In Vitro and in Vivo Metabolism of Lu-AMBA, a GRP-Receptor Binding Compound, and the Synthesis and Characterization of Its Metabolites

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• 作者：Karen E. Linder ; Edmund Metcalfe ; Thangavel Arunachalam ; Jianqing Chen ; Stephen M. Eaton ; Weiwei Feng ; Hong Fan ; Natarajan Raju ; Aldo Cagnolini ; Laura E. Lantry ; Adrian D. Nunn ; Rolf E. Swenson
• 刊名：Bioconjugate Chemistry
• 出版年：2009
• 出版时间：June 17, 2009
• 年：2009
• 卷：20
• 期：6
• 页码：1171-1178
• 全文大小：187K
• 年卷期：v.20,no.6(June 17, 2009)
• ISSN：1520-4812

文摘

The metabolism of ¹⁷⁷Lu-AMBA (AMBA = DO3A-CH₂CO-G-(4-aminobenzoyl)-QWAVGHLM-NH₂), a radiotherapeutic compound in clinical development that binds to GRP and NMB receptors, was studied in vitro (mouse, rat and human plasma, mouse kidney homogenate) and in vivo (by analysis of mouse and rat plasma and urine following IV injection of ¹⁷⁷Lu-AMBA). The primary metabolites were Lu-DO3A-CH₂CO-G-Abz4-R, where R = -Q-OH (A), -QW-OH (B), and -QWAVGH-OH (C). Minor amounts of (D) where R = -QWAVGHLM-OH and (E) -QWAVGHL-OH were also observed. Clearance of ¹⁷⁷Lu-AMBA and of radioactivity from mouse and rat blood was rapid in vivo. In mouse and rat urine, only metabolites Lu-A and Lu-B were found—no parent drug was excreted. Unmetalated ligands and ^natLu and ¹⁷⁷Lu complexes for Lu-AMBA metabolites A−E were synthesized, characterized by HPLC and MS, and used to perform in vitro competition and direct binding studies on GRP receptor-positive PC-3 (human prostate) cancer cells. Biodistribution studies with ¹⁷⁷Lu-labeled metabolites A−E were performed in PC-3 tumor-bearing mice and the results compared with intact ¹⁷⁷Lu-AMBA. IC₅₀ values for unmetalated metabolite ligands A−E were >400 nM in PC-3 cells in competition binding studies against ¹⁷⁷Lu-AMBA. No direct binding to PC-3 cells was observed with ¹⁷⁷Lu-labeled A−C, confirming IC₅₀ results. ¹⁷⁷Lu-labeled metabolites A−E showed no uptake in GRP-receptor positive tumor or pancreas in PC-3 tumor bearing mice. All metabolites were rapidly excreted via the renal route (78−87%) within 1 h. These results demonstrate that the tumor uptake observed with ¹⁷⁷Lu-AMBA is due to parent drug and not due to any of its identified metabolites.