Biomedical subjects

P M van Koetsveld

Publications and source records attributed to P M van Koetsveld.

At least 19 recordsLinked to original sources

PubMed2001

Effect of inflammatory cytokines and growth factors on tumour cell adhesion to the peritoneum.

In this experimental study, the effect of inflammatory cytokines and growth factors on tumour cell adhesion to the peritoneum was investigated. A reproducible in vitro assay was developed to study the adhesion of CC531 colon carcinoma cells to an autologous monolayer of rat mesothelial cells. Tumour cell adhesion to mesothelium pre-incubated with interleukin-1beta (IL-1beta) and epidermal growth factor (EGF) resulted in at least 60% more tumour cell adhesion at maximal stimulation (p</=0.001). Transforming growth factor-beta (TGF-beta) pre-incubation resulted in minor, though significant stimulation of cell adhesion (maximal 16%, p<0.05). The effect of IL-1beta was time- and dose-dependent. No mesothelial cell proliferation took place after pretreatment with IL-1beta, indicating that enhanced adhesion was not based on an increase in the number of mesothelial cells. Pretreatment with EGF stimulated mesothelial cell growth as measured by DNA analysis. This effect on cell growth and adhesion was dose-dependent. Additional blocking experiments with anti-IL-1beta resulted in statistically significant inhibition of IL-1beta-stimulated tumour cell adhesion (p</=0.01), demonstrating the specificity of this effect. Interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), IL-6, and insulin-like growth factor (IGF-I) pre-incubation had no effect on tumour cell adhesion. These results prove that IL-1beta and EGF are significant promoting factors in tumour cell adhesion to mesothelium in vitro and may therefore account for tumour recurrence in the peritoneum in vivo.

Animals↗

PubMed2001

In vitro secretion of FSH by cultured clinically nonfunctioning and gonadotroph pituitary adenomas is directly correlated with locally produced levels of activin A.

OBJECTIVE: Expression of mRNAs encoding activin and its antagonists inhibin and follistatin has been described in human pituitary adenomas, including clinically nonfunctioning adenomas (NFAs) and gonadotroph adenomas (Gn-omas). Since many of the NFAs and Gn-omas secrete FSH in vitro, we hypothesized that locally produced activin may stimulate secretion of FSH in these pituitary adenomas. PATIENTS AND METHODS: Pituitary adenoma tissue was obtained from 38 patients diagnosed preoperatively as having NFAs (n = 17), Gn-omas (n = 5), prolactinomas (n = 6) or growth hormone (GH)-producing adenomas (n = 10). Actual protein levels of activin, inhibin, follistatin, FSH and LH were measured in media of these 38 cultured pituitary adenomas. In addition, we investigated correlations between concentrations of these growth factors and hormones in NFAs and Gn-omas. RESULTS: Gn-omas were found to secrete significantly more activin A in their culture medium than PRL- and GH-producing adenomas (P < 0.05). Inhibin A and inhibin B protein levels in culture media were very low. A positive correlation between levels of activin A and FSH (r = 0.56, P < 0.005) was found, while no correlation between activin A and LH could be detected. Furthermore, levels of follistatin were positively correlated with activin A levels (r = 0.73, P < 0.0005). Comparison of the activin A:follistatin ratio with the measured FSH protein levels showed an even stronger relationship (r = 0.79, P < 0.0005). CONCLUSIONS: It is concluded that levels of activin A, follistatin and FSH in media of cultured nonfunctioning adenomas and gonadotroph adenomas are positively correlated. This suggests that these adenomas secrete FSH in response to the relatively high locally produced levels of activin A.

Activins↗

PubMed2000

Somatostatin receptor subtypes in human thymoma and inhibition of cell proliferation by octreotide in vitro.

Somatostatin (SS) and SS receptor (SSR) subtypes, code-named sst1-5, are heterogeneously expressed in the normal human thymus. This suggests their involvement in controlling the immune and/or neuroendocrine functions in this organ. Moreover, recently a high in vivo uptake of [111In-DTPA-D-Phe1]octreotide has been reported in patients bearing thymoma. The present study characterizes in vivo and in vitro, functional SS-binding sites in a human thymoma. A high uptake of [111In-DTPA-D-Phe1]octreotide was observed in the chest of a patient with myasthenia gravis due to a cortical thymoma. Specific binding of [125I-Tyr11] SS-14 was found on a membrane preparation of the surgically removed thymoma. Scatchard analysis showed high affinity binding sites (Kd, 47.5 +/- 2.5 pmol/L) with low maximum binding capacity (23.5 +/- 2.5 fmol/mg membrane protein). RT-PCR analysis showed the presence of sst1, sst2A, and a predominant sst3 messenger RNA (mRNA) expression in the tumor tissue. Primary cultured tumor cells expressed sst3 mRNA only. In contrast to the normal thymus, SS mRNA was not expressed. By immunohistochemistry, the tumor cells highly expressed sst3 receptors, weakly expressed sst1 receptors, and showed no immunostaining for sst2A receptors. sst2A immunoreactivity was found in the stromal compartment of the tumor, particularly on the endothelium of small intratumoral blood vessels. In primary cultured tumor cells, both SS and octreotide (10 nmol/L) significantly inhibited [3H]thymidine incorporation by 40.6% and 43.2%, respectively. The following conclusions were reached. 1) As this tumor displayed a high immunoreactivity for sst3 and the cultured tumor cells expressed the sst3 mRNA only, this SSR may be the subtype involved in the inhibition of epithelial tumor cell proliferation by octreotide in vitro. 2) A loss of endogenous SS production in this thymoma might be implicated in the uncontrolled cell growth. 3) In this case, the sst3 may play a role in determining the uptake of [111In-DTPA-D-Phe1]octreotide by in vivo SS receptor scintigraphy.

Antineoplastic Agents, Hormonal↗

PubMed1999

Red blood cells inhibit tumour cell adhesion to the peritoneum.

BACKGROUND: Perioperative blood transfusion has been associated with increased tumour recurrence and poor prognosis in colorectal cancer. Blood loss in the peritoneal cavity might be a tumour-promoting factor for local recurrence. The aim of this study was to investigate whether blood in the peritoneal cavity affects local tumour recurrence. METHODS: In an established in vivo rat model the effect of 1.5 ml syngeneic whole blood on tumour cell adhesion and tumour growth was investigated. In the same model the effect of 1.5 ml pure red blood cell (RBC) concentrate and 1.5 ml RBC-derived substances on tumour cell adhesion was studied. In an established in vitro model the effect of increasing numbers of RBCs (0-250 bx 10(6)) on tumour cell adhesion and tumour growth was assessed. RESULTS: Both the presence of blood and RBC concentrate in the peritoneal cavity prevented tumour cell adhesion in vivo (overall P </= 0.001 and P </= 0.05 respectively), rather than promoting adherence. RBC concentrate and RBC-derived substances had a comparable inhibitory effect on tumour cell adhesion. In in vitro studies RBCs inhibited tumour cell adhesion but not tumour growth. CONCLUSION: RBC-derived factors prevent tumour cell adhesion to the peritoneum, and consequently tumour recurrence.

Animals↗

PubMed1999

In vitro characterization of somatostatin receptors in the human thymus and effects of somatostatin and octreotide on cultured thymic epithelial cells.

Somatostatin (SS) and its analogs exert inhibitory effects on secretive and proliferative processes of various cells via high affinity SS receptors (SS-R). SS analogs bind with different affinity to the five cloned SS-R subtypes. Octreotide, an octapeptide SS analog, binds with high affinity to the SS-R subtype 2 (sst2). SS-R have been demonstrated in vivo and in vitro on cells from endocrine and immune systems. Among the lymphatic tissues, the thymus has been shown to contain the highest amount of SS, suggesting a local functional role of the peptide. We investigated the SS distribution and SS-R expression pattern in the normal human thymus using autoradiography, membrane homogenate binding studies, and RT-PCR. In addition, the effect of SS and octreotide on growth of cultured thymic epithelial cells (TEC) was studied. By autoradiography, binding of [125I-Tyr0]-SS-28 and [125I-Tyr3]-octreotide was detected in all seven thymuses studied. Specific [125I-Tyr3]-octreotide binding was shown on membrane preparations from thymuses, while not from cultured thymocytes. RT-PCR showed the expression of sst1, sst2A and sst3 messenger RNA (mRNA) in the thymic tissue, whereas sst1 and sst2A mRNAs were found in isolated TEC. SS mRNA was present in thymic tissue and in isolated TEC. SS and octreotide significantly inhibited 3H-thymidine incorporation in 3 of 3 and 6 of 6 TEC cultures, respectively. The percent inhibition ranged from 38.8 to 66.8% for SS and from 19.1 to 59.5% for octreotide. In conclusion, SS mRNA and sst1, sst2A, and sst3 mRNAs are expressed in the normal human thymus. Cultured TEC selectively express sst1 and sst2A mRNA and respond in vitro to SS and octreotide administration with an inhibition of cell proliferation. These data suggest a paracrine/autocrine role of SS and its receptors in the regulation of cell growth in thymic microenvironment.

Adolescent↗

PubMed1999

Interferon-alpha-2a is a potent inhibitor of hormone secretion by cultured human pituitary adenomas.

Interferon-alpha (IFN alpha) may exert direct inhibitory effects on cell proliferation and on the production of different peptide hormones. We investigated the effect of IFN alpha on hormone production by 15 GH-secreting pituitary adenomas, 4 clinically nonfunctioning or gonadotroph pituitary adenomas, and 4 prolactinomas in vitro. In the GH-secreting pituitary adenoma cultures, a short term (72-h) incubation with IFN alpha (50-100 U/mL) significantly inhibited GH secretion in 3 of 7 cases and PRL secretion in 6 of 7 cultures. During prolonged incubation (14 days) with IFN alpha, GH and/or PRL secretion was significantly inhibited in 7 of 8 cultures (GH, 17-78% inhibition; PRL, 39-88% inhibition). In the clinically nonfunctioning or gonadotroph cultures, incubation with IFN alpha resulted in inhibition of the secretion of gonadotropins and/or alpha-subunit in all cases (27-62%), whereas in the prolactinoma cultures PRL secretion was inhibited by IFN alpha in all cases (37-76%). The effect of IFN alpha was additive to the inhibitory effects of the dopamine agonist bromocriptine (10 nmol/L) or the somatostatin analog octreotide (10 nmol/L). The inhibition of hormone secretion by IFN alpha was accompanied by inhibition of the intracellular hormone concentrations. The effect of IFN alpha was dose dependent, with an IC50 for inhibition of hormone secretion of 2.3 +/- 0.3 U/mL (n = 5), which is relatively low compared with the concentrations that are reached in patients treated with IFN alpha for various malignancies. In conclusion, the potent antihormonal effect of IFN alpha on cultured pituitary adenomas suggests that this drug might be of benefit in the treatment of selected patients with secreting pituitary adenomas. As treatment with IFN alpha is associated with considerable adverse reactions, studies with this drug should only be considered in inoperable, invasive aggressive, and dopamine agonist- and/or somatostatin analog-resistant functioning pituitary macroadenomas.

Adenoma↗

PubMed1999

Somatostatin receptor subtype expression in cells of the rat immune system during adjuvant arthritis.

Somatostatin is a neuropeptide that is widely distributed throughout the body. It acts as a neurohormone and a neurotransmitter and may also have an immunomodulatory role. The genes for five subtypes of somatostatin receptors (sst) have been cloned, suggesting that the diverse effects of the peptide might be mediated by different receptors. We are interested in studying the role of sst ininflammation, using an animal model. Because of the up-regulation of sst expression in inflamed joints in human rheumatoid arthritis, we chose rat adjuvant arthritis as an experimental model. In order to determine which of the sst subtypes might be important in immune modulation, subtype expression in leukocytes isolated from different lymphoid tissues of the rat was studied. Also, the expression levels of the most abundantly expressed sst mRNAs in leukocytes from spleen and blood were compared in rats with adjuvantarthritis and controls, using a semi-quantitative approach. Furthermore, the effect of systemic administration of a long-acting somatostatin analogue, octreotide, which binds selectively to sst subtypes 2 and 5 (sst2 and sst5), on the incidence and the severity of rat adjuvant arthritis, was studied. The main sst expressed in cells of the rat immune system, both resting and activated, were found to be sst3 and sst4. This contrasts with the human and murine situations, in which sst2 appears to be the main subtype expressed in the immune system. No quantitative differences in sst subtype mRNA levels in leukocytes from spleen and blood were found between rats with adjuvant arthritis and controls. Finally, no effect of systemic administration of octreotide on either the incidence or severity of adjuvant arthritis in Lewis rats was found. As octreotide binds selectively to sst2 and sst5, the absence of an immunomodulatory effect of this analogue in rat adjuvant arthritis corroborates our finding that these sst subtypes are not expressed in cells of the rat immune system. In conclusion, cells of the rat immune system appear to express a spectrum of sst (sst3 and sst4) different from that found in human granulomatous and autoimmune disease (mainly sst2). Therefore, the rat adjuvant arthritis model appears to be suitable only for studying the immunomodulatory effects of somatostatin analogues which have a high affinity for sst3 and sst4, but not for studying the immunomodulatory effects of octreotide, which has a high affinity only for sst2 and sst5.

Animals↗

PubMed1997

Paracrine interactions between mesothelial and colon-carcinoma cells in a rat model.

This study used a co-culture system with Transwell tissue-culture inserts to investigate the role of primary cultures of rat peritoneal mesothelial cells on the proliferation of rat colon-carcinoma cells (CC531 cells). Mesothelial cells significantly inhibited the growth of CC531 cells, while, conversely, CC531 cells stimulated the growth of mesothelial cells. Receptor-binding studies demonstrated the presence of high-affinity IGF-I receptors on the mesothelial and CC531 cells. Both cell types also produced IGF-I, as measured by radioimmunoassay. IGF-I stimulated DNA synthesis in mesothelial cells, but had no effect on the growth of CC531 cells. In co-culture, it was found that IGF-I potentiated the inhibitory effect of mesothelial cells on CC531 cells. The effect of IGF-I on mesothelial-cell proliferation was additive to the stimulatory effect of CC531 cells. TGF-beta had no effect on the growth of the CC531 cells, suggesting that this growth (-inhibitory) factor is not involved in the inhibitory effect of mesothelial cells on CC531 cell growth. The study provides evidence for the existence of a paracrine loop between mesothelial and colon-carcinoma cells, giving more insight into the basic cellular mechanisms that may modulate the growth of intraperitoneal colon carcinoma. Inhibition of CC531-cell proliferation by rat mesothelial cells might explain the earlier finding that tumour cells grow poorly in a surgically uncompromised abdomen.

Animals↗

PubMed1996

Internalisation of isotope-coupled somatostatin analogues.

With the technique of in vivo somatostatin (SRIF) receptor (sst) scintigraphy a variety of human sst-positive tumours can be visualised 24-48 h after intravenous injection of the radiolabelled (SRIF) analogue [111In-DTPA-D-Phe1]octreotide. This rather long residence time of radioactivity on tumours suggests that the radioligand is internalised by the tumour cells; literature data for normal pituitary and pancreatic islet cells agree with this. Internalised SRIF has been found to be associated with cytoplasmic organelles, especially the Golgi apparatus, lysosomes and secretory granules. We have found that mouse AtT20 and primary cultures of human growth-hormone-secreting pituitary adenoma cells internalised a high amount of radio-iodinated [Tyr3]octreotide. Since octreotide binds with high affinity to the sst2 and sst5 subtypes and because both sst subtypes are expressed in these cells, one or both subtypes may be involved in this process. We also found that unlabelled octreotide, SRIF-14 or SRIF-28 can increase the internalisation of the radioligand. These observations, together with other studies on the manipulation of sst expression, may help to optimise the uptake of radioligand in in vivo sst scintigraphy in humans and improve the potential effect of radiotherapy with radiolabelled (subtype-specific) SRIF analogues.

Animals↗

PubMed1996

Somatostatin receptor manipulation.

The expression of somatostatin receptors (ssts) on human tumours is the basis for the successful therapeutic and diagnostic application of (radiolabelled) somatostatin analogues. Manipulation (up-regulation) of sst expression might improve the uptake of radioligand in in vivo scintigraphy of human sst-positive tumours, as well as the potential success of radiotherapy using radiolabelled SRIF analogues. In colonal pituitary cell lines, agonist exposure (SRIF-14, SRIF-28, octreotide) has been shown to either reduce or increase sst (subtype) expression, suggesting cell-type-specific responsiveness. In addition, glucocorticoids and oestrogens were shown to down- and up-regulate, respectively, sst numbers. So far, little information is available with respect to sst (subtype) regulation in non-pituitary-derived cell types. We have found that sst expression in the model of the transplantable prolactin (PRL)-secreting rat pituitary tumour 7315b is mainly dependent upon the presence of oestradiol (E2), both in vivo and in vitro. This tumour is sst negative in vivo. In vitro, the addition of E2 induces sst expression (sst2 and sst3 subtypes). The in vivo administration of E2 (20 micrograms/day subcutaneously) to 7315b-tumour-bearing rats induces sst2 mRNA expression. The absence of sst expression in 7315b tumours in vivo may be due to the inhibition of ovarian E2 production by the high circulating PRL levels in the 7315b-prolactinoma-bearing rats. Indeed, no detectable E2 levels were found in the serum of 7315b-tumour-bearing rats. Taken together, our data suggest that the 7315b rat prolactinoma can indirectly manipulate (down-regulate) its own sst expression, in vivo, via its host. This experimental 7315b prolactinoma model might be representative for most untreated female prolactinoma patients. Clinically, patients with microprolactinomas do not benefit from octreotide treatment.

Animals↗

PubMed1995

Role of tumor-derived fibroblasts in the growth of primary cultures of human breast-cancer cells: effects of epidermal growth factor and the somatostatin analogue octreotide.

In the present study we have investigated the role of human breast-cancer-derived fibroblasts in the proliferation of primary cultures of epithelial cells derived from the same tumor. For this purpose, a co-culture system, using Transwell tissue-culture inserts with microporous membranes was employed. Fibroblasts and epithelial cells were enriched according to differences in their density on Percoll density gradients. The co-culture system was first established using MCF-7 breast cancer cells and a human fibroblast line (HF cells). Insulin, 17 beta-estradiol, EGF and HF cells all significantly stimulated the growth of MCF-7 breast cancer cells. The stimulatory effects of insulin, E2 and EGF were additive to the stimulatory effect of HF cells. These data suggest that (unique) factor(s), other than the above-mentioned growth-promoting compounds, are responsible for the growth-promoting effects of fibroblasts. In half of the human breast cancers investigated, tumor-derived fibroblasts stimulated tumor-derived epithelial cell proliferation. EGF significantly stimulated epithelial cell proliferation in 4 out of 6 cultures. The stimulatory effects of fibroblasts and EGF were additive or synergistic, and were observed in the additional presence of FCS, again suggesting production of unique factor(s) by the fibroblasts. In one culture the fibroblasts significantly inhibited epithelial tumor-cell proliferation. Conversely, the epithelial cells significantly stimulated proliferation of fibroblasts in 3 out of 3 cultures. The somatostatin analogue octreotide significantly inhibited epithelial cell proliferation by 46% in one tumor-cell culture in the absence, but not in the presence, of fibroblasts. In one culture, octreotide significantly inhibited the proliferation of fibroblasts co-cultured with epithelial cells.

Adult↗

PubMed1995

Somatostatin receptors: clinical implications for endocrinology and oncology.

Somatostatin receptors are present on most hormone-secreting tumours. They are the pathophysiological basis for the successful control of hormonal hypersecretion by pituitary adenomas, metastatic islet cell tumours and carcinoids during treatment with the long-acting somatostatin analogue octreotide. There is also evidence for inhibition of tumour growth in some of these patients. Visualization of somatostatin receptor-positive tumours is possible in vivo after the administration of ([111In]diethylenetriaminepentaacetic acid)octreotide. Primary tumours are detected and often metastases that were previously unrecognized. Tumours that secrete growth hormone or thyroid-stimulating hormone and non-functioning pituitary adenomas, islet cell tumours, carcinoids, paragangliomas, phaeochromocytomas, medullary thyroid carcinomas and small-cell lung cancers are visualized in 70-100% of cases. Meningiomas, renal cell cancers, breast cancers and malignant lymphomas are often somatostatin receptor positive, allowing their localization with this scanning procedure. In some of these tumours discrepancies have been noted between binding studies with somatostatin-14, somatostatin-28 and octreotide, which suggests the presence of somatostatin receptor subtypes on some tumours. Most hormone-secreting tumours react in vitro to octreotide with an inhibition of hormone release and growth. Cultured meningioma cells react to octreotide with a stimulation in growth, possibly by interference with the autocrine inhibitory growth control by interleukin 6. This suggests that the presence of somatostatin receptors on human tumours does not automatically imply a beneficial effect of somatostatin analogue therapy.

Animals↗

PubMed1995

Internalization of the radioiodinated somatostatin analog [125I-Tyr3]octreotide by mouse and human pituitary tumor cells: increase by unlabeled octreotide.

Recently, we developed a technique that allows the in vivo visualization in man of somatostatin receptor-positive neuroendocrine tumors after i.v. injection of [125I-Tyr3]octreotide or [111In-DTPA-D-Phe1]octreotide. Radiotherapy of such tumors using somatostatin analogs coupled to alpha- or beta-emitting radionuclides has been proposed as an application for radiolabeled somatostatin analogs. To develop this concept further, it is of importance to know whether the above-mentioned radiolabeled somatostatin analogs are internalized by the tumor cells, and whether it might be possible to manipulate the degree of internalization. In the present study we investigated the internalization of a stable somatostatin analog, [125I-Tyr3]octreotide, by mouse AtT20/D16V pituitary tumor cells and primary cultures of human GH-secreting pituitary tumor cells. Treatment of the cells with low pH was used to distinguish between membrane-bound (acid-releasable) and internalize (acid-resistant) radioligand. [125I-Tyr3]octreotide showed a time-dependent increasing accumulation in AtT20 cells; after 4 h of incubation, values up to 6-8% of the dose of radioligand added were obtained. Binding and internalization of [125I-Tyr3]octreotide were temperature dependent and inhibited by pertussis toxin. Inhibitors of lysosomal degradation did not increase the amount of internalized radioligand. After 4 h of incubation, 88% of the radioactivity present in the cells was still peptide bound, suggesting a low intracellular breakdown of this radioligand. Six of seven human GH-secreting adenoma cell cultures also internalized [125I-Tyr3]octreotide (variation between 0.24-4.98% of the dose radioligand added). Displacement of binding and internalization of [125I-Tyr3]octreotide by unlabeled octreotide showed a bell-shaped curve in AtT20 cells. At low concentrations (0.1 and 1 nM), binding and internalization were increased, whereas at higher concentrations, saturation occurred. In contrast to this, binding of [125I-Tyr3]octreotide to a broken cell preparation of AtT20 cells was displaced in a dose-dependent manner by unlabeled octreotide, with an IC50 of 0.1 nM. Similar observations were made in the human GH-secreting adenoma cell cultures. In conclusion, a high amount of [125I-Tyr3]octreotide is internalized in a specific-, time-, temperature-, and pertussis toxin-sensitive GTP-binding protein-dependent manner by mouse AtT20 and human GH-secreting pituitary tumor cells. In the presence of a low concentration of unlabeled octreotide, a rapid increase in the amount of [125I-Tyr3]octreotide internalized by AtT20 cells and by the majority of the human GH-secreting adenoma cell cultures was found.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenoma↗

PubMed1994

Relative potencies of the somatostatin analogs octreotide, BIM-23014, and RC-160 on the inhibition of hormone release by cultured human endocrine tumor cells and normal rat anterior pituitary cells.

In the present study we investigated the effects of the somatostatin (SS) analogs octreotide, RC-160, and BIM-23014 on GH release by cultured cells of human GH-secreting pituitary tumors, in normal rat anterior pituitary cells, and on gastrin release by cultured cells from a human gastrinoma. In all GH-secreting adenomas and in rat anterior pituitary cells, RC-160 was the most potent compound. RC-160 significantly inhibited GH-, PRL, and/or alpha-subunit release by human GH-secreting pituitary adenoma cells in concentrations as low as 10(-12)-10(-14) M, whereas at the same concentrations, octreotide and BIM-23014 did not inhibit or were significantly less effective in inhibiting GH release (P < 0.01, RC-160 vs. octreotide and BIM-23014). In rat anterior pituitary cell cultures, the IC50 values for inhibition of GH release were, in rank order of potency, 0.1, 5.3, 47, 48, and 99 pM for RC-160, SS-14, BIM-23014, octreotide, and SS-28, respectively. Maximal inhibitory effects by the three analogs were the same in the human GH adenoma cell cultures and the rat anterior pituitary cell cultures (-60%). On the basis of these data, RC-160 appears to be about 500 times more potent than octreotide and BIM-23014 in inhibiting GH release by rat anterior pituitary cells in vitro. Forskolin (100 microM) as well as pretreatment of the cells with pertussis toxin significantly diminished the inhibitory effects of the three SS analogs and those of SS-14 and SS-28 to the same extent. The latter data suggest that octreotide, RC-160, and BIM-23014 act mainly via a pertussis toxin-sensitive G-protein and an adenylyl cyclase-dependent mechanism. In the human gastrinoma culture, RC-160 inhibited gastrin release significantly more than octreotide at 10(-12)- and 10(-14)-M concentrations (P < 0.01). In conclusion, the SS analogs octreotide, RC-160, and BIM-23014 may have significant different potencies of inhibition of hormone release in vitro, with RC-160 being the most potent SS analog and octreotide and BIM-23014 having similar potencies. Depending on the pharmacokinetic properties of these three octapeptide SS analogs, these observations may have consequences for the medical therapy of patients with SS receptor-positive endocrine tumors.

Adenoma↗

PubMed1994

Uptake of thyroxine in cultured anterior pituitary cells of euthyroid rats.

The uptake of [125I]T4 was investigated in cultured anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. Experiments were performed with [125I]T4 (10(5) to 2 x 10(6) cpm; 0.35-7 nM) in medium containing 0.5% or 0.1% BSA. The uptake of [125I]T4 increased with time and showed equilibrium after around 1 h of incubation. The presence of 10 microM unlabeled T4 during incubation decreased the uptake of [125I]T4 by 65-70% at all time intervals. After 24 h of incubation, 1.5% iodide and 3.2% conjugates were detected in the medium, whereas around 20% of cellular radioactivity represented [125I]T3. The 15-min uptake of [125I]T4 was significantly reduced by simultaneous incubation with 100 nM T4 (by 24%; P < 0.05), 100 nM T3 (by 38%; P < 0.001), or 10 microM rT3 (by 32%; P < 0.001), whereas 10 microM tetraiodothyroacetic acid (Tetrac) had no effect. Furthermore, preincubation (30 min) and incubation (15 min) with 10 microM monodansylcadaverine, oligomycin, or monensin reduced the uptake of [125I]T4 by 30%, 50%, and 40%, respectively (all P < 0.001). Substitution of Na+ in the buffer by K+ diminished the uptake of [125I]T4 by 39% (P < 0.005); 2 mM phenylalanine, tyrosine, or tryptophan reduced [125I]T4 uptake by 18% (P < 0.05), 18% (P = NS), and 33% (P < 0.005), respectively. Our data suggest that the pituitary contains a specific carrier-mediated energy-requiring mechanism for [125I]T4 uptake that is partly dependent on the Na+ gradient. In addition, part of [125I]T4 uptake in the pituitary might occur through an amino acid transport system. When expressed per pM of free hormone, the 15-min uptake of [125I]T4 was approximately as high as that of [125I]T3. Because the reduction of [125I]T4 uptake by T4, T3, monodansylcadaverine, oligomycin, and monensin was roughly the same as the previously reported reduction of [125I]T3 uptake by the same compounds, it is further suggested that T4 and T3 share a common carrier in cultured anterior pituitary cells.

Animals↗

PubMed1994

A new radiolabelled somatostatin analogue [111In-DTPA-D-Phe1]RC-160: preparation, biological activity, receptor scintigraphy in rats and comparison with [111In-DTPA-D-Phe1]octreotide.

We have evaluated the potential usefulness of indium-111 labelled [DTPA-D-Phe1]RC-160, derived from the octapeptide somatostatin analogue RC-160, as a radiopharmaceutical for the in vivo detection of somatostatin receptor-positive tumours. For this purpose 111In-and 115In-labelled [DTPA-D-Phe1]RC-160 was tested for its biological activity, and applied for somatostatin receptor scintigraphy in vivo to rats bearing the transplantable rat pancreatic tumour CA20948, which expresses somatostatin receptors. We previously described the development of the 111In-labelled somatostatin analogue [DTPA-D-Phe1]octreotide and its use in the in vivo visualization of somatostatin receptor-positive tumours in rats and in humans. Like [111In-DTPA-D-Phe1]octreotide, [111In-DTPA-D-Phe1]RC-160 showed uptake in and specific binding in vivo to somatostatin receptor-positive organs and tumours, and the tumours were clearly visualized by gamma camera scintigraphy. However, as compared to [111In-DTPA-D-Phe1]octreotide, blood radioactivity (background) was higher, resulting in a lower tumour to blood (background) ratio. Using this animal model we therefore conclude that [111In-DTPA-D-Phe1]RC-160 has no advantage over [111In-DTPA-D-Phe1]octreotide as a radiopharmaceutical in the visualization of somatostatin receptors which bind both analogues. However, recent reports suggest the existence of different somatostatin receptor subtypes on some human cancers, which differentially bind RC-160 and not octreotide. These tumours include cancers of the breast, ovary, exocrine pancreas, prostate and colon. [111In-DTPA-D-Phe1]RC-160 might be of interest for future use in such cancer patients as a radiopharmaceutical for imaging somatostatin receptor-positive tumours, which do not bind octreotide.

Animals↗

PubMed1993

Radioiodinated somatostatin analogue RC-160: preparation, biological activity, in vivo application in rats and comparison with [123I-Tyr3]octreotide.

We have evaluated the potential usefulness of the radioiodinated octapeptide RC-160, a somatostatin analogue, which might serve as a radiopharmaceutical for the in vivo detection of somatostatin receptor-positive tumours. For this purpose, iodine-123 and iodine-125 labelled RC-160 was tested for biological activity and applied in vivo in rats bearing the transplantable rat pancreatic tumour CA20948, which expresses somatostatin receptors. Our group has recently described the in vivo visualization of such tumours in rats and in humans with the radioiodinated somatostatin analogue [Tyr3]octreotide. Like [123I-Tyr3]octreotide, 123I-RC-160 showed uptake in and specific binding in vivo to somatostatin receptor-positive organs and tumors. However, blood radioactivity (background) was higher, resulting in a lower tumour to blood (background) ratio. We therefore conclude that in this animal model 123I-RC-160 has no advantage over [123I-Tyr3]octreotide as a radiopharmaceutical for the in vivo use as a somatostatin receptor imager, although, like [123I-Tyr3]octreotide, 123I-RC-160 shows specific binding to different somatostatin receptor-positive organs. Recently differences were reported in affinity between somatostatin and its analogues for somatostatin receptors expressed in different human cancers, like those of the breast, ovary, exocrine pancreas, prostate and colon. Therefore 123I-RC-160 might be of interest for future use in humans as a radiopharmaceutical for imaging octreotide receptor-negative tumours.

Animals↗

PubMed1993

Evidence for carrier-mediated uptake of triiodothyronine in cultured anterior pituitary cells of euthyroid rats.

T3 uptake and TSH secretion were investigated in anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. TSH release during culture increased linearly with the number of cells in the range of 80,000-800,000 cells/well. Uptake and incubation experiments were performed at 37 C in medium containing 0.5% BSA. Incubation with TRH (0.1 microM) for 2 h stimulated TSH release 2.6-fold, and this effect was partly (approximately 45%) suppressed by preexposure for 2 h to T3 (0.01-1 microM) or T4 (1 microM). Similar concentrations of T3 and T4 reduced the cellular uptake of [125I]T3 (50 pM) during 1 h of incubation by 55%. After 15 min of incubation, [125I]T3 uptake (percent dose) amounted to 1.26 +/- 0.05% (mean +/- SE; n = 9)/500,000 cells. The major part (75%) of the [125I]T3 was found in the extranuclear fraction. Simultaneous incubation with unlabeled T3 (1 or 10 microM) reduced [125I]T3 uptake by 43% (n = 3; P < 0.001) and 52% (n = 6; P < 0.001), respectively. Reduction of the temperature to 20 C diminished the T3-suppressible fraction of [125I]T3 uptake approximately 3-fold. After preincubation (30 min) and incubation (15 min) with monodansylcadaverine (100 microM), the uptake of [125I]T3 was reduced by 32% (n = 3; P < 0.01). When the Na+ gradient was reduced by preincubation and incubation with ouabain (0.5 mM) or monensin (10 or 100 microM), T3 uptake was inhibited by 25% (n = 5; P < 0.01), 37% (n = 6; P < 0.001), and 61% (n = 3; P < 0.001), respectively. It is concluded that 1) T3 is taken up by the pituitary by a carrier-mediated mechanism, and 2) this uptake is at least partly dependent on the Na+ gradient.

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