Toll-like receptors (TLRs) are a class of pattern recognition receptors that play a bridging role in innate immunity and adaptive immunity. The activated TLRs not only induce inflammatory responses, but also elicit the development of antigen specific immunity. TLR7, a member of TLR family, is an intracellular receptor expressed on the membrane of endosomes. TLR7 can be triggered not only by ssRNA during viral infections, but also by immune modifiers that share a similar structure to nucleosides. Its powerful immune stimulatory action can be potentially used in the anti-tumor therapy. This article reviewed the anti-tumor activity and mechanism of TLR7 agonists that are frequently applied in preclinical and clinical investigations, and mainly focused on small synthetic molecules, including imiquimod, resiquimod, gardiquimod, and 852A, etc.

Recent studies show that redox-active small molecules are selectively cytotoxic to chronic lymphocytic leukemia (CLL). Although elevated levels of reactive oxygen species in CLL cells have been implicated, the molecular mechanism underlying this selectivity is unclear. In other cell types, the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway regulates the oxidative stress response. We found elevated Nrf2 signaling in untreated CLL cells compared with normal lymphocytes. Therefore, we tested 27 known electrophilic and antioxidant compounds with drug-like properties and determined their CLL-selective cytotoxicity and effect on Nrf2 signaling. The selected compounds were from five distinct structural classes; α-β unsaturated carbonyls, isothiocyanates, sulfhydryl reactive metals, flavones, and polyphenols. Our results show that compounds containing α-β unsaturated carbonyls, sulfhydryl reactive metals, and isothiocyanates are strong activators of Nrf2 in a reporter assay system and in primary human CLL based on increased expression of the Nrf2 target heme oxygenase-1. α-β Unsaturated carbonylcontaining compounds were selectively cytotoxic to CLL, and loss of the α-β unsaturation abrogated Nrf2 activity and CLL toxicity. The α-β unsaturated carbonyl containing compounds ethacrynic acid and parthenolide activated Nrf2 in normal peripheral blood mononuclear cells, but had a less potent effect in CLL cells. Furthermore, ethacrynic acid bound directly to the Nrf2-negative regulator Kelchlike ECH-associated protein 1 (Keap1) in CLL cells. These experiments document the presence of Nrf2 signaling in human CLL and suggest that altered Nrf2 responses may contribute to the observed selective cytotoxicity of electrophilic compounds in this disease.antioxidant response | electrophilic stress response activators | natural product | dietary component

The enzymes involved in the biosynthesis of riboflavin represent attractive targets for the development of drugs against bacterial pathogens, because the inhibitors of these enzymes are not likely to interfere with enzymes of the mammalian metabolism. Lumazine synthase catalyzes the penultimate step in the riboflavin biosynthesis pathway. A number of substituted purinetrione compounds represent a new class of highly specific inhibitors of lumazine synthase from Mycobacterium tuberculosis. To develop potent antibiotics for the treatment of tuberculosis, we have determined the structure of lumazine synthase from M. tuberculosis in complex with two purinetrione inhibitors and have studied binding via isothermal titration calorimetry. The structures were determined by molecular replacement using lumazine synthase from Saccharomyces cerevisiae as a search model and refined at 2 and 2.3 A resolution. The R-factors were 14.7 and 17.4%, respectively, and the R(free) values were 19.3 and 26.3%, respectively. The enzyme was found to be a pentamer consisting of five subunits related by 5-fold local symmetry. The comparison of the active site architecture with the active site of previously determined lumazine synthase structures reveals a largely conserved topology with the exception of residues Gln141 and Glu136, which participate in different charge-charge interactions in the core space of the active site. The impact of structural changes in the active site on the altered binding and catalytic properties of the enzyme is discussed. Isothermal titration calorimetry measurements indicate highly specific binding of the purinetrione inhibitors to the M. tuberculosis enzyme with dissociation constants in micromolar range.

Lumazine synthase and riboflavin synthase catalyze the last two steps in the biosynthesis of riboflavin, an essential metabolite that is involved in electron transport processes. To obtain structural probes of these two enzymes, as well as inhibitors of potential value as antibiotics, a series of ribitylpurinetriones bearing alkyl phosphate and alpha,alpha-difluorophosphonate substituents were synthesized. Since the purinetrione ring system and the ribityl hydroxyl groups can be alkylated, the synthesis required the generation of these two moieties in protected form before the desired alkylation reaction could be carried out. These substances were designed as intermediate analogue inhibitors of lumazine synthase that would bind to its phosphate-binding site. All of the compounds were found to be effective inhibitors of both Bacillus subtilis lumazine synthase as well as Escherichia coli riboflavin synthase. Molecular modeling of the binding of 3-(1,3,7,9-tetrahydro-9-D-ribityl-2,6,8-trioxopurin-7-yl)propane 1-phosphate provided a structural explanation for how these compounds are able to effectively inhibit both enzymes. Interestingly, the enzyme kinetics of these new compounds in comparison with the parent purinetrione demonstrated unexpectedly that the phosphate and phosphonate substituents contributed negatively to the binding. A possible explanation for these effects on lumazine synthase would be that the inorganic phosphate in the assay buffer competes with the substituted purinetriones for binding to the enzyme. This would be consistent with the observed increase in K(m) of the 3,4-dihydroxybutanone-4-phosphate substrate from 5.2 microM in Tris buffer or from 6.7 microM in MOPS buffer to 50 microM in phosphate buffer when tested on Bacillus subtilis lumazine synthase. However, when tested in Tris buffer vs Mycobacterium tuberculosis lumazine synthase, three of the phosphate inhibitors displayed inhibition constants in the 4-5 nM range, indicating that they are much more potent than the parent purinetrione. Under these conditions, the phosphate moieties of the inhibitors do contribute positively to their binding. The alpha,alpha-difluorophosphonate analogue, which is expected to have enhanced metabolic stability relative to the phosphates, was also found to be an inhibitor of Mycobacterium tuberculosis lumazine synthase with a K(i) of 60 nM.

We describe herein the synthesis and biological activity of two indoloazepines that are structurally related to the marine sponge metabolite hymenialdisine. The natural product hymenialdisine was found to be a potent inhibitor of interleukin-2 (IC(50) = 2.4 microM) and tumor necrosis factor alpha (IC(50) = 1.4 microM) production. One of the hymenialdisine derived indoloazepines was found to also inhibit interleukin-2 (IC(50) = 3.5 microM) and tumor necrosis factor alpha (IC(50) = 8.2 microM) production.

Conventional chemotherapy remains the primary treatment option for triple-negative breast cancer (TNBC). However, the current chemotherapeutic drugs have limited effects on TNBC, and often lead to serious side effects as well as drug resistance. Thus, more effective therapeutic options are sorely needed. As c-MYC oncogene is highly expressed during TNBC pathogenesis, inhibiting c-MYC expression would be an alternative anti-TNBC strategy. In this study, we designed and synthesized a serial of quinoxaline analogs that target c-MYC promoter G-quadruplex (G4), which is believed to be a repressor of c-MYC transcription. Among them, a difluoro-substituted quinoxaline QN-1 was identified as the most promising G4-stabilizing ligand with high selectivity to c-MYC G4 over other G4s, which is distinguished from many other reported ligands. Intracellular studies indicated that QN-1 induced cell cycle arrest and apoptosis, repressed metastasis and inhibited TNBC cell growth, primarily due to the downregulation of c-MYC transcription by a G4-dependent mechanism. Notably, inhibition by QN-1 was significantly greater for c-MYC than other G4-driven genes. Cancer cells with c-MYC overexpression were more sensitive to QN-1, relative to normal cells. Furthermore, QN-1 effectively suppressed tumor growth in a TNBC mouse model. Accordingly, this work provides an alternative strategy for treating TNBC.

BackgroundConventional chemotherapy and radiotherapy for the treatment of lymphoma have notable drawbacks, and passive immunotherapy using a monoclonal antibody is restricted to CD20-positive B cell lymphoma. Therefore, new treatment types are urgently required, especially for T cell lymphoma. One type of new antitumour therapy is the use of active immunotherapeutic agents, such as agonists of the Toll-like receptors (TLRs), which facilitate the induction of prolonged antitumour immune responses.MethodsWe have synthesised a novel TLR7 agonist called SZU-101 and investigated the systemic antitumour effect on a murine model of T cell lymphoma in vivo.ResultsHere, we report that the intratumoural administration of SZU-101 enhanced the effectiveness of a conventionally used chemotherapeutic agent, doxorubicin (DOX). SZU-101 administration improved tumour clearance in a murine model of T cell lymphoma. The novel combination of intratumourally administered SZU-101 and DOX generated strong cytokine production and enhanced the cytotoxic T lymphocyte response, leading to the eradication of both local and distant tumours in tumour-bearing mice.ConclusionsThese findings suggested that combined active immunotherapy can be developed as a promising treatment for T cell lymphoma, which may further improve the effectiveness of the current standard cyclophosphamide, DOX, vincristine and prednisone (CHOP) therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-015-0121-9) contains supplementary material, which is available to authorized users.

The penultimate step in the biosynthesis of riboflavin is catalyzed by lumazine synthase. Three metabolically stable analogues of the hypothetical intermediate proposed to arise after phosphate elimination in the lumazine synthase-catalyzed reaction were synthesized and evaluated as lumazine synthase inhibitors. All three intermediate analogues were inhibitors of Mycobacterium tuberculosis lumazine synthase, Bacillus subtilis lumazine synthase, and Schizosaccharomyces pombe lumazine synthase, while one of them proved to be an extremely potent inhibitor of Escherichia coli riboflavin synthase with a Ki of 1.3 nM. The crystal structure of M. tuberculosis lumazine synthase in complex with one of the inhibitors provides a model of the conformation of the intermediate occurring immediately after phosphate elimination, supporting a mechanism in which phosphate elimination occurs before a conformational change of the Schiff base intermediate toward a cyclic structure.