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.

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.

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.

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.

Glioma; Pancreatic neoplasms; Membrane proteins; Isotope labeling; Gallium radioisotopes; Positron-emission tomography; Tomography, X-ray computed; Mice, nude