Differences in the Renal Accumulation of Radiogallium-Labeled (Glu)14 Peptides Containing Different Optical Isomers of Glutamic Acid.

Acidic amino acid peptides have a high affinity for bone. Previously, we demonstrated that radiogallium complex-conjugated oligo-acidic amino acids possess promising properties as bone-seeking radiopharmaceuticals. Here, to elucidate the effect of stereoisomers of Glu in Glu-containing peptides [(Glu)14] on their accumulation in the kidney, the biodistributions of [67Ga]Ga-N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid-conjugated (l-Glu)14 ([67Ga]Ga-HBED-CC-(l-Glu)14), [67Ga]Ga-HBED-CC-(d-Glu)14, [67Ga]Ga-HBED-CC-(dl-Glu)14, and [67Ga]Ga-HBED-CC-(d-Glu-l-Glu)7 were compared. Although the accumulation of these compounds in the bone was comparable, their kidney accumulation and retention were strikingly different, with [67Ga]Ga-HBED-CC-(d-Glu-l-Glu)7 exhibiting the lowest level of kidney accumulation among these compounds. Repeated d- and l-peptides may be a useful method for reducing renal accumulation in some cases.

Synthesis and Evaluation of Radiogallium Labeled Bone-Imaging Probes Using Oligo-γ-Carboxy Glutamic Acid Peptides as Carriers to Bone.

We investigated the importance of the carboxy group density in bone affinity during the development of peptide-based bone-seeking radiopharmaceuticals and carriers. Oligo-γ-carboxy glutamic acid peptides [(Gla)n] with higher carboxy group density than oligo-glutamic acid peptides [(Glu)n] and oligo-aspartic acid peptides [(Asp)n] were chosen. Using the radiogallium chelator N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC), we synthesized [67Ga]Ga-HBED-CC-(Gla)n (n = 1, 2, 5, 8, 11, or 14) with high yields. Hydroxyapatite-binding assays, biodistribution, and SPECT imaging showed higher affinity and bone accumulation for [67Ga]Ga-HBED-CC-(Gla)n compared to [67Ga]Ga-HBED-CC-(Glu)n. Notably, [67Ga]Ga-HBED-CC-(Gla)8 and [67Ga]Ga-HBED-CC-(Gla)11 exhibited superior bone accumulation and rapid blood clearance. SPECT/CT imaging with [67Ga]Ga-HBED-CC-(Gla)8 exclusively visualized the bone tissue. These findings support the potential use of [67Ga]Ga-HBED-CC-(Gla)n as excellent bone-imaging PET probes, suggesting (Gla)n peptides are superior bone-seeking carriers.

Astatine-211-labeled aza-vesamicol derivatives as sigma receptor ligands for targeted alpha therapy.

INTRODUCTION: As sigma receptors are abundantly expressed on different types of cancer cells, several radiolabeled sigma receptor ligands have been developed for cancer imaging and therapy. Previously, we synthesized and evaluated radioiodinated aza-vesamicol derivatives, [125I]pIC3NV, [125I]mIC2N5V, and [125I]mIC3N5V. They accumulated in tumors, and [125I]mIC2N5V and [125I]mIC3N5V showed higher tumor to non-target tissue ratios than [125I]pIC3NV. Therefore, we synthesized and evaluated the corresponding 211At-labeled compounds, [211At]mAtC2N5V and [211At]mAtC3N5V, for targeted alpha therapy (TAT). METHODS: [211At]mAtC2N5V and [211At]mAtC3N5V were prepared by the standard method of electrophilic astatodestannylation of the corresponding trimethylstannyl precursors. Cellular uptake experiments, and biodistribution experiments and therapeutic experiments in tumor-bearing mice were performed. RESULTS: The radiochemical yields of [211At]mAtC2N5V and [211At]mAtC3N5V were 45.5 ± 14.4% and 56.9 ± 13.8%, respectively. After HPLC purification, their radiochemical purities were over 95%. [211At]mAtC2N5V and [211At]mAtC3N5V showed high uptake in DU-145 cells. They demonstrated high accumulation in tumors (6.9 ± 1.4%injected dose/g and 5.1 ± 1.4%injected dose/g at 1 h, respectively) and similar biodistribution tendencies compared with the corresponding 125I-labeled compounds. A single injection of [211At]mAtC2N5V (0.48 MBq) or [211At]mAtC3N5V (0.48 MBq) significantly inhibited tumor growth. CONCLUSION: These results indicated that [211At]mAtC2N5V and [211At]mAtC3N5V could be potential candidates for TAT.