Monitoring Gene Therapy by External Imaging of mRNA: Pilot Study on Murine ErythropoietinSegura, J PhD*‡; Fillat, C PhD†; Andreu, D PhD‡; Llop, J PhD§; Millan, O PhD§; de la Torre, B G PhD‡; Nikolovski, Z BSc*; Gomez, V BSc§; Andreu, N PhD†; Pinyot, A BSc*; Castelo, R PhD‡; Gispert, J D PhD§; Pascual, J A PhD*‡Therapeutic Drug Monitoring: October 2007 - Volume 29 - Issue 5 - pp 612-618 doi: 10.1097/FTD.0b013e31811f3af6 Original Article Abstract Author Information Gene therapy is anticipated as being an important medical development. Essential to its effectiveness is the appropriate activity (protein expression) in the expected target cells. A noninvasive diagnostic procedure of successful gene expression will be of paramount importance to validate its use or its misuse (eg, sports gene doping). Externally detectable labeled oligonucleotide hybridizing with the messenger RNA generated by the transferred gene has been proposed as a possibility to monitor successful gene therapy. The authors selected the erythropoietin gene (Epo) for a pilot study on erythropoietin protein expression in mouse muscle. Oligonucleotides of peptide nucleic acid (PNA) type capable of antisense binding to unique murine Epo-mRNA sequences were synthesized by solid phase methods, and elongated at the N-terminus with the HIV Tat (48-60) cell penetrating peptide. They were labeled with fluorescence and radioactive tags to verify penetration and longer half-life properties in Epo gene transfected C2C12 mouse muscle cells as compared with corresponding wild-type cells. Downregulation of newly expressed erythropoietin protein in such cells additionally confirmed the penetration and hybridizing properties of the selected labeled oligonucleotide. 123I-labeled Tat-PNAs were intravenously injected into mice that had previously received the Epo gene into the right tibialis muscle by DNA electrotransfer. Preferential accumulation of radioactivity in the transferred limb as compared with the contralateral limb was ascertained, especially for 123I-Tat-CTA CGT AGA CCA CT (labeled Tat-PNA 1). This study provides experimental data to support the potential use of external noninvasive image detection to monitor gene therapy. The extension of the approach to more sensitive methods for whole-body external detection such as positron emission tomography appears feasible. From the *Institut Municipal d'Investigació Mèdica IMIM-Hospital del Mar; †Centre de Regulació Genòmica; ‡Universitat Pompeu Fabra; and §Institut d'Alta Tecnologia, Barcelona, Spain. Received for publication March 9, 2007; accepted April 27, 2007. This project was carried out with the support of the World Anti-Doping Agency (WADA, project “Imagene”) and the Spanish Ministry of Education and Science (DEP2005-00188). Correspondence: IMIM-Hospital del Mar Barcelona, Biomedical Research Park, carrer Dr. Aiguader, 88 08006 Barcelona, Spain (e-mail: firstname.lastname@example.org). © 2007 Lippincott Williams & Wilkins, Inc.