Molecular Imaging and Biology

, Volume 20, Issue 2, pp 240–248 | Cite as

Detection of Enzyme Activity and Inhibition during Studies in Solution, In Vitro and In Vivo with CatalyCEST MRI

  • Sanhita Sinharay
  • Edward A. Randtke
  • Christine M. Howison
  • Natalia A. Ignatenko
  • Mark D. Pagel
Research Article



The detection of enzyme activities and evaluation of enzyme inhibitors have been challenging with magnetic resonance imaging (MRI). To address this need, we have developed a diamagnetic, nonmetallic contrast agent and a protocol known as catalyCEST MRI that uses chemical exchange saturation transfer (CEST) to detect enzyme activity as well as enzyme inhibition.


We synthesized a diamagnetic MRI contrast agent that has enzyme responsive and enzyme unresponsive CEST signals. We tested the ability of this agent to detect the activity of kallikrein 6 (KLK6) in biochemical solutions, in vitro and in vivo, with and without a KLK6 inhibitor.


The agent detected KLK6 activity in solution and also detected KLK6 inhibition by antithrombin III. KLK6 activity was detected during in vitro studies with HCT116 colon cancer cells, relative to the detection of almost no activity in a KLK6-knockdown HCT116 cell line and HCT116 cells treated with antithrombin III inhibitor. Finally, strong enzyme activity was detected within an in vivo HCT116 tumor model, while lower enzyme activity was detected in a KLK6 knockdown tumor model and in the HCT116 tumor model treated with antithrombin III inhibitor. In all cases, comparisons of the enzyme responsive and enzyme unresponsive CEST signals were critical for the detection of enzyme activity.


This study has established that catalyCEST MRI with an exogenous diaCEST agent can evaluate enzyme activity and inhibition in solution, in vitro and in vivo.

Key words

CEST MRI Enzyme activity Enzyme inhibition Colon cancer Molecular imaging 



The authors thank Ms. Jasmine Acfalle for laboratory assistance. These studies were supported by NIH grants R01CA169774, R01CA157595, and P30CA23074.

Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no conflict of interest.

Supplementary material

11307_2017_1092_MOESM1_ESM.pdf (589 kb)
ESM 1 (PDF 588 kb)


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Copyright information

© World Molecular Imaging Society 2017

Authors and Affiliations

  • Sanhita Sinharay
    • 1
  • Edward A. Randtke
    • 2
  • Christine M. Howison
    • 2
  • Natalia A. Ignatenko
    • 3
    • 4
  • Mark D. Pagel
    • 1
    • 2
    • 4
    • 5
  1. 1.Department of Chemistry and BiochemistryUniversity of ArizonaTucsonUSA
  2. 2.Department of Medical ImagingUniversity of ArizonaTucsonUSA
  3. 3.Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonUSA
  4. 4.University of Arizona Cancer CenterUniversity of ArizonaTucsonUSA
  5. 5.Department of Cancer Systems ImagingMD Anderson Cancer CenterHoustonUSA

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