Functional biomarkers of musculoskeletal syndrome (MSS) for early in vivo screening of selective MMP-13 inhibitors

IntroductionLong-term administration of non-selective matrix metalloproteinase (MMP) inhibitors, such as marimastat, in humans elicits musculoskeletal syndrome (MSS), a syndrome 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.MethodsMSS was induced by minipump infusion of marimastat (5–10 mg/kg/day). In marimastat-treated or vehicle-control groups, three possible functional biomarkers were assessed: paw volume (PV), landing foot splay separation (LFSS), and rotarod performance (n = 6 rats/group for each endpoint).ResultsHistologically, 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 rotarod performance from 180 ± 0 s (D0) to 135 ± 30 s (D9) using a constant speed protocol (10 rpm, 180 s) and from 180 ± 0 s (D0) to 96 ± 6 s (D6) employing a variable speed protocol (increasing from 5 to 25 rpm over 180 s).DiscussionResults of the present study demonstrate that rotarod performance can be used as a predictive longitudinal, in vivo functional biomarker of MSS concomitant with histological evidence of joint damage to effectively facilitate compound selection during drug discovery. Moreover, for targets with a mechanistic risk for MSS, the model is also conducive to inclusion in secondary pharmacodynamic studies during lead optimization to identify the best (safest) compounds for advancement into clinical trials.