Somatostatin Analogs and Tumor Localization Do Not Influence Vitamin D Concentration in Patients with Neuroendocrine Tumors.

Patients with neuroendocrine tumors (NETs), malignancies of rare but still rising incidence, may be a group at higher risk of vitamin D insufficiency. The gastrointestinal tumor prevalence and somatostatin analog (SSA) therapy may cause vitamin D malabsorption. The aim of this study was to evaluate the serum level of vitamin D in NET patients. A total of 36 NET patients were enrolled into the experimental group and 16 individuals were enrolled into the control group. All patients were further classified into subgroups according to primary tumor localization (gastropancreatic, lung, and other NETs) or therapy (with or without SSA treatment). The concentrations of total 25(OH)D were assayed with Electrochemiluminescence immunoassay (ECLIA). Serum concentration of 25(OH)D in NET patients did not differ significantly from that of the control group. However, the average level of 25(OH)D in both groups met the criteria of vitamin D deficiency. Importantly, SSA therapy did not aggravate vitamin D deficiency. Moreover, the concentration of 25(OH)D in the studied group was not significantly influenced by primary tumor localization, patient age, or season. Vitamin D deficiency is a widespread disorder affecting both NET patients and individuals without other health problems, and SSA and gastrointestinal tumor localization do not exacerbate this condition.

Interferon alpha and rapamycin inhibit the growth of carcinoid and medullary thyroid cancer in vitro.

Neuroendocrine tumors (NETs) are highly vascularized neoplasms characterized by rising incidence. Moreover, the neuroendocrine cells were shown to express vascular endothelial growth factor (VEGF) and VEGF receptors. Therefore, angiomodulators could be potentially a new group of drugs enhancing still unsatisfactory effectiveness of NET therapy. The aim of this study was to assess the direct influence of angiomodulators: VEGF and five endogenous and exogenous antiangiogenic compounds (endostatin, interferon alpha [IFNα], rapamycin, JV1-36, semaxinib [SU5416]) on the growth of two NET cell lines: lung carcinoid H727 cell line and medullary thyroid cancer TT cell line in vitro. IFNα and rapamycin induced the inhibitory effect on H727 and TT cell viability and proliferation, increasing apoptosis and arresting the cell cycle. Also semaxinib (10(-5)M) inhibited proliferation of both cell lines. VEGF and endostatin did not influence the growth of H727 and TT cells. The inhibitory effect of IFNα, rapamycin and semaxinib on carcinoid and medullary thyroid cancer growth was revealed in our in vitro study, although some other antiangiogenic agents did not directly influence H727 and TT cell growth. Thus, IFNα and mTOR inhibitors as multidirectionally acting drugs with antiangiogenic effect could be potentially efficient in treatment of neuroendocrine tumors and are worth further studies.

Interferon alpha and rapamycin inhibit the growth of pheochromocytoma PC12 line in vitro.

INTRODUCTION: Pheochromocytomas are benign or malignant neuroendocrine tumours. The unsatisfactory efficacy of the traditional therapeutic methods for patients with metastatic disease results in a continuing search for more effective and targeted agents. Due to the increased vascularisation of these tumours, inhibitors of angiogenesis could be potentially a new group of drugs in pheochromocytoma/paraganglioma therapy. MATERIAL AND METHODS: The aim of this study was to evaluate the influence of angiomodulators: VEGF (vascular endothelial growth factor) and five endogenous and exogenous antiangiogenic compounds (endostatin; IFN-alpha [interferon alpha]; rapamycin - mTOR [mammalian target of rapamycin] inhibitor; JV1-36 and SU5416 (semaxinib]) on the growth of rat pheochromocytoma PC12 cell line. RESULTS: IFN-alpha (10(5) U/mL) strongly inhibited PC12 growth in a 72 h culture, increasing apoptosis and arresting the cell cycle. Rapamycin in a wide range of concentrations (10(-5) to 10(-8) M) induced a slight inhibitory effect on PC12 viability and decreased cell proliferation at the concentration of 10(-5) M. VEGF, endostatin and JV1-36 did not influence the growth of PC12. CONCLUSIONS: The study has shown for the first time that IFN-a inhibited the growth of pheochromocytoma PC12 line and confirmed the inhibitory action of rapamycin on these cells. The results suggest that IFN-alpha and mTOR inhibitors could be potentially effective in the therapy of malignant pheochromocytoma, and encourage further study in this field.

Modulation of ghrelin axis influences the growth of colonic and prostatic cancer cells in vitro.

BACKGROUND: The risk of different cancers seems to be associated with obesity. Moreover, low ghrelin levels observed in obese people may be implicated in cancer development and progression. The aim of this study was to examine the direct effects of both forms of ghrelin (acylated and unacylated) and ghrelin receptor type 1a antagonist (D-Lys-GHRP-6) on the growth of murine colon cancer MC38 and human prostate cancer DU145 cell lines in vitro. METHODS: The cells were cultured for 72 h in the presence of rat or human acylated ghrelin (rG, hG), human unacylated ghrelin (hUAG), D-Lys-GHRP-6 (GHS-RA) applied either alone or jointly. The cell line growth was assessed by the colorimetric Mosmann method. RESULTS: hUAG (10(-6), 10(-7) and 10(-10) M) inhibited MC38 cancer cell growth and, at some concentrations (10(-8), 10(-9), 10(-10) M), enhanced the antineoplastic effect of GHS-RA(10(-4) M). In turn, GHS-RA evoked a biphasic effect on MC38 cancer growth: inhibitory at 10(-4) M and stimulatory at 10(-5) and 10(-6) M. Moreover, GHS-RA at the highest examined concentration (10(-4) M) enhanced the cytostatic effect of FU. Human acylated and unacylated ghrelin and GHS-RA inhibited DU145 cancer growth with moderate and different potencies. A dose-response effect was observed for the inhibitory action of hG together with the synergistic effect of hUAG and GHS-RA. CONCLUSION: The obtained results indicate an involvement of the ghrelin axis in the growth regulation of colon and prostate cancers and may suggest new therapeutic options for these neoplasms.

D-Lys(3)-GHRP-6 antagonizes the effect of unacylated but not of acylated ghrelin on the growth of HECa10 murine endothelial cells.

Recent studies demonstrate that ghrelin can be an endogenous regulator of angiogenesis. We studied direct effects of human acylated (hAG) and unacylated (hUAG) ghrelin, as well as of rat acylated ghrelin (rAG) on the growth of HECa10 murine endothelial cells. Ghrelin was applied separately or together with D-Lys(3)-GHRP-6, which is commonly used as an antagonist of ghrelin receptor type 1a - GHS-R1a. The growth of HECa10 cells was assessed with Mosmann and in selected study conditions also with BrdU and TUNEL methods. Both hAG and hUAG (10(-5) M to 10(-12) M) inhibited the growth of HECa10 cells in 24h and 72 h cultures. Similarly, rAG decreased the growth of the cells after 24h (10(-7) M and 10(-11) M), and after 72 h (10(-7) M, 10(-8) M and 10(-11) M). Unexpectedly, D-Lys(3)-GHRP-6 itself also inhibited the growth of these cells at 10(-4) to 10(-6) M in 24h, 48 h (dose-response effect) and 72 h cultures. D-Lys(3)-GHRP-6 did not modify the inhibitory effect of rAG. However, D-Lys(3)-GHRP-6 at the concentration of 10(-4) M diminished, abolished or even reversed the inhibitory effect of hUAG in 72 h culture and this was dependent on ghrelin concentrations. These data indicate that both AG and UAG have antiangiogenic properties at least at the level of endothelial growth, through decreased metabolic activity of the cells or stimulation of apoptosis. D-Lys(3)-GHRP-6 (inhibitor of GHS-R1a) seems not to be an appropriate antagonist in this experimental condition. Similar effects of these substances on HECa10 cells suggest that they are not mediated by GHS-R1a.

Elevated peripheral blood plasma concentrations of tie-2 and angiopoietin 2 in patients with neuroendocrine tumors.

BACKGROUND: Gastro-entero-pancreatic/neuroendocrine (NET) tumors are highly vascularized neoplasms. However, our knowledge concerning circulating levels of the angiogenic factors in NET patients still remains insufficient. METHODS: The aim of this study was to measure plasma concentrations of VEGF, angiopoietin 1 (Ang-1), angiopoietin 2 (Ang-2), soluble Tie-2, endostatin, osteopontin (OPN) and chromogranin A (CgA) in 36 NET patients and 16 controls. RESULTS: Only the plasma concentrations of Tie-2 and CgA were higher in NET patients as compared to controls. These levels were within the reference range in controls; however one control demonstrated slightly elevated Tie-2 and 4 elevated CgA. Similarly, in the subgroup of patients with carcinoid syndrome, only Tie-2 and CgA concentrations were higher than those in patients with non-functioning NETs. In turn, in the subgroup of metastatic patients, only Ang-2 levels were higher than in those with localized disease. A positive correlation was found between Ang-2 and Tie-2 levels in metastatic patients and between Ang-1 and Tie-2 in localized NETs. CONCLUSIONS: The plasma concentration of Tie-2 is proposed as an additional marker for NET patients and seems to be similarly effective as the currently used CgA level. Moreover, higher plasma levels of Ang-2 together with the positive correlation between Ang-2 and Tie-2 levels in metastatic subjects, implies that cases with a Tie-2 level above the upper limits, together with higher level of Ang-2 seem to be highly predictive of metastases.

Antineoplastic action of growth hormone-releasing hormone (GHRH) antagonists.

Some of the antagonists of growth hormone-releasing hormone (GHRH) are able to inhibit the growth of various experimental human cancers. The antitumor effects of first antagonists seemed to be dependent mainly on the disruption of pituitary secretion of growth hormone (GH), followed by the reduction in the levels of circulating insulin-like growth factor (IGF)-1, an important growth factor for cancer cells. It seems obvious, that growth hormone deficiency (GHD) induced by GHRH antagonists with all its complications, could limit the beneficial effects of GHRH antagonists therapy, and decrease patients' quality of life. The discovery of local autocrine/paracrine production of GHRH and other related growth factors in many tumoral tissues, in combination with the wide expression of GHRH receptors on cancer cells, directed the research to the synthesis of more potent GHRH antagonists. These compounds exert strong inhibitory effects directly on tumor growth, with scarce endocrine action. The receptor-mediated mechanisms comprise complex and still not completely understood effects on intracellular signaling pathways that are strictly related to human tumorigenesis. This review summarizes recent patents and latest observations on the antineoplastic role of GHRH antagonists in human tumors with emphasis on potential therapeutic applications in clinical oncology.

The inhibitory influence of adiponectin on the growth of the murine endothelial cell line HECa 10 in vitro.

BACKGROUND: Adiponectin, a peptide hormone secreted from the adipose tissue, has anti-diabetic, anti-atherogenic, and anti-inflammatory properties and is also involved in the regulation of angiogenesis. However, there are discrepancies among the results of the published data regarding its pro- or anti-angiogenic properties. The aim of our study was to examine the direct effect of various adiponectin concentrations applied separately or in combination with thalidomide on the growth of the murine endothelial cell line HECa 10 in 24- and 72-hour cell cultures. MATERIAL AND METHODS: We used immortalized murine endothelial cell line received from endothelial cells of the mouse peripheral lymph node. The effect of adiponectin was examined at concentrations from 10(-5) to 10(-12)M. Thalidomide was used at 10(-3)M concentration. The growth of HECa10 cells was assessed by the colorimetric Mosmann method. RESULTS: We found that adiponectin inhibited the growth of HECa 10 line at all examined concentrations in the 24-hour culture, with moderate potency. There were no dose- or time-response effects. In the 72-hour cell culture, adiponectin inhibited the growth with the same or weaker potency and we did not observe its inhibitory effect at 10(-12)M concentration. There was no beneficial interaction between adiponectin and thalidomide. In this study, however, thalidomide alone did not cause any inhibitory effect on this cell line. CONCLUSIONS: The obtained data show that adiponectin inhibits endothelial cell growth and may participate in angiogenesis regulation as an endogenous antiangiogenic factor.

The inhibitory effect of diarylpropionitrile, a selective agonist of estrogen receptor beta, on the growth of MC38 colon cancer line.

The protective role of estrogens in the colon carcinogenesis has been suggested for many years and attributed mainly to estrogen receptor beta (ERbeta). However, the direct effect of estrogens and their action through ERbeta on the growth of colon cancer have been rarely studied. The aim of this study was to examine the effect of various concentrations (10(-4)-10(-12)M) of diarylpropionitrile (DPN)--a selective agonist of ERbeta--on the growth of murine MC38 colon cancer line. Moreover, the aim of this paper was the immunohistochemical assessment of estrogen and progesterone receptor expression in human colon tissues and in MC38 cells (only ERbeta). We found that DPN induced a growth inhibition of MC38 cancer (50-94% of control group) at the highest (10(-4)M) and two lowest concentrations (10(-11) and 10(-12)M). Furthermore, we detected a nuclear-cytoplasmic expression of ERbeta in human normal and neoplastic colon tissues and in the studied MC38 cancer cells. The inhibitory effect of DPN on the growth of MC38 colon cancer line suggests a possibility of using a selective estrogen receptor agonist in the treatment of colon cancer.

Estrone and progesterone inhibit the growth of murine MC38 colon cancer line.

The unsatisfactory effectiveness of reference chemotherapy in colon cancer (fluorouracil - FU) results in continuous search for agents, which could enhance the action of FU. Some epidemiological data such as a decreased risk of colorectal cancer among menopausal women receiving hormonal replacement therapy indicate the role of female sex hormones in the pathogenesis of this disease. The aim of this study was to examine the direct effects of various concentrations of estrone and progesterone (10(-4) to 10(-12)M) applied alone or together with FU on the growth of murine MC38 colon cancer in vitro. Estrone inhibited MC38 cancer growth in a wide range of concentrations (10(-12) to 10(-4)M) with similar potency and at some concentrations (10(-6) and 10(-4)M) augmented also the cytotoxic action of FU. Progesterone induced MC38 cancer growth inhibition at high concentrations (10(-5) to 10(-4)M) in dose- and time-dependent manner but it did not intensify antineoplastic effect of FU. A weak inhibitory effect of progesterone was also observed for lower concentrations (10(-5) to 10(-10)M) in long lasting cultures (72h). The results indicate that estrone and progesterone inhibit the MC38 cancer growth and that estrone increases also the cytotoxic effect of FU, what confirms the role of female sex steroids in modulation of colon cancer growth.

Oestradiol and tamoxifen inhibit murine Colon 38 cancer growth and increase the cytotoxic effect of fluorouracil.

The poor efficacy of reference chemotherapy (fluorouracil -FU) in colon cancer has resulted in a constant search for agents which could augment the action of FU. Epidemiological data, such as the decreased risk of colorectal cancer among menopausal women receiving hormonal replacement therapy, indicate the role of oestrogen in the pathogenesis of this disease. The differences between normal and neoplastic colon cells in the expression of oestrogen receptor beta (ERbeta) could confirm this association. However, the direct influence of oestrogen or tamoxifen (SERM, selective oestrogen receptor modulator) on colon cancer growth has rarely been studied. The aim of the present study was to examine the direct effects of various concentrations of oestradiol and tamoxifen (10(-4) to 10(-12) M), applied alone or together with FU, on the growth of murine Colon 38 cancer in vitro as assessed by three colorimetric methods: Mosmann's method, incorporation of BrdU into cell nuclei and the TUNEL method. At high concentrations oestradiol and tamoxifen decreased the cancer growth in a dose- and time-dependent manner (the Mosmann and BrdU methods) and at some concentrations augmented the cytotoxic action of FU (Mosmann's method). Tamoxifen exerted a very early and potent inhibitory effect, inducing even total cancer growth inhibition at the concentration of 10(-4) M (the Mosmann and BrdU methods). All the substances studied at different concentrations and at different incubation time points increased the apoptosis of tumour cells (the TUNEL method). The results indicate that oestradiol and tamoxifen inhibit Colon 38 cancer growth and increase the cytotoxic effect of FU, which confirms the role of sex steroids in colon carcinogenesis and even suggests new therapeutic schemes.

Leptin promotes the growth of Colon 38 cancer cells and interferes with the cytotoxic effect of fluorouracil in vitro.

INTRODUCTION: Epidemiological studies underline the fact that obesity represents a significant risk factor for the development of several cancers, one of which is cancer of the colon. Moreover, multiple recent data indicate that some adipose tissue-derived hormones may influence the growth of malignant cells. Leptin, the product of the ob gene, is one of these. However, the evidence from research is still contradictory regarding the role of leptin in colon cancer. The aim of our study was to examine the direct effect of leptin at various concentrations (from 10(-5) to 10(-12) M) when applied alone or jointly with fluorouracil (the classical cytotoxic drug for colon cancer) at two concentrations (0.25 mg/ml and 2.5 mg/ml) on the growth of murine Colon 38 cancer cells in vitro. MATERIAL AND METHODS: Colon 38 cancer cells were preincubated in RPMI 1640 medium supplemented with foetal calf serum for 24 hours. The cells were then cultured for a further 72 hours in the presence of various concentrations of the substances under examination, applied either alone or jointly. The growth of the Colon 38 cell line was assessed by a colorimetric kit based on the modified Mosmann method. RESULTS: We found that leptin increased the growth of murine Colon 38 cancer at concentrations of 10(-6), 10(-7) M and 10(-10), 10(-11), 10(-12) M. Its stimulatory effect was fairly slight, with an increase in cancer growth of 5% to 15% as compared to controls. As we expected, fluorouracil at both the concentrations examined inhibited the growth of Colon 38 cancer maximally up to 28% (2.5 mg/ml) and 34% (0.25 mg/ml) of controls, with a stronger effect obtained from higher doses. Leptin did not modulate the cytotoxic effect of fluorouracil applied at the higher concentration (2.5 mg/ml) but, unexpectedly, at concentrations of 1(-9) and 10(-10) M it heightened the cytotoxic effect of fluorouracil given at a lower concentration (0.25 mg/ml). CONCLUSIONS: These data indicate that leptin is involved in the regulation of colon cancer growth and it may even heighten the cytotoxic effect of fluorouracil.

Inhibition of estrogen-induced pituitary tumor growth and angiogenesis in Fischer 344 rats by the matrix metalloproteinase inhibitor batimastat.

The development of estrogen-induced pituitary prolactinoma in Fischer 344 (F344) rats is associated with enhanced neovascularization. Based on the significance of matrix metalloproteinases (MMPs) for tumor growth and angiogenesis, we have studied the effect of batimastat (BB-94), a synthetic MMPs inhibitor (MMPI) on the progression of prolactin-secreting pituitary adenoma in rats. Pituitary tumors were induced in male F344 rats by s.c. implantation of Silastic tubes containing diethylstilbestrol (DES). The effects of chronic treatment with BB-94 (30 mg/kg b.w.) on pituitary weight, cell proliferation, apoptosis and vascular density were evaluated. We have stated that chronic treatment with batimastat caused a significant reduction in the pituitary weight. Batimastat has been found to decrease cell proliferation evaluated by a number of PCNA-positive stained cell nuclei. A marked increase in the apoptotic index within the pituitary was observed in the study group. Moreover, the density of microvessels identified by CD31 was reduced in the group treated with BB-94. The results of our study provide evidence for an inhibitory effect of batimastat, a synthetic MMPI, on the growth and angiogenesis in an experimental model of human prolactinoma. The ability of BB-94 to suppress established pituitary tumor growth suggests a possible application of MMPIs in the treatment of pituitary adenomas.

The place of somatostatin analogs in the diagnosis and treatment of the neuoroendocrine glands tumors.

Somatostatin (SS) was originally discovered as a hypothalamic neurohormone which inhibits growth hormone secretion. The synthesis of the first two metabolically stabilized and more potent SS analogs, octreotide and lanreotide leads to the establishment of applications for them and to introduction into routine therapies. The effectiveness of octreotide or lanreotide in controlling symptoms and GH/IGF-I hypersecretion in acromegalic patients, both preoperatively and postoperatively is well proven. Similarly, these drugs are also very effective in the treatment of TSH-secreting adenomas. The introduction of these drugs into therapy of the functional neuroendocrine tumors of the gastrointestinal tract was a crucial step in the treatment. Octreotide and lanreotide are the drugs of choice in the treatment of patients with: VIPoma, glucagonoma and carcinoid syndrome. Somatostatin receptor scintigraphy with OctreoScan has been recommended as the best imaging technique in these tumors in the localization and staging procedure. SS analogs, coupled to radioisotope or cytotoxic drugs, create another class of SS molecules, very promising in the therapy of the endocrine glands tumors and in other tumors. Another class of SS analogs comprises hybrid molecules, which are chimera of sst2 agonist and D2 agonist, possessing more potent activity than these agonists, applied together.

[Molecular aspects of pituitary tumors]. / Molekularne aspekty guzów przysadki.

Pituitary adenomas are common benign neoplasms, accounting for approximately 15% of intracranial tumors. In systematic autopsy, pituitary tumors are found in 25%, of the population, but only one-third of these tumors give rise to clinical manifestations. Why most of these neoplasms remain undiagnosed and pituitary carcinomas are extremely rare? The progress in the studies concerning pituitary tumorigenesis is rather slow and, due to several limitations, including the anatomic inaccessibility of human pituitary gland, the lack of functional human cell lines in culture and the discrepancies between human and animal pituitary oncogenesis (in rodents pituitary hyperplasia is a prerequisite for adenoma development). In humans, the majority of pituitary tumors are monoclonal in origin and derived from single mutated pituicyte, rarely hyperplasia is a prerequisite for adenoma formation. As in the case of other tumors, activating mutations in oncogenes (GNAS1, PTTG) and inactivating mutations in tumor suppressor genes (MEN1, CNC1) lead to pituitary tumors development. However, mutations in classic oncogenes are very rarely associated with these tumors. Moreover, the important role of some hypothalamic hormones, peripheral hormones and their receptors (e.g. GHRH, dopamine D2 receptor, PRL receptor, estrogens, thyroid hormone receptor) and growth factors (e.g. FGF, EGF, TGF) is postulated and partially proved in promotion of pituitary tumorigenesis. Further studies are required to determine which of these events are truly primary changes in pituitary tumorigenesis, what may allow development of gene therapy.

The combined effects of proglumide and fluorouracil on the growth of murine Colon 38 cancer cells in vitro.

The role of gastrins and their receptors in the pathogenesis of colon cancer has been discussed for many years but it still remains unresolved. Although fluorouracil (FU) remains to be reference chemotherapy for colon cancer, its efficacy is unsatisfactory. Recently, we have shown a synergistic effect of proglumide (a non-selective blocker of cholecystokinin-gastrin receptors) applied together with FU, on the proliferation and apoptosis of transplantable Colon 38 cancer cells in vivo. The aim of this study was to examine direct effects of proglumide (10(-5)-10(-10) M) applied either alone or together with FU (0.25, 2.5 and 25 microg/ml) on the proliferation of murine Colon 38 cancer cells in vitro. Cell proliferation was assessed by the modified colorimetric Mosmann method. Proglumide inhibited the proliferation of Colon 38 cells at the concentrations of 10(-6), 10(-8) and 10(-10) M. FU inhibited the proliferation of cancer cells in all studied concentrations, exerting the most profound antiproliferative effect at the concentrations of 2.5 and 25 microg/ml. Thus, the former concentration was chosen to study its interactions with proglumide. Proglumide applied together with FU exerted a synergistic effect on the inhibition of proliferation of Colon 38 cells at 10(-8), 10(-9), 10(-10) M concentrations. The most profound inhibitory effect was observed in the group incubated with FU and 10(-10) M of proglumide. The obtained results indicate a possibility of new therapeutic options for colon cancer, but further studies are needed to elucidate, if the synergistic effect of FU and proglumide occurs also in the colon cancer in humans.

Effect of monthly administration of GHRH (fragment 1-29) with osmotic pump on the rat anterior pituitary.

Growth Hormone-Releasing Hormone (GHRH) is the main factor, which regulates GH secretion and somatotrope proliferation. However, its chronic effect on anterior pituitary gland is still unknown. It is known that excessive GHRH secretion in patients with gastroenteropancreatic tumors secreting GHRH results in acromegaly and somatotrope hyperplasia. In mice transgenic for GHRH somatotrope tumors develop. Thus, the aim of this paper was to examine the effect of GHRH chronic administration on somatotrope secretion, their percentage and cell proliferation in anterior pituitary gland in rats. The experiment was performed on male Fischer 344 rats weighing 200+/-20 g. The animals were divided into two groups: group I-controls (13 rats) received solvent for GHRH (5% ethanol in demineralized water); group II (10 rats) received GHRH (Growth Hormone Releasing Factor, fragment 1-29 amide) at a dose of 5 microg/day. The substances were given for 1 month via osmotic pump (ALZET), which were implanted subcutaneously in the dorsal region under ketamin anesthesia. After 4 weeks all rats were decapitated and the blood was collected. In the microscopic preparations of anterior pituitary gland the morphology of pituitary (Herlant staining) and the percentage of somatotrope cells and proliferation index based on PCNA staining were assessed. It was found that the chronic treatment with GHRH caused a statistically significant increase in serum rGH concentration and in percentage of somatotropes, but did not change proliferation index and did not induce pathological changes in the morphology of the anterior pituitary gland when compared to the control group. Summing up, monthly GHRH administration did not induce somatotrope adenomas but it caused serum GH level elevation, what seems to depend partially on the increase of somatotrope number.

Somatostatin analogs - from new molecules to new applications.

Somatostatin (SST) was firstly discovered as a hypothalamic hormone inhibiting GH secretion. Despite its broad inhibitory effects on both endocrine and exocrine secretions, natural SST has limited therapeutic potential owing to its short plasma half-life. The synthesis of the first two metabolically stabilized and more potent SST analogs (octreotide and lanreotide) established the use of SST peptide therapy. The discovery of the five SST receptor (sst(1-5)) subtypes in the 1990s further enhanced our understanding of the biological roles of SST, created new therapeutic opportunities and highlighted the limitation of 'classical' SST analogs, which act mainly via receptor subtype 2 and are unable to reproduce all actions of native SST. To diminish these limitations, new SST analogs highly selective for particular receptor subtypes, together with so-called 'universal' analogs acting on multiple receptor subtypes, have been developed. These compounds have shown promise in preclinical studies and might further advance the use of SST analog therapy in the future. The development of SST analogs coupled to radioisotopes or cytotoxic drugs, which allows the selective destruction of tumor cells overexpressing sst receptors, constitutes another field of progress.

Perspectives of new potential therapeutic applications of somatostatin analogs.

At the present time only two long-acting somatostatin (SS) analogs, octreotide and lanreotide, are commonly used in the routine therapy. Both analogs have a high affinity mainly to a somatostatin receptor subtype 2 (SSTR2). The established indications for SS analogs treatment include acromegaly, neuroendocrine tumors of the pancreas and gastrointestinal tract, and some gastro-enterologic diseases (pancreatitis, gastrointestinal bleedings, refractory diarrheas, pancreatic and intestinal fistulas). The recent investigations allow to predict the enlargement of therapeutic applications of SS analogs. It concerns pituitary tumors other than somatotropinoma, tumors of other endocrine glands like thyroid and adrenal gland, as well as some non-endocrine tumors. The progress depends on the introduction of new SS analogs with high affinity for SS receptor subtypes other than SSTR2, because some tumors present the high expression of SSTR1 (e.g. prostatic cancers) or SSTR5 (e.g. colonic cancers). Great hopes are connected with the coupling of SS analogs with the radioactive isotopes or non-radioactive cytotoxic agents to destruct the neoplastic cells highly expressing the specific subtypes of SS receptors. The pre- or postoperative in vivo imaging of SS receptors by means of the receptor scintigraphy, as well as the post-operative identification of SS receptor subtypes in the excised tumor tissues using immunohistochemistry, should play an important role in the prediction of the effects of SS analog treatment. Beside oncology, new therapeutic applications of SS analogs could be presumed among others in ophthalmology; it concerns the treatment of progressive Graves-Basedow ophtalmopathy, diabetic retinopathy, glaucoma and corneal diseases connected with corneal vascularization.