title: DNA binding chelates for nonviral gene delivery imaging.
abstract: Noninvasive in vivo monitoring of gene delivery would provide a critically important information regarding the spatial distribution, local concentration, kinetics of removal and/or biodegradation of the expression vector. We developed a novel approach to noninvasive gene delivery imaging using heterobifunctional peptide-based chelates (PBC) bearing double-stranded DNA-binding groups and a technetium-binding amino acid motif. One of such chelates: Gly-Cys(Acm)-Gly-Cys(Acm)-Gly-Lys(4)-Lys-(N-epsilon-[4-(psoralen-8-yloxy)]butyrate)-NH(2) has been characterized and labeled with reduced (99m)Tc pertechnetate (oxotechnetate). The psoralen moiety (a DNA binding group of PBC) allowed linking to double-stranded DNA upon short-term irradiation with the near UV range light (>320 nm). Approximately 30-40% of added (99m)Tc-labeled PBC was nonextractable and co-eluted with a model pCMV-GFP vector during the gel-permeation chromatography. Nuclear imaging of "naked" DNA and DNA complexes with lipid-based transfection reagents ("lipoplexes") has been performed after systemic or local administration of (99m)Tc-PBC-labeled DNA in mice. Imaging results were corroborated with the biodistribution using (99m)Tc-PBC and (32)P-labeled DNA and lipoplexes. A markedly different biodistribution of (99m)Tc PBC-labeled DNA and lipoplexes was observed with the latter being rapidly trapped in the liver, spleen and lung. (99m)Tc PBC-DNA was used as an imaging tracer during in vivo transfection of B16 melanoma by local injection of "naked" (99m)Tc PBC-DNA and corresponding lipoplexes. As demonstrated by nuclear imaging, (99m)Tc PBC-DNA lipoplexes showed a slower elimination from the site of injection than (99m)Tc PBC-DNA alone. This result correlated with a higher expression of marker mRNA and green fluorescent protein as determined using RT-PCR and immunohistochemistry, respectively.
authors.affiliation: Center for Molecular Imaging Research, Department of Radiology, Massachusetts General Hospital, Building 149, 13th Street, Charlestown, MA 02129, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bogdanov
authors.forename: C H
authors.initials: CH
authors.lastname: Tung
authors.forename: S
authors.initials: S
authors.lastname: Bredow
authors.forename: R
authors.initials: R
authors.lastname: Weissleder
mesh_terms: D000818:Animals; D002614:Chelating Agents; D004247:DNA / Q000493:pharmacokinetics*; D005260:Female; D018014:Gene Transfer Techniques; D005822:Genetic Vectors / Q000493:pharmacokinetics*; D008546:Melanoma, Experimental / Q000000981:diagnostic imaging / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D011877:Radionuclide Imaging; D013667:Technetium; D014018:Tissue Distribution; D014162:Transfection
chemical_list: D002614:Chelating Agents; D013667:Technetium; D004247:DNA