Molecular magnetic resonance imaging of gene therapy-induced apoptosis and gene transfer A role for 1 H spectroscopic imaging and iron oxide labelled viral particles

Cancer is a heterogeneous collection of diseases that affect many people each year in the world. It can originate from nearly every cell type from every organ. For example, gliomas (derived from glial cells) comprise the biggest group of all primary brain tumours and aggressive gliomas related deaths are common amongst patients, despite them having a low incidence in the general population. Non-surgical cancer treatment methods, such as gene therapies, are already a part of modern cancer treatment landscape. Using these methods, apoptosis is the desired way of inducing cancer cell death because of its precision in the death of the target cell and the cleanliness of the removal of the dead cell material afterwards. In order to improve the effectiveness of these therapies, it has been acknowledged that the detection of treatment responses in the early stages of the therapy has become more important. At the tissue level, apoptosis generally appears as a subtle process, but with profound changes in morphology, structure and biochemistry brought forth by the activation of distinct proteases and lipases underlie this. These carefully orchestrated molecular changes are available for visualizing apoptosis in vivo as well. Now a days, widely used clinical visualization methods such as magnetic resonance imaging, X-ray (computed tomography), nuclear imaging and ultrasound, together with optical imaging are providing new possibilities for biophysical, biochemical and biomedical research. Gene delivery can be achieved by using several methods, amongst which viruses, such as adenoviruses and retroviruses are the most potent ones. To ensure that gene transfection is efficient enough to delivery a sufficient gene therapy dose to a patient, techniques for the noninvasive, real time in vivo detection of viral vectors will be required. In the current study, an ultra-short echo time magnetic resonance spectroscopic imaging (MRSI) sequence with water suppression was developed to measure accurately metabolites with short T2-relaxation times, such as lipids. H nuclear magnetic resonance (MR) visible lipids were found to accumulate mostly in the peripheral zones of rat BT4C herpes simplex thymidine kinasetransfected gliomas undergoing apoptosis using this technique, findings which were confirmed by post mortem invasive neutral lipid histology staining of the same tumours. The majority of apoptotic cells were also found in the same regions. A quantitative relationship between membrane lipid catabolism and H MR-visible lipid accumulation in vivo was also found; the biological analyses revealed that the expression of PLA2 together with catabolism of intracellular membrane phosphatidylethanolamine in BT4C gliomas was significantly increased during apoptosis. The biochemical analyses of the tumour cell membranes revealed that membrane fatty acyl moiety losses appear to be reflected in the storage lipid concentrations as observed by H MRSI. Additionally, magnetic resonance spectroscopy (MRS) was used to detect and follow up the cholesterol backbone containing metabolites in BT4C non-invasively during treatment in vivo. The group of molecules containing a cholesterol backbone was found to constitute a remarkable proportion of the H MRS visible lipids and thus cannot be bypassed in accurate tumour lipid analysis of MRS data. The accumulation of the cholesterol backbone containing molecules component was found to take place during the apoptotic cell death of BT4C tumours. Finally, by using unique, biotinylated ultra-small superparamagnetic iron oxide particle (USPIO) -labelled Baavi viruses, it was demonstrated that the biodistribution of these viruses in rat brain could be imaged after intraventricular injection in vivo. With these studies several technical, biochemical, biophysical issues have been resolved in the use of molecular MRI and MRS in the fields of gene transfection and tumour gene therapy. The findings are likely to lead to better diagnostic techniques and a deeper understanding of tumour metabolism in the clinical setting. National Library of Medicine Classification: WN 185, QZ 52, QZ 200, QU 470, QW 160 Medical Subject Headings: magnetic resonance spectroscopy; magnetic resonance imaging; diagnostic imaging; gene therapy; genetic vectors; transfection; viruses; neoplasms; glioma; apoptosis; lipids; cholesterol; contrast media; iron; oxides; biotinylation; baculoviridae