Molecular imaging: A new way to study molecular processes in vivo

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Abstract

Non-invasive imaging of reporter gene expression using different imaging modalities is increasing its role for the in vivo assessment of molecular processes. Multimodality imaging protocols overcome limitations to a single imaging modality and provide a thorough view of specific processes, often allowing a quantitative measurement and direct visualization of the process in a specific target organ or tissue. The use of the right reporter gene for the development of animal models and the characterization of its expression in different conditions and tissues is fundamental for basic, translational and future pharmacological applications of a given model. This paper summarizes the major steps in the development and evaluation of a specific animal model for in vivo molecular imaging studies and describes the first example of an animal model designed for the in vivo assessment of a specific receptor activity and its possible evolution towards multimodality imaging analysis.

Introduction

The term “molecular imaging” refers to the convergence of approaches from various disciplines (cell and molecular biology, chemistry, medicine, pharmacology, physics, bioinformatics, and engineering) to exploit and integrate imaging techniques in the evaluation of specific molecular processes at the cellular and sub-cellular levels in living organisms.

In the assessment of physical, physiological or metabolic processes, classical imaging technologies can differentiate, under clinical circumstances, pathological from normal conditions but are rather non-specific. Molecular imaging techniques, instead, have led to the development of novel procedures with enhanced specificity. As a result, imaging nowadays focuses on an in-depth understanding of biological processes, early detection and characterization of diseases, and treatment evaluation based on molecular processes assessment (Massoud and Gambhir, 2003).

The advent of genetic engineering has brought about major changes to applied science, including, for example, the drug discovery pipeline. In the same way, the development and exploitation of animal imaging procedures is providing new means for pre-clinical studies (Maggi and Ciana, 2005).

By combining animal engineering with molecular imaging techniques, it has become possible to conduct dynamic studies on specific molecular processes in living animals. This approach could potentially impact on pre-clinical protocols, thus widely changing all aspects of medicine (Maggi et al., 2004a).

Section snippets

Molecular imaging applications

The main goal of molecular imaging techniques is to directly assess in living organisms specific processes at the cellular level, including gene expression, protein-protein interaction, dynamic cell tracking throughout the entire organism, and drug action analysis. Molecular imaging techniques may therefore contribute tremendously to our understanding of the physiology of living organisms and provide new means for drug target identification and pre-clinical testing to improve drug discovery.

Imaging modalities

Imaging transgene expression in living animals is principally based on the external detection of bioluminescence (optical imaging) or γ-photon (radionuclide-based imaging) emitted by a reporter located within the body. The reporter can be an enzyme that catalyses a reaction that produces light or that modifies a labeled substrate trapped within the cells, which in turn permits the localization of cells expressing the reporter gene (Massoud and Gambhir, 2003). Otherwise, a reporter can be an

Imaging living animals

The choice of the reporter gene is the most important step in the generation of a new animal reporter model. But candidate reporter genes must satisfy several prerequisites before they can be used for molecular imaging studies. First, they must be detectable by in vivo studies, in other words, their expression must provide information about the location, the magnitude and the persistence of gene expression directly in vivo. Second, their expression must reflect the expression of the gene

Development of new models and new strategies

Multimodality imaging strategies could help to improve approaches to visualizing molecular processes in vivo. The ERE-Luc mouse is a paradigmatic model for molecular imaging in pharmacological studies, but it is restricted by limitations intrinsic to optical imaging: bi-dimensional images, tissue scattering and absorption of photons, it is not fully quantitative and is exploitable only in small animal models.

To overcome the shortcomings each imaging modality has, a multimodality approach should

Conclusions

The studies outlined in this review demonstrate that the ERE-Luc mouse is a paradigm of animal model for the in vivo study of a molecular process (ER activity) by imaging techniques. The ability to visualize the state of ER activity in a living animal endows the model with novel, unique features because changes in ER activity can be now evaluated in the same animal at different times, thus allowing a detailed analysis of the dynamic action of physiological and exogenous compounds.

Compared with

Acknowledgements

The laboratory work was funded by the European NoE CASCADE, EMIL and DIMI, The Italian Ministry of Research and Education PRIN 2004, RBNE01PASK_003 and RBNE0157EH_007, and private foundations: AIRC and CARIPLO.

References (52)

  • J.F. Thompson

    Modulation of firefly luciferase stability and impact on studies of gene regulation

    Gene

    (1991)
  • M.H. Wyckoff

    Plasma membrane estrogen receptors are coupled to endothelial nitric-oxide synthase through Galpha(i)

    J. Biol. Chem.

    (2001)
  • L. Bjornstrom et al.

    Signal transducers and activators of transcription as downstream targets of non-genomic estrogen receptor actions

    Mol. Endocrinol.

    (2002)
  • G. Bunone

    Activation of the unliganded estrogen receptor by EGF involves the MAP kinase pathway and direct phosphorylation

    EMBO J.

    (1996)
  • Burgess-Beusse

    The insulation of genes from external enhancers and silencing chromatin

    Proc. Natl. Acad. Sci. U.S.A.

    (2002)
  • A. Chatziioannou

    Detector development for microPET II: a 1 microl resolution PET scanner for small animal imaging

    Phys. Med. Biol.

    (2001)
  • P. Ciana

    Engineering of a mouse for the in vivo profiling of estrogen receptor activity

    Mol. Endocrinol.

    (2001)
  • P. Ciana

    In vivo imaging of transcriptionally active estrogen receptors

    Nat. Med.

    (2003)
  • P. Ciana

    The ERE-luc Reporter Mouse. Ernst Schering Res

    Found. Workshop

    (2004)
  • C.H. Contag

    Visualizing gene expression in living mammals using a bioluminescent reporter

    Photochem. Photobiol.

    (1997)
  • C.H. Contag et al.

    Advances in in vivo bioluminescence imaging of gene expression

    Annu. Rev. Biomed. Eng.

    (2002)
  • D. Delbeke et al.

    Metabolic imaging with FDG: a primer

    Cancer J.

    (2004)
  • D. Di Lorenzo

    Isomer-specific activity of dichlorodyphenyltrichloroethane with estrogen receptor in adult and suckling estrogen reporter mice

    Endocrinology

    (2002)
  • S.S. Gambhir

    A mutant herpes simplex virus type I thymidine kinase reporter gene shows improved sensitivity for imaging reporter gene expression with positron emission tomography

    Proc. Natl. Acad. Sci. U.S.A.

    (2000)
  • J.A. Gossen

    Efficient rescue of integrated shuttle vectors from transgenic mice: a model for studying mutations in vivo

    Proc. Natl. Acad. Sci. U.S.A.

    (1989)
  • S. Kato

    Activation of the estrogen reporter through phosphorylation by mitogen-activated protein kinase

    Science

    (1995)
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      Psoralen and isopsoralen as ERα agonists promoted MCF-7 cell proliferation significantly but could be completely suppressed by the estrogen antagonist ICI 182, 780. However, the luciferase expression was blocked by ER antagonists, demonstrating the specificity of the rodent in reporting ERs activity but not estrogen-related receptors (ERRs) activity at the level of ER transcriptional activity (Ottobrini et al., 2006). In other studies, wedelolactone, luteolin, and apigenin derived from Wedelia chinensis acted synergistically to suppress both the growth of androgen receptor (AR)-dependent prostate cancer 22Rv1cell lines and prostate-specific antigen luciferase of the 22Rv1-derived 103E cell lines in vitro and prostate cancer 22Rv1 xenografts in vivo (Lin et al., 2007; Tsai et al., 2009).

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