MCL1 nuclear translocation induces chemoresistance in colorectal carcinoma

Colorectal cancer (CRC) is one of the most common and deadliest forms of cancer. Myeloid Cell Leukemia 1 (MCL1), a pro-survival member of the Bcl-2 protein family is associated with chemo-resistance in CRC. The ability of MCL1 to inhibit apoptosis by binding to the BH3 domains of pro-apoptotic Bcl-2 family members is a well-studied means by which this protein confers resistance to multiple anti-cancer therapies. We found that specific DNA damaging chemotherapies promote nuclear MCL1 translocation in CRC models. In p53null CRC, this process is associated with resistance to chemotherapeutic agents, the mechanism of which is distinct from the classical mitochondrial protection. We previously reported that MCL1 has a noncanonical chemoresistance capability, which requires a novel loop domain that is distinct from the BH3-binding domain associated with anti-apoptotic function. Herein we disclose that upon treatment with specific DNA-damaging chemotherapy, this loop domain binds directly to alpha-enolase which in turn binds to calmodulin; we further show these protein−protein interactions are critical in MCL1’s nuclear import and chemoresistance. We additionally observed that in chemotherapy-treated p53−/− CRC models, MCL1 nuclear translocation confers sensitivity to Bcl-xL inhibitors, which has significant translational relevance given the co-expression of these proteins in CRC patient samples. Together these findings indicate that chemotherapy-induced MCL1 translocation represents a novel resistance mechanism in CRC, while also exposing an inherent and targetable Bcl-xL co-dependency in these cancers. The combination of chemotherapy and Bcl-xL inhibitors may thus represent a rational means of treating p53−/− CRC via exploitation of this unique MCL1-based chemoresistance mechanism.

A Multimodal Approach to Discover Biomarkers for Taxane-Induced Peripheral Neuropathy (TIPN): A Study Protocol

Introduction: Taxanes are a class of chemotherapeutics commonly used to treat various solid tumors, including breast and ovarian cancers. Taxane-induced peripheral neuropathy (TIPN) occurs in up to 70% of patients, impacting quality of life both during and after treatment. TIPN typically manifests as tingling and numbness in the hands and feet and can cause irreversible loss of function of peripheral nerves. TIPN can be dose-limiting, potentially impacting clinical outcomes. The mechanisms underlying TIPN are poorly understood. As such, there are limited treatment options and no tools to provide early detection of those who will develop TIPN. Although some patients may have a genetic predisposition, genetic biomarkers have been inconsistent in predicting chemotherapy-induced peripheral neuropathy (CIPN). Moreover, other molecular markers (eg, metabolites, mRNA, miRNA, proteins) may be informative for predicting CIPN, but remain largely unexplored. We anticipate that combinations of multiple biomarkers will be required to consistently predict those who will develop TIPN. Methods: To address this clinical gap of identifying patients at risk of TIPN, we initiated the Genetics and Inflammatory Markers for CIPN (GENIE) study. This longitudinal multicenter observational study uses a novel, multimodal approach to evaluate genomic variation, metabolites, DNA methylation, gene expression, and circulating cytokines/chemokines prior to, during, and after taxane treatment in 400 patients with breast cancer. Molecular and patient reported data will be collected prior to, during, and after taxane therapy. Multi-modal data will be used to develop a set of comprehensive predictive biomarker signatures of TIPN. Conclusion: The goal of this study is to enable early detection of patients at risk of developing TIPN, provide a tool to modify taxane treatment to minimize morbidity from TIPN, and improved patient quality of life. Here we provide a brief review of the current state of research into CIPN and TIPN and introduce the GENIE study design.

CoA Synthase (COASY) Mediates Radiation Resistance via PI3K Signaling in Rectal Cancer

Neoadjuvant radiation is standard of care for locally advanced rectal cancer. Response to radiation is highly variable and directly linked with survival. However, there currently are no validated biomarkers or molecular targets to predict or improve radiation response, which would help develop personalized treatment and ideally targeted therapies. Here, we identified a novel biomarker, coenzyme A synthase (COASY), whose mRNA expression was consistently elevated in radioresistant human rectal cancers. This observation was validated in independent patient cohorts and further confirmed in colorectal cancer cell lines. Importantly, genetic overexpression and knockdown yielded radioresistant and sensitive phenotypes, respectively, in vitro and in vivo. COASY-knockdown xenografts were more vulnerable to radiation, showing delayed tumor growth, decreased proliferation, and increased apoptosis. Mechanistically, COASY protein directly interacted with the PI3K regulatory subunit PI3K-P85α, which increased AKT and mTOR phosphorylation, enhancing cell survival. Furthermore, shRNA COASY knockdown disrupted downstream PI3K pathway activation and also hindered DNA double-strand break repair, which both led to improved radiosensitivity. Collectively, this work reveals for the first time the biological relevance of COASY as a predictive rectal cancer biomarker for radiation response and offers mechanistic evidence to support COASY as a potential therapeutic target. SIGNIFICANCE: COASY is a novel radiotherapy response modulator in rectal cancer that regulates PI3K activation and DNA repair. Furthermore, COASY levels directly correlate with radiation response and serve as a predictive biomarker.

Abstract 4013: CoA Synthase (COASY): A novel predictive marker and functional protein that mediates radiation resistance via PI3K signaling in rectal cancer

Purpose: Rectal cancer response to neoadjuvant chemoradiation is prognostic for disease-free and overall survival, with better responders enjoying better outcomes. Understanding the biology underlying better responses to therapy could lead to more personalized treatment approaches. The purpose of this study was to evaluate a newly identified biomarker and explore its mechanism of action.

Experimental Design: Pretreatment human rectal cancer samples underwent DNA microarray analysis and profiles were compared to post-chemoradiation histologic regression scores. A candidate gene, COASY (which encodes for Coenzyme A Synthase), was stably knocked down by shRNA in colorectal cell lines, and the effects on response to radiation were tested in a xenograft model. The biological function of COASY was first assessed by Gene Set Enrichment Assay (GSEA). Its effects on cell death, cell survival, and DNA repair capacity in colorectal cell lines was analyzed. Immunoprecipitation of COASY followed by LC-MS/MS analysis was done to identify COASY partners.

Results: COASY gene expression was overexpressed in rectal cancer compared to normal rectum and was significantly correlated to the tumor regression score. Tumors from cell lines knocked down for COASY had a strong delayed tumor growth, less proliferation, and more apoptosis after irradiation than the control cell line using in vivo xenograft models. In addition, a higher cell death rate after irradiation was observed in vitro in two colorectal cancer cell lines knocked

down for COASY. Mechanistically, a physical interaction between COASY and the PI3K regulatory subunit PI3K-P85α was identified; which led to a modulation of AKT and mTOR phosphorylation after irradiation. Furthermore, there were more residual double DNA strand breaks after irradiation in cell lines knocked down for COASY accompanied by a decrease in DNA-PK and MRE11 protein levels.

Conclusion: COASY serves as a predictive biomarker for rectal cancer response to neoadjuvant chemoradiation and its increased levels correlate with poor response. In addition to its role as a predictive biomarker, COASY has biological relevance leading to increased radiation resistance via the PI3K pathway-dependent increase in DNA repair capacity.

Citation Format: Sylvain Ferrandon, Jennifer DeVecchio, Leonardo Duares, Hanuman Chouhan, Jacqueline Davenport, Georgios Karagkounis, Matthew Orloff, David Liska, Matthew F. Kalady. CoA Synthase (COASY): A novel predictive marker and functional protein that mediates radiation resistance via PI3K signaling in rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4013.

Methylated SEPTIN9 plasma test for colorectal cancer detection may be applicable to Lynch syndrome

OBJECTIVE

The plasma-based methylated SEPTIN9 (mSEPT9) is a colorectal cancer (CRC) screening test for adults aged 50-75 years who are at average risk for CRC and have refused colonoscopy or faecal-based screening tests. The applicability of mSEPT9 for high-risk persons with Lynch syndrome (LS), the most common hereditary CRC condition, has not been assessed. This study sought preliminary evidence for the utility of mSEPT9 for CRC detection in LS.

DESIGN

Firstly, SEPT9 methylation was measured in LS-associated CRC, advanced adenoma, and subject-matched normal colorectal mucosa tissues by pyrosequencing. Secondly, to detect mSEPT9 as circulating tumor DNA, the plasma-based mSEPT9 test was retrospectively evaluated in LS subjects using the Epi proColon 2.0 CE assay adapted for 1mL plasma using the "1/1 algorithm". LS case groups included 20 peri-surgical cases with acolonoscopy-based diagnosis of CRC (stages I-IV), 13 post-surgical metastatic CRC, and 17 pre-diagnosis cases. The control group comprised 31 cancer-free LS subjects.

RESULTS

Differential hypermethylation was found in 97.3% (36/37) of primary CRC and 90.0% (18/20) of advanced adenomas, showing LS-associated neoplasia frequently produce the mSEPT9 biomarker. Sensitivity of plasma mSEPT9 to detect CRC was 70.0% (95% CI, 48%-88%)in cases with a colonoscopy-based CRC diagnosis and 92.3% (95% CI, 64%-100%) inpost-surgical metastatic cases. In pre-diagnosis cases, plasma mSEPT9 was detected within two months prior to colonoscopy-based CRC diagnosis in 3/5 cases. Specificity in controls was 100% (95% CI 89%-100%).

CONCLUSION

These preliminary findings suggest mSEPT9 may demonstrate similar diagnostic performance characteristics in LS as in the average-risk population, warranting a well-powered prospective case-control study.

Poly(ADP-Ribose) Polymerase Inhibition Sensitizes Colorectal Cancer-Initiating Cells to Chemotherapy

Colorectal cancer (CRC) remains a leading killer in the U.S. with resistance to treatment as the largest hurdle to cure. Colorectal cancer-initiating cells (CICs) are a self-renewing tumor population that contribute to tumor relapse. Here, we report that patient-derived CICs display relative chemoresistance compared with differentiated progeny. In contrast, conventional cell lines failed model therapeutic resistance. CICs preferentially repaired chemotherapy-induced DNA breaks, prompting us to interrogate DNA damage pathways against which pharmacologic inhibitors have been developed. We found that CICs critically depended on the key single-strand break repair mediator, poly(ADP-ribose) polymerase (PARP), to survive treatment with standard-of-care chemotherapy. Small molecule PARP inhibitors (PARPi) sensitized CICs to chemotherapy and reduced chemotherapy-treated CIC viability, self-renewal, and DNA damage repair. Although PARPi monotherapy failed to kill CICs, combined PARPi therapy with chemotherapy attenuated tumor growth in vivo. Clinical significance of PARPi for CRC patients was supported by elevated PARP levels in colorectal tumors compared with normal colon, with further increases in metastases. Collectively, our results suggest that PARP inhibition serves as a point of fragility for CICs by augmenting therapeutic efficacy of chemotherapy. Stem Cells 2019;37:42-53.

Abstract A01: Development and application of DNA Repair Dysregulation Score in predicting response to neoadjuvant therapy in patients with rectal cancer

Purpose/Background: Neoadjuvant chemoradiation (nCRT) may lead to complete tumor regression in a proportion of patients and may offer the opportunity for organ-preserving strategies. Pretreatment prediction of tumor response to nCRT would allow identification of ideal candidates for this alternative treatment, avoiding the unnecessary detrimental effects of radiation for patients unlikely to develop complete response (CR). Dysregulation of DNA repair pathways is involved in several carcinogenetic processes of human cancers, including colorectal malignancies. The purpose of this study was to develop and test the performance of DNA Repair Dysregulation Score (DS) in the prediction of tumor response to neoadjuvant CRT by comparing gene expression profiles of patients with CR and incomplete response (IR) to nCRT.

Methods/Interventions: 46 patients with T2-3N0-1M0 distal rectal cancer underwent pretreatment biopsy collection prior to nCRT. All patients underwent radiation and 5FU-based chemotherapy. Patients were divided in two groups: a training group composed of 25 patients (9 patients with CR and 16 patients with IR) and a validation group composed of 21 patients (8 patients CR and 13 patients with IR). We performed global gene expression analysis using RNA-seq in the training group to search for differentially expressed genes according to tumor response. To develop the DS, RNA-seq expression values in RPKM of upregulated genes among CR patients were multiplied by +1. Expression values for downregulated genes among IR patients were multiplied by -1. The sum of all expression values for all genes was used to determine individual DS for each patient. Average DS values between CR and IR were compared using Mann-Whitney test and ROC curve was used to estimate the predictive value of the score. To assess the predictive value of our DS, in an independent set of patients, we used qRT-PCR to evaluate gene expression of dysregulated DNA repair genes. Relative expression for dysregulated genes was calculated by ∆∆Ct method. Expression values for upregulated genes among CR patients were multiplied by +1 and expression values for downregulated genes among IR patients were multiplied by -1. The sum of all relative expression values for all genes was performed to determine individual score. Average DS values between CR and IR in this independent group were also compared using Mann-Whitney test and ROC curve was used to estimate the predictive value of the score.

Results/Outcome: Using RNA-seq we identified 7 differentially expressed genes between CR and IR patients to develop the DS (XPA, XRCC3, ATRIP, UBE2A, NEIL2, XRCC4). The average DS value in the training group was 27 RPKM for CR and 14 for IR (p<0.001). The ROC curve resulted in an AUC of 0.94 with high sensitivity (87%) and specificity (100%) to predict response to nCRT using a cutoff of >19.5 for the prediction of response. The average DS score in the validation set was 11.5 for CR and 9.2 for IR (p<0.006). The ROC curve resulted in an AUC 0.85 with high sensitivity (62.5%) and specificity (92.3%) to predict response using a cutoff of >10.7 for the prediction or response.

Conclusions: Our DS may provide accurate prediction of tumor response to nCRT and may be useful in clinical practice to optimized nCRT stratification and adopt organ-preserving strategies for selected patients.

Citation Format: Leandro Jimenez, Fernanda Koyama, Jennifer DeVecchio, Mathew Kalady, Angelita Habr-Gama, Rodrigo Perez, Anamaria Camargo. Development and application of DNA Repair Dysregulation Score in predicting response to neoadjuvant therapy in patients with rectal cancer [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A01.

Structure-Function Analysis of the Mcl-1 Protein Identifies a Novel Senescence-regulating Domain

Unlike other antiapoptotic Bcl-2 family members, Mcl-1 also mediates resistance to cancer therapy by uniquely inhibiting chemotherapy-induced senescence (CIS). In general, Bcl-2 family members regulate apoptosis at the level of the mitochondria through a common prosurvival binding groove. Through mutagenesis, we determined that Mcl-1 can inhibit CIS even in the absence of its apoptotically important mitochondrion-localizing domains. This finding prompted us to generate a series of Mcl-1 deletion mutants from both the N and C termini of the protein, including one that contained a deletion of all of the Bcl-2 homology domains, none of which impacted anti-CIS capabilities. Through subsequent structure-function analyses of Mcl-1, we identified a previously uncharacterized loop domain responsible for the anti-CIS activity of Mcl-1. The importance of the loop domain was confirmed in multiple tumor types, two in vivo models of senescence, and by demonstrating that a peptide mimetic of the loop domain can effectively inhibit the anti-CIS function of Mcl-1. The results from our studies appear to be highly translatable because we discerned an inverse relationship between the expression of Mcl-1 and of various senescence markers in cancerous human tissues. In summary, our findings regarding the unique structural properties of Mcl-1 provide new approaches for targeted cancer therapy.

Glioma cancer stem cells secrete Gremlin1 to promote their maintenance within the tumor hierarchy

In glioblastomas, cancer stem cells (CSCs) reside in functional niches that provide essential cues to maintain the cellular hierarchy. Bone morphogenetic proteins (BMPs) are proposed as anti-CSC therapies to induce differentiation, but, paradoxically, tumors express high levels of BMPs. Yan et al. demonstrate that the BMP antagonist Gremlin1 is specifically expressed by CSCs as protection from endogenous BMPs. Gremlin1-overexpressing cells display increased growth and tumor formation, while targeting Gremlin1 in CSCs impairs growth and self-renewal associated with inhibition of p21WAF1/CIP1, a key CSC signaling node.

Glioblastomas are the most prevalent and lethal primary brain tumor and are comprised of hierarchies with self-renewing cancer stem cells (CSCs) at the apex. Like neural stem cells (NSCs), CSCs reside in functional niches that provide essential cues to maintain the cellular hierarchy. Bone morphogenetic proteins (BMPs) instruct NSCs to adopt an astrocyte fate and are proposed as anti-CSC therapies to induce differentiation, but, paradoxically, tumors express high levels of BMPs. Here we demonstrate that the BMP antagonist Gremlin1 is specifically expressed by CSCs as protection from endogenous BMPs. Gremlin1 colocalizes with CSCs in vitro and in vivo. Furthermore, Gremlin1 blocks prodifferentiation effects of BMPs, and overexpression of Gremlin1 in non-CSCs decreases their endogenous BMP signaling to promote stem-like features. Consequently, Gremlin1-overexpressing cells display increased growth and tumor formation abilities. Targeting Gremlin1 in CSCs results in impaired growth and self-renewal. Transcriptional profiling demonstrated that Gremlin1 effects were associated with inhibition of p21^WAF1/CIP1, a key CSC signaling node. This study establishes CSC-derived Gremlin1 as a driving force in maintaining glioblastoma tumor proliferation and glioblastoma hierarchies through the modulation of endogenous prodifferentiation signals.

Chemotherapy activates cancer-associated fibroblasts to maintain colorectal cancer-initiating cells by IL-17A

Chemotherapy stimulates cancer-associated fibroblasts to secrete interleukin-17A to provide maintenance cues to support the growth of colorectal cancer-initiating cells.

Many solid cancers display cellular hierarchies with self-renewing, tumorigenic stemlike cells, or cancer-initiating cells (CICs) at the apex. Whereas CICs often exhibit relative resistance to conventional cancer therapies, they also receive critical maintenance cues from supportive stromal elements that also respond to cytotoxic therapies. To interrogate the interplay between chemotherapy and CICs, we investigated cellular heterogeneity in human colorectal cancers. Colorectal CICs were resistant to conventional chemotherapy in cell-autonomous assays, but CIC chemoresistance was also increased by cancer-associated fibroblasts (CAFs). Comparative analysis of matched colorectal cancer specimens from patients before and after cytotoxic treatment revealed a significant increase in CAFs. Chemotherapy-treated human CAFs promoted CIC self-renewal and in vivo tumor growth associated with increased secretion of specific cytokines and chemokines, including interleukin-17A (IL-17A). Exogenous IL-17A increased CIC self-renewal and invasion, and targeting IL-17A signaling impaired CIC growth. Notably, IL-17A was overexpressed by colorectal CAFs in response to chemotherapy with expression validated directly in patient-derived specimens without culture. These data suggest that chemotherapy induces remodeling of the tumor microenvironment to support the tumor cellular hierarchy through secreted factors. Incorporating simultaneous disruption of CIC mechanisms and interplay with the tumor microenvironment could optimize therapeutic targeting of cancer.

Hedgehog signaling regulates telomerase reverse transcriptase in human cancer cells

The Hedgehog (HH) signaling pathway is critical for normal embryonic development, tissue patterning and cell differentiation. Aberrant HH signaling is involved in multiple human cancers. HH signaling involves a multi-protein cascade activating the GLI proteins that transcriptionally regulate HH target genes. We have previously reported that HH signaling is essential for human colon cancer cell survival and inhibition of this signal induces DNA damage and extensive cell death. Here we report that the HH/GLI axis regulates human telomerase reverse transcriptase (hTERT), which determines the replication potential of cancer cells. Suppression of GLI1/GLI2 functions by a C-terminus truncated GLI3 repressor mutant (GLI3R), or by GANT61, a pharmacological inhibitor of GLI1/GLI2, reduced hTERT protein expression in human colon cancer, prostate cancer and Glioblastoma multiforme (GBM) cell lines. Expression of an N-terminus deleted constitutively active mutant of GLI2 (GLI2ΔN) increased hTERT mRNA and protein expression and hTERT promoter driven luciferase activity in human colon cancer cells while GANT61 inhibited hTERT mRNA expression and hTERT promoter driven luciferase activity. Chromatin immunoprecipitation with GLI1 or GLI2 antibodies precipitated fragments of the hTERT promoter in human colon cancer cells, which was reduced upon exposure to GANT61. In contrast, expression of GLI1 or GLI2ΔN in non-malignant 293T cells failed to alter the levels of hTERT mRNA and protein, or hTERT promoter driven luciferase activity. Further, expression of GLI2ΔN increased the telomerase enzyme activity, which was reduced by GANT61 administration in human colon cancer, prostate cancer, and GBM cells. These results identify hTERT as a direct target of the HH signaling pathway, and reveal a previously unknown role of the HH/GLI axis in regulating the replication potential of cancer cells. These findings are of significance in understanding the important regulatory mechanisms that determine the functions of HH/GLI signaling in cancer cells.

Abstract 4699A: Hedgehog signaling (HH/Gli) transcriptionally regulates hTERT gene expression in human cancer cells

Tightly coordinated Hedgehog (HH) signaling is critical during normal embryonic development. Aberrant HH signaling is involved in driving cell proliferation in multiple human cancers. Classical HH signaling involves the interaction of the soluble HH ligands with their receptor, Patched (Ptch), thereby releasing a transmembrane protein Smoothened (Smo) from Ptch-mediated inhibition. Smo then activates the Gli family of transcription factors that regulate HH target genes. We have previously reported that HH signaling provides essential survival support to human colon cancer cells and inhibition of this signal induces DNA damage and extensive cell death. However the downstream targets that govern the regulation of cell survival by HH/Gli in cancer cells are not completely defined. This study demonstrates that the Gli proteins transcriptionally regulate the expression of human telomerase reverse transcriptase (hTERT) gene in human cancer cells. hTERT is a known regulator of telomere homeostasis, which determines the replicative potential and hence the life span of cells. Suppression of both Gli1 and Gli2 functions by exogenous expression of a C-terminus truncated Gli3 repressor mutant (Gli3R), or by GANT61, a pharmacological inhibitor of Gli1 and Gli2 activity, reduced hTERT protein expression over a period of 72 hr in human colon, prostate and brain cancer cell lines. Further, exogenously expressed Gli2 significantly increased hTERT protein expression in human colon cancer cell lines. Exposure to GANT61 also inhibited hTERT mRNA expression within 24 hr in human colon cancer cell lines. Insilico analysis of the hTERT promoter revealed 7 putative Gli binding sites suggesting a transcriptional mode of regulation of hTERT expression by Gli2. Chromatin immunoprecipitation with Gli2 antibody precipitated fragments of the hTERT promoter in human colon cancer cell lines, indicating a direct interaction between Gli2 and the hTERT promoter. The binding between Gli2 and hTERT promoter was significantly reduced upon exposure to GANT61. Further, overexpression of the wild type hTERT cDNA in cancer cells prevented the cytotoxic effects of blocking the HH signaling pathway with GANT61. These findings demonstrate hTERT to be a direct transcriptional target and a critical mediator of the HH/Gli signaling pathway, and identify a previously unknown role of the HH/Gli axis in regulating the replication potential of cancer cells. These findings are of significance in understanding important regulatory mechanisms that determine the role of HH/Gli signaling in cancer cell survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4699A. doi:1538-7445.AM2012-4699A

The GLI genes as the molecular switch in disrupting Hedgehog signaling in colon cancer

The Hedgehog (HH) signaling pathway leads to activation of GLI, which transcriptionally regulate target genes. Regulated HH signaling activity is critical during embryogenesis while aberrantly activated HH signaling is evident in a variety of human cancers. Canonical HH signaling engages the transmembrane receptor Patched (PTCH) and the signaling intermediate Smoothened (SMO) to activate GLI1 and GLI2. In addition GLI1 and GLI2 are activated by non-canonical oncogenic signaling pathways to further drive HH-dependent survival. We have demonstrated in human colon carcinoma cells that inhibition of the RAS/RAF pathway by U0126 decreases p-ERK protein expression and also inhibits GLI-luciferase activity and GLI1 mRNA and protein levels. Of importance is the demonstration that targeting of SMO (using cyclopamine) has minimal effect on cell survival in comparison to the inhibition of GLI (using GANT61), which induced extensive cell death in 7/7 human colon carcinoma cell lines. Genetic inhibition of the function of GLI1 and GLI2 by transient transfection of the C-terminus deleted repressor GLI3R, reduced proliferation and induced cleavage of caspase-3 and cell death in HT29 cells, similar to the effects of GANT61. Mechanistically, downstream of GLI1 and GLI2 inhibition, γH2AX (a marker of DNA double strand breaks) expression was upregulated, and γH2AX nuclear foci were demonstrated in cells that expressed GLI3R. Activation of the ATM/Chk2 axis with co-localization of γH2AX and p-Chk2 nuclear foci were demonstrated following GLI1/GLI2 inhibition. GANT61 induced cellular accumulation at G1/S and early S with no further progression before cells became subG1, while cDNA microarray gene profiling demonstrated downregulation of genes involved in DNA replication, the DNA damage response, and DNA repair, mechanisms that are currently being pursued. These studies highlight the importance of targeting the GLI genes downstream of SMO for terminating HH-dependent survival, suggesting that GLI may constitute a molecular switch that determines the balance between cell survival and cell death in human colon carcinoma.

Abstract 1656: Termination of hedgehog (HH) survival signaling at the level of the GLI genes induces DNA damage and extensive cell death in human colon carcinoma cells

Temporally and spatially regulated activity of the HH signaling pathway is important for normal embryonic development and organ patterning while aberrant activation of this pathway is involved in the development of genomic instability and dysregulated proliferation in several human cancers. There is emerging evidence that HH signaling progresses during colon carcinogenesis and in metastatic disease, however little is known functionally about this signaling pathway and how it affects the survival and pathogenesis of colon cancer. Canonical HH signaling occurs via Ptch1, Smo, and activation of Gli1 and Gli2, which transcriptionally regulate HH target genes. We demonstrate that a small molecule inhibitor of Gli1 and Gli2, GANT61, in contrast to cyclopamine (Smo inhibitor), induced extensive cell death in six human colon carcinoma cell lines. Detailed mechanistic studies in HT29 cells demonstrated that GANT61 induced transient accumulation of cells at the G1/S boundary and in early S at 24 hr and 32 hr, respectively, along with upregulation of p21Cip1, cyclin E and cyclin A in G1- and S- phase cells. By 40 hr, GANT61-treated cells (but not cells treated with cyclopamine) became subG1. shRNA-mediated knockdown of p21Cip1 failed to alter the cytotoxicity of GANT61. cDNA microarray gene profiling in GANT61-treated cells identified significant changes in expression of genes involved in DNA damage signaling, DNA replication and DNA repair. In single cell assays (Comet), GANT61 induced DNA damage by 24 hr with increased Tail Moment and in particular Tail Length; within 4 hr, γH2AX foci were detected at sites of DNA breaks (confocal microscopy). Upregulation of activated forms of ATM and Chk2 but not ATR or Chk1 at 4 hr, that were sustained (24 hr), was observed by western analysis following GANT61 exposure. Further, by 4 hr, p-Chk2 foci co-localized with γH2AX foci in nuclei. Partial knockdown of GLI1 and GLI2 using shRNA partially protected HT29 cells from GANT61-induced cell death, and reduced nuclear γH2AX foci. Studies of the extrinsic and intrinsic pathways of apoptosis demonstrated increased expression of Fas and DR5 receptors, decreased expression of PDGFRα (GLI1 target which regulates Fas), and decreased Bcl-2 expression (GLI2 target) following GANT61 treatment. Expression of DNFADD (to abrogate death receptor signaling) and/or over-expression of Bcl-2 (to block mitochondria-mediated apoptosis) partially rescued from GANT61-induced cell death. Data demonstrate the critical role of HH signaling in colon cancer cell survival, and that inhibition of this pathway at the level of the GLI genes in contrast to Smo induces 1) DNA damage, 2) transient accumulation of cells at G1/S and early S, 3) ineffective checkpoint activation, and 4) extensive cell death.

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 1656. doi:10.1158/1538-7445.AM2011-1656

Hedgehog signaling drives cellular survival in human colon carcinoma cells

Aberrant activation of Hedgehog (HH) signaling is implicated in many human cancers. Classical HH signaling is characterized by Smoothened (Smo)-dependent activation of Gli1 and Gli2, which transcriptionally regulate target genes. A small molecule inhibitor of Gli1 and Gli2, GANT61, was used to block HH signaling in human colon carcinoma cell lines that express HH signaling components. GANT61 administration induced robust cytotoxicity in 5 of 6 cell lines and moderate cytotoxicity in the remaining 1 cell line. In comparison, the classical Smo inhibitor, cyclopamine, induced modest cytotoxicity. Further, GANT61 treatment abolished the clonogenicity of all six human colon carcinoma cell lines. Analysis of the molecular mechanisms of GANT61-induced cytotoxicity in HT29 cells showed increased Fas expression and decreased expression of PDGFRα, which also regulates Fas. Furthermore, DR5 expression was increased whereas Bcl-2 (direct target of Gli2) was downregulated following GANT61 treatment. Suppression of Gli1 by shRNA mimicked the changes in gene expression observed in GANT61-treated cells. Overexpression of dominant-negative FADD (to abrogate Fas/DR5-mediated death receptor signaling) and/or Bcl-2 (to block mitochondria-mediated apoptosis) partially rescued GANT61-induced cytotoxicity in HT29 cells. Thus, activated GLI genes repress DR5 and Fas expressions while upregulating Bcl-2 and PDGFRα expressions to inhibit Fas and facilitate cell survival. Collectively, these results highlight the importance of Gli activation downstream of Smo as a therapeutic target in models of human colon carcinoma.

cDNA microarray gene expression profiling of hedgehog signaling pathway inhibition in human colon cancer cells

Background

Hedgehog (HH) signaling plays a critical role in normal cellular processes, in normal mammalian gastrointestinal development and differentiation, and in oncogenesis and maintenance of the malignant phenotype in a variety of human cancers. Increasing evidence further implicates the involvement of HH signaling in oncogenesis and metastatic behavior of colon cancers. However, genomic approaches to elucidate the role of HH signaling in cancers in general are lacking, and data derived on HH signaling in colon cancer is extremely limited.

Methodology/Principal Findings

To identify unique downstream targets of the GLI genes, the transcriptional regulators of HH signaling, in the context of colon carcinoma, we employed a small molecule inhibitor of both GLI1 and GLI2, GANT61, in two human colon cancer cell lines, HT29 and GC3/c1. Cell cycle analysis demonstrated accumulation of GANT61-treated cells at the G1/S boundary. cDNA microarray gene expression profiling of 18,401 genes identified Differentially Expressed Genes (DEGs) both common and unique to HT29 and GC3/c1. Analyses using GenomeStudio (statistics), Matlab (heat map), Ingenuity (canonical pathway analysis), or by qRT-PCR, identified p21^Cip1 (CDKN1A) and p15^Ink4b (CDKN2B), which play a role in the G1/S checkpoint, as up-regulated genes at the G1/S boundary. Genes that determine further cell cycle progression at G1/S including E2F2, CYCLIN E2 (CCNE2), CDC25A and CDK2, and genes that regulate passage of cells through G2/M (CYCLIN A2 [CCNA2], CDC25C, CYCLIN B2 [CCNB2], CDC20 and CDC2 [CDK1], were down-regulated. In addition, novel genes involved in stress response, DNA damage response, DNA replication and DNA repair were identified following inhibition of HH signaling.

Conclusions/Significance

This study identifies genes that are involved in HH-dependent cellular proliferation in colon cancer cells, and following its inhibition, genes that regulate cell cycle progression and events downstream of the G1/S boundary.

Inhibition of NF-kappaB signaling by quinacrine is cytotoxic to human colon carcinoma cell lines and is synergistic in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or oxaliplatin

Colorectal cancer is the third most common malignancy in the United States. Modest advances with therapeutic approaches that include oxaliplatin (L-OHP) have brought the median survival rate to 22 months, with drug resistance remaining a significant barrier. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is undergoing clinical evaluation. Although human colon carcinomas express TRAIL receptors, they can also demonstrate TRAIL resistance. Constitutive NF-kappaB activation has been implicated in resistance to TRAIL and to cytotoxic agents. We have demonstrated constitutive NF-kappaB activation in five of six human colon carcinoma cell lines; this activation is inhibited by quinacrine. Quinacrine induced apoptosis in colon carcinomas and potentiated the cytotoxic activity of TRAIL in RKO and HT29 cells and that of L-OHP in HT29 cells. Similarly, overexpression of IkappaBalpha mutant (IkappaBalphaM) or treatment with the IKK inhibitor, BMS-345541, also sensitized these cells to TRAIL and L-OHP. Importantly, 2 h of quinacrine pretreatment resulted in decreased expression of c-FLIP and Mcl-1, which were determined to be transcriptional targets of NF-kappaB. Extended exposure for 24 h to quinacrine did not further sensitize these cells to TRAIL- or L-OHP-induced cell death; however, exposure caused the down-regulation of additional NF-kappaB-dependent survival factors. Short hairpin RNA-mediated knockdown of c-FLIP or Mcl-1 significantly sensitized these cells to TRAIL and L-OHP. Taken together, data demonstrate that NF-kappaB is constitutively active in colon cancer cell lines and NF-kappaB, and its downstream targets may constitute an important target for the development of therapeutic approaches against this disease.

Abstract 3341: Molecular mechanisms of hedgehog (HH) signaling in human colon carcinoma (cc)

HH signaling is essential for normal embryonic development and tissue patterning, and absent in most adult tissues. Aberrant HH signaling is implicated in many human cancers. The classical HH signaling cascade is initiated by ligation of secretory HH molecules to their receptor, Patched, thereby releasing the inhibition on Smoothened (Smo), which then causes the activation of Gli1 and Gli2. The active Gli molecules transcriptionally modulate HH target gene expression. Non-classical pathways, including Ras/Raf/MEK/Erk and PI3K-Akt, can also activate Gli molecules in lymphomas. We have observed that inhibition of PI3K (using LY294002) or ERK (with U0126) decrease Gli1-luciferase activity (by 20% and 50%, respectively) as well as Gli1 mRNA expression in the human cc cell line, HT29, indicating the existence of a Smo-independent HH signaling axis. Inhibition of classical HH signaling using Cyclopamine, a natural inhibitor of Smo, or CUR61414, a synthetic Smo antagonist, demonstrated activity in mouse models of human cancers (basal cell carcinoma [BCC]), but with absence of activity in clinical trials. In the current study 1) the cytotoxicity of HH signaling inhibition by Cyclopamine or GANT61 (a synthetic small molecule Gli antagonist), and 2) the molecular mechanism(s) downstream of HH signaling inhibition leading to cytotoxicity, are being elucidated in human cc cell lines. Data demonstrate that GANT61 (IC50: 20-30 μM) elicits greater cytotoxicity in human cc than Cyclopamine (Annexin V/PI staining; clonogenic survival). Furthermore in HT29 cells, GANT61 increases Fas expression (a known regulator of apoptosis in cc cells), concomitantly with decreased PDGFRα expression (directly regulated by Gli1), which also regulates Fas. We previously determined that interferon-gamma (IFN-γ) promotes Fas-induced apoptosis via Fas upregulation in cc. Thus, co-treatment of HT29 with non-cytotoxic concentrations of GANT61 (10μM) + IFN-γ (100IU/ml) was synergistic in the induction of cell death, increasing both Fas receptor and Fas ligand expression at the transcriptional level. Immunoprecipitation of the Fas receptor complex demonstrated recruitment of increased FADD and decreased c-FLIP when GANT61 and IFN-γ were combined, confirming the importance of Fas in the cytotoxic response downstream of HH signaling inhibition. Data suggest in cc 1) Gli1 is regulated by both canonical HH and non-canonical PI3K and ERK pathways, 2) the importance of Gli activation downstream and independent of Smo activation as a therapeutic target, 3) activated Gli represses Fas expression via PDGFRα, and 4) Fas plays a critical role downstream of Gli1-targeted HH signaling inhibition. Supported by NCI awards CA32613 and CA108929 to JAH.

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 3341.

Abstract C153: Both TRAIL receptor DR5 isoforms are required for the induction of cell death in human colon carcinoma

Colorectal cancer continues to be the third most common malignancy in the United States. This disease remains resistant to treatment, with only 25–30% of patients disease-free long term; for the rest, median su rvival is only 18–22 months. We previously demonstrated synergistic interaction between FUra/LV combined with IFN- (which potentiates FUra/LV-induced DNA damage and requires the death receptor Fas) in human colon carcinoma cell lines and xenografts. FUra/LV/IFN- also demonstrated responses in heavily pretreated and previously untreated patients in Phase I trial and is currently completing Phase II evaluation in Stage IV colorectal cancer. Further, lexatumumab, an agonistic TRAIL-R2 (DR5) monoclonal antibody, is highly synergistic with FUra/LV/IFN- in xenograft models, dependent on TRAIL receptor activation. Lexatumumab demonstrated the broadest spectrum in vitro activity in a panel of 6 human colon carcinoma cell lines when compared to the activity of the recombinant ligand, TRAIL (targeting DR4 and DR5).

To further understand the mechanism of lexatumumab-induced cell death via DR5, DR5 expression, was determined in human colon carcinoma cell lines (Western, RT-PCR) and primary colon tumors (RT-PCR). The short isoform of the receptor (DR5S) was expressed at a higher level than the long isoform (DR5L). To determine the specific function of each isoform in regulating death signaling, a BJAB-derived cell line lacking DR5 expression (DR5−/−) was employed. DR5 −/− cells were resistant to lexatumumab-induced apoptosis, even when each DR5 isoform was expressed individually, despite the fact that the individual isoforms could still bind ligand (lexatumumab). Analysis of receptor complex formation indicated that DR5, FADD, and caspase-8 were recruited; however, caspase-8 was not processed. Apoptotic signaling was restored when both DR5 isoforms were re-expressed in DR5−/− cells. Lexatumumab sensitivity of HCT8 cells was eliminated by stable shRNA knockdown of both DR5 isoforms, as was the recruitment of FADD and caspase-8 to the receptor complex. In contrast, following 1 hr lexatumumab treatment in wild type HCT8 cells, both DR5 isoforms were recruited to the receptor complex; cell death correlated with recruitment of FADD, cleavage of caspase-8, cleavage of RIP, and reduced expression of c-FLIPS and c-FLIPL. TRAF2 and c-IAP2, but not TRAF1 or c-IAP1, were also recruited; however, the significance of these signaling molecules in the cell death response is currently unknown.

Overall, data indicate that both DR5S and DR5L are required for lexatumumab-induced cell death via the DR5 receptor. Although the significance of this is currently unknown, factors that regulate lexatumumab-induced cell death vs survival at the level of receptor complexes are currently being elucidated.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C153.

CpG-induced IFNgamma expands TLR4-specific IL-18 responses in vivo

Serum IL-18 responses to LPS increase after pretreatment with CpG-containing DNA. Compared to saline-pretreated controls, mice pretreated with CpG for two days produced 20-fold more serum IL-18 when challenged with lipopolysaccharide (LPS). In contrast, IFNgamma-deficiency or anti-IFNgamma pretreatment reduced CpG-expanded IL-18 responses to LPS by 67 and 83%, respectively. Mice pretreated with either IFNgamma or CpG comparably increased LPS-inducible serum IL-18 responses. LPS, compared to challenge with other TLR agonists, was best able to trigger high serum IL-18 levels in CpG-pretreated mice and this response was TLR4-dependent. CpG, compared to pretreatment with other TLR agonists, optimally expanded LPS-induced IL-18 responses that correlated with higher levels of circulating IFNgamma levels prior to LPS challenge. High-level serum IL-18 responses were caspase-1-dependent and P2X7 receptor-independent. We conclude that CpG promotes high-level IL-18 synthesis by an IFNgamma-dependent and IFNgamma-sufficient mechanism in vivo that is optimally triggered by LPS.

Fms-like tyrosine kinase 3-based immunoprophylaxis against infection is improved by adjuvant treatment with anti-interleukin-10 antibody

BACKGROUND

Fms-like tyrosine kinase 3 ligand (Flt3L) expands dendritic-cell populations in vivo and protects against microbial infection in healthy and immunocompromised hosts. Approaches for optimizing the protective effects of Flt3L in vivo are not well known.METHODS. BALB/c mice were treated for 9 days with 10 microg of recombinant (r) Flt3L with or without the addition of 250 microg of anti--interleukin (IL)-10 antibody on day 9. After Leishmania major infection, disease progression was determined by measuring cutaneous lesions. Production of IL-12 and interferon (IFN)- gamma were determined.RESULTS. Flt3L pretreatment increased the synthesis of CD40-inducible IL-12 p40 but not of bioactive p70. Coculture with anti--IL-10 antibody increased p70 production. Combined Flt3L and single-dose anti--IL-10 antibody pretreatment improved lesion cure rates from 40% to 87% relative to mice pretreated with rFlt3L only (P<.01, chi (2) test) and increased T helper 1 (Th1)--type cytokine production 4 weeks after infection but did not cure Rag-2-- and IFN- gamma -knockout BALB/c mice. Flt3L and anti-IL-10 antibody pretreatments increased frequencies of IL-12- and IFN- gamma -secreting cells 2 and 4 days after infection. Both natural killer and CD4(+) cells contributed to increased early IFN- gamma production.CONCLUSION. A single dose of anti--IL-10 antibody significantly improves Flt3L immunoprophylaxis against infection mediated by Th1-type adaptive responses.