Common and varied molecular responses of Escherichia coli to five different inhibitors of the lipopolysaccharide biosynthetic enzyme LpxC

A promising yet clinically unexploited antibiotic target in difficult-to-treat Gram-negative bacteria is LpxC, the key enzyme in the biosynthesis of lipopolysaccharides, which are the major constituents of the outer membrane. Despite the development of dozens of chemically diverse LpxC inhibitor molecules, it is essentially unknown how bacteria counteract LpxC inhibition. Our study provides comprehensive insights into the response against five different LpxC inhibitors. All compounds bound to purified LpxC from Escherichia coli. Treatment of E. coli with these compounds changed the cell shape and stabilized LpxC suggesting that FtsH-mediated proteolysis of the inactivated enzyme is impaired. LpxC inhibition sensitized E. coli to vancomycin and rifampin, which poorly cross the outer membrane of intact cells. Four of the five compounds led to an accumulation of lyso-phosphatidylethanolamine, a cleavage product of phosphatidylethanolamine, generated by the phospholipase PldA. The combined results suggested an imbalance in lipopolysaccharides and phospholipid biosynthesis, which was corroborated by the global proteome response to treatment with the LpxC inhibitors. Apart from LpxC itself, FabA and FabB responsible for the biosynthesis of unsaturated fatty acids were consistently induced. Upregulated compound-specific proteins are involved in various functional categories, such as stress reactions, nucleotide, or amino acid metabolism and quorum sensing. Our work shows that antibiotics targeting the same enzyme do not necessarily elicit identical cellular responses. Moreover, we find that the response of E. coli to LpxC inhibition is distinct from the previously reported response in Pseudomonas aeruginosa.

(p)ppGpp and moonlighting RNases influence the first step of lipopolysaccharide biosynthesis in Escherichia coli

The outer membrane (OM) protects Gram-negative bacteria from harsh environmental conditions and provides intrinsic resistance to many antimicrobial compounds. The asymmetric OM is characterized by phospholipids in the inner leaflet and lipopolysaccharides (LPS) in the outer leaflet. Previous reports suggested an involvement of the signaling nucleotide ppGpp in cell envelope homeostasis in Escherichia coli. Here, we investigated the effect of ppGpp on OM biosynthesis. We found that ppGpp inhibits the activity of LpxA, the first enzyme of LPS biosynthesis, in a fluorometric in vitro assay. Moreover, overproduction of LpxA resulted in elongated cells and shedding of outer membrane vesicles (OMVs) with altered LPS content. These effects were markedly stronger in a ppGpp-deficient background. We further show that RnhB, an RNase H isoenzyme, binds ppGpp, interacts with LpxA, and modulates its activity. Overall, our study uncovered new regulatory players in the early steps of LPS biosynthesis, an essential process with many implications in the physiology and susceptibility to antibiotics of Gram-negative commensals and pathogens.

LapB (YciM) orchestrates protein-protein interactions at the interface of lipopolysaccharide and phospholipid biosynthesis

The outer membrane (OM) of Gram-negative bacteria functions as an essential barrier and is characterized by an asymmetric bilayer with lipopolysaccharide (LPS) in the outer leaflet. The enzyme LpxC catalyzes the first committed step in LPS biosynthesis. It plays a critical role in maintaining the balance between LPS and phospholipids (PL), which are both derived from the same biosynthetic precursor. The essential inner membrane proteins YejM (PbgA, LapC), LapB (YciM), and the protease FtsH are known to account for optimal LpxC levels, but the mechanistic details are poorly understood. LapB is thought to be a bi-functional protein serving as an adaptor for FtsH-mediated turnover of LpxC and acting as a scaffold in the coordination of LPS biosynthesis. Here, we provide experimental evidence for the physical interaction of LapB with proteins at the biosynthetic node from where the LPS and PL biosynthesis pathways diverge. By a total of four in vivo and in vitro assays, we demonstrate protein-protein interactions between LapB and the LPS biosynthesis enzymes LpxA, LpxC, and LpxD, between LapB and YejM, the anti-adaptor protein regulating LapB activity, and between LapB and FabZ, the first PL biosynthesis enzyme. Moreover, we uncovered a new adaptor function of LapB in destabilizing not only LpxC but also LpxD. Overall, our study shows that LapB is a multi-functional protein that serves as a protein-protein interaction hub for key enzymes in LPS and PL biogenesis presumably by virtue of multiple tetratricopeptide repeat (TPR) motifs in its cytoplasmic C-terminal region.

An Integrated Proteomic Approach Uncovers Novel Substrates and Functions of the Lon Protease in Escherichia coli

Controlling the cellular abundance and proper function of proteins by proteolysis is a universal process in all living organisms. In Escherichia coli, the ATP-dependent Lon protease is crucial for protein quality control and regulatory processes. To understand how diverse substrates are selected and degraded, unbiased global approaches are needed. We employed a quantitative Super-SILAC (stable isotope labeling with amino acids in cell culture) mass spectrometry approach and compared the proteomes of a lon mutant and a strain producing the protease to discover Lon-dependent physiological functions. To identify Lon substrates, we took advantage of a Lon trapping variant, which is able to translocate substrates but unable to degrade them. Lon-associated proteins were identified by label-free LC-MS/MS. The combination of both approaches revealed a total of 14 novel Lon substrates. Besides the identification of known pathways affected by Lon, for example, the superoxide stress response, our cumulative data suggests previously unrecognized fundamental functions of Lon in sulfur assimilation, nucleotide biosynthesis, amino acid and central energy metabolism.

Sequence and Length Recognition of the C-terminal Turnover Element of LpxC, a Soluble Substrate of the Membrane-bound FtsH Protease

The membrane-anchored FtsH protease is essential in Escherichia coli as it adjusts the cellular amount of LpxC, the key enzyme in lipopolysaccharide (LPS) biosynthesis. Both accumulation and depletion of LpxC are toxic to E. coli. By continuous proteolysis of LpxC, FtsH maintains a low concentration of LpxC and, hence, the proper equilibrium between LPS and phospholipids. The C terminus of LpxC is required for turnover. By adding this tail to glutathione-S-transferase (GST) we show that it is necessary but not sufficient for FtsH-mediated degradation. A detailed mutational analysis revealed six non-polar residues in the C terminus of LpxC that are critical for degradation. Alteration of the C-terminal AVLA motif towards the SsrA-like sequence ALAA directed LpxC to other cellular proteases reinforcing the importance of the C-terminal tail for targeting to FtsH. Short C-terminal truncations stabilized LpxC. Most mutations in the C terminus of LpxC left its enzymatic activity intact as was shown by growth assays, microscopy and 2-keto-3-deoxyoctonate (KDO) determination. The critical length of the turnover element was defined by internal deletions. A C-terminal tail of about 20 amino acids length is required for proteolysis of LpxC by FtsH.

Structure-function studies of linear and cyclized peptide antagonists of the GnRH receptor

Structurally new analogs of the peptidic GnRH receptor antagonist Cetrorelix as well as conformationally constrained cyclized deca- or pentapeptides were synthesized and selected peptides evaluated comprehensively. To understand how structural variations of the antagonistic peptide effect pharmacodynamic properties, binding affinities and antagonistic potencies toward the human and rat GnRH receptor were determined. Whereas large substituents in position 6 of linear peptides are compatible with high binding affinity (K(D) < 0.5 nM), all cyclized peptides except the cyclo[3-10] analog D-52391 depicted low binding affinity (K(D) > 10 nM). Binding affinity and antagonistic potency in vitro correlated for all peptides and surprisingly no discrimination between human and rat receptor proteins was observed. Since receptor residues W(101) and N(102) are involved in agonist and antagonist binding, equally potent but structurally different antagonists were tested for binding to the respective W(101)A and N(102)A mutants. In contrast to linear decapeptides, residues N(102) and W(101) are not involved in binding of D-23938 and W(101) is the critical residue for D-52391 binding. We conclude that although equally potent, peptidic GnRH receptor antagonists do have distinct interactions within the ligand binding pocket. Finally, selected antagonists were tested for testosterone suppression in male rats. The duration of testosterone suppression below castration levels differed largely from 1 day for Ganirelix to 27 days for D-23487. Systemic availability became evident as the most important parameter for in vivo efficacy.

Stability of several LHRH antagonists against proteolytic enzymes and identification of degradation products by mass spectrometry

In this study stabilities of several LHRH antagonists against proteolytic enzymes are compared. For the enzymatic tests 15 proteases which differ in both substrate specificity and pH optimum were selected. The cyclic and two linear antagonists proved to be extraordinarily stable against the enzymes used over an incubation time of 50 h. Some degradation products were identified by high-performance liquid chromatography combined with mass spectrometry.

Changes of intracellular calcium, fatty acids and phospholipids during miltefosine-induced apoptosis monitored by fluorescence- and 13C NMR-spectroscopy

The alkylphosphocholine Miltefosine (hexadecylphosphocholine, HePC) induces apoptosis in human epithelial KB cells, whereas no such effect can be observed in a resistant clone (KBres). Its mode of action is mediated via the cell membrane, whereas the mechanism is still widely unknown. The use of various spectroscopic methods (fluorescence spectroscopy with Fura-2/AM on viable cells, 13C NMR spectroscopy on lipid extracts) reveals osmotic and metabolic changes in HePC treated sensitive cells. Intracellular free Ca(2+)-concentration increased over 300% of control in apoptotic cells, whereas KBres cells showed only a minor increase and no morphological response typical for apoptosis. The Ca(2+)-influx was mediated via calcium channels in the cell membrane. The HePC-induced influx is prevented by Gd3+, which blocks those calcium channels. Cells, grown in Ca(2+)-free medium, showed no apoptotic behaviour after treatment with HePC. If apoptosis was induced, an increased fatty acid and subsequent phospholipid biosynthesis was observed. This effect seems to be a specific marker of apoptosis in KB cells.

New N-(pyridin-4-yl)-(indol-3-yl)acetamides and propanamides as antiallergic agents

A series of new N-(pyridin-4-yl)-(indol-3-yl)alkylamides 44-84 has been prepared in the search of novel antiallergic compounds. Synthesis of the desired ethyl (2-methyindol-3-yl)acetates 1-4 was achieved by indolization under Fischer conditions; Japp-Klingemann method followed by 2-decarboxylation afforded the ethyl (indol-3-yl)alkanoates 17-25. Amidification was successfully carried out by condensation of the corresponding acids or their N-aryl(methyl) derivatives with 4-aminopyridine promoted by 2-chloro-1-methylpyridinium iodide. Efforts to improve the antiallergic potency of the title series by variation of the indole substituents (R1, R2, R) and the length of the alkanoic chain (n = 1, 2, 3) led to the selection of N-(pyridin-4-yl)-[1-(4-fluorobenzyl)indol-3-yl]acetamide 45, out of 41 compounds. This amide was 406-fold more potent than astemizole in the ovalbumin-induced histamine release assay, using guinea pig peritoneal mast cells, with an IC50 = 0.016 microM. Its inhibitory activity in IL-4 production test from Th-2 cells was identical to that of the reference histamine antagonist (IC50 = 8.0 microM) and twice higher in IL-5 assay: IC50 = 1.5 and 3.3 microM, respectively. In vivo antiallergic activity evaluation confirmed efficiency of 45 in sensitized guinea pig late phase eosinophilia inhibition, after parenteral and oral administration at 5 and 30 mg/kg, respectively. Its efficiency in inhibition of microvascular permeability was assessed in two rhinitis models; ovalbumin and capsaicin-induced rhinorrhea could be prevented after topical application of submicromolar concentrations of 45 (IC50 = 0.25 and 0.30 microM); and it also exerted significant inhibitory effect in the first test after iv and oral administration, with ID50 = 0.005 and 0.46 mg/kg.

New N-(pyridin-4-yl)-(indol-3-yl)acetamides and propanamides as antiallergic agents

A series of new N-(pyridin-4-yl)-(indol-3-yl)alkylamides 44-84 has been prepared in the search of novel antiallergic compounds. Synthesis of the desired ethyl (2-methyindol-3-yl)acetates 1-4 was achieved by indolization under Fischer conditions; Japp-Klingemann method followed by 2-decarboxylation afforded the ethyl (indol-3-yl)alkanoates 17-25. Amidification was successfully carried out by condensation of the corresponding acids or their N-aryl(methyl) derivatives with 4-aminopyridine promoted by 2-chloro-1-methylpyridinium iodide. Efforts to improve the antiallergic potency of the title series by variation of the indole substituents (R1, R2, R) and the length of the alkanoic chain (n = 1, 2, 3) led to the selection of N-(pyridin-4-yl)-[1-(4-fluorobenzyl)indol-3-yl]acetamide 45, out of 41 compounds. This amide was 406-fold more potent than astemizole in the ovalbumin-induced histamine release assay, using guinea pig peritoneal mast cells, with an IC50 = 0.016 microM. Its inhibitory activity in IL-4 production test from Th-2 cells was identical to that of the reference histamine antagonist (IC50 = 8.0 microM) and twice higher in IL-5 assay: IC50 = 1.5 and 3.3 microM, respectively. In vivo antiallergic activity evaluation confirmed efficiency of 45 in sensitized guinea pig late phase eosinophilia inhibition, after parenteral and oral administration at 5 and 30 mg/kg, respectively. Its efficiency in inhibition of microvascular permeability was assessed in two rhinitis models; ovalbumin and capsaicin-induced rhinorrhea could be prevented after topical application of submicromolar concentrations of 45 (IC50 = 0.25 and 0.30 microM); and it also exerted significant inhibitory effect in the first test after iv and oral administration, with ID50 = 0.005 and 0.46 mg/kg.

Polymorphism and desolvation of flupirtine maleate

Crystallizates of the analgesic agent flupirtine maleate (Katadolon; ASTA Medica, Dresden, Germany) obtained from isopropanol are examined by X-ray diffractometry, polarization microscopy and thermoanalysis. Depending on the crystallizing conditions, the modifications A and B as well as an isopropanol solvate are observed. The inversion temperature A-->B of the enantiotropic modifications is 164 degrees C (differential scanning calorimetry (DSC) onset). During thermal desolvation, modification B is formed well below the inversion temperature. In concentrated isopropanol suspensions, the solvate and modification B are rapidly transformed into modification A. It is shown how phase-pure products consisting of modification A, which is better wettable with water and stable at room temperature, can be obtained.

Synthesis of Dolastatin 15 mimetic peptoids

Eight peptoids have been synthesized as peptidomimetics of the cytostatic Dolastatin 15, a depsipeptide isolated from the Indian sea hare Dolabella auricularia. The compounds have been tested against several human cancer cell lines and did not show any cytostatic properties.

1,5-Disubstituted indazol-3-ols with anti-inflammatory activity

A series of new indazol-3-ol derivatives was synthesized. Some of these compounds exhibit interesting anti-inflammatory activities in various models of inflammation. 5-Methoxy-1-[quinoline-2-yl-methoxy)-benzyl]-1H-indazol-3-ol (27) strongly inhibits the oxidation of arachidonic acid to 5-hydroperoxyeicosatetraenoic acid catalyzed by 5-lipoxygenase (IC50 = 44 nM). 27 also inhibits the contraction of sensitized guinea pig tracheal segments (IC50 = 2.9 microM). In guinea pigs treated with 27 (1 mg/kg i.p.) 2 h before antigen provocation, there was a marked inhibition (47%) of the antigen-induced airway eosinophilia. After topical application of 1 microgram/ear 27 inhibits the arachidonic acid induced mouse ear edema (41%).

Small peptide libraries: combinatorial split-mix synthesis followed by combinatorial amino acid analysis of selected variants

Peptides from small combinatorial libraries, covalently attached to polymeric TentaGel beads, can be directly sequenced using amino acid analysis. For libraries with restricted diversity, generated by the split-mix synthesis method, the amino acids on a selected single bead identified by pre-column derivatization with o-phthaldialdehyde (OPA) correlate directly with the sequence of a given peptide. This is shown on a tripeptide (343 different compounds) and a tetrapeptide (4096 different compounds) library. This method allows for rapid peptide sequence determination without relying on complex encoding strategies.

D-21266, a new heterocyclic alkylphospholipid with antitumour activity

The aim of this study was to determine the antitumour effects of D-21266 in a rodent tumour model. Hexadecylphosphocholine (INN: Miltefosine) represents the first anticancer agent which was specifically formulated for topical use in cancer patients. The development as an oral drug was hampered by the gastrointestinal toxicity. Hexadecylphosphocholine derivatives were sought with a better therapeutic index. Octadecyl-(1,1-dimethyl-4-piperidylio) phosphate (D-21266) was identified as a suitable candidate. This compound is highly active in vitro inhibiting the growth of a number of human cancer cell lines. Mammary carcinomas were induced in Sprague-Dawley rats using DMBA, and oral doses of D-21266, in various schedules, were given to the animals. A high antineoplastic potency was observed without inducing loss of body weight at highly effective doses. The antitumour effect could be enhanced by introducing a dose schedule consisting of a high loading dose followed by a low maintenance dose, both of which are only marginally active when given alone. Therefore, D-21266 with its favourable pharmacological and toxicological profile, warrants evaluation in the clinic. However, the concept of clinical trials requires new approaches to dose finding and response evaluation, because the dose-response relationship of this compound is distinctly different from that of classical cytostatic agents.

Alkylphosphate esters as inhibitors of phospholipase D

Alkylphosphate esters were shown to be potent inhibitors of phospholipase D. Using phosphatidyl choline/sodium dodecylsulfate (2:1) as substrate, IC50 values were determined for alkylphosphocholines of different chain length (C10-C18) and for various octadecylphosphate esters with different polar head groups. The inhibitory potency strongly increased with increasing chain length of the alkyl chain. The substitution of choline for heterocyclic nitrogen compounds or for 2-trimethylarsonio-ethanol also affected the inhibition of phospholipase D. Octadecylphosphocholine proved to be the most efficient inhibitor (IC50 = 6.4 microM).

Early stage monitoring of miltefosine induced apoptosis in KB cells by multinuclear NMR spectroscopy

Synthetic ether lipids, like miltefosine (hexadecylphosphocholine), an alkylphosphocholine, are antineoplastic agents in vitro and in vivo. Their mode of action is mediated via the cell membrane, but the mechanism is still unclear. Miltefosine induces apoptosis in human epithelial KB cells, but slows down only proliferation in rat C6 glioma cells. NMR spectroscopy on lipid extracts reveals increased diacylglycerol and triacyglycerol biosynthesis in KB cells prior to DNA fragmentation indicating a CTP:phosphocholine-cytidylyl-transferase (CT) inhibition by the drug. Although C6 cells were morphologically affected by alterations in phospholipid composition and metabolism by a long term treatment (23 days) with the drug, no persistent diacylglycerol increase is observed.

D-23129: a new anticonvulsant with a broad spectrum activity in animal models of epileptic seizures

The anticonvulsant activity of the novel drug D-23129 (N-(2-amino-4-(4-fluorobenzylamino)phenyl)carbamic acid ethyl ester) was evaluated in animal models of epileptic seizures. D-23129 was active after oral and intraperitoneal administration in rats and mice in a range of anticonvulsant tests at nontoxic doses. The compound was active against electrically induced seizures (MES, ED50 rat p.o. = 2.87 mg/kg), against seizures induced chemically by pentylenetetrazole (s.c. PTZ, ED50 mouse p.o. = 13.5 mg/kg), picrotoxin and N-methyl-D-aspartate (NMDA) and in a genetic animal model, the DBA/2 mouse. It was not active against seizures induced by bicuculline and strychnine. Motor impairment, evaluated with the rotarod test and by observation in the open field, was minimal at doses showing anticonvulsant activity. D-23129 was very effective in elevating the threshold for electrically and chemically induced seizures. Considering the dose increasing the MES threshold by 50% (TID50 mouse i.p. = 1.6 mg/kg; TID50 rat i.p. = 0.72 mg/kg) and the TD50 obtained in the rotarod test, the protective index of D-23129 is better than that of valproate and phenytoin. During 14 days chronic oral treatment with 15 mg/kg, no development of tolerance was observed. D-23129 thus presents an orally active, safe, broad spectrum anticonvulsant agent, which is structurally unrelated to anticonvulsants currently used. We expect that D-23129 will improve the treatment of refractory seizures in humans.

Evaluation of the in vitro and in vivo activity of the L-, D,L- and D-Cit6 forms of the LH-RH antagonist Cetrorelix (SB-75)

The objective of this study was to examine the in vivo and in vitro gonadotropin-inhibiting potencies, edematogenic activities and the receptor binding affinities of the D-Cit6, D,L-Cit6 and L-Cit6 forms of the LH-RH antagonist Cetrorelix (SB-75) [Ac-D-Nal(2)1,D-Phe(4Cl)2,D-Pal(3)3,D-Cit6,D-Ala10]LH- RH. In order to demonstrate the suppressive effects of two different diastereomers of SB-75 and their racemic mixture on LH and FSH release, [D-Cit6] SB-75 was injected subcutaneously in doses of 2.5 and 10 micrograms/rat, [D,L-Cit6]-SB-75 in doses of 5 and 20 micrograms/rat and [L-Cit6] SB-75 in doses of 12.5 and 50 micrograms/rat to castrated male rats. Two hours after administration, there was no difference in LH levels between rats injected with the L-form and control animals, indicating a low activity and/or a rapid enzymatic degradation of this peptide. The (1:1) diastereomeric mixture was only about half as potent in suppression of LH release compared to [D-Cit6] SB-75. Serum FSH levels were suppressed significantly (p < 0.01) for more than 48 h after the administration of 10 micrograms [D-Cit6] SB-75 and 20 micrograms of [D,L-Cit6] SB-75, respectively. [D-Cit6] SB-75 administered at a dose of 2 micrograms/rat induced 100% inhibition of ovulation, while 4 micrograms/rat of the D,L-Cit6 peptide were necessary to produce the same effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and antitumor activity of two ifosfamide analogs with a five-membered ring

Two ifosfamide (CAS 3778-73-2) analogs with a five-membered ring, i.e. the oxazaphospholidine derivatives 6 and 7, were synthesized and their cytotoxic activity in vitro, acute toxicity and antitumor activity in vivo determined in comparison with the oxazaphorinane ifosfamide 1. The observed low biological activity gives evidence that both, the six-membered oxazaphosphorinane ring and the two N-2-chloroethyl-side chains are necessary for the generation of the ultimate alkylator, i.e. the ifosfamide mustard 5.

Chemical and biological evaluation of hydrolysis products of cyclophosphamide

31P NMR spectroscopy was used to study the products of the decomposition of cyclophosphamide (1) in buffered solutions at pH's ranging between 1.2 and 8.6 at 20 degrees C and at pH 7.4 at 37 degrees C. At pH 1.2, 1 undergoes a rapid breakdown (t1/2 = 1.4 days) of the two P-N bonds, giving compounds 2 [HN(CH2CH2Cl)2] and 3 [H2N(CH2)3OP(O)(OH)2] as hydrochlorides. No intermediates were detected. At pH's between 5.4 and 8.6, hydrolysis of 1 during 17 days leads to the sole and previously unknown nine-membered ring compound 13. 13 results from the intramolecular alkylation of 1 giving the bicyclic compound 7 followed by the exothermal hydrolytic breakdown of the P-N bond of its six-membered ring. At pH 2.2 and 3.4, the two hydrolytic pathways coexist since, beside compounds 2 and 3, the hydrochloride of compound 9 [Cl(CH2)2NH(CH2)2NH(CH2)3OP(O)(OH)2] is formed, resulting from the acid-catalyzed breakdown of the P-N bond in the nine-membered ring compound 13. At pH 2.2, the presence of chloride ion affected neither the stability of 1 nor the contribution of the two competing hydrolytic pathways. At pH's ranging from 3.4 to 8.6, there is little degradation of 1 since more than 95% of initial 1 was still present after 7 days at 20 degrees C. Under physiological conditions (pH 7.4, 37 degrees C) after 6 days, 45% of 1 is hydrolyzed (t1/2 = 6.6 days), leading essentially (30% of initial 1) to the nine-membered ring compound 13. The rate of hydrolysis of 13 and the nature of its hydrolysis products were found to depend on pH over the range 0-8.6. After a single ip injection to mice, compounds 3, 9, and 13 were less toxic than 1. They did not exhibit any direct cytotoxic efficacy on the colony-forming capacity of L1210 cells in vitro, and they had no antitumor activity in vivo against P388 leukemia.

Synthesis and quantitative structure-activity relationships of anticonvulsant 2,3,6-triaminopyridines

The synthesis of 2,3,6-triaminopyridine derivatives, representing a unique chemical structure for anticonvulsants, is described. The synthetic program was performed (a) to identify more potent analogs, (b) to determine structural properties controlling potency as well as neurotoxicity, and (c) to reduce the requirements for animal testing. As a result, besides other structural properties, the overall molecular lipophilicity (log k', octanol-coated column) explained changes in anticonvulsant potency and neurotoxicity. Mimicking the interaction of the amphiphilic triaminopyridines with biological membranes, NMR experiments in the presence of lecithin vesicles were conducted in order to measure the phospholipid-binding parameter log delta (1/T2). Replacement of log k' with log delta (1/T2) in the correlation analysis afforded a more significant equation describing the anticonvulsant activity of 21 derivatives.

Structural investigation of Cetrorelix, a new potent and long-acting LH-RH antagonist

The new decapeptide SB-75 (INN: Cetrorelix) has been characterized as a potent antagonist of luteinizing-hormone releasing hormone (LH-RH). Such derivatives are of great medicinal interest owing to their potential application in areas such as hormone-dependent tumors, uterine fibroids, and in diseases and conditions which result from inappropriate hormone levels or which can be treated by suppression of estrogens. SB-75 is the subject of intensive ongoing clinical evaluation and is an accepted standard for the design of new LH-RH antagonists. We characterized SB-75 by means of modern MS and NMR techniques to demonstrate the significance of both sequencing methods on a complicated unnatural decapeptide. Our structural elucidations with nuclear Overhauser (NOE) experiments revealed clear evidence for a highly flexible molecule with no single predominant conformation even in sodium dodecyl sulfate (SDS) mimicking a cellular membrane.

Antineoplastic activity and tolerability of a novel heterocyclic alkylphospholipid, D-20133

Octadecyl-[2-(N-methylpiperidinio)ethyl]-phosphate (OMPEP, D-20133), a heterocyclic analogue of hexadecylphosphocholine (MIL), has been synthesized in an attempt to increase the therapeutic range of the parent compound. The antineoplastic activity of the novel alkylphospholipid was compared with that of MIL in dimethylbenz(a)anthracene-induced mammary carcinoma of the rat. Using tumors of different sizes and repeated daily doses as well as high single doses, we achieved marked remissions with either compound. However, the therapeutic range of OMPEP was broader than that of the parent drug. Furthermore, the emetic potential of OMPEP tested on ferrets was distinctly less pronounced than that of MIL. In vitro the new alkylphospholipid proved to be more active than MIL in all cell lines tested, and its differentiation-inducing capacity turned out to be superior to that of MIL. No hematological toxicity was observed at various OMPEP doses during a 3-week treatment period.

Chemistry and pharmacology of the non-benzodiazepine anxiolytic enciprazine and related compounds

In the course of studies on tranquilizers, new non-benzodiazepine-like compounds were synthesized. These are 1-(3,4,5-trimethoxyphenoxy)-3-[4-(2-methoxyphenyl)piperazinyl]prop an-2-ol (INN: enciprazine) and derivatives thereof which were screened pharmacologically in order to evaluate their central nervous system activity. Compounds with marked antiaggressive and anxiolytic properties but without dependence potential could be detected. Enciprazine was selected for clinical investigations.