Frida Bällgren: Translational Aspects of Brain-Specific Drug Delivery by Targeting Active Uptake at Brain Barriers

Abstract

Challenges in central nervous system (CNS) drug development often arise from difficulties in achieving safe and effective brain drug delivery. Key to addressing this issue is ensuring sufficient drug concentrations at the CNS target site. This requires efficient drug transport across brain barriers and reliable translation of preclinical findings to clinical settings. The proton-coupled organic cation (H+/OC) antiporter, associated with blood-brain barrier (BBB) uptake of several marketed CNS drugs, has emerged as a promising target in this regard. However, several critical questions are unresolved for fully leveraging this system in drug development. The studies in this thesis investigated key translational pharmacokinetic questions of the CNS delivery of antiporter substrates. This included characterization of the uptake across several CNS barriers, potential sex and species differences, the impact of inflammation, in vitro-in vivo correlations, and regional CNS distribution. Oxycodone served as the primary model substrate across in vitro and in vivo studies, including microdialysis, the Combinatory Mapping Approach for Regions of Interest, and in vitro BBB cell models. Active uptake was confirmed at the BBB and revealed at the blood-cerebrospinal fluid barrier (BCSFB) and blood-spinal cord barrier in rats. Novel evidence of active uptake at the pig BBB and BCSFB was presented, suggesting potential translatability to humans. Cerebrospinal fluid, often used as a proxy for brain concentrations in the clinic, underestimated antiporter substrate exposure, necessitating caution in its use as a surrogate for brain interstitial fluid. Importantly, no sex-related differences were observed in BBB uptake, supporting the antiporter as a viable target in CNS drug development. Lipopolysaccharide-induced inflammation significantly reduced the uptake. Although the active uptake was reduced, net uptake was still present during inflammation. In vitro BBB models of various origins (mouse, rat, pig, human) reflected in vivo findings, supporting the utility of these models for verification of active uptake. A consistent net uptake, with minor regional differences, was observed in the CNS delivery of antiporter substrates. These findings contribute to advancing CNS drug development by highlighting the significance of active uptake transporters and the necessity for comprehensive neuropharmacokinetic evaluations both in vitro and in vivo.