Ramoplanin Imaging Conjugates – Synthesis and Evaluation
Sumbla Sheikh, Alexander Sturzu, Hubert Kalbacher, Uwe Klose, Thomas Nagele, Bushra Amin, Martin Deeg, Marius Horger, Ulrike Ernemann and Stefan Heckl
Affiliation: Department of Neuroradiology, University of Tübingen, Hoppe-Seyler-Str.3, 72076 Tübingen, Germany.
In a previous study we found that fluorescence-marked vancomycin – a glycopeptide antibiotic – is taken up
into human tumor cells. To expand on these investigations we now used the lipoglycodepsipeptide antibiotic ramoplanin.
Compared to vancomycin it is not only a bigger molecule, but it also has two potential binding sites for coupling to the
Three different ramoplanin imaging conjugates were synthesized, two used for fluorescence imaging and one for magnetic
resonance imaging. The two fluorescent dyes used in confocal laser scanning microscopy (CLSM) and fluorescence activated
cell sorting (FACS) were fluorescein isothiocyanate (FITC) and rhodamine isothiocyanate (RITC). The third was
the magnetic resonance imaging (MRI) contrast agent gadolinium-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic
The uptake of ramoplanin conjugates, their specificity for different cell lines and the accessibility of the conjugates by
imaging methods were evaluated on 8 human cell lines (two benign, six malignant) by CLSM, FACS and MRI experiments.
Cytotoxicity of the ramoplanin conjugates was determined in the FACS experiments with the propidium iodide and
Annexin-V-Fluos indicating any disruption in the cell membranes.
Cytoplasmic uptake of the ramoplanin conjugates was observed in confocal laser scanning images and was measured
using FACS and MRI experiments.
Compared to the vancomycin conjugates the ramoplanin conjugates showed much weaker and slower uptake. Additionally,
uptake of the ramoplanin conjugates led to strong membrane disruption and cell death.
Keywords: Ramoplanin conjugates, fluorescence imaging, magnetic resonance imaging.
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