Impact of prior therapies and subsequent transplantation on outcomes in adult patients with relapsed or refractory B-cell acute lymphoblastic leukemia treated with brexucabtagene autoleucel in ZUMA-3

BACKGROUND

Brexucabtagene autoleucel (brexu-cel) is an autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy approved in the USA for adults with relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) and in the European Union for patients ≥26 years with R/R B-ALL. After 2 years of follow-up in ZUMA-3, the overall complete remission (CR) rate (CR+CR with incomplete hematological recovery (CRi)) was 73%, and the median overall survival (OS) was 25.4 months in 78 Phase 1 and 2 patients with R/R B-ALL who received the pivotal dose of brexu-cel. Outcomes by prior therapies and subsequent allogeneic stem cell transplantation (alloSCT) are reported.

METHODS

Eligible adults had R/R B-ALL and received one infusion of brexu-cel (1×10⁶ CAR T cells/kg) following conditioning chemotherapy. The primary endpoint was the CR/CRi rate per central review. Post hoc subgroup analyses were exploratory with descriptive statistics provided.

RESULTS

Phase 1 and 2 patients (N=78) were included with median follow-up of 29.7 months (range, 20.7-58.3). High CR/CRi rates were observed across all prior therapy subgroups examined: 1 prior line of therapy (87%, n=15) and ≥2 prior lines (70%, n=63); prior blinatumomab (63%, n=38) and no prior blinatumomab (83%, n=40); prior inotuzumab (59%, n=17) and no prior inotuzumab (77%, n=61); and prior alloSCT (76%, n=29) and no prior alloSCT (71%, n=49). The frequency of Grade ≥3 cytokine release syndrome, neurological events, and treatment-related Grade 5 adverse events were largely similar among prior therapy subgroups.Median duration of remission (DOR) in responders with (n=14) and without (n=43) subsequent alloSCT was 44.2 (95% CI, 8.1 to not estimable (NE)) and 18.6 months (95% CI, 9.4 to NE); median OS was 47.0 months (95% CI, 10.2 to NE) and not reached (95% CI, 23.2 to NE), respectively. Median DOR and OS were not reached in responders without prior or subsequent alloSCT (n=22).

CONCLUSIONS

In ZUMA-3, adults with R/R B-ALL benefited from brexu-cel, regardless of prior therapies and subsequent alloSCT status, though survival appeared better in patients without certain prior therapies and in earlier lines of therapy. Additional studies are needed to determine the impact prior therapies and subsequent alloSCT have on outcomes of patients who receive brexu-cel.

Referral to and receipt of allogeneic hematopoietic stem cell transplantation in older adults with acute myeloid leukemia

INTRODUCTION

Recent data have shown improved outcomes in selected older adults with acute myeloid leukemia (AML) following allogeneic hematopoietic stem cell transplantation (HSCT). Nonetheless, practice patterns for referring and performing HSCT vary. We aimed to evaluate referral, utilization, and reasons for not referring/proceeding to HSCT in older adults with AML.

MATERIALS AND METHODS

This is a single center retrospective analysis of patients aged ≥60 years diagnosed with AML evaluating rates of HSCT referral and utilization. Fisher's exact test was used to compare rates of referral and utilization across age groups and years of diagnosis.

RESULTS

Median age of the 97 patients was 70 years (range 61-95); 30% (29/97) were referred for HSCT and of these, 69% (20/29) received HSCT. Common documented reasons (can be multiple) for not referring were performance status (n = 21), advanced age (n = 16), patient refusal (n = 15), refractory disease (n = 14), and prohibitive comorbidity (n = 6). Among patients who were referred but did not receive HSCT (n = 9/29), documented reasons for not proceeding with HSCT were refractory disease (n = 5), advanced age (n = 2), and prohibitive comorbidity (n = 2). HSCT referral and utilization rates significantly decreased with age (p < 0.01) but were generally stable over time from 2014 to 2017 (p = 0.40 for referral and p = 0.56 for utilization).

DISCUSSION

Despite improvements in supportive care and HSCT techniques, HSCT referral and utilization rates remained low among older adults with AML but stable over time.

Two-year follow-up of KTE-X19, an anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, in adult patients (Pts) with relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) in ZUMA-3

7010

Background: Brexucabtagene autoleucel (KTE-X19) is an autologous anti-CD19 CAR T-cell therapy approved in the US to treat adult R/R B-ALL based on the ZUMA-3 study. The overall complete remission (CR) rate (CR + CR with incomplete hematologic recovery [CRi]) was 71% (95% CI, 57-82) after 16.4 mo median follow-up (N = 55; Shah et al. Lancet 2021). Here, we report updated outcomes with longer follow-up in these pts and in a larger pooled analysis of Phase (Ph) 1 and 2 pts who received the pivotal dose of KTE-X19. Methods: Eligible adults (≥18 years) had R/R B-ALL and received a single infusion of KTE-X19 at the pivotal dose (1×106 CAR T cells/kg) following leukapheresis and conditioning chemotherapy. The primary endpoint was CR/CRi rate by central review. Results: As of 23 July 2021, median follow-up was 26.8 mo (range, 20.7-32.6) for treated Ph 2 pts (N = 55). The CR/CRi rate per central review was 71% (95% CI, 57-82; 56% CR; 15% CRi). Eleven pts (20%; 8 CR and 2 CRi) proceeded to subsequent allogeneic stem cell transplant (alloSCT). Median duration of remission (DOR) censored at subsequent alloSCT was 14.6 mo (9.4-not estimable [NE]); not censored: 18.6 mo (9.6-NE); 6/39 responders (15%) had ongoing responses at data cutoff. Median (95% CI) relapse-free survival (RFS) was 11.6 mo (2.7-20.5) censored at subsequent alloSCT and 11.7 mo (2.8-20.5) not censored at subsequent alloSCT; 18-mo RFS rates (95% CI) were 35% (20.5-50.6) and 42% (28.0-55.0), respectively. Median (95% CI) overall survival (OS) was 25.4 mo (16.2-NE) among all KTE-X19-treated pts and not reached (25.4-NE) in pts with CR (n = 31). For Ph 1/2 pts (N = 78) who received the pivotal KTE-X19 dose (median follow-up: 29.7 mo; range 20.7-58.3), the CR/CRi rate by independent review was 73% (95% CI, 62-82). Medians (95% CI) for DOR, RFS, and OS were 18.6 mo (9.6-NE), 11.7 mo (6.1-20.5), and 25.4 mo (16.2-NE), respectively. A subgroup analysis revealed that in pts aged 18-39 (n = 36), 40-59 (n = 27), and ≥60 (n = 15) years, the CR/CRi rates (95% CI) were 69% (52-84), 70% (50-86), and 87% (60-98); 24-mo OS rates (95% CI) were 48% (30-64), 54% (33-71), and 57% (28-78), respectively. In pts with pre-KTE-X19 infusion marrow blast percentages > 25 to ≤50 (n = 12), > 50 to ≤75 (n = 14), and > 75 to 100 (n = 30), CR/CRi rates (95% CI) were 83% (52-98), 86% (57-98), and 57% (37-75); 24-mo OS rates (95% CI) were 58% (27-80), 55% (26-77) and 37% (19-55), respectively. There were no new safety signals; the proportion of treated Ph 2 pts with Gr ≥3 treatment emergent adverse events was unchanged since prior data cutoff. One pt had an ongoing neurologic event of Gr 1 finger numbness. Conclusions: With longer follow-up and an expanded data set by independent review, outcomes remain durable in adults with R/R B-ALL, most of whom were heavily pretreated, with median OS not yet reached in pts with CR. Long-term safety was favorable. Clinical trial information: NCT02614066.

SWOG 1318: A Phase II Trial of Blinatumomab Followed by POMP Maintenance in Older Patients With Newly Diagnosed Philadelphia Chromosome-Negative B-Cell Acute Lymphoblastic Leukemia

PURPOSE

Chemotherapy outcomes in older patients with Philadelphia (Ph) chromosome-negative B-acute lymphoblastic leukemia (ALL) are very poor. Here, we evaluated blinatumomab as induction and consolidation therapy followed by prednisone, vincristine, 6-mercaptopurine, and methotrexate (POMP) maintenance chemotherapy in this patient population.

PATIENTS AND METHODS

Patients were treated at National Clinical Trial Network sites. Eligibility criteria included age ≥ 65 years and newly diagnosed Ph chromosome-negative B-ALL. Patients received blinatumomab as induction for one-two cycles until attainment of response (complete remission (CR) and CR with incomplete count recovery). Patients then received three cycles of consolidation with blinatumomab followed by 18 months of POMP maintenance chemotherapy. Eight doses of intrathecal methotrexate were administered as central nervous system prophylaxis.

RESULTS

Twenty-nine eligible patients were enrolled. The median age was 75 years, and the median bone marrow blast count at diagnosis was 87%. Cytogenetic risk was poor in 10 patients (34%), and five of 14 patients (36%) tested had the Ph-like ALL gene signature. Nineteen patients (66%; 95% CI, 46 to 82) achieved CR. Kaplan-Meier 3-year disease-free survival and overall survival estimates were 37% (95% CI, 17 to 57) and 37% (95% CI, 20 to 55), respectively.

CONCLUSION

Blinatumomab was well tolerated and effective in the treatment of older patients with newly diagnosed Ph chromosome-negative B-ALL, including patients with poor-risk cytogenetics. The 3-year disease-free survival and overall survival results are encouraging and suggest that this approach should be further explored.

A phase II study of sequential decitabine and rapamycin in acute myelogenous leukemia

A phase II study was conducted to ascertain whether sequential exposure to decitabine followed by rapamycin, an mTOR (mechanistic target of rapamycin) inhibitor would result in better responses than decitabine alone. Newly diagnosed acute myelogenous leukemia (AML) patients who were >65 years old and not eligible for intensive induction regimens or patients with relapsed or refractory AML received 10 days of decitabine followed by 12 days of rapamycin in cycle 1 and 5 days of decitabine followed by 17 days of rapamycin in subsequent cycles. The composite complete remission rate (CR) was 33 % (CR plus CR with incomplete count recovery). Median overall survival was 7.7 months in newly diagnosed elderly AML patients and 6.6 months in relapsed/refractory AML patients. Twenty-four evaluable patients were enrolled, and the study did not meet its primary endpoint of demonstrating a significant improvement in composite CR rate with the combination as compared to an established historical CR rate of 25 % with decitabine alone. Despite that, the survival rates in relapsed/refractory cases appear comparable to what is reported with other salvage regimens, and no significant patterns of non-hematologic toxicity were noted. 50 % of subjects in the de novo group achieved a composite CR which is significantly higher (p = 0.02) than the rate of 25 % with decitabine alone. This trial is registered at clinical trials.gov as NCT02109744.

KTE-X19 for relapsed or refractory adult B-cell acute lymphoblastic leukaemia: phase 2 results of the single-arm, open-label, multicentre ZUMA-3 study

BACKGROUND

Despite treatment with novel therapies and allogeneic stem-cell transplant (allo-SCT) consolidation, outcomes in adult patients with relapsed or refractory B-precursor acute lymphoblastic leukaemia remain poor, underlining the need for more effective therapies.

METHODS

We report the pivotal phase 2 results of ZUMA-3, an international, multicentre, single-arm, open-label study evaluating the efficacy and safety of the autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy KTE-X19 in adult patients with relapsed or refractory B-precursor acute lymphoblastic leukaemia. Patients were enrolled at 25 sites in the USA, Canada, and Europe. Eligible patients were aged 18 years or older, with Eastern Cooperative Oncology Group performance status of 0-1, and morphological disease in the bone marrow (>5% blasts). After leukapheresis and conditioning chemotherapy, patients received a single KTE-X19 infusion (1 × 10⁶ CAR T cells per kg bodyweight). The primary endpoint was the rate of overall complete remission or complete remission with incomplete haematological recovery by central assessment. Duration of remission and relapse-free survival, overall survival, minimal residual disease (MRD) negativity rate, and allo-SCT rate were assessed as secondary endpoints. Efficacy and safety analyses were done in the treated population (all patients who received a dose of KTE-X19). This study is registered with ClinicalTrials.gov, NCT02614066.

FINDINGS

Between Oct 1, 2018, and Oct 9, 2019, 71 patients were enrolled and underwent leukapheresis. KTE-X19 was successfully manufactured for 65 (92%) patients and administered to 55 (77%). The median age of treated patients was 40 years (IQR 28-52). At the median follow-up of 16·4 months (13·8-19·6), 39 patients (71%; 95% CI 57-82, p<0·0001) had complete remission or complete remission with incomplete haematological recovery, with 31 (56%) patients reaching complete remission. Median duration of remission was 12·8 months (95% CI 8·7-not estimable), median relapse-free survival was 11·6 months (2·7-15·5), and median overall survival was 18·2 months (15·9-not estimable). Among responders, the median overall survival was not reached, and 38 (97%) patients had MRD negativity. Ten (18%) patients received allo-SCT consolidation after KTE-X19 infusion. The most common adverse events of grade 3 or higher were anaemia (27 [49%] patients) and pyrexia (20 [36%] patients). 14 (25%) patients had infections of grade 3 or higher. Two grade 5 KTE-X19-related events occurred (brain herniation and septic shock). Cytokine release syndrome of grade 3 or higher occurred in 13 (24%) patients and neurological events of grade 3 or higher occurred in 14 (25%) patients.

INTERPRETATION

KTE-X19 showed a high rate of complete remission or complete remission with incomplete haematological recovery in adult patients with relapsed or refractory B-precursor acute lymphoblastic leukaemia, with the median overall survival not reached in responding patients, and a manageable safety profile. These findings indicate that KTE-X19 has the potential to confer long-term clinical benefit to these patients.

FUNDING

Kite, a Gilead Company.

A phase 4 study to evaluate outpatient blinatumomab in patients with minimal/measurable residual disease (MRD) positivity (+) of B-cell precursor acute lymphoblastic leukemia (BCP-ALL)

TPS7051

Background: The prognosis for adults with relapsed or refractory BCP-ALL is poor. MRD+ is the strongest predictor of relapse. Blinatumomab, a CD3/CD19-directed BiTE® (bispecific T-cell engager) molecule, is an effective treatment for patients with MRD+.1 Blinatumomab is administered as a continuous intravenous infusion (cIV) 28 days per cycle. Severe adverse events (AEs) such as cytokine release syndrome (CRS) and neurologic toxicity (NT) may occur; thus, hospitalization is recommended for the first 3 days of cycle 1 and the first 2 days of cycle 2 for MRD+ patients. However, the incidence of severe AEs is low in MRD+ BCP-ALL patients (CRS: 2%, NT: 13%).1 We believe that with the use of effective digital monitoring devices, blinatumomab can be safely administered for the entire 28-day cIV cycle as an outpatient. Methods: Adult patients (n = 45) with BCP-ALL in complete remission and MRD+ (≥0.1% blasts) are being enrolled at 25 planned treatment sites, endpoint: grade ≥3 AE during monitoring (Amgen NCT04506086). Patient suitability for blinatumomab and outpatient monitoring is established. Patients will receive 2-4 cycles of blinatumomab. Cycles are initiated in the outpatient setting, digital monitoring devices activated and attached, and patients sent home. Once home, patients set up the home hub and real-time remote data transfer to the healthcare professional (HCP) begins. The devices are worn continuously, 24 hours a day for the first 3 days of cycle 1 and the first 2 days of cycle 2 only. Devices: Current Health’s Wearable Monitoring System (CHWMS) is an FDA-cleared platform for wireless and wearable health monitoring of patients at home. The CHWMS provides continuous oxygen saturation, respiratory rate, and heart rate; an axillary temperature sensor is worn and provides continuous temperature. Patients manually measure blood pressure every 3-6 hours around the clock. Patients have an integrated mobile device (tablet) to initiate contact with the HCP if needed. HCP/designee has a mobile device (smart phone) and receives vital signs as a constant live feed transmitted from the CHWMS device. The CHWMS platform generates a loud audible alert based on pre-specified vital sign alarming thresholds or if there is an interruption in data transfer. HCP may initiate direct audio and video contact with the patient, assess the patient’s condition, and make an appropriate intervention. HCP may also initiate patient contact in the absence of an alert. Patients are required to have a caregiver present during the entire period of outpatient monitoring. Patients have a full set of replacement devices as well as a 24/7 hotline for device support. Trial enrollment is underway. This study may generate feasibility data on the effectiveness of home monitoring during blinatumomab infusion in patients with MRD+ BCP-ALL. 1Gökbuget, Blood, 2018. Clinical trial information: NCT04506086.

Phase 2 results of the ZUMA-3 study evaluating KTE-X19, an anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, in adult patients (pts) with relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL)

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Background: ZUMA-3 is a Phase 1/2 multicenter study evaluating KTE-X19, an autologous anti-CD19 CAR T-cell therapy, in adult pts with R/R B-ALL. Phase 1 efficacy results at the recommended Phase 2 dose (1×106 CAR T cells/kg) were encouraging (Shah et al. ASCO 2019 #7006). Here, we present the pivotal Phase 2 results. Methods: Eligible adults had R/R B-ALL, > 5% bone marrow (BM) blasts by local evaluation, and ECOG 0–1. Pts received a single infusion of KTE-X19 after conditioning chemotherapy. The primary endpoint was the overall complete remission (CR) rate (CR + CR with incomplete hematologic recovery [CRi]) by central review. Key secondary endpoints were duration of remission (DOR), relapse-free survival (RFS), overall survival (OS), measurable residual disease negativity (MRD–) rate by flow cytometry, and safety. Data are reported in all treated pts. Results: As of 9/2020, 55 of 71 enrolled pts received KTE-X19, with a median follow-up of 16.4 mo (range, 10.3–22.1). Adverse events (AEs; n = 8) and ineligibility (n = 4) were the most common reasons enrolled pts did not receive KTE-X19 infusion. Median age was 40 y (range, 19–84), median BM blasts at screening were 65% (range, 5–100), and 47% of pts had ≥3 prior therapies, with 45%, 22%, and 42% having previously received blinatumomab, inotuzumab ozogamicin, or allogeneic stem cell transplant (alloSCT), respectively. The CR/CRi rate was 71% (95% CI, 57–82; 56% CR, 15% CRi); 31% of responders had ongoing responses. Median (95% CI) DOR, RFS, and OS were 12.8 mo (8.7–not estimable [NE]), 11.6 mo (2.7–15.5), and 18.2 mo (15.9–NE), respectively. In responders, median (95% CI) RFS and OS were 14.2 mo (11.6–NE) and not reached (16.2–NE). The MRD– rate was 97% among pts with CR/CRi. Among 25 pts with prior blinatumomab treatment, the CR/CRi rate was 60%. Ten pts (18%) received subsequent alloSCT at a median 98 days post–KTE-X19 infusion. Median DOR remained unchanged when not censoring for alloSCT. Grade ≥3 AEs occurred in 95% of pts, most commonly anemia (49%) and neutropenia (49% [febrile 13%]). Grade ≥3 cytokine release syndrome (CRS; per Lee at al. Blood 2014) and neurologic events occurred in 24% and 25% of pts, respectively, and were generally reversible. Two Grade 5 KTE-X19–related events occurred (brain herniation, n = 1; septic shock, n = 1). Median times to onset of CRS and neurologic events were 5 d and 9 d, with median durations of 7.5 d and 7 d, respectively. Median peak CAR T-cell levels (cells/µL) were 40.5 (range, 1.3–1533.4) in pts with CR and 0 in nonresponders. CAR T cells were undetectable by 9 mo in ongoing responders. Conclusions: After a median follow-up of 16.4 mo, KTE-X19 demonstrated compelling clinical benefit in heavily pretreated adults with R/R B-ALL, with the median OS not yet reached for responding pts and a manageable safety profile. Clinical trial information: NCT02614066.

The challenge to further improvements in survival of patients with T-ALL: Current treatments and new insights from disease pathogenesis

Survival rates for children and adult patients with T-cell acute lymphoblastic leukemia (T-ALL) have improved during the past decade due to optimization of frontline multiagent chemotherapy regimens. The outcome for relapsed T-ALL after initial intensive chemotherapy is frequently fatal, however, because no effective salvage regimens have been developed. Immunotherapy and small molecule inhibitors are beginning to be tested in T-ALL and have the potential to advance the treatment, especially the frontline regimen by eradicating minimal residual disease thus inducing more durable remissions. In this paper, I review the current chemotherapy regimens for adult patients with T-ALL and summarize the novel immunotherapies and small molecule inhibitors that are currently in early phase clinical trials.

Novel mHealth App to Deliver Geriatric Assessment-Driven Interventions for Older Adults With Cancer: Pilot Feasibility and Usability Study

Background

Older patients with cancer are at an increased risk of adverse outcomes. A geriatric assessment (GA) is a compilation of reliable and validated tools to assess domains that are predictors of morbidity and mortality, and it can be used to guide interventions. However, the implementation of GA and GA-driven interventions is low due to resource and time limitations. GA-driven interventions delivered through a mobile app may support the complex needs of older patients with cancer and their caregivers.

Objective

We aimed to evaluate the feasibility and usability of a novel app (TouchStream) and to identify barriers to its use. As an exploratory aim, we gathered preliminary data on symptom burden, health care utilization, and satisfaction.

Methods

In a single-site pilot study, we included patients aged ≥65 years undergoing treatment for systemic cancer and their caregivers. TouchStream consists of a mobile app and a Web portal. Patients underwent a GA at baseline with the study team (on paper), and the results were used to guide interventions delivered through the app. A tablet preloaded with the app was provided for use at home for 4 weeks. Feasibility metrics included usability (system usability scale of >68 is considered above average), recruitment, retention (number of subjects consented who completed postintervention assessments), and percentage of days subjects used the app. For the last 8 patients, we assessed their symptom burden (severity and interference with 17-items scored from 0-10 where a higher score indicates worse symptoms) using a clinical symptom inventory, health care utilization from the electronic medical records, and satisfaction (6 items scored on a 5-point Likert Scale for both patients and caregivers where a higher score indicates higher satisfaction) using a modified satisfaction survey. Barriers to use were elicited through interviews.

Results

A total of 18 patients (mean age 76.8, range 68-87) and 13 caregivers (mean age 69.8, range 38-81) completed the baseline assessment. Recruitment and retention rates were 67% and 80%, respectively. The mean SUS score was 74.0 for patients and 72.2 for caregivers. Mean percentage of days the TouchStream app was used was 78.7%. Mean symptom severity and interference scores were 1.6 and 2.8 at preintervention, and 0.9 and 1.5 at postintervention, respectively. There was a total of 27 clinic calls during the intervention period and 15 during the postintervention period (week 5-8). One patient was hospitalized during the intervention period (week 1-4) and two patients during the postintervention period (week 5-8). Mean satisfaction scores of patients and caregivers with the mobile app were 20.4 and 23.4, respectively. Barriers fell into 3 themes: general experience, design, and functionality.

Conclusions

TouchStream is feasible and usable for older patients on cancer treatment and their caregivers. Future studies should evaluate the effects of the TouchStream on symptoms and health care utilization in a randomized fashion.

Chemoenzymatic synthesis and antileukemic activity of novel C9- and C14-functionalized parthenolide analogs

Parthenolide is a naturally occurring terpene with promising anticancer properties, particularly in the context of acute myeloid leukemia (AML). Optimization of this natural product has been challenged by limited opportunities for the late-stage functionalization of this molecule without affecting the pharmacologically important α-methylene-γ-lactone moiety. Here, we report the further development and application of a chemoenzymatic strategy to afford a series of new analogs of parthenolide functionalized at the aliphatic positions C9 and C14. Several of these compounds were determined to be able to kill leukemia cells and patient-derived primary AML specimens with improved activity compared to parthenolide, exhibiting LC50 values in the low micromolar range. These studies demonstrate that different O-H functionalization chemistries can be applied to elaborate the parthenolide scaffold and that modifications at the C9 or C14 position can effectively enhance the antileukemic properties of this natural product. The C9-functionalized analogs 22a and 25b were identified as the most interesting compounds in terms of antileukemic potency and selectivity toward AML versus healthy blood cells.

Targeting aberrant glutathione metabolism to eradicate human acute myelogenous leukemia cells

The development of strategies to eradicate primary human acute myelogenous leukemia (AML) cells is a major challenge to the leukemia research field. In particular, primitive leukemia cells, often termed leukemia stem cells, are typically refractory to many forms of therapy. To investigate improved strategies for targeting of human AML cells we compared the molecular mechanisms regulating oxidative state in primitive (CD34(+)) leukemic versus normal specimens. Our data indicate that CD34(+) AML cells have elevated expression of multiple glutathione pathway regulatory proteins, presumably as a mechanism to compensate for increased oxidative stress in leukemic cells. Consistent with this observation, CD34(+) AML cells have lower levels of reduced glutathione and increased levels of oxidized glutathione compared with normal CD34(+) cells. These findings led us to hypothesize that AML cells will be hypersensitive to inhibition of glutathione metabolism. To test this premise, we identified compounds such as parthenolide (PTL) or piperlongumine that induce almost complete glutathione depletion and severe cell death in CD34(+) AML cells. Importantly, these compounds only induce limited and transient glutathione depletion as well as significantly less toxicity in normal CD34(+) cells. We further determined that PTL perturbs glutathione homeostasis by a multifactorial mechanism, which includes inhibiting key glutathione metabolic enzymes (GCLC and GPX1), as well as direct depletion of glutathione. These findings demonstrate that primitive leukemia cells are uniquely sensitive to agents that target aberrant glutathione metabolism, an intrinsic property of primary human AML cells.

BCL-2 inhibition targets oxidative phosphorylation and selectively eradicates quiescent human leukemia stem cells

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 overexpress 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.