Strain-Promoted Azide-Alkyne Cycloaddition-Based PSMA-Targeting Ligands for Multimodal Intraoperative Tumor Detection of Prostate Cancer

Bioconjug Chem. 2022 Jan 19;33(1):194-205. doi: 10.1021/acs.bioconjchem.1c00537. Epub 2021 Dec 25.

Abstract

Strain-promoted azide-alkyne cycloaddition (SPAAC) is a straightforward and multipurpose conjugation strategy. The use of SPAAC to link different functional elements to prostate-specific membrane antigen (PSMA) ligands would facilitate the development of a modular platform for PSMA-targeted imaging and therapy of prostate cancer (PCa). As a first proof of concept for the SPAAC chemistry platform, we synthesized and characterized four dual-labeled PSMA ligands for intraoperative radiodetection and fluorescence imaging of PCa. Ligands were synthesized using solid-phase chemistry and contained a chelator for 111In or 99mTc labeling. The fluorophore IRDye800CW was conjugated using SPAAC chemistry or conventional N-hydroxysuccinimide (NHS)-ester coupling. Log D values were measured and PSMA specificity of these ligands was determined in LS174T-PSMA cells. Tumor targeting was evaluated in BALB/c nude mice with subcutaneous LS174T-PSMA and LS174T wild-type tumors using μSPECT/CT imaging, fluorescence imaging, and biodistribution studies. SPAAC chemistry increased the lipophilicity of the ligands (log D range: -2.4 to -4.4). In vivo, SPAAC chemistry ligands showed high and specific accumulation in s.c. LS174T-PSMA tumors up to 24 h after injection, enabling clear visualization using μSPECT/CT and fluorescence imaging. Overall, no significant differences between the SPAAC chemistry ligands and their NHS-based counterparts were found (2 h p.i., p > 0.05), while 111In-labeled ligands outperformed the 99mTc ligands. Here, we demonstrate that our newly developed SPAAC-based PSMA ligands show high PSMA-specific tumor targeting. The use of click chemistry in PSMA ligand development opens up the opportunity for fast, efficient, and versatile conjugations of multiple imaging moieties and/or drugs.

MeSH terms

  • Alkynes* / chemistry
  • Animals
  • Antigens, Surface* / metabolism
  • Azides* / chemistry
  • Cell Line, Tumor
  • Cycloaddition Reaction*
  • Glutamate Carboxypeptidase II* / metabolism
  • Humans
  • Ligands
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude*
  • Optical Imaging / methods
  • Prostatic Neoplasms* / diagnostic imaging
  • Tissue Distribution

Substances

  • Ligands
  • Glutamate Carboxypeptidase II
  • Alkynes
  • FOLH1 protein, human
  • Antigens, Surface
  • Azides