title: Normalisation to blood activity is required for the accurate quantification of Na/I symporter ectopic expression by SPECT/CT in individual subjects.
abstract: The utilisation of the Na/I symporter (NIS) and associated radiotracers as a reporter system for imaging gene expression is now reaching the clinical setting in cancer gene therapy applications. However, a formal assessment of the methodology in terms of normalisation of the data still remains to be performed, particularly in the context of the assessment of activities in individual subjects in longitudinal studies. In this context, we administered to mice a recombinant, replication-incompetent adenovirus encoding rat NIS, or a human colorectal carcinoma cell line (HT29) encoding mouse NIS. We used (99m)Tc pertechnetate as a radiotracer for SPECT/CT imaging to determine the pattern of ectopic NIS expression in longitudinal kinetic studies. Some animals of the cohort were culled and NIS expression was measured by quantitative RT-PCR and immunohistochemistry. The radioactive content of some liver biopsies was also measured ex vivo. Our results show that in longitudinal studies involving datasets taken from individual mice, the presentation of non-normalised data (activity expressed as %ID/g or %ID/cc) leads to 'noisy', and sometimes incoherent, results. This variability is due to the fact that the blood pertechnetate concentration can vary up to three-fold from day to day. Normalisation of these data with blood activities corrects for these inconsistencies. We advocate that, blood pertechnetate activity should be determined and used to normalise the activity measured in the organ/region of interest that expresses NIS ectopically. Considering that NIS imaging has already reached the clinical setting in the context of cancer gene therapy, this normalisation may be essential in order to obtain accurate and predictive information in future longitudinal clinical studies in biotherapy.
authors.affiliation: INSERM U948, Biothérapies Hépatiques, CHU Hôtel Dieu, Nantes, France.
authors.forename: Peggy
authors.initials: P
authors.lastname: Richard-Fiardo
authors.forename: Philippe R
authors.initials: PR
authors.lastname: Franken
authors.forename: Audrey
authors.initials: A
authors.lastname: Lamit
authors.forename: Robert
authors.initials: R
authors.lastname: Marsault
authors.forename: Julien
authors.initials: J
authors.lastname: Guglielmi
authors.forename: Béatrice
authors.initials: B
authors.lastname: Cambien
authors.forename: Fanny
authors.initials: F
authors.lastname: Graslin
authors.forename: Sabine
authors.initials: S
authors.lastname: Lindenthal
authors.forename: Jacques
authors.initials: J
authors.lastname: Darcourt
authors.forename: Thierry
authors.initials: T
authors.lastname: Pourcher
authors.forename: Georges
authors.initials: G
authors.lastname: Vassaux
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D018014:Gene Transfer Techniques; D017930:Genes, Reporter; D019073:HT29 Cells; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008137:Longitudinal Studies; D051379:Mice; D008807:Mice, Inbred BALB C; D012313:RNA / Q000378:metabolism / Q000592:standards; D019275:Radiopharmaceuticals / Q000097:blood; D060888:Real-Time Polymerase Chain Reaction / Q000592:standards; D013670:Sodium Pertechnetate Tc 99m / Q000097:blood; D027981:Symporters / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon; D000099209:Sodium-Iodide Symporters
chemical_list: D012313:RNA; D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m; D027981:Symporters; D000099209:Sodium-Iodide Symporters