Investigation of sterile hydrogels as topical vehicles for APOSEC ^TM , a stressed peripheral blood mononuclear cell secretome for the treatment of poorly healing wounds

Abstract APOSEC TM , a complex mixture of secreted proteins, lipids, and extracellular vesicles from stressed peripheral blood monocytes, is currently in clinical trials for the treatment of chronic, poorly healing wounds. When applied to open wounds, 1 mL reconstituted APOSEC TM lyophilisate is syringe-mixed with 3 g sterile hydrogel prior to administration. This study investigates the pharmaceutical performance of this novel administration system. A gel formulation (APOgel) was developed for terminal sterilisation in pre-filled syringes with post-sterilisation viscosity (∼325-350□Pa*s at 1□s -1 ) comparable to a commercial benchmark gel. Syringe mixing of APOgel with a liquid APOSEC TM surrogate (3:1) reduced viscosity by ∼67% but was highly reproducible across different operators (CV < 6%). Administration of three sequential dose units of the mixture from the syringe revealed an ∼20% higher content of active ingredients in the first and final dispensed compared to the middle unit, indicating non-uniform mixing in the closed syringe system. In vitro release studies over 72□h showed a 32% and 48% higher release of a small molecule marker and total proteins from the sterile APOgel compared to the benchmark gel as well as more pronounced gel swelling. However, efficacy studies in a murine wound healing model showed no significant difference between APOgel and the benchmark. These findings indicate that terminal sterilisation of gels for topical applications may provide benefits for more rapid release of active agents but syringe mixing of gels and a liquid requires optimisation to ensure uniform drug distribution. Highlights An autoclavable hydrogel for APOSEC TM delivery was developed A novel syringe-mixing system for combining a gel with a liquid with subsequent dispensing of different volume units showed non-homogenous active ingredient distribution Final optimised APOSEC TM -APOgel formulation maintains functional wound-healing efficacy