Noninvasive imaging of infection after treatment with tumor-homing bacteria using Chemical Exchange Saturation Transfer (CEST) MRI.

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PubMed URL:
van Zijl PC
Author List: 
Liu G
Bettegowda C
Qiao Y
Staedtke V
Chan KW
Bai R
Li Y
Riggins GJ
Kinzler KW
Bulte JW
McMahon MT
Gilad AA
Vogelstein B
Zhou S
van Zijl PC
Magn Reson Med
PubMed ID: 
To develop a noninvasive MRI method for determining the germination and infection of tumor-homing bacteria in bacteriolytic cancer therapy using endogenous CEST contrast.The 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.CEST 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).Endogenous 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.
Published Date: 
December, 2013

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