Catheter-based in vivo imaging of enzyme activity and gene expression: feasibility study in mice.
OBJECTIVE
To construct and evaluate an interventional catheter-based imaging system for intravital monitoring of molecularly sensitive near-infrared fluorescent probes and optical marker genes.


METHODS
An imaging device that was based on a miniaturized fiberoptic sensor (MIFS) was built in which images created with a 2.7-F fiberoptic catheter were relayed through a dichroic mirror, through a bandpass filter, and on two independent cameras. This system permitted simultaneous recording of white-light and fluorescent images. Spatial resolution, spectral transmissions, and sensitivity were determined in vitro. In vivo testing was performed in nude mice bearing intraperitoneal tumors that express green fluorescent protein and in a mouse model of ovarian carcinoma with enzyme-activatable near-infrared probes sensitive to tumoral protease activity. Signal intensity on images of tumors and that on images of normal tissue were measured and compared with t test.


RESULTS
The catheter, which was advanced through an 18-gauge sheath, showed resolution of 7 line pairs per millimeter and detection limit for fluorochrome Cy5.5 of 1-10 pmol. Detection of endogenous green fluorescent protein gene expression was feasible in tumor nodules smaller than 1 mm in diameter (mean tumor signal intensity, 153.26 +/- 26.45 [SD], compared with that of adjacent nontumoral tissue of 36.73 +/- 11.69; P <.008). Similarly, activation of the near-infrared probe by tumoral proteases could be detected in peritoneal tumor seeds of ovarian cancer model with mean tumor signal intensity of 246.33 +/- 7.77 compared with that of adjacent nontumoral tissue of 41.56 +/- 18.64 (P <.001). Mean contrast-to-noise ratio in the near-infrared channel exceeded white-light contrast-to-noise ratio by a factor of 6.7 (P <.02).


CONCLUSIONS
With this system, in vivo MIFS imaging of gene expression, enzyme activity, and potentially other molecular events is feasible, through direct interventional access to several organs and body cavities and potentially through transvascular approaches.
Funovics
Martin A
MA
Center for Molecular Imaging Research, Massachusetts General Hospital, Harvard Medical School, 13th Street, Bldg 149, Rm 5408, Boston, MA 02129, USA.
Weissleder
Ralph
R
Mahmood
Umar
U
D000818:Animals; D002401:Cathepsin B / Q000378:metabolism; D002404:Catheterization; D004789:Enzyme Activation; D005240:Feasibility Studies; D005260:Female; D005336:Fiber Optic Technology; D005456:Fluorescent Dyes; D015870:Gene Expression; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008904:Miniaturization; D009368:Neoplasm Transplantation; D010051:Ovarian Neoplasms / Q000201:enzymology* / Q000235:genetics; D010534:Peritoneal Neoplasms / Q000235:genetics*; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared; D014162:Transfection
D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D008156:Luciferases; D002401:Cathepsin B