Solid-phase synthesis and pharmacological evaluation of a library of peptidomimetics as potential farnesyltransferase inhibitors: an approach to new lead compounds

Oncogenic Ras proteins whose activation is farnesylation by farnesyltransferase have been seen as important targets for novel anticancer drugs. Inhibitors of this enzyme have already been developed as potential anti-cancer drugs, particularly by rational design based on the structure of the CA(1)A(2)X carboxyl terminus of Ras. Synthesis of a peptidomimetics library via solid-phase synthesis using the Multipin method is described here. The most active hits on cellular assays were resynthesized and enzymatic activity was measured. Compounds A1, A5 and A7 present significant activity on the isolated enzyme (IC(50)=117, 57.3 and 28.5 nM) and their molecular docking in the active site of the enzyme provides details on key interactions with the protein.

A flexible approach to the design of new potent substance P receptor ligands

The development of small-molecule antagonists of the substance-P-preferring tachykinin NK1 receptor offers an excellent opportunity to exploit these molecules as novel therapeutic agents in diverse pathologies such as depression, emesis or asthma. GR71251 has previously been identified as a potent and selective substance-P-receptor antagonist. We have therefore undertaken the synthesis of new pseudopeptidic analogues based on the C-terminal sequence of GR71251. The evaluation of binding affinities toward NK1 and NK2 receptors has enabled us to propose new selective NK1 ligands with high affinity. Structure-activity relationships showed that the Trp-OBzl(CF3)2 moiety is essential for NK1 affinity and that the introduction of building units such as spirolactam, lactam or proline, leading to a constrained peptide, increased selectivity for NK1 receptors. These compounds constitute a useful starting point for new substance P antagonists and represent an attractive lead series for further studies on the design of specific NK1 antagonists.

Conformation of the tripeptide Cbz-Pro-Leu-Trp-OBzl(CF3)2 deduced from two-dimensional 1H-NMR and conformational energy calculations is related to its affinity for NK1-receptor

Chemical modifications of dual NK1/NK2 ligand Cbz-Gly-Leu-Trp-OBzl(CF3)2 (1) enabled us to create a high NK1 selective ligand Cbz-Pro-Leu-Trp-OBzl(CF3)2 (2). A determination of the conformational behavior of tripeptide 2 in solution is described. The 1D and 2D 1H-NMR techniques (COSY and ROESY) were used to assign resonances. Observed interproton distance restraints were considered to characterize conformational behavior. Spectral data indicate that tripeptide 2 presents a rigidified structure in DMSO stabilized by H-bond in two gamma-turns. Agreement with experimental data was obtained by averaging the 1H-NMR parameters over several combinations of low-energy conformations.

DNA interaction of the tyrosine protein kinase inhibitor PD153035 and its N-methyl analogue

The brominated anilinoquinazoline derivative PD153035 exhibits a very high affinity and selectivity for the epidermal growth factor receptor tyrosine kinase (EGF-R TK) and shows a remarkable cytotoxicity against several types of tumor cell lines. In contrast, its N-methyl derivative, designated EBE-A22, has no effect on EGF-R TK but maintains a high cytotoxic profile. The present study was performed to explore the possibility that PD153035 and its N-methyl analogue might interact with double-stranded DNA, which is a primary target for many conventional antitumor agents. We studied the strength and mode of binding to DNA of PD153035 and EBE-A22 by means of absorption, fluorescence, and circular and linear dichroism as well as by a relaxation assay using human DNA topoisomerases. The results of various optical and gel electrophoresis techniques converge to show that both drugs bind to DNA and behave as typical intercalating agents. In particular, EBE-A22 unwinds supercoiled plasmid, stabilizes duplex DNA against heat denaturation, and produces negative CD and ELD signals, as expected for an intercalating agent. Extensive DNase I footprinting experiments performed with a large range of DNA substrates show that EBE-A22, but not PD153035, interacts preferentially with GC-rich sequences and discriminates against homooligomeric runs of A and T which are often cut more readily by the enzyme in the presence of the drug compared to the control. Altogether, the results provide the first experimental evidence that DNA is a target of anilinoquinazoline derivatives and suggest that this N-methylated ring system is a valid candidate for the development of DNA-targeted cytotoxic compounds. The possible relevance of selective DNA binding to activity is considered. The unexpected GC-selective binding properties of EBE-A22 entreat further exploration into the use of N-methylanilinoquinazoline derivatives as tools for designing sequence-specific DNA binding ligands.

N-Aminoindoline derivatives as inhibitors of 5-lipoxygenase

N-Aminoindoline derivatives were prepared and their 5-lipoxygenase inhibitory activities were evaluated in vitro and compared with those of phenidone and NDGA. Compound 4 presents the most effective 5-LO inhibition.

Synthesis and pharmacological evaluation of new pyrazolidine-3, 5-diones as AT(1) angiotensin II receptor antagonists

On the basis of the structure of the non-peptide receptor antagonist irbesartan, a new series of AT(1) ligands was designed. In these compounds the central imidazolone nucleus of irbesartan was replaced by a pyrazolidine-3,5-dione structure. The key intermediate N-alkylpyrazolidine-3,5-diones were synthesized according to a new and general method. The most active compounds possess a spirocyclopentane ring at position 4, a linear butyl chain at position 1, and the [2'-(5-tetrazolyl)biphenyl-4-yl]methyl or [2'-(benzoylaminosulfonyl)biphenyl-4-yl]methyl group at position 2. Affinity toward the AT(1) and AT(2) receptors was assessed by the ability of the compounds to competitively displace [(3)H]AII from its specific binding sites. The most active compounds, 28 and 48, displayed high affinity for the AT(1) receptor, good selectivity AT(1) versus AT(2), and potent in vitro antagonist activity.

Synthesis, DNA binding, topoisomerases inhibition and cytotoxic properties of 4-arylcarboxamidopyrrolo-2-carboxyanilides

Three 4-arylcarboxamidopyrrolo-2-carboxyanilides bearing different substituents on the pyrrole nitrogen were synthesized and evaluated for their capacities to bind to specific sequences within the minor groove of DNA and to inhibit human topoisomerases I and II in vitro. The cytotoxicity of the drugs correlates with their DNA binding affinities. The two drugs bearing a N-methyl or N-benzyl pyrrole stabilize topoisomerase I-DNA complexes.

Synthesis and cytotoxicity of analogues of the antibiotic BE 10988 inhibitors of DNA topoisomerase II

Indolequinone derivatives of the antitumour antibiotic BE 10988 were synthesized and evaluated for their cytotoxicity and action mechanism. The quinone system is essential to biological activity and the thiazole ring plays a major role in the poisoning of topoisomerase II.

Synthesis and antiproliferative properties of 4-aminoquinazoline derivatives as inhibitors of EGF receptor-associated tyrosine kinase activity

The mitogenic action of EGF is mediated by ligand-induced autophosphorylation of the EGF receptor (EGF-R), which is commonly overexpressed in numerous human cancers. Inhibitors of receptor tyrosine kinase (RTK) activity could therefore be considered as effective potential antitumor agents. For this purpose, 4-aminoquinazoline derivatives were prepared and evaluated for their ability to inhibit RTK activity and the autophosphorylation of EGF-R. In addition, these compounds were tested on A431 cell growth to estimate their antiproliferative effect. The results showed that the substituent at the 4-position of the quinazoline ring must be an aromatic amine carrying small lipophilic electron-withdrawing groups on the 3- (or 2-) position of the phenyl ring. This aromatic moiety might be far from the quinazoline provided that the linking group is conformationally restricted, such as with piperazine. Hydrophilic and non-aromatic substituents such as morpholine gave completely inactive compounds. Introduction of a bulk at the 2-position of the quinazoline ring in 2,4-diaminoquinazolines or tricyclic compounds led to inactive products. This study reports additional structure-activity relationships of a well-characterized series to develop new inhibitors of EGF-R-associated tyrosine kinase activity.

One-electron oxidation of ergothioneine and analogues investigated by pulse radiolysis: redox reaction involving ergothioneine and vitamin C

Redox reactions of endogenous and exogenous sulphur-containing compounds are involved in protection against oxidative damage arising from the incidence and/or treatment of many diseases, including cancer. We have investigated, via pulse radiolysis, the one-electron oxidation of ergothioneine, a molecule with antioxidant properties which is detected at millimolar concentrations in certain tissues and fluids subject to oxidative stress, including erythrocytes and plasma. The spectrum of the transient species, assigned to the product of one-electron oxidation, observed after reaction of ergothioneine with the oxidizing radicals OH., N3. and CCl3O2. has a maximum absorption at 520 nm and is very similar to that obtained by oxidation of analogous molecules such as 2-mercaptoimidazole, 1-methyl-2-mercaptoimidazole, S-methyl- and S,N-dimethyl-ergothioneine. In the presence of vitamin C, the oxidized form of ergothioneine is repaired by a rapid reduction (k = 6.3 x 10(8) M(-1).s(-1)) producing ascorbyl radicals. This co-operative interaction between ergothionine and ascorbate, similar to that previously observed between vitamin E and ascorbate, may contribute to essential biological redox protection.

[Conformational analysis of peptide antagonists in the design of pseudopeptide and non-peptide antagonists]

The comparative conformational analysis of four Substance P antagonists (NK1-) having different chemical structures allowed to formulate an hypothesis for a peptidic NK1 pharmacophore. The salient features of this pharmacophore (three aromatic groups and two carbonyl functions) belong to a beta-turn conformation. Thus, this kind of conformation might be the basis for the design of newer pseudo-peptidic and non-peptidic NK1 antagonists.

Influence of the methyl substituents of a thiazole-containing lexitropsin on the mode of binding to DNA

We have studied the DNA-binding properties of two thiazole-containing analogues of netropsin which differ by the absence (Thia-Nt) or presence (Methia-Nt) of methyl groups on the thiazole rings. The mode of binding to DNA of the two lexitropsins was investigated by circular dichroism, electric linear dichroism and viscosity measurements. The spectroscopic and hydrodynamic results indicate that the non-methylated lexitropsin binds to the minor groove of DNA, whereas the methylated analogue behaves as an intercalator. Our findings led to the notion that the methyl substituents on the thiazole rings might play a significant part in the intercalation process.

Antitumor combilexin. A thiazole-containing analogue of netropsin linked to an acridine chromophore

We report the synthesis, DNA-binding properties and antitumor activity of ThiaNetGA, a hybrid molecule in which are conjugated a thiazole-lexitropsin and an intercalating anilinoacridine chromophore. This combilexin molecule binds to DNA via a bimodal process involving minor groove binding of the lexitropsin moiety and intercalation of the acridine moiety. The uptake and distribution of the hybrid in L1210 leukemia cells were investigated by ESR spectroscopy using a spin-labeled derivative. The nitroxide-containing conjugate accumulates preferentially in the cell nuclei and rapidly saturates the nuclear receptor sites. Both in vitro and in vivo assays indicate that the drug is practically nontoxic but exhibits moderate antitumor activity against P388 leukemia cells in mice.

Comparative subcellular distribution of the copper complexes of bleomycin-A2 and deglycobleomycin-A2

We have compared the cellular uptake and subcellular localization of 14C-labeled bleomycin-A2 (BLM) and deglycobleomycin-A2 in living KB3 cells. Both drugs exhibit poor internalization into cells but reveal significantly different intracellular distribution, with low and high accumulation into the cell nuclei for BLM and deglyco-BLM, respectively. The results indicate that the carbohydrate chain does not constitute a limiting factor for BLM permeation and is directly implicated in the intracellular distribution of the drug into cells.

Binding properties and DNA sequence-specific recognition of two bithiazole-linked netropsin hybrid molecules

We report the DNA binding properties of two hybrid molecules which result from the combination of the DNA sequence-specific minor groove ligand netropsin with the bithiazole moiety of the antitumor drug bleomycin. The drug-DNA interaction has been investigated by means of electric linear dichroism (ELD) spectroscopy and DNase I footprinting. In compound 1 the two moieties are linked by a flexible aliphatic tether while in compound 2 the two aromatic ring systems are directly coupled by a rigid peptide bond. The results are consistent with a model in which the netropsin moiety of compound 1 resides in the minor groove of DNA and where the appended bithiazole moiety is projected away from the DNA groove. This monocationic hybrid compound has a weak affinity for DNA and shows a strict preference for A and T stretches. ELD measurements indicate that in the presence of DNA compound 2 has an orientation typical of a minor groove binder. Similar orientation angles were measured for netropsin and compound 2. This ligand which has a biscationic nature tightly binds to DNA (Ka = 6.3 x 10(5) M-1) and is mainly an AT-specific groove binder. But, depending on the nature of the sequence flanking the AT site first targeted by its netropsin moiety, the bithiazole moiety of 2 can accommodate various types of nucleotide motifs with the exception of homooligomeric sequences. As evidenced by footprinting data, the bithiazole group of bleomycin acts as a DNA recognition element, offering opportunities to recognize GC bp-containing DNA sequences with apparently a preference (although not absolute) for a pyrimidine-G-pyrimidine motif. Thus, the bithiazole unit of bleomycin provides an additional anchor for DNA binding and is also capable of specifically recognizing particular DNA sequences when it is appended to a strongly sequence selective groove binding entity. Finally, a model which schematizes the binding of compound 2 to the sequence 5'-TATGC is proposed. This model readily explains the experimentally observed specificity of this netropsin-bithiazole conjugate.

DNA-binding properties of a distamycin-ellipticine hybrid molecule

We have synthesized a distamycin-ellipticine hybrid compound and investigated its interaction with DNA, using various optical and gel electrophoresis techniques. Binding of the hybrid to DNA is evidenced by spectral shifts, fluorescence quenching, and induced linear dichroism. Absorbance measurements have been used to generate Scatchard plots, which reveal that the interaction cannot be described adequately in terms of a single binding mode, probably because of simultaneous intercalation and minor groove binding of the ligand. Competition with added distamycin has been used to verify involvement of the N-methyl-pyrrole portion of the hybrid molecule in the binding reaction. From electric linear dichroism experiments, it is estimated that the orientation of the DNA-bound ellipticine chromophore in the hybrid differs by about 10 degrees from the orientation of the equivalent chromophore lacking a distamycin tail. Topoisomerase assays establish that binding of the hybrid unwinds the DNA helix by a minimum of 11 degrees, which is consistent with intercalation but notably smaller than the unwinding angle of ellipticine. In footprinting experiments, it is found that the AT- and GC-specificity of distamycin and ellipticine, respectively, appear to be merged in the binding of the hybrid, which produces a pattern of protection distinct from the characteristic patterns for either of the parent compounds. The hybrid is an extremely effective inhibitor of cutting by DNase I.

DNA-sequence specific recognition by a thiazole analogue of netropsin: a comparative footprinting study

Four different footprinting techniques have been used to probe the DNA sequence selectivity of Thia-Net, a bis-cationic analogue of the minor groove binder netropsin in which the N-methylpyrrole moieties are replaced by thiazole groups. In Thia-Net the ring nitrogen atoms are directed into the minor groove where they could accept hydrogen bonds from the exocyclic 2-amino group of guanine. Three nucleases (DNAase I, DNAase II, and micrococcal nuclease) were employed to detect binding sites on the 160bp tyr T fragment obtained from plasmid pKM delta-98, and further experiments were performed with 117mer and 253mer fragments cut out of the plasmid pBS. MPE.Fe(II) was used to footprint binding sites on an EcoRI/HindIII fragment from pBR322. Thia-Net binds to sites in the minor groove containing 4 or 5 base pairs which are predominantly composed of alternating A and T residues, but with significant acceptance of intrusive GC base pairs. Unlike the parent antibiotic netropsin, Thia-Net discriminates against homooligomeric runs of A and T. The evident preference of Thia-Net for AT-rich sites, despite its containing thiazole nitrogens capable of accepting GC sites by hydrogen bonding, supports the view that the biscationic nature of the ligand imposes a bias due to the electrostatic potential differences in the receptor which favour the ligand reading alternating AT sequences.

A high performance liquid chromatographic method for the quantitation of flecainide in plasma

A routine high performance liquid chromatographic method for the rapid determination of flecaïnide (Flecaine), using a novel internal standard, N-methylflecaïnide, has been developed. After deproteinization of spiked samples, flecaïnide was totally recovered at neutral pH. Flecaïnide and the internal standard were separated on a reversed phase XL 3 microns ODS column using 10 mM phosphate buffer, pH 3.0: acetonitrile (70:30) as mobile phase, in less than 10 min. With spectrofluorometric detection, the limit of quantitation for flecaïnide was 10 ng/mL. Intra- and inter-assay precision variations were 0.24% and 1.4%.

Design, synthesis, DNA binding, and biological activity of a series of DNA minor-groove-binding intercalating drugs

A group of pseudopeptides, molecular combination of the natural antitumor agents distamycin or netropsin and the anilinoacridine chromophore (which is related to the synthetic antileukemic drug amsacrine) has been synthesized. Their DNA binding properties were determined and discussed in terms of their structural differences and in relation to their observed base-dependent binding. Binding data are consistent with a model in which the acridine nucleus occupies an intercalation site and the netropsin or distamycin residue resides in the DNA minor groove. Cytostatic and cytotoxic activities against a murine cell line are reported, as well as significant differences in the inhibition of DNA synthesis.

Synthesis, biological activity and DNA interaction of anilinoacridine and bithiazole peptide derivatives related to the anti-tumor drugs m-AMSA and bleomycin

The synthesis of two depsipeptides including a peptide metal-chelating moiety (Gly-His-Lys) and a moiety with DNA affinity, namely either glycyl-anilino-9-aminoacridine 1 or 2'-(2-aminoethyl)-4-methoxycarbonyl-2",4'-bithiazole 2, has been carried out. The goal was to introduce separately on the same molecule the two factors contributing to the biological activity of many anti-tumor drugs. The interaction of both drugs with DNA has been studied and the acridine ring of 1 was found to intercalate in the double helix. The production of free radicals has been evidenced by spin-trapping for 1 although both compounds were revealed to be good copper-chelating agents. In vitro cytostatic activity and inhibition of [3H]-thymidine incorporation were obtained for 1 while 2 exhibited no activity in both tests. In view of these results, it can be pointed out that the anti-tumor properties of such drugs rely (1) on their ability to reach and to bind DNA and (2) on redox mechanisms involving interactions between the drugs, metals and molecular oxygen. The latter phenomenon leads to the formation of active radical species, able to degrade the DNA.

The role of the gulose-mannose part of bleomycin in activation of iron-molecular oxygen complexes

A comparison of the complexing properties of metal ions and O2 activation by bleomycin-A2 (BLM-A2) and deglyco-BLM-A2 is presented. Deglyco-BLM-A2 is obtained from the parent derivative by HF cleavage of the sugar moiety followed by h.p.l.c. purification. Complexing of Cu(II) and Fe(III) is studied by using c.d. and e.s.r. spectroscopy. Spin-trapping experiments in the presence of phenyl N-t-butylnitrone indicated lower production of free radicals by deglyco-BLM-A2. Finally, a proposal is made to explain this discrepancy, focusing on the probable role of the gulose-mannose moiety acting as a protecting pocket, comparable with the pocket and picket-fence porphyrins described for haemoproteins.

DNA-binding and DNA-cleaving properties of a synthetic model AGAGLU related to the antitumour drugs AMSA and bleomycin

We have previously described two synthetic models gathering a simplified model of the complexing part of Bleomycin (Blm) and the intercalating moiety of m-AMSA. These molecules, namely AGGA and AGAMGA, do not seem able to cleave DNA as Blm does. The present work is devoted to the study of a new derivative, AGAGLU, which includes in its structure a judiciously chosen connector between the two parts of the molecule. This compound, the chelating and DNA-binding properties of which are described here, has been shown to induce single-strand breakage of duplex DNA in a high level.

Complexation of copper(II) by a peptide hybrid of bleomycin and amsacrine. Circular dichroism and electron spin resonance studies

A model incorporating the metal chelating moiety of bleomycin and an anilinoacridine ring able to intercalate in DNA has been synthesized. The copper(II) complex of that molecule has been studied using circular dichroism and electron spin resonance by comparison with bleomycin. The introduction of the anilinoacridine ring involves a modification in the geometry of the complex. A distortion of the square-pyramidal form (type II complex) gives rise to a type I complex in which the metallic atom is drawn out of the plane of the four square-planar ligands and displaced slightly towards the fifth ligand.

Chelating, DNA-binding and DNA-cleaving properties of a synthetic model for bleomycin

We have previously described a simplified model of the complexing part of bleomycin, namely methyl 2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidinate (AMPHIS), and disubstituted bithiazoles structurally related to the 'tripeptide S' moiety of bleomycin. The present work is devoted to the study of a new derivative, [3-[2-[2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidyl-3 -aminobutyryl-glycyl]-2',4-bithiazole-4-carboxamido]-propyl]- dimethylsulphonium iodide (AMBI-A2), which includes both AMPHIS and a judiciously chosen synthetic bithiazole. This compound, the synthesis of which is described here, has been shown to mimic the chelating and binding properties of the parent drug bleomycin A2, but to cleave DNA at higher concentration.

Design of two metal-chelating, DNA-binding models: molecular combinations of bleomycin and amsacrine anti-tumour drugs

In the course of studies on bleomycin, we recently showed that the bithiazole ring is a poor intercalator into DNA. Therefore we have designed new models, replacing this heterocyclic moiety by an anilinoacridine ring in order to increase the affinity for DNA. This work presents results obtained for two model compounds showing (i) that the anilinoacridine nucleus leads to a good stabilization of the DNA helix, and (ii) that the presence of a bulky group near the complexing part of bleomycin is essential to the activation of molecular oxygen.

A new bithiazole derivative with intercalative properties

In the course of studies related to new molecules with intercalative properties, we have been led to design and synthesize a bithiazole derivative, namely the 2-phenyl-6-[2'-(4'-(ethoxy-carbonyl)thiazolyl)]thiazolo[3,2- b][1,2,4]triazole (PETT). Its interaction with calf thymus DNA was studied using thermal denaturation and viscometry. Our results set in evidence that PETT acts as an intercalator, giving delta Tm, elongation and unwinding of DNA comparable to the values obtained for daunorubicin. The discrepancy between the data presented herein and those precedently obtained for bleomycin and bleomycin models provide evidence that these bithiazole derivatives interact differently with DNA.

Molecular interaction between bleomycin and amsacrine in the presence of cupric ions

The antineoplastic activity of m-AMSA [4'-(9-acridinylamino)-methanesulfon-m-anisidide] has been related to its ability to produce oxygenated free radical during its oxidation to a quinonimine form, in the presence of cupric ions. It has been demonstrated here that the rate of the oxidation is greatly increased by the addition of bleomycin (Blm), another antitumor agent, which is able to complex metallic ions. The catalytic role of Blm has been established on the basis of kinetics measurements and the occurrence of an intermediary ternary complex Blm-m-AMSA-Cu(II) has been demonstrated by circular dichroism and polarography experiments.

Is the bithiazole moiety of bleomycin a classical intercalator?

Bleomycin is a widespread anticancerous drug, the biological activity of which having been extensively studied. Its metal ion-chelating portion has been shown to cleave DNA whereas the role of the bithiazole moiety is still questionable. In order to elucidate this problem some 2', 4-disubstituted bithiazoles structurally related to the "tripeptide S" moiety of bleomycin were synthesized and their interaction with DNA was studied using delta Tm, fluorescence, EPR and viscometry techniques. The results of delta Tm and fluorescence quenching determinations were in favour of a binding of the bithiazole part by an intercalation process. Nevertheless, the use of the spin-label probes indicated only a partial intercalation of the ring between the base-pairs. Moreover, viscometry data which clearly exhibited a slight decrease of DNA length in the presence of bithiazole derivative led to the proposal of a binding model involving a partial insertion of a thiazole ring which wedges in between the bases at a bending point of DNA.

Copper(II)- and iron(II)-complexes of methyl 2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidinate (AMPHIS), a peptide mimicking the metal-chelating moiety of bleomycin. An ESR investigation

Methyl 2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidinate (AMPHIS), a synthetic analogue of the chelating part of bleomycin (BLM), has been studied for its metal binding properties. Electron spin resonance parameters of AMPHIS-Cu(II) and BLM-Cu(II) have been found to be closely similar likewise spectra of oxygen radicals spin-adducts induced by AMPHIS-Fe(II)-O2 and BLM-Fe(II)-O2 systems. Thus, AMPHIS could constitute a very useful tool for the study of BLM mode of action.

Opiate receptor interaction of a new analgesic drug 2-piperidinoethyl dibenzylglycolate

The pharmacological properties of a new analgesic drug, 2-piperidinoethyl dibenzylglycolate (PDG), have been demonstrated by classical tests. The technique of iontophoresis was used in order to compare the effects of PDG with those of Tyr-D-Ser-Gly-Phe-Leu-Thr (DSTLE), syndyphalin, morphine and naloxone (NAL) on hypothalamic neurones. PDG as other four substances evoked only inhibitory responses. Some neurones, on which were tested three substances, were sensitive to one, two or three of these substances. The differential responses so obtained suggested that PDG does not act on mu- and delta-receptors but on an unidentified receptor for which morphine and NAL have a high affinity as agonist. Structural requirements for activity on different receptors were also proposed on the basis of crystallographic data and the above results.

Subcellular distribution of spin-labeled bithiazoles and bleomycin in living KB cells: an ESR study

Spin-labeled derivatives of bithiazole and bleomycin were studied with respect to their uptake and localization in KB cells in vivo. It was found that the amidification of the C-terminal carboxylic group of bleomycinic acid was essential for the penetration of the probes in the cells and that the subcellular localization depended on the number and spacing of positively charged groups.

Structure-neuromuscular blocking activity relationships of ketophosphonium salts

Three ketophosphonium salts containing a morpholino group were prepared and evaluated for their neuromuscular blocking effect. Solution and crystal conformations were studied. An attempt was made to explain, in structural terms, different activity levels in connection with the interatomic distances.