Triple-helical peptide inhibitors (THPIs) of matrix metalloproteinases (MMPs) have recently been demonstrated to be effective in a variety of animal models of disease, coincidental with knockout studies. However, passenger mutations have been described in MMP knockout mice that impact the activity of other proteins, including caspase-11. Thus, it is possible that the results observed with THPIs may be based on inhibition of caspase-11, not MMPs. The present study evaluated whether THPIs were cross-reactive with caspase-11. Two different THPIs were tested, one that is known to inhibit MMP-1 and MMP-8 (GlyΨ{PO2H-CH2}Ile-His-Lys-Gln THPI) and one that is selective for MMP-2 and MMP-9 (α1(V)GlyΨ{PO2H-CH2}Val [mep14,32,Flp15,33] THPI). No inhibition of caspase-11 was observed with GlyΨ{PO2H-CH2}Ile-His-Lys-Gln THPI, even at an inhibitor concentration of 5 μM, while 5 μM α1(V)GlyΨ{PO2H-CH2}Val [mep14,32,Flp15,33] THPI exhibited 40% inhibition of caspase-11. Further testing of GlyΨ{PO2H-CH2}Ile-His-Lys-Gln THPI revealed nM inhibition of MMP-2, MMP-9, and MMP-13. Thus, the effectiveness of GlyΨ{PO2H-CH2}Ile-His-Lys-Gln THPI observed in a sepsis animal model may not be due to caspase-11 inhibition, but may be due to broader MMP inhibition than previously thought.
Keywords: caspase; matrix metalloproteinase; phosphinate; protease inhibitor; sepsis; triple-helical peptide inhibitor.