Year of Publication

2011

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Dr. Michael Jay

Second Advisor

Dr. Paul Bummer

Abstract

Pre-clinical and clinical trials suggest that pre-treatment with dexamethasone (Dex) may facilitate enhanced uptake of subsequently administered chemotherapeutic agents. To reduce the side effects associated with systemic administration of Dex, solid lipid nanoparticles (SLNs) containing dexamethasone palmitate (Dex-P) were prepared as a means of achieving tumor-targeted drug delivery. These studies were aimed at evaluating the physicochemical properties and both the physiological and storage stability of the SLNs.

SLNs were prepared using nanotemplate engineering technology. Stearyl alcohol (SA) was used as the lipid phase with Brij® 78 and Polysorbate 60 as surfactants and PEG6000 monostearate as a long-chain PEGylating agent. Both formulations exhibited a small particle size, ellipsoidal shape, and low polydispersity. 1H-NMR spectroscopy confirmed that SLNs have the expected solid core and PEGylated surface. Analysis of the bulk materials indicated that a number of complex interactions are present among the SLN components, including a eutectic between SA and Brij® 78.

Dex-P could be incorporated in SLNs at 10-30% w/w SA with encapsulation efficiencies >85%. A preferential interaction with the SA-Brij® 78 eutectic was identified, indicating a possible interfacial localization. For comparison, SLNs were also prepared with ascorbyl palmitate (AP) and curcumin. Higher drug loads were achieved with both palmitate-containing prodrugs than curcumin, though all appeared to align differently within the SLNs.

SLNs undergo a concentration-dependent particle size growth when incubated at physiological temperature. However, they appear to remain intact with over 85% of the added Dex-P retained at 24 h in conditions mimicking human plasma. In the presence of carboxylesterase, SLNs became turbid and showed a reduction in particle size as compared to controls. This instability was shown to be a result of the hydrolysis of PEG6000 monostearate and Polysorbate 60.

To enhance storage stability, a lyophilization protocol designed to minimize changes in the physicochemical properties of SLNs was developed. During a 3 month period, lyophilized SLNs stored at 4°C demonstrated the greatest stability, showing a consistent particle size and an encapsulation efficiency >80%. Overall, these results indicate that Dex-P loaded SLNs possess the physicochemical properties and stability desirable for development as a tumor-targeted drug delivery system.

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