Oncogenic NRAS Primes Primary Acute Myeloid Leukemia Cells for Differentiation

Disruption of dNTP homeostasis by ribonucleotide reductase hyperactivation overcomes AML differentiation blockade

Differentiation blockade is a hallmark of acute myeloid leukemia (AML). A strategy to overcome such a blockade is a promising approach against the disease. The lack of understanding of the underlying mechanisms hampers development of such strategies. Dysregulated ribonucleotide reductase (RNR) is considered a druggable target in proliferative cancers susceptible to deoxynucleoside triphosphate (dNTP) depletion. Herein, we report an unanticipated discovery that hyperactivating RNR enables differentiation and decreases leukemia cell growth. We integrate pharmacogenomics and metabolomics analyses to identify that pharmacologically (eg, nelarabine) or genetically upregulating RNR subunit M2 (RRM2) creates a dNTP pool imbalance and overcomes differentiation arrest. Moreover, R-loop-mediated DNA replication stress signaling is responsible for RRM2 activation by nelarabine treatment. Further aggravating dNTP imbalance by depleting the dNTP hydrolase SAM domain and HD domain-containing protein 1 (SAMHD1) enhances ablation of leukemia stem cells by RRM2 hyperactivation. Mechanistically, excessive activation of extracellular signal-regulated kinase (ERK) signaling downstream of the imbalance contributes to cellular outcomes of RNR hyperactivation. A CRISPR screen identifies a synthetic lethal interaction between loss of DUSP6, an ERK-negative regulator, and nelarabine treatment. These data demonstrate that dNTP homeostasis governs leukemia maintenance, and a combination of DUSP inhibition and nelarabine represents a therapeutic strategy.

Guanosine primes acute myeloid leukemia for differentiation via guanine nucleotide salvage synthesis

Differentiation arrest represents a distinct hallmark of acute myeloid leukemia (AML). Identification of differentiation-induction agents that are effective across various subtypes remains an unmet challenge. GTP biosynthesis is elevated in several types of cancers, considered to support uncontrolled tumor growth. Here we report that GTP overload by supplementation of guanosine, the nucleoside precursor of GTP, poises AML cells for differentiation and growth inhibition. Transcriptome profiling of guanosine-treated AML cells reveals a myeloid differentiation pattern. Importantly, the treatment compromises leukemia progression in AML xenograft models. Mechanistically, GTP overproduction requires sequential metabolic conversions executed by the purine salvage biosynthesis pathway including the involvement of purine nucleoside phosphorylase (PNP) and hypoxanthine phosphoribosyltransferase 1 (HPRT1). Taken together, our study offers novel metabolic insights tethering GTP homeostasis to myeloid differentiation and provides an experimental basis for further clinical investigations of guanosine or guanine nucleotides in the treatment of AML patients.

Advances in Diagnosis and Risk Stratification of Acute Myeloid Leukemia and Myelodysplastic Syndromes

Advances in high-throughput DNA sequencing technology in the past decade have made a tremendous impact on basic science and clinical practice. Methods using the latest next generation sequencing technology can sequence an entire human genome within a few hours. Diagnosis and prognostication of hematologic neoplasms have moved from traditional histology and immunophenotyping to integration of cytogenetic and genomic alterations. Using illustrative cases, this chapter provides an overview of the utility of using genomic data for prognostication as well as treatment decision-making for patients with bone marrow neoplasms.

Revealing the anticancer potential of candidate drugs in vivo using Caenorhabditis elegans mutant strains

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Mutations in the Wnt, Notch, and Ras-ERK signaling pathways in C. elegans lead to infertility, sterility, and multivulva formation.

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Phenotypic assays using C. elegans mutant strains can be used as in vivo models for drug repurposing.

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Itraconazole, disulfiram, etodolac, and ouabain have anticancer potential that can specifically target the Wnt, Notch, and RAS-ERK signaling pathways.

Drug repurposing is used as a strategy for finding new drugs for cancer. The process is a faster and a more cost-effective way of providing new indications for drugs that can address emerging drug resistance and numerous side effects of chemotherapeutic drugs. In this study, the in vivo anticancer potential of itraconazole, disulfiram, etodolac, and ouabain were assessed using five different C. elegans mutant strains. Each strain contains mutations in genes involved in different signaling pathways such as Wnt (JK3476), Notch (JK1107 and BS3164), and Ras-ERK (SD939 and MT2124) that result to phenotypes of sterility, infertility, and multivulva formation. These same signaling pathways have been shown to be defective in several human cancer types. The four candidate drugs were tested on the C. elegans mutant strains to determine if they rescue the mutant phenotypes. Both ouabain and etodolac significantly reduced the sterile and infertile phenotypes of JK3476, JK1107, BS3164, and SD939 strains (p=0.0010). Finally, itraconazole and etodolac significantly reduced multivulva formation (p=0.0021). The degrees of significant phenotypic rescues of each mutant were significantly higher than vehicle only (1% DMSO). Therefore, this study demonstrated that the four candidate drugs have anticancer potential in vivo, and etodolac had the highest anticancer potential.