Characterization and regulation of MT1-MMP cell surface-associated activity.

Quantitative assessment of MT1-MMP cell surface-associated proteolytic activity remains undefined. Presently, MT1-MMP was stably expressed and a cell-based FRET assay developed to quantify activity toward synthetic collagen-model triple-helices. To estimate the importance of cell surface localization and specific structural domains on MT1-MMP proteolysis, activity measurements were performed using a series of membrane-anchored MT1-MMP mutants and compared directly with those of soluble MT1-MMP. MT1-MMP activity (kcat /KM ) on the cell surface was 4.8-fold lower compared with soluble MT1-MMP, with the effect largely manifested in kcat . Deletion of the MT1-MMP cytoplasmic tail enhanced cell surface activity, with both kcat and KM values affected, while deletion of the hemopexin-like domain negatively impacted KM and increased kcat . Overall, cell surface localization of MT1-MMP restricts substrate binding and protein-coupled motions (based on changes in both kcat and KM ) for catalysis. Comparison of soluble and cell surface-bound MT2-MMP revealed 12.9-fold lower activity on the cell surface. The cell-based assay was utilized for small molecule and triple-helical transition state analog MMP inhibitors, which were found to function similarly in solution and at the cell surface. These studies provide the first quantitative assessments of MT1-MMP activity and inhibition in the native cellular environment of the enzyme.

Second Generation Triple-Helical Peptide Inhibitors of Matrix Metalloproteinases.

The design of selective matrix metalloproteinase (MMP) inhibitors that also possess favorable solubility properties has proved to be especially challenging. A prior approach using collagen-model templates combined with transition state analogs produced a first generation of triple-helical peptide inhibitors (THPIs) that were effective in vitro against discrete members of the MMP family. These THPI constructs were also highly water-soluble. The present study sought improvements in the first generation THPIs by enhancing thermal stability and selectivity. A THPI selective for MMP-2 and MMP-9 was redesigned to incorporate non-native amino acids (Flp and mep), resulting in an increase of 18 °C in thermal stability. This THPI was effective in vivo in a mouse model of multiple sclerosis, reducing clinical severity and weight loss. Two other THPIs were developed to be more selective within the collagenolytic members of the MMP family. One of these THPIs was serendipitously more effective against MMP-8 than MT1-MMP and was utilized successfully in a mouse model of sepsis. The THPI targeting MMP-8 minimized lung damage, increased production of the anti-inflammatory cytokine IL-10, and vastly improved mouse survival.

Early matrix metalloproteinase-9 inhibition post-myocardial infarction worsens cardiac dysfunction by delaying inflammation resolution.

Matrix metalloproteinase-9 (MMP-9) is robustly elevated in the first week post-myocardial infarction (MI). Targeted deletion of the MMP-9 gene attenuates cardiac remodeling post-MI by reducing macrophage infiltration and collagen accumulation through increased apoptosis and reduced inflammation. In this study, we used a translational experimental design to determine whether selective MMP-9 inhibition early post-MI would be an effective therapeutic strategy in mice. We enrolled male C57BL/6J mice (3-6months old, n=116) for this study. Mice were subjected to coronary artery ligation. Saline or MMP-9 inhibitor (MMP-9i; 0.03µg/day) treatment was initiated at 3h post-MI and the mice were sacrificed at day (D) 1 or 7 post-MI. MMP-9i reduced MMP-9 activity by 31±1% at D1 post-MI (p<0.05 vs saline) and did not affect survival or infarct area. Surprisingly, MMP-9i treatment increased infarct wall thinning and worsened cardiac function at D7 post-MI. While MMP-9i enhanced neutrophil infiltration at D1 and macrophage infiltration at D7 post-MI, CD36 levels were lower in MMP-9i compared to saline, signifying reduced phagocytic potential per macrophage. Escalation and prolongation of the inflammatory response at D7 post-MI in the MMP-9i group was evident by increased expression of 18 pro-inflammatory cytokines (all p<0.05). MMP-9i reduced cleaved caspase 3 levels at D7 post-MI, consistent with reduced apoptosis and defective inflammation resolution. Because MMP-9i effects on inflammatory cells were significantly different from previously observed MMP-9 null mechanisms, we evaluated pre-MI (baseline) systemic differences between C57BL/6J and MMP-9 null plasma. By mass spectrometry, 34 plasma proteins were significantly different between groups, revealing a previously unappreciated altered baseline environment pre-MI when MMP-9 was deleted. In conclusion, early MMP-9 inhibition delayed inflammation resolution and exacerbated cardiac dysfunction, highlighting the importance of using translational approaches in mice.

Matrix metalloproteinase inhibition by heterotrimeric triple-helical Peptide transition state analogues.

Matrix metalloproteinases (MMPs) have been implicated in numerous pathologies. An overall lack of selectivity has rendered active-site-targeted MMP inhibitors problematic. The present study describes MMP inhibitors that function by binding both secondary binding sites (exosites) and the active site. Heterotrimeric triple-helical peptide transition-state analogue inhibitors (THPIs) were assembled utilizing click chemistry. Three different heterotrimers were constructed, allowing for the inhibitory phosphinate moiety to be present uniquely in the leading, middle, or trailing strand of the triple helix. All heterotrimeric constructs had sufficient thermally stability to warrant analysis as inhibitors. The heterotrimeric THPIs were effective against MMP-13 and MT1-MMP, with Ki values spanning 100-400 nM. Unlike homotrimeric THPIs, the heterotrimeric THPIs offered complete selectivity between MT1-MMP and MMP-1. Exosite-based approaches such as this provide inhibitors with desired MMP selectivities.

Evaluation of a triple-helical peptide with quenched FluorSophores for optical imaging of MMP-2 and MMP-9 proteolytic activity.

Matrix metalloproteinases (MMP) 2 and 9, the gelatinases, have consistently been associated with tumor progression. The development of gelatinase-specific probes will be critical for identifying in vivo gelatinoic activity to understand the molecular role of the gelatinases in tumor development. Recently, a self-assembling homotrimeric triple-helical peptide (THP), incorporating a sequence from type V collagen, with high substrate specificity to the gelatinases has been developed. To determine whether this THP would be suitable for imaging protease activity, 5-carboxyfluorescein (5FAM) was conjugated, resulting in 5FAM3-THP and 5FAM6-THP, which were quenched up to 50%. 5FAM6-THP hydrolysis by MMP-2 and MMP-9 displayed kcat/KM values of 1.5 × 104 and 5.4 × 103 M-1 s-1, respectively. Additionally 5FAM6-THP visualized gelatinase activity in gelatinase positive HT-1080 cells, but not in gelatinase negative MCF-7 cells. Furthermore, the fluorescence in the HT-1080 cells was greatly attenuated by the addition of a MMP-2 and MMP-9 inhibitor, SB-3CT, indicating that the observed fluorescence release was mediated by gelatinase proteolysis and not non-specific proteolysis of the THPs. These results demonstrate that THPs fully substituted with fluorophores maintain their substrate specificity to the gelatinases in human cancer cells and may be useful in in vivo molecular imaging of gelatinase activity.

Development of a Förster resonance energy transfer assay for monitoring bacterial collagenase triple-helical peptidase activity.

Due to their efficiency in the hydrolysis of the collagen triple helix, Clostridium histolyticum collagenases are used for isolation of cells from various tissues, including isolation of the human pancreatic islets. However, the instability of clostridial collagenase I (Col G) results in a degraded Col G that has weak collagenolytic activity and an adverse effect on islet isolation and viability. A Förster resonance energy transfer triple-helical peptide substrate (fTHP) has been developed for selective evaluation of bacterial collagenase activity. The fTHP [sequence: Gly-mep-Flp-(Gly-Pro-Hyp)4-Gly-Lys(Mca)-Thr-Gly-Pro-Leu-Gly-Pro-Pro-Gly-Lys(Dnp)-Ser-(Gly-Pro-Hyp)4-NH2] had a melting temperature (Tm) of 36.2°C and was hydrolyzed efficiently by bacterial collagenase (k(cat)/K(M)=25,000s(-1)M(-1)) but not by clostripain, trypsin, neutral protease, thermolysin, or elastase. The fTHP bacterial collagenase assay allows for rapid and specific assessment of enzyme activity toward triple helices and, thus, potential application for evaluating the efficiency of cell isolation by collagenases.

The role of collagen charge clusters in the modulation of matrix metalloproteinase activity.

Members of the matrix metalloproteinase (MMP) family selectively cleave collagens in vivo. Several substrate structural features that direct MMP collagenolysis have been identified. The present study evaluated the role of charged residue clusters in the regulation of MMP collagenolysis. A series of 10 triple-helical peptide (THP) substrates were constructed in which either Lys-Gly-Asp or Gly-Asp-Lys motifs replaced Gly-Pro-Hyp (where Hyp is 4-hydroxy-L-proline) repeats. The stabilities of THPs containing the two different motifs were analyzed, and kinetic parameters for substrate hydrolysis by six MMPs were determined. A general trend for virtually all enzymes was that, as Gly-Asp-Lys motifs were moved from the extreme N and C termini to the interior next to the cleavage site sequence, kcat/Km values increased. Additionally, all Gly-Asp-Lys THPs were as good or better substrates than the parent THP in which Gly-Asp-Lys was not present. In turn, the Lys-Gly-Asp THPs were also always better substrates than the parent THP, but the magnitude of the difference was considerably less compared with the Gly-Asp-Lys series. Of the MMPs tested, MMP-2 and MMP-9 most greatly favored the presence of charged residues with preference for the Gly-Asp-Lys series. Lys-Gly-(Asp/Glu) motifs are more commonly found near potential MMP cleavage sites than Gly-(Asp/Glu)-Lys motifs. As Lys-Gly-Asp is not as favored by MMPs as Gly-Asp-Lys, the Lys-Gly-Asp motif appears advantageous over the Gly-Asp-Lys motif by preventing unwanted MMP hydrolysis. More specifically, the lack of Gly-Asp-Lys clusters may diminish potential MMP-2 and MMP-9 collagenolytic activity. The present study indicates that MMPs have interactions spanning the P23-P23' subsites of collagenous substrates.

Stabilization of collagen-model, triple-helical peptides for in vitro and in vivo applications.

The triple-helical structure of collagen has been accurately reproduced in numerous chemical and recombinant model systems. Triple-helical peptides and proteins have found application for dissecting collagen-stabilizing forces, isolating receptor- and protein-binding sites in collagen, mechanistic examination of collagenolytic proteases, and development of novel biomaterials. Introduction of native-like sequences into triple-helical constructs can reduce the thermal stability of the triple-helix to below that of the physiological environment. In turn, incorporation of nonnative amino acids and/or templates can enhance triple-helix stability. We presently describe approaches by which triple-helical structure can be modulated for use under physiological or near-physiological conditions.

Peptide-based selective inhibitors of matrix metalloproteinase-mediated activities.

The matrix metalloproteinases (MMPs) exhibit a broad array of activities, some catalytic and some non-catalytic in nature. An overall lack of selectivity has rendered small molecule, active site targeted MMP inhibitors problematic in execution. Inhibitors that favor few or individual members of the MMP family often take advantage of interactions outside the enzyme active site. We presently focus on peptide-based MMP inhibitors and probes that do not incorporate conventional Zn²âº binding groups. In some cases, these inhibitors and probes function by binding only secondary binding sites (exosites), while others bind both exosites and the active site. A myriad of MMP mediated-activities beyond selective catalysis can be inhibited by peptides, particularly cell adhesion, proliferation, motility, and invasion. Selective MMP binding peptides comprise highly customizable, unique imaging agents. Areas of needed improvement for MMP targeting peptides include binding affinity and stability.

Synthesis of Fmoc-Gly-Ile Phosphinic Pseudodipeptide: Residue Specific Conditions for Construction of Matrix Metalloproteinase Inhibitor Building Blocks.

The efficient synthesis of an Fmoc-Gly-Ile phosphinic pseudodipeptide was desired as an eventual building block for construction of matrix metalloproteinase inhibitors. A Michael-type addition reaction of bis(tri-methylsilyl) phosphonite with the appropriate acrylate generated the pseudodipeptide bond. Additional of adamantyl (Ad) protection by our prior route (reaction of in situ generated phosphinic acid chloride with the sodium salt of adamantanol) was surprisingly inefficient. Adamantyl protection was achieved in high yield by refluxing the phosphinic acid, Ag2O, and 1-AdBr in chloroform. Subsequently a concise one-pot three-step reaction comprising a double deprotection of the N- and C-termini under catalytic hydrogenation conditions followed by selective protection of the N-terminus with an Fmoc group yielded Fmoc-NHCH2PO(OAd)CH2CH(2-butyl)CO2H in 41 % overall yield. These results indicate that, as the diversity of phosphinic pseudodipeptides is increased to create selective matrix metalloproteinase inhibitors, different synthetic pathways may be required for efficient building block preparation.

Efficient synthesis of Fmoc-protected phosphinic pseudodipeptides: Building blocks for the synthesis of matrix metalloproteinase inhibitors.

A convenient route for the synthesis of Fmoc-protected phosphinic dipeptide building blocks is described. The protected amino acid isosteres benzyloxycarbonyl aminomethyl phosphinic acid (glycine surrogate), benzyl α-isopropyl acrylate (valine surrogate), and benzyl α-isobutyl acrylate (leucine surrogate) were synthesized starting from commercially available materials. Reaction of either the valine or leucine surrogate with bis(trimethylsilyl) phosphonite generated the pseudodipeptide bond. The synthesis concluded with an efficient one-pot three-step procedure involving a bis-deprotection of the N- and C-termini under catalytic hydrogenation conditions followed by selective capping of the N-terminus with an Fmoc group to yield either Fmoc-NHCH(2) PO(OAd)CH(2) CH(Pr(i) )CO(2) H or Fmoc-NHCH(2) PO(OAd)CH(2) CH(Bu(i) )CO(2) H.

Manganese η2-complexes as auxiliaries for stereoselective aldol synthesis of allenyl carbinols.

A convenient and robust manganese auxiliary was linked via an η(2)-bond to alkynyl esters and ketones using a mild complexation reaction with methylcyclopentadienyl manganese tricarbonyl. This complex readily underwent aldol reactions with exclusive α-substitution and in good diastereoselectivities especially with aryl ketone substrates. This selectivity has been rationalized using a cyclic transition state model in which the manganese auxiliary plays a critical role in promoting E(O)-geometry of the cumulenolate intermediate.

Design and synthesis of chiral N-chloroimidodicarbonates: application to asymmetric chlorination of silyl enol ethers.

New chiral N-chloroimidodicarbonates, which function as efficient chiral chlorinating agents, were designed and synthesized. Among these, C(2)-symmetric (1R,2S,5R)-(-)-menthyl-N-chloroimidodicarbonate 2a provided moderate to good enantioselectivity (up to 40%) for the chlorination of silyl enol ethers to afford alpha-chloroketones only in the presence of a suitable Lewis acid such as Sm(OTf)(3).

Metal triflate catalyzed reactions of alkenes, NBS, nitriles, and TMSN3: synthesis of 1,5-disubstituted tetrazoles.

A versatile and highly efficient protocol for the synthesis of 1,5-disubstituted tetrazoles has been developed by metal triflate catalyzed one-pot reaction of alkenes, NBS, nitriles, and TMSN3. Among the metal triflates, Zn(OTf)2 was found to be the best catalyst. Use of different combinations of alkenes and nitriles generate a variety of 1,5-disubstituted tetrazoles containing an additional alpha-bromo functionality of the N1-alkyl substituent.

Highly regio- and stereoselective asymmetric bromoazidation of chiral alpha,beta-unsaturated carboxylic acid derivatives: scope and limitations.

Lewis acid catalyzed asymmetric bromoazidation of chiral alpha,beta-unsaturated carboxylic acid derivatives was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN3) as the bromine and azide sources. Among the Lewis acids, Yb(OTf)3 was found to be the best catalyst. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity (up to 89:11) with good yields were obtained when Oppolzer's bornane sultam chiral auxilairy was used. Diastereoselectivity of >95:05 was observed when (2S,5S)-2,5-diphenylpyrrolidine was used as the chiral auxiliary.