Noninvasive molecular imaging of c-Myc activation in living mice

• Published in: Proceedings of the National Academy of Sciences - PNAS 2010-09, Vol.107 (36), p.15892-15897
• Main Authors: Fan-Minogue, Hua, Cao, Zhongwei, Paulmurugan, Ramasamy, Chan, Carmel T., Massoud, Tarik F., Felsher, Dean W., Gambhir, Sanjiv S., Phelps, Michael E.
• Format: Article
• Language: English
• Subjects: Animals; Antibodies; Biological Sciences; Cancer; Cell growth; Cell lines; Complementation; Gene expression; Heterologous transplantation; Imaging; Mice; Molecular structure; Phosphorylation; Proteins; Proto-Oncogene Proteins c-myc - physiology; Rodents; Scientific imaging; Sensors; Signal transduction; Truncation; Tumors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1007443107

The cytoplasmic Myc protein (c-Myc) regulates various human genes and is dysregulated in many human cancers. Phosphorylation mediates the protein activation of c-Myc and is essential for the function of this transcription factor in normal cell behavior and tumor growth. To date, however, the targeting of Myc as a therapeutic approach for cancer treatment has been achieved primarily at the nonprotein level. We have developed a molecular imaging sensor for noninvasive imaging of c-Myc activity in living subjects using a split Firefly luciferase (FL) complementation strategy to detect and quantify the phosphorylation-mediated interaction between glycogen synthase kinase 3β (GSK3β) and c-Myc. This sensor system consists of two fusion proteins, GSK 35—433-CFL and NFL-c-Myc, in which specific fragments of GSK3β and c-Myc are fused with C-terminal and N-terminal fragments of the split FL, respectively. The sensor detects phosphorylation-specific GSK3β–c-Myc interaction, the imaging signal of which correlates with the steady-state and temporal regulation of c-Myc phosphorylation in cell culture. The sensor also detects inhibition of c-Myc activity via differential pathways, allowing noninvasive monitoring of c-Myc-targeted drug efficacy in intact cells and living mice. Notably, this drug inhibition is detected before changes in tumor size are apparent in mouse xenograft and liver tumor models. This reporter system not only provides an innovative way to investigate the role of functional c-Myc in normal and cancer-related biological processes, but also facilitates c-Myc–targeted drug development by providing a rapid quantitative approach to assessing cancer response to therapy in living subjects.