A pharmacokinetic approach to intra-brain distribution with a focus on cyclic peptides

Abstract: When designing treatments for disorders of the central nervous system (CNS) reaching the site of action is a major hurdle in the development process. Regardless if the target is extra- or intracellular, precise measurements to understand the distribution within the CNS are required. There is however a lack of understanding of differences in blood-brain barrier transport and intra-brain distribution of both small and large molecules. In this thesis the regional Blood-Brain Barrier transport of antipsychotic agents, along with their brain tissue binding and regional cellular accumulation was quantified. Furthermore, a novel LC-MS/MS method was developed for the quantitative analysis of the cyclic peptide kalata B1 was developed for analysis of brain tissue and plasma samples. The Blood-Brain Barrier transport, permeability, intra-brain distribution and cellular accumulation were assessed for two cyclic peptides, SFTI-1 and kalata B1. The antipsychotics exhibited clear differences in their regional BBB transport as well as their brain tissue binding, with the most dramatic spatial differences in BBB transport being observed for the p-glycoprotein substrates risperidone and paliperidone. The highest level of transporter mediated protection was observed in the cerebellum, with pronounced efflux for several of the antipsychotics. The development of a quantitative method for the cyclic peptide kalata B1 was successfully validated and applied to measure low concentration of the peptide in biological matrices. The BBB transport of SFTI-1 was markedly higher than that of kalata B1 whereas both peptides exhibited similar permeability across an in vitro BBB model. It was also shown that SFTI-1 resides mainly within the interstitial fluid within the brain, but that kalata B1 readily enters the cells of the brain parenchyma. The cellular accumulation of kalata B1 was abolished under cold conditions, and was not observable in lung tissue, suggesting an active process that is tissue specific. It was also shown that both peptides are taken up into cell cultures of neurons and astrocytes.In conclusion this thesis and the studies herein contribute to a better understanding of distribution patterns of both antipsychotics and cyclic peptides and provides valuable lessons in terms of what types of studies should be prioritized for the development of such molecules into therapeutic agents.