Emerging understanding of Bcl-2 biology: Implications for neoplastic progression and treatment

Bcl-2, the founding member of a family of apoptotic regulators, was initially identified as the protein product of a gene that is translocated and overexpressed in greater than 85% of follicular lymphomas (FLs). Thirty years later we now understand that anti-apoptotic Bcl-2 family members modulate the intrinsic apoptotic pathway by binding and neutralizing the mitochondrial permeabilizers Bax and Bak as well as a variety of pro-apoptotic proteins, including the cellular stress sensors Bim, Bid, Puma, Bad, Bmf and Noxa. Despite extensive investigation of all of these proteins, important questions remain. For example, how Bax and Bak breach the outer mitochondrial membrane remains poorly understood. Likewise, how the functions of anti-apoptotic Bcl-2 family members such as eponymous Bcl-2 are affected by phosphorylation or cancer-associated mutations has been incompletely defined. Finally, whether Bcl-2 family members can be successfully targeted for therapeutic advantage is only now being investigated in the clinic. Here we review recent advances in understanding Bcl-2 family biology and biochemistry that begin to address these questions.

Targeting immune checkpoints in unresectable metastatic cutaneous melanoma: a systematic review and meta-analysis of anti-CTLA-4 and anti-PD-1 agents trials

Anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and anti-programmed cell death-1 (PD-1) inhibitors have been shown to significantly improve survival in patients with metastatic cutaneous melanoma. However, there was some heterogeneity as well as some variation in the degree of benefit across studies. We reviewed randomized trials and performed a meta-analysis to determine the efficacy and safety of immune checkpoint inhibitors in comparison with conventional regimens. Eligible studies were limited to randomized controlled trials comparing anti-CTLA-4 or anti-PD-1 inhibitors to chemotherapy or vaccination treatment in adult patients with unresectable cutaneous metastatic melanoma. Progression-free survival (PFS) rate at 6 months was 28.5% versus 17.7% (RR: 0.84, 95% CI: 0.76-0.93), overall survival (OS) rate at 1 year was 51.2% versus 38.8% (RR: 0.72, 95% CI: 0.59-0.88), and overall response rate (ORR) at 6 months was 29.6% versus 17.7% (RR: 0.85, 95% CI: 0.76-0.95) favoring immune check point inhibitors over chemotherapies or vaccination. Immune check point inhibitors were associated with more frequent immune-related adverse events at 13.7% versus 2.4% of treated patients (RR: 6.74, 95% CI: 4.65-9.75). Subgroup analyses demonstrated significant PFS (RR: 0.92 vs. 0.74, P < 0.00001) and ORR (RR: 0.95 vs. 0.76, P = 0.0004) improvement with anti-PD-1 treatment compared to anti-CTLA-4 when each of them was compared to control treatments. Collectively, these results demonstrate that immune checkpoint inhibitors have superior outcomes compared to conventional chemotherapies or vaccination, and support the results of recent randomized trials that showed superior outcomes with anti-PD-1 agents over ipilimumab in unresectable metastatic cutaneous melanoma patients.

Risk of Atrial Fibrillation and Bleeding Diathesis Associated With Ibrutinib Treatment: A Systematic Review and Pooled Analysis of Four Randomized Controlled Trials

BACKGROUND

Clinical trials raised concern that ibrutinib may increase the risk of atrial fibrillation/flutter (Afib/Aflutter) and major bleeding. However, the association has not been statistically validated, and there is no consensus regarding optimal management of anticoagulation among patients receiving ibrutinib who develop Afib/Aflutter. We performed a systematic review and pooled analysis to precisely assess the risk of Afib/Aflutter and bleeding associated with ibrutinib treatment in patients with hematologic malignancies.

PATIENTS AND METHODS

We searched PubMed, EMBASE, Cochrane Database, and meeting abstracts up to May 15, 2016, for randomized controlled trials comparing ibrutinib to chemotherapy, monoclonal antibody, or a combination. Primary outcomes were serious Afib/Aflutter and major bleeding. Secondary outcomes were all-grade Afib/Aflutter and bleeding. We calculated the Mantel-Haenszel risk ratio (RR) and estimated the effect of the treatments using a fixed-effects model.

RESULTS

Ibrutinib treatment was associated with a significantly higher incidence of serious Afib/Aflutter (3.03% vs. 0.80%, RR = 3.80, 95% confidence interval [CI] = 1.56-9.29, P = .003), all-grade Afib/Aflutter (8.18% vs. 0.93%, RR = 8.81, 95% CI = 2.70-28.75, P = .0003), and all-grade bleeding (4.85% vs. 1.55%, RR = 2.93, 95% CI = 1.14-7.52, P = .03) compared to control treatments. The observed between-treatment difference in major bleeding rates was not statistically significant (3.69% vs. 2.13%, RR = 1.72, 95% CI = 0.95-3.11, P = .07). The risk of these adverse events was not different between subgroups on the basis of pathology, treatment setting, dose, and duration of ibrutinib exposure.

CONCLUSION

The risks of Afib/Aflutter and all-grade bleeding were significantly higher in the ibrutinib group. These results indicate the need for vigilant monitoring while the patient is receiving ibrutinib therapy, and careful assessment of the risks and benefits of anticoagulation is required.

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.

Targeting epigenetic pathways in acute myeloid leukemia and myelodysplastic syndrome: a systematic review of hypomethylating agents trials

Background

Aberrant DNA methylation has been identified as a key molecular event regulating the pathogenesis of myelodysplastic syndromes (MDS); myeloid neoplasms with an inherent risk of transformation to acute myeloid leukemia (AML). Based on the above findings, DNA hypomethylating agents (HMA) have been widely used to treat AML and MDS, especially in elderly patients and in those who are not eligible for allogeneic stem cell transplantation (SCT). Our goal was to determine if there is any therapeutic advantage of HMA vs. conventional care regimens (CCR) and indirectly compare the efficacy of azacitidine and decitabine in this patient population.

Methods

Eligible studies were limited to randomized controlled trials comparing HMA to CCR in adult patients with AML or MDS.

Results

Overall survival (OS) rate was 33.2 vs. 21.4 % (RR 0.83, 95 % CI 0.71–0.98) and overall response rate (ORR) 23.7 vs. 13.4 % (RR 0.87, 95 % CI 0.81–0.93) for HMA and CCR, respectively. In subgroup analyses, only azacitidine treatment showed OS improvement (RR 0.75, 95 % CI 0.64–0.98) and not decitabine. Cytogenetic risk or bone marrow blast count did not have independent prognostic impact.

Conclusion

Collectively, these results demonstrate that HMA have superior outcomes compared to CCR and suggest that azacitidine in comparison to decitabine, may be more effective.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0233-2) contains supplementary material, which is available to authorized users.

Assessment of ASC specks as a putative biomarker of pyroptosis in myelodysplastic syndromes: an observational cohort study

BACKGROUND

NLRP3 inflammasome-directed pyroptotic cell death drives ineffective haemopoiesis in myelodysplastic syndromes. During inflammasome assembly, the apoptosis-associated speck-like protein containing a CARD (PYCARD, commonly known as ASC) adaptor protein polymerises into large, filamentous clusters termed ASC specks that are released upon cytolysis. Specks are resistant to proteolytic degradation because of their prion-like structure, and therefore might serve as a biomarker for pyroptotic cell death in myelodysplastic syndromes.

METHODS

This observational cohort study was done at the H Lee Moffitt Cancer Center (Tampa, FL, USA). Patients with myelodysplastic syndromes, healthy controls, and patients with non-myelodysplastic syndrome haematological cancers or type 2 diabetes were recruited. We used confocal and electron microscopy to visualise, and flow cytometry to quantify, ASC specks in peripheral blood and bone marrow plasma samples. Speck percentages were compared by t test or ANOVA, correlations were assessed by Spearman's rank correlation coefficient, and biomarker efficiency was assessed by receiver operating characteristics and area under the curve (AUC) analysis.

FINDINGS

Between Jan 1, 2005, and Jan 12, 2017, we obtained samples from 177 patients with myelodysplastic syndromes and 29 healthy controls for the discovery cohort, and 113 patients with myelodysplastic syndromes and 31 healthy controls for the validation cohort. We also obtained samples from 22 patients with del(5q) myelodysplastic syndromes, 230 patients with non-myelodysplastic syndrome haematological cancers and 23 patients with type 2 diabetes. After adjustment for glucose concentration, the log₁₀-transformed mean percentage of peripheral blood plasma-derived ASC specks was significantly higher in the 177 patients with myelodysplastic syndromes versus the 29 age-matched, healthy donors (-0·41 [SD 0·49] vs -0·67 [0·59], p=0·034). The percentages of ASC specks in samples from patients with myelodysplastic syndromes were significantly greater than those in samples from individuals with every other haematological cancer studied (all p<0·05) except myelofibrosis (p=0·19). The findings were confirmed in the independent validation cohort (p<0·0001). Peripheral blood plasma danger-associated molecular pattern protein S100-A8 and protein S100-A9 concentrations from 144 patients with myelodysplastic syndromes from the discovery cohort directly correlated with ASC speck percentage (r=0·4, p<0·0001 for S100-A8 and r=0·2, p=0·017 for S100-A9). Patients with at least two somatic gene mutations had a significantly greater mean percentage of peripheral blood plasma ASC specks than patients with one or no mutation (-0·22 [SD 0·63] vs -0·53 [0·44], p=0·008). The percentage of plasma ASC specks was a robust marker for pyroptosis in myelodysplastic syndromes (AUC=0·888), in which a cutoff of 0·80 maximised sensitivity at 0·84 (95% CI 0·65-0·91) and specificity at 0·87 (0·58-0·97).

INTERPRETATION

Our results underscore the pathobiological relevance of ASC specks and suggest that ASC specks are a sensitive and specific candidate plasma biomarker that provides an index of medullary pyroptotic cell death and ineffective haemopoiesis in patients with myelodysplastic syndromes.

FUNDING

T32 Training Grant (NIH/NCI 5T32 CA115308-08), Edward P Evans Foundation, The Taub Foundation Grants Program, the Flow Cytometry, Analytic Microscopy, and Tissue Core Facilities at the H Lee Moffitt Cancer Center and Research Institute, a National Cancer Institute-designated Comprehensive Cancer Center (P30-CA076292).

Update on iron metabolism and molecular perspective of common genetic and acquired disorder, hemochromatosis

Iron is an essential component of erythropoiesis and its metabolism is tightly regulated by a variety of internal and external cues including iron storage, tissue hypoxia, inflammation and degree of erythropoiesis. There has been remarkable improvement in our understanding of the molecular mechanisms of iron metabolism past decades. The classical model of iron metabolism with iron response element/iron response protein (IRE/IRP) is now extended to include hepcidin model. Endogenous and exogenous signals funnel down to hepcidin via wide range of signaling pathways including Janus Kinase/Signal Transducer and Activator of Transcription 3 (JAK/STAT3), Bone Morphogenetic Protein/Hemojuvelin/Mothers Against Decapentaplegic Homolog (BMP/HJV/SMAD), and Von Hippel Lindau/Hypoxia-inducible factor/Erythropoietin (VHL/HIF/EPO), then relay to ferroportin, which directly regulates intra- and extracellular iron levels. The successful molecular delineation of iron metabolism further enhanced our understanding of common genetic and acquired disorder, hemochromatosis. The majority of the hereditary hemochromatosis (HH) patients are now shown to have mutations in the genes coding either upstream or downstream proteins of hepcidin, resulting in iron overload. The update on hepcidin centered mechanisms of iron metabolism and their clinical perspective in hemochromatosis will be discussed in this review.

TFEB links MYC signaling to epigenetic control of myeloid differentiation and acute myeloid leukemia

MYC oncoproteins regulate transcription of genes directing cell proliferation, metabolism and tumorigenesis. A variety of alterations drive MYC expression in acute myeloid leukemia (AML) and enforced MYC expression in hematopoietic progenitors is sufficient to induce AML. Here we report that AML and myeloid progenitor cell growth and survival rely on MYC-directed suppression of Transcription Factor EB (TFEB), a master regulator of the autophagy-lysosome pathway. Notably, although originally identified as an oncogene, TFEB functions as a tumor suppressor in AML, where it provokes AML cell differentiation and death. These responses reflect TFEB control of myeloid epigenetic programs, by inducing expression of isocitrate dehydrogenase-1 (IDH1) and IDH2, resulting in global hydroxylation of 5-methycytosine. Finally, activating the TFEB-IDH1/IDH2-TET2 axis is revealed as a targetable vulnerability in AML. Thus, epigenetic control by a MYC-TFEB circuit dictates myeloid cell fate and is essential for maintenance of AML.

Prognostic significance of MYC oncoprotein expression on survival outcome in patients with acute myeloid leukemia with myelodysplasia related changes (AML-MRC)

MYC is an oncoprotein that coordinates the expression of genes involved in metabolism, cell differentiation and survival in various types of malignancies. However, the underlying oncogenic mechanisms and the clinical significance of MYC expression in the acute myeloid leukemia with myelodysplasia related changes (AML-MRC) remain to be answered. A total of 135 patients were retrospectively identified using Total Cancer Care (TCC) Moffitt Cancer Center (MCC) databases. Diagnosis of AML-MRC was based on the 2016 WHO classification utilizing bone marrow (BM) evaluation. MYC protein expression level was assessed by immunohistochemistry (IHC) staining using paraffin-embedded BM trephine biopsy samples obtained at the time of diagnosis or relapse. Concurrent somatic mutations were assessed using targeted next generation sequencing that include 54 genes. A total of 38% (n = 51) and 62% (n = 84) patients had high and low MYC expression, respectively. The most common somatic mutation in our cohort was TP53 followed by DNMT3A, and ASXL1. The median OS was significantly longer in low MYC patients (median OS 42.3 vs. 17.05 months, p = 0.0109). Multivariate analysis including MYC expression level, transplantation status, gender and age demonstrated high MYC expression (HR 1.77, 95% CI 1.004-3.104, p = 0.045) to be an independent poor prognostic factor. Further studies are needed to identify the underlying mechanism of MYC driven oncogenesis in AML-MRC. Additionally, the prognostic impact of MYC on the AML survival in a larger cohort that include diverse somatic mutations and chromosomal abnormalities requires further investigation.

Somatic gene mutations expose cytoplasmic DNA to co-opt the cGAS-STING-NLRP3 axis in Myelodysplastic syndromes

NLRP3 inflammasome and IFN-stimulated gene (ISG) induction are key biological drivers of ineffective hematopoiesis and inflammation in myelodysplastic syndromes (MDSs). Gene mutations involving mRNA splicing and epigenetic regulatory pathways induce inflammasome activation and myeloid lineage skewing in MDSs through undefined mechanisms. Using immortalized murine hematopoietic stem and progenitor cells harboring these somatic gene mutations and primary MDS BM specimens, we showed accumulation of unresolved R-loops and micronuclei with concurrent activation of the cytosolic sensor cyclic GMP-AMP synthase. Cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) signaling caused ISG induction, NLRP3 inflammasome activation, and maturation of the effector protease caspase-1. Deregulation of RNA polymerase III drove cytosolic R-loop generation, which upon inhibition, extinguished ISG and inflammasome response. Mechanistically, caspase-1 degraded the master erythroid transcription factor, GATA binding protein 1, provoking anemia and myeloid lineage bias that was reversed by cGAS inhibition in vitro and in Tet2^–/– hematopoietic stem and progenitor cell–transplanted mice. Together, these data identified a mechanism by which functionally distinct mutations converged upon the cGAS/STING/NLRP3 axis in MDS, directing ISG induction, pyroptosis, and myeloid lineage skewing.

Oxidized Mitochondrial DNA Engages TLR9 to Activate the NLRP3 Inflammasome in Myelodysplastic Syndromes

Myelodysplastic Syndromes (MDSs) are bone marrow (BM) failure malignancies characterized by constitutive innate immune activation, including NLRP3 inflammasome driven pyroptotic cell death. We recently reported that the danger-associated molecular pattern (DAMP) oxidized mitochondrial DNA (ox-mtDNA) is diagnostically increased in MDS plasma although the functional consequences remain poorly defined. We hypothesized that ox-mtDNA is released into the cytosol, upon NLRP3 inflammasome pyroptotic lysis, where it propagates and further enhances the inflammatory cell death feed-forward loop onto healthy tissues. This activation can be mediated via ox-mtDNA engagement of Toll-like receptor 9 (TLR9), an endosomal DNA sensing pattern recognition receptor known to prime and activate the inflammasome propagating the IFN-induced inflammatory response in neighboring healthy hematopoietic stem and progenitor cells (HSPCs), which presents a potentially targetable axis for the reduction in inflammasome activation in MDS. We found that extracellular ox-mtDNA activates the TLR9-MyD88-inflammasome pathway, demonstrated by increased lysosome formation, IRF7 translocation, and interferon-stimulated gene (ISG) production. Extracellular ox-mtDNA also induces TLR9 redistribution in MDS HSPCs to the cell surface. The effects on NLRP3 inflammasome activation were validated by blocking TLR9 activation via chemical inhibition and CRISPR knockout, demonstrating that TLR9 was necessary for ox-mtDNA-mediated inflammasome activation. Conversely, lentiviral overexpression of TLR9 sensitized cells to ox-mtDNA. Lastly, inhibiting TLR9 restored hematopoietic colony formation in MDS BM. We conclude that MDS HSPCs are primed for inflammasome activation via ox-mtDNA released by pyroptotic cells. Blocking the TLR9/ox-mtDNA axis may prove to be a novel therapeutic strategy for MDS.

Outcome Comparison of Allogeneic versus Autologous Stem Cell Transplantation in Transformed Low-Grade Lymphoid Malignancies: A Systematic Review and Pooled Analysis of Comparative Studies

BACKGROUND

Some patients with low-grade lymphoid malignancies develop transformed disease, requiring stem cell transplantation (SCT). SCT outcomes in transformed low-grade lymphoid malignancies may differ from those of nontransformed disease or other aggressive non-Hodgkin lymphomas. We conducted a pooled analysis of the clinical outcomes of allogeneic versus high-dose therapy (HDT) with autologous SCT in adult patients with transformed low-grade lymphoid malignancies.

METHODS

A PubMed, EMBASE, and Cochrane search yielded 4 comparative studies reporting allogeneic versus HDT with autologous SCT outcomes in adults (age ≥18) with transformed low-grade lymphoid malignancies, including follicular, chronic/small lymphocytic, and marginal zone lymphoma. Risk ratio (RR) and 95% CI were calculated using random-effects models.

RESULTS

Rates for overall survival (OS) were 51.0 versus 69.5% (RR = 1.55, 95% CI 1.19-2.02, p = 0.001), rates of relapse were 37.3 versus 35.3% (RR = 1.04, 95% CI 0.70-1.55, p = 0.84), and rates of transplant-related mortality (TRM) were 33.3 versus 7.2% (RR = 4.52, 95% CI 2.75-7.43, p < 0.00001) for allogeneic versus autologous SCT. Previous rituximab treatment, reduced intensity conditioning regimen prior to SCT, or original pathology had no prognostic impact.

CONCLUSION

HDT followed by autologous SCT was associated with lower TRM and a better OS, but there was no difference in relapse versus allogeneic SCT. Autologous SCT may be the better therapeutic option, considering the second chance of allogeneic SCT in the case of relapse.

Blinatumomab-induced donor T-cell activation for post-stem cell transplant-relapsed acute CD19-positive biphenotypic leukemia

Post-stem cell transplantation (SCT) relapsed acute lymphoblastic leukemia (ALL) has extremely poor prognosis with median survival of less than 1 year. Donor lymphocyte infusion, second transplantation, chemotherapy or cytokine treatment have been tried as a salvage regimen without significant clinical benefit. Recently, blinatumomab, a bispecific monoclonal antibody targeting CD3-expressing T cells and CD19-expressing B-cell lineage malignant cells demonstrated promising outcomes in relapsed/refractory ALL patients. Literature on blinatumomab use in biphenotypic ALL along with Philadelphia chromosome positive (Ph+) ALL is limited. We report a case of post-SCT relapsed CD19 expressing biphenotypic lymphoblastic leukemia patient who achieved complete remission after blinatumomab treatment and has lasting remission for 1 year.

Effect of CHK1 Inhibition on CPX-351 Cytotoxicity in vitro and ex vivo

CPX-351 is a liposomally encapsulated 5:1 molar ratio of cytarabine and daunorubicin that recently received regulatory approval for the treatment of therapy-related acute myeloid leukemia (AML) or AML with myelodysplasia-related changes based on improved overall survival compared to standard cytarabine/daunorubicin therapy. Checkpoint kinase 1 (CHK1), which is activated by DNA damage and replication stress, diminishes sensitivity to cytarabine and anthracyclines as single agents, suggesting that CHK1 inhibitors might increase the effectiveness of CPX-351. The present studies show that CPX-351 activates CHK1 as well as the S and G2/M cell cycle checkpoints. Conversely, CHK1 inhibition diminishes the cell cycle effects of CPX-351. Moreover, CHK1 knockdown or addition of a CHK1 inhibitor such as MK-8776, rabusertib or prexasertib enhances CPX-351-induced apoptosis in multiple TP53-null and TP53-wildtype AML cell lines. Likewise, CHK1 inhibition increases the antiproliferative effect of CPX-351 on primary AML specimens ex vivo, offering the possibility that CPX-351 may be well suited to combine with CHK1-targeted agents.

Spontaneous tumour lysis syndrome associated with contrast dye iohexol use in mantle cell lymphoma

We describe a case of a 73-year-old man who presented with right-sided abdominal pain associated with palpable mass. Initial laboratory examination was normal except lactate dehydrogenase level. Subsequent CT image showed situs inversus and splenic mass with multiple lymph nodes enlargement. Biopsy taken from the splenic mass demonstrated mantle cell lymphoma. Staging CT examination was performed with intravenous contrast, and patient developed altered mental status, respiratory failure and acute kidney injury requiring intensive care unit care. Laboratory examination revealed hyperuricaemia, hyperphosphataemia, hyperkalaemia and hypocalcaemia, which are consistent with spontaneous tumour lysis syndrome. The patient was successfully treated with rasburicase and haemodialysis, and completed the first course of chemotherapy without further complications.

Acute renal failure and type B lactic acidosis as first manifestation of extranodal T-cell lymphoblastic lymphoma

We describe a rare case of a 19-year-old male patient with a history of epilepsy and developmental delay who presented with acute renal failure (ARF) and lactic acidosis (LA) as the first manifestation of T-cell lymphoblastic lymphoma. Renal ultrasound and CT of the abdomen showed renal parenchymal infiltration, and renal biopsy demonstrated T-cell lymphoblastic lymphoma. LA, ARF and electrolyte abnormalities were refractory to the initial treatment of bicarbonate infusion and hydration. However, these abnormalities rapidly normalised after the initiation of chemotherapy, suggesting that the LA and ARF were secondary to lymphomatous renal infiltration.

Abstract 3479: CPX-351 (cytarabine:daunorubicin liposome for injection) anti-leukemia activity is potentiated by Chk1 inhibition

Background: Cytarabine and an anthracycline, the mainstay of AML therapy, affords a five-year survival below 30%. Accordingly, there is a continuing need for improved AML therapies. CPX-351 encapsulates within liposomes a fixed 5:1 molar ratio of cytarabine and daunorubicin that is synergistic (in vitro) and markedly improved in anti-leukemic activity (in vivo). Promising evidence of improved remission and survival rates with CPX-351 compared to standard of care treatments has also been observed clinically and a pivotal Phase 3 trial is currently ongoing. Because Chk1 inhibition has been shown to enhance the actions of both cytarabine and anthracyclines, there has been interest in assessing the effect of CPX-351 when combined with Chk1 inhibitors. Here we describe the evaluation of CPX-351 alone and in combination with the Chk1 inhibitors MK-8776 and LY2603618 in AML cell lines and in clinical AML samples ex vivo. Methods: Effects of CPX-351 on Chk1 phosphorylation and cell cycle distribution in the human AML lines U937 and HL-60 were analyzed by immunoblotting and flow cytometry. Effects of Chk1 inhibitors on CPX-351-induced apoptosis were assessed by flow cytometry after propidium iodide staining (DNA cleavage), Hoechst staining (nuclear fragmentation) and colony formation in soft agar (long-term survival). Effects CPX-351 ± MK-8776 on clinical AML samples were assayed using clonogenic assays. Results: Treatment of U937 cells with CPX-351 resulted in phosphorylation of Chk1 on Ser317 and Ser296 (sites of ATR-mediated phosphorylation and autophosphorylation, respectively) as well as S phase slowing consistent with Chk1 activation. Co-treatment of AML cell lines with Chk1 inhibitors + CPX-351 resulted in increased apoptotic morphological changes and DNA fragmentation as well as diminished clonogenic survival compared to CPX-351 alone. The CPX-351/MK-8776 combination displayed enhanced antiproliferative effects against some clinical AML isolates ex vivo compared to CPX-351 alone, with additional assays ongoing. Conclusions: Collectively, these results show that Chk1 inhibition enhances the cytotoxicity of CPX-351 in AML cell lines and some clinical AML samples, offering the possibility that CPX-351 may be well suited for combining with such molecularly targeted agents.

Citation Format: Nicole D. Vincelette, Larry M. Karnitz, Judith E. Karp, Douglas B. Smith, Allan D. Hess, Lawrence D. Mayer, Scott H. Kaufmann. CPX-351 (cytarabine:daunorubicin liposome for injection) anti-leukemia activity is potentiated by Chk1 inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3479. doi:10.1158/1538-7445.AM2015-3479

CDK2-Mediated Upregulation of TNFα as a Mechanism of Selective Cytotoxicity in Acute Leukemia

Although inhibitors of the kinases CHK1, ATR, and WEE1 are undergoing clinical testing, it remains unclear how these three classes of agents kill susceptible cells and whether they utilize the same cytotoxic mechanism. Here we observed that CHK1 inhibition induces apoptosis in a subset of acute leukemia cell lines in vitro, including TP53-null acute myeloid leukemia (AML) and BCR/ABL-positive acute lymphoid leukemia (ALL), and inhibits leukemic colony formation in clinical AML samples ex vivo. In further studies, downregulation or inhibition of CHK1 triggered signaling in sensitive human acute leukemia cell lines that involved CDK2 activation followed by AP1-dependent TNF transactivation, TNFα production, and engagement of a TNFR1- and BID-dependent apoptotic pathway. AML lines that were intrinsically resistant to CHK1 inhibition exhibited high CHK1 expression and were sensitized by CHK1 downregulation. Signaling through this same CDK2-AP1-TNF cytotoxic pathway was also initiated by ATR or WEE1 inhibitors in vitro and during CHK1 inhibitor treatment of AML xenografts in vivo. Collectively, these observations not only identify new contributors to the antileukemic cell action of CHK1, ATR, and WEE1 inhibitors, but also delineate a previously undescribed pathway leading from aberrant CDK2 activation to death ligand-induced killing that can potentially be exploited for acute leukemia treatment. SIGNIFICANCE: This study demonstrates that replication checkpoint inhibitors can kill AML cells through a pathway involving AP1-mediated TNF gene activation and subsequent TP53-independent, TNFα-induced apoptosis, which can potentially be exploited clinically.

MYC overexpression is associated with an early disease progression from MDS to AML

Recent studies demonstrated that MYC epigenetically regulates AML cell survival and differentiation by suppressing IDH1/2-TET2-5hmC signaling and that MYC overexpression is associated with poor survival outcomes in multiple AML patient cohorts. However, the oncogenic roles of MYC in MDS remain to be explored. A total of 41 patients with de novo MDS were retrospectively identified using the Total Cancer Care database at the Moffitt Cancer Center. A total of 61 % of patients had low MYC expression and 39 % of patients had high MYC expression defined as MYC reactivity by immunohistochemical staining in ≥5% of bone marrow (BM) cells at the time of MDS diagnosis. The median MDS-to-AML progression free survival (PFS) was significantly shorter in the high MYC group (median PFS 9.3 vs. 17.7 months, HR = 2.328, p = 0.013). Further, overall survival (OS) was also shorter in the high MYC patients (median OS 19.7 vs. 51.7 months, HR = 2.299, p = 0.053). Multivariate analyses demonstrated that high MYC expression is an independent poor prognostic factor for the MDS-to-AML progression (HR = 2.275, p = 0.046). Our observations indicate that MYC may play a crucial role in MDS transformation to AML and the underlying mechanisms of MYC-driven MDS clonal expansion and leukemic transformation require further investigation.