Imaging of differential protease expression in breast cancers for detection of aggressive tumor phenotypes.
OBJECTIVE
To determine if different expression levels of tumor cathepsin-B activity in well differentiated and undifferentiated breast cancers could be revealed in vivo with optical imaging.


METHODS
A well differentiated human breast cancer (BT20, n = 8) and a highly invasive metastatic human breast cancer (DU4475, n = 8) were implanted orthotopically in athymic nude mice. Tumor-bearing animals were examined in vivo with near-infrared fluorescence (NIRF) imaging 24 hours after intravenous injection of an enzyme-sensing imaging probe. Immunohistochemistry, Western blotting (on cells and whole tumor samples), and correlative fluorescence microscopy were performed.


RESULTS
Both types of breast cancers activated the NIRF probe so that tumors became readily detectable. However, in tumors of equal size, there was a 1.5-fold higher fluorescence signal in the highly invasive breast cancer (861 arbitrary units +/- 88) compared with the well differentiated lesion (566 arbitrary units +/- 36, P <.01). Western blotting confirmed a higher cathepsin-B protein content in the highly invasive breast cancer (DU4475) of about 1.4-fold (whole tumor samples) to 1.7-fold (cells). Immunohistochemistry and fluorescence microscopy findings confirmed the imaging findings.


CONCLUSIONS
Cathepsin-B enzyme activity can be determined in vivo with NIRF optical imaging, while differences in tumoral expression may correlate with tumor aggressiveness.
Bremer
Christoph
C
Center for Molecular Imaging Research, Massachusetts General Hospital and Harvard Medical School, Boston, USA. bremerc@uni-muenster.de
Tung
Ching-Hsuan
CH
Bogdanov
Alex
A
Weissleder
Ralph
R
D000230:Adenocarcinoma / Q000737:chemistry* / Q000473:pathology / Q000556:secondary; D000818:Animals; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000737:chemistry / Q000473:pathology; D002401:Cathepsin B / Q000032:analysis*; D005260:Female; D005456:Fluorescent Dyes; D006801:Humans; D007150:Immunohistochemistry; D008325:Mammary Neoplasms, Experimental / Q000737:chemistry* / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D019265:Spectroscopy, Near-Infrared; D014407:Tumor Cells, Cultured
D005456:Fluorescent Dyes; D002401:Cathepsin B