A novel integrin αvβ3-targeted isoDGR probe for SPECT/CT imaging of glioma

Abstract

Objective To prepare 99Tcm-HYNIC-c(isoDGRKy) as a SPECT/CT imaging molecular probe targeting integrin αvβ3, and evaluate its biodistribution and feasibility on SPECT/CT imaging for integrin αvβ3-positive tumor in U87MG human glioma xenograft mouse models. Methods The bifunctional chelator HYNIC was conjugated to c(isoDGRKy), and tricine and TPPTS were used as coligands for 99Tcm labeling to prepare 99Tcm-HYNIC-c(isoDGRKy). The radiochemical purity and stability of the product were measured. The expression of integrin αvβ3 and binding affinity (half maximal inhibitory concentration, IC50) of c(isoDGRKy) was detected in U87MG cells by cell experiments in vitro. Biodistribution and SPECT/CT imaging of 99Tcm-HYNIC-c(isoDGRKy) including blocking experiments were performed respectively in nude mice bearing U87MG human glioma xenografts. Results The radiochemical purity of 99Tcm-HYNIC-c(isoDGRKy) was over 99%, and was still over 99% after 4 h incubation in saline at room temperature. Flow cytometry assay showed that U87MG cells were integrin αvβ3-positive (expressive rate: 70%). The IC50 of c(isoDGRKy) was 6.67×10-8 mol/L. Biodistribution results showed 99Tcm-HYNIC-c(isoDGRKy) with a rapid clearance from blood was excreted mainly via the kidneys. The 99Tcm-HYNIC-c(isoDGRKy) uptake values in U87MG tumors were (7.31±1.42) and (1.09±0.11) %ID/g at 15 and 45 min post-injection respectively, and tumor-to-muscle ratio reached 5.01±1.47 at 15 min post-injection. The tumors were clearly visualized with low background from 0.5 to 1 h post-injection in tumor bearing mice. In the blocking experiment, the tumor was barely visualized after co-injection of excess cold c(RGDfK) peptide with 99Tcm-HYNIC-c(isoDGRKy). Conclusions 99Tcm-HYNIC-c(isoDGRKy) may be easily and steadily prepared. It may be a RGD-like promising SPECT/CT imaging probe for integrin αvβ3-positive tumor. Key words: Isoaspartate-glycine-arginine; Technetium; Integrin alphaVbeta3; Glioma; Tomography, emission-computed, single-photon; Tomography, X-ray computed; Mice, nude