Resveratrol induces Notch2-mediated apoptosis and suppression of neuroendocrine markers in medullary thyroid cancer

BACKGROUND

Currently, complete surgical resection is the only curative option for medullary thyroid cancer (MTC). Previous work has shown the Notch pathway is a potent tumor suppressor in MTC and that resveratrol activates the Notch pathway in carcinoid cancer, a related neuroedocrine malignancy. In this study, we hypothesized that the effects observed on carcinoid cells could be extended to MTC.

METHODS

MTC cells treated with varying doses of resveratrol were assayed for viability by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Western blot analysis for achaete-scute complex-like 1 (ASCL1), chromogranin A (CgA), full-length and cleaved caspase 3, and poly-ADP ribose polymerase (PARP) was performed. Quantitative real-time polymerase chain reaction (qPCR) was used to measure relative mRNA expression.

RESULTS

Treatment with resveratrol resulted in growth suppression and an increase in the cleavage of caspase-3 and PARP. A dose-dependent inhibition of ASCL1, a neuroedocrine transcription factor, was observed at the protein and mRNA levels. Protein levels of CgA, a marker of hormone secretion, were also reduced after treatment with resveratrol. A dose-dependent induction of Notch2 mRNA was observed by qPCR.

CONCLUSIONS

Resveratrol suppresses in vitro growth, likely through apoptosis, as demonstrated by cleavage of caspase-3 and PARP. Furthermore, resveratrol decreased neuroedocrine markers ASCL1 and chromogranin A. Induction of Notch2 mRNA suggests that this pathway may be central in the anti-MTC effects observed.

Identification and validation of Notch pathway activating compounds through a novel high-throughput screening method

BACKGROUND

Carcinoids are neuroendocrine (NE) tumors with limited treatment options. Notch activation has been shown to suppress growth and hormone production in carcinoid cells.

METHODS

The purpose of this study was to provide a process for identifying Notch activating compounds via high-throughput screening (HTS) and to validate the effects of the strongest hit from the 7264 compounds analyzed: resveratrol (RESV).

RESULTS

Treatment of carcinoid cells with RESV resulted in up-regulation of the Notch signaling pathway as measured by suppression of its downstream target achaete-scute complex-like 1. Luciferase reporter assays incorporating the centromere-binding factor 1 binding site also confirmed the functional activity of RESV-induced Notch. Because activation of the Notch pathway has been shown to suppress carcinoid proliferation, RESV treatment of carcinoid cells led to a dose-dependent inhibition of cellular growth. Immunoblotting revealed phosphorylation of cdc2 (Tyr15) and up-regulation of p21Cip1/Waf, markers of cell cycle arrest, with RESV treatment. Flow cytometry confirmed the mechanism of RESV-induced growth inhibition is S phase cell cycle arrest. Furthermore, because Notch has been shown to inhibit bioactive hormone production from NE tumors, RESV also suppressed expression of the NE peptides/hormones chromogranin A and serotonin. RNA interference assays demonstrated that the hormone suppressing capacity of RESV was due to up-regulation of the Notch2 isoform.

CONCLUSIONS

HTS can be used to identify novel Notch activating compounds, which may have the potential to suppress carcinoid tumor growth and the associated endocrinopathies. Cancer 2011. © 2010 American Cancer Society.

MicroRNA profiling of benign and malignant pheochromocytomas identifies novel diagnostic and therapeutic targets

MicroRNAs (miRNAs) are small RNAs ( approximately 22 bp) that post-transcriptionally regulate protein expression and are found to be differentially expressed in a number of human cancers. There is increasing evidence to suggest that miRNAs could be useful in cancer diagnosis, prognosis, and therapy. We performed miRNA microarray expression profiling on a cohort of 12 benign and 12 malignant pheochromocytomas and identified a number of differentially expressed miRNAs. These results were validated in a separate cohort of ten benign and ten malignant samples using real-time quantitative RT-PCR; benign samples had a minimum follow-up of at least 2 years. It was found that IGF2 as well as its intronic miR-483-5p was over-expressed, while miR-15a and miR-16 were under-expressed in malignant tumours compared with benign tumours. These miRNAs were found to be diagnostic and prognostic markers for malignant pheochromocytoma. The functional role of miR-15a and miR-16 was investigated in vitro in the rat PC12 pheochromocytoma cell line, and these miRNAs were found to regulate cell proliferation via their effect on cyclin D1 and apoptosis. These data indicate that miRNAs play a pivotal role in the biology of malignant pheochromocytoma, and represent an important class of diagnostic and prognostic biomarkers and therapeutic targets warranting further investigation.

Lithium inhibits carcinoid cell growth in vitro

Carcinoids are slow growing neuroendocrine tumors that often cause debilitating symptoms due to excessive secretion of hormones such as serotonin. Surgery is the only potentially curative treatment, but many patients have unresectable metastatic disease. Lithium is a non- competitive inhibitor of GSK-3 with an established safety profile. The objective of this study was to investigate the effects of lithium on carcinoid cell growth in vitro. Lithium treatment caused a dose-dependent reduction in carcinoid cancer cell (BON and H727) growth. Western blot analysis revealed increased expression of cleaved poly (ADP-ribose) polymerase (PARP), indicating the induction of apoptosis. Lithium treatment also suppressed cellular levels of serotonin and chromogranin A. In summary, lithium inactivates GSK-3, induces apoptosis, and suppresses carcinoid cancer cell growth in vitro. The drug has been used clinically since the 19(th) century to treat a variety of diseases including bipolar disorder, and its safety profile is well documented. Therefore, based on these findings, we have undertaken a clinical trial of lithium chloride in the treatment of patients with unresectable carcinoid cancer.

Xanthohumol inhibits the neuroendocrine transcription factor achaete-scute complex-like 1, suppresses proliferation, and induces phosphorylated ERK1/2 in medullary thyroid cancer

BACKGROUND

Achaete-scute complex-like 1 (ASCL1) is a transcription factor important in the malignant development of medullary thyroid cancer (MTC). Activation of Raf-1 signaling is associated with ASCL1 suppression and growth inhibition. Xanthohumol, a natural compound, has recently been shown to have anticancer properties. We thus hypothesized that xanthohumol would suppress growth by activating Raf-1 signaling, thus altering the malignant phenotype of MTC.

METHODS

Human MTC cells were treated with xanthohumol (0-30 micromol/L) for up to 6 days. Proliferation was measured by a methylthiazolyldiphenyl-tetrazolium bromide (MTT) colorimetric assay. Western blot analysis was performed for ASCL1 and markers of Raf-1 pathway activation.

RESULTS

Treatment of MTC cells with xanthohumol resulted in a dose dependent inhibition of growth. Additionally, induction of phosphorylated ERK1/2 and a reduction of ASCL1 protein was noted.

CONCLUSIONS

Xanthohumol is a potent Raf-1 activator in MTC cells. This compound suppresses MTC growth, alters the malignant phenotype, and warrants further preclinical study.

Focal adhesion kinase, a downstream mediator of Raf-1 signaling, suppresses cellular adhesion, migration, and neuroendocrine markers in BON carcinoid cells

We have recently reported that activation of the Raf-1/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase 1/2 (MEK1/2)/ERK1/2 signaling cascade in gastrointestinal carcinoid cell line (BON) alters cellular morphology and neuroendocrine phenotype. The mechanisms by which Raf-1 mediates these changes in carcinoid cells are unclear. Here, we report that activation of the Raf-1 signaling cascade in BON cells induced the expression of focal adhesion kinase (FAK) protein, suppressed the production of neuroendocrine markers, and resulted in significant decreases in cellular adhesion and migration. Importantly, inactivation of MEK1/2 by 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene or abolition of FAK induction in Raf-1-activated BON cells by targeted siRNA led to reversal of the Raf-1-mediated reduction in neuroendocrine markers and cellular adhesion and migration. Phosphorylation site-specific antibodies detected the phosphorylated FAK(Tyr407), but not FAK(Tyr397), in these Raf-1-activated cells, indicating that FAK(Tyr407) may be associated with changes in the neuroendocrine phenotype. Overexpression of constitutively active FAK plasmids (wild-type FAK or FAK(Tyr397) mutant) into BON cells reduced neuroendocrine markers, whereas the FAK(Tyr407) mutant plasmid did not show any decrease in the levels of neuroendocrine markers, indicating that phosphorylation of FAK at the Tyr(407) residue may be important for these effects. Our results showed for the first time that FAK is an essential downstream effector of the Raf-1/MEK1/2/ERK1/2 signaling cascade and negatively regulated the neuroendocrine and metastatic phenotype in BON cells.

Abstract 3085: Overexpression of the NOTCH3 intracellular domain alters neuroendocrine phenotype in carcinoid tumor cells

Introduction: There are four mammalian Notch receptors (Notch1-4), which exhibit unique and overlapping expression pattern and act as oncogenes or tumor suppressor genes depending on the cell and context type. We previously reported that Notch1 pathway is minimally active in neuroendocrine (NE) tumors. Furthermore, induction of the Notch1 signaling pathway by over- expression or by pharmacological treatment with valproic acid (VPA) and suberoyl bis-hydroxamic acid (SBHA) suppresses hormone secretion. However, the role of other Notch isoforms is not clear in carcinoid. In this study, we analyzed the presence of Notch isoforms and their regulatory role on chromogranin A (CgA), a clinically important NE marker, and achaete-scute complex-like1 (ASCL1), a known downstream target of Notch.

Methods: Expression of four Notch isoforms was quantified by real time RT-PCR from parental BON cells (GI carcinoid) and VPA treated BON cells. pcDNA3.3 TOPO plasmid containing constitutively expressed human active portion of Notch3, NICD3, was transiently transfected into BON cells and the cell lysates were tested for the presence of NOTCH3. The levels of NE markers such as CgA and ASCL1 were analyzed by Western blot.

Results: Gene expression analysis showed that the parental BON cells had very minimal levels of Notch1-3. Notch4 expression was not detected. In VPA treated cells, the levels of Notch1, 2 and 3 were increased significantly. Overall, the Notch3 expression level was higher than Notch1 and 2 in VPA treated cells. Importantly, there was a 60-fold induction of Notch3 expression in VPA treated cells compared to parental untreated cells. VPA treatment also resulted in a 15-fold and 20-fold increase for Notch1 and Notch2 respectively whereas Notch4 was not detected in these cells. The constitutive expression of NICD3 in BON cells resulted in a reduction in ASCL1 and CgA.

Conclusions: Carcinoid tumor cells have a paucity of all Notch isoforms, including Notch3. For the first time, we demonstrate that Notch3 regulates the NE phenotype, and may play an important role in regulating carcinoid tumor progression. These findings warrant further investigation on targeting Notch3 for carcinoid cancer therapy.

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 3085.

Abstract 4142: The effects of SBHA on Notch 1 expression and platinum sensitivity in ovarian cancer cells

Objective: Despite advances in radical surgical debulking and intraperitoneal chemotherapy, ovarian cancer remains the most deadly gynecologic malignancy. The Notch signaling pathway plays an important role in cellular differentiation, proliferation, and apoptosis. We have previously found Notch 1 intracellular domain (NICD) to be highly expressed in the most platinum resistant ovarian cancer cell lines. Recent evidence has shown that histone deacetylase inhibitors (HDACi's) decrease platinum resistance in oral squamous cell cancers. In addition, the HDACi suberoyl bis-hydroxamic acid (SBHA) has been found to modify Notch 1 expression in other cancers. We hypothesized that SBHA would reduce ovarian cancer cell proliferation through inhibition of the Notch 1 signaling pathway and help sensitize ovarian cancer cells to platinum.

Methods: Following treatment with SBHA, NICD expression in the ovarian carcinoma cell lines OVCAR3, SKOV3, and CaOV3 was analyzed by Western blot. The effects of SBHA and cisplatin on ovarian cancer cell growth were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) growth assay.

Results: NICD expression by Western blot was consistently reduced in all 3 cell lines following treatment with SBHA. Dose-dependent growth inhibition of ovarian cancer cells was demonstrated with SBHA treatment. Furthermore, the addition of SBHA to cisplatin resulted in additional reduction of NICD and further growth suppression in SKOV3, the most platinum resistant cell line tested.

Conclusions: SBHA treatment of ovarian cancer cells led to decreased NICD expression and dose dependent growth reduction in ovarian cancer cells. In addition, we found that SBHA in combination with platinum further reduced NICD expression and growth in SKOV3 cells. These findings provide a compelling argument for further study into the role that Notch 1 signaling may be playing in platinum resistance and ovarian cancer.

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 4142.

Azacytidine induces cell cycle arrest and suppression of neuroendocrine markers in carcinoids

Neuroendocrine tumors (NETs) hypersecrete neuropeptides that cause debilitating symptoms of carcinoid syndrome, including cardiac abnormalities. Surgical resection is the only potentially curative treatment for NETs; however, 90% of NE cancer patients are not candidates for surgery due to extensive hepatic sites involved with NETs. Recently, DNA methyltransferase inhibitors (DNMTI) such as azacytidine (AzaC) have shown efficacy in clinical treatments of hematological malignancies, but effects on NETs are not well-studied. We hypothesized that this novel class of drugs inhibits NET cell growth and decreases NE markers. Three carcinoid types-human midgut (CDNT2.5), pulmonary (H727), and gastrointestinal (BON)- were treated with AzaC (0-100uM) over 6 days. MTT Assays were used to measure cellular proliferation. Western blots were performed with antibodies against chromogranin A (CgA), Neuron-Specific Enolase (NSE), and Cyclin B1. Flow cytometric data was collected from AzaC-treated CNDT2.5 cells for DNA cell cycle analysis. Results showed that treatment of CDNT2.5, H727, and BON carcinoid cells with AzaC resulted in a dose-dependent reduction in tumor cell proliferation. Flow cytometric analysis showed that AzaC-treated cells accumulate in the G2 Phase of cell cycle. AzaC treatment led to: significant decreases in CgA and NSE, indicating that AzaC inhibits neuroendocrine markers; and significant increases in the levels of Cyclin B1, further supporting the flow cytometric data and conclusion that AzaC induces G2/M arrest. The data indicate that AzaC suppresses cell growth in three different carcinoid types, reduces neuroendocrine markers in CNDT2.5 cells, and inhibits cell proliferation by inducing G2/M phase arrest. The results suggest that DNMTIs may be a novel class of therapeutic agents that can effectively control tumor growth and the release of bioactive peptides in patients with NETs.

Identification of a novel Raf-1 pathway activator that inhibits gastrointestinal carcinoid cell growth

Carcinoids are neuroendocrine tumors (NET) that secrete hormones, including serotonin, resulting in the malignant carcinoid syndrome. In addition to the significant morbidity associated with the syndrome, carcinoids are frequently metastatic at diagnosis, and untreated mortality at 5 years exceeds 70%. Surgery is the only curative option, and the need for other therapies is clear. We have previously shown that activation of Raf-1 inhibits carcinoid cell proliferation. We investigated the ability of leflunomide (LFN), a Food and Drug Administration-approved medication for the treatment of rheumatoid arthritis, and its active metabolite teriflunomide (TFN) as a potential anti-NET treatment. LFN and TFN inhibit the in vitro proliferation of gastrointestinal carcinoid cells and induce G(2)-M phase arrest. Daily oral gavage of nude mice with subcutaneous xenografted carcinoid tumors confirms that LFN can inhibit NET growth in vivo. Treatment with TFN suppresses the cellular levels of serotonin and chromogranin A, a glycopeptide co-secreted with bioactive hormones. Additionally, TFN reduces the level of achaete-scute complex-like 1 (ASCL1), a NET marker correlated with survival. These effects are associated with the activation of the Raf-1/mitiogen-activated protein kinase kinase/extracellular signal-regulated kinase-1/2 pathway, and blockade of mitiogen-activated protein kinase kinase signaling reversed the effects of TFN on markers of the cell cycle and ASCL1 expression. In summary, LFN and TFN inhibit carcinoid cell proliferation in vitro and in vivo and alter the expression of NET markers. This compound thus represents an attractive target for further clinical investigation.

Notch 1 signaling is active in ovarian cancer

OBJECTIVE.: Despite advances in chemotherapy and radical surgery, most advanced stage ovarian cancer patients die from their disease, highlighting the need for the development of novel treatment strategies. The Notch signaling pathway plays an important role in cellular differentiation, proliferation and apoptosis. We hypothesized that the active form of Notch 1, the Notch 1 intracellular domain (NICD), would be overexpressed in ovarian cancer cells and that depletion of NICD would lead to growth reduction. METHODS.: Following institutional review board approval, NICD expression was analyzed in human ovarian cancer specimens as well as the ovarian cancer cell lines OVCAR3, SKOV3, and CaOV3. In addition, the effects of Notch 1 depletion on ovarian cancer cell growth were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) growth assay for 6 days following transfection with siRNA against Notch 1. RESULTS.: Western blot analysis revealed abundant NICD expression in all 3 ovarian cancer cell lines, as well as in 16 of 21 (76%) human ovarian cancer samples. Following treatment with Notch 1 siRNA, expression of NICD was greatly reduced in all three cell lines. Furthermore, this depletion of NICD was associated with significant growth inhibition of all three ovarian cancer cell lines. CONCLUSIONS.: NICD was frequently expressed in ovarian cancer cell lines and human ovarian cancer specimens. Importantly, depletion of Notch 1 led to growth inhibition of ovarian cancer cells. These findings support the hypothesis that Notch 1 plays a role in ovarian cancer proliferation, encouraging the investigation of this pathway as a therapeutic target.

MG-132 inhibits carcinoid growth and alters the neuroendocrine phenotype

BACKGROUND

Carcinoid cancers are the most common neuroendocrine (NE) tumors, and limited treatment options exist. The inhibition of glycogen synthase kinase-3beta (GSK-3beta) has been shown to be a potential therapeutic target for the treatment of carcinoid disease. In this study, we investigate the ability of MG-132, a proteasome inhibitor, to inhibit carcinoid growth, the neuroendocrine phenotype, and its association with GSK-3beta.

MATERIALS AND METHODS

Human pulmonary (NCI-H727) and gastrointestinal (BON) carcinoid cells were treated with MG-132 (0-4microM). Cellular growth was measured by the 3-[4,5-dimethylthiazole-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay. Levels of total and phosphorylated GSK-3beta and the NE markers chromogranin A (CgA), Achaete-Scute complex-like 1 (ASCL1), as well as the apoptotic markers poly (ADP-ribose), polymerase (PARP), and cleaved caspase-3 were determined by Western blot.

RESULTS

Treating carcinoid cells with MG-132 resulted in growth inhibition, a dose-dependent inhibition of CgA and ASCL1, as well as an increase in the levels of cleaved PARP and cleaved caspase-3. Additionally, an increase in the level of phosphorylated GSK-3beta was observed.

CONCLUSION

MG-132 inhibits cellular growth and the neuroendocrine phenotype. This proteasome inhibitor warrants further preclinical investigation as a possible therapeutic strategy for intractable carcinoid disease.

ZM336372 induces apoptosis associated with phosphorylation of GSK-3beta in pancreatic adenocarcinoma cell lines

INTRODUCTION

ZM336372 is small molecule tyrosine kinase modulator. It has been shown to inhibit glycogen synthase kinase-3beta (GSK-3beta) through phosphorylation of GSK-3beta at Ser 9. GSK-3beta has previously been shown to mediate cell survival in pancreatic cancer cells. Here we determine the effects of ZM336372 on GSK-3beta phosphorylation, apoptosis, and growth in pancreatic adenocarcinoma cell lines.

METHODS

Panc-1 and MiaPaCa-2 cells were treated with ZM336372 or lithium chloride (LiCl) and compared with solvent control. The effects on proliferation for each cell line were determined using the MTT assay. Western blot analysis was performed to examine the effects of treatment on the phosphorylation of GSK-3beta. In addition, western blot was utilized to examine the cleavage of poly (ADP-ribose) polymerase (PARP), a marker of apoptosis.

RESULTS

A dose-dependent increase in phosphorylation of GSK-3beta was observed after treatment with both ZM336372 and LiCl. Growth inhibition due to treatment with ZM336372 and LiCl also occurred in a dose-dependent fashion. An increase in cleaved PARP was demonstrated after treatment with both agents, as was seen previously with GSK-3beta inhibition in pancreatic adenocarcinoma cells.

CONCLUSION

This is the first description of growth inhibition and apoptosis in pancreatic cancer cells related to GSK-3beta inhibition through treatment with ZM336372.

Inhibition of phosphatidylinositol 3-kinase/Akt signaling suppresses tumor cell proliferation and neuroendocrine marker expression in GI carcinoid tumors

BACKGROUND

Overactivation of PI3K/Akt signaling facilitates tumor proliferation in several cancers. We have shown that various signal transduction pathways promote tumorigenesis in carcinoid tumors, which exhibit endogenously high levels of active, phosphorylated Akt. Therefore, we hypothesized that inhibition of the PI3K/Akt pathway would suppress carcinoid tumor cell growth and neuroendocrine (NE) marker production.

METHODS

Human carcinoid BON cells were treated in vitro with LY294002, a PI3-kinase inhibitor, or transfected with Akt1 siRNA. Tumor cell proliferation was measured by MTT for 6 days. The effect of LY294002 or Akt1 siRNA treatment was assessed by Western analysis. We examined the levels of phosphorylated Akt, total Akt, Akt1, and the NE markers human achaete-scute homolog1 (ASCL1) and chromogranin A (CgA).

RESULTS

Treatment of BON cells with LY294002 reduced tumor cell proliferation (76%) in a dose-dependent manner. Growth also decreased in Akt1 siRNA transfected cells (26%). Levels of active, phosphorylated Akt and the NE tumor markers, ASCL1 and CgA, were diminished with both LY294002 and Akt1 siRNA treatments proportional to the degree of Akt inhibition. Total Akt, Akt2, and Akt3 levels were unaffected by these experiments.

CONCLUSIONS

These data indicate that PI3K/Akt signaling performs a critical role in human carcinoid tumor cell survival and NE hormone generation. Furthermore, the development of novel therapeutics targeting Akt1 or components of the PI3K/Akt pathway may enhance the management of carcinoid disease.

Characterization of the tumor marker muc16 (ca125) expressed by murine ovarian tumor cell lines and identification of a panel of cross-reactive monoclonal antibodies

OBJECTIVES

The ovarian tumor marker CA125 is expressed on human MUC16, a cell surface bound mucin that is also shed by proteolytic cleavage. Human MUC16 is overexpressed by ovarian cancer cells. MUC16 facilitates the binding of ovarian tumor cells to mesothelial cells lining the peritoneal cavity. Additionally, MUC16 also is a potent inhibitor of natural killer cell mediated anti-tumor cytotoxic responses. Extensive studies using human as well as murine ovarian tumor cell models are required to clearly define the function of MUC16 in the progression of ovarian tumors. The major objective of this study was to determine if the murine ovarian tumor cells, MOVCAR, express Muc16 and to characterize antibodies that recognize this mucin.

METHODS

RT-PCR analysis was used for detecting the Muc16 message and size exclusion column chromatography for isolating Muc16 produced by MOVCAR cells. Soluble and cell-associated murine Muc16 were analyzed, respectively, by Western blotting and flow cytometry assays using a new panel of antibodies. The presence of N-linked oligosaccharides on murine Muc16 was determined by ConA chromatography.

RESULTS

We demonstrate that murine Muc16 is expressed by mouse ovarian cancer cells as an ~250 kDa glycoprotein that carries both O-linked and N-linked oligosaccharides. In contrast to human MUC16, the murine ortholog is primarily released from the cells and cannot be detected on the cell surface. Since the released murine Muc16 is not detected by conventional anti-CA125 assays, we have for the first time identified a panel of anti-human MUC16 antibodies that also recognizes the murine counterpart.

CONCLUSION

The antibodies identified in this study can be used in future purification of murine Muc16 and exhaustive study of its properties. Furthermore, the initial identification and characterization of murine Muc16 is a vital preliminary step in the development of effective murine models of human ovarian cancer. These models will aid in the further elucidation of the role that human MUC16 plays in the etiology and progression of ovarian tumors.

Tautomycetin and tautomycin suppress the growth of medullary thyroid cancer cells via inhibition of glycogen synthase kinase-3beta

Medullary thyroid cancer (MTC) is a relatively uncommon neuroendocrine tumor that arises from the calcitonin-secreting parafollicular cells of the thyroid gland. Unfortunately, MTC frequently metastasizes, precluding curative surgical resection and causing significant morbidity. Thus, there is an urgent need for new treatment modalities. Tautomycin and tautomycetin are antifungal antibiotics isolated from Streptomyces spiroverticillatus and Streptomyces griseochromogens, respectively. Glycogen synthase kinase-3beta is a serine/threonine protein kinase that regulates multiple cellular processes and is important in various cancers, including MTC. Treatment with tautomycin and tautomycetin decreased neuroendocrine markers, suppressed hormonal secretion, and inhibited growth through apoptosis in MTC cells. Importantly, we describe a novel action of these compounds: inhibition of glycogen synthase kinase-3beta.

Tautomycin suppresses growth and neuroendocrine hormone markers in carcinoid cells through activation of the Raf-1 pathway

BACKGROUND

Carcinoids are neuroendocrine (NE) tumors with limited treatment options. Raf-1 pathway activation has been shown to suppress hormone production in carcinoid cells. We investigated a novel treatment for carcinoid cell growth based on pharmacologic Raf-1 activation using the compound tautomycin (TTY).

METHODS

Human carcinoid cells were treated with TTY for 48 hours. Western blot analysis was used to demonstrate Raf-1 pathway activation by phosphorylation of ERK1/2 and to determine the effect on NE tumor markers. Cellular growth was measured by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay.

RESULTS

Treatment with TTY resulted in dose-dependent activation of the Raf-1 pathway. Furthermore, a significant decrease in NE tumor markers was seen. Importantly, TTY inhibited carcinoid cellular growth and induced the cell-cycle inhibitors p21 and p27.

CONCLUSION

TTY activates the Raf-1 pathway, limits carcinoid cell growth, and suppresses NE marker production in vitro. This new compound warrants further investigation in animal models of carcinoid cancer.

AKT and PTEN expression in human gastrointestinal carcinoid tumors

Activation of Akt (protein kinase B) and loss of phosphatase and tensin homolog (PTEN) expression have been associated with disease recurrence and reduced survival in several cancers. We evaluated the expression patterns and prognostic value of active, phosphorylated Akt (pAkt) and PTEN in gastrointestinal (GI) carcinoid tumors. Total Akt, pAkt, and PTEN expression was assessed by Western blot analysis in 14 tumor samples from patients with GI carcinoid tumors. Expression levels were quantified with volume analysis software and correlated with clinical parameters. Total Akt, pAkt, and PTEN proteins were detectable in all tumor samples. The expression of activated pAkt and pAkt:PTEN ratios were significantly associated with elevated serum chromogranin A measurements (r=0.77 and 0.78, respectively, P</=0.02 for both). In addition, pAkt:PTEN expression ratios positively correlated with older age (r=0.65, P=0.017). Increased pAkt and pAkt:PTEN expression both were associated with reduced survival (r= -0.51, P=0.06 and r= -0.50, P=0.09, respectively). Patients with pAkt:PTEN ratios greater than one also had dramatically reduced overall survival, but this finding did not achieve statistical significance (36 vs. 153 months, P=0.19). These data suggest that pAkt and PTEN expression levels may be useful tools in understanding tumor biology and perhaps predicting survival in patients with carcinoid tumors. Furthermore, cumulative mutations may lead to upregulation of pAkt and loss of PTEN expression as patients age explaining why older age is associated with a worse prognosis in patients with carcinoid tumors.