The PPP1R15 Family of eIF2-alpha Phosphatase Targeting Subunits (GADD34 and CReP).

The vertebrate PPP1R15 family consists of the proteins GADD34 (growth arrest and DNA damage-inducible protein 34, the product of the PPP1R15A gene) and CReP (constitutive repressor of eIF2α phosphorylation, the product of the PPP1R15B gene), both of which function as targeting/regulatory subunits for protein phosphatase 1 (PP1) by regulating subcellular localization, modulating substrate specificity and assembling complexes with target proteins. The primary cellular function of these proteins is to facilitate the dephosphorylation of eukaryotic initiation factor 2-alpha (eIF2α) by PP1 during cell stress. In this review, we will provide a comprehensive overview of the cellular function, biochemistry and pharmacology of GADD34 and CReP, starting with a brief introduction of eIF2α phosphorylation via the integrated protein response (ISR). We discuss the roles GADD34 and CReP play as feedback inhibitors of the unfolded protein response (UPR) and highlight the critical function they serve as inhibitors of the PERK-dependent branch, which is particularly important since it can mediate cell survival or cell death, depending on how long the stressful stimuli lasts, and GADD34 and CReP play key roles in fine-tuning this cellular decision. We briefly discuss the roles of GADD34 and CReP homologs in model systems and then focus on what we have learned about their function from knockout mice and human patients, followed by a brief review of several diseases in which GADD34 and CReP have been implicated, including cancer, diabetes and especially neurodegenerative disease. Because of the potential importance of GADD34 and CReP in aspects of human health and disease, we will discuss several pharmacological inhibitors of GADD34 and/or CReP that show promise as treatments and the controversies as to their mechanism of action. This review will finish with a discussion of the biochemical properties of GADD34 and CReP, their regulation and the additional interacting partners that may provide insight into the roles these proteins may play in other cellular pathways. We will conclude with a brief outline of critical areas for future study.

Synthesis and antiprotozoal activity of mono- and bis-uracil isatin conjugates against the human pathogen Trichomonas vaginalis.

A library of mono- and bis-uracil isatin conjugates were synthesized and subjected for the assessment of their in vitro activity against the protozoal pathogen Trichomonas vaginalis. The structure activity studies (SAR) revealed that the bis-uracil-isatin based conjugates were more effective than their corresponding mono conjugates in inhibiting the growth of T. vaginalis at approximately 10 µM with no visual effect on mammalian cells at the same concentration.

Synthesis and preliminary in vitro activity of mono- and bis-1H-1,2,3-triazole-tethered ß-lactam-isatin conjugates against the human protozoal pathogen Trichomonas vaginalis.

In this study, we describe the synthesis of mono- and bis-1H-1,2,3-triazole-tethered ß-lactam-isatin conjugates using copper-catalysed azide-alkyne cycloaddition reaction between mono- and di-propargylated azetidin-2-ones and N-alkylazido isatins. The synthesized conjugates were evaluated for their preliminary in vitro analysis against Trichomonas vaginalis at 50 µM. The efficacy of synthesized hybrids was observed to depend on the substituent at N-1 position of ß-lactam ring, as well as the presence of single/double 1H-1,2,3-triazole linker. Among the synthesized conjugates, the presence of a p-tolyl substituent at N-1 of ß-lactam ring was preferred for good activity profiles while the increase in spacer length did not influence the efficacy of the compounds. Compounds with high levels of potency were further analysed to determine their IC50 values, as well as cytotoxicity profiles against mammalian cells. The most active compound in the synthesized conjugates displayed an IC50 value of 10.49 µM against cultured G3 strain of T. vaginalis and was non-toxic to cultured mammalian HeLa cells at the same concentration.

Gold(I) Phosphine Derivatives with Improved Selectivity as Topically Active Drug Leads to Overcome 5-Nitroheterocyclic Drug Resistance in Trichomonas vaginalis.

Trichomonas vaginalis causes the most common, nonviral sexually transmitted infection. Only metronidazole (Mz) and tinidazole are approved for treating trichomoniasis, yet resistance is a clinical problem. The gold(I) complex, auranofin, is active against T. vaginalis and other protozoa but has significant human toxicity. In a systematic structure-activity exploration, we show here that diversification of gold(I) complexes, particularly as halides with simple C1-C3 trialkyl phosphines or as bistrialkyl phosphine complexes, can markedly improve potency against T. vaginalis and selectivity over human cells compared to that of the existing antirheumatic gold(I) drugs. All gold(I) complexes inhibited the two most abundant isoforms of the presumed target enzyme, thioredoxin reductase, but a subset of compounds were markedly more active against live T. vaginalis than the enzyme, suggesting that alternative targets exist. Furthermore, all tested gold(I) complexes acted independently of Mz and were able to overcome Mz resistance, making them candidates for the treatment of Mz-refractory trichomoniasis.

AdoHcy hydrolase of Trichomonas vaginalis: studies of the effects of 5'-modified adenosine analogues and related 6-N-cyclopropyl derivatives.

Trypanosoma brucei and Trichomonas vaginalis are both parasitic protozoans that are known to share many similar biochemical pathways. Aristeromycin, as well as 5'-iodovinyl and 5'-oxime analogues of adenosine, are potent inhibitors of AdoHcy hydrolase in T. brucei, an enzyme that catalyses the hydrolysis of AdoHcy to adenosine and L-homocysteine. To help determine the role of this enzyme in T. vaginalis, we have tested a library of 5'-modified adenosine derivatives, including 5'-deoxy-5'-(iodomethylene)-adenosine and related 6-N-cyclopropyl analogues. Our results indicate that these inhibitors are effective at inhibiting the growth of T. vaginalis, by as much as 95%.

Preliminary studies of 3,4-dichloroaniline amides as antiparasitic agents: structure-activity analysis of a compound library in vitro against Trichomonas vaginalis.

Trichomonas vaginalis, a human-infectious protozoan, can display resistance to treatment by metronidazole. A library of 3,4-dichloroaniline amides based on propanil, an herbicide, has been synthesized and screened to test susceptibility to these analogs. From this preliminary study, the most effective compound 15, inhibits growth of the organism by 66% and 69% on the two strains tested, T1 and G3, respectively.

Production of hydrogen peroxide and redox cycling can explain how sanguinarine and chelerythrine induce rapid apoptosis.

Sanguinarine and chelerythrine are naturally occurring benzophenanthridines with multiple biological activities. Sanguinarine is believed to be a potential anticancer agent but its mechanism of action has not been fully elucidated. We previously found that it causes oxidative DNA damage and very rapid apoptosis that is not mediated by p53-dependent DNA damage signaling. Here we show that sanguinarine and chelerythrine cause the production of large amounts of reactive oxygen species (ROS), in particular hydrogen peroxide, which may deplete cellular antioxidants and provide a signal for rapid execution of apoptosis. Several oxidoreductases contribute to cell death induced by sanguinarine and chelerythrine which appear to be reduced upon entering the cell. We propose a model in which the generation of lethal amounts of hydrogen peroxide is explained by enzyme-catalyzed redox cycling between the reduced and oxidized forms of the phenanthridines and discuss the implications of such a mechanism for potential pharmaceutical applications.

Sanguinarine causes DNA damage and p53-independent cell death in human colon cancer cell lines.

The benzophenanthridine alkaloid sanguinarine has antimicrobial and possibly anticancer properties but it is not clear to what extent these activities involve DNA damage. Thus, we studied its ability to cause DNA single and double strand breaks, as well as increased levels of 8-oxodeoxyguanosine, in human colon cancer cells and found DNA damage consistent with oxidation. Since the tumor suppressor p53 is frequently involved in inducing apoptosis following DNA damage we investigated the effect of sanguinarine in wild type, p53-mutant and p53-null colon cancer cell lines. We found them to be equally sensitive to this plant compound, indicating that cell death is not mediated by p53 in this case. In addition, our observation that apoptosis induced by sanguinarine is initiated very rapidly raised the question whether there is enough time for cellular signaling in response to DNA damage. Moreover, the abundance of double strand breaks is not consistent with only oxidative damage to DNA. We conclude that the majority of DNA double strand breaks in sanguinarine-treated cells are likely the result, rather than the cause, of apoptotic cell death and that apoptosis induced by sanguinarine is independent of p53 and most likely independent of DNA damage.

Auranofin inactivates Trichomonas vaginalis thioredoxin reductase and is effective against trichomonads in vitro and in vivo.

Trichomoniasis, caused by the protozoan parasite Trichomonas vaginalis, is the most common, non-viral, sexually transmitted infection in the world, but only two closely related nitro drugs are approved for its treatment. New antimicrobials against trichomoniasis remain an urgent need. Several organic gold compounds were tested for activity against T. vaginalis thioredoxin reductase (TrxR) in cell-free systems as well as for activity against different trichomonads in vitro and in a murine infection model. The organic gold(I) compounds auranofin and chloro(diethylphenylphosphine)gold(I) inhibited TrxR in a concentration-dependent manner in assays with recombinant purified reductase and in cytoplasmic extracts of T. vaginalis transfected with a haemagglutinin epitope-tagged form of the reductase. Auranofin potently suppressed the growth of three independent clinical T. vaginalis isolates as well as several strains of another trichomonad (Tritrichomonas foetus) in a 24 h-assay, with 50% inhibitory concentrations of 0.7-2.5 µM and minimum lethal concentrations of 2-6 µM. The drug also compromised the ability of the parasite to overcome oxidant stress, supporting the notion that auranofin acts, in part, by inactivating TrxR-dependent antioxidant defences. Chloro(diethylphenylphosphine)gold(I) was 10-fold less effective against T. vaginalis in vitro than auranofin. Oral administration of auranofin for 4 days cleared the parasites in a murine model of vaginal T. foetus infection without displaying any apparent adverse effects. The approved human drug auranofin may be a promising agent as an alternative treatment of trichomoniasis in cases when standard nitro drug therapies have failed.

Recruitment of the proneural gene scute to the Drosophila sex-determination pathway.

In flies, scute (sc) works with its paralogs in the achaete-scute-complex (ASC) to direct neuronal development. However, in the family Drosophilidae, sc also acquired a role in the primary event of sex determination, X chromosome counting, by becoming an X chromosome signal element (XSE)-an evolutionary step shown here to have occurred after sc diverged from its closest paralog, achaete (ac). Two temperature-sensitive alleles, sc(sisB2) and sc(sisB3), which disrupt only sex determination, were recovered in a powerful F1 genetic selection and used to investigate how sc was recruited to the sex-determination pathway. sc(sisB2) revealed 3' nontranscribed regulatory sequences likely to be involved. The sc(sisB2) lesion abolished XSE activity when combined with mutations engineered in a sequence upstream of all XSEs. In contrast, changes in Sc protein sequence seem not to have been important for recruitment. The observation that the other new allele, sc(sisB3), eliminates the C-terminal half of Sc without affecting neurogenesis and that sc(sisB1), the most XSE-specific allele previously available, is a nonsense mutant, would seem to suggest the opposite, but we show that housefly Sc can substitute for fruit fly Sc in sex determination, despite lacking Drosophilidae-specific conserved residues in its C-terminal half. Lack of synergistic lethality among mutations in sc, twist, and dorsal argue against a proposed role for sc in mesoderm formation that had seemed potentially relevant to sex-pathway recruitment. The screen that yielded new sc alleles also generated autosomal duplications that argue against the textbook view that fruit fly sex signal evolution recruited a set of autosomal signal elements comparable to the XSEs.

Discovery of highly selective 7-chloroquinoline-thiohydantoins with potent antimalarial activity.

A series of C-3 thiourea functionalized ß-lactams, ß-lactam-7-chloroquinoline conjugates and 7-chloroquinoline-thiohydantoin derivatives were prepared with the aim of probing antimalarial structure-activity relationships. 7-Chlorquinoline-thiohydantoin derivatives were found to be potent inhibitors of cultured Plasmodium falciparum, with the most potent and non-cytotoxic compound exhibiting an IC50 of 39.8 nM. Studies of ß-hematin formation suggested that inhibition of haemozoin formation could be primary mechanism of action, with IC50 values comparable to those of chloroquine. Evaluation of cytotoxicity against HeLa cells demonstrated high selective indices.

Two closely related nickel complexes have different effects on DNA damage and cell viability.

Nickel is considered a weak carcinogen. It is known to interact with DNA and DNA-binding proteins. The ability of certain nickel compounds to cleave DNA has been exploited mainly for research purposes and less for developing new anticancer drugs. Here we compare the interactions of two closely related nickel complexes, [NiCR]2+ and [Ni(CR-2H)]2+, with DNA. CR stands for 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene. [NiCR]2+ has been used in the past as a structure-specific probe for RNA and DNA oligonucleotides in the presence of oxidizing agent but little is known about the biological effects of either complex. Our results show that [Ni(CR-2H)]2+ can damage DNA in vivo and in vitro in the absence of an added oxidizing agent and has an IC50 of 70 microM in human breast cancer cells whereas [NiCR]2+ and NiCl2 do not exhibit significant cytotoxicity. However, both [NiCR]2+ and [Ni(CR-2H)]2+ bind to the minor groove of double-stranded DNA.