Structure-activity relationship study of small molecule interfering proteoglycan catabolism in nucleus pulposus cells

Abstract

Intervertebral discs (IVDs) are semi-cartilaginous connective tissues between vertebral bodies for spinal motion. Function of IVD relies on the integrity of the gelatinous core nucleus pulposus. IVD degeneration (IDD) is associated with low back pain. IDD is characterized by a reduction of proteoglycans within the nucleus pulposus (NP) with a replacement of fibrocartilaginous matrix, leading to a loss of mechanical strength and shock-absorbing capacity of IVD. The reduction is linked to an enhanced degradation of proteoglycans, which is mainly mediated by matrixdegrading enzymes (e.g. metalloproteinases (MMPs)) under proinflammatory cytokines (e.g. IL-1 and TNF) stimulation.

Through a high-throughput chemical screen, we previously identified a small molecule termed CSG-1 that could interfere interleukin-1 alpha (IL- 1α)-driven proteoglycan catabolism in degenerative human NP cells. To identify the functional motifs within CSG-1, we generated a series of analogues, and conducted a small scale structure-activity relationship (SAR) study. In this study, we firstly test the effects of bulk substitution (methyl/ ether groups, or chlorobenzene ring) in an attempt to narrow down the functional moiety. The performance of 28 analogues in inhibiting IL-1 a-induced proteoglycan degradation was further assessed using an alginate-bovine NP cell culture system. Data suggested that the core structure/functional (position R1,R2 and R3 on GSG-1) motifs of CSG- 1 are essential to its biological activity. Interestingly, we identified an analogue with a higher efficacy than CSG-1 in countering IL-1-induced proteoglycans degradation. Our findings may facilitate subsequent target identification of CSG-1 in the future study and drug discovery for modifying IVD degeneration as well as other degenerative disorders associated with deregulated proteoglycan expression such as osteoarthritis.