Clinicopathological and Molecular Profile of Sellar Neurocytoma

OBJECTIVE

To investigate the clinical features, imaging characteristics and molecular profile of Sellar neurocytoma (SN).

METHODS

Clinical, imaging, and pathological features of eleven cases of sellar neurocytoma were retrospectively analyzed. Electron microscopy was performed in five cases. Molecular features were detected in tumor tissue by RNA sequencing, qPCR and IHC.

RESULTS

The clinical features of SN patients showed high incidence of hyponatremia (73%,8/11) and the tumors tended to invaded lateral side of saddle area from preoperative imaging analysis. The tumors had positive NeuN, SYN, NF, SSTR2 immunohistochemistry staining. Tumor transcriptomic analysis suggested a new LMCD1-AS1:GRM7-AS1 fusion gene event and increased expression of 10 hypothalamus-secreted hormones in SN. 15 differentially expressed genes were verified for qPCR verification. SSTR2 has been verified by immunohistochemistry.

CONCLUSIONS

Hyponatremia is the dominant clinical features of SN. Preoperative imaging suggests that growth toward the dorsal region is the imaging feature of SN. SSTR2 expression and LMCD1-AS1:GRM7-AS1 fusion gene event expected to become a new molecular marker for SN. Somatostatin receptor ligand therapy may be a potential therapy for SN.

Efficacy of [67Cu]Cu-EB-TATE Theranostic Against Somatostatin Receptor Subtype-2-Positive Neuroendocrine Tumors

β--emitting 177Lu-octreotate is an approved somatostatin receptor subtype 2 (SSTR2)-directed peptide receptor radionuclide therapy for the treatment of gastroenteropancreatic neuroendocrine tumors (NETs). However,177Lu-octreotate has fast pharmacokinetics, requiring up to 4 treatment doses. Moreover, 177Lu is less than ideal for theranostics because of the low branching ratio of its γ-emissions, which limits its SPECT imaging capability. Compared with 177Lu, 67Cu has better decay properties for use as a theranostic. Here, we report the preclinical evaluation of a long-lived somatostatin analog, [67Cu]Cu-DOTA-Evans blue-TATE (EB-TATE), against SSTR2-positive NETs. Methods: The in vitro cytotoxicity of [67Cu]Cu-EB-TATE was investigated on 2-dimensional cells and 3-dimensional spheroids. In vivo pharmacokinetics and dosimetry were studied in healthy BALB/c mice, whereas ex vivo biodistribution, micro-SPECT/CT imaging, and therapy studies were done on athymic nude mice bearing QGP1.SSTR2 and BON1.SSTR2 xenografts. Therapeutic efficacy was compared with [177Lu]Lu-EB-TATE. Results: Projected human effective doses of [67Cu]Cu-EB-TATE for male (0.066 mSv/MBq) and female (0.085 mSv/MBq) patients are tolerable. In vivo micro-SPECT/CT imaging of SSTR2-positive xenografts with [67Cu]Cu-EB-TATE showed tumor-specific uptake and prolonged accumulation. Biodistribution showed tumor accumulation, with concurrent clearance from major organs over a period of 72 h. [67Cu]Cu-EB-TATE was more effective (60%) at eliminating tumors that were smaller than 50 mm3 within the first 15 d of therapy than was [177Lu]Lu-EB-TATE (20%) after treatment with 2 doses of 15 MBq administered 10 d apart. Mean survival of [67Cu]Cu-EB-TATE-treated groups was 90 d and more than 90 d, whereas that of [177Lu]Lu-EB-TATE was more than 90 d and 89 d against vehicle control groups (26 d and 53 d), for QGP1.SSTR2 and BON1.SSTR2 xenografts, respectively. Conclusion: [67Cu]Cu-EB-TATE exhibited high SSTR2-positive NET uptake and retention, with favorable dosimetry and SPECT/CT imaging capabilities. The antitumor efficacy of [67Cu]Cu-EB-TATE is comparable to that of [177Lu]Lu-EB-TATE, with [67Cu]Cu-EB-TATE being slightly more effective than [177Lu]Lu-EB-TATE for complete remission of small tumors. [67Cu]Cu-EB-TATE therefore warrants clinical development.

SSTR2 Mediates the Inhibitory Effect of SST/CST on Lipolysis in Chicken Adipose Tissue

Somatostatin shows an anti-lipolytic effect in both chickens and ducks. However, its molecular mediator remains to be identified. Here, we report that somatostatin type 2 receptor (SSTR2) is expressed at a high level in chicken adipose tissue. In cultured chicken adipose tissue, the inhibition of glucagon-stimulated lipolysis by somatostatin was blocked by an SSTR2 antagonist (CYN-154086), supporting an SSTR2-mediated anti-lipolytic effect. Furthermore, a significant pro-proliferative effect was detected in SST28-treated immortalized chicken preadipocytes (ICP-1), and this cell proliferative effect may be mediated through the MAPK/ERK signaling pathway activated by SSTR2. In summary, our results demonstrate that SSTR2 may regulate adipose tissue development by affecting the number and volume of adipocytes in chickens.

Low-dose targeted radionuclide therapy synergizes with CAR T cells and enhances tumor response

Ionizing radiation has garnered considerable attention as a combination partner for immunotherapy due to its potential immunostimulatory effects. In contrast to the more commonly used external beam radiation, we explored the feasibility of combining chimeric antigen receptor (CAR) T cell therapy with targeted radionuclide therapy (TRT), which is achieved by delivering β-emitting 177Lu-DOTATATE to tumor via tumor-infiltrating CAR T cells that express somatostatin receptor 2 (SSTR2). We hypothesized that the delivery of radiation to tumors could synergize with CAR T therapy, resulting in enhanced antitumor immunity and tumor response. To determine the optimal dosage and timing of 177Lu-DOTATATE treatment, we measured CAR T cell infiltration and expansion in tumors longitudinally through positron emission tomography (PET) using a SSTR2-specific positron-emitting radiotracer,18F-NOTA-Octreotide. In animals receiving CAR T cells and a low-dose (2.5 Gy) of TRT following the administration of 177Lu-DOTATATE, we observed a rapid regression of large subcutaneous tumors, which coincided with a dramatic increase in serum proinflammatory cytokines. Tumor burden was also reduced when a higher radiation dose (6 Gy) was delivered to the tumor. However, this higher dose led to cell death in both the tumor and CAR T cells. Our study suggests that there may exist an optimum range of TRT dosage that can enhance T cell activity and sensitize tumor cells to T cell killing, which may result in more durable tumor control compared to a higher radiation dose.

Structural modifications toward improved lead-203/lead-212 peptide-based image-guided alpha-particle radiopharmaceutical therapies for neuroendocrine tumors

PURPOSE

The lead-203 (203Pb)/lead-212 (212Pb) elementally identical radionuclide pair has gained significant interest in the field of image-guided targeted alpha-particle therapy for cancer. Emerging evidence suggests that 212Pb-labeled peptide-based radiopharmaceuticals targeting somatostatin receptor subtype 2 (SSTR2) may provide improved effectiveness compared to beta-particle-based therapies for neuroendocrine tumors (NETs). This study aims to improve the performance of SSTR2-targeted radionuclide imaging and therapy through structural modifications to Tyr3-octreotide (TOC)-based radiopharmaceuticals.

METHODS

New SSTR2-targeted peptides were designed and synthesized with the goal of optimizing the incorporation of Pb isotopes through the use of a modified cyclization technique; the introduction of a Pb-specific chelator (PSC); and the insertion of polyethylene glycol (PEG) linkers. The binding affinity of the peptides and the cellular uptake of 203Pb-labeled peptides were evaluated using pancreatic AR42J (SSTR2+) tumor cells and the biodistribution and imaging of the 203Pb-labeled peptides were assessed in an AR42J tumor xenograft mouse model. A lead peptide was identified (i.e., PSC-PEG2-TOC), which was then further evaluated for efficacy in 212Pb therapy studies.

RESULTS

The lead radiopeptide drug conjugate (RPDC) - [203Pb]Pb-PSC-PEG2-TOC - significantly improved the tumor-targeting properties, including receptor binding and tumor accumulation and retention as compared to [203Pb]Pb-DOTA0-Tyr3-octreotide (DOTATOC). Additionally, the modified RPDC exhibited faster renal clearance than the DOTATOC counterpart. These advantageous characteristics of [212Pb]Pb-PSC-PEG2-TOC resulted in a dose-dependent therapeutic effect with minimal signs of toxicity in the AR42J xenograft model. Fractionated administrations of 3.7 MBq [212Pb]Pb-PSC-PEG2-TOC over three doses further improved anti-tumor effectiveness, resulting in 80% survival (70% complete response) over 120 days in the mouse model.

CONCLUSION

Structural modifications to chelator and linker compositions improved tumor targeting and pharmacokinetics (PK) of 203/212Pb peptide-based radiopharmaceuticals for NET theranostics. These findings suggest that PSC-PEG2-TOC is a promising candidate for Pb-based targeted radionuclide therapy for NETs and other types of cancers that express SSTR2.

PPY-cell hyperplasia accompanying NENs: Immunohistochemical and nuclear medicine analysis

Pancreatic polypeptide cell hyperplasia (PPY-H) is a multiplication of the neuroendocrine cells producing pancreatic polypeptide (PPY). The development and role of PPY-H and its corresponding clinical and imaging findings still need to be fully elucidated. We present 12 cases of PPY-H accompanying pancreatic neuroendocrine neoplasias (NEN). PPY-H was analyzed with the help of immunohistochemistry and confocal microscopy; preoperative clinical data and imaging studies were evaluated retrospectively. We observed PPY-H emerging from pancreatic ducts, and in some cases, we observed simultaneous NKX6.1 positivity in ducts and PPY-H. Additional clinical-pathological correlations suggests that gastrointestinal symptoms (e.g., epigastric pain and cholestasis) could be more related to PPY-H than to NEN hormonal production. In particular cases, SSTR2 expression was strong in PPY-H and correlated with distinguishable accumulation of activity next to NEN on 99 mTc EDDA/Hynic-TOC SPECT/CT. In another case, 18F-FDG-PET/CT showed increased metabolic activity in the area of PPY-H surrounding NEN. Our data suggest that PPY-H originates in the lining of pancreatic ducts. Confirmation of SSTR2 in PPY-H, using immunohistochemistry, suggests the utility of 99 mTc EDDA/Hynic-TOC or 68Ga-DOTA radiotracers in clinical diagnostics; however, studies with larger cohort are needed.

Challenging Tumor Heterogeneity with HER2, p16 and Somatostatin Receptor 2 Expression in a Case of EBV-Associated Lymphoepithelial Carcinoma of the Salivary Gland

BACKGROUND

Lymphoepithelial carcinoma of the salivary glands (LECSG) is a rare disease in the Western hemisphere that is typically associated with an EBV infection. The molecular mechanisms of LECSG tumorigenesis are poorly understood.

RESULTS

Here we report a case of EBV-associated LECSG with an unusual immunophenotype. The tumor exhibited bi-morphic histological features with a mutually exclusive expression of HER2 and p16. The p16-positive domain of the tumor immunohistochemically co-expressed late membrane protein 1 (LMP-1), while the HER2 positive domain did not. Both tumor regions expressed SSTR2.

METHODS

In situ hybridization confirmed the EBV origin of the tumor while extensive immunohistochemical characterization and the recently established RNA-based next generation sequencing panel ("SalvGlandDx" panel) did not reveal evidence for another salivary gland neoplasm. No HPV co-infection was detected by in situ hybridization or PCR-based screenings and no ERBB2 gene amplification was detected by fluorescence in situ hybridization.

CONCLUSION

These findings suggest tumor heterogeneity and lack of genomic aberrations in EBV-associated LECSGs. The heterogenous and unusual immunohistochemical features explain the diagnostic difficulties and simultaneously extend the immunophenotype spectrum of this tumor entity.

Novel Discovery of the Somatostatin Receptor (SSTR2) in Pleomorphic Adenomas via Immunohistochemical Analysis of Tumors of the Salivary Glands

Reliable preoperative diagnosis between salivary gland tumor entities is difficult. In this monocentric retrospective study, we examined the somatostatin receptor 2 (SSTR2) status of salivary gland tumors after salivary gland tumor resection via immunohistochemistry (IHC), and stains were compared in analogy to the HER2 mamma scale. A total of 42.3% of all pleomorphic adenoma (PA) tumors (42 of 99, 95% confidence interval 32.5-52.8%) demonstrated ≥20% of cells displaying the SSTR2 as compared to just 1% of all other tumors (1/160, 95% CI 0.02-3.4%). The other tumor was a neuroendocrine carcinoma. PA had a higher intensity of SSTR2 staining, with 90.9% staining ≥ an intensity of 2 (moderate). Tumors with an intensity of SSTR2 expression equal to or greater than 2 had an 89.9% likelihood of being a PA (95% CI: 82.2-95.0%, AUC: 0.928). Only one Warthin tumor demonstrated a 'strong' SSTR2 staining intensity. No Warthin tumor showed a percentage of cells staining for SSTR2 above ≥20%. This result demonstrates consistent and strong expression of SSTR2 in PAs as compared to Warthin tumors, which may allow physicians to utilize radioligand-somatostatin analog PET CT/MR imaging to diagnose the PA. SSTR2 positivity, if shown to be clinically relevant, may allow peptide receptor radionuclide therapy in the future.

[212Pb]Pb-eSOMA-01: A Promising Radioligand for Targeted Alpha Therapy of Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) has been applied to the treatment of neuroendocrine tumors (NETs) for over two decades. However, improvement is still needed, and targeted alpha therapy (TAT) with alpha emitters such as lead-212 (²¹²Pb) represents a promising avenue. A series of ligands based on octreotate was developed. Lead-203 was used as an imaging surrogate for the selection of the best candidate for the studies with lead-212. ^203/212Pb radiolabeling and in vitro assays were carried out, followed by SPECT/CT imaging and ex vivo biodistribution in NCI-H69 tumor-bearing mice. High radiochemical yields (≥99%) and purity (≥96%) were obtained for all ligands. [²⁰³Pb]Pb-eSOMA-01 and [²⁰³Pb]Pb-eSOMA-02 showed high stability in PBS and mouse serum up to 24 h, whereas [²⁰³Pb]Pb-eSOMA-03 was unstable in those conditions. All compounds exhibited a nanomolar affinity (2.5-3.1 nM) for SSTR2. SPECT/CT images revealed high tumor uptake at 1, 4, and 24 h post-injection of [²⁰³Pb]Pb-eSOMA-01/02. Ex vivo biodistribution studies confirmed that the highest uptake in tumors was observed with [²¹²Pb]Pb-eSOMA-01. [²¹²Pb]Pb-eESOMA-01 displayed the highest absorbed dose in the tumor (35.49 Gy/MBq) and the lowest absorbed dose in the kidneys (121.73 Gy/MBq) among the three tested radioligands. [²¹²Pb]Pb-eSOMA-01 is a promising candidate for targeted alpha therapy of NETs. Further investigations are required to confirm its potential.

First preclinical evaluation of [225Ac]Ac-DOTA-JR11 and comparison with [177Lu]Lu-DOTA-JR11, alpha versus beta radionuclide therapy of NETs

BACKGROUND

The [¹⁷⁷Lu]Lu-DOTA-TATE mediated peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs) is sometimes leading to treatment resistance and disease recurrence. An interesting alternative could be the somatostatin antagonist, [¹⁷⁷Lu]Lu-DOTA-JR11, that demonstrated better biodistribution profile and higher tumor uptake than [¹⁷⁷Lu]Lu-DOTA-TATE. Furthermore, treatment with alpha emitters showed improvement of the therapeutic index of PRRT due to the high LET offered by the alpha particles compared to beta emitters. Therefore, [²²⁵Ac]Ac-DOTA-JR11 can be a potential candidate to improve the treatment of NETs (Graphical abstract). DOTA-JR11 was radiolabeled with [²²⁵Ac]Ac(NO₃)₃ and [¹⁷⁷Lu]LuCl₃. Stability studies were performed in phosphate buffered saline (PBS) and mouse serum. In vitro competitive binding assay has been carried out in U2OS-SSTR2 + cells for ^natLa-DOTA-JR11, ^natLu-DOTA-JR11 and DOTA-JR11. Ex vivo biodistribution studies were performed in mice inoculated with H69 cells at 4, 24, 48 and 72 h after injection of [²²⁵Ac]Ac-DOTA-JR11. A blocking group was included to verify uptake specificity. Dosimetry of selected organs was determined for [²²⁵Ac]Ac-DOTA-JR11 and [¹⁷⁷Lu]Lu-DOTA-JR11.

RESULTS

[²²⁵Ac]Ac-DOTA-JR11 has been successfully prepared and obtained in high radiochemical yield (RCY; 95%) and radiochemical purity (RCP; 94%). [²²⁵Ac]Ac-DOTA-JR11 showed reasonably good stability in PBS (77% intact radiopeptide at 24 h after incubation) and in mouse serum (~ 81% intact radiopeptide 24 h after incubation). [¹⁷⁷Lu]Lu-DOTA-JR11 demonstrated excellent stability in both media (> 93%) up to 24 h post incubation. Competitive binding assay revealed that complexation of DOTA-JR11 with ^natLa and ^natLu did not affect its binding affinity to SSTR2. Similar biodistribution profiles were observed for both radiopeptides, however, higher uptake was noticed in the kidneys, liver and bone for [²²⁵Ac]Ac-DOTA-JR11 than [¹⁷⁷Lu]Lu-DOTA-JR11.

CONCLUSION

[²²⁵Ac]Ac-DOTA-JR11 showed a higher absorbed dose in the kidneys compared to [¹⁷⁷Lu]Lu-DOTA-JR11, which may limit further studies with this radiopeptide. However, several strategies can be explored to reduce nephrotoxicity and offer opportunities for future clinical investigations with [²²⁵Ac]Ac-DOTA-JR11.

Circulating hsa-miR-5096 predicts 18F-FDG PET/CT positivity and modulates somatostatin receptor 2 expression: a novel miR-based assay for pancreatic neuroendocrine tumors

Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) are rare diseases encompassing pancreatic (PanNETs) and ileal NETs (SINETs), characterized by heterogeneous somatostatin receptors (SSTRs) expression. Treatments for inoperable GEP-NETs are limited, and SSTR-targeted Peptide Receptor Radionuclide Therapy (PRRT) achieves variable responses. Prognostic biomarkers for the management of GEP-NET patients are required. ¹⁸F-FDG uptake is a prognostic indicator of aggressiveness in GEP-NETs. This study aims to identify circulating and measurable prognostic miRNAs associated with ¹⁸F-FDG-PET/CT status, higher risk and lower response to PRRT.

Methods

Whole miRNOme NGS profiling was conducted on plasma samples obtained from well-differentiated advanced, metastatic, inoperable G1, G2 and G3 GEP-NET patients enrolled in the non-randomized LUX (NCT02736500) and LUNET (NCT02489604) clinical trials prior to PRRT (screening set, n= 24). Differential expression analysis was performed between ¹⁸F-FDG positive (n=12) and negative (n=12) patients. Validation was conducted by Real Time quantitative PCR in two distinct well-differentiated GEP-NET validation cohorts, considering the primary site of origin (PanNETs n=38 and SINETs n=30). The Cox regression was applied to assess independent clinical parameters and imaging for progression-free survival (PFS) in PanNETs. In situ RNA hybridization combined with immunohistochemistry was performed to simultaneously detect miR and protein expression in the same tissue specimens. This novel semi-automated miR-protein protocol was applied in PanNET FFPE specimens (n=9). In vitro functional experiments were performed in PanNET models.

Results

While no miRNAs emerged to be deregulated in SINETs, hsa-miR-5096, hsa-let-7i-3p and hsa-miR-4311 were found to correlate with ¹⁸F-FDG-PET/CT in PanNETs (p-value:<0.005). Statistical analysis has shown that, hsa-miR-5096 can predict 6-month PFS (p-value:<0.001) and 12-month Overall Survival upon PRRT treatment (p-value:<0.05), as well as identify ¹⁸F-FDG-PET/CT positive PanNETs with worse prognosis after PRRT (p-value:<0.005). In addition, hsa-miR-5096 inversely correlated with both SSTR2 expression in PanNET tissue and with the ⁶⁸Gallium-DOTATOC captation values (p-value:<0.05), and accordingly it was able to decrease SSTR2 when ectopically expressed in PanNET cells (p-value:<0.01).

Conclusions

hsa-miR-5096 well performs as a biomarker for ¹⁸F-FDG-PET/CT and as independent predictor of PFS. Moreover, exosome-mediated delivery of hsa-miR-5096 may promote SSTR2 heterogeneity and thus resistance to PRRT.

Case Report: Octreotide plus CVD chemotherapy for the treatment of multiple metastatic paragangliomas after double resection for functional bladder paraganglioma and urothelial papilloma

Background

Metastatic pheochromocytomas and paragangliomas are rare neuroendocrine tumors with a poor prognosis. Bladder paraganglioma concomitant with urothelial papilloma is even rarer. However, the rate of tumor response to cyclophosphamide-vincristine-dacarbazine (CVD) chemotherapy and 5-year overall survival for patients with metastatic PPGLs remained lower. We described, for the first time, a case of a patient with multiple metastatic bladder PGL who received octreotide LAR combined with CVD chemotherapy after urological surgery and then octreotide therapy was continued during follow-up.

Case presentation

A 43-year-old male patient was admitted to the urology department for frequent micturition syncope concomitant with malignant hypertension. Preoperative findings were elevated levels of normetanephrine in 24-h urine or plasma. CT and MRI indicated diagnosis of suspicious bladder paraganglioma. Transurethral resection of bladder tumor combined with laparoscopic partial cystectomy was performed successfully after preoperative phenoxybenzamine with aggressive volume repletion for 7 days. The result of postoperative pathology was immediate-risk functional bladder paraganglioma (T2N0M0, Stage II) concomitant with urothelial papilloma, and the immunohistochemistry results of PPGL were positive for Ki-67 (15%), SDHB, CgA, and SSTR2. The patient achieved enhanced recovery with normal urination and no syncope after surgery. However, the results of ¹⁸F-FDG and ¹⁸F-DOTATATE PET/CT found that the metastatic localizations of bladder PGLs were in the liver, lung, and bones at the 8th month after surgery. The patient received octreotide long-acting repeatable plus six courses of CVD chemotherapy for 6 months, and then octreotide therapy was continued every 3 months until now. Metastatic localizations were stable in CT scans, and vanillylmandelic acid in 24-h urine was maintained at lower levels during follow-up.

Conclusion

Octreotide long-acting repeatable plus CVD chemotherapy after surgery could achieve stable disease in the case with multiple metastatic bladder PGLs, and the following octreotide therapy could maintain a state of stable disease during the period of 6-month follow-up.

Resistance to Somatostatin Analogs in Italian Acromegaly Patients: The MISS Study

Approximately 60% of acromegaly patients are not adequately controlled by first-generation somatostatin receptor ligands. This multicenter retrospective study aimed to identify the most relevant biomarkers specific for the Italian acromegaly population. Resistant patients were enrolled consecutively based on time of neurosurgery, while responders were collected in a 1:2 ratio. Clinical characteristics and T2-intensity on MRI scans at diagnosis were retrospectively re-evaluated. Histological analyses of CAM5.2 granulation patterns and SSTR2 expression were centrally performed. Sixty-three resistant patients and thirty-three responders were enrolled. A low-grade SSTR2 expression was the most relevant predictor of resistance identified (OR 4.58, p = 0.013), even considering CAM5.2 immunohistochemistry (OR 2.65, p = 0.047). T2-iso/hyperintense pattern on MRI was also associated with a 3.3-fold greater probability of poor response to medical treatment (p = 0.027), as well as a young age at diagnosis (OR 0.96, p = 0.035). In those patients treated only after neurosurgery due to persistent GH-hypersecretion (51, 53.1%) the absence of any appreciable adenomatous remnant on postoperative MRI was associated with a negligible risk of resistance (OR 0.04, p = 0.003). In the Italian acromegaly population, a low-grade SSTR2 expression seems to be the most relevant predictor of resistance to first-generation somatostatin receptor ligands, followed by a SG/intermediate cytokeratin pattern and a T2-iso/hyperintense MRI signal.

Aberrant Methylation of Somatostatin Receptor 2 Gene Is Initiated in Aged Gastric Mucosa Infected with Helicobacter pylori and Consequential Gene Silencing Is Associated with Establishment of Inflammatory Microenvironment In Vitro Study

The loss-of-function variants are thought to be associated with inflammation in the stomach. We here aimed to evaluate the extent and role of methylation at the SSTR2 promoter in inflammation and gastric tumor formation. A whole-genome bisulfite sequencing analysis revealed that the SSTR2 promoter was significantly hypermethylated in gastric tumors, dysplasia, and intestinal metaplasia compared to non-tumor tissues from patients with gastric cancer. Using public data, we confirmed SSTR2 promoter methylation in primary gastric tumors and intestinal metaplasia, and even aged gastric mucosae infected with Helicobacter pylori, suggesting that aberrant methylation is initiated in normal gastric mucosa. The loss-of-function of SSTR2 in SNU638 cell-induced cell proliferation in vitro, while stable transfection of SSTR2 in AGS and MKN74 cells inhibited cell proliferation and tumorigenesis in vitro and in vivo. As revealed by a comparison of target genes differentially expressed in these cells with hallmark molecular signatures, inflammation-related pathways were distinctly induced in SSTR2-KO SNU638 cell. By contrast, inflammation-related pathways were inhibited in AGS and MKN74 cells ectopically expressing SSTR2. Collectively, we propose that SSTR2 silencing upon promoter methylation is initiated in aged gastric mucosae infected with H. pylori and promotes the establishment of an inflammatory microenvironment via the intrinsic pathway. These findings provide novel insights into the initiation of gastric carcinogenesis.

Exploring the Potential of High-Molar-Activity Samarium-153 for Targeted Radionuclide Therapy with [(153)Sm]Sm-DOTA-TATE

Samarium-153 is a promising theranostic radionuclide, but low molar activities (Am) resulting from its current production route render it unsuitable for targeted radionuclide therapy (TRNT). Recent efforts combining neutron activation of 152Sm in the SCK CEN BR2 reactor with mass separation at CERN/MEDICIS yielded high-Am 153Sm. In this proof-of-concept study, we further evaluated the potential of high-Am 153Sm for TRNT by radiolabeling to DOTA-TATE, a well-established carrier molecule binding the somatostatin receptor 2 (SSTR2) that is highly expressed in gastroenteropancreatic neuroendocrine tumors. DOTA-TATE was labeled with 153Sm and remained stable up to 7 days in relevant media. The binding specificity and high internalization rate were validated on SSTR2-expressing CA20948 cells. In vitro biological evaluation showed that [153Sm]Sm-DOTA-TATE was able to reduce CA20948 cell viability and clonogenic potential in an activity-dependent manner. Biodistribution studies in healthy and CA20948 xenografted mice revealed that [153Sm]Sm-DOTA-TATE was rapidly cleared and profound tumor uptake and retention was observed whilst these were limited in normal tissues. This proof-of-concept study showed the potential of mass-separated 153Sm for TRNT and could open doors towards wider applications of mass separation in medical isotope production.

Epigenetic potentiation of somatostatin-2 by guadecitabine in neuroendocrine neoplasias as a novel method to allow delivery of peptide receptor radiotherapy

BACKGROUND

Somatostatin receptor-2 (SSTR2) is expressed on cell surface of neuroendocrine neoplasias; its presence is exploited for the delivery of peptide receptor radionuclide therapy (PRRT). Patients with no or low expression of SSTR2 are not candidates for PRRT. SSTR2 promotor undergoes epigenetic modification, known to regulate gene expression. We investigated whether the demethylation agent, guadecitabine, could enhance the expression of SSTR2 in NET models, using radioligand uptake/PET imaging as a biomarker of epigenetic modification.

METHODS

The effects of guadecitabine on the transcriptional, translational, and functional regulation of SSTR2 both in vitro and in vivo using low (QGP-1) and high (BON-1) methylated neuroendocrine neoplasia models was characterised. Promotor region methylation profiling of clinical samples (n = 61) was undertaken. Safety of combination guadecitabine and PRRT was assessed in vivo.

RESULTS

Pyrosequencing of cell lines illustrated differential methylation indices - BON: 1 94%, QGP: 1 21%. Following guadecitabine treatment, a dose-dependent increase in SSTR2 in BON-1 at a transcriptional, translational, and functional levels using the SSTR2-directed radioligand, ¹⁸F-FET-βAG-TOCA ([¹⁸F]-FETO) (150% increase [¹⁸F]-FETO uptake, p < 0.05) was observed. In vivo, guadecitabine treatment resulted in a 70% increase in [¹⁸F]-FETO uptake in BON-1 tumour models compared models with low baseline percentage methylation (p < 0.05). No additive toxicity was observed with the combination treatment of PRRT and guadecitabine in vivo. Methylation index in clinical samples was 10.5% compared to 5.2% in controls (p = 0.03) and correlated with SSTR2 expression (Wilcoxon rank sign -3.75,p < 0.01).

CONCLUSION

Guadecitabine increases SSTR2 expression both in vitro and in vivo. The combination of demethylation agents with PRRT warrants further investigation.

Changes in dorsal root ganglion CGRP expression in mouse pinch nerve injury model: Modulation by Somatostatin type-2 receptor

INTRODUCTION

Our previous work has shown that somatostatin effectively inhibits neuropathic pain by activating its type 2 receptor (SSTR2) in the dorsal root ganglion (DRG) and spinal cord of mice. However, the underlying mechanism of this activation has not been elucidated.

METHODS

To explore further mechanisms, we examined pain behavior and the expression of neuropeptides such as calcitonin gene-related peptide (CGRP) in dorsal root ganglion neurons(DRGs) as well as the changes of the number of CGRP-IR DRGs in the mouse model of sciatic pinch nerve injury.

RESULTS

In this model, the number of medium and small DRG neurons in ipsilateral CGRP-IR was slightly increased, but not significantly, compared with sham animals at 3, 7, and 9 days after pinch nerve injury. This correlated with the behavioral readouts of hypersensitivity at the same time points. However, the magnitude of the painful behavior (Autotomy) was observed after application of SSTR2 antagonist (CYN154806, 5 mg/kg) in the injured nerve groups compared to the saline-treated injured group as well as the sham-operated group. Following pinch nerve injury, there was a significant decrease in the number of ipsilateral CGRP-IR small and medium DRG neurons in SSTR2 antagonist (anti-SSTR2)- but not saline-treated mice. These data also correlated with painful behavioral readouts where hypersensitivity was significantly increased by anti-SSTR2 but not saline treatment.

DISCUSSION/CONCLUSION

In all, application of the SSTR2 antagonist to the pinched sciatic nerve suppressed CGRP expression and aggravated painful behavior, suggesting that CGRP expression in DRG neurons can be an important component of the pain mechanism and an indicator of pain behavior.

Correlation of Somatostatin Receptor 2 Expression, 68Ga-DOTATATE PET Scan and Octreotide Treatment in Thymic Epithelial Tumors

Somatostatin receptor 2 (SSTR2) has been shown to be expressed in a subset of neuroendocrine tumors and carcinomas and plays a role in imaging studies and guiding therapy. Patients with tumors expressing SSTR2 may be successfully treated with somatostatin inhibitors or radiolabeled somatostatin analogues. We studied SSTR2 expression in TET and correlated it with 68Ga-DOTATATE PET/CT or 68Ga-DOTATATE PET/MR results and treatment outcome. An institutional database of TET was searched for thymoma, thymic carcinoma, and thymic neuroendocrine tumor (TNET) with available resection specimens. Cases were subtyped (2021 WHO classification) and staged (8^th AJCC/UICC staging). A section was stained with anti-SSTR2 antibody (clone UMB1). Percent tumor cells with membranous staining was recorded if present in ≥1% of tumor cells. Medical records were searched for 68Ga-DOTATATE PET scans and treatment. Statistical analysis was performed. Eighty patients (1969-2021) with a median age of 61.3 years (range, 19.1-87.3) (37 males, 46.3%) had thymic carcinoma (N=33), TNET (N=7), or thymoma (N=40). SSTR2 expression was identified in 29 (of 80, 36.3%) TET including 2/2 (100%) small cell carcinomas, 2/5 (40.0%) atypical carcinoid tumors, 16/23 (69.6%) squamous cell carcinomas, 2/2 (100%) lymphoepithelial carcinomas, 1/1 (100%) adenosquamous carcinoma, and 6/40 (15.0%) thymomas. SSTR2 expression in ≥50% of tumor cells (vs 1-49%) was associated with younger age (p=0.023) and shorter recurrence/metastasis-free survival (p=0.007). 68Ga-DOTATATE PET scans (N=9) revealed a Krenning score of 3 in patients with atypical carcinoid tumor, small cell carcinoma, and squamous cell carcinoma (N=1 each) with SSTR2 expression in 95, 100, and 5% of tumor cells, respectively. Scans with Krenning scores of ≤2 (N=5) were seen in tumors with no SSTR2 expression in 80% of cases and a single atypical carcinoid tumor with SSTR2 expression in 10% of tumor cells. One scan resulted as "increased uptake" was in a patient with no SSTR2 expression. In conclusion, 68Ga-DOTATATE PET scans correlated with SSTR2 expression in TET in most patients and appeared to be useful to identify patients with TET who may be amenable to treatment with somatostatin analogues. Larger studies including more patients with 68Ga-DOTATATE PET scans are necessary to independently and prospectively validate our findings.

The Effect of VPA Treatment on Radiolabeled DOTATATE Uptake: Differences Observed In Vitro and In Vivo

Background: To improve peptide receptor radionuclide therapy (PRRT), we aimed to enhance the expression of somatostatin type-2 receptors (SSTR2) in vitro and in vivo, using valproic acid (VPA). Methods: Human NCI-H69 small-cell lung carcinoma cells were treated with VPA, followed by [¹¹¹In]In-DOTATATE uptake studies, RT-qPCR and immunohistochemistry analysis. Furthermore, NCI-H69 xenografted mice were treated with VPA or vehicle, followed by [¹⁷⁷Lu]Lu-DOTATATE injection. Biodistribution studies were performed, and tissues were collected for further analysis. Results: VPA significantly increased SSTR2 expression in vitro. In animals, a statistically significant increased [¹⁷⁷Lu]Lu-DOTATATE tumoral uptake was observed when VPA was administered eight hours before [¹⁷⁷Lu]Lu-DOTATATE administration, but increased tumor SSTR2 expression levels were lacking. The animals also presented significantly higher [¹⁷⁷Lu]Lu-DOTATATE blood levels, as well as an elevated renal tubular damage score. This suggests that the enhanced tumor uptake was presumably a consequence of the increased radiotracer circulation and the induced kidney damage. Conclusions: VPA increases SSTR2 expression in vitro. In vivo, the observed increase in tumoral [¹⁷⁷Lu]Lu-DOTATATE uptake is not caused by SSTR2 upregulation, but rather by other mechanisms, e.g., an increased [¹⁷⁷Lu]Lu-DOTATATE circulation time and renal toxicity. However, since both drugs are safely used in humans, the potential of VPA to improve PRRT remains open for investigation.

Design, synthesis, and biological evaluation of novel somatostatin receptor subtype-2 agonists: Optimization for potency and risk mitigation of hERG and phospholipidosis

Somatostatin receptors are members of G-protein coupled receptor superfamily. Receptors can be classified into five subtypes, SSTR1 to 5. The highly potent and orally active SSTR2 agonist 7, which had been identified by our group, was found out to have toxicological liabilities such as hERG inhibition and phospholipidosis (PLD). We investigated the relationship between in silico physicochemical properties and hERG and PLD, and explored well-balanced agonists to identify amide 19 and benzimidazole 30. As a result of this exploration, we found out that the value of (cLogP) [2] + (pKa) [2] needs to be less than 110 to mitigate the liabilities.

Somatostatin receptor imaging with [68Ga]Ga-DOTATATE positron emission tomography/computed tomography (PET/CT) in patients with nasopharyngeal carcinoma

PURPOSE

To explore the feasibility of [⁶⁸Ga]Ga-DOTATATE positron emission tomography/computed tomography (PET/CT) in patients with non-keratinizing nasopharyngeal carcinoma (NPC) and to evaluate whether [⁶⁸Ga]Ga-DOTATATE PET/CT could be used for non-invasive determination of somatostatin receptor 2 (SSTR2) expression in NPC.

METHODS

This prospective study included patients with NPC who underwent [⁶⁸Ga]Ga-DOTATATE PET/CT between February and May 2021. The [⁶⁸Ga]Ga-DOTATATE and [¹⁸F]FDG uptakes in primary and metastatic NPC lesions were calculated and compared, and the [⁶⁸Ga]Ga-DOTATATE uptake between SSTR2 score groups was analysed.

RESULTS

A total of 36 participants (25 patients, initial staging; 11 patients, recurrence detection) were included; 33 patients also underwent [¹⁸F]FDG PET/CT for staging/restaging as a part of their routine diagnostic workup. [⁶⁸Ga]Ga-DOTATATE PET/CT showed an intense tracer uptake in primary and metastatic NPC lesions. The radiotracer uptake was higher with [⁶⁸Ga]Ga-DOTATATE than with [¹⁸F]FDG PET in primary NPC lesions (SUVmax: 12.03 vs. 10.07, P = 0.048; tumour-to-brain ratio: 36.16 vs. 0.86, P < 0.001) and regional lymph node metastases (median SUVmax: 9.11 vs. 6.12, P < 0.001) and comparable in bone and visceral metastases. Importantly, most NPC lesions showed intense SSTR2 expression (85.7%), which was strongly correlated with the [⁶⁸Ga]Ga-DOTATATE uptake. The SUVmax of SSTR2-negative lesions was significantly lower than that of SSTR2-positive lesions (SUVmax: 4.95 vs. 12.61, P = 0.013).

CONCLUSION

[⁶⁸Ga]Ga-DOTATATE PET/CT is a promising imaging modality for detecting primary and metastatic NPC, with favourable image contrast and comparable diagnostic efficacy when compared to [¹⁸F]FDG PET/CT. An intense SSTR2 expression was observed in most NPCs, and this expression was significantly correlated with the [⁶⁸Ga]Ga-DOTATATE uptake.

SSTR2 is a prognostic factor and a promising therapeutic target in glioma

Gliomas are the most prevalent primary malignant central nervous system tumors among all tumors occurring in the brain and spinal cord. The poor outcome of glioma requires the discovery of novel biomarkers with potential therapeutic value. Somatostatin receptor subtype 2 (SSTR2) represents a diagnostic biomarker and potential therapeutic target in many cancers, such as meningioma and neuroendocrine tumors (NETs). However, the relationship of SSTR2 and glioma was unclear. Therefore, this study aimed to investigate the expression of SSTR2 and assess its prognostic and potential therapeutic value in a large cohort of patients with WHO grade I to IV glioma from a single Chinese center. Immunohistochemical analysis revealed that SSTR2 was highly expressed in 23.84% (72 of 302) of glioma (I-IV grade) samples. Among all glioma subtypes, high SSTR2 expression was detected mainly in oligodendroglioma, anaplastic oligodendroglioma, and astrocytoma, whereas SSTR2 was expressed at a low level, or not at all, in glioblastoma. Western blotting also confirmed the low expression of SSTR2 in glioblastoma cell lines. Statistical analysis showed that SSTR2 protein expression correlated significantly with WHO grade, the location of the tumor, epilepsy syndrome, mitosis (PHH3), proliferation index (Ki-67), IDH and 1p/19q-codeleted status. Kaplan-Meier analysis indicated that SSTR2 high expression was a good prognostic factor in glioma. In summary, this study demonstrated that SSTR2 might be a valuable prognostic factor and therapeutic target in certain glioma subtypes.

TGF-β1/Smad2/3 signaling pathway modulates octreotide antisecretory and antiproliferative effects in pituitary somatotroph tumor cells

Octreotide (OCT) is used to inhibit hormone secretion and growth in somatotroph tumors, although a significant percentage of patients are resistant. It has also been tested in nonfunctioning (NF) tumors but with poor results, with these outcomes having been associated with SSTR2 levels and impaired signaling. We investigated whether OCT inhibitory effects can be improved by TGF-β1 in functioning and nonfunctioning somatotroph tumor cells. OCT effects on hormone secretion and proliferation were analyzed in the presence of TGF-β1 in WT and SSTR2-overexpressing secreting GH3 and silent somatotroph tumor cells. The mechanism underlying these effects was assessed by studying SSTR and TGFβR signaling pathways mediators. In addition, we analyzed the effects of OCT/TGF-β1 treatment on tumor growth and cell proliferation in vivo. The inhibitory effects of OCT on GH- and PRL-secretion and proliferation were improved in the presence of TGF-β1, as well as by SSTR2 overexpression. The OCT/TGF-β1 treatment induced downregulation of pERK1/2 and pAkt, upregulation of pSmad3, and inhibition of cyclin D1. In vivo experiments showed that OCT in the presence of TGF-β1 blocked tumor volume growth, decreased cell proliferation, and increased tumor necrosis. These results indicate that SSTR2 levels and the stimulation of TGF-β1/TGFβR/Smad2/3 pathway are important for strengthening the antiproliferative and antisecretory effects of OCT.

Evaluation of 68Ga-DOTATATE uptake at the pituitary region and the biochemical response to somatostatin analogs in acromegaly

PURPOSE

Acromegaly is associated with many comorbidities and increased mortality. The first-line treatment is transsphenoidal surgery. However, many patients also need adjuvant drug treatment after surgery. Somatostatin analog (SSA), which suppresses GH secretion by somatotrophs by binding to the SSTR2 receptor, is the first choice. Nevertheless, 50% of patients are partially or totally resistant to SSA, so predictive factors of response are helpful to individualize drug treatment. ⁶⁸GaDOTATATE PET/CT has emerged as the gold-standard method in the diagnosis and follow-up of gastroenteropancreatic neuroendocrine tumors, which also express SSTR. Our objective was to evaluate whether ⁶⁸Ga-DOTATATE uptake (SUV max) at the pituitary region of patients on SSA therapy would be useful as a drug response predictor without the need of tumoral tissue.

METHODS

Fifteen acromegalics patients on SSA treatment for at least 6 months were underwent to ⁶⁸Ga-DOTATATE PET/CT at the nuclear medicine service. There was an SSA complete response group (n = 5), defined as GH < 1 µg/L and IFG-1 in the normal range for gender and age, and a group that did not meet these criteria (n = 10).

RESULTS

As a result, we did not find out a significantly higher SUV max in the complete response group (p = 0.0576) to SSA. However, we found a significant inverse relationship between postoperative GH values and the SUVmax at the sella turcica (p = 0.0188), probably reflecting tumor SSTR2 expression.

CONCLUSION

Thus, after this initial evaluation, ⁶⁸GaDOTATATE PET/CT should be better studied to assess its usefulness in the follow-up of acromegalic patients.

Comparing the Effect of Multiple Histone Deacetylase Inhibitors on SSTR2 Expression and [111In]In-DOTATATE Uptake in NET Cells

Simple Summary

Patients diagnosed with neuroendocrine tumors (NETs) are often treated with peptide receptor radionuclide therapy (PRRT). This therapy targets the somatostatin type-2 receptors (SSTR2) frequently overexpressed on these types of tumors. Although this therapy has proven to be effective, complete responses are rare and therapy improvement is desirable. We aimed to increase SSTR2 expression on NET cells, potentially increasing the number of patients eligible for SSTR2-targeted PRRT and improving clinical outcomes. We used histone deacetylase inhibitors (HDACis) to manipulate the epigenetic machinery and hereby aimed to increase SSTR2 gene transcription. Our results showed that the HDACis increased SSTR2 expression in several NET cell lines. Moreover, the uptake of radiolabeled DOTATATE, the tracer used for PRRT, was enhanced. The observed reversibility profile after HDACi withdrawal of the induced effects suggests that proper timing of HDACi treatment is likely essential.

Abstract

The aim of this study was to increase somatostatin type-2 receptor (SSTR2) expression on neuroendocrine tumor (NET) cells using histone deacetylase inhibitors (HDACis), potentially increasing the uptake of SSTR2-targeted radiopharmaceuticals and subsequently improving treatment efficacy of peptide receptor radionuclide therapy (PRRT). Human NET cell lines BON-1, NCI-H727, and GOT1 were treated with HDACis (i.e., CI-994, entinostat, LMK-235, mocetinostat, panobinostat, or valproic acid (VPA); entinostat and VPA were the HDACis tested in GOT1 cells) to examine SSTR2 mRNA expression levels and uptake of SSTR2-targeting radiotracer [¹¹¹In]In-DOTATATE. Reversibility of the induced effects was examined after drug-withdrawal. Finally, the effect of VPA on radiosensitivity was investigated. A strong stimulatory effect in BON-1, NCI-H727, and GOT1 cells was observed after HDACi treatment, both on SSTR2 mRNA expression levels and [¹¹¹In]In-DOTATATE uptake. The effects of the HDACis were largely reversible over a period of seven days, demonstrating largest reductions within the first day. The reversibility profile of the induced effects suggests that proper timing of HDACi treatment is most likely essential for a beneficial outcome. In addition to increasing SSTR2 expression levels, VPA enhanced the radiosensitivity of all cell lines. In conclusion, HDACi treatment increased SSTR2 expression, and radiosensitivity was also enhanced upon VPA treatment.

Clinicopathologic features and BRAF mutation status of tracheal glomus tumors - Characterization of 4 cases and the distinction from low-grade neuroendocrine tumors

BACKGROUND

Glomus tumors are uncommon and mostly benign mesenchymal neoplasms of the perivascular family. To date, only a few cases of glomus tumors occurring in the trachea have been reported. Tracheal glomus tumors simulated low-grade neuroendocrine tumors on clinical and histomorphological examination, so the differential diagnosis between these two entities is very necessary. The latest studies showed that BRAF mutation may be associated with a malignant phenotype of glomus tumors.

METHODS

We investigated the clinical, histopathologic, immunohistochemical, and BRAF V600E mutation status of four cases of tracheal glomus tumors.

RESULTS

The cases showed a female predilection (male:female, 1:3) with a median age of 35.5. All of the cases had the typical morphological characteristics of glomus tumors, such as uniform round tumor cells with nest-like distribution surrounding thin-walled vessels; two of them met the malignant diagnostic criteria based on the 5th edition of WHO classification, including marked nuclear atypia and any level of mitotic activity. Immunohistochemistry showed diffusely positive for vimentin (4/4), α-SMA (4/4) and collagen IV (4/4), variably reactive for synaptophysin (3/4) and SSTR2 (2/2), and negative for AE1/AE3 (0/4) and chromogranin A (0/4). Three tested cases harbored no BRAF V600E mutation. Three follow-up cases were alive and free of disease with an average follow-up of 89.3 months.

CONCLUSIONS

Tracheal glomus tumors are rare mesenchymal tumors that have overlapping morphologic and immunohistochemical features with neuroendocrine neoplasms. Our cases highlight the importance of careful histomorphological examination and comprehensive immunohistochemical study in reaching a correct diagnosis of glomus tumors of the trachea. Other than BRAF mutation, malignant glomus tumors may have a complex mutational profile.

Somatostatin receptor 2 is highly sensitive and specific for Epstein-Barr virus-associated nasopharyngeal carcinoma

Viruses are known drivers of head and neck squamous cell carcinomas (HNSCC), particularly Epstein-Barr virus (EBV) and human papillomavirus (HPV). Both EBV-positive nasopharyngeal carcinoma (EBVNPC) and HPV-positive oropharyngeal SCC (OPSCC) can have overlapping histomorphology and molecular signatures, including nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB) pathway mutations. A recent study showed that NFKB activation in EBVNPC drives somatostatin receptor 2 (SSTR2) expression that is detectable by immunohistochemistry and by imaging with 68-Gadolinium-DOTA-peptide radioconjugate. However, whether a similar NFKB-SSTR2 signaling mechanism exists for other virus-positive HNSCC, namely HPV-positive sinonasal carcinomas and OPSCC, remains unclear. Here we examined SSTR2 expression in a cohort of EBV-positive, HPV-positive, and virus-negative HNSCC with immunohistochemistry. SSTR2 immunohistochemistry was performed on our cohort of primary and/or metastatic EBVNPC, HPV-positive sinonasal SCC, OPSCC, HPV-negative sinonasal and oral cavity SCC, and benign tonsil and adenoid tissue. For SSTR2 staining, the extent was categorized as focal, multifocal, or diffuse, and the intensity was categorized as weak, moderate, or strong. Multifocal/diffuse SSTR2 staining of any intensity was considered positive. Among primary, recurrent, and/or undifferentiated NPC, 90% showed multifocal to diffuse strong SSTR2 expression. One HPV-positive sinonasal carcinoma showed patchy SSTR2 staining. None of the remaining HPV-positive sinonasal carcinomas, OPSCC, or oral cavity HNSCC showed significant SSTR2 staining. Overall, SSTR2 is highly sensitive and specific for EBVNPC and could represent a surrogate biomarker. Among HNSCC assessed here, we recommend testing primary NPC for SSTR2 because of its relevance for diagnosis, associated imaging modalities, and its therapeutic implications for patient care.

A physiologically based pharmacokinetic (PBPK) model to describe organ distribution of 68Ga-DOTATATE in patients without neuroendocrine tumors

Background

Physiologically based pharmacokinetic (PBPK) models combine drug-specific information with prior knowledge on the physiology and biology at the organism level. Whole-body PBPK models contain an explicit representation of the organs and tissue and are a tool to predict pharmacokinetic behavior of drugs. The aim of this study was to develop a PBPK model to describe organ distribution of ⁶⁸Ga-DOTATATE in a population of patients without detectable neuroendocrine tumors (NETs).

Methods

Clinical ⁶⁸Ga-DOTATATE PET/CT data from 41 patients without any detectable somatostatin receptor (SSTR) overexpressing tumors were included. Scans were performed at 45 min (range 30–60 min) after intravenous bolus injection of ⁶⁸Ga-DOTATATE. Organ (spleen, liver, thyroid) and blood activity levels were derived from PET scans, and corresponding DOTATATE concentrations were calculated. A whole-body PBPK model was developed, including an internalization reaction, receptor recycling, enzymatic reaction for intracellular degradation and renal clearance. SSTR2 expression was added for several organs. Input parameters were fixed or estimated using a built-in Monte Carlo algorithm for parameter identification.

Results

⁶⁸Ga-DOTATATE was administered with a median peptide amount of 12.3 µg (range 8.05–16.9 µg) labeled with 92.7 MBq (range 43.4–129.9 MBq). SSTR2 amounts for spleen, liver and thyroid were estimated at 4.40, 7.80 and 0.0108 nmol, respectively. Variability in observed organ concentrations was best described by variability in SSTR2 expression and differences in administered peptide amounts.

Conclusions

To conclude, biodistribution of ⁶⁸Ga-DOTATATE was described with a whole-body PBPK model, where tissue distribution was mainly determined by variability in SSTR2 organ expression and differences in administered peptide amounts.

Quantitative digital image analysis of somatostatin receptor 2 immunohistochemistry in pancreatic neuroendocrine tumors

Immunohistochemical analysis of somatostatin receptor 2 (SSTR2) provides important information regarding the potential therapeutic efficacy of somatostatin analogues (SSAs) in patients with neuroendocrine tumors. HER2 scoring has been proposed to interpret SSTR2 immunoreactivity but their reproducibility was relatively low because of its intrinsic subjective nature. Digital image analysis (DIA) has recently been proposed as an objective and more precise method of evaluating immunoreactivity. Therefore, in this study, we used DIA for analyzing SSTR2 immunoreactivity in pancreatic neuroendocrine tumors (PanNETs) to obtain its H score and "(%) strong positive cells" and compared the results with those of manually obtained HER2 scores. Membranous SSTR2 immunoreactivity evaluated by DIA was calculated by two scales as: "Membrane Optical Density" and "Minimum Membrane Completeness". PanNETs with HER2 score of > 2 demonstrated the highest concordance with results of "(%) strong positive cells" obtained by DIA when "Minimum Membrane Completeness" was tentatively set at 80%. The SSTR2 immunoreactivity, evaluated based on all scoring systems, was different between grades G1 and G2 in insulinoma but not in non-functional PanNETs. DIA provided reproducible results of SSTR2 immunoreactivity in PanNETs and yielded important information as to the potential application of SSAs.

A new pathological classification of intrahepatic cholangiocarcinoma according to protein expression of SSTR2 and Bcl2

Background

No universal classification method for intrahepatic cholangiocarcinoma (IHCC) has been reported based on the embryological origin of biliary epithelial cells. The aim of this study was to classify IHCC according to protein expression levels of somatostatin receptor 2 (SSTR2) and b-cell leukemia/lymphoma 2 (Bcl2) and to elucidate the clinicopathological features of each group.

Methods

Fifty-two IHCC patients who underwent hepatic resection were enrolled in this study. Protein expression levels of SSTR2 and Bcl2 were examined using immunohistochemistry. Clinicopathological factors were compared between the three groups and prognostic factors were investigated.

Results

The patients were divided into three groups: SSTR2 positive and Bcl2 negative (p-Group H, n = 21), SSTR2 negative and Bcl2 positive (p-Group P, n = 14), and the indeterminate group (p-Group U, n = 17) for cases where SSTR2 and Bcl2 were both positive or both negative. All p-Group P cases displayed curability A or B. The 5-year survival rates of p-Group H and U patients were worse than those in p-Group P. p-Group H had higher T-factor, clinical stage, and incidence of periductal infiltration than p-Group P.

Conclusions

This method could be used to classify IHCC into peripheral and perihilar type by embryological expression patterns of SSTR2 and Bcl2.

SSTR2 Expression in Olfactory Neuroblastoma: Clinical and Therapeutic Implications

Somatostatin receptor 2 (SSTR2) expression has previously been documented in olfactory neuroblastoma (ONB). Here, we fully characterize SSTR2 expression in ONB and correlate staining results with clinicopathologic parameters including Hyams grade. We also assess SSTR2 immunohistochemistry expression in various histologic mimics of ONB to assess its diagnostic functionality. 78 ONBs (51 primary biopsies/excisions and 27 recurrences/metastases) from 58 patients were stained for SSTR2. H-scores based on intensity (0-3 +) and percentage of tumor cells staining were assigned to all cases. 51 histologic mimics were stained and scored in an identical fashion. 77/78 (99%) ONB cases demonstrated SSTR2 staining (mean H-score: 189, range: 0-290). There were no significant differences in staining between primary tumors and recurrences/metastases (mean H-score: 185 vs 198). Primary low-grade ONB had somewhat stronger staining than high-grade tumors (mean H-score: 200 vs 174). SSTR2 expression had no prognostic value when considering disease-free or disease-specific survival. SSTR2 staining is significantly higher in ONB than its histologic mimics (mean H-score: 189 vs 12.9, p < 0.001) suggesting a potential use of the marker in diagnosis of ONB. In conclusion, SSTR2 is consistently expressed in ONB suggesting a role for somatostatin-analog based imaging and therapy in this disease. More generally, SSTR2 may be another marker of neuroendocrine differentiation in ONB.

A Cyanine-Bridged Somatostatin Hybrid Probe for Multimodal SSTR2 Imaging in Vitro and in Vivo: Synthesis and Evaluation

Multimodal imaging probes have attracted the interest of ongoing research, for example, for the surgical removal of tumors. Modular synthesis approaches allow the construction of hybrid probes consisting of a radiotracer, a fluorophore and a targeting unit. We present the synthesis of a new asymmetric bifunctional cyanine dye that can be used as a structural and functional linker for the construction of such hybrid probes. 68 Ga-DOTATATE, a well-characterized radiopeptide targeting the overexpressed somatostatin receptor subtype 2 (SSTR2) in neuroendocrine tumors, was labeled with our cyanine dye, thus providing additional information along with the data obtained from the radiotracer. We tested the SSTR2-targeting and imaging properties of the resulting probe 68 Ga-DOTA-ICC-TATE in vitro and in a tumor xenograft mouse model. Despite the close proximity between dye and pharmacophore, we observed a high binding affinity towards SSTR2 as well as elevated uptake in SSTR2-overexpressing tumors in the positron emission tomography (PET) scan and histological examination.

Transcriptome analysis of the transdifferentiation of canine BMSCs into insulin producing cells

Background

Bone marrow mesenchymal stem cells are a potential resource for the clinical therapy of certain diseases. Canine, as a companion animal, living in the same space with human, is an ideal new model for human diseases research. Because of the high prevalence of diabetes, alternative transplantation islets resource (i.e. insulin producing cells) for diabetes treatment will be in urgent need, which makes our research on the transdifferentiation of Bone marrow mesenchymal stem cells into insulin producing cells become more important.

Result

In this study, we completed the transdifferentiation process and achieved the transcriptome profiling of five samples with two biological duplicates, namely, “BMSCs”, “islets”, “stage 1”, “stage 2” and “stage 3”, and the latter three samples were achieved on the second, fifth and eighth day of induction. A total of 11,530 differentially expressed transcripts were revealed in the profiling data. The enrichment analysis of differentially expressed genes revealed several signaling pathways that are essential for regulating proliferation and transdifferentiation, including focal adhesion, ECM-receptor interaction, tight junction, protein digestion and absorption, and the Rap1 signaling pathway. Meanwhile, the obtained protein–protein interaction network and functional identification indicating involvement of three genes, SSTR2, RPS6KA6, and VIP could act as a foundation for further research.

Conclusion

In conclusion, to the best of our knowledge, this is the first survey of the transdifferentiation of canine BMSCs into insulin-producing cells according with the timeline using next-generation sequencing technology. The three key genes we pick out may regulate decisive genes during the development of transdifferentiation of insulin producing cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07426-3.

Detection and therapy of neuroblastoma minimal residual disease using [64/67Cu]Cu-SARTATE in a preclinical model of hepatic metastases

Background

A major challenge to the long-term success of neuroblastoma therapy is widespread metastases that survive initial therapy as minimal residual disease (MRD). The SSTR2 receptor is expressed by most neuroblastoma tumors making it an attractive target for molecularly targeted radionuclide therapy. SARTATE consists of octreotate, which targets the SSTR2 receptor, conjugated to MeCOSar, a bifunctional chelator with high affinity for copper. Cu-SARTATE offers the potential to both detect and treat neuroblastoma MRD by using [⁶⁴Cu]Cu-SARTATE to detect and monitor the disease and [⁶⁷Cu]Cu-SARTATE as the companion therapeutic agent. In the present study, we tested this theranostic pair in a preclinical model of neuroblastoma MRD. An intrahepatic model of metastatic neuroblastoma was established using IMR32 cells in nude mice. The biodistribution of [⁶⁴Cu]Cu-SARTATE was measured using small-animal PET and ex vivo tissue analysis. Survival studies were carried out using the same model: mice (6–8 mice/group) were given single doses of saline, or 9.25 MBq (250 µCi), or 18.5 MBq (500 µCi) of [⁶⁷Cu]Cu-SARTATE at either 2 or 4 weeks after tumor cell inoculation.

Results

PET imaging and ex vivo biodistribution confirmed tumor uptake of [⁶⁴Cu]Cu-SARTATE and rapid clearance from other tissues. The major clearance tissues were the kidneys (15.6 ± 5.8% IA/g at 24 h post-injection, 11.5 ± 2.8% IA/g at 48 h, n = 3/4). Autoradiography and histological analysis confirmed [⁶⁴Cu]Cu-SARTATE uptake in viable, SSTR2-positive tumor regions with mean tumor uptakes of 14.1–25.0% IA/g at 24 h. [⁶⁷Cu]Cu-SARTATE therapy was effective when started 2 weeks after tumor cell inoculation, extending survival by an average of 13 days (30%) compared with the untreated group (mean survival of control group 43.0 ± 8.1 days vs. 55.6 ± 9.1 days for the treated group; p = 0.012). No significant therapeutic effect was observed when [⁶⁷Cu]Cu-SARTATE was started 4 weeks after tumor cell inoculation, when the tumors would have been larger (control group 14.6 ± 8.5 days; 9.25 MBq group 9.5 ± 1.6 days; 18.5 MBq group 15.6 ± 4.1 days; p = 0.064).

Conclusions

Clinical experiences of peptide-receptor radionuclide therapy for metastatic disease have been encouraging. This study demonstrates the potential for a theranostic approach using [^64/67Cu]Cu-SARTATE for the detection and treatment of SSTR2-positive neuroblastoma MRD.

Clinical Significance of Somatostatin Receptor (SSTR) 2 in Meningioma

Somatostatin receptor (SSTR) 2, widely expressed in meningioma, is a G-protein-coupled receptor and can be activated by somatostatin or its synthetic analogs. SSTR2 is therefore extensively studied as a marker and target for the diagnosis and treatment of meningioma. Accumulating studies have revealed the crucial clinical significance of SSTR2 in meningioma. Summarizing the progress of these studies is urgently needed as it may not only provide novel and better management for patients with meningioma but also indicate the direction of future research. Pertinent literature is reviewed to summarize the recent collective knowledge and understanding of SSTR2’s clinical significance in meningioma in this review. SSTR2 offers novel ideas and approaches in the diagnosis, treatment, and prognostic prediction for meningioma, but more and further studies are required.

Characterization of agonist-dependent somatostatin receptor subtype 2 trafficking in neuroendocrine cells

BACKGROUND

Somatostatin (SOM) receptor subtype 2 (SSTR2) is the major receptor subtype mediating SOM effects throughout the neuraxis. We previously demonstrated that the non-selective agonist [D-Trp⁸]-SOM induces intracellular sequestration of SSTR2, whereas this receptor is maintained at the cell surface after treatment with the SSTR2-selective agonist L-779,976 in cells co-expressing SSTR2 and SSTR5.

METHODS AND RESULTS

In this study, we knocked-out SSTR5 in AtT20 cells endogenously expressing both SSTR2 and SSTR5 and used immuno-labeling and confocal microscopy to investigate the effect of SSTR5 on regulation of SSTR2 trafficking. Our results indicate that unlike [D-Trp⁸]-SOM-induced intracellular sequestration, L-779,976 stimulation results in the maintenance of SSTR2 at the cell surface regardless of whether SSTR5 is present or not. We then examined the trafficking pathways of SSTR2 upon stimulation by either agonist. We found that both [D-Trp⁸]-SOM and L-779,976 induce SSTR2 internalization via transferrin-positive vesicles. However, SSTR2 internalized upon L-779,976 treatment undergoes rapid recycling to the plasma membrane, whereas receptors internalized by [D-Trp⁸]-SOM recycle slowly after washout of the agonist. Furthermore, [D-Trp⁸]-SOM stimulation induces degradation of a fraction of internalized SSTR2 whereas L-779,976-dependent, rapid SSTR2 recycling appears to protect internalized SSTR2 from degradation. In addition, Octreotide which has preferential SSTR2 affinity, induced differential effects on both SSTR2 trafficking and degradation.

CONCLUSION

Our results indicate that the biased agonistic property of L-779,976 protects against SSTR2 surface depletion by rapidly initiating SSTR2 recycling while SSTR5 does not regulate L-779-976-dependent SSTR2 trafficking.

The effect of miR-10b on growth hormone in pituitary cells of Yanbian yellow cattle by somatostatin receptor 2

This study aimed to evaluate the effect of miR-10b on growth hormone (GH) in pituitary cells of Yanbian yellow cattle. According to analysis of GH and somatostatin receptor 2 (SSTR2) mRNA and protein expression levels, we found that miR-10b targeted 3'UTR of SSTR2. Compared with the negative control (NC) group, GH mRNA transcription and protein expression in pituitary cells of Yanbian yellow cattle were significantly increased by adding miR-10b mimics (p < .01), while these were significantly decreased by adding miR-10b inhibitor (p < .05); compared with the NC group, SSTR2 mRNA transcription and protein expression were significantly inhibited by the addition of miR-10b mimics (p < .01), while these were significantly increased by the addition of miR-10b inhibitor compared with the iNC group (p < .05). This study suggested that miR-10b could regulate GH level by regulating SSTR2 gene expression in pituitary cells of Yanbian yellow cattle.

Advances in Molecular Classification and Therapeutic Opportunities in Meningiomas

PURPOSE OF REVIEW

Our understanding of the genetic and epigenetic alterations in meningioma and the underlying tumor biology of meningioma has significantly changed over the past decade and resulted in revision of prognostically relevant meningioma subclasses within and beyond the WHO classification of CNS tumors.

RECENT FINDINGS

The 2016 WHO classification of CNS tumors recognizes WHO grade I, II, and III based on histopathological features. Recent work has identified genetic alterations with prognostic implications, including mutations of the TERT promoter, loss of function of the DMD gene, and inactivation of the tumor suppressor BAP-1. Studies of DNA methylation patterns in meningiomas have resulted in a novel and prognostically relevant meningioma subclassification schema. There have been major advances in our understanding of prognostically relevant genetic and epigenetic changes in meningioma which will hopefully allow for improvement in clinical trial design and the development of more effective therapies for meningioma.

Molecular profiling for acromegaly treatment: a validation study

Pharmacologic treatment of acromegaly is currently based upon assay-error strategy, the first-generation somatostatin receptor ligands (SRL) being the first-line treatment. However, about 50% of patients do not respond adequately to SRL. Our objective was to evaluate the potential usefulness of different molecular markers as predictors of response to SRL. We used somatotropinoma tissue obtained after surgery from a national cohort of 100 acromegalic patients. Seventy-one patients were treated with SRL during at least 6 months under maximal therapeutic doses according to IGF1 values. We analyzed the expression of SSTR2, SSTR5, AIP, CDH1 (E-cadherin), MKI67 (Ki-67), KLK10, DRD2, ARRB1, GHRL, In1-Ghrelin, PLAGL1 and PEBP1 (RKIP) by RT-qPCR and mutations in GNAS gene by Sanger sequencing. The response to SRL was categorized as complete response (CR), partial (PR) or non-response (NR) if IGF1 was normal, between >2<3 SDS or >3 SDS IGF1 at 6 months of follow-up, respectively. From the 71 patients treated, there were 27 CR (38%), 18 PR (25%) and 26 NR (37%). SSTR2, Ki-67 and E-cadherin were associated with SRL response (P < 0.03, P < 0.01 and P < 0.003, respectively). E-cadherin was the best discriminator for response prediction (AUC = 0.74, P < 0.02, PPV of 83.7%, NPV of 72.6%), which was validated at protein level. SSTR5 expression was higher in patients pre-treated with SRL before surgery. We conclude that somatotropinomas showed heterogeneity in the expression of genes associated with SRL response. E-cadherin was the best molecular predictor of response to SRL. Thus, the inclusion of E-cadherin in subsequent treatment-decision after surgical failure may be useful in acromegaly.

Discovery and SAR Studies of Orally Active Somatostatin Receptor Subtype-2 (SSTR2) Agonists for the Treatment of Acromegaly

Acromegaly is a disease caused by the oversecretion of growth hormone. It is currently treated by intravenous injection with cyclic peptide drugs that activate somatostatin receptor subtype 2 (SSTR2). Here, novel nonpeptidic, small-molecule, and orally active SSTR2 agonists were identified from a hit compound (13). Pharmacophore studies enabled scaffold hopping to obtain a unique 3,4,5-trisubstituted pyridine motif. Further optimization conferred potent SSTR2 agonistic activity and metabolic stability. Several compounds were evaluated and these showed good oral pharmacokinetic profiles in rats, and one representative compound (25) showed highly potent inhibition of growth hormone secretion induced by growth hormone-releasing hormone in rats. Based on these results, 25 was identified as a promising lead for further optimization. A structure-activity relationship (SAR) study and the metabolic stability data for this compound are also described.

Somatostatin receptor-2 negative meningioma: pathologic correlation and imaging implications

Meningiomas are the most common non-malignant primary intracranial tumors, accounting for nearly 40% of all primary brain tumors, usually expressing high levels of somatostatin receptors (SSTR), particularly SSTR2. Because ⁶⁸Ga-DOTATATE targets SSTR2, it is increasingly used clinically for meningioma evaluation. While previous apparent lack of SSTR expression in meningiomas has been reported in isolated cases, these prior studies utilized Indium-111 (¹¹¹In) Octreotide, which is of lesser diagnostic accuracy compared to ⁶⁸Ga-DOTATATE, as well as Technetium-99m (^99mTc)-DTPA scintigraphy, which necessitates an intact blood-tumor-permeability barrier. This paper presents a histopathologic proven atypical meningioma, WHO Grade II, with low level avidity on ⁶⁸Ga-DOTATATE PET/MRI, subsequently proven to be SSTR2-negative by immunohistochemistry, with a review and discussion of the current literature and imaging implications.

Pharmacokinetic analysis of [68Ga]Ga-DOTA-TOC PET in meningiomas for assessment of in vivo somatostatin receptor subtype 2

PURPOSE

DOTA-D-Phe¹-Tyr³-octreotide with gallium-68 ([⁶⁸Ga]Ga-DOTA-TOC) is one of the PET tracers that forms the basis for peptide receptor radionuclide therapy based on somatostatin receptor subtype 2 (SSTR2) expression in meningiomas. Yet, the quantitative relationship between [⁶⁸Ga]Ga-DOTA-TOC accumulation and SSTR2 is unknown. We conducted a correlative analysis of a range of [⁶⁸Ga]Ga-DOTA-TOC PET metric(s) as imaging surrogate(s) of the receptor binding in meningiomas by correlating the PET results with SSTR2 expression from surgical specimens. We additionally investigated possible influences of secondary biological factors such as vascularization, inflammation and proliferation.

METHODS

Fifteen patients with MRI-presumed or recurrent meningiomas underwent a 60-min dynamic [⁶⁸Ga]Ga-DOTA-TOC PET/CT before surgery. The PET data comprised maximum and mean standardized uptake values (SUV_max, SUV_mean) with and without normalization to reference regions, and quantitative measurements derived from kinetic modelling using a reversible two-tissue compartment model with the fractional blood volume (V_B). Expressions of SSTR2 and proliferation (Ki-67, phosphohistone-H3, proliferating cell nuclear antigen) were determined by immunohistochemistry and/or quantitative polymerase chain reaction (qPCR), while biomarkers of vascularization (vascular endothelial growth factor A (VEGFA), endothelial marker CD34) and inflammation (cytokine interleukin-18, microglia/macrophage-specific marker CD68) by qPCR.

RESULTS

Histopathology revealed 12 World Health Organization (WHO) grade I and three WHO grade II meningiomas showing no link to SSTR2. The majority of [⁶⁸Ga]Ga-DOTA-TOC PET metrics showed significant associations with SSTR2 protein, while all PET metrics were positively correlated with SSTR2 mRNA with the best results for mean tumour-to-blood ratio (TBR_mean) (r = 0.757, P = 0.001) and SUV_mean (r = 0.714, P = 0.003). Significant positive correlations were also found between [⁶⁸Ga]Ga-DOTA-TOC PET metrics, and VEGFA and V_B. SSTR2 mRNA was moderately correlated with VEGFA (r = 0.539, P = 0.038). Neither [⁶⁸Ga]Ga-DOTA-TOC PET metrics nor SSTR2 were correlated with proliferation or inflammation.

CONCLUSION

[⁶⁸Ga]Ga-DOTA-TOC accumulation in meningiomas is associated with SSTR2 binding and vascularization with TBR_mean being the best PET metric for assessing SSTR2.

Clinicopathologic characteristics and novel biomarkers of aggressive B-cell lymphomas in the nasopharynx

BACKGROUND

The most common nasopharyngeal lymphoma in the United States are B-cell non-Hodgkin lymphomas (B-NHL). Relatively little is known about the clinicopathologic features of these cases. In this study, we characterize a bi-institutional cohort of aggressive B-NHL primary to the nasopharyngeal area. We compare and contrast EBV-positive versus EBV-negative cases and evaluate expression of SSTR2, CD30, and PD-L1, potential markers for targeted therapeutics.

METHODS AND RESULTS

We retrieved 53 cases of aggressive B-NHL from the two institutions. Staining was performed for in situ EBV (EBER), CD30, SSTR2 and PD-L1. The response to initial therapy, disease-free interval, and survival at two- and five-year following initial diagnosis were used as primary clinical outcome. Overall, 13 out of 53 cases (23%) were EBV positive. CD30 expression was more frequent in EBV-positive than in EBV-negative cases (4/6 vs 1/17). Seven of 14 (50%) cases tested demonstrated expression of PD-L1 within tumor cells; the two EBV-positive DLBCL tested showed substantial PD-L1 reactivity. Six of 15 (40%) cases tested were positive for SSTR2. The three EBV-positive patients with available outcome data died within one year of diagnosis; in contrast, the EBV-negative cases showed survival rate of 100% (8/8) and 83% (5/6) at two- and five-year follow-up, respectively.

DISCUSSION

The aggressive B-NHLs of the nasopharynx show differences between EBV-positive versus EBV-negative cases. The association of EBV-positive cases with expression of CD30 and PD-L1 may be particularly informative for targeted therapies. A significant number of cases expresses SSTR2, which could render them susceptible to somatostatin analogue and peptide receptor radionuclide therapies. Finally, our limited case series suggest that EBV negativity may be associated with a better prognosis.

Somatostatin Serves a Modulatory Role in the Mouse Olfactory Bulb: Neuroanatomical and Behavioral Evidence

Somatostatin (SOM) and somatostatin receptors (SSTR1-4) are present in all olfactory structures, including the olfactory bulb (OB), where SOM modulates physiological gamma rhythms and olfactory discrimination responses. In this work, histological, viral tracing and transgenic approaches were used to characterize SOM cellular targets in the murine OB. We demonstrate that SOM targets all levels of mitral dendritic processes in the OB with somatostatin receptor 2 (SSTR2) detected in the dendrites of previously uncharacterized mitral-like cells. We show that inhibitory interneurons of the glomerular layer (GL) express SSTR4 while SSTR3 is confined to the granule cell layer (GCL). Furthermore, SOM cells in the OB receive synaptic inputs from olfactory cortical afferents. Behavioral studies demonstrate that genetic deletion of SSTR4, SSTR2 or SOM differentially affects olfactory performance. SOM or SSTR4 deletion have no major effect on olfactory behavioral performances while SSTR2 deletion impacts olfactory detection and discrimination behaviors. Altogether, these results describe novel anatomical and behavioral contributions of SOM, SSTR2 and SSTR4 receptors in olfactory processing.

The Search for an Alternative to [68Ga]Ga-DOTA-TATE in Neuroendocrine Tumor Theranostics: Current State of 18F-labeled Somatostatin Analog Development

The trend to inform personalized molecular radiotherapy with molecular imaging diagnostics, a concept referred to as theranostics, has transformed the field of nuclear medicine in recent years. The development of theranostic pairs comprising somatostatin receptor (SSTR)-targeting nuclear imaging probes and therapeutic agents for the treatment of patients with neuroendocrine tumors (NETs) has been a driving force behind this development. With the Neuroendocrine Tumor Therapy (NETTER-1) phase 3 trial reporting encouraging results in the treatment of well-differentiated, metastatic midgut NETs, peptide radioligand therapy (RLT) with the 177Lu-labeled somatostatin analog (SSA) [177Lu]Lu-DOTA-TATE is now anticipated to become the standard of care. On the diagnostics side, the field is currently dominated by 68Ga-labeled SSAs for the molecular imaging of NETs with positron emission tomography-computed tomography (PET/CT). PET/CT imaging with SSAs such as [68Ga]Ga-DOTA-TATE, [68Ga]Ga-DOTA-TOC, and [68Ga]Ga-DOTA-NOC allows for NET staging with high accuracy and is used to qualify patients for RLT. Driven by the demand for PET/CT imaging of NETs, a commercial kit for the production of [68Ga]Ga-DOTA-TATE (NETSPOT) was approved by the U.S. Food and Drug Administration (FDA). The synthesis of 68Ga-labeled SSAs from a 68Ge/68Ga-generator is straightforward and allows for a decentralized production, but there are economic and logistic difficulties associated with these approaches that warrant the search for a viable, generator-independent alternative. The clinical introduction of an 18F-labeled SSTR-imaging probe can help mitigate the shortcomings of the generator-based synthesis approach, but despite extensive research efforts, none of the proposed 18F-labeled SSAs has been translated past prospective first-in-humans studies so far. Here, we review the current state of probe-development from a translational viewpoint and make a case for a clinically viable, 18F-labeled alternative to the current standard [68Ga]Ga-DOTA-TATE.

Long-lasting actions of somatostatin on pyramidal cell excitability in the mouse cingulate cortex

Many neurological diseases are related to disturbances of somatostatin- (SOM-) expressing interneurons in the cingulate cortex. Therefore, their role within the circuitry of the cingulate cortex needs to be investigated. We describe here the physiological time course of SOM effects onto pyramidal cell excitability and action potential discharge pattern. Furthermore, we show that the GRK2 inhibitor Gallein had no effect on the reduced SOM-induced response following repetitive SOM applications.

Regulation of somatostatin receptor 2 by proinflammatory, microbial and obesity-related signals in periodontal cells and tissues

Background

Periodontitis is a chronic disease characterized by a progressive and irreversible destruction of the tooth-supporting tissues, including gingiva and periodontal ligament (PDL). Microorganisms, such as Fusobacterium nucleatum, evoke an inflammatory host response, which leads to increased levels of inflammatory mediators, such as interleukin (IL)-1β. Periodontitis has been linked to obesity, and adipokines have been suggested to represent a pathomechanistic link. The hormone somatostatin (SST) exerts antiproliferative, antiangiogenetic, proapoptotic, anti-nociceptive and other effects through binding to its receptors, such as SSTR2. Therefore, the objective of the present study was to examine the regulation of SSTR2 in periodontal cells and tissues under inflammatory, microbial and obesity-related conditions.

Methods

In-vitro, human PDL fibroblasts were exposed to IL-1β, F. nucleatum, leptin or visfatin. The SSTR2 regulation was assessed by real-time PCR and immunocytochemistry. In-vivo, the SSTR2 expression was analyzed in gingival biopsies of periodontally diseased and healthy subjects by real-time PCR and immunohistochemistry. Additionally, the SSTR2 expression was determined in gingival biopsies of rats with ligature-induced periodontitis, rats with diet-induced obesity, and periodontally and systemically healthy control animals. For statistical analyses, the Mann-Whitney-U test and ANOVA with post-hoc tests were applied (p < 0.05).

Results

Exposure of PDL cells to IL-1β and F. nucleatum caused a significant SSTR2 upregulation by 2.6-fold and 6.4-fold, respectively. Additionally, leptin and visfatin increased significantly the SSTR2 gene expression by 3.0-fold and 2.8-fold, respectively. These stimulatory effects were also observed at protein level. SSTR2 expressions in human gingival biopsies from sites of periodontitis were significantly higher than those in healthy biopsies. Similarly, SSTR2 expression levels were significantly enhanced at periodontally-diseased sites in rat experimental periodontitis. Finally, the SSTR2 expression was significantly upregulated in gingival biopsies of obese rats as compared to normal weight control animals.

Conclusions

Our study provides original insights into the SSTR2 regulation in cells and tissues of the periodontium. We demonstrate for the first time that proinflammatory, microbial and obesity-associated molecules result in an SSTR2 upregulation. Since SST has been shown to be antiproliferative, antiangiogenetic, and proapoptotic, our study suggests that SSTR2 might play a critical role in the aetiopathogenesis of periodontitis.

Toward a better understanding of the interaction between somatostatin receptor 2 and its ligands: a structural characterization study using molecular dynamics and conceptual density functional theory

This study is a part of the extensive research intending to provide the structural insights on somatostatin and its receptor. Herein, we have studied the structural complexity involved in the binding of somatostatin receptor 2 (SSTR2) with its agonists and antagonist. A 3D QSAR study based on comparative molecular field analysis and comparative molecular similarity analysis (CoMSIA) discerned that a SSTR2 ligand with electronegative, less-bulkier, and hydrogen atom donating/accepting substitutions is important for their biological activity. A conceptual density functional theory (DFT) study was followed to study the chemical behavior of the ligands based on the molecular descriptors derived using the Fukui's molecular orbital theory. We have performed molecular dynamics simulations of receptor-ligand complexes for 100 ns to analyze the dynamic stability of the backbone Cα atoms of the receptor and strength and approachability of the receptor-ligand complex. The findings of this study could be efficacious in the further studies understanding intricate structural features of the somatostatin receptors and in discovering novel subtype-specific ligands with higher affinity. Communicated by Ramaswamy H. Sarma.

SSTR2 associated with neuronal apoptosis after intracerebral hemorrhage in adult rats

Objective SSTR2 is a member of superfamily of SST receptor (SSTR), and widely expressed in the brain; however, the knowledge of its functions in area adjacent to hematoma after intracerebral hemorrhage (ICH) is still limited. Method The role of SSTR2 in the processes of ICH was explored by conducting an ICH rat model. Western blot and immunohistochemistry were employed to examine the level of SSTR2 in area adjacent to hematoma after ICH. Immunofluorescent staining was used to observe the spatial correlation of SSTR2 with cellular types adjacent to hematoma after ICH. RNA interference specific to SSTR2 was adopted in PC12 cells to clarify the causal correlation between SSTR2 and neuronal activities. Results Increased expression of SSTR2 was observed and restricted to the neurons adjacent to hematoma following ICH. Immunofluorescent staining showed that SSTR2 was significant increased in neurons, but not astrocytes or microglia. Increasing SSTR2 level was found to be accompanied by the up-regulation of activated caspase-3 and the down-expression of p-Akt in a time-dependent manner. What's more, using SSTR2 RNA interference (SSTR2-RNAi) in PC12 cells, we indicated that SSTR2 might have a pro-apoptotic role in neurons. Conclusion We speculated that SSTR2 might exert its pro-apoptotic function in neurons through inhibiting Akt activity following ICH.