Sustained Release Relaxin-2 for the Treatment of Frozen Shoulder

PROJECT SUMMARY/ABSTRACT This proposal describes an innovative and restorative treatment for shoulder arthrofibrosis, also known as frozen shoulder. Of the 15 million individuals in the United States suffering from shoulder arthrofibrosis, more than 1.6 million seek medical care each year. Current treatment options, including intraarticular corticosteroid injections, non-steroidal anti-inflammatory drugs (NSAIDs), and nerve blockers, provide only marginal and temporary relief of patient symptoms and do not address the underlying cause of the disease – the accumulation of fibrotic collagenous tissue. Physical therapy is a main treatment option but it is prolonged and suboptimal. Surgical interventions are used in severe cases, but these procedures are fraught with complications and can further aggravate the fibrosis. We propose the use of human relaxin-2 (RLX) as a novel therapeutic for the treatment of shoulder arthrofibrosis. RLX is an endogenous 6-kDa peptide hormone that primarily aids in softening of the pubic symphysis and pelvic ligaments prior to childbirth via extracellular matrix remodeling. Repurposing this antifibrotic peptide to treat arthrofibrosis represents a first-of-its-kind protein therapy for this disease. Specifically, we describe detailed mechanism-of-action studies for RLX in the joint space combined with encapsulation and sustained delivery of RLX from microparticles prepared from both novel and well-established biocompatible and biodegradable polymers. The proposed experiments will define the molecular and structural basis for RLX signaling in the joint space and will use an in vivo shoulder joint contracture immobilization model to test the hypothesis that RLX reduces arthrofibrosis by inhibiting TGF-β1 signaling via the NO-sGC-cGMP pathway, thereby decreasing joint stiffness and increasing shoulder range of motion (ROM). Further, we hypothesize that sustained release of RLX from a single intraarticular injection of RLX-loaded polymeric microparticles will alleviate both the symptoms and causes of arthrofibrosis. Importantly, preliminary data support the proposed studies, well-characterized materials and rigorous experimental designs are established, and essential cross-disciplinary collaborations and expertise are in place to address the hypotheses. The specific aims of this five-year proposal are as follows. Aim 1 defines the molecular mechanism of by which RLX binds its receptor, RXFP1, providing a framework for structure-based optimization of RLX. Aim 2 determines the material property characteristics of RLX-loaded biodegradable and biocompatible polymeric microparticles, including RLX release kinetics and particle degradation. Aim 3 assesses the pharmacokinetics and efficacy of the optimal RLX-loaded microparticle formulation identified in Aim 2 using an established in vivo shoulder contracture model.