Publications by authors named "Vadym Zaberezhnyy"

16 Publications

  • Page 1 of 1

The Hematopoietic Oxidase NOX2 Regulates Self-Renewal of Leukemic Stem Cells.

Cell Rep 2019 04;27(1):238-254.e6

Division of Hematology, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA. Electronic address:

The NADPH-dependent oxidase NOX2 is an important effector of immune cell function, and its activity has been linked to oncogenic signaling. Here, we describe a role for NOX2 in leukemia-initiating stem cell populations (LSCs). In a murine model of leukemia, suppression of NOX2 impaired core metabolism, attenuated disease development, and depleted functionally defined LSCs. Transcriptional analysis of purified LSCs revealed that deficiency of NOX2 collapses the self-renewal program and activates inflammatory and myeloid-differentiation-associated programs. Downstream of NOX2, we identified the forkhead transcription factor FOXC1 as a mediator of the phenotype. Notably, suppression of NOX2 or FOXC1 led to marked differentiation of leukemic blasts. In xenotransplantation models of primary human myeloid leukemia, suppression of either NOX2 or FOXC1 significantly attenuated disease development. Collectively, these findings position NOX2 as a critical regulator of malignant hematopoiesis and highlight the clinical potential of inhibiting NOX2 as a means to target LSCs.
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http://dx.doi.org/10.1016/j.celrep.2019.03.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6931909PMC
April 2019

Targeting Glutamine Metabolism and Redox State for Leukemia Therapy.

Clin Cancer Res 2019 07 2;25(13):4079-4090. Epub 2019 Apr 2.

Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado.

Purpose: Acute myeloid leukemia (AML) is a hematologic malignancy characterized by the accumulation of immature myeloid precursor cells. AML is poorly responsive to conventional chemotherapy and a diagnosis of AML is usually fatal. More effective and less toxic forms of therapy are desperately needed. AML cells are known to be highly dependent on the amino acid glutamine for their survival. These studies were directed at determining the effects of glutaminase inhibition on metabolism in AML and identifying general weaknesses that can be exploited therapeutically.

Experimental Design: AML cancer cell lines, primary AML cells, and mouse models of AML and acute lymphoblastic leukemia (ALL) were utilized.

Results: We show that blocking glutamine metabolism through the use of a glutaminase inhibitor (CB-839) significantly impairs antioxidant glutathione production in multiple types of AML, resulting in accretion of mitochondrial reactive oxygen species (mitoROS) and apoptotic cell death. Moreover, glutaminase inhibition makes AML cells susceptible to adjuvant drugs that further perturb mitochondrial redox state, such as arsenic trioxide (ATO) and homoharringtonine (HHT). Indeed, the combination of ATO or HHT with CB-839 exacerbates mitoROS and apoptosis, and leads to more complete cell death in AML cell lines, primary AML patient samples, and using mouse models of AML. In addition, these redox-targeted combination therapies are effective in eradicating ALL cells and .

Conclusions: Targeting glutamine metabolism in combination with drugs that perturb mitochondrial redox state represents an effective and potentially widely applicable therapeutic strategy for treating multiple types of leukemia.
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http://dx.doi.org/10.1158/1078-0432.CCR-18-3223DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6642698PMC
July 2019

SIX2 Mediates Late-Stage Metastasis via Direct Regulation of and Induction of a Cancer Stem Cell Program.

Cancer Res 2019 02 3;79(4):720-734. Epub 2019 Jan 3.

Integrated Physiology Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado.

The capacity for tumor cells to metastasize efficiently is directly linked to their ability to colonize secondary sites. Here we identify Six2, a developmental transcription factor, as a critical regulator of a breast cancer stem cell program that enables metastatic colonization. In several triple-negative breast cancer (TNBC) models, Six2 enhanced the expression of genes associated with embryonic stem cell programs. Six2 directly bound the Srr2 enhancer, promoting expression and downstream expression of , which are both key pluripotency factors. Regulation of by Six2 enhanced cancer stem cell properties and increased metastatic colonization. and expression correlated highly in breast cancers including TNBC, where a Six2 expression signature was predictive of metastatic burden and poor clinical outcome. Our findings demonstrate that a SIX2/SOX2 axis is required for efficient metastatic colonization, underscoring a key role for stemness factors in outgrowth at secondary sites. SIGNIFICANCE: These findings provide novel mechanistic insight into stemness and the metastatic outgrowth of triple-negative breast cancer cells. http://cancerres.aacrjournals.org/content/canres/79/4/720/F1.large.jpg.
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http://dx.doi.org/10.1158/0008-5472.CAN-18-1791DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6586234PMC
February 2019

Glutaminase inhibition improves FLT3 inhibitor therapy for acute myeloid leukemia.

Exp Hematol 2018 02 22;58:52-58. Epub 2017 Sep 22.

Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO. Electronic address:

Acute myeloid leukemia (AML) is a blood cancer that is poorly responsive to conventional cytotoxic chemotherapy and a diagnosis of AML is usually fatal. More effective and better-tolerated therapies for AML are desperately needed. Activating mutations in FMS-like tyrosine kinase 3 (FLT3) are one of the most frequently observed genetic defects in AML. FLT3 inhibitors have shown impressive anti-leukemic activity in clinical trials; however, sustained remissions using these inhibitors as monotherapy have not been achieved. Our previous studies have implicated impaired glutamine metabolism in response to FLT3 inhibitors as a dominant factor causing AML cell death. In this study, we have employed metabolic flux analysis to examine the effects of FLT3 inhibition on glutamine utilization in FLT3-mutated AML cells using stable isotope tracers. We found that the FLT3 inhibitor AC220 inhibited glutamine flux into the antioxidant factor glutathione profoundly due to defective glutamine import. We also found that the glutaminase inhibitor CB-839 similarly impaired glutathione production by effectively blocking flux of glutamine into glutamate. Moreover, the combination of AC220 with CB-839 synergized to deplete glutathione, induce mitochondrial reactive oxygen species, and cause loss of viability through apoptotic cell death. In vivo, glutaminase inhibition with CB-839 facilitated leukemic cell elimination by AC220 and improved survival significantly in a patient-derived xenograft AML mouse model. Therefore, targeting glutaminase in combination with FLT3 may represent an effective therapeutic strategy for improving treatment of FLT3-mutated AML.
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http://dx.doi.org/10.1016/j.exphem.2017.09.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5815916PMC
February 2018

Folate dietary insufficiency and folic acid supplementation similarly impair metabolism and compromise hematopoiesis.

Haematologica 2017 12 7;102(12):1985-1994. Epub 2017 Sep 7.

Department of Biochemistry and Molecular Genetics, University of Colorado AMC, Aurora, CO, USA

While dietary folate deficiency is associated with increased risk for birth defects and other diseases, evidence suggests that supplementation with folic acid can contribute to predisposition to some diseases, including immune dysfunction and cancer. Herein, we show that diets supplemented with folic acid both below and above the recommended levels led to significantly altered metabolism in multiple tissues in mice. Surprisingly, both low and excessive dietary folate induced similar metabolic changes, which were particularly evident for nucleotide biosynthetic pathways in B-progenitor cells. Diet-induced metabolic changes in these cells partially phenocopied those observed in mice treated with anti-folate drugs, suggesting that both deficiency and excessive levels of dietary folic acid compromise folate-dependent biosynthetic pathways. Both folate deficiency and excessive dietary folate levels compromise hematopoiesis, resulting in defective cell cycle progression, persistent DNA damage, and impaired production of lymphocytes. These defects reduce the reconstitution potential in transplantation settings and increase radiation-induced mortality. We conclude that excessive folic acid supplementation can metabolically mimic dietary folate insufficiency, leading to similar functional impairment of hematopoiesis.
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http://dx.doi.org/10.3324/haematol.2017.171074DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5709097PMC
December 2017

AZ1366: An Inhibitor of Tankyrase and the Canonical Wnt Pathway that Limits the Persistence of Non-Small Cell Lung Cancer Cells Following EGFR Inhibition.

Clin Cancer Res 2017 Mar 23;23(6):1531-1541. Epub 2016 Sep 23.

Department of Biochemistry and Molecular Genetics.

The emergence of EGFR inhibitors such as gefitinib, erlotinib, and osimertinib has provided novel treatment opportunities in EGFR-driven non-small cell lung cancer (NSCLC). However, most patients with EGFR-driven cancers treated with these inhibitors eventually relapse. Recent efforts have identified the canonical Wnt pathway as a mechanism of protection from EGFR inhibition and that inhibiting tankyrase, a key player in this pathway, is a potential therapeutic strategy for the treatment of EGFR-driven tumors. We performed a preclinical evaluation of tankyrase inhibitor AZ1366 in combination with multiple EGFR-inhibitors across NSCLC lines, characterizing its antitumor activity, impingement on canonical Wnt signaling, and effects on gene expression. We performed pharmacokinetic and pharmacodynamic profiling of AZ1366 in mice and evaluated its therapeutic activity in an orthotopic NSCLC model. In combination with EGFR inhibitors, AZ1366 synergistically suppressed proliferation of multiple NSCLC lines and amplified global transcriptional changes brought about by EGFR inhibition. Its ability to work synergistically with EGFR inhibition coincided with its ability to modulate the canonical Wnt pathway. Pharmacokinetic and pharmacodynamic profiling of AZ1366-treated orthotopic tumors demonstrated clinically relevant serum drug levels and intratumoral target inhibition. Finally, coadministration of an EGFR inhibitor and AZ1366 provided better tumor control and improved survival for Wnt-responsive lung cancers in an orthotopic mouse model. Tankyrase inhibition is a potent route of tumor control in EGFR-dependent NSCLC with confirmed dependence on canonical Wnt signaling. These data strongly support further evaluation of tankyrase inhibition as a cotreatment strategy with EGFR inhibition in an identifiable subset of EGFR-driven NSCLC. .
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http://dx.doi.org/10.1158/1078-0432.CCR-16-1179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5354947PMC
March 2017

Aging-associated inflammation promotes selection for adaptive oncogenic events in B cell progenitors.

J Clin Invest 2015 Dec 9;125(12):4666-80. Epub 2015 Nov 9.

The incidence of cancer is higher in the elderly; however, many of the underlying mechanisms for this association remain unexplored. Here, we have shown that B cell progenitors in old mice exhibit marked signaling, gene expression, and metabolic defects. Moreover, B cell progenitors that developed from hematopoietic stem cells (HSCs) transferred from young mice into aged animals exhibited similar fitness defects. We further demonstrated that ectopic expression of the oncogenes BCR-ABL, NRAS(V12), or Myc restored B cell progenitor fitness, leading to selection for oncogenically initiated cells and leukemogenesis specifically in the context of an aged hematopoietic system. Aging was associated with increased inflammation in the BM microenvironment, and induction of inflammation in young mice phenocopied aging-associated B lymphopoiesis. Conversely, a reduction of inflammation in aged mice via transgenic expression of α-1-antitrypsin or IL-37 preserved the function of B cell progenitors and prevented NRAS(V12)-mediated oncogenesis. We conclude that chronic inflammatory microenvironments in old age lead to reductions in the fitness of B cell progenitor populations. This reduced progenitor pool fitness engenders selection for cells harboring oncogenic mutations, in part due to their ability to correct aging-associated functional defects. Thus, modulation of inflammation--a common feature of aging--has the potential to limit aging-associated oncogenesis.
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http://dx.doi.org/10.1172/JCI83024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4665776PMC
December 2015

TWIST1-Induced miR-424 Reversibly Drives Mesenchymal Programming while Inhibiting Tumor Initiation.

Cancer Res 2015 May 25;75(9):1908-21. Epub 2015 Feb 25.

Program in Molecular Biology, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado.

Epithelial-to-mesenchymal transition (EMT) is a dynamic process that relies on cellular plasticity. Recently, the process of an oncogenic EMT, followed by a reverse mesenchymal-to-epithelial transition (MET), has been implicated as critical in the metastatic colonization of carcinomas. Unlike governance of epithelial programming, regulation of mesenchymal programming is not well understood in EMT. Here, we describe and characterize the first microRNA that enhances exclusively mesenchymal programming. We demonstrate that miR-424 is upregulated early during a TWIST1 or SNAI1-induced EMT, and that it causes cells to express mesenchymal genes without affecting epithelial genes, resulting in a mixed/intermediate EMT. Furthermore, miR-424 increases motility, decreases adhesion, and induces a growth arrest, changes associated with a complete EMT that can be reversed when miR-424 expression is lowered, concomitant with an MET-like process. Breast cancer patient miR-424 levels positively associate with TWIST1/2 and EMT-like gene signatures, and miR-424 is increased in primary tumors versus matched normal breast. However, miR-424 is downregulated in patient metastases versus matched primary tumors. Correspondingly, miR-424 decreases tumor initiation and is posttranscriptionally downregulated in macrometastases in mice, suggesting the need for biphasic expression of miR-424 to transit the EMT-MET axis. Next-generation RNA sequencing revealed miR-424 regulates numerous EMT and cancer stemness-associated genes, including TGFBR3, whose downregulation promotes mesenchymal phenotypes, but not tumor-initiating phenotypes. Instead, we demonstrate that increased MAPK-ERK signaling is critical for miR-424-mediated decreases in tumor-initiating phenotypes. These findings suggest miR-424 plays distinct roles in tumor progression, potentially facilitating earlier, but repressing later, stages of metastasis by regulating an EMT-MET axis.
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http://dx.doi.org/10.1158/0008-5472.CAN-14-2394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4417413PMC
May 2015

Tyrosine kinase inhibition in leukemia induces an altered metabolic state sensitive to mitochondrial perturbations.

Clin Cancer Res 2015 Mar 29;21(6):1360-72. Epub 2014 Dec 29.

Integrated Department of Immunology, University of Colorado Anschutz Medical Campus, Aurora, Colorado. School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Cancer Biology Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Department of Pediatrics, Division of Hematology, Oncology, and Bone Marrow Transplantation, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Department of Medicine, Section of Hematology, University of Colorado Anschutz Medical Campus, Aurora, Colorado.

Purpose: Although tyrosine kinase inhibitors (TKI) can be effective therapies for leukemia, they fail to fully eliminate leukemic cells and achieve durable remissions for many patients with advanced BCR-ABL(+) leukemias or acute myelogenous leukemia (AML). Through a large-scale synthetic lethal RNAi screen, we identified pyruvate dehydrogenase, the limiting enzyme for pyruvate entry into the mitochondrial tricarboxylic acid cycle, as critical for the survival of chronic myelogenous leukemia (CML) cells upon BCR-ABL inhibition. Here, we examined the role of mitochondrial metabolism in the survival of Ph(+) leukemia and AML upon TK inhibition.

Experimental Design: Ph(+) cancer cell lines, AML cell lines, leukemia xenografts, cord blood, and patient samples were examined.

Results: We showed that the mitochondrial ATP-synthase inhibitor oligomycin-A greatly sensitized leukemia cells to TKI in vitro. Surprisingly, oligomycin-A sensitized leukemia cells to BCR-ABL inhibition at concentrations of 100- to 1,000-fold below those required for inhibition of respiration. Oligomycin-A treatment rapidly led to mitochondrial membrane depolarization and reduced ATP levels, and promoted superoxide production and leukemia cell apoptosis when combined with TKI. Importantly, oligomycin-A enhanced elimination of BCR-ABL(+) leukemia cells by TKI in a mouse model and in primary blast crisis CML samples. Moreover, oligomycin-A also greatly potentiated the elimination of FLT3-dependent AML cells when combined with an FLT3 TKI, both in vitro and in vivo.

Conclusions: TKI therapy in leukemia cells creates a novel metabolic state that is highly sensitive to particular mitochondrial perturbations. Targeting mitochondrial metabolism as an adjuvant therapy could therefore improve therapeutic responses to TKI for patients with BCR-ABL(+) and FLT3(ITD) leukemias.
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http://dx.doi.org/10.1158/1078-0432.CCR-14-2146DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4359967PMC
March 2015

Contrasting roles for C/EBPα and Notch in irradiation-induced multipotent hematopoietic progenitor cell defects.

Stem Cells 2015 Apr;33(4):1345-58

Department of Immunology, University of Colorado, Aurora, Colorado, USA.

Ionizing radiation (IR) is associated with reduced hematopoietic function and increased risk of hematopoietic malignancies, although the mechanisms behind these relationships remain poorly understood. Both effects of IR have been commonly attributed to the direct induction of DNA mutations, but evidence supporting these hypotheses is largely lacking. Here we demonstrate that IR causes long-term, somatically heritable, cell-intrinsic reductions in hematopoietic stem cell (HSC) and multipotent hematopoietic progenitor cell (mHPC) self-renewal that are mediated by C/EBPα and reversed by Notch. mHPC from previously irradiated (>9 weeks prior), homeostatically restored mice exhibit gene expression profiles consistent with their precocious differentiation phenotype, including decreased expression of HSC-specific genes and increased expression of myeloid program genes (including C/EBPα). These gene expression changes are reversed by ligand-mediated activation of Notch. Loss of C/EBPα expression is selected for within previously irradiated HSC and mHPC pools and is associated with reversal of IR-dependent precocious differentiation and restoration of self-renewal. Remarkably, restoration of mHPC self-renewal by ligand-mediated activation of Notch prevents selection for C/EBPα loss of function in previously irradiated mHPC pools. We propose that environmental insults prompt HSC to initiate a program limiting their self-renewal, leading to loss of the damaged HSC from the pool while allowing this HSC to temporarily contribute to differentiated cell pools. This "programmed mediocrity" is advantageous for the sporadic genotoxic insults animals have evolved to deal with but becomes tumor promoting when the entire HSC compartment is damaged, such as during total body irradiation, by increasing selective pressure for adaptive oncogenic mutations.
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http://dx.doi.org/10.1002/stem.1936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4376650PMC
April 2015

Homeoprotein Six2 promotes breast cancer metastasis via transcriptional and epigenetic control of E-cadherin expression.

Cancer Res 2014 Dec 27;74(24):7357-70. Epub 2014 Oct 27.

Department of Pharmacology, University of Colorado School of Medicine, Aurora, Colorado. Program in Molecular Biology, University of Colorado School of Medicine, Aurora, Colorado. Program in Cancer Biology, University of Colorado School of Medicine, Aurora, Colorado. Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, Colorado.

Misexpression of developmental transcription factors occurs often in human cancers, where embryonic programs may be reinstated in a context that promotes or sustains malignant development. In this study, we report the involvement of the kidney development transcription factor Six2 in the metastatic progression of human breast cancer. We found that Six2 promoted breast cancer metastasis by a novel mechanism involving both transcriptional and epigenetic regulation of E-cadherin. Downregulation of E-cadherin by Six2 was necessary for its ability to increase soft agar growth and in vivo metastasis in an immunocompetent mouse model of breast cancer. Mechanistic investigations showed that Six2 represses E-cadherin expression by upregulating Zeb2, in part, through a microRNA-mediated mechanism and by stimulating promoter methylation of the E-cadherin gene (Cdh1). Clinically, SIX2 expression correlated inversely with CDH1 expression in human breast cancer specimens, corroborating the disease relevance of their interaction. Our findings establish Six2 as a regulator of metastasis in human breast cancers and demonstrate an epigenetic function for SIX family transcription factors in metastatic progression through the regulation of E-cadherin.
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http://dx.doi.org/10.1158/0008-5472.CAN-14-0666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4268359PMC
December 2014

Inhibition of calcineurin combined with dasatinib has direct and indirect anti-leukemia effects against BCR-ABL1(+) leukemia.

Am J Hematol 2014 Sep 19;89(9):896-903. Epub 2014 Jun 19.

Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045.

Treatment of BCR-ABL1(+) leukemia has been revolutionized with the development of tyrosine kinase inhibitors. However, patients with BCR-ABL1(+) acute lymphoblastic leukemia and subsets of patients with chronic myeloid leukemia are at high risk of relapse despite kinase inhibition therapy, necessitating novel treatment strategies. We previously reported synthetic lethality in BCR-ABL1(+) leukemia cells by blocking both calcineurin/NFAT signaling and BCR-ABL1, independent of drug efflux inhibition by cyclosporine. Here, using RNA-interference we confirm that calcineurin inhibition sensitizes BCR-ABL1(+) cells to tyrosine kinase inhibition in vitro. However, when we performed pharmacokinetic and pharmacodynamic studies of dasatinib and cyclosporine in mice, we found that co-administration of cyclosporine increases peak concentrations and the area under the curve of dasatinib, which contributes to the enhanced disease control. We also report the clinical experience of two subjects in whom we observed more hematopoietic toxicity than expected while enrolled in a Phase Ib trial designed to assess the safety and tolerability of adding cyclosporine to dasatinib in humans. Thus, the anti-leukemia benefit of co-administration of cyclosporine and dasatinib is mechanistically pleiotropic, but may not be tolerable, at least as administered in this trial. These data highlight some of the challenges associated with combining targeted agents to treat leukemia.
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http://dx.doi.org/10.1002/ajh.23776DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4134764PMC
September 2014

Declining lymphoid progenitor fitness promotes aging-associated leukemogenesis.

Proc Natl Acad Sci U S A 2010 Dec 22;107(50):21713-8. Epub 2010 Nov 22.

Department of Biochemistry and Molecular Genetics and Pediatrics, School of Medicine, University of Colorado Denver, Aurora, CO 80045, USA.

Aging is associated with the functional decline of cells, tissues, and organs. At the same time, age is the single most important prognostic factor in the development of most human cancers, including chronic myelogenous and acute lymphoblastic leukemias initiated by Bcr-Abl oncogenic translocations. Prevailing paradigms attribute the association between aging and cancers to the accumulation of oncogenic mutations over time, because the accrual of oncogenic events is thought to be the rate-limiting step in initiation and progression of cancers. Conversely, aging-associated functional decline caused by both cell-autonomous and non-cell-autonomous mechanisms is likely to reduce the fitness of stem and progenitor cell populations. This reduction in fitness should be conducive for increased selection of oncogenic mutations that can at least partially alleviate fitness defects, thereby promoting the initiation of cancers. We tested this hypothesis using mouse hematopoietic models. Our studies indicate that the dramatic decline in the fitness of aged B-lymphopoiesis coincides with altered receptor-associated kinase signaling. We further show that Bcr-Abl provides a much greater competitive advantage to old B-lymphoid progenitors compared with young progenitors, coinciding with restored kinase signaling pathways, and that this enhanced competitive advantage translates into increased promotion of Bcr-Abl-driven leukemias. Moreover, impairing IL-7-mediated signaling is sufficient to promote selection for Bcr-Abl-expressing B progenitors. These studies support an unappreciated causative link between aging and cancer: increased selection of oncogenic mutations as a result of age-dependent alterations of the fitness landscape.
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http://dx.doi.org/10.1073/pnas.1005486107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3003039PMC
December 2010

Wnt/Ca2+/NFAT signaling maintains survival of Ph+ leukemia cells upon inhibition of Bcr-Abl.

Cancer Cell 2010 Jul;18(1):74-87

Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO 80045, USA.

Although Bcr-Abl kinase inhibitors have proven effective in the treatment of chronic myeloid leukemia (CML), they generally fail to eradicate Bcr-Abl(+) leukemia cells. To identify genes whose inhibition sensitizes Bcr-Abl(+) leukemias to killing by Bcr-Abl inhibitors, we performed an RNAi-based synthetic lethal screen with imatinib mesylate in CML cells. This screen identified numerous components of a Wnt/Ca(2+)/NFAT signaling pathway. Antagonism of this pathway led to impaired NFAT activity, decreased cytokine production, and enhanced sensitivity to Bcr-Abl inhibition. Furthermore, NFAT inhibition with cyclosporin A facilitated leukemia cell elimination by the Bcr-Abl inhibitor dasatinib and markedly improved survival in a mouse model of Bcr-Abl(+) acute lymphoblastic leukemia (ALL). Targeting this pathway in combination with Bcr-Abl inhibition could improve treatment of Bcr-Abl(+) leukemias.
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http://dx.doi.org/10.1016/j.ccr.2010.04.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2904512PMC
July 2010

Irradiation selects for p53-deficient hematopoietic progenitors.

PLoS Biol 2010 Mar 2;8(3):e1000324. Epub 2010 Mar 2.

Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America.

Identification and characterization of mutations that drive cancer evolution constitute a major focus of cancer research. Consequently, dominant paradigms attribute the tumorigenic effects of carcinogens in general and ionizing radiation in particular to their direct mutagenic action on genetic loci encoding oncogenes and tumor suppressor genes. However, the effects of irradiation are not limited to genetic loci that encode oncogenes and tumor suppressors, as irradiation induces a multitude of other changes both in the cells and their microenvironment which could potentially affect the selective effects of some oncogenic mutations. P53 is a key tumor suppressor, the loss of which can provide resistance to multiple genotoxic stimuli, including irradiation. Given that p53 null animals develop T-cell lymphomas with high penetrance and that irradiation dramatically accelerates lymphoma development in p53 heterozygous mice, we hypothesized that increased selection for p53-deficient cells contributes to the causal link between irradiation and induction of lymphoid malignancies. We sought to determine whether ionizing irradiation selects for p53-deficient hematopoietic progenitors in vivo using mouse models. We found that p53 disruption does not provide a clear selective advantage within an unstressed hematopoietic system or in previously irradiated BM allowed to recover from irradiation. In contrast, upon irradiation p53 disruption confers a dramatic selective advantage, leading to long-term expansion of p53-deficient clones and to increased lymphoma development. Selection for cells with disrupted p53 appears to be attributable to several factors: protection from acute irradiation-induced ablation of progenitor cells, prevention of irradiation-induced loss of clonogenic capacity for stem and progenitor cells, improved long-term maintenance of progenitor cell fitness, and the disabling/elimination of competing p53 wild-type progenitors. These studies indicate that the carcinogenic effect of ionizing irradiation can in part be explained by increased selection for cells with p53 disruption, which protects progenitor cells both from immediate elimination and from long-term reductions in fitness following irradiation.
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http://dx.doi.org/10.1371/journal.pbio.1000324DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2830447PMC
March 2010

Irradiation alters selection for oncogenic mutations in hematopoietic progenitors.

Cancer Res 2009 Sep 8;69(18):7262-9. Epub 2009 Sep 8.

Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, USA.

Exposure to ionizing radiation and other DNA-damaging carcinogens is strongly associated with induction of malignancies. Prevailing paradigms attribute this association to the induction of oncogenic mutations, as the incidence of oncogenic events is thought to limit initiation and progression of cancers. On the other hand, random mutagenic and genotoxic effects of irradiation are likely to alter progenitor cell populations and the microenvironment, thus altering the selective effects of oncogenic mutations. Using competitive bone marrow transplantation experiments in mice, we show that ionizing irradiation leads to a persistent decline in the numbers and fitness of hematopoietic stem cells, in part resulting from persistent induction of reactive oxygen species. Previous irradiation dramatically alters the selective effects of some oncogenic mutations, substantially inhibiting clonal expansion and leukemogenesis driven by Bcr-Abl or activated N-Ras oncogenes but enhancing the selection for and leukemogenesis driven by the activated Notch1 mutant ICN. Irradiation-dependent selection for ICN expression occurs in a hematopoietic stem cell-enriched pool, which should facilitate the accumulation of additional oncogenic events at a committed T-progenitor stage critical for formation of T-lymphocytic leukemia stem cells. Enhancement of ICN-driven selection and leukemogenesis by previous irradiation is in part non-cell autonomous, as partial restoration of normal hematopoiesis can reverse these effects of irradiation. These studies show that irradiation substantially alters the adaptive landscape in hematopoietic progenitors and suggest that the causal link between irradiation and carcinogenesis might involve increased selection for particular oncogenic mutations.
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http://dx.doi.org/10.1158/0008-5472.CAN-09-0604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2745506PMC
September 2009