(W1130-03-17) Enabling Oral Delivery of Exenatide by Designing Phospholipid Complexes for Self-nanoemulsifying Drug Delivery Systems

Purpose: Exenatide is a 39 amino acid GLP-1 analogue, used in the treatment of type II diabetes mellitus by subcutaneous injection and is applied as a model drug in this study. Since frequent injections can negatively affect patient compliance, oral administration of peptide drugs is desired by the patients, healthcare professionals and the pharmaceutical industry¹. Additionally, the oral administration route mimicks the physiological GLP-1 secretion from intestine to systemic circulation through L-cells. However, upon oral administration, exenatide is labile to acid and enzymatic hydrolysis and has poor permeability across the intestinal wall due to its large size and hydrophilicity. Self nano-emulsifying drug delivery system (SNEDDS) possess protperties which could enable overcoming such barriers. SNEDDS are isotropic mixtures of oil, surfactant and co-surfactant, which upon dispersion in aqueous media form a nano-sized oil-in-water emulsion. SNEDDS possess advantages such as gentle preparation and innate permeation enhancement. Improving the lipophilicity of exenatide by complexing it with phospholipids (PL) may improve loading into self-nanoemulsifying drug delivery systems (SNEDDS). In this study, exenatide was complexed with soybean phosphatidylcholine (SPC; Ex:SPC) using freeze-drying and loaded into SNEDDS containing medium chain (C₈-C₁₀) glycerides. The aims of the study were to develop and evaluate the protective effects of SNEDDS loaded with Ex:SPC against enzymatic degradation in an in vitro proteolysis set-up, to assess whether the proteolysis set-up is able to predict in vivo absorption of exenatide by an in vivo pharmacokinetic (PK) study, and a further aim was to evaluate the influence of lipid (SNEDDS) volume on absorption of exenatide (loaded as Ex:SPC) in vivo in rats.

Methods: Exenatide and SPC were dissolved and freeze dried in a solution of tertiary butyl alcohol and water (60:40 w/w; pH 1.5). Molar ratio of Ex:SPC (1:60) were chosen based on previous studies (data not shown). SNEDDS were developed by utilizing design of experiments (DoE) using weight fractions of C₈-C₁₀ triglycerides (MCT) (0.35-0.60), C₈-C₁₀ mono-diglyceride (MGDG) (0.30-0.45), polyoxyl-40 hydrogenated castor oil (Kolliphor®RH40) (0.10-0.30) and MAPC (constant at 0.10). The generated SNEDDS were loaded with 2.0 mg of exenatide (as Ex:SPC) and were evaluated in the in vitro proteolysis set-up for 60 mins, using α-chymotrypsin (0.25 U/mL) as a protease. Based on the proteolysis study, SNEDDS which exhibited high, intermediate and low protection of exenatide were selected for PK-studies. 150 µg of exenatide (as Ex:SPC) loaded in SNEDDS (80 µL) was administered to fasted rats by oral gavage. In the second PK-study 120 µL (1.5x), 160 µL (2.0x) and 240 µL (3.0x) of selected SNEDDS loaded with 150 µg of exenatide (as Ex:SPC) was administered to fasted rats by oral gavage.

Results: 15 different SNEDDS compositions were obtained by using D-Optimal design, which were loaded with Ex:SPC (2 mg/g) and subjected to proteolysis studies. Fig. 1 shows the response contour plot depicting the percentage of exenatide remaining after 60 min of in vitro proteolysis of Ex:SPC loaded into the SNEDDS. Ex:SPC loaded in N1, N4 and N7 SNEDDS (composition in Fig. 1 (b)) resulted in 40%, 64% and 76% of exenatide remaining, which represented three different zones in the response contour plot, and were thus selected for the PK-study. Fig. 2 shows the mean plasma concentration of exenatide dosed as Ex:SPC in different SNEDDS. The maximum plasma concentration (C_max), time to reach C_max (T_max) and the bioavailability (AUC_0-8h) are displayed in Table 1. N7 resulted in significantly higher C_max than N1 and N4 (p < 0.05). The AUC_0-8h for Ex:SPC loaded in N7 and N4 was significantly higher than for N1 (p < 0.05).
Since N7 SNEDDS displayed the highest absorption of exenatide (as Ex:SPC), this formulation was chosen for the following PK- study. Fig. 3 shows the mean plasma concentration of 150 µg of exenatide dosed as Ex:SPC in different volumes of N7 SNEDDS. Increasing the volume of N7-SNEDDS to 2.0x and 3.0x resulted in significantly higher AUC_0-8h when compared to N7-1.0x SNEDDS (plasma profile obtained from Fig. 2) (p < 0.05). Furthermore, there was a (nonsignificant) tendency for a reduced T_max in N7-SNEDDS- 2.0x and 3.0x.

Conclusion: Different SNEDDS loaded with Ex:SPC offered protection to exenatide ranging from 40 to 80%, indicating a significant role of the composition of SNEDDS in proteolytic protection of exenatide. Ex:SPC loaded SNEDDS selected for in vivo PK-studies displayed a rank order correlation between C_max and AUC_0-8h and in vitro proteolytic protection in the order of N7 > N4 > N1. Upon dosing increasing volumes (80 (1.0x) to 240 (3.0x) µL) of N7-SNEDDS, there was a significant difference observed in the AUC_0-8h, however, the increase plateued at 2.0x N7-SNEDDS dose, indicating that the influence of SNEDDS/ digested SNEDDS has a limited role in increasing the absorption of exenatide. This study paves a rational approach on development and evaluation (in vitro and in vivo) of SNEDDS intended for delivery of therapeutic peptides via the oral route.

References: 1. Brayden, D. J. Evolving peptides for oral intake. Nature Biomedical Engineering 4, 487–488 (2020).