68Ga-DOTA-VAP molecular probe targeted glucose-regulated protein 78 for specific microPET/CT imaging of tumors / 中华核医学与分子影像杂志

ABSTRACT

Objective:To evaluate the specificity of 68Ga-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA)-Ser-Asn-Thr-Arg-Val-Ala-Pro (SNTRVAP, VAP) molecular probe targeting glucose-regulated protein 78(GRP78) in vivo and in vitro and the feasibility of 68Ga-DOTA-VAP microPET/CT imaging in the diagnosis of GRP78-positive tumors. Methods:68Ga-DOTA-VAP was prepared by the combination of bifunctional chelating agent DOTA and VAP, followed by 68Ga labeling. Western blotting experiment was perfomed to detect the expression of GRP78 in U87MG, BxPC-3, and 293T cell lines, at the same time, cold polypeptide blocked experiments were conducted to verify the specific binding of 68Ga-DOTA-VAP to cells. U87MG and BxPC-3 subcutaneous transplantation tumor mouse models were established and the biodistribution of 68Ga-DOTA-VAP were explored in vivo. The imaging effect of 68Ga-DOTA-VAP in GRP78-positive tumor-bearing mouse models was evaluated by microPET/CT. Independent-sample t test, one-way analysis of variance and Dunnett t test were used for data analysis. Results:68Ga-DOTA-VAP was easily prepared with labeling yield and radiochemical purity >98%. It had good stability in vitro, and its radiochemical purity was still (98.27±0.22)% after 2 h. GRP78 was highly expressed in U87MG and BxPC-3 cells, but lowly expressed in 293T cells ((0.78±0.02), (0.53±0.05) and (0.36±0.03), F=102.22, P<0.001; t values: 0.43, 0.18, both P<0.01). The uptake of 68Ga-DOTA-VAP in U87MG cells was higher than that in BxPC-3 cells (5 154.00±216.70 vs 4 344.00±60.88; t=3.10, P=0.027). Excessive unlabeled VAP polypeptide could significantly reduce the uptake of 68Ga-DOTA-VAP both in U87MG and BxPC-3 cells (3 324.00±54.14, 3 270.00±131.10; t values: 8.19, 7.43, both P<0.01). The uptake of 68Ga-DOTA-VAP in U87MG tumor tissue was higher than that in BxPC-3 tumor tissue ((1.98±0.20) vs (1.30±0.08) percentage activity of injection dose per gram of tissue (%ID/g); t=5.48, P=0.005), while co-injection of excessive unlabeled VAP polypeptide significantly reduced the uptake in U87MG and BxPC-3 tumors ((0.99±0.02) and (0.62±0.05) %ID/g; t values: 8.32, 12.25, both P<0.05). MicroPET/CT imaging showed that 68Ga-DOTA-VAP could clearly display U87MG and BxPC-3 tumors, and U87MG had a better imaging effect. The tumors could not be clearly visualized after co-injection of excessive VAP polypeptide. Conclusion:68Ga-DOTA-VAP molecular probe binds with GRP78 specifically and can reflect the expression level of GRP78 in vivo, which may be a promising probe for the specific imaging diagnosis of GRP78-positive tumors.