title: Design of (Gd-DO3A)n-polydiamidopropanoyl-peptide nucleic acid-D(Cys-Ser-Lys-Cys) magnetic resonance contrast agents.
abstract: We hypothesized that chelating Gd(III) to 1,4,7-tris(carboxymethylaza)cyclododecane-10-azaacetylamide (DO3A) on peptide nucleic acid (PNA) hybridization probes would provide a magnetic resonance genetic imaging agent capable of hybridization to a specific mRNA. Because of the low sensitivity of Gd(III) as an magnetic resonance imaging (MRI) contrast agent, a single Gd-DO3A complex per PNA hybridization agent could not provide enough contrast for detection of cancer gene mRNAs, even at thousands of mRNA copies per cell. To increase the Gd(III) shift intensity of MRI genetic imaging agents, we extended a novel DO3An-polydiamidopropanoyl (PDAPm) dendrimer, up to n = 16, from the N-terminus of KRAS PNA hybridization agents by solid phase synthesis. A C-terminal D(Cys-Ser-Lys-Cys) cyclized peptide analog of insulin-like growth factor 1 (IGF1) was included to enable receptor-mediated cellular uptake. Molecular dynamic simulation of the (Gd-DO3A-AEEA)16-PDAP4-AEEA2-KRAS PNA-AEEA-D(Cys-Ser-Lys-Cys) genetic imaging nanoparticles in explicit water yielded a pair correlation function similar to that of PAMAM dendrimers, and a predicted structure in which the PDAP dendron did not sequester the PNA. Thermal melting measurements indicated that the size of the PDAP dendron included in the (DO3A-AEEA)n-PDAPm-AEEA2-KRAS PNA-AEEA-D(Cys-Ser-Lys-Cys) probes (up to 16 Gd(III) cations per PNA) did not depress the melting temperatures (Tm) of the complementary PNA/RNA hybrid duplexes. The Gd(III) dendrimer PNA genetic imaging agents in phantom solutions displayed significantly greater T1 relaxivity per probe (r1 = 30.64 +/- 2.68 mM(-1) s(-1) for n = 2, r1 = 153.84 +/- 11.28 mM(-1) s(-1) for n = 8) than Gd-DTPA (r1 = 10.35 +/- 0.37 mM(-1) s(-1)), but less than that of (Gd-DO3A)32-PAMAM dendrimer (r1 = 771.84 +/- 20.48 mM(-1) s(-1)) (P < 0.05). Higher generations of PDAP dendrimers with 32 or more Gd-DO3A residues attached to PNA-D(Cys-Ser-Lys-Cys) genetic imaging agents might provide greater contrast for more sensitive detection.
authors.affiliation: Laboratory of Nucleic Acids Chemistry, Institute of Chemical Biology and Fundamental Medicine, Philadelphia, PA 19107, USA.
authors.forename: Nariman V
authors.initials: NV
authors.lastname: Amirkhanov
authors.forename: Ivan
authors.initials: I
authors.lastname: Dimitrov
authors.forename: Armin W
authors.initials: AW
authors.lastname: Opitz
authors.forename: Kaijun
authors.initials: K
authors.lastname: Zhang
authors.forename: John P
authors.initials: JP
authors.lastname: Lackey
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Cardi
authors.forename: Song
authors.initials: S
authors.lastname: Lai
authors.forename: Norman J
authors.initials: NJ
authors.lastname: Wagner
authors.forename: Mathew L
authors.initials: ML
authors.lastname: Thakur
authors.forename: Eric
authors.initials: E
authors.lastname: Wickstrom
mesh_terms: D000873:Anthracenes / Q000737:chemistry; D001483:Base Sequence; D002614:Chelating Agents / Q000737:chemistry; D003198:Computer Simulation; D003545:Cysteine; D005682:Gadolinium / Q000737:chemistry; D019786:Gadolinium DTPA / Q000737:chemistry*; D008239:Lysine; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008958:Models, Molecular; D008968:Molecular Conformation; D009841:Oligonucleotides / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry; D020135:Peptide Nucleic Acids / Q000737:chemistry*; D012694:Serine; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000873:Anthracenes; D002614:Chelating Agents; D009841:Oligonucleotides; D009842:Oligopeptides; D020135:Peptide Nucleic Acids; C501244:dendron; D012694:Serine; D005682:Gadolinium; D019786:Gadolinium DTPA; D008239:Lysine; D003545:Cysteine