Cell-Penetrating Peptide-Bismuth Bicycles.

Cell-penetrating peptides (CPPs) play a significant role in the delivery of cargos into human cells. We report the first CPPs based on peptide-bismuth bicycles, which can be readily obtained from commercially available peptide precursors, making them accessible for a wide range of applications. These CPPs enter human cells as demonstrated by live-cell confocal microscopy using fluorescently labelled peptides. We report efficient sequences that demonstrate increased cellular uptake compared to conventional CPPs like the TAT peptide (derived from the transactivating transcriptional activator of human immunodeficiency virus 1) or octaarginine (R8 ), despite requiring only three positive charges. Bicyclization triggered by the presence of bismuth(III) increases cellular uptake by more than one order of magnitude. Through the analysis of cell lysates using inductive coupled plasma mass spectrometry (ICP-MS), we have introduced an alternative approach to examine the cellular uptake of CPPs. This has allowed us to confirm the presence of bismuth in cells after exposure to our CPPs. Mechanistic studies indicated an energy-dependent endocytic cellular uptake sensitive to inhibition by rottlerin, most likely involving macropinocytosis.

Kinetics, Thermodynamics, and Structural Effects of Quinoline-2-Carboxylates, Zinc-Binding Inhibitors of New Delhi Metallo-ß-lactamase-1 Re-sensitizing Multidrug-Resistant Bacteria for Carbapenems.

Carbapenem resistance mediated by metallo-ß-lactamases (MBL) such as New Delhi metallo-ß-lactamase-1 (NDM-1) has become a major factor threatening the efficacy of essential ß-lactam antibiotics. Starting from hit fragment dipicolinic acid (DPA), 8-hydroxy- and 8-sulfonamido-quinoline-2-carboxylic acids were developed as inhibitors of NDM-1 with highly improved inhibitory activity and binding affinity. The most active compounds formed reversibly inactive ternary protein-inhibitor complexes with two zinc ions as proven by native protein mass spectrometry and bio-layer interferometry. Modification of the NDM-1 structure with remarkable entropic gain was shown by isothermal titration calorimetry and NMR spectroscopy of isotopically labeled protein. The best compounds were potent inhibitors of NDM-1 and other representative MBL with no or little inhibition of human zinc-binding enzymes. These inhibitors significantly reduced the minimum inhibitory concentrations (MIC) of meropenem for multidrug-resistant bacteria recombinantly expressing blaNDM-1 as well as for several multidrug-resistant clinical strains at concentrations non-toxic to human cells.

A Formylglycine-Peptide for the Site-Directed Identification of Phosphotyrosine-Mimetic Fragments.

Discovery of protein-binding fragments for precisely defined binding sites is an unmet challenge to date. Herein, formylglycine is investigated as a molecular probe for the sensitive detection of fragments binding to a spatially defined protein site . Formylglycine peptide 3 was derived from a phosphotyrosine-containing peptide substrate of protein tyrosine phosphatase PTP1B by replacing the phosphorylated amino acid with the reactive electrophile. Fragment ligation with formylglycine occurred in situ in aqueous physiological buffer. Structures and kinetics were validated by NMR spectroscopy. Screening and hit validation revealed fluorinated and non-fluorinated hit fragments being able to replace the native phosphotyrosine residue. The formylglycine probe identified low-affinity fragments with high spatial resolution as substantiated by molecular modelling. The best fragment hit, 4-amino-phenyl-acetic acid, was converted into a cellularly active, nanomolar inhibitor of the protein tyrosine phosphatase SHP2.

Nanoparticular Inhibitors of Flavivirus Proteases from Zika, West Nile and Dengue Virus Are Cell-Permeable Antivirals.

Viral proteases have been established as drug targets in several viral diseases including human immunodeficiency virus and hepatitis C virus infections due to the essential role of these enzymes in virus replication. In contrast, no antiviral therapy is available to date against flaviviral infections including those by Zika virus (ZIKV), West Nile virus (WNV), or dengue virus (DENV). Numerous potent inhibitors of flaviviral proteases have been reported; however, a huge gap remains between the in vitro and intracellular activities, possibly due to low cellular uptake of the charged compounds. Here, we present an alternative, nanoparticular approach to antivirals. Conjugation of peptidomimetic inhibitors and cell-penetrating peptides to dextran yielded chemically defined nanoparticles that were potent inhibitors of flaviviral proteases. Peptide-dextran conjugates inhibited viral replication and infection in cells at nontoxic, low micromolar or even nanomolar concentrations. Thus, nanoparticular antivirals might be alternative starting points for the development of broad-spectrum antiflaviviral drugs.

Catching a Moving Target: Comparative Modeling of Flaviviral NS2B-NS3 Reveals Small Molecule Zika Protease Inhibitors.

The pivotal role of viral proteases in virus replication has already been successfully exploited in several antiviral drug design campaigns. However, no efficient antivirals are currently available against flaviviral infections. In this study, we present lead-like small molecule inhibitors of the Zika Virus (ZIKV) NS2B-NS3 protease. Since only few nonpeptide competitive ligands are known, we take advantage of the high structural similarity with the West Nile Virus (WNV) NS2B-NS3 protease. A comparative modeling approach involving our in-house software PyRod was employed to systematically analyze the binding sites and develop molecular dynamics-based 3D pharmacophores for virtual screening. The identified compounds were biochemically characterized revealing low micromolar affinity for both ZIKV and WNV proteases. Their lead-like properties together with rationalized binding modes represent valuable starting points for future lead optimization. Since the NS2B-NS3 protease is highly conserved among flaviviruses, these compounds may also drive the development of pan-flaviviral antiviral drugs.

Rhenium mixed-ligand complexes with S,N,S-tridentate thiosemicarbazone/thiosemicarbazide ligands.

Rhenium(V) complexes containing tridentate thiosemicarbazones/thiosemicarbazides (H2L1) derived from N-[N',N'-dialkylamino(thiocarbonyl)]benzimidoyl chlorides with 4,4-dialkylthiosemicarbazides have been synthesized by ligand-exchange reactions starting from [ReOCl(L1)]. The chlorido ligand of [ReOCl(L1)] (4) is readily replaced and reactions with ammonium thiocyanate or potassium cyanide give [ReO(NCS)(L1)] (6) and [ReO(CN)(L1)] (7), respectively. The reaction of (NBu4)[ReOCl4] with H2L1 and two equivalents of ammonium thiocyanate, however, gives in a one-pot reaction [ReO(NCS)2(HL1)] (8), in which the pro-ligand H2L1 is only singly deprotonated. An oxo-bridged, dimeric nitridorhenium(V) compound of the composition [{ReN(HL1)}2O] (11) is obtained from a reaction of (NBu4)[ReOCl4], H2L1 and sodium azide. The six-coordinate complexes [ReO(L1)(Ph2btu)] (12), where HPh2btu is N,N-diphenyl-N'-benzoylthiourea, can be obtained by treatment of [ReOCl(L1)] with HPh2btu in the presence of NEt3. Studies of the antiproliferative effects of the [ReOX(L1)] system (X = Cl−, NCS− or CN−) on breast cancer cells show that the lability of a monodentate ligand seems to play a key role in the cytotoxic activity of the metal complexes, while the substitution of this ligand by the chelating ligand Ph2btu− completely terminates the cytotoxicity.

Neutral gold complexes with tridentate SNS thiosemicarbazide ligands.

Na[AuCl(4)]·2H(2)O reacts with tridentate thiosemicarbazide ligands, H(2)L1, derived from N-[N',N'-dialkylamino(thiocarbonyl)]benzimidoyl chloride and thiosemicarbazides under formation of air-stable, green [AuCl(L1)] complexes. The organic ligands coordinate in a planar SNS coordination mode. Small amounts of gold(I) complexes of the composition [AuCl(L3)] are formed as side-products, where L3 is an S-bonded 5-diethylamino-3-phenyl-1-thiocarbamoyl-1,2,4-triazole. The formation of the triazole L3 can be explained by the oxidation of H(2)L1 to an intermediate thiatriazine L2 by Au(3+), followed by a desulfurization reaction with ring contraction. The chloro ligands in the [AuCl(L1)] complexes can readily be replaced by other monoanionic ligands such as SCN(-) or CN(-) giving [Au(SCN)(L1)] or [Au(CN)(L1)] complexes. The complexes described in this paper represent the first examples of fully characterized neutral Gold(III) thiosemicarbazone complexes. All the [AuCl(L1)] compounds present a remarkable cell growth inhibition against human MCF-7 breast cancer cells. However, systematic variation of the alkyl groups in the N(4)-position of the thiosemicarbazone building blocks as well as the replacement of the chloride by thiocyanate ligands do not considerably influence the biological activity. On the other hand, the reduction of Au(III) to Au(I) leads to a considerable decrease of the cytotoxicity.

Synthesis, characterisation and biological evaluation of copper and silver complexes based on acetylsalicylic acid.

Metalcarbonyl complexes with ligands derived from acetylsalicylic acid demonstrated high cytotoxic potential against various tumor cell lines and strong inhibition of the cyclooxygenase enzymes COX-1 and 2. In this study we tried to achieve comparable effects with [alkyne]silver or copper trifluoromethanesulfonate complexes which are more hydrophilic then the uncharged metalcarbonyl derivatives. All compounds were evaluated for growth inhibition against breast (MCF-7, MDA-MB 231) and colon cancer (HT-29) cell lines and for COX-1 and COX-2 inhibitory effects at isolated isoenzymes. Pure ligands showed neither cytotoxic nor COX-inhibitory effects. While the silver complexes of (but-2-ynyl)-2-acetoxybenzoate (But-ASS-Ag) and (but-2-yne-1,4-diyl)-bis(2-acetoxybenzoate) (Di-ASS-But-Ag) were strong cytostatics, only the copper complex Di-ASS-But-Cu was active. At the COX enzymes the complexes were more effective than their ligands and aspirin.

[Cyclopentadienyl]metalcarbonyl complexes of acetylsalicylic acid as neo-anticancer agents.

[(Prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS), a derivative of the nonsteroidal anti-inflammatory drug aspirin(®) (ASS), demonstrated high cytotoxic potential against various tumor cells. The [acetylene]Co(2)(CO)(6) cluster strongly increased the biological effects compared to aspirin(®). In this study we evaluated the use of [cyclopentadienyl]metalcarbonyl as cytotoxic moiety with a broader series of metals: molybdenum, manganese, cobalt and rhodium. All compounds were tested for cytotoxicity against breast (MCF-7, MDA-MB-231) and colon cancer (HT-29) cell lines. Their COX-1 and COX-2 inhibitory effects were evaluated at isolated isoenzymes. Additionally, the influence on the level of the major COX metabolite prostaglandin E(2) (PGE(2)) was quantified in MDA-MB-231 breast cancer cells. Whereas the pure ligands or ASS did not show any cytotoxic effect, all metal complexes inhibited the tumor cell growth. The inhibitory effects at COX-1 and COX-2 enzymes were low. Only the Prop-Cp-ASS-Rh complex (10 µM) caused an important inhibition of COX-1 by 60% and COX-2 by 30%. ASS showed at the same concentration only a marginal repression of COX-1 activity (30%) and no effect on COX-2.

Synthesis and biological activities of transition metal complexes based on acetylsalicylic acid as neo-anticancer agents.

[(µ(4)-η(2))-(Prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS), a derivative of aspirin (ASS), demonstrated high growth-inhibitory potential against various tumor cells with interference in the arachidonic acid cascade as probable mode of action. The significance of the kind of metal and cluster was verified in this structure-activity study: Co(2)(CO)(6) was respectively exchanged by a tetrameric cobalt-, trimeric ruthenium-, or trimeric ironcarbonyl cluster. Furthermore, the metal binding motif was changed from alkyne to 1,3-butadiene. Compounds were evaluated for growth inhibition, antiproliferative effects, and apoptosis induction in breast (MCF-7, MDA-MB 231) and colon cancer (HT-29) cell lines and for COX-1/2 inhibitory effects at isolated isoenzymes. Additionally, the major COX metabolite prostaglandin E2 (PGE(2)) was quantified in arachidonic acid-stimulated MDA-MB 231 breast tumor cells. It was demonstrated that the metal cluster was of minor importance for effects on cellular activity if an alkyne was used as ligand. Generally, no correlation existed between growth inhibition and COX activity. Cellular growth inhibition and antiproliferative activity at higher concentrations of the most active compounds Prop-ASS-Co(4) and Prop-ASS-Ru(3) correlated well with apoptosis induction.

Synthesis, structural characterization, and biological evaluation of oxorhenium(V) complexes with a novel type of thiosemicarbazones derived from N-[N',N'-dialkylamino(thiocarbonyl)]benzimidoyl chlorides.

Reactions of N-[N',N'-diethylamino(thiocarbonyl)]benzimidoyl chloride with 4,4-dialkylthiosemicarbazides give a novel class of thiosemicarbazides/thiosemicarbazones, H(2)L, which causes a remarkable reduction of cell growth in in vitro experiments. These strong antiproliferative effects are also observed for oxorhenium(V) complexes of the general composition [ReOCl(L)], which are formed by reactions of the potentially tridentate ligands with (NBu(4))[ReOCl(4)]. A systematic substitution of the alkyl groups in the thiosemicarbazone building blocks of the ligands do not significantly influence the biological activity of the metal complexes, while the replacement of the chloro ligand by a PPh(3) ligand (by the replacement of the oxo unit by a nitrido ligand) completely terminated the cytotoxicity of the metal complexes.

Two novel series of allocolchicinoids with modified seven membered B-rings: design, synthesis, inhibition of tubulin assembly and cytotoxicity.

Two new attractive series of allocolchicinoids were designed as inhibitors of tubulin assembly using the potent ketone 4 and the tetracyclic, pyrazole annulated NCME variant 7 (NCME = N-acetyl colchinol-O-methylether (2)) as lead structures. The first group of inhibitors of type 6 with novel oxepine and azepine B-ring structures belongs to the NCME-series and was synthesized via a multistep total synthesis starting from simple and cheap 3-methoxybenzaldehyde (12) and 3,4,5-trimethoxybenzaldehyde (13). Biaryl-coupling of the starting materials 12 and 13 was accomplished via Ziegler-Ullmann-reaction to furnish the biphenyl 11 equipped with two carbaldehyde functions. The subsequent Cannizzaro reaction of this dicarbaldehyde 11 proceeded with high regioselectivity to yield almost exclusively the key compound, the hydroxymethyl carboxylic acid 9. Ring closure to the o,o'-bridged biphenyls was accomplished by two routes: on the one hand, treatment of 9 with aqueous hydrochloric acid yielded the lactone 15. On the other hand, a four step sequence starting from the isomeric mixture 9/10 furnished the constitutionally isomeric lactams 23 and 24; these could be converted to the corresponding thiolactams 25 and 26 and to the tetrazole annulated NCME-type derivatives 27 and 28. The second series of bioactive compounds are congeners of allocolchicine (3). The well known desacetyl allocolchicine (29) was easily oxidized to the oxime 30, which was further transformed to the corresponding ketone 31. This served as key precursor for the syntheses of various tetracyclic allocolchicine modifications 33-36 annulated with a pyrazole, isoxazole, pyrimidine or 2-aminopyrimidine heterocycle, respectively. Unexpectedly, all the NCME-variants with a substituent in position 7 like in NCME (2) inhibited the tubulin assembly only moderately. In contrast, the new series of allocolchicine modifications proved to be highly potent antimicrotubule agents. Inhibition of tubulin assembly occurred at lower concentrations compared to those measured for the reference colchicine (1). Surprisingly, these promising results could not be confirmed in the cytotoxicity tests against the human MCF-7 breast cancer cell line, where an unexpected loss of effectiveness compared to the corresponding NCME-derivatives was observed.

Non-thiol farnesyltransferase inhibitors: FTase-inhibition and cellular activity of benzophenone-based bisubstrate analogue farnesyltransferase inhibitors.

Some 5-acylaminoacylamino-benzophenone derivatives were designed as bisubstrate analogue farnesyltransferase inhibitors. These compounds turned out to be only weakly active against farnesyltransferase, but displayed an antiproliferative effect rendering them suitable for further development as a novel type of cytostatic agents.

Novel B-ring modified allocolchicinoids of the NCME series: design, synthesis, antimicrotubule activity and cytotoxicity.

Two new series of allocolchicinoids mimicking the structure of (-)-N-acetylcolchinol O-methyl ether (2, NCME) were synthesized and evaluated for their abilities to inhibit tubulin assembly. Possible antitumor properties resulting thereof were evaluated in vitro on the human MCF-7 breast cancer cell line. The first series of NCME-derivatives was brought about by extending the seven membered B-ring to novel semisynthetic variations with a nitrogen containing eight-membered B-ring similar, for example, to the artificial, potent steganacin aza-analogue 3. In the second series the seven-membered B-ring of NCME (2) was modified by annulation with a heterocyclic ring system. The racemic ketone 7a serving as key precursor involved in the syntheses of all the target NCME variants 9-13 and 15, 16 was easily transformed into the eight-membered B-ring lactams 9 and 10 via a Beckmann rearrangement of the corresponding E-oxime 8. The tetrazole annulated congener 11 was prepared via azidotrimethylsilane-mediated Schmidt rearrangement. Treatment of educt 7a with Bredereck's reagent led to the enamino ketone 14, which was easily converted into the pyrazole- or pyrimidine-annulated allocolchicinoids 15 and 16. Remarkably, all the allocolchicinoids 9-13 with an azocin-B-ring affected the tubulin/microtubule equilibrium only moderately. In contrast, the novel heterocycle annulated seven membered B-ring variants 15 and 16 proved to be highly potent tubulin-inhibitory, antimitotic agents. Interaction with tubulin occured at concentrations similar to those observed for colchicine (1) or the lead NCME (2). In all cases the antiproliferative effects correlated roughly with the inhibition of tubulin assembly.