Synthesis of Novel, Dual-Targeting 68Ga-NODAGA-LacN-E[c(RGDfK)]2 Glycopeptide as a PET Imaging Agent for Cancer Diagnosis

Abstract

Radiolabeled peptides possessing an Arg-Gly-Asp (RGD) motif are widely used radiopharmaceuticals for PET imaging of tumor angiogenesis due to their high affinity and selectivity to αvβ3 integrin. This receptor is overexpressed in tumor and tumor endothelial cells in the case of numerous cancer cell lines, therefore, it is an excellent biomarker for cancer diagnosis. The galectin-3 protein is also highly expressed in tumor cells and N-acetyllactosamine is a well-established ligand of this receptor. We have developed a synthetic method to prepare a lactosamine-containing radiotracer, namely 68Ga-NODAGA-LacN-E[c(RGDfK)]2, for cancer diagnosis. First, a lactosamine derivative with azido-propyl aglycone was synthetized. Then, NODAGA-NHS was attached to the amino group of this lactosamine derivative. The obtained compound was conjugated to an E[c(RGDfK)]2 peptide with a strain-promoted click reaction. We have accomplished the radiolabeling of the synthetized NODAGA-LacN-E[c(RGDfK)]2 precursor with a positron-emitting 68Ga isotope (radiochemical yield of >95%). The purification of the labeled compound with solid-phase extraction resulted in a radiochemical purity of >99%. Subsequently, the octanol–water partition coefficient (log P) of the labeled complex was determined to be −2.58. In addition, the in vitro stability of 68Ga-NODAGA-LacN-E[c(RGDfK)]2 was investigated and it was found that it was stable under the examined conditions.

Recent Advances in Bioorthogonal Click Chemistry for Enhanced PET and SPECT Radiochemistry

“…Compared with CuAAC, SPAAC reaction can form a more stable 1,2,3-triazole by the conjugation of cyclooctynes with azides in the absence of Cu (I/II) cations, driven by ring strain from cyclic alkynes including DBCO derivatives [e.g., oxadibenzocyclooctyne (ODIBO) and azadibenzocyclooctyne (ADIBO)] and difluorinated cyclooctyne (DIFO) (Figure A), affording fewer byproducts, lower cell toxicity, and higher reaction kinetics . In fact, the radiolabeling protocol involving the incorporation of 18 F/ 68 Ga-labeled scaffolds into clickable tumor-targeted peptides was utilized with high radiochemical yields to radiolabel the RGD peptide, cyclic RGD (cRGD) peptide, mesenchymal-epithelial transition factor (c-Met) binding peptide (cMBP), bombesin (BBN) peptide, apoptosis targeting peptide (ApoPep), dual-targeting α v β 3 integrin and galectin-3 peptide, and integrin α v β 6 -specific peptide in high radiochemical yields. − Azide analogues were radiolabeled to provide 18 F-labeled scaffolds for the synthesis of peptide-based radiotracers. The radiolabeling of the di-cRGD-PEG5-ADIBO precursor with 18 F-labeled azide was performed to synthesize the 18 F-labeled di-cRGD peptide-based probe in 92% decay-corrected radiochemical yield (Figure C), and the PEG-containing probe displayed the highest binding affinity compared to the other RGD derivatives (Figure B) .…”

Role of Peptides in Diagnostics

“…Therefore, this novel approach for dual α v β 3 integrin and GRPR, targeting PET radiotracers, demonstrated a great potential in diagnosis and staging of primary prostate cancers as well as metastases lesions. Recently, another novel dual-targeting 68 Ga-NODAGA-LacN-E[c(RGDfK)] 2 Glycopeptide has also been developed for PET imaging of cancer patients, which can diagnose integrin α v β 3 and galectin-3 expression in tumor and tumor endothelial cells [104]. As evident from the details above, enough novel radiolabeled peptides are now available in the clinical setting and many more peptides are currently in preclinical investigation and indifferent clinical trial stages; therefore, there is no doubt that it will have enormous clinical impact in diagnostics in the coming years.…”

Synthesis of 68Ga-Labeled cNGR-Based Glycopeptides and In Vivo Evaluation by PET Imaging

“…To investigate the effect of glycosylation and pegylation on the in vivo properties of a radiotracer, three NGR-based radiopeptides were synthesized. We have previously reported the synthesis and radiochemical investigation of a glycopeptide, 68 Ga-NODAGA-LacN-E[c(RGDfK)] 2 , which may be suitable for the detection of α v β 3 integrin and galectin-3 expression in tumor endothelial and cancer cells by PET imaging [31]. In this report, a similar synthetic approach was used to prepare NGR-based radioligands as previously applied for 68 Ga-NODAGA-LacN-E[c(RGDfK)] 2 .…”