Assessing gene expression in vivo: magnetic resonance imaging and spectroscopy

Recent developments in magnetic resonance imaging and spectroscopy afford the possibility of detecting and assessing transfer, expression and subsequent therapeutic changes of effector or marker transgenes noninvasively. In the field of MR imaging, 'smart' MR contrast agents are being developed, so called because they change their conformational structure and in so doing induce MR detectable changes in a given tissue. These agents become 'switched on' in response to physiological changes brought about by the enzymatic action of a given gene product (enzymes), and are being developed for use in intact cells, isolated organs and animal models. Ultimately, these agents hold the promise of bridging the gap between the laboratory and the patient with noninvasive detection of transgene expression in vivo in man. Similarly, magnetic resonance spectroscopy is being developed as a noninvasive method to assess transgene expression indirectly by means of MR visible intracellular markers. These markers take the form of intracellular endo/exogenous metabolites associated with exogenous enzyme expression and function. Again, this technique will be applicable to a variety of different situations, from cell suspensions through to clinical imaging of the whole body. In this article the unique opportunities for laboratory-based and clinical studies afforded by MR techniques are discussed.