Somatostatin Receptor Binding Research Articles

Modeling Early Radiation DNA Damage Occurring During 177Lu-DOTATATE Radionuclide Therapy.

The aim of this study was to build a simulation framework to evaluate the number of DNA double-strand breaks (DSBs) induced by invitro targeted radionuclide therapy (TRT). This work represents the first step toward exploring underlying biologic mechanisms and the influence of physical and chemical parameters to enable a better response prediction in patients. We used this tool to characterize early DSB induction by 177Lu-DOTATATE, a commonly used TRT for neuroendocrine tumors. Methods: A multiscale approach was implemented to simulate the number of DSBs produced over 4 h by the cumulated decays of 177Lu distributed according to the somatostatin receptor binding. The approach involves 2 sequential simulations performed with Geant4/Geant4-DNA. The radioactive source is sampled according to uptake experiments on the distribution of activities within the medium and the planar cellular cluster, assuming instant and permanent internalization. A phase space is scored around the nucleus of the central cell. Then, the phase space is used to generate particles entering the nucleus containing a multiscale description of the DNA in order to score the number of DSBs per particle source. The final DSB computations are compared with experimental data, measured by immunofluorescent detection of p53-binding protein 1 foci. Results: The probability of electrons reaching the nucleus was significantly influenced by the shape of the cell compartment, causing a large variance in the induction pattern of DSBs. A significant difference was found in the DSBs induced by activity distributions in cell and medium, as is explained by the specific energy ([Formula: see text]) distributions. The average number of simulated DSBs was 14 DSBs per cell (range, 7-24 DSBs per cell), compared with 13 DSBs per cell (range, 2-30 DSBs per cell) experimentally determined. We found a linear correlation between the mean absorbed dose to the nucleus and the number of DSBs per cell: 0.014 DSBs per cell mGy-1 for internalization in the Golgi apparatus and 0.017 DSBs per cell mGy-1 for internalization in the cytoplasm. Conclusion: This simulation tool can lead to a more reliable absorbed-dose-to-DNA correlation and help in prediction of biologic response.

The Use of Radioimmunotherapy for the Treatment of Metastatic Melanoma

In 2017, an estimated 7 200 Canadians (91 000 Americans) were diagnosed with melanoma skin cancer. While surgical resection of the primary tumour can be effectively accomplished, there is no satisfactory treatment for patients with metastatic melanoma who do not respond or become resistant to immunotherapy. This reality projected that approximately 1 250 diagnosed Canadians (9 300 Americans) will have succumbed to the disease by the end 2017. Thus, there is a need for alternative effective approaches to treatment of metastatic melanoma. The approval of 223-Radium chloride (Xofigo) for treatment of metastatic prostate cancer and of 177-Lutetium-labeled somatostatin receptor binding peptides for neuroendocrine tumors, as well as recent successes of 177-Lu-A617 compound in patients with metastatic prostate cancer demonstrate the potential of targeted alpha or beta emitting radionuclides in treatment of cancers resistant to all other therapies. Through the use of targeted antibodies containing therapeutic radionuclides it becomes possible to deliver a site-specific lethal dose of radiation to cancer cells providing a direct and effective method for the treatment of metastatic melanoma. Biodistribution and microSPECT/CT imaging results show that a humanized antibody that targets “free” melanin in the tumour microenvironment, has high tumour uptake in B16F10 murine melanoma tumours in C57Bl/6 mice, while little to no uptake in naturally melanized tissues. Initial results indicate that 213Bi (alpha emitter) is more effective than 177Lu (beta emitter) for treatment of metastatic melanoma while both radiolabels did not produce significant side effects. Currently MTD and fractionation studies are underway to determine the best course of treatment.

The Use of Radioimmunotherapy for the Treatment of Metastatic Melanoma

In 2017, an estimated 7 200 Canadians (91 000 Americans) were diagnosed with melanoma skin cancer. While surgical resection of the primary tumour can be effectively accomplished, there is no satisfactory treatment for patients with metastatic melanoma who do not respond or become resistant to immunotherapy. This reality projected that approximately 1 250 diagnosed Canadians (9 300 Americans) will have succumbed to the disease by the end 2017. Thus, there is a need for alternative effective approaches to treatment of metastatic melanoma. The approval of 223-Radium chloride (Xofigo) for treatment of metastatic prostate cancer and of 177-Lutetium-labeled somatostatin receptor binding peptides for neuroendocrine tumors, as well as recent successes of 177-Lu-A617 compound in patients with metastatic prostate cancer demonstrate the potential of targeted alpha or beta emitting radionuclides in treatment of cancers resistant to all other therapies. Through the use of targeted antibodies containing therapeutic radionuclides it becomes possible to deliver a site-specific lethal dose of radiation to cancer cells providing a direct and effective method for the treatment of metastatic melanoma. Biodistribution and microSPECT/CT imaging results show that a humanized antibody that targets “free” melanin in the tumour microenvironment, has high tumour uptake in B16F10 murine melanoma tumours in C57Bl/6 mice, while little to no uptake in naturally melanized tissues. Initial results indicate that 213Bi (alpha emitter) is more effective than 177Lu (beta emitter) for treatment of metastatic melanoma while both radiolabels did not produce significant side effects. Currently MTD and fractionation studies are underway to determine the best course of treatment.

Synthesis, Characterization, and In Vitro Evaluation of New (99m)Tc/Re(V)-Cyclized Octreotide Analogues: An Experimental and Computational Approach.

Radiolabeled proteolytic degradation-resistant somatostatin analogues have been of long-standing interest as cancer imaging and radiotherapy agents for targeting somatostatin receptor-positive tumors. Our interest in developing (186)Re- and (188)Re-based therapeutic radiopharmaceuticals led to investigation of a new Re(V)-cyclized octreotide analogue, Re(V)-cyclized, thiolated-DPhe(1)-Cys(2)-Tyr(3)-DTrp(4)-Lys(5)-Thr(6)-Cys(7)-Thr(OH)(8) (Re-SDPhe-TATE) using both experimental and quantum chemical methods. The metal is directly coordinated to SDPhe-TATE through cyclization of the peptide around the [ReO](3+) core. Upon complexation, four isomers were observed; the isolated/semi-isolated isomers exhibited different somatostatin receptor (sstr) binding affinities, 0.13 to 1.5 μM, in rat pancreatic tumor cells. Two-dimensional NMR experiments and electronic structure calculations were employed to elucidate the structural differences among the different isomers. According to NMR studies, the metal is coordinated to three thiolates and the backbone amide of Cys(2) in isomers 1 and 4, whereas the metal is coordinated to three thiolates and the backbone amide of Tyr(3) in isomer 2. Quantum chemical methods clarified the stereochemistry of Re-SDPhe-TATE and the possible peptide arrangements around the [ReO](3+) core. The re-cyclization reaction was translated to the (99m)Tc radiotracer level with four isomers observed on complexation with comparable HPLC retention times as the Re-SDPhe-TATE isomers. About 85% total (99m)Tc labeling yield was achieved by ligand exchange from (99m)Tc-glucoheptonate at 60 °C for an hour. About 100% and 51% of (99m)Tc(V)-cyclized SDPhe-TATE remained intact in phosphate buffered saline and 1 mM cysteine solution under physiological conditions at 6 h, respectively.

Next Generation of SiFAlin-Based TATE Derivatives for PET Imaging of SSTR-Positive Tumors: Influence of Molecular Design on In Vitro SSTR Binding and In Vivo Pharmacokinetics.

The Silicon-Fluoride-Acceptor (SiFA)-(18)F-labeling strategy has been shown before to enable the straightforward and efficient (18)F-labeling of complex biologically active substances such as proteins and peptides. Especially in the case of peptides, the radiolabeling proceeds kit-like in short reaction times and without the need of complex product workup. SiFA-derivatized, (18)F-labeled Tyr(3)-octreotate (TATE) derivatives demonstrated, besides strong somatostatin receptor (SSTR) binding, favorable in vivo pharmacokinetics as well as excellent tumor visualization by PET imaging. In this study, we intended to determine the influence of the underlying molecular design and used molecular scaffolds of SiFAlin-TATE derivatives on SSTR binding as well as on the in vivo pharmacokinetics of the resulting (18)F-labeled peptides. For this purpose, new SiFAlin-(Asp)n-PEG1-TATE analogs (where n = 1-4) were synthesized, efficiently radiolabeled with (18)F in a kit-like manner and obtained in radiochemical yields of 70-80%, radiochemical purities of ≥97%, and nonoptimized specific activities of 20.1-45.2 GBq/μmol within 20-25 min starting from 0.7-1.5 GBq of (18)F. In the following, the radiotracer's lipophilicities and stabilities in human serum were determined. Furthermore, the SSTR-specific binding affinities were evaluated by a competitive displacement assay on SSTR-positive AR42J cells. The obtained in vitro results support the assumption that aspartic acids are able to considerably increase the radiotracer's hydrophilicity and that their number does not affect the SSTR binding potential of the TATE derivatives. The most promising tracer (18)F-SiFAlin-Asp3-PEG1-TATE [(18)F]6 (LogD = -1.23 ± 0.03, IC50 = 20.7 ± 2.5 nM) was further evaluated in vivo in AR42J tumor-bearing nude mice via PET/CT imaging against the clinical gold standard (68)Ga-DOTATATE as well as the previously developed SiFAlin-TATE derivative [(18)F]3. The results of these evaluations showed that [(18)F]6-although showing very similar chemical and in vitro properties to [(18)F]3-exhibits not only a slowed renal clearance compared to [(18)F]3, but also a higher absolute tumor uptake compared to (68)Ga-DOTATATE, and furthermore enables excellent tumor visualization with high image resolution. These results emphasize the importance of systematic study of the influence of molecular design and applied structure elements of peptidic radiotracers, as these may considerably influence in vivo pharmacokinetics while not affecting other parameters such as radiochemistry, lipophilicity, serum stability, or receptor binding potential.

Assessment of the absorption, metabolism and excretion of [14C]pasireotide in healthy volunteers using accelerator mass spectrometry

Pasireotide (SOM230) is a multireceptor-targeted somatostatin analog designed to have a broader somatostatin receptor binding profile than other currently available somatostatin analogs. The purpose of this study was to evaluate the absorption, metabolism and excretion of pasireotide in healthy male subjects (N = 4) following a single, subcutaneous (sc), 600 μg dose of [¹⁴C]pasireotide. Blood, plasma, urine and feces were collected for 240 h post-dose and analyzed for total ¹⁴C and metabolite profile by accelerator mass spectrometry (AMS) or high-performance liquid chromatography-AMS. Parent drug levels were analyzed by radioimmunoassay. [¹⁴C]pasireotide was rapidly absorbed, with a mean peak plasma ¹⁴C concentration of 16.6 ± 5.28 ngEq/mL at 0.5 h in plasma. The parent drug to total ¹⁴C AUC(0-24h) ratio was 1.08, indicating that little metabolite was present in plasma up to 24 h post-dose. In pooled plasma samples (0-12 h), only unchanged [¹⁴C]pasireotide was detected. Unchanged [¹⁴C]pasireotide accounted for approximately 84 % of total excretion (feces and urine). Approximately 56 % of the administered radioactive dose was recovered within 240 h, eliminated primarily in feces (48.3 ± 8.16 %) and minimally in urine (7.63 ± 2.03 %). No serious adverse events were reported. A single dose of [¹⁴C]pasireotide 600 μg sc administered to healthy male subjects was rapidly absorbed and excreted in its unchanged form primarily via the hepatic route.

Abstract 2125: AN-162, a targeted cytotoxic analog of somatostatin, suppresses growth of human hormone refractory prostate cancers in vitro and in vivo.

Abstract BACKGROUND: Prostate cancer is the most common non-cutaneous human cancer found in the US. Although generally prostate cancer does not have overwhelming effects on patient mortality, the management of hormone refractory prostate cancers (HRPC) has been found to be challenging because of the limitations of current therapeutic modalities. Due to these cancers being hormone refractory alternative therapies have been sought after. One such therapy focuses on the unusual expression of somatostatin receptors in a large percentage of human HRPC samples. Here we tested targeted somatostatin analog, AN-162, consisting of doxorubicin (DOX) conjugated to a somatostatin analog which acts as a carrier in cell lines of human hormone refractory prostate cancer in vitro and in vivo. METHODS: Expression of mRNA for the five subtypes of the somatostatin receptor in PC-3 and DU-145 human prostate cancer cell lines was evaluated by RT-PCR. Somatostatin receptor binding was measured with radioligand assays. The influence of AN-162 and DOX on the viability of PC-3 and DU-145 cells was assessed by MTS assay. Nude mice bearing PC-3 and DU-145 tumors were randomized to 5 groups (control, AN-162, DOX, somatostatin analog RC-160 as a control, and DOX + RC-160). Treatment consisted i.v. injections of AN-162, DOX, RC-160, DOX + RC-160, or vehicle once a week for 4 weeks. Tumor volume was measured every week; the study lasted 28 days. The doses of AN-162 were equivalent to 1.45 mg/kg DOX (2.5 μmol/kg). In addition, cell cycle analysis was performed via laser flow cytometry at concentrations of 1μM for each group. RESULTS: The expression of mRNA for the five subtypes of the somatostatin receptor were demonstrated in PC-3 and DU-145 cell lines and xenografts. Specific, high-affinity binding sites for somatostatin were demonstrated. AN-162 and DOX (0.10-10 μM) suppressed the proliferation of PC-3 and DU-145 prostate cancer cells in a dose-dependent manner. In vivo, AN-162 exerted a stronger inhibition of growth than DOX alone; but in vitro the difference was not significant. In vivo, AN-162 significantly inhibited growth of both tumor models’ compared with the controls and with the groups given equimolar doses of doxorubicin, RC-160, or doxorubicin plus RC-160. Treatment of these cell lines with 1μM of AN-162, Doxorubicin, and the combination of Doxorubicin with RC-160 all expressed significant blocks in the G2/M phase with AN-162 exhibiting the most effective blockage of cell growth and leading to an increased number of apoptotic cells. CONCLUSIONS: Our work establishes potent inhibitory effects of AN-162 on somatostatin receptor positive hormone refractory prostate cancers. The effects were superior to any of the components of AN-162. The mechanisms of action of targeted cytotoxic somatostatin analog, AN-162, in HRPC should be explored. Our findings suggest a possible use of AN-162 in HRPC patients. Citation Format: Ferenc G. Rick, Andrew Abi-Chaker, Luca Szalontay, Norman L. Block, Gabor Halmos, Andrew V. Schally. AN-162, a targeted cytotoxic analog of somatostatin, suppresses growth of human hormone refractory prostate cancers in vitro and in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2125. doi:10.1158/1538-7445.AM2013-2125

324 TARGETED CYTOTOXIC ANALOG OF SOMATOSTATIN AN-162 [AEZS-124] INHIBITS PROLIFERATION OF PC-3 AND DU-145 HUMAN ANDROGEN-INDEPENDENT PROSTATE CANCERS IN VITRO AND IN VIVO

You have accessJournal of UrologyProstate Cancer: Basic Research (II)1 Apr 2013324 TARGETED CYTOTOXIC ANALOG OF SOMATOSTATIN AN-162 [AEZS-124] INHIBITS PROLIFERATION OF PC-3 AND DU-145 HUMAN ANDROGEN-INDEPENDENT PROSTATE CANCERS IN VITRO AND IN VIVO Ferenc Rick, Andrew Abi-Chaker, Luca Szalontay, Norman Block, Gabor Halmos, and Andrew Schally Ferenc RickFerenc Rick Miami, FL More articles by this author , Andrew Abi-ChakerAndrew Abi-Chaker Miami, FL More articles by this author , Luca SzalontayLuca Szalontay Miami, FL More articles by this author , Norman BlockNorman Block Miami, FL More articles by this author , Gabor HalmosGabor Halmos Debrecen, Hungary More articles by this author , and Andrew SchallyAndrew Schally Miami, FL More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.1709AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The management of castration-resistant prostate cancer (CRPC) presents a clinical challenge because of limitations in durability and efficacy of current therapeutic modalities. A clear need exists for novel therapeutic strategies for the treatment of CRPC. Somatostatin receptors are expressed in human CRPC. Here we tested targeted somatostatin analog, AN-162, consisting of doxorubicin (DOX) conjugated to a somatostatin analog which acts as a carrier in cell lines of human androgen-independent prostate cancer in vitro and in vivo. METHODS Somatostatin receptor binding was measured with radioligand assays. Expression of mRNA for the five subtypes of the somatostatin receptor in PC-3 and DU-145 human prostate cancer cell lines was evaluated by RT-PCR. The effect of AN-162 and DOX on the viability of PC-3 and DU-145 cells was assessed by MTS assay. Nude mice bearing PC-3 and DU-145 tumors were randomized to 5 groups (control, AN-162, DOX, somatostatin analog RC-160 as a control, and DOX + RC-160). Treatment consisted i.v. injections of AN-162, DOX, RC-160, DOX + RC-160, or vehicle once a week for 4 weeks. Tumor volume was measured every week; the study lasted 28 days. The doses of AN-162 were equivalent to 1.45 mg/kg DOX (2.5 μmol/kg). RESULTS Specific, high-affinity binding sites for somatostatin were demonstrated. The PC-3 and DU-145 cell lines were each positive for the five subtypes of the somatostatin receptor. AN-162 and DOX (0.10-10 μM) inhibited the proliferation of PC-3 and DU-145 prostate cancer cells in a dose-dependent manner. In vivo, AN-162 exerted a stronger suppression of growth than DOX alone; but in vitro the difference was not statistically significant. In vivo, AN-162 significantly inhibited growth of both tumor models' compared with the controls and with the groups given equimolar doses of doxorubicin, RC-160, or doxorubicin plus RC-160. CONCLUSIONS Our work demonstrates potent inhibitory effects of AN-162 on somatostatin receptor positive androgen-independent prostate cancers The effects were greater than any of the components of AN-162. The mechanisms of action of targeted cytotoxic somatostatin analog, AN-162, in CRPC should be explored. Our findings suggest a possible use of AN-162 in these patients. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e131 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Ferenc Rick Miami, FL More articles by this author Andrew Abi-Chaker Miami, FL More articles by this author Luca Szalontay Miami, FL More articles by this author Norman Block Miami, FL More articles by this author Gabor Halmos Debrecen, Hungary More articles by this author Andrew Schally Miami, FL More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Long-term efficacy and safety of subcutaneous pasireotide in acromegaly: results from an open-ended, multicenter, Phase II extension study

Pasireotide has a broader somatostatin receptor binding profile than other somatostatin analogues. A 16-week, Phase II trial showed that pasireotide may be an effective treatment for acromegaly. An extension to this trial assessed the long-term efficacy and safety of pasireotide. This study was an open-label, single-arm, open-ended extension study (primary efficacy and safety evaluated at month 6). Patients could enter the extension if they achieved biochemical control (GH ≤ 2.5 μg/L and normal IGF-1) or showed clinically relevant improvements during the core study. Thirty of the 60 patients who received pasireotide (200–900 μg bid) in the core study entered the extension. At extension month 6, of the 26 evaluable patients, six were biochemically controlled, of whom five had achieved control during the core study. Normal IGF-1 was achieved by 13/26 patients and GH ≤ 2.5 μg/L by 12/26 at month 6. Nine patients received pasireotide for ≥24 months in the extension; three who were biochemically controlled at month 24 had achieved control during the core study. Of 29 patients with MRI data, nine had significant (≥20 %) tumor volume reduction during the core study; an additional eight had significant reduction during the extension. The most common adverse events were transient gastrointestinal disturbances; hyperglycemia-related events occurred in 14 patients. Twenty patients had fasting plasma glucose shifted to a higher category during the extension. However, last available glucose measurements were normal for 17 patients. Pasireotide has the potential to be an effective, long-term medical treatment for acromegaly, providing sustained biochemical control and significant reductions in tumor volume.Electronic supplementary materialThe online version of this article (doi:10.1007/s11102-013-0478-0) contains supplementary material, which is available to authorized users.

Experimental therapy of PC-3 and DU-145 human androgen-independent prostate cancers with targeted cytotoxic analog of somatostatin AN-162.

236 Background: Management of castration-resistant prostate cancer (CRPC) is challenging because of limitations in efficacy of current therapies. Somatostatin receptors are expressed in human CRPC. Here we tested targeted somatostatin AN-162 analog consisting of doxorubicin (DOX) conjugated to octapeptide RC-121, acting as a carrier, in human androgen-independent prostate cancer cell lines in vitro and in vivo. Methods: Expression of mRNA for the five subtypes of the somatostatin receptor in PC-3 and DU-145 human prostate cancer cell lines was evaluated by RT-PCR. Somatostatin receptor binding was measured with radioligand assays. The effect of AN-162 and DOX on the viability of PC-3 and DU-145 cells was assessed by MTS assay. Nude mice bearing PC-3 and DU-145 tumors were randomized to 5 groups (control, AN-162, DOX, somatostatin analog RC-160 as a control, and DOX + RC-160). Treatment consisted i.v. injections of AN-162, DOX, RC-160, DOX + RC-160, or vehicle once a week for 4 weeks. Tumor volume was measured every week; the study lasted 28 days. The doses of AN-162 were equivalent to 1.45 mg/kg DOX (2.5 μmol/kg). Results: The PC-3 and DU-145 cell lines were positive for the five subtypes of the somatostatin receptor. AN-162 and DOX (0.10–10 µM) inhibited the proliferation of PC-3 and DU-145 prostate cancer cells in a dose-dependent manner. AN-162 exerted a stronger inhibition of proliferation than DOX alone, but in vitro the difference was not significant. In vivo, AN-162 significantly inhibited growth of both tumor models’ compared with the controls and the groups given equimolar doses of doxorubicin, RC-160, or doxorubicin unconjugated to RC-160. Conclusions: Our work demonstrates potent inhibitory effects of AN-162 on somatostatin receptor positive androgen-independent prostate cancers, which were greater than any of the components of AN-162. The mechanisms of action of targeted cytotoxic analog of somatostatin AN-162 in CRPC should be explored. Our findings suggest the possible use of AN-162 in patients with CRPC.

68Ga-Autoclabeling of DOTA-TATE and DOTA-NOC

IntroductionA new method combining 68Ga-labeling and steam sterilization, here called autoclabeling, has been evaluated for two somatostatin receptor binding tracers used for positron emission tomography (PET) imaging of neuroendocrine tumors; DOTA-TATE and -NOC. MethodsThe two peptides DOTA-TATE and -NOC were labeled with 68Ga by heating for 15min at 121°C in the presence of acetate buffer at pH 4.3. The product solutions were tested for sterility, presence of endotoxins, degradation of peptide and osmolality. ResultsComplete incorporation of 68Ga was obtained after the autoclabeling reaction and no degradation of the peptides was observed. Sterility was verified and the presence of endotoxins was well within Ph. Eur limits (175IU/maximum injected volume). ConclusionsThe autoclabeling method provides a convenient procedure for 68Ga-labeling by combining the labeling reaction and steam sterilization into one single step.

A 12-Month Phase 3 Study of Pasireotide in Cushing's Disease

BackgroundCushing's disease is associated with high morbidity and mortality. Pasireotide, a potential therapy, has a unique, broad somatostatin-receptor–binding profile, with high binding affinity for somatostatin-receptor subtype 5.MethodsIn this double-blind, phase 3 study, we randomly assigned 162 adults with Cushing's disease and a urinary free cortisol level of at least 1.5 times the upper limit of the normal range to receive subcutaneous pasireotide at a dose of 600 μg (82 patients) or 900 μg (80 patients) twice daily. Patients with urinary free cortisol not exceeding 2 times the upper limit of the normal range and not exceeding the baseline level at month 3 continued to receive their randomly assigned dose; all others received an additional 300 μg twice daily. The primary end point was a urinary free cortisol level at or below the upper limit of the normal range at month 6 without an increased dose. Open-label treatment continued through month 12.ResultsTwelve of the 82 patients in the 600-μg group and 21 of the 80 patients in the 900-μg group met the primary end point. The median urinary free cortisol level decreased by approximately 50% by month 2 and remained stable in both groups. A normal urinary free cortisol level was achieved more frequently in patients with baseline levels not exceeding 5 times the upper limit of the normal range than in patients with higher baseline levels. Serum and salivary cortisol and plasma corticotropin levels decreased, and clinical signs and symptoms of Cushing's disease diminished. Pasireotide was associated with hyperglycemia-related adverse events in 118 of 162 patients; other adverse events were similar to those associated with other somatostatin analogues. Despite declines in cortisol levels, blood glucose and glycated hemoglobin levels increased soon after treatment initiation and then stabilized; treatment with a glucose-lowering medication was initiated in 74 of 162 patients.ConclusionsThe significant decrease in cortisol levels in patients with Cushing's disease who received pasireotide supports its potential use as a targeted treatment for corticotropin-secreting pituitary adenomas. (Funded by Novartis Pharma; ClinicalTrials.gov number, NCT00434148.)

Somatostatin Receptor Subtype 2A Immunohistochemistry Using a New Monoclonal Antibody Selects Tumors Suitable for In Vivo Somatostatin Receptor Targeting

High overexpression of somatostatin receptors in neuroendocrine tumors allows imaging and radiotherapy with radiolabeled somatostatin analogues. To ascertain whether a tumor is suitable for in vivo somatostatin receptor targeting, its somatostatin receptor expression has to be determined. There are specific indications for use of immunohistochemistry for the somatostatin receptor subtype 2A, but this has up to now been limited by the lack of an adequate reliable antibody. The aim of this study was to correlate immunohistochemistry using the new monoclonal anti-somatostatin receptor subtype 2A antibody UMB-1 with the gold standard in vitro method quantifying somatostatin receptor levels in tumor tissues. A UMB-1 immunohistochemistry protocol was developed, and tumoral UMB-1 staining levels were compared with somatostatin receptor binding site levels quantified with in vitro I-[Tyr]-octreotide autoradiography in 89 tumors. This allowed defining an immunohistochemical staining threshold permitting to distinguish tumors with somatostatin receptor levels high enough for clinical applications from those with low receptor expression. The presence of >10% positive tumor cells correctly predicted high receptor levels in 95% of cases. In contrast, absence of UMB-1 staining truly reflected low or undetectable somatostatin receptor expression in 96% of tumors. If 1% to 10% of tumor cells were stained, a weak staining intensity was suggestive of low somatostatin receptor levels. This study allows for the first time a reliable recommendation for eligibility of an individual patient for in vivo somatostatin receptor targeting based on somatostatin receptor immunohistochemistry. Under optimal methodological conditions, UMB-1 immunohistochemistry may be equivalent to in vitro receptor autoradiography.

Technetium-99m depreotide imaging by single photon emission tomography/low resolution computed tomography in malignant lymphomas: comparison with gallium-67 citrate

Previous studies have demonstrated the feasibility of targeting lymphoma lesions with somatostatin receptor binding agents, mainly with In-111-pentetreotide. In the present work another somatostatin analog, Tc-99m depreotide, is investigated. One-hundred and six patients, 47 with Hodgkin's (HL) and 59 with various types of non-Hodgkin's lymphoma (NHL), were imaged with both Tc-99m depreotide and Ga-67 citrate. Planar whole-body and single photon emission tomography/low resolution computerized tomography (SPECT/CT) images were obtained. A total of 142 examinations were undertaken at different phases of the disease. Depreotide and gallium findings were compared visually and semi-quantitatively, with reference to the results of conventional work-up and the patients' follow-up data. In most HL, intermediate- and low-grade B-cell, as well as in T-cell NHL, depreotide depicted more lesions than Ga-67 and/or exhibited higher tumor uptake. The opposite was true in aggressive B-cell NHL. However, there were notable exceptions in all lymphoma subtypes. During initial staging, 93.3% of affected lymph nodes above the diaphragm, 100% of inguinal nodes and all cases with splenic infiltration were detected by depreotide. On the basis of depreotide findings, 32% of patients with early-stage HL were upstaged. However, advanced HL and NHL cases were frequently downstaged, due to low sensitivity for abdominal lymph node (22.7%), liver (45.5%) and bone marrow involvement (36.4%). Post-therapy, depreotide detected 94.7% of cases with refractory disease or recurrence. Its overall specificity was moderate (57.1%). Rebound thymic hyperplasia, various inflammatory processes and sites of unspecific uptake were the commonest causes of false positive findings. The combination of depreotide and gallium enhanced sensitivity (100%), while various false positive results of either agent could be avoided. Except perhaps for early-stage HL, Tc-99m depreotide as a stand-alone imaging modality has limited value for the initial staging of lymphomas. Post-therapy, however, depreotide scintigraphy seems useful in the evaluation of certain anatomic areas, particularly in non-aggressive lymphoma types. The combination with Ga-67 potentially enhances sensitivity and specificity. If fluorodeoxyglucose positron emission tomography is not available or in case of certain indolent lymphoma types, Tc-99m depreotide may have a role as an adjunct to conventional imaging procedures.

Effects of octreotide exposure during pregnancy in acromegaly

Only six women who were treated with somatostatin analogues (SSAs) throughout their pregnancies have been described so far. The influence of SSAs on the course of pregnancy and newborn outcomes remains largely unknown. Many aspects of SSAs pharmacokinetics in mother and foetus have not yet been defined. We report a case study on the effects of octreotide on uterine artery blood flow, octreotide concentrations in biological fluids of mother and newborn, and somatostatin (SST) receptor expression and binding at the level of the maternal-foetal barrier tissues in an acromegalic woman treated with short-acting octreotide throughout her pregnancy. An acute decrease in uterine artery blood flow was observed after octreotide injections, without affecting the pregnancy course, delivery, or foetal development. Octreotide concentrations were high in maternal serum and colostrum and lower in umbilical cord serum, amniotic fluid, and newborn serum. All SST receptor subtypes can be expressed in placental tissue but their binding profile was weak both in the placenta and umbilical cord. The child was healthy and developed normally up to age 6 from an anthropometric, metabolic, and endocrine point of view. We reviewed all published reports on pregnancy SSA exposure and outcomes were compared to a time-matched group of acromegalic women not exposed to SSA. No significant effect on the mother or foetus was observed. Short-acting octreotide appears not to affect the function of the maternal-foetal barrier or foetal development, except for the occurrence of acute, reversible, and clinically irrelevant haemodynamic changes. These data support the feasibility and safety of treatment with short-acting octreotide in acromegalic women during pregnancy and excludes major matters of concern about the effects of this medication on pregnancy itself and its outcome.

Molecular imaging in thyroid cancer

Molecular imaging plays an important role in the evaluation and management of thyroid cancer. The routine use of thyroid scanning in all thyroid nodules is no longer recommended by many authorities. In the initial work-up of a thyroid nodule, radioiodine imaging can be particularly helpful when the thyroid stimulating hormone level is low and an autonomously functioning nodule is suspected. Radioiodine imaging can also be helpful in the 10–15% of cases for which fine-needle aspiration biopsy is indeterminate. Therapy of confirmed thyroid cancer frequently involves administration of iodine-131 after surgery to ablate remnant tissue. In the follow-up of thyroid cancer patients, increased thyroglobulin levels will often prompt the empiric administration of 131I followed by whole body radioiodine imaging in the search for recurrent or metastatic disease. 131I imaging of the whole body and blood pharmacokinetics can be used to determine if higher doses of 131I can be given in thyroid cancer. The utility of [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) is steadily increasing. FDG is primarily taken up by dedifferentiated thyroid cancer cells, which are poorly iodine avid. Thus, it is particularly helpful in the patient with an increased thyroglobulin but negative radioiodine scan. FDG PET is also useful in the patient with a neck mass but unknown primary, in patients with aggressive (dedifferentiated) thyroid cancer, and in patients with differentiated cancer where histologic transformation to dedifferentiation is suspected. In rarer types of thyroid cancer, such as medullary thyroid cancer, FDG and other tracers such as 99mTc sestamibi, [11C]methionine, [111In]octreotide, and [68Ga]somatostatin receptor binding reagents have been utilized. 124I is not widely available, but has been used for PET imaging of thyroid cancer and will likely see broader applicability due to the advantages of PET methodology.

Radiolabeled Peptides and Proteins in Cancer Therapy

With the advances in genomics, molecular biology including gene vector technologies today's molecular imaging modalities have strongly been improved. The major progress is based on peptide and antibody targeting vectors. When labeled with beta(-)-emitting radioisotopes these agents are applicable for endoradiotherapy and exploit the targeting potential for highly specific therapeutic applications. This novel class of pharmaceuticals offers the potential to develop patient specific therapies and might provide the means to go beyond the possibilities of current chemotherapy and radiation therapy. In this review the basic principles of endoradiotherapeutics based on peptides and proteins are presented. Several of these drugs such as (90)Y-rituximab (Zevalin), (131)I-tositumomab (Bexxar) and the somatostatin receptor binding (90)Y-DOTATOC that are nowadays successfully applied in oncological therapy are discussed. Future generations of endoradiopharmaceuticals will address yet unknown targets which might be identified by screening techniques such as ribosome and phage display peptide libraries.

Value of 111In-DOTA-lanreotide and 111In-DOTA-DPhe1-Tyr3-octreotide in differentiated thyroid cancer: results of in vitro binding studies and in vivo comparison with 18F-FDG PET

Radioiodine-negative thyroid cancer presents diagnostic and therapeutic difficulties, warranting the implementation of new imaging and treatment strategies. The purpose of this study was twofold. First, we investigated in vitro the binding characteristics of 111In-DOTA-lanreotide (111In-DOTA-LAN) and 111In-DOTA-D: Phe1-Tyr3-octreotide (111In-DOTA-TOC) to cells derived from differentiated thyroid cancer (DTC). Second, we evaluated the value of somatostatin receptor (SSTR) scintigraphy with these radioligands, as compared with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), for the detection of tumour lesions in DTC patients. Binding of 111In-DOTA-LAN and 111In-DOTA-TOC to cells isolated from surgically removed thyroid tissue was evaluated in vitro by performing saturation and displacement studies. Eighteen DTC patients with elevated thyroglobulin (12 radioiodine-negative, six radioiodine-positive) were investigated with 111In-DOTA-LAN, 111In-DOTA-TOC and 18F-FDG PET scans. Large numbers of SSTR binding sites for 111In-DOTA-LAN and 111In-DOTA-TOC were found on the cells investigated. Both SSTR radioligands exhibited a high binding affinity for these SSTR binding sites. 111In-DOTA-LAN and 111In-DOTA-TOC scintigraphy detected 37 and 33 lesions, respectively, in 17 (94%) patients each, whereas 18F-FDG PET revealed 30 lesions in 15 (83%) patients. Uptake of both SSTR radioligands was found in several radioiodine-negative sites. No striking differences in lesion imaging by 111In-DOTA-LAN and 111In-DOTA-TOC were found. In both radioiodine-negative and radioiodine-positive patients, more lesions were SSTR-positive/18F-FDG-negative than were 18F-FDG-positive/SSTR-negative. Adding a SSTR scan with these radioligands to the diagnostic work-up increases the diagnostic capacity in DTC, and should be considered particularly in radioiodine-negative patients with elevated thyroglobulin levels.

Somatostatin receptor subtypes: basic pharmacology and tissue distribution

The heptahelical receptor superfamily constitutes the largest single family of transmembrane-signalling molecules that regulate a wide range of physiological processes. The five somatostatin receptors represent a distinct subgroup of this seven transmembrane receptor superfamily. They range in size from 356 to 391 amino acids with 39–57% protein identity between the subtypes with 100 residues strictly conserved among the somatostatin receptor sequences. A high grade of mRNA homology exists in somatostatin receptor subtypes cloned from different species. Following somatostatin receptor binding and functional activity studies, two alternative models of ligand-binding interaction have been hypothesised. One relies on the presence of a binding pocket within the receptor structure constituted by specific amino acids residues, the other denies the presence of such binding structures and suggests that it is the interaction of agonists with specific extracellular and/or transmembrane domains that determine stable receptor structure conformation. Somatostatin receptors, as, indeed, all G-protein-coupled receptors are able to regulate their responsiveness to agonist exposure. This agonist-specific regulation includes three main events, namely, desensitisation, receptor internalisation and receptor degradation. The cell expression of somatostatin receptor subtypes, at the mRNA level, has been characterised in rodent and in human organs with multiple subtype expression in brain and peripheral tissues.

DOTA-NOC, a high-affinity ligand of somatostatin receptor subtypes 2, 3 and 5 for labelling with various radiometals

Earlier studies have shown that modification of the octapeptide octreotide in positions 3 and 8 may result in compounds with increased somatostatin receptor affinity that, if radiolabelled, display improved uptake in somatostatin receptor-positive tumours. The aim of a recent research study in our laboratory was to employ the parallel peptide synthesis approach by further exchanging the amino acid in position 3 of octreotide and coupling the macrocyclic chelator DOTA(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to these peptides for labelling with radiometals like gallium-67 or -68, indium-111, yttrium-90 and lutetium-177. The purpose was to find radiopeptides with an improved somatostatin receptor binding profile in order to extend the spectrum of targeted tumours. A first peptide, [111In,90Y-DOTA]-1-Nal3-octreotide (111In,90Y-DOTA-NOC), was isolated which showed an improved profile. InIII-DOTA-NOC exhibited the following IC50 values (nM) when studied in competition with [125I][Leu8, d-Trp22, Tyr25]somatostatin-28 (values for YIII-DOTA-NOC are shown in parentheses): sstr2, 2.9 +/- 0.1 (3.3 +/- 0.2); sstr3, 8 +/- 2 (26 +/- 1.9); sstr5, 11.2 +/- 3.5 (10.4 +/- 1.6). Affinity towards sstr1 and 4 was very low or absent. InIII-DOTA-NOC is superior to all somatostatin-based radiopeptides having this particular type of binding profile, including DOTA-lanreotide, and has three to four times higher binding affinity to sstr2 than InIII,YIII-DOTA-Tyr3-octreotide (InIII,YIII-DOTA-TOC). In addition, [111In]DOTA-NOC showed a specific and high rate of internalization into AR4-2J rat pancreatic tumour cells which, after 4 h, was about two times higher than that of [111In]DOTA-TOC and three times higher than that of [111In]DOTA-octreotide ([111In]DOTA-OC). The internalized radiopeptides were externalized intact upon 2 h of internalization followed by an acid wash. After 2-3 h of externalization a plateau is reached, indicating a steady-state situation explained by reactivation of the receptors followed by re-endocytosis. Biodistribution studies in CA 20948 tumour-bearing rats showed rapid clearance from all sstr-negative tissues except the kidneys. At 4 h the uptake of [111In]DOTA-NOC in the tumour and sstr-positive tissues, such as adrenals, stomach and pancreas, was three to four times higher than that of [111In]DOTA-TOC. Differential blocking studies indicate that this is at least partially due to the uptake mediated by sstr3 and sstr5. These very promising preclinical data justify the use of this new radiopeptide for imaging and potentially internal radiotherapy studies in patients.