Differential effects of LHRH and somatostatin analogs on human breast cancer

Localization of luteinizing-hormone releasing hormone binding sites in the gastric mucosa of suckling rats

Luteinizing-hormone releasing hormone (LHRH) is a hypothalamic and milk-borne hormone that inhibits the cell proliferation of gastric epithelium in developing rats, although the mechanism of such action is unknown. We investigated the presence of binding sites for LHRH in the stomach of suckling rats after the injection of the hormone. Immunofluorescence at the confocal microscopy level revealed that LHRH binds to gastric cells, being particularly abundant over the gland. Different fluorescent lectins were used to identify gastric cell types and determine which were labeled by the hormone. Colocalization studies in these double-labeling experiments showed that LHRH staining colocalizes with parietal cells, suggesting the presence of binding sites in these cells. The three-dimensional (3-D) reconstruction of isolated parietal cells revealed the localization of the signal, which appears to be in the membrane of the canalicular region. These results suggest that there are binding sites for LHRH in the gastric epithelium, specifically in parietal cells, and they might play a role in the control of cell proliferation during suckling.

LHRH antagonist inhibits gastric cell proliferation in suckling rats

The cell proliferation of the gastric epithelium is stimulated by food deprivation in suckling rats, and LHRH inhibits this process as it does in other hyperproliferating tissues. However, as LHRH antagonist is also being used as a potent antiproliferative agent for tumors, this study aims to investigate whether it plays any role on the cell proliferation of the gastric epithelium. Seventeen-day-old rats were fasted for 20 h and treated with LHRH antagonist, LHRH, or both during this period. The following morning, animals were injected with BrDU to label proliferating cells, and were sacrificed 1 h later. Paraffin sections of the gastric mucosa were processed for immunohistochemistry and BrDU labeled and non-labeled epithelial cells were counted to determine the labeling index (LI). None of the hormone treatments changed body weight or the morphology of the stomach. Apoptotic cells were observed in the gastric gland in treated rats. The LI were inhibited by the antagonist, LHRH or both, showing that the LHRH antagonist plays an inhibitory role on the hyperproliferating gastric epithelium. These results suggest that both LHRH agonist and antagonist can influence the proliferative activity in suckling rats, though the mode of action remains to be determined.

Phase II study of RC-160 (vapreotide), an octapeptide analogue of somatostatin, in the treatment of metastatic breast cancer

RC-160 (octastatin/vapreotide) is a potent octapeptide analogue of somatostatin with growth inhibitory activity in experimental tumours in vitro and in vivo, including breast cancer. We evaluated the efficacy and tolerability of high-dose RC-160, 3 mg day(-1) on week 1 increased to 4.5 mg day(-1) for weeks 2-4 and subsequently 6 mg day(-1) until the end of treatment, administered by continuous subcutaneous infusion in the management of 14 women with previously treated metastatic breast cancer. The age range was 37-80 years (median 58.5 years) and performance status 0-2. The treatment was well tolerated with no dose reductions being required. No grade 3 or 4 toxicities were seen. Abscess formation developed at the infusion site in eight patients and erythema and discomfort was seen in a further three patients. A significant reduction in IGF-I levels occurred by day 7 and was maintained throughout the treatment. The lowest dose of RC-160 produced the maximal IGF-I response. Although there was no reduction in prolactin levels in patients whose baseline levels were normal, elevated prolactin levels found in three patients fell to within the normal range 7 days after commencing RC-160 treatment. A small but significant rise in fasting blood glucose levels was also recorded, the highest level on treatment being 7.6 mmol l(-1). No objective tumour responses were observed, all patients showing disease progression within 3 months of commencing treatment. These findings demonstrate that high-dose RC-160, administered as a continuous subcutaneous infusion, can reduce serum levels of the breast growth factors IGF-I and prolactin but is ineffective in the management of metastatic breast cancer. Encouraging preclinical anti-tumour activity and the favourable toxicity profile in patients suggest the merit of future studies combining RC-160 with anti-oestrogen, cytotoxic and anti-angiogenic agents.

Expression of the messenger RNA for gonadotropin-releasing hormone and its receptor in human cancer cell lines

The presence of gonadotropin-releasing hormone (GnRH) binding sites in biopsy samples of human epithelial ovarian cancer and ovarian tumor cell lines as well as the demonstration of the inhibitory effects of GnRH analogues on the growth of these cells raised the possibility that GnRH is produced locally by ovarian cancer cells. In order to investigate an autocrine/paracrine regulatory mechanism in human carcinomas, we have studied the expression of GnRH and GnRHR mRNA in human ovarian epithelial cell lines (OVCAR-3 and SKOV-3), human choriocarcinoma cell line (JEG-3) and human hepatocarcinoma cell line (HepG 2). Using primers corresponding to published human GnRH and GnRHR cDNA sequences, predicted PCR products were obtained from these cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and confirmed by Southern hybridization. Sequencing analysis of GnRH PCR products showed that their sequences have 100% identity to the published human GnRH cDNA sequence. These results indicated that GnRH and GnRHR genes are expressed in all the cell lines tested in the present study, and strengthen the concept that GnRH may act as an autocrine regulator on the growth of cancer cells.

LHRH and somatostatin effects on the cell proliferation of the gastric epithelium of suckling and weaning rats

The aim of this study was to investigate the effects of LHRH and somatostatin on the cell proliferation of the gastric epithelium of suckling and weaning rats after fasting treatment. Previous studies on the cell proliferation of the gastric epithelium have shown that fasting stimulates this process in suckling, but not in weaning and adult rats. As milk is the most important source of nutrients and hormones during the suckling phase, and luteinizing hormone-releasing hormone (LHRH) and somatostatin are found in milk, their possible inhibitory roles on the gastric epithelium were investigated. Metaphasic index was achieved by vincristine blockade in 18- and 22-day-old treated and non-treated rats. The results showed that at 18 days, both hormones inhibited the enhanced proliferation activity due to fasting treatment, while at 22 days, no effect was detected. Therefore, LHRH and somatostatin were considered to have inhibitory roles on the cell proliferation of the gastric epithelium in suckling rats only.

LHRH agonist treatment of breast cancer and gynecological malignancies: a review

Since 1982 LHRH agonists have been used as a treatment modality in patients with disseminated breast cancer and gynecologic malignancies, based on the assumption of steroid dependence of these cancers. They have been successfully used in the treatment of premenopausal women with breast cancer; response rates reported are 31-63%. Less optimistic results have been reported in postmenopausal breast cancer patients as well as in the treatment of women suffering from ovarian cancer. Response rates for treatment of postmenopausal breast- and ovarian cancer patients appear to be up to 22% and 29%, respectively. Studies using LHRH agonists to treat endometrial and cervical intra-epithelial neoplasia are still rare and, until now, no data about the efficacy of LHRH agonists in treating these malignancies have been reported. This paper reviews clinically important studies of LHRH agonists, including a rationale for the use of LHRH agonists in breast cancer and gynecological cancer treatment. In view of the changed endocrine state in postmenopausal women on the one hand and alterations in endocrine metabolism in breast cancer tissue on the other hand, it is concluded that it might be more effective to use a combination of LHRH agonists and other endocrine modalities to treat disseminated breast cancer and gynecological malignancies.

Somatostatin receptor expression in lung cancer

Experimental evidence suggests that somatostatin analogues may have a role to play in the management of lung tumours. We evaluated membrane preparations of nine small cell lung cancer (SCLC) cell lines and of tumour samples from 3 patients with non-small cell lung cancer (NSCLC), 1 patient with an atypical carcinoid and another with a bronchial carcinoid for the presence of specific binding sites for RC-160, a potent growth inhibitory octapeptide analogue of somatostatin. Specific binding was noted on six of nine SCLC lines. Radio-receptor assay on the cell line NCI H 69 showed evidence of two specific binding sites for RC-160, one with high affinity and the other with low affinity. Binding sites were also found on all five tumour samples. Scatchard analysis indicated the presence of a single class of receptors with high affinity in each case. Histological assessment of the resected specimens before binding assay showed them to be comprised of tumour cells and necrotic tissue, stroma and/or inflammatory cells. Therefore, the specific binding of RC-160 may be to tissues other than the tumour cells. In 3 patients, from whom the tumour samples were obtained, radiolabelled somatostatin analogue scintigraphy using [111In] pentetreotide was performed prior to surgery. In all cases, the radiolabel localised the disease. This study demonstrates the presence of specific binding sites for RC-160 in SCLC. Furthermore, the detection of specific binding in vitro and in vivo in NSCLC and intrapulmonary carcinoids demonstrates that these tumours contain cells which express specific binding sites for somatostatin. These results suggest that RC-160 may have a role to play as a therapeutic agent in lung cancer.