(T1030-10-56) Optimized Aqueous Remote Encapsulation of Setmelanotide in PLGA for Monthly Controlled Release Treatment of Syndromic Obesity

Purpose: Setmelanotide (Imcivree™), a cyclic melanocortin peptide with two cationic arginine residues, was developed as a daily injectable for treating rare forms of syndromic obesity, such as POMC deficiency and leptin receptor deficiency. To reduce the frequency of injections, microencapsulation of peptides in polymers like poly(lactic-co-glycolic acid) (PLGA) is often employed due to its long-interval release and biocompatibility. Recently, we demonstrated that PLGA microspheres with a carboxylic acid end group for monthly administration can bind and absorb setmelanotide, enabling remote encapsulation in an aqueous environment without organic solvents, which is advantageous for large-scale manufacturing. This study aimed to optimize the remote encapsulation method to achieve high loading capacity and encapsulation efficiency, low initial burst, and a monthly continuously release profile.

Methods: We investigated the effects of polymer molecular weight, polymer L:G ratio, and aqueous buffer ionic strength on the pH drop and encapsulation efficiency after remote loading, and resulting in vitro initial burst and long-term release profiles. Encapsulation efficiency was evaluated using mass loss and nitrogen analysis. The in vitro release was characterized using the sample-and-separate method in phosphate buffered saline + 0.02%Tween 80 at 37 °C, and setmelanotide concentration was analyzed by UPLC.

Results: Decreasing polymer molecular weight positively impacted encapsulation efficiency. The initial burst was significantly influenced by buffer ionic strength and pH drop associated with the peptide-proton exchange with the polymer end-group binding sites post remote loading. The L:G ratio affected the total duration of release. An optimal formulation achieved a loading capacity as high as 9.9% (99% encapsulation efficiency), which sustained the release of setmelanotide continuously over 35 days with a low initial burst in vitro.

Conclusion: This study presents an alternative to conventional peptide encapsulation method for multi-cationic peptides, demonstrating optimal loading capacity and potential for clinical translation of monthly slow-release of setmelanotide from PLGA microspheres. The aqueous remote loading method can bypass complicated aseptic processing and unit operations associated with organic solvents, providing a simplified and more cost-effective manufacturing pathway for monthly PLGA depots.

References: 1. Giles, M. B., et al., Efficient aqueous remote loading of peptides in poly(lactic-co-glycolic acid), Nature Communication, 2022, 13, 1-9.
2. Wang, S., et al. Aqueous remote loading of setmelanotide in poly(lactic-co-glycolic acid) microspheres for long-term obesity treatment. Journal of Controlled Release, 2023, 364, 589-600.

Acknowledgements: This work was supported in part by NIH Grant 2R42DK127817-02.

A. Drug loading and pH drop for the formulations with different molecular weights and L:G ratios. B. Cumulative release profiles for different formulations. C. Ionic strength affects the initial burst. D. Initial burst release amount is proportional to pH drop after remote loading.