In vivo use of a radioiodinated somatostatin analogue: dynamics, metabolism, and binding to somatostatin receptor-positive tumors in man

Somatostatin analogues, labeled with gamma-emitting radionuclides, are of potential value in the localization of somatostatin receptor-positive tumors with gamma camera imaging. We investigated the application in man of a radioiodinated analogue of somatostatin, 123I-Tyr-3-octreotide, which has similar biologic characteristics as the native peptide. The radiopharmaceutical is cleared rapidly from the circulation (up to 85% of the dose after 10 min) mainly by the liver. Liver radioactivity is rapidly excreted into the biliary system. Until 3 hr after injection, radioactivity in the circulation is mainly in the form of 123I-Tyr-3-octreotide. Thereafter, plasma samples contain increasing proportions of free iodide. Similarly, during the first hours after injection, radioactivity in the urine exists mainly in the form of the unchanged peptide. Thereafter, a progressive increase in radioiodide excretion is observed, indicating degradation of the radiopharmaceutical in vivo. Fecal excretion of radioactivity amounts to only a few percent of the dose. The calculated median effective dose equivalent is comparable with values for applications of other 123I-radiopharmaceuticals (0.019 mSv/MBq).

Thyroxine and 3,3',5-triiodothyronine are glucuronidated in rat liver by different uridine diphosphate-glucuronyltransferases

Male Wistar rats were treated with 50 mg 3,3',4,4'-tetrachlorobiphenyl (TCB)/kg BW or vehicle. After 4 days, the livers were isolated and perfused for 90 min with 2 nM [125I]T3 or 10 nM [125I]T4 in Krebs-Ringer medium containing 1% albumin. Deiodination and conjugation products and remaining substrates were determined in bile and medium samples by Sephadex LH-20 chromatography and HPLC. TCB treatment did not affect hepatic uptake and metabolism of T3. However, biliary excretion of T4 glucuronide was strongly increased by TCB, resulting in an augmented T4 disappearance from the medium, although initial hepatic uptake of T4 was not altered. Measurement of the microsomal UDP-glucuronyltransferase (UDPGT) activities confirmed that T4 UDPGT was induced by TCB, whereas T3 glucuronidation was unaffected. T3 UDPGT activity showed a discontinuous variation, which completely matched the genetic heterogeneity in androsterone glucuronidation in Wistar rats. These results indicate that different isozymes catalyze the glucuronidation of T3 and T4.

In vivo application of [111In-DTPA-D-Phe1]-octreotide for detection of somatostatin receptor-positive tumors in rats

Radioiodinated somatostatin analogues are useful ligands for the in vitro and in vivo detection of somatostatin receptors. [111In-DTPA-D-Phe1]-octreotide, a somatostatin analogue labeled with a different radionuclide, also binds specifically to somatostatin receptors in vitro. In this study we investigated its in vivo application in the visualization of somatostatin receptor-positive tumors in rats. The distribution of the radiopharmaceutical was investigated after intravenous injection in normal rats and in rats bearing the somatostatin receptor-positive rat pancreatic carcinoma CA 20948. After injection the radiopharmaceutical was rapidly cleared (50% decrease in maximal blood radioactivity in 4 min), predominantly by the kidneys. Excreted radioactivity was mainly in the form of the intact radiopharmaceutical. Ex vivo autoradiographic studies showed that specific accumulation of radioactivity occurred in somatostatin receptor-containing tissue (anterior pituitary gland). However, in contrast to the adrenals and pituitary, the tracer accumulation in the kidneys was not mediated by somatostatin receptors. Increasing radioactivity over the somatostatin receptor-positive tumors was measured rapidly after injection and the tumors were clearly visualized by gamma camera scintigraphy. In rats pretreated with 1 mg octreotide accumulation of [111In-DTPA-D-Phe1]-octreotide in the tumors was prevented. Because of its relatively long effective half-life, [111In-DTPA-D-Phe1]-octreotide is a radionuclide-coupled somatostatin analogue which can be used to visualize somatostatin receptor-bearing tumors efficiently after 24 hr, when interfering background radioactivity is minimized by renal clearance. This is an advantage over the previously used [123I-Tyr3]-octreotide which has a shorter effective half-life and shows high abdominal interference due to its hepato-biliary clearance. Therefore, [111In-DTPA-D-Phe1]-octreotide seems a better alternative for scintigraphic imaging of somatostatin receptor-bearing tumors.

Euro-Collins solution versus UW-solution for long-term liver preservation in the isolated rat-liver perfusion model

To compare UW-solution (UW) and Euro-Collins (EC) for long-term liver preservation we investigated the morphology and metabolic capacity of rat liver after 18 and 42-hours cold-storage in either UW or EC. After harvesting the rat liver was transferred to a perfusion chamber where it was perfused for 10 min with UW or EC at 4 degrees C. Thereafter livers were stored at 4 degrees C in UW or EC for 18 hours (both groups n = 6) or for 42 hours (both groups n = 8). After 18-hr or 42-hr cold-storage a 2-hr warm perfusion (37 degrees C) was started with Krebs-Ringer solution with carbogen to which 125Iodine-triiodothyronine (T3) was added. Control livers (n = 8) were immediately perfused with Krebs-Ringer without cold-storage. The following parameters were assessed: ASAT-levels in the perfusate, T3-metabolites in the bile and the perfusate, the perfusion pressure, the volume of bile secreted and light-microscopical morphology at the end of the warm perfusion period. After cold storage in UW-solution the ASAT-levels in the perfusate were lower than after storage in EC as well as the perfusion pressures. These livers demonstrated a better T3-metabolism and secreted more bile than EC-stored livers. Histological examination showed more tissue damage in the EC-stored livers than in the UW stored livers. We conclude that cold-storage of rat liver in UW-solution resulted in a better morphology and metabolic capacity as compared with EC-solution.

Somatostatin receptor imaging in vivo localization of tumors with a radiolabeled somatostatin analog

This paper presents the results of the visualization of somatostatin (SS) receptor positive tumors in man after the i.v. administration of the SS analog Tyr3-octreotide coupled to 123I. It is an easy, quick and harmless procedure which allows imaging of primary and (often unexpected) secondary deposits and/or multiple localizations of the majority of endocrine pancreatic tumors, metastatic carcinoids and pituitary tumors, as well as of a multitude of tumors with neuroendocrine characteristics and well-differentiated brain tumors and meningiomas. In the case of hormone-secreting tumors a positive scan in most instances also predicts the subsequent successful therapy with octreotide.

Somatostatin-receptor imaging in the localization of endocrine tumors

BACKGROUND AND METHODS

A number of different tumors have receptors for somatostatin. We evaluated the efficacy of scanning with 123I-labeled Tyr3-octreotide, a somatostatin analogue, for tumor localization in 42 patients with carcinoid tumors, pancreatic endocrine tumors, or paragangliomas. We then evaluated the response to octreotide therapy in some of these patients.

RESULTS

Primary tumors or metastases, often previously unrecognized, were visualized in 12 of 13 patients with carcinoid tumors and in 7 of 9 patients with pancreatic endocrine tumors. The endocrine symptoms of these patients responded well to therapy with octreotide. Among 20 patients with paragangliomas, 8 of whom had more than one tumor, 10 temporal (tympanic or jugular), 9 carotid, and 10 vagal tumors could be visualized. One small tympanic tumor and one small carotid tumor were not seen on the scan.

CONCLUSIONS

The 123I-labeled Tyr3-octreotide scanning technique is a rapid and safe procedure for the visualization of some tumors with somatostatin receptors. A positive scan may predict the ability of octreotide therapy to control symptoms of hormonal hypersecretion.

Pulmonary clearance of 99mTc-DTPA during halothane anaesthesia

We studied the integrity of the alveolo-capillary barrier during different forms of anaesthesia by measuring the pulmonary clearance of inhaled 99mTc-DTPA. We studied four groups of rabbits. Groups I and II were anaesthetized with nembuthal only and the fractional concentration of inspired oxygen (F1O2) was 0.30 and 1.00, respectively. Groups III and IV were anaesthetized with 1% halothane and F1O2 was 0.30 and 0.99, respectively. 99mTc-DTPA was administered as a fine aerosol and the clearance of the tracer from the lungs was subsequently measured with a gamma camera. The mean half-life of the tracer in the lungs in Groups I-IV was 60, 58, 59 and 26 min, respectively. The rapid pulmonary clearance of 99mTc-DTPA in Group IV indicates that halothane in combination with high oxygen concentration increases the permeability of the alveolo-capillary barrier. This may be due to effects on the pulmonary surfactant system and/or the alveolar epithelium.

Treatment with Sandostatin and in vivo localization of tumors with radiolabeled somatostatin analogs

The presence of high numbers of somatostatin receptors seems to be the basis for the successful control by Sandostatin of hormonal hypersecretion by most growth hormone-secreting pituitary adenomas, endocrine pancreatic tumors, and carcinoids. In this report, we present preliminary data on in vivo somatostatin receptor imaging with a 123I-coupled somatostatin analog (204-090) in patients with these types of tumors.

Somatostatin receptor imaging with 123I-Tyr3-Octreotide

Somatostatin receptors have been shown to be present at all main sites of its action, such as the anterior pituitary gland, the exocrine and endocrine pancreas, the mucosa of the gastrointestinal tract and the central nervous system (1, 2). Somatostatin receptors can be measured by two different approaches (3). First by direct biochemical techniques, i.e. binding studies on tissue homogenates in vitro, which allow precise characterization of the affinities and kinetics of these receptors. Secondly, receptors can also be visualized in tissue sections with autoradiography. This last method has the advantage of identifying histologically the tissues containing these receptors. High numbers of high affinity somatostatin receptors have been found on most growth hormone secreting pituitary tumors, as well as on many endocrine pancreatic tumors and carcinoids (4, 5). These receptors probably form the pathophysiological basis for the successful control of hormonal hypersecretion by most of these tumors during treatment with octreotide (Sandostatin). Several other human tumor types have also been recognized to contain large numbers of high affinity somatostatin receptors. All 27 meningiomas investigated contained these receptors, while well-differentiated glia-derived brain tumors like most oligo-dendrogliomas and (low-grade) astrocytomas, but not glioblastomas contain somatostatin receptors (6-9). Somatostatin receptors have also been found on 20-40% of human breast cancers (10).

Receptor scintigraphy with a radioiodinated somatostatin analogue: radiolabeling, purification, biologic activity, and in vivo application in animals

Radioiodinated Tyr-3-octreotide, a somatostatin analogue, is a useful ligand for the in vitro detection of somatostatin receptors. In this study, we have investigated the possible in vivo application of this radioligand in the detection of somatostatin receptor-bearing tumors by scintigraphy. The specific somatostatin-like biologic activity of radioiodinated Tyr-3-octreotide was confirmed in vitro: (a) radioiodinated Tyr-3-octreotide competes in the nanomolar range with specific receptor binding of somatostatin to suspended human meningioma membranes and (b) the secretion of growth hormone by cultured rat pituitary cells was similarly inhibited by iodinated Tyr-3-octreotide and somatostatin. In rats, intravenously injected 123I-Tyr-3-octreotide is rapidly cleared from the circulation mainly by the liver. Although this rapid clearance limits the amount of tracer available for somatostatin receptor-bearing tumors, the advantage of this rapid clearance is that the background level is rapidly reduced in favor of scintigraphic imaging of these tumors. Pancreatic tumors in rats were localized by scintigraphy after intravenous injection of 123I-Tyr-3-octreotide.

Parallel in vivo and in vitro detection of functional somatostatin receptors in human endocrine pancreatic tumors: consequences with regard to diagnosis, localization, and therapy

The effects of octreotide in vivo and in vitro on hormone release, in vivo [123I]Tyr3-octreotide scanning, and in vitro [125I]Tyr3-octreotide autoradiography were compared in five patients with endocrine pancreatic tumors. [123I]Tyr3-octreotide scanning localized the primary tumor and/or previously unknown metastases in four of the five patients. The patient with a negative scan had an insulinoma that did not respond to octreotide in vivo. No Tyr3-octreotide-binding sites were subsequently found at autoradiography of the tumor, whereas somatostatin-14 receptors were present at a high density. In parallel, culture studies with the cells prepared from this adenoma showed that insulin release was not affected by octreotide, while both somatostatin-14 and -28 significantly suppressed hormone release. Culture studies of the tumor cells from two gastrinomas showed a dose-dependent inhibition of gastrin release by octreotide. Octreotide exerted direct antiproliferative effects in one of these gastrinomas, which had been shown to be rapidly growing in vivo. Both gastrinomas had specific somatostatin receptors, as measured by in vitro receptor autoradiography. Somatostatin release by the cultured somatostatinoma cells from one of these patients was suppressed by octreotide. In conclusion, 1) the [123I]Tyr3-octreotide scanning procedure is valuable in the localization of primary endocrine pancreatic tumors as well their often clinically not yet recognized metastases; 2) the in vitro detection of somatostatin receptors in those tumors that were also visualized in vivo after injection of [123I] Tyr3-octreotide indicates that the ligand binding to the tumor in vivo indeed represents binding to specific somatostatin receptors; and 3) the parallel between the presence of somatostatin receptors on tumors and in in vivo and in vitro effects of octreotide on hormonal release from these tumors indicate that a positive scan predicts a good suppressive effect of octreotide on hormonal hypersecretion by these tumors.

The clinical use of somatostatin analogues in the treatment of cancer

Somatostatin is a regulatory hormone or tissue factor which plays an inhibitory role in the normal regulation of several organ systems, including the central nervous system, hypothalamus and pituitary gland, the gastrointestinal tract and the exocrine and endocrine pancreas. Sandostatin is an analogue of somatostatin which has characteristics which makes it a better compound for clinical use than native somatostatin: it inhibits GH preferentially over insulin. It has a long half-life in the circulation, causing a prolonged inhibitory effect in somatostatin-responsive target organs. It is active after subcutaneous administration and rebound hypersecretion does not occur. Sandostatin is very well tolerated by most patients. Somatostatin receptors remain present on a variety of tumours which arise in tissues that contain these receptors normally. High numbers of somatostatin receptors have been found on GH-secreting pituitary tumours and on most metastatic endocrine pancreatic tumours and carcinoids. Sandostatin treatment ameliorates clinical symptoms in most acromegalic patients while GH hypersecretion and elevated concentrations of circulating IGF-I are well controlled. In most patients hormonal hypersecretion from endocrine pancreatic tumours and carcinoids is also suppressed during Sandostatin therapy. This results in an instant improvement in the quality of life. There is preliminary evidence of control of tumour growth. The presence of high numbers of somatostatin receptors on tumours enables in vivo receptor-imaging, with 123iodine coupled to a somatostatin analogue. This newly developed technique provides for the first time the possibility of localization of the primary tumours and their metastases and a prediction of which patients may respond to treatment with Sandostatin. Theoretically this somatostatin-receptor imaging technique represents a new approach which may be extended to other receptor-containing tumours. Therefore it may provide a new, powerful alternative to tumour localization performed with monoclonal antibody technology. Another potential development is the use of beta-emitting isotopes coupled to somatostatin analogues for therapeutic irradiation. Somatostatin analogues exert potent inhibitory effects on the growth of a variety of experimental tumour models in animals. Several mechanisms of action have been proposed including the direct antiproliferative effects of somatostatin and its analogues in a variety of tumour cell cultures. Most well-differentiated human brain tumours like meningiomas and low-grade astrocytomas contain somatostatin receptors, while undifferentiated brain tumours mainly contain EGF receptors. Fifteen percent of human breast carcinomas contain somatostatin receptors; those which do have a better prognosis. It can be concluded that somatostatin is an endogenous, naturally occurring inhibitory growth factor.(ABSTRACT TRUNCATED AT 400 WORDS)

Development and use of a mathematical two-pool model of distribution and metabolism of 3,3',5-triiodothyronine in a recirculating rat liver perfusion system: albumin does not play a role in cellular transport

To describe the T3 kinetics in a recirculating rat liver perfusion system, we have developed a mathematical two-pool model consisting of medium and liver. It appeared that all parameters of the model could be fully resolved by using the time-dependent disappearance of radioactive T3 (2 nM) from the medium only. The model calculates the T3 medium pool, the T3 liver pool, and the amount of hormone metabolized at different times after the start of the perfusion. To check the validity of the model, metabolism was also estimated from the appearance of labeled metabolites (glucuronides, sulfates, and I-) in the medium and the cumulative excretion of T3 and metabolites into the bile. The medium pool was also estimated by the product of medium volume and remaining T3 concentration, and the liver pool as the amount of T3 at time zero minus medium pool minus T3 metabolized). These results were in excellent agreement with the predicted values from the model. Taking the metabolites appearing in medium and bile together, about 38% of the total amount of T3 metabolized during 60 min was converted into T3 glucuronide, 12% into T3 sulfate, and 48% into I-, respectively, while about 3% was excreted in the bile unaltered. The results show that not all T3 transported to the liver is being metabolized, but part is bound outside the cellular compartment. This latter pool of T3 is dependent on the albumin concentration in the medium. The amount of T3 metabolized is solely determined by the free T3 concentration and is independent of total T3 or albumin concentration in the medium.

Clinical applications of somatostatin analogs

The somatostatin analog Sandostatin is successfully used in the treatment of metastatic endocrine pancreatic tumors, carcinoids, and acromegaly. In addition, somatostatin receptors are also present on other tumors in man, therefore making it possible to demonstrate these tumors by the administration of (123)I-coupled to a somatostatin analog.

Prednisone and cyclosporine in the treatment of severe Graves' ophthalmopathy

It is uncertain what is the most appropriate medical therapy for patients with severe Graves' ophthalmopathy. Therefore, we carried out a single-blind, randomized clinical trial to compare the efficacy of prednisone with that of cyclosporine in 36 patients who had been euthyroid for at least two months. The two groups, each consisting of 18 patients, were similar in age, sex, and the duration and severity of ophthalmopathy. The initial dose of cyclosporine was 7.5 mg per kilogram of body weight per day, and that of prednisone was 60 mg per day, which was subsequently tapered to 20 mg per day. During the 12-week treatment period, 11 prednisone-treated and 4 cyclosporine-treated patients responded to therapy (61 percent vs. 22 percent; P = 0.018); response was manifested by decreases in eye-muscle enlargement and proptosis and improved visual acuity and total and subjective eye scores. There were no differences at base line between the patients who later responded and those who did not. Prednisone was tolerated less well than cyclosporine. After 12 weeks, patients who did not respond were treated for another 12 weeks with a combination of cyclosporine and a low dose of prednisone. Among the 9 patients who initially received prednisone, the addition of cyclosporine resulted in improvement in 5 (56 percent); among the 13 patients who received cyclosporine initially, 8 (62 percent) improved after the addition of prednisone. Combination therapy was better tolerated than prednisone treatment alone. We conclude that single-drug therapy with prednisone is more effective than cyclosporine in patients with severe Graves' ophthalmopathy. The combination can be effective in patients who do not respond to either drug alone.

Auxiliary partial liver transplantation: imaging evaluation in 10 patients

Auxiliary partial liver transplantation involves placement of a heterotopic graft in the subhepatic space, with the liver of the recipient left unaltered. We studied the values of three imaging procedures (Doppler sonography, diisopropyl iminodiacetic acid [DISIDA] scintigraphy, and cholangiography) to evaluate the transplant and the native liver after surgery in 10 patients. Special attention was paid to the Doppler waveform of the hepatic artery of the graft and to the resistive index. An increase of the index above 0.80 was not specific for, but was always associated with graft dysfunction (rejection, primary nonfunction, multiple organ failure, or portal vein thrombosis). DISIDA scintigraphy also lacked specificity and was of limited value in the detection of postoperative complications. It proved useful in routine imaging to monitor atrophy of the native liver and hypertrophy of the transplant. Cholangiography was useful for visualization of the biliary tree. Our experience suggests that these three noninvasive imaging procedures are sufficient for the proper postoperative evaluation of patients after auxiliary partial liver transplantation.

Congenital hypothyroidism and partial thyroid hormone unresponsiveness of the pituitary in a patient with congenital thyroxine binding albumin elevation

We describe a girl who presented at the age of 6 weeks with cardiogenic shock due to congenital hypothyroidism (serum thyroxine (T4) less than 12 nmol/l). Thyroxine replacement therapy was instituted. In spite of high total serum T4 levels, thyroid stimulating hormone (TSH) serum values remained elevated. The raised serum T4 levels were the result of congenital elevation of thyroid binding albumin (TBA). Toxic doses of both T4 and triiodothyronine (T3) normalized the elevated TSH levels indicating that the pituitary is responsive to thyroid hormone, albeit at a higher threshold. In patients with congenital TBA elevation and an altered T4 pituitary response requiring thyroid replacement therapy, the measurement of serum free T4 levels is the parameter of choice to monitor treatment.

[The effect of immunoscintigraphy with monoclonal antibodies on assays of hormones and tumor markers. This is not the end of the matter!]

The use of monoclonal antibodies in medicine for in-vivo diagnostic methods and for therapeutic purposes will increase in the future. Although monoclonal antibodies possess a high specificity, the animal origin of these antibodies remains a problem. Repeated administration of animal monoclonal antibodies (in vivo) may induce the formation of human antibodies against these monoclonal antibodies. Because animal monoclonal antibodies are also used in laboratory assays (in vitro), the presence of human antibodies against these animal monoclonal antibodies may cause spuriously elevated or depressed results of these assays. The clinician should be alert to this possibility. A case history is presented to demonstrate the problem.

Combined measurements of plasma aromatic L-amino acid decarboxylase and DOPA as tumour markers in diagnosis and follow-up of neuroblastoma

As neuroblastoma, the most common solid tumour in childhood, may contain all the constituents of the catecholamine biosynthesis cascade, some of these constituents may be produced in excess in a varying mixture reflecting the wide variability in expression of differentiated features of the tumour. We have measured plasma levels of norepinephrine (NE), epinephrine (E), dopamine (DA) and 3,4-dihydroxyphenylalanine (DOPA), and plasma activities of dopamine beta-hydroxylase (DBH) and aromatic L-amino acid decarboxylase (ALAAD) in 18 patients with neuroblastoma, in 13 at various times during the course of their disease. Activities of serum lactic dehydrogenase (LDH), serum levels of ferritin (FER) and neuron-specific enolase (NSE), and urinary vanilmandelic acid (VMA) were also determined. NE, E and DBH were found not to reflect tumour activity. In untreated active neuroblastoma DOPA or ALAAD (10 out of 10) or both (six out of 10) were clearly elevated. In all 13 patients where samples were obtained during chemotherapy, ALAAD activities fell within the normal range, while DOPA decreased more slowly. During relapse, DOPA and, especially, ALAAD, rapidly increased; in all six patients who had a relapse both DOPA and ALAAD were elevated. In complete remission (eight patients), ALAAD was normal in all patients, but DOPA remained elevated in the one patient who later experienced a relapse. Our preliminary conclusion is that combined measurements of plasma ALAAD and DOPA may be useful markers for neuroblastoma activity at diagnosis, but even more so in indicating residual disease (DOPA) and in the early detection of relapse (ALAAD).

Localisation of endocrine-related tumours with radioiodinated analogue of somatostatin

Various endocrine-related tumours contain large numbers of high-affinity somatostatin receptors. 123I-labelled tyr-3-octreotide (tyr-3-SMS 201-995, a synthetic derivative of somatostatin) was used to localise such tumours in vivo with a gamma-camera. Positive scans were obtained for two meningiomas, two gastrinomas, and one carcinoid; negative scans were obtained for one insulinoma (in which unlabelled octreotide had no effect on insulin levels), one phaeochromocytoma, one adrenal carcinoma (octreotide had no effect on cortisol levels), and three medullary thyroid carcinomas (octreotide had no effect on calcitonin levels). Thus radioiodinated tyr-3-octreotide can label somatostatin receptors in endocrine-related tumours in vivo and can therefore be used for tumour localisation.