Liver enzyme delayed clearance in rat treated by CSF1 receptor specific antagonist Sotuletinib

Sotuletinib (BLZ945), a CSF1-R specific kinase inhibitor developed for the treatment of Amyotrophic Lateral Sclerosis, induced liver enzyme elevation in absence of hepatocellular lesions in preclinical rat and monkey studies. The monocytic cell family, including Kupffer cells, e.g., the liver-resident macrophages, are dependent upon CSF1 pathway activation for their survival, proliferation, and differentiation. Kupffer cells act as the main body compartment responsible for elimination of some blood-borne proteins, like ALT, AST, and few others. The depletion of Kupffer cells through CSF1 pathway inhibition has already been hypothesized as responsible for apparent liver enzyme elevation without detectable corresponding liver damage. However, a release of these biomarkers from unseen hepatic lesions or from other organs cannot be excluded. In order to eliminate a potential contribution of ALT elevation from an internal organ source, we injected recombinant his-Tagged ALT1 into rats pretreated with Sotuletinib. The elimination rate of the exogenous ALT1 was significantly lower in treated animals, demonstrating a delayed clearance independently of any potential organ lesions.