Potential role of somatostatin analogues in the treatment of cancer

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Streptozotocin-induced diabetes models: pathophysiological mechanisms and fetal outcomes

Glucose homeostasis is controlled by endocrine pancreatic cells, and any pancreatic disturbance can result in diabetes. Because 8% to 12% of diabetic pregnant women present with malformed fetuses, there is great interest in understanding the etiology, pathophysiological mechanisms, and treatment of gestational diabetes. Hyperglycemia enhances the production of reactive oxygen species, leading to oxidative stress, which is involved in diabetic teratogenesis. It has also been suggested that maternal diabetes alters embryonic gene expression, which might cause malformations. Due to ethical issues involving human studies that sometimes have invasive aspects and the multiplicity of uncontrolled variables that can alter the uterine environment during clinical studies, it is necessary to use animal models to better understand diabetic pathophysiology. This review aimed to gather information about pathophysiological mechanisms and fetal outcomes in streptozotocin-induced diabetic rats. To understand the pathophysiological mechanisms and factors involved in diabetes, the use of pancreatic regeneration studies is increasing in an attempt to understand the behavior of pancreatic beta cells. In addition, these studies suggest a new preventive concept as a treatment basis for diabetes, introducing therapeutic efforts to minimize or prevent diabetes-induced oxidative stress, DNA damage, and teratogenesis.

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.

Somatostatin receptor (SSTR) scintigraphy in patients with osteosarcoma

To investigate somatostatin receptors (SSTRs) in primary or metastatic high-grade osteosarcoma, 18 patients (12 without metastases, 4 with synchronous lung, and 2 with metachronous bone metastases) underwent SSTR scintigraphy. After intravenous (i.v.) injection of 200-250 MPq of 111In-pentreotide, images were recorded at 4 and 24 hours. All patients underwent 99mTc-methylene diphosphonate (MDP) bone scan (BS). Scans were interpreted both with qualitative evaluation and with semiquantitative image processing, by means of tumor-to-background ratio modification over time. Primary tumor: SSTR scintigraphy was positive in 12 (75%) patients: 10 (83%) of the 12 nonmetastatic patients, and 2 (50%) of those with synchronous metastases. Metastases: SSTR scintigraphy was positive only in one (17%) of the six patients with metastatic disease. No relation was found between SSTR scintigraphy results and gender, histologic subtype, site, and size of the tumor. After primary chemotherapy, 15 patients underwent surgery of primary tumor; a good histologic response was found in 7 (64%) of the 11 patients with positive SSTR scintigraphy versus 1 (25%) of the 4 patients with negative SSTR scintigraphy. High-grade osteosarcoma exhibits somatostatin receptors, usually detectable in the primary tumor, but not in the metastatic lesions. The different expression of somatostatin receptors observed in primary and metastatic lesions, and in patients with tumors having different chemosensitivity, could indicate a possible relation between somatostatin receptors and biological behavior of the tumor.

Cholecystokinin-B (CCK-B)/gastrin receptor targeting peptides for staging and therapy of medullary thyroid cancer and other CCK-B receptor expressing malignancies

Nuclear medicine is engaged with the detection of pathological processes with the help of radionuclides. An interesting approach is to target antigens, symporters, or receptors with diagnostic and therapeutic radionuclides. Different peptide receptors like somatostatin, bombesin/GRP or VIP are (over)expressed on cancer cells, and are therefore an ideal target for the diagnosis and therapy in nuclear medicine with radiolabeled peptides. The somatostatin analogue OctreoScan [octreotide coupled with diethylene-triamine-pentaacetate (DTPA)] can be labeled with In-111 and is widely used in nuclear oncology for the staging of different tumors (e.g., carcinoids). Other peptides like neurotensin, bombesin/GRP, and VIP are under (pre)clinical investigations. The staging of metastatic medullary thyroid cancer (MTC) with the conventional radiological procedures is sometimes difficult. The high sensitivity of the pentagastrin stimulation test in detecting primary or metastatic MTC indicates the presence of tumor, but its localization is often not possible. This reaction of the tumor cells to the pentagastrin stimulation test suggests a widespread expression of the corresponding receptor type on human MTC. Indeed, autoradiographic studies demonstrated cholecystokinin (CCK)-B/gastrin receptors not only in over 90% of MTCs, but in a high percentage of small cell lung cancers, stromal ovarian, and potentially a variety of other tumors, including gastrointestinal adenocarcinomas, neuroendocrine tumors, and malignant glioma. The aim of our recent work was to develop and systematically optimize suitable radioligands for targeting CCK-B receptors in vivo and to investigate their role in the staging and therapy of MTC and other CCK-B receptor expressing malignancies. For this purpose, a variety of CCK/gastrin-related peptides, all having in common the C-terminal CCK receptor binding tetrapeptide sequence -Trp-Met-Asp-PheNH(2) or derivatives thereof, were investigated. They were members of the gastrin- or cholecystokinin families, or possessed characteristics of both, which differ by the intramolecular position of a tyrosyl moiety. Their stability and affinity were studied and optimized in vitro and in vivo; their biodistribution and therapeutic efficacy were tested in preclinical models. Best tumor uptake and tumor-to-nontumor ratios were obtained with members of the gastrin family, due to their superior selectivity and affinity for the CCK-B receptor subtype. Radiometal-labeled derivatives of minigastrin showed excellent targeting of CCK-B receptor expressing tissues in animals and healthy human volunteers. Preclinical therapy experiments in MTC-bearing animals showed significant antitumor efficacy. In a subsequent clinical study, 75 MTC patients with metastatic MTC were investigated; 43 suffered of known, 32 of occult disease. CCK-B receptor scintigraphy was performed with (111)In-DTPA-D-Glu(1)-minigastrin. The normal organ uptake was essentially confined to the stomach (and to a lower extent, to the gallbladder and, in premenopausal women, to normal breast tissue) as a result of CCK-B receptor specific binding, and to the kidneys as excretory organs. All tumor manifestations known from conventional imaging were visualized as early as 1 h p.i., with increasing tumor-to-background ratios over time; at least one lesion was detected in 29/32 patients with occult disease (patient-based sensitivity 91%). Among them were local recurrences, lymph node, pulmonary, hepatic, splenic, and bone (marrow) metastases. Eight patients with advanced metastatic disease were injected in a dose-escalation study with potentially therapeutic activities of a (90)Y-labeled minigastrin derivative at 4-6-weekly intervals (30-50 mCi/m(2) per injection for a maximum of four injections). Hematologic and renal were identified as the dose-limiting toxicities at the 40 and 50 mCi/m(2) levels. Two patients experienced partial remissions, 4 stabilization of their previously rapidly progressing disease. These data suggest that CCK-B receptor ligands may be a useful new class of receptor binding peptides for diagnosis and therapy of a variety of (CCK-B receptor expressing) tumor types. They allow for a sensitive and reliable staging of patients with metastatic MTC. Initial therapeutic results are promising, but nephrotoxicity is a major concern to be solved.

Biotherapeutic approaches to pancreatic cancer

The incidence of adenocarcinoma of the pancreas has risen steadily over the past four decades. Since pancreatic cancer is usually diagnosed at an advanced stage and because of the lack of effective therapies, the prognosis of such patients is extremely poor. Despite advances in our understanding of the molecular biology of pancreatic cancer, the systemic treatment of this disease remains unsatisfactory. Conventional chemotherapy has not produced dramatic improvements in response rates or patient survival. New treatment strategies are clearly needed. This paper will review emerging therapies for pancreatic carcinoma. A deeper understanding of the molecular biology of cell growth and proliferation, as well as of neoplastic cell transformation, has led to advances in several areas, including the use of hormones and antihormones as adjuvant therapy; inhibition of tumour growth and metastasis by inhibitors of matrix metalloproteases and angiogenesis, and by small molecules, such as retinoids, which interfere with progression through the cell cycle; immunotherapy with monoclonal antibodies; disruption of intracellular signal transduction with farnesyltransferase inhibitors; and, finally, gene therapy with specifically designed vaccines.

The clinical role of somatostatin analogues as antineoplastic agents: much ado about nothing?

BACKGROUND

Somatostatin (SST) analogues represent a novel approach for the treatment of certain cancers. The objective of this article is to summarise the current knowledge on SST analogues in the treatment of cancer patients.

METHODS

Computerised (Medline) and manual searches were performed to identify publications on clinical trials published in the English-speaking literature between 1966 and 2000. Information abstracted included patients' pre-treatment status, histology, SST receptor (SSTR) evaluation, type of SST analogue, application schedule and dose, duration of treatment, side-effects, response criteria applied (i.e. WHO response criteria, biochemical criteria or symptomatic investigations) and survival.

RESULTS

Our search disclosed 22 case reports, five phase 1 and 47 phase II trials, and eight randomised clinical trials using SST analogues (octreotide, lanreotide and vapreotide) as antineoplastic agents. With regard to the phase II trials, conflicting results have been demonstrated in almost all tumour entities investigated. The few randomised studies published so far have shown an impact on survival in patients with hepatocellular cancer, while the effect attributed to treatment in patients with gastrointestinal adenocarcinomas might well have been due to an exceptionally short survival in the control group. There appears to be evidence that SST analogues are able to enhance the therapeutic effects of hormonal intervention in patients with breast cancer, prostate cancer and probably pancreatic cancer. Interpretation of the findings, however, is complicated by the fact that patients were heavily pre-treated in some studies and response criteria have not been uniformly applied. In addition, most studies have not been designed to distinguish between receptor-mediated (direct) and indirect effects of SST analogues in tumour patients.

CONCLUSIONS

According to the results obtained so far, there can be no doubt about the wide therapeutic index and the high efficacy of SST analogues in the symptomatic management of neuroendocrine tumours. Apart from these indications, the data do not justify recommendation of SST analogues as antineoplastic agents outside of clinical trials, as the optimal dose and schedule of application for antineoplastic activity has not been defined for currently used agents. Carefully designed clinical trials including investigation of SSTR status before treatment, evaluation of an indirect mechanism of SST analogues, and assessment of optimal combination of hormone therapy and chemotherapy with SST analogues are clearly needed in the near future.

Cholecystokinin-B/Gastrin receptor-targeting peptides for staging and therapy of medullary thyroid cancer and other cholecystokinin-B receptor-expressing malignancies

The high sensitivity of the pentagastrin stimulation test in detecting primary or metastatic medullary thyroid cancer (MTC) suggests a widespread expression of the corresponding receptor type on human MTC. Indeed, autoradiographic studies demonstrated cholecystokinin (CCK)-B/gastrin receptors not only in more than 90% of MTCs, but also in a high percentage of small-cell lung cancers, stromal ovarian tumors, and potentially a variety of other tumors, including gastrointestinal adenocarcinomas, neuroendocrine tumors, and malignant glioma. The aim of our work was to develop and systematically optimize suitable radioligands for targeting CCK-B receptors in vivo and to investigate their role in the staging and therapy of MTC and other CCK-B receptor expressing malignancies. For this purpose, a variety of CCK/gastrin-related peptides, all having in common the C-terminal CCK-receptor binding tetrapeptide sequence-Trp-Met-Asp-PheNH(2) or derivatives thereof, were investigated. They were members of the gastrin or cholecystokinin families or possessed characteristics of both, which differ by the intramolecular position of a tyrosyl moiety. Their stability and affinity were studied and optimized in vitro and in vivo; their biodistribution and therapeutic efficacy were tested in preclinical models. Best tumor uptake and tumor to nontumor ratios were obtained with members of the gastrin family, because of their superior selectivity and affinity for the CCK-B receptor subtype. Radiometal-labeled derivates of minigastrin showed excellent targeting of CCK-B receptor expressing tissues in animals and healthy human volunteers. Preclinical therapy experiments in MTC-bearing animals showed significant antitumor efficacy. In a subsequent clinical study, 45 MTC patients with metastatic MTC were investigated; 23 had known and 22 had occult disease. CCK-B receptor scintigraphy was performed with (111)In-diethylenetriamine pentaacetic acid-d-Glu(1)-minigastrin. The normal organ uptake was essentially confined to the stomach (and, to a lesser extent, to the gallbladder and, in premenopausal women, to normal breast tissue) as a result of CCK-B receptor specific binding and to the kidneys, as excretory organs. All tumor manifestations known from conventional imaging were visualized as early as 1 hour postinjection, with increasing tumor to background ratios over time; at least 1 lesion was detected in 20 of 22 patients with occult disease (patient-based sensitivity, 91%). Among them were local recurrences and lymph node, pulmonary, hepatic, splenic, and bone (marrow) metastases. Eight patients with advanced metastatic disease were injected in a dose-escalation study with potentially therapeutic activities of a (90)Y-labeled minigastrin derivative at 4 to 6-week intervals (30-50 mCi/m(2) per injection for a maximum of 4 injections). Hematologic and renal toxicities were identified as the dose-limiting toxicities at the 40 and 50 mCi/m(2) levels. Two patients experienced partial remissions, and 4 experienced stabilization of their previously rapidly progressing disease. These data suggest that CCK-B receptor ligands may be a useful new class of receptor-binding peptides for diagnosis and therapy of a variety of (CCK-B receptor expressing) tumor types. They allow for sensitive and reliable staging of patients with metastatic MTC. Initial therapeutic results are promising, but nephrotoxicity is a major concern to be solved.

Type-2 somatostatin receptor mRNA levels in breast and colon cancer determined by a quantitative RT-PCR assay based on dual label fluorogenic probe and the TaqMan technology

We reported previously that the expression of type 2 somatostatin receptor (sst2) was positively related to patient outcome in the childhood tumor neuroblastoma. To quantitate the expression of mRNA sst2 expression, we used a competitive RT-PCR assay. To improve the practicability of this measurement and its applicability to large groups of patients, we present here an original 'real-time' quantitative RT-PCR method, based on a dual-labeled fluorogenic probe and the TaqMan technology. By this method, we have measured sst2 mRNA expression in 24 breast cancer samples and 26 colon carcinomas as well as on the corresponding non-adjacent non-neoplastic tissue of the same patients. The proposed method has a dynamic range of 4 x 10(4) to 4 x 10(8) molecules of sst2 mRNA. The intra-assay precision of the test, evaluated as signal detection variability, was 2.4%. Accuracy, evaluated by the addition of standard RNA to unknown samples, provided a mean recovery of 98+/-2%. A significant correlation has been observed in a study performed in 24 neuroblastoma samples measured both with the proposed method and with a competitive RT-PCR assay (r=0.913, p<0.001). In our preliminary clinical study, no significant differences were observed in sst2 mRNA levels between normal and tumor specimens in both colorectal (normal tissue 5.1 x 10(7)+/-2.0 x 10(7) molecules/microg total RNA, cancer tissue 9.7 x 10(7)+/-4.2 x 10(7)) and breast tumors (normal tissue 5.5 x 10(8)+/-2.0 x 10(8), cancer tissue 4.4 x 10(8)+/-3,7 x 10(8)).However, in colorectal cancer, sst2 mRNA values of subjects with high circulating carcinoembryonic antigen (CEA) levels (>5 ng/ml) were statistically lower (2.3 x 10(7)+/-6.2 x 10(6) molecules/, microg total RNA; p<0.05) than those of subjects with low CEA concentration (1.4 x 10(8)+/-6.7 x 10(7)). Also, the sst2 mRNA ratio between normal and tumor tissue (N/T ratio) resulted significantly inversely related to CEA levels. In breast cancer, a significant difference was found between the mean N/T ratio of negative (below 10 fmol/mg protein) and positive estrogen receptor tumors (p<0.05). Analogous results were found selecting breast tumors on the basis of the progesterone receptor status (p<0.05). The proposed method is accurate, precise, sensitive and less labor-intensive than the competitive RT-PCR assay. For a correct evaluation of sst2 mRNA expression, it seems very important to measure the sst2 expression both in tumor and in the non-tumoral non-adjacent tumor specimens.

Pancreatic cancer: a review of emerging therapies

The incidence of adenocarcinoma of the pancreas has risen steadily over the past 4 decades. Since pancreatic cancer is diagnosed at an advanced stage, and because of the lack of effective therapies, the prognosis of such patients is extremely poor. Despite advances in our understanding of the molecular biology of pancreatic cancer, the systemic treatment of this disease remains unsatisfactory. Conventional chemotherapy has not produced dramatic improvements in response rates or patient survival. New treatment strategies are clearly needed. This paper reviews emerging therapies for pancreatic carcinoma. A more profound understanding of the molecular biology of cell growth and proliferation, as well as of neoplastic cell transformation, has led to advances in several areas, including the use of somatostatin analogues and antiandrogens as adjuvant therapy; inhibition of tumour growth and metastasis by inhibitors of matrix metalloproteinases and angiogenesis, and by small molecules such as retinoids, which interfere with progression through the cell cycle; immunotherapy with monoclonal antibodies; disruption of intracellular signal transduction with farnesyltransferase inhibitors; and finally gene therapy with specifically designed vaccines.

Rat somatostatin sst2(a) and sst2(b) receptor isoforms mediate opposite effects on cell proliferation

We have investigated the actions of somatostatin (SRIF) and angiopeptin on cell proliferation of CHO-K1 cells expressing the recently cloned rat sst2(b) receptor (CHOsst2(b)) and compared these to their effects in cells expressing the sst2(a) receptor (CHOsst2(a)). In contrast to the sst2(a) receptor, the sst2(b) receptor did not mediate inhibition of bFGF (10 ng ml(-1))-stimulated re-growth and cell proliferation. Rather, SRIF (0.1-1000 nM) and angiopeptin (0.1-1000 nM) stimulated basal re-growth and proliferation of CHOsst2(b) cells in a concentration-dependent manner (estimated pEC50 values of 7.8 and 7.9, respectively). The opposite effects of SRIF on cell proliferation mediated through the two sst2 receptor isoforms were both abolished by 18 h pre-treatment with pertussis toxin. The proliferative effect via the sst2(b) receptor was also abolished by the tyrosine kinase inhibitor, genistein. In conclusion, the present study shows that the rat sst2(a) and sst2(b) receptor splice variants mediate opposite effects on cell proliferation.

[125I][Tyr3]octreotide labels human somatostatin sst2 and sst5 receptors

Human somatostatin (somatotropin release inhibiting factor = SRIF) receptor subtypes sst2 and sst5 were stably expressed in Chinese hamster lung fibroblast (CCL39) cells. [125I][Tyr3]octreotide labelled with high affinity and in a saturable manner both sst2 (pKd = 9.89+/-0.02, Bmax = 210+/-10 fmol/mg, n = 3) and sst5 sites (pKd = 9.64+/-0.04, Bmax = 920+/-170 fmol/mg, n = 3). The pharmacological profile of sst2 sites established in CCL39 cells using SRIF and various peptide analogues was very similar to that described previously in CHO cells and in human cortex: SRIF14 = SRIF28 > or = seglitide > BIM 23014 = RC 160 > octreotide > CGP 23996 > or = L362,855 > BIM 23052 > L361,301 = cortistatin14 > BIM 23030 > BIM 23056 > cycloantagonist SA. However, peptides classically perceived as sst2 receptor selective (e.g., seglitide, octreotide, vapreotide) showed also high affinity for human sst5 receptors labelled with [125I][Tyr3]octreotide: SRIF28 > seglitide > SRIF14 > L361,301 = octreotide > cortistatin14 = BIM 23014 = BIM 23052 > L362,855 = RC160 > CGP 23996 > BIM 23056 > cycloantagonist SA > BIM 23030. Further radioligand binding studies were performed with [Leu8,D-Trp22,125I-Tyr25]SRIF28 ([125I]LTT-SRIF28) and [125I]CGP 23996. At sst2 receptors, Bmax values determined with [125I][Tyr3]octreotide, [125I]LTT-SRIF28 and [125I]CGP 23996 were in the same range (180-370 fmol/mg). 5'-Guanylyl-imidodiphosphate (GppNHp) displaced all three radioligands to the same extent (85%) and the pharmacological profiles were superimposable. By contrast, at sst5 receptors Bmax values were very different: [125I][Tyr3]octreotide (920 fmol/mg), [125I]CGP 23996 (3530 fmol/mg) and [125I]LTT-SRIF28 (6950 fmol/mg). GppNHp affected [125I][Tyr3]octreotide more than [125I]CGP 23996 binding, whereas [125I]LTT-SRIF28 was much less affected. In addition, the affinity values determined in competition experiments at sst5 receptors, varied markedly; whereas SRIF14, cortistatin14 and SRIF28 showed 2-, 4- and 8-fold differences in affinity at sst5 receptors labelled with [125I][Tyr3]octreotide and [125I]LTT-SRIF28 compounds such as RC160, L363,301, L362,855, octreotide or CGP 23996 showed between 42- and 123-fold lower affinity when sst5 sites were labelled with [125I]LTT-SRIF28. The present data suggest caution to be used when comparing affinity profiles determined in binding studies using different radioligands. In addition, the present results suggest that effects produced by octreotide and related short chain SRIF analogues on hormone release, modulation of tumour growth and central effects may be mediated by either sst2 and/or sst5 receptors.

Differential effects of somatostatin and angiopeptin on cell proliferation

1. Somatostatin (SRIF) exerts antiproliferative effects, and angiopeptin (an sst2/sst5 receptor-selective analogue) has recently been evaluated in clinical trials for the prophylaxis of restenosis following coronary angioplasty. Using an in vitro model of cell growth we have examined the effects of SRIF and angiopeptin on cell proliferation in CHO-K1 cells stably transfected with the human or rat recombinant sst2 or sst5 receptor and compared these with their effects on rat aortic vascular smooth muscle cells (VSMC) expressing endogenous somatostatin receptors. 2. In CHO-KI cells, expressing either human or rat recombinant sst2 or sst5 receptors, or in rat aortic VSMC, SRIF and angiopeptin (0.1-1000 nM) had no effect on basal re-growth of cells into a denuded area of a previously confluent monolayer. In contrast, basic fibroblast growth factor (bFGF, 10 ng ml(-1)) stimulated re-growth of these cells. 3. SRIF (0.1-1000 nM) caused a concentration-dependent inhibition of the bFGF-stimulated re-growth in CHO-K1 cells expressing human sst2 (h sst2) or sst5 (h sst5) receptors (pIC50=8.05+/-0.03 and 8.56+/-0.12, respectively). In contrast, angiopeptin (0.1-1000 nM) acted as a partial agonist at the h sst2 receptor (44.6+/-2.7% inhibition of the bFGF-stimulated re-growth at 100 nM; pIC50=8.69+/-0.25) but was devoid of any agonist activity at the h sst5 receptor. 4. In CHO-K1 cells stably expressing rat recombinant sst2 (r sst2) or sst5 (r sst5) receptors, SRIF (0.1-1000 nM) was able to inhibit the bFGF-stimulated re-growth (pIC50=7.98+/-24 and 8.50+/-0.12, respectively). Angiopeptin (0.1-1000 nM) caused a concentration-dependent inhibition of bFGF-stimulated re-growth at the r sst2 receptor (pIC50=8.08+/-0.24) but acted as a partial agonist at the r sst5 receptor (maximum response= 57.7+/-3.6% inhibition of bFGF-stimulated re-growth at 100 nM; pIC50=8.60+/-0.16). 5. Although angiopeptin was inactive as an agonist at the h sst5 receptor, 100 nM angiopeptin potently antagonized the SRIF-induced inhibition of proliferation in CHO h sst5 (estimated pKB= 10.4+/-0.3). 5-Hydroxytryptamine (0.1 nM-10 microM) also inhibited bFGF-stimulated re-growth (pIC50=8.36+/-0.11) and angiopeptin had no effect on this response (pKB<7). 6. SRIF (0.1-1000 nM) caused a concentration-dependent (pIC50=8.04+/-0.08) inhibition of bFGF-stimulated re-growth in VSMC, whereas angiopeptin displayed weak agonist activity, only inhibiting bFGF-stimulated re-growth at concentrations greater than 100 nM. Angiopeptin (100 nM) caused a rightward displacement of the concentration-effect curve to SRIF with an estimated pKB value of 7.70+/-0.12. 7. These findings suggest that the low intrinsic activity of angiopeptin at the h sst2 receptor, combined with its lack of agonist activity at the h sst5 receptor, may explain the poor clinical efficacy of angiopeptin in trials for coronary artery restenosis, which contrasts with encouraging data found in equivalent in vivo animal studies.

Selenium, calcium channel blockers, and cancer risk--the Yin and Yang of apoptosis?

It is increasingly clear that apoptosis plays a crucial role in the promotional phase of cancer development. Initiated pre-neoplastic clones in rat liver experience a high rate of apoptosis, and this rate has an important impact on the survival and growth of these clones. Suppression of apoptosis appears to be a universal property of cancer promoters, suggesting conversely that agents which inhibit cancer induction during the promotional phase increase the rate of apoptosis in initiated cells. Modulation of apoptosis is a likely explanation for recent striking evidence that use of calcium channel blockers substantially increases, whereas supplemental selenium substantially decreases, human cancer incidence. Non-genotoxic measures which are likely to upregulate apoptosis in pre-neoplastic/neoplastic cells--and thus may be useful in prevention and/or therapy--include selenium, retinoids/carotenoids, green tea polyphenols, caloric restriction, downregulation of IGF-I activity, high-dose tamoxifen and other protein kinase C antagonists, withdrawal or blockade of trophic hormones, isoflavones, limonene, vitamin D and cholecalciferol analogs, dietary fiber/sodium butyrate, hyperthermia, benzaldehyde derivatives, and creatine.

Somatostatin decreases somatostatin messenger ribonucleic acid levels in the rat periventricular nucleus

Growth hormone (GH) secretion from the pituitary is known to be under the dual control of GH-releasing factor (GRF) and somatostatin (SRIF). Hypothalamic SRIF, the major inhibitor of pituitary growth hormone secretion, inhibits its own release by a negative ultrashort-loop feedback mechanism. However, it is not known whether this negative regulation is mediated by inhibition of SRIF mRNA production. GRF may also inhibit its own release, thereby modifying pituitary GH secretion, possibly through an ultrashort-loop feedback mechanism. Thus, SRIF production and GRF release are both regulated by SRIF. Periventricular nucleus (PeN) and mediobasal hypothalamus (MBH) from adult male rats were incubated for 6 h in Waymouth's medium with either SRIF or the SRIF agonist analog RC 160 (10(-9) to 10(-6) M). Levels of SRIF mRNA were determined by an S1 nuclease protection assay using a 32[P]-labeled rat SRIF riboprobe. SRIF (10(-7) M) and RC 160 (10(-8), 10(-7) M) significantly (p< or =0.01) decreased SRIF mRNA levels in the PeN. The levels of SRIF mRNA in the MBH were not modified by either SRIF or RC 160. SRIF (10(-7) and 10(-6) M) significantly (p < or = 0.01 and p < or = 0.001, respectively) inhibited the release of GRF at 30 min in the MBH. Likewise, the release of GRF was slightly decreased by 10(-7) M RC 160, and significantly inhibited by 10(-6) M (p < or = 0.001) at 30 min. At 6 h, the levels of GRF were significantly reduced by 10(-7) M SRIF (p < or = 0.05) and by RC 160 (10(-7), 10(-6) M; p < or = 0.001 and p < or = 0.05, respectively). In contrast with these results, the SRIF analog was unable to alter SRIF release at 30 min. At 6 h incubation, RC 160 (10(-7) M) significantly (p < or = 0.001) reduced SRIF release from MBH fragments. These results demonstrate that SRIF and a SRIF analog decrease SRIF mRNA levels in the PeN and inhibit the release of SRIF from the nerve terminals of the MBH. Thus, SRIF appears to regulate its own gene expression by negative ultrashort-loop feedback. Therefore, when SRIF is secreted from these neurons in response to GRF, it down-regulates the preceding stimulatory input as well as its own secretion.

Treatment of pancreatic cancer. Promises and problems of tamoxifen, somatostatin analogs, and gemcitabine

The clinical problem posed by pancreatic cancer is introduced, and the epidemiology and pathology of the disease are briefly presented. The natural history of this tumor is then described in order to highlight the deficiencies of current therapeutic modalities. The extremely poor results of the early drug trials are reviewed, followed by a detailed discussion and critique of the trials of novel treatments that include gemcitabine, somatostatin analogs, and tamoxifen. Finally, areas for future development are indicated.

Molecular Events as Targets of Anticancer Drug Therapy

The aim of this review is to introduce some molecular targets for cancer chemotherapy, with comments on their mode of action, preclinical and clinical results. The representatives of the following groups are covered: phosphorylation inhibitors, protein kinase modulators, receptor antagonists, immunomodulators, differentiating agents, multidrug resistance modulation, telomerase inhibitors, and bioreductive agents.

The diagnostic utility of somatostatin receptor scintigraphy in oncology

Somatostatin receptor scintigraphy (SRS) with the diethylenetriaminopentaacetic-acid-conjugated somatostatin analogue [111In-DTPA-D-Phe1] octreotide, also known as 111In-pentetreotide, is a new non-invasive modality for the evaluation of tumours that express receptors for somatostatin. These receptors are present on neuroendocrine and other tumours, including lymphomas and some breast cancers. In oncology SRS is a promising diagnostic tool for localizing primary tumours, staging, control and follow-up after therapy, and for identification of patients who may benefit from therapy with unlabelled octreotide or, in the future, with radiolabelled octreotide. In the past few years many small and large studies investigating various aspects of SRS have been reported. In this review the value of SRS in the management of individual tumour types is explored. For many tumours the best sensitivity in lesion detection is only achieved by very careful imaging after the administration of at least 200 MBq 111In-pentetreotide. On the basis of the current experience the main value of SRS in oncology is in the staging and evaluation of gastroenteropancreatic tumours, paragangliomas, small-cell lung cancer and lymphomas. Promising areas for SRS are the evaluation of breast cancer, non-medullary thyroid cancer and melanoma, and initial results with targeted radionuclide therapy using radiolabelled octreotide have been reported.

Somatostatin receptor-binding peptides labeled with technetium-99m: chemistry and initial biological studies

The synthesis of peptides which possess a high affinity for the somatostatin receptor and contain a chelator for the radionuclide technetium-99m is described. The target compounds were designed such that they would form stable, oxotechnetium(V) chelate complexes in which the Oxorhenium(V) chelate complexes of these peptides were prepared as nonradioactive surrogates for the technetium complexes. Peptide oxorhenium complexes and Tc-99m complexes eluted closely upon HPLC analysis. The receptor-binding affinities of both the free and rhenium-coordinated species were measured in vitro. The binding affinities of the free peptides (Ki's in the 0.25 - 10 nM range) compared favorably with [DTPA]octreotide (Ki = 1.6 nM), which, as the indium-111 complex, is already approved for somatostatin receptor (SSTR)-expressing tumor imaging in the United States and Europe. Furthermore, the rhenium-coordinated peptides had binding affinities which, in many cases, were higher than those of the corresponding free peptides, with several complexes having a Ki's of 0.1 nM. Some of the more potent SSTR-binding peptides were labeled with technetium-99m and assessed in an in vivo study with tumor-bearing rats. The 99m Tc-labeled peptides prepared in this study should be useful as SSTR-expressing tumor-imaging agents due to their high SSTR-binding affinities, ease of preparation, and, because they are low molecular weight peptides, expected pharmacokinetics characterized by rapid tracer excretion from the body resulting in high-contrast images.

Octreotide differentially modulates human Caco-2 intestinal epithelial cell proliferation and differentiation by decreasing intracellular cAMP

Somatostatin modulates gastrointestinal mucosal growth and differentiation indirectly via inhibition of bioactive peptides and directly by less well understood mechanisms. We studied the direct effects of the somatostatin analog octreotide on proliferation, brush-border enzyme activity, cell-matrix interactions and intracellular cAMP in Caco-2 human intestinal epithelial cells. Proliferation was assessed by cell counting and [3H]thymidine uptake. The brush-border enzymes alkaline phosphatase (AP) and dipeptidyl dipeptidase (DP) were quantitated by synthetic substrate digestion. Adhesion and migration on purified matrix proteins were also measured. Octreotide (10(-9)-10(-5)M) shortened doubling time (46.5 +/- 6.2% at 10(-5) M, n = 20, P < 0.0001) and stimulated [3H]thymidine uptake. Octreotide decreased intracellular cAMP by 19.4 +/- 5.0% (n = 7, P < 0.0001) while dibutyryl-cAMP (10(-6) M) prolonged doubling time by 10.1 +/- 1.5% (n = 8, P < 0.0001), and blocked the octreotide effect. Octreotide decreased AP and DP with maximal effect at 10(-6) M (36.8 +/- 8.3% and 20.5 +/- 9.1%, n > 7, P < 0.0005 respectively). However, mitomycin proliferative blockade prevented octreotide inhibition of AP and DP, suggesting that the mitogenic effects of octreotide had simply decreased average maturity of the cells. Octreotide did not alter Caco-2 adhesion, EGF-or matrix-modulated motility, or integrin surface expression. Octreotide appears to directly stimulate Caco-2 proliferation by decreasing cAMP. These proliferative effects modulate Caco-2 differentiation but do not affect cell-matrix interactions.

Somatostatin and its cyclic octapeptide analog SMS 201-995 as inhibitors of proliferation of human acute lymphoblastic and acute myeloid leukemia

Somatostatin (SS) is a 14 amino acid peptide which is secreted by the hypothalamus and the pancreatic islets. It expresses antiproliferative activity in various organ systems, experiments have suggested effects of SS on hematopoietic cells. Here we present investigations regarding the effect of SS and its analog SMS 201-995 (SMS) on the in vitro proliferation of acute lymphoblastic leukemia (ALL; n = 7 cases), acute myeloid leukemia (AML; n = 21 cases) and chronic lymphocytic leukemia (CLL; n = 2 cases). Both SS and SMS inhibited spontaneous leukemic cell growth in approximately 1/3 of cases (i.e. 7/19). G-CSF stimulated AML cells were inhibited by SMS in 11/21 cases. AML cell proliferation induced by IL-3 or GM-CSF was suppressed in only 3/21 and 6/21 cases, respectively. In ALL cells, IL-7-induced proliferation was suppressed by SMS in 3/7 cases. The effect of SMS seemed to depend on the type of the hematopoietic growth factor, and on their concentrations. In fact, high concentrations of G-CSF could override SMS blocking completely. Colony formation by normal marrow progenitors and DNA synthesis by HL-60 and T11/65 leukemic cell lines were not affected by SMS. In conclusion, somatostatin may act as a negative regulator of the proliferative activity of human leukemia.

A phase I study of the somatostatin analogue somatuline in patients with metastatic hormone-refractory prostate cancer

BACKGROUND

Somatuline, a somatostatin analogue, has proven to be effective in several animal models of prostate cancer. Preliminary clinical studies also have suggested antitumor activity in patients with prostate cancer. The authors conducted a dose-escalation trial of 25 patients with metastatic hormone-refractory prostate cancer.

METHODS

Dosages of 4, 7, 10, 13, 18, and 24 mg/day were administered by continuous intravenous infusion for at least 28 days.

RESULTS

Plasma levels of insulin-like growth factor-I (IGF-I), but not those of IGF-II, declined modestly during therapy. Toxicities included grade I diarrhea, bloating, infection, nausea, and flatus. The gastrointestinal side effects were typically self-limiting and occurred during the initial portion of treatment cycles. In addition, three patients experienced grade II catheter-related infections. No clinical response was noted by either radiographic or tumor marker criteria. The maximally tolerated dose of somatuline was not determined.

CONCLUSION

A continuous intravenous infusion of 24 mg/day of somatuline is well tolerated and could be evaluated in other types of cancer or possibly in less advanced prostate cancer, but no clinical activity was noted at this dose in patients with advanced metastatic hormone-refractory prostate cancer.

A randomised trial of octreotide vs best supportive care only in advanced gastrointestinal cancer patients refractory to chemotherapy

Octreotide, a somatostatin analogue, has been shown to inhibit the growth of gastrointestinal cancers in vitro and in vivo. To assess the anti-tumour effect of octreotide, we performed a randomised trial comparing octreotide with best supportive care in advanced gastrointestinal cancer patients refractory to chemotherapy. A total of 107 patients with advanced gastrointestinal cancer refractory to chemotherapy were randomised to receive octreotide at the dose of 200 micrograms three times a day for 5 days a week, or the best supportive care only. The primary outcome variable was the survival duration. Response rate was an outcome variable of secondary importance. Fifty-five patients (15 stomach, 16 pancreas, 24 colon-rectum) received octreotide, while 52 (14 stomach, 16 pancreas, 22 colon-rectum) received the best supportive care. Patients treated with octreotide had a significant advantage in duration of survival with a median survival time of 20 weeks vs 11 in the control group (P < 0.0001). This advantage was present also considering the survival data for each tumour group. Twenty-five patients (45%) given octreotide showed stable disease vs only eight (15%) in the control group (P < 0.001). In conclusion, octreotide therapy seems to confer a survival benefit in advanced gastrointestinal cancer patients refractory to chemotherapy. Additional studies will be needed to confirm these results and to clarify other questions about dose and schedule of octreotide.

Low dose octreotide and tamoxifen in the treatment of adenocarcinoma of the pancreas

BACKGROUND

Data from experimental studies suggest that a combination of octreotide, the long acting somatostatin analogue, octreotide, and tamoxifen improves the survival of animals with pancreatic cancer.

METHODS

Twelve patients with a tissue diagnosis of ductal adenocarcinoma of the pancreas were treated with 100 micrograms of octreotide three times per day and tamoxifen 10 mg twice daily. The survival of the octreotide-tamoxifen group was compared with a historic cohort of 68 untreated patients with pancreatic cancer, matched for age, sex, and TNM stage.

RESULTS

The median survival times for the octreotide-tamoxifen-treated group compared with the historic cohort were 12 and 3, months respectively. Actuarial one-year survival rates for the octreotide-tamoxifen-treated group compared with the historic cohort were 59% and 16%, respectively.

CONCLUSIONS

In this study, patients with unresectable and resected ductal adenocarcinoma of the pancreas had an apparently increased survival when treated with a combination of octreotide and tamoxifen. A randomized controlled trial to examine this potential therapeutic benefit is now indicated.

Phase I-II study of the somatostatin analogue lanreotide in hormone-refractory prostate cancer

Lanreotide (BIM 32014), a somatulin analogue, was found to be as effective as castration in a rat prostate tumor model. Therapeutic benefit was also demonstrated in the hormone-resistant phase of this tumor model. The activity of lanreotide may be due to a reduction in the levels of growth factors such as insulin growth factor 1 (IGF1). A total of 30 patients with hormone-refractory prostate cancer were treated with a slow-release formulation of lanreotide. The mean age was 71 years. Patients were treated with one intramuscular injection of 30 mg BIM 23014 once a week and were followed for prostate-specific antigen (PSA) level evolution until disease progression or WHO grade 3 or 4 toxicity and for survival. The patients were treated for a mean duration of 12 weeks (range, 2-60 weeks). The performance status and bone pain were improved in 40% and 35% of patients respectively. In all, 20% of the patients had a decrease of > or = 50% in PSA levels and 16% showed a stabilization. The biological response was correlated with clinical improvement. The 1-year global survival rate was 72%, with the rate being 89% in the group of patients who were responders on PSA plasma level and 64% in patients with progressive disease. The response duration ranged from 16 to 60 weeks. Toxicity was minor, with transient grade I digestive side effects being noted in a few patients. Lanreotide given at 30 mg once a week to patients with metastatic hormone-refractory prostate cancer was well tolerated. The response rate was higher than that reported in recent published series. Higher doses of lanreotide should be evaluated.

Somatostatin receptor imaging of small cell lung cancer (SCLC) by means of 111In-DTPA octreotide scintigraphy

Somatostatin receptors have been described on the membrane of neoplastic cells derived from the APUD system and their expression has also been demonstrated on small cell lung cancer (SCLC) in vitro and in vivo. 21 patients with SCLC were studied using 111In-octreotide (111In-OCT) scintigraphy. Scintigraphic examinations were performed following intravenous (i.v.) injection of 111 MBq 111In-OCT with whole-body scintigraphy and planar scintigraphy of the thorax as well as the SPET technique. No short-term side effects were described following 111In-OCT administration. We studied the 111In-OCT biodistribution in 3 patients with serial scintigraphies at 1, 5 and 24 h. We used the 5 h as standard scanning time for the following 18 patients. The scintigraphic results were compared with those of other conventional diagnostic procedures. 111In-OCT detected 86% (48/56) of the lesions already known at the time of scintigraphy. It was positive in all 20 SCLC patients and negative in one lung adenocarcinoma. 111In-OCT showed high sensitivity for mediastinal metastases (94%) and good sensitivity for bone metastases (75%) and abdominal lymph node metastases (71%). 111In-OCT did not detect two liver metastases. 111In-OCT detected five unknown lesions which were confirmed by other diagnostic examinations. 111In-OCT was also effective in cancer patients with low levels of NSE. Our study shows that 111In-OCT scintigraphy is a reliable, non-invasive technique to detect primary SLCL and its locoregional or distant metastases. The clinical utility of receptor status characterisation obtained with 111In-OCT scintigraphy should be evaluated by means of an appropriate prospective study.

Somatostatin receptor-dependent growth inhibition of liver metastases by octreotide

Rats were administered the somatostatin analogue octreotide 15 micrograms intraperitoneally twice daily for 4 weeks after intraportal injection of somatostatin receptor-positive pancreatic tumour cells (CA-20948) and somatostatin receptor-negative colonic tumour cells (CC531). Octreotide significantly inhibited the growth and development of somatostatin receptor-positive tumour cells in the liver. The median number of liver tumours was 286 (range 146 to greater than 500) in the treated animals and more than 500 (range 250 to in excess of 500) in the controls (P < 0.05). This significant difference in tumour load was also represented in the mean(s.e.m.) liver weight (14.5(3.7) g in animals given octreotide versus 17.9(3.0) g in the controls). No effect of octreotide treatment was found on the growth and development of somatostatin receptor-negative tumour cells in the liver. The median (range) number of tumours was 6.5 (0-425) in the treated animals and 11.0 (0-475) in the controls. Mean(s.e.m.) liver weights were 14.0(5.7) g and 11.8(4.5) g respectively. There was no difference in serum levels of growth hormone, prolactin and insulin-like growth factor between control and octreotide-treated rats. The growth inhibition of somatostatin receptor-positive tumour cells was unlikely to be the result of suppressed secretion of one of these tumour growth factors. Octreotide may be useful for the treatment of patients with somatostatin receptor-positive hepatic metastases, which can be demonstrated by somatostatin receptor scintigraphy.

Long-acting somatostatin analogue therapy and protein metabolism in patients with jejunostomies

BACKGROUND/AIMS

Previous studies have shown that secretory losses in patients with end jejunostomy syndrome (EJS) on home parenteral nutrition (HPN) can be suppressed by the somatostatin analogue, octreotide, thus facilitating fluid balance. However, the hormone also has antianabolic actions that may interfere with the use of infused amino acids.

METHODS

Amino acid metabolism, pancreatic enzyme synthesis and secretion, and mucosal protein turnover were measured by primed/continuous intravenous infusion of [1-14C] leucine tracer, duodenal aspiration, and endoscopic mucosal biopsy techniques during hormonal stimulation with pentagastrin and cholecystokinin 8.

RESULTS

In comparison with normal healthy controls, baseline measurements of amino acid metabolism were normal in patients with EJS/HPN, but pancreatic enzyme synthesis and secretion were elevated. Octreotide therapy improved fluid balance but suppressed gut hormone (insulin, gastrin, glucagon, peptide YY) levels in blood and the uptake of amino acids into pancreatic enzyme and mucosal proteins, increasing oxidative losses.

CONCLUSIONS

Octreotide improves fluid balance in patients who have undergone jejunostomy but reduces the use of amino acids for splanchnic protein synthesis. This may interfere with the physiological process of adaptation to intestinal resection.

Effect of the slow-release formulation of somatuline (BIM 23014) on estrogen-induced hyperprolactinemia and lactotroph hyperplasia in the female rat

Somatuline, in common with other SRIH analogues, exerts antiproliferative and antisecretory activities on various tumors. Our purpose was to test the effectiveness of a slow-release formulation of somatuline on lactotroph hyperplasia and PRL hypersecretion induced by estrogens (17 beta E2) in rats. Female rats were primed with 17 beta E2 for 6 weeks before receiving somatuline (2 mg/kg) intramuscular injections every 10 days for one month. The mean anterior pituitary weight was 11.22 +/- 0.32 mg (mean +/- SEM) in non-estrogenized rats, 29.62 +/- 1.63 mg in 17 beta E2-primed rats and 23.58 +/- 1.26 mg in 17 beta E2-primed somatuline-treated rats. Mean plasma PRL level was 5.63 +/- 0.97 ng/ml, 182.37 +/- 27.55 ng/ml and 113.89 +/- 15.07 ng/ml in the same groups respectively. Thus, the 17 beta E2-induced pituitary enlargement and hyperprolactinemia were 20% and 38% lower respectively when animals were treated with somatuline during the last month of estrogenization. The 17 beta E2-induced increase in PRL cell density was also reduced by somatuline treatment. We conclude that the slow-release formulation of somatuline impedes 17 beta E2-induced hyperprolactinemia and pituitary enlargement concomittantly, at least in part by acting on lactotroph proliferation.

Somatostatin binding in human gastrointestinal tissues: effect of cations and somatostatin analogues

This study characterises the somatostatin binding site in human gastrointestinal cancer and mucosa in terms of cationic specificity and relative affinity for three somatostatin analogues. Competitive displacement assays were performed on plasma membranes from human gastric and colonic tissues using radiolabelled somatostatin-14 as ligand. Comparison was made with the somatostatin binding site in rat cerebral cortex. In gastrointestinal tissue, magnesium decreased and sodium increased specific binding. By contrast, in rat cerebral cortex, the converse cationic effect was seen. These changes resulted from alterations in receptor density, with no change in receptor affinity. Displacement studies were then performed with somatostatin-14 and somatostatin analogues RC-160, somatuline, and octreotide. RC-160 and somatuline displaced radiolabel from binding sites in gastric and colonic cancer and mucosa with 10-fold lower affinity than the native peptide. Octreotide did not displace radioligand in gastric or colonic cancer at any concentration tested. By contrast, in rat cortex, although all three analogues displaced with a lower affinity than the native peptide, there was no difference between analogues. These data suggest a distinct somatostatin receptor subtype in gastrointestinal tissues.

Somatostatin analog sandostatin and inhibition of tumor growth in patients with metastatic endocrine gastroenteropancreatic tumors

A prospective study was performed to determine the efficacy of octreotide (Sandostatin; SMS 201-995) 200 micrograms tid in controlling tumor growth. The study included 21 patients with metastasized endocrine GEP tumors: 6 gastrinomas, 8 carcinoid syndromes, 7 nonfunctioning tumors. Treatment was performed for 3 to 59 months (median 15 months). Evaluation of the response to octreotide was facilitated in 12 patients by a pretreatment observation period of 3 to 47 months (median 17 months) during which the natural growth behavior was determined. Based on the presence or absence of a control period prior to treatment, 5 patients were considered to be responders, 7 as questionable responders (no pretreatment phase available), and 9 as nonresponders. None of the 21 patients had documented shrinkage of the tumor mass. The most favorable response was tumor standstill. In all but one responder an escape to an initially favorable response occurred after 6 to 28 months (median 14 months). Proved inhibition of growth was paralleled by a reduction of serum and urine hormone parameters, whereas unaltered progression of tumor growth was observed also in the presence of hormone suppression. Tumor growth and hormone release was inhibited in the absence and presence of somatostatin receptors on the tumor. It is concluded that octreotide exerts a limited effect on metastatic GEP tumor growth. The evaluation of a response to octreotide is facilitated by an observation period prior to the drug that provides information on growth characteristics of the tumor. The presence of octreotide receptors does not predict the success of therapy.

Localization of neuroendocrine tumours and insulinomas using radiolabelled somatostatin analogues, 123I-Tyr3-octreotide and 111In-pentatreotide

OBJECTIVE

A number of neoplasms are known to express somatostatin receptors; the use of somatostatin receptor imaging in their localization has recently been described, but the resolution and discrimination of the isotopes used remains sub-optimal. We have looked at the use of a new 111In-labelled analogue of somatostatin, pentatreotide, in the visualization and functional characterization of a number of neoplastic conditions.

PATIENTS

Thirteen patients with proven neoplasms were scanned using this agent. Planar and single-photon-emission computerized tomographic (SPECT) images of the relevant part of the body were obtained using a gamma-camera at 10 minutes and 4 and 21 hours after injection of the radiopharmaceutical. In six patients (three carcinoid, three insulinomas) scanning was also performed using 123I-Tyr-3-octreotide.

RESULTS

Primary tumours or metastases were visualized in six of the seven patients with neuroendocrine tumours, and three of six patients with insulinoma. One patient with an insulinoma who had a positive scan showed absent uptake when rescanned after tumour removal. A rise in blood glucose (more than twice basal) in response to octreotide was seen only in those insulinoma patients with positive scans. In cases where both 111In-pentratreotide and 123I-Tyr-3-octreotide scans were performed, both radiopharmaceuticals identified the same 4/6 tumours; however, tumour definition (reflecting high tumour to background ratio) was better with pentatreotide on the 21-hour images with minimum biliary and gut activity, allowing better resolution of the tumour image.

CONCLUSION

It appears that 111In-pentatreotide scintigraphy is a rapid and safe procedure for the visualization of neuroendocrine tumours possessing somatostatin binding sites. A positive scan may be predictive of neuroendocrine responsiveness to octreotide therapy. In addition, it also appears that 111In-pentatreotide has superior kinetics compared to 123I-Tyr-3-octreotide, typically achieving more satisfactory tumour to background ratios, and may thus be more useful in the localization of endocrine tumours.

Potential role for somatostatin analogues in breast cancer: rationale and description of an ongoing trial

Somatostatin analogues such as octreotide have been shown in experimental systems to exhibit antineoplastic activity. Further laboratory and clinical research is needed to clarify the mechanism of action of somatostatin analogues as antineoplastics, and to determine if the encouraging preclinical results will lead to novel endocrine approaches to the treatment of breast cancer.

Cytotoxic analog of somatostatin containing methotrexate inhibits growth of MIA PaCa-2 human pancreatic cancer xenografts in nude mice

Nude mice bearing xenografts of MIA PaCa-2 human pancreatic cancer cell line were treated for 4 weeks with AN-51, a somatostatin octapeptide analog D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (RC-121) containing methotrexate attached to the alpha-amino group of D-Phe in position 1. Control groups of mice received saline, RC-121 or methotrexate. Drugs were given in equimolar doses by daily s.c. injections. After 7 days of treatment with 25 micrograms/day of AN-51, tumor growth was completely inhibited although the treatment had to be suspended because of toxic side effects, especially on the gastrointestinal tract, accompanied by major weight loss of the animals. Mice were allowed to recover for 1 week and treatment was continued with 12.5 micrograms/day AN-51. After 2 weeks of additional therapy, tumor volume, percentage change in tumor volume, and tumor weights were significantly decreased, compared with controls, only in the group treated with AN-51. Methotrexate and RC-121 also inhibited tumor growth, but their effects were not statistically significant. AN-51 retained its hormonal activity and decreased serum growth hormone levels in mice. Binding affinity of AN-51 for somatostatin receptors on MIA PaCa-2 cells was found to be 2.5-times lower than that of parent compound RC-121. This is the first report on inhibition of human pancreatic cancer growth in vivo by somatostatin analogs carrying cytotoxic radicals.

Pituitary imaging using a labelled somatostatin analogue in acromegaly

OBJECTIVE

A number of neoplasms are known to express somatostatin receptors, and the use of somatostatin receptor imaging in their localization has recently been described. We have looked at the use of an 123I-labelled Tyr3-octreotide analogue of somatostatin in the visualization and functional characterization of growth hormone-secreting pituitary adenomas.

PATIENTS

Fifteen patients with biochemically-proven acromegaly were scanned using this agent. In eight of these we also assessed acute GH responses to octreotide in order to correlate these responses with tumour uptake characteristics.

MEASURES

Planar and single-photon-emission computerized tomographic (SPECT) images of the head were obtained using a gamma-camera at 10 minutes, and 4 and 24 hours, after injection of the radiopharmaceutical. Blood for serum GH was sampled for 12 hours after administration of a single dose of 100 micrograms octreotide.

RESULTS

Twelve of the acromegalic subjects showed significant uptake of the radiopharmaceutical in the pituitary fossa. Of the eight patients in whom we assessed acute GH responses, five demonstrated a significant fall in GH in response to octreotide. These subjects also showed positive uptake in the pituitary on scanning. The three patients who had no fall in GH had no uptake on scanning.

CONCLUSIONS

Uptake of 123I-labelled Tyr3-octreotide in the pituitary fossa appears to correlate closely with the presence of a therapeutic response to octreotide.

Growth factors and cancer

Signaling pathways that mediate the normal functions of growth factors are commonly subverted in cancer. Oncogenes identified by a variety of approaches have been shown to function at critical steps in mitogenic signaling. Progression through the cell cycle requires the coordinated actions of members of two complementary classes of growth factors, and oncogenes appear to replace the actions of one set of these growth factors. Growth factors can also influence normal cell differentiation, and constitutive activation of growth-promoting pathways in cancer cells can modulate the cell phenotype as well. Paracrine actions of growth factors and cytokines may also influence the stepwise series of genetic events that lead to malignancy. New approaches for cancer therapy are being developed that intervene at various steps in growth factor signaling pathways.

The interrelationship between the anti-mitotic action of the somatostatin analog octreotide and that of cytostatic drugs and suramin

In the present study we used the model of cultured somatostatin-receptor-positive prolactin (PRL)-secreting rat pituitary tumor cells to investigate the possible interrelationships between the anti-mitotic and hormone-release-inhibitory effects of the somatostatin analog octreotide (SMS 201-955) and the effects of vincristine, methotrexate, fluouracil and suramin. Dose-dependent inhibitory effects of all compounds were shown both on the DNA content and on PRL release. Octreotide and these cytostatic compounds were slightly additive in their anti-proliferative and anti-secretory effects. The somatostatin analog did not alter drug sensitivity in these tumor cells, however. The data obtained in this tumor model suggest that octreotide can be effectively administered in combination with cytostatic drugs and/or suramin.

Octapeptide analogues of somatostatin inhibit the clonal growth and vasoactive intestinal peptide-stimulated cyclic AMP formation in human small cell lung cancer cells

Two endocrinologically active octapeptide analogues (BIM-23014 C and BIM-23034) of somatostatin (SRIF) containing either an N- or C-terminal 3-(2-naphthyl)-D-Ala residue were examined for their ability to inhibit the in vitro receptor binding, clonal growth, and vasoactive intestinal peptide (VIP)-stimulated cyclic AMP formation in human small cell lung cancer cell (SCLC) line NCI-H345. Both SRIF peptides inhibited [125I]SRIF(Tyr11)-14 binding with IC50 values in the low nM range. Colony formation in the in vitro SCLC growth assay was also inhibited in the same concentration range, as was VIP-stimulated cyclic AMP formation. Therefore, octapeptide analogues of SRIF function as SCLC SRIF receptor agonists.

The effect of a somatostatin analogue on the release of hormones from human midgut carcinoid tumour cells

The use of a somatostatin analogue (SMS 201-995) has greatly facilitated the treatment of patients with the midgut carcinoid syndrome. Clinical studies have shown that SMS reduces the peripheral levels of tumour-produced serotonin (5-HT) and tachykinins, e.g. neuropeptide K (NPK), basally and after pentagastrin provocation. Some studies have indicated an inhibitory effect of SMS on tumour cell growth as well. In the present study we have investigated the effects of SMS on four different human midgut carcinoid tumours maintained in long term culture. Media levels of 5-HT and NPK-LI in tumour cell cultures decreased rapidly during incubation with SMS (10(-8)-10(-10) M) in all four tumours studied without evidence for tachyphylaxis (up to 6 weeks observation period). SMS treatment (10(-8) M) during 4 days reduced the media concentrations of 5-HT by 56%, while the intracellular contents of 5-HT were decreased by 27% indicating dual inhibitory effects on synthesis and secretion of 5-HT from tumour cells. The DNA contents of cultures were not affected by SMS (10(-8) M or 10(-10) M) treatment for 4 or 14 days. When tumour cell cultures were challenged with isoprenaline (IP) (10(-6) M) no reduction of the IP induced release of 5-HT could be detected after pretreatment of tumour cell cultures with SMS (10(-8) M) for 1 h, 4 h or 4 days. These studies provide evidence for a direct action of the somatostatin analogue on midgut carcinoid tumour cells, reducing both synthesis and secretion of hormones from tumour cells. This effect appears not to be related to inhibition of tumour cell growth. The inhibition of 5-HT secretion from tumour cells by SMS seems to operate via a second messenger system different from the one mediating the beta-adrenoceptor stimulated release of 5-HT.

Somatostatin and analogues in the treatment of cancer. A review

Somatostatin is a naturally occurring cyclic tetradecapeptide that inhibits release of growth hormone and all gastrointestinal hormones. The beneficial effect of somatostatin in the treatment of certain hypersecretory disorders of hormone excess in well recognized; however its clinical usefulness has been limited in the past by its extremely short plasma half-life. The development of long-acting somatostatin analogues has provided clinically useful agents for treatment of hormone-producing tumors. In addition to well-known inhibiting effects on hormone release and actions, recent studies using experimental tumor models have demonstrated an antiproliferative effect of somatostatin and its analogues on growth of a variety of neoplasms. The exact role of somatostatin analogues in cancer therapy has yet to be established; however studies suggest that these agents could provide a useful and relatively nontoxic adjuvant therapy in the treatment of certain tumors. In this review, the oncologic application of somatostatin and possible mechanism of action are examined and current clinical and experimental studies are summarized.