Highly shifted proton MR imaging: cell tracking by using direct detection of paramagnetic compounds.
OBJECTIVE
To explore the feasibility of tracking thulium (Tm)-1,4,7,10-tetraazacyclododecane-α,α',α'',α'''-tetramethyl-1,4,7,10-tetraacetic acid (DOTMA)-labeled cells in vivo by means of highly shifted proton magnetic resonance (MR) imaging as a potential alternative to established cell-tracking methods.


METHODS
All animal experiments were approved by the local ethics committee for animal experiments. Highly shifted proton MR imaging is based on the principle that the shifted resonances on Tm and dysprosium (Dy)-DOTMA can be detected separately from the tissue water signal at MR imaging with very short echo time and radial center-out readout (UTE, or "ultrashort echo time"). MR imaging of aqueous solutions and in mice in vivo was performed at 9.4 T. Human fibrosarcoma cells (HT-1080) and murine macrophages were labeled with different amounts of Tm-DOTMA. Labeled fibrosarcoma cells were injected subcutaneously into three mice. For cell tracking, labeled macrophages were administered intravenously into eight mice bearing local granulomatous inflammation. Three-dimensional UTE MR imaging was performed during 1 week. Macrophage viability and activity and fibrosarcoma cell viability were statistically analyzed by performing an unpaired two-tailed t test for labeled versus unlabeled cells by using data of at least six independent experiments.


RESULTS
The strongly shifted MR lines of Tm- and Dy-DOTMA can be separated from the tissue water signal and from each other. A detection limit of about 25 µmol/L of Tm-DOTMA was calculated from in vitro MR measurements. A mean ± standard error of the mean intracellular uptake of (4.19 ± 0.88) × 10(9) (HT-1080) and (10.1 ± 3.0) × 10(10) (macrophages) of Tm-DOTMA molecules per cell was achieved. In vivo, Tm-DOTMA signal was detectable for 1 week in both tumors and macrophages, with a detection limit of approximately 10(4) HT-1080 and 600 macrophages. Histologic examination results and elemental bioimaging confirmed labeled cells as source of MR signal.


CONCLUSIONS
Strongly shifted proton three-dimensional UTE MR imaging of Tm-DOTMA-labeled cells is a highly specific and sensitive tool for in vivo cell tracking.
From the Department of Clinical Radiology (R.S., K.S., M.M., C.H., U.K., C.B., C.F.) and Clinic of Dermatology-General Dermatology and Venerology (N.N., C.S.), University Hospital Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany; Institute of Inorganic and Analytical Chemistry, University of Münster, Münster, Germany (O.R., U.K.); Department of Molecular Biotechnologies and Health Sciences, University of Torino, Turin, Italy (D.D.C., S.A.); Cluster of Excellence EXC 1003, Cells in Motion, Münster, Germany (U.K., C.S., C.B., C.F.); and Bruker Biospin GmbH, Ettlingen, Germany (K.S.).
Rebecca
R
Schmidt
Nadine
N
Nippe
Klaus
K
Strobel
Max
M
Masthoff
Olga
O
Reifschneider
Daniela Delli
DD
Castelli
Carsten
C
Höltke
Silvio
S
Aime
Uwe
U
Karst
Cord
C
Sunderkötter
Christoph
C
Bremer
Cornelius
C
Faber
D000818:Animals; D045744:Cell Line, Tumor; D058948:Cell Tracking / Q000379:methods*; D003287:Contrast Media; D005260:Female; D005354:Fibrosarcoma / Q000473:pathology*; D006099:Granuloma / Q000473:pathology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008264:Macrophages / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D008819:Mice, Nude; D011522:Protons; D000644:Quaternary Ammonium Compounds; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003287:Contrast Media; D011522:Protons; D000644:Quaternary Ammonium Compounds; C054005:N-(1-(2,3-dioleyloxy)propyl)-N,N,N-trimethylammonium