Using various synthetic strategies, we designed several libraries of novel polysaccharide mixed ester derivatives for oral drug delivery applications. Cellulose and cellulose esters have been extensively studied and utilized for different applications such as separation membranes, sustainable plastics, and enteric coatings in oral drug delivery carriers. We sought to exploit the ring-opening of cyclic anhydrides, succinic and glutaric anhydride, to append ω-carboxyl groups to commercially available cellulose and cellulose ester substrates. We used scalable synthetic strategies and widely available and cheap reagents to show a proof-of-concept for the manufacturability of these different polymer derivatives. We incorporated different degrees of substitution of ω-carboxyl groups to impart a range of water solubility in these polymers. The derivatives displayed excellent <i>T</i>g values for ASD applications, adequate water solubility, and good amphiphilic properties. We designed very effective amorphous solid dispersion (ASD) oral drug delivery polymers that prevented recrystallization of felodipine for hours and had excellent congruent polymer-drug release from the formulation at 20% drug loading. During the ring-opening reactions of the cellulose derivatives with glutaric anhydride we discovered that crosslinking and gelation can occur, especially with cellulose and cellulose ester substrates with a high degree of substitution (DS) of hydroxy groups. We isolated and characterized these gelled products using rheology, and solid-state 1D and 2D NMR spectroscopy, to evaluate whether the gels are physical or chemical in nature and proposed a mechanism for gelation. We determined that the gels are mostly physical but can proceed to chemical crosslinking over time. We designed a library of cellulose ester derivatives, and we investigated their performance as amorphous solid dispersion (ASD) drug delivery vehicles for the lipophilic drug felodipine, through <i>in vitro</i> experiments. Aside from felodipine, many other active pharmaceutical ingredients (APIs) are also highly crystalline and poorly water-soluble. ASDs are used to disrupt the crystalline packing of these drugs through dispersing them in amorphous polymeric carriers, facilitating their water-solubility, and preventing their recrystallization. We showed that our polymers performed remarkably well in the <i>in vitro</i> studies and inhibited crystallization of model compound felodipine for several hours while providing optimal drug release, affording highly promising ASD polymers. If company formulators are unable to develop an effective oral-delivery carrier to prevent a drug from recrystallizing, then the drug cannot be tested in <i>in vivo</i> toxicology studies, and therefore cannot be brought to market because of its poor aqueous solubility and subsequent low bioavailability. To test the robustness of our polymers, we also performed <i>in vitro</i> ASD experiments at the pharmaceutical company AbbVie with their most rapidly crystallizing pipeline compounds, and several commercially available drugs (Compound A, axitinib, and ziprasidone). We demonstrated that our polymers could also prevent drug recrystallization with these rapid crystallizers, outperforming commercial polymers like FDA-approved hydroxypropyl methyl cellulose acetate succinate (HPMCAS (MF)), even at exceptionally high drug loading ratios of 40 times the concentration of polymer. α-1,3-Glucans are an emerging class of polysaccharides and are structurally different than cellulose due to their α (1→3) linkage versus the cellulose β (1→4) glycosidic linkage. We demonstrated that we could modify these derivatives using a variety of esterification strategies and TEMPO-mediated C6 selective oxidation, affording a myriad of different novel polymer products, some of which are structural analogs of the cellulose ester derivatives we previously created. The polymers had higher <i>T</i>g values than the cellulose ester polymers, which may be useful for applications where heat resistance is desired. In the future, we will screen some of these α-1,3-glucan derivatives with poorly water-soluble enzalutamide, posaconazole and celecoxib model drugs, to evaluate their crystallization inhibition properties and the influence of polymer morphology upon structure-property relationships. We expect that these synthetic polymer strategies will offer scalable routes to novel ASD polymers, which we demonstrated to be highly effective drug crystallization inhibitors against a variety of different hydrophobic pharmaceutical compounds. / Doctor of Philosophy / Polysaccharides are polymers comprised of many linked sugar molecules and are an incredibly abundant and renewable resource. They are found everywhere in nature such as the wood from trees, the shells of crabs, the exoskeletons of bugs, and the mushrooms that sprout in damp forests. The research in this dissertation focuses on the use and chemical modification of polysaccharides for designing new, polysaccharide-based oral drug delivery systems called amorphous solid dispersions (ASDs), which significantly aid in the solubility and bioavailability of important medications. We started with the chemical modification of cellulose, the most abundant plant polysaccharide on planet Earth, and previously modified commercial cellulose substrates (known as cellulose esters) to create novel polymers for ASDs. We successfully modified these polymers, characterized them, and evaluated their potential as oral drug delivery vehicles by formulating them with several different classes of potent drugs used to treat a variety of diseases such as hypertension and schizophrenia. We showed that our designed cellulose ester polymers kept these hydrophobic drugs water-soluble for long-enough so that they can be adequately absorbed in the human body through the gastrointestinal tract, significantly outperforming commercial polymers in many cases. During the chemical modification of the cellulose esters, we also observed that they were prone to form gels, and we investigated this gelation phenomena in more detail through rheometry, 1D and 2D solid-state nuclear magnetic resonance spectroscopy (similar in principle to the medical diagnostic method, magnetic resonance imaging or MRI). We discovered that these gels can be physically and/or chemically linked together, and that different gelation mechanisms can dominate depending on the polysaccharide substrate and the esterification reagent used. We extended our research to other polysaccharide derivatives called α-1,3-glucans, which can be sourced from fungi, and/or enzymatically synthesized in the lab. Using various synthetic esterification and oxidation chemical methods to functionalize this polysaccharide, we designed a library of entirely novel polymers with different physical structures relative to the cellulose ester polymers. The polymers displayed thermal properties that show promise in drug delivery vehicle applications and in applications where high heat resistance is required. Overall, we developed next-generation polymers for amorphous solid dispersion oral drug delivery applications. We displayed the versatility of using a select few chemistry strategies to create a variety of different polymers with very different physicochemical properties. We hope that this work will help researchers design sustainable, plant-based polymers for ASD applications and we hope to nurture future structure-function studies to improve ASD performance for the benefit of patients in need.

The use of amorphous solid dispersions (ASDs) is an effective and increasingly widely adopted approach for solubility and bioavailability enhancement of hydrophobic drugs. Cellulose derivatives have strong potential as ASD polymers. We demonstrate herein design, synthesis and structure-property relationship characterization of a new series of organo-soluble cellulose omega-carboxyalkanoates for ASDs, by two different synthetic approaches. These carboxyl-containing cellulose mixed-esters possessed relatively high Tg values with sufficient differences versus ambient temperature, useful to prevent drug mobility and crystallization during storage or transport. Screening experiments were utilized to study the impact of ASD polymers including our new family of cellulose Ω-carboxyesters on both nucleation induction time and crystal growth rate of three poorly soluble model drugs from supersaturated solutions. Attributed to relatively rigid structures and bulky substituent groups, cellulose derivatives were more significant crystallization inhibitors compared to the synthetic polymers. The effective cellulose omega-carboxyesters were identified as possessing a similar hydrophobicity to the drug molecule and high number of ionization groups. Among them, cellulose acetate suberate prepared by us was an extraordinary solution crystal growth inhibitor for ritonavir and its formulated solid dispersions provided a substantial 15-fold enhancement of apparent solution concentration vs. the equilibrium solubility of the crystalline drug. To offset the issue of slow drug release from some cellulose omega-carboxyester based formulations, a new class of amphiphilic cellulosic polymers with hydrophilic oligo(ethylene oxide)-containing side chains was developed via versatile synthetic pathways, and the evaluation of these materials alone or by pairwise polymer blends will be performed as ASD matrices for the enhancement of drug solubility and stability. / Ph. D.

In an effort to produce new derivatives of cellulose for drug delivery applications, methods were developed to regioselectively modify C-6 halo cellulose esters to produce cationic derivatives via nucleophilic substitution. Reaction of C-6 substituted bromo and iodo cellulose with trialkylated amines and phosphines produced new cationic ammonium and phosphonium cellulose derivatives which can be explored as delivery agents for nucleic acids, proteins and other anionic drug molecules. It was anticipated that these new derivatives would not only be capable of complexing anionic drug molecules but would have greatly improved aqueous solubility compared to their precursors. The phosphonium derivatives described in this work are an obvious example of such improved solubility properties. Given the importance of cellulose derivatives in making amorphous dispersions with critical drugs, it has also been important to analyze commercially available polymers for the potential impact in oral drug delivery formulations. To do so pairwise blends of cellulosics and synthetic polymers commonly used as excipients were tested for miscibility using techniques such as DSC, mDSC, FTIR and film clarity. Miscible combinations highlight the potential to use combinations of polymers currently available commercially to provide drug delivery solutions for specific drug formulations. The use of melt extrusion in processing some of these drug/polymer dispersions provides a means of highlighting the capability for the use of these cellulosics in melt extruded amorphous dispersions. This solvent free, high pressure method significantly reduces cost and time and can be applied on a large scale. The analysis of long chain cellulose esters and ultimately the novel omega carboxy esters for melt processability significantly impacts the possibilities available for use of those excellent drug delivery agents on a much larger scale. / Ph. D.

Chemical modification of naturally occurring cellulose into ester and ether derivatives has been of growing interest due to inexhaustible cellulose resources, and to excellent properties and extremely broad applications of these derivatives. However, traditional esterification and etherification involve relatively harsh conditions (strongly acidic or strongly alkaline), greatly limiting the content and range of functional groups that may be installed onto the cellulose backbone. Amorphous solid dispersion (ASD) is an effective method to promote oral delivery of poorly-soluble drugs by dispersing crystalline drugs in a polymer matrix, creating drug supersaturation upon release. Cellulose 𝜔-carboxyesters have been proven to be effective ASD matrices for many different drugs; however, synthesis of such polymers involves protecting-deprotecting chemistry and one synthetic route only leads to one structure. Developing a new generation of cellulosic polymers for oral drug delivery such as ASD matrices requires new synthetic techniques and powerful tools. Olefin cross-metathesis (CM) is a mild, efficient and modular chemistry with extensive applications in organic, polymer, and polysaccharide chemistry. Successful CM can be achieved by appending olefin “handles” from cellulose esters and reacting with electron-deficient olefins like acrylic acid. Cellulose ethers have much better hydrolytic stability compared to esters and are also commercially very important. The overarching theme of this dissertation is to investigate modification of cellulose ether derivatives, and to design and synthesize effective ASD polymers by olefin CM. We first validated the strategy of performing CM by appending metathesis “handles” through etherification and then subjected these terminal olefins to various partners (acrylic acid and different acrylates). After demonstration of the concept, we applied different starting materials (e.g. ethyl cellulose, methyl cellulose, microcrystalline cellulose, and hydroxypropyl cellulose) with distinctive hydrophobicity/hydrophilicity balance. Furthermore, α,β-unsaturated CM products tended to undergo radical crosslinking through abstraction of 𝛾-protons and recombination of polymer radicals. In order to resolve this issue, we first applied post-CM hydrogenation and then explored a thiol-Michael addition to the α,β-unsaturation, which also incorporates an extra functional group through the thioether. We have successfully prepared a collection of cellulose 𝜔-carboxyether derivatives through the above-mentioned method and preliminary drug induction experiments also revealed that these derivatives hold high promise for ASD application. We also explored the possibility of conducting CM in a reverse order: i.e. appending electron-deficient acrylate groups to the polymer, then subjecting it to electron-rich small molecule terminal olefins. The failure of this metathesis approach was speculated to be due mainly to low acrylate reactivity on an already crowded polymer backbone and the high reactivity of rapidly diffusing, small molecule terminal olefins. Last but not least, we further utilized olefin CM to conjugate bile salt derivatives (e.g. lithocholic acid and deoxycholic acid) to a cellulose backbone by converting bile salts into acrylate substrates. Successful CM of bile salt acrylates to cellulose olefin “handles” further demonstrated the great versatility, excellent tolerance, and very broad applicability of this strategy. Overall, we have founded the strategy for performing successful olefin CM in many cellulose ether derivatives with acrylic acid and a variety of different acrylates. Post-CM hydrogenation efficiently removes the α,β-unsaturation and provides stable and effective cellulose 𝜔-carboxyether derivatives for ASD application. Tandem CM/thiol-Michael addition not only eliminates the crosslinking tendency but also enables an even broader library of polymer structures and architectures for structure-property investigations. We anticipate these methods can be readily adapted by polysaccharide chemists and applied with numerous complex structures, which would greatly broaden the range of cellulose and other polysaccharide derivatives for applications including ASDs, P-glycoprotein inhibition, antimicrobial, coating, and other biomedical applications. / Ph. D.

<p>The subject of this thesis was to study two intestinal barriers to oral drug bioavailability, drug efflux proteins of the ABC-transporter family, and in particular ABCB1/P-glycoprotein (Pgp), and the drug metabolizing enzyme cytochrome P450 (CYP) 3A4. At the onset of this thesis, similarities between CYP3A4 and Pgp in terms of their tissue distribution and gene regulation, along with overlapping substrate specificities, had generated the hypothesis that CYP3A4 and Pgp may have a complementary function and thus form a coordinated intestinal barrier to drug absorption and gut wall metabolism.</p><p>In the first part of this thesis, a cell culture model of the intestinal epithelium that expressed both functional Pgp and CYP3A4 was developed. This model was then used to investigate the steroselective drug efflux and metabolism of R/S-verapamil. In summary, the results indicated that the two barriers in the cell culture model were in agreement with those in the human intestine.</p><p>Both ABC-transporters and CYPs are regulated by drugs that interact with nuclear receptors. However, while the regulation of CYPs is quite well understood, less is known about how repeated drug administration regulates the most abundantly expressed ABC-transporters. Therefore, in the second part of this thesis, the effects of repeated drug administration on the gene regulation of four ABC-transporters and CYP3A4 were studied in intestinal epithelial cell lines in vitro and in the perfused human jejunum in vivo. The in vitro studies revealed that the ABC-transporters are induced by drugs that interact with slightly different sets of nuclear receptors. The in vivo study showed that repeated oral administration of St John’s wort decreased the bioavailability of verapamil, predominantly by induction of intestinal CYP3A4. This part of the thesis provides new information about the regulation of ABC-transporters, shows that the intestinal metabolism is the most significant barrier to oral bioavailability of verapamil and provides evidence for a clinically significant interaction between verapamil and St John’s wort in vivo.</p>

The subject of this thesis was to study two intestinal barriers to oral drug bioavailability, drug efflux proteins of the ABC-transporter family, and in particular ABCB1/P-glycoprotein (Pgp), and the drug metabolizing enzyme cytochrome P450 (CYP) 3A4. At the onset of this thesis, similarities between CYP3A4 and Pgp in terms of their tissue distribution and gene regulation, along with overlapping substrate specificities, had generated the hypothesis that CYP3A4 and Pgp may have a complementary function and thus form a coordinated intestinal barrier to drug absorption and gut wall metabolism. In the first part of this thesis, a cell culture model of the intestinal epithelium that expressed both functional Pgp and CYP3A4 was developed. This model was then used to investigate the steroselective drug efflux and metabolism of R/S-verapamil. In summary, the results indicated that the two barriers in the cell culture model were in agreement with those in the human intestine. Both ABC-transporters and CYPs are regulated by drugs that interact with nuclear receptors. However, while the regulation of CYPs is quite well understood, less is known about how repeated drug administration regulates the most abundantly expressed ABC-transporters. Therefore, in the second part of this thesis, the effects of repeated drug administration on the gene regulation of four ABC-transporters and CYP3A4 were studied in intestinal epithelial cell lines in vitro and in the perfused human jejunum in vivo. The in vitro studies revealed that the ABC-transporters are induced by drugs that interact with slightly different sets of nuclear receptors. The in vivo study showed that repeated oral administration of St John’s wort decreased the bioavailability of verapamil, predominantly by induction of intestinal CYP3A4. This part of the thesis provides new information about the regulation of ABC-transporters, shows that the intestinal metabolism is the most significant barrier to oral bioavailability of verapamil and provides evidence for a clinically significant interaction between verapamil and St John’s wort in vivo.

Oral mucositis is a painful and debilitating chronic inflammatory condition that can result from chemo and/or radiotherapy. While current treatment strategies which provide temporary relief exist, there is still an unmet clinical need for a robust long active barrier strategy which can simultaneously provide protection and release drug to enhance the wound healing response. It is proposed that an affinity based layer-by-layer self-assembled barrier administered as a series of mouth rinses can allow for wound specific drug delivery, providing an effective regenerative therapy. In this work, biotinylated poly(acrylic acid) is used to develop LBL assemblies based upon biotin-streptavidin affinity interactions. To explore the ability of developed LBL assemblies to resist the harsh intraoral environment, in vitro chemical and ex vivo mechanical tests are performed. The stability results demonstrate significant LBL barrier stability with wear resistance. From principal component regression analysis, factors such as polymer MW and number of layers in assemblies contributed significantly to chemical barrier stability. Also it is observed that the extent of biotin conjugation plays a significant role in LBL development and in mechanical stability. Thus, the proposed affinity based multilayered assemblies with their excellent barrier properties offer a modular treatment approach in oral mucosal injuries.

One of the pathological hallmarks of Alzheimer's disease (AD) is the amyloid plaque deposition in aging brains by aggregation of amyloid-β (Aβ) peptides. In this study, the effect of chloroplast derived myelin basic protein (MBP) fused with cholera toxin subunit B (CTB) was investigated in advanced diseased stage of human and mouse AD brains. The CTB-fusion protein in chloroplasts facilitates transmucosal delivery in the gut by the natural binding ability of CTB pentameric form with GM1 receptors on the intestinal epithelium. Further, bioencapsulation of the MBP within plant cells confers protection from enzymes and acids in the digestive system. Here, 12-14 months old triple transgenic AD mice were fed with CTB-MBP bioencapsulated in the plant cells for 3 months. A reduction of 67.3% and 33.3% amyloid levels in hippocampal and cortical regions, respectively were observed by immunostaining of brain sections with anti- Aβ antibody. Similarly, 70% decrease in plaque number and 40% reduction of plaque intensity was observed through thioflavin S (ThS) staining that specifically stains amyloid in the AD brain. Furthermore, ex vivo 3xTg AD mice brain sections showed up to 45% reduction of ThS stained amyloid levels when incubated with enriched CTB-MBP in a concentration dependent manner. Similarly, incubation of enriched CTB-MBP with ex vivo postmortem human brain tissue sections with advanced stage of AD resulted up to 47% decrease of ThS stained amyloid plaque intensity. Lastly, lyophilization of plant material facilitates dehydration and long term storage of capsules at room temperature, in addition to increasing CTB-MBP concentration by 17 fold. These observations offer a low cost solution for treatment of even advanced stages of the AD by facilitating delivery of therapeutic proteins to central nervous system to address other neurodegenerative disease.

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