Ester Prodrug NLRP3 Inflammasome Inhibitor NT-0796 is Brain Active due to Activation by Local Expression of Carboxylesterase-1

NLRP3 inflammasome activation has been implicated in the pathogenesis of human disorders, including a number of neurodegenerative diseases of the central nervous system. Pharmacological inhibition of NLRP3-mediated neuroinflammation via a brain-penetrant therapeutic agent, therefore, is an attractive target for the treatment of neurodegenerative disorders. The NLRP3 inflammasome inhibitor NT-0796 is an ester-containing prodrug that is metabolized intracellularly into its active metabolite NDT-19795 by carboxylesterase-1 (CES1). NT-0796 shows high <i>in vitro</i> permeability in an induced pluripotent stem cells (iPSC)-derived human brain endothelial blood-brain barrier (BBB) model, while nonhuman primate pharmacokinetics studies demonstrate the ability of NT-0796 to cross the BBB, which is then metabolized locally to give rise to its active metabolite, NDT-19795 <i>in vivo</i>. While human and nonhuman primate cerebrospinal fluid are incapable of NT-0796 metabolism, brain parenchymal tissue homogenates obtained from either species metabolized NT-0796 to NDT-19795. Data presented in this manuscript also offer a mechanistic explanation for the central exposure levels of NDT-19795 achieved following NT-0796 administration in our Phase 1b open-label study conducted in elderly healthy volunteers and patients with Parkinson's disease, recently published in Movement Disorders. Immunolocalization of nonhuman primate frontal tissues indicates that CES1 is expressed by a subpopulation of cells, many of which were also ionized calcium-binding adapter molecule 1 (IBA1) positive. Collectively, these data show that the ester-containing prodrug, NT-0796, is highly brain penetrant and, after crossing the BBB, NT-0796 is metabolized predominantly by CES1 in brain parenchyma. Immunolocalization studies also suggest that the subset of cells in the brain expressing CES1 is microglial in origin.