Engineered Coiled-Coil Protein for Delivery of Inverse Agonist for Osteoarthritis

Osteoarthritis (OA) results from degenerative and abnormal function of joints, with localized biochemistry playing a critical role in its onset and progression. As high levels of all-trans retinoic acid (ATRA) in synovial fluid have been identified as a contributive factor to OA, the synthesis of de novo antagonists for retinoic acid receptors (RARs) has been exploited to interrupt the mechanism of ATRA action. BMS493, a pan-RAR inverse agonist, has been reported as an effective inhibitor of ATRA signaling pathway; however, it is unstable and rapidly degrades under physiological conditions. We employed an engineered cartilage oligomeric matrix protein coiled-coil (Ccc(S)) protein for the encapsulation, protection, and delivery of BMS493. In this study, we determine the binding affinity of Ccc(S) to BMS493 and the stimulator, ATRA, via competitive binding assay, in which ATRA exhibits approximately 5-fold superior association with Ccc(S) than BMS493. Interrogation of the structure of Ccc(S) indicates that ATRA causes about 10% loss in helicity, while BMS493 did not impact the structure. Furthermore, Ccc(S) self -assembles into nanofibers when bound to BMS493 or ATRA as expected, displaying 11-15 nm in diameter. Treatment of human articular chondrocytes in vitro reveals that Ccc(S) SBMS493 demonstrates a marked improvement in efficacy in reducing the mRNA levels of matrix metalloproteinase-13 (MMP-13), one of the main proteases responsible for the degradation of the extracellular cartilage matrix compared to BMS493 alone in the presence of ATRA, interleukin-1 beta (IL -1 ss), or IL -1 ss together with ATRA. These results support the feasibility of utilizing coiled -coil proteins as drug delivery vehicles for compounds of relatively limited bioavailability for the potential treatment of OA.