99mTc]-labeling and evaluation of a new linear peptide for imaging of glioblastoma as a αvβ3-positive tumor.

Abstract

In this study, we designed a new linear 6-Hydrazinonicotinamide (HYNIC)-conjugated peptide (HYNIC-KRWrNM) (M-6) and labeled with technetium-99m for gamma imaging of glioblastoma as a αvβ3-positive tumor. We evaluated tumor targeting ability of this radio-peptide and compared with previous 99mTc-labeled HYNIC-conjugated RGD analogue peptides. One new linear peptide (HYNIC-KRWrNM) (M-6) was designed and labeled with technetium-99m in the presence of 2-[[1,3-dihydroxy-2-(hydroxymethyl) propan-2-yl] amino] acetic acid (Tricine)/Ethylenediamine-N,N'-diacetic acid(EDDA) as co-ligand system. Then, this 99mTc-labeled peptide ([99mTc]Tc-M-7) was evaluated for in vitro stability in saline and serum, specific binding assay, internalization, and binding affinity (Kd). In addition, we performed biodistribution study and planar imaging on nude mice bearing U87-MG xenograft as a αvβ3-positive tumor. The radiochemical yield of [99mTc]Tc-M-7 was obtained ˃95%. This 99mTc-labeled peptide remained stable and intact in saline solution after 24h incubation. In addition, metabolic stability of this 99mTc-labeled peptide was obtained ˃60% after 4h incubation in serum. The Kd value for [99mTc]Tc-M-7 was obtained 5.2 ± 1.0nM. Based on biodistribution results in nude mice bearing U87-MG xenograft, tumor/muscle activity ratio was 6.22 and decreased to 1.89 in blocking group at the same time point (4h p.i.). The blocking experiment results also indicated that tumor uptake and kidney uptake were αvβ3-mediated. In comparison with previous HYNIC-conjugated RGD analogue peptides, kidneys had the highest uptake of this 99mTc-labeled peptide (52.29 ± 11.48 at 1.5h p.i. and 27.04 ± 0.66%ID/g at 4h p.i.). Finally, similar to previous 99mTc-labeled HYNIC-conjugated RGD analogue peptides, [99mTc]Tc-M-7 showed acceptable tumor uptake after 4h post-injection (based on ROI technique, target-to-background activity ratio = 3.80). This small linear 99mTc-labeled peptide, with high affinity to αvβ3 integrin, desirable water solubility, and cost efficient, demonstrates a potent tumor targeting ability as well as previous HYNIC-conjugated RGD analogue peptides. Hence, [99mTc]Tc-M-7 can be of service to as a new candidate for early detection of αvβ3-positive tumors.