Octreotide: an active agent in epithelial ovarian carcinoma?

Synthetic paclitaxel-octreotide conjugate reverses the resistance of paclitaxel in A2780/Taxol ovarian cancer cell line

The high mortality of ovarian cancer is partly due to the frequent resistance of ovarian cancer to current chemotherapy agents such as paclitaxel and platinum. Somatostatin analogue (SSTA) has been shown to inhibit the proliferation of some tumors through binding to somatostatin receptor (SSTR) and activation of Ras-, Rapl- and B-Raf-dependent extracellular signal-regulated kinase 2 (Erk2). It was reported that paclitaxel-octreotide conjugate (POC) exhibited enhanced tumor growth inhibition with reduced toxicity. In the present study, we prepared the POC and investigated its effects and mechanism for the reversal of drug resistance in paclitaxel-resistant ovarian cancer cell line. We demonstrated that treatment with POC led to more cell apoptosis than either paclitaxel or octreotide (OCT) alone. Moreover, the expression of multidrug resistance 1 (MDR1) and vascular endothelial growth factor (VEGF) mRNA, and protein decreased in a dose-dependent manner while the expression of SSTR remained stable following treatment with POC. Although the exact action, in vivo effects and pharmacologic kinetics of POC remain to be investigated, we have demonstrated the feasibility for the synthesis of POC, and more significantly, provided a potential approach to overcome the resistance of ovarian cancer against taxol. The findings also shed some new light on the mechanisms underlying the development of resistance to taxol by ovarian cancer cells.

Octreotide enhances the sensitivity of the SKOV3/DDP ovarian cancer cell line to cisplatin chemotherapy in vitro

The present study aimed to investigate the effects of octreotide (OCT) on the reversal of resistance of cisplatin-resistant cancer cells and on enhancement of the cisplatin sensitivity of cancer cells. The 3-(4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide method and flow cytometry were used to investigate the effect of cisplatin, OCT or the combination of these two compounds on the proliferation and apoptosis of SKOV3/DDP cells. Real-time, quantitative RT-PCR was used to detect the mRNA expression of SSTR2, MDR1, MRP2, GST-π and EGFR in SKOV3/DDP cells following OCT treatment. At the concentration of 2.5-20 μg/ml, OCT significantly reduced the IC(50) value (P<0.05) and promoted apoptosis (P<0.05) in the SKOV3/DDP cells in response to cisplatin. The synergistic effect of OCT and cisplatin on SKOV3/DDP cell proliferation was observed. SSTR2 was expressed on the SKOV3/DDP cell surface. OCT increased GST-π expression (P<0.05) and reduced MRP2 and EGFR expression (P<0.05) in a dose-dependent manner. However, it had no effect on the expression of MDR1 (P>0.05). It is suggested that OCT inhibits ovarian cancer proliferation and promotes apoptosis, via the cell surface expression of SSRT2, and reverses cisplatin resistance through the inhibition of MRP2 and EGFR expression.

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.

Identification and characterization of two novel truncated but functional isoforms of the somatostatin receptor subtype 5 differentially present in pituitary tumors

CONTEXT

Somatostatin and its related peptide cortistatin exert multiple actions on normal and tumoral tissue targets through a family of receptors termed somatostatin receptor (sst)1-5. Despite the considerable advances in the knowledge on these receptors and their (patho)physiological roles, there is still evidence that additional receptors for these peptides should exist to fully explain their actions.

OBJECTIVE

The growing number of spliced variants found in similar receptor families, often present in tumors, and results from our group obtained on sst5 from other species (pig) led us to explore the existence of new human sst5 isoforms.

DESIGN AND RESULTS

A rapid amplification of cDNA ends PCR approach on samples from a human pituitary tumor and a cell line enabled identification of two novel alternatively spliced sst5 receptor variants. The sequences obtained encode putative proteins that correspond to truncated isoforms of five and four transmembrane domains (TMDs), accordingly named sst5TMD5 and sst5TMD4, respectively. Both novel receptors show a differential expression pattern in normal tissues and are also present in pituitary tumors of diverse etiology including nonfunctioning adenomas, corticotropinomas, somatotropinomas, and a prolactinoma. In contrast to the predominant plasma membrane localization of full-length sst5, both sst5TMD5 and sst5TMD4 show a preferentially intracellular localization. Despite their truncated nature, both receptors are functional, as shown by their ability to mediate selective, ligand-induced rises in free cytosolic calcium concentration. Specifically, whereas sst5TMD5 is selectivity activated by somatostatin compared with cortistatin, cells transfected with sst5TMD4 almost exclusively respond to cortistatin and not to somatostatin.

CONCLUSIONS

Our results demonstrate the existence of two previously unidentified sst5 spliced variants with distinct distribution in normal tissues and pituitary tumors, unique ligand-selective signaling properties, and subcellular distribution, which could contribute to somatostatin and cortistatin signaling in normal and tumoral cells.

Malignant irreversible intestinal obstruction: the powerful association of octreotide to corticosteroids, antiemetics, and analgesics

In the case of malignant intestinal obstruction, surgery often carries important mortality and morbidity risks, and feasibility is neither realistic nor reasonable. A total of 4 clinical cases of intestinal obstruction caused by advanced gastrointestinal cancers in their terminal phase are described. The association of analgesics, corticosteroids, antiemetics, and octreotide was effective to relieve symptoms of intestinal obstruction for the remaining lifetime. The insertion of a nasogastric tube was avoided in 3 of 4 cases. Death occurred 51, 56, and 64 days after clinical and radiological diagnosis of irreversible intestinal obstruction. This combination of drugs appears very powerful and well tolerated. The relatively long survival that was observed should encourage future studies of longer half-life somatostatin analogues with no need of continuous infusion or multiple daily injections.

Long-acting octreotide for the treatment and symptomatic relief of bowel obstruction in advanced ovarian cancer

Symptoms of malignant bowel obstruction in patients with recurrent ovarian cancer lead to a poor quality of life. Sandostatin LAR Depot (LAR) is an intramuscular, monthly administered, long-acting form of octreotide. LAR's safety and utility were evaluated in a pilot study enrolling 15 advanced ovarian cancer patients with bowel dysfunction. Once safety with subcutaneous (SQ) octreotide was assessed, patients were given 30 mg LAR on Day 1 and octreotide SQ for 2 weeks. Of 13 evaluable patients, three patients had a major response to LAR treatment with reduction in bowel obstruction symptoms, two had a minor response, four had no response, and four had progressive symptoms. Three patients remained on LAR for more than 9 months. No significant toxicities were attributable to octreotide or LAR. Because three patients received nine or more monthly injections of LAR, possible direct antitumor effects of LAR or synergy with chemotherapy needs to be explored.