This project specifically proposes:
i) to develop efficient and general procedures for labelling ODNs of specified sequence with a range of positron-emitting isotopes of differing half-lives.
ii) to demonstrate that specific hybridisation of a positron-emitting probe in vivo combined with image treatment methods will be able to provide the tissue distribution of the target mRNA.
This project aims to combine European expertise to extend PET (Positron Emission Tomography) to an entirely new area: the imaging of antisense oligodeoxynucleotide (ODN) hybridisation to mRNA in humans in vivo. The advance represented by being able to image antisense hybridisation in vivo could be immense. In principle, the PET imaging of any target mRNA could be addressed by merely changing the ODN sequence of the labelled probe and the half-life of the label to suit localisation kinetics. By the use of such positron-emitting antisense probes, genetic factors, such as point mutations, associated with the prognosis of severe or even lethal diseases could be studied in vivo. The method could also be applied to longitudinal studies of the results of grafting, gene therapy and antisense therapy. Exogenous mRNA from viral infection might be detected and its tissue distribution studied. The development of an array of general procedures for labelling antisense ODNs with positronemitters of differing half-life could also be useful to Academia and Pharmaceutical Industry as a procedure for assessing the pharmacokinetics and accumulation of novel antisense therapeutics at target sites in vivo. Diagnostic applications of labelled antisense ODNs could ultimately be envisaged.
Most of the positron-emitting isotopes suitable to the project are currently produced by each of the participating PET centres. Several strategies for labelling ODNs with positron-emitters will be explored. The London Cyclotron Unit of the MRC Clinical Science Centre, and the Groningen PET Centre, who have experience in direct labelling with fluorine-18 at a selected heterocyclic base, will develop chemical methodology to extend these procedures at the ODN level. Other procedures, like labelling at the terminal 5'-position by coupling labelled amino acids, inorganic positron-emitters or iodine- 120 will also be attempted. The CEA PET centre of Orsay, SHFJ, will realise the labelling of fluorobenzyliodoacetamide or bromobenzyliodoacetamide with fluorine- 18 or bromine-76, respectively, and their coupling to ODNs via an intermediate phosphothioate in the 3'-position. Biological models will be conceived to test the labelled ODNs produced by the chemists. The INSERM U.334 unit of Orsay will develop a cellular and a mouse model. The cellular model will be the retina, which offers the advantage of a stratified structure of different cell families and requires small amounts of labelled ODN injected into the eye. The mouse model will consist in a viral infection (Friend's Virus) concentrated in a target organ (the spleen).
Funding SchemeCSC - Cost-sharing contracts
W12 0NN London
9700 RBF Groningen
1381 CP Weesp