Browsing by Subject "Drug Delivery"

Now showing 1 - 5 of 5
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    Degradable Polymersomes for Targeted Drug Delivery
    (2013-08) Petersen, Matthew
    Chemotherapy today is often accompanied by major side effects due to delivery of toxic drugs to healthy tissue in addition to diseased cells. Targeted drug delivery offers the possibility of minimizing these side effects by specific delivery to cancer cells using targeted nanocarriers that enhance drug accumulation in tumors and facilitate target-specific cellular uptake. Polymersomes, vesicles self-assembled from polymeric amphiphiles, are an attractive targeted vehicle, as they are capable of encapsulating both hydrophobic and hydrophilic drugs, have lengthy circulation times in vivo, and can employ degradable functionality for triggered release of payload and clearance from the body. This thesis reports on efforts to enhance the capabilities of degradable polymersomes for targeted delivery. First, targeting functionality is incorporated into polymersomes of the block copolymer poly(ethylene oxide)-b-poly(γ-methyl-ε-caprolactone) by incorporating the reactive vinyl sulfone group into the amphiphile's hydrophilic terminus, allowing site-selective reaction with cysteine-functionalized targeting peptides following self-assembly. The performance of targeted delivery using this polymersome is then evaluated in vitro. Binding and delivery to model cell lines for targeted and bystander cells is tracked using nontargeted polymersomes and compared to that for polymersomes using a high- or low-affinity ligand. Polymer degradation is also tracked both in simple media and during cellular delivery. Finally, a new monomer is developed incorporating acid-labile acetal functionality into a cyclic polyester. The polymerization of this monomer to two distinct polymers is also characterized and the degradation behavior of both polymers evaluated.
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    Engineering Antimicrobial Probiotics for the Treatment of Vancomycin-Resistant Enterococcus
    (2016-12) Geldart, Kathryn
    The rise of antibiotic resistance in bacteria has become an urgent concern in global healthcare. There is now a strong drive for the preservation of our current antibiotics as well as for the rapid development of new antibacterial therapies. Antimicrobial peptides (AMPs) are a vast collection of proteins naturally produced by living organisms as a defense mechanism against invading microbes. Unfortunately, though society has been aware of the therapeutic potential of AMPs for many years, their utility has been limited to topical applications because of toxicity and degradation in the body. Moreover, many bacterial infections originate in the gastrointestinal (GI) tract, which is largely unreachable for most AMPs by oral administration. To overcome this delivery challenge, we are engineering probiotic bacteria that can actively produce and deliver AMPs inside the GI tract. Vancomycin-resistant enterococci (VRE) are among the most difficult to treat pathogens in hospital environments. These bacteria frequently reside in the GI tract, often in low counts because of competition from the surrounding microbiota. When patients are given broad-spectrum antibiotics, the competition is reduced and VRE dominate in numbers. The pathogen can then spread to other host organs or to the surrounding hospital environment. Delivery of AMPs targeting VRE by probiotics may provide an alternative treatment or prevention option against these deadly pathogens. Importantly, the elimination of VRE from the GI tract using VRE-specific AMPs may allow removal of VRE while minimizing disruption of the surrounding bacteria. In this thesis, we describe the development of two different probiotic delivery systems for the reduction of the two major causative species of VRE infections, Enterococcus faecium and Enterococcus faecalis. The first probiotic platform employs the Gram-positive species, Lactococcus lactis, for the production of three class IIa bacteriocins, AMPs endogenously produced by bacteria. We have developed a chloride-inducible expression vector for AMP delivery from L. lactis, which we show to be activated by physiologically-relevant chloride concentrations. Herein, we demonstrate the ability of this system to inhibit VRE, first in in vitro cultures. VRE intestinal colonization models in mice were then developed and used to test the efficacy of our engineered L. lactis in the GI tract. Multiple trials showed statistically significant reduction of Enterococcus faecium in L. lactis treated mice compared to untreated mice. The second probiotic delivery system uses probiotic Escherichia coli Nissle 1917 (EcN). Currently, no anti-enterococcal peptides are known to be naturally produced from E. coli. In this project, we developed a modular AMP expression system that can be used in E. coli to express and secrete a variety of AMPs derived from a wide range of producer strains. With this system, we are able to produce AMPs targeting not only Gram-positive pathogens like VRE, but also Gram-negative pathogens including Salmonella and diarrheagenic E. coli. We show this system can be used to simultaneously express multiple anti-enterococcal peptides in vitro. Lastly, we demonstrate the efficacy of Nissle producing Enterocin B, Enterocin A, and Hiracin JM79 in reducing VRE colonization in mice. The final section of this thesis addresses the concern of bacterial resistance development to our antimicrobial probiotics. Class IIa bacteriocins are currently the most thoroughly-studied class of AMPs targeting enterococci. Though the mechanism of resistance to these peptides has been studied in E. faecalis, it has never been examined in E. faecium. In this project, we identified a mannose phosphotransferase in E. faecium that appears to be directly involved in E. faecium susceptibility to class IIa bacteriocins. We show that resistant mutants exhibit either downregulation or direct mutation of this transporter and that heterologous expression of this transporter in L. lactis confers susceptibility to the otherwise unsusceptible strain. We then include a brief discussion of the implications of this mode of resistance and potential methods for preventing resistance development in the future.
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    Intrapericardial delivery of anti-arrhythmic agents.
    (2009-05) Richardson, Eric Stephen
    Anti-arrhythmic agents are known for their narrow therapeutic window and common side effects. Delivery of anti-arrhythmic agents into the pericardium has shown to increase their efficacy and minimize their side effects. My work has focused on evaluating the clinical potential of intrapericardial (IP) anti-arrhythmic delivery. This has included working with physicians to identify appropriate clinical applications, developing devices to aid in pericardial drug delivery, and carrying out several large animal studies to test efficacy. In swine models of sinus tachycardia, atrial fibrillation, and ischemia-induced ventricular tachycardias, we have shown the pharmacodynamic benefits of IP-delivered metoprolol, amiodarone, and docosahexaenoic acid. Pharmacokinetic data show that minimal amounts of drug reach the systemic circulation. We propose that IP delivery of anti-arrhythmic agents has potential to maximize therapeutic benefits while minimizing side effects, particularly in the settings of post-operative atrial fibrillation and inappropriate sinus tachycardia.
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    Polymer Reservoirs to Solubilize Hydrophobic Drugs
    (2018-08) Li, Ziang
    Research and development of new drug delivery formulations for hydrophobic drugs hold great promise for patients worldwide in the ever-growing pharmaceutical industry. A large portion of the drugs, both in the current market and the development pipeline, suffer from low aqueous solubility, therefore limiting their efficacy for oral administration. One effective way to resolve this problem is the use of an amorphous solid dispersion (ASD), a blend of drug and polymer. An ideal polymer candidate can kinetically stabilize the dispersed drug in its amorphous form in the solid state, while enhancing drug solubility and dissolution in the solution state. Despite recent advances in polymer development for oral drug delivery, the structure-property relationships and the underlying solubility enhancement mechanisms are not fully understood for ASDs. The goals of this dissertation are to develop effective polymers for oral drug delivery, and more importantly, to elucidate the mechanism(s) of drug solubility and dissolution enhancement by using well-defined polymer platforms. Specifically, three model systems were designed and synthesized, including blends of a commercially available polymer and self-assembled micelles in Chapter 3, micelle-forming statistical copolymers and diblock polymers in Chapter 4, and chemically crosslinked polymer nanogels in Chapter 5. It was observed universally in all these three systems that hydrophobic drugs can be sequestered in the slightly hydrophobic polymer reservoirs, and that the drug-polymer partitioning is stronger when the polymer chains are more crowded. The partitioning inhibits drug nucleation and crystal growth in aqueous solution, resulting in enhanced drug solubility. This mechanism is supported by a battery of state-of-the-art characterization experiments, including light scattering, nuclear Overhauser effect and diffusion ordered spectroscopy, cryogenic transmission electron microscopy, small-angle X-ray scattering, and in vitro dissolution tests. Potential applications of the discovered mechanism and the characterization experiments to other drug/polymer systems are discussed as future directions.
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    Role of ß-Glucuronidase in the Chemopreventive Efficacy of Oral Curcumin: A Prodrug Hypothesis
    (2015-11) Liu, Garvey
    Curcumin, a dietary polyphenol, has been shown to have several preventive and therapeutic benefits in epidemiological studies. The chemopreventive potential of curcumin is related to its anti-inflammatory activity and is largely mediated through inhibition of the transcription factor NF-kB. However, curcumin has rather poor oral bioavailability (<1%). Much of orally dosed curcumin undergoes glucuronidation, resulting in the formation of inactive glucuronides. Thus, it is not clear how dietary curcumin exhibits chemopreventive activity despite not being absorbed into the systemic circulation in its active form. We proposed a prodrug hypothesis to explain this ‘bioavailability paradox’ of curcumin. β-glucuronidase is an enzyme that hydrolyzes the glycosidic bond of glucuronides. Previous studies have shown that the expression of this enzyme is elevated under inflammatory conditions and overexpressed in necrotic regions of tumors. Increased β-glucuronidase activity in the tumor tissue in comparison to its relatively minimal activity in normal cells potentially explains the bioavailability paradox with curcumin. We hypothesized that curcumin glucuronide is an inflammation-responsive natural prodrug that gets converted back to curcumin ‘on-demand’ at the site of action. Our studies were aimed at determining specific activity of β-glucuronidase based on mammary tumor type, stage, and model. β-glucuronidase activity was determined in mammary tumor tissues with HER-2+ (BALB-neuT, TuBo) and triple negative (4T1, JC, MDA-MB-231) phenotypes. Activity assay results showed that the highest rate of conversion was in 4T1 tumors as compared to the other tumor types. Immunohistochemistry (IHC) studies on primary human breast tumor tissue samples showed β-glucuronidase expression levels to be highest in HER-2+ type breast cancer compared to triple negative and ER/PR+ types. Also determined from the microarray of human tissue samples, as well as from Western blotting and fluorescence imaging studies, was the strong correlation between enzyme expression levels and stage of cancer: normal and benign stages showed the lowest levels of β-glucuronidase while the invasive/metastatic stage showed the highest expression levels. Using a self-microemulsifying drug delivery system (SMEDDS) formulation that was developed to improve the oral absorption, we aimed next to investigate the chemopreventive efficacy of curcumin following oral administration. Daily oral dosing of curcumin for one month in the orthotopic models described above showed that those with higher β-glucuronidase specific activities (JC, MDA-MB-231, and 4T1) benefitted the most from curcumin in limiting tumor growth rate. Pharmacokinetic studies with oral dosing of curcumin SMEDDS showed elevated levels of the glucuronide metabolite in plasma as compared to negligible levels of curcumin while the trend was reversed in the tumor tissue, providing further support to the prodrug activation hypothesis. The pharmacokinetics of curcumin glucuronide following intravenous dosing also confirmed conversion of the glucuronide to the parent compound in the tumor tissue. Overall, the work presented in this thesis demonstrated the potential of oral curcumin for breast cancer chemoprevention based on the enzymatic prodrug activation hypothesis.