Isothiocyanate-Functionalized Bifunctional Chelates and fac-[MI(CO)3]+ (M = Re, 99mTc) Complexes for Targeting uPAR in Prostate Cancer

Benjamin B. Kasten, Xiaowei Ma, Kai Cheng, Lihong Bu, Winston S. Slocumb, Thomas R. Hayes, Steven Trabue, Zhen Cheng, Paul D. Benny

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Developing new strategies to rapidly incorporate the fac-[MI(CO)3]+ (M = Re, 99mTc) core into biological targeting vectors in radiopharmaceuticals continues to expand as molecules become more complex and as efforts to minimize nonspecific binding increase. This work examines a novel isothiocyanate-functionalized bifunctional chelate based on 2,2′-dipicolylamine (DPA) specifically designed for complexing the fac-[MI(CO)3]+ core. Two strategies (postlabeling and prelabeling) were explored using the isothiocyanate-functionalized DPA to determine the effectiveness of assembly on the overall yield and purity of the complex with amine containing biomolecules. A model amino acid (lysine) examined (1) amine conjugation of isothiocyanate-functionalized DPA followed by complexation with fac-[MI(CO)3]+ (postlabeling) and (2) complexation of fac-[MI(CO)3]+ with isothiocyanate-functionalized DPA followed by amine conjugation (prelabeling). Conducted with stable Re and radioactive 99mTc analogs, both strategies formed the product in good to excellent yields under macroscopic and radiotracer concentrations. A synthetic peptide (AE105) which targets an emerging biomarker in CaP prognosis, urokinase-type plasminogen activator receptor (uPAR), was also explored using the isothiocyanate-functionalized DPA strategy. In vitro PC-3 (uPAR+) cell uptake assays with the 99mTc-labeled peptide (8a) showed 4.2 ± 0.5% uptake at 4 h. In a murine model bearing PC-3 tumor xenografts, in vivo biodistribution of 8a led to favorable tumor uptake (3.7 ± 0.7% ID/g) at 4 h p.i. with relatively low accumulation (<2% ID/g) in normal organs not associated with normal peptide excretion. These results illustrate the promise of the isothiocyanate-functionalized approach for labeling amine containing biological targeting vectors with fac-[MI(CO)3]+.

Original languageEnglish
Pages (from-to)130-142
Number of pages13
JournalBioconjugate Chemistry
Volume27
Issue number1
DOIs
StatePublished - Jan 20 2016
Externally publishedYes

Funding

The authors wish to thank Mary Dyszlewski of Covidien, Inc., for the Isolink kits and Dr. Gerhard Munske of the Washington State University Molecular Biology and Genomics Core for performing the MALDI-TOF analysis. This research was funded in part by the Office of Science (BER), U.S. Department of Energy (DE-SC0008397), the NIH/NIGMS Biotechnology Training Program at Washington State University (Institutional Award T32 GM008336), the Auvil Fellows Program, the College of Arts and Sciences, and the Chemistry Department at Washington State University.

FundersFunder number
Chemistry Department at Washington State University
Mary Dyszlewski of Covidien, Inc.
NIH/NIGMST32 GM008336
U.S. Department of EnergyDE-SC0008397
U.S. Department of Energy
National Institute of Neurological Disorders and StrokeT32NS048039
National Institute of Neurological Disorders and Stroke
Office of Science
Biological and Environmental Research
Washington State University
College of Arts and Sciences, Boston University

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