# Fluorescent Deferoxamine Complexes of Cu(II) and Zr(IV): Insights in the Development of Dual Imaging Probes

## TL;DR

A new fluorescent deferoxamine derivative, DFOKC, can bind Cu(II) and Zr(IV) and is suitable for both optical and PET imaging, with improved cell uptake and no toxicity.

## Contribution

DFOKC introduces a fluorescent coumarin unit via a lysine linker, enabling dual-mode imaging with enhanced metal binding and cell internalization.

## Key findings

- DFOKC forms more stable complexes with Cu(II) and Zr(IV) than DFO while retaining fluorescence.
- DFOKC shows improved tumor cell internalization via pinocytosis compared to DFOC.
- DFOKC exhibits no cytotoxicity or mitochondrial impairment at high concentrations.

## Abstract

Deferoxamine (DFO) is widely regarded as benchmark chelator for 89Zr(IV), a commonly used PET (positron emission tomography) tracer. We have introduced a novel fluorescent coumarin derivative of DFO (DFOKC), characterized by chelating unit and fluorophore covalently linked via a lysine molecule. This design introduces a free primary amine group, which, in perspective, can be functionalized with biological vectors, potentially improving tumor tissue selectivity. Its acid‐base and metal coordination properties toward Cu(II) and Zr(IV) ions were thoroughly characterized using UV‐Vis and fluorescence emission spectroscopy. DFOKC strongly coordinates both metal ions, forming somewhat more stable complexes than DFO, while retaining fluorescence emission, thus enabling dual‐mode optical and PET imaging. Biodistribution assays conducted on NIH‐3T3 fibroblasts, and MDA‐MB‐231 mammary adenocarcinoma cell lines demonstrated that the presence of primary amine groups favors Zr‐DFOKC complex cell internalization via pinocytosis compared to the parent molecule DFOC, in which the fluorophore is linked to the amine group of DFO. Furthermore, crystal violet and MTT assays revealed no cytotoxic effects or mitochondrial impairment, even at concentrations higher than those typically used for radio‐diagnostic applications. These results strongly support the potential of DFOKC as a versatile and promising tool for dual imaging, offering significant advantages in molecular imaging.

The insertion of a fluorescent coumarin unit by using a lysine‐based linker on deferoxamine leads to a chelating agent (DFOKC), whose Cu(II) and Zr(IV) complexes can be used for both optical imaging and positron emission tomography. DFOKC shows increased binding ability for Cu(II) and Zr(II) and improved tumor cell internalization via pinocytosis.