Bioluminescent Molecular Imaging of Endogenous and Exogenous p53-Mediated Transcription In Vitro and In Vivo Using an HCT116 Human Colon Carcinoma Xenograft Model

Real-time p53 activity in tumor cells was detected non-invasively both in vitro and in vivo by bioluminescent imaging. HCT116 colon cancer cells were stably transduced with PG13-luc, a p53 reporter with a Firefly luciferase gene under the control of 13 p53 response elements, together with a Renilla luciferase gene under an MMLV long terminal repeat promoter. Basic conditions for both in vivo and in vitro imaging were explored. Signals from as few as three thousand cells in a 96-well plate were detected following addition of D-luciferin, a substrate of Firefly luciferase at a concentration of 100 microg/ml. Bioluminescence from fifteen thousand cells with PG13-luc inoculated subcutaneously was detected following intravenous injection of D-luciferin at a dose of 100 mg/kg. Intraperitoneal injection serves as an alternative and effective route for D-luciferin delivery, although the maximal luminescent intensity was 4-10 times lower than that from intravenous injection. Bioluminescence from Renilla luciferase constitutively expressed in tumor cells was also imaged both in vitro and in vivo and served as an internal control to monitor the physiological state of the cells or tumor volume. Infection of the cells with adenovirus carrying p53 increased the bioluminescent intensity both in vitro and in vivo. Non-invasive imaging of p53 transcriptional activity provides a practical way to monitor the p53 response in cell culture and in animal models.