Secondary ion mass spectrometry and optical imaging analysis of membranes and tissues: Part A: Biodegradable polymer membranes for controlled protein drug delivery, Part B: chemotherapeutic agents in xenograft tissue
Burns, Sarah A.
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This thesis project consisted of two separate projects which were connected by roots in biological analysis. The first was to characterize the release kinetics of a protein from a biodegradable polymer membrane which had not previously been formulated on a scale large enough for clinical medicine. This scaled up membrane was assessed using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and fluorescence spectroscopy for physical properties such as composition and release kinetics but was also analyzed using optical microscopy methods for biocompatibility. The second was to use of ToF-SIMS chemical imaging to determine the distribution of a drug called methylselenocysteine (MSC) in xenograft tumor tissue. MSC had previously been found to increase tumor vasculature which will in turn increase the distribution of CPT-11 throughout the tumor. This type of study had not previously been attempted with the ToF-SIMS chemical imaging method. Based on the work done on both of these projects, three chapters are included in this thesis document and are summarized below. A new, low mass aggregation pattern was observed using ToF-SIMS for solid Aerosol-OT (AOT) thin films cast from concentrations above the critical micelle concentration (CMC) (10 -3 - 10 -5 M in chloroform). Conventional methods typically used to calculate the aggregation number of AOT include optical methods such as visible spectroscopy, dynamic light scattering, or infrared spectroscopy which use the appearance (or disappearance) of a pattern to discern the CMC. These methods all use a secondary molecule such as water to determine when a physical change in the AOT has occurred. ToF-SIMS analysis allows for the direct analysis of an ion fragmentation pattern specific to the solution concentration of AOT to determine the CMC. Two molecularly distinct polymer membranes based on optimization of KGF activity were formulated to release biologically active KGF into solution. The protein that was used for this study is Keratinocyte Growth Factor (KGF). The membrane was formulated with an anionic surfactant called AOT, which was hypothesized to contain the protein in an aqueous environment thereby preserving the activity during the formulation and delivery process. Each of these membranes was found to release a biologically relevant concentration of KGF and was able to sustain cell growth/adherence in vitro. ToF-SIMS chemical imaging was conducted using tissue that had been treated first with methylselenocystine (MSC) followed by the anticancer drug CPT-11. ToF-SIMS analysis found that tumor and liver tissue that had been treated with MSC had characteristic ion signals that could be associated with this drug. Imaging with ToF-SIMS was confirmed with fluorescence microscopy and found that the drug segregated to the vasculature of the liver and tumor tissue.