Targeting matrix metalloproteinases in inflammatory conditions.

The matrix metalloproteinases (MMPs) and their endogenous regulators, the tissue inhibitors of MMPs (TIMPs) are responsible for the physiological remodelling of the extracellular matrix (ECM) in healthy connective tissues. MMPs are also involved in the regulation of cell behaviour via the release of growth factors and cytokines from the substrates they cleave, increasing the magnitude of their effects. Excess MMP activity is associated with ECM destruction in various inflammatory conditions, such as osteoarthritis (OA), while MMP under-activity potentially impairs healing by promoting fibrosis and preventing the effective removal of scar tissue. Both direct (TIMPs, small molecule MMP inhibitor drugs, blocking antibodies and anti-sense technologies) and indirect (glucocorticoids and non-steroidal anti-inflammatory drugs, statins, anti-sense technologies and various phytochemicals) strategies for MMP inhibition have been proposed and investigated. The strategy of MMP inhibition for degenerative and neoplastic diseases has been relatively unsuccessful due to undesired sequelae, often caused by non-selectivity of the MMP inhibition method. Therapeutic strategies for MMP-related conditions ideally should regulate MMP activity in order to maintain the optimum balance between MMPs and TIMPs. By avoiding complete inhibition it may be possible to prevent the complications of MMP over- and under-activity. Furthermore, MMP sub-type specificity is critical for minimising detrimental off-target effects that have been observed with broad-spectrum MMP inhibitors. Any potential MMP inhibitor or modulator must be subjected to rigorous pharmacokinetic, toxicity and safety studies and data obtained using in vitro models must be verified in clinically relevant animal models before therapeutic use is considered.