Systematic review and meta-analysis: Prognostic impact of time from diagnosis to treatment in patients with acute myeloid leukemia.

BACKGROUND: Acute myeloid leukemia (AML) has been considered an oncologic emergency that requires initiation of chemotherapy immediately after diagnosis. With the introduction of novel targeted therapies, there is a potential benefit associated with delaying definitive treatment for identification of actionable therapeutic targets. Unfortunately, cytogenetic/molecular testing can take >7 days to return, and there is not a consensus regarding the prognostic impact of time from diagnosis to treatment (TDT) in AML. METHODS: A literature review and meta-analysis of studies done to date that evaluate TDT was conducted. Studies that reported baseline characteristics, TDT, and outcomes for patients with AML were selected. Outcomes included overall survival (OS), complete remission (CR), and mortality. Studies that measured CR rates within each TDT range and data to calculate odds ratios were included in the meta-analysis. The remaining outcomes were synthesized descriptively for literature review. RESULTS: Thirteen studies were identified, which comprised a total of 14,946 patients. Median TDT values were between 1 and 8 days. Several studies found a significant association between prolonged TDT and older age and lower proliferation burden. Four of 11 studies did not detect a significant relationship between TDT and OS. No studies found a significant association between TDT and early death. Six of eight studies did not find a significant association between TDT and CR rate. The meta-analysis found a significant association between prolonged TDT and decreased achievement of CR (p < .05). CONCLUSIONS: Results were highly variable but suggest it may be feasible to pursue cytogenetic/molecular testing in patients who are clinically stable, particularly in those aged 60 years and older.

Constitutive BAK activation as a determinant of drug sensitivity in malignant lymphohematopoietic cells.

Mitochondrial outer membrane permeabilization (MOMP), a key step in the intrinsic apoptotic pathway, is incompletely understood. Current models emphasize the role of BH3-only BCL2 family members in BAX and BAK activation. Here we demonstrate concentration-dependent BAK autoactivation under cell-free conditions and provide evidence that this autoactivation plays a key role in regulating the intrinsic apoptotic pathway in intact cells. In particular, we show that up to 80% of BAK (but not BAX) in lymphohematopoietic cell lines is oligomerized and bound to anti-apoptotic BCL2 family members in the absence of exogenous death stimuli. The extent of this constitutive BAK oligomerization is diminished by BAK knockdown and unaffected by BIM or PUMA down-regulation. Further analysis indicates that sensitivity of cells to BH3 mimetics reflects the identity of the anti-apoptotic proteins to which BAK is constitutively bound, with extensive BCLXL•BAK complexes predicting navitoclax sensitivity, and extensive MCL1•BAK complexes predicting A1210477 sensitivity. Moreover, high BAK expression correlates with sensitivity of clinical acute myelogenous leukemia to chemotherapy, whereas low BAK levels correlate with resistance and relapse. Collectively, these results inform current understanding of MOMP and provide new insight into the ability of BH3 mimetics to induce apoptosis without directly activating BAX or BAK.

Hypoalbuminemia as a prognostic biomarker for higher mortality and treatment complications in acute myeloid leukemia.

Older age and poor performance status lead to worse outcomes in acute myeloid leukemia (AML) patients. Hypoalbuminemia is a negative predictor of morbidity and mortality in several malignancies. We evaluated the relationship between baseline serum albumin levels on treatment-related complications, as well as short-term mortality and overall survival (OS) in 756 newly diagnosed AML patients. We conducted a retrospective multicenter study to examine treatment-related complications and OS according to pretreatment serum albumin levels: normal albumin ≥3.5 g/dl, marked hypoalbuminemia <2.5 g/dl, and hypoalbuminemia 2.5-3.4 g/dl. In an adjusted multivariate analysis, a lower baseline albumin was independently associated with a higher number of grade ≥3 complications when adjusting for age, secondary AML, sex and intensive treatment. When comparing normal to markedly low albumin levels, the estimated mean number of complications increases by a factor of 1.35. Patients who had a normal baseline albumin had a 30 day-mortality rate of 4.8%, which was significantly lower compared with patients with hypoalbuminemia (16.5%) and marked hypoalbuminemia (33.9%; p < 0.01). Similarly, 60-day mortality rate was significantly higher in the hypoalbuminemia group (24.0%) and marked hypoalbuminemia group (45%) compared with normal albumin group (8.3%; p < 0.01). Patients with lower baseline albumin levels have increased treatment-related morbidity and mortality, suggesting that pre-treatment serum albumin is an important independent prognostic marker.

A randomized trial of three novel regimens for recurrent acute myeloid leukemia demonstrates the continuing challenge of treating this difficult disease.

To improve the outcome of relapsed/refractory acute myeloid leukemia (AML), a randomized phase II trial of three novel regimens was conducted. Ninety patients were enrolled and were in first relapse or were refractory to induction/re-induction chemotherapy. They were randomized to the following regimens: carboplatin-topotecan (CT), each by continuous infusion for 5 days; alvocidib (formerly flavopiridol), cytarabine, and mitoxantrone (FLAM) in a timed sequential regimen; or sirolimus combined with mitoxantrone, etoposide, and cytarabine (S-MEC). The primary objective was attainment of a complete remission (CR). A Simon two-stage design was used for each of the three arms. The median age of the patients in the FLAM arm was older at 62 years compared with 55 years for the CT arm and the S-MEC arm. The overall response was 14% in the CT arm (5/35, 90% CI 7%-35%), 28% in the FLAM arm (10/36, 90% CI, 16%-43%), and 16% in the S-MEC arm (3/19, 90% CI, 4%-36%). There were nine treatment-related deaths, seven of which occurred in the FLAM arm with four of these in elderly patients. We conclude that the FLAM regimen had an encouraging response rate and should be considered for further clinical development but should be used with caution in elderly patients.

4EBP1/c-MYC/PUMA and NF-κB/EGR1/BIM pathways underlie cytotoxicity of mTOR dual inhibitors in malignant lymphoid cells.

The mammalian target of rapamycin (mTOR), a kinase that regulates proliferation and apoptosis, has been extensively evaluated as a therapeutic target in multiple malignancies. Rapamycin analogs, which partially inhibit mTOR complex 1 (mTORC1), exhibit immunosuppressive and limited antitumor activity, but sometimes activate survival pathways through feedback mechanisms involving mTORC2. Thus, attention has turned to agents targeting both mTOR complexes by binding the mTOR active site. Here we show that disruption of either mTOR-containing complex is toxic to acute lymphocytic leukemia (ALL) cells and identify 2 previously unrecognized pathways leading to this cell death. Inhibition of mTORC1-mediated 4EBP1 phosphorylation leads to decreased expression of c-MYC and subsequent upregulation of the proapoptotic BCL2 family member PUMA, whereas inhibition of mTORC2 results in nuclear factor-κB-mediated expression of the Early Growth Response 1 (EGR1) gene, which encodes a transcription factor that binds and transactivates the proapoptotic BCL2L11 locus encoding BIM. Importantly, 1 or both pathways contribute to death of malignant lymphoid cells after treatment with dual mTORC1/mTORC2 inhibitors. Collectively, these observations not only provide new insight into the survival roles of mTOR in lymphoid malignancies, but also identify alterations that potentially modulate the action of mTOR dual inhibitors in ALL.

BCL2 mutations are associated with increased risk of transformation and shortened survival in follicular lymphoma.

Follicular lymphoma (FL), an indolent neoplasm caused by a t(14;18) chromosomal translocation that juxtaposes the BCL2 gene and immunoglobulin locus, has a variable clinical course and frequently undergoes transformation to an aggressive lymphoma. Although BCL2 mutations have been previously described, their relationship to FL progression remains unclear. In this study, we evaluated the frequency and nature of BCL2 mutations in 2 independent cohorts of grade 1 and 2 FLs, along with the correlation between BCL2 mutations, transformation risk, and survival. The prevalence of BCL2 coding sequence mutations was 12% in FL at diagnosis and 53% at transformation (P < .0001). The presence of these BCL2 mutations at diagnosis correlated with an increased risk of transformation (hazard ratio 3.6; 95% CI, 2.0-6.2; P < .0001) and increased risk of death due to lymphoma (median survival of 9.5 years with BCL2 mutations vs 20.4 years without; P = .012). In a multivariate analysis, BCL2 mutations and high FL international prognostic index were independent risk factors for transformation and death due to lymphoma. Some mutant Bcl-2 proteins exhibited enhanced antiapoptotic capacity in vitro. Accordingly, BCL2 mutations can affect antiapoptotic Bcl-2 function, are associated with increased activation-induced cytidine deaminase expression, and correlate with increased risk of transformation and death due to lymphoma.

Population pharmacokinetics and site of action exposures of veliparib with topotecan plus carboplatin in patients with haematological malignancies.

AIMS: Veliparib is a potent inhibitor of poly(ADP-ribose) polymerase (PARP) enzyme. The objectives of the analysis were to evaluate the effect of baseline covariates and co-administration of topotecan plus carboplatin (T + C) on pharmacokinetics of veliparib in patients with refractory acute leukaemia, and compare veliparib concentration in various biological matrices. METHODS: A population pharmacokinetic model was developed and effect of age, body size indices, sex, creatinine clearance (CrCL) and co-administration of T + C on the pharmacokinetics of veliparib were evaluated. The final model was qualified using bootstrap and quantitative predictive check. Linear regression was conducted to correlate concentrations of veliparib in various biological matrices. RESULTS: A two compartment model with first-order absorption with Tlag described veliparib pharmacokinetics. The apparent clearance (CL/F) and volume (Vc /F) were 16.5 l h-1 and 122.7 l, respectively. The concomitant administration of T + C was not found to affect veliparib CL/F. CrCL and lean body mass (LBM) were significant covariates on CL/F and Vc/F, respectively. While a strong positive relationship was observed between veliparib concentrations in plasma and bone marrow supernatant, no correlation was observed between plasma and peripheral blood or bone marrow blasts. CONCLUSIONS: Consistent with veliparib's physiochemical properties and its elimination mechanism, LBM and CrCL were found to affect pharmacokinetics of veliparib while concomitant administration of T + C did not affect veliparib's CL/F. Plasma concentrations were found to be a reasonable surrogate for veliparib concentrations in peripheral blood and bone marrow supernatant but not blasts. The current model will be utilized to conduct exposure-response analysis to support dosing recommendations.

Histone Deacetylase Inhibitors Target the Leukemic Microenvironment by Enhancing a Nherf1-Protein Phosphatase 1α-TAZ Signaling Pathway in Osteoblasts.

Disrupting the protective signals provided by the bone marrow microenvironment will be critical for more effective combination drug therapies for acute myeloid leukemia (AML). Cells of the osteoblast lineage that reside in the endosteal niche have been implicated in promoting survival of AML cells. Here, we investigated how to prevent this protective interaction. We previously showed that SDF-1, a chemokine abundant in the bone marrow, induces apoptosis of AML cells, unless the leukemic cells receive protective signals provided by differentiating osteoblasts (8, 10). We now identify a novel signaling pathway in differentiating osteoblasts that can be manipulated to disrupt the osteoblast-mediated protection of AML cells. Treating differentiating osteoblasts with histone deacetylase inhibitors (HDACi) abrogated their ability to protect co-cultured AML cells from SDF-1-induced apoptosis. HDACi prominently up-regulated expression of the Nherf1 scaffold protein, which played a major role in preventing osteoblast-mediated protection of AML cells. Protein phosphatase-1α (PP1α) was identified as a novel Nherf1 interacting protein that acts as the downstream mediator of this response by promoting nuclear localization of the TAZ transcriptional modulator. Moreover, independent activation of either PP1α or TAZ was sufficient to prevent osteoblast-mediated protection of AML cells even in the absence of HDACi. Together, these results indicate that HDACi target the AML microenvironment by enhancing activation of the Nherf1-PP1α-TAZ pathway in osteoblasts. Selective drug targeting of this osteoblast signaling pathway may improve treatments of AML by rendering leukemic cells in the bone marrow more susceptible to apoptosis.

Poly(ADP-ribose) polymerase inhibitors sensitize cancer cells to death receptor-mediated apoptosis by enhancing death receptor expression.

Recombinant human tumor necrosis factor-α-related apoptosis inducing ligand (TRAIL), agonistic monoclonal antibodies to TRAIL receptors, and small molecule TRAIL receptor agonists are in various stages of preclinical and early phase clinical testing as potential anticancer drugs. Accordingly, there is substantial interest in understanding factors that affect sensitivity to these agents. In the present study we observed that the poly(ADP-ribose) polymerase (PARP) inhibitors olaparib and veliparib sensitize the myeloid leukemia cell lines ML-1 and K562, the ovarian cancer line PEO1, non-small cell lung cancer line A549, and a majority of clinical AML isolates, but not normal marrow, to TRAIL. Further analysis demonstrated that PARP inhibitor treatment results in activation of the FAS and TNFRSF10B (death receptor 5 (DR5)) promoters, increased Fas and DR5 mRNA, and elevated cell surface expression of these receptors in sensitized cells. Chromatin immunoprecipitation demonstrated enhanced binding of the transcription factor Sp1 to the TNFRSF10B promoter in the presence of PARP inhibitor. Knockdown of PARP1 or PARP2 (but not PARP3 and PARP4) not only increased expression of Fas and DR5 at the mRNA and protein level, but also recapitulated the sensitizing effects of the PARP inhibition. Conversely, Sp1 knockdown diminished the PARP inhibitor effects. In view of the fact that TRAIL is part of the armamentarium of natural killer cells, these observations identify a new facet of PARP inhibitor action while simultaneously providing the mechanistic underpinnings of a novel therapeutic combination that warrants further investigation.

A phase 1b/2 study of vosaroxin in combination with cytarabine in patients with relapsed or refractory acute myeloid leukemia.

Vosaroxin is a first-in-class anticancer quinolone derivative that intercalates DNA and inhibits topoisomerase II. This study assessed the safety and tolerability of vosaroxin plus cytarabine in patients with relapsed/refractory acute myeloid leukemia. Escalating vosaroxin doses (10-minute infusion; 10-90 mg/m(2); days 1, 4) were given in combination with cytarabine on one of two schedules: schedule A (24-hour continuous intravenous infusion, 400 mg/m(2)/day, days 1-5) or schedule B (2-hour intravenous infusion, 1 g/m(2)/day, days 1-5). Following dose escalation, enrollment was expanded at the maximum tolerated dose. Of 110 patients enrolled, 108 received treatment. The maximum tolerated dose of vosaroxin was 80 mg/m(2) for schedule A (dose-limiting toxicities: grade 3 bowel obstruction and stomatitis) and was not reached for schedule B (recommended phase 2 dose: 90 mg/m(2)). In the efficacy population (all patients in first relapse or with primary refractory disease treated with vosaroxin 80-90 mg/m(2); n=69), the complete remission rate was 25% and the complete remission/complete remission with incomplete blood count recovery rate was 28%. The 30-day all-cause mortality rate was 2.5% among all patients treated at a dose of 80-90 mg/m(2). Based upon these results, a phase 3 trial of vosaroxin plus cytarabine was initiated in patients with relapsed/refractory acute myeloid leukemia. (Clinicaltrials.gov identifier: NCT00541866).

Randomized multicenter phase II study of flavopiridol (alvocidib), cytarabine, and mitoxantrone (FLAM) versus cytarabine/daunorubicin (7+3) in newly diagnosed acute myeloid leukemia.

Serial studies have demonstrated that induction therapy with FLAM [flavopiridol (alvocidib) 50 mg/m(2) days 1-3, cytarabine 667 mg/m(2)/day continuous infusion days 6-8, and mitoxantrone (FLAM) 40 mg/m(2) day 9] yields complete remission rates of nearly 70% in newly diagnosed poor-risk acute myeloid leukemia. Between May 2011-July 2013, 165 newly diagnosed acute myeloid leukemia patients (age 18-70 years) with intermediate/adverse-risk cytogenetics were randomized 2:1 to receive FLAM or 7+3 (cytarabine 100 mg/m(2)/day continuous infusion days 1-7 and daunorubicin 90 mg/m(2) days 1-3), across 10 institutions. Some patients on 7+3 with residual leukemia on day 14 received 5+2 (cytarabine 100 mg/m(2)/day continuous infusion days 1-5 and daunorubicin 45 mg/m(2) days 1-2), whereas patients on FLAM were not re-treated based on day 14 bone marrow findings. The primary objective was to compare complete remission rates between one cycle of FLAM and one cycle of 7+3. Secondary end points included safety, overall survival and event-free survival. FLAM led to higher complete remission rates than 7+3 alone (70% vs. 46%; P=0.003) without an increase in toxicity, and this improvement persisted after 7+3+/-5+2 (70% vs. 57%; P=0.08). There were no significant differences in overall survival and event-free survival in both arms but post-induction strategies were not standardized. These results substantiate the efficacy of FLAM induction in newly diagnosed AML. A phase III study is currently in development. This study is registered with clinicaltrials.gov identifier: 01349972.

CXCR4 chemokine receptor signaling induces apoptosis in acute myeloid leukemia cells via regulation of the Bcl-2 family members Bcl-XL, Noxa, and Bak.

The CXCR4 chemokine receptor promotes survival of many different cell types. Here, we describe a previously unsuspected role for CXCR4 as a potent inducer of apoptosis in acute myeloid leukemia (AML) cell lines and a subset of clinical AML samples. We show that SDF-1, the sole ligand for CXCR4, induces the expected migration and ERK activation in the KG1a AML cell line transiently overexpressing CXCR4, but ERK activation did not lead to survival. Instead, SDF-1 treatment led via a CXCR4-dependent mechanism to apoptosis, as evidenced by increased annexin V staining, condensation of chromatin, and cleavage of both procaspase-3 and PARP. This SDF-1-induced death pathway was partially inhibited by hypoxia, which is often found in the bone marrow of AML patients. SDF-1-induced apoptosis was inhibited by dominant negative procaspase-9 but not by inhibition of caspase-8 activation, implicating the intrinsic apoptotic pathway. Further analysis showed that this pathway was activated by multiple mechanisms, including up-regulation of Bak at the level of mRNA and protein, stabilization of the Bak activator Noxa, and down-regulation of antiapoptotic Bcl-XL. Furthermore, adjusting expression levels of Bak, Bcl-XL, or Noxa individually altered the level of apoptosis in AML cells, suggesting that the combined modulation of these family members by SDF-1 coordinates their interplay to produce apoptosis. Thus, rather than mediating survival, SDF-1 may be a means to induce apoptosis of CXCR4-expressing AML cells directly in the SDF-1-rich bone marrow microenvironment if the survival cues of the bone marrow are disrupted.

Osteoblasts protect AML cells from SDF-1-induced apoptosis.

The bone marrow provides a protective environment for acute myeloid leukemia (AML) cells that often allows leukemic stem cells to survive standard chemotherapeutic regimens. Targeting these leukemic stem cells within the bone marrow is critical for preventing relapse. We recently demonstrated that SDF-1, a chemokine abundant in the bone marrow, induces apoptosis in AML cell lines and in patient samples expressing high levels of its receptor, CXCR4. Here we show that a subset of osteoblast lineage cells within the bone marrow can protect AML cells from undergoing apoptosis in response to the SDF-1 naturally present in that location. In co-culture systems, osteoblasts at various stages of differentiation protected AML cell lines and patient isolates from SDF-1-induced apoptosis. The differentiation of the osteoblast cell lines, MC3T3 and W-20-17, mediated this protection via a cell contact-independent mechanism. In contrast, bone marrow-derived mesenchymal cells, the precursors of osteoblasts, induced apoptosis in AML cells via a CXCR4-dependent mechanism and failed to protect AML cells from exogenously added SDF-1. These results indicate that osteoblasts in the process of differentiation potently inhibit the SDF-1-driven apoptotic pathway of CXCR4-expressing AML cells residing in the bone marrow. Drugs targeting this protective mechanism could potentially provide a new approach to treating AML by enhancing the SDF-1-induced apoptosis of AML cells residing within the bone marrow microenvironment.

Epidemiology of Candida kefyr in patients with hematologic malignancies.

Candida kefyr is an emerging pathogen among patients with hematologic malignancies (HM). We performed a retrospective study at Johns Hopkins Hospital to evaluate the epidemiology of C. kefyr colonization and infection in HM patients between 2004 and 2010. Eighty-three patients were colonized and/or infected with C. kefyr, with 8 (9.6%) having invasive candidiasis (IC). The yearly incidence of C. kefyr colonization and candidemia increased over the study period (P < 0.01), particularly after 2009. In 2010, C. kefyr caused 16.7% of candidemia episodes. The monthly incidence of C. kefyr was higher during the summer throughout the study. In a cohort of patients with acute myelogenic leukemia receiving induction chemotherapy, risks for C. kefyr colonization included the summer season (odds ratio [OR], 3.1; P = 0.03); administration of an azole (OR, 0.06; P < 0.001) or amphotericin B (OR, 0.35; P = 0.05) was protective. Fingerprinting of 16 isolates by repetitive sequence-based PCR showed that all were different genotypes. The epidemiology of C. kefyr candidemia was evaluated in another hospital in Montreal, Canada; data confirmed higher rates of C. kefyr infection in the summer. C. kefyr appears to be increasing in HM patients, with prominent summer seasonality. These findings raise questions about the effect of antifungal agents and health care exposures (e.g., yogurt) on the epidemiology of this yeast.

Dual mTORC1/mTORC2 inhibition diminishes Akt activation and induces Puma-dependent apoptosis in lymphoid malignancies.

The mammalian target of rapamycin (mTOR) plays crucial roles in proliferative and antiapoptotic signaling in lymphoid malignancies. Rapamycin analogs, which are allosteric mTOR complex 1 (mTORC1) inhibitors, are active in mantle cell lymphoma and other lymphoid neoplasms, but responses are usually partial and short-lived. In the present study we compared the effects of rapamycin with the dual mTORC1/mTORC2 inhibitor OSI-027 in cell lines and clinical samples representing divers lymphoid malignancies. In contrast to rapamycin, OSI-027 markedly diminished proliferation and induced apoptosis in a variety of lymphoid cell lines and clinical samples, including specimens of B-cell acute lymphocytic leukemia (ALL), mantle cell lymphoma, marginal zone lymphoma and Sezary syndrome. Additional analysis demonstrated that OSI-027-induced apoptosis depended on transcriptional activation of the PUMA and BIM genes. Overexpression of Bcl-2, which neutralizes Puma and Bim, or loss of procaspase 9 diminished OSI-027-induced apoptosis in vitro. Moreover, OSI-027 inhibited phosphorylation of mTORC1 and mTORC2 substrates, up-regulated Puma, and induced regressions in Jeko xenografts. Collectively, these results not only identify a pathway that is critical for the cytotoxicity of dual mTORC1/mTORC2 inhibitors, but also suggest that simultaneously targeting mTORC1 and mTORC2 might be an effective anti-lymphoma strategy in vivo.

A clinically relevant population of leukemic CD34(+)CD38(-) cells in acute myeloid leukemia.

Relapse of acute myeloid leukemia (AML) is thought to reflect the failure of current therapies to adequately target leukemia stem cells (LSCs), the rare, resistant cells presumed responsible for maintenance of the leukemia and typically enriched in the CD34(+)CD38(-) cell population. Despite the considerable research on LSCs over the past 2 decades, the clinical significance of these cells remains uncertain. However, if clinically relevant, it is expected that LSCs would be enriched in minimal residual disease and predictive of relapse. CD34(+) subpopulations from AML patients were analyzed by flow cytometry throughout treatment. Sorted cell populations were analyzed by fluorescence in situ hybridization for leukemia-specific cytogenetic abnormalities (when present) and by transplantation into immunodeficient mice to determine self-renewal capacity. Intermediate (int) levels of aldehyde dehydrogenase (ALDH) activity reliably distinguished leukemic CD34(+)CD38(-) cells capable of engrafting immunodeficient mice from residual normal hematopoietic stem cells that exhibited relatively higher ALDH activity. Minimal residual disease detected during complete remission was enriched for the CD34(+)CD38(-)ALDH(int) leukemic cells, and the presence of these cells after therapy highly correlated with subsequent clinical relapse. ALDH activity appears to distinguish normal from leukemic CD34(+)CD38(-) cells and identifies those AML cells associated with relapse.

Multi-institutional phase 2 clinical and pharmacogenomic trial of tipifarnib plus etoposide for elderly adults with newly diagnosed acute myelogenous leukemia.

Tipifarnib (T) exhibits modest activity in elderly adults with newly diagnosed acute myelogenous leukemia (AML). Based on preclinical synergy, a phase 1 trial of T plus etoposide (E) yielded 25% complete remission (CR). We selected 2 comparable dose levels for a randomized phase 2 trial in 84 adults (age range, 70-90 years; median, 76 years) who were not candidates for conventional chemotherapy. Arm A (T 600 mg twice a day × 14 days, E 100 mg days 1-3 and 8-10) and arm B (T 400 mg twice a day × 14 days, E 200 mg days 1-3 and 8-10) yielded similar CR, but arm B had greater toxicity. Total CR was 25%, day 30 death rate 7%. A 2-gene signature of high RASGRP1 and low aprataxin (APTX) expression previously predicted for T response. Assays using blasts from a subset of 40 patients treated with T plus E on this study showed that AMLs with a RASGRP1/APTX ratio of more than 5.2 had a 78% CR rate and negative predictive value 87%. This ratio did not correlate with outcome in 41 patients treated with conventional chemotherapies. The next T-based clinical trials will test the ability of the 2-gene signature to enrich for T responders prospectively. This study is registered at www.clinicaltrials.gov as #NCT00602771.

CHK1 and WEE1 inhibition combine synergistically to enhance therapeutic efficacy in acute myeloid leukemia ex vivo.

Novel combinations targeting new molecular vulnerabilities are needed to improve the outcome of patients with acute myeloid leukemia. We recently identified WEE1 kinase as a novel target in leukemias. To identify genes that are synthetically lethal with WEE1 inhibition, we performed a short interfering RNA screen directed against cell cycle and DNA repair genes during concurrent treatment with the WEE1 inhibitor MK1775. CHK1 and ATR, genes encoding two replication checkpoint kinases, were among the genes whose silencing enhanced the effects of WEE1 inhibition most, whereas CDK2 short interfering RNA antagonized MK1775 effects. Building on this observation, we examined the impact of combining MK1775 with selective small molecule inhibitors of CHK1, ATR and cyclin-dependent kinases. The CHK1 inhibitor MK8776 sensitized acute myeloid leukemia cell lines and primary leukemia specimens to MK1775 ex vivo, whereas smaller effects were observed with the MK1775/MK8776 combination in normal myeloid progenitors. The ATR inhibitor VE-821 likewise enhanced the antiproliferative effects of MK1775, whereas the cyclin-dependent kinase inhibitor roscovitine antagonized MK1775. Further studies showed that MK8776 enhanced MK1775-mediated activation of the ATR/CHK1 pathway in acute leukemia cell lines and ex vivo. These results indicate that combined cell cycle checkpoint interference with MK1775/MK8776 warrants further investigation as a potential treatment for acute myeloid leukemia.

A phase II trial of sequential ribonucleotide reductase inhibition in aggressive myeloproliferative neoplasms.

Myeloproliferative neoplasms are a varied group of disorders that can have prolonged chronic phases, but eventually accelerate and can transform into a secondary acute myeloid leukemia that is ultimately fatal. Triapine is a novel inhibitor of the M2 subunit of ribonucleotide reductase. Sequential inhibition of ribonucleotide reductase with triapine and an M1 ribonucleotide reductase inhibitor (fludarabine) was noted to be safe, and led to a 29% complete plus partial response rate in myeloproliferative neoplasms. This article reports the findings of a phase II trial of triapine (105 mg/m(2)/day) followed by fludarabine (30 mg/m(2)/day) daily for 5 consecutive days in 37 patients with accelerated myeloproliferative neoplasms and secondary acute myeloid leukemia. The overall response rate was 49% (18/37), with a complete remission rate of 24% (9/37). Overall response rates and complete remissions were seen in all disease subsets, including secondary acute myeloid leukemia, in which the overall response rate and complete remission rate were 48% and 33%, respectively. All patients with known JAK2 V617F mutations (6/6) responded. The median overall survival of the entire cohort was 6.9 months, with a median overall survival of both overall responders and complete responders of 10.6 months. These data further demonstrate the promise of sequential inhibition of ribonucleotide reductase in patients with accelerated myeloproliferative neoplasms and secondary acute myeloid leukemia. This study was registered with clinicaltrials.gov (NCT00381550).

Farnesyltransferase inhibitor tipifarnib inhibits Rheb prenylation and stabilizes Bax in acute myelogenous leukemia cells.

Although farnesyltransferase inhibitors have shown promising activity in relapsed lymphoma and sporadic activity in acute myelogenous leukemia, their mechanism of cytotoxicity is incompletely understood, making development of predictive biomarkers difficult. In the present study, we examined the action of tipifarnib in human acute myelogenous leukemia cell lines and clinical samples. In contrast to the Ras/MEK/ERK pathway-mediated Bim upregulation that is responsible for tipifarnib-induced killing of malignant lymphoid cells, inhibition of Rheb-induced mTOR signaling followed by dose-dependent upregulation of Bax and Puma occurred in acute myelogenous leukemia cell lines undergoing tipifarnib-induced apoptosis. Similar Bax and Puma upregulation occurred in serial bone marrow samples harvested from a subset of acute myelogenous leukemia patients during tipifarnib treatment. Expression of FTI-resistant Rheb M184L, like knockdown of Bax or Puma, diminished tipifarnib-induced killing. Further analysis demonstrated that increased Bax and Puma levels reflect protein stabilization rather than increased gene expression. In U937 cells selected for tipifarnib resistance, neither inhibition of signaling downstream of Rheb nor Bax and Puma stabilization occurred. Collectively, these results not only identify a pathway downstream from Rheb that contributes to tipifarnib cytotoxicity in human acute myelogenous leukemia cells, but also demonstrate that FTI-induced killing of lymphoid versus myeloid cells reflects distinct biochemical mechanisms downstream of different farnesylated substrates. (ClinicalTrials.gov identifier NCT00602771).