Bioluminescence imaging of live HCT-8 colon carcinoma cells treated with shRNAi against MDR1. HCT-8 control cells (left) and shRNAi transduced cells (right), each transiently transfected with Renilla luciferase, were imaged with coelenterazine, the fluorogenic substrate for Renilla luciferase. Coelenterazine is outwardly transported by MDR1 P-glycoprotein, thereby enabling P-glycoprotein transport activity to be monitored in intact cells with noninvasive bioluminescence imaging. The bioluminescence signal was increased 7.5-fold upon knockdown of MDR1. For further details, please see Pichler et al. on page 4487 in this issue.

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