Microscopic detection of quenched activity-based optical imaging probes using an antibody detection system:...

The family of cathepsin proteases plays an important physiological role in both normal physiology and in the physiology of many human diseases. This activity, which is upregulated in many cancers, can be exploited for tumor imaging both in vivo and ex vivo. To characterize the behavior of a topically applied quenched fluorescent activity-based probe, GB119, ex vivo, we developed a basic immunohistochemistry technique to identify unquenched GB119 within tissue.

Immunoblot assays were used to validate the utility of an anit-Cy5 antibody for the detection of unquenched GB119 generated by cathepsin-L. Following validation of the anti-Cy5 antibody, an immunohistochemical procedure was developed to detect the presence of unquenched GB119 in frozen sections of brain tumors derived from an orthotopic mouse model.

These studies demonstrate that the anti-Cy5 antibody preferentially recognizes unquenched GB119 and that this differential can be used to identify the regions within the brain and the tumor that contained unquenched GB119. Using H&E staining and antibodies against other biochemical markers, it was further determined that unquenched GB119 was localized to the peri-tumor space and co-localized with cathepsin-L expression.

Our data indicate that this methodology allows high-resolution detection of unquenched GB119 that can be correlated with other immunohistological stains.