Abstract
As the limits of existing treatments for cancer are recognized, clearly novel therapies must be considered for successful treatment; cancer therapy using adenovirus vectors is a promising strategy. However tracking the biodistribution of adenovirus vectors in vivo is limited to invasive procedures such as biopsies, which are error prone, non-quantitative, and do not give a full representation of the pharmacokinetics involved. Current non-invasive imaging strategies using reporter gene expression have been applied to analyze adenoviral vectors. The major drawback to approaches that tag viruses with reporter genes is that these systems require initial viral infection and subsequent cellular expression of a reporter gene to allow non-invasive imaging. As an alternative to conventional vector detection techniques, we developed a specific genetic labeling system whereby an adenoviral vector incorporates a fusion between capsid protein IX and human metallothionein. Our study herein clearly demonstrates our ability to rescue viable adenoviral particles that display functional metallothionein (MT) as a component of their capsid surface. We demonstrate the feasibility of 99mTc binding in vitro to the pIX-MT fusion on the capsid of adenovirus virions using a simple transchelation reaction. SPECT imaging of a mouse after administration of a 99mTc-radiolabeled virus showed clear localization of radioactivity to the liver. This result strongly supports imaging using pIX-MT, visualizing the normal biodistribution of Ad primarily to the liver upon injection into mice. The ability we have developed to view real-time biodistribution in their physiological milieu represents a significant tool to study adenovirus biology in vivo.
Highlights
Barrier to gene therapy approaches for cancer As the limits of existing treatments for cancer are recognized, clearly novel therapies must be considered for successful treatment; cancer therapy using adenovirus (Ad) vectors is a promising strategy
Current detection methods are inadequate for Ad vector systems Several imaging studies have attempted to address this problem, including the use of positron emission tomography (PET) scanning to detect herpes simplex virus thymidine kinase (HSV-TK) as a reporter of oncolytic herpes simplex virus replication [2]
This band corresponds to the expected molecular weight of the pIX-MT, and was absent in purified Ad-CMV-enhanced GFP (EGFP) virus
Summary
Barrier to gene therapy approaches for cancer As the limits of existing treatments for cancer are recognized, clearly novel therapies must be considered for successful treatment; cancer therapy using adenovirus (Ad) vectors is a promising strategy. Other conventional imaging systems for adenovirus based gene therapy have been designed to detect transgene expression of reporters such as green fluorescent protein (GFP) [4], somatostatin receptor type 2 (SSTR-2) [5,6], sodium iodide symporter [7], luciferase [8], and HSV-TK [9]. Despite their utility for assessing gene delivery and expression, PLoS ONE | www.plosone.org pIX-Metallothionein Incorporation into Adenovirus these reporters by themselves are not suitable for monitoring physical biodistribution. The major drawback to approaches that tag viruses with reporter genes is that these systems require initial viral infection and subsequent cellular expression of a reporter gene to allow non-invasive imaging
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