Assessment of an 18F-Labeled Phosphoramidate Peptidomimetic as a New Prostate-Specific Membrane Antigen–Targeted Imaging Agent for Prostate Cancer

Journal of Nuclear Medicine

Hilla Wahnishe¹  Ella F. Jones¹  Jessie R. Nedrow-Byers¹  Clifford E. Berkman¹  David Pham¹  Tiancheng Liu¹  Kaveh Vejdani¹  Henry F. VanBrocklin¹  Lisa Y. Wu¹  Suzanne E. Lapi¹ 

关键词: molecular imaging;    PET;    radiopharmaceuticals;    ¹⁸F;    PSMA;    phosphoramidate;    prostate cancer;   

DOI  :  10.2967/jnumed.109.066589

学科分类：医学（综合）

来源: Society of Nuclear Medicine

【 摘 要 】

Prostate-specific membrane antigen (PSMA) is a transmembrane protein commonly found on the surface of late-stage and metastatic prostate cancer and a well-known imaging biomarker for staging and monitoring therapy. Although 111In-labeled capropmab pendetide is the only approved agent available for PSMA imaging, its clinical use is limited because of its slow distribution and clearance that leads to challenging image interpretation. A small-molecule approach using radiolabeled urea-based PSMA inhibitors as imaging agents has shown promise for prostate cancer imaging. The motivation of this work is to explore phosphoramidates as a new class of potent PSMA inhibitors to develop more effective prostate cancer imaging agents with improved specificity and clearance properties. Methods: N-succinimidyl-4-18F-fluorobenzoate (18F-SFB) was conjugated to S-2-((2-(S-4-amino-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (Phosphoramidate (1)), yielding S-2-((2-(S-4-(4-18F-fluorobenzamido)-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (3). In vivo studies were conducted in mice bearing either LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors. PET images were acquired at 1 and 2 h with or without a preinjection of a nonradioactive version of the fluorophosphoramidate. Tissue distribution studies were performed at the end of the 2 h imaging sessions. Results: Phosphoramidate (1) and its fluorobenzamido conjugate (2) were potent inhibitors of PSMA (inhibitory concentration of 50% [IC50], 14 and 0.68 nM, respectively). PSMA-mediated tumor accumulation was noted in the LNCaP versus the PC-3 tumor xenografts. The LNCaP tumor uptake was also blocked by the administration of nonradioactive (2) prior to imaging studies. With the exception of the kidneys, tumor-to-tissue and tumor-to-blood ratios were greater than 5:1 at 2 h. The strong kidney uptake may be due to the known PSMA expression in the mouse kidney, because significant reduction (>6-fold) in kidney activity was seen in mice injected with (2). Conclusion: 18F-labeled phosphoramidate (3) is a representative of a new class of PSMA targeting peptidomimetic molecules that shows great promise as imaging agents for detecting PSMA+ prostate tumors.

【 授权许可】

Unknown