Title

DNA-Capped Gold Nanoparticles as Intercalative Anticancer Drug Delivery Vehicles

Date of Award

8-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

James C. Dabrowiak

Keywords

anticancer, drug delivery, gold nanoparticles

Subject Categories

Chemistry

Abstract

Gold nanoparticles (AuNP) are excellent platforms for the delivery of chemotherapy drugs. They are biocompatible, their surface can be easily modified with ligands, and they are readily taken up by cells. In this work, DNA-functionalized gold nanoparticles (AuNP) were developed as delivery vehicles for the clinically used anticancer drugs doxorubicin (DOX) and actinomycin D (ActD). Each vehicle contains a tailorable number of DNA duplexes (typically ~60), each possessing three high-affinity sequences for intercalation. Drug binding was evaluated by measuring changes to DNA melting temperature (Tm), particle hydrodynamic diameter (Dh), and AuNP surface plasmon resonance wavelength (ëspr) as a function of drug loading. These studies demonstrated that DOX intercalates at its high-affinity sequence bound at the AuNP, and that ActD exhibits relatively weaker binding to its preferred sequence. The binding constant (K) and drug dissociation rate constant (â) were shown to be enhanced in DOX-vehicle binding compared to DOX-calf thymus binding, but no such effect was noted in the ActD system. Cytotoxicity toward neuroblastoma cells was similar for each vehicle compared to the corresponding free drug, DOX or ActD.

A second generation of vehicles was developed to overcome potential limitations of the initial design. First, the vehicle was functionalized with folic acid (FA) to enable cancer cell targeting and to enhance cytotoxicity. FA-modified vehicles were synthesized and extensively characterized. A second modification to the vehicle involved functionalization with a temperature-responsive pNIPAAm-co-pAAm polymer (p) to improve the kinetic and equilibrium properties of drug release. By sterically impeding the release of drug from surface bound DNA at physiological temperature, the K doubled for the p-modified vehicle. The vehicle was also functionalized with polyethylene glycol (PEG) to enable evasion of the mononuclear phagocyte system (MPS). Confocal microscopy studies showed moderate DOX uptake for the first generation vehicle, with little DOX located in the nucleus. In contrast, DOX uptake was significantly enhanced for vehicles modified with FA, p, and both. Neuroblastoma cell culture studies showed ~5-fold enhanced cytotoxicity for the p-modified vehicle relative to DOX, presumably due to an increase in K. Cytotoxicity was enhanced ~1.2-fold for vehicles with low to moderate FA loading, demonstrating that there may be an optimal FA loading to achieve targeting. PEG functionalization did not affect cell growth. Finally, the cytotoxicity of vehicles co-functionalized with both FA and p was enhanced ~10-fold, making it the most cytotoxic vehicle investigated.

In another class of studies, the gravitational sedimentation of citrate- and ascorbate-capped spherical AuNP was investigated by measuring the absorption-vs.-time trend produced as the particles slowly sediment. For comparison, theoretical sedimentation curves were generated using the Mason-Weaver sedimentation-diffusion equation. This was done by solving the equation for various particle diameters and weighting the solution with the TEM histogram and the size-dependent extinction coefficients. For particles having average AuNP core diameters of 12.1 ± 0.6, 65.0 ± 5.2, and 82.5 ± 5.2 nm, very good agreement existed between the theoretical and observed sedimentation curves. Size histograms were also generated based on the measured sedimentation data.

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