• Guanshu Liu, Chetan Bettegowda, Yuan Qiao, Verena Staedtke, Kannie W Y Chan, Renyuan Bai, Yuguo Li, Gregory J Riggins, Kenneth W Kinzler, Jeff W M Bulte, Michael T McMahon, Assaf A Gilad, Bert Vogelstein, Shibin Zhou, and Peter C M van Zijl.
• F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA; Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
• Magn Reson Med. 2013 Dec 1;70(6):1690-8.

PurposeTo develop a noninvasive MRI method for determining the germination and infection of tumor-homing bacteria in bacteriolytic cancer therapy using endogenous CEST contrast.MethodsThe CEST parameters of the anaerobic gram-positive bacterium Clostridium novyi-NT (C. novyi-NT) were first characterized in vitro, then used to detect C. novyi-NT germination and infection in subcutaneous CT26 colorectal tumor-bearing mice (n = 6) after injection of 300 million bacterial spores. Lipopolysacharide (LPS) injected mice were used to exclude that the changes of CEST MRI were due to inflammation.ResultsCEST contrast was observed over a broad frequency range for bacterial suspensions in vitro, with the maximum contrast around 2.6 ppm from the water resonance. No signal could be detected for bacterial spores, demonstrating the specificity for germination. In vivo, a significant elevation of CEST contrast was identified in C. novyi-NT infected tumors as compared to those before bacterial germination and infection (P < 0.05; n = 6). No significant change was observed in tumors with LPS-induced sterile inflammation (P > 0.05; n = 4).ConclusionEndogenous bacterial CEST contrast (bacCEST) can be used to monitor the germination and proliferation of the therapeutic bacterium C. novyi-NT without a need for exogenous cell labeling probes.Copyright © 2013 Wiley Periodicals, Inc.

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