Development of membrane type‐1 matrix metalloproteinase‐specific activatable fluorescent probe for malignant tumor detection

Membrane type‐1 matrix metalloproteinase (MT1‐MMP) is a protease that activates pro‐MMP‐2 and pro‐MMP13, which are related to tumor malignancy. Therefore, probes that specifically image MT1‐MMP would be useful for malignant tumor diagnosis. In the present study, we prepared rhodamine X‐conjugated anti‐MT1‐MMP antibody (anti‐MT1‐MMP mAb‐ROX) as an activatable fluorescent probe and evaluated its usefulness for MT1‐MMP‐specific imaging. Anti‐MT1‐MMP mAb‐ROX was obtained in a quenched form with approximately three ROX molecules per mAb. Its fluorescence intensity increased approximately 14‐fold in the presence of detergent, which is suitable for activatable systems. C6 glioma cells and MCF‐7 human breast adenocarcinoma cells were used as MT1‐MMP‐positive and MT1‐MMP‐negative models, respectively. The fluorescence intensity of C6 cells treated with anti‐MT1‐MMP mAb‐ROX, but not ROX‐conjugated isotype control antibody (NC Ab‐ROX), increased with time and was significantly higher than that of MCF‐7 cells at 6 h ( P  < 0.001). The fluorescence intensity of cells treated with anti‐MT1‐MMP mAb‐ROX was also suppressed by pre‐treatment with a MT1‐MMP endocytosis inhibitor ( P  < 0.05). Furthermore, the probes were intravenously administered to C6 and MCF‐7 xenografted mice. The tumor‐to‐muscle (T/M) ratio of the anti‐MT1‐MMP mAb‐ROX group was 15.1 ± 3.2 at 48 h and was significantly higher than that of the NC Ab‐ROX group (T/M ratio = 4.6 ± 3.0, P  < 0.05) in C6 xenografted mice, while the T/M ratio of the anti‐MT1‐MMP mAb‐ROX and NC Ab‐ROX groups was not different in MCF‐7 xenografted mice. These findings suggest that anti‐MT1‐MMP mAb‐ROX is a promising probe for specifically detecting MT1‐MMP‐expressing tumors. ( Cancer Sci 2011; 102: 1897–1903)