In vitro studies of a bradykinin B1/B2 antagonist linked to a human neutrophil elastase inhibitor; a heterodimer for the treatment of inflammatory disorders.

Inflammatory disorders typically have a complex etiology and involve a multitude of inflammatory mediators, and hence, a polytherapeutic approach to these diseases would seem appropriate. In certain chronic inflammatory conditions, we believe that bradykinin (BK) and human neutrophil elastase (HNE) are cooperatively involved. We have previously synthesized compounds with inhibitory activity toward both the BK B2 receptor and HNE. The present study describes single compounds designed to incorporate HNE inhibitory activity and BK B1 and B2 antagonist activity. A proprietary HNE inhibitor (HNEI, CP-955) was directly linked via amide bond formation to a peptide-based combined BK B1/B2 antagonist (B-9430). Three compounds were made using different linking positions in the antagonist peptide. For all compounds, B1 and B2 receptor binding in human cloned receptors was at least 10-fold less than that of B-9430, whereas in the in vitro guinea pig ileum B2 receptor functional assay, the compounds had potencies equivalent to B-9430. Compound I was found to have a fourfold increase in HNEI activity compared with CP-955, whereas compounds II and III were inactive. These data clearly demonstrate that it is possible to retain BK B1/B2 receptor antagonist and HNE activity in a heterodimer.

Solid-phase synthesis of (tyrosyl-alanyl-glutamyl)n by segment condensation.

(Tyr-Ala-Glu)n, n = 1-9, were synthesized by segment condensation using the Fmoc/tert-butyl protection strategy and solid-phase techniques. The C-terminal residue was coupled to the resin and the peptides were built out by adding Fmoc-Glu(O-t-Bu)-Tyr(t-Bu)-Ala-OH units. When the desired lengths were reached the peptides were capped with Fmoc-Tyr(t-Bu)-Ala-OH units. Fmoc-Tyr(t-Bu)-Ala-OH and Fmoc-Glu(O-t-Bu)-Tyr(t-Bu)-Ala-OH were synthesized in aqueous solution by the successive addition of N-hydroxysuccinimide esters of Fmoc-Tyr(t-Bu) and Fmoc-Glu(O-t-Bu) to the growing chain. Neither sequential amino acid addition or segment condensation techniques were successful on polystyrene supports. However, the segment condensations were highly successful on kieselguhr-supported polydimethylacrylamide based resins. (Tyr-Ala-Glu)n, n = 1-9, were tested as inhibitors of the protein tyrosine kinase, pp60c-src. Inhibition, as measured by IC50 values, increased with increasing size of the peptide.

Cyclic peptide substrates of pp60c-src. Synthesis and evaluation.

To study the effects of constrained conformation and amino acid sequence on their kinetic parameters, a series of cyclic peptides were synthesized and each was tested as both a substrate and an inhibitor of pp60c-src, the product of the src proto-oncogene. The amino acid sequences were derived from Glu-Leu-Pro-Tyr-Ala-Gly and from the autophosphorylation site of pp60c-src (Ile-Glu-Asp-Asn-Glu-Tyr-Ala-Ala-Arg-Gln-Gly). Linear precursor peptides were synthesized by SPPS on aminomethylated polystyrene resin using the Fmoc-tert-butyl protection scheme with 4-hydroxymethyl-3-methoxyphenoxyacetic acid as the linkage agent. The peptides were cleaved from the support with 1% TFA in dichloromethane with the N-terminal Fmoc and the side-chain protecting groups in place. Removal of the Fmoc group with diethylamine and cyclization with BOP afforded cyclic peptides in 55-78% yield. Side-chain deprotection and further purification gave the final products in 25-48% yields based on their linear precursors. Based on the activities of the linear analogues, cyclization had little effect on the binding (Ki and Km) and rate of phosphorylation (Vmax) of cyclo(Glu-Leu-Pro-Tyr-Ala-Gly) and cyclo(Ile-Glu-Asp-Asn-Glu-Tyr-Ala-Ala-Arg-Gln). A series of cyclic decapeptides that contained the dipeptide D-Phe-Pro inserted in various positions in the autophosphorylation sequence showed marked differences in Ki, Km and Vmax. Compared to the well characterized linear substrate Val-5 angiotensin II, the D-Phe-Pro-containing cyclic peptides have higher Vmax values but differ little in Km, with values in the millimolar range.

Monitoring protein cleavage and concurrent disulfide bond assignment using thermospray LC/MS.

The arrangement of the disulfide bridges of Cucurbita maxima trypsin inhibitor, CMTI I, has been confirmed by enzymatic and chemical cleavages of the native protein and analysis of the resulting disulfide-bridged fragments using thermospray liquid chromatography/mass spectrometry. Although the disulfide bridges of CMTI I have recently been assigned from the x-ray crystallographic structure, direct chemical analysis of the S-S bonds using classical techniques proved difficult. The CMTI I molecule is extremely resistant to enzymatic digestion, and only one site of the peptide chain (Met-8) can be used efficiently for chemical cleavage. A series of degradative conditions were employed in the studies reported here. The progress of protein modification was monitored directly by high-performance liquid chromatography/thermospray mass spectrometry. The disulfide pairings could be deduced directly from the mass spectra of the peptides produced by the fragmentation processes and resolved by high-performance liquid chromatography. In two instances, fragments involving a disulfide bond were isolated and further analyzed, and these confirmed the mass spectral assignments. The disulfide bridges identified, 3-20, 10-22 and 16-28, correspond to those of the x-ray structure and are consistent with those assigned for two other closely related trypsin inhibitors.

Peptide mapping using thermospray LC/MS detection: rapid identification of hemoglobin variants.

A rapid and easily interpreted method for peptide mapping is demonstrated with hemoglobin A and three variants. Digests of the globin chains are generated in columns containing immobilized trypsin. The resulting protein fragments are resolved by reverse phase HPLC and then analyzed by thermospray mass spectrometry. The entire process is carried out on-line. The result is a chromatographic trace which is two dimensional; in addition to the standard elution pattern, the individual mass spectra collected for each peak contain information about their identity and their purity. In two of the variants used, hemoglobin C and hemoglobin Baylor, the exact nature of the amino acid substitution could be determined unambiguously in a single analysis, from the masses of the new tryptic peptides observed. In the third case, hemoglobin S, the mass of the peptide containing the amino acid replacement is consistent with two separate sites of substitution. This ambiguity was resolved in a second analysis, using immobilized carboxypeptidase Y, prior to mass spectral analysis. The resulting partial digest permits reconstruction of the critical sequence region and correct assignment of the allelic site.

Recognition of neuropeptides FMRFamide and LPLRFamide by chicken cerebellum avian pancreatic polypeptide binding sites.

Binding isotherms were constructed for the binding of synthetic tetrapeptide and pentapeptide fragments to membranes prepared from chicken cerebellar tissue. Both the tetrapeptide (FMRFamide), which was originally isolated from ganglia of mollusks, and the pentapeptide (LPLRFamide) previously isolated from chicken brain are known to increase blood pressure and modulate brain neurons in rats. The C-terminal dipeptide sequences of the two peptides are identical and both show similarity to the dipeptide sequence established for the pancreatic polypeptide (PP) family. Specific high-affinity binding sites exist for the latter peptide, sites which are competed for (though with less affinity) by neuropeptide Y (NPY). Affinity for cerebellar membranes was virtually equivalent for the synthetic peptide LPLRFamide and FRMFamide; the binding affinities (IC50) of all fragments tested (C-terminal pentapeptides of avian PP and NPY, and FMRFamide and LPLRFamide) fell in the same approximate range. Since the N-terminal residues of FMRFamide and LPLRFamide are not homologous with equivalent residues of APP or NPY, our results indicate that only Arg-Tyr-NH2 or Arg-Phe-NH2 sequences are necessary for binding of the carboxy terminus peptides of the PP family. In this respect, these sequences are functionally equivalent.

Binding of C-terminal segments of neuropeptide Y to chicken brain.

The C-terminal pentapeptide amide segment of neuropeptide Y (NPY) binds specifically to chicken brain membrane preparations. The contribution of each residue of the C-terminus to this binding has been investigated through the synthesis and evaluation of a series of pentapeptide analogs. The binding of these molecules is strongly dependent on the presence of certain functional groups, in particular the guanidinium group of Arg-35 and the C-terminal aromatic amide function. The significance of these results for the binding to chicken brain tissue of NPY, pancreatic polypeptide and other potentially related neuropeptides is discussed.

Evidence for hemiketals as intermediates in the inactivation of serine proteinases with halomethyl ketones.

The mechanism of inactivation of serine proteinases by peptide halomethyl ketone inhibitors was studied through the inhibition of trypsin with a series of model peptide ketones (Lys-Ala-LysCH2X). In this series, X is a poor leaving group with increasing electron-withdrawing capacity (X = H, CH2CO2CH3, COCH3, OCOCH3, and F), and as expected, the peptide ketones are reversible, competitive inhibitors of trypsin. The strength of binding of these inhibitors to trypsin increases with the electron-withdrawing ability of X, indicating that the inhibition constant Ki obtained is a measure of reversible hemiketal formation between the inhibitor ketone carbonyl group and the hydroxyl group of the active site serine. A Hammett plot of -log Ki vs. sigma I, the inductive substituent constant of X, reveals a linear relationship between the free energy of binding and the electron-withdrawing power of X. The reversible binding constant obtained for the corresponding chloromethyl ketone Lys-Ala-LysCH2Cl falls on this line, indicating that the reversible binding involves hemiketal formation, which is followed by alkylation of the enzyme.

Direct monitoring of sequential enzymatic hydrolysis of peptides by thermospray mass spectrometry.

A procedure for peptide sequencing using an immobilized exopeptidase column directly coupled to a thermospray mass spectrometer is described. The amino acids sequentially released from the C-terminus of the peptide chain are directly introduced into a thermospray ion source by a flowing aqueous buffer. The buffer is essential for the direct production of ions from solution. The method eliminates the need to derivatize the amino acids for detection and, by comparison to standard injections, amino acid sequence information can be obtained in less than two minutes. With the present configuration, detection limits are typically in the low picomolar range.

In vitro binding and degradation of avian pancreatic polypeptide by chicken and rat tissues.

The interaction of pancreatic polypeptide (PP) with possible chicken and rat target tissues was investigated by characterizing the binding and degradation of [125I]iodo-PP by plasma membrane preparations in vitro. Membranes from chick brain and liver possessed highly specific avian PP (APP)-binding sites, while those from chick whole pancreas and proventricular and duodenal mucosa exhibited little or no specific [125I]iodo-APP binding. The affinity of the specific chick liver binding sites for APP was low; 500 ng unlabeled APP/ml (1.2 X 10(-7) M) were required for half-maximal displacement of [125I]iodo-APP. Chick brain membranes, on the other hand, possessed two orders of APP binding sites, a high affinity site (Kd = 3.3 X 10(-10) M) and a low affinity site (Kd = 1.8 X 10(-7) M). The binding process to chick brain membranes retained specificity for intact APP1-36, as unlabeled bovine PP1-36 (BPP1-36) inhibited specific binding of [125I]iodo-APP by 50% at a concentration of 7 X 10(-9) M (10 times the IC50 level of unlabeled APP). Carboxy-terminal pentapeptides of APP and BPP (APP32-36 and BPP32-36) interacted with the chick brain membrane APP-binding sites, but did not possess the full binding activity of the intact molecule. Membranes from rat brain exhibited little APP-specific binding and no BPP-specific binding. Chick kidney membranes degraded more [125I]iodo-APP than any other chicken tissue. The degradation process was specifically inhibited by unlabeled APP and yielded reaction products of lower molecular weight than intact APP. The antiprotease bacitracin was capable of virtually complete degradation inhibition, but its presence failed to increase APP binding by kidney membranes. It is concluded that chick brain possesses high affinity APP-binding sites, potentially functional at physiological concentrations of the polypeptide. APP-binding sites on liver membranes are probably physiologically nonfunctional, while the kidney is most active relative to other tissues in the degradation and, probably, clearance of APP.

A synthetic 13-residue peptide designed to resemble the primary binding site of the basic pancreatic trypsin inhibitor.

A peptide, AC-Pro-Cys-Lys-Ala-Arg-Ile-DPhe-Pro-Tyr-Gly-Gly-Cys-Arg-NH2, which resembles the binding site of the basic pancreatic trypsin inhibitor, has been prepared by solid-phase peptide synthesis. A partially protected peptide was first obtained from the solid-phase product by removal of all side-chain protecting groups except the acetamidomethyl (Acm) groups on the cysteines. This di-Acm-peptide was deprotected, with concomitant formation of the cyclic product, by treatment with I2 in AcOH. The cyclic 13-residue peptide is a reversible, competitive inhibitor of trypsin with a Ki (app) of 2 . 10(-6) M, but loses its inhibitory activity upon incubation with trypsin. The di-Acm-peptide precursor has a Ki (app) of 5 . 10(-5) M and is deactivated more rapidly by trypsin. The effectiveness of the 13-residue peptides as inhibitors is in part attributed to the conformation induced by the beta-turn directing the -DPhe-Pro portion of the sequence.

Interaction of dansylated peptidyl chloromethanes with trypsin, chymotrypsin, elastase, and thrombin.

A series of N alpha-1-(dimethylamino)-5-naphthalenesfulfonyl (dansyl) derivatives of peptidyl chloromethanes (chloromethyl ketones) were synthesized and employed to introduce the fluorescent dansyl moiety specifically into the active sites of proteinases via affinity labeling. Dansylalanyllysychloromethane (DALCM) was utilized to inactivate and fluorescently label trypsin and the trypsin-like enzyme thrombin. Dansylleucylphenylalanylchloromethane (DLPCM) was synthesized and selectively employed as an inhibitor of chymotrypsin. The di-, tri-, and tetrapeptides--dansylprolylalanylchloromethane (DPACM), dansylalanylprolylalanylchloromethane (DAPACM), and dansylprolylalanylprolylalanylchloromethane (DPAPACM)--were synthesizedand their interaction with elastase was evaluated. The compounds DALCM, DLPCM, and DAPACM all proved to be effective, fast-acting proteinase inhibitors. Studies of energy transfer in the enzyme-inhibitor conjugates led to results entirely consistent with the proposed conformational bomology of thrombin with the other serine proteinases studied. The fluorescent affinity labels are believed to posses enormous potential for the localization, isolation, and characterization of enzymes.

Synthesis and biological effect of the C-terminal pentapeptide amide of avian pancreatic hormone III (APP).

Model building studies and analogies drawn from peptides of similar biological activity have indicated that the C-terminus of avian pancreatic hormone III may possess significant biological information. To test this hypothesis, the C-terminal pentapeptide amide sequence has been synthesized by the Merrifield method. The synthesis, purification and characterization of this compound are reported here in detail. In vivo studies indicate that this synthetic segment possesses none of the secretogogic activity of the parent hormone; rather, it reduces "gastric" secretion levels even in the presence of the intact hormone.

Synthesis, characterization and fluorescence studies on N-alpha-dansylalanyllysyl trypsino (HIS-46)-methane.

The 1-dimethylamino-5-naphthalene sulfonyl (dansyl) derivative of alanyllsyl chloromethane was synthesized and employed to introduce the fluorescent dansyl moiety specifically into the active site of trypsin via affinity labelling. The potential of dansylalanyllysyl chloromethane lies in its high degree of selectivity and markedly faster rate of enzyme inactivation when compared to previously synthesized, single residue affinity label chromophores. This permits the practical utilization of stoichiometric amounts of the inhibitor to achieve 100% inactivation of trypsin, even at high dilutions. The transfer of energy between the four tryptophan residues of trypsin and the bound dansyl group has been investigated in the fluorescent inhibitor-enzyme conjugate. From transfer efficiency measurements mean distances of 19.0 A and 19.3 A between the point of attachment of the dansyl group and the four tryptophan residues of trypsin have been calculated. These compare well with the mean value of 18.8 A derived from calculations based on crystallographic model studies.

[52-Homoserine]-basic pancreatic trypsin inhibitor. Preparation and properties of a protein analog.

Treatment of basic pancreatic trypsin inhibitor (BPTI) with cyanogen bromide smoothly cleaves the polypeptide chain at the single methionyl residue. The newly formed homoserine lactone and alpha-amino functions are held in proximity by a disulfide linkage, and in neutral aqueous solution react together spontaneously to re-form the peptide chain. The resulting analog, [52-homoserine]-BPTI is very similar to the native molecule in most properties measured. The rate of formation of this analog from the chain-cleaved intermediate has been determined. It is apparent that the facility of analog synthesis is due in large part to the retention of the native protein conformation in the cyanogen bromide-cleaved intermediate.

Studies on the partial synthesis of protein analogs by direct coupling to terminal homoserine lactone derivatives. Experiments with basic pancreatic trypsin inhibitor.

Treatment of basic pancreatic trypsin inhibitor (BPTI, I) with cyanogen bromide smoothly yields the chain cleaved derivative II. The utility of the seco-lactone (II) in the partial synthesis of protein analogues has been investigated. It is shown that the homoserine lactone ring is sufficiently reactive to combine directly with the radiolabelled synthetic peptide glycylglycylanine t-butyl ester in both aqueous and non-aqueous solution, leading to a BPTI analogue which has been purified and characterized.