title: 99mTc-peptide-peptide nucleic acid probes for imaging oncogene mRNAs in tumours.
abstract: Imaging oncogene mRNA in tumours would provide a powerful tool for the early detection of occult malignant lesions. The goal was to prepare a chimera consisting of a dodecamer antisense peptide nucleic acid (PNA) specific for c-MYC oncogene overexpressed in human breast cancer cells and a chelating moiety that facilitates quantitative radiolabelling with 99mTc and evaluate it for hybridization and tissue distribution in laboratory animals. The pentapeptide chelator-PNA dodecamer specific for c-MYC mRNA was extended from a solid support by 9-fluorenylmethyloxycarbonyl (Fmoc) coupling. Similarly, a chelator-PNA chimera with four central mismatches was also prepared which served as a control. The chimeras were purified, characterized and evaluated for hybridization to c-MYC mRNA by fluorescent, real-time polymerase chain reaction (RT-PCR). The chimeras were labelled with 99mTc and their tissue distribution was examined in athymic nude mice bearing experimental human breast tumours. 99mTc radiolabelling was quantitative and presented a single peak in reversed phase liquid chromatography. Fluorescent real-time polymerase chain reactions using primer and fluorescent probe sets previously calculated for c-MYC mRNA demonstrated inhibition of reverse transcription by the c-MYC specific chimera as compared to that of the control. Tissue distribution studies of antisense and mismatch chimeras at 4 h and 24 h after administration displayed modest accumulation in the liver, and appreciable levels in tumours. These observations suggest that 99mTc-peptide-PNA probes might be useful for imaging gene expression in tumours, and the approach is worthy of further investigation.
authors.affiliation: Departments of Radiology, Thomas Jefferson University, Philadelphia 19107, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Rao
authors.forename: X
authors.initials: X
authors.lastname: Tian
authors.forename: W
authors.initials: W
authors.lastname: Qin
authors.forename: M R
authors.initials: MR
authors.lastname: Aruva
authors.forename: E R
authors.initials: ER
authors.lastname: Sauter
authors.forename: M L
authors.initials: ML
authors.lastname: Thakur
authors.forename: E
authors.initials: E
authors.lastname: Wickstrom
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D020135:Peptide Nucleic Acids / Q000493:pharmacokinetics*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D017556:Technetium Compounds / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: D014408:Biomarkers, Tumor; D020135:Peptide Nucleic Acids; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D019275:Radiopharmaceuticals; D017556:Technetium Compounds