Targeting CHAF1B Enhances IFN Activity against Myeloproliferative Neoplasm Cells

Interferons (IFNs) are cytokines with potent antineoplastic and antiviral properties. IFNα has significant clinical activity in the treatment of myeloproliferative neoplasms (MPN), but the precise mechanisms by which it acts are not well understood. Here, we demonstrate that chromatin assembly factor 1 subunit B (CHAF1B), an Unc-51-like kinase 1 (ULK1)-interactive protein in the nuclear compartment of malignant cells, is overexpressed in patients with MPN. Remarkably, targeted silencing of CHAF1B enhances transcription of IFNα-stimulated genes and promotes IFNα-dependent antineoplastic responses in primary MPN progenitor cells. Taken together, our findings indicate that CHAF1B is a promising newly identified therapeutic target in MPN and that CHAF1B inhibition in combination with IFNα therapy might offer a novel strategy for treating patients with MPN.

Significance

Our findings raise the potential for clinical development of drugs targeting CHAF1B to enhance IFN antitumor responses in the treatment of patients with MPN and should have important clinical translational implications for the treatment of MPN and possibly in other malignancies.

SLFN11 Negatively Regulates Noncanonical NFκB Signaling to Promote Glioblastoma Progression

Glioblastoma (GBM) is an aggressive and incurable brain tumor in nearly all instances, whose disease progression is driven in part by the glioma stem cell (GSC) subpopulation. Here, we explored the effects of Schlafen family member 11 (SLFN11) in the molecular, cellular, and tumor biology of GBM. CRISPR/Cas9-mediated knockout of SLFN11 inhibited GBM cell proliferation and neurosphere growth and was associated with reduced expression of progenitor/stem cell marker genes, such as NES, SOX2, and CD44. Loss of SLFN11 stimulated expression of NFκB target genes, consistent with a negative regulatory role for SLFN11 on the NFκB pathway. Furthermore, our studies identify p21 as a direct transcriptional target of NFκB2 in GBM whose expression was stimulated by loss of SLFN11. Genetic disruption of SLFN11 blocked GBM growth and significantly extended survival in an orthotopic patient-derived xenograft model. Together, our results identify SLFN11 as a novel component of signaling pathways that contribute to GBM and GSC with implications for future diagnostic and therapeutic strategies.

Significance:

We identify a negative regulatory role for SLFN11 in noncanonical NFκB signaling that results in suppression of the cell-cycle inhibitor p21. We provide evidence that SLFN11 contributes to regulation of stem cell markers in GBM, promoting the malignant phenotype. In addition, SLFN11 targeting triggers p21 expression and antitumor responses. Our studies define a highly novel function for SLFN11 and identify it as a potential therapeutic target for GBM.

Schlafen 5 as a novel therapeutic target in pancreatic ductal adenocarcinoma

We provide evidence that a member of the human Schlafen (SLFN) family of proteins, SLFN5, is overexpressed in human pancreatic ductal adenocarcinoma (PDAC). Targeted deletion of SLFN5 results in decreased PDAC cell proliferation and suppresses PDAC tumorigenesis in in vivo PDAC models. Importantly, high expression levels of SLFN5 correlate with worse outcomes in PDAC patients, implicating SLFN5 in the pathophysiology of PDAC that leads to poor outcomes. Our studies establish novel regulatory effects of SLFN5 on cell cycle progression through binding/blocking of the transcriptional repressor E2F7, promoting transcription of key genes that stimulate S phase progression. Together, our studies suggest an essential role for SLFN5 in PDAC and support the potential for developing new therapeutic approaches for the treatment of pancreatic cancer through SLFN5 targeting.

Inhibitory effects of SEL201 in acute myeloid leukemia

MAPK interacting kinase (MNK), a downstream effector of mitogen-activated protein kinase (MAPK) pathways, activates eukaryotic translation initiation factor 4E (eIF4E) and plays a key role in the mRNA translation of mitogenic and antiapoptotic genes in acute myeloid leukemia (AML) cells. We examined the antileukemic properties of a novel MNK inhibitor, SEL201. Our studies provide evidence that SEL201 suppresses eIF4E phosphorylation on Ser209 in AML cell lines and in primary patient-derived AML cells. Such effects lead to growth inhibitory effects and leukemic cell apoptosis, as well as suppression of leukemic progenitor colony formation. Combination of SEL201 with 5'-azacytidine or rapamycin results in synergistic inhibition of AML cell growth. Collectively, these results suggest that SEL201 has significant antileukemic activity and further underscore the relevance of the MNK pathway in leukemogenesis.

Pharmacological mTOR targeting enhances the antineoplastic effects of selective PI3Kα inhibition in medulloblastoma

Despite recent advances in the treatment of medulloblastoma, patients in high-risk categories still face very poor outcomes. Evidence indicates that a subpopulation of cancer stem cells contributes to therapy resistance and tumour relapse in these patients. To prevent resistance and relapse, the development of treatment strategies tailored to target subgroup specific signalling circuits in high-risk medulloblastomas might be similarly important as targeting the cancer stem cell population. We have previously demonstrated potent antineoplastic effects for the PI3Kα selective inhibitor alpelisib in medulloblastoma. Here, we performed studies aimed to enhance the anti-medulloblastoma effects of alpelisib by simultaneous catalytic targeting of the mTOR kinase. Pharmacological mTOR inhibition potently enhanced the suppressive effects of alpelisib on cancer cell proliferation, colony formation and apoptosis and additionally blocked sphere-forming ability of medulloblastoma stem-like cancer cells in vitro. We identified the HH effector GLI1 as a target for dual PI3Kα and mTOR inhibition in SHH-type medulloblastoma and confirmed these results in HH-driven Ewing sarcoma cells. Importantly, pharmacologic mTOR inhibition greatly enhanced the inhibitory effects of alpelisib on medulloblastoma tumour growth in vivo. In summary, these findings highlight a key role for PI3K/mTOR signalling in GLI1 regulation in HH-driven cancers and suggest that combined PI3Kα/mTOR inhibition may be particularly interesting for the development of effective treatment strategies in high-risk medulloblastomas.

Discovery of novel Mnk inhibitors using mutation-based induced-fit virtual high-throughput screening

Mnk kinases (Mnk1 and 2) are downstream effectors of Map kinase pathways and regulate phosphorylation of eukaryotic initiation factor 4E. Engagement of the Mnk pathway is critical in acute myeloid leukemia (AML) leukemogenesis and Mnk inhibitors have potent antileukemic properties in vitro and in vivo, suggesting that targeting Mnk kinases may provide a novel approach for treating AML. Here, we report the development and application of a mutation-based induced-fit in silico screen to identify novel Mnk inhibitors. The Mnk1 structure was modeled by temporarily mutating an amino acid that obstructs the ATP-binding site in the Mnk1 crystal structure while carrying out docking simulations of known inhibitors. The hit compounds display activity in Mnk biochemical and cellular assays, including acute myeloid leukemia progenitors. This approach will enable further rational structure-based drug design of new Mnk inhibitors and potentially novel ways of therapeutically targeting this kinase.

Potent Antineoplastic Effects of Combined PI3Kα-MNK Inhibition in Medulloblastoma

Medulloblastoma is a highly malignant pediatric brain tumor associated with poor outcome. Developing treatments that target the cancer stem cell (CSC) population in medulloblastoma are important to prevent tumor relapse and induce long-lasting clinical responses. We utilized medulloblastoma neurospheres that display CSC characteristics and found activation of the PI3K/AKT pathway in sphere-forming cells. Of all class IA PI3Ks, only the PI3Kα isoform was required for sphere formation by medulloblastoma cells. Knockdown of p110α, but not p110β or p110δ, significantly disrupted cancer stem cell frequencies as determined by extreme limiting dilution analysis (ELDA), indicating an essential role for the PI3Kα catalytic isoform in medulloblastoma CSCs. Importantly, pharmacologic inhibition of the MAPK-interacting kinase (MNK) enhanced the antineoplastic effects of targeted PI3Kα inhibition in medulloblastoma. This indicates that MNK signaling promotes survival in medulloblastoma, suggesting dual PI3Kα and MNK inhibition may provide a novel approach to target and eliminate medulloblastoma CSCs. We also observed a significant reduction in tumor formation in subcutaneous and intracranial mouse xenograft models, which further suggests that this combinatorial approach may represent an efficient therapeutic strategy for medulloblastoma. IMPLICATIONS: These findings raise the possibility of a unique therapeutic approach for medulloblastoma, involving MNK targeting to sensitize medulloblastoma CSCs to PI3Kα inhibition.

Differential Response of Glioma Stem Cells to Arsenic Trioxide Therapy Is Regulated by MNK1 and mRNA Translation

Mesenchymal (MES) and proneural (PN) are two distinct glioma stem cell (GSC) populations that drive therapeutic resistance in glioblastoma (GBM). We screened a panel of 650 small molecules against patient-derived GBM cells to discover compounds targeting specific GBM subtypes. Arsenic trioxide (ATO), an FDA-approved drug that crosses the blood-brain barrier, was identified as a potent PN-specific compound in the initial screen and follow-up validation studies. Furthermore, MES and PN GSCs exhibited differential sensitivity to ATO. As ATO has been shown to activate the MAPK-interacting kinase 1 (MNK1)-eukaryotic translation initiation factor 4E (eIF4E) pathway and subsequent mRNA translation in a negative regulatory feedback manner, the mechanistic role of ATO resistance in MES GBM was explored. In GBM cells, ATO-activated translation initiation cellular events via the MNK1-eIF4E signaling axis. Furthermore, resistance to ATO in intracranial PDX tumors correlated with high eIF4E phosphorylation. Polysomal fractionation and microarray analysis of GBM cells were performed to identify ATO's effect on mRNA translation and enrichment of anti-apoptotic mRNAs in the ATO-induced translatome was found. Additionally, it was determined that MNK inhibition sensitized MES GSCs to ATO in neurosphere and apoptosis assays. Finally, examination of the effect of ATO on patients from a phase I/II clinical trial of ATO revealed that PN GBM patients responded better to ATO than other subtypes as demonstrated by longer overall and progression-free survival.Implications: These findings raise the possibility of a unique therapeutic approach for GBM, involving MNK1 targeting to sensitize MES GSCs to drugs like arsenic trioxide. Mol Cancer Res; 16(1); 32-46. ©2017 AACR.

Pre-clinical evidence of PIM kinase inhibitor activity in BCR-ABL1 unmutated and mutated Philadelphia chromosome-positive (Ph+) leukemias

We investigated the efficacy of targeting the PIM kinase pathway in Philadelphia chromosome-positive (Ph+) leukemias. We provide evidence that inhibition of PIM, with the pan-PIM inhibitor SGI-1776, results in suppression of classic PIM effectors and also elements of the mTOR pathway, suggesting interplay between PIM and mTOR signals. Our data demonstrate that PIM inhibition enhances the effects of imatinib mesylate on Ph+ leukemia cells. We also found that PIM inhibition results in suppression of leukemic cell proliferation and induction of apoptosis of Ph+ leukemia cells, including those resistant to imatinib mesylate. Importantly, inhibition of PIM results in enhanced suppression of primary leukemic progenitors from patients with CML. Altogether these findings suggest that pharmacological PIM targeting may provide a unique therapeutic approach for the treatment of Ph+ leukemias.

Central role of ULK1 in type I interferon signaling

We provide evidence that the Unc-51-like kinase 1 (ULK1) is activated during engagement of the type I interferon (IFN) receptor (IFNR). Our studies demonstrate that the function of ULK1 is required for gene transcription mediated via IFN-stimulated response elements (ISRE) and IFNγ activation site (GAS) elements and controls expression of key IFN-stimulated genes (ISGs). We identify ULK1 as an upstream regulator of p38α mitogen-activated protein kinase (MAPK) and establish that the regulatory effects of ULK1 on ISG expression are mediated possibly by engagement of the p38 MAPK pathway. Importantly, we demonstrate that ULK1 is essential for antiproliferative responses and type I IFN-induced antineoplastic effects against malignant erythroid precursors from patients with myeloproliferative neoplasms. Together, these data reveal a role for ULK1 as a key mediator of type I IFNR-generated signals that control gene transcription and induction of antineoplastic responses.

Direct binding of arsenic trioxide to AMPK and generation of inhibitory effects on acute myeloid leukemia precursors

Arsenic trioxide (As2O3) exhibits potent antineoplastic effects and is used extensively in clinical oncology for the treatment of a subset of patients with acute myeloid leukemia (AML). Although As2O3 is known to regulate activation of several signaling cascades, the key events, accounting for its antileukemic properties, remain to be defined. We provide evidence that arsenic can directly bind to cysteine 299 in AMPKα and inhibit its activity. This inhibition of AMPK by arsenic is required in part for its cytotoxic effects on primitive leukemic progenitors from patients with AML, while concomitant treatment with an AMPK activator antagonizes in vivo the arsenic-induced antileukemic effects in a xenograft AML mouse model. A consequence of AMPK inhibition is activation of the mTOR pathway as a negative regulatory feedback loop. However, when AMPK expression is lost, arsenic-dependent activation of the kinase RSK downstream of MAPK activity compensates the generation of regulatory feedback signals through phosphorylation of downstream mTOR targets. Thus, therapeutic regimens with As2O3 will need to include inhibitors of both the mTOR and RSK pathways in combination to prevent engagement of negative feedback loops and maximize antineoplastic responses.

Autophagy is a survival mechanism of acute myelogenous leukemia precursors during dual mTORC2/mTORC1 targeting

PURPOSE

To examine whether induction of autophagy is a mechanism of leukemic cell resistance to dual mTORC1/mTORC2 inhibitors in acute myelogenous leukemia (AML) leukemic progenitors.

EXPERIMENTAL DESIGN

Combinations of different experimental approaches were used to assess induction of autophagy, including immunoblotting to detect effects on LC3II and p62/SQTM1 expression and on ULK1 phosphorylation, immunofluorescence, and electron microscopy. Functional responses were assessed using cell viability and apoptosis assays, and clonogenic leukemic progenitor assays in methylcellulose.

RESULTS

We provide evidence that treatment of AML cells with catalytic mTOR inhibitors results in induction of autophagy, which acts as a regulatory mechanism to promote leukemic cell survival. Such induction of autophagy by dual mTORC1/mTORC2 inhibitors partially protects primitive leukemic precursors from the inhibitory effects of such agents and limits their activities. Simultaneous blockade of the autophagic process using chloroquine or by knockdown of ULK1 results in enhanced antileukemic responses.

CONCLUSIONS

Dual targeting of mTORC2 and mTORC1 results in induction of autophagy in AML cells. Combinations of catalytic mTOR targeting agents and autophagy inhibitors may provide a unique approach to target primitive leukemic precursors in AML.

The evolution of the TOR pathway and its role in cancer

The target of rapamycin (TOR) pathway is highly conserved among eukaryotes and has evolved to couple nutrient sensing to cellular growth. TOR is found in two distinct signaling complexes in cells, TOR complex 1 (TORC1) and TOR complex 2 (TORC2). These complexes are differentially regulated and act as effectors for the generation of signals that drive diverse cellular processes such as growth, proliferation, protein synthesis, rearrangement of the cytoskeleton, autophagy, metabolism and survival. Mammalian TOR (mTOR) is very important for development in embryos, while in adult organisms it is linked to aging and lifespan effects. In humans, the mTOR pathway is implicated in the tumorigenesis of multiple cancer types and its deregulation is associated with familial cancer syndromes. Because of its high biological relevance, different therapeutic strategies have been developed to target this signaling cascade, resulting in the emergence of unique pharmacological inhibitors that are either already approved for use in clinical oncology or currently under preclinical or clinical development. Multimodal treatment strategies that simultaneously target multiple nodes of the pathway and/or negative feedback regulatory loops may ultimately provide the best therapeutic advantage in targeting this pathway for the treatment of malignancies.

A new era for an ancient drug: arsenic trioxide and Hedgehog signaling

Arsenic has been used for ages as a therapeutic agent. Currently, it is an FDA approved drug to treat acute promyelocytic leukemia where it leads to degradation of the PML-RAR fusion protein. It has been shown to have various other targets in cells such as JNK, NFκB, thioredoxin reductase, and MAPK pathways. Most of its effects in cells have been through arsenic's ability to bind to thiol groups in cysteine residues. Recent evidence has shown that arsenic can inhibit the Hedgehog pathway by inhibiting GLI proteins. The proposed mechanism of action is through direct binding. Potential binding sites include the critical cysteine residues in GLI zinc finger domains. The role of the Hedgehog pathway has been implicated in many cancers such as basal cell carcinoma, medulloblastoma, Ewing sarcoma, and rhabdoid tumors. Current Hedgehog pathway inhibitors have been fraught with resistance issues and so arsenic trioxide may provide an alternative therapy when combined with these other inhibitors or after acquired resistance.

Beta-catenin accelerates human papilloma virus type-16 mediated cervical carcinogenesis in transgenic mice

Human papilloma virus (HPV) is the principal etiological agent of cervical cancer in women, and its DNA is present in virtually all of these tumors. However, exposure to the high-risk HPV types alone is insufficient for tumor development. Identifying specific collaborating factors that will lead to cervical cancer remains an unanswered question, especially because millions of women are exposed to HPV. Our earlier work using an in vitro model indicated that activation of the canonical Wnt pathway in HPV-positive epithelial cells was sufficient to induce anchorage independent growth. We therefore hypothesized that constitutive activation of this pathway might function as the "second hit." To address this possibility, we developed two double-transgenic (DT) mouse models, K14-E7/ΔN87βcat and K14-HPV16/ΔN87βcat that express either the proteins encoded by the E7 oncogene or the HPV16 early region along with constitutively active β-catenin, which was expressed by linking it to the keratin-14 (K14) promoter. We initiated tumor formation by treating all groups with estrogen for six months. Invasive cervical cancer was observed in 11% of the K14-ΔN87βcat mice, expressing activated β-catenin and in 50% of the animals expressing the HPV16 E7 oncogene. In double-transgenic mice, coexpression of β-catenin and HPV16 E7 induced invasive cervical cancer at about 7 months in 94% of the cases. We did not observe cervical cancer in any group unless the mice were treated with estrogen. In the second model, K14-HPV16 mice suffered cervical dysplasias, but this phenotype was not augmented in HPV16/ΔN87βcat mice. In summary, the phenotypes of the K14-E7/ΔN87βcat mice support the hypothesis that activation of the Wnt/β-catenin pathway in HPV-associated premalignant lesions plays a functional role in accelerating cervical carcinogenesis.

YK-4-279 inhibits ERG and ETV1 mediated prostate cancer cell invasion

Background

Genomic rearrangements involving the ETS family of transcription factors occur in 40–70% of prostate cancer cases. ERG and ETV1 are the most common ETS members observed in these genetic alterations. The high prevalence of these rearrangements and their biological significance represents a novel therapeutic target for the treatment of prostate cancer.

Methods and Findings

We recently reported the development of YK-4-279, a small molecule inhibitor of EWS-FLI1 oncoprotein in Ewing's Sarcoma. Since ERG and ETV1 belong to the same class of ETS factors as FLI1, we tested the ability of YK-4-279 to inhibit biological functions of ERG and ETV1 proteins in prostate cancer. YK-4-279 inhibited ERG and ETV1 mediated transcriptional activity in a luciferase assay. YK-4-279 also decreased ERG and ETV1 downstream target mRNA and protein expression in ETV1-fusion positive LNCaP and ERG fusion positive VCaP cells. YK-4-279 reduced the motility of LNCaP cells in a scratch assay and the invasive phenotype of both LNCaP and VCaP cells in a HUVEC invasion assay. Fusion-negative PC3 cells were unresponsive to YK-4-279. SiRNA mediated ERG knockdown in VCaP cells resulted in a loss of drug responsiveness. Concurrently, transient ERG expression in PC-3 cells resulted in increased invasive potential, which was reduced by YK-4-279.

Conclusion

These data demonstrate that YK-4-279 inhibits ERG and ETV1 biological activity in fusion-positive prostate cancer cells leading to decreased motility and invasion. Therefore, YK-4-279 may have an impact on metastasis in prostate cancer and it may be further evaluated for its clinical applications in prostate cancer in addition to Ewing's sarcoma.

Abstract 4328: Beta-catenin accelerates human papillomavirus type16 -E7 mediated cervical carcinogenesis in transgenic mice

Human papilloma virus (HPV) is the principal etiological agent of cervical cancer in women and its DNA is present and expressed in virtually all cervical cancers. Exposure to the high-risk HPV types is not sufficient for tumor development. Approximately 80% of women will be infected with HPV in their lifetime, however only a small percentage of infected women develop cervical cancer. It is unknown who among the millions of women infected with HPV will go on to develop cervical cancer. Therefore, it remains critical to discover additional cellular changes that lead to malignant transformation. The persistence of viral infection is one critical factor in the predisposition to cancer, presumably providing genetic instability that leads to additional genetic/epigenetic changes. Our earlier work using an in vitro model indicated that activation of the canonical Wnt pathway in HPV-positive epithelial cells was sufficient to induce anchorage independent growth. Therefore, we hypothesized that constitutive activation of the Wnt pathway might function as a second hit. To address this possibility, we generated two new double transgenic (DT) mouse models. The first model, K14-HPV16/ΔN87βcat is established by crossing K14-ΔN87βcat mice with K14-HPV16 mice. These mice express wild type HPV16 early region oncoproteins including E6 and E7 and constitutively active -catenin protein in cervical epithelia under the control of tissue specific K14 promoter. The second model, K14-E7/ΔN87βcat mice were generated by crossing K14-ΔN87cat cat mice with K14-E7 mice and they express only the E7 oncoprotein and constitutively active -catenin under the same K14 promoter. All the transgenic animals in both crosses were maintained as heterozygotes. Within the K14-HPV16/ΔN87βcat model, we did not observe any cervical pathology in the wild type and K14-ΔN87βcat mice, whereas we observed CINIII in 26.7% of K14-HPV16 animals and CINIII and invasive tumors in 30% of the double transgenic animals at an average of 6 months of age. Within the K14-E7/ΔN87βcat model, wild type animals did not develop any cervical pathology. Invasive cervical cancer was observed in 10.5% of the animals expressing activated β-catenin and in 50% of the animals expressing HPV16-E7 oncogene. In double transgenic animals, expression of β-catenin and the HPV16-E7 oncogene induced invasive cervical cancer at an average age of 6 months in 93.75% of the cases. In summary, our data support the hypothesis that activation of the Wnt/β-catenin pathway in HPV pre-malignant lesions has a functional role in accelerating cervical carcinogenesis. These findings may have both preventive and therapeutic applications for cervical cancer patients. HPV positive patients may be screened for activation of Wnt signaling for early intervention. Late stage patients may benefit from novel anti-beta-catenin agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4328. doi:10.1158/1538-7445.AM2011-4328

Abstract 4505: Development of small molecules to target ezrin as anti-metastatic agents

The most common cause for mortality in osteosarcoma (OS) is respiratory failure due to metastasis to lungs. Thus targeting underlying molecular events that lead to metastasis can provide a significant benefit to patients with fatal metastatic disease. Accumulating evidence from experimental animal models and human cases suggests that ezrin is a key factor in the metastasis of OS cells. Ezrin is a multifunctional protein that connects the actin cytoskeleton to extracellular matrix through transmembrane proteins. We screened small molecule libraries for compounds that directly interact with ezrin protein. Two small molecules that directly bind to ezrin with low micromolar affinity were selected based on inhibiting ezrin function in multiple assays. They inhibited ezrin phosphorylation, ezrin-actin interaction, and ezrin mediated motility of OS cells in culture. These compounds were unique in their mechanism of action such that they inhibited in vitro phosphorylation of ezrin by protein kinase C (PKC) by binding to the substrate not by inhibiting the kinase activity of the enzyme. PKC was able to phosphorylate other substrates in the presence of these novel ezrin inhibitors. They also mimicked the ezrin morpholino phenotype and caused a unique developmental defect consistent with reduced cell motility in zebrafish. Following tail vein injection of osteosarcoma cells to mice, both molecules inhibited lung metastasis of ezrin-sensitive cells, but not ezrin-resistant cells. These two molecules demonstrate a novel targeted therapy that directly inhibits ezrin protein as an approach to prevent tumor metastasis in osteosarcoma and other tumors with elevated ezrin in their metastatic subclones.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4505. doi:10.1158/1538-7445.AM2011-4505

Abstract 663: YK-4-279 inhibits ERG and ETV1 mediated prostate cancer cell invasion

Chromosomal translocations involving the ETS family of transcription factors are found in a majority of prostate cancers, including the most clinically aggressive forms. These translocations produce a chimeric gene, which fuses the promoter region of an androgen responsive gene, such as TMPRSS2, to the coding region of ETS factors, most frequently ETV1 or ERG. Over-expression of ETS factors in prostate cancer cells results in a more invasive phenotype. The high prevalence of these rearrangements, and their biological significance represents a novel therapeutic target for the treatment of prostate cancer. We recently reported the development of YK-4-279, a small molecule inhibitor of EWS-FLI1 oncoprotein in Ewing's Sarcoma. ERG and ETV1 belong to the same class of ETS factors as FLI1. Due to the close homology of FLI1 with ERG and ETV1, we tested the ability of YK-4-279 to inhibit ETS biological activity in prostate cell-lines such as VCaP and LNCaP that demonstrate androgen dependent ERG and ETV1 expression, respectively. YK-4-279 inhibited ERG and ETV1 mediated transcription of target genes such as PLAU, PLAT, ADAM19 and MMP-13, which are involved in breakdown of the extracellular matrix and metastasis. YK-4-279 reduced the motility and invasive phenotype of ETV1-fusion positive LNCaP cells and ERG fusion-positive VCaP cells in in vitro invasion assays. However, ETS fusion-negative PC-3 cells were unresponsive to YK-4-279. ERG knockdown in VCaP cells resulted in a loss of drug responsiveness. Transient ERG expression in PC-3 cells resulted in an increased invasive phenotype, which was reduced by YK-4-279. Our results demonstrate that YK-4-279 inhibits ERG and ETV1 biological activity in fusion-positive prostate cancer cells leading to decreased motility and invasion. Therefore, YK-4-279 may have an impact on metastasis in prostate cancer, which is a leading cause of death, and it may be further evaluated for its clinical applications in prostate cancer, in addition to Ewing's sarcoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 663. doi:10.1158/1538-7445.AM2011-663

Arsenic trioxide inhibits human cancer cell growth and tumor development in mice by blocking Hedgehog/GLI pathway

The Hedgehog (Hh) pathway is activated in some human cancers, including medulloblastoma. The glioma-associated oncogene homolog (GLI) transcription factors are critical mediators of the activated Hh pathway, and their expression may be elevated in some tumors independent of upstream Hh signaling. Thus, therapies targeting GLI transcription factors may benefit a wide spectrum of patients with mutations at different nodal points of the Hh pathway. In this study, we present evidence that arsenic trioxide (ATO) suppresses human cancer cell growth and tumor development in mice by inhibiting GLI1. Mechanistically, ATO directly bound to GLI1 protein, inhibited its transcriptional activity, and decreased expression of endogenous GLI target genes. Consistent with this, ATO inhibited the growth of human cancer cell lines that depended on upregulated GLI expression in vitro and in vivo in a xenograft model of Ewing sarcoma. Furthermore, ATO improved survival of a clinically relevant spontaneous mouse model of medulloblastoma with activated Hh pathway signaling. Our results establish ATO as a Hh pathway inhibitor acting at the level of GLI1 both in vitro and in vivo. These results warrant the clinical investigation of ATO for tumors with activated Hh/GLI signaling, in particular patients who develop resistance to current therapies targeting the Hh pathway upstream of GLI.

Abstract 3409: Arsenic trioxide inhibits Ewing sarcoma growth by blocking Hedgehog/GLI pathway

Ewing's Sarcoma Family of Tumors (ESFT) is an undifferentiated neoplasm of the bone and soft tissue. ESFT is characterized by a specific chromosomal translocation occurring between chromosome 22 and (in most cases) chromosome 11, which generates an aberrant transcription factor, EWS-FLI1. We have previously shown that GLI1 is a direct transcriptional target of EWS-FLI1, and is important for ESFT tumorigenicity. Thus, GLI1 is a potential therapeutic target in ESFT. Arsenic Trioxide (ATO) is an FDA approved drug used for the treatment of Acute Promyelocytic Luekemia (APL) as a second line of therapy for those patients who don't response or relapse on All-trans-retinoic acid therapy. We show that Arsenic Trioxide inhibits GLI1 transcriptional activity. Arsenic Trioxide can also decrease the expression of GLI target genes without affecting GLI1 protein levels. We also show that ATO can inhibit the growth of ESFT cell lines in vitro and in vivo in a mouse xenograft model. To further prove that ATO is causing tumor cell growth inhibition by affecting GLI, we treated a mouse medulloblastoma model that is driven by an activating Smoothened mutation SMOA1. We were able to significantly improve survival of these mice with ATO treatment. Our results establish ATO as a hedgehog pathway inhibitor, and warrant the investigation of ATO in clinical trials as a new therapy for ESFT, basal cell carcinoma and medulloblastoma patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3409.