RNAi screening of the kinome with cytarabine in leukemias

Sequential drug treatment targeting cell cycle and cell fate regulatory programs blocks non-genetic cancer evolution in acute lymphoblastic leukemia

BACKGROUND

Targeted therapies exploiting vulnerabilities of cancer cells hold promise for improving patient outcome and reducing side-effects of chemotherapy. However, efficacy of precision therapies is limited in part because of tumor cell heterogeneity. A better mechanistic understanding of how drug effect is linked to cancer cell state diversity is crucial for identifying effective combination therapies that can prevent disease recurrence.

RESULTS

Here, we characterize the effect of G2/M checkpoint inhibition in acute lymphoblastic leukemia (ALL) and demonstrate that WEE1 targeted therapy impinges on cell fate decision regulatory circuits. We find the highest inhibition of recovery of proliferation in ALL cells with KMT2A-rearrangements. Single-cell RNA-seq and ATAC-seq of RS4;11 cells harboring KMT2A::AFF1, treated with the WEE1 inhibitor AZD1775, reveal diversification of cell states, with a fraction of cells exhibiting strong activation of p53-driven processes linked to apoptosis and senescence, and disruption of a core KMT2A-RUNX1-MYC regulatory network. In this cell state diversification induced by WEE1 inhibition, a subpopulation transitions to a drug tolerant cell state characterized by activation of transcription factors regulating pre-B cell fate, lipid metabolism, and pre-BCR signaling in a reversible manner. Sequential treatment with BCR-signaling inhibitors dasatinib, ibrutinib, or perturbing metabolism by fatostatin or AZD2014 effectively counteracts drug tolerance by inducing cell death and repressing stemness markers.

CONCLUSIONS

Collectively, our findings provide new insights into the tight connectivity of gene regulatory programs associated with cell cycle and cell fate regulation, and a rationale for sequential administration of WEE1 inhibitors with low toxicity inhibitors of pre-BCR signaling or metabolism.

Synergistic interactions of cytarabine-adavosertib in leukemic cell lines proliferation and metabolomic endpoints

Drug synergy allows reduced dosing, side effects and tolerance. Optimization of drug synergy chemotherapy is fundamental in acute lymphocytic leukemia and other cancers. This study aimed to analyze the pharmacodynamic synergy between the anti-metabolite cytarabine and WEE1 inhibitor adavosertib on acute leukemia cell lines CCRF-CEM and Jurkat. In both cell lines analysis of concentration-inhibition curves of adavosertib-cytarabine combinations and synergy matrixes supported mutually synergistic drug interactions. Overall mean ( ± SD) synergy scores were higher in Jurkat than CCRF-CEM: Jurkat, ZIP 22.51 ± 1.1, Bliss 22.49 ± 1.1, HSA 23.44 ± 1.0, Loewe 14.16 ± 1.2; and, CCRF-CEM, ZIP 9.17 ± 1.9, Bliss 8.13 ± 2.1, HSA 11.48 ± 1.9 and Loewe 4.99 ± 1.8. Jurkat also surpassed CCRF-CEM in high-degree synergistic adavosertib-cytarabine interactions with mean across-models synergy values of ∼89.1% ± 2.9 for 63 nM cytarabine-97 nM adavosertib (91.4% inhibition synergy barometer). Combination sensitivity scores scatter plots confirmed combination's synergy efficacy. This combined approach permitted identification and prioritization of 63 nM cytarabine-97 nM adavosertib for multiple endpoints analysis. This combination did not affect PBMC viability, while exhibiting Jurkat selective synergy. Immunoblots also revealed Jurkat selective synergistically increased γH2AX phosphorylation, while CDC2 phosphorylation effects were attributed to adavosertib's WEE1 inhibition. In conclusion, the high synergistic efficacy combination of cytarabine (63 nM) and adavosertib (97 nM) was associated with remarkable alterations in metabolites related to the Krebs cycle in Jurkat. The metabolic pathways and processes are related to gluconeogenesis, amino acids, nucleotides, glutathione, electron transport and Warburg effect. All above relate to cell survival, apoptosis, and cancer progression. Our findings could pave the way for novel biomarkers in treatment, diagnosis, and prognosis of leukemia and other cancers.

Targeting WEE1 kinase as a p53-independent therapeutic strategy in high-risk and relapsed acute lymphoblastic leukemia

BACKGROUND

Outcomes for patients with relapsed acute lymphoblastic leukemia (ALL) are poor and there is a need for novel therapies to improve outcomes. Targeted inhibition of WEE1 with small-molecule inhibitor adavosertib (AZD1775) has emerged as a therapeutic strategy to sensitize cancer cells to DNA-damaging chemotherapeutics, particularly in the context of TP53-mutated tumors. However, WEE1 inhibition as a potential therapeutic strategy for patients with high-risk and relapsed ALL, including those with TP53 mutations, has not been definitively evaluated.

METHODS

Anti-leukemic effects of adavosertib were investigated using a relapsed TP53 isogenic cell model system, primary patient, and patient-derived ALL samples (n = 27) in an ex vivo co-culture model system with bone marrow-derived mesenchymal stem cells. Combination effects with drugs currently used for relapsed ALL were quantified by Excess over Bliss analyses. Investigations for alterations of cell cycle and apoptosis as well as related proteins were examined by flow cytometry and Western blot, respectively.

RESULTS

Our study demonstrates the potent anti-leukemic activity of the clinically advanced WEE1 inhibitor adavosertib in a large majority (n = 18/27) of high-risk and relapsed ALL specimens at lower than clinically attainable concentrations, independent of TP53 mutation status. We show that treatment with adavosertib results in S-phase disruption even in the absence of DNA-damaging agents and that premature mitotic entry is not a prerequisite for its anti-leukemic effects. We further demonstrate that WEE1 inhibition additively and synergistically enhances the anti-leukemic effects of multiple conventional chemotherapeutics used in the relapsed ALL treatment setting. Particularly, we demonstrate the highly synergistic and cytotoxic combination of adavosertib with the nucleoside analog cytarabine and provide mechanistic insights into the combinational activity, showing preferential engagement of apoptotic cell death over cell cycle arrest. Our findings strongly support in vivo interrogation of adavosertib with cytarabine in xenograft models of relapsed and high-risk ALL.

CONCLUSIONS

Together, our data emphasize the functional importance of WEE1 in relapsed ALL cells and show WEE1 as a promising p53-independent therapeutic target for the improved treatment of high-risk and relapsed ALL.

Cyclers' kinases in cell division: from molecules to cancer therapy

Faithful eucaryotic cell division requires spatio-temporal orchestration of multiple sequential events. To ensure the dynamic nature of these molecular and morphological transitions, a swift modulation of key regulatory pathways is necessary. The molecular process that most certainly fits this description is phosphorylation, the post-translational modification provided by kinases, that is crucial to allowing the progression of the cell cycle and that culminates with the separation of two identical daughter cells. In detail, from the early stages of the interphase to the cytokinesis, each critical step of this process is tightly regulated by multiple families of kinases including the Cyclin-dependent kinases (CDKs), kinases of the Aurora, Polo, Wee1 families, and many others. While cell-cycle-related CDKs control the timing of the different phases, preventing replication machinery errors, the latter modulate the centrosome cycle and the spindle function, avoiding karyotypic abnormalities typical of chromosome instability. Such chromosomal abnormalities may result from replication stress (RS) and chromosome mis-segregation and are considered a hallmark of poor prognosis, therapeutic resistance, and metastasis in cancer patients. Here, we discuss recent advances in the understanding of how different families of kinases concur to govern cell cycle, preventing RS and mitotic infidelity. Additionally, considering the growing number of clinical trials targeting these molecules, we review to what extent and in which tumor context cell-cycle-related kinases inhibitors are worth exploiting as an effective therapeutic strategy.

Cytarabine-induced destabilization of MCL1 mRNA and protein triggers apoptosis in leukemia cells

Although cytarabine (Ara-C) is the mainstay of treatment for acute myeloid leukemia (AML), its cytotoxic mechanisms for inducing apoptosis are poorly understood. Therefore, we investigated the Ara-C-induced cell death pathway in human AML U937 cells. Ara-C-induced downregulation of MCL1 is associated with the induction of mitochondrial depolarization and apoptosis. Ara-C triggered NOX4-mediated ROS production, which in turn activated p38 MAPK but inactivated AKT. Ara-C-induced DNA damage modulates p38 MAPK activation without affecting AKT inactivation in U937 cells. Inactivated AKT promotes GSK3β-dependent CREB phosphorylation, which in turn increases NOXA transcription, thereby triggering the degradation of MCL1 protein. Activated p38 MAPK induces HuR downregulation, leading to accelerated MCL1 mRNA turnover. A similar pathway also explains the Ara-C-induced THP-1 cell death. Collectively, our data confirm that Ara-C-triggered apoptosis in the AML cell lines U937 and THP-1 is mediated through the destabilization of MCL1 mRNA and protein. Furthermore, Ara-C acts synergistically with the BCL2 inhibitor ABT-199 to induce cell death in ABT-199-resistant and parental U937 cells by inhibiting MCL1 expression.

Wee1 promotes cell proliferation and imatinib resistance in chronic myeloid leukemia via regulating DNA damage repair dependent on ATM-γH2AX-MDC1

BACKGROUND

The treatment of chronic myeloid leukemia (CML) is facing the dilemma of tyrosine kinase inhibitors (TKIs) resistance and disease recurrence. The dysfunctional DNA damage repair mechanism plays an essential role not only in the initiation and progression of hematological malignancies but also links to the development of TKI resistance. Deciphering the abnormally regulated DNA damage repair and proteins involved brings new insights into the therapy of leukemias. As a G2/M phase checkpoint kinase and a DNA damage repair checkpoint kinase engaged in the DNA damage response (DDR), along with an oncogenic driver present in various cancers, the particular involvement of Wee1 in DNA damage is far from clear. Deciphering its function and targeting it via modulating DNA repair pathways is important for improving our understanding of cancer treatment.

METHODS

Wee1 expression was assessed in cell lines using RT-qPCR and western blot, and Wee1 knockdown efficacy was validated using RT-qPCR, western blot, and immunofluorescence. Wee1 function was investigated by CCK-8, colony formation, and flow cytometry assay in vitro. Wee1 role in DNA repair and its interactions with other proteins were then studied using western blot, immunofluorescence, and double plasmid-repair studies. Finally, the CCK-8 and flow cytometry assay was utilized to investigate Wee1 and imatinib's synergistic effect, and a CML mouse model was constructed to study Wee1's role in carcinogenesis in vivo.

RESULTS

Wee1 was reported to respond quickly to DDR in an ATM-γH2AX-MDC1-dependent way upon DNA double-strand breaks (DSBs) occurrence, and it regulated homologous recombination by stimulating the recruitment of critical proteins RAD51/BRCA1 upon DSB sites. Wee1 was also revealed to be abnormally upregulated in CML cells. Further suppression of Wee1 not only causes cell cycle arrest and inhibits the proliferation of cancer cells but also enhances CML cell sensitivity to Imatinib in vitro and in vivo, possibly through an excessive accumulation of overall DSBs.

CONCLUSION

Wee1 is extensively involved in the DRR signaling and DSB repair pathway. Inhibiting abnormally elevated Wee1 benefits CML therapy in both IM-resistant and IM-sensitive cells. Our data demonstrated that Wee1 participated in promoting cell proliferation and imatinib resistance in chronic myeloid leukemia via regulating DNA damage repair dependent on ATM-γH2AX-MDC1. In the fight against CML, Wee1's dysregulation in the DNA damage repair mechanism of CML pathogenesis makes it a viable therapeutic target in clinical applications.

Targeting the DNA Damage Response for Cancer Therapy by Inhibiting the Kinase Wee1

Cancer cells typically heavily rely on the G2/M checkpoint to survive endogenous and exogenous DNA damage, such as genotoxic stress due to genome instability or radiation and chemotherapy. The key regulator of the G2/M checkpoint, the cyclin-dependent kinase 1 (CDK1), is tightly controlled, including by its phosphorylation state. This posttranslational modification, which is determined by the opposing activities of the phosphatase cdc25 and the kinase Wee1, allows for a more rapid response to cellular stress than via the synthesis or degradation of modulatory interacting proteins, such as p21 or cyclin B. Reducing Wee1 activity results in ectopic activation of CDK1 activity and drives premature entry into mitosis with unrepaired or under-replicated DNA and causing mitotic catastrophe. Here, we review efforts to use small molecule inhibitors of Wee1 for therapeutic purposes, including strategies to combine Wee1 inhibition with genotoxic agents, such as radiation therapy or drugs inducing replication stress, or inhibitors of pathways that show synthetic lethality with Wee1. Furthermore, it become increasingly clear that Wee1 inhibition can also modulate therapeutic immune responses. We will discuss the mechanisms underlying combination treatments identifying both cell intrinsic and systemic anti-tumor activities.

Targeting Wee1 kinase as a therapeutic approach in Hematological Malignancies

Hematologic malignancies include various diseases that develop from hematopoietic stem cells of bone marrow or lymphatic organs. Currently, conventional DNA-damage-based chemotherapy drugs are approved as standard therapeutic regimens for these malignancies. Although many improvements have been made, patients with relapsed or refractory hematological malignancies have a poor prognosis. Therefore, novel and practical therapeutic approaches are required for the treatment of these diseases. Interestingly several studies have shown that targeting Wee1 kinase in the Hematological malignancies, including AML, ALL, CML, CLL, DLBCL, BL, MCL, etc., can be an effective therapeutic strategy. It plays an essential role in regulating the cell cycle process by abrogating the G2-M cell-cycle checkpoint, which provides time for DNA damage repair before mitotic entry. Consistently, Wee1 overexpression is observed in various Hematological malignancies. Also, in healthy normal cells, repairing DNA damages occurs due to G1-S checkpoint function; however, in the cancer cells, which have an impaired G1-S checkpoint, the damaged DNA repair process depends on the G2-M checkpoint function. Thus, Wee1 inhibition could be a promising target in the presence of DNA damage in order to potentiate multiple therapeutic drugs. This review summarized the potentials and challenges of Wee1 inhibition combined with other therapies as a novel effective therapeutic strategy in Hematological malignancies.

Wee1 Kinase: A Potential Target to Overcome Tumor Resistance to Therapy

During the cell cycle, DNA suffers several lesions that need to be repaired prior to entry into mitosis to preserve genome integrity in daughter cells. Toward this aim, cells have developed complex enzymatic machinery, the so-called DNA damage response (DDR), which is able to repair DNA, temporarily stopping the cell cycle to provide more time to repair, or if the damage is too severe, inducing apoptosis. This DDR mechanism is considered the main source of resistance to DNA-damaging therapeutic treatments in oncology. Recently, cancer stem cells (CSCs), which are a small subset of tumor cells, were identified as tumor-initiating cells. CSCs possess self-renewal potential and persistent tumorigenic capacity, allowing for tumor re-growth and relapse. Compared with cancer cells, CSCs are more resistant to therapeutic treatments. Wee1 is the principal gatekeeper for both G2/M and S-phase checkpoints, where it plays a key role in cell cycle regulation and DNA damage repair. From this perspective, Wee1 inhibition might increase the effectiveness of DNA-damaging treatments, such as radiotherapy, forcing tumor cells and CSCs to enter into mitosis, even with damaged DNA, leading to mitotic catastrophe and subsequent cell death.

Discovery of ZN-c3, a Highly Potent and Selective Wee1 Inhibitor Undergoing Evaluation in Clinical Trials for the Treatment of Cancer

Wee1 inhibition has received great attention in the past decade as a promising therapy for cancer treatment. Therefore, a potent and selective Wee1 inhibitor is highly desirable. Our efforts to make safer and more efficacious Wee1 inhibitors led to the discovery of compound 16, a highly selective Wee1 inhibitor with balanced potency, ADME, and pharmacokinetic properties. The chiral ethyl moiety of compound 16 provided an unexpected improvement of Wee1 potency. Compound 16, known as ZN-c3, showed excellent in vivo efficacy and is currently being evaluated in phase 2 clinical trials.

Targeting WEE1 by adavosertib inhibits the malignant phenotypes of hepatocellular carcinoma

Targeting the cell cycle checkpoints and DNA damage response are promising therapeutic strategies for cancer. Adavosertib is a potent inhibitor of WEE1 kinase, which plays a critical role in regulating cell cycle checkpoints. However, the effect of adavosertib on hepatocellular carcinoma (HCC) treatment, including sorafenib-resistant HCC, has not been thoroughly studied. In this study, we comprehensively investigated the efficacy and pharmacology of adavosertib in HCC therapy. Adavosertib effectively inhibited the proliferation of HCC cells in vitro and suppressed tumor growth in HCC xenografts and patient-derived xenograft (PDX) models in vivo. Additionally, adavosertib treatment effectively inhibited the motility of HCC cells by impairing pseudopodia formation. Further, we revealed that adavosertib induced DNA damage and premature mitosis entrance by disturbing the cell cycle. Thus, HCC cells accumulating DNA damage underwent mitosis without G2/M checkpoint arrest, thereby leading to mitotic catastrophe and apoptosis under adavosertib administration. Given that sorafenib resistance is common in HCC in clinical practice, we also explored the efficacy of adavosertib in sorafenib-resistant HCC. Notably, adavosertib still showed a desirable inhibitory effect on the growth of sorafenib-resistant HCC cells. Adavosertib markedly induced G2/M checkpoint arrest and cell apoptosis in a dose-dependent manner, confirming the similar efficacy of adavosertib in sorafenib-resistant HCC. Collectively, our results highlight the treatment efficacy of adavosertib in HCC regardless of sorafenib resistance, providing insights into exploring novel strategies for HCC therapy.

Cell cycle inhibitors for the treatment of acute myeloid leukemia: a review of phase 2 & 3 clinical trials

Introduction: Acute myeloid leukemia (AML) is a clinically heterogeneous hematologic malignancy with poor long term outcomes. Cytotoxic chemotherapy remains the backbone of therapy especially among younger patients; however the effective incorporation of targeted therapies continues to be an area of active research in an effort to improve response durations and survival. Cell cycle inhibitors (CCI) are a novel class of agents which may be of particular interest for development in patients with AML. Areas covered: We will review the concept of CCIs along with available pre-clinical and clinical data in the treatment of AML both in North America and abroad. Specific drug targets reviewed include cyclin D kinase, Aurora kinase, CHK1, and WEE1. Expert opinion: Utilization of CCIs in patients with AML is an emerging approach that has shown promise in pre-clinical models. It has been challenging to translate this concept into clinical success thus far, due to marginal single-agent activity and significant toxicity profiles, however clinical evaluation is ongoing. Addition of these agents to cytotoxic chemotherapy and other targeted therapies provides a potential combinatorial path forward for this novel class of therapies. Developing optimal combinations while balancing toxicity are among the top clinical challenges that must be overcome before we can anticipate adoption of these agents into the armamentarium of AML therapy.

A WEE1 family business: regulation of mitosis, cancer progression, and therapeutic target

The inhibition of the DNA damage response (DDR) pathway in the treatment of cancer has recently gained interest, and different DDR inhibitors have been developed. Among them, the most promising ones target the WEE1 kinase family, which has a crucial role in cell cycle regulation and DNA damage identification and repair in both nonmalignant and cancer cells. This review recapitulates and discusses the most recent findings on the biological function of WEE1/PKMYT1 during the cell cycle and in the DNA damage repair, with a focus on their dual role as tumor suppressors in nonmalignant cells and pseudo-oncogenes in cancer cells. We here report the available data on the molecular and functional alterations of WEE1/PKMYT1 kinases in both hematological and solid tumors. Moreover, we summarize the preclinical information on 36 chemo/radiotherapy agents, and in particular their effect on cell cycle checkpoints and on the cellular WEE1/PKMYT1-dependent response. Finally, this review outlines the most important pre-clinical and clinical data available on the efficacy of WEE1/PKMYT1 inhibitors in monotherapy and in combination with chemo/radiotherapy agents or with other selective inhibitors currently used or under evaluation for the treatment of cancer patients.

Therapeutic Target Discovery Using High-Throughput Genetic Screens in Acute Myeloid Leukemia

The development of high-throughput gene manipulating tools such as short hairpin RNA (shRNA) and CRISPR/Cas9 libraries has enabled robust characterization of novel functional genes contributing to the pathological states of the diseases. In acute myeloid leukemia (AML), these genetic screen approaches have been used to identify effector genes with previously unknown roles in AML. These AML-related genes centralize alongside the cellular pathways mediating epigenetics, signaling transduction, transcriptional regulation, and energy metabolism. The shRNA/CRISPR genetic screens also realized an array of candidate genes amenable to pharmaceutical targeting. This review aims to summarize genes, mechanisms, and potential therapeutic strategies found via high-throughput genetic screens in AML. We also discuss the potential of these findings to instruct novel AML therapies for combating drug resistance in this genetically heterogeneous disease.

Preclinical evaluation of the combination of AZD1775 and irinotecan against selected pediatric solid tumors: A Pediatric Preclinical Testing Consortium report

INTRODUCTION

WEE1 is a serine kinase central to the G₂ checkpoint. Inhibition of WEE1 can lead to cell death by permitting cell-cycle progression despite unrepaired DNA damage. AZD1775 is a WEE1 inhibitor that is in clinical development for children and adults with cancer.

METHODS

AZD1775 was tested using a dose of 120 mg/kg administered orally for days 1 to 5. Irinotecan was administered intraperitoneally at a dose of 2.5 mg/kg for days 1 to 5 (one hour after AZD1775 when used in combination). AZD1775 and irinotecan were studied alone and in combination in neuroblastoma (n = 3), osteosarcoma (n = 4), and Wilms tumor (n = 3) xenografts.

RESULTS

AZD1775 as a single agent showed little activity. Irinotecan induced objective responses in two neuroblastoma lines (PRs), and two Wilms tumor models (CR and PR). The combination of AZD1775 + irinotecan-induced objective responses in two neuroblastoma lines (PR and CR) and all three Wilms tumor lines (CR and 2 PRs). The objective response measure improved compared with single-agent treatment for one neuroblastoma (PR to CR), two osteosarcoma (PD1 to PD2), and one Wilms tumor (PD2 to PR) xenograft lines. Of note, the combination yielded CR (n = 1) and PR (n = 2) in all the Wilms tumor lines. The event-free survival was significantly longer for the combination compared with single-agent irinotecan in all models tested. The magnitude of the increase was greatest in osteosarcoma and Wilms tumor xenografts.

CONCLUSIONS

AZD1775 potentiates the effects of irinotecan across most of the xenograft lines tested, with effect size appearing to vary across tumor panels.

Increased HDAC Activity and c-MYC Expression Mediate Acquired Resistance to WEE1 Inhibition in Acute Leukemia

WEE1 is a cell cycle and DNA damage response kinase that is emerging as a therapeutic target for cancer. AZD1775 is a small molecule inhibitor of WEE1, currently in early phase clinical trials as a single agent and in combination with more conventional anti-neoplastic agents. As resistance to kinase inhibitors is frequent, we sought to identify mechanisms of resistance to WEE1 inhibition in acute leukemia. We found that AZD1775 resistant cell lines are dependent upon increased HDAC activity for their survival, in part due to increased KDM5A activity. In addition, gene expression analyses demonstrate HDAC dependent increase in MYC expression and c-MYC activity in AZD1775 treated resistant cells. Overexpression of c-MYC confers resistance to AZD1775 in cell lines with low baseline expression. Pharmacologic inhibition of BRD4, and thereby c-MYC, partially abrogated resistance to AZD1775. Thus, acquired resistance to WEE1 inhibition may be reversed by HDAC or BRD4 inhibition in leukemia cells.

Transcriptional Silencing of MCL-1 Through Cyclin-Dependent Kinase Inhibition in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common adult acute leukemia. Survival remains poor, despite decades of scientific advances. Cytotoxic induction chemotherapy regimens are standard-of-care for most patients. Many investigations have highlighted the genomic heterogeneity of AML, and several new targeted therapeutic options have recently been approved. Additional novel therapies are showing promising clinical results and may rapidly transform the therapeutic landscape of AML. Despite the emerging clinical success of B-cell lymphoma (BCL)-2 targeting in AML and a large body of preclinical data supporting myeloid leukemia cell (MCL)-1 as an attractive therapeutic target for AML, MCL-1 targeting remains relatively unexplored, although novel MCL-1 inhibitors are under clinical investigation. Inhibitors of cyclin-dependent kinases (CDKs) involved in the regulation of transcription, CDK9 in particular, are being investigated in AML as a strategy to target MCL-1 indirectly. In this article, we review the basis for CDK inhibition in oncology with a focus on relevant preclinical mechanism-of-action studies of CDK9 inhibitors in the context of their therapeutic potential specifically in AML.

Challenges and Opportunities for Childhood Cancer Drug Development

Cancer in children is rare with approximately 15,700 new cases diagnosed in the United States annually. Through use of multimodality therapy (surgery, radiation therapy, and aggressive chemotherapy), 70% of patients will be "cured" of their disease, and 5-year event-free survival exceeds 80%. However, for patients surviving their malignancy, therapy-related long-term adverse effects are severe, with an estimated 50% having chronic life-threatening toxicities related to therapy in their fourth or fifth decade of life. While overall intensive therapy with cytotoxic agents continues to reduce cancer-related mortality, new understanding of the molecular etiology of many childhood cancers offers an opportunity to redirect efforts to develop effective, less genotoxic therapeutic options, including agents that target oncogenic drivers directly, and the potential for use of agents that target the tumor microenvironment and immune-directed therapies. However, for many high-risk cancers, significant challenges remain.

FLT3-ITD cooperates with Rac1 to modulate the sensitivity of leukemic cells to chemotherapeutic agents via regulation of DNA repair pathways

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm, and patients with an internal tandem duplication (ITD) mutation of the FMS-like tyrosine kinase-3 (FLT3) receptor gene have a poor prognosis. FLT3-ITD interacts with DOCK2, a G effector protein that activates Rac1/2. Previously, we showed that knockdown of DOCK2 leads to decreased survival of FLT3-ITD leukemic cells. We further investigated the mechanisms by which Rac1/DOCK2 activity affects cell survival and chemotherapeutic response in FLT3-ITD leukemic cells. Exogenous expression of FLT3-ITD led to increased Rac1 activity, reactive oxygen species, phosphorylated STAT5, DNA damage response factors and cytarabine resistance. Conversely, DOCK2 knockdown resulted in a decrease in these factors. Consistent with the reduction in DNA damage response factors, FLT3-ITD cells with DOCK2 knockdown exhibited significantly increased sensitivity to DNA damage response inhibitors. Moreover, in a mouse model of FLT3-ITD AML, animals treated with the CHK1 inhibitor MK8776 + cytarabine survived longer than those treated with cytarabine alone. These findings suggest that FLT3-ITD and Rac1 activity cooperatively modulate DNA repair activity, the addition of DNA damage response inhibitors to conventional chemotherapy may be useful in the treatment of FLT3-ITD AML, and inhibition of the Rac signaling pathways via DOCK2 may provide a novel and promising therapeutic target for FLT3-ITD AML.

SETD2 mutations confer chemoresistance in acute myeloid leukemia partly through altered cell cycle checkpoints

SETD2, an epigenetic tumor suppressor, is frequently mutated in MLL-rearranged (MLLr) leukemia and relapsed acute leukemia (AL). To clarify the impact of SETD2 mutations on chemotherapy sensitivity in MLLr leukemia, two loss-of-function (LOF) Setd2-mutant alleles (Setd2^F2478L/WT or Setd2^Ex6-KO/WT) were generated and introduced, respectively, to the Mll-Af9 knock-in leukemia mouse model. Both alleles cooperated with Mll-Af9 to accelerate leukemia development that resulted in resistance to standard Cytarabine-based chemotherapy. Mechanistically, Setd2-mutant leukemic cells showed downregulated signaling related to cell cycle progression, S, and G2/M checkpoint regulation. Thus, after Cytarabine treatment, Setd2-mutant leukemic cells exit from the S phase and progress to the G2/M phase. Importantly, S and G2/M cell cycle checkpoint inhibition could resensitize the Mll-Af9/Setd2 double-mutant cells to standard chemotherapy by causing DNA replication collapse, mitotic catastrophe, and increased cell death. These findings demonstrate that LOF SETD2 mutations confer chemoresistance on AL to DNA-damaging treatment by S and G2/M checkpoint defects. The combination of S and G2/M checkpoint inhibition with chemotherapy can be explored as a promising therapeutic strategy by exploiting their unique vulnerability and resensitizing chemoresistant AL with SETD2 or SETD2-like epigenetic mutations.

Targeting WEE1 to enhance conventional therapies for acute lymphoblastic leukemia

BACKGROUND

Despite the recent progress that has been made in the understanding and treatment of acute lymphoblastic leukemia (ALL), the outcome is still dismal in adult ALL cases. Several studies in solid tumors identified high expression of WEE1 kinase as a poor prognostic factor and reported its role as a cancer-conserving oncogene that protects cancer cells from DNA damage. Therefore, the targeted inhibition of WEE1 kinase has emerged as a rational strategy to sensitize cancer cells to antineoplastic compounds, which we evaluate in this study.

METHODS

The effectiveness of the selective WEE1 inhibitor AZD-1775 as a single agent and in combination with different antineoplastic agents in B and T cell precursor ALL (B/T-ALL) was evaluated in vitro and ex vivo studies. The efficacy of the compound in terms of cytotoxicity, induction of apoptosis, and changes in gene and protein expression was assessed using different B/T-ALL cell lines and confirmed in primary ALL blasts.

RESULTS

We showed that WEE1 was highly expressed in adult primary ALL bone marrow and peripheral blood blasts (n = 58) compared to normal mononuclear cells isolated from the peripheral blood of healthy donors (p = 0.004). Thus, we hypothesized that WEE1 could be a rational target in ALL, and its inhibition could enhance the cytotoxicity of conventional therapies used for ALL. We evaluated the efficacy of AZD-1775 as a single agent and in combination with several antineoplastic agents, and we elucidated its mechanisms of action. AZD-1775 reduced cell viability in B/T-ALL cell lines by disrupting the G2/M checkpoint and inducing apoptosis. These findings were confirmed in human primary ALL bone marrow and peripheral blood blasts (n = 15). In both cell lines and primary leukemic cells, AZD-1775 significantly enhanced the efficacy of several tyrosine kinase inhibitors (TKIs) such as bosutinib, imatinib, and ponatinib, and of chemotherapeutic agents (clofarabine and doxorubicin) in terms of the reduction of cell viability, apoptosis induction, and inhibition of proliferation.

CONCLUSIONS

Our data suggest that WEE1 plays a role in ALL blast's survival and is a bona fide target for therapeutic intervention. These data support the evaluation of the therapeutic potential of AZD-1775 as chemo-sensitizer agent for the treatment of B/T-ALL.

Development of Potent Pyrazolopyrimidinone-Based WEE1 Inhibitors with Limited Single-Agent Cytotoxicity for Cancer Therapy

WEE1 kinase regulates the G₂ /M cell-cycle checkpoint, a critical mechanism for DNA repair in cancer cells that can confer resistance to DNA-damaging agents. We previously reported a series of pyrazolopyrimidinones based on AZD1775, a known WEE1 inhibitor, as an initial investigation into the structural requirements for WEE1 inhibition. Our lead inhibitor demonstrated WEE1 inhibition in the same nanomolar range as AZD1775, and potentiated the effects of cisplatin in medulloblastoma cells, but had reduced single-agent cytotoxicity. These results prompted the development of a more comprehensive series of WEE1 inhibitors. Herein we report a series of pyrazolopyrimidinones and identify a more potent WEE1 inhibitor than AZD1775 and additional compounds that demonstrate that WEE1 inhibition can be achieved with reduced single-agent cytotoxicity. These studies support that WEE1 inhibition can be uncoupled from the potent cytotoxic effects observed with AZD1775, and this may have important ramifications in the clinical setting where WEE1 inhibitors are used as chemosensitizers for DNA-targeted chemotherapy.

STK3 is a therapeutic target for a subset of acute myeloid leukemias

Acute myeloid leukemia (AML) is characterized by uncontrolled proliferation and accumulation of immature myeloblasts, which impair normal hematopoiesis. While this definition categorizes the disease into a distinctive group, the large number of different genetic and epigenetic alterations actually suggests that AML is not a single disease, but a plethora of malignancies. Still, most AML patients are not treated with targeted medication but rather by uniform approaches such as chemotherapy. The identification of novel treatment options likely requires the identification of cancer cell vulnerabilities that take into account the different genetic and epigenetic make-up of the individual tumors. Here we show that STK3 depletion by knock-down, knock-out or chemical inhibition results in apoptotic cells death in some but not all AML cell lines and primary cells tested. This effect is mediated by a premature activation of cyclin dependent kinase 1 (CDK1) in presence of elevated cyclin B1 levels. The anti-leukemic effects seen in both bulk and progenitor AML cells suggests that STK3 might be a promising target in a subset of AML patients.

New therapeutic strategies to treat human cancers expressing mutant p53 proteins

The tumor suppressor p53 plays a critical role to preserve DNA fidelity from diverse insults through the regulation of cell-cycle checkpoints, DNA repair, senescence and apoptosis. The TP53 is the most frequently inactivated gene in human cancers. This leads to the production of mutant p53 proteins that loose wild-type p53 tumor suppression functions and concomitantly acquire new oncogenic properties among which deregulated cell proliferation, increased chemoresistance, disruption of tissue architecture, promotion of migration, invasion and metastasis and several other pro-oncogenic activities. Mouse models show that the genetic reconstitution of the wild type p53 tumor suppression functions rescues tumor growth. This strongly supports the notion that either restoring wt-p53 activity or inhibiting mutant p53 oncogenic activity could provide an efficient strategy to treat human cancers. In this review we briefly summarize recent advances in the study of small molecules and compounds that subvert oncogenic activities of mutant p53 protein into wt-p53 tumor suppressor functions. We highlight inhibitors of signaling pathways aberrantly modulated by oncogenic mutant p53 proteins as promising therapeutic strategies. Finally, we consider the clinical applications of compounds targeting mutant p53 and the use of currently available drugs in the treatment of tumors expressing mutant p53 proteins.

In Vitro High-Throughput RNAi Screening to Accelerate the Process of Target Identification and Drug Development

High-throughput RNA interference (HT-RNAi) is a powerful tool that can be used to knock down gene expression in order to identify novel genes and pathways involved in many cellular processes. It is a systematic, yet unbiased, approach to identify essential or synthetic lethal genes that promote cell survival in diseased cells as well as genes that confer resistance or sensitivity to drug treatment. This information serves as a foundation for enhancing current treatments for cancer and other diseases by identifying new drug targets, uncovering potential combination therapies, and helping clinicians match patients with the most effective treatment based on genetic information. Here, we describe the method of performing an in vitro HT-RNAi screen using chemically synthesized siRNA.

Regulation of G2/M Transition by Inhibition of WEE1 and PKMYT1 Kinases

In the cell cycle, there are two checkpoint arrests that allow cells to repair damaged DNA in order to maintain genomic integrity. Many cancer cells have defective G1 checkpoint mechanisms, thus depending on the G2 checkpoint far more than normal cells. G2 checkpoint abrogation is therefore a promising concept to preferably damage cancerous cells over normal cells. The main factor influencing the decision to enter mitosis is a complex composed of Cdk1 and cyclin B. Cdk1/CycB is regulated by various feedback mechanisms, in particular inhibitory phosphorylations at Thr14 and Tyr15 of Cdk1. In fact, Cdk1/CycB activity is restricted by the balance between WEE family kinases and Cdc25 phosphatases. The WEE kinase family consists of three proteins: WEE1, PKMYT1, and the less important WEE1B. WEE1 exclusively mediates phosphorylation at Tyr15, whereas PKMYT1 is dual-specific for Tyr15 as well as Thr14. Inhibition by a small molecule inhibitor is therefore proposed to be a promising option since WEE kinases bind Cdk1, altering equilibria and thus affecting G2/M transition.

Understanding the molecular basis of acute myeloid leukemias: where are we now?

Although the treatment modalities for acute myeloid leukemia (AML) have not changed much over the past 40 years, distinct progress has been made in deciphering the basic biology underlying the pathogenesis of this group of hematological disorders. Studies show that AML development is a multicause, multistep and multipathway process. Accordingly, AMLs constitute a heterogeneous group of diseases. The thorough understanding of the molecular basis of AML is paving the way for better therapeutic approaches. Multiple novel drugs are being introduced and new, more efficient and less toxic formulations of conventional therapeutics are becoming available. Here, we review the recent advances in the comprehension of the molecular processes that lead to the onset of AML and its translation into clinical practice.

Increased activity of both CDK1 and CDK2 is necessary for the combinatorial activity of WEE1 inhibition and cytarabine

Inhibition of WEE1 is emerging as a promising chemosensitization strategy in many cancers including acute leukemia. Our lab and others have demonstrated that a small-molecule inhibitor of WEE1, AZD1775, sensitizes acute leukemia cells to cytarabine; however, a mechanism of combinatorial activity has remained elusive. Thus, we sought to determine the relative contribution of WEE1 targets CDK1 and CDK2 to the combinatorial activity of AZD1775 and cytarabine. To accomplish this, we expressed "WEE1 resistant" CDK1 (CDK1-AF) and CDK2 (CDK2-AF) constructs in a T-ALL cell line. Expression of CDK1/2-AF together, but neither alone, enhanced the anti-proliferative effects, DNA damage and apoptosis induced by cytarabine. Furthermore, pharmacologic inhibition of CDK1 alone or CDK1 and CDK2 together reduced the combinatorial activity of AZD1775 and cytarabine. Thus, increased activity of both CDK1 and CDK2 in response to WEE1 inhibition is necessary for the combinatorial activity of AZD1775 and cytarabine. This suggests the role of WEE1 in cells with accumulated DNA damage extends beyond regulation of CDK1 and the G2/M checkpoint and highlights the importance of WEE1 in mediating progression through the cell cycle.

Recent Advances of Cell-Cycle Inhibitor Therapies for Pediatric Cancer

This review describes the pivotal roles of cell-cycle and checkpoint regulators and discusses development of specific cell-cycle inhibitors for therapeutic use for pediatric cancer. The mechanism of action as well as the safety and tolerability of drugs in pediatric patients, including compounds that target CDK4/CDK6 (palbociclib, ribociclib, and abemaciclib), aurora kinases (AT9283 and MLN8237), Wee1 kinase (MK-1775), KSP (ispinesib), and tubulin (taxanes, vinca alkaloids), are presented. The design of mechanism-based combinations that exploit the cross-talk of signals activated by cell-cycle arrest, as well as pediatric-focused drug development, are critical for the advancement of drugs for rare childhood diseases. Cancer Res; 77(23); 6489-98. ©2017 AACR.

Randomized phase II trial of cytosine arabinoside with and without the CHK1 inhibitor MK-8776 in relapsed and refractory acute myeloid leukemia

PURPOSE

Cytosine arabinoside (AraC) remains the backbone of most treatment regimens for acute myeloid leukemia (AML). Incorporation of AraC into DNA activates checkpoint kinase 1 (Chk1), leading to cell-cycle arrest and diminished AraC cytotoxicity, which can be reversed by the selective Chk1 inhibitor MK-8776. Building on a Phase I trial, we conducted a phase II trial comparing timed sequential AraC with or without MK-8776.

METHODS

Patients with relapsed or primary refractory AML were randomized 1:1 to receive either AraC with MK-8776 (Arm A); or AraC alone (Arm B).

RESULTS

32 patients were treated: 14 assigned to Arm A and 18 to Arm B. There were 5 (36%) complete responses (CR/CRi) and 1 (7%) partial response (PR) in Arm A, and 8 (44%) CR/CRis and 1 (6%) PR in Arm B. Median survival did not differ significantly between the two groups (5.9months in Arm A vs. 4.5 months in Arm B). MK-8776 led to a robust increase in DNA damage in circulating leukemic blasts as measured by increased γ-H2AX (16.9%±6.1% prior and 36.4%±6.8% at one hour after MK-8776 infusion, p=0.016).

CONCLUSION

Response rates and survival were similar between the two groups in spite of evidence that MK-8776 augmented DNA damage in circulating leukemic blasts. Better than expected results in the control arm using timed sequential AraC and truncated patient enrollment may have limited the ability to detect clinical benefit from the combination.

Association of Therapy for Autoimmune Disease With Myelodysplastic Syndromes and Acute Myeloid Leukemia

Importance

Therapy-related myeloid neoplasms are a potentially life-threatening consequence of treatment for autoimmune disease (AID) and an emerging clinical phenomenon.

Objective

To query the association of cytotoxic, anti-inflammatory, and immunomodulating agents to treat patients with AID with the risk for developing myeloid neoplasm.

Design, Setting, and Participants

This retrospective case-control study and medical record review included 40 011 patients with an International Classification of Diseases, Ninth Revision, coded diagnosis of primary AID who were seen at 2 centers from January 1, 2004, to December 31, 2014; of these, 311 patients had a concomitant coded diagnosis of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Eighty-six cases met strict inclusion criteria. A case-control match was performed at a 2:1 ratio.

Main Outcomes and Measures

Odds ratio (OR) assessment for AID-directed therapies.

Results

Among the 86 patients who met inclusion criteria (49 men [57%]; 37 women [43%]; mean [SD] age, 72.3 [15.6] years), 55 (64.0%) had MDS, 21 (24.4%) had de novo AML, and 10 (11.6%) had AML and a history of MDS. Rheumatoid arthritis (23 [26.7%]), psoriasis (18 [20.9%]), and systemic lupus erythematosus (12 [14.0%]) were the most common autoimmune profiles. Median time from onset of AID to diagnosis of myeloid neoplasm was 8 (interquartile range, 4-15) years. A total of 57 of 86 cases (66.3%) received a cytotoxic or an immunomodulating agent. In the comparison group of 172 controls (98 men [57.0%]; 74 women [43.0%]; mean [SD] age, 72.7 [13.8] years), 105 (61.0%) received either agent (P = .50). Azathioprine sodium use was observed more frequently in cases (odds ratio [OR], 7.05; 95% CI, 2.35- 21.13; P < .001). Notable but insignificant case cohort use among cytotoxic agents was found for exposure to cyclophosphamide (OR, 3.58; 95% CI, 0.91-14.11) followed by mitoxantrone hydrochloride (OR, 2.73; 95% CI, 0.23-33.0). Methotrexate sodium (OR, 0.60; 95% CI, 0.29-1.22), mercaptopurine (OR, 0.62; 95% CI, 0.15-2.53), and mycophenolate mofetil hydrochloride (OR, 0.66; 95% CI, 0.21-2.03) had favorable ORs that were not statistically significant. No significant association between a specific length of time of exposure to an agent and the drug's category was observed.

Conclusions and Relevance

In a large population with primary AID, azathioprine exposure was associated with a 7-fold risk for myeloid neoplasm. The control and case cohorts had similar systemic exposures by agent category. No association was found for anti-tumor necrosis factor agents. Finally, no timeline was found for the association of drug exposure with the incidence in development of myeloid neoplasm.

Emerging cell cycle inhibitors for acute myeloid leukemia

INTRODUCTION

AML therapy remains very challenging despite our increased understanding of its molecular heterogeneity. Outcomes with chemotherapy and targeted therapy remain poor. Targeting cell cycle regulators might complement chemotherapy and targeted therapy and help in improving outcomes. Areas covered: Here we cover the pre-clinical and clinical data for both for cyclin dependent kinase (CDK) and cell-cycle checkpoint inhibitors. While CDK inhibition can inhibit proliferation, checkpoint inhibitors can facilitate cell cycle progression in presence of DNA damage and can induce mitotic catastrophe. Expert opinion: Though the preclinical data for cell cycle inhibitors in AML is compelling, the clinical translation so far has proven to be challenging. This is a reflection of the complexity of both, AML and cell cycle regulators. However, early introduction of cell-cycle active agents in combination with chemotherapy or targeted agents, identifying right sequence of use and identifying right biomarkers might pave the way into successful clinical translation.

The cell cycle checkpoint inhibitors in the treatment of leukemias

The inhibition of the DNA damage response (DDR) pathway in the treatment of cancers has recently reached an exciting stage with several cell cycle checkpoint inhibitors that are now being tested in several clinical trials in cancer patients. Although the great amount of pre-clinical and clinical data are from the solid tumor experience, only few studies have been done on leukemias using specific cell cycle checkpoint inhibitors. This review aims to summarize the most recent data found on the biological mechanisms of the response to DNA damages highlighting the role of the different elements of the DDR pathway in normal and cancer cells and focusing on the main genetic alteration or aberrant gene expression that has been found on acute and chronic leukemias. This review, for the first time, outlines the most important pre-clinical and clinical data available on the efficacy of cell cycle checkpoint inhibitors in single agent and in combination with different agents normally used for the treatment of acute and chronic leukemias.

Identification of Interleukin-1 by Functional Screening as a Key Mediator of Cellular Expansion and Disease Progression in Acute Myeloid Leukemia

Secreted proteins in the bone marrow microenvironment play critical roles in acute myeloid leukemia (AML). Through an ex vivo functional screen of 94 cytokines, we identified that the pro-inflammatory cytokine interleukin-1 (IL-1) elicited profound expansion of myeloid progenitors in ∼67% of AML patients while suppressing the growth of normal progenitors. Levels of IL-1β and IL-1 receptors were increased in AML patients, and silencing of the IL-1 receptor led to significant suppression of clonogenicity and in vivo disease progression. IL-1 promoted AML cell growth by enhancing p38MAPK phosphorylation and promoting secretion of various other growth factors and inflammatory cytokines. Treatment with p38MAPK inhibitors reversed these effects and recovered normal CD34+ cells from IL-1-mediated growth suppression. These results highlight the importance of ex vivo functional screening to identify common and actionable extrinsic pathways in genetically heterogeneous malignancies and provide impetus for clinical development of IL-1/IL1R1/p38MAPK pathway-targeted therapies in AML.

Mechanisms responsible for the synergistic antileukemic interactions between ATR inhibition and cytarabine in acute myeloid leukemia cells

Acute myeloid leukemia (AML) continues to be a challenging disease to treat, thus new treatment strategies are needed. In this study, we investigated the antileukemic effects of ATR inhibition alone or combined with cytarabine in AML cells. Treatment with the ATR-selective inhibitor AZ20 caused proliferation inhibition in AML cell lines and primary patient samples. It partially abolished the G2 cell cycle checkpoint and caused DNA replication stress and damage, accompanied by CDK1-independent apoptosis and downregulation of RRM1 and RRM2. AZ20 synergistically enhanced cytarabine-induced proliferation inhibition and apoptosis, abolished cytarabine-induced S and G2/M cell cycle arrest, and cooperated with cytarabine in inducing DNA replication stress and damage in AML cell lines. These key findings were confirmed with another ATR-selective inhibitor AZD6738. Therefore, the cooperative induction of DNA replication stress and damage by ATR inhibition and cytarabine, and the ability of ATR inhibition to abrogate the G2 cell cycle checkpoint both contributed to the synergistic induction of apoptosis and proliferation inhibition in AML cell lines. Synergistic antileukemic interactions between AZ20 and cytarabine were confirmed in primary AML patient samples. Our findings provide insight into the mechanism of action underlying the synergistic antileukemic activity of ATR inhibition in combination with cytarabine in AML.

Synergistic anti-leukemic interactions between panobinostat and MK-1775 in acute myeloid leukemia ex vivo

MK-1775 is the first-in-class selective Wee1 inhibitor which has been demonstrated to synergize with CHK1 inhibitors in various malignancies. In this study, we report that the pan-histone deacetylase inhibitor (HDACI) panobinostat synergizes with MK-1775 in acute myeloid leukemia (AML), a malignancy which remains a clinical challenge and requires more effective therapies. Using both AML cell line models and primary patient samples, we demonstrated that panobinostat and MK-1775 synergistically induced proliferation arrest and cell death. We also demonstrated that panobinostat had equal anti-leukemic activities against primary AML blasts derived from patients either at initial diagnosis or at relapse. Interestingly, treatment with panobinostat alone or in combination with MK-1775 resulted in decreased Wee1 protein levels as well as downregulation of the CHK1 pathway. shRNA knockdown of CHK1 significantly sensitized AML cells to MK-1775 treatment, while knockdown of Wee1 significantly enhanced both MK-1775- and panobinostat-induced cell death. Our results demonstrate that panobinostat synergizes with MK-1775 in AML cells, at least in part through downregulation of CHK1 and/or Wee1, providing compelling evidence for the clinical development of the combination treatment in AML.

Targeting WEE1 Kinase in Cancer

WEE1 kinase plays a crucial role in the G2-M cell-cycle checkpoint arrest for DNA repair before mitotic entry. Normal cells repair damaged DNA during G1 arrest; however, cancer cells often have a deficient G1-S checkpoint and depend on a functional G2-M checkpoint for DNA repair. WEE1 is expressed at high levels in various cancer types including breast cancers, leukemia, melanoma, and adult and pediatric brain tumors. Many of these cancers are treated with DNA-damaging agents; therefore, targeting WEE1 for inhibition and compromising the G2-M checkpoint presents an opportunity to potentiate therapy. In this review we summarize the current WEE1 inhibitors, the potential for further inhibitor development, and the challenges in the clinic for the WEE1 inhibitor strategy.

The kinome 'at large' in cancer

Over the past decade, rapid advances in genomics, proteomics and functional genomics technologies that enable in-depth interrogation of cancer genomes and proteomes and high-throughput analysis of gene function have enabled characterization of the kinome 'at large' in human cancers, providing crucial insights into how members of the protein kinase superfamily are dysregulated in malignancy, the context-dependent functional role of specific kinases in cancer and how kinome remodelling modulates sensitivity to anticancer drugs. The power of these complementary approaches, and the insights gained from them, form the basis of this Analysis article.

A scalable method for molecular network reconstruction identifies properties of targets and mutations in acute myeloid leukemia

A key aim of systems biology is the reconstruction of molecular networks. We do not yet, however, have networks that integrate information from all datasets available for a particular clinical condition. This is in part due to the limited scalability, in terms of required computational time and power, of existing algorithms. Network reconstruction methods should also be scalable in the sense of allowing scientists from different backgrounds to efficiently integrate additional data. We present a network model of acute myeloid leukemia (AML). In the current version (AML 2.1), we have used gene expression data (both microarray and RNA-seq) from 5 different studies comprising a total of 771 AML samples and a protein-protein interactions dataset. Our scalable network reconstruction method is in part based on the well-known property of gene expression correlation among interacting molecules. The difficulty of distinguishing between direct and indirect interactions is addressed by optimizing the coefficient of variation of gene expression, using a validated gold-standard dataset of direct interactions. Computational time is much reduced compared to other network reconstruction methods. A key feature is the study of the reproducibility of interactions found in independent clinical datasets. An analysis of the most significant clusters, and of the network properties (intraset efficiency, degree, betweenness centrality, and PageRank) of common AML mutations demonstrated the biological significance of the network. A statistical analysis of the response of blast cells from 11 AML patients to a library of kinase inhibitors provided an experimental validation of the network. A combination of network and experimental data identified CDK1, CDK2, CDK4, and CDK6 and other kinases as potential therapeutic targets in AML.

The Hedgehog pathway as targetable vulnerability with 5-azacytidine in myelodysplastic syndrome and acute myeloid leukemia

Background

Therapy and outcome for elderly acute myeloid leukemia (AML) patients has not improved for many years. Similarly, there remains a clinical need to improve response rates in advanced myelodysplastic syndrome (MDS) patients treated with hypomethylating agents, and few combination regimens have shown clinical benefit. We conducted a 5-azacytidine (5-Aza) RNA-interference (RNAi) sensitizer screen to identify gene targets within the commonly deleted regions (CDRs) of chromosomes 5 and 7, whose silencing enhances the activity of 5-Aza.

Methods and results

An RNAi silencing screen of 270 genes from the CDRs of chromosomes 5 and 7 was performed in combination with 5-Aza treatment in four AML cell lines (TF-1, THP-1, MDS-L, and HEL). Several genes within the hedgehog pathway (HhP), specifically SHH, SMO, and GLI3, were identified as 5-Aza sensitizing hits. The smoothened (SMO) inhibitors LDE225 (erismodegib) and GDC0449 (vismodegib) showed moderate single-agent activity in AML cell lines. Further studies with erismodegib in combination with 5-Aza demonstrated synergistic activity with combination index (CI) values of 0.48 to 0.71 in seven AML lines. Clonogenic growth of primary patient samples was inhibited to a greater extent in the combination than with single-agent erismodegib or 5-Aza in 55 % (6 of 11) primary patient samples examined. There was no association of the 5-Aza/erismodegib sensitization potential to clinical-cytogenetic features or common myeloid mutations. Activation of the HhP, as determined by greater expression of HhP-related genes, showed less responsiveness to single-agent SMO inhibition, while synergy between both agents was similar regardless of HhP gene expression. In vitro experiments suggested that concurrent dosing showed stronger synergy than sequential dosing.

Conclusions

Inhibition of the HhP with SMO inhibitors in combination with the hypomethylating agent 5-Aza demonstrates synergy in vitro and inhibits long-term repopulation capacity ex vivo in AML and MDS. A clinical trial combining 5-Aza with LDE225 (erismodegib) in MDS and AML is ongoing based on these results as well as additional publications suggesting a role for HhP signaling in myeloid disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0211-8) contains supplementary material, which is available to authorized users.

AZD1775 sensitizes T cell acute lymphoblastic leukemia cells to cytarabine by promoting apoptosis over DNA repair

While some children with acute lymphoblastic leukemia (ALL) have excellent prognoses, the prognosis for adults and children with T cell ALL is more guarded. Treatment for T-ALL is heavily dependent upon antimetabolite chemotherapeutics, including cytarabine. Targeted inhibition of WEE1 with AZD1775 has emerged as a strategy to sensitize cancer cells to cytarabine and other chemotherapeutics. We sought to determine if this strategy would be effective for T-ALL with clinically relevant anti-leukemia agents. We found that AZD1775 sensitizes T-ALL cells to several traditional anti-leukemia agents, acting synergistically with cytarabine by enhancing DNA damage and apoptosis. In addition to increased phosphorylation of H2AX at serine 139 (γH2AX), AZD1775 led to increased phosphorylation of H2AX at tyrosine 142, a signaling event associated with promotion of apoptosis over DNA repair. In a xenograft model of T-ALL, the addition of AZD1775 to cytarabine slowed leukemia progression and prolonged survival. Inhibition of WEE1 with AZD1775 sensitizes T-ALL to several anti-leukemia agents, particularly cytarabine and that mechanistically, AZD1775 promotes apoptosis over DNA repair in cells treated with cytarabine. These data support the development of clinical trials including AZD1775 in combination with conventional chemotherapy for acute leukemia.

RNAi profiling of primary human AML cells identifies ROCK1 as a therapeutic target and nominates fasudil as an antileukemic drug

Acute myeloid leukemia (AML) is characterized by a marked genetic heterogeneity, which complicates the development of novel therapeutics. The delineation of pathways essential within an individual patient's mutational background might overcome this limitation and facilitate personalized treatment. We report the results of a large-scale lentiviral loss-of-function RNA interference (RNAi) screen in primary leukemic cells. Stringent validation identified 6 genes (BNIPL1, ROCK1, RPS13, STK3, SNX27, WDHD1) whose knockdown impaired growth and viability of the cells. Dependence on these genes was not caused by mutation or overexpression, and although some of the candidates seemed to be rather patient specific, others were essential in cells isolated from other AML patients. In addition to the phenotype observed after ROCK1 knockdown, treatment with the approved ROCK inhibitor fasudil resulted in increased apoptosis and decreased viability of primary AML cells. In contrast to observations in some other malignancies, ROCK1 inhibition did not foster growth of immature malignant progenitors but was toxic to this cell fraction in feeder coculture and xenotransplant experiments, indicating a distinct effect of ROCK1 inhibition on leukemic progenitors. We conclude that large-scale RNAi screens in primary patient-derived cells are feasible and can complement other methods for personalized cancer therapies, such as expression and mutation profiling.

Rational Combinations of Targeted Agents in AML

Despite modest improvements in survival over the last several decades, the treatment of AML continues to present a formidable challenge. Most patients are elderly, and these individuals, as well as those with secondary, therapy-related, or relapsed/refractory AML, are particularly difficult to treat, owing to both aggressive disease biology and the high toxicity of current chemotherapeutic regimens. It has become increasingly apparent in recent years that coordinated interruption of cooperative survival signaling pathways in malignant cells is necessary for optimal therapeutic results. The modest efficacy of monotherapy with both cytotoxic and targeted agents in AML testifies to this. As the complex biology of AML continues to be elucidated, many “synthetic lethal” strategies involving rational combinations of targeted agents have been developed. Unfortunately, relatively few of these have been tested clinically, although there is growing interest in this area. In this article, the preclinical and, where available, clinical data on some of the most promising rational combinations of targeted agents in AML are summarized. While new molecules should continue to be combined with conventional genotoxic drugs of proven efficacy, there is perhaps a need to rethink traditional philosophies of clinical trial development and regulatory approval with a focus on mechanism-based, synergistic strategies.

Targeting cell cycle regulators in hematologic malignancies

Hematologic malignancies represent the fourth most frequently diagnosed cancer in economically developed countries. In hematologic malignancies normal hematopoiesis is interrupted by uncontrolled growth of a genetically altered stem or progenitor cell (HSPC) that maintains its ability of self-renewal. Cyclin-dependent kinases (CDKs) not only regulate the mammalian cell cycle, but also influence other vital cellular processes, such as stem cell renewal, differentiation, transcription, epigenetic regulation, apoptosis, and DNA repair. Chromosomal translocations, amplification, overexpression and altered CDK activities have been described in different types of human cancer, which have made them attractive targets for pharmacological inhibition. Mouse models deficient for one or more CDKs have significantly contributed to our current understanding of the physiological functions of CDKs, as well as their roles in human cancer. The present review focuses on selected cell cycle kinases with recent emerging key functions in hematopoiesis and in hematopoietic malignancies, such as CDK6 and its role in MLL-rearranged leukemia and acute lymphocytic leukemia, CDK1 and its regulator WEE-1 in acute myeloid leukemia (AML), and cyclin C/CDK8/CDK19 complexes in T-cell acute lymphocytic leukemia. The knowledge gained from gene knockout experiments in mice of these kinases is also summarized. An overview of compounds targeting these kinases, which are currently in clinical development in various solid tumors and hematopoietic malignances, is presented. These include the CDK4/CDK6 inhibitors (palbociclib, LEE011, LY2835219), pan-CDK inhibitors that target CDK1 (dinaciclib, flavopiridol, AT7519, TG02, P276-00, terampeprocol and RGB 286638) as well as the WEE-1 kinase inhibitor, MK-1775. The advantage of combination therapy of cell cycle inhibitors with conventional chemotherapeutic agents used in the treatment of AML, such as cytarabine, is discussed.

The Efficacy of the Wee1 Inhibitor MK-1775 Combined with Temozolomide Is Limited by Heterogeneous Distribution across the Blood-Brain Barrier in Glioblastoma

PURPOSE

Wee1 regulates key DNA damage checkpoints, and in this study, the efficacy of the Wee1 inhibitor MK-1775 was evaluated in glioblastoma multiforme (GBM) xenograft models alone and in combination with radiation and/or temozolomide.

EXPERIMENTAL DESIGN

In vitro MK-1775 efficacy alone and in combination with temozolomide, and the impact on DNA damage, was analyzed by Western blotting and γH2AX foci formation. In vivo efficacy was evaluated in orthotopic and heterotopic xenografts. Drug distribution was assessed by conventional mass spectrometry (MS) and matrix-assisted laser desorption/ionization (MALDI)-MS imaging.

RESULTS

GBM22 (IC50 = 68 nmol/L) was significantly more sensitive to MK-1775 compared with five other GBM xenograft lines, including GBM6 (IC50 >300 nmol/L), and this was associated with a significant difference in pan-nuclear γH2AX staining between treated GBM22 (81% cells positive) and GBM6 (20% cells positive) cells. However, there was no sensitizing effect of MK-1775 when combined with temozolomide in vitro. In an orthotopic GBM22 model, MK-1775 was ineffective when combined with temozolomide, whereas in a flank model of GBM22, MK-1775 exhibited both single-agent and combinatorial activity with temozolomide. Consistent with limited drug delivery into orthotopic tumors, the normal brain to whole blood ratio following a single MK-1775 dose was 5%, and MALDI-MS imaging demonstrated heterogeneous and markedly lower MK-1775 distribution in orthotopic as compared with heterotopic GBM22 tumors.

CONCLUSIONS

Limited distribution to brain tumors may limit the efficacy of MK-1775 in GBM.

Tumour suppressive effects of WEE1 gene silencing in breast cancer cells

BACKGROUND

WEE1 is a G2/M checkpoint regulator protein. Various studies have indicated that WEE1 could be a good target for cancer therapy. The main aim of this study was to asssess the tumor suppressive potential of WEE1 silencing in two different breast cancer cell lines, MCF7 which carries the wild-type p53 and MDA-MB468 which contains a mutant type.

MATERIALS AND METHODS

After WEE1 knockdown with specific shRNAs downstream effects on cell viability and cell cycle progression were determined using MTT and flow cytometry analyses, respectively. Real-time PCR and Western blotting were conducted to assess the effect of WEE1 inhibition on the expression of apoptotic (p53) and anti-apoptotic (Bcl2) factors and also a growth marker (VEGF).

RESULTS

The results showed that WEE1 inhibition could cause a significant decrease in the viability of both MCF7 and MDA-MB-468 breast cancer cell lines by more than 50%. Interestingly, DNA content assays showed a significant increase in apoptotic cells following WEE1 silencing. WEE1 inhibition also induced up- regulation of the apoptotic marker, p53, in breast cancer cells. A significant decrease in the expression of VEGF and Bcl-2 was observed following WEE1 inhibition in both cell lines.

CONCLUSIONS

In concordance with previous studies, our data showed that WEE1 inhibition could induce G2 arrest abrogation and consequent cell death in breast cancer cells. Moreover, in this study, the observed interactions between the pro- and anti-apoptotic proteins and decrease in the angiogenesis marker expression confirm the susceptibility to apoptosis and validate the tumor suppressive effect of WEE1 inhibition in breast cancer cells. Interestingly, the levels of the sensitivity to WEE1 silencing in breast cancer cells, MCF7 and MDA-MB468, seem to be in concordance with the level of p53 expression.

Targeting histone deacetylases (HDACs) and Wee1 for treating high-risk neuroblastoma

BACKGROUND

Despite advances in treatment regimens, patients with high-risk neuroblastoma have long-term survival rates of < 40%. Wee1 inhibition in combination with CHK1 inhibition has shown promising results in neuroblastoma cells. In addition, it has been demonstrated that panobinostat can downregulate CHK1. Therefore, combination of panobinostat and MK-1775 may result in synergistic cytotoxicity against neuroblastoma cell lines.

PROCEDURE

In vitro cytotoxicities of panobinostat and MK-1775 at clinically achievable concentrations, either alone or in combination, were evaluated in SK-N-AS, SK-N-DZ, and SK-N-BE(2) high-risk neuroblastoma cell lines using MTT assays. The mechanism of antitumor interaction was investigated using propidium iodide (PI) staining and flow cytometry analysis to determine apoptosis, as well as Western blotting to assess expression of phosphorylated CDK1/2, CHK1, and H2AX.

RESULTS

Treatment of neuroblastoma cell lines with 500 nM MK-1775 caused growth arrest and apoptosis in SK-N-DZ and SK-N-AS, while it had minimal effect on the SK-N-BE(2) cell line. The combination of panobinostat and MK-1775 resulted in synergistic antitumor interactions in all three of the cell lines tested. MK-1775 treatment in SK-N-BE(2) cells induced increased levels of p-CHK1(S345) , which could be decreased by the addition of panobinostat. This was accompanied by increased DNA damage and apoptosis.

CONCLUSIONS

The combination of panobinostat and MK-1775 has synergistic antitumor activity against neuroblastoma cell lines and holds promise as a potential treatment strategy for the management of high-risk neuroblastoma patients.