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Gallium-68 Complex of a Macrobicyclic Cage Amine Chelator Tethered to Two Integrin-Targeting Peptides for Diagnostic Tumor Imaging

Ma, M.; Neels, O.; Denoyer, D.; Roselt, P.; Karas, J.; Scanlon, D.; White, J.; Hicks, R.; Donnelly, P.
Tumor-targeting peptides radiolabeled with positron-emitting 68Ga are promising candidates as new noninvasive diagnostic agents for positron emission tomography (PET). The targeting peptides are tethered to a chelator that forms a stable coordination complex with Ga3+ that is inert to dissociation of Ga3+in vivo. Metal complexes of macrobicyclic hexaamine “sarcophagine” (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) ligands exhibit remarkable stability as a result of the encapsulating nature of the cage amine ligand. A Ga3+ sarcophagine complex, [Ga-(1-NH3-8-NH2-sar)]4+, has been characterized using X-ray crystallography, demonstrating that Ga3+ is coordinated to six nitrogen atoms in a distorted octahedral complex. A bifunctional derivative of (NH2)2sar, possessing two aliphatic linkers with carboxylic acid functional groups has been attached to two cyclic-RGD peptides that target the αvβ3 integrin receptor that is overexpressed in some types of tumor tissue. This dimeric species can be radiolabeled with 68Ga3+ in >98% radiochemical yield and 68Ga3+ does not dissociate from the ligand in the presence of transferrin, an endogenous protein with high affinity for Ga3+. Biodistribution and micro-PET imaging studies in tumor-bearing mice indicate that the tracer accumulates specifically in tumors with high integrin expression. The high tumor uptake is coupled with low nonspecific uptake and clearance predominantly through the kidneys resulting in high-quality PET images in animal models.


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Publ.-Id: 31006