ISG20 is an interferon-induced antiviral exoribonuclease that acts on single-stranded RNA and also has minor activity towards single-stranded DNA. It belongs to the DEDDh group of RNases of the DEDD ...exonuclease superfamily. We have solved the crystal structure of human ISG20 complexed with two Mn
2+ ions and uridine 5
′-monophosphate (UMP) at 1.9 Å resolution. Its structure, including that of the active site, is very similar to those of the corresponding domains of two DEDDh-group DNases, the ε subunit of
Escherichia coli DNA polymerase III and
E. coli exonuclease I, strongly suggesting that its catalytic mechanism is identical to that of the two DNases. However, ISG20 also has distinctive residues, Met14 and Arg53, to accommodate hydrogen bonds with the 2
′-OH group of the UMP ribose, and these residues may be responsible for the preference of ISG20 for RNA substrates.
Escherichia coli ferredoxin (Fdx) is an adrenodoxin-type 2Fe-2S ferredoxin. Recent genetic analyses show that it has an essential role in the maturation of various iron-sulfur (Fe-S) proteins. Fdx ...probably functions as a component of the complex machinery responsible for the biogenesis of Fe-S clusters. Its crystal structure was determined by the multiple-wavelength anomalous dispersion method using the iron atoms in the 2Fe-2S cluster of the protein and then refined to R and R(free) values of 0.255 and 0.278, respectively, at 1.7 A resolution. The structure of Fdx is similar to the structures of bovine adrenodoxin (Adx) and Pseudomonas putida putidaredoxin (Pdx) whose respective root-mean-square deviations of the corresponding Calpha atoms are 1.8 and 2.2 A. This analysis also revealed the structure of the C-terminal residues protruding into the solvent, which is missing in Adx and Pdx. The 2Fe-2S cluster is located at the edge of the molecule and bonds with the Sgamma atoms of Cys42, Cys48, Cys51, and Cys87. Electrostatic potential analysis showed that the surface of Fdx has two negatively charged areas separated by a hydrophobic lane. One is conserved on the surface of Adx which is an area of interaction with adrenodoxin reductase. Cys46 is located on the molecular surface in the vicinity of the 2Fe-2S cluster, an indication that it may be involved in Fe-S cluster formation.
We have investigated the mechanism of resistance of leukemia cells to Ara-C using an in-house cDNA microarray designed for the analysis of leukemia cells. We produced Ara-C-resistant cells from the ...CCRF-CEM (acute lymphoblastic leukemia) cell line and compared their gene-expression profile with that of wild-type cells. The adenosine deaminase (ADA) gene was highly up-regulated in Ara-C-resistant cells, while equilibrative nucleoside transporter 1 (ENT1) and several cell-cycle-related genes were down-regulated. Of all these genes, ENT1 seemed the most likely to be relevant to Ara-C resistance. To investigate the role of ENT1 in Ara-C-resistant cells, we transfected the cells with the gene. ENT1-transfected Ara-C-resistant cells resembled wild-type CCRF-CEM cells more closely than untransfected Ara-C-resistant cells in terms of growth rate, Ara-C-uptake characteristics, and ADA expression levels. The down-regulation of the ENT1 gene is expected to result in nucleotide deficiency in addition to blockage of Ara-C influx. Accordingly, Ara-C-resistant cells showed low growth rates, which were restored by transfection with ENT1. These low growth rates were also correlated with the phosphorylation level of cell-cycle checkpoint kinase 2. In this study we identified down-regulation of ENT1 as the factor responsible for Ara-C resistance, and this knowledge may be used to devise a clinical regimen that will overcome the resistance.
Human chronic myelogenous leukemia K562 cells are relatively resistant to the anti‐metabolite cytosine arabinoside (Ara‐C) and, when treated with Ara‐C, they differentiate into erythrocytes without ...undergoing apoptosis. In this study we investigated the mechanism by which Ara‐C induces K562 cells to differentiate. We first observed that Ara‐C‐induced differentiation of these cells is completely inhibited by the radiosensitizing agent caffeine, an inhibitor of ATM and ATR protein kinases. We next found that Ara‐C activates Chk1 and Chk2 in the cells, and that the activation of Chk1, but not of Chk2, was almost completely inhibited by caffeine. Proteasome‐mediated degradation of Cdc25A and phosphorylation of Cdc25C were induced by Ara‐C treatment, presumably due to the activation of Chk2 and Chk1, respectively. To directly observe the effects of checkpoint kinase activation in Ara‐C‐induced differentiation, we suppressed Chk1 or Chk2 with the Chk1‐specific inhibitor Gö6976, by generating cell lines stably over‐expressing dominant‐negative forms of Chk2, or by siRNA‐mediated knock‐down of the Chk1 or the Chk2 gene. The results suggest that Ara‐C‐induced erythroid differentiation of K562 cells depends on both Chk1 and Chk2 pathways.
A single somatic mutation, V617F, in Janus kinase 2 (JAK2) is one of the causes of myeloproliferative neoplasms (MPN), including primary myelofibrosis, and the mutant kinase JAK2V617F is a ...therapeutic target in MPN. However, inhibition of wild-type JAK2 (JAK2WT) can decrease the red blood cell (RBC) or platelet count. Therefore, a JAK2 inhibitor that produces a smaller reduction in the RBC and platelet counts in the therapeutic window would have clinical benefit.
NS-018 is a potent and selective inhibitor of JAK2 and Src-family kinases which is currently in an early-phase clinical trial for MPN. To compare the inhibitory effect of NS-018 on JAK2WT and JAK2V617F in the cell, we assessed the antiproliferative activity of NS-018 against Ba/F3 cells expressing murine JAK2WT or JAK2V617F. NS-018 suppressed the growth of Ba/F3-JAK2V617F cells with an IC50 value of 470 nM, whereas it suppressed the growth of Ba/F3-JAK2WT cells stimulated with IL-3 with an IC50value of 2000 nM. Thus, NS-018 showed 4.3-fold selectivity for Ba/F3-JAK2V617F over Ba/F3-JAK2WT cells (V617F/WT ratio). Other JAK2 inhibitors also showed selectivity for Ba/F3-JAK2V617F over Ba/F3-JAK2WT cells, though their selectivity was lower. For example, INCB018424 (ruxolitinib) and TG101348 showed V617F/WT ratios of 2.0 and 1.5, respectively. Among the eight JAK2 inhibitors tested, NS-018 showed the highest selectivity for JAK2V617F cells. NS-018 also inhibited erythroid colony formation in JAK2V617F transgenic mice at significantly lower concentrations than in wild-type mice.
To assess the ability of NS-018 to selectively inhibit JAK2V617F-harboring cells in vivo, we established a JAK2V617F bone marrow transplantation (BMT) mouse model. NS-018 was administered by oral gavage twice a day for 40 days at a dose of 50 mg/kg. When assessment was carried out 50 days after the start of the study, NS-018 was found to have significantly prolonged the survival of JAK2V617F BMT mice, decreased their splenomegaly and restored their disrupted splenic architecture. NS-018 also partially suppressed bone marrow fibrosis in JAK2V617F BMT mice. All vehicle-treated mice that had survived to the study endpoint had mild-to-moderate reticulin fibrosis, whereas all mice treated with NS-018 had slight-to-little reticulin fibrosis, except for one mouse with mild fibrosis. Although vehicle-treated JAK2V617F BMT mice showed marked leukocytosis, NS-018 treatment achieved a 95% suppression of this increase. In spite of the marked effects of NS-018 in JAK2V617F BMT mice described above, NS-018 treatment had not decreased the RBC or reticulocyte count after 50 days of administration. JAK2V617F BMT mice showed a 78% decrease in the platelet count compared with control mice, and NS-018 treatment did not further decrease the count.
To better understand the ability of NS-018 to preferentially inhibit the mutated form of JAK2, we explored the X-ray co-crystal structure of NS-018 bound to activated JAK2 and focused on the flipped carbonyl group of Gly933, which is located immediately N-terminal to the DFG (Asp-Phe-Gly) motif in the activation loop of JAK2. We identified two kinds of hydrogen-bonding interactions between NS-018 and the carbonyl group of Gly993: water-mediated hydrogen bonding involving a nitrogen atom of NS-018 and a CH•••O hydrogen bond involving an aromatic CH of NS-018. The unique mode of binding of NS-018 to activated JAK2 provides a plausible explanation for its JAK2V617F selectivity.
In summary, NS-018 preferentially inhibited the growth of JAK2V617F-harboring cells over JAK2WT-harboring cells. NS-018 was also effective against leukocytosis, splenomegaly, and bone marrow fibrosis, and prolonged survival in JAK2V617F BMT mice with no reduction in the RBC or platelet counts. These characteristics of NS-018 may be explained at least in part by its unique mode of binding to the activated form of JAK2. NS-018 may have therapeutic benefit for MPN patients in virtue of its simultaneous satisfaction of the two requirements of efficacy and reduced hematologic adverse effects.
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Inhibition and structural studies show that dual inhibition of Abl and Lyn kinases by 3-substituted benzamides can be explained by a high similarity in their modes of interaction with both kinases.
...To investigate why 3-substituted benzamide derivatives show dual inhibition of Abl and Lyn protein tyrosine kinases, we determined their inhibitory activities against Abl and Lyn, carried out molecular modeling, and conducted a structure–activity relationship study with the aid of a newly determined X-ray structure of the Abl/Lyn dual inhibitor INNO-406 (formerly known as NS-187) bound to human Abl. We found that this series of compounds interacted with both kinases in very similar ways, so that they can inhibit both kinases effectively.
The acute lymphoblastic leukemia cell line CCRF-CEM is sensitive to Ara-C and undergoes apoptosis. In contrast, the chronic myelogenous leukemia (CML) cell line K562 is highly resistant to Ara-C, ...which causes the cells to differentiate into erythrocytes before undergoing apoptosis. We used cDNA microarrays to monitor the alterations in gene expression in these two cell lines under conditions leading to apoptosis or differentiation. Ara-C-treated CCRF-CEM cells were characterized by a cluster of down-regulated chaperone genes, whereas Ara-C-treated K562 cells were characterized by a cluster of up-regulated hemoglobin genes. In K562 cells, Ara-C treatment induced significant down-regulation of the asparagine synthetase gene, which is involved in resistance to
l-asparaginase. Sequential treatment with Ara-C and
l-asparaginase had a synergistic effect on the inhibition of K562 cell growth, and combination therapy with these two anticancer agents may prove effective in the treatment of CML, which cannot be cured by either drug alone.
Anaplastic lymphoma kinase (ALK) rearrangement-positive non-small-cell lung cancers can be effectively treated with an ALK tyrosine kinase inhibitor (TKI) such as crizotinib, but the response ...magnitude and duration are heterogeneous. Several ALK variants have been identified, but few studies have focused on the effects of different ALK variants on the efficacy of crizotinib.
Among 55 patients treated with crizotinib as the initial ALK-TKI between January 2007 and December 2014, we identified 35 patients with tumor specimens that could be evaluated for ALK variants by reverse transcription polymerase chain reaction. We retrospectively evaluated the efficacy of crizotinib on the basis of the objective response rate and progression-free survival (PFS) according to the ALK variants.
The most frequent ALK variant was variant 1 in 19 patients (54%), followed by variant 2 in five patients (14%), variant 3a/3b in four patients (12%), and other variants in seven patients (20%). Objective response rate was 69% in all patients, whereas it was 74% and 63% in the variant 1 and non-variant 1 groups, respectively. The median PFS time was significantly longer in patients with variant 1 than in those with non-variant 1 (median PFS, 11.0 months 95% CI, 6.5 to 43.0 months v 4.2 months 95% CI, 1.6 to 10.2 months, respectively; P < .05). Multivariable analysis identified two significant factors associated with PFS duration, ALK variant 1 (hazard ratio, 0.350; 95% CI, 0.128 to 0.929; P < .05) and advanced stage (hazard ratio, 4.646; 95% CI, 1.381 to 21.750; P < .05).
Our results indicate the better efficacy of crizotinib in patients with ALK variant 1 versus non-variant 1. The ALK variant status might affect the efficacy of ALK-TKIs.
Nivolumab offers a superior survival benefit over docetaxel in patients with advanced, previously treated non-small-cell lung cancer (NSCLC). An association between programmed cell death ligand-1 ...(PD-L1) expression and the efficacy of nivolumab has been reported in many studies. However, the association between the clinical parameters and efficacy of nivolumab remains unclear in advanced NSCLC patients.
Among 124 patients, 108 (88%) were performance status (PS) 0 to 1. PD-L1 expression was assessed in 89 patients, with 51 (57%) patients having PD-L1 positive expression. In all patients, the objective response rate (ORR) in patients with elevated CRP levels (≥ 1 mg/dl) was significantly worse than those without elevated CRP levels (< 1 mg/dl) (8.3 vs 23.4%,
= 0.0180). The PS (≥ 2), smoking index (< 400), CRP levels (≥ 1 mg/dl) and LDH (≥ 245 IU/L) were significantly associated with a shorter PFS and OS in patients treated with nivolumab. Multivariate analyses showed that the PS (≥ 2), smoking index (< 400), CRP levels (≥ 1 mg/dl) and LDH (≥ 245 IU/L) and PD-L1 expression were significant factors associated with a longer PFS of nivolumab.
We retrospectively analyzed 124 patients who received nivolumab as a subsequent treatment. The patient characteristics, laboratory data at baseline (C-reactive protein CRP and lactate dehydrogenase LDH), PD-L1 expression, nivolumab response, progression-free survival (PFS), and overall survival (OS) were evaluated.
Clinical parameters, such as PS, serum CRP, serum LDH, and smoking status, were significantly associated with the response duration and survival in patients treated with nivolumab.
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