Functionalized Bis(thiosemicarbazonato) Complexes of Zinc and Copper:  Synthetic Platforms Toward Site-Specific Radiopharmaceuticals

Abstract

Two new types of unsymmetrical bis(thiosemicarbazone) proligands and their neutral zinc(II) and copper(II) complexes have been synthesized. These bifunctional ligands both chelate the metal ions and provide pendent amino groups that can be readily functionalized with biologically active molecules. Functionalization has been demonstrated by the synthesis of three water-soluble glucose conjugates of the new zinc(II) bis(thiosemicarbazonato) complexes, and their copper(II) analogues have been prepared in aqueous solution via transmetalation. A range of techniques including NMR, electron paramagnetic resonance, cyclic voltammetry, high-performance liquid chromatography (HPLC), UV/vis, and fluorescence emission spectroscopy have been used to characterize the complexes. Four compounds, including two zinc(II) complexes, have been characterized by X-ray crystallography. The connectivity and conformation of the glucose conjugates have been assigned by NMR spectroscopy. Time-dependent density functional theory calculations have been used to assign the electronic transitions of the copper(II) bis(thiosemicarbazonato) chromophore. Two copper-64-radiolabeled complexes, including one glucose conjugate, have been prepared and characterized using radio-HPLC, and transmetalation is shown to be a viable method for radiolabeling compounds with copper radionuclides. Preliminary cell washout studies have been performed under normoxic conditions, and the uptake and intracellular distribution have been studied using confocal fluorescence microscopy.

In Vitro and In Vivo Evaluations of a Hydrophilic 64Cu-Bis(Thiosemicarbazonato)–Glucose Conjugate for Hypoxia Imaging

“…2B) and demonstrated that copper-zinc exchange could be used to prepare the 64 Cu-radiolabeled compound 64 Cu-ATSE/ A-G (Fig. 2C) (19). In this article, we describe the oxygendependent uptake of 64 Cu-ATSE/A-G into HeLa cells in vitro and preliminary in vivo imaging results obtained in male BDIX rats with implanted P22 syngeneic carcinosarcomas.…”

“…The proligand H 2 -ATSM, Zn-ATSM, and Zn-ATSE/A-G were prepared according to published methods (17)(18)(19)(20).…”

“…1, R 1 and R 2 ) (16,17). We have developed methods for the synthesis of Cu-ATSM nonsymmetrically substituted at R 3 and R 4 and have shown that variations in the exocyclic amine substituents have a relatively minor influence on the redox potential of the copper(II) center (18,19) and should not affect hypoxia selectivity. When R 3 or R 4 is a reactive amino group ( Fig.…”

“…When R 3 or R 4 is a reactive amino group ( Fig. 2A), the bis(thiosemicarbazonato) core can be conjugated to a biologically active molecule, such as glucose (19). Glucose is of particular interest because it is hydrophilic and is avidly metabolized by many types of tumors.…”

In Vitro and In Vivo Evaluation of Bifunctional Bisthiosemicarbazone 64Cu-Complexes for the Positron Emission Tomography Imaging of Hypoxia

“…26 Complexes were prepared at a specific activity range of 1-1000 mCi/μg ligand. All complexes were prepared in sufficient radiochemical purity (>95%, determined by radio-TLC and identity confirmed by direct comparison with the elution profile of the authentic nonradioactive analog) to undertake in vitro and in vivo studies.…”