Arginine addiction in AML

Amino acid metabolism: challenges and opportunities for the therapeutic treatment of leukemia and lymphoma

Leukemia and lymphoma-the most common hematological malignant diseases-are often accompanied by complications such as drug resistance, refractory diseases and relapse. Amino acids (AAs) are important energy sources for malignant cells. Tumor-mediated AA metabolism is associated with the immunosuppressive properties of the tumor microenvironment, thereby assisting malignant cells to evade immune surveillance. Targeting abnormal AA metabolism in the tumor microenvironment may be an effective therapeutic approach to address the therapeutic challenges of leukemia and lymphoma. Here, we review the effects of glutamine, arginine and tryptophan metabolism on tumorigenesis and immunomodulation, and define the differences between tumor cells and immune effector cells. We also comment on treatments targeting these AA metabolism pathways in lymphoma and leukemia and discuss how these treatments have profound adverse effects on tumor cells, but leave the immune cells unaffected or mildly affected.

Phase I study of ADI-PEG20 plus low-dose cytarabine for the treatment of acute myeloid leukemia

Most acute myeloid leukemia (AML) cells are argininosuccinate synthetase‐deficient. Pegylated arginine deiminase (ADI‐PEG20) monotherapy depletes circulating arginine, thereby selectively inducing tumor cell death. ADI‐PEG20 was shown to induce complete responses in ~10% of relapsed/refractory or poor‐risk AML patients. We conducted a phase I, dose‐escalation study combining ADI‐PEG20 and low‐dose cytarabine (LDC) in AML patients. Patients received 20 mg LDC subcutaneously twice daily for 10 days every 28 days and ADI‐PEG20 at 18 or 36 mg/m² (dose levels 1 and 2) intramuscularly weekly. An expansion cohort for the maximal tolerated dose of ADI‐PEG20 was planned to further estimate the toxicity and preliminary response of this regimen. The primary endpoints were safety and tolerability. The secondary endpoints were time on treatment, overall survival (OS), overall response rate (ORR), and biomarkers (pharmacodynamics and immunogenicity detection). Twenty‐three patients were included in the study, and seventeen patients were in the expansion cohort (dose level 2). No patients developed dose‐limiting toxicities. The most common grade III/IV toxicities were thrombocytopenia (61%), anemia (52%), and neutropenia (30%). One had an allergic reaction to ADI‐PEG20. The ORR in 18 evaluable patients was 44.4%, with a median OS of 8.0 (4.5‐not reached) months. In seven treatment‐naïve patients, the ORR was 71.4% and the complete remission rate was 57.1%. The ADI‐PEG20 and LDC combination was well‐tolerated and resulted in an encouraging ORR. Further combination studies are warranted. (This trial was registered in ClinicalTrials.gov as a Ph1 Study of ADI‐PEG20 Plus Low‐Dose Cytarabine in Older Patients With AML, NCT02875093).

Arginine deprivation as a strategy for cancer therapy: An insight into drug design and drug combination

Extensive studies have shown that cancer cells have specific nutrient auxotrophy and thus have much a higher demand for certain nutrients than normal cells. Amino acid deprivation has attracted much attention in cancer therapy with positive outcomes from clinical trials. Arginine, as one of the conditionally essential amino acids, plays a pivotal role in cellular division and metabolism. Since many types of cancer cells exhibit decreased expression of argininosuccinate synthetase and/or ornithine transcarbamylase, they are auxotrophic for arginine, which makes arginine deprivation an accessible choice for cancer treatment. Arginine deiminase (ADI) and human arginase (hArg) are the two major protein drugs used for arginine deprivation and are undergoing many clinical trials. However, the clinical application of ADI and hArg is facing some common problems, including their short half-lives, immunogenicity and inconsistent production, which underlines the importance of improving these drugs using protein engineering techniques. Thus, we systematically review the latest studies of protein engineering and anti-cancer studies based on in vitro, in vivo and clinical models of ADI and hArg, and we include the latest studies on drug combinations consisting of ADI/hArg with chemotherapeutic drugs.

Metabolic regulation of the bone marrow microenvironment in leukemia

Most leukemia patients experience little benefit from immunotherapy, in part due to the immunosuppressive bone marrow microenvironment. Various metabolic mechanisms orchestrate the behaviors of immune cells and leukemia cells in the bone marrow microenvironment. Furthermore, leukemia cells regulate the bone marrow microenvironment through metabolism to generate an adequate supply of energy and to escape antitumor immune surveillance. Thus, the targeting of the interaction between leukemia cells and the bone marrow microenvironment provides a new therapeutic avenue. In this review, we describe the concept of the bone marrow microenvironment and several important metabolic processes of leukemia cells within the bone marrow microenvironment, including carbohydrate, lipid, and amino acid metabolism. In addition, we discuss how these metabolic pathways regulate antitumor immunity and reveal potential therapeutic targets.

Identification of a metabolic gene panel to predict the prognosis of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is clonal disease featured by ineffective haematopoiesis and potential progression into acute myeloid leukaemia (AML). At present, the risk stratification and prognosis of MDS need to be further optimized. A prognostic model was constructed by the least absolute shrinkage and selection operator (LASSO) regression analysis for MDS patients based on the identified metabolic gene panel in training cohort, followed by external validation in an independent cohort. The patients with lower risk had better prognosis than patients with higher risk. The constructed model was verified as an independent prognostic factor for MDS patients with hazard ratios of 3.721 (1.814-7.630) and 2.047 (1.013-4.138) in the training cohort and validation cohort, respectively. The AUC of 3-year overall survival was 0.846 and 0.743 in the training cohort and validation cohort, respectively. The high-risk score was significantly related to other clinical prognostic characteristics, including higher bone marrow blast cells and lower absolute neutrophil count. Moreover, gene set enrichment analyses (GSEA) showed several significantly enriched pathways, with potential indication of the pathogenesis. In this study, we identified a novel stable metabolic panel, which might not only reveal the dysregulated metabolic microenvironment, but can be used to predict the prognosis of MDS.

A Phase II Study of Arginine Deiminase (ADI-PEG20) in Relapsed/Refractory or Poor-Risk Acute Myeloid Leukemia Patients

Exogenous arginine is required for growth in some argininosuccinate synthetase (ASS)-deficient cancers. Arginine deiminase (ADI) inhibits growth in various ASS-deficient cancers by depleting arginine. The efficacy of pegylated ADI (ADI-PEG20) in relapsed/refractory/poor-risk acute myeloid leukemia (AML) was evaluated in 43 patients in a prospective, phase II trial (NCT01910012 (10/07/2013), https://clinicaltrials.gov/ct2/show/NCT01910012?term = ADI-PEG20&rank = 12). Despite almost all pre-treatment tumor samples showing ASS deficiency, the best response among 21 evaluable patients was complete response (CR) in 2 (9.5%) and stable disease in 7 (33.3%), yielding a disease control rate (DCR) of 42.9%. The response durations of the two patients with CR were 7.5 and 8.8 months. DCR was correlated with a median of 8 weeks of arginine depletion to ≤10 μM. Using whole transcriptome sequencing, we compared gene expression profiling of pre- and post-treatment bone marrow samples of the two responders and three non-responders. The expression levels of some markers for AML subtypes and c-MYC regulated genes were considered potential predictors of response to ADI-PEG20. These results suggest that ASS deficiency is a prerequisite but not a sufficient condition for response to ADI-PEG20 monotherapy in AML. Predictive biomarkers and mechanistic explorations will be critical for identifying appropriate patients for future AML trials of ADI-PEG20.

Marketed drugs used for the management of hypercholesterolemia as anticancer armament

The design of novel pharmacologic agents as well as their approval for sale in markets all over the world is a tedious and pricey process. Inevitably, oncologic patients commonly experience unwanted effects of new anticancer drugs, while the acquisition of clinical experience for these drugs is largely based on doctor–patient partnership which is not always effective. The repositioning of marketed non-antineoplastic drugs that hopefully exhibit anticancer properties into the field of oncology is a challenging option that gains ground and attracts preclinical and clinical research in an effort to override all these hindrances and minimize the risk for reduced efficacy and/or personalized toxicity. This review aims to present the anticancer properties of drugs used for the management of hypercholesterolemia. A global view of the antitumorigenicity of all marketed antihypercholesterolemic drugs is of major importance, given that atherosclerosis, which is etiologically linked to hypercholesterolemia, is a leading worldwide cause of morbidity and mortality, while hypercholesterolemia and tumorigenesis are known to be interrelated. In vitro, in vivo and clinical literature data accumulated so far outline the mechanistic basis of the antitumor function of these agents and how they could find application at the clinical setting.

The creatine kinase pathway is a metabolic vulnerability in EVI1-positive acute myeloid leukemia

Expression of the MECOM (also known as EVI1) proto-oncogene is deregulated by chromosomal translocations in some cases of acute myeloid leukemia (AML) and is associated with poor clinical outcome. Here, through transcriptomic and metabolomic profiling of hematopoietic cells, we reveal that EVI1 overexpression alters cellular metabolism. A screen using pooled short hairpin RNAs (shRNAs) identified the ATP-buffering, mitochondrial creatine kinase CKMT1 as necessary for survival of EVI1-expressing cells in subjects with EVI1-positive AML. EVI1 promotes CKMT1 expression by repressing the myeloid differentiation regulator RUNX1. Suppression of arginine-creatine metabolism by CKMT1-directed shRNAs or by the small molecule cyclocreatine selectively decreased the viability, promoted the cell cycle arrest and apoptosis of human EVI1-positive cell lines, and prolonged survival in both orthotopic xenograft models and mouse models of primary AML. CKMT1 inhibition altered mitochondrial respiration and ATP production, an effect that was abrogated by phosphocreatine-mediated reactivation of the arginine-creatine pathway. Targeting CKMT1 is thus a promising therapeutic strategy for this EVI1-driven AML subtype that is highly resistant to current treatment regimens.

Molecular basis and current strategies of therapeutic arginine depletion for cancer

Renewed interest in the use of therapeutic enzymes combined with an improved knowledge of cancer cell metabolism, has led to the translation of several arginine depletion strategies into early phase clinical trials. Arginine auxotrophic tumors are reliant on extracellular arginine, due to the downregulation of arginosuccinate synthetase or ornithine transcarbamylase-key enzymes for intracellular arginine recycling. Engineered arginine catabolic enzymes such as recombinant human arginase (rh-Arg1-PEG) and arginine deiminase (ADI-PEG) have demonstrated cytotoxicity against arginine auxotrophic tumors. In this review, we discuss the molecular events triggered by extracellular arginine depletion that contribute to tumor cell death.