title: Synthesis, characterization, and evaluation of a novel 99mTc(CO)3 pyrazolyl conjugate of a peptide nucleic acid sequence.
abstract: The 16-mer peptide nucleic acid sequence H-A GAT CAT GCC CGG CAT-Lys-NH2 (1), which is complementary to the translation start region of the N-myc oncogene messenger RNA, was synthesized and conjugated to a pyrazolyl diamine bifunctional chelator (pz). The novel conjugate pz-A GAT CAT GCC CGG CAT-Lys-NH2 (2) was labeled with technetium tricarbonyl, yielding quantitatively the complex fac-[99mTc(CO)3(kappa3-pz-A GAT CAT GCC CGG CAT-Lys-NH2)]2+ (4). Complex 4 was obtained with high radiochemical purity and high specific activity, revealing high stability in human serum and in cell culture medium. The identity of 4 was confirmed by comparing its reversed-phase high performance liquid chromatography profile with that of the rhenium analog fac-[Re(CO)3(kappa3-pz-A GAT CAT GCC CGG CAT-Lys-NH2)]2+ (3), prepared by conjugation of fac-[Re(CO)3(3,5-Me2pz(CH2)2N((CH2)3COOH)(CH2)2NH2)]+ to 1, using solid-phase techniques. UV melting experiments of 1 and 3 with the complementary DNA sequence led to the formation of stable duplexes, indicating that the conjugation of 1 to the pyrazolyl chelator and to the metal fragment fac-[M(CO)3]+ did not affect the recognition of the complementary sequence as well as the duplex stability. For a first screening, SH-SY5Y human neuroblastoma cells, which express N-myc, were treated with 4. The results show that 4 internalizes (7% of the activity goes into the cells, after 4 h at 37 degrees C), presenting also a relatively high cellular retention (only 40% of internalized activity is released from the cells after 5 h).
authors.affiliation: Unidade de Ciências Químicas e Radiofarmacêuticas, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953, Sacavém, Portugal.
authors.forename: Catarina
authors.initials: C
authors.lastname: Xavier
authors.forename: Clelia
authors.initials: C
authors.lastname: Giannini
authors.forename: Sergio
authors.initials: S
authors.lastname: Dall'Angelo
authors.forename: Lurdes
authors.initials: L
authors.lastname: Gano
authors.forename: Stefano
authors.initials: S
authors.lastname: Maiorana
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
authors.forename: Isabel
authors.initials: I
authors.lastname: Santos
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D003959:Diamines / Q000737:chemistry; D006801:Humans; D008956:Models, Chemical; D015336:Molecular Probe Techniques; D015335:Molecular Probes / Q000138:chemical synthesis* / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D015609:Organotechnetium Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D020135:Peptide Nucleic Acids / Q000737:chemistry* / Q000235:genetics; D011720:Pyrazoles / Q000737:chemistry*; D013667:Technetium / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D003959:Diamines; D015335:Molecular Probes; D015609:Organotechnetium Compounds; D020135:Peptide Nucleic Acids; D011720:Pyrazoles; D013667:Technetium
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