(T1130-10-55) Physicochemical Stability Investigation of Insulin in a Mesoporous Carrier Used for Oral Delivery

Purpose: There has been increasing interest in oral delivery of large molecules, such as peptides and proteins, for treating chronic diseases due to the convenience of administration. Apart from physiological barriers to oral delivery of large molecules, such as low permeability and susceptibility to digestive enzymes, manufacturing also presents serious challenges including inadequate powder flow and instability under ambient conditions. This project aimed at developing a platform technology for successful manufacturing of oral tablets that contain such molecules by loading them into a mesoporous carrier to prepare composites with good manufacturability and stability.

Methods: Insulin was used as a model drug because of its common use and well documented properties. Aeroperl^® 300 was used as mesoporous carrier because of its commercial availability and use in marketed oral dosage forms. To load insulin into the carrier, a solution of 30 mg/mL insulin in pH 2 HCl was prepared and a NaOH solution (~10 M) was added to shift pH 3-4 to maintain chemical stability of insulin.  The pH 3-4 insulin solution was immediately added to Aeroperl^® 300 powder at a solution-to-carrier ratio of 1.6 mL/g with constant stirring in a glass beaker until complete absorption of the solution by the carrier, followed by drying to a constant weight under vacuum at room temperature to obtain a composite containing 4.8% (w/w) insulin. When co-loading an excipient was desired, insulin was loaded (after the excipient was loaded) following the same procedure described earlier but at a lower solution-to-carrier ratio of 1 mL/g to ensure complete absorption of solution into carrier. Stability was assessed by storing samples at 40 °C and 11% RH for 0, 7, 14, and 30 days. Chemical stability (degradation of insulin) was assessed using an HPLC method, while physical stability (aggregation of insulin) was assessed by SEC as described in the USP. Release of insulin from composites co-loaded with 2.5 M PBS (P-I-2.5 M) and 0.72 M sucrose (S-I-0.72 M) was investigated in simulated gastric fluid (pH 2 HCl solution) and simulated intestinal fluid (pH 6.8 PBS, 0.05 M) solution at room temperature.

Results: Chemical degradation of insulin was accelerated when loaded in the mesoporous carrier (Figure 1). At 30 days, only 71.92 ± 0.14 % of insulin remained intact in the composite with Aeroperl^® 300 (I-A composite), whereas 93.52 ± 0.23 % insulin remained intact in the insulin powder. Co-loading of excipients stabilized insulin in composites in a concentration dependent manner. The fact that co-loading PBS in composites resulted in higher stability than pure insulin powder (Figure 1a) suggests that the stabilization mechanism of PBS is not just simply providing a physical barrier between insulin and the carrier. Sucrose also exhibited stabilizing effect of insulin in the carrier (Figure 1b). However, the stabilization effect was less than PBS (Figure 1a & b). The I-A composite exhibited comparable physical stability to that of insulin powder (Figure 2). Co-loading with either PBS or sucrose significantly lowered aggregation tendency of insulin (Figure 2a & b). In the simulated gastric fluid (pH 2 HCl solution), a negligible amount of insulin was released from the P-I-2.5 M after 10 min and ~ 20% of the insulin was released after 60 min. This release rate is significantly lower than that from the I-A composite (~70% after 10 min) and S-I-0.72 M (80% after 10 min) (Figure 3a). In the simulated intestinal fluid (pH 6.8), P-I-2.5 M demonstrated nearly complete release within 10 minutes. In contrast, both the I-A composite and S-I-0.72 M showed only ~10% release (Figure 3b). The slow release in simulated gastric and fast release in simulated intestinal fluid of P-I-2.5 M is advantageous to the stability and absorption of insulin when administered orally

Conclusion: Using insulin as a model compound, our results confirm the feasibility of developing a carrier based platform technology to enable manufacturing of oral dosage forms of large molecules. Co-loading with PBS or sucrose effectively stabilized insulin for both chemical and physical stability in a concentration dependent manner. The release of insulin from a composite with excellent physical and chemical stability, P-I-2.5 M, is minimum in simulated gastric fluid but rapid in simulated intestinal fluid, providing favorable controlled release when administered orally. This API engineering approach potentially enables continuous manufacturing of tablets of peptides or large molecules via direct compaction.

Acknowledgements: The authors thank Eli Lilly and Company for support through the Lilly Research Award Program (LRAP) and the National Science Foundation for support through the Industry University Collaborative Research Center (IUCRC) grant IIP-2137264, Center for Integrated Materials Science and Engineering for Pharmaceutical Products (CIMSEPP).

Figure 1. Chemical stability of insulin in I-A composite and composites with co-loaded excipients, a) PBS, B) sucrose, n=3

Figure 2. Physical stability of insulin in I-A composite and composites with co-loaded excipients, a) PBS, b) sucrose, n=1. Aggregation of insulin is quantified by an increase in high molecular weight entities (ΔHMWs),

Figure 3. Release of the insulin from its composites in a) pH 1.2 HCl solution, and b) pH 6.8 PBS solution