Molecular mechanisms of resistance to kinase inhibitors and redifferentiation in thyroid cancers

Protein kinases play critical roles in cell survival, proliferation, and motility. Their dysregulation is therefore a common feature in the pathogenesis of a number of solid tumors, including thyroid cancers. Inhibiting activated protein kinases has revolutionized thyroid cancer therapy, offering a promising strategy in treating tumors refractory to radioactive iodine treatment or cytotoxic chemotherapies. However, despite satisfactory early responses, these drugs are not curative and most patients inevitably progress due to drug resistance. This review summarizes up-to-date knowledge on various mechanisms that thyroid cancer cells develop to bypass protein kinase inhibition and outlines strategies that are being explored to overcome drug resistance. Understanding how cancer cells respond to drugs and identifying novel molecular targets for therapy still represents a major challenge for the treatment of these patients.

Abstract P120: Novel in vitro targeted combination therapies for anaplastic thyroid cancer

Purpose: To identify effective drug combination strategies targeting multiple oncogenic pathways in anaplastic thyroid cancer. Background: Treatments with BRAF and MEK inhibitors induce impressive tumor size reduction in most BRAF-mutated anaplastic thyroid carcinoma (ATC) patients. However, these drugs are ultimately ineffective due to resistance development, probably because ATC cells express multiple oncogenic pathways that can be used to bypass the treatments. Therefore, the identification of novel therapeutic strategies is still urgently needed. We had previously identified additional pathways/targets (TWIST1, MMP9, BCL2, TGFβR, and the stress kinase MAPK14/p38α) by reverse-phase protein arrays (RPPA) and microarray analysis. In this study, we report the in vitro effects of inhibitors specific for the identified targets used alone or in combination with BRAF inhibitors. Methods: We established mouse ATC cell lines (MCH2.2-Luc and PPA6-Luc) to graft into immunocompetent syngeneic animals. As a first step, these lines were treated in vitro for 72 hours with increasing concentrations of nine different inhibitors for the above targets, and the MTS colorimetric assay determined viability/IC50. We also tested the combinatorial effects of these compounds with BRAF inhibitors (vemurafenib or dabrafenib) and compared them to single agents’ effects. Also, we investigated the colony-forming ability and apoptotic response of these cell lines. Results: IC50 concentrations for nine different compounds were calculated. Both cell lines showed similar IC50 values, except that PPA6-Luc was more resistant to the BRAF inhibitor dabrafenib than MCH2.2-Luc. The MMP-9 inhibitor and the PARP inhibitor olaparib did not significantly affect the growth of these lines. Among three different MAPK14/p38α inhibitors tested, ralimetinib was the most effective (IC50 @ 15 mM). Importantly, venetoclax (BCL2 inhibitor) and harmine (TWIST1 inhibitor) effectively inhibited cell growth with an IC50 of 8 µM and 25 mM, respectively. Treatments using 0.1mM dabrafenib or 1mM vemurafenib in combination with 4 other drugs (5 mM each below the IC50) resulted in significant synergy only with ralimetinib (38% growth decrease) and harmine (37% growth decrease) compared to treatments with single agents. Colony-forming assays confirmed the growth suppression. Conclusions: Inhibiting specific targets previously identified by RPPA and microarray analysis demonstrated, for the first time, in differential ATC cell growth suppression. Notably, only a combination of specific inhibitors (dabrafenib combined with the TWIST1 or the MAPK14/p38α inhibitors) resulted in synergy, suggesting that these targeted combinations will be more effective in our preclinical ATC mouse model than the other drugs. By treating these combinations in a mouse model may contribute, in the future, to the development of clinical and therapeutic strategies for aggressive thyroid cancer.

Citation Format: Muthusamy Kunnimalaiyaan, Parag Parekh, Jalyn Golden, Ying Anderson, Stephen Lai, Maria Cabanillas, Marc Zafereo, Ramona Dadu, Marie-Claude Hofmann. Novel in vitro targeted combination therapies for anaplastic thyroid cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P120.

A novel gene panel for prediction of lymph-node metastasis and recurrence in patients with thyroid cancer

BACKGROUND

Although well-differentiated papillary thyroid cancer may remain indolent, lymph node metastases and the recurrence rates are approximately 50% and 20%, respectively. No current biomarkers are able to predict metastatic lymphadenopathy and recurrence in early stage papillary thyroid cancer. Hence, identifying prognostic biomarkers predicting cervical lymph-node metastases would prove very helpful in determining treatment.

METHODS

The database of the Cancer Genome Atlas included 495 papillary thyroid cancer samples. Using this database, we developed a machine learning model to define a gene signature that could predict lymph-node metastasis (N0 or N1). Kruskal-Wallis tests, univariate and multivariate logistic and Cox regression models, and Kaplan-Meier analyses were performed to correlate the gene signature with clinical outcomes.

RESULTS

We identified a panel of 25 genes and constructed a risk score that can differentiate N0 and N1 papillary thyroid cancer samples (P < .001) with a sensitivity of 86%, a specificity of 62%, a positive predictive value of 93%, and a negative predictive value of 42%. This panel represents an independent biomarker to predict metastatic lymphadenopathy (OR = 8.06, P < .001) specifically in patients with T1 lesions (OR = 7.65, P = .002) and disease-free survival (HR = 2.64, P = .043).

CONCLUSION

This novel 25-gene panel may be used as a potential prognostic marker for accurately predicting lymph-node metastasis and disease-free survival in patients with early-stage papillary thyroid cancer.

Xanthohumol increases death receptor 5 expression and enhances apoptosis with the TNF-related apoptosis-inducing ligand in neuroblastoma cell lines

High-risk neuroblastoma (NB) is lethal childhood cancer. Published data including ours have reported the anti-proliferative effect of Xanthohumol (XN), a prenylated chalcone, in various cancer types suggesting that XN could be a useful small molecule compound against cancer. The TNF-Related Apoptosis-Inducing Ligand (TRAIL) is an endogenous ligand that is expressed in various immune cells. TRAIL mediates apoptosis through binding of transmembrane receptors, death receptor 4 (DR4) and/or death receptor 5 (DR5). Cancer cells are frequently resistant to TRAIL-mediated apoptosis, and the cause of this may be decreased expression of death receptors. This study aimed to identify combination therapies that exploit XN for NB. First, the effect of XN on cellular proliferation in human NB cell lines NGP, SH-SY-5Y, and SK-N-AS were determined via MTT assay, colony forming assay, and real-time live cell imaging confluency. XN treatment causes a statistically significant decrease in the viability of NB cells with IC50 values of approximately 12 μM for all three cell lines. Inhibition of cell proliferation via apoptosis was evidenced by an increase in pro-apoptotic markers (cleaved PARP, cleaved caspase-3/-7, and Bax) and a decrease in an anti-apoptotic marker, Bcl-2. Importantly, XN treatment inhibited PI3K/Akt pathway and associated with increased expression of DR5 by both mRNA and protein levels. Furthermore, a statistically significant synergistic reduction was observed following combination treatment (50%) compared to either TRAIL (5%) or XN (15%) alone in SK-N-AS cells. Therefore, this study shows XN treatment reduces NB cell growth via apoptosis in a dose-dependent manner, and enhanced growth reduction was observed in combination with TRAIL. This is the first study to demonstrate that XN alters the expression of DR5 as well as the synergistic effect of XN on TRAIL in NB and provides a strong rationale for further preclinical analysis.

Antiproliferative and apoptotic effect of LY2090314, a GSK-3 inhibitor, in neuroblastoma in vitro

Background

Neuroblastoma (NB) is a devastating disease. Despite recent advances in the treatment of NB, about 60% of high-risk NB will have relapse and therefore long-term event free survival is very minimal. We have reported that targeting glycogen synthase kinase-3 (GSK-3) may be a potential strategy to treat NB. Consequently, investigating LY2090314, a clinically relevant GSK-3 inhibitor, on NB cellular proliferation and may be beneficial for NB treatment.

Methods

The effect of LY2090314 was compared with a previously studied GSK-3 inhibitor, Tideglusib. Colorimetric, clonogenic, and live-cell image confluency assays were used to study the proliferative effect of LY2090314 on NB cell lines (NGP, SK-N-AS, and SH-SY-5Y). Western blotting and caspase glo assay were performed to determine the mechanistic function of LY2090314 in NB cell lines.

Results

LY2090314 treatment exhibited significant growth reduction starting at a 20 nM concentration in NGP, SK-N-AS, and SH-SY-5Y cells. Western blot analysis indicated that growth suppression was due to apoptosis as evidenced by an increase in pro-apoptotic markers cleaved PARP and cleaved caspase-3 and a reduction in the anti-apoptotic protein, survivin. Further, treatment significantly reduced the level of cyclin D1, a key regulatory protein of the cell cycle and apoptosis. Functionally, this was confirmed by an increase in caspase activity. LY2090314 treatment reduced the expression levels of phosphorylated GSK-3 proteins and increased the stability of β-catenin in these cells.

Conclusions

LY2090314 effectively reduces growth of both human MYCN amplified and non-amplified NB cell lines in vitro. To our knowledge, this is the first study to look at the effect of LY2090314 in NB cell lines. These results indicate that GSK-3 may be a therapeutic target for NB and provide rationale for further preclinical analysis using LY2090314.

Antiproliferative and apoptotic effects of xanthohumol in cholangiocarcinoma

Cholangiocarcinoma remains the second most prevalent hepatic neoplasm in the United States with a 5-year survival rate of less than 10%. Currently, no systemic therapy has demonstrated efficacy. Therefore, an urgent need for the identification of molecularly targeted compound(s) remains. The Notch signaling pathway has been shown to be dysregulated in cholangiocarcinoma, exhibiting hyperactivity while also possibly mediating chemotherapeutic resistance. We analyzed the effects of xanthohumol, a prenylated chalcone, on cholangiocarcinoma proliferation utilizing human cholangiocarcinoma cell lines CCLP1, SG-231 and CC-SW-1 while gaining insight into the associated mechanism. Xanthohumol potently reduced cellular proliferation, colony formation, and cell confluency in all three cell lines. Xanthohumol induced cell cycle arrest as well as apoptosis through the reduction of cell cycle regulatory proteins as well as an increase in pro-apoptotic markers (cleaved poly ADP ribose polymerase, cleaved caspase-3) and a decrease in anti-apoptotic markers (X-linked inhibitor of apoptosis and survivin). At the molecular level, xanthohumol reduced Notch1 and AKT expression in a step-wise and time-dependent fashion, with Notch1 reductions preceding AKT. Additionally, xanthohumol reduced cholangiocarcinoma growth in both CCLP-1 and SG-231 derived mice xenografts. In summary, we show that xanthohumol significantly reduced cholangiocarcinoma growth through the Notch1/AKT signaling axis. Furthermore, known pharmacokinetics and bioavailability of XN supports continued development of treatment for cholangiocarcinoma.

Suberoylanilide hydroxamic Acid, a histone deacetylase inhibitor, alters multiple signaling pathways in hepatocellular carcinoma cell lines

INTRODUCTION

Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, has preclinical efficacy in hepatocellular carcinoma (HCC), despite an unclear molecular mechanism. We sought to further investigate the effects of SAHA on HCC. We hypothesize SAHA will inhibit HCC cellular proliferation through apoptosis and aid in further profiling SAHA's effect on HCC oncogenic pathways.

METHODS

HCC cell lines were treated with various concentrations of SAHA. Cell proliferation was determined by MTT and colonogenic assays. Cell lysates were analyzed via Western blotting for apoptotic and oncogenic pathway markers. Caspase glo-3/7 was used to assess apoptosis.

RESULTS

SAHA treatment demonstrated significant (<0.05) reduction in cell growth and colony formation through apoptosis and cell cycle arrest. Western analysis showed reduction in Notch, pAKT and pERK1/2 proteins. Interestingly, phosphorylated STAT3 was increased in all cell lines.

CONCLUSIONS

SAHA inhibits Notch, AKT, and Raf-1 pathways but not the STAT3 pathway. We believe that STAT3 may lead to cancer cell progression, reducing SAHA efficacy in HCC. Therefore, combination of SAHA and STAT or Notch inhibition may be a strategy for HCC treatment.

Potential Molecular Targeted Therapeutics: Role of PI3-K/Akt/mTOR Inhibition in Cancer

Primary liver cancer is one of the most commonly occurring cancers worldwide. Hepatocellular carcinoma (HCC) represents the majority of primary liver cancer and is the 3rd most common cause of cancer-related deaths globally. Survival rates of patients with HCC are dependent upon early detection as concomitant liver dysfunction and advanced disease limits traditional therapeutic options such as resection or ablation. Unfortunately, at the time of diagnosis, most patients are not eligible for curative surgery and have a five-year relative survival rate less than 20%, leading to systemic therapy as the only option. Currently, sorafenib is the only approved systemic therapy; however, it has a limited survival advantage and low efficacy prompting alternative strategies. The inception of sorafenib for HCC systemic therapy and the understanding involved of cancer therapy have led to an enhanced focus of the PI3-k/Akt/mTOR pathway as a potential area of targeting including pan and isoform-specific PI3-K inhibitors, Akt blockade, and mTOR suppression. The multitude, expanding roles, and varying clinical trials of these inhibitors have led to an increase in knowledge and availability for current and future studies. In this review, we provide a review of the literature with the aim to focus on potential targets for HCC therapies as well as an in depth focus on Akt inhibition.

Role of Akt inhibition on Notch1 expression in hepatocellular carcinoma: potential role for dual targeted therapy

BACKGROUND

We have shown that an Akt inhibitor, MK2206, reduces hepatocellular carcinoma (HCC) proliferation. To further delineate MK2206, we sought to investigate the Notch1 pathway and hypothesize that MK2206 treatment will result in Notch1 inhibition with either subsequent or parallel Akt suppression.

METHODS

HCC cell lines were treated with various concentrations of MK2206. Cell proliferation was determined via real-time live cell imaging. Knockdown of Notch1 was used to observe interaction between Notch1 and pAkt. Cell lysates were analyzed via Western blotting for Notch and Akt pathway targets.

RESULTS

After treatment with MK2206 (up to 2 μM), there was a 60% reduction in cell viability at 48 hours with a concomitant reduction in Notch1 expression. Knockdown of Notch1 in HCC cell lines correlated with reduction in Akt phosphorylation.

CONCLUSIONS

MK2206 inhibits both the PI3-K/Akt and Notch1 pathways. Therefore, further characterization of MK2206 comparing the 2 pathways is warranted and the effect of dual targeting in HCC.

Glycogen synthase kinase-3 inhibitor AR-A014418 suppresses pancreatic cancer cell growth via inhibition of GSK-3-mediated Notch1 expression

BACKGROUND

Glycogen synthase kinase-3 (GSK-3) can act as either a tumour promoter or suppressor by its inactivation depending on the cell type. There are conflicting reports on the roles of GSK-3 isoforms and their interaction with Notch1 in pancreatic cancer. It was hypothesized that GSK-3α stabilized Notch1 in pancreatic cancer cells thereby promoting cellular proliferation.

METHODS

The pancreatic cancer cell lines MiaPaCa2, PANC-1 and BxPC-3, were treated with 0-20 μM of AR-A014418 (AR), a known GSK-3 inhibitor. Cell viability was determined by the MTT assay and Live-Cell Imaging. The levels of Notch pathway members (Notch1, HES-1, survivin and cyclinD1), phosphorylated GSK-3 isoforms, and apoptotic markers were determined by Western blot. Immunoprecipitation was performed to identify the binding of GSK-3 specific isoform to Notch1.

RESULTS

AR-A014418 treatment had a significant dose-dependent growth reduction (P < 0.001) in pancreatic cancer cells compared with the control and the cytotoxic effect is as a result of apoptosis. Importantly, a reduction in GSK-3 phosphorylation lead to a reduction in Notch pathway members. Overexpression of active Notch1 in AR-A014418-treated cells resulted in the negation of growth suppression. Immunoprecipitation analysis revealed that GSK-3α binds to Notch1.

CONCLUSIONS

This study demonstrates for the first time that the growth suppressive effect of AR-A014418 on pancreatic cancer cells is mainly mediated by a reduction in phosphorylation of GSK-3α with concomitant Notch1 reduction. GSK-3α appears to stabilize Notch1 by binding and may represent a target for therapeutic development. Furthermore, downregulation of GSK-3 and Notch1 may be a viable strategy for possible chemosensitization of pancreatic cancer cells to standard therapeutics.

Abstract 52: Glycogen synthase kinase inhibition associated with Notch-1 reduction in cholangiocarcinoma

Introduction: Cholangiocarcinoma (CCA) is the most common biliary cancer and the second most common hepatic malignancy after hepatocellular carcinoma with incidence in the United States steadily increasing. It is a highly malignant adenocarcinoma characterized by poor prognosis and chemotherapeutic inefficacy with 5-year survival rates remaining at less than 10%. Currently, surgical resection is the only effective strategy; however, the majority of patients (90%) are not candidates due to metastasis and concomitant liver disease. Furthermore, local and distant recurrence and high morbidity rates are common following resection. Therefore, new targeted molecular strategies against CCA are imperative. The glycogen synthase kinase-3 (GSK-3) pathway is a potential therapeutic target as it is overexpressed in various cancer types including CCA acting as an oncogene in these cancers. However, the role of the GSK-3 isoform and their interaction with Notch-1 remains unclear in CCA. Our findings and other reports demonstrate that the inhibition of Notch-1 in CCA leads to growth suppression. We hypothesize that GSK-3 stabilizes Notch-1 and thereby promoting cellular proliferation in CCA. In this study, we investigated the effect of the GSK-3 inhibitor AR-A014418 (AR) on the levels of GSK-3 isoforms and further delineated the effect of specific GSK-3 inhibition on Notch-1 signaling and growth in CCA.

Methods: The effects of AR on CCA cell lines (CCLP-1 and SG-231) were assessed by MTT assay and live cell imaging. Cell lysates were analyzed via Western blotting for active and total GSK-3, β-catenin, Notch-1, pro-apoptotic and anti-apoptotic proteins. Transient knockout against Notch-1 was used to determine the interaction of Notch-1 in CCA whereas knockout of GSK-3α or β was used to analyze the interaction with Notch-1 and delineate isoform specificity in CCA.

Results: Increasing AR treatment (0μM - 20μM) had a significant dose-dependent growth reduction (p&lt;0.001); starting at 5μM in CCA cells, compared to control. Upon Western analysis, growth suppression due to apoptosis was evidenced by increased expression of pro-apoptotic and reduced anti-apoptotic proteins. Inhibition of GSK-3 by AR reduced the levels of active GSK-3 expression with concomitant reduction in Notch-1 expression in a dose-dependent manner. Importantly, specific knock-down of GSK-3α resulted in Notch-1 reduction compared to GSK-3β knock-down. However, shRNA against Notch-1 had no effect on the expression of either GSK-3 isoform.

Conclusion: AR-A014418, a GSK-3 inhibitor, effectively inhibits CCA growth in cell culture through both GSK-3 and Notch-1 pathways. Transient knockout of GSK-3 isoforms demonstrated specificity toward GSK-3α in reducing Notch-1 suggesting GSK-3α may be required for Notch-1 stability. This is the first study to effectively correlate GSK-3α with Notch-1 in cholangiocarcinoma.

Citation Format: Kevin M. Sokolowski, Selvi Kunnimalaiyaan, T Clark Gamblin, Muthusamy Kunnimalaiyaan. Glycogen synthase kinase inhibition associated with Notch-1 reduction in cholangiocarcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 52. doi:10.1158/1538-7445.AM2015-52

Abstract 5342: Xanthohumol induces apoptosis and reduces notch in neuroblastoma

Background: Neuroblastoma (NB) is a common neuroendocrine tumor with a high incidence of malignancy and recurrence. It signifies the most common extracranial solid cancer in childhood and accounts for 15% of childhood cancer-related deaths. More than 40% of patients present at diagnosis with aggressive disease and distant metastases which poses numerous therapeutic challenges. Despite intensive treatment options, the 5-year disease free survival remains less than 50%. Therefore, effective treatment approaches are required. Although recent studies revealed deregulated expression of Notch signaling in NB, therapeutic targeting of Notch represents a significant challenge. Xanthohumol (XN) (3′-[3,3-dimethyl allyl]-2′,4′,4-trihydroxy-6′-methoxychalcone), prenylated flavonoid from the Humulus lupulus L. (hops) exerts anti-proliferative activity against various cancers but the molecular mechanism of action remains unclear.

In addition, the effect of XN on NB is not known. Based on our findings, we hypothesize that the XN treatment will reduce NB growth and the growth suppression may be mediated by Notch reduction. Therefore, the present study is designed to elicit, for the first time, anti-proliferative effect of XN on NB cell lines as well as understanding the molecular mechanism of action of XN.

Methods: The proliferation effects of XN on a panel of human NB cell lines (SK-NA-S, NGP and

SH-5Y-SY) were assessed by MTT assay as well as in real-time cellular proliferation assay using IncuCyte Live-Cell Imaging system. The expression levels of pro-apoptotic (c-PARP and cleaved caspase-3) and anti-apoptotic proteins (Bcl2, and survivin) were analyzed by Western blotting after XN treatment. Effects of XN on Notch pathway proteins (Notch3, Hes1, and ASCL1) were studied by Western blotting in addition to quantitative RT-PCR. Short hairpin RNA (shRNAs) targeting Notch3 was used to determine the XN sensitivity in NB.

Results: NB cells treated with increasing concentrations of XN (0-30 μM) had a dose-dependent reduction in growth. A significant reduction in growth was noted at or above 10 μM of XN (40% or above; p&lt;0.01) in all three cell lines tested. This was confirmed by real-time imaging of the cells after treatment with XN. The growth suppression effect is due to apoptosis as evidenced by increased expression of c-PARP and cleaved caspase-3 and decreased levels of Bcl2 and survivin proteins. Furthermore, XN inhibited

Notch signaling by reducing Notch3 and associated downstream targets; Hes1 and ASCL1. Concomitant treatment with XN and Notch3 shRNA augmented growth suppression.

Conclusions: We report for the first time that XN targets Notch3 signaling in NB cells. In summary, the similarity of XN metabolism between animals and humans, the antiproliferative effects on various cancers, and safety profile, we anticipate that XN could potentially be used in future clinical studies on patients with disease.

Citation Format: Mariappan Balamurugan, Selvi Kunnimalaiyaan, T.Clark Gamblin, Muthusamy Kunnimalaiyaan. Xanthohumol induces apoptosis and reduces notch in neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5342. doi:10.1158/1538-7445.AM2015-5342

Xanthohumol inhibits Notch signaling and induces apoptosis in hepatocellular carcinoma

Despite improvement in therapeutic strategies, median survival in advanced hepatocellular carcinoma (HCC) remains less than one year. Therefore, molecularly targeted compounds with less toxic profiles are needed. Xanthohumol (XN), a prenylated chalcone has been shown to have anti-proliferative effects in various cancers types in vitro. XN treatment in healthy mice and humans yielded favorable pharmacokinetics and bioavailability. Therefore, we determined to study the effects of XN and understand the mechanism of its action in HCC. The effects of XN on a panel of HCC cell lines were assessed for cell viability, colony forming ability, and cellular proliferation. Cell lysates were analyzed for pro-apoptotic (c-PARP and cleaved caspase-3) and anti-apoptotic markers (survivin, cyclin D1, and Mcl-1). XN concentrations of 5μM and above significantly reduced the cell viability, colony forming ability and also confluency of all four HCC cell lines studied. Furthermore, growth suppression due to apoptosis was evidenced by increased expression of pro-apoptotic and reduced expression of anti-apoptotic proteins. Importantly, XN treatment inhibited the Notch signaling pathway as evidenced by the decrease in the expression of Notch1 and HES-1 proteins. Ectopic expression of Notch1 in HCC cells reverses the anti-proliferative effect of XN as evidenced by reduced growth suppression compared to control. Taken together these results suggested that XN mediated growth suppression is appeared to be mediated by the inhibition of the Notch signaling pathway. Therefore, our findings warrants further studies on XN as a potential agent for the treatment for HCC.

Xanthohumol-Mediated Suppression of Notch1 Signaling Is Associated with Antitumor Activity in Human Pancreatic Cancer Cells

Pancreatic cancer remains a lethal disease with limited treatment options. At the time of diagnosis, approximately 80% of these patients present with unresectable tumors caused by either locally advanced lesions or progressive metastatic growth. Therefore, development of novel treatment strategies and new therapeutics is needed. Xanthohumol (XN) has emerged as a potential compound that inhibits various types of cancer, but the molecular mechanism underlying the effects of XN remains unclear. In the present study, we have assessed the efficacy of XN on pancreatic cancer cell lines (AsPC-1, PANC-1, L3.6pl, MiaPaCa-2, 512, and 651) against cell growth in real time and using colony-forming assays. Treatment with XN resulted in reduction in cellular proliferation in a dose- and time-dependent manner. The growth suppression effect of XN in pancreatic cancer cell lines is due to increased apoptosis via the inhibition of the Notch1 signaling pathway, as evidenced by reduction in Notch1, HES-1, and survivin both at mRNA as well as protein levels. Notch1 promoter reporter analysis after XN treatment indicated that XN downregulates Notch promoter activity. Importantly, overexpression of active Notch1 in XN-treated pancreatic cancer cells resulted in negation of growth suppression. Taken together, these findings demonstrate, for the first time, that the growth suppressive effect of XN in pancreatic cancer cells is mainly mediated by Notch1 reduction.

Curcumin-mediated regulation of Notch1/hairy and enhancer of split-1/survivin: molecular targeting in cholangiocarcinoma

BACKGROUND

Cholangiocarcinoma (CCA) is highly malignant and characterized by poor prognosis with chemotherapeutic resistance. Therefore, continued development of novel, effective approaches are needed. Notch expression is markedly upregulated in CCA, but the utility of Notch1 inhibition is not defined. Based on recent findings, we hypothesized that curcumin, a polyphenolic phytochemical, suppresses CCA growth in vitro via inhibition of Notch1 signaling.

METHODS

Established CCA cell lines CCLP-1 and SG-231 were treated with varying concentrations of curcumin (0-20 μM). Viability was assessed through 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and clonogenic assays. Evaluation of apoptosis was determined via Western analysis for apoptotic markers and Caspase-Glo 3/7 assay. Cell lysates were further analyzed via Western blotting for Notch1/HES-1/survivin pathway expression, cell cycle progression, and survival.

RESULTS

Curcumin-treated CCA cells exhibited reduced viability compared with control treatment. Statistically significant reductions in cell viability were observed with curcumin treatment at concentrations of 7.5, 10, and 15 μM by approximately 10%, 48%, and 56% for CCLP-1 and 13%, 25%, and 50% for SG-231, respectively. On Western analysis, concentrations of ≥10 μM showed reductions in Notch1, HES-1, and survivin. Apoptosis was evidenced by an increase in expression of cleaved poly [ADP] ribose polymerase and an increase in caspase activity. Cyclin D1 (cell cycle progression) expression levels were also reduced with treatment.

CONCLUSIONS

Curcumin effectively induces CCA (CCLP-1 and SG-231) growth suppression and apoptosis at relatively low treatment concentrations when compared with the previous research. A concomitant reduction of Notch1, HES-1, and survivin expression in CCA cell lines provides novel evidence for a potential antitumorigenic mechanism-of-action. To our knowledge, this is the first report showing reduction in HES-1 expression via protein analysis after treatment with curcumin. Such findings merit further investigation of curcumin-mediated inhibition of Notch signaling in CCA either alone or in combination with chemotherapeutic agents.

Inhibition of the AKT pathway in cholangiocarcinoma by MK2206 reduces cellular viability via induction of apoptosis

Introduction

Cholangiocarcinoma (CCA) is an aggressive disease with limited effective treatment options. The PI3K/Akt/mTOR pathway represents an attractive therapeutic target due to its frequent dysregulation in CCA. MK2206, an allosteric Akt inhibitor, has been shown to reduce cellular proliferation in other cancers. We hypothesized that MK2206 mediated inhibition of Akt would impact CCA cellular viability.

Study methods

Post treatment with MK2206 (0-2 μM), cellular viability was assessed in two human CCA cell lines—CCLP-1 and SG231—using an MTT assay. Lysates from the MK2206 treated CCA cells were then examined for apoptotic marker expression levels using Western blot analysis. Additionally, the effect on cellular proliferation of MK2206 treatment on survivin depleted cells was determined.

Results

CCLP-1 and SG231 viability was significantly reduced at MK2206 concentrations of 0.5, 1, and 2 μM by approximately 44%, 53%, and 64% (CCLP-1; p = 0.01) and 32%, 32%, and 42% (SG231; p < 0.00005) respectively. Western analysis revealed a decrease in AKT^Ser473, while AKT^Thr308 expression was unchanged. In addition, cleaved PARP as well as survivin expression increased while pro-caspase 3 and 9 levels decreased with treatment. Depletion of survivin in CCLP-1 cells resulted in apoptosis as evidenced by increased cleaved PARP. In addition, survivin siRNA further enhanced the antitumor activity of MK2206.

Conclusions

This study demonstrates that by blocking phosphorylation of Akt at serine473, CCA cellular growth is reduced. The growth suppression appears to be mediated via apoptosis. Importantly, combination of survivin siRNA transfection and MK2206 treatment significantly decreased cell viability.

MK2206 inhibits hepatocellular carcinoma cellular proliferation via induction of apoptosis and cell cycle arrest

BACKGROUND

Hepatocellular carcinoma (HCC) is commonly diagnosed at an advanced stage and has limited effective treatment options. The aberrant regulation of the phosphoinositide 3-kinase/Akt pathway in HCC makes it an attractive therapeutic target. The effect of MK2206, a novel, allosteric Akt inhibitor, on HCC cells is not yet fully understood. We hypothesized that inhibition of Akt by MK2206 would impact cellular viability.

MATERIALS AND METHODS

Human Huh7, Hep3B, and HepG2 cell lines were treated with 0-2 μM of MK2206 for 96 h. Cell viability was determined by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Western blot analysis was used to examine the expression level of various protein markers to assess the mechanism of drug action and proliferation inhibition.

RESULTS

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed a reduction in cellular viability by ≥55% for all cell lines (control versus 2 μM MK2206; P <0.001). Western blot analysis revealed reduction in the level of phosphorylated AKT-Ser473 with no change in AKT-thr308 expression confirming the specificity of MK2206. There was an observed reduction in caspase-9 and survivin. Importantly, there were increases in p21 and p27 along with decreased cyclinD1 expression after treatment.

CONCLUSIONS

This study demonstrates the anti-tumor activity of MK2206 in HCC cells. The observed reduction in survivin and pro-caspase 9 suggests that MK2206 induces apoptosis. However, HCC proliferation is also halted via induction of cell cycle arrest as indicated by the increase in p21 and p27 expression and decrease in cyclinD1. Importantly, the concentration needed to achieve growth inhibition in HCC is lower than that needed for other cancer types.

Specific glycogen synthase kinase-3 inhibition reduces neuroendocrine markers and suppresses neuroblastoma cell growth

OBJECTIVE

Neuroblastoma is a common neuroendocrine (NE) tumor that presents in early childhood, with a high incidence of malignancy and recurrence. The glycogen synthase kinase-3 (GSK-3) pathway is a potential therapeutic target, as this pathway has been shown to be crucial in the management of other NE tumors. However, it is not known which isoform is necessary for growth inhibition. In this study, we investigated the effect of the GSK-3 inhibitor AR-A014418 on the different GSK-3 isoforms in neuroblastoma.

METHODS

NGP and SH-5Y-SY cells were treated with 0-20 μM of AR-A014418 and cell viability was measured by MTT assay. Expression levels of NE markers CgA and ASCL1, GSK-3 isoforms, and apoptotic markers were analyzed by western blot.

RESULTS

Neuroblastoma cells treated with AR-A014418 had a significant reduction in growth at all doses and time points (P<0.001). A reduction in growth was noted in cell lines on day 6, with 10 μM (NGP-53% vs. 0% and SH-5Y-SY-38% vs. 0%, P<0.001) treatment compared to control, corresponding with a noticeable reduction in tumor marker ASCL1 and CgA expression.

CONCLUSION

Treatment of neuroblastoma cell lines with AR-A014418 reduced the level of GSK-3α phosphorylation at Tyr279 compared to GSK-3β phosphorylation at Tyr216, and attenuated growth via the maintenance of apoptosis. This study supports further investigation to elucidate the mechanism(s) by which GSK-3α inhibition downregulates the expression of NE tumor markers and growth of neuroblastoma.

MK-2206 causes growth suppression and reduces neuroendocrine tumor marker production in medullary thyroid cancer through Akt inhibition

BACKGROUND

Development of targeted therapies for medullary thyroid cancer (MTC) has focused on inhibition of the rearranged during transfection (RET) proto-oncogene. Akt has been demonstrated to be a downstream target of RET via the key mediator phosphoinositide-3-kinase. MK-2206 is an orally administered allosteric Akt inhibitor that has exhibited minimal toxicity in phase I trials. We explored the antitumor effects of this compound in MTC.

METHODS

Human MTC-TT cells were treated with MK-2206 (0-20 μM) for 8 days. Assays for cell viability were performed at multiple time points with MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide). The mechanism of action, mechanism of growth inhibition, and production of neuroendocrine tumor markers were assessed with Western blot analysis.

RESULTS

MK-2206 suppressed MTC cell proliferation in a dose-dependent manner (p ≤ 0.001). Levels of Akt phosphorylated at serine 473 declined with increasing doses of MK-2206, indicating successful Akt inhibition. The apoptotic proteins cleaved poly (ADP-ribose) polymerase and cleaved caspase-3 increased in a dose-dependent manner with MK-2206, while the apoptosis inhibitor survivin was markedly reduced. Importantly, the antitumor effects of MK-2206 were independent of RET inhibition, as the levels of RET protein were not blocked.

CONCLUSIONS

MK-2206 significantly suppresses MTC proliferation without RET inhibition. Given its high oral bioavailability and low toxicity profile, phase II studies with this drug alone or in combination with RET inhibitors are warranted.

Leflunomide suppresses growth in human medullary thyroid cancer cells

BACKGROUND

Medullary thyroid cancer (MTC) is a neuroendocrine tumor that arises from the calcitonin-secreting parafollicular cells of the thyroid gland. Leflunomide (LFN) is a disease-modifying antirheumatic drug approved for the treatment of rheumatoid arthritis, and its active metabolite teriflunomide has been identified as a potential anticancer drug. In this study we investigated the ability of LFN to similarly act as an anticancer drug by examining the effects of LFN treatment on MTC cells.

METHODS

Human MTC-TT cells were treated with LFN (25-150 μmol/L) and Western blotting was performed to measure levels of neuroendocrine markers. MTT assays were used to assess the effect of LFN treatment on cellular proliferation.

RESULTS

LFN treatment downregulated neuroendocrine markers ASCL1 and chromogranin A. Importantly, LFN significantly inhibited the growth of MTC cells in a dose-dependent manner.

CONCLUSIONS

Treatment with LFN decreased neuroendocrine tumor marker expression and reduced the cell proliferation in MTC cells. As the safety of LFN in human beings is well established, a clinical trial using this drug to treat patients with advanced MTC may be warranted.

Resveratrol induces differentiation markers expression in anaplastic thyroid carcinoma via activation of Notch1 signaling and suppresses cell growth

Anaplastic thyroid carcinoma (ATC) is an extremely aggressive malignancy with undifferentiated features, for which conventional treatments, including radioactive iodine ablation, are usually not effective. Recent evidence suggests that the Notch1 pathway is important in the regulation of thyroid cancer cell growth and expression of thyrocyte differentiation markers. However, drug development targeting Notch1 signaling in ATC remains largely underexplored. Previously, we have identified resveratrol out of over 7,000 compounds as the most potent Notch pathway activator using a high-throughput screening method. In this study, we showed that resveratrol treatment (10-50 μmol/L) suppressed ATC cell growth in a dose-dependent manner for both HTh7 and 8505C cell lines via S-phase cell-cycle arrest and apoptosis. Resveratrol induced functional Notch1 protein expression and activated the pathway by transcriptional regulation. In addition, the expression of thyroid-specific genes including TTF1, TTF2, Pax8, and sodium iodide symporter (NIS) was upregulated in both ATC cell lines with resveratrol treatment. Notch1 siRNA interference totally abrogated the induction of TTF1 and Pax8 but not of TTF2. Moreover, Notch1 silencing by siRNA decreased resveratrol-induced NIS expression. In summary, our data indicate that resveratrol inhibits cell growth and enhances redifferentiation in ATC cells dependent upon the activation of Notch1 signaling. These findings provide the first documentation for the role of resveratrol in ATC redifferentiation, suggesting that activation of Notch1 signaling could be a potential therapeutic strategy for patients with ATC and thus warrants further clinical investigation.

Synergistic effect of pasireotide and teriflunomide in carcinoids in vitro

BACKGROUND/AIM

Somatostatin (SST) analogs are mainstay for controlling tumor proliferation and hormone secretion in carcinoid patients. Recent data suggest that extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation may potentiate the anti-tumor effects of SST analogs in carcinoids. Additionally, ERK1/2 phosphorylating agents have been shown to suppress biomarker expression in carcinoids. Thus, Raf-1/MEK/ERK1/2 pathway activating drugs may be synergistic with SST analogs such as pasireotide (SOM230), which may be more effective than others in its class given its elevated receptor affinity and broader binding spectrum. Here, we investigate the effects of SOM230 in combination with teriflunomide (TFN), a Raf-1 activator, in a human carcinoid cell line.

METHODS

Human pancreatic carcinoid cells (BON) were incubated in TFN, SOM230 or a combination. Cell proliferation was measured using a rapid colorimetric assay. Western analysis was performed to analyze expression levels of achaete-scute complex-like 1 (ASCL1), chromogranin A (CgA), phosphorylated and total ERK1/2, and markers for apoptosis.

RESULTS

Combination treatment with SOM230 and TFN reduced cell growth beyond the additive effect of either drug alone. Combination indices (CI) fell below 1, thus quantifiably verifying synergy between both drugs as per the Chou-Talalay CI scale. Combined treatment also reduced ASCL1 and CgA expression beyond the additive effect of either drug alone. Furthermore, it increased levels of phosphorylated ERK1/2, cleaved poly(ADP)-ribose polymerase and caspase-3, and reduced levels of anti-apoptotic biomarkers. Elevated phosphorylated ERK1/2 expression following combination therapy may underlie the synergistic interaction between the two drugs.

CONCLUSION

Since efficacy is achieved at lower doses, combination therapy may palliate symptoms at low toxicity levels. Because each drug has already been evaluated in clinical trials, combinatorial drug trials are warranted.

Co-delivery of doxorubicin and siRNA using octreotide-conjugated gold nanorods for targeted neuroendocrine cancer therapy

A multifunctional gold (Au) nanorod (NR)-based nanocarrier capable of co-delivering small interfering RNA (siRNA) against achaete-scute complex-like 1 (ASCL1) and an anticancer drug (doxorubicin (DOX)) specifically to neuroendocrine (NE) cancer cells was developed and characterized for combined chemotherapy and siRNA-mediated gene silencing. The Au NR was conjugated with (1) DOX, an anticancer drug, via a pH-labile hydrazone linkage to enable pH-controlled drug release, (2) polyarginine, a cationic polymer for complexing siRNA, and (3) octreotide (OCT), a tumor-targeting ligand, to specifically target NE cancer cells with overexpressed somatostatin receptors. The Au NR-based nanocarriers exhibited a uniform size distribution as well as pH-sensitive drug release. The OCT-conjugated Au NR-based nanocarriers (Au-DOX-OCT, targeted) exhibited a much higher cellular uptake in a human carcinoid cell line (BON cells) than non-targeted Au NR-based nanocarriers (Au-DOX) as measured by both flow cytometry and confocal laser scanning microscopy (CLSM). Moreover, Au-DOX-OCT-ASCL1 siRNA (Au-DOX-OCT complexed with ASCL1 siRNA) resulted in significantly higher gene silencing in NE cancer cells than Au-DOX-ASCL1 siRNA (non-targeted Au-DOX complexed with ASCL1 siRNA) as measured by an immunoblot analysis. Additionally, Au-DOX-OCT-ASCL1 siRNA was the most efficient nanocarrier at altering the NE phenotype of NE cancer cells and showed the strongest anti-proliferative effect. Thus, combined chemotherapy and RNA silencing using NE tumor-targeting Au NR-based nanocarriers could potentially enhance the therapeutic outcomes in treating NE cancers.

Abstract 951: Preclinical evaluation of Xanthohumol in carcinoid cancer growth in vitro and in vivo

Background: Besides surgery, there is no potential curative treatment for carcinoid tumors. Because these cancers are metastatic in nature and produce excessive amounts of various bioactive hormones, patients diagnosed with this malignancy will have poor quality of life due to carcinoid syndrome. Therefore, new anticarcinogenic agents are required to improve the effectiveness of treatment. Xanthohumol (XN) (Tetrahydroxy-3′-prenylchalcone) is a prenylated chalconoid found in hops and beer that has been found to have potential anticancer and bioactive properties. Therefore, the purpose of this study was to evaluate the effectiveness of xanthohumol (XN) on carcinoid cancer growth in vitro and in vivo. Methods: To examine the anticancer activity of XN, we treated human gastrointestinal carcinoid BON and bronchopulmonary carcinoid H727 cells with up to 15 μmol/L of XN or carrier (DMSO), and analyzed the effect on cell growth by colony formation assay. The mechanism of growth inhibition was examined by flow cytometry and western analysis for the levels of pro-apoptotic and cell cycle regulatory proteins. To examine the anticancer activity of XN in vivo, subcutaneous BON carcinoid tumors developed in murine xenografts were subjected to intraperitoneal injections of XN (3 mg/kg bwt) or an appropriate volume of DMSO carrier every other day. Results: Treatment with xanthohumol significantly reduced the ability of carcinoid cells to form colonies in a dose-dependent manner. Flow cytometry and western analysis confirmed the observed decrease in cell viability, and showed the decrease was mediated through apoptosis. The carcinoid tumors in the mouse xenograft experiment showed a significant reduction in growth. Conclusions: XN treatment reduced cell viability, colony forming ability and increased cell death through apoptosis. In addition, administration of XN suppressed cancer cell growth in an in vivo xenograft mouse model. Our findings demonstrate for the first time the anti-proliferative effects of xanthohumol in carcinoid cell lines in vivo. Xanthohumol is already being used as a dietary supplement to encourage overall health and has shown few side effects. This fact combined with the potential anticarcinogenic activity found here warrants clinical investigation on patients with carcinoid disease.

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 951. doi:1538-7445.AM2012-951

Hesperetin, a potential therapy for carcinoid cancer

BACKGROUND

The investigators' laboratory has demonstrated that the Notch1 signaling pathway acts as a tumor suppressor in carcinoid tumors. The aim of this study was to examine hesperetin, a flavonoid, as a potential Notch1 activator and carcinoid tumor suppressor.

METHODS

A high-throughput drug screen revealed hesperetin as a Notch1 activator. Human gastrointestinal carcinoid (BON) cell growth after hesperetin treatment was assessed with a 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide assay. Western blots were used to measure neuroendocrine tumor markers, human achaete-scute complex-like 1, and chromogranin A. Notch1 expression was measured using western blot analysis and real-time polymerase chain reaction.

RESULTS

Hesperetin induced cell death in a dose-dependent manner and reduced achaete-scute complex-like 1 and chromogranin A expression, with a concomitant rise in Notch1 levels. It also induced Notch1 messenger ribonucleic acid, indicating regulation at the transcriptional level.

CONCLUSION

Hesperetin induces Notch1 expression in carcinoid cells, subsequently suppressing tumor cell proliferation and bioactive hormone production. This provides evidence for further study into hesperetin as a potential treatment for carcinoid cancer.

Antiproliferative effect of chrysin on anaplastic thyroid cancer

BACKGROUND

Anaplastic thyroid cancer (ATC) is an undifferentiated, aggressive malignancy, for which there are no effective therapies. Though ATCs only make up less than 2% of all thyroid cancer cases, they represent over half of the thyroid cancer-related deaths. Chrysin, a natural flavonoid, has recently been reported as a potential anti-cancer agent. However, the effect of this compound on ATC cells is not known. Thus, in this study, we evaluated the antiproliferative nature of chrysin in ATC cells.

METHODS

HTH7 and KAT18 cells, derived from patients with ATC, were treated with chrysin (25-50 μM) for up to 6 d. Cell proliferation was measured every 2 d using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Western blot analysis for molecular makers of apoptosis was carried out to investigate the effect and mechanism of Chrysin on ATC.

RESULTS

Chrysin inhibited proliferation of HTH7 and KAT18 in a dose- and time-dependent manner. HTH7 and KAT18 cells with Chrysin treatment showed a significant increase in cleaved caspase-3, cleaved PolyADP Ribose Polymerase (PARP), along with a decrease in cyclin D1, Mcl-1, and XIAP. Furthermore, the ratio of Bax to Bcl-2 expression in ATC cells revealed an increase after the treatment.

CONCLUSIONS

Chrysin inhibits growth in ATC cells via apoptosis in vitro. Therefore, the natural flavonoid chrysin warrants further clinical investigation as a new potential drug for the treatment for ATC.

Abstract 2181: Tumor suppressor role of Notch3 in medullary thyroid carcinoma

Introduction: NOTCH3 is a transmembrane receptor that appears to be absent in the neuroendocrine (NE) tumors. We have previously demonstrated that transient expression of the active portion of NOTCH3 (NICD3) alters the NE phenotype and inhibits the proliferation of carcinoid tumor cells in vitro. However, the long term effect of activation this pathway is not clearly understood in Medullary Thyroid Carcinoma (MTC). To elucidate the role of Notch3 in NE, we established a doxycycline inducible NOTCH3 intracellular domain in MTC TT cells. The aim of this study was to assess the long term effect of NOTCH3 and determine the mechanism of inhibition of TT cells growth.

Methods: Doxycycline inducible TT-NOTCH3 cells were created by stable transfection of Tet-On vector followed by transfection of pRevTRE-NOTCH3 plasmid. Functional analysis of NICD3 was done by measuring the degree of luciferase activity by CBF binding assay. Quantification of HES and HEY gene expression (Notch signaling mediators) was done by real time RT-PCR. Effect of Notch3 on NE markers -chromogranin A (CgA) and achaete-scute complex-like1 (ASCL1) – was assessed by Western blot analysis. The influence of NOTCH3 overexpression on TT-NOTCH cell proliferation was measured by the methylthiazolyldiphenyl-tetrazolium bromide (MTT) rapid colorimetric assay. The mechanism of growth inhibition was determined for apoptosis markers by Western blot and flow cytometry analyses.

Results: Treatment of TT-NOTCH3 cells with doxycycline led to an induction of NOTCH3 protein in a dose-dependent manner. Increase in the CBF1 binding activity showed that the NOTCH3 protein is functional and this is associated with changes in transcriptional level of HES and HEY families. More importantly, NOTCH3 activation led to a dose dependant reduction of NE markers ASCL1 and CgA. In addition, NOTCH3 activity is required to suppress MTC cell proliferation and the level of growth regression depends on the amount of NOTCH3 protein expressed. Finally, Western blot analysis and flow cytometry experiments indicated that the growth inhibition is due to apoptosis.

Conclusions: We demonstrate, for the first time, that overexpression of NOTCH3 in MTC cells suppresses tumor cells growth by promoting apoptosis. Moreover, Notch3 pathway is functional as active NOTCH3 triggers the CBF-dependent transcriptional network. Finally, the activation of Notch3 in the in vitro model resulted in down-regulation of NE markers indicated that this pathway is conserved in MTC. Therefore, activation of Notch3 could be a therapeutic strategy to treat patients with MTC.

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 2181. doi:10.1158/1538-7445.AM2011-2181

Expression of the active Notch1 decreases MTC tumor growth in vivo

BACKGROUND

Human medullary thyroid cancer (MTC) is a neuroendocrine (NE) tumor, derived from thyroid C-cells. Besides surgery, there are no curative therapies for MTC. This emphasizes the need for the development of new therapies. In MTC, Notch1 signaling pathway is absent and Notch1 activation in MTC-TT cells has been shown to reduce growth and NE markers in vitro. While the in vitro studies will provide insight into the potential mechanisms by which Notch inhibits growth, only by in vivo model one can recreate the conditions found in patients with MTC and assess effects on metastatic potential and microscopic disease.

MATERIALS AND METHODS

Doxycycline inducible TT-NOTCH1 cells were utilized in a murine subcutaneous xenograft model to study tumor development and growth. Doxycycline was used to induce the expression of Notch1 in these tumors.

RESULTS

Measurements of tumor volume showed that doxycycline treated mice had slower tumor growth than control mice. Western blot analysis of tumor lysates demonstrated activation of Notch1 protein only in doxycycline treated mice suggesting that active Notch1 slowed tumor growth. Furthermore, this activation led to a significant reduction in the levels of achaete-scute complex-like1 and chromogranin A important NE markers.

CONCLUSION

Based on these data, activation of Notch signaling pathway could be a therapeutic strategy to treat patients with MTC.

A preclinical and clinical study of lithium in low-grade neuroendocrine tumors

BACKGROUND

Low-grade neuroendocrine tumors (NETs) respond poorly to chemotherapy; effective, less toxic therapies are needed. Glycogen synthase kinase (GSK)-3β has been shown to regulate growth and hormone production in NETs. Use of lithium chloride in murine models suppressed carcinoid cell growth, reduced GSK-3β levels, and reduced expression of chromogranin A. This study assessed the efficacy of lithium chloride in patients with NETs.

DESIGN

Eligible patients had low-grade NETs. A single-arm, open-label phase II design was used. Lithium was dosed at 300 mg orally three times daily, titrated to serum levels of 0.8-1.0 mmol/L. The primary endpoint was objective tumor response by the Response Evaluation Criteria in Solid Tumors. Secondary endpoints included overall survival, progression-free survival, GSK-3β phosphorylation, and toxicity.

RESULTS

Fifteen patients were enrolled between October 3, 2007 and July 17, 2008, six men and nine women. The median age was 58 years. Patient diagnoses were carcinoid tumor for eight patients, islet cell tumor for five patients, and two unknown primary sites. Eastern Cooperative Oncology Group performance status scores were 0 or 1. Two patients came off study because of side effects. The median progression-free survival interval was 4.50 months. There were no radiographic responses. Because of an early stopping rule requiring at least one objective response in the first 13 evaluable patients, the study was closed to further accrual. Patients had pre- and post-therapy biopsies.

CONCLUSIONS

Lithium chloride was ineffective at obtaining radiographic responses in our 13 patients who were treated as part of this study. Based on the pre- and post-treatment tumor biopsies, lithium did not potently inhibit GSK-3β at serum levels used to treat bipolar disorders.

The Phosphatidylinositol 3-kinase/Akt Signaling Pathway in Neuroendocrine Tumors

The phosphatidylinositol 3-kinase (PI3K)-Akt pathway is often aberrantly activated in neuroendocrine-derived cancers. Therefore, selectively targeting this pathway using small-molecule inhibitors may reduce neuroendocrine tumor burden, potentiate adjunct therapies, and achieve symptomatic control for patients with hormonally active and inoperable disease. Here, we discuss the role of the PI3K-Akt pathway in the malignant transformation of neuroendocrine tumors, specifically carcinoids and small cell lung cancers. The collective findings presented in this review propose that selective targeting of the PI3K-Akt pathway may mitigate neuroendocrine tumor progression, thus offering a viable therapeutic approach for managing systemic disease.