PSMA-targeted SPECT agents: mode of binding effect on in vitro performance.
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.
Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, USA.
Jessie R
JR
Nedrow-Byers
Adam L
AL
Moore
Tanushree
T
Ganguly
Mark R
MR
Hopkins
Melody D
MD
Fulton
Paul D
PD
Benny
Clifford E
CE
Berkman
D000954:Antigens, Surface / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D016503:Drug Delivery Systems / Q000379:methods*; D043425:Glutamate Carboxypeptidase II / Q000378:metabolism*; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D011485:Protein Binding / Q000502:physiology; D011868:Radioisotopes / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon
D000954:Antigens, Surface; D011868:Radioisotopes; C473848:FOLH1 protein, human; D043425:Glutamate Carboxypeptidase II