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Protozoa depend on purine salvage for nucleic acid synthesis. An abundant salvage enzyme in Crithidia fasciculata is the inosine-uridine nucleoside hydrolase (IU-nucleoside hydrolase). The enzyme was cloned by polymerase chain reaction techniques using primers corresponding to the amino acid sequences of tryptic fragments and to the miniexon of C. fasciculata. The full-length cDNA was expressed in Escherichia coli and the protein purified to > 99% homogeneity. The open reading frame encodes a protein of 315 amino acids. Enzyme purified from C. fasciculata was missing the N-terminal Met and gave a major mass peak of 34 194 amu by mass spectrometry. Predicted mass from the DNA sequence for the Met-processed enzyme was 34 196. A pET3d-IUNH construct expressed in E. coli introduced MetAla instead of MetPro at the N-terminus. Enzyme purified from this construct also had a processed N-terminus and gave predicted and observed masses of 34 168 and 34 170 amu, respectively. The amino acid sequence for IU-nucleoside hydrolase has no close relatives among the known proteins. A cDNA clone of unknown function from Leishmania major shows near identity in the N-terminal deduced amino acid sequence. Open reading frames near 1 and 47 min on the E. coli chromosome and from two yeast genomes encode for proteins of similar size with substantial amino acid identity. Mutation of His241Ala caused a 2100-fold loss in k(cat) for inosine but a 2.8-fold increase in k(cat) with p-nitrophenyl beta-D-ribofuranoside, establishing the location of the catalytic site and implicating His241 as a proton donor for leaving group activation. IU-nucleoside hydrolase from C. fasciculata and the protein expressed in E. coli were crystallized and diffract to 2.5 and 2.1 A resolution, respectively. Both belong to the P2(1)2(1)2 orthorhombic space group with unit cell parameters a = 63.5 A, b = 131.9 A, c = 90.1 A, and alpha = beta = gamma = 90 degrees. Two subunits of the tetrameric enzyme are present in the asymmetric unit. The following paper reports the X-ray crystal structure for this enzyme.

The roles of aberrant expression of constitutively active ALK chimeric proteins in the pathogenesis of anaplastic large-cell lymphoma (ALCL) have been well defined; nevertheless, the notion that ALK is a molecular target for the therapeutic modulation of ALK ؉ ALCL has not been validated thus far. Select fused pyrrolocarbazole (FP)-derived small molecules with ALK inhibitory activity were used as pharmacologic tools to evaluate whether functional ALK is essential for the prolifera- IntroductionChromosomal translocations occur frequently in a select group of human cancers, including most lymphomas, leukemias, and sarcomas. Individual translocations have shown a high degree of specificity for particular cancer types and the presence of a particular translocation often correlates well with clinical behavior and outcome for specific types of cancer. 1 Consequently, therapies directed at molecular targets dysregulated by tumor-specific genetic aberrations will potentially provide more effective and less toxic therapies than conventional chemotherapy. 1,2 Anaplastic large-cell lymphomas (ALCLs) comprise a group of non-Hodgkin lymphomas (NHLs) that are usually of T-cell origin and often present with extranodal disease, especially the skin, and are characterized by the expression of the CD30/Ki-1 antigen. Roughly 2500 to 3000 new cases of ALCLs are diagnosed in the United States each year and 50% to 60% of these ALCLs are associated with a specific t(2;5) (p23;q35) chromosome translocation. 4,5 The genes altered in the t(2;5) translocation contain the N-terminal portion of nucleophosmin (NPM) gene, a nuclear phosphoprotein, fused to the catalytic domain of anaplastic lymphoma kinase (ALK) gene. ALK is a cell-membrane-spanning receptor tyrosine kinase and a member of the insulin receptor superfamily. Although the precise physiologic function and regulation of ALK have not been well defined, the NPM-ALK fusion gene encodes for an 80-kDa NPM-ALK chimeric oncoprotein with constitutively active ALK tyrosine kinase activity, which plays a key role in lymphomagenesis by the aberrant phosphorylation of multiple intracellular substrates downstream of NPM-ALK. 4,5 Subsequently, other fusion partners of ALK were also reported in ALCL, and dysregulated expression and constitutive activation of the ALK protein was demonstrated in approximately 60% to 70% of ALCLs, termed ALK ϩ lymphomas. 4,[6][7][8] Preclinical experimental data have demonstrated that the aberrant expression of constitutively active ALK is directly implicated in the pathogenesis of ALCL and that ALK down-regulation or inhibition of ALK-mediated pathways can markedly impair the growth of ALK ϩ lymphoma cells. 9-15 Currently there is no optimal therapeutic regimen for ALK ϩ ALCL. Doxorubicin-based combination chemotherapy has limited effectiveness, resulting in a substantial number of patients with ALK ϩ ALCL with a poor outcome, either failing to enter remission or relapsing within a few months from the start of treatment. 3 Thus, optimal and more effective therapeu...

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A series of potent vascular endothelial growth factor R2 (VEGF-R2) tyrosine kinase inhibitors from a new indenopyrrolocarbazole template is reported. The structure-activity relationships for a series of 9-alkoxymethyl-12-(3-hydroxypropyl)indeno[2,1-a]pyrrolo[3,4-c]carbazole-5-ones revealed an optimal R9 substitution with ethoxymethyl 19 (VEGF-R2 IC(50) = 4 nM) and isopropoxymethyl 21 (VEGF-R2 IC(50) = 8 nM) being the most potent inhibitors in the series. The VEGF-R2 activity was reduced appreciably by increasing the size of the R9 alkoxy group or by alpha-methyl branching adjacent to the ring. The combined R9 alkoxymethyl and N12 hydroxypropyl substitutions were required for potent VEGF-R2 activity, and the corresponding thioether analogues were weaker than their ether counterparts. Compound 21 (R9 isopropoxymethyl, CEP-5214) was identified as a potent, low-nanomolar pan inhibitor of human VEGF-R tyrosine kinases, displaying IC(50) values of 16, 8, and 4 nM for VEGF-R1/FLT-1, VEGF-R2/KDR, and VEGF-R3/FLT-4, respectively, with cellular activity equivalent to the isolated enzyme activity. Compound 21 exhibited good selectivity against numerous tyrosine and serine/threonine kinases including PKC, Tie2, TrkA, CDK1, p38, JNK, and IRK. To increase water solubility and oral bioavailability, the N,N-dimethylglycine ester 40 was prepared. In pharmacokinetic studies in mice and rats, increased plasma levels of 21 were observed after oral administration of 40. Compound 21 demonstrated significant in vivo antitumor activity in numerous tumor models and was advanced into phase I clinical trials as the water-soluble N,N-dimethylglycine ester prodrug 40 (CEP-7055).