Summary Most forms of chemotherapy employ mechanisms involving induction of oxidative stress, a strategy that can be effective due to the elevated oxidative state commonly observed in cancer cells. However, recent studies have shown that relative redox levels in primary tumors can be heterogeneous, suggesting that regimens dependent on differential oxidative state may not be uniformly effective. To investigate this issue in hematological malignancies, we evaluated mechanisms controlling oxidative state in primary specimens derived from acute myelogenous leukemia (AML) patients. Our studies demonstrate three striking findings. First, the majority of functionally-defined leukemia stem cells (LSCs) are characterized by relatively low levels of reactive oxygen species (termed “ROS-low”). Second, ROS-low LSCs aberrantly over-express BCL-2. Third, BCL-2 inhibition reduced oxidative phosphorylation and selectively eradicated quiescent LSCs. Based on these findings, we propose a model wherein the unique physiology of ROS-low LSCs provides an opportunity for selective targeting via disruption of BCL-2-dependent oxidative phosphorylation.

Background: Eradication of primary human leukemia cells represents a major challenge. Therapies have not substantially changed in over 30 years. Results: Using normal versus leukemia specimens enriched for primitive cells, we document aberrant regulation of glutathione metabolism. Conclusion: Aberrant glutathione metabolism is an intrinsic property of human leukemia cells. Significance: Interventions based on modulation of glutathione metabolism represent a powerful means to improve therapy.

We hypothesized that chronic tissue stress due to interaction of alloreactive donor cells with host epithelium after allogeneic hematopoietic cell transplantation (allo-HCT) may cause genomic alterations. We therefore analyzed 176 buccal samples obtained from 71 unselected allotransplanted patients for microsatellite instability (MSI). MSI was observed in 52% of allotransplanted patients but never in 31 healthy or autotransplanted controls. The patient age, the donor age, a female-tomale transplantation and a low number of CD34 þ cells in the graft were significantly correlated with genomic instability. There was a trend for increasing risk of MSI for patients who experienced severe graft-vs-host disease. Secondary malignancy was diagnosed in five (14%) of the MSI þ and only in one (3%) MSI À patient. In an in vitro model of mutation analysis we found significant induction of frameshift mutations and DNA strand breaks in HaCaT keratinocytes co-cultured with mixed lymphocyte cultures (MLCs) but not after their exposure to interferon-c, tumor necrosis factor-a, transforming growth factor-b (TGF-b), MLC supernatant, peripheral blood mononuclear cells (PBMCs) or phytohemagglutinin-stimulated PBMC. A reactive oxygen species-mediated mechanism is implicated. The in vivo and in vitro data of our study show that alloreactions after allo-HCT may induce genomic alterations in epithelium. Progress in understanding DNA damage and repair after allo-HCT can potentially provide molecular biomarkers and therapeutic targets.

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Identification of agents that target human leukemia stem cells (LSCs) is an important consideration for the development of new therapies. The present study demonstrates that rocaglamide and silvestrol, closely related natural products from the flavagline class of compounds, are able to preferentially kill functionally defined LSCs while sparing normal stem and progenitor cells. In addition to efficacy as single agents, flavaglines sensitize leukemia cells to several anti-cancer compounds, including front-line chemotherapeutic drugs used to treat leukemia patients. Mechanistic studies indicate that flavaglines strongly inhibit protein synthesis, leading to the reduction of short-lived anti-apoptotic proteins. Notably though, treatment with flavaglines alone or in combination with other drugs, yields a much stronger cytotoxic activity towards leukemia cells than the translational inhibitor temsirolimus. These results indicate that the underlying cell death mechanism of flavaglines is more complex than simply inhibiting general protein translation. Global gene expression profiling and cell biological assays identified Myc inhibition and the disruption of mitochondrial integrity to be features of flavaglines, which we propose contribute to their efficacy in targeting leukemia cells. Together, these findings indicate that rocaglamide and silvestrol are distinct from clinically available translational inhibitors and represent promising candidates for the treatment of leukemia.