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Most medicines are taken orally. To enter the systemic circulation, they dissolve in the intestinal fluid, cross the epithelial barrier, and pass through the liver. Intestinal absorption is driven by the unique features of the gastrointestinal tract, including the bile colloids formed in the lumen and the mucus layer covering the intestinal epithelium. Neglecting this multifaceted environment can lead to poor drug development decisions, especially for poorly water-soluble drugs that interact with bile and mucus. However, there is a lack of a rationale nexus of molecular interactions between oral medicines and gastrointestinal components with drug bioavailability. Against this background, this thesis aims to develop biopharmaceutical strategies to optimize the presentation of oral therapeutics to the intestinal epithelial barrier.
In Chapter 1, the dynamics of bile colloids upon solubilization of the poorly-water soluble drug Perphenazine was studied. Perphenazine impacted molecular arrangement, structure, binding thermodynamics, and induced a morphological transition from vesicles to worm-like micelles. Despite these dynamics, the bile colloids ensured stable relative amounts of free drug substance. The chapter was published in Langmuir.
Chapter 2 examined the impact of pharmaceutical polymeric excipients on bile-mediated drug solubilization. Perphenazine and Imatinib were introduced as model compounds interacting with bile, whereas Metoprolol did not. Some polymers altered the arrangement and geometry of bile colloids, thereby affecting the molecularly soluble amount of those drugs interacting with bile. These insights into the bile-drug-excipient interplay provide a blueprint to optimizing formulations leveraging bile solubilization. The chapter was published in Journal of Controlled Release.
Chapter 3 deals with the impact of bile on porcine intestinal mucus. Mucus exposed to bile solution changed transiently, it stiffened, and the overall diffusion rate increased. The bile-induced changes eased the transport of the bile-interacting drug substance Fluphenazine, whereas Metoprolol was unaffected. This dichotomous pattern was linked to bioavailability in rats and generalized based on two previously published data sets. The outcomes point to a bile-mucus interaction relevant to drug delivery. The chapter is submitted.
The Appendix provides a guide for biopharmaceutical characterization of drug substances by nuclear magnetic resonance spectroscopy aiming at establishing a predictive algorithm.
In summary, this thesis deciphers bile-driven mechanisms shaping intestinal drug absorption. Based on these molecular insights, pharmaceuticals can be developed along a biopharmaceutical optimization, ultimately leading to better oral drugs of tomorrow.
Recent progress in nanotechnology has attracted interest to a biomedical application of the carbon nanoparticle C60 fullerene (C60) due to its unique structure and versatile biological activity. In the current study the dual functionality of C60 as a photosensitizer and a drug nanocarrier was exploited to improve the efficiency of chemotherapeutic drugs towards human leukemic cells.
Pristine C60 demonstrated time-dependent accumulation with predominant mitochondrial localization in leukemic cells. C60’s effects on leukemic cells irradiated with high power single chip LEDs of different wavelengths were assessed to find out the most effective photoexcitation conditions. A C60-based noncovalent nanosized system as a carrier for an optimized drug delivery to the cells was evaluated in accordance to its physicochemical properties and toxic effects. Finally, nanomolar amounts of C60-drug nanocomplexes in 1:1 and 2:1 molar ratios were explored to improve the efficiency of cell treatment, complementing it with photodynamic approach.
A proposed treatment strategy was developed for C60 nanocomplexes with the common chemotherapeutic drug Doxorubicin, whose intracellular accumulation and localization, cytotoxicity and mechanism of action were investigated. The developed strategy was revealed to be transferable to an alternative potent anticancer drug – the herbal alkaloid Berberine.
Hereafter, a strong synergy of treatments arising from the combination of C60-mediated drug delivery and C60 photoexcitation was revealed. Presented data indicate that a combination of chemo- and photodynamic treatments with C60-drug nanoformulations could provide a promising synergetic approach for cancer treatment.