Clinical Correlates of Venetoclax-Based Combination Sensitivities to Augment Acute Myeloid Leukemia Therapy

The BCL2 inhibitor venetoclax combined with the hypomethylating agent azacytidine shows significant clinical benefit in a subset of patients with acute myeloid leukemia (AML); however, resistance limits response and durability. We prospectively profiled the ex vivo activity of 25 venetoclax-inclusive combinations on primary AML patient samples to identify those with improved potency and synergy compared with venetoclax + azacytidine (Ven + azacytidine). Combination sensitivities correlated with tumor cell state to discern three patterns: primitive selectivity resembling Ven + azacytidine, monocytic selectivity, and broad efficacy independent of cell state. Incorporation of immunophenotype, mutation, and cytogenetic features further stratified combination sensitivity for distinct patient subtypes. We dissect the biology underlying the broad, cell state-independent efficacy for the combination of venetoclax plus the JAK1/2 inhibitor ruxolitinib. Together, these findings support opportunities for expanding the impact of venetoclax-based drug combinations in AML by leveraging clinical and molecular biomarkers associated with ex vivo responses.

SIGNIFICANCE

By mapping drug sensitivity data to clinical features and tumor cell state, we identify novel venetoclax combinations targeting patient subtypes who lack sensitivity to Ven + azacytidine. This provides a framework for a taxonomy of AML informed by readily available sets of clinical and genetic features obtained as part of standard care. See related commentary by Becker, p. 437 . This article is featured in Selected Articles from This Issue, p. 419.

Entospletinib with decitabine in acute myeloid leukemia with mutant TP53 or complex karyotype: A phase 2 substudy of the Beat AML Master Trial

BACKGROUND

Patients with acute myeloid leukemia (AML) who have tumor protein p53 (TP53) mutations or a complex karyotype have a poor prognosis, and hypomethylating agents are often used. The authors evaluated the efficacy of entospletinib, an oral inhibitor of spleen tyrosine kinase, combined with decitabine in this patient population.

METHODS

This was a multicenter, open-label, phase 2 substudy of the Beat AML Master Trial (ClinicalTrials.gov identifier NCT03013998) using a Simon two-stage design. Eligible patients aged 60 years or older who had newly diagnosed AML with mutations in TP53 with or without a complex karyotype (cohort A; n = 45) or had a complex karyotype without TP53 mutation (cohort B; n = 13) received entospletinib 400 mg twice daily with decitabine 20 mg/m² on days 1-10 every 28 days for up to three induction cycles, followed by up to 11 consolidation cycles, in which decitabine was reduced to days 1-5. Entospletinib maintenance was given for up to 2 years. The primary end point was complete remission (CR) and CR with hematologic improvement by up to six cycles of therapy.

RESULTS

The composite CR rates for cohorts A and B were 13.3% (95% confidence interval, 5.1%-26.8%) and 30.8% (95% confidence interval, 9.1%-61.4%), respectively. The median duration of response was 7.6 and 8.2 months, respectively, and the median overall survival was 6.5 and 11.5 months, respectively. The study was stopped because the futility boundary was crossed in both cohorts.

CONCLUSIONS

The combination of entospletinib and decitabine demonstrated activity and was acceptably tolerated in this patient population; however, the CR rates were low, and overall survival was short. Novel treatment strategies for older patients with TP53 mutations and complex karyotype remain an urgent need.

Integrative analysis of drug response and clinical outcome in acute myeloid leukemia

Acute myeloid leukemia (AML) is a cancer of myeloid-lineage cells with limited therapeutic options. We previously combined ex vivo drug sensitivity with genomic, transcriptomic, and clinical annotations for a large cohort of AML patients, which facilitated discovery of functional genomic correlates. Here, we present a dataset that has been harmonized with our initial report to yield a cumulative cohort of 805 patients (942 specimens). We show strong cross-cohort concordance and identify features of drug response. Further, deconvoluting transcriptomic data shows that drug sensitivity is governed broadly by AML cell differentiation state, sometimes conditionally affecting other correlates of response. Finally, modeling of clinical outcome reveals a single gene, PEAR1, to be among the strongest predictors of patient survival, especially for young patients. Collectively, this report expands a large functional genomic resource, offers avenues for mechanistic exploration and drug development, and reveals tools for predicting outcome in AML.

A phase 1b/2 study of TP-0903 and decitabine targeting mutant TP53 and/or complex karyotype in patients with untreated acute myeloid leukemia ≥ age 60 years: Phase 1b interim results

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Background: TP-0903 is a multi-kinase inhibitor designed to target AXL, a receptor tyrosine kinase, and also inhibits cell cycle regulators such as Chk1/2 and other AML associated kinases. TP-0903 has shown prior anti-tumor activity at a safe dose in solid tumors. In pre-clinical AML studies, TP-0903 shows potent cytotoxicity in TP53 mutant ( TP53m) AML cell lines, an adverse prognostic genomic sub-group of AML. TP-0903 also had synergistic activity with decitabine (dec) in TP53m AML and prolonged survival in xenograft and genetically engineered mouse models. We report here on the initial safety and clinical results from the Leukemia and Lymphoma Society’s ongoing Beat AML phase 1b/2 (Ph1b/2) trial of TP-0903 in combination with dec (ClinicalTrials.gov NCT03013998). Methods: Newly diagnosed AML pts ≥60 years with TP53m and/or complex karyotype (≥3 abnormalities) were selected for a Ph1b/2 dose escalation study of TP-0903 combined with dec. Seven Ph1b pts were given TP-0903 every 28-day cycle from days 1-21 (Dose level (DL) 1 = 37 mg/day) and dec IV days 1-10 (20 mg/m2). A standard 3+3 design was used to evaluate the safety and tolerability. Nine additional patients enrolled onto Ph2 at DL1, but further assessments of safety, pharmacokinetics (PK) and correlative data was used to update the final recommended Ph2 dose (RP2D) of TP-0903 to DL-1 (25 mg/day) with dec. Results: At data cutoff (10Jan2022), 16 total pts were accrued. Ph1b treated 7 pts at DL1, 6 were DLT evaluable, and no DLTs were observed. Ph2 enrolled and treated 9 pts at DL1 before concerns of delayed count recovery led to the reduction of the Ph2 dose of TP-0903 to DL-1 (25 mg/day). For all 16 pts treated at DL1, 1 pt achieved CR, 4 pts CRh, and 1 pt CRi, for a composite CR (CR/CRh/CRi) rate of 37.5% (95% CI, 15.2-64.6), with 4 pts achieving MRD negativity by central flow cytometry. For the remaining 10 pts, 1 pt achieved MLFS (6%), 6 pts had stable disease (37.5%), 1 pt had treatment failure (6%), and 2 pts were not evaluable (12.5%) due to withdrawal of consent and death from early disease progression. Two pts (1 CR and 1 CRh) proceeded to stem cell transplantation. The most common grade 3 and above treatment-related AEs include decreased neutrophil counts (37.5%), platelet counts (31.3%), and anemia (18.8%). Finally, PK and correlative data analysis looking at soluble Axl and Gas6 also supported reduction to DL-1. Conclusions: Initial results with DL1 suggest that TP-0903/dec shows preliminary clinical activity in the prognostically poor TP53m/complex karyotype AML sub-group, with 4 pts achieving MRD negative status out of 6 patients who achieved a CR/CRh/CRi (66%). After further patients were treated on DL1, the toxicity profile and correlative data supported the de-escalation to DL-1 as the RP2D. The Ph2 study is ongoing to determine the clinical activity of this new RP2D (DL-1). Clinical trial information: NCT03013998.

Model-based analysis to support dose selection of pevonedistat (PEV) combined with azacitidine (AZA) in patients (pts) with higher-risk myelodysplastic syndromes (MDS)/chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML)

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Background: PEV+AZA has been studied in higher-risk MDS/CMML and AML, with encouraging efficacy and an acceptable safety profile without added myelosuppression. This pooled analysis was performed to evaluate the impact of PEV exposure on safety and efficacy. Methods: Data from three studies (NCT01814826, NCT02782468 and NCT02610777) were used in the PEV exposure–safety analyses, including ≥ grade 3 neutropenia (NEU3), febrile neutropenia (FN), ≥ grade 3 thrombocytopenia, ≥ grade 3 alanine aminotransferase elevation, ≥ grade 3 aspartate aminotransferase elevation and ≥ grade 3 treatment-emergent adverse event (TEAE3), in pts with higher-risk MDS/CMML and AML who received PEV+AZA. Data from NCT02610777 were used for exposure–efficacy analyses, including overall survival (OS), event-free survival (EFS), complete response (CR) and CR+partial response (PR), in pts with higher-risk MDS/CMML who received PEV+AZA. The exposure metrics for individual pts were derived from a previously developed population pharmacokinetic model with pooled data from eight phase 1/2 studies. PEV exposure–safety relationships for the toxicity endpoints, exposure–CR and exposure–CR+PR, were estimated by logistic regression. Age, sex, race, baseline Eastern Cooperate Oncology Group (ECOG) Performance Status score and disease type were evaluated as covariates. Cox proportional-hazards models were used to evaluate the PEV exposure–survival for higher-risk MDS/CMML, with age, sex, baseline ECOG PS score, Revised International Prognostic Scoring System score (IPSS-R) and disease type as potential covariates. Results: In total, 135 pts (median age, 74 years; male, 64%; Caucasian, 82%) and 41 pts (median age, 74 years; male, 76%; Caucasian, 90%; median IPSS-R, 5.5) were included in PEV exposure–safety and exposure–efficacy analyses, respectively. PEV exposure was significantly related to the incidence of NEU3 ( p = 0.003), FN ( p = 0.02) and TEAE3 ( p = 0.02), supporting PEV dose reductions for pts with treatment-related toxicities. Relationships between PEV exposures and CR, CR+PR, EFS or OS indicated consistent clinical benefit across ranges of PEV exposure following a starting dose of 20 mg/m2. Conclusions: The association between exposure and safety supports PEV dose reductions for pts with treatment-related toxicities. The exposure–efficacy analyses indicated consistent clinical benefit across ranges of PEV exposure following a starting dose of 20 mg/m2. These results support a favorable benefit–risk profile of the 20 mg/m2 PEV dose on days 1, 3 and 5 in combination with AZA 75 mg/m2 for 7 days in 28-day cycles. Clinical trial information: NCT01814826 , NCT02782468 , NCT02610777.

A systematic review of higher-risk myelodysplastic syndromes clinical trials to determine the benchmark of azacitidine and explore alternative endpoints for overall survival

The hypomethylating agent azacitidine can prolong overall survival (OS) in patients with higher risk-myelodysplastic syndromes (HR-MDS) compared to conventional regimens. However, outcomes differ largely between studies, making it challenging to determine the contribution of novel therapies added to azacitidine. Further, a discrepancy is seen between complete (CR) or partial (PR) response rates and OS improvement with azacitidine, making it challenging to rely on earlier endpoints than OS. We conducted a systematic literature search and study-level systematic review of 237 clinical studies to better understand outcomes for HR-MDS patients treated with azacitidine. Pooled marrow CR was 9% (N = 2654; 95% CI: 6-13 %), CR rate was 17 % (N = 6943; 95% CI: 15-20 %), and median OS (mOS) was 18.6 months (N = 2820; 95% CI: 15.3-21.9). A weak correlation to mOS was detected with CR rate (207 patient cohorts, Pearson's r = 0.315; P < 0.0005), and a much stronger correlation with median progression-free survival (mPFS) (r=0.88, P = 3 × 10^-14). Six-months progression-free survival rates correlated with 1-year OS rates but were only infrequently reported (N = 41 patient cohorts) therefore not allowing a robust recommendation for a surrogate to the established OS endpoint. Larger patient numbers and patient-level data appear necessary, especially for designing future clinical trials using azacitidine combinations.

Clinical Responsiveness to All-trans Retinoic Acid Is Potentiated by LSD1 Inhibition and Associated with a Quiescent Transcriptome in Myeloid Malignancies

PURPOSE

In preclinical studies, the lysine-specific histone demethylase 1A (LSD1) inhibitor tranylcypromine (TCP) combined with all-trans retinoic acid (ATRA) induces differentiation and impairs survival of myeloid blasts in non-acute promyelocytic leukemia acute myeloid leukemia (AML). We conducted a phase I clinical trial (NCT02273102) to evaluate the safety and activity of ATRA plus TCP in patients with relapsed/refractory AML and myelodysplasia (MDS).

PATIENTS AND METHODS

Seventeen patients were treated with ATRA and TCP (three dose levels: 10 mg twice daily, 20 mg twice daily, and 30 mg twice daily).

RESULTS

ATRA-TCP had an acceptable safety profile. The MTD of TCP was 20 mg twice daily. Best responses included one morphologic leukemia-free state, one marrow complete remission with hematologic improvement, two stable disease with hematologic improvement, and two stable disease. By intention to treat, the overall response rate was 23.5% and clinical benefit rate was 35.3%. Gene expression profiling of patient blasts showed that responding patients had a more quiescent CD34⁺ cell phenotype at baseline, including decreased MYC and RARA expression, compared with nonresponders that exhibited a more proliferative CD34⁺ phenotype, with gene expression enrichment for cell growth signaling. Upon ATRA-TCP treatment, we observed significant induction of retinoic acid-target genes in responders but not nonresponders. We corroborated this in AML cell lines, showing that ATRA-TCP synergistically increased differentiation capacity and cell death by regulating the expression of key gene sets that segregate patients by their clinical response.

CONCLUSIONS

These data indicate that LSD1 inhibition sensitizes AML cells to ATRA and may restore ATRA responsiveness in subsets of patients with MDS and AML.

Functional genomic landscape of acute myeloid leukaemia

The implementation of targeted therapies for acute myeloid leukaemia (AML) has been challenging because of the complex mutational patterns within and across patients as well as a dearth of pharmacologic agents for most mutational events. Here we report initial findings from the Beat AML programme on a cohort of 672 tumour specimens collected from 562 patients. We assessed these specimens using whole-exome sequencing, RNA sequencing and analyses of ex vivo drug sensitivity. Our data reveal mutational events that have not previously been detected in AML. We show that the response to drugs is associated with mutational status, including instances of drug sensitivity that are specific to combinatorial mutational events. Integration with RNA sequencing also revealed gene expression signatures, which predict a role for specific gene networks in the drug response. Collectively, we have generated a dataset-accessible through the Beat AML data viewer (Vizome)-that can be leveraged to address clinical, genomic, transcriptomic and functional analyses of the biology of AML.

Leveraging Hypomethylating Agents for Better MDS Therapy

PURPOSE OF REVIEW

Myelodysplastic syndrome (MDS) is a clinically and molecularly heterogeneous disease, which primarily occurs in older adults. Although hypomethylating agents have survival benefit and are the current standard of care, many MDS patients will not garner a response from therapy. For those who do respond, most responses are not durable, and the only hope for a cure is allogeneic stem cell transplant. New therapies to improve outcomes are urgently needed.

RECENT FINDINGS

Clinical trials combining standard hypomethylating agents with novel experimental agents are underway in an effort to improve clinical outcomes in MDS patients. Several of these small molecules have demonstrated the ability to augment the response rates of hypomethylating agents alone, including complete remission rates, in both the front line and refractory settings. Combination approaches utilizing hypomethylating agents and novel-targeted therapies have demonstrated the ability to improve response rates in MDS patients in both the front line and salvage settings, and thus may change the standard of care.

A new approach to the treatment of acute myeloid leukaemia targeting the receptor for growth hormone-releasing hormone

Growth hormone-releasing hormone (GHRH) is secreted by the hypothalamus and acts on the pituitary gland to stimulate the release of growth hormone (GH). GHRH can also be produced by human cancers, in which it functions as an autocrine/paracrine growth factor. We have previously shown that synthetic antagonistic analogues of GHRH are able to successfully suppress the growth of 60 different human cancer cell lines representing over 20 cancers. Nevertheless, the expression of GHRH and its receptors in leukaemias has never been examined. Our study demonstrates the presence of GHRH receptor (GHRH-R) on 3 of 4 human acute myeloid leukaemia (AML) cell lines-K-562, THP-1, and KG-1a-and significant inhibition of proliferation of these three cell lines in vitro following incubation with the GHRH antagonist MIA-602. We further show that this inhibition of proliferation is associated with the upregulation of pro-apoptotic genes and inhibition of Akt signalling in leukaemic cells. Treatment with MIA-602 of mice bearing xenografts of these human AML cell lines drastically reduced tumour growth. The expression of GHRH-R was further confirmed in 9 of 9 samples from patients with AML. These findings offer a new therapeutic approach to this malignancy and suggest a possible role of GHRH-R signalling in the pathology of AML.

Inhibition of the NEDD8 conjugation pathway induces calcium-dependent compensatory activation of the pro-survival MEK/ERK pathway in acute lymphoblastic leukemia

De novo and acquired drug resistance and subsequent relapse remain major challenges in acute lymphoblastic leukemia (ALL). We previously identified that pevonedistat (TAK-924, MLN4924), a first-in-class inhibitor of NEDD8 activating enzyme (NAE), elicits ER stress and has potent in vitro and in vivo efficacy against ALL. However, in pevonedistat-treated ALL cell lines, we found consistent activation of the pro-survival MEK/ERK pathway, which has been associated with relapse and poor outcome in ALL. We uncovered that inhibition of the MEK/ERK pathway in vitro and in vivo sensitized ALL cells to pevonedistat. The observed synergistic apoptotic effect appears to be mediated by inhibition of the MEK/ERK pro-survival cascade leading to de-repression of the pro-apoptotic BIM protein. Mechanistically, Ca²⁺ influx via the Ca²⁺-release-activated Ca²⁺ (CRAC) channel induced protein kinase C β2 (PKC-β2) was responsible for activation of the MEK/ERK pathway in pevonedistat-treated ALL cells. Sequestration of Ca²⁺ using BAPTA-AM or blockage of store-operated Ca²⁺ entry (SOCE) using BTP-2 both attenuated the compensatory activation of MEK/ERK signaling in pevonedistat-treated ALL cells. Pevonedistat significantly altered the expression of Orai1 and stromal interaction molecule 1 (STIM1), resulting in significantly decreased STIM1 protein levels relative to Orai1. Further, we identified eIF2α as an important post-transcriptional regulator of STIM1, suggesting that pevonedistat-induced eIF2α de-phosphorylation selectively down-regulates translation of STIM1 mRNA. Consequently, our data suggest that pevonedistat potentially activates SOCE and promotes Ca²⁺ influx leading to activation of the MEK/ERK pathway by altering the stoichiometric Orai1:STIM1 ratio and inducing ER stress in ALL cells.

Ex-vivo sensitivity profiling to guide clinical decision making in acute myeloid leukemia: A pilot study

A precision medicine approach is appealing for use in AML due to ease of access to tumor samples and the significant variability in the patients' response to treatment. Attempts to establish a precision medicine platform for AML, however, have been unsuccessful, at least in part due to the use of small compound panels and having relatively slow turn over rates, which restricts the scope of treatment and delays its onset. For this pilot study, we evaluated a cohort of 12 patients with refractory AML using an ex vivo drug sensitivity testing (DST) platform. Purified AML blasts were screened with a panel of 215 FDA-approved compounds and treatment response was evaluated after 72h of exposure. Drug sensitivity scoring was reported to the treating physician, and patients were then treated with either DST- or non-DST guided therapy. We observed survival benefit of DST-guided therapy as compared to the survival of patients treated according to physician recommendation. Three out of four DST-treated patients displayed treatment response, while all of the non-DST-guided patients progressed during treatment. DST rapidly and effectively provides personalized treatment recommendations for patients with refractory AML.

Enasidenib in mutant IDH2 relapsed or refractory acute myeloid leukemia

Recurrent mutations in isocitrate dehydrogenase 2 (IDH2) occur in ∼12% of patients with acute myeloid leukemia (AML). Mutated IDH2 proteins neomorphically synthesize 2-hydroxyglutarate resulting in DNA and histone hypermethylation, which leads to blocked cellular differentiation. Enasidenib (AG-221/CC-90007) is a first-in-class, oral, selective inhibitor of mutant-IDH2 enzymes. This first-in-human phase 1/2 study assessed the maximum tolerated dose (MTD), pharmacokinetic and pharmacodynamic profiles, safety, and clinical activity of enasidenib in patients with mutant-IDH2 advanced myeloid malignancies. We assessed safety outcomes for all patients and clinical efficacy in the largest patient subgroup, those with relapsed or refractory AML, from the phase 1 dose-escalation and expansion phases of the study. In the dose-escalation phase, an MTD was not reached at doses ranging from 50 to 650 mg per day. Enasidenib 100 mg once daily was selected for the expansion phase on the basis of pharmacokinetic and pharmacodynamic profiles and demonstrated efficacy. Grade 3 to 4 enasidenib-related adverse events included indirect hyperbilirubinemia (12%) and IDH-inhibitor-associated differentiation syndrome (7%). Among patients with relapsed or refractory AML, overall response rate was 40.3%, with a median response duration of 5.8 months. Responses were associated with cellular differentiation and maturation, typically without evidence of aplasia. Median overall survival among relapsed/refractory patients was 9.3 months, and for the 34 patients (19.3%) who attained complete remission, overall survival was 19.7 months. Continuous daily enasidenib treatment was generally well tolerated and induced hematologic responses in patients for whom prior AML therapy had failed. Inducing differentiation of myeloblasts, not cytotoxicity, seems to drive the clinical efficacy of enasidenib. This trial was registered at www.clinicaltrials.gov as #NCT01915498.

Enasidenib in mutant-IDH2 relapsed or refractory acute myeloid leukemia (R/R AML): Results of a phase I dose-escalation and expansion study

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Background: Recurrent mutations in isocitrate dehydrogenase 2 (m IDH2) occur in 8-15% of AML pts. mIDH2 proteins synthesize an oncometabolite, 2-hydroxyglutarate (2HG), causing DNA and histone hypermethylation and blocked myeloid differentiation. Enasidenib (AG-221) is an oral, selective, small-molecule inhibitor of mIDH2 protein. Methods: This phase 1/2 study assessed the maximum tolerated dose (MTD), pharmacokinetic and pharmacodynamic profiles, safety, and clinical activity of enasidenib in pts with m IDH2 myeloid malignancies. Safety for all pts and efficacy outcomes for R/R AML pts from the phase 1 dose-escalation and expansion phases are reported. Results: In all, 239 pts received enasidenib. In the dose-escalation (n=113), the MTD was not reached at doses up to 650 mg daily. Median 2HG reductions from baseline were 92%, 90%, and 93% for pts receiving <100 mg, 100 mg, and >100 mg daily, respectively. Enasidenib 100 mg QD was chosen for the expansion phase (n=126) based on PK/PD profiles and demonstrated efficacy. Median number of enasidenib cycles was 5 (range 1–25). Grade 3-4 drug-related investigator reported AEs included indirect hyperbilirubinemia (12%) and IDH-inhibitor-associated differentiation syndrome (ie, retinoic acid syndrome; 7%). For R/R AML pts, overall response rate (ORR) was 40.3%, including 34 (19.3%) complete remissions (CR; Table). Response was associated with cellular differentiation, typically with no evidence of aplasia. Median overall survival (OS) for R/R AML pts was 9.3 months (mos). For pts who attained CR, OS was 19.7 mos. Pts who had received ≥2 prior AML regimens (n=94; 53%) had median OS of 8.0 mos. Conclusions: Enasidenib was well tolerated, induced CRs, and was associated with OS of >9 mos in pts who had failed prior AML therapies. Differentiation of myeloblasts, not cytotoxicity, appears to drive the clinical efficacy of enasidenib. Clinical trial information: NCT01915498. [Table: see text]

KB004, a first in class monoclonal antibody targeting the receptor tyrosine kinase EphA3, in patients with advanced hematologic malignancies: Results from a phase 1 study

EphA3 is an Ephrin receptor tyrosine kinase that is overexpressed in most hematologic malignancies. We performed a first-in-human multicenter phase I study of the anti-EphA3 monoclonal antibody KB004 in refractory hematologic malignancies in order to determine safety and tolerability, along with the secondary objectives of pharmacokinetics (PK) and pharmacodynamics (PD) assessments, as well as preliminary assessment of efficacy. Patients were enrolled on a dose escalation phase (DEP) initially, followed by a cohort expansion phase (CEP). KB004 was administered by intravenous infusion on days 1, 8, and 15 of each 21-day cycle in escalating doses. A total of 50 patients (AML 39, MDS/MPN 3, MDS 4, DLBCL 1, MF 3) received KB004 in the DEP; an additional 14 patients were treated on the CEP (AML 8, MDS 6). The most common toxicities were transient grade 1 and grade 2 infusion reactions (IRs) in 79% of patients. IRs were dose limiting above 250mg. Sustained exposure exceeding the predicted effective concentration (1ug/mL) and covering the 7-day interval between doses was achieved above 190mg. Responses were observed in patients with AML, MF, MDS/MPN and MDS. In this study, KB004 was well tolerated and clinically active when given as a weekly infusion.

The NEDD8-activating enzyme inhibitor pevonedistat activates the eIF2α and mTOR pathways inducing UPR-mediated cell death in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the leading cause of cancer-related death in children, and cure rates for adults remain dismal. Further, effective treatment strategies for relapsed/refractory ALL remain elusive. We previously uncovered that ALL cells are prone to apoptosis via endoplasmic reticulum (ER) stress/unfolded protein response (UPR)-mediated mechanisms. We investigated the antineoplastic activity of pevonedistat^®, a novel NEDD8-activating enzyme inhibitor that targets E3 cullin-RING ligases (CRLs) dependent proteasomal protein degradation, in ALL. Herein, we report that pevonedistat induces apoptosis in ALL cells by dysregulating the translational machinery leading to induction of proteotoxic/ER stress and UPR-mediated cell death. Mechanistically, pevonedistat led to P-eIF2a dephosphorylation causing atypical proteotoxic/ER stress from failure to halt protein translation via the UPR and upregulation of mTOR/p70S6K. Additional studies revealed that pevonedistat re-balanced the homeostasis of pro- and anti-apoptotic proteins to favor cell death through altered expression and/or activity of Mcl-1, NOXA, and BIM, suggesting that pevonedistat has a "priming" effect on ALL by altering the apoptotic threshold through modulation of Mcl-1 activity. Further, we demonstrated that pevonedistat synergizes with selected anti-leukemic agents in vitro, and prolongs survival of NSG mice engrafted with ALL cells, lending support for the use of pevonedistat as part of a multi-agent approach.

Abstract 4547: Rebalancing of Bcl-2 family proteins mediate the vulnerability of pevonedistat-treated acute lymphoblastic leukemia cells towards MEK/ERK pathway inhibition

Acute lymphoblastic leukemia (ALL) is the leading cause of cancer-related death in children and the relapse rate in adult ALL patients is about 50%, highlighting the need for new therapeutic strategies. Data from our laboratory and others showed that ALL cells are sensitive to drugs that induce endoplasmic reticulum (ER) stress/unfolded protein response (UPR). In search for novel strategies to target the ER stress/UPR in ALL, we tested the efficacy of the NEDD8-activating enzyme (NAE) inhibitor pevonedistat (MLN4924, pevo) in ALL. We found ALL cells exhibited significant in vitro and in vivo sensitivity to pevo-induced ER stress/UPR. Specifically, proteotoxic/ER stress was observed in pevo-treated ALL cells secondary to their inability to halt protein translation following pevo-induced activation of the mTOR pathway and concomitant de-phosphorylation of p-eIF2α (S51). In addition, aberrant activation of MEK/ERK has been correlated with resistance/relapse in pediatric ALL (Blood 2014; 124: 3420-3430). In our Bp- and T-ALL cell line models, we found consistent induction of p-ERK1/2 (T202/Y204) following pevo treatment, suggesting phosphorylation of ERK1/2 as a compensatory survival mechanism in response to pevo's cytotoxicity. Supporting this hypothesis, we observed significant in vitro synergy between the MEK inhibitor selumetinib (SEL) and pevo (CI = 0.017). On this basis, we tested the in vivo efficacy of pevo + SEL in NSG mice injected with NALM6 cells expressing the luciferase gene (NALM6/LUC). Engrafted NSG mice were treated with pevo (s.c., 66 mg/kg) and SEL (p.o., 50 mg/kg) twice daily on weekdays and once per day on weekends. Bioluminescence analysis of animals 21 days post ALL injection revealed significant reduction of tumor burden in mice treated with pevo alone or pevo + SEL (p&lt;0.05 for both vs. control). Kaplan-Meier curves showed a significant survival advantage for mice treated with pevo + SEL compared with the control group (p&lt;0.05). Mechanistic studies showed that pevo led to induction of NOXA and BIM whereas Mcl-1 levels were stabilized, suggesting sequestration of the pro-survival activity of Mcl-1 by NOXA/BIM. Indeed, co-IP analysis demonstrated that binding between NOXA and/or BIM with Mcl-1 was enhanced in pevo-treated ALL cells. Further, significant downregulation of Mcl-1 was observed in ALL cells co-treated with pevo + SEL. We found that the synergy of this combination was prevented by co-treatment with the pan-caspase inhibitor Z-VAD, but observed persistence of Mcl-1downregulation whereas BIM expression remained unchanged. We conclude that MEK/ERK pathway inhibition rebalances the Bcl-2 family proteins in favor of synergistic apoptotic death in ALL cells treated in vitro and in vivo with the NAE inhibitor pevonedistat. Our data supports further investigations of agents targeting NAE and the MEK/ERK pathway in relapsed/refractory ALL.

Citation Format: Shuhua Zheng, Gilles M. Leclerc, Guy J. Leclerc, Joanna DeSalvo, Ronan T. Swords, Julio C. Barredo. Rebalancing of Bcl-2 family proteins mediate the vulnerability of pevonedistat-treated acute lymphoblastic leukemia cells towards MEK/ERK pathway inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4547.

MK-0457, an Aurora kinase and BCR-ABL inhibitor, is active in patients with BCR-ABL T315I leukemia

MK-0457, an Aurora kinase and BCR-ABL inhibitor, was studied on a Phase I/II study in 77 patients with refractory hematologic malignancies. The average number of cycles per patient was 3 (range 1-21). Maximum tolerated doses for a 5-day short infusion and continuous infusion regimens were 40 mg/m(2)/h and 144 mg/m(2)/h, respectively. Drug-related adverse events (AEs) included transient mucositis and alopecia. Eight of 18 patients with BCR-ABL T315I-mutated chronic myelogenous leukemia (44%) had hematologic responses and one of three patients (33%) with Philadelphia chromosome-positive acute lymphoblastic leukemia obtained complete remission. MK-0457 has important activity in patients with leukemias expressing the highly resistant T315I BCR-ABL mutation.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.

Targeting protein neddylation: a novel therapeutic strategy for the treatment of cancer

INTRODUCTION

The NEDD8 (neural precursor cell-expressed developmentally downregulated 8) conjugation pathway regulates the post-translational modification of oncogenic proteins. This pathway has important potential for cancer therapeutics. Several proteins vital in cancer biology are regulated by protein neddylation. These observations led to the development of a small molecule inhibitor that disrupts protein neddylation and leads to cancer cell death and important activity in early phase clinical trials.

AREAS COVERED

This review provides an extensive coverage of cellular protein homeostasis with particular emphasis on the NEDD8 conjugation pathway. Insights into a new investigational drug that specifically disrupts the NEDD8 pathway are discussed. The clinical data for this agent are also updated.

EXPERT OPINION

Neddylation controls key cellular pathways found to be dysregulated in many cancers. Protein neddylation is a relatively under-explored pathway for pharmacologic inhibition in cancer. Selective disruption of this pathway has demonstrated clinical activity in patients with myeloid neoplasms and is worth exploring further in combination with other anti-leukemia agents.

Rotary powered device for bone marrow aspiration and biopsy yields excellent specimens quickly and efficiently

Recently, a new FDA-cleared battery powered bone marrow biopsy system was developed to allow operators access to the bone marrow space quickly and efficiently. A pre-clinical evaluation of the device (OnControl, Vidacare Corporation, San Antonio, TX, USA) on anesthetized pigs was conducted, in addition to a clinical evaluation in hematology clinic patients requiring a bone marrow biopsy. Twenty-six samples were collected from the swine model. No cellular artifact or thermal damage was reported in any of the samples obtained. For the clinical evaluation of the device, 16 patients were recruited. Mean time from needle contact with skin to needle removal was 38.5 +/- 13.94 seconds. No complications were reported. In this study, the manual and powered samples were equivalent in specimen quality. In the patients evaluated, the device was safe, easy to use and the mean procedural time was significantly faster than previously reported with a manual technique.

Abstract B272: The novel PIM kinase inhibitor SGI-1776 significantly enhances the preclinical activity of sunitinib in renal cell carcinoma

The PIM kinases (PIM1, PIM2, and PIM3) are constitutively active serine/threonine kinases that promote tumorigenesis in mouse models and are associated with drug resistance. Upregulation of PIM kinase expression has been reported in many malignancies including renal cell carcinoma (RCC), suggesting that inhibition of PIM kinase activity may be an attractive therapeutic strategy. SGI-1776 is a novel orally available small molecule inhibitor of PIM kinase activity that is currently in Phase I clinical trials. We hypothesized that inhibition of PIM kinase activity would reduce the viability of RCC cells and enhance the activity of the multi-targeted receptor tyrosine kinase (RTK) inhibitor sunitinib. Cell viability and apoptosis assays demonstrated that SGI-1776 possessed significant in vitro activity in a panel of RCC cell lines. One of the mechanisms by which the PIM kinases have been reported to inhibit apoptosis is by phosphorylating the BH3-only protein Bad to abrogate its pro-apoptotic function. Accordingly, SGI-1776-mediated apoptosis was associated with decreased levels of the phosphorylated form of Bad. Moreover, targeted knockdown of Bad expression significantly decreased sensitivity to SGI-1776 indicating that Bad is an important mediator of the anticancer activity of this agent. Treatment with SGI-1776 also led to a markedly decrease in phosphorylated and total c-Myc levels and enhanced the activity of sunitinib in RCC cells. The addition of sunitinib to SGI-1776 further reduced c-Myc expression. Silencing of the gene suggested that c-Myc plays a significant role in sensitivity to the SGI-1776/sunitinib combination. To further evaluate this drug combination, Caki-1 and 786-O RCC xenografts were established in nude mice and they were treated orally with SGI-1776, sunitinib, or the combination. The SGI-1776/sunitinib combination significantly reduced tumor burden in both xenograft models compared to single agent therapy and was very well tolerated. Analysis of the tumors revealed that the drug combination strongly decreased tumor proliferation and induced apoptosis as measured by PCNA and TUNEL immunohistochemistry, respectively. These data indicate that PIM kinase signaling has a significant role in the biology of RCC and warrants further investigation.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B272.

Emerging drugs in the treatment of pancreatic cancer

BACKGROUND

Pancreatic cancer is the fourth leading cause of cancer-related death in the US. However, there is a growing belief that novel biological agents could improve survival of patients with this cancer. Gemcitabine-based chemotherapy remains the cornerstone treatment for advanced pancreatic cancers. So far, the current targeted agents that have been used in combination with gemcitabine have failed to improve clinical outcomes. This failure may stem from the heterogeneous molecular pathogenesis of pancreatic cancers, which involves several oncogenic pathways and defined genetic mutations.

OBJECTIVE

The aims of this review are: i) to define the existing treatments available at present for patients with pancreatic cancers in the neo-adjuvant, adjuvant, locally advanced and metastatic settings; ii) to highlight the molecular heterogeneity of the cancers and the rationale for targeting specific oncogenic pathways; iii) to give an overview of targeted agents that may potentially have an impact in the treatment of pancreatic cancers.

CONCLUSIONS

Molecular pathogenesis of pancreatic cancer involves several pathways and defined genetic mutations. Targeting these complex molecular pathways with a combination of novel biological and chemotherapeutic agents could potentially improve patient outcome.