Matrix Metalloproteinase-9 as a Novel Target and a First-in-Class Therapeutic Agent for Treatment of Diabetic Foot Ulcers

Diabetic patients are fatally affected by a common complication-diabetic foot ulcers (DFUs), or wounds that are recalcitrant to healing, and more prone to the risk of infection and amputation. Matrix metalloproteinases (MMPs) are implicated to play important roles in normal wound healing, as well as in the pathology of DFUs. The challenge remains as to which MMP(s) among the 24 known human variants plays a role in the ailment, compounded by the fact that MMPs exist in three forms: the latent, the activated in complex with protein inhibitors TIMPs, and the activated uninhibited form. The first two are catalytically incompetent.

Active MMP-8 and MMP-9 are the only active MMPs were identified and quantified in the wound healing of both diabetic and non-diabetic mice with the use of a novel affinity resin. Topical application of ND-336-a MMP-9 selective inhibitor- accelerates wound repair of diabetic mice, and it demonstrates that upregulation of active MMP-9 is detrimental to diabetic wound healing. Topical application of active recombinant MMP-8 improves the rate of wound closure, indicating that MMP-8 plays a role in the repair process. A combination treatment of ND-336 and MMP-8 enhanced wound closure even further, in a strategy that holds considerable promise in healing of chronic wounds.

Topical application of active MMP-8 and MMP-13 (another collagenase) facilitates wound healing in both diabetic and non-diabetic mice. MMP-2 and MMP-9 are gelatinases that have been implicated to play roles in the process of wound healing. However, current methodology cannot distinguish an active MMP among its three forms. In fact, unlike MMP-9, MMP-2 most likely has no role in wound healing because this proteinase is in complex with its inhibitors TIMPs in vivo.

Aclerastide, a peptide analog of angiotensin II, recently failed in phase III clinical trials for treatment of DFUs. Topical treatment of aclerastide to wounds of diabetic mice results in elevated levels of reactive oxygen species (ROS) and of active MMP-9, which is likely an important contributor to the failure of aclerastide in clinical trials.

Using an affinity resin that pulls down only active MMPs coupled with proteomics, active MMP-8 and MMP-9 are identified and quantified in patients’ DFUs. Thirty four-fold higher levels of the detrimental active MMP-9 are observed in diabetic patients with the more severe and infected DFUs compared to control tissues. The enantiomerically pure (R)-ND-336 exhibits superior efficacy in inhibiting MMP-9, lowering ROS while improving diabetic wound healing significantly. (R)-ND-336 represents a first-in-class therapeutic agent to treat DFUs.