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Noninvasive Assessment of E2F-1–Mediated Transcriptional Regulation In vivo

¹ Laboratory for Gene Therapy and Molecular Imaging at the Max-Planck Institute for Neurological Research with Klaus-Joachim-Zülch-Laboratories of the Max Planck Society and the Faculty of Medicine of the University of Cologne, ² Center for Molecular Medicine, ³ Institute of Genetics, and ⁴ Departments of Neurology, University of Cologne, Cologne, Germany; and ⁵ Klinikum Fulda, Fulda, Germany

Requests for reprints: Andreas H. Jacobs, Laboratory for Gene Therapy and Molecular Imaging, Max Planck Institute for Neurological Research, Gleuelerstr. 50, 50931 Cologne, Germany. Phone: 49-221-4726-310; Fax: 49-221-4726-298; E-mail: Andreas.Jacobs{at}nf.mpg.de.

Key Words: glioma • molecular imaging • E2F-1 • transcriptional regulation • BCNU • bioluminescence imaging

Targeted therapies directed against individual cancer-specific molecular alterations offer the development of disease-specific and individualized treatment strategies. Activation of the transcription factor E2F-1 via alteration of the p16-cyclinD-Rb pathway is one of the key molecular events in the development of gliomas. E2F-1 binds to and activates the E2F-1 promoter in an autoregulatory manner. The human E2F-1 promoter has been shown to be selectively activated in tumor cells with a defect in the pRb pathway. Paradoxically, E2F-1 also carries tumor suppressor function. Our investigations focused on analyzing the dynamics of the activity of the E2F-1 responsive element under basal conditions and certain stimuli such as chemotherapy using molecular imaging technology. We constructed a retrovirus bearing the Cis-E2F-TA-LITG reporter system to noninvasively assess E2F-1–dependent transcriptional regulation in culture and in vivo. We show that our reporter system is sensitive to monitor various changes in cellular E2F-1 levels and its transcriptional control of our reporter system to follow the state of the Rb/E2F pathway and the DNA damage–induced up-regulation of E2F-1 activity in vivo. Exposure to 1,3-bis(2-chloroethyl)-1-nitrosourea leads to increased E2F-1 expression levels in a dose- and time-dependent manner, which can be quantified by imaging in vivo, leading to an alteration of cell cycle progression and caspase 3/7 activity. In summary, noninvasive imaging of E2F-1 as a common downstream regulator of cell cycle progression using the Cis-E2F-TA-LUC-IRES-TKGFP reporter system is highly attractive for evaluating the kinetics of cell cycle regulation and the effects of novel cell cycle targeting anticancer agents in vivo. [Cancer Res 2008;68(14):5932–40]