Monitoring Human Neutrophil Activation by a Proteinase 3 Near-Infrared Fluorescence Substrate-Based Probe

Abstract

A near-infrared fluorescent (NIRF) substrate-based probe (SBP) was conceived to monitor secreted human proteinase 3 (hPR3) activity. This probe, called pro3-SBP, is shaped by a fused peptide hairpin loop-structure, which associates a hPR3 recognition domain (Val-Ala-Asp-Nva-Ala-Asp-Tyr-Gln, with Nva: norvaline) and an electrostatic zipper (consisting of complementary polyanionic (D-Glu)5 and polycationic (D-Arg)5 sequences) driving a tight vicinity of the N-and C-terminal FRET couple (fluorescent donor: sulfoCy5.5; dark quencher: QSY21). Beside its subsequent stability, no intermolecular fluorescence quenching was detected following its complete hydrolysis by hPR3, advocating that pro3-SBP could further afford unbiased imaging. Pro3-SBP was specifically hydrolyzed by hPR3 (kcat/Km = 440,000 ± 5,500 M -1 . s -1 ) and displayed a sensitive detection threshold for hPR3 (sub-nanomolar concentration range), while neutrophil elastase showed a weaker potency. Conversely, pro3-SBP was not cleaved by cathepsin G. Pro3-SBP was successfully hydrolyzed by conditioned media of activated human neutrophils, but not by quiescent neutrophils. Moreover, unlike unstimulated neutrophils, a strong NIRF signal was specifically detected by confocal microscopy following neutrophil ionomycin-induced degranulation. Fluorescence release was abolished in the presence of a selective hPR3 inhibitor, indicating that pro3-SBP is selectively cleaved by extracellular hPR3. Taken together, present data support that pro3-SBP could be a convenient tool allowing a straightforward monitoring of human neutrophil activation.

Neutrophil serine proteases

“…Cyclic peptide compounds containing SFTI-variants can be an attractive group of new reversible, competitive inhibitors of PR3 with high stability in human serum. The most potent selective inhibitor toward PR3, from a synthesized set, was compound 3, c[GTCTAbuSIPPICNPN], a cyclized Gly1-Asn14 including a disulfide bond between Cys3-Cys11, with a K i value of 9.8 ± 1.2 nM [66] .…”