Reaction hijacking inhibition of Plasmodium falciparum asparagine tRNA synthetase

Malaria poses an enormous threat to human health. With ever increasing resistance to currently deployed drugs, breakthrough compounds with novel mechanisms of action are urgently needed. Here, we explore pyrimidine-based sulfonamides as a new low molecular weight inhibitor class with drug-like physical parameters and a synthetically accessible scaffold. We show that the exemplar, OSM-S-106, has potent activity against parasite cultures, low mammalian cell toxicity and low propensity for resistance development. In vitro evolution of resistance using a slow ramp-up approach pointed to the Plasmodium falciparum cytoplasmic asparaginyl-tRNA synthetase (PfAsnRS) as the target, consistent with our finding that OSM-S-106 inhibits protein translation and activates the amino acid starvation response. Targeted mass spectrometry confirms that OSM-S-106 is a pro-inhibitor and that inhibition of PfAsnRS occurs via enzyme-mediated production of an Asn-OSM-S-106 adduct. Human AsnRS is much less susceptible to this reaction hijacking mechanism. X-ray crystallographic studies of human AsnRS in complex with inhibitor adducts and docking of pro-inhibitors into a model of Asn-tRNA-bound PfAsnRS provide insights into the structure-activity relationship and the selectivity mechanism.

A conserved complex of microneme proteins mediates rhoptry discharge in Toxoplasma

Apicomplexan parasites discharge specialized organelles called rhoptries upon host cell contact to mediate invasion. The events that drive rhoptry discharge are poorly understood, yet essential to sustain the apicomplexan parasitic life cycle. Rhoptry discharge appears to depend on proteins secreted from another set of organelles called micronemes, which vary in function from allowing host cell binding to facilitation of gliding motility. Here we examine the function of the microneme protein CLAMP, which we previously found to be necessary for Toxoplasma gondii host cell invasion, and demonstrate its essential role in rhoptry discharge. CLAMP forms a distinct complex with two other microneme proteins, the invasion-associated SPATR, and a previously uncharacterized protein we name CLAMP-linked invasion protein (CLIP). CLAMP deficiency does not impact parasite adhesion or microneme protein secretion; however, knockdown of any member of the CLAMP complex affects rhoptry discharge. Phylogenetic analysis suggests orthologs of the essential complex components, CLAMP and CLIP, are ubiquitous across apicomplexans. SPATR appears to act as an accessory factor in Toxoplasma, but despite incomplete conservation is also essential for invasion during Plasmodium falciparum blood stages. Together, our results reveal a new protein complex that mediates rhoptry discharge following host-cell contact.

Reaction hijacking inhibition of Plasmodium falciparum asparagine tRNA synthetase

Malaria poses an enormous threat to human health. With ever increasing resistance to currently deployed drugs, breakthrough compounds with novel mechanisms of action are urgently needed. Here, we explore pyrimidine-based sulfonamides as a new low molecular weight inhibitor class with drug-like physical parameters and a synthetically accessible scaffold. We show that the exemplar, OSM-S-106, has potent activity against parasite cultures, low mammalian cell toxicity and low propensity for resistance development. In vitro evolution of resistance using a slow ramp-up approach pointed to the Plasmodium falciparum cytoplasmic asparaginyl tRNA synthetase (PfAsnRS) as the target, consistent with our finding that OSM-S-106 inhibits protein translation and activates the amino acid starvation response. Targeted mass spectrometry confirms that OSM-S-106 is a pro-inhibitor and that inhibition of PfAsnRS occurs via enzyme-mediated production of an Asn-OSM-S-106 adduct. Human AsnRS is much less susceptible to this reaction hijacking mechanism. X-ray crystallographic studies of human AsnRS in complex with inhibitor adducts and docking of pro-inhibitors into a model of Asn-tRNA-bound PfAsnRS provide insights into the structure activity relationship and the selectivity mechanism.

The anticancer human mTOR inhibitor sapanisertib potently inhibits multiple Plasmodium kinases and life cycle stages

Compounds acting on multiple targets are critical to combating antimalarial drug resistance. Here, we report that the human "mammalian target of rapamycin" (mTOR) inhibitor sapanisertib has potent prophylactic liver stage activity, in vitro and in vivo asexual blood stage (ABS) activity, and transmission-blocking activity against the protozoan parasite Plasmodium spp. Chemoproteomics studies revealed multiple potential Plasmodium kinase targets, and potent inhibition of Plasmodium phosphatidylinositol 4-kinase type III beta (PI4Kβ) and cyclic guanosine monophosphate-dependent protein kinase (PKG) was confirmed in vitro. Conditional knockdown of PI4Kβ in ABS cultures modulated parasite sensitivity to sapanisertib, and laboratory-generated P. falciparum sapanisertib resistance was mediated by mutations in PI4Kβ. Parasite metabolomic perturbation profiles associated with sapanisertib and other known PI4Kβ and/or PKG inhibitors revealed similarities and differences between chemotypes, potentially caused by sapanisertib targeting multiple parasite kinases. The multistage activity of sapanisertib and its in vivo antimalarial efficacy, coupled with potent inhibition of at least two promising drug targets, provides an opportunity to reposition this pyrazolopyrimidine for malaria.

GERMPLASM BANKING AND ITS ROLE IN THE DEVELOPMENT OF THE FISH GENETIC IMPROVEMENT PROGRAMME IN BRAZIL

BACKGROUND

Over the last ten years, Brazilian fish farming has become more focused, resulting in the development of genetic improvement programmes (GIP) for two South American species Colossoma macropomum (tambaqui) and Pseudoplatystoma reticulatum (cachara).

OBJECTIVE

To describe the action plan used for setting up the GIP and to detail the germplasm bank composition.

MATERIALS AND METHODS

Semen of both species was collected, frozen and transported between locations in Brazil. To start the programme, full and half-sib families of both species were established from 120 males and 60 females.

RESULTS

New species-specific protocols for semen cryopreservation s were established of value to commercial application in fish farming.

CONCLUSION

Germplasm banking has enabled the exchange of biological material and reduced the overall GIP costs. Germplasm banking can be very important to the dissemination of the selected genetic material of these species among fish farmers.

Untargeted Proteomics and Systems-Based Mechanistic Investigation of Artesunate in Human Bronchial Epithelial Cells

The antimalarial drug artesunate is a semisynthetic derivative of artemisinin, the principal active component of a medicinal plant Artemisia annua. It is hypothesized to attenuate allergic asthma via inhibition of multiple signaling pathways. We used a comprehensive approach to elucidate the mechanism of action of artesunate by designing a novel biotinylated dihydroartemisinin (BDHA) to identify cellular protein targets of this anti-inflammatory drug. By adopting an untargeted proteomics approach, we demonstrated that artesunate may exert its protective anti-inflammatory effects via direct interaction with multiple proteins, most importantly with a number of mitochondrial enzymes related to glucose and energy metabolism, along with mRNA and gene expression, ribosomal regulation, stress responses, and structural proteins. In addition, the modulatory effects of artesunate on various cellular transcription factors were investigated using a transcription factor array, which revealed that artesunate can simultaneously modulate multiple nuclear transcription factors related to several major pro- and anti-inflammatory signaling cascades in human bronchial epithelial cells. Artesunate significantly enhanced nuclear levels of nuclear factor erythroid-2-related factor 2 (Nrf2), a key promoter of antioxidant mechanisms, which is inhibited by the Kelch-like ECH-associated protein 1 (Keap1). Our results demonstrate that, like other electrophilic Nrf2 regulators, artesunate activates this system via direct molecular interaction/modification of Keap1, freeing Nrf2 for transcriptional activity. Altogether, the molecular interactions and modulation of nuclear transcription factors provide invaluable insights into the broad pharmacological actions of artesunate in inflammatory lung diseases and related inflammatory disorders.

Discovery of a rare pterosaur bone bed in a cretaceous desert with insights on ontogeny and behavior of flying reptiles

A pterosaur bone bed with at least 47 individuals (wing spans: 0.65–2.35 m) of a new species is reported from southern Brazil from an interdunal lake deposit of a Cretaceous desert, shedding new light on several biological aspects of those flying reptiles. The material represents a new pterosaur, Caiuajara dobruskii gen. et sp. nov., that is the southermost occurrence of the edentulous clade Tapejaridae (Tapejarinae, Pterodactyloidea) recovered so far. Caiuajara dobruskii differs from all other members of this clade in several cranial features, including the presence of a ventral sagittal bony expansion projected inside the nasoantorbital fenestra, which is formed by the premaxillae; and features of the lower jaw, like a marked rounded depression in the occlusal concavity of the dentary. Ontogenetic variation of Caiuajara dobruskii is mainly reflected in the size and inclination of the premaxillary crest, changing from small and inclined (∼115°) in juveniles to large and steep (∼90°) in adults. No particular ontogenetic features are observed in postcranial elements. The available information suggests that this species was gregarious, living in colonies, and most likely precocial, being able to fly at a very young age, which might have been a general trend for at least derived pterosaurs.

Spatiotemporal intracellular nitric oxide signaling captured using internalized, near-infrared fluorescent carbon nanotube nanosensors

Fluorescent nanosensor probes have suffered from limited molecular recognition and a dearth of strategies for spatial-temporal operation in cell culture. In this work, we spatially imaged the dynamics of nitric oxide (NO) signaling, important in numerous pathologies and physiological functions, using intracellular near-infrared fluorescent single-walled carbon nanotubes. The observed spatial-temporal NO signaling gradients clarify and refine the existing paradigm of NO signaling based on averaged local concentrations. This work enables the study of transient intracellular phenomena associated with signaling and therapeutics.

Mechanism-based triarylphosphine-ester probes for capture of endogenous RSNOs

Nitrosothiols (RSNOs) have been proposed as important intermediates in nitric oxide (NO^•) metabolism, storage, and transport as well as mediators in numerous NO-signaling pathways. RSNO levels are finely regulated, and dysregulation is associated with the etiology of several pathologies. Current methods for RSNO quantification depend on indirect assays that limit their overall specificity and reliability. Recent developments of phosphine-based chemical probes constitute a promising approach for the direct detection of RSNOs. We report here results from a detailed mechanistic and kinetic study for trapping RSNOs by three distinct phosphine probes, including structural identification of novel intermediates and stability studies under physiological conditions. We further show that a triarylphosphine-thiophenyl ester can be used in the absolute quantification of endogenous GSNO in several cancer cell lines, while retaining the elements of the SNO functional group, using an LC–MS-based assay. Finally, we demonstrate that a common product ion (m/z = 309.0), derived from phosphine–RSNO adducts, can be used for the detection of other low-molecular weight nitrosothiols (LMW-RSNOs) in biological samples. Collectively, these findings establish a platform for the phosphine ligation-based, specific and direct detection of RSNOs in biological samples, a powerful tool for expanding the knowledge of the biology and chemistry of NO^•-mediated phenomena.

Abstract 894: Melanoma fights cisplatin with NO: S-nitrosation as a mechanism supporting drug-resistance

Melanoma patients experience inferior survival after bio-chemotherapy when their tumors contain numerous cells expressing the inducible isoform of NO synthase (iNOS), and elevated levels of nitrotyrosine, a product derived from nitric oxide (NO). Although several lines of evidence suggest that NO promotes tumor growth and increases resistance to chemotherapy, it is unclear how it shapes these outcomes. Here we demonstrate that modulation of NO-mediated S-nitrosation of cellular proteins is strongly associated with the pattern of response to the anti-cancer agent cisplatin in human melanoma cells in vitro. Cells were shown to express iNOS constitutively, and to generate sustained nanomolar levels of NO intracellularly. Inhibition of NO synthesis or scavenging of NO enhanced cisplatin-induced apoptotic cell death. Additionally, pharmacologic agents disrupting S-nitrosation markedly increased cisplatin toxicity, whereas treatments favoring stabilization of S-nitrosothiols decreased its cytotoxic potency. Activity of the pro-apoptotic enzyme caspase-3 was higher in cells treated with a combination of cisplatin and chemicals that decreased NO/S-nitrisothiols, whereas lower activity resulted from cisplatin combined with stabilization of S-nitrisothiols. Constitutive protein S-nitrosation in cells was detected by analysis with biotin switch and reduction/chemiluminescence techniques. Moreover, intracellular NO concentration increased significantly in cells that survived cisplatin treatment, resulting in augmented S-nitrosation of caspase-3 and prolyl-hydroxylase-2 (PHD2), the enzyme responsible for targeting the pro-survival transcription factor HIF-1α for proteasomal degradation. Because activities of these enzymes are inhibited by S-nitrosation, our data thus indicate that modulation of intrinsic intracellular NO levels substantially affects cisplatin toxicity in melanoma cells. The underlying mechanisms may thus represent potential targets for adjuvant strategies to improve the efficacy of chemotherapy.

Citation Format: Luiz C. Godoy, Chase C.T. Anderson, Rajdeep Chowdhury, Laura J. Trudel, Gerald N. Wogan. Melanoma fights cisplatin with NO: S-nitrosation as a mechanism supporting drug-resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 894. doi:10.1158/1538-7445.AM2013-894

Nitric oxide produced endogenously is responsible for hypoxia-induced HIF-1α stabilization in colon carcinoma cells

Hypoxia-inducible factor-1α (HIF-1α) is a critical regulator of cellular responses to hypoxia. Under normoxic conditions, the cellular HIF-1α level is regulated by hydroxylation by prolyl hydroxylases (PHDs), ubiquitylation, and proteasomal degradation. During hypoxia, degradation decreases, and its intracellular level is increased. Exogenously administered nitric oxide (NO)-donor drugs stabilize HIF-1α; thus, NO is suggested to mimic hypoxia. However, the role of low levels of endogenously produced NO generated during hypoxia in HIF-1α stabilization has not been defined. Here, we demonstrate that NO and reactive oxygen species (ROS) produced endogenously by human colon carcinoma HCT116 cells are responsible for HIF-1α accumulation in hypoxia. The antioxidant N-acetyl-L-cysteine (NAC) and NO synthase inhibitor N(G)-monomethyl L-arginine (L-NMMA) effectively reduced HIF-1α stabilization and decreased HIF-1α hydroxylation. These effects suggested that endogenous NO and ROS impaired PHD activity, which was confirmed by reversal of L-NMMA- and NAC-mediated effects in the presence of dimethyloxaloylglycine, a PHD inhibitor. Thiol reduction with dithiothreitol decreased HIF-1α stabilization in hypoxic cells, while dinitrochlorobenzene, which stabilizes S-nitrosothiols, favored its accumulation. This suggested that ROS- and NO-mediated HIF-1α stabilization involved S-nitrosation, which was confirmed by demonstrating increased S-nitrosation of PHD2 during hypoxia. Our results support a regulatory mechanism of HIF-1α during hypoxia in which endogenously generated NO and ROS promote inhibition of PHD2 activity, probably by its S-nitrosation.

Increasing storage capability of pacu (Piaractus mesopotamicus) embryos by chilling: development of a useful methodology for hatcheries management

Cryopreservation of fish gametes has been studied extensively in the last few decades, but the successful cryopreservation of fish embryos remains elusive. However, recent studies using short-term chilling techniques have shown that it is possible to store embryos at low temperatures with no significant loss in viability. Information on cryopreservation of Neotropical freshwater fish embryos has so far been very limited in the literature. In the present study, chilling protocols for storage of pacu embryos at -8°C for up to 24 h were studied using different concentrations of sucrose in methanol. Embryos tolerated the subzero temperature for up to 6 h with no adverse effects (P > 0.05). After 12 h chilling, hatching rate of 64.0 +/- 3.5 percent was recorded. Low temperature storage of pacu embryos by chilling is detailed here for the first time. Further studies are needed to extend the storage time and to improve the hatching rate.

PPARγ expression is increased in systemic lupus erythematosus patients and represses CD40/CD40L signaling pathway

Systemic lupus erythematosus (SLE) is a heterogeneous disease involving several immune cell types and pro-inflammatory signals, including the one triggered by binding of CD40L to the receptor CD40. Peroxisome-proliferator activated receptor gamma (PPARγ) is a transcription factor with anti-inflammatory properties. Here we investigated whether CD40 and PPARγ could exert opposite effects in the immune response and the possible implications for SLE. Increased PPARγ mRNA levels were detected by real-time PCR in patients with active SLE, compared to patients with inactive SLE PPARγ/GAPDH mRNA = 2.21 ± 0.49 vs. 0.57 ± 0.14, respectively (p < 0.05) or patients with infectious diseases and healthy subjects (p < 0.05). This finding was independent of the corticosteroid therapy. We further explored these observations in human THP1 and in SLE patient-derived macrophages, where activation of CD40 by CD40L promoted augmented PPARγ gene transcription compared to non-stimulated cells (PPARγ/GAPDH mRNA = 1.14 ± 0.38 vs. 0.14 ± 0.01, respectively; p < 0.05). This phenomenon occurred specifically upon CD40 activation, since lipopolysaccharide treatment did not induce a similar response. In addition, increased activity of PPARγ was also detected after CD40 activation, since higher PPARγ-dependent transcription of CD36 transcription was observed. Furthermore, CD40L-stimulated transcription of CD80 gene was elevated in cells treated with PPARγ-specific small interfering RNA (small interfering RNA, siRNA) compared to cells treated with CD40L alone (CD80/GAPDH mRNA = 0.11 ± 0.04 vs. 0.05 ± 0.02, respectively; p < 0.05), suggesting a regulatory role for PPARγ on the CD40/CD40L pathway. Altogether, our findings outline a novel mechanism through which PPARγ regulates the inflammatory signal initiated by activation of CD40, with important implications for the understanding of immunological mechanisms underlying SLE and the development of new treatment strategies.

Abstract 204: Disruption of S-nitrosothiols decreases chemoresistance in melanoma cells

Exposure to nitric oxide (NO•) during inflammation has been implicated in the development of various forms of cancer, including melanoma. Clinical and epidemiologic studies indicate that expression of inducible nitric oxide synthase (NOS2), as well as NO• production by tumor cells, correlate with patient mortality. NO• favors resistance to drug-induced apoptosis in melanoma cells and may do so by caspases inactivation through S-nitrosation, which could represent a mechanism responsible for NO• inhibition of apoptosis. Here we further investigate how S-nitrosation impacts apoptotic and survival pathways in human melanoma. We demonstrate that A375, SK-Mel 100 and SK-Mel 28 cells constitutively express NOS2 and that an inhibitor of NO• synthesis decreases cell proliferation. Moreover, this same treatment, or the pre-incubation with the NO• scavenger carboxy-PTIO, leads to enhanced toxicity of cisplatin, suggesting that endogenous NO• regulates growth and enhances anti-apoptotic mechanisms in melanoma cells. This anti-apoptotic effect may be due to protein S-nitrosation promoted by endogenous NO•, because disruption of nitrosothiols by dithiothreitol promotes a remarkable increase in cisplatin-induced cell death in comparison with cells treated with cisplatin alone (80% vs. 20% cell death, respectively). On the other hand, when accumulation of cellular nitrosothiols is favored via inhibition of thioredoxin reductase by 1-chloro-2,4-dinitrobenzene, increased resistance to cisplatin is seen in A375 cells. Using the biotin switch technique (BST), a low, yet detectable level of endogenous protein S-nitrosation is seen in A375 cells. The properties conferred by exogenous NO• to melanoma cells were studied in a controlled-delivery system to simulate NO• concentrations known to occur in inflamed tissues. Using this system, the toxicity of NO• was shown to be lower in A375, SK-Mel 100 and SK-Mel 28 cells when compared to other non-melanoma cell lines. The possible protective effect of a chronic exposure to a non-toxic dose of exogenous NO• was investigated. A375 cells were treated with 0.64 µM NO• or argon (control) for 24 hours and then cisplatin was added to the system. Cell viability was assessed 24 hours later with trypan blue staining. While nearly 50% cell death was seen in argon+cisplatin-treated cells, no significant cell death occurred under NO•+cisplatin treatment, which points to an anti-apoptotic effect of low, sustained doses of NO• in this system. Finally, using the BST, the level of global protein S-nitrosation in the cells exposed to 0.64 µM NO• was shown to be considerably increased. Collectively, these results show that NO• favors survival and proliferation of melanoma cells in vitro, possibly by S-nitrosation of components of the signaling cascades. Identification of the proteins susceptible to this NO•-mediated modification will help to devise rational strategies for disease intervention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 204.

Role of distinct immune components in the radiation-induced abrogation of systemic lupus erythematosus development in mice

The New Zealand Black x New Zealand White F1 [(NZB/NZW) F1] mouse develops an autoimmune condition resembling aspects of human systemic lupus erythematosus (SLE). We investigated the effects of a novel prophylactic thoraco-abdominal gamma irradiation protocol on the onset and evolution of lupus in these animals. Survival of irradiated mice was higher when compared with nonirradiated mice. Kidney lesions were milder and autoantibody levels were lower in irradiated mice. To identify possible mechanisms involved in the radiation-induced improvement of disease, distinct components of humoral and cellular immune responses were evaluated. Because B-1 cells are known to be involved in various autoimmune diseases, we investigated the participation of these cells in SLE progression. Unexpectedly, B-1 cells were not depleted in (NZB/NZW) F1, even after several rounds of irradiation. No alterations were found in viability and physiology of B-1 cells in SLE animals with the exception of constitutive overexpression of the anti-apoptotic molecule Bcl-2, which may account for the observed radioresistance. Thus, a role for B-1 cells in murine SLE cannot be excluded, since the irradiation protocol did not effectively eliminate these cells. Additionally, we demonstrate a marked delay in the ability of splenocytes to repopulate the spleen after irradiation in (NZB/NZW) F1, in contrast to leucocytes in other cellular compartments. The implications of these findings for the fate of SLE in this model are discussed.

Low coronary driving pressure is associated with subendocardial remodelling and left ventricular dysfunction in aortocaval fistula

1. The role of haemodynamic changes in left ventricular remodelling has been poorly investigated, especially in the context of volume overload cardiac hypertrophy. Low diastolic blood pressure and high left ventricular filling pressure are expected to affect coronary driving pressure negatively and thereby put in jeopardy subendocardial perfusion in particular. The consequences to global left ventricular remodelling remain undetermined. The aim of the present study was to investigate the role of coronary driving pressure in the development of subendocardial remodelling and the conceivable effects on cardiac function, using a rat model of aortocaval fistula. 2. Wistar rats, weighing 330-350 g, were submitted to aortocaval fistula (ACF group) or sham (control group) operations. Two haemodynamic measurements were determined following surgery, the initial measurement at week 1 and the final measurement at week 8. Cytokine expression, myeloperoxidase (MPO) activity, metalloproteinase expression and activity and fibrosis were assessed in two distinct left ventricular myocardial layers: the subendocardium (SE) and the non-subendocardium (non-SE). 3. The ACF group showed lower initial and final coronary driving pressure and lower final +dP/dt and -dP/dt compared with the control group. Multivariate analyses disclosed initial coronary driving pressure as the only haemodynamic parameter independently associated with SE fibrosis (R(2) = 0.76; P < 0.0001) and with +dP/dt (R(2) = 0.55; P = 0.0004) and -dP/dt (R(2) = 0.91; P < 0.0001). Matrix metalloproteinase (MMP)-2 expression and activity predominated in the SE of ACF animals, particularly in those with low coronary driving pressure. Increased levels of interleukin (IL)-6 and IL-1beta also predominated in the SE of the ACF group. Otherwise, MPO activity and levels of tumour necrosis factor-alpha and IL-10 were similar in both groups. Final coronary driving pressure correlated with both the expression and activity of MMP-2. 4. Low coronary driving pressure early in the course of ACF determines SE damage and, by this mechanism, interferes negatively in left ventricular function.