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.