Novel “bi-modal” H2dedpa derivatives for radio- and fluorescence imaging

• Published in: Journal of inorganic biochemistry 2016-09, Vol.162, p.253-262
• Main Authors: Ramogida, Caterina F., Murphy, Lisa, Cawthray, Jacqueline F., Ross, James D., Adam, Michael J., Orvig, Chris
• Format: Article
• Language: English
• Subjects: Bifunctional chelates; Fluorescence imaging; Gallium-68; Nitroimidazole; Positron-emission tomography; Spheroids
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2015.11.021

A novel pyridyl functionalized analog of the promising hexadentate 68Ga3+ chelate H2dedpa (N4O2, 1,2-[[6-carboxy-pyridin-2-yl]-methylamine]ethane) was successfully synthesized and characterized. This new bifunctional chelate (BFC) was used to prepare the first proof-of-principle bi-modal H2dedpa derivative for fluorescence and nuclear imaging. Two bi-modal H2dedpa derivatives were prepared: H2dedpa-propylpyr-FITC and H2dedpa-propylpyr-FITC-(N,N′-propyl-2-NI) (FITC=fluorescein, pyr=pyridyl functionalized, NI=nitroimidazole). The ligands possess the strong gallium-coordinating atoms contained within dedpa2− that are ideal for radiolabeling with 68Ga3+ for positron-emission tomography (PET) imaging, and two fluorophores for optical imaging. In addition, one analog contains two NI moieties for specific entrapment of the tracer in hypoxic cells. These new bi-modal analogs were compared to the native unfunctionalized H2dedpa scaffold to determine the extent to which the addition of pyridyl functionalization would affect metal coordination, and complex stability. The non-radioactive gallium complexes were tested in a 3D tumor spheroid model. The novel pyridyl bis-functionalized H2dedpa ligand, H2dedpa-propylpyr-NH2, was quantitatively radiolabeled with 67Ga (RCY>99%) under reaction conditions commensurate with unfunctionalized H2dedpa (10min at room temperature) at ligand concentrations as low as 10−5M. The resultant 67Ga-complex withstood transchelation to the in vivo metal-binding competitor apo-transferrin (2h at 37°C, 93% intact), signifying that [Ga(dedpa-propylpyr-NH2)]+ is a kinetically inert complex suitable for in vivo use, but exhibited slightly reduced stability compared to the native [67Ga(dedpa)] scaffold (>99% intact). Finally, bi-model fluorescent Ga-dedpa compounds were successfully imaged in a 3D tumor spheroid model. The Ga-dedpa-FITC-NI derivative was specifically localized in the central hypoxic core of the spheroid. A novel bifunctional analog of the promising gallium(III) ligand H2dedpa (N4O2, 1,2-[[6-carboxy-pyridin-2-yl]-methylamine]ethane) was synthesized, and screened for its ability to bind Ga3+ isotopes. This new bifunctional chelate was conjugated to fluorescein isothiocyanate (FITC), and tested in vitro as a first proof-of-principle bimodal imaging agent for positron emission tomography and optical imaging. [Display omitted] •H2dedpa (N4O2, 1,2-[[6-carboxy-pyridin-2-yl]-methylamine]ethane) is a Ga3+ chelate.•A novel pyridyl functiona