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Open AccessArticle

Modulating the Properties of Fe(III) Macrocyclic MRI Contrast Agents by Appending Sulfonate or Hydroxyl Groups

1
Department of Chemistry, University at Buffalo, The State University of New York, Amherst, NY 14260, USA
2
Department of Cell Stress Biology, Roswell Park Comprehensive Cancer Center, Buffalo, NY 14263, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Zoltan Kovacs
Molecules 2020, 25(10), 2291; https://doi.org/10.3390/molecules25102291
Received: 7 April 2020 / Revised: 7 May 2020 / Accepted: 10 May 2020 / Published: 13 May 2020
(This article belongs to the Special Issue Recent Advances on MRI Contrast Agents)
Complexes of Fe(III) that contain a triazacyclononane (TACN) macrocycle, two pendant hydroxyl groups, and a third ancillary pendant show promise as MRI contrast agents. The ancillary group plays an important role in tuning the solution relaxivity of the Fe(III) complex and leads to large changes in MRI contrast enhancement in mice. Two new Fe(III) complexes, one with a third coordinating hydroxypropyl pendant, Fe(L2), and one with an anionic non-coordinating sulfonate group, Fe(L1)(OH2), are compared. Both complexes have a deprotonated hydroxyl group at neutral pH and electrode potentials representative of a stabilized trivalent iron center. The r1 relaxivity of the Fe(L1)(OH2) complex is double that of the saturated complex, Fe(L2), at 4.7 T, 37 °C in buffered solutions. However, variable-temperature 17O-NMR experiments show that the inner-sphere water of Fe(L1)(OH2) does not exchange rapidly with bulk water under these conditions. The pendant sulfonate group in Fe(L1)(OH2) confers high solubility to the complex in comparison to Fe(L2) or previously studied analogues with benzyl groups. Dynamic MRI studies of the two complexes showed major differences in their pharmacokinetics clearance rates compared to an analogue containing a benzyl ancillary group. Rapid blood clearance and poor binding to serum albumin identify Fe(L1)(OH2) for development as an extracellular fluid contrast agent. View Full-Text
Keywords: Fe(III) complexes; T1 contrast agents; MRI; macrocyclic ligands; TACN; sulfonate group; pharmacokinetics; in vivo; kidney image; relaxivity Fe(III) complexes; T1 contrast agents; MRI; macrocyclic ligands; TACN; sulfonate group; pharmacokinetics; in vivo; kidney image; relaxivity
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Asik, D.; Smolinski, R.; Abozeid, S.M.; Mitchell, T.B.; Turowski, S.G.; Spernyak, J.A.; Morrow, J.R. Modulating the Properties of Fe(III) Macrocyclic MRI Contrast Agents by Appending Sulfonate or Hydroxyl Groups. Molecules 2020, 25, 2291.

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