Remarkable Enhancement in Boron Uptake Within Glioblastoma Cells With Carboranyl-Indole Carboxamides.

Novel boron-rich, carboranyl-indole carboxamide ligands were prepared and found to effectively target the 18 kDa translocator protein (TSPO), an upregulated mitochondrial membrane-bound protein which has been observed in variety of tumor cell lines and its expression appears to be proportional to the degree of tumorigenicity, emphasizing a key role in cancer cell proliferation. Both boronated compounds displayed remarkably high affinities for the TSPO. In addition, the in vitro uptake of these compounds into T98G human glioma cells was found to be 25- to 100-fold greater than that of clinical boron neutron capture therapy (BNCT) agents.

Site-specific synthesis of a hybrid boron-graphene salt.

We report the first example of an ionic graphene salt containing boron. An anionic charge is introduced to the graphene surface by means of 7,8-nido-[C2B9H11](-) carborane clusters covalently and electronically bound to the graphene lattice, and this new material was isolated as its Cs(+) salt.

Targeting key dioxygenases in tryptophan-kynurenine metabolism for immunomodulation and cancer chemotherapy.

Tryptophan to kynurenine metabolism is controlled by three distinct dioxygenase enzymes: tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 1 (IDO1), and indoleamine 2,3-dioxygenase 2 (IDO2). Collectively, the activity of these enzymes contributes to tumour immune tolerance and immune dysregulation in a variety of disease pathologies, including cancer. Whereas IDO1 inhibitor drug design has been the focus of study for more than two decades (with novel compounds currently in Phase II clinical trials), only recently have the roles of TDO and IDO2 been elucidated in immunosuppression. Consequently, little comparative work on inhibitor cross-reactivity and selectivity has been performed. Here, we provide an overview of the current and future drug discovery landscape for targeting TDO, IDO1, and IDO2 (individually and collectively) for pharmacological intervention.

The Fe-heme structure of met-indoleamine 2,3-dioxygenase-2 determined by X-ray absorption fine structure.

Multiple-scattering (MS) analysis of EXAFS data on met-indoleamine 2,3-dioxygenase-2 (IDO2) and analysis of XANES have provided the first direct structural information about the axial donor ligands of the iron center for this recently discovered protein. At 10K, it exists in a low-spin bis(His) form with Fe-Np(av)=1.97Å, the Fe-NIm bond lengths of 2.11Å and 2.05Å, which is in equilibrium with a high-spin form at room temperature. The bond distances in the low-spin form are consistent with other low-spin hemeproteins, as is the XANES spectrum, which is closer to that of the low-spin met-Lb than that of the high-spin met-Mb. The potential physiological role of this spin equilibrium is discussed.

The first indoleamine-2,3-dioxygenase-1 (IDO1) inhibitors containing carborane.

Indoleamine-2,3-dioxygenase-1 (IDO1) is a critical immunoregulatory enzyme responsible for the metabolism of tryptophan during inflammation and disease. Based upon a pyranonaphthoquinone framework, the first examples of indoleamine-2,3-dioxygenase-1 (IDO1) inhibitors containing a carborane cage are reported. The novel closo-1,2-carboranyl-N-pyranonaphthoquinone derivatives display low µM binding affinity for the human recombinant enzyme, with IC50 values ranging from 0.78 to 1.77 µM.

Molecular and functional alterations in a mouse cardiac model of Friedreich ataxia: activation of the integrated stress response, eIF2α phosphorylation, and the induction of downstream targets.

Friedreich ataxia (FA) is a neurodegenerative and cardiodegenerative disease resulting from marked frataxin deficiency. The condition is characterized by ataxia with fatal cardiomyopathy, but the pathogenic mechanisms are unclear. We investigated the association between gene expression and progressive histopathological and functional changes using the muscle creatine kinase conditional frataxin knockout (KO) mouse; this mouse develops a severe cardiac phenotype that resembles that of FA patients. We examined KO mice from 3 weeks of age, when they are asymptomatic, to 10 weeks of age, when they die of the disease. Positive iron staining was identified in KO mice from 5 weeks of age, with markedly reduced cardiac function from 6 weeks. We identified an early and marked up-regulation of a gene cohort responsible for stress-induced amino acid biosynthesis and observed markedly increased phosphorylation of eukaryotic translation initiation factor 2α (p-eIF2α), an activator of the integrated stress response, in KO mice at 3 weeks of age, relative to wild-type mice. Importantly, the eIF2α-mediated integrated stress response has been previously implicated in heart failure via downstream processes such as autophagy and apoptosis. Indeed, expression of a panel of autophagy and apoptosis markers was enhanced in KO mice. Thus, the pathogenesis of cardiomyopathy in FA correlates with the early and persistent eIF2α phosphorylation, which precedes activation of autophagy and apoptosis.

Hepcidin bound to α2-macroglobulin reduces ferroportin-1 expression and enhances its activity at reducing serum iron levels.

Hepcidin regulates iron metabolism by down-regulating ferroportin-1 (Fpn1). We demonstrated that hepcidin is complexed to the blood transport protein, α2-macroglobulin (α2M) (Peslova, G., Petrak, J., Kuzelova, K., Hrdy, I., Halada, P., Kuchel, P. W., Soe-Lin, S., Ponka, P., Sutak, R., Becker, E., Huang, M. L., Suryo Rahmanto, Y., Richardson, D. R., and Vyoral, D. (2009) Blood 113, 6225-6236). However, nothing is known about the mechanism of hepcidin binding to α2M or the effects of the α2M·hepcidin complex in vivo. We show that decreased Fpn1 expression can be mediated by hepcidin bound to native α2M and also, for the first time, hepcidin bound to methylamine-activated α2M (α2M-MA). Passage of high molecular weight α2M·hepcidin or α2M-MA·hepcidin complexes (≈725 kDa) through a Sephadex G-25 size exclusion column retained their ability to decrease Fpn1 expression. Further studies using ultrafiltration indicated that hepcidin binding to α2M and α2M-MA was labile, resulting in some release from the protein, and this may explain its urinary excretion. To determine whether α2M-MA·hepcidin is delivered to cells via the α2M receptor (Lrp1), we assessed α2M uptake and Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells. Interestingly, α2M·hepcidin or α2M-MA·hepcidin demonstrated similar activities at decreasing Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells, indicating that Lrp1 is not essential for Fpn1 regulation. In vivo, hepcidin bound to α2M or α2M-MA did not affect plasma clearance of α2M/α2M-MA. However, serum iron levels were reduced to a significantly greater extent in mice treated with α2M·hepcidin or α2M-MA·hepcidin relative to unbound hepcidin. This effect could be mediated by the ability of α2M or α2M-MA to retard kidney filtration of bound hepcidin, increasing its half-life. A model is proposed that suggests that unlike proteases, which are irreversibly bound to activated α2M, hepcidin remains labile and available to down-regulate Fpn1.

Mutation of cysteine residues alters the heme-binding pocket of indoleamine 2,3-dioxygenase-1.

The hemoprotein indoleamine 2,3-dioxygenase-1 (IDO1) is the first and rate-limiting enzyme in mammalian tryptophan metabolism. Interest in IDO1 continues to grow, due to the ever expanding influence IDO1 plays in the immune response. This study examined the contribution of all individual cysteine residues towards the overall catalytic properties and stability of recombinant human IDO1 via mutagenesis studies using a range of biochemical and spectroscopic techniques, including in vitro kinetic assessment, secondary structure identification via circular dichroism spectroscopy and thermal stability assessment. Upon mutation of cysteine residues we observed changes in secondary structure (principally, shifting from α-helix/ß-sheet features to random coil structures) that produced out of plane heme torsion and puckering, changes to thermal stability (including gains in stability for one mutant protein) and differences in enzymatic activity (such as, increased ability to convert non-natural substrates, e.g.d-tryptophan) from wild type IDO1 enzyme.

The translocator protein (TSPO): a novel target for cancer chemotherapy.

The translocator protein (TSPO) is an 18 kDa transmembrane protein primarily found in the outer mitochondrial membrane where it forms a key part of the mitochondrial permeability transition pore (MPTP). Omnipresent in almost all tissues, TSPO up-regulation has been connected to neuronal damage and inflammation, making the protein an important bio-imaging marker for disease progression. More recently, TSPO has attracted attention as a possible molecular target for tumour imaging and chemotherapy. In this review we summarize TSPO's molecular characteristics and highlight research progress in recent years in the field of TSPO-targeted cancer diagnostics and treatments.

Synchrotron X-ray fluorescence studies of a bromine-labelled cyclic RGD peptide interacting with individual tumor cells.

The first example of synchrotron X-ray fluorescence imaging of cultured mammalian cells in cyclic peptide research is reported. The study reports the first quantitative analysis of the incorporation of a bromine-labelled cyclic RGD peptide and its effects on the biodistribution of endogenous elements (for example, K and Cl) within individual tumor cells.

1-L-methyltryptophan is a more effective inhibitor of vertebrate IDO2 enzymes than 1-D-methyltryptophan.

1-D-methyltryptophan (D-1MT) is an effective anti-cancer agent in mouse tumour models. It has been suggested to be a selective inhibitor of the recently described tryptophan-degrading enzyme indoleamine 2,3-dioxygenase 2 (IDO2) rather than the closely related enzyme IDO1. We found that mammalian (mouse, opossum and platypus), chicken, frog, and fish IDO2 could be functional tryptophan-catabolising enzymes. The characteristics of pH-dependent activity and inhibitor selectivity were conserved amongst the vertebrate IDO2 proteins tested. Like IDO1 enzymes, the enzymatic activity of all IDO2s was inhibited by L-1MT but not by D-1MT in a cell-free assay. When IDO2s were expressed in mammalian cells, L-1MT was also a better inhibitor than D-1MT.

Characterization and evolution of vertebrate indoleamine 2, 3-dioxygenases IDOs from monotremes and marsupials.

Indoleamine 2,3-dioxygenase (IDO1) and tryptophan 2,3-dioxygenase (TDO) are tryptophan-degrading enzymes that catalyze the first step in tryptophan catabolism via the kynurenine pathway. TDO is widely distributed in both eukaryotes and bacteria. In contrast, IDO has been found only in mammals and yeast. In 2007, a third enzyme, indoleamine 2,3-dioxygenase-2 (IDO2), was discovered. IDO2 is found not only in mammals but also in lower vertebrates. Interestingly, the K(m) value of IDO2 for L-Trp was 500-1000 fold higher than that of IDO1. In this study, we isolated both IDO1 and IDO2 cDNA from a monotreme, the platypus (Ornithorhynchus anatinus), and a marsupial, the gray short-tailed opossum (Monodelphis domestica). We characterized the recombinant proteins and those of other known IDO1/IDO2 in intact cells and a cell-free system. It was found that methylene blue may not be suitable reductant for IDO2, hence resulting in an underestimation of recombinant IDO2 activity. In intact cells, the K(m) value of IDO2 for L-Trp was estimated to be much higher than that of IDO1 and this high K(m) value appears to have been conserved during the evolution of IDO2. The protein encoded by the ancestor gene of IDO1 and IDO2 is likely to have had properties more similar to present day IDO2 than to IDO1.

Characterization and evolution of vertebrate indoleamine 2, 3-dioxygenases IDOs from monotremes and marsupials.

Indoleamine 2,3-dioxygenase (IDO1) and tryptophan 2,3-dioxygenase (TDO) are tryptophan-degrading enzymes that catalyze the first step in tryptophan catabolism via the kynurenine pathway. TDO is widely distributed in both eukaryotes and bacteria. In contrast, IDO has been found only in mammals and yeast. In 2007, a third enzyme, indoleamine 2,3-dioxygenase-2 (IDO2), was discovered. IDO2 is found not only in mammals but also in lower vertebrates. Interestingly, the Km value of IDO2 for L-Trp was 500-1000 fold higher than that of IDO1. In this study, we isolated both IDO1 and IDO2 cDNA from a monotreme, the platypus (Ornithorhynchus anatinus), and a marsupial, the gray short-tailed opossum (Monodelphis domestica). We characterized the recombinant proteins and those of other known IDO1/IDO2 in intact cells and a cell-free system. It was found that methylene blue may not be suitable reductant for IDO2, hence resulting in an underestimation of recombinant IDO2 activity. In intact cells, the Km value of IDO2 for L-Trp was estimated to be much higher than that of IDO1 and this high Km value appears to have been conserved during the evolution of IDO2. The protein encoded by the ancestor gene of IDO1 and IDO2 is likely to have had properties more similar to present day IDO2 than to IDO1.

Mouse and human indoleamine 2,3-dioxygenase display some distinct biochemical and structural properties.

The hemoprotein indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in the most significant pathway for mammalian tryptophan metabolism. It has received considerable attention in recent years, particularly due to its dual role in immunity and the pathogenesis of many diseases. Reported here are differences and similarities between biochemical behaviour and structural features of recombinant human IDO and recombinant mouse IDO. Significant differences were observed in the conversion of substrates and pH stability. Differences in inhibitor potency and thermal stability were also noted. Secondary structural features were broadly similar but variation between species was apparent, particularly in the alpha-helix portion of the enzymes. With mouse models substituting for human diseases, the differences between mouse and human IDO must be recognised before applying experimental findings from one system to the next.

Indoleamine 2,3-dioxygenase-2; a new enzyme in the kynurenine pathway.

The kynurenine pathway of tryptophan metabolism converts the amino acid tryptophan into a number of biologically active metabolites. The first and rate-limiting step in this pathway is the conversion of tryptophan to N-formylkynurenine and until recently this reaction was thought to be performed by either of two enzymes, tryptophan 2,3-dioxygenase and indoleamine 2,3-dioxygenase. A third enzyme, indoleamine 2,3-dioxygenase-2, indoleamine 2,3-dioxygenase-like protein or proto-indoleamine 2,3-dioxygenase (IDO2, IDO-2, INDOL1 or proto-IDO), with this activity recently has been described. The gene encoding IDO2 is adjacent and structurally similar to the indoleamine 2,3-dioxygenase gene and both mouse genes use multiple promoters to express transcripts with alternate 5' exons. The IDO2 protein is expressed in the murine kidney, liver, male and female reproductive system. The two IDO enzymes can utilise a similar range of substrates, however they differ in their selectivity for some inhibitors. The selective inhibition of IDO2 by 1-methyl-D-tryptophan suggests that IDO2 activity may have a role in the inhibition of immune responses to tumours.

Characterization of an indoleamine 2,3-dioxygenase-like protein found in humans and mice.

Indoleamine 2,3-dioxygenase (INDO) and tryptophan 2,3-dioxygenase (TDO) each catalyze the first step in the kynurenine pathway of tryptophan metabolism. We describe the discovery of another enzyme with this activity, indoleamine 2,3-dioxygenase-like protein (INDOL1), which is closely related to INDO and is expressed in mice and humans. The corresponding genes have a similar genomic structure and are situated adjacent to each other on human and mouse chromosome 8. They are likely to have arisen by gene duplication before the origin of the tetrapods. The expression of INDOL1 is highest in the mouse kidney, followed by epididymis, and liver. Expression of mouse INDOL1 was further localized to the tubular cells in the kidney and the spermatozoa. INDOL1 was assigned its name because of its structural similarity to INDO. We demonstrate that INDOL1 catalyses the conversion of tryptophan to kynurenine therefore a more appropriate nomenclature for the enzymes might be INDO-1 and INDO-2, or the more commonly-used abbreviations, IDO-1 and IDO-2. Although the two proteins have similar enzymatic activities, their different expression patterns within tissues and during malaria infection, suggests a distinct role for each protein. This identification of INDOL1 may help to explain the regulation of the diversity of physiological and patho-physiological processes in which the kynurenine pathway is involved.

Optimised expression and purification of recombinant human indoleamine 2,3-dioxygenase.

The hemoprotein indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in mammalian tryptophan metabolism. It has received considerable attention in recent years, particularly due to its role in the pathogenesis of many diseases. Here, we report attempts to improve soluble expression and purification of hexahistidyl-tagged recombinant human IDO from Escherichia coli (EC538, pREP4, and pQE9-IDO). Significant formation of inclusion bodies was noted at the growth temperature of 37 degrees C, with reduced formation at 30 degrees C. The addition of the natural biosynthetic precursor of protoporphrin IX, delta-aminolevulinic acid (ALA), coupled with optimisation of IPTG induction levels during expression at 30 degrees C and purification by nickel-agarose and size exclusion chromatography, resulted in protein with 1 mol of heme/mol of protein and a specific activity of 160 micromol of kynurenine/h/mg of protein (both identical to native human IDO). The protein was homogeneous in terms of electrophoretic analysis. Yields of soluble protein (3-5 mg/L of bacterial culture) and heme content are greater than previously reported.