Lysosomal acid lipase A modulates leukemia stem cell response to venetoclax/tyrosine kinase inhibitor combination therapy in blast phase chronic myeloid leukemia.

The treatment of blast phase chronic myeloid leukemia (bpCML) remains a challenge due at least in part to drug resistance of leukemia stem cells (LSCs). Recent clinical evidence suggests that the BCL-2 inhibitor venetoclax in combination with ABL-targeting tyrosine kinase inhibitors (TKIs) can eradicate bpCML LSCs. In this report, we employed preclinical models of bpCML to investigate the efficacy and underlying mechanism of LSC-targeting with venetoclax/TKI combinations. Transcriptional analysis of LSCs exposed to venetoclax and dasatinib revealed upregulation of genes involved in lysosomal biology, in particular lysosomal acid lipase A (LIPA), a regulator of free fatty acids. Metabolomic analysis confirmed increased levels of free fatty acids in response to venetoclax/dasatinib. Pre-treatment of leukemia cells with bafilomycin, a specific lysosome inhibitor, or genetic perturbation of LIPA, resulted in increased sensitivity of leukemia cells toward venetoclax/dasatinib, implicating LIPA in treatment resistance. Importantly, venetoclax/dasatinib treatment does not affect normal stem cell function, suggestive of a leukemia-specific response. These results demonstrate that venetoclax/dasatinib is an LSCselective regimen in bpCML and that disrupting LIPA and fatty acid transport enhances venetoclax/dasatinib response in targeting LSCs, providing a rationale for exploring lysosomal disruption as an adjunct therapeutic strategy to prolong disease remission.

White blood cell count nadir to zero following intensive chemotherapy as a predictive factor for patients with acute myeloid leukemia.

Predictors for response to intensive therapy in AML have focused on baseline factors: percent leukemic blasts in marrow, cytogenetic/molecular genetic abnormalities, and presence of secondary AML. Non-baseline dynamic factors, occurring after induction but before response, may be useful for decisions related to salvage chemotherapy. We hypothesized white blood cell (WBC) count nadir after induction may be a real time indicator of treatment efficacy. We also examined whether time to stem cell transplant (SCT) or baseline molecular genetic abnormalities are associated with a low nadir. Data showed WBC nadir = 0 was a negative predictor for response to intensive induction and was correlated with reduced overall survival and progression free survival. Patients with WBC nadir = 0 did not have a significantly longer time to SCT, and none of the mutations increased the likelihood of reaching WBC nadir = 0. WBC nadir may be a useful real-time monitor in AML patients receiving intensive induction chemotherapy.

Targeting Acute Myeloid Leukemia Stem Cells Through Perturbation of Mitochondrial Calcium.

Acute myeloid leukemia stem cells (LSCs) are uniquely reliant on oxidative phosphorylation (OXPHOS) for survival. Moreover, maintenance of OXPHOS is dependent on BCL-2, creating a therapeutic opportunity to target LSCs using the BCL-2 inhibitor venetoclax. While venetoclax-based regimens have shown promising clinical activity, the emergence of drug resistance is prevalent. Thus, in the present study, we investigated how mitochondrial properties may influence venetoclax responsiveness. Our data show that utilization of mitochondrial calcium is fundamentally different between drug-responsive and non-responsive LSCs. By comparison, venetoclax-resistant LSCs demonstrate a more active metabolic (i.e. OXPHOS) status with relatively high levels of calcium. Consequently, we tested genetic and pharmacological approaches to target the mitochondrial calcium uniporter, MCU. We demonstrate that inhibition of calcium uptake reduces OXPHOS and leads to eradication of venetoclax-resistant LSCs. These findings demonstrate a central role for calcium signaling in LSCs and provide an avenue for clinical management of venetoclax resistance.

Chronic Myeloid Leukemia, Version 2.2024, NCCN Clinical Practice Guidelines in Oncology.

Chronic myeloid leukemia (CML) is defined by the presence of Philadelphia chromosome resulting from a reciprocal translocation between chromosomes 9 and 22 [t9;22] that gives rise to a BCR::ABL1 fusion gene. CML occurs in 3 different phases (chronic, accelerated, and blast phase) and is usually diagnosed in the chronic phase in developed countries. Tyrosine kinase inhibitor (TKI) therapy is a highly effective treatment option for patients with chronic phase-CML. The primary goal of TKI therapy in patients with chronic phase-CML is to prevent disease progression to accelerated phase-CML or blast phase-CML. Discontinuation of TKI therapy with careful monitoring is feasible in selected patients. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with chronic phase-CML.

Targeting Acute Myeloid Leukemia Stem Cells Through Perturbation of Mitochondrial Calcium.

We previously reported that acute myeloid leukemia stem cells (LSCs) are uniquely reliant on oxidative phosphorylation (OXPHOS) for survival. Moreover, maintenance of OXPHOS is dependent on BCL2, creating a therapeutic opportunity to target LSCs using the BCL2 inhibitor drug venetoclax. While venetoclax-based regimens have indeed shown promising clinical activity, the emergence of drug resistance is prevalent. Thus, in the present study, we investigated how mitochondrial properties may influence mechanisms that dictate venetoclax responsiveness. Our data show that utilization of mitochondrial calcium is fundamentally different between drug responsive and non-responsive LSCs. By comparison, venetoclax-resistant LSCs demonstrate a more active metabolic (i.e., OXPHOS) status with relatively high steady-state levels of calcium. Consequently, we tested genetic and pharmacological approaches to target the mitochondrial calcium uniporter, MCU. We demonstrate that inhibition of calcium uptake sharply reduces OXPHOS and leads to eradication of venetoclax-resistant LSCs. These findings demonstrate a central role for calcium signaling in the biology of LSCs and provide a therapeutic avenue for clinical management of venetoclax resistance.

A Novel Type of Monocytic Leukemia Stem Cell Revealed by the Clinical Use of Venetoclax-Based Therapy.

The BCL2 inhibitor venetoclax has recently emerged as an important component of acute myeloid leukemia (AML) therapy. Notably, use of this agent has revealed a previously unrecognized form of pathogenesis characterized by monocytic disease progression. We demonstrate that this form of disease arises from a fundamentally different type of leukemia stem cell (LSC), which we designate as monocytic LSC (m-LSC), that is developmentally and clinically distinct from the more well-described primitive LSC (p-LSC). The m-LSC is distinguished by a unique immunophenotype (CD34-, CD4+, CD11b-, CD14-, CD36-), unique transcriptional state, reliance on purine metabolism, and selective sensitivity to cladribine. Critically, in some instances, m-LSC and p-LSC subtypes can co-reside in the same patient with AML and simultaneously contribute to overall tumor biology. Thus, our findings demonstrate that LSC heterogeneity has direct clinical significance and highlight the need to distinguish and target m-LSCs as a means to improve clinical outcomes with venetoclax-based regimens. SIGNIFICANCE: These studies identify and characterize a new type of human acute myeloid LSC that is responsible for monocytic disease progression in patients with AML treated with venetoclax-based regimens. Our studies describe the phenotype, molecular properties, and drug sensitivities of this unique LSC subclass. This article is featured in Selected Articles from This Issue, p. 1949.

Venetoclax is safe and tolerable as post-transplant maintenance therapy for AML patients at high risk for relapse.

Relapse is the most common cause of mortality in acute myeloid leukemia (AML) patients after allogeneic stem cell transplant (SCT). Post-SCT maintenance strategies that prevent relapse are desirable but must be well tolerated and convenient to administer. We hypothesized single agent venetoclax (ven) may be an effective maintenance therapy among high relapse risk patients. Between February 2019 and December 2021, we administered post-SCT ven maintenance to 49 AML patients at high-risk for relapse as a prospectively defined off-label practice at our institution. Ven was planned to be administered until 1-year post-SCT. While temporary interruptions were common (67.3% of all patients), of those with >1 year follow up, 22/25 (88%) completed the full year of planned therapy. Cytopenias (40.8%) and gastrointestinal adverse events (34.7%) were the most common toxicities. At 1-year post-SCT, overall survival (OS) and relapse-free survival (RFS) were 70% and 67% respectively. Our experience demonstrates single agent ven is a safe, tolerable, and feasible maintenance therapy that may improve RFS and OS in high relapse risk post-SCT patients.

Higher-dose venetoclax with measurable residual disease-guided azacitidine discontinuation in newly diagnosed acute myeloid leukemia.

Venetoclax+azacitidine is the standard of care for newly-diagnosed patients with acute myeloid leukemia (AML) for whom intensive chemotherapy is inappropriate. Efforts to optimize this regimen are necessary. We designed a clinical trial to investigate two hypotheses: i) higher doses of venetoclax are tolerable and more effective, and ii) azacitidine can be discontinued after deep remissions. Forty-two newly diagnosed AML patients were enrolled in the investigator-initiated High Dose Discontinuation Azacitidine+Venetoclax (HiDDAV) Study (clinicaltrials gov. Identifier: NCT03466294). Patients received one to three "induction" cycles of venetoclax 600 mg daily with azacitidine. Responders received MRD-positive or MRDnegative "maintenance" arms: azacitidine with 400 mg venetoclax or 400 mg venetoclax alone, respectively. The toxicity profile of HiDDAV was similar to 400 mg venetoclax. The overall response rate was 66.7%; the duration of response (DOR), event-free survival (EFS) and overall survival were 12.9, 7.8 and 9.8 months, respectively. The MRD negativity rate was 64.3% by flow cytometry and 25.0% when also measured by droplet digital polymerase chain recation. MRD-negative patients by flow cytometry had improved DOR and EFS; more stringent measures of MRD negativity were not associated with improved OS, DOR or EFS. Using MRD to guide azacitidine discontinuation did not lead to improved DOR, EFS or OS compared to patients who discontinued azacitidine without MRD guidance. Within the context of this study design, venetoclax doses >400 mg with azacitidine were well tolerated but not associated with discernible clinical improvement, and MRD may not assist in recommendations to discontinue azacitidine. Other strategies to optimize, and for some patients, de-intensify, venetoclax+azacitidine regimens are needed.

Review of the chewing louse fauna of the invasive common myna (Acridotheres tristis), with new records from Palestine and a redescription of Brueelia chayanh Ansari, 1955 (Phthiraptera, Ischnocera, Brueelia-complex).

Palestine hosts a large diversity of birds, with 393 recorded species, but little data are available on the chewing lice fauna found on these birds. In this study, we surveyed the species of chewing lice found on the common myna, Acridotheres tristis, which is one of the most invasive bird species in the world. Forty-five mynas were examined to collect their ectoparasites, which were preserved and slide mounted. Among the 1004 chewing lice processed, we identified two species: Menacanthus eurysternus (Burmeister, 1838) (prevalence 100%) and Brueelia chayanh Ansari, 1955 (prevalence 82.2%). No other species of chewing louse known from A. tristis in its native range was found, showing a possible sorting event in the founding population of common myna in the region. Prevalence (100%) and abundance (22.3) were high compared to similar studies of the common myna. To contribute to future research on the lice of common mynas, we provide an annotated checklist of the louse species reported from this host globally. Also, we redescribe and illustrate Brueelia chayanh, and place Sturnidoecus tristisae Bughio et al., 2018 as a new junior synonym of Sturnidoecus bannoo Ansari, 1968.

Cambio rutinario de instrumental y guantes quirúrgicos en cirugía abdominal: ¿cuál es el impacto sobre el riesgo de infección? / Routine change of surgical instruments and gloves in abdominal surgery: what is the impact on the risk of infection?

Objetivo: Analizar la evidencia más actualizada sobre el cambio rutinario de instrumental y guantes quirúrgicos en cirugía abdominal, y su impacto en el riesgo de infecciones. Métodos: Se realizó una búsqueda bibliográfica, en las bases de datos PubMed, ScienceDirect, Web of Science, y MEDLINE. Resultados: A la fecha, la evidencia sumamente escasa sobre el potencial impacto del cambio rutinario de instrumental y guantes quirúrgicos en cirugía abdominal, y su relación con la incidencia de infección en el sitio operatorio. Sin embargo, no deja de ser un tema de interés en cirugía global. El estudio ChEETAh, ensayo realizado en siete países de bajos y medianos ingresos, que evaluó el cambio rutinario tanto de guantes como de instrumental quirúrgico en cirugía abdominal y su relación con la infección, demostró que, la frecuencia de infección en sitio operatorio fue del 16% (n=931) en el grupo intervención, comparado a un 18,9% (n=1280) en el grupo control (RR 0,87; IC 95%: 0,79 ­ 0,95; p=0,0032). Así, podría existir cierta protección adicional con el cambio rutinario de guantes e instrumental en cirugía abdominal. Conclusión: Aunque la evidencia es limitada y heterogénea, existe una tendencia respecto a un potencial beneficio frente a la incidencia de infección en sitio operatorio, en el cambio rutinario de guantes e instrumental quirúrgico en cirugía abdominal(AU)

Objective: To analyze the most recent evidence regarding the routine change of surgical instruments and gloves in abdominal surgery and its impact on the risk of infections. Methods: A literature search was conducted in the PubMed, ScienceDirect, Web of Science, and MEDLINE databases. Results: To date, the evidence regarding the potential impact of routine changes in surgical instruments and gloves in abdominal surgery and their relationship with the incidence of surgical site infections is extremely scarce. Nevertheless, it remains a topic of interest in global surgery. The ChEETAh study, conducted in seven low and middle-income countries, which assessed the routine change of both gloves and surgical instruments in abdominal surgery and its relation to infection, demonstrated that the frequency of surgical site infection was 16% (n=931) in the intervention group compared to 18.9% (n=1280) in the control group (RR 0.87; 95% CI: 0.79 ­ 0.95; p=0.0032). Thus, there may be some additional protection with the routine change of gloves and instruments in abdominal surgery. Conclusion: Although the evidence is limited and heterogeneous, there is a trend suggesting a potential benefit in reducing the incidence of surgical site infections through the routine change of gloves and surgical instruments in abdominal surgery(AU)

Machine Learning-Based Exploratory Clinical Decision Support for Newly Diagnosed Patients With Acute Myeloid Leukemia Treated With 7 + 3 Type Chemotherapy or Venetoclax/Azacitidine.

PURPOSE: There are currently limited objective criteria to help assist physicians in determining whether an individual patient with acute myeloid leukemia (AML) is likely to do better with induction with either standard 7 + 3 chemotherapy or targeted therapy with venetoclax plus azacitidine. The study goal was to address this need by developing exploratory clinical decision support methods. PATIENTS AND METHODS: Univariable and multivariable analysis as well as comparison of a range of machine learning (ML) predictors were performed using cohorts of 120 newly diagnosed 7 + 3-treated AML patients compared with 101 venetoclax plus azacitidine-treated patients. RESULTS: A variety of features in the two patient cohorts were identified that may potentially correlate with short- and long-term outcomes, toxicities, and other considerations. A subset of these diagnostic features was then used to develop ML-based predictors with relatively high areas under the curve of short- and long-term outcomes, hospital stays, transfusion requirements, and toxicities for individual patients treated with either venetoclax/azacitidine or 7 + 3. CONCLUSION: Potential ML-based approaches to clinical decision support to help guide individual patients with newly diagnosed AML to either 7 + 3 or venetoclax plus azacitidine induction therapy were identified. Larger cohorts with separate test and validation studies are necessary to confirm these initial findings.

The power of local research to inform adverse childhood experiences in substance use prevention in adolescents and adults.

BACKGROUND: The impact of adverse childhood experiences on substance use has been well reported, however, less well documented is looking at the comparison of youth and adult substance use and their respective adverse childhood experiences. This study leveraged local data sources to support prevention efforts inside a state-level working group and examined research questions that explored the relationship between reported adverse childhood experiences and substance use for youth and adult samples at the state level. METHODS: This study conducted a series of logistic regression models (95% CI) between substance use outcomes with different age group populations to investigate the relationship between adverse childhood experiences and substance use for each group. Adverse childhood experiences scores and substance use were examined using two Arizona datasets: 1) Arizona Youth Survey (n = 42,009) and 2) the Behavioral Risk Factor Surveillance System (n = 5328). RESULTS: The results of youth and adult datasets were consistent: users with adverse childhood experiences scores of 4 to 6 had a positive association with more substance use. When the variables were examined, showing the entire sample of youth and adult groups compared to those subgroups with a score of zero, a score of 1 to 3, and a score of 4 to 6, the overall pattern was the same; the more frequent use of substances was directly associated to the group with higher scores. Additionally, findings support increased attention on prevention and intervention efforts with higher reports of adverse childhood experiences as well as substance use. CONCLUSIONS: These findings demonstrate how local research can help prioritize prevention resources and increase the value of data-based decision-making. Policy-makers and providers can examine youth and adult data to compare priorities and assess for planning purposes. Specifically, it is possible to replicate known research findings, identify the most impacted subpopulations, and forecast the community's future needs.

Atraumatic Splenic Rupture due to Chronic Myelomonocytic Leukemia Treated with Partial Splenic Artery Embolization.

Splenic rupture can be categorized into two groups: traumatic and atraumatic. Traumatic rupture is frequently associated with blunt abdominal trauma, while atraumatic splenic rupture (ASR) is more uncommon and has been associated with both benign and malignant hematological disorders. In general, most cases of splenic rupture are managed with splenectomy, which carries significant mortality and morbidity; more recently, splenic artery embolization (SAE) has become a mainstay of management particularly after traumatic rupture. We describe a patient with chronic myelomonocytic leukemia (CMML) who presented to the emergency department for acute abdominal pain and was found to have an ASR. He underwent partial SAE, with postoperative complications of leukocytosis and tumor lysis syndrome (TLS) requiring rasburicase and allopurinol. On follow-up in clinic 2 months post-discharge, the patient was doing well on hydroxyurea, without need for further intervention at that time. In patients with hematologic malignancies presenting with abdominal pain and splenomegaly, it is important to consider ASR as a rare, but possible complication. To our knowledge, this is the only reported patient treated with SAE in the context of ASR from CMML, demonstrating that SAE can be an effective nonoperative strategy for treatment of CMML-associated ASR. This case report also highlights postoperative complications and management in this patient population, specifically a profound leukocytosis and TLS, for which close monitoring should be performed.

The STAT3-MYC axis promotes survival of leukemia stem cells by regulating SLC1A5 and oxidative phosphorylation.

Acute myeloid leukemia (AML) is characterized by the presence of leukemia stem cells (LSCs), and failure to fully eradicate this population contributes to disease persistence/relapse. Prior studies have characterized metabolic vulnerabilities of LSCs, which demonstrate preferential reliance on oxidative phosphorylation (OXPHOS) for energy metabolism and survival. In the present study, using both genetic and pharmacologic strategies in primary human AML specimens, we show that signal transducer and activator of transcription 3 (STAT3) mediates OXPHOS in LSCs. STAT3 regulates AML-specific expression of MYC, which in turn controls transcription of the neutral amino acid transporter gene SLC1A5. We show that genetic inhibition of MYC or SLC1A5 acts to phenocopy the impairment of OXPHOS observed with STAT3 inhibition, thereby establishing this axis as a regulatory mechanism linking STAT3 to energy metabolism. Inhibition of SLC1A5 reduces intracellular levels of glutamine, glutathione, and multiple tricarboxylic acid (TCA) cycle metabolites, leading to reduced TCA cycle activity and inhibition of OXPHOS. Based on these findings, we used a novel small molecule STAT3 inhibitor, which binds STAT3 and disrupts STAT3-DNA, to evaluate the biological role of STAT3. We show that STAT3 inhibition selectively leads to cell death in AML stem and progenitor cells derived from newly diagnosed patients and patients who have experienced relapse while sparing normal hematopoietic cells. Together, these findings establish a STAT3-mediated mechanism that controls energy metabolism and survival in primitive AML cells.

Venetoclax and azacitidine compared with induction chemotherapy for newly diagnosed patients with acute myeloid leukemia.

Venetoclax (ven) plus azacitidine (aza) is the standard of care for patients with newly diagnosed acute myeloid leukemia (AML) who are not candidates for intensive chemotherapy (IC). Some patients who are IC candidates instead receive ven/aza. We retrospectively analyzed patients with newly diagnosed AML who received ven/aza (n = 143) or IC (n = 149) to compare outcomes, seek variables that could predict response to 1 therapy or the other, and ascertain whether treatment recommendations could be refined. The response rates were 76.9% for ven/aza and 70.5% for IC. The median overall survival (OS) was 884 days for IC compared with 483 days for ven/aza (P = .0020). A propensity-matched cohort was used to compare outcomes in the setting of equivalent baseline variables, and when matched for age, biological risk, and transplantation, the median OS was 705 days for IC compared with not reached for ven/aza (P = .0667). Variables that favored response to ven/aza over IC included older age, secondary AML, and RUNX1 mutations. AML M5 favored response to IC over ven/aza. In the propensity-matched cohort analyzing OS, older age, adverse risk, and RUNX1 mutations favored ven/aza over IC, whereas intermediate risk favored IC over ven/aza. In conclusion, patients receiving IC have improved OS compared with those receiving ven/aza. However, in a propensity-matched cohort of patients with equivalent baseline factors, there was a trend toward favorable OS for ven/aza. Specific variables, such as RUNX1 mutations, reported here for the first time, can be identified that favor ven/aza or IC, helping to guide treatment decisions for patients who may be eligible candidates for either therapy.

The propriety of upgrading responses to venetoclax + azacitidine in newly diagnosed patients with acute myeloid leukemia.

Widely-used response criteria, conditional upon count recovery, were developed for acute myeloid leukemia (AML) in the context of intensive chemotherapy (IC). Extending these definitions to continuously-administered venetoclax-based therapies might underestimate responses. Best practices for venetoclax-based therapies mandate interruption after an end-of-cycle 1 bone marrow biopsy shows morphologic remission with cytopenias. We analyzed 435 patients with newly-diagnosed AML and follow-up response assessments. Of the 101 who responded to venetoclax + azacitidine, overall survival for patients whose response was upgraded due to count recovery during a 14-day post-disease assessment period, from complete remission (CR) with incomplete recovery of blood counts to CR, was not different compared to patients who did not need the 14-day period for count recovery. These results were distinct from 138 IC patients. Although sample sizes for the comparison groups were small, and conclusions are exploratory and must be verified, these findings support consideration of new response criteria for venetoclax-based regimens.

Accumbal TRH is downstream of the effects of isolation stress on hedonic food intake in rats.

Emotional stress, through elevating corticosterone (CORT) levels may reduce feeding in rodents however when offered palatable food, stressed animals ingest more food compared to non-stressed controls. Nucleus accumbens (NAc) is part of the mesocorticolimbic system and participates in processing rewarding characteristics of food modulating palatable food intake, mainly when glucocorticoids are elevated. A possible mediator of CORT effects is accumbal thyrotropin-releasing hormone (TRH), which reduces chow intake in rats when administered into the NAc. We aimed to study the TRH role in hedonic feeding in stressed rats. For 14 days, animals with ad libitum access to chow or chow plus chocolate milk were either group-housed or singly-housed to induce stress. Rats with access to chocolate milk showed hyperphagia and decreased accumbal TRH mRNA levels, which were potentiated by stress. Results suggest that TRH downregulation was permissive of the increased palatable food intake. TRH injections into NAc of singly-housed animals with palatable food access reduced their food intake and increased serum CORT levels. The accumbal injections of a glucocorticoid receptor antagonist (mifepristone) in stressed rats with palatable food access, reduced only palatable food intake and increased accumbal TRH expression and serum CORT levels. This modulation of TRH mRNA when CORT signaling is modified suggests that accumbal TRH is downstream of glucocorticoids activity, which specifically increase palatable food intake. Our results strengthen the TRH involvement in regulating emotional aspects of hedonic feeding in stressed animals. Finding new therapies directed towards increasing TRHergic activity in NAc may be protective against overeating.

The Hepatic Microenvironment Uniquely Protects Leukemia Cells through Induction of Growth and Survival Pathways Mediated by LIPG.

Due to the disseminated nature of leukemia, malignant cells are exposed to many different tissue microenvironments, including a variety of extramedullary sites. In the present study, we demonstrate that leukemic cells residing in the liver display unique biological properties and also contribute to systemic changes that influence physiologic responses to chemotherapy. Specifically, the liver microenvironment induces metabolic adaptations via upregulating expression of endothelial lipase in leukemia cells, which not only stimulates tumor cell proliferation through polyunsaturated fatty acid-mediated pathways, but also promotes survival by stabilizing antiapoptotic proteins. Additionally, hepatic infiltration and tissue damage caused by malignant cells induces release of liver-derived enzymes capable of degrading chemotherapy drugs, an event that further protects leukemia cells from conventional therapies. Together, these studies demonstrate a unique role for liver in modulating the pathogenesis of leukemic disease and suggest that the hepatic microenvironment may protect leukemia cells from chemotherapeutic challenge. SIGNIFICANCE: The studies presented herein demonstrate that the liver provides a microenvironment in which leukemia cells acquire unique metabolic properties. The adaptations that occur in the liver confer increased resistance to chemotherapy. Therefore, we propose that therapies designed to overcome liver-specific metabolic changes will yield improved outcomes for patients with leukemia.This article is highlighted in the In This Issue feature, p. 211.

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.