title: Synthesis and biological testing of aminoxyls designed for long-term retention by living cells.
abstract: Owing to recent advances in electron paramagnetic resonance (EPR) imaging methodologies, it is now potentially possible to track and image, in real time in vivo, cells that had been tagged with aminoxyl spin probes. We had previously reported that living cells can accumulate 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl [1] to high (millimolar) intracellular concentrations through passive incubation with the corresponding acetoxymethyl (AM) ester [2]. In the present study, we show that under physiological conditions aminoxyl [1] is rapidly extruded by cells through an organic anion transport mechanism, resulting in an intracellular exponential lifetime (t(1/e) or tau) of just 9.84 min at 37 degree C. Through successive rational structural modifications, we arrived at (2,2,5,5-tetramethylpyrrolidin-1-oxyl-3-ylmethyl)amine-N,N-diacetic acid [10], which can still be accumulated by cells to high intracellular concentrations, but which, with an intracellular exponential lifetime of tau]= 114 min, is well retained by cells for long periods of time, where one expects 14% retention even after 5 h. These results suggest that it should be feasible to use EPR imaging to perform in vivo tracking of populations of cells that have accumulated high intracellular levels of aminoxyls.
authors.affiliation: Department of Pharmaceutical Sciences and the Center for Very Low Frequency EPR Imaging for In Vivo Physiology, University of Maryland School of Pharmacy, Baltimore, MD 21201, USA.
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Rosen
authors.forename: Scott R
authors.initials: SR
authors.lastname: Burks
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Kohr
authors.forename: Joseph P Y
authors.initials: JP
authors.lastname: Kao
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004952:Esters; D006801:Humans; D019169:Jurkat Cells; D015335:Molecular Probes / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D027361:Organic Anion Transporters / Q000037:antagonists & inhibitors / Q000378:metabolism; D010879:Piperazines / Q000737:chemistry; D011339:Probenecid / Q000494:pharmacology; D011759:Pyrrolidines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
chemical_list: D004952:Esters; D015335:Molecular Probes; D027361:Organic Anion Transporters; D010879:Piperazines; D011759:Pyrrolidines; D011339:Probenecid