Gastrointestinal cancer refractory to chemotherapy: a role for octreotide?

Promoter hypermethylation-related reduced somatostatin production promotes uncontrolled cell proliferation in colorectal cancer

BACKGROUND

Somatostatin (SST) has anti-proliferative and pro-apoptotic effects. Our aims were to analyze and compare the SST expression during normal aging and colorectal carcinogenesis at mRNA and protein levels. Furthermore, we tested the methylation status of SST in biopsy samples, and the cell growth inhibitory effect of the SST analogue octreotide in human colorectal adenocarcinoma cell line.

METHODS

Colonic samples were collected from healthy children (n1 = 6), healthy adults (n2 = 41) and colorectal cancer patients (CRCs) (n3 = 34) for SST mRNA expression analysis, using HGU133 Plus2.0 microarrays. Results were validated both on original (n1 = 6; n2 = 6; n3 = 6) and independent samples ((n1 = 6; n2 = 6; n3 = 6) by real-time PCR. SST expressing cells were detected by immunohistochemistry on colonic biopsy samples (n1 = 14; n2 = 20; n3 = 23). The effect of octreotide on cell growth was tested on Caco-2 cell line. SST methylation percentage in biopsy samples (n1 = 5; n2 = 5; n3 = 9) was defined using methylation-sensitive restriction enzyme digestion.

RESULTS

In case of normal aging SST mRNA expression did not alter, but decreased in cancer (p < 0.05). The ratio of SST immunoreactive cells was significantly higher in children (0.70% ± 0.79%) compared to CRC (0% ± 0%) (p < 0.05). Octreotide significantly increased the proportion of apoptotic Caco-2 cells. SST showed significantly higher methylation level in tumor samples (30.2% ± 11.6%) compared to healthy young individuals (3.5% ± 1.9%) (p < 0.05).

CONCLUSIONS

In cancerous colonic mucosa the reduced SST production may contribute to the uncontrolled cell proliferation. Our observation that in colon cancer cells octreotide significantly enhanced cell death and attenuated cell proliferation suggests that SST may act as a regulator of epithelial cell kinetics. The inhibition of SST expression in CRC can be epigenetically regulated by promoter hypermethylation.

A review of the use of somatostatin analogs in oncology

Somatostatin is a neuropeptide produced by paracrine cells that are located throughout the gastrointestinal tract, lung, and pancreas, and is also found in various locations of the nervous system. It exerts neural control over many physiological functions including inhibition of gastrointestinal endocrine secretion through its receptors. Potent and biologically stable analogs of somatostatin have been developed. These somatostatin analogs show different efficacy on different receptors, and receptors are varyingly concentrated in specific tissues. Antitumor and antisecretory effects of somatostatin analogs in cancer have been shown in several in vivo and in vitro studies. However, these activities have not always yielded into clinically relevant patient outcome benefit. Somatostatin analogs are of clinical benefit in treating symptoms of ectopic hormone secretion (adrenocorticotropic hormone, growth hormone-releasing hormone) in lung cancer, without inducing a significant tumor response. They have also been shown to induce a statistically significant decrease in bone pain and increase in Karnofsky performance status in patients with metastatic prostate cancer. Somatostatin analogs alone or in combination with other agents have only limited antitumoral effect in breast cancer. In gastrointestinal cancers, studies have not shown an objective tumor response to somatostatin analogs except in endocrine tumors of the liver with symptomatic and biochemical improvement. In neuroendocrine tumors of the gastrointestinal system and pancreas, very high symptomatic and biochemical response rates have been achieved with somatostatin analogs. Antiproliferative activity has been clearly shown in metastatic midgut neuroendocrine tumors.

Somatostatin and somatostatin receptors: implications for neoplastic growth and cancer biology

Somatostatin agonists (SM-As) are capable of achieving durable symptomatic relief and significant clinical responses in certain tumours. Herein, we review the diverse direct and indirect mechanisms of antineoplastic activity elicited by SM-As as well as the hurdles that complicate their use as monotherapies in a broader range of malignancies. Emphasis is placed on recent clinical attempts to neutralise the IGF-mediated survival factor effects in the bone metastasis microenvironment in advanced prostate cancer. The first clinical trials of this 'anti-survival factor manipulation' strategy utilised the ability of SM-As to suppress the growth hormone-dependent liver-derived IGF-I bioavailability in combination with other drugs, such as dexamethasone, zolendronate and oestrogens, acting systemically and at the bone metastasis microenvironment. These regimens restored androgen ablation responsiveness in stage D3 prostate cancer patients and successfully produced objective clinical responses while only mild toxicities were observed. Furthermore, we focus on the preclinical experimental data of a targeted SM-A coupled to the super-potent doxorubicin derivative AN-201. The resulting conjugate (AN-238) has shown increased antitumour potency with a favourable toxicity profile. The potential use of novel SM-As as anticancer drugs is discussed in relation to data suggesting other direct and indirect treatment approaches pertaining to the somatostatin system.

Future clinical prospects in somatostatin/cortistatin/somatostatin receptor field

Somatostatin receptors (sst), somatostatin (SS) and cortistatin (CST) are widely expressed in the various systems in the human and rodent organisms and are "responsible" for maintaining homeostasis, which is essential for survival. Because of their broad expression pattern sst, SS and CST interactions may play regulatory roles in both physiology and pathophysiology in mammalian organisms. SS analogue treatment strategies as well as the use of SS analogues for diagnostic purposes have been established in diseases of different origins. This review focuses on the currently determined role for SS analogues in today's clinical practice and the potential clinical prospects for SS, CST and sst interactions in the future, with a focus on neuroendocrine and non-neuroendocrine tumours and immune-mediated diseases. Moreover, the role of new SS analogues and new insights in sst physiology will be discussed.

Uniform Potent Activity of the Antiproliferative Metal Chelate Trans-Bis(resorcylaldoximato)copper(II) against a Large Panel of Human Tumor Cell Lines in vitro

BACKGROUND

The copper chelate trans-bis(salicylaldoximato)copper(II), CuSAO2, is a powerful antitumor agent in vivo, being capable of drastically increasing the life span of mice bearing Ehrlich ascites carcinoma, and has in many cases even a curative effect. This compound as well as some congeners, most notably the 4-hydroxylated analogue trans-bis(resorcylaldoximato)copper(II), CuRES2, also have potent antiproliferative activity against tumor cells in vitro.

METHODS

CuRES2 was tested in vitro against a panel of 37 different types of human tumor cells (leukemias, small cell and non-small cell lung tumors, melanomas, as well as colon, breast, central nervous system, ovarian and renal tumors). The cells were incubated on microculture plates for 6 days, and the amount of viable cells was determined with the agent XTT, whose metabolic reduction gives a colored formazan compound.

RESULTS

CuRES2 inhibited the proliferation of all the 37 cell lines studied. The IC50 values ranged between 0.575 and 8.57 microg/ml and the IC90 values between 1.74 and 20.6 microg/ml. Thus, it had distinct and very potent activity against all the cell lines studied, and the differences between the susceptibilities of different tumor types and cell lines were not very large.

DISCUSSION

Clearly, CuRES2 is active against all the tumor cell lines studied. None of the cell lines (tumor types) demonstrates a significantly higher or lower susceptibility, but some trends appear to exist. Thus, most (but not all) of the leukemia and melanoma cell lines, the two ovarian cancer lines and one small cell lung cancer and one CNS cancer cell line were somewhat more susceptible than the cell lines on average. The results obtained for the melanomas are of special interest, since CuRES2 (and even more so CuSAO2) have very low aqueous solubilities. In cutaneous melanomas, their administration might, however, be very easy, since both compounds are soluble in dimethyl sulfoxide and could thus easily be administered topically in this solvent whose ability to be absorbed through the skin is well known.

CONCLUSION

The present results on human tumor cell lines are in line with previous observations that CuSAO2 and CuRES2 essentially totally inhibit the proliferation of leukemia L1210 and Ehrlich ascites carcinoma cells in vitro in a concentration as low as approximately 5 microg/ml.