Synthesis of DOTA-conjugated multimeric [Tyr3]octreotide peptides via a combination of Cu(I)-catalyzed "click" cycloaddition and thio acid/sulfonyl azide "sulfo-click" amidation and their in vivo evaluation

C. Yim, I. Dijkgraaf, R. Merkx, C. Versluis, A. Eek, G. Mulder, D. Rijkers, O. Boerman and R. Liskamp

Department of Pharmaceutical Sciences, Faculty of Science, Division of Medicinal Chemistry and Chemical Biology, Utrecht University, Utrecht, The Netherlands.
May, 2010



Herein, we describe the design, synthesis, and biological evaluation of a series of DOTA-conjugated monomeric, dimeric, and tetrameric [Tyr(3)]octreotide-based analogues as a tool for tumor imaging and/or radionuclide therapy. These compounds were synthesized using a Cu(I)-catalyzed 1,3-dipolar cycloaddition ("click" reaction) between peptidic azides and dendrimer-derived alkynes and a subsequent metal-free introduction of DOTA via the thio acid/sulfonyl azide amidation ("sulfo-click" reaction). In a competitive binding assay using rat pancreatic AR42J tumor cells, the monomeric [Tyr(3)]octreotide conjugate displayed the highest binding affinity (IC(50) = 1.32 nM) followed by dimeric [Tyr(3)]octreotide (2.45 nM), [DOTA(0),Tyr(3)]octreotide (2.45 nM), and tetrameric [Tyr(3)]octreotide (14.0 nM). Biodistribution studies with BALB/c nude mice with subcutaneous AR42J tumors showed that the (111)In-labeled monomeric [Tyr(3)]octreotide conjugate had the highest tumor uptake (42.3 +/- 2.8 \%ID/g) at 2 h p.i., which was better than [(111)In-DOTA(0),Tyr(3)]octreotide (19.5 +/- 4.8 \%ID/g). The (111)In-labeled dimeric [Tyr(3)]octreotide conjugate showed a long tumor retention (25.3 +/- 5.9 \%ID/g at 2 h p.i. and 12.1 +/- 1.3 \%ID/g at 24 h p.i.). These promising results can be exploited for therapeutic applications.