Defining and engineering specificity of tissue inhibitors of metalloproteinases (TIMPs)
TIMPs inhibit MMPs using a broad contact interface, as illustrated by TIMP-1 inhibition of MMP-10. The binding surface of TIMP-1 (bottom) involves three distinct protein regions: the core epitope (green), AB-loop (cyan) and C-terminal domain (yellow). The contact footprint of these binding epitopes on the catalytic domain of MMP-10 is shown in corresponding colors (top).
TIMP-MMP contact surface
Gene silencing (knockdown) of MMP-9 expression in breast cancer cells (KD) blocks the cells from invading through artificial basement membrane, compared with control cells (NT) that express MMP-9.
MMP-9 drives invasion
Breast cancer cells with knockdown of MMP-9 (KD) show blocked metastasis to the lung in an orthotopic mouse model, compared with MMP-9-expressing breast cancer cells (NT), which show extensive metastasis. New drugs capable of selectively blocking MMP-9 may similarly prevent the spread of breast cancer.
MMP-9 drives metastasis
Despite proven and important roles for matrix metalloproteinases (MMPs) in promoting cancer progression, small-molecule MMP inhibitors have fared poorly in clinical trials. This is in part because of a lack of selectivity, a problem that might be overcome by inhibitors highly selective for individual tumor-promoting MMPs.
An alternative to small-molecule MMP inhibitor development could be the engineering of naturally occurring protein inhibitors of MMPs — the tissue inhibitors of metalloproteinases (TIMPs). TIMPs offer an unparalleled scaffold for developing new MMP inhibitors of novel selectivity.
Unlike synthetic MMP inhibitors, TIMPs feature a broad and extensive contact surface for interaction with MMP targets, encompassing more than 20 amino acid residues. This large interface offers an outstanding opportunity for molecular optimization.
Using both structure-guided approaches and directed evolution techniques, the Radisky Proteases in Cancer Laboratory is exploring the idea that TIMPs, like antibodies, may be engineered as targeted protein therapeutics of remarkable affinity and exquisite selectivity.
The Proteases in Cancer Laboratory is working to develop selective inhibitors for several MMPs known to promote cancer progression by modifying the natural human TIMPs. These include MMP-3, a key inducer of epithelial-mesenchymal transition (EMT) and tumor progression in lung and breast cancers; MMP-10, an enzyme necessary for lung tumors for maintenance of the cancer stem cell phenotype; and MMP-9, a critical inducer of EMT, invasion, metastasis and angiogenesis in breast cancer and many other tumor types.