Synthesis and biological evaluation of analogues of the tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of primitive haematopoietic cell proliferation

Synthesis and Identification of a Novel Peptide, Ac-SDK (Biotin) Proline, That Can Elicit Anti-Fibrosis Effects in Rats Suffering from Silicosis

Background

N-Acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a short peptide with an anti-silicosis effect. However, the short biological half-life and low plasma concentration of Ac-SDKP hamper discovery of specific targets in organisms and reduce the anti-silicosis effect. A novel peptide, Ac-SDK (biotin) proline, termed “Ac-B”, with anti-fibrotic properties was synthesized.

Methods

Ac-B was detected quantitatively by high-performance liquid chromatography. Phagocytosis of Ac-B by the alveolar epithelial cell line A549 was investigated by confocal laser scanning microscopy and flow cytometry. To further elucidate the cellular-uptake mechanism of Ac-B, chemical inhibitors of specific uptake pathways were used. After stimulation with transforming growth factor-β1, the effects of Ac-B on expression of the myofibroblast marker vimentin and accumulation of collagen type I in A549 cells were analyzed by Western blotting. Sirius Red staining and immunohistochemical analyses of the effect of Ac-B on expression of α-smooth muscle actin (SMA) in a rat model of silicosis were undertaken.

Results

Ac-B had good traceability during the uptake, entry, and distribution in cells. Ac-B treatment prevented an increase in α-SMA expression in vivo and in vitro and was superior to that of Ac-SDKP. Caveolae-mediated uptake of Ac-B by A549 cells led to achieving anti-epithelial–mesenchymal transformation (EMT) effects.

Conclusion

Ac-B had an anti-fibrotic effect and could be a promising agent for the fibrosis observed in silicosis in the future.

Synthesis and bioactivity of a Goralatide analog with antileukemic activity

Natural tetrapeptide Goralatide (AcSDKP) is a selective inhibitor of primitive haematopoietic cell proliferation. It is not stable in vivo and decomposes within 4.5min when applied to live cells. In this work we developed an analog of Goralatide that exhibits cytotoxicity towards human myeloid HL-60, HEL, Nalm-6 leukemia cells, endothelial HUVEC, glioblastoma U251 and transformed kidney 293T cells. The Goralatide analog showed significant stability in organic solution with no tendency to degrade oxidatively.

Synthesis of L-Lys-Aminoxy-Goralatide

Natural tetrapeptide Goralatide inhibits primitive hematopoietic cell proliferation but reported to be rather unstable in solution (half-life 4.5 min). In this work, we report the synthesis of an aminoxy analog of Goralatide. Aminoxy moiety is expected to provide increased stability and bioavailability of the Goralatide analog.

Mass spectrometric quantification of AcSDKP-NH2 in human plasma and urine and comparison with an immunoassay

RATIONALE

Precise assessment of renal glomerular filtration rate (GFR) is essential for the early detection of chronic kidney disease. AcSDKP-NH(2), an analogue of the endogenous tetrapeptide AcSDKP, is not degraded in vivo and is freely filtered by the kidney and eliminated in urine; for that reason this analogue is an ideal candidate marker for the assessment of GRF after administration to humans. Proof-of-concept demonstration and lack of toxicity in animals have allowed an ongoing clinical study in which AcSDKP-NH(2) was administered intravenously at a dose of 100 µg and compared with currently available GFR markers. The use of the AcSDKP analogue in clinical practice requires that this novel marker be associated with an analytical method that combines specificity, robustness and high accuracy. We have developed a liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay and compared it with an existing enzyme immunoassay (EIA) for AcSDKP-NH(2).

METHODS

Human urine and plasma samples from the clinical study were analyzed by EIA and LC/MS/MS. Before LC/MS/MS assessment, AcSDKP-NH(2) was extracted using mixed-mode cation-exchange solid-phase extraction cartridges. Chromatographic separation was performed by hydrophilic interaction liquid chromatography (HILIC), before analysis with an electrospray ionization triple quadrupole mass spectrometer.

RESULTS

Mass spectrometry, through the use of an internal standard, tailored sample preparation and chromatographic separation, has better intra- and inter-assay precision (accuracies between 95 and 101% with CVs <8% for LC/MS/MS vs. accuracies between 90 and 115% with CVs <18% for EIA) and allows greater steadiness in intra-subject concentrations during the infusion (4.4% for LC/MS/MS vs. 8.6% for EIA). Moreover, the LC/MS/MS assay circumvents matrix effects observed in certain instances for the EIA and which may reduce its accuracy.

CONCLUSIONS

Although the EIA can provide sufficient information in most subjects, the LC/MS/MS assay associated with this new marker should be the reference method.

Peptide screening to knockdown Bcl-2's anti-apoptotic activity: implications in cancer treatment

Bcl-2 (B cell lymphoma-2) is an anti-apoptotic member of Bcl-2 family and its overexpression causes development of several types of cancer. The BH3 domain of pro-apoptotic and BH3-only proteins is capable of binding to Bcl-2 protein to induce apoptosis. This binding is the basis for the development of novel anticancer drug which would likely antagonize Bcl-2 overexpression. In this study we have identified BH3 domain of Bax (Bax BH3) as potentially the best Bcl-2 antagonist by performing docking of BH3 peptides (peptides representing BH3 domain of pro-apoptotic and BH3-only proteins) into the Bcl-2 hydrophobic groove formed by BH3, BH1 and BH2 domains (also referred as BH3 cleft). To predict the best small antagonist for Bcl-2, three groups of small peptides (pentapeptide, tetrapeptide and tripeptide) were designed and screened against Bcl-2 which revealed the structural importance of a set of residues playing a vital role in interaction with Bcl-2. The docking and scoring function identified KRIG and KRI as specific peptides among the screened small peptides responsible for Bcl-2 neutralization and would induce apoptosis. The applied pharmacokinetic and pharmacological filters to all small peptides signify that only IGD has drug-like properties and displayed good oral bioavailability. However, the obtained binding affinity of IGD to Bcl-2 was diminutive. Hence deprotonation, amidation, acetylation, benzoylation, benzylation, and addition of phenyl, deoxyglucose and glucose fragments were performed to increase the binding affinity and to prevent its rapid degradation. Benzoylated IGD tripeptide (IGD(bzo)) was observed to have increased binding affinity than IGD with acceptable pharmacokinetic filters. In addition, stability of Bcl-2/IGD(bzo) complex was validated by Molecular Dynamics (MD) simulations revealing improved binding energy, salt bridges and strong interaction energies. This study suggests a new molecule that inhibits Bcl-2 associated cancer/tumor regression.

Fluorescent Profiling of Natural Product Producers

The identification of natural product producer organisms remains a problem for both isolation and natural product classification. A concise screen is developed through fluorescent modification of a set of natural products that offer a common activity. Through real-time multicolor microscopy, the processing, storage, and effects of a natural product are rapidly screened at the level of the strain and individual organism.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Comparative evaluation of four trityl-type amidomethyl polystyrene resins in Fmoc solid phase peptide synthesis

Four trityl-type (i.e. non-substituted trityl-, o-Cl-trityl-, o-F-trityl- and p-CN-trityl-) amidomethyl polystyrene resins were evaluated comparatively, in terms of the stability of the trityl-ester bond in slightly acidic dichloromethane solutions, and the p-CN-trityl-amidomethyl polystyrene resin was found to be the most stable of them. The above resins were applied, in parallel with Wang benzyl-type resin, well known for its stability in mild acidic conditions, to the Fmoc solid phase synthesis of the 43-amino acid residue long bioactive peptide thymosin beta-4. Independent of their differences in acid sensitivity, the resins seemed to function equally well under the conditions used, since pure thymosin beta-4 was obtained with a final yield of approximately 30% from each resin. The trityl-type amidomethyl polystyrene resins were also applied, in parallel with the Wang resin, to the Fmoc solid phase synthesis of a bioactive peptide containing proline at its C-terminus, i.e. the N-terminal tetrapeptide of thymosin beta-4, AcSDKP. In this case, the best yield (87%) was obtained with the o-Cl-trityl-amidomethyl polystyrene resin, which may be the resin of choice, of those studied, for the Fmoc solid phase peptide synthesis.

Engineering new peptidic inhibitors from a natural chymotrypsin inhibitor

Three model peptides of different sizes (17-24 amino acid residues) mimicking the chymotrypsin inhibitor SCGI (a peptide of 35 amino acid residues) isolated from Schistocerca gregaria were designed and prepared by convergent peptide synthesis. Selective formation of disulphide bridges in the closing step was achieved without selective protection of cysteine residues. The natural pattern of the two disulphide bridges was determined by 2D homonuclear 1H NMR techniques. All three model peptides were characterized by amino acid analysis. MS and CD spectra. Preliminary results revealed that the two smaller model peptides exhibit no Inhibitory activity, whereas the larger one shows limited inhibition of chymotrypsin.