Development of disease microenvironment-targeting bilirubin-based nanomedicine

Abstract

For diagnosis and therapy of certain diseases, conventional approaches only utilize passive delivery strategy to target damaged tissues. However, it has been proven that the disease specific targeting strategies can improve diagnostic and therapeutic efficacy, so number of trials are reported. Base on this approach, I utilize bilirubin-based nanoparticles for effective disease targeting and treatment. The endogenous molecule, bilirubin, is made from catabolism of heme and has potential to apply for various clinical purposes. At first, it is strong anti-oxidative and anti-inflammatory signaling molecule which could regulate immune responses. In addition, bilirubin can coordinate with metal ion or nanoparticle surface, so bilirubin can be a carrier or surface stabilizer. This molecule is also reactive to several chemicals like reactive oxygen species or glutathione, and its ridge-tile like structure can stabilize nanoparticle formulation with its self-assembling feature. Therefore, bilirubin-based nanoparticles are potent platform to effectively target the diseased environment. In chapter 1, the detail characteristics of bilirubin, which are utilized for therapeutic and diagnostic approach, are explained. Additionally, previous bilirubin-based therapy, diagnosis or targeting strategies are introduced. In chapter 2, glutathione (GSH) responsive CT imaging probe is suggested. Glutathione (GSH) is produced at high levels in normal liver, but its production is considerably reduced under certain pathological conditions. Accordingly, an imaging probe capable of visualizing altered GSH level in the liver would be a useful tool for monitoring hepatic function or disease. This chapter reports a gold nanoparticle (AuNP)-based computed tomography (CT) contrast agent that undergoes a change in colloidal stability in response to GSH levels, resulting in differential CT signal intensity between normal (higher intensity) and pathological (lower intensity) livers, enabling imaging of hepatic function. This GSH-responsive CT contrast agent, prepared by coating AuNPs with PEGylated bilirubin (PEG-BR), shows serum stability as well as high sensitivity to GSH. The resulting PEG-BR@AuNPs preferentially accumulate in normal liver, as evidenced by strongly enhanced CT intensity, but fail to do so in a GSH-depleted mouse model, where the CT signal in the liver was substantially decreased. In addition, injection of PEG-BR@AuNPs caused a greater reduction in CT signals in liver in a drug-induced acute liver failure model than in healthy normal mice. These findings suggest that GSH-responsive PEG-BR@AuNPs have the potential to be used as a CT contrast agent to detect various hepatic function-related diseases and liver-metastasized tumors. In chapter 3, glycocalyx mimic targeting strategy for treatment of inflammatory bowel disease is suggested. Gut is major organ where large portion of immune cells and various commensal bacteria or exogenous molecules are located. Therefore, the potential impact of inflammatory bowel disease can easily extend beyond gut-localized inflammation by affecting systemic immune homeostasis that governs our overall health. However, the common treatments of inflammatory bowel disease, including anti-inflammatory small molecule, or biologics against inflammatory signals, can disturb immune system and induce unexpected diseases. During colitis pathogenesis, lectin expression by immune cells or glycocalyx components are dramatically changed. So, we constructed bacterial glycocalyx-mimicking nanoparticles library for identifying effective sugar ligand to target specific molecular changes of colitis lesion. The library contains 31 types of glycopolymers which contains the combination of five different sugar ligands (β-glucose, β-galactose, α-mannose, β-N-acetyl glucosamine, and β-N-acetyl galactosamine). The glycopolymers are finally conjugated with bilirubin, an endogenous anti-inflammatory molecule, to form the nanoparticles, denoted as GlyNPs$_{(BR)}$. Through a series of in-vivo therapeutic screening, we deduced GlyNPCD$_{(BR)}$ displaying Man/GlcNAc as the prime nanomedicine candidate for targeted IBD therapy. Finally, we traced the GlyNPs and identify target cell, macrophage, whose pro-inflammatory activity was inhibited by GlyNP$_{(BR)}$. It was demonstrated that the cellular targeting mediated by combinatorial sugar moieties effectively support the therapeutic performance of GlyNPs$_{(BR)}$.