PSMA-targeted SPECT agents: mode of binding effect on in vitro performance

Prostate. 2013 Mar;73(4):355-62. doi: 10.1002/pros.22575. Epub 2012 Aug 21.


Background: The enzyme-biomarker prostate-specific membrane antigen (PSMA) is an active target for imaging and therapeutic applications for prostate cancer. The internalization of PSMA has been shown to vary with inhibitors' mode of binding: irreversible, slowly reversible, and reversible.

Methods: In the present study, PSMA-targeted clickable derivatives of an irreversible phosphoramidate inhibitor DBCO-PEG(4) -CTT-54 (IC(50) = 1.0 nM) and a slowly reversible phosphate inhibitor, DBCO-PEG(4) -CTT-54.2 (IC(50) = 6.6 nM) were clicked to (99m) Tc(CO)(3) -DPA-azide to assemble a PSMA-targeted SPECT agent. The selectivity, percent uptake, and internalization of these PSMA-targeted SPECT agents were evaluated in PSMA-positive and PSMA-negative cells.

Results: In vitro studies demonstrated that PSMA-targeted SPECT agents exhibited selective cellular uptake in the PSMA-positive LNCaP cells compared to PSMA-negative PC3 cells. More importantly, it was found that (99m) Tc(CO)(3) -DPA-DBCO-PEG(4) -CTT-54 based on an irreversible PSMA inhibitor core, exhibited greater uptake and internalization than (99m) Tc(CO)(3) -DPA-DBCO-PEG(4) -CTT-54.2 constructed from a slowly reversible PSMA inhibitor core.

Conclusions: We have demonstrated that a PSMA-targeted SPECT agent can be assembled efficiently using copper-less click chemistry. In addition, we demonstrated that mode of binding has an effect on internalization and percent uptake of PSMA-targeted SPECT agents; with the irreversible targeting agent demonstrating superior uptake and internalization in PSMA+ cells. The approach demonstrated in this work now supports a modular approach for the assembly of PSMA-targeted imaging and therapeutic agents.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Antigens, Surface / metabolism*
  • Cell Line, Tumor
  • Cell Survival / physiology
  • Drug Delivery Systems / methods*
  • Glutamate Carboxypeptidase II / metabolism*
  • Humans
  • Male
  • Prostatic Neoplasms / diagnosis
  • Prostatic Neoplasms / metabolism*
  • Prostatic Neoplasms / pathology
  • Protein Binding / physiology
  • Radioisotopes / metabolism
  • Tomography, Emission-Computed, Single-Photon*


  • Antigens, Surface
  • Radioisotopes
  • FOLH1 protein, human
  • Glutamate Carboxypeptidase II