Exploitation Of P-Glycoprotein At The Blood Brain Barrier For Targeted Drug Delivery

Other Titles
Abstract

Drug development for the central nervous system (CNS) has struggled to reach clinical approval. One reason many drugs do not advance into clinical applications is their low uptake in the CNS due to the blood brain barrier (BBB). Targeted drug delivery to the CNS has been well-studied for over 30 years, and recently has been focused on methods of BBB disruption (e.g., focused ultrasound), circumvention (e.g., convection enhanced delivery) or exploitation (e.g., receptor mediated targeting). Receptor mediated targeting is a method of active transport across the BBB by exploiting endogenous receptorligand interactions. The work outlined in this dissertation has studied a novel drug delivery method for receptor mediated targeting through the exploitation of P-glycoprotein (P-gp). P-gp is naturally overexpressed at the BBB and therefore makes an attractive target for CNS drug delivery. It was hypothesized that this new approach to CNS delivery could be accomplished by creating a polymeric nanoparticle delivery system with a P-gp substrate as a targeting moiety. The work focused on the development of a polylactide (PLA) nanoparticle containing a surfacetethered polyethylene glycol (PEG) linker terminated with rhodamine as a P-gp targeting moiety. Rhodamine dyes are a well-known class of P-gp substrates and the two used in this study, rhodamine 6G (Rho6G) and rhodamine 123 (Rho123) show high and moderate affinity to P-gp, respectively. Due to the novelty of this system, the PEG-Rho linker was first assessed in vitro to determine if it was still capable of interacting with P-gp as a substrate. It was evident that the conjugates of PEG-Rho still remained P-gp substrates; therefore, the PLA-PEG nanoparticle was developed to assess targeting of the drug delivery system in vivo. Before targeting efficiency could be measured in vivo a nanoparticle detection method was needed. The autofluorescence of various tissues poses a problem when considering nanoparticle detection by fluorescence in vivo. Therefore, the time resolved fluorescent properties of europium chelates were utilized to overcome autofluorescence challenges. Europium chelates continue to emit photons microseconds after excitation, whereas the autofluorescent molecules in tissues emit photons for only nanoseconds. By measuring photon emittance at microsecond timescales following excitation, the autofluorescent background was eliminated allowing sensitive detection of the nanoparticles in vivo. Once the Rho-PEG-PLA nanoparticle was synthesized and a detection method to track and quantify the particles in vivo was developed, the targeting efficiency of the systems was assessed. In a mouse model, Rho6G-PEG-PLA nanoparticles accumulated 2.6 times greater in the brain than untargeted control mPEG-PLA nanoparticles. Using a P-gp knockout mouse, the accumulation of Rho6G-PEG-PLA nanoparticles was shown to significantly decrease in the brain compared to the wild type mouse. Thus the conclusion was made that Rho6G-PEG-PLA nanoparticles can actively target P-gp at the BBB and can enhance the accumulation of drug delivery nanoparticles in the CNS.

Journal / Series
Volume & Issue
Description
Sponsorship
Date Issued
2015-08-17
Publisher
Keywords
P-glycoprotein; Targeted Drug Delivery; Blood Brain Barrier
Location
Effective Date
Expiration Date
Sector
Employer
Union
Union Local
NAICS
Number of Workers
Committee Chair
Putnam,David A.
Committee Co-Chair
Committee Member
Fischbach,Claudia
King,Michael R.
Degree Discipline
Chemical Engineering
Degree Name
Ph. D., Chemical Engineering
Degree Level
Doctor of Philosophy
Related Version
Related DOI
Related To
Related Part
Based on Related Item
Has Other Format(s)
Part of Related Item
Related To
Related Publication(s)
Link(s) to Related Publication(s)
References
Link(s) to Reference(s)
Previously Published As
Government Document
ISBN
ISMN
ISSN
Other Identifiers
Rights
Rights URI
Types
dissertation or thesis
Accessibility Feature
Accessibility Hazard
Accessibility Summary
Link(s) to Catalog Record