UBASH3B/Sts-1-CBL axis regulates myeloid proliferation in human preleukemia induced by AML1-ETO

The t(8;21) rearrangement, which creates the AML1-ETO fusion protein, represents the most common chromosomal translocation in acute myeloid leukemia (AML). Clinical data suggest that CBL mutations are a frequent event in t(8;21) AML, but the role of CBL in AML1-ETO-induced leukemia has not been investigated. In this study, we demonstrate that CBL mutations collaborate with AML1-ETO to expand human CD34+ cells both in vitro and in a xenograft model. CBL depletion by shRNA also promotes the growth of AML1-ETO cells, demonstrating the inhibitory function of endogenous CBL in t(8;21) AML. Mechanistically, loss of CBL function confers hyper-responsiveness to thrombopoietin and enhances STAT5/AKT/ERK/Src signaling in AML1-ETO cells. Interestingly, we found the protein tyrosine phosphatase UBASH3B/Sts-1, which is known to inhibit CBL function, is upregulated by AML1-ETO through transcriptional and miR-9-mediated regulation. UBASH3B/Sts-1 depletion induces an aberrant pattern of CBL phosphorylation and impairs proliferation in AML1-ETO cells. The growth inhibition caused by UBASH3B/Sts-1 depletion can be rescued by ectopic expression of CBL mutants, suggesting that UBASH3B/Sts-1 supports the growth of AML1-ETO cells partly through modulation of CBL function. Our study reveals a role of CBL in restricting myeloid proliferation of human AML1-ETO-induced leukemia, and identifies UBASH3B/Sts-1 as a potential target for pharmaceutical intervention.

A stem cell-like gene expression signature associates with inferior outcomes and a distinct microRNA expression profile in adults with primary cytogenetically normal acute myeloid leukemia

Acute myeloid leukemia (AML) is hypothesized to be sustained by self-renewing leukemia stem cells (LSCs). Recently, gene expression signatures (GES) from functionally defined AML LSC populations were reported, and expression of a 'core enriched' (CE) GES, representing 44 genes activated in LCSs, conferred shorter survival in cytogenetically normal (CN) AML. The prognostic impact of the CE GES in the context of other molecular markers, including gene mutations and microRNA (miR) expression alterations, is unknown and its clinical utility is unclear. We studied associations of the CE GES with known molecular prognosticators, miR expression profiles, and outcomes in 364 well-characterized CN-AML patients. A high CE score (CE(high)) associated with FLT3-internal tandem duplication, WT1 and RUNX1 mutations, wild-type CEBPA and TET2, and high ERG, BAALC and miR-155 expression. CE(high) patients had a lower complete remission (CR) rate (P=0.003) and shorter disease-free (DFS, P<0.001) and overall survival (OS, P<0.001) than CE(low) patients. These associations persisted in multivariable analyses adjusting for other prognosticators (CR, P=0.02; DFS, P<0.001; and OS, P<0.001). CE(high) status was accompanied by a characteristic miR expression signature. Fifteen miRs were upregulated in both younger and older CE(high) patients, including miRs relevant for stem cell function. Our results support the clinical relevance of LSCs and improve risk stratification in AML.

NPM1 mutations as an independent prognosticator for older cytogenetically normal acute myeloid leukemia (CN AML)

7000

Background: In younger CN AML without FLT3-ITD, NPM1 mutations predict favorable outcome. Their prognostic impact in older [≥60 years (y)] patients (pts) requires further evaluation. Methods: Pretreatment marrow was studied in 189 older CN AML pts [median age 69 y (60 - 83 y); 162 de novo & 27 secondary (s; prior hematologic disorders) cases] enrolled on CALGB 9720 (n=106) & 10201 (n=83). Both protocols had standard-dose (100 mg/m2/d) cytarabine (AraC)/daunorubicin (DN)-based induction; consolidation was based on standard-dose AraC/DN/etoposide (1 cycle) in 9720 & intermediate-dose (2 g/m2/d) AraC (2 cycles) in 10201. Pts transplanted in 1st complete remission (CR) were excluded. Median follow-up was 3.3 y for pts alive. Analyses of NPM1 exon 12 by direct sequencing, gene & microRNA (miR) expression profiling by Affymetrix U133 plus 2.0 & OSU CCC v4.0 arrays, & other markers (FLT3-ITD, FLT3-TKD, WT1mut) were performed centrally. Results: In de novo CN AML, NPM1 mutated (NPM1mut) pts (54%) had more CRs (85% v 45%, P<.0001) & longer relapse-free (RFS) (P=.02; 3 y rates 23% v 10%) & overall survival (OS) (P<.0001; 3 y 34% v 7%) than NPM1 wild-type (NPM1wt) pts. In multivariable models, NPM1 mutations independently predicted favorable outcome (Table) - NPM1mut pts had 10-fold higher odds of CR & 64% reduction in relapse risk. In genome-wide analyses, miR-10 & miR-16 were upregulated in NPM1mut pts, accompanied by highly expressed HOX genes & downregulated BCL2, respectively. NPM1mut were rare in sAML pts (15%), precluding study of their impact. Conclusions: NPM1 mutations independently predict better outcome in older CN AML. Upregulation of proapoptotic microRNAs & downregulation of antiapoptotic microRNA targets may explain the impact of NPM1 mutations.

[Table: see text]

No significant financial relationships to disclose.

MicroRNA 181a (miR-181a) expression as a prognosticator in cytogenetically normal acute myeloid leukemia (CN AML)

7001

Background: We showed recently that CEBPA mutations (mut) in CN AML are associated with better outcome and a unique microRNA expression profile, including miR-181a upregulation. Here we tested if miR-181a expression can predict outcome independently. Methods: We analyzed 187 de novo CN AML adult patients (pts) aged <60 years (y; median 45) similarly treated on CALGB 9621 and 19808. Of these, 122 had molecular high risk [FLT3-ITD or NPM1 wild type (wt)] and 65 low risk (no FLT3-ITD, NPM1 mut) CN AML. FLT3, NPM1, CEBPA, MLL, and WT1 mutations, and ERG and BAALC expression were analyzed centrally. miR-181a expression was measured in pretherapy marrow using OSUCCC v3.0 arrays. The mean of 2 miR-181a probe log intensities was used as a continuous variable for analyses. Results: Higher miR-181a levels (miR-181a↑) were associated with CEBPA mut, NPM1 wt, no FLT3-TKD, lower ERG expression, higher %FAB M1/M2, lower WBC and age, higher blood blasts, and lower % gum hypertrophy. miR-181a↑ tended to associate with more complete remissions (CRs; p = .07) and significantly associated with longer disease-free (DFS; p = .05) and overall (OS; p = .01) survival (median follow-up 6.5 y for pts alive). A stronger prognostic impact of miR-181a was observed in the molecular high risk group, where miR-181a↑ predicted more CRs (p = .03), and longer DFS (p = .0002) and OS (p = .0001). In multivariable analyses of the molecular high risk group, miR-181a↑independently predicted CR, and longer DFS and OS (Table). For descriptive purposes, we dichotomized pts at the median miR-181a expression value. For high v low miR-181a expressers, CR rates were 84% vs 72% and 5 y DFS and OS rates 43% vs 18% and 48% vs 19%, respectively. Conclusions: miR-181a expression is a prognostic marker in CN AML, mainly in the molecular high risk group, where it predicts outcome independently of other variables including CEBPA mutations. As miR-181a↑ confer better treatment response, novel approaches increasing miR-181a levels might benefit not only CN but also other AML pts.

[Table: see text]

No significant financial relationships to disclose.

Improving the molecular risk classification for younger (<60 years) de novo cytogenetically normal acute myeloid leukemia (CN AML) patients (pts)

7002

Background: CN AML pts are currently stratified into Low-risk [FLT3-ITD negative (neg)/NPM1 mutated (mut)] and High-risk [FLT3-ITD positive (pos) or NPM1 wild type (wt)] groups (FLT3-ITD/NPM1-only classification). We recently showed that low ERG expression and CEBPAmut identify pts with better outcome within, respectively, the Low- and High-risk groups, and that WT1mut confers poor outcome regardless of FLT3-ITD/NPM1 status. Here, we assess if adding CEBPA and WT1 mutation and ERG expression testing improves the currently used CN AML molecular risk classification. Methods: FLT3, NPM1, CEBPA and WT1 mutations and ERG and BAALC expression were tested at diagnosis in 143 CN AML adults enrolled on CALGB treatment protocols 9621 and 19808. Pts were divided into two molecular risk groups: i) CALGB Group I that included Low-risk pts with low ERG & High-risk pts with CEBPAmut and ii) CALGB Group II that included WT1mut pts & Low-risk pts with high ERG & High- risk pts with CEBPAwt. Results: CALGB Group I (n=56) v Group II (n=87) had more complete remissions (CRs) (P=.005; 96% v 79%), and longer disease-free (DFS; P<.0001; 5 year (y) 69% v 21%) and overall (OS; P<.0001; 5 y 70% v 31%) survival [median follow-up for pts alive 6 y]. In multivariable (MV) analyses, Group I predicted higher rate of CR (P=.02), and longer DFS (P<.0001) and OS (P=.0002), after correcting for other variables (Table). In contrast, for the same cohort of pts grouped by the FLT3-ITD/NPM1-only classification, CRs were 94% v 82% and 5 y DFS 59% v 32% and OS 67% v 36% in the Low- v High-risk groups. Based on the Akaike Information Criterion, MV models for DFS and OS using the CALGB risk Groups were better than those using the FLT3-ITD/NPM1-only risk groups. Conclusions: Prognostic classification of younger de novo CN AML pts is improved by adding CEBPA and WT1 mutation and ERG expression testing. While mutational analyses are ready for use in clinical trials, quantification of ERG expression is yet to be standardized.

[Table: see text]

No significant financial relationships to disclose.

High BAALC expression associates with other molecular prognostic markers, poor outcome and a distinct gene expression signature in cytogenetically normal acute myeloid leukemia (CN AML): A Cancer and Leukemia Group B (CALGB) study

7013

Background: High BAALC expression predicts poor outcome in CN AML patients (pts). Yet, little is known about BAALC's function or its relation to other prognostic markers. We evaluated BAALC expression in the context of molecular markers and clinical outcome in 172 de novo CN AML adults, aged <60 years (y) treated on similar CALGB protocols (9621 and 19808). Methods: BAALC expression was measured by quantitative real-time RT-PCR in pretreatment blood samples. Pts were grouped as high (n=86) or low BAALC (n=86) expressers using the median expression value, by protocol, as a cutoff. Gene expression profiling (Affymetrix U133 plus 2.0 GeneChip) was performed on high (n=26) and low (n=24) pts. Results: BAALC expression was associated with several molecular markers ( Table ). Complete remission (CR) rate was lower in high BAALC pts (79% v 90%), for whom achieving CR was almost 4 times less likely than for low BAALC pts (P=.02; odds ratio=0.27), after adjusting for age (P=.004), ERG expression (P=.05) and white blood cell count (WBC; P=.04). With a median follow-up of 4.3 y, high BAALC pts had shorter overall survival (OS) (P=.002; 3-y OS: 42% v 59%). In a multivariable model, high BAALC provided further adverse prognostic information (P=.06; hazard ratio=1.66) independent of FLT3 ITD (P<.001), WBC (P=.007) and NPM1 (P=.02). A gene expression signature was identified consisting of 312 probe sets differentially expressed (P<.001) between BAALC groups. High BAALC was associated with overexpression of, among other genes, PROM1, CD34 and KIT indicating a less differentiated phenotype in these pts. Conclusions: Although associated with other prognostic markers, high BAALC expression independently predicts outcome and is associated with a distinct gene expression profile, potentially identifying new therapeutic targets in this pt subset.

No significant financial relationships to disclose.

[Table: see text]

FLT3 D835/I836 mutations predict worse disease-free survival (DFS) in younger adults with cytogenetically normal acute myeloid leukemia (CN AML) without FLT3 internal tandem duplications (ITD): A Cancer and Leukemia Group B (CALGB) study

10532

Background: The adverse prognostic impact of FLT3 ITD is well-recognized in younger adults with CN AML, whereas the clinical relevance of D835/I836 mutations in the second tyrosine kinase domain of FLT3 (FLT3 TKD), that occur in 5%-14% of patients (pts), remains controversial. We evaluated the prognostic impact of FLT3 TKD, alone and with other prognostic markers, in 139 de novo CN AML adults, aged <60 years, without FLT3 ITD, and treated on similar CALGB protocols (9621 and 19808). Methods: FLT3 TKD was detected by RT-PCR/EcoRV digestion. Affymetrix U133 plus 2.0 gene expression profiles derived from FLT3 TKD+ and FLT3 wild-type (FLT3 WT) pts with available RNA were compared. Results: Relative to FLT3 WT pts, FLT3 TKD+ pts [n=16 (11.5%)] presented with higher white blood cell counts (WBC) (median: 57.2 v 14.6 × 109/L; P<.001), % bone marrow (BM) blasts (median: 75.5 v 63; P=.001), and % blood blasts (median: 62.5 v 46; P=.03). All 16 FLT3 TKD+ pts achieved complete remission versus 85% of FLT3 WT pts (P=.13). With a median follow-up of 4.6 years, FLT3 TKD+ pts had worse DFS (P=.01; 3-year DFS rates: 31% v 60%) and a trend for worse overall survival (OS) (P=.17, 3-year OS rates: 40% v 65%) compared to FLT3 WT pts. Other variables moderately associated with a worse DFS (P<.10) included higher % BM blasts and NPM1 WT. Adjusting for these two variables, FLT3 TKD remained significantly associated with adverse DFS (P=.02; hazard ratio=2.3). A gene expression signature consisting of 333 probe sets (P<.001) differentiated FLT3 TKD+ (n=9) from FLT3 WT (n=50) pts. Genes represented in this signature include those involved in cell motility (e.g., C3AR1, VNN1, VNN2, ADAM8; all over-expressed in FLT3 TKD+), development (e.g., HOXB5, HOXB6; both over-expressed in FLT3 TKD+) and stress response (e.g., MPO; under-expressed in FLT3 TKD+). Conclusions: FLT3 TKD appears to be an independent predictor for DFS among younger CN AML adult pts without FLT3 ITD. Gene expression profiling provides additional insight into the biology of FLT3 TKD+ AML and may lead to identification of additional targets for improved therapy.

No significant financial relationships to disclose.

MicroRNA (miR) expression signatures in molecular subsets of cytogenetically normal (CN) acute myeloid leukemia (AML): A Cancer and Leukemia Group B (CALGB) study

7010

Background: Aberrantly expressed miRs contribute to malignant transformation by hybridizing to specific mRNA targets and suppressing their translation into proteins. In CN AML, the largest cytogenetic AML subset, several molecular markers are associated with favorable [e.g., NPM1 mutation (mutNPM1)] or unfavorable [e.g., FLT3 internal tandem duplication (ITD) or high ERG expression (↑ERG)] outcome. We explored if differentially expressed miRs are associated with the aforementioned markers. If so, this might indicate a role for miRs in leukemogenesis and prognosis in CN AML. Methods: Diagnostic samples from 100 adults <60 years, treated on CALGB 19808 (Blood 2005; 106:122a), were analyzed on miR microarrays. Among 305 miR probes, we identified differentially expressed miRs (P<0.005) when comparing patients (pts) with or without mutNPM1, FLT3 ITD or ↑ERG. Results: Nine miRs were differentially expressed in FLT3 ITD compared with FLT3 wild-type pts. miR 155, previously reported in aggressive cancers, was upregulated in FLT3 ITD pts. Strong signatures were associated with mutNPM1 (42 miR probes) and ↑ERG groups (54 miR probes). Consistent with their better prognosis, pts with mutNPM1 had upregulated miRs 10 and 196 targeting HOX genes, miRs 15 and 16 targeting BCL2 and let-7 targeting RAS. Consistent with a more aggressive phenotype, ↑ERG pts had downregulation of let-7 and miR 15 and 16 but also miRs 30, 103, and 24 which target, respectively, CDK6, FBXW11 and MAPK14, all involved in cell cycle regulation and proliferation. Four miRs were associated with event free survival (EFS); all were also associated with ↑ERG. High expression of miRs 124, 129, and 194 was significantly associated with worse EFS and ↑ERG. Low expression of miR 181 was associated with worse EFS and ↑ERG. Notably, downregulation of mir 181 has also been reported in pts with aggressive B-cell chronic lymphocytic leukemia. Conclusions: We report the first miR expression signatures within molecular subsets of CN AML. Further study is warranted to elucidate mechanisms by which miRs contribute to leukemogenesis and impact prognosis, and to determine whether miRs can be therapeutically targeted.

No significant financial relationships to disclose.

Outcome prediction in adult core binding factor (CBF) acute myeloid leukemia (AML) with gene expression profiling: A Cancer and Leukemia Group B (CALGB) study

7011

Background: In CBF AML with t(8;21)(q22;q22) or inv(16)(p13q22)/t(16;16)(p13;q22) [abbreviated inv(16)], KIT mutations (mutKIT) and, in inv(16), trisomy 22 predict outcome and may guide the development of novel risk-adapted therapies. However, prognosis of patients (pts) lacking the aforementioned markers is less clear. Therefore, we profiled gene expression in t(8;21) (n=22) or sole inv(16) (n=25) pts who lacked mutKIT to identify signatures predictive of outcome. All pts were treated on CALGB trials incorporating consolidation therapy with multiple courses of higher dose cytarabine. Methods: Gene expression profiling was performed using Affymetrix U133 plus 2.0 arrays on diagnostic samples. As differences in gene expression distinguished all t(8;21) pts from all inv(16) pts, indicating two different biological entities, we pursued outcome prediction separately for each cytogenetic group. Gene expression-based outcome predictors for event-free survival (EFS) were constructed using a cross-validated prediction algorithm. Results: Among t(8;21) pts, EFS for predicted good (n=13) and poor (n=9) outcome groups differed strikingly (P=0.005; estimated 3-year EFS rates: 69% v 11%). Prediction was correct for 77% of pts. Among sole inv(16) pts, EFS for predicted good (n=18) and poor (n=7) outcome groups also differed (P=0.08; 3-year EFS rates: 78% v 29%). Prediction was correct for 76% of pts. FLT3 mutations appeared not to account for differences in EFS between the predicted groups; only the predicted outcome groups were associated with EFS (all baseline clinical characteristics at P>0.10). Pts with predicted poor outcome had higher expression of genes with leukemogenic potential such as WT1 [t(8;21) and inv(16)], CCNA1 [t(8;21)] and the oncogene MYCN [inv(16)]. Conclusions: Gene expression profiling improves outcome prediction in CBF AML pts lacking the known prognostic markers. Future studies should explore the clinical usefulness of targeting products of over- expressed genes, such as WT1 encoding a potential target for immunotherapy in AML.

No significant financial relationships to disclose.

Depsipeptide (FR 901228) promotes histone acetylation, gene transcription, apoptosis and its activity is enhanced by DNA methyltransferase inhibitors in AML1/ETO-positive leukemic cells

In t(8;21) acute myeloid leukemia (AML), the AML1/ETO fusion protein promotes leukemogenesis by recruiting histone deacetylase (HDAC) and silencing AML1target genes important for hematopoietic differentiation. We hypothesized that depsipeptide (FR901228), a novel HDAC inhibitor evaluated in ongoing clinical trials, restores gene transcription and cell differentiation in AML1/ETO-positive cells. A dose-dependent increase in H3 and H4 histone acetylation was noted in depsipeptide-treated AML1/ETO-positive Kasumi-1 cells and blasts from a patient with t(8;21) AML. Consistent with this biological effect, we also showed a dose-dependent increase in cytotoxicity, expression of IL-3, here used as read-out for silenced AML1-target genes, upregulation of CD11b with other morphologic changes suggestive of partial cell differentiation in Kasumi-1 cells. Some of these biologic effects were also attained in other myeloid leukemia cell lines, suggesting that depsipeptide has differentiation and cytotoxic activity in AML cells, regardless of the underlying genomic abnormality. Notably, the activity of depsipeptide was enhanced by 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor (DNMT). These two agents in combination resulted in enhanced histone acetylation, IL-3 expression, and cytotoxicity, suggesting HDAC and DNMT activities as a potential dual target in future therapeutic strategies for AML1/ETO and other molecular subgroups of AML.

Absence of the wild-type allele predicts poor prognosis in adult de novo acute myeloid leukemia with normal cytogenetics and the internal tandem duplication of FLT3: a cancer and leukemia group B study

The FLT3 gene is mutated by an internal tandem duplication (ITD) in 20-25% of adults with acute myeloid leukemia (AML). We studied 82 adults <60 years of age with primary AML and normal cytogenetics, who received uniform high-dose therapy and found FLT3 ITD in 23 (28%) patients. When the 23 FLT3 ITD+ cases were compared with the 59 cases with wild-type (WT) FLT3, disease-free survival (DFS) was inferior (P = 0.03), yet overall survival (OS) was not different (P = 0.14). However, 8 (35%) of 23 FLT3 ITD/+ cases also lacked a FLT3 WT allele (FLT3(ITD-R)) as determined by PCR and loss of heterozygosity. Thus, three genotypic groups were identified: normal FLT3(WT/WT), heterozygous FLT3(ITD/WT), and hemizygous FLT3(ITD/-). DFS and OS were significantly inferior for patients with FLT3(ITD/-) (P = 0.0017 and P = 0.0014, respectively). Although DFS and OS for FLT3(WT/WT) and FLT3(ITD/WT) groups did not differ (P = 0.32 and P = 0.98, respectively), OS of the FLT3(ITD/-) group was worse than the FLT3(WT/WT) (P = 0.0005) and FLT3(ITD/WT) (P = 0.008) groups. We propose a model in which FLT3(ITD/-) represents a dominant positive, gain-of-function mutation providing AML cells with a greater growth advantage compared with cells having the FLT3(WT/WT) or FLT3(ITD/WT) genotypes. In conclusion, we have identified the FLT3(ITD/-) genotype as an adverse prognostic factor in de novo AML with normal cytogenetics. A poor prognosis of the relatively young FLT3(ITD/-) adults (median age, 37 years), despite treatment with current dose-intensive regimens, suggests that new treatment modalities, such as therapy with a FLT3 tyrosine kinase inhibitor, are clearly needed for this group of patients.

The partial nontandem duplication of the MLL (ALL1) gene is a novel rearrangement that generates three distinct fusion transcripts in B-cell acute lymphoblastic leukemia

A partial nontandem duplication (PNTD) of mixed lineage leukemia (MLL) gene is described in B-cell acute lymphoid leukemia without structural cytogenetic abnormalities at 11q23 and 9p22. A duplicated portion of MLL is interrupted by the insertion of a region of 9p22 that includes the 3'-end of the AF9 gene. The PNTD encodes: (a) a PNTD transcript; (b) a partial tandem duplication of MLL; and (c) a chimeric transcript fusing MLL to the 3'-end of AF9, mimicking the t(9;11)(p22;q23) and expressed 1024-fold higher than the other two. The MLL PNTD, therefore, contributes toward leukemogenesis through simultaneous production of fusion transcripts that are otherwise encoded by three distinct genetic defects.

Coordinate transcriptional and translational regulation of ferritin in response to oxidative stress

The global increase in transcription of cytoprotective genes induced in response to oxidative challenge has been termed the antioxidant response. Ferritin serves as the major iron-binding protein in nonhematopoietic tissues, limiting the catalytic availability of iron for participation in oxygen radical generation. Here we demonstrate that ferritin is a participant in the antioxidant response through a genetically defined electrophile response element (EpRE). The EpRE of ferritin H identified in this report exhibits sequence similarity to EpRE motifs found in antioxidant response genes such as those encoding NAD(P)H:quinone reductase, glutathione S-transferase, and heme oxygenase. However, the EpRE of ferritin H is unusual in structure, comprising two bidirectional motifs arranged in opposing directions on complementary DNA strands. In addition to EpRE-mediated transcriptional activation, we demonstrate that ferritin is subject to time-dependent translational control through regulation of iron-regulatory proteins (IRP). Although IRP-1 is initially activated to its RNA binding (ferritin-repressing) state by oxidants, it rapidly returns to its basal state. This permits the translation of newly synthesized ferritin transcripts and ultimately leads to increased levels of ferritin protein synthesis following oxidant exposure. Taken together, these results clarify the complex transcriptional and translational regulatory mechanisms that contribute to ferritin regulation in response to prooxidant stress and establish a role for ferritin in the antioxidant response.

Differential cytokine and chemokine gene expression by human NK cells following activation with IL-18 or IL-15 in combination with IL-12: implications for the innate immune response

NK cells constitutively express monocyte-derived cytokine (monokine) receptors and secrete cytokines and chemokines following monokine stimulation, and are therefore a critical component of the innate immune response to infection. Here we compared the effects of three monokines (IL-18, IL-15, and IL-12) on human NK cell cytokine and chemokine production. IL-18, IL-15, or IL-12 alone did not stimulate significant cytokine or chemokine production in resting NK cells. The combination of IL-18 and IL-12 induced extremely high amounts of IFN-gamma protein (225 +/- 52 ng/ml) and a 1393 +/- 643-fold increase in IFN-gamma gene expression over those in resting NK cells. IL-15 and IL-12 induced less IFN-gamma protein (24 +/- 10 ng/ml; p < 0.007) and only a 45 +/- 19-fold increase in IFN-gamma gene expression over those in resting NK cells. The CD56bright NK cell subset produced significantly more IFN-gamma following IL-18 and IL-12 compared with CD56dim NK cells (p < 0.008). However, the combination of IL-15 and IL-12 was significantly more potent than that of IL-18 and IL-12 for NK cell production of IL-10, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, and TNF-alpha at the protein and transcript levels. Granulocyte-macrophage CSF was optimally induced by IL-15 and IL-18. Resting CD56+ NK cells expressed IL-18R transcript that was up-regulated by IL-12 or IL-15. Our results show that distinct cytokine and chemokine patterns are induced in NK cells in response to different costimulatory signals from these three monokines. This suggests that NK cell cytokine production may be governed in part by the monokine milieu induced during the early proinflammatory response to infection and by the subset of NK cells present at the site of inflammation.

Tumor cell cytotoxicity of a novel metal chelator

We have synthesized a novel six-coordinate metal chelator from the triamine cis-1,3,5-triaminocyclohexane by the addition of a 2-pyridylmethyl pendant arm on each nitrogen, which we term tachpyr. The experiments described here were designed to explore whether this compound exhibits potential antitumor activity. When added to MBT2 or T24 cultured bladder cancer cells, tachpyr was profoundly cytotoxic, with an IC50 of approximately 4.6 micromol/L compared with 70 micromol/L for desferioxamine. To explore the mode of action of tachpyr, several metal complexes were prepared, including Fe(II), Ca(II), Mn(II), Mg(II), Cu(II), and Zn(II) tachpyr complexes. Of these, the Zn(II), Cu(II), and Fe(II) complexes were without toxic effect, whereas the Ca(II), Mn(II), and Mg(II) complexes remained cytotoxic. To further probe the role of Zn(II) and Cu(II) chelation in the cytotoxicity of tachpyr, sterically hindered tachpyr derivatives were prepared through N-alkylation of tachpyr. These derivatives were unable to strongly bind Fe(III) or Fe(II) but were able to bind Zn(II) and Cu(II). When added to cells, these sterically hindered tachpyr derivatives were nontoxic, consistent with a role of iron depletion in the cytotoxic mechanism of tachpyr. Further, the addition of tachpyr to proliferating cultures resulted in an early and selective inhibition of ferritin synthesis, an iron storage protein whose translation is critically dependent on intracellular iron pools. Taken together, these experiments suggest that tachpyr is a cytotoxic metal chelator that targets intracellular iron, and that the use of tachpyr in cancer therapy deserves further exploration.

Protein kinase CbetaII activation by 1-beta-D-arabinofuranosylcytosine is antagonistic to stimulation of apoptosis and Bcl-2alpha down-regulation

1-beta-D-Arabinofuranosylcytosine (ara-C) stimulates the formation of both diglyceride and ceramide in the acute myelogenous leukemia cell line HL-60 (Strum, J. C., Small, G. W., Pauig, S. B., and Daniel, L. W. (1994) J. Biol. Chem 269, 15493-15497). ara-C also causes apoptosis in HL-60 cells which can be mimicked by exogenous ceramide. However, the signaling role for ara-C-induced diacylglycerol (DAG) is not defined. We found that Bcl-2 levels were increased by treatment of HL-60 cells with exogenous DAG or 12-O-tetradecanoylphorbol-13-acetate (TPA). In contrast, exogenous ceramide treatment caused a decrease in cellular Bcl-2 levels. Thus, ara-C stimulates the synthesis of two second messengers with opposing effects on Bcl-2. Since the effects of ara-C-induced DAG could be due to protein kinase C (PKC) activation, we determined the effects of ara-C on PKC isozymes. ara-C caused an increase in membrane-bound PKCbetaII (but not PKCalpha or PKCdelta). ara-C or TPA-induced translocation of PKCbetaII was inhibited by 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3), and ara-C-induced apoptosis was stimulated by pretreatment of the cells with ET-18-OCH3. ET-18-OCH3 also inhibited stimulation of Bcl-2 by TPA and enhanced the decrease in Bcl-2 observed in ara-C-treated cells. These data indicate that ara-C-induced apoptosis is limited by ara-C-stimulated PKCbetaII through effects on Bcl-2. To further determine the role of PKC, we used antisense oligonucleotides directed toward PKCbetaII. The antisense, but not the sense, oligonucleotide inhibited PKCbetaII activation and enhanced ara-C-induced apoptosis. These data demonstrate that the stimulation of apoptosis by ara-C is self-limiting and can be enhanced by inhibition of PKC.