Octreotide attenuates intestinal barrier damage by maintaining basal autophagy in Caco2 cells

The intestinal mucosal barrier is of great importance for maintaining the stability of the internal environment, which is closely related to the occurrence and development of intestinal inflammation. Octreotide (OCT) has potential applicable clinical value for treating intestinal injury according to previous studies, but the underlying molecular mechanisms have remained elusive. This article is based on a cell model of inflammation induced by lipopolysaccharide (LPS), aiming to explore the effects of OCT in protecting intestinal mucosal barrier function. A Cell Counting Kit‑8 assay was used to determine cell viability and evaluate the effectiveness of OCT. Gene silencing technology was used to reveal the mediated effect of somatostatin receptor 2 (SSTR2). The changes in intestinal permeability were detected through trans‑epithelial electrical resistance and fluorescein isothiocyanate‑dextran 4 experiments, and the alterations in tight junction proteins were detected using immunoblotting and reverse transcription fluorescence‑quantitative PCR technology. Autophagosomes were observed by electron microscopy and the dynamic changes of the autophagy process were characterized by light chain (LC)3‑II/LC3‑I conversion and autophagic flow. The results indicated that SSTR2‑dependent OCT can prevent the decrease in cell activity. After LPS treatment, the permeability of monolayer cells decreased and intercellular tight junctions were disrupted, resulting in a decrease in tight junction protein zona occludens 1 in cells. The level of autophagy‑related protein LC3 was altered to varying degrees at different times. These abnormal changes gradually returned to normal levels after the combined application of LPS and SSTR2‑dependent OCT, confirming the role of OCT in protecting intestinal barrier function. These experimental results suggest that OCT maintains basal autophagy and cell activity mediated by SSTR2 in intestinal epithelial cells, thereby preventing the intestinal barrier dysfunction in inflammation injury.

From biology to clinical practice: antiproliferative effects of somatostatin analogs in neuroendocrine neoplasms

Somatostatin analogs (SSA), specifically octreotide and lanreotide, have demonstrated antiproliferative effects in patients with neuroendocrine tumors (NET), a group of rare malignancies of diverse origin and presentation. A prominent feature of NET cells is the expression of G protein-coupled receptors called somatostatin receptors (SSTR). Although these SSTR are not uniformly present in NET, they can be instrumental in the diagnosis and treatment of NET. Apart from their application in nuclear imaging and radionuclide therapy, SSA have proven invaluable in the treatment of hormonal syndromes associated with certain NET (antisecretory effects of SSA), but it took more than two decades to convincingly demonstrate the antiproliferative effects of SSA in metastatic NET with the two pivotal studies PROMID and CLARINET. The current review summarizes three decades of SSA treatment and provides an overview of the clinical trial landscape for SSA monotherapy and combination therapy, including clinical implications and quality of life aspects, as well as ongoing fields of research.

Somatostatin receptors and the associated intracellular machinery: the two sides of the coin

Somatostatin receptors (SSTs) are widely expressed in pituitary tumors and neuroendocrine neoplasms (NENs) of different origins, i.e. the gastrointestinal tract and the thorax (lungs and thymus), thus representing a well-established target for medical treatment with SST ligands (SRLs). However, the response to SRLs is highly heterogeneous between tumors. Two main factors can contribute to this variability: (i) the differential SST expression among tumor types and (ii) the differential expression/modulation of the SST-related intracellular machinery. In this literature review, we provide an overview of available data on the variable expression of SSTs in pituitary tumors and NENs, together with the resulting clinical implications. Moreover, we aim to describe the complex intracellular machinery involved in SST signaling and trafficking. Particularly, we will focus on β-arrestins and describe their role in receptor internalization and recycling, as well as the various functions of these scaffold molecules in tumor pathogenesis and progression. This review highlights the interplay between membrane receptors and intracellular machinery, together with its role in determining the clinical behavior of the tumor and the response to treatment in patients with pituitary tumors or NENs.

Case Report: Opposite Tumoral and Hormonal Responses to Low-dose Pasireotide in Cushing's Disease

BACKGROUND

Pasireotide is a multireceptor somatostatin analogue approved for the treatment of patients with Cushing's disease (CD) who are ineligible or poor candidates for pituitary surgery. Here we present a patient with severe recurrent CD who was treated with pasiretide and showed opposite results between hormonal levels and pituitary tumour size.

CASE PRESENTATION

A 54-year-old woman was diagnosed with CD, a first surgical transsphenoidal procedure was performed at the time of diagnosis, and the disease recurred seven years later. She underwent a second transsphenoidal surgery, but despite apparent complete removal of the adenoma, the hypercortisolism worsened. Magnetic resonance imaging showed a tiny remnant of the adenoma adjacent to the cavernous sinus, and ketoconazole was started at a dose of 800 mg/day. Due to the persistence of pathological urinary free cortisol levels, 600 μg bid pasireotide was added. The combination therapy induced first normalisation of urinary free cortisol and later hypoadrenalism, so that ketoconazole was discontinued and pasireotide was maintained. A marked clinical improvement was achieved with pasireotide. Adrenal insufficiency persisted despite progressive tapering of the pasireotide dose to 150 mg once daily. Pituitary magnetic resonance imaging performed at 12 and 24 months during low-dose pasireotide treatment showed a few millimetres increase of the remnant.

CONCLUSIONS

This report suggests that CD Pas induces an opposite effect between hormonal profile and increase of pituitary tumor size. This peculiar phenomenon may be a consequence of the unusually low doses of pasireotide needed to control hormonal hypersecretion.

New horizon of radiopharmaceuticals in management of neuroendocrine tumors

Neuroendocrine neoplasms are rare and heterogenous group of tumors with varying degrees of clinical presentations and involvement of multiple organ systems in the body. In the modern clinical practice somatostatin receptor molecular imaging and targeted radioligand therapy plays a vital role in the diagnosis and management of the disease. Several new and promising radiotracers for NET imaging and theranostics, belonging to various groups and classes are being studied and investigated. This exponential growth of radiotracers poses concerns about the indication, clinical benefit, and safety profile of the agents. We discuss the basis behind these radiotracers clinical use, receptor targeting and intra and inter tumor heterogeneity. Furthermore, role of dual tracer imaging, combination therapy and potential applications of dosimetry in predicting treatment outcome and safety profile is reviewed. Individualized precision medicine with better tumor characterization, maximum therapeutic benefit and minimum toxicity is the way forward for future medicine.

Imaging surveillance in multiple endocrine neoplasia type 1: Ten years of experience with somatostatin receptor positron emission tomography

Guidelines for multiple endocrine neoplasia type 1 (MEN1) recommend intensive imaging surveillance without specifying a superior regimen, including the role of somatostatin receptor imaging (SRI) with positron emission tomography (PET). The primary outcomes were to: (1) Assess change in treatment of duodenal-pancreatic neuroendocrine neoplasms (DP-NENs), bronchopulmonary NENs, and thymic tumors attributed to use of SRI PET/computed tomography (CT) and (2) estimate radiation from imaging and risk of cancer death attributed to imaging radiation. This was a retrospective single center study, including all MEN1 patients, who had had at least one SRI PET/CT. A total of 60 patients, median age 42 (range 21-54) years, median follow-up 6 (range 1-10) years were included. Of 470 cross sectional scans (MRI, CT, SRI PET/CT), 209 were SRI PET/CT. The additional information from SRI PET had implications in 1/14 surgical interventions and 2/12 medical interventions. The estimated median radiation dose per patient was 104 (range 51-468) mSv of which PET contributed with 13 (range 5-55) mSv and CT with 91 mSv (range 46-413 mSv), corresponding to an estimated increased median risk of cancer death of 0.5% during 6 years follow-up. SRI PET had a significant impact on 3/26 decisions to intervene in 60 MEN1 patients followed for a median of 6 years with SRI PET/CT as the most frequently used modality. The surveillance program showed a high radiation dose. Multi-modality imaging strategies designed to minimize radiation exposure should be considered. Based on our findings, SRI-PET combined with CT cannot be recommended for routine surveillance in MEN1 patients.

Improving Overall Survival and Quality of Life in Patients with Prostate Cancer and Neuroendocrine Tumors Using 177Lu-iPSMA and 177Lu-DOTATOC: Experience after 905 Treatment Doses

¹⁷⁷Lu-iPSMA is a novel radioligand developed at ININ-Mexico with a high affinity for the PSMA protein heavily expressed in cancer cells of approximately 95% of patients with metastatic castration-resistant prostate cancer (mCRPC). ¹⁷⁷Lu-DOTATOC is a patent-free radioligand, molecularly recognized by somatostatin receptors (SSTR-2) overexpressed in cancer cells of about 80% of patients with metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NET). This translational research aimed to determine the efficacy and safety of ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC developed as GMP pharmaceutical formulations for treating progressive and advanced mCRPC and NET. One hundred and forty-five patients with mCRPC and one hundred and eighty-seven subjects with progressive NET (83% GEP-NET and 17% other NET), treated with ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC, respectively, were evaluated. Patients received a mean dose of 7.4 GBq per administration of ¹⁷⁷Lu-iPSMA (range 1-5 administrations; 394 treatment doses) or ¹⁷⁷Lu-DOTATOC (range 2-8 administrations; 511 treatment doses) at intervals of 1.5-2.5 months. Efficacy was assessed by SPECT/CT or PET/CT. Results were stratified by primary tumor origin and number of doses administered. Patients with mCRPC showed overall survival (OS) of 21.7 months with decreased radiotracer tumor uptake (SUV) and PSA level in 80% and 73% of patients, respectively. In addition, a significant reduction in pain (numerical scale from 10-7 to 3-1) was observed in 88% of patients with bone metastases between one and two weeks after the second injection. In the GEP-NET population, the median progression-free survival was 34.7 months, with an OS of >44.2 months. The treatments were well tolerated. Only ten patients experienced grade ≥ 3 myelosuppression (3% of all patients). The observed safety profiles and favorable therapeutic responses demonstrated the potential of ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC to improve overall survival and quality of life in patients with progressive and advanced mCRPC and NET.

Diagnosis, Management and Theragnostic Approach of Gastro-Entero-Pancreatic Neuroendocrine Neoplasms

Gastro-entero-pancreatic neuroendocrine neoplasms (GEP-NENs) constitute an ideal target for radiolabeled somatostatin analogs. The theragnostic approach is able to combine diagnosis and therapy by the identification of a molecular target that can be diagnosed and treated with the same radiolabeled compound. During the last years, advances in functional imaging with the introduction of somatostatin analogs and peptide receptor radionuclide therapy, have improved the diagnosis and treatment of GEP-NENs. Moreover, PET/CT imaging with ¹⁸F-FDG represents a complementary tool for prognostic evaluation of patients with GEP-NENs. In the field of personalized medicine, the theragnostic approach has emerged as a promising tool in diagnosis and management of patients with GEP-NENs. The aim of this review is to summarize the current evidence on diagnosis and management of patients with GEP-NENs, focusing on the theragnostic approach.

Immunohistochemical somatostatin receptor expression in insulinomas

Insulinomas are rare pancreatic neuroendocrine tumours. Most patients can be cured with surgery, but patients with a metastatic disease show impaired survival. The aim of this study was to evaluate somatostatin receptor (SSTR) 1-5 expression in insulinomas and to correlate the expression profile with clinicopathological variables and with patient outcome. This retrospective study involved 52 insulinoma patients. After histological re-evaluation, formalin-fixed paraffin-embedded tissue samples were processed into tissue microarrays and stained immunohistochemically with monoclonal SSTR1-5 antibodies. All the 52 tumours (49 non-metastatic, 3 metastatic) expressed at least one SSTR subtype. SSTR2 was expressed most frequently (71%), followed by SSTR3 (33%), SSTR1 (27%), SSTR5 (6%) and SSTR4 (0%). SSTR3 expression was associated with a larger tumour size (median diameter 19 mm vs. 13 mm, p = 0.043), and SSTR3 and SSTR5 expression were associated with impaired overall survival [HR 3.532 (95% CI 1.106-11,277), p = 0.033, and HR 6.805 (95% CI 1.364-33.955), p = 0.019 respectively]. Most insulinomas express SSTR2, which may be utilized in diagnostic imaging, and in planning individualized treatment strategies for insulinoma patients. Further studies are needed to clarify the association between SSTR profile and overall survival.

Standardized Uptake Values on SPECT/CT: A Promising Alternative Tool for Treatment Evaluation and Prognosis of Metastatic Neuroendocrine Tumours

(1) Background: The aim of our study was to assess the feasibility of 99mTcEDDA/HYNIC-TOC SPECT/CT quantitative analysis in evaluating treatment response and disease progression in patients with NETs. (2) Methods: This prospective monocentric study evaluated 35 SPECT/CT examinations performed on 14 patients with neuroendocrine tumours who underwent a baseline and at least one follow-up 99mTcEDDA/HYNIC-TOC scan as part of their clinical management. The examination protocol included a whole-body scan acquired 2 h after the radiotracer’s administration, with the SPECT/CT performed 4 h post-injection. Images were analyzed by two experienced physicians and patients were classified into response categories based on their changes in SUV values. (3) Results: We evaluated 14 baseline studies and 21 follow-up scans, accounting for 123 lesions. A statistically positive correlation has been found between the SUVmax and SUVpeak values in tumoral lesions (p < 0.05). No correlation has been found between the SUV values and the ki67 proliferation index. Finally, 64.29% patients were classified as SD at the end of the study, with only 14.29% of patients exhibiting PD and 21.43% patients with PR. (4) Conclusions: The quantitative analysis of 99mTcEDDA/HYNIC-TOC SPECT/CT data in patients with neuroendocrine tumours could represent an alternative to 68Ga-DOTA-peptides PET/CT for the monitoring and prognosis of NETs.

Validation of the HPLC Analytical Method for the Determination of Chemical and Radiochemical Purity of Ga-68-DOTATATE

Purpose of the Study

Ga-68-DOTA-peptides targeting somatostatin receptors have been assessed as a valuable tool in neuroendocrine tumors imaging using positron emission tomography (PET). A new selective and sensitive high-pressure liquid chromatography (HPLC) method was developed for determining chemical and radiochemical purity of Ga-68-DOTATATE (PET) tracer. The identification of peaks was achieved on a symmetry C18 column 3 μm 120Å (3.0 mm × 150 mm spherical particles) using (A) water + 0.1% trifluoroacetic acid (TFA) and (B) acetonitrile + 0.1% TFA, as the mobile phases at a flow rate of 0.600 mL/min and monitored at 220 nm. The run time was 16 min.

Materials and Methods

The method was validated to fulfill International Conference on Harmonization requirements and EDQM guidelines, and it included specificity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, and precision.

Results

The calibration curve was linear over the concentration range from 0.5 to 3 μg/ml, with a correlation coefficient (r2) equal to 0.999, average coefficient of variation (CV%) 2%, and average bias% did not deviate more than 5% for all concentrations. The LOD and LOQ for DOTATATE were 0.5 and 0.1 μg/mL, respectively. The method was considered precise, obtaining coefficients of variation between 0.22% and 0.52% for intraday and 0.20% and 0.61% for interday precision. Accuracy of method was confirmed with average bias% that did not deviate more than 5% for all concentrations.

Conclusion

All results were acceptable and this confirmed that the method is suitable for its intended use in routine quality control of Ga-68-DOTATATE to guarantee the high quality of the finished product before release.

Second line treatment of acromegaly: Pasireotide or Pegvisomant?

Acromegaly is a chronic disease with an increased mortality in case of persistently active disease. The treatment of acromegaly is mainly based on the surgical resection of the GH secreting pituitary tumor and, in cases with persistent disease, on the medical therapy with first generation somatostatin analogues (first gen-SSAs). Data from national registries, meta-analysis and epidemiology studies showed that 24%-65% of acromegaly patients treated with first gen-SSA did not reach the control of disease, requiring second line therapies, as the second gen-SSAs and the GH receptor antagonist. According to the high efficacy of these treatments and their molecular mechanisms of action, the choice of second line therapies should be personalized. In this review, we summarize the evidence on clinical, molecular and morphological aspects that may predict the response to second line therapies, in order to integrate and translate in the clinical practice for a patient-tailored therapeutic approach.

Diagnostic performance and impact on patient management of [68Ga]Ga-DOTA-TOC PET/CT in colorectal neuroendocrine tumors derived from hindgut

The main purpose of this retrospective study was to determine the diagnostic performance of [68Ga]Ga-DOTA-D-Phe1-Try3-octreotide(DOTA-TOC) positron emission tomography/computed tomography (PET/CT) in patients with well-differentiated colorectal Neuroendocrine Tumours (NETs) originating from the hindgut. The other aims were to assess the impact of the examination on patient management and to analyze the results of 2-[18F]FDG and/or 6-[18F]FDOPA PET/CT when they were performed. [68Ga]Ga-DOTA-TOC PET/CT and clinical data from 30 patients with biopsy-proven well-differentiated NETs originating from the hindgut were retrospectively reviewed and analyzed by comparing the [68Ga]Ga-DOTA-TOC PET/CT findings with pathological and/or follow-up data. We also compared the [68Ga]Ga-DOTA-TOC PET/CT results with 2-[18F]FDG and/or 6-[18F]FDOPA PET/CT results in 6 patients. The impact on management was determined in hindsight by comparing the patient management decided before and after the TEP examination based on data from multidisciplinary team meetings. On a patient basis, [68Ga]Ga-DOTA-TOC PET/CT was accurate in 30 of the 30 examinations. [68Ga]Ga-DOTA-TOC PET/CT correctly identified the primary tumor in all patients with primary tumors not resected before the examination and allowed the detection of unexpected distant metastases in 36% of the patients referred for initial staging. [68Ga]Ga-DOTA-TOC PET/CT findings affected patient management in 57% of cases with generally major intermodality changes. Intraindividual comparison of the results of the different PET radiopharmaceuticals showed a clear superiority of [68Ga]Ga-DOTA-TOC PET/CT considering both the number of lesions and the intensity of uptake. [68Ga]Ga-DOTA-TOC PET/CT is an accurate imaging modality for the assessment of well-differentiated colorectal NETs that highly impact patient management. Thus, we suggest that [68Ga]Ga-DOTA-TOC PET/CT be employed as a first choice for the assessment of these tumors in nuclear medicine.

Dissecting the in vitro efficacy of octreotide and cabergoline in GH- and GH/PRL-secreting pituitary tumors

CONTEXT

Cabergoline (CAB) is an off-label medical therapy for acromegaly, overshadowed by first-generation somatostatin receptor ligands, e.g. octreotide (OCT).

OBJECTIVE

Head-to-head comparison between OCT and CAB in inhibiting growth hormone (GH) secretion in primary cultures of GH- and GH/PRL-secreting tumors. To investigate the role of somatostatin (SST) and dopamine type 2 (D2R) receptor expression.

DESIGN

To evaluate the antisecretory effect of OCT and CAB, together with receptor mRNA expression, in 23 tumor cultures.

SETTING AND PATIENTS

Acromegaly patients referred to the Erasmus Medical Center (Rotterdam, The Netherlands).

INTERVENTIONS

72-hour OCT and CAB treatment (10 nM).

MAIN OUTCOME MEASURES

GH concentrations in cell culture media.

RESULTS

OCT showed a slightly higher efficacy compared with CAB (GH decrease -39.5% vs. -32.5%, p = 0.079). The effect of the two drugs was superimposable in GH/PRL co-secreting tumors (-42.1% vs. -44.8%), where SST1 and D2R had a higher expression compared to the pure GH-secreting ones (p = 0.020 and p = 0.026). OCT was more effective than CAB in 8/23 cultures, while CAB was more effective than OCT in 3/23 (CAB + group). In CAB + tumors, SST1 expression was higher compared to the other groups (p = 0.034). At ROC curve analysis, SST1 and D2R discriminated between GH and GH/PRL co-secretion (AUC 0.856, p = 0.013; AUC 0.822, p = 0.024). SST1 was the best predictor of CAB response (≥50% GH reduction, AUC 0.913, p = 0.006; 80% sensitivity, 94% specificity).

CONCLUSIONS

OCT is 5-10% more effective than CAB in vitro. SST1 mRNA expression can represent a reliable marker of GH/PRL co-secreting tumors showing a preferential response to CAB treatment.

Value of Somatostatin Receptor PET/CT in Patients With MEN1 at Various Stages of Their Disease

CONTEXT

Despite the growing evidence of the clinical value of somatostatin receptor (SSTR) positron emission tomography (PET) in the evaluation of neuroendocrine tumors (NETs), its role remains to be clarified at different time points in the journey of patients with multiple endocrine neoplasia type 1 (MEN1). The rarity of the disease is however a significant impediment to prospective clinical trials.

OBJECTIVE

The goals of the study were to assess the indications and value of SSTR PET/computed tomography (CT) in patients with MEN1.

METHODS

We retrospectively included patients from 7 French expert centers for whom data on SSTR PET/CT and morphological imaging performed at the same period were available. Detection rates of PET study were analyzed.

RESULTS

One hundred and 8 patients were included. SSTR PET/CT was performed at screening (n = 33), staging (n = 34), restaging (n = 37), and for peptide receptor targeted radiotherapy selection (n = 4). PET detected positive pancreatic lesions in 91% of cases at screening, with results comparable with magnetic resonance imaging but superior to CT (P = .049). Metastases (mostly lymph node [LN]) were present at the screening phase in 28% of cases, possibly due to the suboptimal value of screening morphological imaging in the assessment of nodal metastases and/or a long delay between imaging studies. SSTR PET/CT was considered superior or complementary to the reference standard in the assessment of LN or distant metastases in the vast majority of cases and regardless of the clinical scenario.

CONCLUSION

This study shows the potential added value of SSTR PET in the assessment of MEN1-associated NETs and provides great impetus toward its implementation in the evaluation of patients with MEN1.

Radiolabeled Somatostatin Analogs-A Continuously Evolving Class of Radiopharmaceuticals

Somatostatin receptors (SSTs) are recognized as favorable molecular targets in neuroendocrine tumors (NETs) and neuroendocrine neoplasms (NENs), with subtype 2 (SST₂) being the predominantly and most frequently expressed. PET/CT imaging with ⁶⁸Ga-labeled SST agonists, e.g., ⁶⁸Ga-DOTA-TOC (SomaKit TOC^®) or ⁶⁸Ga-DOTA-TATE (NETSPOT^®), plays an important role in staging and restaging these tumors and can identify patients who qualify and would potentially benefit from peptide receptor radionuclide therapy (PRRT) with the therapeutic counterparts ¹⁷⁷Lu-DOTA-TOC or ¹⁷⁷Lu-DOTA-TATE (Lutathera^®). This is an important feature of SST targeting, as it allows a personalized treatment approach (theranostic approach). Today, new developments hold promise for enhancing diagnostic accuracy and therapeutic efficacy. Among them, the use of SST₂ antagonists, such as JR11 and LM3, has shown certain advantages in improving image sensitivity and tumor radiation dose, and there is evidence that they may find application in other oncological indications beyond NETs and NENs. In addition, PRRT performed with more cytotoxic α-emitters, such as ²²⁵Ac, or β^- and Auger electrons, such as ¹⁶¹Tb, presents higher efficacy. It remains to be seen if any of these new developments will overpower the established radiolabeled SST analogs and PRRT with β^--emitters.

Molecular mechanisms involved in somatostatin receptor regulation in corticotroph tumors: the role of cytoskeleton and USP8 mutations

Adrenocorticotropic hormone (ACTH)-secreting pituitary tumors mainly express somatostatin receptor 5 (SSTR5) since SSTR2 is downregulated by the elevated levels of glucocorticoids that characterize patients with Cushing's disease (CD). SSTR5 is the molecular target of pasireotide, the only approved pituitary tumor-targeted drug for the treatment of CD. However, the molecular mechanisms that regulate SSTR5 are still poorly investigated. This review summarizes the experimental evidence supporting the role of the cytoskeleton actin-binding protein filamin A (FLNA) in the regulation of SSTR5 expression and signal transduction in corticotroph tumors. Moreover, the correlations between the presence of somatic USP8 mutations and the expression of SSTR5 will be reviewed. An involvement of glucocorticoid-mediated β-arrestins modulation in regulating SSTRs expression and function in ACTH-secreting tumors will also be discussed.

Role of Ga-68 DOTANOC Positron Emission Tomography/ Computed Tomography Scan in Clinical Management of Patients with Neuroendocrine Tumors and its Correlation with Conventional Imaging- Experience in a Tertiary Care Center in India

Purpose of Study

Aim of the study was to evaluate the role of ⁶⁸Gallium-DOTANOC positron emission tomography/computed tomography (⁶⁸Ga-DOTANOC PET/CT), a pan somatostatin receptor (SSTR) analog in the clinical management of patients with neuroendocrine tumors (NETs) and its correlation with conventional imaging.

Materials and Methods

We retrospectively evaluated 69 patients of known/suspected NETs who underwent ⁶⁸Ga-DOTANOC PET/CT scan for tumor localization (n = 15), stage modification (primary staging, n = 26 and restaging, n = 25) and therapy monitoring (n = 3). We also compared PET scan with conventional imaging as reference standard and evaluated the impact of PET/CT in the clinical management of patients.

Results

The concordant findings on ⁶⁸Ga-DOTANOC PET/CT and conventional imaging seen in 33 and discordant in 36 patients. Among discordant group, disease was upstaged in 32 patients; down staged in 3 patients; no stage change in one patient. PET/CT localized primary tumor in 4 patients. Among patients with raised tumor markers (39/69), PET was positive in 29 and negative in 10 patients. Patients were followed for mean duration of 27 months to assess management. We found strong agreement between positive PET and raised tumor markers (Kappa value = 0.8). Sensitivity and specificity of PET/CT for primary tumor localization, stage modification, and therapy monitoring was >90% (P < 0.05).

Conclusions

Study shows that DOTANOC, a broad spectrum SSTRs binding peptide labeled with Ga-68 in PET/CT scan is an excellent modality in the management of NETs patients.

Correlation of Somatostatin Receptor 1-5 Expression, [68Ga]Ga-DOTANOC, [18F]F-FDG PET/CT and Clinical Outcome in a Prospective Cohort of Pancreatic Neuroendocrine Neoplasms

Simple Summary

The need for prognostic and predictive biomarkers in pancreatic neuroendocrine neoplasms (PNENs) is great. Overexpression of somatostatin receptors (SSTRs) provides a molecular basis for imaging these tumors with ⁶⁸Ga-labeled somatostatin (SST) PET/CT and for treatment with somatostatin analogs. We evaluated all 5 somatostatin receptors (SSTR1-5) with immunohistochemistry and prospectively compared the results with both [⁶⁸Ga]Ga-DOTANOC and [¹⁸F]F-FDG PET/CT in a cohort of 21 non-functional (NF) PNENs. SSTR2 was the only SSTR subtype to correlate with [⁶⁸Ga]Ga-DOTANOC PET/CT. High SSTR5 expression correlated with a low Ki-67 proliferation index, suggesting a better prognosis for these patients. Thus, our results confirm that SSTR2 has the highest impact on SSTR PET signaling of PNENs.

Abstract

Purpose: The aim of this study was to correlate immunohistochemical (IHC) tissue levels of SSTR1-5 with the receptor density generated from [⁶⁸Ga]Ga-DOTANOC uptake in a prospective series of NF-PNENs. Methods: Twenty-one patients with a total of thirty-five NF-PNEN-lesions and twenty-one histologically confirmed lymph node metastases (LN+) were included in this prospective study. Twenty patients were operated on, and one underwent endoscopic ultrasonography and core-needle biopsy. PET/CT with both [⁶⁸Ga]Ga-DOTANOC and [¹⁸F]F-FDG was performed on all patients. All histological samples were re-classified and IHC-stained with monoclonal SSTR1-5 antibodies and Ki-67 and correlated with [⁶⁸Ga]Ga-DOTANOC and [¹⁸F]F-FDG PET/CT. Results: Expression of SSTR1-5 was detected in 74%, 91%, 80%, 14%, and 77% of NF-PNENs. There was a concordance of SSTR2 IHC with positive/negative [⁶⁸Ga]Ga-DOTANOC finding (Spearman’s rho 0.382, p = 0.043). All [⁶⁸Ga]Ga-DOTANOC-avid tumors expressed SSTR2 or SSTR3 or SSTR5. Expression of SSTR5 was higher in tumors with a low Ki-67 proliferation index (PI) (−0.353, 95% CI −0.654–0.039, p = 0.038). The mean Ki-67 PI for SSTR5 positive tumors was 2.44 (SD 2.56, CI 1.0–3.0) and 6.38 (SD 7.25, CI 2.25–8.75) for negative tumors. Conclusion: SSTR2 was the only SSTR subtype to correlate with [⁶⁸Ga]Ga-DOTANOC PET/CT. Our prospective study confirms SSTR2 to be of the highest impact for SST PET/CT signal.

Prognostic Value of Volume-Based Parameters Measured by SSTR PET/CT in Neuroendocrine Tumors: A Systematic Review and Meta-Analysis

Purpose: A meta-analysis was conducted to investigate the value of the volume parameters based on somatostatin receptor (SSTR)-positron emission tomography (PET) in predicting the prognosis in patients with neuroendocrine tumors (NETs). Material: PUBMED, EMBASE, Cochrane library, and Web of Knowledge were searched from January 1990 to May 2021 for studies evaluating prognostic value of volume-based parameters of SSTR PET/CT in NETs. The terms used were "volume," "positron emission tomography," "neuroendocrine tumors," and "somatostatin receptor." Pooled hazard ratio (HR) values were calculated to assess the correlations between volumetric parameters, including total tumor volume (TTV) and total-lesion SSTR expression (TL-SSTR), with progression-free survival (PFS) and overall survival (OS). Heterogeneity and subgroup analysis were performed. Funnel plots, Begg's and Egger's test were used to assess possible underlying publication bias. Results: Eight eligible studies involving 593 patients were included in the meta-analysis. In TTV, the pooled HRs of its prognostic value of PFS and OS were 2.24 (95% CI: 1.73-2.89; P < 0.00001) and 3.54 (95% CI, 1.77-7.09; P = 0.0004), respectively. In TL-SSTR, the pooled HR of the predictive value was 1.61 (95% CI, 0.48-5.44, P = 0.44) for PFS. Conclusion: High TTV was associated with a worse prognosis for PFS and OS in with patients NETs. The TTV of SSTR PET is a potential objective prognosis predictor.

Somatostatin and Somatostatin Receptors: From Signaling to Clinical Applications in Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NENs) are heterogeneous neoplasms which arise from neuroendocrine cells that are distributed widely throughout the body. Although heterogenous, many of them share their ability to overexpress somatostatin receptors (SSTR) on their cell surface. Due to this, SSTR and somatostatin have been a large subject of interest in the discovery of potential biomarkers and treatment options for the disease. The aim of this review is to describe the molecular characteristics of somatostatin and somatostatin receptors and its application in diagnosis and therapy on patients with NENs as well as the use in the near future of somatostatin antagonists.

Metastatic Medullary Thyroid Cancer: The Role of 68Gallium-DOTA-Somatostatin Analogue PET/CT and Peptide Receptor Radionuclide Therapy

CONTEXT

Metastatic medullary thyroid cancer (MTC) is a rare malignancy with minimal treatment options. Many, but not all, MTCs express somatostatin receptors.

OBJECTIVE

Our aim was to explore the role of 68Ga-DOTA-somatostatin analogue (SSA) positron emission tomography (PET)/computed tomography (CT) in patients with metastatic MTC and to determine their eligibility for peptide receptor radionuclide therapy (PRRT).

METHODS

We retrospectively identified patients with metastatic MTC who had 68Ga-DOTA-SSA PET/CT at 5 centers. We collected characteristics on contrast-enhanced CT, 68Ga-DOTA-SSA and 18F-FDG PET/CT. The efficacy of PRRT was explored in a subgroup of patients. Kaplan-Meier analysis was used to estimate time to treatment failure (TTF) and overall survival (OS).

RESULTS

Seventy-one patients were included (10 local recurrence, 61 distant disease). Of the patients with distant disease, 16 (26%) had ≥50% of disease sites with tracer avidity greater than background liver, including 10 (10/61, 16%) with >90%. In 19 patients with contemporaneous contrast-enhanced CT, no disease regions were independently identified on 68Ga-DOTA-SSA PET/CT. Thirty-five patients had an 18F-FDG PET/CT, with 18F-FDG positive/68Ga-DOTA-SSA negative metastases identified in 15 (43%). Twenty-one patients had PRRT with a median TTF of 14 months (95% CI 8-25) and a median OS of 63 months (95% CI 21-not reached). Of the entire cohort, the median OS was 323 months (95% CI 152-not reached). Predictors of poorer OS included a short calcitonin doubling-time (≤24 months), strong 18F-FDG avidity, and age ≥60 years.

CONCLUSIONS

The prevalence of high tumor avidity on 68Ga-DOTA-SSA PET/CT is low in the setting of metastatic MTC; nevertheless, PRRT may still be a viable treatment option in select patients.

Somatostatin Receptors in Human Meningiomas-Clinicopathological Aspects

Simple Summary

Meningioma diagnostics and grading are currently based on subjective histopathological criteria given by the 2016 World Health Organization (WHO) classification. However, biomarkers may provide a more objective approach to diagnostics. This study was designed to elucidate the diagnostic and prognostic value of somatostatin receptors (SSTRs) as biomarkers in meningiomas, which could help to identify patients with a higher risk of recurrence and provide more personalized treatment. We have confirmed, in a population of 162 patients, that SSTRs have diagnostic value and may aid in the differentiation between WHO grade 1 and grade 2 tumors. Furthermore, SSTR1, SSTR2 and SSTR5 were associated with higher malignancy grades. SSTR2 expression was found to be characteristic in meningiomas. To maintain objectiveness, we scoped for a digital evaluation of immunoreactivity. We aim to impact and motivate researchers to further investigations towards more objective criteria in meningioma diagnostics, which in turn will improve patient care.

Abstract

Meningiomas have high recurrence rates despite frequently benign histopathological appearances. Somatostatin receptors (SSTRs) may be reliable biomarkers that could identify patients with increased risk of recurrence. Even though SSTRs are previously detected in meningiomas, their associations to clinicopathological features remain unclear. The aim of this study was to investigate the diagnostic and prognostic value of SSTRs in a large series of human meningiomas with long follow-up data. Immunohistochemistry was used to measure the expression of SSTR1-SSTR5 in tissue samples from 162 patients diagnosed with intracranial meningiomas of World Health Organization (WHO) grade 1 or 2. Digital scoring and a manual staining index were applied to assess immunoreactivity. All SSTRs, except SSTR4, were upregulated in our series of meningiomas. SSTR1 (p = 0.036), SSTR2 (p = 0.036) and SSTR5 (p = 0.029) were associated with a higher malignancy grade. SSTR2 presented as the most reliable marker. Only SSTR2 was associated with time to recurrence (TTR) in univariate Cox regression analyses. Manual staining index was strongly correlated with digital scoring for all SSTRs (r > 0.65, p < 0.001). SSTRs, and especially SSTR2, are useful in the diagnostics of meningiomas, even though their prognostic value appears limited. Digital scoring is valuable to ensure reproducibility.

Targeted paclitaxel-octreotide conjugates inhibited the growth of paclitaxel-resistant human non-small cell lung cancer A549 cells in vitro

The application of chemotherapy in non‐small cell lung cancer (NSCLC) is limited by the toxicity to normal cells and the development of multi‐drug resistance. Targeted chemotherapy using cytotoxic analogs against specific receptors on cancer cells could be a less toxic and more efficacious approach. We identified that the expressions of somatostatin receptor (SSTR) 2 and 5 in tumor tissues from NSCLC patients were higher than those in the adjacent normal tissues by immunohistochemistry, and therefore, cytotoxic somatostatin analogues might be applied for SSTRs‐mediated targeted therapy against NSCLC. Two cytotoxic analogs, paclitaxel‐octreotide (PTX‐OCT) and 2paclitaxel‐octreotide (2PTX‐OCT), were synthesized by linking one or two molecules of paclitaxel to one molecule of somatostatin analog octreotide. PTX‐OCT and 2PTX‐OCT significantly inhibited the growth and induced apoptosis of SSTR2‐ and SSTR5‐positive A549 cells, compared with the control (p < 0.01), and had less inhibitory effect on SSTR2‐ and SSTR5‐negative H157 cells than paclitaxel (p < 0.01). Moreover, compared with paclitaxel, PTX‐OCT conjugates induced lower expression of MDR‐1 gene both in vitro and in vivo. Three A549 paclitaxel‐resistant cell lines were established through different approaches, and the paclitaxel‐resistant cell showed higher sensitivity to PTX‐OCT conjugates than to paclitaxel, which might be because of the differential MDR‐related gene expressions and cell‐cycle distribution in paclitaxel‐resistant A549 cells. Our results suggested that PTX‐OCT conjugates could be potentially used for SSTRs‐mediated targeted therapy for NSCLC, especially for those with paclitaxel resistance and induced less multidrug resistance.

Molecular and Clinical Implications of Somatostatin Receptor Profile and Somatostatin Analogues Treatment in Oral Cavity Squamous Cell Carcinoma

Simple Summary

The treatment of oral squamous cell carcinoma (OSCC) represents a significant problem worldwide. Among cancers with the highest incidence, OSCC renders one of the worst prognoses. Therefore, novel prognostic biomarkers and therapeutic tools to tackle OSCC are urgently needed. Somatostatin-analogues (SSA) are an invaluable therapeutic option in the treatment of several cancers. We aimed to determine the expression levels of all somatostatin-receptors (SSTs) in OSCC, compared to adjacent healthy control tissues, to analyze the relationship of SSTs expression with key clinical and histopathological data, and to explore the direct in vitro effect of different SSAs on OSCC cancer cells. Our findings highlight a potential role of SST₂ as a good prognostic biomarker for recurrence and metastasis in OSCC and unveil that SSA exerts antitumoral effects on OSCC cells, providing a relevant clinical conclusion, which should be soon tested for their use in humans.

Abstract

Oral squamous cell carcinoma (OSCC) incidence has increased by 50% over the last decade. Unfortunately, surgery and adjuvant radiotherapy and chemotherapy are still the mainstream modality of treatment, underscoring the need for alternative therapies. Somatostatin-analogues (SSA) are efficacious and safe treatments for a variety of tumors, but the presence of somatostatin-receptors (SSTs) and pharmacological effects of SSA on OSCC are poorly known. In this study, we demonstrated that SST₂ and SST₃ levels were significantly higher in OSCC, compared to adjacent healthy control tissues. SST₂ expression was associated with less regional metastasis and a lower recurrence rate. Moreover, SST₂ was elevated in OSCC and associated with histopathological good prognosis factors, such as high peritumoral inflammation, smaller depth of invasion, and expansive vs. infiltrative front of tumor invasion. Importantly, treatment with different SSA (octreotide, lanreotide, and pasireotide) significantly reduced cell-proliferation in OSCC primary cell cultures. Altogether, this study demonstrated that SST₂ is overexpressed in OSCC vs. healthy tissues and could represent a novel prognostic biomarker, since its expression is associated with tumors that show better prognostic factors and less recurrent rate. Moreover, our data unveil clear antitumoral effects of SSAs on OSCC, opening new avenues to explore their potential as targeting therapy to OSCC.

The new WHO classification of gastrointestinal neuroendocrine tumors and immunohistochemical expression of somatostatin receptor 2 and 5

The 2019 World Health Organization (WHO) classification of gastrointestinal tumors defines well-differentiated grade 3 neuroendocrine tumors, the mixed neuroendocrine-non-neuroendocrine tumors (MiNENs) and classifies goblet cell carcinoid as goblet cell adenocarcinoma. The expression of somatostatin receptors (SSTRs) is the foundation for somatostatin analogue therapy. At present, there are only a few studies that have analyzed the immunohistochemical reactivity of SSTRs in gastrointestinal neuroendocrine neoplasms (NENs). The aim of the present study was to evaluate the immunohistochemical expression of SSTR2 and SSTR5 in gastrointestinal NENs and goblet cell adenocarcinomas and the correlation of these markers with clinical and morphological factors. The study included 67 patients with NENs and 4 patients with adenocarcinoma ex-goblet cell carcinoid diagnosed between January 2008 and December 2018. Tumors were reclassified according to the 2019 WHO classification. Immunohistochemical staining for chromogranin A, synaptophysin, Ki-67, p53, SSTR2, and SSTR5 were performed in all the cases. The results showed that, G1 and G2 neuroendocrine tumors were more common SSTR2-positive in comparison with G3 carcinomas (P<0.0001). In addition, 33.3% of neuroendocrine carcinomas and 2 cases of low-grade adenocarcinoma ex-goblet cell carcinoid were SSTR2-positive. Neuroendocrine carcinomas had significantly lower SSTR2 and SSTR5 expression compared with well-differentiated neuroendocrine tumors (P=0.0130; P=0.0437, respectively). The SSTR2 expression in the early tumor stages was 100%, more often than in advanced stages (55.6%; P=0.0011). The results demonstrated the decrease in SSTR2 expression with increasing malignancy and tumor stage. The SSTR2-positive expression in neuroendocrine carcinomas and adenocarcinoma ex-goblet cell carcinoid provides evidence for the benefits of somatostatin analog treatment associated with surgery and chemotherapy.

Labeling and receptor affinity of an ultra-short somatostatin analogue Thz-Phe-D-Trp-Lys-Thr-DOTA

Somatostatin analogues play an important role in the therapy of neuroendocrine tumors by binding to somatostatin receptors on the surface of cancer cells. In this work, we analyze the receptor-binding affinity and in vitro stability of a novel ultra-short somatostatin analogue Thz-Phe-D-Trp-Lys-Thr-DOTA (DOTA-P4). This conjugate is successfully radiolabeled with ⁴⁴ Sc, ⁹⁰ Y, ¹⁵² Eu, and ²⁰⁷ Bi, characterized and validated by thin layer and high-performance liquid chromatography. The optimum conditions for M-DOTA-P4 labeling are found. In vitro stability studies are performed in saline, in the presence of serum proteins, and with biologically relevant metal cations. All complexes demonstrate no cation release in vitro within 4-24 h. The conformations of DOTA-conjugates are studied by circular dichroism spectroscopy. The circular dichroism spectra of DOTA-P4 conjugates show a negative peak at 225 nm, which may correspond to the required β-sheet conformation. The binding to somatostatin receptors of types 2 and 5 is performed with the IMR-32 cells at 4°C, with non-specific binding representing 26% of the total binding. A two-line approximation of the Scatchard plot results in the apparent dissociation constants of 0.10 and 2.25 nM. It is shown that the chelator position with respect to the amino acid sequence significantly affects the labeling conditions with cations of different ionic radii. For the first time, the binding of a linear type ultra-short peptide conjugate with DOTA to somatostatin receptors is demonstrated. The obtained results are promising for experiments with DOTA-P4 in vivo in mice with inoculated tumors.

Gender-Specific Efficacy Revealed by Head-to-Head Comparison of Pasireotide and Octreotide in a Representative In Vivo Model of Nonfunctioning Pituitary Tumors

Simple Summary

No effective medical therapy exists for residual/recurrent nonfunctioning pituitary tumors (NFPTs). First-generation somatostatin analogs (SSAs) like octreotide targeting somatostatin receptor type 2 (SSTR2) are the mainstay therapy for functioning PTs, but have shown little effect in NFPTs. This is in agreement with an SSTR profile characterized by low SSTR2, and high SSTR3 levels in the latter. Pasireotide a multi-SSTR-preferring SSA, should be effective against NFPTs. To test this hypothesis, we conducted a head-to-head comparison of octreotide and pasireotide in the only spontaneous in vivo model of NFPTs (MENX rats), which recapitulates the human disease. Pasireotide showed a superior anti-tumor effect vs. octreotide, especially in females. Interestingly, Sstr3 levels were higher in female vs. male NFPTs. A sex-related SSTR3 expression may extend to human NFPTs, thereby representing a tool for patient stratification. Our results have translational relevance for the medical treatment of patients with residual/recurrent NFPTs currently lacking efficacious therapeutic options.

Abstract

Invasive nonfunctioning pituitary tumors (NFPTs) are non-resectable neoplasms associated with frequent relapse and significant comorbidities. Current treatments, including somatostatin receptor 2 (SSTR2)-directed somatostatin analogs (SSAs), often fail against NFPTs. Thus, identifying effective therapies is clinically relevant. As NFPTs express SSTR3 at high levels, pasireotide, a multireceptor-targeted SSA, might be beneficial. Here we evaluated pasireotide in the only representative model of spontaneous NFPTs (MENX rats) in vivo. Octreotide long-acting release (LAR), pasireotide LAR, or placebo, were administered to age-matched, tumor-bearing MENX rats of both sexes for 28 d or 56 d. Longitudinal high-resolution magnetic resonance imaging monitored tumor growth. While tumors in placebo-treated rats increased in volume over time, PTs in drug-treated rats displayed significant growth suppression, and occasional tumor shrinkage. Pasireotide elicited stronger growth inhibition. Radiological responses correlated with tumors’ proliferation rates. Both SSAs, but especially pasireotide, were more effective in female vs. male rats. Basal Sstr3 expression was significantly higher in the former group. It is noteworthy that female human NFPTs patients also have a trend towards higher SSTR3 expression. Altogether, our studies provide the rationale for testing pasireotide in patients with residual/recurrent NFPTs. If confirmed, the sex-related SSTR3 expression might be used as criteria to stratify NFPTs patients for treatment with pasireotide.

Gene expression in rat placenta after exposure to di(2-ethylhexyl) phthalate

The organic compound di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in many products. Exposure to DEHP has been reported to lead to adverse pregnancy outcomes by suppressing placenta growth and development. The aim of this study was to determine the gene expression profiles of rat placenta exposed to (DEHP) and identify genes crucial for the DEHP response. Three groups of Wistar rats were administered an intragastric dose of 1,000 mg/kg DEHP, 500 mg/kg DEHP, or corn oil, RNA was isolated from placenta tissue, and hybridization was performed. Gene expression profiles were analyzed by identifying functional enrichment, differentially expressed genes (DEGs), protein-protein interaction (PPI) networks and modules, and transcription factor (TF)-miRNA-target regulatory networks. We obtained 2,032 DEGs, including cytochrome P450, family 2, subfamily R, polypeptide 1 (CYP2R1), sterol O-acyltransferase 2 (SOAT2), and 24-dehydrocholesterol reductase (DHCR24) from the steroid biosynthesis pathway and somatostatin receptor 4 (SSTR4) and somatostatin receptor 2 (SSTR2) in the neuroactive ligand-receptor interaction pathway. The PPI network included 476 nodes, 2,682 interaction pairs, and three sub-network modules. Moreover, eight miRNAs, three TFs, and 176 regulatory pairs were obtained from the TF-miRNA-target regulatory network. CYP2R1, SOAT2, DHCR24, SSTR4, and SSTR2 may affect DEHP influence on rat placenta development.

Physiological Biodistribution of 68Ga-DOTA-TATE in Normal Subjects

Objectives:

Somatostatin is an endocrine peptide hormone that regulates neurotransmission and cell proliferation by interacting with G protein-coupled somatostatin receptors (SSTRs). SSTRs are specific molecular targets of several radiotracers for neuroendocrine tumor (NET) imaging. Gallium-68 (⁶⁸Ga)-DOTA-TATE is widely used for positron emission tomography/computed tomography (PET/CT) imaging of SSTRs and has shown a higher affinity for SSTR2, the most common SSTR subtype found in NETs. We aimed to analyze the distribution pattern of ⁶⁸Ga-DOTA-TATE in normal subjects.

Methods:

A total of 617 consecutive ⁶⁸Ga-DOTA-TATE PET/CT whole-body scans performed in our department from May 2015 through April 2020 with known or suspected neuroendocrine malignancies, mostly to evaluate adrenal adenomas, were retrospectively analyzed by 2 nuclear medicine physicians. One hundred eighteen subjects without a diagnosis of NET, with no tracer avid lesion of NET on ⁶⁸Ga-DOTA-TATE PET/CT, and followed up for at least 6 months (average 2-3 years) without any biochemical, clinical, or imaging findings suggestive of NET were included in this study.

Results:

The highest uptake of ⁶⁸Ga-DOTA-TATE was noted in the spleen followed by the kidneys, adrenal glands, liver, stomach, small intestine, prostate gland, pancreas head, pancreas body, thyroid gland, and uterus, in descending order. Minimal to mild uptake was detected in the submandibular glands, parotid glands, thymus, muscles, bones, breast, lungs, and mediastinum.

Conclusion:

Our study shows the biodistribution pattern of ⁶⁸Ga-DOTA-TATE in normal subjects and the ranges of the maximum standard uptake value (SUV_max) and SUV_mean values of 68Ga-DOTA-TATE obtained in several tissues for reliably identifying malignancy in ⁶⁸Ga-DOTA-TATE PET/CT studies.

Somatostatin-Dopamine Chimeric Molecules in Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NENs) are a widely heterogeneous family of neoplasms arising from neuroendocrine cells, which are interspersed throughout the body. Despite NENs are relatively rare, their incidence and prevalence are constantly increasing probably due to the improvement in earlier diagnosis and patients’ management. When surgery is not curative, particularly for patients with metastatic disease, several medical options are available. Somatostatin analogues (SSA) are the first-line medical therapy for well-differentiated NENs. Interestingly, the heterodimerization of somatostatin receptors (SSTs) with dopamine receptors (DRs) has been discovered in NENs. This phenomenon results in hybrid receptors with enhanced functional activity. On these bases, chimeric molecules embracing somatostatin and dopamine features have been recently developed. The aim of this review is to provide a comprehensive overview of the available preclinical and clinical data regarding chimeric somatostatin-dopamine agonists as a new class of “magic bullet” in the therapy of NENs.

Somatostatin Receptors and Analogs in Pheochromocytoma and Paraganglioma: Old Players in a New Precision Medicine World

Neuroendocrine tumors overexpress somatostatin receptors, which serve as important and unique therapeutic targets for well-differentiated advanced disease. This overexpression is a well-established finding in gastroenteropancreatic neuroendocrine tumors which has guided new medical therapies in the administration of somatostatin analogs, both "cold", particularly octreotide and lanreotide, and "hot" analogs, chelated to radiolabeled isotopes. The binding of these analogs to somatostatin receptors effectively suppresses excess hormone secretion and tumor cell proliferation, leading to stabilization, and in some cases, tumor shrinkage. Radioisotope-labeled somatostatin analogs are utilized for both tumor localization and peptide radionuclide therapy, with ⁶⁸Ga-DOTATATE and ¹⁷⁷Lu-DOTATATE respectively. Benign and malignant pheochromocytomas and paragangliomas also overexpress somatostatin receptors, irrespective of embryological origin. The pattern of somatostatin receptor overexpression is more prominent in succinate dehydrogenase subunit B gene mutation, which is more aggressive than other subgroups of this disease. While the Food and Drug Administration has approved the use of ⁶⁸Ga-DOTATATE as a radiopharmaceutical for somatostatin receptor imaging, the use of its radiotherapeutic counterpart still needs approval beyond gastroenteropancreatic neuroendocrine tumors. Thus, patients with pheochromocytoma and paraganglioma, especially those with inoperable or metastatic diseases, depend on the clinical trials of somatostatin analogs. The review summarizes the advances in the utilization of somatostatin receptor for diagnostic and therapeutic approaches in the neuroendocrine tumor subset of pheochromocytoma and paraganglioma; we hope to provide a positive perspective in using these receptors as targets for treatment in this rare condition.

Calcitriol-Mediated Hypercalcemia, Somatostatin Receptors Expression and 25-Hydroxyvitamin D3-1α- Hydroxylase in GIST Tumors

Hypercalcemia is a common complication in cancer patients Mainly caused by Parathyroid hormone-related protein (PTHrP) secretion and metastasis. Calcitriol secretion is a rare source of hypercalcemia in solid tumors, especially in gastrointestinal stromal tumors (GIST). We present a case report of a female patient with a 23 cm gastric GIST that expressed somatostatin-receptors and presented with severe hypercalcemia due to calcitriol secretion. Calcium control was achieved with medical treatment before the use of targeted-directed therapies. Surgery was performed and allowed complete tumor resection. Two years later, patient remains free of disease. Molecular analysis revealed the mRNA expression of 25-hydroxyvitamin D₃-1-hydroxylase (1αOHase) and vitamin-D receptors in the tumor cells, confirming the calcitriol-mediated mechanism. Furthermore, the expression of the endotoxin recognition factors CD14 and TLR4 suggests an inflammatory mediated mechanism. Finally, the expression of somatostatin-receptors, especially SST2 might have been related with clinical evolution and prognosis in this patient.

Expression of Somatostatin Receptor Subtypes (SSTR-1-SSTR-5) in Pediatric Hematological and Oncological Disorders

Hematological and oncological disorders represent leading causes of childhood mortality. Neuropeptide somatostatin (SST) has been previously demonstrated in various pediatric tumors, but limited information exists on the expression and characteristics of SST receptors (SSTR) in hematological and oncological disorders of children. We aimed to investigate the expression of mRNA for SSTR subtypes (SSTR-1–5) in 15 pediatric hematological/oncological specimens by RT-PCR. The presence and binding characteristics of SSTRs were further studies by ligand competition assay. Our results show that the pediatric tumor samples highly expressed mRNA for the five SSTR subtypes with various patterns. The mRNA for SSTR-2 was detected in all specimens independently of their histological type. A Hodgkin lymphoma sample co-expressed mRNA for all five SSTR subtypes. SSTR-3 and SSTR-5 were detected only in malignant specimens, such as rhabdomyosarcoma, Hodgkin lymphoma, acute lymphoblastic leukemia, and a single nonmalignant condition, hereditary spherocytosis. The incidence of SSTR-1 and SSTR-4 was similar (60%) in the 15 specimens investigated. Radioligand binding studies demonstrated the presence of specific SSTRs and high affinity binding of SST analogs in pediatric solid tumors investigated. The high incidence of SSTRs in hematological and oncological disorders in children supports the merit of further investigation of SSTRs as molecular targets for diagnosis and therapy.

Fluorescent Nanoparticles Coated with a Somatostatin Analogue Target Blood Monocyte for Efficient Leukaemia Treatment

BACKGROUND

Leukaemia is the most prevalent form of cancer-causing death in a large number of populations and needs prompt and effective treatment. Chemotherapeutics can be used to treat leukaemia, but their pronounced killing effects to other living cells is still an issue. Active targeting to certain specific receptors in leukaemic cells is the best way to avoid damage to other living cells. Leukaemic cells can be targeted using novel nanoparticles (NPs) coated with a specific ligand, such as octreotide (OCD), to target somatostatin receptor type 2 (SSTR₂), which is expressed in leukaemic cells.

METHODS

Amino-PEGylated quantum dots (QDs) were chosen as model NPs. The QDs were first succinylated using succinic anhydride and then coated with OCD. The reactivity and selectivity of the formulated QDs-OCD were studied in cell lines with well-expressed SSTR₂, while fluorescence was detected using confocal laser scanning microscopy (CLSM) and flow cytometry (FACS). Conclusively, QD-OCD targeting to blood cells was studied in vivo in mice and detected using inductively coupled plasma mass spectrometry and CLSM in tissues.

RESULTS

Highly stable QDs coated with OCD were prepared. FACS and CLSM showed highly definite interactions with overexpressed SSTR₂ in the investigated cell lines. Moreover, the in vivo results revealed a higher concentration of QDs-OCD in blood cells. The fluorescence intensity of the QDs-OCD was highly accumulated in blood cells, while the unmodified QDs did not accumulate significantly in blood cells.

CONCLUSION

The formulated novel QDs-OCD can target SSTR₂ overexpressed in blood cells with great potential for treating blood cancer.

Validation of Quality Control Parameters of Cassette-Based Gallium-68-DOTA-Tyr3-Octreotate Synthesis

Purpose of the Study:

Gallium (Ga)-68-DOTA peptides targeting somatostatin receptors have been assessed as a valuable tool in neuroendocrine tumor imaging using positron emission tomography. However, at the moment, a specific monograph in the European Pharmacopoeia (Ph. Eur.) does exist only for Ga-68-edotreotide (DOTATOC) injection. Here, we report on the validation process of Ga-68-DOTA-Tyr3-octreotate (DOTATATE) cassette-based production and quality control (QC).

Materials and Methods:

Preparation of Ga-68-DOTATATE was performed according to the current European Union-good manufacturing practices, the current good radiopharmacy practice, the Ph. Eur., and the guidelines on validation of analytical methods for radiopharmaceuticals. Process was validated via three consecutive production runs to ensure that the methods are reproducible and reliable in routine use. The QC tests for Ga-68-DOTATATE were radiochemical purity (RCP – high-pressure liquid chromatography [HPLC]), radiochemical impurities ⁶⁸Ga³⁺ (HPLC and instant thin layer chromatography [ITLC]), chemical purity (HPLC and gas chromatography [GC]), pH (pH-strips), radionuclidic purity (principal γ-photon), germanium-breakthrough (⁶⁸Ge-content), Ga-68 half-life (γ-ray spectrometry), and sterility/endotoxin assay.

Results:

Radiolabeling procedure of Ga-68-DOTATATE fits all the applicable Ph. Eur. specifications. RCP measured via ITLC was >99% in the three validation batches. HPLC-measured RCP resulted 99.45%, 99.78%, and 99.75%. Germanium-breakthrough was far below the recommended level established in the Ph. Eur. Ga-68-DOTATOC injection (#2482). Residual ethanol tested with GC was less than 10%. All the batches were tested for endotoxin content, which always resulted lower than 17.5 EU/ml. All preparations passed the sterility tests. pH of the final product was 7 in all samples.

Conclusion:

Ga-68-DOTATATE fulfilled all the pre-set QCs and release criteria in the batches considered for this validation study. The results demonstrated a batch-to-batch reproducibility, ensuring that synthesis process leads to the expected final product in terms of yield, quality, reliability, safety, and efficacy.

Evaluation of the expression of somatostatin receptors by immunohistochemistry in neuroendocrine tumors of the small intestine

Most neuroendocrine neoplasms (NEN) are characterized by the presence of somatostatin receptors (SSTR) which we use in location diagnostics and treatment. The aim of this study was to evaluate the expression of somatostatin receptors by immunohistochemistry in tissue obtained after surgery of the primary focus in the small intestine. The group of patients consisted of 41 people, in 18 cases the primary tumor was in the jejunum and in 23 in the ileum. The immunohistochemical method was used to visualize the receptors, using polyclonal antibodies in a two-stage peroxidase method. In patients with NEN of the small intestine, the SSTR2a and SSTR5 receptors are most commonly expressed, followed by SSTR2b and 3. In statistical analysis, it was shown that the expression of somatostatin receptors was not dependent on the primary site of the tumor (p > 0.05). The dependence of SSTR expression on histological maturity is evident. SSTR1, SSTR2b, SSTR3 and SSTR5 are more common in tumors with grading G1 (p < 0.05). In the study group, the exception was SSTR2a, whose incidence was comparable in both groups (p = 0.35). In NEN of the small intestine, the expression SSTR2a and SSTR5 is the most common.

Targeting vulnerable atherosclerotic plaque via PET-tracers aiming at cell-surface overexpression of somatostatin receptors

Cardiovascular disease (CD) is the leading cause of death in the developed world, with major atherothrombotic events, being mainly attributed to the rupture of unstable, vulnerable atherosclerotic lesions, leading to blood flow obstruction. Since unstable atherosclerotic plaques frequently do not cause hemodynamically significant blood flow restriction, conventional stress imaging tests cannot depict the vulnerable, high-risk for rupture atherosclerotic lesions. Therefore, molecular imaging techniques targeting specific pathophysiologic features related to atherosclerotic plaque rupture mechanism, hold promise for precise and individualized treatment strategies of CD. In the current report, we describe in a patient diagnosed with pancreatic neuroendocrine tumor, the selective uptake of ⁶⁸Ga-DOATATE by an atherosclerotic lesion in the thoracic aorta. This data indicates that ⁶⁸Ga-DOTATATE, which is a positron emitting tomography tracer, targeting the recruitment of macrophages taking place in the vulnerable plaque, could potentially serve as an imaging probe for the detection of high-risk, prone to rupture plaques.

Coexisting Somatostatin Receptor Expressing Gastric Neuroendocrine Tumor Primary and Lymph Nodal Tuberculosis on 68Ga-DOTANOC Positron Emission Tomography/Computed Tomography

Gastric neuroendocrine tumors (G-NETs) express somatostatin receptors (SSTR), which can be imaged using radiolabeled somatostatin analogs, including ⁶⁸Ga-DOTA octreotide analogs. SSTR expression is also seen in activated lymphocytes and macrophages, which might result in false-positive results on SSTR imaging, in patients with coexistent granulomatous pathologies including tuberculosis, sarcoidosis, and Wegener's granulomatosis. We present a case where ⁶⁸Ga-DOTANOC positron emission tomography/computed tomography (PET/CT) showed primary G-NET, with SSTR expressing nonregional lymph nodes which on histopathology showed necrotizing granulomas with Langhans histiocytes. Antitubercular therapy was started, and a decrease in size and SSTR expression in involved lymph nodes was noted on follow-up ⁶⁸Ga-DOTANOC PET/CT.

Neuroendocrine Carcinoma of the Uterine Cervix: A Clinicopathologic and Immunohistochemical Study with Focus on Novel Markers (Sst2-Sst5)

BACKGROUND

Gynecological neuroendocrine neoplasms (NENs) are extremely rare, accounting for 1.2-2.4% of the NENs. The aim of this study was to test cervical NENs for novel markers of potential utility for differential diagnosis and target therapy.

METHODS

All cases of our center (n = 16) were retrieved and tested by immunohistochemistry (IHC) for 12 markers including markers of neuroendocrine differentiation (chromogranin A, synaptophysin, CD56), transcription factors (CDX2 and TTF1), proteins p40, p63, p16INK4a, and p53, somatostatin receptors subtypes (SST2-SST5) and the proliferation marker Ki67 (MIB1).

RESULTS

All cases were poorly differentiated neuroendocrine carcinomas (NECs), 10 small cell types (small cell-neuroendocrine carcinomas, SCNECs) and 6 large cell types (large cell-neuroendocrine carcinomas, LCNECs); in 3 cases a predominant associated adenocarcinoma component was observed. Neuroendocrine cancer cells expressed at least 2 of the 3 tested neuroendocrine markers; p16 was intensely expressed in 14 (87.5%) cases; SST5 in 11 (56.25%, score 2-3, in 9 cases); SST2 in 8 (50%, score 2-3 in 8), CDX2 in 8 (50%), TTF1 in 5 (31.25%), and p53 in 1 case (0.06%). P63 and p40 expressions were negative, with the exception of one case that showed moderate expression for p63.

CONCLUSIONS

P40 is a more useful marker for the differential diagnosis compared to squamous cell carcinoma. Neither CDX2 nor TTF1 expression may help the differential diagnosis versus potential cervical metastasis. P16 expression may suggest a cervical origin of NEC; however, it must be always integrated by clinical and instrumental data. The expression of SST2 and SST5 could support a role for SSAs (Somatostatin Analogues) in the diagnosis and therapy of patients with cervical NECs.

A plausible way for excretion of metal nanoparticles via active targeting

Even so, the metal nanoparticles (metal NPs) have attractive optical and biomedical applications, the translation of metal NPs into the clinical practice remains a challenge due to their severe accumulation in the body. Active targeting to renal podocytes opens the door for enhancing kidney targeting and clearance. The goal of this study was to assess the excretion of larger particle size through kidney podocyte via active targeting. To reach this goal, PEGylated quantum dots (QDs) were coated with vapreotide (VAP) for selectively reaching somatostatin receptors (SSTRs) expressed in the podocyte cells. This QDs-VAP was tested on isolated primary podocytes, while the flow cytometry (FACS), confocal microscopy (CLSM), and inductively coupled plasma mass spectrometry (ICP-MS) were used to confirm this hypothesis. The results showed highly specific interactions with podocyte cells as detected by FACS, and CLSM. Moreover, ICP-MS demonstrated higher amount of QDs in the podocyte cells one-hour post-incubation (67.99% ID/g tissue), while the unmodified QDs did not accumulate. This study confirmed that QDs-VAP can target the podocyte's SSTRs then can be cleared via podocyte cells. Moreover, these results are considered as a highly promising approach for future therapy, targeting, clearance, and diagnosis of podocyte-associated diseases.

Role of Somatostatin in the Regulation of Central and Peripheral Factors of Satiety and Obesity

Obesity is one of the major social and health problems globally and often associated with various other pathological conditions. In addition to unregulated eating behaviour, circulating peptide-mediated hormonal secretion and signaling pathways play a critical role in food intake induced obesity. Amongst the many peptides involved in the regulation of food-seeking behaviour, somatostatin (SST) is the one which plays a determinant role in the complex process of appetite. SST is involved in the regulation of release and secretion of other peptides, neuronal integrity, and hormonal regulation. Based on past and recent studies, SST might serve as a bridge between central and peripheral tissues with a significant impact on obesity-associated with food intake behaviour and energy expenditure. Here, we present a comprehensive review describing the role of SST in the modulation of multiple central and peripheral signaling molecules. In addition, we highlight recent progress and contribution of SST and its receptors in food-seeking behaviour, obesity (orexigenic), and satiety (anorexigenic) associated pathways and mechanism.

Paracrine crosstalk between intestinal L- and D-cells controls secretion of glucagon-like peptide-1 in mice

DPP-4 inhibitors, used for treatment of type 2 diabetes, act by increasing the concentrations of intact glucagon-like peptide-1 (GLP-1), but at the same time, they inhibit secretion of GLP-1, perhaps by a negative feedback mechanism. We hypothesized that GLP-1 secretion is feedback regulated by somatostatin (SS) from neighboring D-cells, and blocking this feedback circuit results in increased GLP-1 secretion. We used a wide range of experimental techniques, including gene expression analysis, immunohistochemical approaches, and the perfused mouse intestine to characterize the paracrine circuit controlling GLP-1 and SS. We show that 1) antagonizing the SS receptor (SSTr) 2 and SSTr5 led to increased GLP-1 and SS secretion in the mouse, 2) SS exhibits strong tonic inhibition of GLP-1 secretion preferentially through SSTr5, and 3) the secretion of S was GLP-1 receptor dependent. We conclude that SS is a tonic inhibitor of GLP-1 secretion, and interventions in the somatostain-GLP-1 paracrine loop lead to increased GLP-1 secretion.

Biological and Biochemical Basis of the Differential Efficacy of First and Second Generation Somatostatin Receptor Ligands in Neuroendocrine Neoplasms

Endogenous somatostatin shows anti-secretory effects in both physiological and pathological settings, as well as inhibitory activity on cell growth. Since somatostatin is not suitable for clinical practice, researchers developed synthetic somatostatin receptor ligands (SRLs) to overcome this limitation. Currently, SRLs represent pivotal tools in the treatment algorithm of neuroendocrine tumors (NETs). Octreotide and lanreotide are the first-generation SRLs developed and show a preferential binding affinity to somatostatin receptor (SST) subtype 2, while pasireotide, which is a second-generation SRL, has high affinity for multiple SSTs (SST₅ > SST₂ > SST₃ > SST₁). A number of studies demonstrated that first-generation and second-generation SRLs show distinct functional properties, besides the mere receptor affinity. Therefore, the aim of the present review is to critically review the current evidence on the biological effects of SRLs in pituitary adenomas and neuroendocrine tumors, by mainly focusing on the differences between first-generation and second-generation ligands.

68Ga-DOTATATE positron emission tomography/computed tomography to detect the recurrence of phosphaturic mesenhcymal tumor-induced osteomalacia

⁶⁸Ga-DOTATATE positron emission tomography/computed tomography (PET/CT) has shown superiority over ¹¹¹Indium-octreotide scanning for the detection of phosphaturic mesenchymal tumors (PMTs). We report a case of tumor-induced osteomalacia resulting from PMT which, although initially clinically suspected, was not localized on octreotide scintigraphy performed several years prior. Subsequent surgical excision of a presumed benign osseous lesion a few years later revealed the diagnosis on pathology. Imaging assessment using ⁶⁸Ga-DOTATATE PET/CT following recent clinical suspicion for recurrence revealed an intense tracer-avid lesion at the primary tumor site. DOTATATE imaging plays an important role in localizing tumors with high somatostatin receptor expression, such as neuroendocrine tumors (pheochromocytoma, paraganglioma, and neuroblastoma), meningioma, and mesenchymal tumors, causing oncogenic osteomalacia.

Design and development of the theranostic pair 177 Lu-OPS201/68 Ga-OPS202 for targeting somatostatin receptor expressing tumors

Radiolabeled somatostatin receptor (sstr) antagonists have shown superiority in different preclinical and clinical settings compared with the well-established and clinically used agonists for targeting sstr-expressing tumors, with regard to pharmacokinetics, tumor uptake, and retention. The theranostic pair ¹⁷⁷ Lu-OPS201/⁶⁸ Ga-OPS202, based on the sstr2 antagonist JR11 (Cpa-c[d-Cys-Aph(Hor)-d-Aph(Cbm)-Lys-Thr-Cys]-d-Tyr-NH₂ ), is the most advanced pair of the antagonist family in terms of preclinical development and is currently under clinical evaluation. OPS201 and OPS202 share the same amino acid sequence (JR11) but feature different conjugated chelators needed for radiolabeling, DOTA for OPS201 and NODAGA for OPS202. In this review, the design and development of the peptidic analog, JR11, and the selection of chelators and radiometals that led to ¹⁷⁷ Lu-OPS201/⁶⁸ Ga-OPS202 are discussed. Furthermore, the preclinical evaluation of both radiolabeled analogs from bench to bedside and the clinical trials involving the theranostic pair are presented.

Recombinant α1-Microglobulin Is a Potential Kidney Protector in 177Lu-Octreotate Treatment of Neuroendocrine Tumors

Treatment of neuroendocrine tumors with ¹⁷⁷Lu-octreotate results in prolonged survival and improved quality of life for the patient. However, the treatment is today limited by side effects on kidney and bone marrow, and complete tumor remission is rarely seen. A possible way to minimize dose-limiting toxicity and to optimize this treatment method is to use radioprotectors in conjunction with radiotherapy. A recombinant form of α₁-microglobulin (rA1M) was recently shown to preserve kidney structure and function after ¹⁷⁷Lu-octreotate injection in mice and was suggested as a radioprotector in peptide receptor radionuclide therapy. The aims of this work were to investigate the influence of rA1M on the in vivo biokinetics of ¹⁷⁷Lu-octreotate, with a focus on tumor tissue, and to study the impact of rA1M on the therapeutic response in tumor tissue subjected to ¹⁷⁷Lu-octreotate treatment. Methods: The biodistribution of ¹⁷⁷Lu-octreotate was examined in BALB/c nude mice with GOT2 tumors 1-168 h after injection with either ¹⁷⁷Lu-octreotate or coadministration of ¹⁷⁷Lu-octreotate and rA1M. The effects of rA1M on the tumor response after ¹⁷⁷Lu-octreotate treatment were studied in BALB/c nude mice with GOT1 tumors. Three groups of mice were administered rA1M, ¹⁷⁷Lu-octreotate, or both. Another group served as untreated controls. Tumor volume was measured to follow the treatment effects. Results: No statistically significant difference in biodistribution of ¹⁷⁷Lu was observed between the groups receiving ¹⁷⁷Lu-octreotate or coinjection of ¹⁷⁷Lu-octreotate and rA1M. The therapy study showed a decrease in mean tumor volume during the first 2 wk for both the ¹⁷⁷Lu-octreotate group and the coadministration group, followed by tumor regrowth. No statistically significant difference between the groups was found. Conclusion: rA1M did not negatively impact absorbed dose to tumor or therapeutic response in combination with ¹⁷⁷Lu-octreotate and may be a promising kidney protector during ¹⁷⁷Lu-octreotate treatment of patients with neuroendocrine tumors.