⁶⁸Ga-Chelation and comparative evaluation of N,N′-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N′-diacetic acid (HBED-CC) conjugated NGR and RGD peptides as tumor targeted molecular imaging probes

Abstract

Peptides containing RGD and NGR motifs display high affinity towards tumor vasculature molecular markers, integrin αβ and CD13 receptors, respectively. In the present study, RGD and NGR peptides were conjugated with the novel acyclic chelator ,'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-,'-diacetic acid (HBED-CC) for radiolabeling with Ga. The radiotracers [Ga-HBED-CC-c(NGR)] and [Ga-HBED-CC-c(RGD)] were quite hydrophilic with respective log values being -2.8 ± 0.14 and -2.1 ± 0.17.Ga-HBED-CC-c(RGD) displayed a significantly higher ( < 0.05) uptake in murine melanoma B16F10 tumors as compared to Ga-HBED-CC-c(NGR) indicating its higher specificity towards integrin αβ-positive tumors. The two radiotracers showed similar uptake in CD13-positive human fibrosarcoma HT-1080 tumor xenografts (∼1.5 ± 0.2% ID g). The tumor uptake of the two radiotracers was significantly reduced ( < 0.05) in both animal models during blocking studies. The tumor-to-blood ratio was observed to be ∼2-2.5 for the two radiotracers, whereas the tumor-to-muscle ratio was significantly higher ( < 0.005) for Ga-HBED-CC-c(RGD) in the two animal models. The two radiotracersGa-HBED-CC-c(NGR) and Ga-HBED-CC-c(RGD) exhibited renal excretion with rapid clearance from blood and other non-target organs. Thus,Ga-chelated HBED-CC conjugated NGR and RGD peptides expressed features conducive towards development as tumor targeted molecular imaging probes. This study further opens avenues for the successful conjugation of different peptides with the acyclic chelator HBED-CC and expansion of Ga-based radiopharmaceuticals.

Comparative evaluation of 68Ga‐labeled NODAGA, DOTAGA, and HBED‐CC‐conjugated cNGR peptide chelates as tumor‐targeted molecular imaging probes

“…The specific activity of radiotracers was determined to be 10–12 GBq/μmol. Radiochemical yield was determined by paper chromatography carried out in acetonitrile/water (1:1, v/v) as the mobile phase . Radiochemical purity of the radiotracers was determined by radio‐HPLC chromatograms.…”

“…The peptide c(KCNGRC) was synthesized according to previously mentioned procedure . The N‐terminus of the peptide (0.1 mmol) was conjugated on resin with either DOTAGA anhydride (0.3 mmol), NODAGA(tBu) 3 (0.3 mmol) or HBED‐CC‐tris(tBu)ester (0.2 mmol) in the presence of HATU (0.3 mmol) and DIPEA (0.6 mmol).…”

“…However, NOTA/NODAGA chelators having suitable cavity size form more thermodynamically stable complexes with 68 Ga, leading to rapid chelation at room temperature . The acyclic chelator HBED‐CC has recently gained popularity for 68 Ga‐chelation due to remarkably high thermodynamic and kinetic stability of 68 Ga‐HBED‐CC complexes . The different chelators influence the charge, hydrophilicity, and stability of radiolabeled peptide ligands, and this would be resonated in pharmacokinetics, tumor uptake, and selectivity.…”

Design, synthesis, and comparative evaluation of 99mTc(CO)3‐labeled N‐terminal and C‐terminal modified asparagine–glycine–arginine peptide constructs

“…The CD13 receptors specifically recognize asparagine–glycine–arginine (NGR) motif containing peptides . Radiometalated NGR peptide constructs are hence being explored as molecular imaging probes for detection and monitoring of CD13 receptor‐expressing malignant sites . According to a literature report, carboxyl terminal of cyclic NGR [cCNGRC] peptide is a favorable position for tagging radioisotopes/drugs rather than N‐terminal that plays more important role in receptor binding .…”

“…Radiometalation of NGR peptides has been reported with 64 Cu, 68 Ga, and 99m Tc for diagnostic purpose . However, single‐photon emission computed tomography (SPECT) radioisotope, 99m Tc has wider coverage in nuclear medicine hospitals because of lower infrastructure and financial requirement in comparison with positron emission tomography (PET) isotopes, 64 Cu and 68 Ga .…”