpose of this study was to utilize radioimmunotherapy (RIT) to target CD133(+) colonic CSCs and observe whether this prevented tumor development, by assessing the maximum tolerated dose (MTD) of HCT116 tumor-bearing nude mice with escalating doses of 131I-AC133.1 monoclonal antibody (mAb), and determining the therapeutic efficacy of RIT with 131I-AC133.1 mAb. For RIT trials, animals were randomly divided into 4 groups of 6 per group, and injected with 131I-AC133.1 mAb (16.65 MBq/100 µl), AC133.1 mAb (173.1 µg/100 µl), saline (100 µl), or unrelated IgG1 as an isotype control. Iodine-131 was radiolabeled to AC133.1 mAb by conjugation with N-succinimidyl 3-(tri-n-butylstannyl) benzoate. The MTD of HCT116 tumor-bearing nude mice was 16.65 MBq. Both of the tumor volume doubling time and the survival time of the 131I-AC133.1 mAb group were significant longer than other groups (P < 0.001). CD133 expression was assessed by flow cytometry. Protein levels of cancer stem-like biomarkers (CD133, ALDH1, Lgr5, Vimentin, Snail1), and the proliferative rate of 131I-AC133.1 mAb group were lower than other groups (P<0.001); while its protein level of E-cadherin was higher than other groups. Furthermore, a large proportion of tumor necrosis was also observed in the 131I-AC133.1 mAb group, suggesting that RIT can destroy CSCs and effectively inhibit tumor development.