Improving Blood Brain Barrier Permeation of Small Molecules Exhibiting Chemotherapeutic and Neuroprotective Effects

Abstract

The blood brain barrier is the body's natural defense system for limiting the brain's exposure to potentially harmful xenobiotics. This barrier exists between the blood of the systemic circulation and the brain and is made up of brain endothelial cells which have tight junctions, reduced pinocytosis, minimal fenestration and increased expression of metabolizing enzymes and membrane transporters capable of efflux. Estimates predict that the blood brain barrier may be capable of limiting up to 98% of all drugs from entering the brain and is therefore a major obstacle in drug delivery. The research presented herein highlights several small molecules that possess chemotherapeutic and neuroprotective properties. These molecules also represent various strategies for improving blood brain barrier penetration. Derivatives of the microtubule stabilizing agent paclitaxel were investigated in which chemical modification was employed to reduce interaction with the efflux transporter P-glycoprotein, which is critical in limiting paclitaxel's entry into the brain. TH-237A, another microtubule stabilizing agent that is structurally very different from paclitaxel was also characterized and was shown to have excellent blood brain barrier penetration. Additionally, derivatives of the monoamine oxidase inhibitor tranylcypromine were explored that have fatty acid and lipoamino acid chains of varying length attached to improve blood brain barrier permeability. In order for these compounds to exert their mechanism of action as either chemotherapeutic or neuroprotective agents, they must be able to penetrate the blood brain barrier. The specific objective of this project was to explore various chemical approaches to improving blood brain barrier permeability using pharmacologically relevant molecules.