Ga-68-labeled cyclic RGD dimers with Gly(3) and PEG(4) linkers: promising agents for tumor integrin alpha(v)beta(3) PET imaging

Department of Radiology, Biophysics & Bio-X, Stanford University, Stanford, CA 94305, USA.
European Journal of Nuclear Medicine (Impact Factor: 4.53). 06/2009; 36(6):947-57. DOI: 10.1007/s00259-008-1045-1
Source: PubMed

ABSTRACT Radiolabeled cyclic RGD (Arg-Gly-Asp) peptides have great potential for the early tumor detection and noninvasive monitoring of tumor metastasis and therapeutic response. (18)F-labeled RGD analogs ([(18)F]-AH111585 and [(18)F]Galacto-RGD) have been investigated in clinical trials for positron emission tomography (PET) imaging of integrin expression in cancer patients. To develop new RGD radiotracers with higher tumor accumulation, improved in vivo kinetics, easy availability and low cost, we developed two new RGD peptides and labeled them with generator-eluted (68)Ga (t(1/2) = 68 min) for PET imaging of integrin alpha(v)beta(3) expression in tumor xenograft models.
The two new cyclic RGD dimers, E[PEG(4)-c(RGDfK)](2) (P(4)-RGD2, PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and E[Gly(3)-c(RGDfK)](2) (G(3)-RGD2, G(3) = Gly-Gly-Gly) were designed, synthesized and conjugated with 1,4,7-triazacyclononanetriacetic acid (NOTA) for (68)Ga labeling. The microPET imaging and biodistribution of the (68)Ga labeled RGD tracers were investigated in integrin alpha(v)beta(3)-positive tumor xenografts.
The new RGD dimers with the Gly(3) and PEG(4) linkers showed higher integrin alpha(v)beta(3) binding affinity than no-linker RGD dimer (RGD2). NOTA-G(3)-RGD2 and NOTA-P(4)-RGD2 could be labeled with (68)Ga within 30 min with higher purity (>98%) and specific activity (8.88-11.84 MBq/nmol). Both (68)Ga-NOTA-P(4)-RGD2 and (68)Ga-NOTA-G(3)-RGD2 exhibited significantly higher tumor uptake and tumor-to-normal tissue ratios than (68)Ga-NOTA-RGD2.
Because of their high affinity, high specificity and excellent pharmacokinetic properties, further investigation of the two novel RGD dimers for clinical PET imaging of integrin alpha(v)beta(3) expression in cancer patients is warranted.

1 Follower
  • [Show abstract] [Hide abstract]
    ABSTRACT: [18 F]FPyKYNE-c(RGDyK) was successfully synthesized by the Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition of alkynes to azides using [18 F]FPyKYNE as a prosthetic group in an overall radiochemical yield of 12%–18% (decay-corrected) and >99.5% chemical and radiochemical purities in 125 min including quality control. This simple, fully automated two-step, two-reactor approach consists of a quick and convenient purification of the prosthetic group using silica gel cartridges and its subsequent use for the labeling of the azido-c(RGDyK) peptide via click chemistry.
    Journal of Labelled Compounds 02/2012; 55(2). DOI:10.1002/jlcr.1948
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of (99m)Tc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD2 and HYNIC-P6D-RGD2 were prepared by reacting P6G-RGD2 and P6D-RGD2, respectively, with excess HYNIC-OSu in the presence of diisopropylethylamine. Their IC50 values were determined to be 31 ± 5 and 41 ± 6 nM, respectively, against (125)I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [(99m)Tc(HYNIC-P6G-RGD2)(tricine)(TPPTS)] ((99m)Tc-P6G-RGD2) and [(99m)Tc(HYNIC-P6D-RGD2)(tricine)(TPPTS)] ((99m)Tc-P6D-RGD2) were prepared in high radiochemical purity (RCP > 95%) and specific activity (37-110 GBq/μmol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between (99m)Tc-P6D-RGD2 and (99m)Tc-P6G-RGD2 was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for (99m)Tc-P6D-RGD2 (4.71 ± 1.00%ID/g) was ∼5× higher than that of (99m)Tc-P6G-RGD2 (0.88 ± 0.05%ID/g), but this difference disappeared at 60 min p.i. (99m)Tc-P6D-RGD2 had much lower tumor uptake (2.20-3.11%ID/g) than (99m)Tc-P6G-RGD2 (7.82-9.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD2 and HYNIC-P6G-RGD2 shared a similar integrin αvβ3 binding affinity (41 ± 6 nM versus 31 ± 5 nM), the difference in their blood activity and tumor uptake is most likely related to the nine negative charges and high protein binding of (99m)Tc-P6D-RGD2. Despite its low uptake in U87MG tumors, the tumor uptake of (99m)Tc-P6D-RGD2 was integrin αvβ3-specific. SPECT/CT studies were performed using (99m)Tc-P6G-RGD2 in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of (99m)Tc-P6G-RGD2, and its tumor uptake depends on the integrin αvβ3 expression levels on tumor cells and neovasculature. It was concluded that the multiple negative charges have a significant impact on the blood clearance kinetics and tumor uptake of (99m)Tc-labeled dimeric cyclic RGD peptides.
    Bioconjugate Chemistry 08/2014; 25(9). DOI:10.1021/bc500309r · 4.82 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Purpose: Tc-99m-3PRGD2, a promising tracer targeting integrin receptor, may serve as a novel tumor-specific agent for single photon emission computed tomography (SPECT). A multi-center study was prospectively designed to evaluate the diagnostic accuracy of Tc-99m-3PRGD2 imaging for bone metastasis in patients with lung cancer in comparison with the conventional Tc-99m-MDP bone scan. Methods: The patients underwent whole-body scan and chest tomography successively at both 1 h and 4 h after intravenous injection of 11.1 MBq/Kg Tc-99m-3PRGD2. Tc-99m-MDP whole-body bone scan was routinely performed within 1 week for comparison. Three experienced nuclear medicine physicians blindly read the Tc-99m-3PRGD2 and Tc-99m-MDP images. The final diagnosis was established based on the comprehensive assessment of all available data. Results: A total of 44 patients (29 male, 59 +/- 10 years old) with suspected lung cancer were recruited from 4 centers. Eighty-nine bone lesions in 18 patients were diagnosed as metastases and 23 bone lesions in 9 patients were benign. In a lesion-based analysis, Tc-99m-3PRGD2 imaging demonstrated a sensitivity, specificity, and accuracy of 92.1%, 91.3%, and 92.0%, respectively. The corresponding diagnostic values for Tc-99m-MDP bone scan were 87.6%, 60.9%, and 82.1%, respectively in the same patients. Tc-99m-MDP bone scan had better contrast in most lesions, whereas the Tc-99m-3PRGD2 imaging seemed to be more effective to exclude pseudo-positive lesions and detect bone metastases without osteogenesis. Conclusion: Tc-99m-3PRGD2 is a novel tumor-specific agent based on SPECT technology with a promising value in diagnosis of bone metastasis in patients with lung cancer.
    PLoS ONE 10/2014; 9(10):e111221. DOI:10.1371/journal.pone.0111221 · 3.53 Impact Factor


Available from
Jun 3, 2014