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1.  Lipidomic analysis of bloodstream and procyclic form Trypanosoma brucei 
Parasitology  2010;137(9):1357-1392.
The biological membranes of Trypanosoma brucei contain a complex array of phospholipids that are synthesized de novo from precursors obtained either directly from the host, or as catabolised endocytosed lipids. This paper describes the use of nanoflow electrospray tandem mass spectrometry and high resolution mass spectrometry in both positive and negative ion modes, allowing the identification of ~500 individual molecular phospholipids species from total lipid extracts of cultured bloodstream and procyclic form T. brucei. Various molecular species of all of the major subclasses of glycerophospholipids were identified including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol as well as phosphatidic acid, phosphatidylglycerol and cardolipin, and the sphingolipids sphingomyelin, inositol phosphoceramide and ethanolamine phosphoceramide. The lipidomic data obtained in this study will aid future biochemical phenotyping of either genetically or chemically manipulated commonly used bloodstream and procyclic strains of Trypanosoma brucei. Hopefully this will allow a greater understanding of the bizarre world of lipids in this important human pathogen.
PMCID: PMC3744936  PMID: 20602846
Phospholipid; Trypanosoma brucei; mass spectrometry; lipidomics
2.  ON 01910.Na is selectively cytotoxic for Chronic Lymphocytic Leukemia cells through a dual mechanism of action involving PI3K/AKT inhibition and induction of oxidative stress 
Clinical Cancer Research  2012;18(7):1979-1991.
Chronic Lymphocytic Leukemia (CLL), a malignancy of mature B-cells, is incurable with chemotherapy. Signals from the microenvironment support leukemic cell survival and proliferation, and may confer chemotherapy resistance. ON 01910.Na (Rigosertib) a multikinase PI3K inhibitor is entering phase III trials for myelodysplastic syndrome. Our aim was to analyze the efficacy of ON 01910.Na against CLL cells in vitro and investigate the molecular effects of this drug on tumor biology.
Experimental design
Cytotoxicity of ON 01910.Na against CLL cells from 34 patients was determined in vitro using flow cytometry of cells stained with Annexin V and CD19. Global gene expression profiling on Affymetrix microarrays, flow cytometry, western blotting, and co-cultures with stroma cells were used to delineate ON 01910.Na mechanism of action.
ON 01910.Na induced apoptosis in CLL B-cells without significant toxicity against T-cells or normal B-cells. ON 01910.Na was equally active against leukemic cells associated with a more aggressive disease course (IGHV unmutated, adverse cytogenetics) than against cells without these features. Gene expression profiling revealed two main mechanisms of action: PI3K/AKT inhibition and induction of ROS that resulted in an oxidative stress response through activating protein 1 (AP-1), c-Jun NH2-terminal kinase, and ATF3 culminating in the upregulation of NOXA. ROS scavengers and shRNA mediated knockdown of ATF3 and NOXA protected cells from drug induced apoptosis. ON 01910.Na also abrogated the pro-survival effect of follicular dendritic cells on CLL cells and reduced SDF-1-induced migration of leukemic cells.
These data support the clinical development of ON 01910.Na in CLL.
PMCID: PMC3321371  PMID: 22351695
3.  CD44 signaling via PI3K/AKT and MAPK/ERK pathways protects CLL cells from spontaneous and drug induced apoptosis through MCL-1 
Leukemia & lymphoma  2011;52(9):1758-1769.
Survival of chronic lymphocytic leukemia (CLL) cells in vivo is supported by the tissue microenvironment, which includes components of the extracellular matrix. Interactions between tumor cells and the extracellular matrix are in part mediated by CD44, whose principle ligand in this respect is hyaluronic acid. Purpose: to evaluate the effect of CD44 engagement on the survival of CLL cells. Experimental Design: CD44 in CLL cells was engaged by anti-CD44 monoclonal antibody, or hyaluronic acid, and the effects of CD44 activation on CLL cell viability and pro-survival pathways were evaluated. Results: engagement of CD44 activated the PI3K/AKT and MAPK/ERK pathways and increased MCL-1 protein expression. Consistent with the induction of these anti-apoptotic mechanisms, CD44 protected CLL cells from spontaneous and fludarabine-induced apoptosis. Leukemic cells of the more aggressive CLL subtype that express unmutated IgVH genes (U-CLL) showed higher CD44 expression than IgVH-mutated CLL (M-CLL) cells, and acquired a greater survival advantage via CD44 activation. Thus, CD44 activation in the tissue microenvironment may contribute to increased MCL-1 protein levels, resistance to apoptosis, and could contribute to the more progressive nature of U-CLL. Furthermore, PI3K or MEK inhibitors as well as obatoclax, an antagonist of MCL-1, blocked the pro-survival effect of CD44. In addition, obatoclax synergized with fludarabine to induce apoptosis of CLL cells. Conclusions: components of the extracellular matrix may provide survival signals to CLL cells through engagement of CD44. Inhibition of MCL-1, PI3K, and MAPK/ERK pathways are promising strategies to reduce the anti-apoptotic effect of the microenvironment on CLL cells.
PMCID: PMC3403533  PMID: 21649540
4.  The role of perforin-mediated cell apoptosis in murine models of infusion-induced bone marrow failure 
Experimental hematology  2009;37(4):477-486.
To investigate the role of perforin-mediated cell apoptosis in murine models of immune-mediated bone marrow (BM) failure.
We compared C57BL/6J (B6) mice carrying a perforin gene deletion (Prf−/−) with wild type (WT) controls for cellular composition in lymphohematopoietic tissues. Lymph node (LN) cells from Prf−/− mice were co-incubated with BM cells from B10-H2b/LilMcdJ (C.B10) mice in an apoptosis assay in vitro. We then infused Prf−/− and WT B6 LN cells into sublethally-irradiated C.B10 and CByB6F1 recipients with mismatches at the minor- and major-histocompatibility loci, respectively, in order to induce BM failure. Cellular composition was analyzed by flow cytometry.
Prf−/− mice showed normal lymphoid cell composition but Prf−/− LN cells had reduced ability to induce C.B10 BM cell apoptosis in vitro. Infusion of 5–10 × 106 Prf−/− LN cells produced obvious BM failure in C.B10 and CByB6F1 recipients; pancytopenia and BM hypocellularity were only slightly less severe than those caused by infusion of 5 × 106 WT B6 LN cells. Infused Prf−/− LN cells showed less T cell expansion, normal T cell activation, and higher proportions of T cells expressing gamma-interferon, tissue necrosis factor alpha and Fas ligand CD178, in comparison to infused WT B6 LN cells. Fas expression was equally high in residual BM cells in recipient of both Prf−/− and B6 LN cells.
Perforin deficiency alters T cell expansion but up-regulates T cell Fas ligand expression. Perforin-mediated cell death appears to play a minor role in mouse models of immune-mediated BM failure.
PMCID: PMC2692757  PMID: 19216020
5.  Biochemical characterization of the initial steps of the Kennedy pathway in Trypanosoma brucei: the ethanolamine and choline kinases 
Biochemical Journal  2008;415(Pt 1):135-144.
Ethanolamine and choline are major components of the trypanosome membrane phospholipids, in the form of GPEtn (glycerophosphoethanolamine) and GPCho (glycerophosphocholine). Ethanolamine is also found as an integral component of the GPI (glycosylphosphatidylinositol) anchor that is required for membrane attachment of cell-surface proteins, most notably the variant-surface glycoproteins. The de novo synthesis of GPEtn and GPCho starts with the generation of phosphoethanolamine and phosphocholine by ethanolamine and choline kinases via the Kennedy pathway. Database mining revealed two putative C/EKs (choline/ethanolamine kinases) in the Trypanosoma brucei genome, which were cloned, overexpressed, purified and characterized. TbEK1 (T. brucei ethanolamine kinase 1) was shown to be catalytically active as an ethanolamine-specific kinase, i.e. it had no choline kinase activity. The Km values for ethanolamine and ATP were found to be 18.4±0.9 and 219±29 μM respectively. TbC/EK2 (T. brucei choline/ethanolamine kinase 2), on the other hand, was found to be able to phosphorylate both ethanolamine and choline, even though choline was the preferred substrate, with a Km 80 times lower than that of ethanolamine. The Km values for choline, ethanolamine and ATP were 31.4±2.6 μM, 2.56±0.31 mM and 20.6±1.96 μM respectively. Further substrate specificity analysis revealed that both TbEK1 and TbC/EK2 were able to tolerate various modifications at the amino group, with the exception of a quaternary amine for TbEK1 (choline) and a primary amine for TbC/EK2 (ethanolamine). Both enzymes recognized analogues with substituents on C-2, but substitutions on C-1 and elongations of the carbon chain were not well tolerated.
PMCID: PMC2552378  PMID: 18489261
choline kinase; ethanolamine kinase; Kennedy pathway; Trypanosoma brucei; C/EK, choline/ethanolamine kinase; EK, ethanolamine kinase; GPCho, glycerophosphocholine; GPEtn, glycerophosphoethanolamine; GPI, glycosylphosphatidylinositol; GPSer, glycerophosphoserine; HPTLC, high-performance TLC; LB, Luria–Bertani; MALDI, matrix-assisted laser-desorption ionization; ORF, open reading frame; PtdCho, phosphotidylcholine; PtdEtn, phosphatidylethanolamine; RT, reverse transcription; Tb, Trypanosome brucei; TEV, tobacco etch virus; TOF, time-of-flight; UTR, untranslated region; VSG, variant-surface glycoprotein
6.  Structure and reactivity of Trypanosoma brucei pteridine reductase: inhibition by the archetypal antifolate methotrexate 
Molecular Microbiology  2006;61(6):1457-1468.
The protozoan Trypanosoma brucei has a functional pteridine reductase (TbPTR1), an NADPH-dependent short-chain reductase that participates in the salvage of pterins, which are essential for parasite growth. PTR1 displays broad-spectrum activity with pterins and folates, provides a metabolic bypass for inhibition of the trypanosomatid dihydrofolate reductase and therefore compromises the use of antifolates for treatment of trypanosomiasis. Catalytic properties of recombinant TbPTR1 and inhibition by the archetypal antifolate methotrexate have been characterized and the crystal structure of the ternary complex with cofactor NADP+ and the inhibitor determined at 2.2 Å resolution. This enzyme shares 50% amino acid sequence identity with Leishmania major PTR1 (LmPTR1) and comparisons show that the architecture of the cofactor binding site, and the catalytic centre are highly conserved, as are most interactions with the inhibitor. However, specific amino acid differences, in particular the placement of Trp221 at the side of the active site, and adjustment of the β6-α6 loop and α6 helix at one side of the substrate-binding cleft significantly reduce the size of the substrate binding site of TbPTR1 and alter the chemical properties compared with LmPTR1. A reactive Cys168, within the active site cleft, in conjunction with the C-terminus carboxyl group and His267 of a partner subunit forms a triad similar to the catalytic component of cysteine proteases. TbPTR1 therefore offers novel structural features to exploit in the search for inhibitors of therapeutic value against African trypanosomiasis.
PMCID: PMC1618733  PMID: 16968221
7.  The ethanolamine branch of the Kennedy pathway is essential in the bloodstream form of Trypanosoma brucei 
Molecular Microbiology  2009;73(5):826-843.
Phosphatidylethanolamine (GPEtn), a major phospholipid component of trypanosome membranes, is synthesized de novo from ethanolamine through the Kennedy pathway. Here the composition of the GPEtn molecular species in the bloodstream form of Trypanosoma brucei is determined, along with new insights into phospholipid metabolism, by in vitro and in vivo characterization of a key enzyme of the Kennedy pathway, the cytosolic ethanolamine-phosphate cytidylyltransferase (TbECT). Gene knockout indicates that TbECT is essential for growth and survival, thus highlighting the importance of the Kennedy pathway for the pathogenic stage of the African trypanosome. Phosphatiylserine decarboxylation, a potential salvage pathway, does not appear to be active in cultured bloodstream form T. brucei, and it is not upregulated even when the Kennedy pathway is disrupted. In vivo metabolic labelling and phospholipid composition analysis by ESI-MS/MS of the knockout cells confirmed a significant decrease in GPEtn species, as well as changes in the relative abundance of other phospholipid species. Reduction in GPEtn levels had a profound influence on the morphology of the mutants and it compromised mitochondrial structure and function, as well as glycosylphosphatidylinositol anchor biosynthesis. TbECT is therefore genetically validated as a potential drug target against the African trypanosome.
PMCID: PMC2784872  PMID: 19555461

Results 1-7 (7)