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

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.

Combined inhibition of the cell cycle related proteins Wee1 and Chk1/2 induces synergistic anti-cancer effect in melanoma

BACKGROUND

Malignant melanoma has an increasing incidence rate and the metastatic disease is notoriously resistant to standard chemotherapy. Loss of cell cycle checkpoints is frequently found in many cancer types and makes the cells reliant on compensatory mechanisms to control progression. This feature may be exploited in therapy, and kinases involved in checkpoint regulation, such as Wee1 and Chk1/2, have thus become attractive therapeutic targets.

METHODS

In the present study we combined a Wee1 inhibitor (MK1775) with Chk1/2 inhibitor (AZD7762) in malignant melanoma cell lines grown in vitro (2D and 3D cultures) and in xenografts models.

RESULTS

Our in vitro studies showed that combined inhibition of Wee1 and Chk1/2 synergistically decreased viability and increased apoptosis (cleavage of caspase 3 and PARP), which may be explained by accumulation of DNA-damage (increased expression of γ-H2A.X)--and premature mitosis of S-phase cells. Compared to either inhibitor used as single agents, combined treatment reduced spheroid growth and led to greater tumour growth inhibition in melanoma xenografts.

CONCLUSIONS

These data provide a rationale for further evaluation of the combination of Wee1 and Chk1/2 inhibitors in malignant melanoma.

Exploiting replicative stress to treat cancer

DNA replication in cancer cells is accompanied by stalling and collapse of the replication fork and signalling in response to DNA damage and/or premature mitosis; these processes are collectively known as 'replicative stress'. Progress is being made to increase our understanding of the mechanisms that govern replicative stress, thus providing ample opportunities to enhance replicative stress for therapeutic purposes. Rather than trying to halt cell cycle progression, cancer therapeutics could aim to increase replicative stress by further loosening the checkpoints that remain available to cancer cells and ultimately inducing the catastrophic failure of proliferative machineries. In this Review, we outline current and future approaches to achieve this, emphasizing the combination of conventional chemotherapy with targeted approaches.

A regimen combining the Wee1 inhibitor AZD1775 with HDAC inhibitors targets human acute myeloid leukemia cells harboring various genetic mutations

AZD1775 targets the cell cycle checkpoint kinase Wee1 and potentiates genotoxic agent cytotoxicity through p53-dependent or -independent mechanisms. Here, we report that AZD1775 interacted synergistically with histone deacetylase inhibitors (HDACIs, for example, Vorinostat), which interrupt the DNA damage response, to kill p53-wild type (wt) or -deficient as well as FLT3-ITD leukemia cells in association with pronounced Wee1 inhibition and diminished cdc2/Cdk1 Y15 phosphorylation. Similarly, Wee1 shRNA knockdown significantly sensitized cells to HDACIs. Although AZD1775 induced Chk1 activation, reflected by markedly increased Chk1 S296/S317/S345 phosphorylation leading to inhibitory T14 phosphorylation of cdc2/Cdk1, these compensatory responses were sharply abrogated by HDACIs. This was accompanied by premature mitotic entry, multiple mitotic abnormalities and accumulation of early S-phase cells displaying increased newly replicated DNA, culminating in robust DNA damage and apoptosis. The regimen was active against patient-derived acute myelogenous leukemia (AML) cells harboring either wt or mutant p53 and various next-generation sequencing-defined mutations. Primitive CD34(+)/CD123(+)/CD38(-) populations enriched for leukemia-initiating progenitors, but not normal CD34(+) hematopoietic cells, were highly susceptible to this regimen. Finally, combining AZD1775 with Vorinostat in AML murine xenografts significantly reduced tumor burden and prolonged animal survival. A strategy combining Wee1 with HDACI inhibition warrants further investigation in AML with poor prognostic genetic aberrations.

Targeting lung cancer through inhibition of checkpoint kinases

Inhibitors of checkpoint kinases ATR, Chk1, and Wee1 are currently being tested in preclinical and clinical trials. Here, we review the basic principles behind the use of such inhibitors as anticancer agents, and particularly discuss their potential for treatment of lung cancer. As lung cancer is one of the most deadly cancers, new treatment strategies are highly needed. We discuss how checkpoint kinase inhibition in principle can lead to selective killing of lung cancer cells while sparing the surrounding normal tissues. Several features of lung cancer may potentially be exploited for targeting through inhibition of checkpoint kinases, including mutated p53, low ERCC1 levels, amplified Myc, tumor hypoxia and presence of lung cancer stem cells. Synergistic effects have also been reported between inhibitors of ATR/Chk1/Wee1 and conventional lung cancer treatments, such as gemcitabine, cisplatin, or radiation. Altogether, inhibitors of ATR, Chk1, and Wee1 are emerging as new cancer treatment agents, likely to be useful in lung cancer treatment. However, as lung tumors are very diverse, the inhibitors are unlikely to be effective in all patients, and more work is needed to determine how such inhibitors can be utilized in the most optimal ways.

WEE1 is a validated target of the microRNA miR-17-92 cluster in leukemia

MicroRNAs are short single-stranded RNAs that regulate target gene expression by binding to complementary sites in the 3' untranslated region (UTR) of their mRNA targets. The polycistronic miR-17-92 cluster, which encodes miR-17, miR-18a, miR-19a, miR-20a, miR-19b, and miR-92a, was previously shown to be overexpressed in multiple types of cancer. In this study, target gene prediction algorithms were used to predict potential targets of the miR-17-92 cluster. WEE1, a kinase that inhibits cell cycle progression, was identified as a possible target of five of the six miRNAs in the cluster. Luciferase reporter assays were used to determine that miR-17, miR-20a, and miR-18a specifically target nucleotides 465-487 of the 3' UTR of WEE1, whereas miR-19a and miR-19b exert control on WEE1 by targeting nucleotides 1069-1091. A negative correlation was determined between endogenous miR-17 or miR-19a expression and endogenous WEE1 protein expression in the same panel of cell lines. We conclude that WEE1 is a valid target of the miR-17-92 cluster in leukemia.

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.

Critical role of lysine 134 methylation on histone H2AX for γ-H2AX production and DNA repair

The presence of phosphorylated histone H2AX (γ-H2AX) is associated with the local activation of DNA-damage repair pathways. Although γ-H2AX deregulation in cancer has previously been reported, the molecular mechanism involved and its relationship with other histone modifications remain largely unknown. Here we find that the histone methyltransferase SUV39H2 methylates histone H2AX on lysine 134. When H2AX was mutated to abolish K134 methylation, the level of γ-H2AX became significantly reduced. We also found lower γ-H2AX activity following the introduction of double-strand breaks in Suv39h2 knockout cells or on SUV39H2 knockdown. Tissue microarray analyses of clinical lung and bladder tissues also revealed a positive correlation between H2AX K134 methylation and γ-H2AX levels. Furthermore, introduction of K134-substituted histone H2AX enhanced radio- and chemosensitivity of cancer cells. Overall, our results suggest that H2AX methylation plays a role in the regulation of γ-H2AX abundance in cancer.

γ-H2AX The Ser139 phosphorylated form of H2AX, γ-H2AX, is generated in response to DNA double-strand breaks and is involved in the repair process. Here, Sone et al. show that H2AX K134 methylation by SUV39H2 is crucial for the production of γ-H2AX, and that loss of methylation correlates with radio- and chemosensitivity.

DNA damage accumulation and repair defects in acute myeloid leukemia: implications for pathogenesis, disease progression, and chemotherapy resistance

DNA damage repair mechanisms are vital to maintain genomic integrity. Mutations in genes involved in the DNA damage response (DDR) can increase the risk of developing cancer. In recent years, a variety of polymorphisms in DDR genes have been associated with increased risk of developing acute myeloid leukemia (AML) or of disease relapse. Moreover, a growing body of literature has indicated that epigenetic silencing of DDR genes could contribute to the leukemogenic process. In addition, a variety of AML oncogenes have been shown to induce replication and oxidative stress leading to accumulation of DNA damage, which affects the balance between proliferation and differentiation. Conversely, upregulation of DDR genes can provide AML cells with escape mechanisms to the DDR anticancer barrier and induce chemotherapy resistance. The current review summarizes the DDR pathways in the context of AML and describes how aberrant DNA damage response can affect AML pathogenesis, disease progression, and resistance to standard chemotherapy, and how defects in DDR pathways may provide a new avenue for personalized therapeutic strategies in AML.

Synergistic antitumor interactions between MK-1775 and panobinostat in preclinical models of pancreatic cancer

Pancreatic cancer remains a clinical challenge, thus new therapies are urgently needed. The selective Wee1 inhibitor MK-1775 has demonstrated promising results when combined with DNA damaging agents, and more recently with CHK1 inhibitors in various malignancies. We have previously demonstrated that treatment with the pan-histone deacetylase inhibitor panobinostat (LBH589) can cause down-regulation of CHK1. Accordingly, we investigated using panobinostat to down-regulate CHK1 in combination with MK-1775 to enhance cell death in preclinical pancreatic cancer models. We demonstrate that MK-1775 treatment results in increased H2AX phosphorylation, indicating increased DNA double-strand breaks, and activation of CHK1, which are both dependent on CDK activity. Combination of MK-1775 and panobinostat resulted in synergistic antitumor activity in six pancreatic cancer cell lines. Finally, our in vivo study using a pancreatic xenograft model reveals promising cooperative antitumor activity between MK-1775 and panobinostat. Our study provides compelling evidence that the combination of MK-1775 and panobinostat has antitumor activity in preclinical models of pancreatic cancer and supports the clinical development of panobinostat in combination with MK-1775 for the treatment of this deadly disease.

Targeting the wee1 kinase for treatment of pediatric Down syndrome acute myeloid leukemia

BACKGROUND

Most Down syndrome children with acute myeloid leukemia (DS-AML) have an overall excellent prognosis, however, patients who suffer an induction failure or relapse, have an extremely poor prognosis. Hence, new therapies need to be developed for this subgroup of DS-AML patients. One new therapeutic approach is preventing cell cycle checkpoint activation by inhibiting the upstream kinase wee1 with the first-in-class inhibitor MK-1775 in combination with the standard genotoxic agent cytarabine (AraC).

PROCEDURE

Using the clinically relevant DS-AML cell lines CMK and CMY, as well as ex vivo primary DS-AML patient samples, the ability of MK-1775 to enhance the cytotoxicity of AraC was investigated with MTT assays. The mechanism by which MK-1775 enhanced AraC cytotoxicity was investigated in the cell lines using Western blots to probe CDK1 and H2AX phosphorylation and flow cytometry to determine apoptosis, cell cycle arrest, DNA damage, and aberrant mitotic entry.

RESULTS

MK-1775 alone had modest single-agent activity, however, MK-1775 was able to synergize with AraC in causing proliferation arrest in both cell lines and primary patient samples, and enhance AraC-induced apoptosis. MK-1775 was able to decrease inhibitory CDK1(Y15) phosphorylation at the relatively low concentration of 100 nM after only 4 hours. Furthermore, it was able to enhance DNA damage induced by AraC and partially abrogate cell cycle arrest. Importantly, the DNA damage enhancement appeared in early S-phase.

CONCLUSIONS

MK-1775 is able to enhance the cytotoxicity of AraC in DS-AML cells and presents a promising new treatment approach for DS-AML.

CHK1 plays a critical role in the anti-leukemic activity of the wee1 inhibitor MK-1775 in acute myeloid leukemia cells

Background

Acute myeloid leukemia (AML) remains a difficult disease to treat and requires new therapies to improve treatment outcome. Wee1 inhibitors have been used to prevent activation of the G2 cell cycle checkpoint, thus enhancing the antitumor activity of DNA damaging agents. In this study, we investigated MK-1775 in AML cell lines and diagnostic blast samples to identify sensitive subtypes as well as possible mechanisms of resistance.

Methods

In vitro MK-1775 cytotoxicities of AML cell lines and diagnostic blasts were measured using MTT assays. The effects of MK-1775 on cell cycle progression and related proteins were determined by propidium iodide (PI) staining and flow cytometry analysis and Western blotting. Drug-induced apoptosis was determined using annexin V/PI staining and flow cytometry analysis.

Results

We found that newly diagnosed and relapsed patient samples were equally sensitive to MK-1775. In addition, patient samples harboring t(15;17) translocation were significantly more sensitive to MK-1775 than non-t(15;17) samples. MK-1775 induced apoptosis in both AML cell lines and diagnostic blast samples, accompanied by decreased phosphorylation of CDK1 and CDK2 on Tyr-15 and increased DNA double-strand breaks (DSBs). Time-course experiments, using AML cell lines, revealed a time-dependent increase in DNA DSBs, activation of CHK1 and subsequent apoptosis following MK-1775 treatment, which could be attenuated by a CDK1/2 inhibitor, Roscovitine. Simultaneous inhibition of CHK1 and Wee1 resulted in synergistic anti-leukemic activity in both AML cell lines and primary patient samples ex vivo.

Conclusions

Our study provides compelling evidence that CHK1 plays a critical role in the anti-leukemic activity of MK-1775 and highlights a possible mechanism of resistance to MK-1775. In addition, our study strongly supports the use of MK-1775 to treat both newly diagnosed and relapsed AML, especially cases with t(15;17) translocation, and supports the development of combination therapies with CHK1 inhibitors.