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Julian A Simon

Publications and source records attributed to Julian A Simon.

14 recordsLinked to original sources
PubMed2006

KN-62 analogues as potent differentiating agents of HL-60 cells.

KN-62, an inhibitor of the calmodulin-dependent protein kinases (CaMKs), enhances the terminal differentiation of retinoic acid sensitive human myeloid leukemia cell lines. In an effort to identify additional CaMK inhibitors that exhibit more potent activity in triggering leukemia cell differentiation, we synthesized 45 analogues of KN-62 and determined their ability to induce HL-60 cell differentiation. Sixteen of these novel analogues exhibited significant differentiation-inducing activity, and one analogue, AS-004, was five times more potent than KN-62 in inhibiting proliferation and inducing differentiation of HL-60 cells. Such KN-62 analogues and/or related compounds may prove useful in treating promyelocytic leukemia.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed2006

Using isoform-specific inhibitors to target lipid kinases.

In this issue of Cell, Knight et al. (2006) present a detailed pharmacological analysis of the PI3 kinase (PI3-K) family using small molecule inhibitors. They conclude that p110alpha, a PI3-K isoform, has a critical role in insulin signaling. In a related Cancer Cell paper, Fan et al. (2006) show that blocking activation of both p110alpha and the kinase mTOR with a small molecule inhibitor limits the growth of gliomas.

Animals↗
PubMed2006

Antitumor activity of a small-molecule inhibitor of human silent information regulator 2 enzymes.

SIRT1 and other NAD-dependent deacetylases have been implicated in control of cellular responses to stress and in tumorigenesis through deacetylation of important regulatory proteins, including p53 and the BCL6 oncoprotein. Hereby, we describe the identification of a compound we named cambinol that inhibits NAD-dependent deacetylase activity of human SIRT1 and SIRT2. Consistent with the role of SIRT1 in promoting cell survival during stress, inhibition of SIRT1 activity with cambinol during genotoxic stress leads to hyperacetylation of key stress response proteins and promotes cell cycle arrest. Treatment of BCL6-expressing Burkitt lymphoma cells with cambinol as a single agent induced apoptosis, which was accompanied by hyperacetylation of BCL6 and p53. Because acetylation inactivates BCL6 and has the opposite effect on the function of p53 and other checkpoint pathways, the antitumor activity of cambinol in Burkitt lymphoma cells may be accomplished through a combined effect of BCL6 inactivation and checkpoint activation. Cambinol was well tolerated in mice and inhibited growth of Burkitt lymphoma xenografts. Inhibitors of NAD-dependent deacetylases may constitute novel anticancer agents.

Acetylation↗
PubMed2006

Telomere length as a quantitative trait: genome-wide survey and genetic mapping of telomere length-control genes in yeast.

Telomere length-variation in deletion strains of Saccharomyces cerevisiae was used to identify genes and pathways that regulate telomere length. We found 72 genes that when deleted confer short telomeres, and 80 genes that confer long telomeres relative to those of wild-type yeast. Among identified genes, 88 have not been previously implicated in telomere length control. Genes that regulate telomere length span a variety of functions that can be broadly separated into telomerase-dependent and telomerase-independent pathways. We also found 39 genes that have an important role in telomere maintenance or cell proliferation in the absence of telomerase, including genes that participate in deoxyribonucleotide biosynthesis, sister chromatid cohesion, and vacuolar protein sorting. Given the large number of loci identified, we investigated telomere lengths in 13 wild yeast strains and found substantial natural variation in telomere length among the isolates. Furthermore, we crossed a wild isolate to a laboratory strain and analyzed telomere length in 122 progeny. Genome-wide linkage analysis among these segregants revealed two loci that account for 30%-35% of telomere length-variation between the strains. These findings support a general model of telomere length-variation in outbred populations that results from polymorphisms at a large number of loci. Furthermore, our results laid the foundation for studying genetic determinants of telomere length-variation and their roles in human disease.

Chromosome Mapping↗
PubMed2004

Inhibitors of Sir2: evaluation of splitomicin analogues.

Splitomicin (1) and 41 analogues were prepared and evaluated in cell-based Sir2 inhibition and toxicity assays and an in vitro Sir2 inhibition assay. Lactone ring or naphthalene (positions 7-9) substituents decrease activity, but other naphthalene substitutions (positions 5 and 6) are well-tolerated. The hydrolytically unstable aromatic lactone is important for activity. Lactone hydrolysis rates were used as a measure of reactivity; hydrolysis rates correlate with inhibitory activity. The most potent Sir2 inhibitors were structurally similar to and had hydrolysis rates similar to 1.

Histone Deacetylase Inhibitors↗
PubMed2004

Disruption of protein-membrane binding and identification of small-molecule inhibitors of coagulation factor VIII.

Factor VIII is a critical member of the blood coagulation cascade. It binds to the membrane surfaces of activated platelets at the site of vascular injury via a highly specific interaction between factor VIII's carboxy-terminal C2 domain and their phosphatidylserine-rich lipid bilayer. We have identified small-molecule inhibitors of factor VIII's membrane binding activity that have IC50 values as low as 2.5 microM. This interaction is approximately 10(3)-fold tighter than that of free o-phospho-L-serine. These compounds also inhibit factor VIII-dependent activation of factor X, indicating that disruption of membrane lipid binding leads to inhibition of the intrinsic coagulation pathway. The tightest binding inhibitor is specific and does not prevent membrane binding by the closely related coagulation factor V. These results indicate that this and related compounds may be used as leads to develop novel antithrombotic agents.

Blood Coagulation Factor Inhibitors↗
PubMed2003

Identification of selective inhibitors of NAD+-dependent deacetylases using phenotypic screens in yeast.

Sir2 and Hst1 are NAD+-dependent deacetylases involved in transcriptional repression in yeast. The two enzymes are highly homologous yet have different sensitivity to the small-molecule inhibitor splitomicin (compound 1) (Bedalov, A., Gatbonton, T., Irvine, W. P., Gottschling, D. E., and Simon, J. A. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 15113-15118). We have now defined a critical amino acid residue within a small helical module of Hst1 that confers relative resistance to splitomicin. Parallel cell-based screens of 100 splitomicin analogues led to the identification of compounds that exhibit a higher degree of selectivity toward Sir2 or Hst1. A series of compounds based on a splitomicin derivative, dehydrosplitomicin (compound 2), effectively phenocopied a yeast strain that lacked Hst1 deacetylase while having no effect on the silencing activities of Sir2. In addition, we identified a compound with improved selectivity for Sir2. Selectivity was affirmed using whole-genome DNA microarray analysis. This study underscores the power of phenotypic screens in the development and characterization of selective inhibitors of enzyme functions.

Amino Acid Sequence↗
PubMed2003

Sir2 flexes its muscle.

A new report reveals a role for the mammalian NAD-dependent deacetylase Sir2 in repressing the muscle cell differentiation program and implicates the cellular redox state as a critical determinant of transcriptional activity of differentiation-specific genes.

Animals↗
PubMed2003

NAD+-dependent deacetylase Hst1p controls biosynthesis and cellular NAD+ levels in Saccharomyces cerevisiae.

Nicotine adenine dinucleotide (NAD(+)) performs key roles in electron transport reactions, as a substrate for poly(ADP-ribose) polymerase and NAD(+)-dependent protein deacetylases. In the latter two processes, NAD(+) is consumed and converted to ADP-ribose and nicotinamide. NAD(+) levels can be maintained by regeneration of NAD(+) from nicotinamide via a salvage pathway or by de novo synthesis of NAD(+) from tryptophan. Both pathways are conserved from yeast to humans. We describe a critical role of the NAD(+)-dependent deacetylase Hst1p as a sensor of NAD(+) levels and regulator of NAD(+) biosynthesis. Using transcript arrays, we show that low NAD(+) states specifically induce the de novo NAD(+) biosynthesis genes while the genes in the salvage pathway remain unaffected. The NAD(+)-dependent deacetylase activity of Hst1p represses de novo NAD(+) biosynthesis genes in the absence of new protein synthesis, suggesting a direct effect. The known Hst1p binding partner, Sum1p, is present at promoters of highly inducible NAD(+) biosynthesis genes. The removal of HST1-mediated repression of the NAD(+) de novo biosynthesis pathway leads to increased cellular NAD(+) levels. Transcript array analysis shows that reduction in cellular NAD(+) levels preferentially affects Hst1p-regulated genes in comparison to genes regulated with other NAD(+)-dependent deacetylases (Sir2p, Hst2p, Hst3p, and Hst4p). In vitro experiments demonstrate that Hst1p has relatively low affinity toward NAD(+) in comparison to other NAD(+)-dependent enzymes. These findings suggest that Hst1p serves as a cellular NAD(+) sensor that monitors and regulates cellular NAD(+) levels.

Adenosine Diphosphate Ribose↗
PubMed2002

Cell-based assays for identification of novel double-strand break-inducing agents.

BACKGROUND: We are developing cell-based assays to identify anticancer agents that are selectively toxic to cells with defined mutations. As a test, we used a three-stage strategy to screen compounds from the National Cancer Institute's repository for agents that are selectively toxic to double-strand break repair-deficient yeast cells. METHODS: Compounds identified in the screen were further analyzed by use of yeast and vertebrate cell-based and in vitroassays to distinguish between topoisomerase I and II poisons. RESULTS: Of the more than 85 000 compounds screened, 126 were selectively toxic to yeast deficient in DNA double-strand break repair. Eighty-seven of these 126 compounds were structurally related to known topoisomerase poisons, and 39 were not. Twenty-eight of the 39 were characterized, and we present data for eight of the compounds. Among these eight compounds, we identified two novel topoisomerase II poisons (NSC 327929 and NSC 638432) that were equipotent to etoposide in biochemical tests and in cells, five (NSC 63599, NSC 65601, NSC 380271, NSC 651646, and NSC 668370) with topoisomerase I-dependent toxicity in yeast that induced DNA damage and toxicity in mammalian cells, and one (NSC 610898) that directly bound to DNA and induced strand breaks. CONCLUSIONS: Cell-based assays can be used to identify molecules that are selectively toxic to cells with a predetermined genetic background, including mutations in genes involved in the cell cycle and its checkpoints, for which there are currently no selectively toxic compounds.

Animals↗