In Vitro and In Vivo Testing of Ultra-Small Gold Nanoparticles as a Novel Drug Delivery Platform for Enhancing the Brain Penetration and Receptor Binding Affiinity of Central Nervous System Drugs.

The endothelial cells of brain capillaries form the so-called blood brain barrier (BBB) which protects the central nervous system (CNS) from the entry of neurotoxins and blood components. Consequently, more than 98% of potential CNS drugs fail to cross the BBB. Therefore in this thesis, we describe the development and testing of ultra-small gold nanoparticles (AuNPs) that can traffic drugs across the BBB into brain parenchyma, with the potential of also increasing the receptor-binding affinity of CNS drugs. In chapter one, we provide an introduction to the global impact of CNS diseases and discuss the anatomy and function of the BBB. Various strategies for CNS drug delivery are presented. Finally, we describe unique features of AuNPs that make them attractive as drug carriers for CNS delivery. Chapter two describes a novel CNS drug-delivery strategy involving the conjugation of 6-mercaptopurine riboside to AuNPs (6-MPR-AuNPs). The 6-MPR-AuNPs drastically decreased the clearance of 6-MPR from 6190 to 22.45 mL/min/kg. Correspondingly, the half-life of 6-MPR increased from 13.8 to 44.16 minutes and the AUC increased about 100-fold. Studies using rat liver homogenate revealed that AuNPs directly inhibited liver xanthine oxidase to stabilize 6-MPR. Chapter three examines the brain penetration of 6-MPR-AuNPs using whole-body imaging and CNS distribution experiments. Compared to control, the fluorescence intensity of FITC-labeled AuNPs was highest in the brain and cerebrospinal fluid. The AUC of CNS and plasma were respectively 5.3 and 142-fold higher with 6MPR-AuNPs. TEM provided direct evidence that 6-MPR-AuNPs penetrated the BBB and was distributed into cerebral parenchyma. In chapter four, we use dopamine-conjugated AuNPs (DA-AuNPs) to overcome the poor brain permeability of dopamine. Binding studies using human dopamine-receptor cells revealed that the binding affinity of DA-AuNPs was 10-fold higher than dopamine. Rat ex vivo studies produced receptor occupancy of 100 and 80%, for DA-AuNPs and DA respectively. The RO of smaller DA-AuNPs (5, 15, 50 nm) were respectively 90, 60, and 20%, whereas larger particles(100, 200nm)had RO of 5%. Finally, in chapter five, key the findings of this thesis are summarized and perspectives on future research are presented.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99801/1/pnkansah_1.pd