Cysteine depletion targets leukemia stem cells through inhibition of electron transport complex II.

We have previously demonstrated that oxidative phosphorylation is required for the survival of human leukemia stem cells (LSCs) from patients with acute myeloid leukemia (AML). More recently, we demonstrated that LSCs in patients with de novo AML rely on amino acid metabolism to drive oxidative phosphorylation. Notably, although overall levels of amino acids contribute to LSC energy metabolism, our current findings suggest that cysteine may be of particular importance for LSC survival. We demonstrate that exogenous cysteine is metabolized exclusively to glutathione. Upon cysteine depletion, glutathione synthesis is impaired, leading to reduced glutathionylation of succinate dehydrogenase A (SDHA), a key component of electron transport chain complex (ETC) II. Loss of SDHA glutathionylation impairs ETC II activity, thereby inhibiting oxidative phosphorylation, reducing production of ATP, and leading to LSC death. Given the role of cysteine in driving LSC energy production, we tested cysteine depletion as a potential therapeutic strategy. Using a novel cysteine-degrading enzyme, we demonstrate selective eradication of LSCs, with no detectable effect on normal hematopoietic stem/progenitor cells. Together, these findings indicate that LSCs are aberrantly reliant on cysteine to sustain energy metabolism, and that targeting this axis may represent a useful therapeutic strategy.

SIX1 and EWS/FLI1 co-regulate an anti-metastatic gene network in Ewing Sarcoma.

Ewing sarcoma (ES), which is characterized by the presence of oncogenic fusion proteins such as EWS/FLI1, is an aggressive pediatric malignancy with a high rate of early dissemination and poor outcome after distant spread. Here we demonstrate that the SIX1 homeoprotein, which enhances metastasis in most tumor types, suppresses ES metastasis by co-regulating EWS/FLI1 target genes. Like EWS/FLI1, SIX1 promotes cell growth/transformation, yet dramatically inhibits migration and invasion, as well as metastasis in vivo. We show that EWS/FLI1 promotes SIX1 protein expression, and that the two proteins share genome-wide binding profiles and transcriptional regulatory targets, including many metastasis-associated genes such as integrins, which they co-regulate. We further show that SIX1 downregulation of integrins is critical to its ability to inhibit invasion, a key characteristic of metastatic cells. These data demonstrate an unexpected anti-metastatic function for SIX1, through coordinate gene regulation with the key oncoprotein in ES, EWS/FLI1.

SIX1 reprograms myogenic transcription factors to maintain the rhabdomyosarcoma undifferentiated state.

Rhabdomyosarcoma (RMS) is a pediatric muscle sarcoma characterized by expression of the myogenic lineage transcription factors (TFs) MYOD1 and MYOG. Despite high expression of these TFs, RMS cells fail to terminally differentiate, suggesting the presence of factors that alter their functions. Here, we demonstrate that the developmental TF SIX1 is highly expressed in RMS and critical for maintaining a muscle progenitor-like state. SIX1 loss induces differentiation of RMS cells into myotube-like cells and impedes tumor growth in vivo. We show that SIX1 maintains the RMS undifferentiated state by controlling enhancer activity and MYOD1 occupancy at loci more permissive to tumor growth over muscle differentiation. Finally, we demonstrate that a gene signature derived from SIX1 loss correlates with differentiation status and predicts RMS progression in human disease. Our findings demonstrate a master regulatory role of SIX1 in repression of RMS differentiation via genome-wide alterations in MYOD1 and MYOG-mediated transcription.

Nicotinamide Metabolism Mediates Resistance to Venetoclax in Relapsed Acute Myeloid Leukemia Stem Cells.

We previously demonstrated that leukemia stem cells (LSCs) in de novo acute myeloid leukemia (AML) patients are selectively reliant on amino acid metabolism and that treatment with the combination of venetoclax and azacitidine (ven/aza) inhibits amino acid metabolism, leading to cell death. In contrast, ven/aza fails to eradicate LSCs in relapsed/refractory (R/R) patients, suggesting altered metabolic properties. Detailed metabolomic analysis revealed elevated nicotinamide metabolism in relapsed LSCs, which activates both amino acid metabolism and fatty acid oxidation to drive OXPHOS, thereby providing a means for LSCs to circumvent the cytotoxic effects of ven/aza therapy. Genetic and pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in nicotinamide metabolism, demonstrated selective eradication of R/R LSCs while sparing normal hematopoietic stem/progenitor cells. Altogether, these findings demonstrate that elevated nicotinamide metabolism is both the mechanistic basis for ven/aza resistance and a metabolic vulnerability of R/R LSCs.

Monocytic Subclones Confer Resistance to Venetoclax-Based Therapy in Patients with Acute Myeloid Leukemia.

Venetoclax-based therapy can induce responses in approximately 70% of older previously untreated patients with acute myeloid leukemia (AML). However, up-front resistance as well as relapse following initial response demonstrates the need for a deeper understanding of resistance mechanisms. In the present study, we report that responses to venetoclax +azacitidine in patients with AML correlate closely with developmental stage, where phenotypically primitive AML is sensitive, but monocytic AML is more resistant. Mechanistically, resistant monocytic AML has a distinct transcriptomic profile, loses expression of venetoclax target BCL2, and relies on MCL1 to mediate oxidative phosphorylation and survival. This differential sensitivity drives a selective process in patients which favors the outgrowth of monocytic subpopulations at relapse. Based on these findings, we conclude that resistance to venetoclax + azacitidine can arise due to biological properties intrinsic to monocytic differentiation. We propose that optimal AML therapies should be designed so as to independently target AML subclones that may arise at differing stages of pathogenesis. SIGNIFICANCE: Identifying characteristics of patients who respond poorly to venetoclax-based therapy and devising alternative therapeutic strategies for such patients are important topics in AML. We show that venetoclax resistance can arise due to intrinsic molecular/metabolic properties of monocytic AML cells and that such properties can potentially be targeted with alternative strategies.

Pregnancy and Cancer Treatment: Developing a Standardized Testing Policy and Procedure

Systematic gaps for pregnancy screening and testing of patients with cancer persist. Absent or inconsistent guidelines and policies are barriers to standardized practice. Awareness among oncology nurses is needed to promote safe cancer care, prevent patient harm, and uphold patient-centered care.

Reducing Patient Uncertainty: Implementation of a Shared Decision-Making Process Enhances Treatment Quality and Provider Communication.

Patients with cancer can experience uncertainty when making treatment decisions. When unaddressed, patient uncertainty can result in decisional conflict and decisional regret. Providers can assist in decreasing these factors by involving patients in the decision-making process. Patients who agree to participate should be informed about their diagnosis, prognosis, and treatment options, including the benefits, the risks and harms, or the option of no treatment. Providers also can help patients to clarify their values, which reveal patient preferences and inform tailoring of care for each patient. When an informed patient's personal preferences align with care decisions, decisional quality is achieved.