Key Points• More than 60% of primary AML blasts constitutively produce high levels of NOXderived reactive oxygen species (ROS), which drives AML proliferation.• High ROS AMLs show depleted antioxidant defenses but evade the oxidative stress response through suppression of p38 MAPK signaling.Excessive production of reactive oxygen species (ROS) is frequently observed in cancer and is known to strongly influence hematopoietic cell function. Here we report that extracellular ROS production is strongly elevated (mean >10-fold) in >60% of acute myeloid leukemia (AML) patients and that this increase is attributable to constitutive activation of nicotinamide adenine dinucleotide phosphate oxidases (NOX). In contrast, overproduction of mitochondrial ROS was rarely observed. Elevated ROS was found to be associated with lowered glutathione levels and depletion of antioxidant defense proteins. We also show for the first time that the levels of ROS generated were able to strongly promote the proliferation of AML cell lines, primary AML blasts, and, to a lesser extent, normal CD34 1 cells, and that the response to ROS is limited by the activation of the oxidative stress pathway mediated though p38 MAPK. Consistent with this, we observed that p38 MAPK responses were attenuated in patients expressing high levels of ROS. These data show that overproduction of NOX-derived ROS can promote the proliferation of AML blasts and that they also develop mechanisms to suppress the stress signaling that would normally limit this response. Together these adaptations would be predicted to confer a competitive advantage to the leukemic clone. (Blood. 2013;122(19):3322-3330)

The introduction of BCR-ABL tyrosine kinase inhibitors has revolutionized the treatment of chronic myeloid leukemia (CML). A major clinical aim remains the identification and elimination of low-level disease persistence, termed "minimal residual disease". The phenomenon of disease persistence suggests that despite targeted therapeutic approaches, BCR-ABLindependent mechanisms exist which sustain the survival of leukemic stem cells (LSCs). Although other markers of a primitive CML LSC population have been identified in the preclinical setting, only CD26 appears to offer clinical utility. Here we demonstrate consistent and selective expression of CD93 on a lin − CD34 + CD38 − CD90 + CML LSC population and show in vitro and in vivo data to suggest increased stem cell characteristics, as well as robust engraftment in patient-derived xenograft models in comparison with a CD93 − CML stem/progenitor cell population, which fails to engraft. Through bulk and single-cell analyses of selected stem cell and cell survival-specific genes, we confirmed the quiescent character and demonstrate their persistence in a population of CML patient samples who demonstrate molecular relapse on TKI withdrawal. Taken together, our results identify that CD93 is consistently and selectively expressed on a lin − CD34 + CD38 − CD90 + CML LSC population with stem cell characteristics and may be an important indicator in determining poor TKI responders.

Inappropriate localization of proteins can interfere with normal cellular function and drive tumor development. To understand how this contributes to the development of acute myeloid leukemia (AML), we compared the nuclear proteome and transcriptome of AML blasts with normal human CD34 + cells. Analysis of the proteome identified networks and processes that significantly affected transcription regulation including misexpression of 11 transcription factors with seven proteins not previously implicated in AML. Transcriptome analysis identified changes in 40 transcription factors but none of these were predictive of changes at the protein level. The highest differentially expressed protein in AML nuclei compared with normal CD34 + nuclei (not previously implicated in AML) was S100A4. In an extended cohort, we found that overexpression of nuclear S100A4 was highly prevalent in AML (83%; 20/24 AML patients). Knock down of S100A4 in AML cell lines strongly impacted their survival whilst normal hemopoietic stem progenitor cells were unaffected. These data are the first analysis of the nuclear proteome in AML and have identified changes in transcription factor expression or regulation of transcription that would not have been seen at the mRNA level. These data also suggest that S100A4 is essential for AML survival and could be a therapeutic target in AML.

Hsp90alpha's vital role in cell cycle progression and apoptosis together with its presence in gliomas and absence in normal tissue, make it a credible target for cancer therapy. Three sets of dsRNA oligos designed to align different regions of the hsp90alpha sequence were used to downregulate hsp90alpha. SiRNA 1, 2, and 3 resulted in significant levels of silencing of hsp90alpha after 48 hr treatment (p < .0001). Concurrent treatment of the glioma cell line U87-MG with siRNA 1 and temozolomide (TMZ) resulted in a 13-fold reduction in the dose of TMZ required to achieve a similar effect if TMZ was used alone.

Hsp90α's vital role in tumour survival and progression, together with its highly inducible expression profile in gliomas and its absence in normal tissue and cell lines validates it as a therapeutic target for glioma. Hsp90α was downregulated using the post-transcriptional RNAi strategy (sihsp90α) and a post-translational inhibitor, the benzoquinone antibiotic 17-AAG. Glioblastoma U87-MG and normal human astrocyte SVGp12 were treated with sihsp90α, 17-AAG and concurrent sihsp90α/17-AAG (combined treatment). Both Hsp90α gene silencing and the protein inhibitor approaches resulted in a dramatic reduction in cell viability. Results showed that sihsp90α, 17-AAG and a combination of sihsp90α/17-AAG, reduced cell viability by 27%, 75% and 88% (p < 0.001), respectively, after 72 h. hsp90α mRNA copy numbers were downregulated by 65%, 90% and 99% after 72 h treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG, respectively. The relationship between Hsp90α protein expression and its client Akt kinase activity levels were monitored following treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG. Akt kinase activity was downregulated as a direct consequence of Hsp90α inhibition. Both Hsp90α and Akt kinase levels were significantly downregulated after 72 h. Although, 17-AAG when used as a single agent reduces the Hsp90α protein and the Akt kinase levels, the efficacy demonstrated by combinatorial treatment was found to be far more effective. Combination treatment reduced the Hsp90α protein and Akt kinase levels to 4.3% and 43%, respectively, after 72 h. hsp90α mRNA expression detected in SVGp12 was negligible compared to U87-MG, also, the combination treatment did not compromise the normal cell viability. Taking into account the role of Hsp90α in tumour progression and the involvement of Akt kinase in cell signalling and the anti-apoptotic pathways in tumours, this double targets treatment infers a novel therapeutic strategy.

The efficacy of glioma therapy can be considerably improved if it eliminates cancer stem cells (CSCs); however, to achieve this, CSCs markers are required. This study investigated the influence of micro-environmental changes on CSCs in hypoxic, serum deprived U87-MG and the corresponding control cells. Proteomic analysis produced a wide dataset, depicting the changes that occur at the proteomic level in the differentiated and undifferentiated U87-MG cell line. With the IPA analysis, HPRD and literature reviews, 11 proteins were proposed as potential differentiated biomarkers for CSCs namely Hsp90β1, vimentin, PGK1, GAPDH, EIF4e, TPI1, HspA8, HNRNPK, NAMPT, CCSNK2A1, and ANXA2.

The molecular chaperone heat shock protein 90 alpha (Hsp90α) has been recognized in various tumours including glioma. This pilot study using a proteomic approach analyses the downstream effects of Hsp90 inhibition using 17-allylamino-17-demethoxygeldanamycin (17AAG) and a short hairpin RNA (shRNA) oligonucleotide targetinghsp90α(shhsp90α) in the U87-MG glioma cell line. Preliminary data coupled with bioinformatic analysis identified several known and unknown Hsp90 client proteins that demonstrated a change in their protein expression after Hsp90 inhibition, signifying an alteration in the canonical pathways of cell cycle progression, apoptosis, cell invasion, angiogenesis, and metastasis. Members of the glycolysis pathway were upregulated, demonstrating increased dependency on glycolysis for energy source by the treated glioma cells. Upregulated proteins also include Hsp70 and members of its family such as Hsp27 and gp96, thereby suggesting the role of Hsp90 co-chaperones in compensating for Hsp90 function after Hsp90 inhibition. Considering Hsp70’s role in antiapoptosis, it was postulated that a combination therapy involving a multitarget approach could be carried out. Consequently inhibition of both Hsp90 and Hsp70 in U87-MG glioma cells resulted in 60% cell death indicating the importance of combination therapy for glioma therapeutics.

Until very recently, understanding the complexity of the stem cell (SC) compartment in both normal and leukemic hematopoiesis has been challenging due to the inability to separate and study normal and leukemic SCs at the single-cell level. Recent advances in cell-sorting techniques and single-cell technologies now make this possible, with the identification of a population of highly quiescent chronic myeloid leukemia (CML) SCs that is enriched following therapy with tyrosine kinase inhibitors (TKIs).