Phenoxy- and Phenylamino-Heterocyclic Quinones: Synthesis and Preliminary Anti-Pancreatic Cancer Activity.

The successful application of fragment-based drug discovery strategy for the efficient synthesis of phenoxy- or phenylamino-2-phenyl-benzofuran, -benzoxazole and -benzothiazole quinones is described. Interestingly, in the final step of the synthesis of the target compounds, unusual results were observed on the regiochemistry of the reaction of bromoquinones with phenol and aniline. A theoretical study was carried out for better understanding the factors that control the regiochemistry of these reactions. The substituted heterocyclic quinones were evaluated in vitro to determine their cytotoxicity by the MTT method in three pancreatic cancer cell lines (MIA-PaCa-2, BxPC-3, and AsPC-1). Phenoxy benzothiazole quinone 26a showed potent cytotoxic activity against BxPC-3 cell lines, while phenylamino benzoxazole quinone 20 was the most potent on MIA-PaCa-2 cells. Finally, electrochemical properties of these quinones were determined to correlate with a potential mechanism of action. All these results, indicate that the phenoxy quinone fragment led to compounds with increased activity against pancreatic cancer cells.

Cytotoxic and Radiosensitising Effects of a Novel Thioredoxin Reductase Inhibitor in Brain Cancers.

The thioredoxin (Trx) system, a key antioxidant pathway, represents an attractive target for cancer therapy. This study investigated the chemotherapeutic and radiosensitising effects of a novel Trx reductase (TrxR) inhibitor, IQ10, on brain cancer cells and the underlying mechanisms of action. Five brain cancer cell lines and a normal cell type were used. TrxR activity and expression were assessed by insulin reduction assay and Western blotting, respectively. IQ10 cytotoxicity was evaluated using growth curve, resazurin reduction and clonogenic assays. Radiosensitivity was examined using clonogenic assay. Reactive oxygen species levels were examined by flow cytometry and DNA damage assessed by immunofluorescence. Epithelial-mesenchymal transition (EMT)-related gene expression was examined by RT-PCR array. IQ10 significantly inhibited TrxR activity but did not affect Trx system protein expression in brain cancer cells. The drug exhibited potent anti-proliferative and cytotoxic effects against brain cancer cells under both normoxic and hypoxic conditions in both 2D and 3D systems, with IC50s in the low micromolar range. It was up to ~ 1000-fold more potent than temozolomide. IQ10 substantially sensitised various brain cancer cells to radiation, with such effect being due, in part, to functional inhibition of TrxR, making cells less able to deal with oxidative stress and leading to increased oxidative DNA damage. IQ10 significantly downregulated EMT-associated gene expression suggesting potential anti-invasive and antimetastatic properties. This study suggests that IQ10 is a potent anticancer agent and could be used as either a single agent or combined with radiation, to treat brain cancers.

Diazophosphonates: Effective Surrogates for Diazoalkanes in Pyrazole Synthesis.

Diazophosphonates, readily prepared from α-ketophosphonates by oxidation of the corresponding hydrazones in batch or in flow, are useful partners in 1,3-dipolar cycloaddition reactions to alkynes to give N-H pyrazoles, including the first intramolecular examples of such a process. The phosphoryl group imbues a number of desirable properties into the diazo 1,3-dipole. The electron-withdrawing nature of the phosphoryl stabilizes the diazo compound making it easier to handle, whilst the ability of the phosphoryl group to migrate readily in a [1,5]-sigmatropic rearrangement enables its transfer from C to N to aromatize the initial cycloadduct, and hence its facile removal from the final pyrazole product. Overall, the diazophosphonate acts as a surrogate for the much less stable diazoalkane in cycloadditions, with the phosphoryl group playing a vital, but traceless, role. The cycloaddition proceeds more readily with alkynes bearing electron-withdrawing groups, and is regiospecific with asymmetrical alkynes. The potential of diazophosphonates for use in bioorthogonal cycloadditions is demonstrated by their facile addition to strained alkynes.

Cytotoxic and radiosensitising effects of a novel thioredoxin reductase inhibitor in breast cancer.

Radiotherapy is an effective treatment modality for breast cancer but, unfortunately, not all patients respond fully with a significant number experiencing local recurrences. Overexpression of thioredoxin and thioredoxin reductase has been reported to cause multidrug and radiation resistance - their inhibition may therefore improve therapeutic efficacy. Novel indolequinone compounds have been shown, in pancreatic cancer models, to inhibit thioredoxin reductase activity and exhibit potent anticancer activity. The present study evaluates, using in vitro breast cancer models, the efficacy of a novel indolequinone compound (IQ9) as a single agent and in combination with ionising radiation using a variety of endpoint assays including cell proliferation, clonogenic survival, enzyme activity, and western blotting. Three triple-negative breast cancer (MDA-MB-231, MDA-MB-468, and MDA-MB-436) and two luminal (MCF-7 and T47D) breast cancer cell lines were used. Results show that treatment with IQ9 significantly inhibited thioredoxin reductase activity, and inhibited cell growth and colony formation of breast cancer cells with IC50 values in the low micromolar ranges. Enhanced radiosensitivity of triple-negative breast cancer cells was observed, with sensitiser enhancement ratios of 1.20-1.43, but with no evident radiosensitisation of luminal breast cancer cell lines. IQ9 upregulated protein expression of thioredoxin reductase in luminal but not in triple-negative breast cancer cells which may explain the observed differential radiosensitisation. This study provides important evidence of the roles of the thioredoxin system as an exploitable radiobiological target in breast cancer cells and highlights the potential therapeutic value of indolequinones as radiosensitisers.***This study was not part of a clinical trial. Clinical trial registration number: N/A.

Origin of the Thiopyrone CTP-431 "Unexpectedly" Isolated from the Marine Sponge Cacospongia mycofijiensis.

An intriguing hypothesis that latrunculin A, a well-known natural product, might have undergone transformation into the unprecedented thiopyrone CTP-431 upon long-term storage in methanol is advanced. Thus, opening of the hemiacetal of latrunculin A, followed by E1CB elimination, and dehydration would give a polyene that could undergo intramolecular Diels-Alder reaction, followed by methanolysis of the thiazolidinone ring and ring closure by intramolecular thiol addition to an enone. Experimental evidence that the novel thiazolidinone to thiopyrone rearrangement can occur is presented.

Total Synthesis of the Cyclic Dodecapeptides Wewakazole and Wewakazole B.

The cyclic dodecapeptides wewakazole and wewakazole B have been synthesized by a divergent strategy via a common tris-proline containing oxazole octapeptide and two separate bis-oxazole containing tetrapeptide units, followed by peptide coupling and macrocyclization. The three oxazole amino acid fragments are readily accessible by rhodium(II)-catalyzed amide N-H insertion of diazocarbonyl compounds, or by the cycloaddition of rhodium carbenoids with nitriles.

Synthesis of the Reported Pyranonaphthoquinone Structure of the Indoleamine-2,3-dioxygenase Inhibitor Annulin B by Regioselective Diels-Alder Reaction.

Annulin B, isolated from the marine hydroid isolated from Garveia annulata, is a potent inhibitor of the tryptophan catabolizing enzyme indoleamine-2,3-dioxygenase (IDO). A synthesis of the reported pyranonaphthoquinone structure is described, in which the key step is a regioselective Diels-Alder reaction between a pyranobenzoquinone dienophile and a silyl ketene acetal diene.

Antitumour indolequinones: synthesis and activity against human pancreatic cancer cells.

An important determinant of the growth inhibitory activity of indolequinones against pancreatic cancer cells is substitution on the 2-position with 2-unsubstituted derivatives being markedly more potent. A series of indolequinones bearing a range of substituents on nitrogen and at the indolylcarbinyl position was prepared by copper(II)-mediated reaction of bromoquinones and enamines, followed by functional group interconversions. The compounds were then assayed for their ability to inhibit the growth of pancreatic cancer cells. The pKa of the leaving group at the 3-position was shown to influence growth inhibitory activity that is consistent with the proposed mechanism of action of reduction, loss of leaving group and formation of a reactive iminium species. Substitutions on the indole nitrogen were well tolerated with little influence on growth inhibitory activity while substitutions at the 5- and 6-positions larger than methoxy led to decreased activity. The studies presented define the range of substitutions of 2-unsubstituted indolequinones required for optimal growth inhibitory activity.

Benzofuranquinones as inhibitors of indoleamine 2,3-dioxygenase (IDO). Synthesis and biological evaluation.

A series of benzofuranquinones, analogues of the marine metabolite annulin A, has been synthesized and evaluated as inhibitors of human indoleamine 2,3-dioxygenase (IDO). The synthesis was carried out by copper(II)-mediated reaction of bromobenzoquinones with 1,3-dicarbonyl compounds followed by functional group interconversions. The most potent compounds were 5-methoxy-2-methylbenzofuranquinones containing a CH2OR group at position-3 with IC50 ~ 0.2 mM. The corresponding hydroquinones were inactive. Compounds based on the benzimidazolequinone framework are also active IDO inhibitors. The quinones do not generate significant levels of oxidative stress at concentrations that inhibit IDO.

Copper(II)-Mediated Synthesis of Indolequinones from Bromoquinones and Enamines.

The reaction of enamines and bromoquinones in the presence of copper(II) acetate and potassium carbonate results in a regiospecific synthesis of indolequinones. The reaction is broad in scope and scalable and provides a route to the core structure that is present in several biologically interesting natural and synthetic compounds.

Carbophilic 3-component cascades: access to complex bioactive cyclopropyl diindolylmethanes.

Naturally occurring indole-3-carbinol and 3,3-diindolylmethane show bioactivity in a number of disparate disease areas, including cancer, prompting substantial synthetic analogue activity. We describe a new approach to highly functionalised derivatives that starts from allene gas and proceeds via the combination of a three-component Pd(0)-catalysed cascade with a one-pot, three-component carbophilic Pt(II) cascade linked to a stereoselective acid-catalysed Mannich-Michael reaction that generates complex cyclopropyl diindolylmethanes which show selective activity against prostate cancer cell lines.

Induction of differentiation and apoptosis in leukaemic cell lines by the novel benzamide family histone deacetylase 2 and 3 inhibitor MI-192.

Histone deacetylase inhibitors (HDACIs) are in advanced clinical development as cancer therapeutic agents. However, first generation HDACIs such as butyrate and valproate are simple short chain aliphatic compounds with moieties resembling acetyl groups, and have a broad spectrum of activity against HDACs. More complex second generation HDACIs undergoing clinical trials, such as the benzamide group compounds MS-275 and MGCD0103, are specific primarily for HDAC1 and HDAC2. To expand the repertoire of available HDACIs and HDAC specificities we created a novel benzamide-based compound named MI-192. When tested against purified recombinant HDACs, MI-192 had marked selectivity for the class I enzymes, HDAC2 and HDAC3. Screening in the NCI60 screen demonstrated that MI-192 had greatly enhanced efficacy against cells of leukaemic origin. When tested in culture against the acute myeloid leukaemic cell lines U937, HL60 and Kasumi-1, MI-192 induced differentiation and was cytotoxic through promotion of apoptosis. MI-192 therefore justifies further investigation and development as a potential therapeutic agent for use in leukaemia.

Histone deacetylases are dysregulated in rheumatoid arthritis and a novel histone deacetylase 3-selective inhibitor reduces interleukin-6 production by peripheral blood mononuclear cells from rheumatoid arthritis patients.

OBJECTIVE: To characterize the role of histone deacetylase (HDAC) activity in rheumatoid arthritis (RA) and to evaluate the effects of MI192, a novel HDAC-3-selective inhibitor, compared with the established nonselective HDAC inhibitor trichostatin A (TSA), on proinflammatory cytokine production. METHODS: Activity of HDAC and histone acetyltransferase was measured in peripheral blood mononuclear cells (PBMCs) from RA patients by spectrophotometric assay, prior to and after 12 weeks of etanercept therapy. The effects of HDAC inhibitor treatment on cytokine production in both RA and healthy PBMCs were assessed by enzyme-linked immunosorbent assay. RESULTS: RA PBMCs exhibited significantly increased HDAC activity (P = 0.007) compared to PBMCs from healthy individuals, and the increase was unaltered after 12 weeks of etanercept therapy. TSA was a potent inhibitor of tumor necrosis factor (TNF) and interleukin-6 (IL-6) production in both RA and healthy PBMCs and of interferon-γ (IFNγ) production in healthy PBMCs; IFNγ was not produced by RA PBMCs. MI192 inhibited TNF production at high concentrations and dose-dependently inhibited IL-6 in RA PBMCs but not healthy PBMCs, across a dose range of 10 µM-5 nM. CONCLUSION: HDAC activity is dysregulated in RA PBMCs and is a potential target for therapeutic intervention, as it is not affected by conventional anti-TNF treatment with etanercept. Both the selective and the nonselective HDAC inhibitors (MI192 and TSA, respectively) were found to regulate cytokine production from PBMCs, but their effects were cell type and compound specific. HDAC inhibitors have potential in the treatment of RA, and HDAC-selective inhibition may improve the therapeutic margin of safety; however, further clinical characterization and evaluation for adverse effects is needed.

Two-step route to indoles and analogues from haloarenes: a variation on the Fischer indole synthesis.

In a new variation on the Fischer indole synthesis, readily available haloarenes are converted into a wide range of indoles in just two steps by halogen-magnesium exchange and quenching with di-tert-butyl azodicarboxylate, followed by reaction with aldehydes or ketones under acidic conditions. The protocol, which is readily extended to the preparation of indole isosteres, 4- and 6-azaindoles and thienopyrroles, obviates the need to prepare potentially toxic aryl hydrazines, simultaneously avoiding undesirable anilines such as naphthylamines.

A two step route to indoles from haloarenes--a versatile variation on the Fischer indole synthesis.

In a new variation on the Fischer indole synthesis, readily available haloarenes are converted into a wide range of indoles in just two steps by halogen-magnesium exchange, quenching with di-tert-butyl azodicarboxylate, followed by reaction with ketones under acidic conditions.

Synthesis of indolequinones from bromoquinones and enamines mediated by Cu(OAc)2.H2O.

A Cu(II)-mediated synthesis of indolequinones from the corresponding bromoquinones and enamines is reported. The key oxidative cyclization proceeds in good yield for a broad range of substrates and can be performed on a multigram scale, allowing access to biologically interesting structures.