Abstracts

Rationale: Cathepsins are elevated in macrophage-like cells in many inflammatory conditions and might play a role in the pathophysiology of epilepsy and other CNS diseases. The goal of this study was to investigate in epileptic mice the biodistribution of the novel fluorescent cathepsin activity-based probe GB123 which has been utilized in diagnostics of peripheral diseases. 

Methods: GB123 biodistribution was evaluated in mice with pilocarpine-induced seizures and in naïve mice (n=4/group) in the presence or absence of the macrophage-targeted cathepsin inhibitor GB111-NH₂. Compounds were injected intravenously and fluorescence was measured in vivo and ex vivo. Interactions of GB123 with P-glycoprotein (P-gp) and the breast cancer-resistance protein (BCRP) were assessed in Madin-Darby Canine Kidney (MDCK)II overexpressing the respective transporters and control MDCKII cells and by the use of an ATPase assay.

Results: The in vivo biodistribution of GB123 was similar in mice with spontaneous seizures and naïve controls. The highest distribution was observed in the liver, whereas the brain signal was low. Efflux ratios were identical between P-gp- or BCRP-MDCK and control cells. ATPase activity was not induced in the presence of GB123 or GB111-NH₂.

Conclusions: The global brain distribution of GB123 in mice (naïve and those with induced seizures) appears to be low. The low CNS distribution cannot be explained by P-gp- or BCRP-mediated efflux. Ongoing studies will characterize GB123 distribution into distinct cell types within the CNS.

Funding: The study was supported by The Israel Ministry of Industry and Trade (Kamin; 60564 and 60565).