Molecular imaging of aberrant crypt foci in the human colon targeting glutathione S-transferase P1-1

Abstract

Aberrant crypt foci (ACF), the earliest precursor lesion of colorectal cancers (CRCs), are a good surrogate marker for CRC risk stratification and chemoprevention. However, the conventional ACF detection method with dye-spraying by magnifying colonoscopy is labor- and skill-intensive. We sought to identify rat and human ACF using a fluorescent imaging technique that targets a molecule specific for ACF. We found that glutathione S-transferase (GST) P1-1 was overexpressed in ACF tissues in a screening experiment. We then synthesized the fluorogenic probe, DNAT-Me, which is fluorescently quenched but is activated by GSTP1-1. A CRC cell line incubated with DNAT-Me showed strong fluorescence in the cytosol. Fluorescence intensities correlated significantly with GST activities in cancer cell lines. When we sprayed DNAT-Me onto colorectal mucosa excised from azoxymethane-treated rats and surgically resected from CRC patients, ACF with strong fluorescent signals were clearly observed. The ACF number determined by postoperative DNAT-Me imaging was almost identical to that determined by preoperative methylene blue staining. The signal-to-noise ratio for ACF in DNAT-Me images was significantly higher than that in methylene blue staining. Thus, we sensitively visualized ACF on rat and human colorectal mucosa by using a GST-activated fluorogenic probe without dye-spraying and magnifying colonoscopy.

A Novel Theranostic Combination of Near-infrared Fluorescence Imaging and Laser Irradiation Targeting c-KIT for Gastrointestinal Stromal Tumors

“…To quantify the fluorescence intensity, regions of interest (ROIs) with a diameter of 7 mm were selected in each tumor and the background skin, and the fluorescence intensities were calculated using software provided by the manufacturer. The signal to noise (S/N) ratio was calculated as described previously 23 .…”

Molecular imaging within the lower gastrointestinal tract: From feasibility to future

“…Just recently, Muguruma and co-workers found that glutathione Stransferase (GST) P1-1 is overexpressed in ACF tissues and synthesized the fluorogenic probe DNAT-Me which is activated by GST P1-1. 39 When DNAT-Me was sprayed onto colorectal mucosa excised from AOM-treated rats and specimens from CRC patients, ACF with strong fluorescent signals were clearly observed with the advantage of a higher signal-to-noise ratio for ACF in DNAT-Me imaging compared to preoperative methylene blue staining. 39 In addition to visualization of colorectal adenomas or direct precursor lesions of CRC such as AFI, a variety of studies has Digestive Endoscopy 2018; 30: 730-738 Molecular imaging within the lower GI-tract 735 successfully provided proof of concept that molecular imaging can also visualize CRC and cancer cells.…”

“…With aberrant crypt foci (ACF) as the earliest precursor lesion of CRC, ACF might act as surrogate markers for CRC risk stratification and chemoprevention. Just recently, Muguruma and co‐workers found that glutathione S‐transferase (GST) P1‐1 is overexpressed in ACF tissues and synthesized the fluorogenic probe DNAT‐Me which is activated by GST P1‐1 . When DNAT‐Me was sprayed onto colorectal mucosa excised from AOM‐treated rats and specimens from CRC patients, ACF with strong fluorescent signals were clearly observed with the advantage of a higher signal‐to‐noise ratio for ACF in DNAT‐Me imaging compared to preoperative methylene blue staining …”

Recent Advances in Molecular Imaging of Colorectal Tumors

“…In addition, enzymes such as glutathione S-transferase-P1 (GST-P1) in the cytosol, γ-glutamyl transpeptidase (GGT) in cell membranes, and cathepsin in lysosomes are highly expressed in certain tumor cell types including colorectal tumors [9, 10]. Molecular imaging studies using a fluorogenic substrate probe, which is fluorescently quenched but activatable by enzyme activity only in the tumor cells, have been reported [11, 12].…”

“…ACF is the earliest form of colorectal tumor lesion, which shows dense staining with methylene blue and is detectable by stereomicroscopy or magnifying endoscopy [21]. Employing a fluorogenic probe (DNAT-Me) activated by GSTP1-1, we performed molecular imaging of ACF, colorectal adenoma, and CRC in an AOM-induced rat carcinogenesis model and in human colorectum ex vivo [11]. DNAT-Me is a fluorescently quenched substrate but is activated by GSTP1-1 in tumor cells to release a strong fluorophore.…”