Assessing gene expression in vivo: magnetic resonance imaging and spectroscopy

Recent developments in magnetic resonance imaging and spectroscopy afford t he possibility of detecting and assessing transfer, expression and subseque nt therapeutic changes of effector or marker transgenes noninvasively. In t he field of MR imaging, 'smart' MR contrast agents are being developed, so called because they change their conformational structure and in so doing i nduce MR detectable changes in a given tissue. These agents become 'switche d on' in response to physiological changes brought about by the enzymatic a ction of a given gene product (enzymes), and are being developed for use in intact cells, isolated organs and animal models. Ultimately these agents h old the promise of bridging the gap between the laboratory and the patient with noninvasive detection of transgene expression in vivo in man. Similarl y, magnetic resonance spectroscopy is being developed as a noninvasive meth od to assess transgene expression indirectly by means of MR visible intrace llular markers. These markers take the form of intracellular endo/exogenous metabolites associated with exogenous enzyme expression and function. Agai n, this technique will be applicable to a variety of different situations, from cell suspensions through to clinical imaging of the whole body. In thi s article the unique opportunities for laboratory-based and clinical studie s afforded by MR techniques are discussed.