Functionalized calcium carbonate based peptide formulation : aspects of the development for oral delivery to the buccal and intestinal mucosa

Summary
Diseases and malfunctions of the gastro intestinal tract belong to the most common illnesses in humans. This includes infections, caused by bacteria and fungi as well as food intolerances against a variety of dietary products. The prevalence of such diseases is increasing due to either bacterial resistances or changes in alimentary behavior.
Peptide drugs are a promising class of active pharmaceutical ingredients that have the potential to overcome the drawbacks of conventional small molecules such as increasing bacterial resistances. Since peptides regulate a variety of functions in the human body, they offer attractive therapeutic strategies such as enzyme replacement therapy or hormone substitution. However, oral delivery of peptide drugs is challenging mainly due to their low physical and chemical stability and poor bioavailability. Therefore, formulation of such compounds is challenging and only a few products exist on the market.
Functionalized Calcium Carbonate (FCC) was recently introduced as a new pharmaceutical excipient. FCC is a microparticulate material composed of calcium carbonate and hydroxyapatite with a high porosity of up to 60%, and an average particle size of approx. 10 μm. It shows excellent compaction behavior due to a nano-structured surface and it combines properties of nanoparticles such as high surface area with the processibility of larger particles.
The aim of this thesis was to explore the possibilities of using FCC for the delivery of sensitive biomolecules such as enzymes, proteins, and peptides via the oral cavity respecting the requirements of a multiparticulate mucoadhesive system. Further, the goal was to improve analytical methods to study material distribution within the porous particles in order to finally improve loading and coating processes.
Therefore, FCC was loaded with the two model substances lysozyme and bovine serum albumin. Release was measured in a customized flow cell, showing that lysozyme was released after 100 minutes, while considerable amounts of BSA remained adsorbed to the particles surface. Structural integrity and enzymatic activity of the released model substances were compared to unloaded material and were shown to be unchanged.
A two-step fluidized bed process, which allows drug loading and mucoadhesive coating of FCC was developed and mucoadhesion was assessed in a flow cell on porcine mucosa from the colon. The process is suitable for scale up and the produced particles showed good mucoadhesion in vitro. Release rate was found to be lower compared to uncoated particles, this was mainly attributed to a reduced surface area of the agglomerated particles.
Loaded particles were imaged by focused ion beam scanning electron microscopy to reveal the internal structure as well as intraparticulate material distribution. The findings were compared to results from mercury intrusion porosimetry mercury intrusion porosimetry in order to point out limitations of each method. It was concluded, that material distribution is dependent on a materials physical properties, and that a combination of the two methods is required for the correct interpretation of material distribution within porous microparticles.
Colloidal electrospray was investigated in a pilot study for its potential to load and coat individual particles. Preliminary trials showed promising results in terms of producibility, particle morphology, and size.
Generally, FCC is a suitable carrier for the models BSA and lysozyme and potentially other peptide drugs. However, poor release of BSA suggests further investigation on adsorption phenomena and how to avoid these. Mucoadhesion of the particles was good in vitro, although its performance in vivo still needs to be evaluated. With the gained knowledge on material distribution and the internal structure of FCC, new loading methods to promote material deposition in deeper regions of the particle should be considered. This might include further investigation of the colloidal electrospray process.