N-Metallocenoylsphingosines as targeted ceramidase inhibitors: Syntheses and antitumoral effects.

Three N-metallocenoylsphingosines with variance in the central metal (Fe, Co, Ru), the charge (neutral or cationic), and the arene ligands (Cp2, Cp*Ph) were synthesized from serine and metallocene carboxylic acids as substrate-analogous inhibitors of human acid ceramidase (AC). Their inhibitory potential was examined using the recombinant full length ASAH1 enzyme, expressed and secreted from High Five insect cells, and the fluorescent substrate Rbm14-12. All complexes inhibited AC, most strongly so ruthenium(II) complex 13a. Some antitumoral effects of the complexes, such as the interference with the microtubular and F-actin cytoskeleton of cancer cells, were correlated to their AC-inhibition, whereas others, e.g. their cytotoxicity and their induction of caspase-3/-7 activity in cancer cells, were not. All complexes accumulated preferentially in the lysosomes of cancer cells like their target AC, arrested the cells in G1 phase of the cell cycle, and displayed cytotoxicity with mostly single-digit micromolar IC50 values while inducing cancer cell apoptosis.

Luminescent Gold(I) Complexes of 1-Pyridyl-3-anthracenylchalcone Inducing Apoptosis in Colon Carcinoma Cells and Antivascular Effects.

The luminescent chalcone gold(I) conjugates [Au(PPh3)(AN3E)]PF6(1) and [Au(SIMes)(AN3E)]PF6 (2) (AN3E = (E)-3-(9-anthracenyl)-1-(4-pyridyl)propenone; SIMes = N,N'-dimesitylimidazolidin-2-ylidene; Mes = 2,4,6-trimethylphenyl)) were prepared and characterized; complex 1 was also characterized by X-ray crystallography. In MTT assays against a panel of three human colon, a melanoma and a breast cancer cell lines both complexes were antiproliferative with low micromolar IC50 values. It is noteworthy that HCT116p53-/- colon carcinoma cells lacking functional p53 (a vital tumor suppressor) were more susceptible to them than the wildtype parent cell line. In flow cytometry analyses, the gold conjugates induced a significant arrest in G2/M phase primarily. Complexes 1 and 2 quickly increased the production of reactive oxygen species (ROS) and induced mitochondrial membrane potential depolarization, higher ROS values being obtained after coadministration with enzymatic inhibitors. The free chalcone AN3E and its gold(I) complex conjugates located in the cell mitochondria according to confocal microscopy. In addition, complexes 1 and 2 showed in vivo antivascular effects on the chorioallantoic membrane (CAM) of fertilized specific-pathogen-free (SPF) chicken eggs.

Oxazole-Bridged Combretastatin A-4 Derivatives with Tethered Hydroxamic Acids: Structure⁻Activity Relations of New Inhibitors of HDAC and/or Tubulin Function.

New inhibitors of tubulin polymerization and/or histone deacetylase (HDAC) activity were synthesized by attaching alkyl tethered hydroxamic acid appendages of varying length to oxazole-bridged combretastatin A-4 analogous caps. While their antiproliferative and microtubule disrupting effect was most pronounced for derivatives with short spacers, HDAC inhibition was strongest for those with longer spacers. These findings were further supported by computational methods such as structure-based docking experiments exploring the target interactions of the derivatives with varying linkers. For instance, compounds featuring short four-atom spacers between cap and hydroxamic acid inhibited the growth of various cancer cell lines and human endothelial hybrid cells with IC50 values in the low nanomolar range. In line with their ability to inhibit the microtubule assembly, four- and five-atom spacered hydroxamic acids caused an accumulation of 518A2 melanoma cells in G2/M phase, whereas a compound featuring a six-atom spacer and performing best in HDAC inhibition, induced a G1 arrest in these cells. All these beneficial anticancer activities together with their selectivity for cancer cells over non-malignant cells, point out the great potential of these novel pleiotropic HDAC and tubulin inhibitors as drug candidates for cancer therapy.

Synthesis and Cytotoxicity Studies of Novel NHC*-Gold(I) Complexes Derived from Lepidiline A.

Ten novel N-heterocyclic carbene gold(I) complexes derived from lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride) are reported here with full characterisation and biological testing. (1,3-Dibenzyl-4,5-diphenylimidazol-2-ylidene)gold(I) chloride (NHC*-AuCl) (1) was modified by substituting the chloride for the following: cyanide (2), dithiocarbamates (3⁻5), p-mercaptobenzoate derivatives (12⁻14) and N-acetyl-l-cysteine derivatives (15⁻17). All complexes were synthesised in good yields of 57⁻78%. Complexes 2, 12, 13, and 14 were further characterised by X-ray crystallography. Initial evaluation of the biological activity was conducted on all ten complexes against the multidrug resistant MCF-7topo breast cancer, HCT-116wt, and p53 knockout mutant HCT-116-/- colon carcinoma cell lines. Across the three cell lines tested, mainly single-digit micromolar IC50 values were observed. Nanomolar activity was exhibited on the MCF-7topo cell line with 3 displaying an IC50 of 0.28 µM ± 0.03 µM. Complexes incorporating a Au⁻S bond resulted in higher cytotoxic activity when compared to complexes 1 and 2. Theoretical calculations, carried out at the MN15/6⁻311++G(2df,p) computational level, show that NHC* is the more favourable ligand for Au(I)-Cl when compared to PPh3.

Exploring the Influence of the Aromaticity on the Anticancer and Antivascular Activities of Organoplatinum(II) Complexes.

A series of new organometallic PtII complexes of the type [Pt(C^N)Cl(DMSO)] (C^N=N,N-dimethyl-1-(2-aryl)methanamine-κ2 C2,N; aryl=phenyl 2 a, biphenyl 2 b, p-terphenyl 2 c, naphthyl 2 d, anthracenyl 2 e, or pyrenyl 2 f) have been synthesized to explore the influence of the aromaticity on their anticancer activity. The best performers, 2 b and d, are more active than cisplatin (CDDP) in epithelial ovarian carcinoma cells A2780, with 2 d having a higher selectivity factor than CDDP in all the tested cell lines. In addition, all the new compounds overcome the acquired resistance in A2780cisR cells and interestingly, show low micromolar IC50 values towards the triple negative breast cancer cell line MDA-MB-231 and the highly metastatic 518A2 melanoma cells. This study shows that the hydrophobicity, accumulation into cells, and metal levels on nuclear DNA for the complexes are consistent with their cytotoxicity. Complexes 2 b and d induce apoptosis in a caspase-independent manner and suppress the intracellular ROS generation without modifying the mitochondria membrane potential. In addition, 2 a-f effectively inhibit angiogenesis in the endothelial cell line EA.hy926 at sub-cytotoxic concentrations and 2 b and d show in vivo antivascular effects on the chorioallantoic membrane (CAM) of fertilized SPF-eggs (SPF=specific-pathogen-free). Inhibition of tubulin polymerization and degeneration of cytoskeleton organization in 518A2 melanoma cells are presented as a preliminary mechanism of its antimetastatic activity.

Antitumoral effects of mitochondria-targeting neutral and cationic cis-[bis(1,3-dibenzylimidazol-2-ylidene)Cl(L)]Pt(ii) complexes.

Recently, we opened a synthetic access to antitumoral platinum complexes of the type cis-[(NHC)1(NHC)2PtIICl(L)] which interact with DNA in a way correlated to the complex charge and to the sterical accessibility of the leaving chlorido ligand. We now identified mitochondria rather than nuclei as the cellular target of the neutral dichlorido complex 1 (L = Cl) and the delocalized lipophilic cationic phosphine complex 2 (L = PPh3), both carrying the same cis-bis(1,3-dibenzylimidazol-2-ylidene) ligands. Their uptake into 518A2 melanoma cells was concentration-dependent and distinctly greater for complex 2 which was also more cytotoxic against sensitive cancer cell lines with submicromolar IC50 values. Both complexes interfered strongly with various forms of DNA in vitro, but only complex 2 caused a melanoma cell cycle arrest in G1-phase, setting both apart from the S-phase arresting drug cisplatin. Studies of the intracellular localisation of 1 and 2 were carried out with their alkyne-tagged analogues 6 and 7, which showed identical patterns of cancer cell cytotoxicity, cell cycle interference and effects on mitochondria. Click reactions with 7-hydroxycoumarin azide, colocalisation with Mitotracker™ and confocal microscopy, proved complexes 6 and 7 to accumulate mainly in the mitochondria rather than the nuclei of melanoma cells. Complex 1 and even more so complex 2 reduced the mitochondrial membrane potential and also increased the cellular ROS levels. As a consequence, both complexes caused stress fibre formation in the F-actin cytoskeleton of melanoma cells, most distinctly so complex 2 which also activated the apoptotic cascade mediated by capases-3 and -7.

Synthesis, structures and cytotoxic effects in vitro of cis- and trans-[PtIVCl4(NHC)2] complexes and their PtII precursors.

Four new bis(N,N-dialkylbenzimidazol-2-ylidene)dichlorido platinum(ii) complexes 2 featuring N-alkyl substituents of increasing size (a: Me, b: Et, c: n-butyl, d: n-octyl) were synthesised and oxidised with PhICl2 to give the corresponding [PtIVCl4(N,N-dialkylbenzimidazol-2-ylidene)2] complexes 4 as potential anticancer prodrugs. The known bis(N,N-dibenzylimidazol-2-ylidene)dichlorido platinum(ii) complex 1 was likewise oxidised to [PtIVCl4(N,N-dibenzylimidazol-2-ylidene)2] 3. In contrast, oxidation of complexes 1 and 2 with H2O2 or hypochlorites, or exchange of chlorido for hydroxo ligands in tetrachlorido complexes 4 failed to give isolable complexes of type [PtIVCl4-n(OH)n(NHC)2]. In MTT assays the [PtIICl2(NHC)2]/[PtIVCl4(NHC)2] complex couples 1/3, 2c/4c, and trans-2c/trans-4c, bearing either N-benzyl or N-butyl substituents, each showed similar single-digit micromolar IC50 values against at least three out of five human cancer cell lines, presumably due to an intracellular reduction of the PtIV complexes to their active PtII congeners. Unlike cisplatin, whose anticancer effect requires functional p53, each of them was active both in wildtype and in p53-negative HCT116 colon carcinoma cells. In ethidium bromide saturation assays with isolated DNA, cis-(bis-NHC)PtII complexes such as 1 caused morphological DNA changes more pronounced than those initiated by cisplatin, while the corresponding cis-(bis-NHC)PtIV complexes such as 3 interacted with DNA in a less structure-modifying way.

New naphthopyran analogues of LY290181 as potential tumor vascular-disrupting agents.

A series of 19 analogues of the antiproliferative naphthopyran LY290181 were prepared for structure-activity relationship studies. We found the best activities for test compounds bearing small substituents at the meta position of the phenyl ring. The mode of action of LY290181 and eight new analogues was studied in detail. The compounds were highly anti-proliferative with IC50 values in the sub-nanomolar to triple-digit nanomolar range. The new analogues led to G2/M arrest due to interruption of the microtubule dynamics. In 518A2 melanoma cells they caused a mitotic catastrophe which eventually led to apoptosis. The naphthopyrans also induced a disruption of the vasculature in the chorioallantoic membrane (CAM) of fertilized chicken eggs as well as in xenograft tumors in mice. In a preliminary therapy trial, the difluoro derivative 2b retarded the growth of resistant xenograft tumors in mice.

Towards New Robust Zn(II) Complexes for the Ring-Opening Polymerization of Lactide Under Industrially Relevant Conditions.

The synthesis of bio-based and biodegradable plastics is a hot topic in research due to growing environmental problems caused by omnipresent plastics. As a result, polylactide, which has been known for years, has seen a tremendous increase in industrial production. Nevertheless, the manufacturing process using the toxic catalyst Sn(Oct)2 is very critical. As an alternative, five zinc acetate complexes have been synthesized with Schiff base-like ligands that exhibit high activity in the ring-opening polymerization of non-purified lactide. The systems bear different side arms in the ligand scaffold. The influence of these substituents has been analyzed. For a detailed description of the catalytic activities, the rate constants k app and k p were determined using in-situ Raman spectroscopy at a temperature of 150 °C. The polymers produced have molar masses of up to 71 000 g mol-1 and are therefore suitable for a variety of applications. Toxicity measurements carried out for these complexes proved the nontoxicity of the systems.

Copper(ii) complexes with tridentate Schiff base-like ligands: solid state and solution structures and anticancer activity.

We report 15 new Cu(ii) complexes with tridentate NNO ß-acylenamino ligands derived from 2-picolylamine and bearing up to three alkyl, alkoxy, alkoxycarbonyl, or (pseudo)halide substituents. The structures of nine complexes were elucidated by single crystal X-ray diffraction analysis. Complexes with an unsubstituted pyridine ring crystallised with a square pyramidal coordination sphere, whereas substitution of the pyridine ring led to a square planar coordination sphere around the metal centre. The solution structures and properties of the complexes were characterised by UV-Vis spectroscopy and cyclic voltammetry. They were also tested for their cytotoxic effect on four human cancer cell lines. Two complexes were identified that were highly active with single-digit IC50 values, exceeding those of cisplatin by far. A tentative structure-activity relationship was proposed as well as topoisomerase I inhibition as a possible mode of action, while any significant interference with DNA and the level of reactive oxygen species could be excluded.

N,N-Dialkylbenzimidazol-2-ylidene platinum complexes - effects of alkyl residues and ancillary cis-ligands on anticancer activity.

Eleven complexes of [(1,3-dialkylbenzimidazol-2-ylidene)LnCl3-n]Pt(n-1)+, with Ln = DMSO (8), Ph3P (9), (Ph3P)2 (10), and alkyl = Me (a), Et (b), Bu (c), octyl (d), were synthesised and tested for cellular accumulation, cytotoxicity, interference with the tumour cell cycle, and interaction with DNA. The delocalised lipophilic cationic bisphosphane complexes 10 were on average found to be more cytotoxic in MTT assays against a panel of seven cancer cell lines than the neutral DMSO and monophosphane complexes 8 and 9. The uptake of complexes 10, at least into HCT116 colon carcinoma cells, was also significantly greater than that of analogues 8 and 9. Their cytotoxicities did not differ significantly with the N-alkyl side chain length. The complexes that were most active, with sub-micromolar IC50 (72 h) values against HCT116wt cells, that is 8b, 9b, 10a-c, worked by a mode of action that was dependent on the functional p53, yet were still far more active than cisplatin in both of the HCT116wt and HCT116-/- variants. In detailed binding analyses 8c, 9c and 10a-c showed a lower affinity to DNA and different binding modes when compared to cisplatin, preferably forming mono-adducts with DNA and distorting it to a lower extent. Also, unlike cisplatin, they arrested the HCT116 cells of both variants predominantly in the G1 phase.

A new C,N-cyclometalated osmium(ii) arene anticancer scaffold with a handle for functionalization and antioxidative properties.

A series of six osmium(ii) complexes of the type [(η6-p-cymene)Os(C^N)X] (X = chlorido or acetato) containing benzimidazole C^N ligands with an ester group as a handle for further functionalization have been synthesized. They exhibit IC50 values in the low micromolar range in a panel of cisplatin (CDDP)-resistant cancer cells (approximately 10× more cytotoxic than CDDP in MCF-7), decrease the levels of intracellular ROS and reduce the NAD+ coenzyme, and inhibit tubulin polymerization. This discovery could open the door to a new large family of osmium(ii)-based bioconjugates with diverse modes of action.

Novel cis-[(NHC)1(NHC)2(L)Cl]platinum(ii) complexes - synthesis, structures, and anticancer activities.

A general synthesis of novel platinum(ii) complexes bearing two different, cis-oriented, N-heterocyclic carbene (NHC) ligands is presented. Easily accessible cis-[PtII(NHC)(DMSO)] precursor complexes were converted to either cis-[PtII(NHC)2Cl2] complexes such as 5a and 5b, or to novel mixed cis-[PtII(NHC)1(NHC)2Cl2] complexes such as 5c-h by successive introduction of the individual carbene ligands. The 'symmetric' complexes 5a and 5b were also converted to cationic cis-[PtII(NHC)2(PPh3)Cl]+Cl- complexes 8a and 8b. The structures of the ten new complexes, comprising benzylated and alkylated imidazol-2-ylidene ligands, were analysed by 1H, 13C and 195Pt NMR spectroscopy and also by X-ray diffraction for 5a, 5d, 5h, and 8a. The neutral complexes 5 were cytotoxic against a panel of seven human cancer cell lines with IC50 values in the low micromolar range, while the cationic complexes 8 reached even nanomolar IC50 values. Complex 5h carrying the substitution pattern of the natural antitumoral agent Combretastatin A-4 showed a conspicuous specificity for cancer cell lines sensitive to this drug. In electrophoretic mobility shift assays, the cis-biscarbene complexes 5b and 8b led to an unwinding or aggregation of plasmid DNA, while the trans-biscarbene complex 1b showed no such effect.