Monitoring gene transfer by adenoviral vectors using in vivo imaging
Karim Benihoud, CNRS UMR 8203, Laboratoire de Vectorologie et Thérapeutiques Anticancéreuses, Univ Paris-Sud, Orsay, France.
Adenovirus-derived vectors have been extensively studied in a large panel of preclinical studies as well as in clinical trials. While these studies have underlined their potential for antitumor therapies, they also raised several concerns. Thus, adenovectors poorly disseminate into solid tumors and bind/transduce non-targeted tissues leading to toxicities.
Different strategies have been developed to overcome these limits. For example, genetic engineering of the capsid was used to modify adenovector tropism. This approach was used on one hand to provide adenovectors with new entry pathways into tumor cells, on the other hand to reduce adenovector uptake by non-targeted tissues, thus limiting liver toxicities. An increase in gene transfer into tumors was also achieved by means of coadministration of adenovectors with replicative adenovirus. Indeed, this combined administration was shown to lead to in vivo amplification of adenovectors and thus to an increased number of transduced cells.
The evaluation of the efficacy of all these approaches is done by biodistribution studies based on the measurement of transgene expression or/and viral DNA levels in different organs. For example, transgene expression is assessed either by the follow up of enzymatic activity in organ extracts or by immunohistology. Both methods provide accurate estimation of transgene expression but require the sacrifice of animals and are costly if a kinetic is to be performed. Different methods of in vivo imaging based of the measurement of fluorescence, luminescence or even positron emission can be used to monitor transgene expression. Interestingly, they allow longitudinal studies of gene delivery in the same animal thus reducing the cost of biodistribution studies.
