Synthesis and Biological Evaluation of Novel Mixed-Ligand 99mTc-Labeled Anthraquinone Complexes as Potential DNA-Targeted Imaging Agents

Anthraquinones are molecules with numerous biological properties that can act as DNA intercalators and topoisomerase IIa inhibitors. In this work, the development of technetium-99m radiotracers was pursued via the technetium-tricarbonyl “2 + 1” mixed-ligand approach, fac-[99mTc][TcI(CO)3(NN′)(N)]+, with a (N,N′) bidentate chelator and a N co-ligand. In one approach, the ligands used were 2,2′-bipyridine (bpy) and N-functionalized-imidazole, where imidazole was conjugated to an anthraquinone moiety. In the other approach, 2-picolylamine and imidazole were used as the mixed-ligand system, where picolylamine was conjugated to an anthraquinone moiety. The synthesis of the ligands was achieved by reaction of 2-picolylamine with a suitably functionalized anthraquinone (Aqpa) or anthrapyrazole (Appa) and imidazole with a suitably functionalized anthraquinone (Aqim). The rhenium reference compounds, fac-[ReI(CO)3(bpy)(Aqim)]+ with bpy as a bidentate chelator and fac-[ReI(CO)3(Aqpa or Appa)(Im)]+, with imidazole (Im) as a co-ligand, were synthesized and characterized with spectroscopic methods. The radiotracer technetium-99m complexes fac-[99mTc][Tc(CO)3(bpy)(Aqim)]+ and fac-[99mTc][Tc(CO)3(Aqpa or Appa)(Im)]+ were prepared and characterized with standard methods. The purified radiotracers displayed high stability (≥90%) after incubation 24 h in 1 mM L-histidine or rat plasma. The tracers’ cell uptake was evaluated in vitro in CT-26 cells, and their pharmacokinetic properties and tumor uptake were evaluated in vivo in CT26-tumor-bearing mice. The “2 + 1” technetium-tricarbonyl approach leads to in vitro stable tracers, and this mixed-ligand system shows promise for further evaluation.