Affinity For Somatostatin Receptors Research Articles

The Novel SSTR3 Agonist ITF2984 Exerts Antimitotic and Proapoptotic Effects in Human Non-Functioning Pituitary Neuroendocrine Tumor (NF-PitNET) Cells.

Somatostatin receptor ligands (SRLs) with high affinity for somatostatin receptors 2 and 5 (SSTR2 and SSTR5) are poorly efficacious in NF-PitNETs, expressing high levels of SSTR3. ITF2984 is a pan-SSTR ligand with high affinity for SSTR3, able to induce SSTR3 activation and to exert antitumoral activity in the MENX rat model. The aim of this study was to test ITF2984's antiproliferative and proapoptotic effects in NF-PitNET primary cultured cells derived from surgically removed human tumors and to characterize their SSTR expression profile. We treated cells derived from 23 NF-PitNETs with ITF2984, and a subset of them with octreotide, pasireotide (SRLs with high affinity for SSTR2 or 5, respectively), or cabergoline (DRD2 agonist) and we measured cell proliferation and apoptosis. SSTR3, SSTR2, and SSTR5 expression in tumor tissues was analyzed by qRT-PCR and Western blot. We demonstrated that ITF2984 reduced cell proliferation (-40.8 (17.08)%, p < 0.001 vs. basal, n = 19 NF-PitNETs) and increased cell apoptosis (+41.4 (22.1)%, p < 0.001 vs. basal, n = 17 NF-PitNETs) in all tumors tested, whereas the other drugs were only effective in some tumors. In our model, SSTR3 expression levels did not correlate with ITF2984 antiproliferative nor proapoptotic effects. In conclusion, our data support a possible use of ITF2984 in the pharmacological treatment of NF-PitNET.

Octreotide-Targeted Lcn2 siRNA PEGylated Liposomes as a Treatment for Metastatic Breast Cancer.

Lcn2 overexpression in metastatic breast cancer (MBC) can lead to cancer progression by inducing the epithelial-to-mesenchymal transition and enhancing tumor angiogenesis. In this study, we engineered a PEGylated liposomal system encapsulating lipocalin 2 (Lcn2) small interfering RNA (Lcn2 siRNA) for selective targeting MBC cell line MCF-7 and triple-negative breast cancer cell line MDA-MB-231. The PEGylated liposomes were decorated with octreotide (OCT) peptide. OCT is an octapeptide analog of somatostatin growth hormone, having affinity for somatostatin receptors, overexpressed on breast cancer cells. Optimized OCT-targeted Lcn2 siRNA encapsulated PEGylated liposomes (OCT-Lcn2-Lipo) had a mean size of 152.00 nm, PDI, 0.13, zeta potential 4.10 mV and entrapment and loading efficiencies of 69.5% and 7.8%, respectively. In vitro uptake and intracellular distribution of OCT-Lcn2-Lipo in MCF-7 and MDA-MB-231 and MCF-12A cells demonstrated higher uptake for the OCT-targeted liposomes at 6 h by flow cytometry and confocal microscopy. OCT-Lcn2-lipo could achieve approximately 55−60% silencing of Lcn2 mRNA in MCF-7 and MDA-MB-231 cells. OCT-Lcn2-Lipo also demonstrated in vitro anti-angiogenic effects in MCF-7 and MDA-MB-231 cells by reducing VEGF-A and reducing the endothelial cells (HUVEC) migration levels. This approach may be useful in inhibiting angiogenesis in MBC.

2038-P: The Somatostatin Analog Pasireotide Reduces Pancreatic ß-Cell Function and Survival, and Both Incretin-Based Drugs and Irisin Revert These Effects

Pasireotide is a new-generation somatostatin analog used for the treatment of acromegaly, Cushing’s disease and neuroendocrine tumors. However, due to its high affinity for somatostatin receptors (SSTR) 2 and 5, highly expressed in enteroendocrine- and pancreatic β-cells, it can reduce insulin, GLP-1 and GIP release and increase glucagonemia, causing marked hyperglycemia in some patients. The diabetogenic effects of pasireotide are significantly reduced in vivo by the co-administration of liraglutide or vildagliptin. The aim of this study was to evaluate the effects of pasireotide on β-cell survival and function, and the ability of molecules with known beneficial action on β-cells (incretin-based drugs and irisin, a myokine with β-cellular trophic properties) to prevent these effects. In INS-1E cells, both acute and chronic administration of pasireotide 10-50 nM reduced glucose-induced insulin secretion by 30% and 50% respectively and proinsulin mRNA levels by 20%, without altering cellular insulin content. Furthermore, pasireotide induced apoptosis in INS-1E cells and human pancreatic islets. Pretreatment with both incretin-based drugs (exendin-4, lixisenatide, liraglutide, saxagliptin) and irisin prevented pasireotide-induced apoptosis in INS-1E cells. In addition, pasireotide increased the protein levels of SSTR2 (2-fold) but not of SSTR5. Among the protective molecules examined, only irisin was able to prevent this increase. In conclusion, pasireotide can induce hyperglycemia and diabetes via direct effects on β-cells, resulting in reduced insulin secretory capacity and survival. Both GLP-1 receptor agonists and DPP-4 inhibitors and irisin can reduce the proapoptotic effects of pasireotide, acting through partially different molecular mechanisms. These results demonstrate for the first time a functional antagonism between SSTR2/5 activation and incretin-based drugs or irisin in pancreatic β-cells. Disclosure A. Natalicchio: Consultant; Self; AstraZeneca, Novo Nordisk Inc., Sanofi-Aventis. G. Biondi: None. N. Marrano: None. L. Vincenti: None. A. Cignarelli: None. S. Perrini: None. L. Laviola: Advisory Panel; Self; Abbott, AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk Inc., Roche Diabetes Care, Sanofi-Aventis. Speaker’s Bureau; Self; Abbott, Medtronic. F. Giorgino: Advisory Panel; Self; AstraZeneca, Eli Lilly and Company, Novo Nordisk Inc., Roche Diabetes Care, Sanofi. Consultant; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., LifeScan, Inc., MedImmune, Merck Sharp &amp; Dohme Corp., Roche Diabetes Care, Sanofi. Research Support; Self; Eli Lilly and Company, LifeScan, Inc., Takeda Development Centre Europe Ltd. Funding Novartis

Design, preparation and biological evaluation of a 177Lu-labeled somatostatin receptor antagonist for targeted therapy of neuroendocrine tumors.

Somatostatin receptor-targeted radionuclide therapy has become an effective treatment in patients with neuroendocrine tumors. Recently, investigations on the development of antagonistic peptides are increasing with possible superior biological properties as opposed to the agonists. Herein, we have reported the development of a new somatostatin receptor peptide ligand labeled with 177Lu to achieve a therapeutic ligand for tumor treatment. The interactions of selected and drown ligands using Avogadro software were docked on somatostatin receptor by Dink algorithm. The best docked peptide-chelator conjugate (DOTA-p-Cl-Phe-Cyclo(d-Cys-l-BzThi-d-Aph-Lys-Thr-Cys)-d-Tyr-NH2) (DOTA-Peptide 2) was synthesized using the Fmoc solid-phase method. DOTA-Peptide 2 was radiolabeled with the 177Lu Trichloride (177LuCl3) solution at 95 °C for 30 min and radiochemical purity (RCP) of 177Lu-DOTA-Peptide 2 solution was monitored by radio-HPLC and radio-TLC procedures. The new radiolabeled peptide was evaluated for stability, receptor binding, internalization, biodistribution and single-photon emission computed tomography (SPECT) imaging using C6 glioma cells and C6 tumor-bearing rats. DOTA-Peptide 2 was obtained with 98% purity and efficiently labeled with 177Lu (RCP > 99%). 177Lu-DOTA-Peptide 2 showed a high value of stability in acetate buffer (91.4% at 312 h) and human plasma (>97% at 24 h). Radioconjugate exhibited low internalization (<5%) and high affinity for somatostatin receptors (Kd = 12.06 nM, Bmax = 0.20 pmol/106 cells) using saturation binding assay. Effective tumor uptake of 7.3% ID/g (percentage of injected dose per gram of tumor) at 4 h post-injection and fast clearance of radiopeptide from blood and other organs led to a high tumor-to-normal organ ratios. SPECT/CT imaging clearly showed the activity localization in tumor. The favorable antagonistic properties of 177Lu-DOTA-Peptide 2 on the somatostatin receptors can make it a suitable candidate for peptide receptor radionuclide therapy (PRRT). In the future study, the therapeutic application of this radiopeptide will be evaluated.

Synthesis and Antitumor Activity of Conjugates Based on the Phe-D-Trp-Lys-Thr Peptide Fragment of Somatostatin

New somatostatin analogs containing the fragments of adamantane, coumarin, tetrahydrocarbazole, and palmitic acid of the general formula R-Phe-D-Trp-Lys(Boc)-Thr-OMe have been synthesized. The structure of the conjugates combines a peptide fragment, which has affinity for somatostatin receptors (sstr), and a nonpeptide fragment, which potentially possesses antitumor activity. Presumably, the compounds synthesized are the agonists of sstr. The amide bond between the peptide and nonpeptide fragments has been formed using the carbodiimide method and the method of activated esters. The structures of the conjugates have been confirmed by mass spectrometry (ESI+) and 1H NMR spectroscopy. The antitumor activity of the conjugates has been examined by the MTT test on human lung adenocarcinoma (A549), human prostate adenocarcinoma (PC3), human colon cancer (HCT-116), human breast cancer (MCF7), and acute human T‑cell leukemia (Jurkat) cell lines. Compounds selectively inhibiting the growth of A549 cells have been identified.

Impact of Tumor Burden on Quantitative [68Ga] DOTATOC Biodistribution

PurposeAs has been previously reported, the somatostatin receptor (SSTR) imaging agent [68Ga]-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotate ([68Ga]DOTATATE) demonstrates lower uptake in normal organs in patients with a high neuroendocrine tumor (NET) burden. Given the higher SSTR affinity of [68Ga] DOTATATE, we aimed to quantitatively investigate the biodistribution of [68Ga]-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotide ([68Ga]DOTATOC) to determine a potential correlation between uptake in normal organs and NET burden.ProceduresOf the 44 included patients, 36/44 (82 %) patients demonstrated suspicious radiotracer uptake on [68Ga] DOTATOC positron emission tomography (PET)/X-ray computed tomography (CT). Volumes of interest (VOIs) were defined for tumor lesions and normal organs (spleen, liver, kidneys, adrenals). Mean body weight corrected standardized uptake value (SUVmean) for normal organs was assessed and was used to calculate the corresponding mean specific activity uptake (Upt: fraction of injected activity per kg of tissue). For the entire tumor burden, SUVmean, maximum standardized uptake value (SUVmax), and the total mass (TBM) was calculated and the decay corrected tumor fractional uptake (TBU) was assessed. A Spearman’s rank correlation coefficient was used to determine the correlations between normal organ uptake and tumor burden.ResultsThe median SUVmean was 18.7 for the spleen (kidneys, 9.2; adrenals, 6.8; liver, 5.6). For tumor burden, the median values were SUVmean 6.9, SUVmax 35.5, TBM 42.6 g, and TBU 1.2 %. With increasing volume of distribution, represented by lean body mass and body surface area (BSA), Upt decreased in kidneys, liver, and adrenal glands and SUVmean increased in the spleen. Correlation improved only for both kidneys and adrenals when the influence of the tumor uptake on the activity available for organ uptake was taken into account by the factor 1/(1-TBU). TBU was neither predictive for SUVmean nor for Upt in any of the organs. The distribution of organ Upt vs. BSA/(1-TBU) were not different for patients with minor TBU (<3 %) vs. higher TBU (>7 %), indicating that the correlations observed in the present study are explainable by the body size effect. High tumor mass and uptake mitigated against G1 NET.ConclusionsThere is no significant impact on normal organ biodistribution with increasing tumor burden on [68Ga] DOTATOC PET/CT. Potential implications include increased normal organ dose with [177Lu-DOTA]0-D-Phe1-Tyr3-Octreotide and decreased absolute lesion detection with [68Ga] DOTATOC in high NET burden.

Abstract LB-061: Systematic, network-based, comparative analysis of differential mechanisms of action of lanreotide and octreotide in neuroendocrine tumor derived cell lines

Abstract Lanreotide and octreotide are somatostatin receptor (SSTR) agonists thought to exhibit overlapping Mechanism of Action (MoA), despite small differences in their SSTRs affinity and differential PK response in vivo [1]. To systematically and quantitatively assess both concentration- and time-dependent MoA differences at the molecular level —by characterizing the full protein repertoire that mediates the compound's pharmacological effects— we assessed the protein-specific activity of lanreotide and octreotide in two gastroenteropancreatic neuroendocrine tumor (GEP-NET) derived cell lines (H-STS and KRJ-1). We performed RNASeq profiling at 4 different time points (24h -96h), following cell perturbation at 4 non-toxic doses (2 nM - 1 μM). RNASeq profiles were used to assess compound activity on 6,276 regulatory proteins, using VIPER, an experimentally-validated algorithm to infer protein activity based on the expression of its targets [2]. The analysis was performed using a GEP-NET-specific regulatory model inferred from a collection of 212 primary and metastatic human samples. Concentrations above the EC50 of the drugs were selected to (a) assess potential off-target effects and (b) discount potential effects from differential compound degradation. Confirming the robust nature of our approach, short-term (24h and 48h) transcriptional and protein activity profiles, following compound perturbation, were virtually identical across both cell lines and drug concentration (FET p-value &amp;lt; 10-12). However, the sensitivity and reproducibility of VIPER analysis, which represents the foundation for two NYS CLIA approved tests, allowed identification of 367 proteins affected differentially by these drugs (FDR &amp;lt; 0.05), which were enriched in cancer-relevant functional categories, including apoptosis, immune response, cell differentiation, cell proliferation and DNA-repair (FDR &amp;lt; 10-5). Most critically, while lanreotide-modulated proteins were virtually unchanged over time (from 24h to 96h, p &amp;lt; 0.05), the effect of octreotide on the same proteins was transient and virtually lost at 72h. This discrepancy cannot be attributed to concentration-related effects, since it was manifested identically across all tested concentrations. This work constitutes the first systematic, genome-wide characterization of the MoA of two clinically relevant SSTR agonists, showing both common as well as differentially affected pathways. Two key elements which may account for differential clinical response in patients emerged from the analysis: (1) Differences in the repertoire of affected proteins (MoA) by each compound, and (2) different response kinetics, with sustained lanreotide response from 24h to 96h vs. transient octreotide response with subsequent adaptive cell response after 48h. [1] Enzler et.al (2017) Sem. Oncol. 44:141.[2] Alvarez et.al (2016) Nat. Genet. 48:838. Citation Format: Mariano J. Alvarez, Gideon Bosker, Roswitha Pfragner, Mark Kidd, Irvin Modlin, Andrea Califano. Systematic, network-based, comparative analysis of differential mechanisms of action of lanreotide and octreotide in neuroendocrine tumor derived cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-061.

Synthesis and evaluation of a 99mTc tricarbonyl-labeled somatostatin receptor-targeting antagonist peptide for imaging of neuroendocrine tumors

IntroductionA somatostatin receptor (SSTR)-targeting antagonist peptide (sst2-ANT) was radiolabeled with 99mTc tricarbonyl via a tridentate [N,S,N]-type ligand (L) to develop a radiodiagnostic agent, 99mTcL-sst2-ANT, for imaging of SSTR-expressing neuroendocrine tumors. MethodsReceptor affinity was assessed in vitro with the nonradioactive analogue, ReL-sst2-ANT, via a challenge experiment in AR42J cells with 125I–SS-14 as the competing radioligand. Preparation of 99mTcL-sst2-ANT was achieved via reaction of [99mTc(CO)3(H2O)3]+ with L-sst2-ANT. To test the stability of the radiolabeled complex, challenge experiments were performed in phosphate-buffered saline solutions containing cysteine or histidine and also in mouse serum. Biodistribution and micro-SPECT/CT imaging studies were performed in AR42J tumor-bearing female ICR SCID mice. ResultsThe half maximal inhibitory concentration (IC50 value) of ReL-sst2-ANT in AR42J cells was 15nM. Preparation of 99mTcL-sst2-ANT was achieved with ≥97% radiochemical yield (RCY) and was verified by HPLC co-elution with the ReL-sst2-ANT analogue. The radiolabeled complex remained intact for up to 24h in high concentration solutions of cysteine and histidine at 37°C. Furthermore, the radiotracer was 90% stable for 1h at 37°C in mouse serum. Micro-SPECT/CT images showed clear uptake in tumors and were supported by the biodistribution data, in which the 3.2% ID/g tumor uptake at 4h was significantly blocked by co-administration of nonradioactive SS-14. ConclusionsA [99mTc(CO)3(N,S,N)]+ chelate was employed for radiolabeling of an SSTR-targeting antagonist peptide. Synthesis of 99mTcL-sst2-ANT was achieved in high RCY, and the resulting complex displayed high in vitro stability. Somatostatin receptor affinity was retained in both cells and in tumor-bearing mice, where the complex successfully targeted SSTR-positive tumors via a receptor-mediated process.Advances in Knowledge and Implications for Patient Care.This first 99mTc-tricarbonyl-labeled SSTR antagonist peptide showed promising in vivo tumor targeting in mice. Future studies may lead to translation of a similar design into the clinic.

Triple targeting of Auger emitters using octreotate conjugated to a DNA-binding ligand and a nuclear localizing signal

Purpose: We investigated the effect of incorporation of a nuclear localization signal (NLS) into a conjugate comprising the DNA binding ligand para-iodoHoechst (PIH) and octreotate on its DNA binding and affinity to the somatostatin receptor (SSTR). Confirmation of these properties would support development of similar conjugates labelled with Auger emitters for their potential in Auger endoradiotherapy. Materials and methods: We synthesized conjugates of PIH and octreotate (PO) or PIH and NLS (PN) and a conjugate comprising PIH, NLS and octreotate (PNO). DNA-binding characteristics of PIH and conjugates were assessed using synthetic DNA oligonucleotides employing spectrophotometric titration of ligand solutions with DNA. We used membranes from the type 2 SSTR (SSTR2) overexpressing human non-small cell lung cancer cell line A427-7 to investigate the binding affinity of PNO. Results: We demonstrated PN and PNO retain specific high affinity DNA-binding properties observed for PIH, and acquire an additional non-specific binding capacity. No DNA binding was observed for PO. PNO retains its binding affinity for SSTR. Conclusions: The DNA-binding properties of PNO and its affinity for SSTR suggests that it could potentially be used for tumour-specific delivery of PIH labelled with an Auger emitter in SSTR expressing tumours.

Phase I study of pasireotide in combination with FOLFIRI in gastrointestinal malignancies.

e15201 Background: Pasireotide (SOM230) is a somatostatin analog with high binding affinity for somatostatin receptors. It is hypothesized to induce apoptosis by decreasing insulin like growth fact...

PET imaging with 68gallium labelled somatostatin analogues in the evaluation of neuroendocrine tumours (NETs)

Neuroendocrine tumours (NETs) are rare tumours arising from cells of the nervous and endocrine systems. Since the 1990's, the use of somatostatin analogues (SSTa) imaging for NETs evaluation has allowed a better understanding of these neoplasms. Recent 68gallium labelled somatostatin analogues with higher affinity for somatostatin receptors are now available for PET/CT imaging of NETs, leading to new imaging protocols for patient care. Three new analogues (DOTATOC, DOTANOC, DOTATATE) were superior to OctreoScan®, and conventional imaging for lesion detection. In this article, recent publications on the diagnostic and care of gastroenteropancreatic (GEP) tumours, pheochromocytomas/paragangliomas (PPGLs), unknown primary tumours, medullary thyroid carcinomas (MTC), Merkel tumours and Cushing syndrome with ectopic ACTH hypersecretion are reviewed.

New options in the treatment of Cushing&rsquo;s disease: a focus on pasireotide

Cushing's disease is caused by a corticotroph pituitary adenoma secreting adreno- corticotropin and can be fatal in the absence of adequate treatment. Transsphenoidal surgery remains the treatment of choice in almost all cases. However, remission rates are relatively low, and recurrence is usual and can be diagnosed up to decades after the initial diagnosis. Repeat surgery or radiation can be useful in these cases, although both have clear limitations with respect to efficacy and/or side effects. Hence, there is a clear unmet need for an effective medical treatment in patients with recurrent or persistent Cushing's disease. Pasireotide is a novel multireceptor-targeted somatostatin analog with a high affinity for somatostatin receptor (sstr)-1, sstr-2, sstr-3, and sstr-5. Compared with octreotide, pasireotide has an in vitro binding affinity 40-fold higher for sstr-5, which is the major receptor subtype expressed by corticotroph pituitary adenoma. Recent studies have suggested a role for this new multireceptor somatosta- tin analog in Cushing's disease. We review in this article the current data available regarding pharmacokinetics, clinical efficiency, and tolerance of pasireotide in patients with de novo, persistent, or recurrent Cushing's disease, with a special focus on the disturbances of glucose metabolism induced by such a treatment.

Growth hormone granulation pattern and somatostatin receptor subtype 2A correlate with postoperative somatostatin receptor ligand response in acromegaly: a large single center experience

Acromegaly is associated with serious morbidity and mortality, if not well controlled. Approved somatostatin receptor ligands (SRLs) are a mainstay of medical therapy and exhibit preferential affinity for somatostatin receptor (SSTR) subtype 2. Our objective was to assess whether characteristic features of individual growth hormone (GH)-secreting adenomas at diagnosis, correlated with SRL sensitivity, using defined tumor markers. A retrospective review of 86 consecutive acromegaly surgeries (70 patients) performed between January 2006 and December 2011 was undertaken. Patients with any preoperative medical treatment were excluded. Response to SRL therapy was defined as normalization of insulin-like growth factor 1 (IGF1) and random GH < 1.0 ng/dl. Immunohistochemical staining pattern: sparsely granulated, densely granulated, mixed growth hormone-prolactin (GH/PRL) and SSRT2 positivity (+) were correlated with clinicopathologic features, adenoma recurrence, and SRL treatment response. Two-tailed t test, univariate ANOVA, Kruskal-Wallis and bivariate correlation were performed using PAWS 18. The cohort eligible for analysis comprised 59 patients (41 female and 18 male). Based on pre-surgery adenoma imaging dimensions, 81.3% (48) were macroadenomas and average maximum tumor diameter was 18.1 ± 9.9 mm. Patients on SRLs were followed for 13.4 ± 15.8 (mean ± SD) months. Sparsely granulated adenomas were significantly larger at diagnosis, exhibited lower SSTR2 positivity and had a lower rate of biochemical normalization to SRLs. Densely granulated adenomas were highly responsive to SRLs. Overall, patients with SSTR2A+ adenomas responded more favorably to SRL treatment than those with SSTR2A- adenomas. Eighty-one percent of patients with SSTR2A+ adenomas were biochemically controlled (both GH and IGF1) on SRL treatment, e.g. a much higher normalization rate than that reported in the unselected acromegaly population (20-30%). Detailed knowledge of adenoma GH granularity and the immunohistochemical SSTR2A+ status is a predictor of SRL response. These immunoreactive markers should be assessed routinely on surgical specimens to assess subsequent SRL responsiveness and potential need for adjunctive therapy after surgery.

Unexpected Sensitivity of sst2 Antagonists to N-Terminal Radiometal Modifications

Chelated somatostatin agonists have been shown to be sensitive to N-terminal radiometal modifications, with Ga-DOTA agonists having significantly higher binding affinity than their Lu-, In-, and Y-DOTA correlates. Recently, somatostatin antagonists have been successfully developed as alternative tracers to agonists. The aim of this study was to evaluate whether chelated somatostatin antagonists are also sensitive to radiometal modifications and how. We have synthesized 3 different somatostatin antagonists, DOTA-p-NO(2)-Phe-c[D-Cys-Tyr-D-Aph(Cbm)-Lys-Thr-Cys]-D-Tyr-NH(2), DOTA-Cpa-c[D-Cys-Aph(Hor)-D-Aph(Cbm)-Lys-Thr-Cys]-D-Tyr-NH(2) (DOTA-JR11), and DOTA-p-Cl-Phe-c[D-Cys-Tyr-D-Aph(Cbm)-Lys-Thr-Cys]-D-Tyr-NH(2), and added various radiometals including In(III), Y(III), Lu(III), Cu(II), and Ga(III). We also replaced DOTA with 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) and added Ga(III). The binding affinity of somatostatin receptors 1 through 5 was evaluated in all cases. In all 3 resulting antagonists, the Ga-DOTA analogs were the lowest-affinity radioligands, with a somatostatin receptor 2 binding affinity up to 60 times lower than the respective Y-DOTA, Lu-DOTA, or In-DOTA compounds. Interestingly, however, substitution of DOTA by the NODAGA chelator was able to increase massively its binding affinity in contrast to the Ga-DOTA analog. The 3 NODAGA analogs are antagonists in functional tests. In vivo biodistribution studies comparing (68)Ga-DOTATATE agonist with (68)Ga-DOTA-JR11 and (68)Ga-NODAGA-JR11 showed not only that the JR11 antagonist radioligands were superior to the agonist ligands but also that (68)Ga-NODAGA-JR11 was the tracer of choice and preferable to (68)Ga-DOTA-JR11 in transplantable HEK293-hsst(2) tumors in mice. One may therefore generalize that somatostatin receptor 2 antagonists are sensitive to radiometal modifications and may preferably be coupled with a (68)Ga-NODAGA chelator-radiometal complex.

Tumour targeting of Auger emitters using DNA ligands conjugated to octreotate

Purpose: The objective of the study was to conjugate the DNA binding ligand para-[125I]-iodoHoechst to octreotate, and to explore the tumour targeting potential of this conjugate in the octreotate-somatostatin receptor system.Methods: We synthesized a Hoechst analogue containing a tri-butylstannyl group in the para position of phenyl ring, conjugated it to the N-terminal amino group of octreotate and prepared 125I-labelled conjugate by iododestannylation. We used the somatostatin receptor (SSTR2) over-expressing cell line A427-7 derived from its parent A427 human non-small cell lung carcinoma cell line to investigate SSTR2 affinity and receptor-mediated internalisation of the conjugate, and the mouse A427-7 tumour xenograft model for in vivo biodistribution studies of the radiolabelled conjugate.Results: A method was developed for convenient preparation of high specific activity radioiodinated conjugate which retains affinity for somatostatin receptors and is internalised into A427-7 SSTR2 over-expressing cells via a receptor-mediated mechanism. The conjugate accumulates in mouse A427-7 tumour xenografts following intravenous administration.Conclusions: A dual targeting strategy for Auger endoradiotherapy, in which a DNA ligand is used to target the Auger decay to DNA, in conjunction with receptor-mediated targeting to specific receptors, using a labelled DNA ligand/peptide conjugate, has been demonstrated for the octreotate-somatostatin receptor system.

The diagnostic role of 68Ga-DOTATATE PET/CT in the detection of neuroendocrine tumours

Positron emission tomography (PET) combined with computer tomography (CT) using (68)Ga-DOTATATE is a promising method for the evaluation of patients with recognised or suspected neuroendocrine tumours (NET). The aim of this study was to assess the diagnostic value of (68)Ga-DOTATATE PET/CT in the visualisation of the expression of somatostatin receptors (SSTR) and identification of new lesions. Between December 2009 and January 2011 ninety-seven patients with confirmed (88 cases) or suspected (9 cases) NET underwent (68)Ga DOTATATE PET/CT. The primary, confirmed or suspected, NET localizations were: GEP tumours--71 patients; medullary thyroid carcinoma--4 patients; cancer of an unknown primary--14 patients; and NET in other localisations--8 patients. PET/CT acquisitions were performed using standard techniques, 45 to 60 minutes after the intravenous injection of 111-185 MBq (68)Ga-DOTATATE. (68)Ga-DOTATATE PET/CT detected the presence of lesions demonstrating the somatostatin receptor affinity in 50 of the 97 patients (51.5%) and was negative in 47 patients (48.5%). Among 14 patients with metastatic unknown primary cancer, in 5 patients (45.5%) the primary tumour site was identified, and in 4 patients with medullary thyroid cancer distant metastases with SSTR expression were localized in only one patient. Our findings confirm the diagnostic role of (68)Ga-DOTATATE PET/CT as an accurate method of identifying primary tumours and distant metastases. It provides information on tumour cell receptors status, which has a significant bearing on planning target radionuclide therapy. Overall, (68)Ga-DOTATATE PET/CT can be used in staging, re-staging, and in regular follow up of oncology patients.

Role of somatostatin receptor ligands in the treatment of acromegaly – review of literature

Acromegaly is a rare disease with typical clinical manifestations. Untreated acromegaly carries a 2-4-fold increase in mortality in long-term outcome. The goal of treatment is double, including biochemical control of the disease (normalization of serum IGF1 levels compared to age and gender matched controls, GH levels below 1 ng/ml after oral glucose load, or random GH below 2.5 ng/ml) and control of the tumor mass. The therapeutic modalities currently available for the treatment of acromegaly are: surgery, medical therapy, radiation therapy and their combinations. The cornerstones of medical therapy in acromegaly are the somatostatin receptor ligands due to their effectiveness in controlling GH excess in 60-70 % of patients and their beneficial effects on tumor volume. Somatostatin analogues have an established role as adjuvant therapy after non-curative surgery, and evidence suggests their use as primary treatment for selected patients. The long-term use of somatostatin receptor ligands is safe and they are well tolerated. Future medical therapy consists of pasireotide, a novel, universal somatostatin receptor agonist, and a new class of drugs named dopastatins. The latter so-called chimeric molecules have strong affinity for somatostatin receptors and dopamine-2 receptors, resulting in a more effective blocking of GH secretion, according to preliminary data. The authors of this paper review the current medical therapy of acromegaly, focusing on the role of somatostatin receptor ligands. Orv. Hetil., 2011, 152, 715–721.

Labeling, stability and biodistribution studies of 99mTc-cyclized Tyr3-octreotate derivatives

To probe the interplay between radiotracer stability and somatostatin receptor affinity, Tyr(3)-octreotate and six variations of its peptide sequence, for which the Re-cyclized products were previously reported, were radiolabeled with (99m)Tc and investigated for their in vitro stability. Radiolabeling of the peptides was effected by ligand exchange from (99m)Tc-glucoheptonate, and the desired products were purified by radio-RP-HPLC. The in vitro stability in phosphate buffered saline, mouse serum and cysteine solutions at physiological temperature and pH for all seven (99m)Tc-cyclized peptides was determined by radio-RP-HPLC and radio-TLC. Normal CF-1 mouse biodistribution studies were performed for three of the (99m)Tc-cyclized peptides. Based on the fully characterized Re-cyclized peptide analogues, four (99m)Tc-coordination motifs were proposed for the (99m)Tc-cyclized peptides. Technetium-99m-cyclized Tyr(3)-octreotate derivatives with N(2)S(2) metal coordination modes and large metal ring sizes were susceptible to oxidation and loss of (99m)Tc in the form of (99m)TcO(4)(-), as evidenced by their instability in the various solutions under physiological conditions (15-58% intact at 24 h). As anticipated, the addition of a third cysteine to the sequence stabilized the (99m)Tc metal coordination, and peptides with NS(3) coordination modes remained >85% intact out to 24 h. No significant differences were observed in the biodistribution studies performed with three peptides of varying stabilities. Improvements in stability were not sufficient to outweigh the low somatostatin receptor affinity for the peptides in this study. Further improvements in the peptide sequence and/or metal coordination are needed to result in a radiodiagnostic/radiotherapeutic pair for targeting the somatostatin receptor.

More on Clinical Renal Genetics

Massive polycystic liver may be the source of severe discomfort, early satiety, pain, dyspnea, and finally denutrition. This is in part due to the increase with age in the number of hepatic cysts, but also because the individual cyst volume grows from 0.25 to 22.8 ml over 20 years. Polycystic liver is found in two inherited disorders—autosomal dominant polycystic kidney disease (ADPKD) and autosomal dominant polycystic liver disease (PCLD), an infrequent disorder in which no kidney cysts are detected caused by mutations in PKRCSH or SEC63 genes. Studies in ADPKD have indicated that total liver cyst volume and the prevalence of massive polycystic liver are greater in women than in men. Liver cysts arise from cholangiocytes. Secretin is a potent stimulator of adenylate cyclase and thus of cAMP generation. cAMP acts by two major mechanisms: increased electrolyte and water secretion and stimulation of cholangiocyte proliferation. Conversely, somatostatin inhibits cAMP production and thus fluid secretion and proliferation. Additional experimental and clinical data supported the project of initiating a clinical trial of somatostatin analogues on liver cyst progression. Octreotide, a somatostatin analogue, prevented outgrowth of liver and kidney cysts in polycystic kidney (PCK) rats. In contrast, antagonists of the V2 vasopressin receptor have no effect on liver cysts that do not express this receptor, whereas they prevent or slow the progression of renal cysts in various experimental models. In two patients with polycystic livers, a 3- to 6-month treatment with somatostatin analogues led to impressive reductions in liver volume (1). Finally, a randomized, placebo-controlled trial in ADPKD patients using slow-release octreotide (40 mg) showed that kidney volume increase could be reduced by 60% at 6 months compared with placebo but there was an ongoing increase of kidney volume—2.2% in the octreotide group versus 5.9% in the placebo group (2). Van Keimpema et al. (1) designed a multicenter, randomized, double-blind, placebo-controlled trial to evaluate the effects of the long-acting somatostatin analogue, lanreotide autosolution (120 mg), or placebo administered subcutaneously every 28 days for 24 weeks in patients with polycystic liver due to ADPKD (32 patients) or PLCD (22 patients). The high percentage of PLCD is explained by the fact that the initiators of and participants in this trial were gastroenterologists and hepatologists. The primary end point was change in liver volume measured on computed tomography (CT) scan at baseline and after 24 weeks of treatment. Health-related quality of life was a secondary end point. Of 113 consecutive patients assessed during the study period, 54 were included in the trial. Relatively more PCLD patients (68%) than ADPKD patients (38%) received lanreotide. The mean liver volume decreased from 4606 to 4471 ml (i.e., an average reduction of 2.9%) whereas there was an average increase of 1.6% in patients receiving lanreotide and in those in the placebo group, respectively. Eighty-five percent of patients on lanreotide showed a decrease of liver volume, compared with 27% of those receiving placebo. Larger livers had proportionally more volume reduction than smaller livers. In the subgroup of patients with ADPKD, mean kidney volume decreased by 1.5% with lanreotide, whereas it increased in the placebo group (P = 0.02). Current health perception improved in lanreotide-treated patients. The most common adverse effect of lanreotide consisted of loose, pale, and fatty stools (19 patients), which were relieved by pancreatic enzymes. Gamma-glutamyl transferase levels increased in the lanreotide group, possibly reflecting increased cyst epithelium degeneration. In this trial, no correlation was found between lanreotide serum levels and response to treatment. Little is known about the optimal dosage of somatostatin analogues. The authors chose for the highest licensed dose of lanreotide. Lanreotide at 120 mg is equivalent to octreotide at 60 mg. However, somatostatin receptor affinity of octreotide is higher compared with that of lanreotide. The results of this trial are very encouraging. Aspiration and sclerosis, laparoscopic fenestration, or hepatic resection have led to disappointing or limited results in women with massive polycystic liver. Combined liver and kidney transplantation has been mandatory in some of them. Noninvasive effective therapy is eagerly awaited. Another trial with a somatostatin analogue is in progress.

Lanreotide for the treatment of acromegaly

Lanreotide is an eight-amino acid peptide, which is an analog of the native somatostatin peptide, physiological inhibitor of growth hormone (GH). The drug shows high binding affinity for somatostatin receptors, SSTR2 and SSTR5, which is the primary mechanism considered to be responsible for decreasing GH secretion and GH cell proliferation in acromegaly. Two different formulations of lanreotide are currently available: lanreotide slow release, which requires intramuscular injection every 7-14 days, and lanreotide autogel, which requires deep subcutaneous injection every 4-8 weeks. Several studies have been published to date on the use of lanreotide in acromegaly. Antisecretory efficacy has been reported in 35%-70% of cases; this huge variability is probably explained by different indications (eg, primary or adjunctive postsurgical treatment), or the fact that some studies were based on patients known to be responders to somatostatin analogs. As a primary treatment, antisecretory efficacy was very similar, confirming the possibility of lanreotide as an option in cases of unsuccessful surgery, contraindication, or surgery refusal. Lanreotide also has antitumoral effects as it induces a decrease in tumor volume of [Symbol: see text]25% in 30%-70% of patients. This could be beneficial before transsphenoidal surgery, as a pretreatment, to decrease tumor volume and ease surgery; however, to date, advantages in terms of final remission or uncured status remain a matter of debate. Side effects are rare; the most frequent being gastrointestinal discomfort and increased risk of gallstone formation, and glucose metabolism modifications. Comparison with the other somatostatin analog, octreotide, tends to show identical levels of efficacy between both drugs. Lanreotide thus seems to be an effective treatment in acromegaly. To date, however, lanreotide is still considered as only suspending GH secretion, thus requiring prolonged and costly treatment.