Peptidomimetic inhibitors of the VEGF-A165/NRP-1 complex obtained by modification of the C-terminal arginine.

Inhibitors of the interaction between Neuropilin-1 (NRP-1) and Vascular Endothelial Growth Factor-A165 (VEGF-A165) hold significant promise as therapeutic and diagnostic agents directed against cancers overexpressing NRP-1. In our efforts in this field, a few series of strong and fairly stable peptide-like inhibitors of the general formula Lys(Har)1-Xaa2-Xaa3-Arg4 have been previously discovered. In the current work, we focused on Lys(Har)-Dap/Dab-Pro-Arg sequence. The aim was to examine whether replacing C-terminal Arg with its homologs and mimetics would yield more stable yet still potent inhibitors. Upon considering the results of modelling and other factors, ten novel analogues with Xaa4 = homoarginine (Har), 2-amino-4-guanidino-butyric acid (Agb), 2-amino-3-guanidino-propionic acid (Agp), citrulline (Cit), 4-aminomethyl-phenylalanine [Phe(4-CH2-NH2)] were designed, synthesized and evaluated. Two of the proposed modifications resulted in inhibitors with activity slightly lower [e.g. IC50 = 14.3 µM for Lys(Har)-Dab-Pro-Har and IC50 = 19.8 µM for Lys(Har)-Dab-Pro-Phe(4-CH2-NH2)] than the parent compounds [e.g. IC50 = 4.7 µM for Lys(Har)-Dab-Pro-Arg]. What was a surprise to us, the proteolytic stability depended more on position two of the sequence than on position four. The Dab2-analogues exhibited half-life times beyond 60 h. Our results build up the knowledge on the structural requirements that effective VEGF-A165/NRP-1 inhibitors should fulfil.

Physicochemical and Biological Characterization of Novel Membrane-Active Cationic Lipopeptides with Antimicrobial Properties.

We have designed and synthesized new short lipopeptides composed of tetrapeptide conjugated to fatty acids with different chain lengths. The amino acid sequence of the peptide moiety included d-phenylalanine, two residues of l-2,4-diaminobutyric acid and l-leucine. To explore the possible mechanism of lipopeptide action, we have provided a physicochemical characterization of their interactions with artificial lipid membranes. For this purpose, we have used monolayers and bilayers composed of lipids representative of Gram-negative and Gram-positive bacterial membranes. Using surface pressure measurements and atomic force microscopy, we were able to monitor the changes occurring within the films upon exposure to lipopeptides. Our experiments revealed that all lipopeptides can penetrate the lipid membranes and affect their molecular ordering. The latter results in membrane thinning and fluidization. However, the effect is stronger in the lipid films mimicking Gram-positive bacterial membranes. The results of the physicochemical characterization were compared with the biological activity of lipopeptides. The effect of lipopeptides on bacterial growth was tested on several strains of bacteria. It was revealed that lipopeptides show stronger antimicrobial activity against Gram-positive bacteria. At the same time, all tested compounds display relatively low hemolytic activity.

ß2-Homo-Amino Acid Scan of µ-Selective Opioid Tetrapeptide TAPP.

TAPP (H-Tyr-d-Ala-Phe-Phe-NH2) is a potent, µ-selective opioid ligand. In order to gain further insights into pharmacophoric features of this tetrapeptide, we have performed a ß2-Homo-amino acid (ß2hAA) scan of the TAPP sequence. To this aim, 10 novel analogues have been synthesized and evaluated for µ-opioid and δ-opioid receptor affinity as well as for stability in human plasma. The derivatives included compounds in which a (R)- or (S)-ß2-Homo-Homologue replaced the amino acids in the TAPP sequence. The derivatives with (R)- or (S)-ß2hPhe4 turned out to bind µOR with affinities equal to that of the parent. ß2hAAs in position 1 and 3 resulted in rather large affinity decreases, but the change differed depending on the stereochemistry. ß2-Homologation in the second position gave derivatives with very poor µOR binding. According to molecular modelling, the presented α/ß-peptides adopt a variety of binding poses with their common element being an ionic interaction between a protonable amine of the first residue and Asp147. A feature required for high µOR affinity seems the ability to accommodate the ring in the fourth residue in a manner similar to that found for TAPP. Contrary to what might be expected, several compounds were significantly less stable in human plasma than the parent compound.

Triazolopeptides Inhibiting the Interaction between Neuropilin-1 and Vascular Endothelial Growth Factor-165.

Inhibiting the interaction of neuropilin-1 (NRP-1) with vascular endothelial growth factor (VEGF) has become an interesting mechanism for potential anticancer therapies. In our previous works, we have obtained several submicromolar inhibitors of this interaction, including branched pentapeptides of general structure Lys(Har)-Xxx-Xxx-Arg. With the intent to improve the proteolytic stability of our inhibitors, we turned our attention to 1,4-disubstituted 1,2,3-triazoles as peptide bond isosteres. In the present contribution, we report the synthesis of 23 novel triazolopeptides along with their inhibitory activity. The compounds were synthesized using typical peptide chemistry methods, but with a conversion of amine into azide completely on solid support. The inhibitory activity of the synthesized derivatives spans from 9.2% to 58.1% at 10 µM concentration (the best compound Lys(Har)-GlyΨ[Trl]GlyΨ[Trl]Arg, 3, IC50 = 8.39 µM). Synthesized peptidotriazoles were tested for stability in human plasma and showed remarkable resistance toward proteolysis, with half-life times far exceeding 48 h. In vitro cell survival test resulted in no significant impact on bone marrow derived murine cells 32D viability. By means of molecular dynamics, we were able to propose a binding mode for compound 3 and discuss the observed structure-activity relationships.

Modulation of Activity of Ultrashort Lipopeptides toward Negatively Charged Model Lipid Films.

Because of the increasing resistance of pathogens to commonly used antibiotics, there is an urgent need to find alternative antimicrobial compounds with different mechanisms of action. Among them, lipopeptides are recognized as promising candidates. In this work, the Langmuir technique and atomic force microscopy were employed to investigate the interactions of two novel lipopeptides with negatively charged phospholipid membranes, which served as a simplified model of inner membrane of Gram-negative bacteria. Lipid films contained phosphatidylethanolamine and phosphatidylglycerol extracts from E. coli bacteria. Lipopeptides were composed of palmitoyl chain covalently coupled to N-terminus of peptide with Trp-Lys-Leu-Lys amino acid sequence and the conformation of third residue was either d-Leu or l-Leu. It was found that chirality of leucine strongly affects interfacial behavior of these compounds, which was ascribed to the difference in effective size of the peptide portion of the molecules. Although the lipopeptides were the same in terms of amino acid sequence, charge, and identity of lipophilic chain, the experiments revealed that the barrier for their insertion into the lipid membrane is significantly different. Namely, it was lower for lipopeptide containing d-Leu residue. We have also found that insertion of the lipopeptides into the model membranes strongly alters lateral distribution of the membrane components and leads to its substantial fluidization. The dynamics of reorganization was noticeably faster in the presence of lipopeptide with smaller size of peptide moiety, i.e., containing d-Leu. It proves that effective size of the peptide headgroup is an important factor determining lipopeptide activity toward the lipid membranes.

Conformational latitude - activity relationship of KPPR tetrapeptide analogues toward their ability to inhibit binding of vascular endothelial growth factor 165 to neuropilin-1.

Neuropilin-1 has been found to be overexpressed in several kinds of malignant tumors, and it is postulated that its interaction with the vascular endothelial growth factor 165 leads to progression of tumor vascularization and growth. Several analogues (KxxR) with various conformational latitudes have been synthesized and found as inhibitors of NRP-1. Detailed insight provided by molecular dynamics simulation allowed forming a clear relationship between flexibility of xx part of the molecule and its inhibitory activity.

Beware of Cocktails: Chain-Length Bidispersity Triggers Explosive Self-Assembly of Poly-L-Glutamic Acid ß2-Fibrils.

Chain-length polydispersity is among the least understood factors governing the fibrillation propensity of homopolypeptides. For monodisperse poly-L-glutamic acid (PLGA), the tendency to form fibrils depends of the main-chain length. Long-chained PLGA, so-called (Glu)200, fibrillates more readily than short (Glu)5 fragments. Here we show that conversion of α-helical (Glu)200 into amyloid-like ß-fibrils is dramatically accelerated in the presence of intrinsically disordered (Glu)5. While separately self-assembled fibrils of (Glu)200 and (Glu)5 reveal distinct morphological and infrared characteristics, accelerated fibrillation in mixed (Glu)200 and (Glu)5 leads to aggregates similar to neat (Glu)200 fibrils, even in excess of (Glu)5. According to molecular dynamics simulations and circular dichroism measurements, local events of "misfolding transfer" from (Glu)5 to (Glu)200 may play a key role in the initial stages of conformational dynamics underlying the observed phenomenon. Our results highlight chain-length polydispersity as a potent, although so-far unrecognized factor profoundly affecting the fibrillation propensity of homopolypeptides.

Synthesis, binding affinities and metabolic stability of dimeric dermorphin analogs modified with ß3-homo-amino acids.

In this study, proteinogenic amino acids residues of dimeric dermorphin pentapeptides were replaced by the corresponding ß(3)-homo-amino acids. The potency and selectivity of hybrid α/ß dimeric dermorphin pentapeptides were evaluated by competetive receptor binding assay in the rat brain using [3H]DAMGO (a µ ligand) and [3H]DELT (a δ ligand). Tha analog containing ß(3)-homo-Tyr in place of Tyr (Tyr-D-Ala-Phe-Gly-ß(3)-homo-Tyr-NH-)2 showed good µ receptor affinity and selectivity (IC50 = 0.302, IC50 ratio µ/δ = 68) and enzymatic stability in human plasma.

Amyloidogenic Properties of Short α-L-Glutamic Acid Oligomers.

Poly-L-glutamic acid (PLGA) forms amyloid-like ß2-fibrils with the main spectral component of vibrational amide I' band unusually shifted below 1600 cm(-1). This distinct infrared feature has been attributed to the presence of bifurcated hydrogen bonds coupling C═O and N-D (N-H) groups of the main chains to glutamate side chains. Here, we investigate how decreasing the chain length of PLGA affects its capacity to form ß2-fibrils. A series of acidified aqueous solutions of synthetic (l-Glu)n peptides (n ≈ 200, 10, 6, 5, 4, and 3) were incubated at high temperature. We observed that n = 4 is the critical chain length for which formation of aggregates with the ß2-like infrared features is still observed under such conditions. Interestingly, according to atomic force microscopy (AFM), the self-assembly of (L-Glu)n chains varying vastly in length produces fibrils with rather uniform diameters of approximately 4-6 nm. Kinetic experiments on (L-Glu)5 and (L-Glu)200 peptides indicate that the fibrillation is significantly accelerated not only in the presence of homologous seeds but also upon cross-seeding, suggesting thereby a common self-assembly theme for (L-Glu)n chains of various lengths. Our results are discussed in the context of mechanisms of amyloidogenic fibrillation of homopolypeptides.

Comparison of the separation performances of cinchona alkaloid-based zwitterionic stationary phases in the enantioseparation of ß2- and ß3-amino acids.

The enantiomers of twelve unusual ß2- and ß3-homoamino acids containing the same side-chains were separated on chiral stationary phases containing a quinine- or quinidine-based zwitterionic ion-exchanger as chiral selector. The effects of the mobile phase composition, the nature and concentration of the acid and base additives and temperature on the separations were investigated. The changes in standard enthalpy, ∆(∆H°), entropy, ∆(∆S°), and free energy, ∆(∆G°), were calculated from the linear van't Hoff plots derived from the ln α vs. 1/T curves in the studied temperature range (10-50 °C). The values of the thermodynamic parameters depended on the nature of the selectors, the structures of the analytes, and the positions of the substituents on the analytes. A comparison of the zwitterionic stationary phases revealed that the quinidine-based ZWIX(-)™ column exhibited much better selectivity for both ß2- and ß3-amino acids than the quinine-based ZWIX(+)™ column, and the separation performances of both the ZWIX(+)™ and ZWIX(-)™ columns were better for ß2-amino acids. The elution sequence was determined in some cases and was observed to be R < S and S < R on the ZWIX(+)™ and ZWIX(-)™ columns, respectively.

De novo designed self-assembling helicomimetic lipooligoureas with antibacterial activity.

The overuse of antibiotics has led to a rise in infections caused by multidrug-resistant bacteria, resulting in a need for new antibacterial compounds with different modes of action. In this paper, we describe a new class of compounds called lipooligoureas, which are foldamer-based mimetics of antimicrobial lipopeptides. The lipooligoureas consist of an acyl chain connected to the N-terminus of an oligourea head group that exhibits a well-defined 2.5-helix secondary structure, which is further stabilized by the attachment of the lipophilic chain to the oligourea moiety. These compounds meet the established criteria for membranolytic compounds by possessing an amphiphilic structure that promotes the internalization and partitioning of the molecules into the lipid membrane. The presence of positively charged urea residues promotes electrostatic interactions with the negatively charged bacterial membrane. The subtle structural differences in oligourea head group influence the compounds' aggregation behavior, with the number and position of positively charged urea residues correlating with their aggregation ability. The biological activity of these compounds in inhibiting bacterial growth is correlated with their ability to aggregate, with stronger antibacterial properties exhibited by those that aggregate more easily. However, the concentration inhibiting bacterial growth is significantly lower than the critical aggregation concentration values, suggesting that the mechanism of action involves the monomeric forms of lipooligoureas. Nonetheless, a mechanism based on membrane-induced aggregation cannot be ruled out. The lipooligoureas exhibit higher activity towards Gram-positive bacteria than against Gram-negative bacteria, which is indicative of certain selectivity of these compounds. It is also demonstrated that lipooligoureas exhibit increased stability against proteolytic degradation in human blood serum.

Scandium-44 Radiolabeled Peptide and Peptidomimetic Conjugates Targeting Neuropilin-1 Co-Receptor as Potential Tools for Cancer Diagnosis and Anti-Angiogenic Therapy.

Pathological angiogenesis, resulting from an imbalance between anti- and pro-angiogenic factors, plays a pivotal role in tumor growth, development and metastasis. The inhibition of the angiogenesis process by the VEGF/VEGFR-2/NRP-1 pathway raises interest in the search for such interaction inhibitors for the purpose of the early diagnosis and treatment of angiogenesis-dependent diseases. In this work we designed and tested peptide-based radiocompounds that selectively bind to the neuropilin-1 co-receptor and prevent the formation of the pro-angiogenic VEGF-A165/NRP-1 complex. Three biomolecules, A7R and retro-inverso DR7A peptides, and the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg (K4R), conjugated with macrocyclic chelator through two linkers' types, were labeled with theranostic scandium-44 radionuclide, and studied in vitro as potential targeted radiopharmaceuticals. ELISA (enzyme-linked immunosorbent assay) studies showed no negative effect of the introduced biomolecules' changes and high NRP-1 affinity in the case of A7R- and K4R-radiocompounds and a lack affinity for DR7A-radiocompounds. All radiopeptides showed a hydrophilic nature as well as high stability against ligand exchange reactions in cysteine/histidine solutions. Unfortunately, all radiocompounds showed unsatisfactory nano-scale stability in human serum, especially for use as therapeutic radioagents. Further work is ongoing and focused on the search for angiogenesis inhibitors that are more human serum stable.

Electron transfer across α-helical peptide monolayers: importance of interchain coupling.

Four helical peptides with the general formula (Boc)-Cys-(S-Acm)-(Ala-Leu)(n)-NH-(CH(2))(2)-SH (n = 4-7) were synthesized and further used for the preparation of self-assembled monolayers (SAMs) on gold substrates. The electron-transfer behavior of these systems was probed using current-sensing atomic force microscopy (CS-AFM). It was found that the electron transmission through SAMs of helical peptides trapped between an AFM conductive tip and a gold substrate occurs very efficiently and that the distance dependence obeys the exponential trend with a decay constant of 4.6 nm(-1). This result indicates that the tunneling mechanism is operative in this case. Conductance measurements under mechanical stress show that peptide-mediated electron transmission occurs with the possible contribution of intermolecular electron tunneling between adjacent helices. It was also demonstrated that an external electric field applied between metallic contacts can affect the structure of the peptide SAM by changing its thickness. This explains the asymmetry of the current-voltage response of metal-monolayer-metal junction.

Synthesis, Physicochemical and Biological Study of Gallium-68- and Lutetium-177-Labeled VEGF-A165/NRP-1 Complex Inhibitors Based on Peptide A7R and Branched Peptidomimetic.

Neuropilin-1 (NRP-1) is a surface receptor found on many types of cancer cells. The overexpression of NRP-1 and its interaction with vascular endothelial growth factor-165 (VEGF165) are associated with tumor growth and metastasis. Therefore, compounds that block the VEGF165/NRP-1 interaction represent a promising strategy to image and treat NRP-1-related pathologies. The aim of the presented work was to design and synthesize radioconjugates of two known peptide-type inhibitors of the VEGF165/NRP-1 complex: A7R peptide and its shorter analog, the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg. Both peptide-type inhibitors were coupled to a radionuclide chelator (DOTA) via a linker (Ahx) and so radiolabeled with Ga-68 and Lu-177 radionuclides, for diagnostic and therapeutic uses, respectively. The synthesized radioconjugates were tested for their possible use as theranostic-like radiopharmaceuticals for the imaging and therapy of cancers that overexpress NRP-1. The obtained results indicate good efficiency of the radiolabeling reaction and satisfactory stability, at least 3t1/2 for the 68Ga- and 1t1/2 for the 177Lu-radiocompounds, in solutions mimicking human body fluids. However, enzymatic degradation of both the studied inhibitors caused insufficient stability of the radiocompounds in human serum, indicating that further modifications are needed to sufficiently stabilize the peptidomimetics with inhibitory properties against VEGF165/NRP-1 complex formation.

The Role of VEGF Receptors as Molecular Target in Nuclear Medicine for Cancer Diagnosis and Combination Therapy.

One approach to anticancer treatment is targeted anti-angiogenic therapy (AAT) based on prevention of blood vessel formation around the developing cancer cells. It is known that vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEGFRs) play a pivotal role in angiogenesis process; hence, application of angiogenesis inhibitors can be an effective approach in anticancer combination therapeutic strategies. Currently, several types of molecules have been utilised in targeted VEGF/VEGFR anticancer therapy, including human VEGF ligands themselves and their derivatives, anti-VEGF or anti-VEGFR monoclonal antibodies, VEGF binding peptides and small molecular inhibitors of VEGFR tyrosine kinases. These molecules labelled with diagnostic or therapeutic radionuclides can become, respectively, diagnostic or therapeutic receptor radiopharmaceuticals. In targeted anti-angiogenic therapy, diagnostic radioagents play a unique role, allowing the determination of the emerging tumour, to monitor the course of treatment, to predict the treatment outcomes and, first of all, to refer patients for AAT. This review provides an overview of design, synthesis and study of radiolabelled VEGF/VEGFR targeting and imaging agents to date. Additionally, we will briefly discuss their physicochemical properties and possible application in combination targeted radionuclide tumour therapy.

Interactions of Linear Analogues of Battacin with Negatively Charged Lipid Membranes.

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this context, amphiphilic lipopeptides belong to the class of the compounds which may fulfill this requirement. In this paper, we describe two linear analogues of battacin with modified acyl chains to tune the balance between the hydrophilic and hydrophobic portion of lipopeptides. We demonstrate that both compounds display antimicrobial activity with the lowest values of minimum inhibitory concentrations found for Gram-positive pathogens. Therefore, their mechanism of action was evaluated on a molecular level using model lipid films mimicking the membrane of Gram-positive bacteria. The surface pressure measurements revealed that both lipopeptides show ability to bind and incorporate into the lipid monolayers, resulting in decreased ordering of lipids and membrane fluidization. Atomic force microscopy (AFM) imaging demonstrated that the exposure of the model bilayers to lipopeptides leads to a transition from the ordered gel phase to disordered liquid crystalline phase. This observation was confirmed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) results, which revealed that lipopeptide action causes a substantial increase in the average tilt angle of lipid acyl chains with respect to the surface normal to compensate for lipopeptide insertion into the membrane. Moreover, the peptide moieties in both molecules do not adopt any well-defined secondary structure upon binding with the lipid membrane. It was also observed that a small difference in the structure of a lipophilic chain, altering the balance between hydrophobic and hydrophilic portion of the molecules, results in different insertion depth of the active compounds.

Novel bifunctional hybrid compounds designed to enhance the effects of opioids and antagonize the pronociceptive effects of nonopioid peptides as potent analgesics in a rat model of neuropathic pain.

ABSTRACT: The purpose of our work was to determine the role of nonopioid peptides derived from opioid prohormones in sensory hypersensitivity characteristics of neuropathic pain and to propose a pharmacological approach to restore the balance of these endogenous opioid systems. Nonopioid peptides may have a pronociceptive effect and therefore contribute to less effective opioid analgesia in neuropathic pain. In our study, we used unilateral chronic constriction injury (CCI) of the sciatic nerve as a neuropathic pain model in rats. We demonstrated the pronociceptive effects of proopiomelanocortin- and proenkephalin-derived nonopioid peptides assessed by von Frey and cold plate tests, 7 to 14 days after injury. The concentration of proenkephalin-derived pronociceptive peptides was increased more robustly than that of Met-enkephalin in the ipsilateral lumbar spinal cord of CCI-exposed rats, as shown by mass spectrometry, and the pronociceptive effect of one of these peptides was blocked by an antagonist of the melanocortin 4 (MC4) receptor. The above results confirm our hypothesis regarding the possibility of creating an analgesic drug for neuropathic pain based on enhancing opioid activity and blocking the pronociceptive effect of nonopioid peptides. We designed and synthesized bifunctional hybrids composed of opioid (OP) receptor agonist and MC4 receptor antagonist (OP-linker-MC4). Moreover, we demonstrated that they have potent and long-lasting antinociceptive effects after a single administration and a delayed development of tolerance compared with morphine after repeated intrathecal administration to rats subjected to CCI. We conclude that the bifunctional hybrids OP-linker-MC4 we propose are important prototypes of drugs for use in neuropathic pain.

Chymase Dependent Pathway of Angiotensin II Generation and Rapeseed Derived Peptides for Antihypertensive Treatment of Spontaneously Hypertensive Rats.

The contribution of chymase, one of the enzymes responsible for angiotensin II generation in non-ACE pathway, remains unclear in the development of hypertension. The aim of the study was to investigate chymase inhibition as potential antihypertensive therapy in spontaneously hypertensive rats (SHR). To block chymase we employed chymostatin, a commercial inhibitor, and new analogues of rapeseed-derived peptides, VWIS and RIY. These simple and easy to obtain peptides not only block chymase, but also possess weak activity to inhibit ACE. This is a first attempt to evaluate the impact of chronic administration of selected inhibitors on blood pressure of SHR in two phases of hypertension. Male SHR (6 or 16 weeks old) were treated daily for two weeks with chymostatin (CH; 2 mg/kg/day), the peptides VWIS (12.5 mg/kg/day) or RIY (7.5 mg/kg/day); control groups received chymostatin solvent (0.15% DMSO in saline) or peptide solvent (saline). The substances were administered intravenously to conscious animals via a chronically cannulated femoral vein. Systolic blood pressure (SBP) was measured by telemetry. Metabolic parameters were measured weekly, and tissue samples were harvested after two weeks of treatment. None of the administered chymase inhibitors affected the development of hypertension in young rats. Only RIY exhibited beneficial properties when administered in the established phase of hypertension: SBP decreased from 165 ± 10 to 157 ± 7 mmHg while the excretion of nitric oxide metabolites increased significantly. The glomerulosclerosis index was lower after RIY treatment in both age groups (significant only in young rats 0.29 ± 0.05 vs 0.48 ± 0.04 in the control group; p < 0.05). Hence, it seems that peptide RIY exhibits some positive effect on renal morphology. The results obtained suggest that the peptide RIY may be a useful tool in the treatment of hypertension, especially in cases when ACE inhibitors are not effective.

Enantioseparation of ß2-amino acids by liquid chromatography using core-shell chiral stationary phases based on teicoplanin and teicoplanin aglycone.

Enantioseparation of nineteen ß2-amino acids has been performed by liquid chromatography on chiral stationary phases based on native teicoplanin and teicoplanin aglycone covalently bonded to 2.7 µm superficially porous silica particles. Separations were carried out in unbuffered (water/methanol), buffered [aqueous triethylammonium acetate (TEAA)/methanol] reversed-phase (RP) mode, and in polar-ionic (TEAA containing acetonitrile/methanol) mobile phases. Effects of pH in the RP mode, acid and salt additives, as well as counter-ion concentrations on chromatographic parameters have been studied. The structure of selectands (ß2-amino acids possessing aliphatic or aromatic side chains) and selectors (native teicoplanin or teicoplanin aglycone) was found to have a considerable influence on separation performance. Analysis of van Deemter plots and determination of thermodynamic parameters were performed to further explore details of the separation performance.

Multifunctional Enkephalin Analogs with a New Biological Profile: MOR/DOR Agonism and KOR Antagonism.

In our previous studies, we developed a series of mixed MOR/DOR agonists that are enkephalin-like tetrapeptide analogs with an N-phenyl-N-piperidin-4-ylpropionamide (Ppp) moiety at the C-terminus. Further SAR study on the analogs, initiated by the findings from off-target screening, resulted in the discovery of LYS744 (6, Dmt-DNle-Gly-Phe(p-Cl)-Ppp), a multifunctional ligand with MOR/DOR agonist and KOR antagonist activity (GTPγS assay: IC50 = 52 nM, Imax = 122% cf. IC50 = 59 nM, Imax = 100% for naloxone) with nanomolar range of binding affinity (Ki = 1.3 nM cf. Ki = 2.4 nM for salvinorin A). Based on its unique biological profile, 6 is considered to possess high therapeutic potential for the treatment of chronic pain by modulating pathological KOR activation while retaining analgesic efficacy attributed to its MOR/DOR agonist activity.