Background The Holy Grail of drug delivery is an autonomous system that titrates the amount of drug released in response to a biological stimulus, ensuring the drug is released only when needed at a therapeutically relevant concentration.1 One of the hallmarks of inflammatory arthritis is its variable disease activity consisting of flares of inflammation punctuated by periods of reduced disease activity.2 We have developed an injectable Inflammation Responsive self-assembled hydrogel (IR-gel) that can encapsulate and release drugs in response to enzymes that are upregulated in a diseased state including matrix metalloproteinases (MMP-2 & MMP-9) and esterases.

Objectives We aim to demonstrate on-demand delivery of the anti-inflammatory agent, triamcinolone acetonide (TA), in response to i) proteolytic enzymes, ii) enzymes secreted from lipopolysaccharide (LPS) activated macrophages and iii) synovial fluid (SF) collected from rheumatoid patient’s knee joint.

Methods TA loaded IR-gel (100 µL) was suspended in PBS (900 µL), and enzyme (100 ng/mL) was added in a dialysis bag and immersed in 40 ml of PBS, followed by incubation at 37°C. At each time-point, an aliquot (2 ml) was collected, lyophilized, dissolved in DMSO and quantified the concentration of the drug using HPLC. Similarly, instead of enzymes, either conditioned media from activated macrophages or inflamed SF were used.

Results IR-gel released TA in response to the enzymes that are expressed within arthritic joints (MMP-2, MMP-9 and esterases) as well as conditioned media of activated macrophages, a mimic of inflammation (Fig. 1). Incubation in phosphate buffer saline (PBS) at 37oC releases moderate amount of drug (<20%) during a 120-day incubation. To evaluate on-demand delivery, enzymes were added to the PBS samples on day-120, which triggered the release of TA (Fig. 1B). In addition, IR-gel released TA in response to SF collected from inflamed joints, but not when incubated with normal SF (Fig. 1D). These results suggest that IR-gel responds to proteolytic enzymes to release drug on-demand.

Conclusions IR-gel can encapsulate drugs, and disassemble in response to proteolytic enzymes, yet is hydrolytically stable in healthy SF. These hydrogels may be useful to deliver drugs in an inflammation dependent manner.

1. Vemula PK, Cruikshank GA, Karp JM, John G. Biomaterials 2009;30:383.

2. Wolfe F, Caplan L, Michaud K. Arthritis Rheum 2006;54:628.

Disclosure of Interest None Declared