High density of somatostatin receptors in veins surrounding human cancer tissue: role in tumor-host interaction?

Targeted Therapy for Medullary Thyroid Cancer: A Review

Medullary thyroid cancers (MTCs) constitute between 2 and 5% of all thyroid cancers. The 10-year overall survival (OS) rate of patients with localized disease is around 95% while that of patients with regional stage disease is about 75%. Only 20% of patients with distant metastases at diagnosis survive 10 years which is significantly lower than for differentiated thyroid cancers. Cases with regional metastases at presentation have high recurrence rates. Adjuvant external radiation confers local control but not improved OS. The management of residual, recurrent, or metastatic disease till a few years ago was re-surgery with local measures such as radiation. Chemotherapy was used with marginal benefit. The development of targeted therapy has brought in a major advantage in management of such patients. Two drugs—vandetanib and cabozantinib—have been approved for use in progressive or metastatic MTC. In addition, several drugs acting on other steps of the molecular pathway are being investigated with promising results. Targeted radionuclide therapy also provides an effective treatment option with good quality of life. This review covers the rationale of targeted therapy for MTC, present treatment options, drugs and methods under investigation, as well as an outline of the adverse effects and their management.

68Ga-DOTATATE PET/CT imaging of indeterminate pulmonary nodules and lung cancer

PURPOSE

18F-FDG PET/CT is widely used to evaluate indeterminate pulmonary nodules (IPNs). False positive results occur, especially from active granulomatous nodules. A PET-based imaging agent with superior specificity to 18F-FDG for IPNs, is badly needed, especially in areas of endemic granulomatous nodules. Somatostatin receptors (SSTR) are expressed in many malignant cells including small cell and non-small cell lung cancers (NSCLCs). 68Ga-DOTATATE, a positron emitter labeled somatostatin analog, combined with PET/CT imaging, may improve the diagnosis of IPNs over 18F-FDG by reducing false positives. Our study purpose was to test this hypothesis in our region with high endemic granulomatous IPNs.

METHODS

We prospectively performed 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT scans in the same 30 patients with newly diagnosed, treatment-naïve lung cancer (N = 14) or IPNs (N = 15) and one metastatic nodule. 68Ga-DOTATATE SUVmax levels at or above 1.5 were considered likely malignant. We analyzed the scan results, correlating with ultimate diagnosis via biopsy or 2-year chest CT follow-up. We also correlated 68Ga-DOTATATE uptake with immunohistochemical (IHC) staining for SSTR subtype 2A (SSTR2A) in pathological specimens.

RESULTS

We analyzed 31 lesions in 30 individuals, with 14 (45%) being non-neuroendocrine lung cancers and 1 (3%) being metastatic disease. McNemar's result comparing the two radiopharmaceuticals (p = 0.65) indicates that their accuracy of diagnosis in this indication are equivalent. 68Ga-DOTATATE was more specific (94% compared to 81%) and less sensitive 73% compared to 93%) than 18F-FDG. 68Ga-DOTATATE uptake correlated with SSTR2A expression in tumor stroma determined by immunohistochemical (IHC) staining in 5 of 9 (55%) NSCLCs.

CONCLUSION

68Ga-DOTATATE and 18F-FDG PET/CT had equivalent accuracy in the diagnosis of non-neuroendocrine lung cancer and 68Ga-DOTATATE was more specific than 18F-FDG for the diagnosis of IPNs. IHC staining for SSTR2A receptor expression correlated with tumor stroma but not tumor cells.

Molecular Imaging using PET/CT Applying 68Ga-Labeled Tracers and Targeted Radionuclide Therapy: Theranostics on the Way to Personalized Medicine

Theranostics is an acronym, which exemplifies the togetherness of diagnostics and therapeutics in the individualized management of disease. The key to personalized medicine in cancer is to determine the molecular phenotypes of neoplasms, so that specific probes can be selected to target the tumor and its microenvironment. Molecular imaging and radionuclide therapy using a particular probe is based on this premise. Neuroendocrine neoplasms express somatostatin receptors, enabling the use of somatostatin analogs for molecular imaging, when labeled with the positron-emitter 68Ga for receptor positron emission tomography/computed tomography (PET/CT), and targeted radionuclide therapy, when labeled with beta-emitters 90Y and 177Lu.

How to cite this article

Kulkarni HR, Baum RP. Molecular Imaging using PET/CT Applying 68Ga-Labeled Tracers and Targeted Radionuclide Therapy: Theranostics on the Way to Personalized Medicine. J Postgrad Med Edu Res 2013; 47(1):47-53.

Somatostatin in inflammatory bowel disease

Intestinal inflammation is controlled by various immunomodulating cells, interacting by molecular mediators. Neuropeptides, released by enteric nerve cells and neuroendocrine mucosa cells, are able to affect several aspects of the general and intestinal immune system, with both pro- as well as anti-inflammatory activities. In inflammatory bowel disease (IBD) there is both morphological as well as experimental evidence for involvement of neuropeptides in the pathogenesis. Somatostatin is the main inhibitory peptide in inflammatory processes, and its possible role in IBD is discussed.

Naposomes: a new class of peptide-derivatized, target-selective multimodal nanoparticles for imaging and therapeutic applications

Modified supramolecular aggregates for selective delivery of contrast agents and/or drugs are examined with a focus on a new class of peptide-derivatized nanoparticles: naposomes. These nanoparticles are based on the co-aggregation of two different amphiphilic monomers that give aggregates of different shapes and sizes (micelles, vesicles and liposomes) with diameters ranging between 10 and 300 nm. Structural properties and in vitro and in vivo behaviors are discussed. For the high relaxitivity values (12–19 mM-1s-1) and to detect for the presence of a surface-exposed peptide, the new peptide-derived supramolecular aggregates are very promising candidates as target-selective MRI contrast agents. The efficiency of surface-exposed peptides in homing these nanovectors to a specific target introduces promising new opportunities for the development of diagnostic and therapeutic agents with high specificity toward the biological target and reduced toxic side effects on nontarget organs.

Effects of somatostatin and octreotide on the interactions between neoplastic gastroenteropancreatic endocrine cells and endothelial cells: a comparison between in vitro and in vivo properties

BACKGROUND/AIMS

Experimental studies in vitro suggest that somatostatin and some of its analogues used in clinical practice, such as octreotide, may have potent antiangiogenic properties. However, the clinical transposition of these data is difficult.

METHODS

To address this issue, we designed a comparative study of the effects of somatostatin and octreotide on the interactions between neoplastic endocrine cells and endothelial cells in several in vitro and in vivo experimental models, including primary cultures of human umbilical vein endothelial cells (HUVEC), indirect cocultures between HUVEC and the somatostatin-producing endocrine cell line STC-1, and an animal model of intrahepatic dissemination of STC-1 cells.

RESULTS

10(-8)M octreotide markedly inhibited both basal and VEGF-stimulated HUVEC proliferation, had no effect on endothelial cell migration, but inhibited endothelial tubule formation. HUVEC cocultured with the somatostatin- and VEGF-producing STC-1 cells presented a markedly decreased proliferation, a slightly increased motility and an increased capacity of tubule formation; in this system, the inhibition of endothelial cell proliferation was abolished by neutralizing anti-somatostatin but was restored in the presence of anti-VEGF antibodies. This suggests that somatostatin is able to antagonize the effects of VEGF on endothelial cell proliferation but not on endothelial cell sprouting. Finally, no significant effect of octreotide on tumor growth and intratumoral microvascular density was detected in an experimental model of intrahepatic dissemination of STC-1 cells.

CONCLUSION

The in vitro antiangiogenic effects of somatostatin and its analogues are likely to be efficiently counterbalanced in the tumor microenvironment by the concomitant release of proangiogenic factors like VEGF.

Treatment of endocrine pancreatic tumors

Endocrine pancreatic tumors are rare with an incidence of 4 per million inhabitants. Most tumors are malignant except for insulinomas that usually are benign. They are slowly growing in the majority of cases but there are exceptions with rapidly progressing malignant carcinomas. Because of the rarity of these tumors large randomized trials are difficult to accomplish. However, most physicians treating these patients agree that surgery should be considered in all cases and that medical treatment with chemotherapy and biotherapy is well established for this group of patients.

Micelles derivatized with octreotide as potential target-selective contrast agents in MRI

New amphiphilic monomers (OCA-DTPAGlu and OCA-DOTA) containing, in the same molecule, three different functions: (i) the chelating agent (DTPAGlu or DOTA) able to coordinate gadolinium ion, (ii) the octreotide bioactive peptide able to target somatostatin receptors, and (iii) a hydrophobic moiety with two 18-carbon atoms alkyl chains have been designed and synthesized by solid-phase methods. The novel amphiphilic monomers aggregate, in water solution, giving stable micelles at very low concentration (cmc values of 2.3 x 10(-6) mol kg(-1) and 2.5 x 10(-6) mol kg(-1) for OCA-DTPAGlu and OCA-DOTA, respectively) as confirmed by fluorescence spectroscopy. Fluorescence studies and circular dichroism experiments indicate, for the two compounds as well as for their gadolinium complexes (OCA-DOTA(Gd) and OCA-DTPAGlu(Gd)), the complete exposure of octreotide on the micelle surface, and the predominant presence of an antiparallel beta-sheet peptide conformation characterized by a beta-like turn. The high relaxivity value (r(1p) = 13.9 mM(-1) s(-1) at 20 MHz and 25 degrees C), measured for micelles obtained by the gadolinium complex OCA-DTPAGlu(Gd), indicates these aggregates as promising target-selective magnetic resonance imaging (MRI) contrast agents.

Intimal Hyperplasia in Rats after Subcutaneous Injection of a Somatostatin Analog

The somatostatin analog octreotide was administered to male and female Sprague-Dawley rats by subcutaneous injection for thirteen weeks at 0 (saline control), 0 (placebo control [mannitol and lactic acid; pH 4.2]), 1.25 mg/kg/day and 2.5 mg/kg/day to explore its potential effect on cutaneous vascular morphology. The placebo caused an increase in the incidence of intimal hyperplasia compared to saline controls in female rats; octreotide increased the incidence and severity of intimal hyperplasia in males and females. Intimal hyperplasia consisted of increased numbers of cells located between the endothelial cell layer and the internal elastic lamina. Severity was based on the degree of compromise of the vascular lumen (regardless of vessel size and number), with severely affected vessels having no visible lumen. Intimal hyperplasia in rats treated with octreotide was considered to be an unexpected and adverse finding, given that this compound and other somatostatin analogs have been investigated as reducers of intimal proliferation or restenosis after angioplasty in humans and that no such lesion has been reported in the literature for this class of compound to date. The induction of intimal hyperplasia by the placebo is also a notable finding; this may be because of the low pH of the formulation.

A “false positive” octreoscan in ileal Crohn’s disease

We present a case report of a patient with a suspicious ileal carcinoid tumour. Clinical examination as well as computer tomography (CT) scan suggested a tumour. Octeotride scan showed uptake in the same bowel loop reported as pathological in CT. The patient underwent surgery and biopsy which reported Crohn’s disease (CD). The interest in the case is due to the fact that this is, to the best of our knowledge, the second report of Crohn’s disease as a cause of false positive octeotride scan. Unfortunately, no somatostatin receptors could be found in the sample, so further studies should be performed.

Targeting vascular endothelial growth factor in advanced carcinoid tumor: a random assignment phase II study of depot octreotide with bevacizumab and pegylated interferon alpha-2b

PURPOSE

Effective systemic therapy for advanced carcinoid is lacking. The combination of bevacizumab (BEV) and pegylated (PEG) interferon alpha-2b was evaluated among patients with metastatic or unresectable carcinoid tumors.

PATIENTS AND METHODS

Forty-four patients on stable doses of octreotide were randomly assigned to 18 weeks of treatment with bevacizumab or PEG interferon alpha-2b. At disease progression (PD) or at the end of 18 weeks (whichever occurred earlier), patients received bevacizumab plus PEG interferon until progression. Functional computer tomography (CT) scans were performed to measure effect on tumor blood flow.

RESULTS

In the bevacizumab arm, four patients (18%) achieved confirmed partial response (PR), 17 patients (77%) had stable disease (SD), and one patient (5%) had PD. In the PEG interferon arm, 15 patients (68%) had SD and six patients (27%) had PD. Progression-free survival (PFS) rates after 18 weeks of monotherapy were 95% in bevacizumab versus 68% on the PEG interferon arm. The overall median PFS for all 44 patients is 63 weeks. Compared with paired baseline measurements on functional CT scans, we observed a 49% (P < .01) and 28% (P < .01) decrease in tumor blood flow at day 2 and week 18 among patients treated with bevacizumab. No significant changes in tumor blood flow were observed following PEG interferon. PEG interferon alpha-2b treatment was associated with decrease in plasma basic fibroblast growth factor (bFGF; P = .04) and increase in plasma interleukin-18 (IL-18; P < .01). No significant changes in bFGF or IL-18 following treatment with bevacizumab were observed.

CONCLUSION

Bevacizumab therapy resulted in objective responses, reduction of tumor blood flow, and longer PFS in patients with carcinoid than PEG interferon treatment.

Diagnostic targeting of colon cancer using a novel fluorescent somatostatin conjugate in a mouse xenograft model

Colorectal carcinoma is one of the more prevalent, highly malignant human tumors, occurring in about 7% of the population. However, if diagnosed and treated in its early stages, colon cancer is curable. In our study, we used a mouse xenograft model to investigate the capability of a fluorescent conjugate of a novel synthetic somatostatin (SST) analog to improve detection of human colorectal tumors that are characterized by over-expressed SST receptors. Human HT-29 colon carcinomas were induced in nude mice. After administration of the fluorescent SST conjugate, in vivo low- and high-magnification fluorescence microscopy, as well as high-resolution spectrally resolved imaging were performed, and the time-dependent biodistribution was determined quantitatively (using fiber-optic spectroscopy). Administration of the conjugate (at concentrations of 6 mg/kg body weight) enabled targeting small (1-5 mm diameter) tumors with high sensitivity and selectivity. Toxicity studies at dosages up to 1,000 mg/kg body weight did not reveal any drug related abnormalities. In conclusion, the SST conjugate significantly enhanced the detection of HT-29 colon tumors by fluorescence imaging because of a 5- to 8-fold increase in the contrast between malignant and normal tissues.

Characterization of somatostatin receptor subtypes

Somatostatin regulates endocrine and exocrine secretion, possesses antiproliferative properties and acts as a neurotransmitter/neuromodulator in the central nervous system. These effects are mediated by G protein-coupled receptors, of which at least five types have been cloned (sstr1-5). In radioligand-binding studies we have compared the binding properties of sstr1-5 with their activities as somatostatin receptors. All receptors identified so far bind somatostatin-14 and somatostatin-28 with high affinity. The similarities in receptor sequence and in the binding profiles of short synthetic somatostastin analogues such as octreotide, MK 678 or RC 160 for sstr1-5 indicate the existence of two classes of receptors sstr1/sstr4 with virtually no or very low affinity and sstr2/sstr3/sstr5 with intermediate to high affinity for the short somatostatin analogues. All five receptors mediate inhibition of adenylyl cyclase; this inhibition is sensitive to pertussis toxin. In vitro and in vivo studies suggest the importance of sstr2 and/or sstr5 in the inhibition of growth hormone release. The sstr2 receptor is apparently the predominant subtype expressed in somatostatin receptor-positive tumours. Evidence exists for the importance of sstr5 receptors in insulin secretion and sstr1 receptors in oncology. Somatostatin receptor-selective agonists and antagonists will help to explore new therapeutic opportunities in oncology as well as in endocrine and gastrointestinal disorders and those of the central nervous system.

Comparative evaluation of 99mTc-depreotide and 201Tl chloride single photon emission tomography in the characterization of pulmonary lesions

PURPOSE

To compare (99m)Tc-depreotide and (201)Tl chloride SPET in the characterization of pulmonary lesions.

METHODS

Fifty-seven pulmonary lesions from 33 patients suspected of malignancy in computed tomography, were assessed by (99m)Tc-depreotide and (201)Tl early and delayed SPET imaging. Images were visually assessed and the tumour-to-normal (T/N) lung activity ratio for early (ER) and delayed (DR) scans and the retention index (RI), were calculated in every lesion. A final diagnosis was reached for all lesions, based either on histology or prolonged clinical and radiological follow-up.

RESULTS

Twenty-three lesions were characterized as malignant and 34 benign. In visual analysis, all malignant lesions accumulated both tracers resulting in sensitivity and negative predictive values of 100%. However, false positive interpretations resulted in a specificity of 64.7% and 67.6% for (99m)Tc-depreotide and (201)Tl, respectively. ER and DR of both agents and the RI of (99m)Tc-depreotide were significantly higher in malignant, compared to benign lesions. In defining thresholds of abnormality from ROC analysis, a significant increase in specificity was observed for both tracers in both scan phases (91.2% for all), as compared to visual analysis (P<0.01). There was no significant difference in the diagnostic performance between (99m)Tc-depreotide DR and (201)Tl DR, although the former provided the highest T/N ratio.

CONCLUSION

This study demonstrates that (99m)Tc-depreotide and (201)Tl SPET are equally effective and may be useful in the non-invasive determination of lung malignancy. The specificity of both techniques is significantly improved by quantifying radiopharmaceutical accumulation in pulmonary lesions.

Somatostatin Receptor-Binding Peptides Suitable for Tumor Radiotherapy with Re-188 or Re-186. Chemistry and Initial Biological Studies

Somatostatin derivative peptides previously designed for radiodiagnostic purposes (99mTc P829 or 99mTc depreotide) were reoptimized for radiotherapy of tumors with rhenium radioisotopes. An optimized pharmacophore peptide P1839 was derived by in vitro binding affinity assay to AR42J rat pancreatic tumor cell membranes. Peptides with chelating domains and their oxorhenium(V) complexes were tested in vitro for binding to NCI H69 human SCLC tumor membranes. Further optimization entailed radiolabeling with 99mTc and biodistribution in an AR42J xenograft mouse model. Kidney uptake was decreased substantially by removing positively charged residues. Neutral N3S diamide amine thiol chelators with no adjacent positive charges had the best overall properties. Substituting an aromatic amino acid into the chelator approximately doubled the tumor uptake. The final optimized peptide P2045 (39) radiolabeled with 99mTc exhibited increased tumor uptake ( approximately 25 %ID/g at 1.5 h), lower kidney uptake ( approximately 4.8 %ID/g at 1.5 h), and extensive urinary excretion (59 %ID at 1.5 h). Finally, comparison biodistribution studies between 99mTc and 188Re (39) showed a good correlation between the two metal complexes and demonstrated prolonged tumor retention (> or =24 h).

Rationale for the use of somatostatin analogs as antitumor agents

BACKGROUND

There is a need for novel antitumor agents that demonstrate efficacy in currently refractory tumors without adding to the toxicity of therapy. The somatostatin analogs, which have demonstrated antineoplastic activities in experimental tumor models, and good tolerability and safety profiles are attractive candidates.

MATERIALS AND METHODS

Data from preclinical studies provide evidence for direct and indirect mechanisms by which somatostatin analogs exert antitumor effects.

RESULTS

Direct antitumor activities, mediated through somatostatin receptors (sst(1)-sst(5)) expressed in tumor cells, include blockade of autocrine/paracrine growth-promoting hormone and growth factor production, inhibition of growth factor-mediated mitogenic signals and induction of apoptosis. Indirect antitumor effects include inhibition of growth-promoting hormone and growth factor secretion, and antiangiogenic actions. Many human tumors express more than one somatostatin receptor subtype, with sst(2) being predominant. Somatostatin analogs such as octreotide and lanreotide, which present a high affinity for sst(2), are in current clinical use to alleviate symptoms in patients with endocrine tumors, and radiolabeled somatostatin analogs have been developed for diagnosis and radiotherapy.

CONCLUSIONS

While the rationale exists for the use of somatostatin analogs as antitumor agents, studies are ongoing to identify analogs with activity across the range of receptor subtypes to maximize the potential of such treatment.

Differential diagnosis of solitary pulmonary nodules based on 99mTc-EDDA/HYNIC-TOC scintigraphy: the effect of tumour size on the optimal method of image assessment

PURPOSE

The aim of the study was to determine an optimal method for the evaluation of scintigrams obtained with (99m)Tc-EDDA/HYNIC-TOC for the purpose of differential diagnosis of solitary pulmonary nodules (SPNs) and to assess the diagnostic value of the method.

METHODS

Eighty-five patients (48 males and 37 females, mean age 57 years, range 34-78 years) were enrolled in the study. Patients underwent (99m)Tc-EDDA/HYNIC-TOC scintigraphy for the purpose of differential diagnosis of SPNs (size between 1 and 4 cm). Images of all patients were evaluated visually in a prospective manner.

RESULTS

Positive scintigraphic results were found in 37 out of 40 (93%) patients with malignant SPNs including 34 out of 35 (97%) patients with primary lung carcinoma. Two remaining false negative cases turned out to be metastatic lesions of malignant melanoma and leiomyosarcoma. Among 45 benign tumours, negative results were obtained in 31 cases (69%) and positive results in 14. The accuracy of the method was 80%. Analysis of the results of the visual assessment of scintigrams revealed a significantly higher frequency of false positive results among larger nodules (diameter at least 1.4 cm). Uptake of the tracer in those nodules was therefore assessed semi-quantitatively (using the tumour-to-background ratio), in expectation of an improvement in the low specificity of the visual method. The semi-quantitative assessment reduced the total number of false positive results in a subgroup of larger nodules from 13 to six, while preserving the high sensitivity of the method.

CONCLUSION

The combination of visual analysis (for lesions smaller than 1.4 cm in diameter) and semi-quantitative assessment (for larger lesions) provided a high sensitivity of the method and significantly improved its specificity (84%) and accuracy (88%) in comparison with visual analysis (p<0.05).

Somatostatin receptor scintigraphy with 111In-DOTA-lanreotide and 111In-DOTA-Tyr3-octreotide in patients with stage IV melanoma: in-vitro and in-vivo results

The overexpression of somatostatin receptors (SST-Rs) on various tumour cells provides the molecular basis for the successful use of radiolabelled SST analogues in clinical oncology. The objective of the study was to evaluate the tumour binding of In-1,4,7,10-tetraazacyclo-dodecane-N,N',N'',N'''-tetraacetic acid-lanreotide (In-DOTA-LAN) and In-DOTA-tyrosine-octreotide (In-DOTA-Tyr-OCT) in patients with stage IV melanoma. In addition, we evaluated the potential antiproliferative effect of SST analogues, together with an assessment of the functionality of SST-Rs, on four melanoma cell lines. Twenty-three patients with advanced metastatic melanoma underwent scintigraphy. Thirty-eight of 61 lesions (62%) were positively imaged with In-DOTA-LAN, whereas 23 (37%) were negative. With In-DOTA-Tyr-OCT, 10 of the 23 documented lesions (43%) were positive and 13 (56%) were negative. In vitro, cell lines showed no growth inhibition in the presence of SST analogues and no influence on cell cycle distribution was found with the addition of SST analogues to cultured cells. In addition, no functional surface SST-Rs could be demonstrated on these cell lines. Taken together, our results demonstrate the visualization of metastatic melanoma in a high percentage of patients, probably due to binding of SST analogues to SST-Rs on tumour vessels or infiltrating immune cells. Judging from our data, however, there is no evidence of functional SST-R expression on melanoma cells.

Characterization of the Bystander Effect of Somatostatin Receptor sst2 After In Vivo Gene Transfer into Human Pancreatic Cancer Cells

Pancreatic cancer is one of the most aggressive and devastating human malignancies. The present study was conducted to determine whether in vivo sst2 gene transfer into human pancreatic tumors would impair tumor progression, and to characterize sst2 antitumoral bystander mechanisms. sst2 administration, using the synthetic vector PEI, strongly inhibited tumor progression of human pancreatic adenocarcinoma, in vivo. sst2 gene transfer induced intratumoral production of its ligand somatostatin. Disruption of this autocrine loop by RNA interference completely reversed sst2 antitumoral activity. Mice depleted of natural killer (NK) cells did not hamper sst2 tumor growth inhibition. However, microvessel density and vascular endothelial growth factor (VEGF) expression were markedly reduced in sst2-transfected tumors, whereas sst3 somatostatin receptor was upregulated. Depleting somatostatin by RNA interference completely abolished the sst2 inhibitory effect on VEGF expression and tumor angiogenesis, and sst2-induced sst3 expression in peripheral tumor vessels. We conclude that in vivo sst2 gene transfer elicited intratumoral somatostatin production and strongly impaired human pancreatic tumor growth. NK cells were not involved in this antitumoral bystander effect. VEGF and tumor vascularization were identified as novel targets for sst2-mediated antitumoral bystander effect. sst3 somatostatin receptor was upregulated in sst2-transfected tumors. Therefore, in vivo gene delivery of sst2 receptor to target the angiogenic process in pancreatic ductal adenocarcinoma might be a new therapeutic approach for treatment of pancreatic cancer in patients with unresectable disease.

Tumour angiogenesis: a novel therapeutic target in patients with malignant disease

Angiogenesis refers to the formation of new blood vessels from an existing vasculature and is recognised as a necessary requirement for most tumours to grow beyond 1-2 mm in diameter. Factors established as playing a role in angiogenesis may be divided into two principal groups: (a) those that stimulate endothelial cell proliferation and/or elongation, migration and vascular morphogenesis including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet derived endothelial cell growth factor (PD-ECGF) and the tie and tek receptors, and (b) proteases and their receptors involved in the breakdown of basement membranes and the extracellular matrix (ECM) including the matrix metalloproteinases (MMPs), cathepsins and those involved in the plasmin cascade. Angiogenesis has been identified as a potential target for development of anticancer agents. The discovery of a range of naturally-occurring factors which negatively regulate angiogenesis, including the thrombospondins, angiostatin and endostatin, and the tissue inhibitors of MMPs (TIMPs), has given added impetus to this approach. Synthetic anti-angiogenic compounds have been developed, including TNP-470, carboxyamidotriazole, VEGF-tyrosine kinase inhibitors and MMP inhibitors (MMPI) which, like the naturally-occurring anti-angiogenic factors, inhibit angiogenesis in vitro and in vivo, and tumour development, growth and metastasis in vivo. Anti-angiogenic agents also enhance the antitumour activity of many conventional cytotoxic chemotherapeutic agents. Such combinations may have a particular role as adjuvant therapies following surgical resection of primary tumours. Unlike tumour cells, tumour associated endothelial cells do not develop resistance to anti-angiogenic agents. Furthermore, anti-angiogenic agents are generally cytostatic rather than cytotoxic. As such, these agents are, in general, likely to be administered over long periods of time. Therefore, as well as having proven antitumour efficacy, an anti-angiogenic compound will need to be well-tolerated if it is to become established in the clinical management of patients with malignant disease.

Somatostatin receptors 2 and 5 are preferentially expressed in proliferating endothelium

Angiogenesis is characterised by activation, migration and proliferation of endothelial cells and is central to the pathology of cancer, cardiovascular disease and chronic inflammation. Somatostatin is an inhibitory polypeptide that acts through five receptors (sst 1, 2, 3, 4, 5). Sst has previously been reported in endothelium, but their role remains obscure. Here, we report the expression of sst in human umbilical vein endothelial cells (HUVECs) in vitro, during proliferation and quiescence. A protocol for culturing proliferating and quiescent HUVECs was established, and verified by analysing cell cycle distribution in propidium-iodide-stained samples using flow cytometry. Sst mRNA was then quantified in nine proliferating and quiescent HUVEC lines using quantitative reverse transcriptase–polymerase chain reaction. Sst 2 and 5 were preferentially expressed in proliferating HUVECs. All samples were negative for sst 4. Sst 1 and 3 expression and cell cycle progression were unrelated. Immunostaining for sst 2 and 5 showed positivity in proliferating but not quiescent cells, confirming sst 2 and 5 protein expression. Inhibition of proliferating cells with somatostatin analogues Octreotide and SOM230, which have sst 5 activity, was found (Octreotide 10⁻¹⁰–10⁻⁶ M: 48.5–70.2% inhibition; SOM230 10⁻⁹–10⁻⁶ M: 44.9–65.4% inhibition) in a dose-dependent manner, suggesting that sst 5 may have functional activity in proliferation. Dynamic changes in sst 2 and 5 expression during the cell cycle and the inhibition of proliferation with specific analogues suggest that these receptors may have a role in angiogenesis.

Clinical usefulness of 99mTc-EDDA/HYNIC-TOC scintigraphy in oncological diagnostics: a pilot study

The clinical usefulness of a new 99mTc-labeled somatostatin analogue has been studied from the standpoint of oncological diagnostics. The group of patients studied included 40 individuals with diagnosed malignant neoplasms (32 primary and 8 metastatic). Among the primary tumors were 7 pituitary adenomas (5 hormonally active and 2 inactive), 1 liposarcoma, 2 carcinoids, 1 breast carcinoma, and 21 cases of lung cancer (2 small cell and 19 non-small cell) were represented. The metastatic tumors consisted of: 3 malignant melanomas, 1 pheochromocytoma, 1 prostatic cancer, 1 leiomyosarcoma, 1 pancreatic carcinoma ectopically secreting ACTH, and 1 carcinoid of the thymus. The radiopharmaceutical, 99mTc-EDDA/HYNIC-octreotide, was i.v. administered at the activity of 740-925 MBq. The imaging was comprized of a whole-body scan and single photon emission computed tomography. Positive scintigrams were obtained in 4 of 5 hormonally active pituitary adenomas, in 1 of 2 cases of carcinoid, in liposarcoma, breast cancer, and all cases of small cell (SCLC) and non-small cell lung cancer (NSCLC). The neoplastic metastases were visualized in 2 of 3 cases of melanoma and in patients with pheochromocytoma, pancreatic carcinoma secreting ACTH, and thymic carcinoid. Scintigrams were negative in both hormonally inactive pituitary adenomas, in one case of metastatic malignant melanoma, leiomyosarcoma, and in cases of metastasis from the prostatic carcinomas. The results of this pilot study indicated that 99mTc-EDDA/HYNIC-TOC is a potentially useful radiopharmaceutical for the imaging of a wide range of primary and metastatic tumors. More detailed indications for the clinical usefulness of the new tracer for the imaging of selected tumor types require studies on much larger groups of patients. Special attention should be paid to the successful imaging of all cases of NSCLC.

Efficacy of 99mTc-EDDA/HYNIC-TOC Scintigraphy in Differential Diagnosis of Solitary Pulmonary Nodules

Fifty consecutive patients with solitary pulmonary nodules (SPN) on chest radiographs were studied scintigraphically after the administration of a somatostatin analog 99mTc-EDDA/HYNIC-TOC. The activity amounted to 740-925 MBq and a single photon emission computed tomography (SPECT) technique was applied. Verification of the nodule etiology was based on histology or cytology and bacteriology. As additional criterion for nodule benignity, its stable size in a chest radiograph for at least 3 years was accepted. In 31 patients, malignant etiologies of nodules were found. The diagnoses included: 11 adenocarcinomas, 6 squamous-cell carcinomas, 2 large-cell carcinomas, 6 nonsmall-cell lung cancers (NSCLC) of unspecified, more detailed morphology, 2 small-cell lung cancers (SCLC), 2 typical carcinoids, and 2 metastatic tumors: leiomyosarcoma and malignant melanoma. In 19 patients, the following benign tumors were diagnosed: 6 tuberculomas, 2 other granulomas, 4 hamartomas, 2 nonspecific inflammatory infiltrates, 1 abscess, 1 peripheral carcinoid of morphological characteristics of a benign tumor, 1 ectopic lesion of thyroid tissue, and 2 benign tumors of unspecified etiology, with stable size over 3 and 5 years. Positive scintigraphic results were obtained in 28 of 31 patients (90%) with malignant SPNs; among these there were 26 of 27 (96%) cases of primary pulmonary carcinoma. The remaining 2 false-negative cases included metastatic tumors: liposarcoma and melanoma. Among 19 benign lesions, 15 (79%) did not accumulate the radiopharmaceutical. The remaining 4 tumors visible on scintigrams included: 1 tuberculoma, 1 hamartoma, 1 abscess, and 1 case of nonestablished diagnosis (with stable size over 3 years). In conclusion, scintigraphy with 99mTc-EDDA/HYNIC-TOC appears to be an effective procedure for differentiation between malignant and benign SPNs.

Inhibition of endothelial proliferation by the somatostatin analogue SOM230

OBJECTIVE

Somatostatin (SST) modulates exocrine and endocrine secretion, proliferation and apoptosis via five G protein-linked receptors (SSTRs 1-5). Long-acting SST analogues such as Octreotide, and the new analogue SOM230, have been developed for the treatment of neuroendocrine tumours. Octreotide has previously been reported to inhibit endothelial proliferation. We wished to determine if SOM230 is a more potent inhibitor of endothelial cell proliferation than Octreotide.

DESIGN

We have determined the expression of SSTRs in proliferating human umbilical vein endothelial cells (HUVECs) in vitro, and determined their response to the somatostatin analogues SOM230 and Octreotide, following vascular endothelial growth factor (VEGF) stimulation.

MEASUREMENTS

Quantitative RT-PCR and western blotting were used to determine the expression of SSTRs 1-5 in proliferating HUVECs. These cells were grown in media containing 200 pg/ml VEGF and treated with 10(-11) to 10(-6) M Octreotide or SOM230. The WST-1 assay was then used to determine the effects of these analogues on HUVEC proliferation.

RESULTS

Using quantitative RT-PCR and western blotting, HUVECs were found to express SSTRs 1, 2 and 5. SSTRs 3 and 4 were not detected. Using the WST-1 assay, SOM230 was found to significantly inhibit proliferation by up to 46.0% +/- 9.4% (10(-6)-10(-7) M; P < 0.05), whereas in parallel studies Octreotide failed to inhibit HUVEC proliferation.

CONCLUSIONS

The pan SST analogue SOM230 inhibits proliferation of HUVECs, which are unaffected by Octreotide. SOM230 may thus represent a suitable candidate drug for antiangiogenic therapy.

Somatostatin analogues: multiple roles in cellular proliferation, neoplasia, and angiogenesis

Angiogenesis, the development of new blood vessels is a crucial process both for tumor growth and metastatic dissemination. Additionally, dysregulation in angiogenesis has been implicated in the pathogenesis of cardiovascular disease, proliferative retinopathy, diabetic nephropathy, and rheumatoid arthritis (RA). The neuropeptide somatostatin has been shown to be a powerful inhibitor of neovascularization in several experimental models. Furthermore, somatostatin receptors (sst) are expressed on endothelial cells; particularly, sst2 has been found to be uniquely up-regulated during the angiogenic switch, from quiescent to proliferative endothelium. The present manuscript reviews the anti-angiogenic activity of somatostatin and its analogues in neoplastic and nonneoplastic disease. The role of sst subtypes particularly sst2 in mediating its angioinhibitory activity is described. Somatostatin agonists may also exert their anti-angiogenic activity indirectly by inhibition of growth factors like vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis or through its immunomodulatory effects. However, the therapeutic utility of somatostatin agonists as anti-angiogenic drugs in these diseases remains confusing because of conflicting results from different studies. More basic research, as well as patient-oriented studies, is required to firmly establish the clinical potential of somatostatin agonists in therapeutic angiogenesis. The currently available somatostatin agonists have high affinity of sst2 with lower affinities for sst3 and sst5. The emergence of novel somatostatin agonists especially bispecific analogues (agonists targeting multiple cellular receptors) and conjugates (synthesized by chemically linking somatostatin analogues with other antineoplastic agents) with improved receptor specificity signify a new generation of anti-angiogenics, which may represent novel strategies in the treatment of neovascularization-related diseases.

Development of targeted somatostatin-based antiangiogenic therapy: a review and future perspectives

Angiogenesis, the development of new blood vessels, is a critical determinant of tumor growth and the dissemination of metastasis. A number of antiangiogenic therapies have been introduced into clinical trials, though few of these are targeted therapies. Somatostatin analogs may be an excellent candidate to develop as targeted antiangiogenic agents alone, or in combination with cytotoxic or cytostatic compounds. Somatostatin analog inhibition of angiogenesis has been demonstrated in the chicken chorioallantoic membrane (CAM) model, the human umbilical vein endothelial cell (HUVEC) proliferation model, and the human placental vein angiogenesis model (HPVAM). This inhibition appears to be the result of a unique upregulation of somatostatin receptor subtype 2 (sst 2) during the angiogenic switch from resting to proliferating endothelium. The distinct overexpression of this receptor provides a unique target for these somatostatin analogs or somatostatin analog conjugates. This manuscript reviews the development of somatostatin analogs as antiangiogenics in both their unlabeled and radiolabeled forms and postulates on future developments in this field.

Tc-99m Depreotide Detecting Malignant Pulmonary Nodules

Tc-99m depreotide is a synthetic somatostatin analog with a low molecular weight of 1358 and binding domains for somatostatin receptors (SSTRs) subtypes 2, 3, and 5. This agent has been used for imaging pulmonary nodules in an effort to differentiate malignancies from infectious processes. To investigate whether there is significant ratio variability predicting a specific lung cancer type, we undertook this study. We analyzed the semiquantitative tumor-to-normal lung ratios among 23 patients with histopathologically proven lung carcinoma. Eleven patients with squamous cell carcinoma had 14 nodular lesions (n = 14); the ratios ranged from 6.0 to 1.4; the mean was 3.500. Nine patients with adenocarcinoma had 9 nodular lesions (n = 9); the ratios ranged from 3.2 to 1.0; mean was 1.89. Three patients with large cell carcinoma had 3 nodular lesions (n = 3); mean was 1.2. There were significantly different ratio values between squamous cell carcinoma and nonsquamous cell carcinoma. On a statistical analysis by t test, this difference proved to have a statistically significant value of P < 0.038. For patients with lung cancer, we could predict the tumor most likely to be squamous cell carcinoma if the uptake ratio was greater than 3.5. Otherwise, the lower ratio appeared to be either the result of large cell carcinoma or adenocarcinoma. High tumor uptake of Tc-99m depreotide reflecting abundant SSTRs of a tumor and/or peritumoral neovasculature such as squamous cell carcinoma could be potentially useful in diagnostic and therapeutic guidance.

Cotargeting tumor and stroma in a novel chimeric tumor model involving the growth of both human prostate cancer and bone stromal cells

Stromal-epithelial interaction contributes to local prostate tumor growth, androgen-independent progression and distant metastasis. We have established in vitro coculture and in vivo chimeric tumor models to evaluate the roles of stromal cells isolated from either osteosarcoma or normal bone, a site where prostate cancer cells frequently metastasize, in contributing to the growth and survival of human prostate cancer cells. We have evaluated extensively the effects of toxic gene therapy using luciferase-tagged chimeric human prostate cancer models both in vitro and in vivo. In the in vitro cocultured cell model, we assessed cancer cell growth and residual cellular proteins after targeting either prostate cancer epithelial cells alone or both prostate cancer and bone stromal cells. In the in vivo animal model, we measured tumor volume and serum prostate-specific antigen (PSA) in mice bearing chimeric prostate tumors comprised of human prostate tumor cells and normal bone stromal cells. Our results demonstrated that: (1) The rate of human prostate cancer cell growth in vitro is accelerated by coculturing with human and rat osteosarcoma or normal mouse bone marrow stromal cell lines. No growth stimulation was noted when cocultured with a human prostate epithelial cell line. (2) Disabling the growth of normal bone stromal cells using transgenic targeting with a bystander gene, herpes simplex virus thymidine kinase (hsv-TK), plus the pro-drug ganciclovir (GCV) or acyclovir markedly depressed the growth of cocultured human prostate cancer cells in vitro and human prostate cancer-mouse normal bone stroma chimeric tumors in vivo. (3) By cotargeting both human prostate cancer and normal mouse bone stromal cells in vitro with an adenoviral construct, Ad-hOC-TK (a replication-defective Ad5 vector with the bystander transgene hsv-TK under the control of a human osteocalcin (hOC) promoter) plus GCV4, we observed greater inhibition of tumor cell growth than by targeting a single cell compartment with Ad-PSA-TK (a vector construct similar to Ad-hOC-TK except that the transgene expression is under regulation by a full-length human PSA promoter). These results, taken together, established a basic principle that cotargeting both tumor and its supporting stroma is more efficacious than targeting a single cell compartment in the treatment of human prostate cancer bone metastasis. This principle can be applied to other clinical conditions of cancer growth where stroma contribute to the overall growth and survival potential of the cancer.

Expression of somatostatin receptor subtypes 1 to 5 in tumor tissue and intratumoral vessels in malignant endocrine pancreatic tumors

Somatostatin analogs are well established in the treatment of malignant endocrine pancreatic tumors (EPTs). Our goal is to individualize their treatment using receptor-subtype-specific analogs and, therefore, exploring the receptor expression is highly important. We have examined the expression of somatostatin receptor (sst) subtypes 1-5 on tumor cells and in intratumoral vessels in 28 tumor tissues from malignant EPTs with immunohistochemistry using sst-subtype-specific polyclonal antibodies. We found that sst(2) and sst(4) stained positive in 90% and sst(1) in 70% of the tumor tissues, whereas sst(3) and sst(5) stained positive in only 50% of the tumor tissues. Sst expression in intratumoral vessels was high for sst(2) and sst(4) (80%), moderate for sst(1) (40%), and low for sst(3) and sst(5) (10%). The ssts were evenly distributed among the different tumor subtypes. However, tumors belonging to the same subgroup of EPTs showed a variable expression of receptor subtypes. No differences in receptor-subtype expression could be seen between poorly and welldifferentiated tumors, nor between primary tumors and metastases. Prior medical treatment did not influence sst expression pattern. In conclusion, sst(2) and sst(4) were expressed in most tumor tissues and intratumoral vessels from EPTs. However, sst(3) and sst(5) were lacking in half of the tumor tissues and in most of the intratumoral vessels. These differences indicate the importance of determining each tumor s subset of receptors before treatment with receptor-subtype-specific analogs is initiated. The importance of sst expression in intratumoral vessels is not yet known.

90Y-DOTA-D-Phe1-Try3-octreotide in therapy of neuroendocrine malignancies

Somatostatin receptors type 2 (sst(2)) are expressed in high concentration on numerous neudoendocrine tumors. The successful use of radiolabeled somatostatin analogs in imaging promoted further studies in utilizing them in radiopeptide therapy. The somatostatin analog [(90)Y-DOTA-D-Phe(1)-Try3]octreotide (DOTATOC) (DOTA: 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) possesses favorable characteristic for its therapeutic use; shows high affinity for sst(2), moderately high affinity for sst(5), and intermediate affinity for sst(3); high hydrophilicity; stable and facile labeling with (111) In and (90) Y. In this article we report our experience with (90)Y-DOTATOC in neuroendocrine tumors. Eighty-seven patients with neuroendocrine tumors were treated with a cumulated activity ranging from 7.4 to 20.2 GBq. Most patients responded with stabilization of disease (48%); however, objective responses were observed in 28% of patients (5% complete response). No major acute reactions were observed up to the activity of 5.55 GBq per cycle. The dose limiting was bone marrow toxicity and the maximal tolerated dose was defined as 5.18 GBq.

The pathophysiological consequences of somatostatin receptor internalization and resistance

Somatostatin receptors expressed on tumor cells form the rationale for somatostatin analog treatment of patients with somatostatin receptor-positive neuroendocrine tumors. Nevertheless, although somatostatin analogs effectively control hormonal hypersecretion by GH-secreting pituitary adenomas, islet cell tumors, and carcinoid tumors, significant differences are observed among patients with respect to the efficacy of treatment. This may be related to a differential expression of somatostatin receptor subtypes among tumors. In addition, the property of somatostatin receptor subtypes to undergo agonist-induced internalization has important consequences for visualizing, as well as for therapy, of receptor-positive tumors using radioisotope- or chemotherapeutic-compound-coupled somatostatin analogs. This review covers the pathophysiological role of somatostatin receptor subtypes in determining the efficacy of treatment of patients with somatostatin receptor-positive tumors using somatostatin analogs, as well as the preclinical and clinical consequences of agonist-induced receptor internalization for somatostatin receptor-targeted radio- and chemotherapy. Herein, the development and potential role of novel somatostatin analogs is discussed.

Somatostatin analogs and radiopeptides in cancer therapy

Since the discovery of somatostatin (sst) in 1973, numerous chemical and biological studies have been carried out to develop sst analogs with enhanced resistance to proteases and prolonged activity. Three highly potent sst analogs-octreotide, lanreotide, and vapreotide-are now available in the clinic, and demonstrate efficacy in the treatment of tumors of the pituitary and the gastroenteropancreatic tract. The most striking effect is the control of hormone hypersecretion associated with these tumors. Available data on growth suppression in patients indicate a limited antiproliferative action, tumor shrinkage is observed in 10-20% patients, and tumor stabilization in about half of the patients for duration of 8-16 months. Eventually, however, all patients escape from sst analog therapy with regard to both hormone hypersecretion and tumor growth, the only exception being observed in acromegalic patients who do not experience tachyphylaxis even after more than 10 years of daily octreotide injection. The mechanism underlying the escape phenomenon is not yet clarified. Regarding the molecular mechanisms involved in sst antineoplastic activity, both indirect and direct effects via specific somatostatin receptors (SSTRs) expressed in the target cells have be described. Direct action may result from blockade of mitogenic growth signal or induction of apoptosis following interaction with SSTRs. Indirect effects may be the result of reduced or inhibited secretion of growth-promoting hormones and growth factors that stimulate the growth of various types of cancer; also, inhibition of angiogenesis or influence on the immune system are important factors. Five SSTR subtypes have been identified so far, which are variably expressed in a variety of tumors such as gastroenteropancreatic (GEP) tumors, pituitary tumors, and carcinoid tumors. Although all five SSTR subtypes are linked to adenylate cyclase, they are now known to affect multiple other cellular signaling systems and hence they differentially participate in the regulation of the various cellular processes. The finding of several laboratories that SSTR-expressing tumors frequently contain two or more SSTR subtypes, and the recent discovery that SSTR subtypes might form homo/heterodimers to create a novel receptor with different functional characteristics, expand the array of selective SSTR activation pathways and subsequent intracellular signaling cascades. This may lead to improved clinical protocols that take into account possible synergistic interactions between the SSTR subtypes present on the same cancer cell. Radiolabeled sst analogs, such as [(111)In]-[diethylenetriamine pentaacetic acid (DTPA)-D-Phe(1)]-octreotide (OcreoScan), have proved to be very useful for tumor scintigraphy and internal radiotherapy of SSTR overexpressing tumors. The recent introduction of the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) considerably improved the stability of the radioconjugates, making possible the incorporation of a variety of radionuclides, such as (90)Y for receptor-mediated radionuclide therapy or (68)Ga for positron emission tomography (PET). Another promising area is the development of sst conjugates incorporating cytotoxic anticancer drugs.

Radiolabeled peptides in the diagnosis and therapy of oncological diseases

There has been an exponential growth in the development of radiolabeled peptides for diagnostic and therapeutic applications in oncology. Peptides have fast clearance, rapid tissue penetration, low antigenicity and can be produced easily and inexpensively. However, peptides have problems with in vivo catabolism, unwanted physiological effects, and chelate attachment. The approved 111In-DTPA-OctreoScan, a somatostatin receptor binder, is well established for diagnosis of neuroendocrine tumors. NeoTect, an approved, 99mTc-labeled, somatostatin-receptor-binding analogue has good specificity for lung cancer detection. The receptors for Vasoactive Intestinal Peptide, Cholecystokinin-B/gastrin, Bombesin, Epidermal Growth Factor, and Alpha Melanocyte Stimulating Hormone and the Integrin, alpha(v)beta(3), are under active investigation as targets. Octreotide and its analogues labeled with 111In, 90Y, 64Cu or 177Lu are under study for the treatment of patients with promising results.

Nuclear medicine applications in molecular imaging

With the emergence of the new field of molecular imaging, there is an increasing demand for development of sensitive and safe novel imaging agents that can be rapidly translated from small animal models into patients. Nuclear medicine and positron emission tomography (PET) techniques have the ability to detect and serially monitor a variety of biologic and pathophysiologic processes, usually with tracer quantities of radiolabeled peptides, drugs, and other molecules at doses free of pharmacologic side effects, unlike the current generation of intravenous agents required for magnetic resonance (MR) and computed tomography (CT) scanning. In this article, we will review a representative sampling of the wide array of radiopharmaceuticals developed specifically for nuclear medicine radionuclide imaging that have been approved for clinical use, and those in pre-clinical trials. We will also review the existing strategies used to select the appropriate biologic markers and targets for radionuclide labeling that have been employed in the development of novel radiotracers and the imaging of small animals with new microSPECT (single photon emission computed tomography) technologies.

Antiangiogenic effects of somatostatin analogues

Inhibition of angiogenesis has become a target for antineoplastic therapy and for treatment of retinal neovascularization. The presence of somatostatin receptors on tumour cells and on the proliferating vascular endothelium has led to several in vitro and in vivo studies to investigate the antiproliferative and antiangiogenic effects of somatostatin analogues. Currently available data suggest that somatostatin analogues might inhibit angiogenesis directly through somatostatin receptors present on endothelial cells and also indirectly through the inhibition of growth factor secretion such as IGF-I and vascular endothelial growth factor (VEGF) and reducing monocyte chemotaxis. However, beneficial effects on inhibition of neovascularization have been questioned by some studies. More work is therefore required to firmly establish the role of somatostatin analogues as potential antiangiogenic therapy. The currently available somatostatin analogues have high affinity for somatostatin receptor subtype 2 (sst2) and, to a lesser extent, sst5 and sst3. However, because vascular endothelial cells express several types of somatostatin receptors, it will be important to investigate somatostatin analogues with different receptor subtype affinities, which might increase the spectrum of available therapy for tumours.

Localisation of somatostatin and somatostatin receptors in benign and malignant ovarian tumours

Somatostatin has been identified as having anti-proliferative, anti-angiogenic and pro-apoptotic actions in many tumour systems, and these effects are mediated through a family of five transmembrane G-protein coupled SRIF receptors. Ovarian cancer is the commonest gynaecological malignancy in the UK and maintenance therapy is urgently required. Native somatostatin expression and its receptors sst(1,2,3 and 5) were studied with immunohistochemistry in 63 malignant and 35 benign ovarian tumours of various histological types. Fifty-seven out of 63 (90%) of malignant and 26/35 (74%) benign tumours expressed somatostatin. Receptors sst(1,2,3 and 5) were expressed variably in epithelial, vascular and stromal compartments for both benign and malignant tumours. Somatostatin was found to correlate significantly with stromal sst(1) (P=0.008), epithelial sst(1) (P<0.001), stromal sst(2) (P=0.019), vascular sst(2) (P=0.026), epithelial sst(3) (P=0.026), stromal sst(5) (P=0.013) and vascular sst(5) (P=0.038). Increased expression of native somatostatin correlating with somatostatin receptors in malignant ovarian tumours raises the possibility that either synthetic somatostatin antagonists or receptor agonists may have therapeutic potential.

Somatostatin receptor 2 expression in the human endometrium through the menstrual cycle

OBJECTIVE

Somatostatin mediates its many inhibitory functions through five G-protein-coupled receptors (sstr1-5); however, it is not known whether somatostatin or its receptors are present in the endometrium.

DESIGN

We have used immunohistochemistry on formalin-fixed paraffin-embedded sections of normal human endometrium from the menstrual (n = 6), proliferative (n = 15) and secretory (n = 10) stages of the endometrial cycle to determine the pattern of expression of somatostatin receptor (sstr) subtype 2. In addition, we have used quantitative polymerase chain reaction (PCR) to determine the level of expression of the sstr2 mRNA in 17 samples of normal human endometrium.

PATIENTS

Endometrial tissue had been removed from patients undergoing dilation and curettage (D&C) for menorrhagia and had been determined to be normal histologically.

MEASUREMENTS

Immunostaining in the epithelium, endothelium and the stroma of the endometrial sections was characterized and was scored positive or negative. The PCR results were analysed using the software provided to standardize the expression of sstr2 against that of constitutively expressed beta-glucoronidase in the same sample. A final percentage value of the level of sstr2 expression was then determined.

RESULTS

sstr2 was expressed variably throughout all the stages of the menstrual cycle in the epithelium, the endothelium and the stroma. In particular, the position of sstr2 expression varied in the epithelial cells surrounding the endometrial glands from being basal or diffuse in the proliferative and secretory phase to being lumenal in the menstrual stage. Quantitative PCR showed that 15 of 17 samples expressed sstr2 mRNA and the level of expression between individual samples varied dramatically.

CONCLUSIONS

These data show that sstr2 is present in the endometrium and its location seems to vary through the menstrual cycle.

Indium-111-pentetreotide prolongs survival in gastroenteropancreatic malignancies

Somatostatin and its analogues bind to somatostatin receptors (sst) 1 through 5 that are overexpressed in neuroendocrine neoplasms such as gastroenteropancreatic (GEP) malignancies. After ligand-receptor binding, a fraction of the ligand-receptor complexes internalize. This internalization process is an effective means of delivering cytotoxic radiolabeled somatostatin analogues, especially those emitting short-range decay particles such as Auger electrons, to the neoplastic cell nucleus. Indium-111-pentetreotide, an sst 2 preferring somatostatin analogue with gamma and Auger electron decay characteristics, is commonly used for the scintigraphic evaluation and management of neuroendocrine cancer patients. This clinical trial was performed to determine the effectiveness and tolerability of therapeutic doses of (111)In-pentetreotide in patients with GEP tumors. GEP tumor patients who had failed all forms of conventional therapy, with worsening of tumor-related signs and symptoms and/or radiographically documented progressive disease, an expected survival less than 6 months, and sst positivity as determined by the uptake on a 6.0 mCi (111)In-pentetreotide scan (OctreoScan; Mallinckrodt Medical, Inc, St. Louis, MO), were treated with at least 2 monthly 180-mCi intravenous injections of (111)In-pentetreotide. Baseline clinical assessments, serum chemistries, and plasma pancreastatin levels were measured and repeated before each (111)In-pentetreotide treatment. From February 1997 to February 1998, 27 GEP (24 carcinoid neoplasms with carcinoid syndrome and 3 pancreatic islet cells) patients were accrued, with 26 patients evaluable for clinical and radiographic responses, 21 patients evaluable for biochemical assessments, and 27 patients evaluable for survival analysis and safety. Toxicity was evaluated by using standard National Cancer Institute (NCI) Common Toxicity Criteria guidelines. Clinical benefit occurred in 16 (62%) patients. Pancreastatin levels decreased by 50% or more in 81% of the patients. Objective partial radiographic responses occurred in 2 (8%) patients, and significant tumor necrosis (defined by 20 Hounsfield units or greater decrease from baseline) developed in 7 (27%) patients. The following transient Grades 3/4 NCI Common Toxicity Criteria side effects were observed, respectively: leukocyte: 1/1; platelets: 0/2; hemoglobin: 3/0; bilirubin: 1/3; creatinine: 1/0; neurologic: 1/0. Myeloproliferative disease and/or myelodysplastic syndrome have not been observed in the 6 patients followed-up for 48+ months. The median survival was 18 months (range, 3-54+ mo). Two doses (180 mCi) of (111)In-pentetreotide are safe, well-tolerated, and improve symptoms in 62% of patients, decrease hormonal markers in 81% of patients, decrease Hounsfield units on computed tomography (CT) scans in 27% of patients, with 8% partial radiographic responses and increased expected survival in GEP cancer patients with somatostatin receptor-expressing tumors. The maximal tolerated dose of (111)In-pentetreotide and the optimal dosing schedules remain under investigation.

Receptor-mediated radiotherapy with Y-DOTA-DPhe-Tyr-octreotide: the experience of the European Institute of Oncology Group

High concentrations of subtype 2 somatostatin tumor receptors (sst(2)) are expressed in numerous tumors, enabling primary and metastatic masses to be localized by scintigraphy after injecting (111)In-labeled somatostatin analogue octreotide. In addition to neuroendocrine tumors, somatostatin receptors have been identified on cancers of the central nervous system, breast, lung, and lymphatic tissue, and the use of radionuclide-labeled somatostatin analogues appeared promising for therapy as well as for diagnosis of such malignancies. The somatostatin analogue [DOTA-(D)Phe(1)-Tyr(3)] octreotide (DOTATOC) possesses favorable characteristics for its potential therapeutic use in that it shows high affinity for sst(2), moderately high affinity for sst(5), and intermediate affinity for sst(3), high hydrophilicity, stable and facile labeling with (111)In and (90)Y. We began to investigate the potential therapeutic applications of (90)Y DOTATOC in 1997 by performing a thorough dosimetric study in 18 patients who were administered (111)In DOTATOC to estimate the absorbed doses during(90)Y-DOTATOC therapy. Then, we moved on and treated an overall number of 256 patients, mostly recruited in 2 distinct protocols with and without the administration of kidney protecting agents, with (90)Y DOTATOC. No major acute reactions were observed up to the activity of 5.55 GBq per cycle. The MTD per cycle was defined as 5.18 GBq. Objective therapeutic responses were documented in more than 20% of patients in terms of partial and complete responses. The present article reports in details our clinical experience (still ongoing) and outcomes with the use of (90)Y DOTATOC.

Head and neck paragangliomas: physiology and biochemistry

Paragangliomas of the head and neck are derivatives of neural crest cells, comprising part of the diffuse neuroendocrine system. Indeed, paragangliomas encompass a unique subset of tumors of the head and neck. Their biochemistry and physiology are similar to other neuroendocrine tumors unlike tumors based on location. This article discusses their distinct biologic attributes.

Radiolabeled peptides in diagnosis and therapy

During the past few years, there has been exponential growth in the development of radiolabeled peptides for diagnosis and therapy. This is because the peptides can be synthesized easily and inexpensively, they have fast clearance and rapid tissue penetration, and they are less likely to be immunogenic. More importantly, most peptides have a high affinity for characteristic receptor molecules that are overexpressed on malignant mammalian cells. Peptides can be labeled with a variety of radionuclides intended for specific applications, diagnostic or therapeutic, by using both conventional and novel chelating moieties, many of which can be incorporated during the solid state synthesis of a chosen peptide. High specific-activity peptides can be prepared and used to minimize unwanted physiologic effects, and known sequences of amino acids can be modified to slow their in vivo catabolic rate. These characteristics have paved the way for the preparation of a large number of radiolabeled peptides for a variety of clinical and experimental applications. This article briefly discusses the peptide chemistry; it also summarizes the preparation of radiolabeled peptides and outlines their applications in imaging vascular thrombosis, detecting infection and inflammation, and localizing tumors. Their therapeutic applications in oncology are also presented and the future directions outlined. Peptides that have been approved for human use, such as AcuTect (Diatide, Londonderry, NH) or OctreoScan (Mallinckrodt, St. Louis, MO), or those that have made it to clinical trials, are emphasized. Also discussed are selected promising agents that are still in preclinical investigation.