Abstract by Freja Fredholt

Achieving systemic delivery via the oral route is particularly challenging for peptide and protein therapeutics. This is largely due to the harsh environment in the gastrointestinal (GI) tract, which results in poor molecular stability, and limited absorption across the mucosal barrier. To overcome these challenges, formulation strategies often incorporate functional excipients such as permeation enhancers (PEs), with the aim to improve transmucosal permeation of co-formulated drugs. Despite the goal being developing a solid dosage form, most exploratory preclinical in vivo studies with peptides in rats rely on dosing liquid formulations. Consequently, there is not knowledge of, and thus a lack of understanding regarding critical parameters involved when translating promising liquid-based peptide - and PE - containing delivery systems into effective solid dosage forms for preclinical in vivo evaluation.

This project aimed to design and characterize mini-tablets with peptide drug (insulin or octreotide) and the PEs sodium decanoate (C10) or sodium N-(8-[2-hydroxybenzoyl]amino) caprylate (SNAC). The mini-tablets should be suitable for administration to rats for evaluation of delivery efficacy when compared to liquid formulations with similar composition.
Additionally, the work aimed to evaluate the compatibility of C10 by evaluating its effect on the rat intestinal mucosal barrier and the rat microbiome.

The formulated mini-tablets containing peptides and PEs demonstrated acceptable tensile strength and disintegrated within 15 min in low fluid volumes mimicking the rat GI environment. In vivo comparisons between mini-tablets and liquid formulations showed that absorption varied depending on the peptide, enhancer, and route of administration. Across all mini-tablet formulations, the inclusion of a PE increased the relative bioavailability (BA) of the peptide compared to controls without PEs. Following intestinal administration, the mini-tablets with insulin and C10 showed no significant difference in BA compared to corresponding liquid formulations. However, after oral gavage, the liquid insulin-C10 solution exhibited higher relative BA than the mini-tablet, although no difference in pharmacodynamic (PD) response was observed, suggesting that these results should be interpreted with caution. In contrast, oral gavage of mini-tablets containing octreotide and SNAC or C10 showed markedly higher relative BA than their liquid counterparts, likely due to prolonged mucosal contact and slower release to the stomach. Additionally, histological analysis confirmed that C10 only caused mild, reversible mucosal effects, and that repeated high-dose administration of C10, particularly as a mini-tablet, reduced the microbial diversity in the gut.

Overall, this thesis demonstrates the feasibility of evaluating solid dosage forms such as mini-tablets in the rat model for oral peptide delivery when including a PE. The findings highlight that the performance of mini-tablets versus liquid formulations is highly dependent on the drug, the enhancer, and the administration route. Further research is needed to understand the benefits and limitations of solid dosage form testing in preclinical rat studies and to assess the translational potential of solid versus liquid peptide formulations.