Radiotracers for different angiogenesis receptors in a melanoma model

Abstract

Early and reliable diagnosis of melanoma, a skin tumor with a poor prognosis, is extremely important. Phage display peptide libraries are a convenient screening resource for identifying bioactive peptides that interact with cancer targets. The aim of this study was to evaluate two technetium-99m tracers for angiogenesis detection in a melanoma model, using cyclic pegylated pentapeptide with RGD and NGR motifs conjugated with the bifunctional chelator mercaptoacetyltriglycine (MAG(3)). The conjugated peptides (10 μl of a μg/μl solution) were labeled with technetium-99m using a sodium tartrate buffer. Radiochemical evaluation was carried out by instant thin-layer chromatography and confirmed by high-performance liquid chromatography. The partition coefficient was determined and internalization assays were performed in two melanoma cell lines (B16F10 and SKMEL28). Biodistribution evaluation of the tracers was carried out in healthy animals at different time points and also in tumor-bearing mice, 120 min post injection. Blocking studies were also conducted by coinjection of cold peptides. The conjugates displayed a rather similar pharmacokinetic profile. They were radiolabeled with high radiochemical purity (>97%) and both were hydrophilic with preferential renal excretion. Yet, tumor uptake was higher for human than for murine melanoma cells, especially for [(99m)Tc]-MAG(3)-PEG(8)-c(RGDyk) (7.85±2.34%injected dose/g 120 min post injection). The performance of [(99m)Tc]-MAG(3)-PEG(8)-c(RGDyk) was better than the NGR tracer with regard to human melanoma uptake. In this sense, it should be considered for future radiotracer studies of tumor diagnosis.

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

“…The radiometalated peptide 6 exhibited slightly higher radioactive accumulation in liver and intestine at 4 hours p.i.. Amongst the few reports of 99m Tc‐labeled NGR peptide, the NGR peptide has been either directly labeled with 99m Tc or using MAG 3 /HYNIC approach. Oliveira et al performed studies with 99m Tc‐MAG 3 ‐c (NGRyk) and reported uptake of 0.85 ± 0.34% ID/g at 2 hours p.i. in murine melanoma B16F10 tumor, whereas in present studies, tumor uptake of 1.9 ± 0.1 and 2.4 ± 0.2% ID/g was observed for 5 and 6 , respectively at 2 hours p.i.…”

“…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 .…”

Synthesis and evaluation of novel Tc-99 m labeled NGR-containing hexapeptides as tumor imaging agents

“…Although different tumor models were used, the tumor/muscle uptake ratio was 6.06 at 4 h, and this value was comparable with our results. Oliveira et al developed Tc‐99 m‐MAG3‐PEG(8)‐c(NGRyk) and reported that tumor uptake in the biodistribution study was 1.07 ± 0.23%ID/g at 120 min post injection in the SK‐MEL‐28 human melanoma model …”

“…8 Because of the good property of NGR peptide binding specifically to APN/CD13, several studies had developed the NGR peptide-based Tc-99 m imaging agents. [11][12][13][14] Ma et al developed Tc-99 m labeled monomeric and dimeric NGR peptides and reported that the NGR dimer showed higher binding affinity and cell uptake in vitro than the NGR-containing monomer. In the biodistribution study, tumor uptake of NGR dimer was 5.03 ± 0.74 at 4 h after injection.…”