A Functional Biomarker of Musculoskeletal Syndrome for Effective in vivo Screening in Drug Discovery

Abstract

Long‐term administration of non‐selective matrix metalloproteinase (MMP) inhibitors, such as marimastat, in humans elicits musculoskeletal syndrome (MSS), a disease characterized by joint damage including pain, stiffness, and inflammation. This pathology is a significant obstacle to the clinical development of MMP inhibitors and in pre‐clinical models MSS can be verified only after terminal histopathology. Consequently, we devised a longitudinal and functional readout of MSS in conscious rats treated with marimastat that was validated against terminal histological assessment. MSS was induced by minipump infusion of marimastat (5–10 mg/kg/day); three possible functional biomarkers were assessed: paw volume (PV), landing foot splay separation (LFSS), and rotarod performance (RRP). Histologically, fibrosis scores in the synovium and ligament increased from 0 on Day 1 (D1) to 4.6±0.2 and 4.7±0.1, respectively, on D15; growth plate thickness was also elevated from 215.0±6.3 μm (D1) to 253.3±8.0 μm (D15). While neither PV nor LFSS were correlative with MSS histopathology, marimastat (10 mg/kg/day) reduced RRP from 180±0 sec (D0) to 135±30 sec (D9) using a constant speed protocol (10 rpm, 180 sec) and from 180±0 sec (D0) to 96±6 sec (D6) employing a variable speed protocol (increasing from 5–25 rpm over 180 sec). Results of the present study demonstrate that rotarod performance can be used as a longitudinal and in vivo functional biomarker of MSS concomitant with histological evidence of joint damage to effectively facilitate compound selection during drug discovery.