Enhanced inhibitive effects of combination of rofecoxib and octreotide on the growth of human gastric cancer

Analysis of somatostatin receptors and somatostatin promoter methylation in human gastric cancer

Somatostatin (SST) is a gut peptide that is able to inhibit the growth of tumor cells in gastric cancer and other types of cancer. The present study investigated the mRNA and protein levels of SST and SST receptors (SSTRs) in human gastric cancer, and detected the DNA methylation of the SST promoter. The protein levels of SST were detected using a radioimmunoassay in 102 human gastric tissue specimens (51 pairs of samples from 51 gastric cancer patients, each pair of samples included a cancer tissue and a normal tissue sample). SST and SSTR mRNA expression was assessed by reverse transcription-PCR (RT-PCR), while SST promoter methylation was examined using quantitative methylation-specific PCR (qMSP) in 51 pairs of tissues. The association between SST protein and RNA levels and SST methylation and gastric cancer were also analyzed. The protein levels of SST were decreased in the gastric cancer group compared with those of the normal group (5.091±0.994 vs. 7.399±0.956 pg/mg; P<0.01). The RT-PCR analysis indicated that the mRNA levels of SST (0.218±0.183 vs. 0.456±0.331; P<0.001) and SSTRs in the gastric cancer group were lower compared with those of the normal gastric tissue group. The methylation proportion of SST was 45.1% (23/51) in the carcinoma group and 3.9% (2/51) in the normal group. In conclusion, SST promoter methylation is a common event in human gastric cancer and is connected with a decrease in SST protein and RNA levels and associated with gastric carcinogens.

Peptide receptor targeting in cancer: the somatostatin paradigm

Peptide receptors involved in pathophysiological processes represent promising therapeutic targets. Neuropeptide somatostatin (SST) is produced by specialized cells in a large number of human organs and tissues. SST primarily acts as inhibitor of endocrine and exocrine secretion via the activation of five G-protein-coupled receptors, named sst1–5, while in central nervous system, SST acts as a neurotransmitter/neuromodulator, regulating locomotory and cognitive functions. Critical points of SST/SST receptor biology, such as signaling pathways of individual receptor subtypes, homo- and heterodimerization, trafficking, and cross-talk with growth factor receptors, have been extensively studied, although functions associated with several pathological conditions, including cancer, are still not completely unraveled. Importantly, SST exerts antiproliferative and antiangiogenic effects on cancer cells in vitro, and on experimental tumors in vivo. Moreover, SST agonists are clinically effective as antitumor agents for pituitary adenomas and gastro-pancreatic neuroendocrine tumors. However, SST receptors being expressed by tumor cells of various tumor histotypes, their pharmacological use is potentially extendible to other cancer types, although to date no significant results have been obtained. In this paper the most recent findings on the expression and functional roles of SST and SST receptors in tumor cells are discussed.

Transcatheter arterial embolization followed by octreotide and celecoxib synergistically prolongs survival of rabbits with hepatic VX2 allografts

OBJECTIVE

To validate the efficacy of an innovative multimodality therapy with transcatheter arterial embolization (TAE) plus octreotide and celecoxib in reducing neoangiogenesis and prolonging the survival of rabbits with hepatocellular carcinoma.

METHODS

Rabbits with hepatic VX2 allografts were divided into four groups: control group, TAE group, octreotide + celecoxib (O + C) group and the multimodality therapy (TAE + O + C) group. Survival of the rabbits was analyzed using the Kaplan-Meier method and the expression of CD31 in tumor tissues was detected by immunohistochemistry.

RESULTS

Rabbits in the TAE + O + C group lived nearly 20 days longer than those in the control group. The survival rate of the TAE + O + C group was 50% at day 80 and was the highest among the four groups (P < 0.05). No VX2 allograft-bearing rabbits in the control group lived longer than 60 days. Compared with the control group, the survival time of the other two intervention groups were not prolonged significantly (P > 0.05). The CD31 expression induced by TAE was reduced significantly in TAE + O + C group (P < 0.05). Less metastasis was detected in TAE + O + C group.

CONCLUSION

TAE followed by the long-term administration of octreotide and celecoxib can synergistically prolong the survival of rabbits with hepatic VX2 allografts by inhibiting potential neoangiogenesis, tumor growth and metastasis.

Clinical significance of protein expression of cyclooxygenase-2 and somatostatin receptors in gastroenteropancreatic neuroendocrine tumors

Purpose

This study was undertaken to evaluate the significance of cyclooxygenase-2 (COX2) overexpression and the expression of somatostatin receptor (SSTR) subtypes in gastroenteropancreatic neuroendocrine tumors (GEP-NETs).

Materials and Methods

Two hundred and forty-seven cases of GEP-NET, comprising 86 foregut and 156 hindgut primary NETs, and 5 metastatic NETs in the liver, were studied retrospectively with immunohistochemistry for COX2, chromogranin A, Ki-67, SSTR1, SSTR2, and SSTR5.

Results

COX2 overexpression was observed in 54%(126 of 234), and SSTR1, SSTR2, and SSTR5 positivity in 84%(196 of 233), 72%(168 of 233), and 55%(128 of 232), respectively. COX2 overexpression was found to be positively correlated with Ki-67 labeling index and inversely correlated with the expression of SSTR subtypes. In addition, the expression of SSTR subtypes was tightly correlated in any comparative pairs. A significant inverse correlation was found between COX2 and SSTR2 expression in the foregut, but not hindgut NETs. Kaplan-Meier analyses showed that COX2 overexpression (p=0.003) and high Ki-67 labeling index (p<0.001) were associated with poor overall survival (OS), whereas expression of SSTR2 (p<0.001) was associated with better OS of GEP-NET patients. Multivariate analysis revealed negative SSTR2 expression as an independent prognostic marker in GEP-NET patients (p<0.001).

Conclusion

Our results suggest that expression of SSTR subtypes is associated with favorable prognosis, whereas COX2 overexpression is associated with poor prognosis in GEP-NETs. Taken together, COX2 could be a possible therapeutic target in some subsets of GEP-NETs.

Somatostatin receptors in non-neuroendocrine malignancies: the potential role of somatostatin analogs in solid tumors

Somatostatin receptors (sstrs) are G-protein-coupled receptors that mediate various physiological effects when activated by the neuropeptide somatostatin or its synthetic analogs. In addition to the well-documented antisecretory effects of sstr2-preferential somatostatin analogs octreotide and lanreotide, ligand binding to sstr initiates an inhibitory action on tumor growth. This effect may result from both indirect actions (suppression of growth factors and growth-promoting hormones [e.g., GH/IGF-1 axis] and inhibition of angiogenesis) and direct actions (activation of antigrowth activities [e.g., apoptosis]). As solid tumor cells express multiple sstrs, there is a rationale to evaluate the potential antitumor effects of pasireotide (SOM230), a multireceptor-targeted somatostatin analog with high binding affinity for sstr1–3 and sstr5. Pasireotide reduces systemic IGF-1 levels more potently than currently available somatostatin analogs and has been well tolerated in clinical trials.

Mouse models of gastric tumors: Wnt activation and PGE2 induction

Accumulating evidence has suggested that cooperation of oncogenic activation and the host responses is important for cancer development. In gastric cancer, activation of Wnt signaling appears to be a major oncogenic pathway that causes tumorigenesis. In the chronic gastritis caused by Helicobacter pylori infection, cyclooxigenase-2 induces prostaglandin E(2) (PGE(2)) biosythesis, which plays an important role in tumorigenesis. We constructed a series of mouse models and investigated the role of each pathway in the gastric tumorigenesis. Wnt activation in gastric epithelial cells suppresses differentiation, and induces development of preneoplastic lesions. On the other hand, induction of the PGE(2) pathway in gastric mucosa induces development of spasmolytic polypeptide-expressing metaplasia (SPEM), which is a possible preneoplastic metaplasia. Importantly, simultaneous activation of Wnt and PGE(2) pathways leads to dysplastic gastric tumor development. Moreover, induction of the PGE(2) pathway also promotes gastric hamartoma development when bone morphogenetic protein (BMP) signaling is suppressed. These results indicate that alteration in the Wnt or BMP signaling impairs epithelial differentiation, and the PGE(2) pathway accelerates tumor formation regardless of the types of oncogenic pathways. We review the phenotypes and gene expression profiles of the respective models, and discuss the cooperation of oncogenic pathways and host responses in gastric tumorigenesis.

BCL2L10 protein regulates apoptosis/proliferation through differential pathways in gastric cancer cells

The reason for and consequences of BCL2L10 down-regulation in gastric carcinoma are poorly understood. Our aim was to investigate the function of the protein BCL2L10 in gastric carcinoma. We investigated BCL2L10 expression using quantitative real-time PCR and immunoblotting. The methylation status of the BCL2L10 gene promoter was examined by bisulphite sequencing in fresh gastric normal and carcinoma tissues. We studied apoptosis and proliferation regulation in gastric cancer cell lines using flow cytometry, fluorescence staining, murine xenografting and immunoblotting. Pathway inhibitors were applied to confirm the major pathways involved in apoptosis or proliferation regulation. We observed significant correlations between lower BCL2L10 expression and CpG island hypermethylation of the BCL2L10 gene promoter in gastric carcinoma, apoptosis induced by over-expressed BCL2L10 through mitochondrial pathways, and proliferation accelerated by BCL2L10 siRNA via the PI3K-Akt signalling pathway in gastric cancer cell lines. The pro-apoptotic effect of BCL2L10 and growth promotion by BCL2L10 siRNA in gastric cancer cells suggest that it may be a tumour suppressor.

Effects of non-cytotoxic drugs on the growth of multidrug-resistance human gastric carcinoma cell line

OBJECTIVE

To investigate the effects of the non-cytotoxic drug (cyclooxygenase-2 (COX-2) inhibitor and octreotide) on growth of the multidrug-resistant human gastric carcinoma cell line SGC-7901/ADR.

METHODS

The effects of non-cytotoxic drug on the growth of SGC-7901 and SGC-7901/ADR cells were evaluated by (3)H-thymidine incorporation assay. The apoptosis of cells was measured by the TdT-mediated dUTP nick end-labeling assay (TUNEL) and flow cytometric assay. Western blotting was used to analysis the expression of cyclooxygenase (COX-2) protein in SGC-7901 cells and SGC-7901/ADR cells and P-glycoprotein (P-gp) from SGC-7901/ADR cells with variable treatments. Activator protein-1 binding activity was examined by electrophoretic mobility shift assay.

RESULTS

(3)H-thymidine incorporation into SGC-7901/ADR cells treated with celecoxib was significantly lower than that of control group (471.3 +/- 79.7 cpm vs 917.5 +/- 130.8 cpm, P < 0.05). When combined with octreotide, celecoxib presented lower (3)H-thymidine incorporations than its used alone and decreased to 53.3% of that amount original. Either celecoxib or the combination group markedly induced apoptosis in SGC-7901/ADR cells. COX-2 protein in the SGC-7901/ADR cells was higher than in that of the SGC-7901 cells (1.543 +/- 0.052 vs 0.564 +/- 0.021, P < 0.05). The inhibition of P-gp could be achieved with celecoxib alone and combination with octreotide (0.486 +/- 0.012, 0.252 +/- 0.014 vs 0.941 +/- 0.033, P < 0.05). Moreover, AP-1 binding activity could be suppressed by non-cytotoxic drug and showed a synergistic effect.

CONCLUSION

The combination of non-cytotoxic drug significantly improved the inhibitive effects on the growth of multidrug-resistant human gastric cancer cells.

Effects of celecoxib on the reversal of multidrug resistance in human gastric carcinoma by downregulation of the expression and activity of P-glycoprotein

We investigated the effects of celecoxib on the cell proliferation and the expression and activity of P-glycoprotein in the human gastric carcinoma multidrug resistance sublines SGC7901/adriamycin and SGC7901/vincristine. The cell proliferation was measured by [3H]thymidine incorporation assay and MTT test. The expression of the multidrug resistant gene (MDR1) was detected by real-time quantitative reverse transcription-polymerase chain reaction. P-glycoprotein was measured by Western blot analysis. The intracellular rhodamine 123 accumulation was analyzed by flow cytometry to evaluate the activity of P-glycoprotein. After treatment with celecoxib, the proliferation inhibitions of SGC7901 cell line and the SGC7901/adriamycin and SGC7901/vincristine sublines increased linearly in a positive dose-dependent pattern in both the [3H]thymidine incorporation assay and in the MTT test. The IC50 value of the MDR1/GAPDH ratio was 5.50 x 10(-6) mol/l in SGC7901/adriamycin and 3.89 x 10(-6) mol/l in SGC7901/vincristine. P-glycoprotein expression levels in the two multidrug resistance sublines treated with celecoxib were significantly lower than those in control groups, 0.28 vs. 0.71 in the SGC7901/adriamycin subline and 0.21 vs. 0.83 in the SGC7901/vincristine subline, respectively, P<0.05. After treatment with celecoxib, intracellular rhodamine 123 accumulation in the SGC7901/adriamycin and SGC7901/vincristine sublines increased positively in a dose-dependent pattern (P<0.05), and reached more than 50% of that in the SGC7901 cell line at the concentration of 1 x 10(-4) mol/l of celecoxib. In conclusion, celecoxib could inhibit proliferation of multidrug resistance in gastric carcinoma sublines. The reversal of multidrug resistance was caused by downregulation of the expression and activity of P-glycoprotein. The results may suggest a new way to reverse P-glycoprotein-dependent multidrug resistance in human gastric carcinoma.

Preoperative growth inhibition of human gastric adenocarcinoma treated with a combination of celecoxib and octreotide

AIM

To gain insight into the histopathological responses and molecular targets in the inhibition of growth of human gastric cancer treated with celecoxib (a cyclooxygenase [COX]-2 inhibitor) combined with octreotide.

METHODS

Seventy five patients with gastric cancer undergoing curative gastrectomy or extended resection were randomly divided into 3 groups. The apoptosis of tumor cells was measured by terminal deoxynucleotide transferase-mediated dUTP nick endlabeling (TUNEL) assay. Gastric cancer microvessel density (MVD) and the expression of COX-2 were evaluated by immunohistochemical staining. The expression of somatostatin receptor (SSTR)-2 was detected with the biomolecular interaction analysis system. The transcription of non-steroidal anti-inflammatory drug-activated gene (NAG)-1 was measured by RT-PCR.

RESULTS

Compared with the control and celecoxib groups, more necrosis in the combination group was observed. The apoptotic rate in the combination group (7.06%+/-0.67%) was significantly higher than that in the control group (6.23%+/-1.29%, P<0.05). The MVD decreased considerably in the combination group. The upregulation of NAG-1 was displayed both in the celecoxib and combination groups. The positive rate of SSTR-2 in gastric cancers treated with celecoxib (48%) was significantly higher than that of control group (12%) after surgery (P<0.05).

CONCLUSION

Celecoxib combined with octreotide significantly promoted necrosis in gastric adenocarcinoma through the induction of apoptosis and the reduction of MVD. NAG-1 and SSTR-2 might be the molecular targets for celecoxib or octreotide.

Cyclooxygenase-2 (COX-2)-independent anticarcinogenic effects of selective COX-2 inhibitors

Nonsteroidal antiinflammatory drugs (NSAIDs) appear to reduce the risk of developing cancer. One mechanism through which NSAIDs act to reduce carcinogenesis is to inhibit the activity of cyclooxygenase-2 (COX-2), an enzyme that is overexpressed in various cancer tissues. Overexpression of COX-2 increases cell proliferation and inhibits apoptosis. However, selective COX-2 inhibitors can also act through COX-independent mechanisms. In this review, we describe the COX-2-independent molecular targets of these COX-2 inhibitors and discuss how these targets may be involved in the anticarcinogenic activities of these selective COX-2 inhibitors. We also compare the concentrations of these inhibitors used in in vitro and in vivo experiments and discuss the implications of the in vitro studies for clinical management of cancer with these drugs.