Somatostatin Receptor Subtype Research Articles

Cortistatin protects against septic cardiomyopathy by inhibiting cardiomyocyte pyroptosis through the SSTR2-AMPK-NLRP3 pathway

BackgroundAlthough the pathophysiological mechanism of septic cardiomyopathy has been continuously discovered, it is still a lack of effective treatment method. Cortistatin (CST), a neuroendocrine polypeptide of the somatostatin family, has emerged as a novel cardiovascular-protective peptide, but the specific mechanism has not been elucidated. PurposeThe aim of our study is to explore the role of CST in cardiomyocytes pyroptosis and myocardial injury in sepsis and whether CST inhibits cardiomyocytes pyroptosis through specific binding with somastatin receptor 2 (SSTR2) and activating AMPK/Drp1 signaling pathway. Methods and ResultsIn this study, plasma CST levels were significantly high and were negatively correlated with N-terminal pro-B type natriuretic peptide (NT-proBNP), a biomarker for cardiac dysfunction, in patients with sepsis. Exogenous administration of CST significantly improved survival rate and cardiac function in mouse models of sepsis by inhibiting the activation of the NLRP3 inflammasome and pyroptosis of cardiomyocytes (decreased cleavage of caspase-1, IL-1β and gasdermin D). Pharmacological inhibition and genetic ablation revealed that CST exerted anti-pyroptosis effects by specifically binding to somatostatin receptor subtype 2 (SSTR2), thus activating AMPK and inactivating Drp1 to inhibit mitochondrial fission in cardiomyocytes. ConclusionsThis study is the first to report that CST attenuates septic cardiomyopathy by inhibiting cardiomyocyte pyroptosis through the SSTR2-AMPK-Drp1-NLRP3 pathway. Importantly, CST specifically binds to SSTR2, which promotes AMPK phosphorylation, inhibits Drp1-mediated mitochondrial fission, and reduces ROS levels, thereby inhibiting NLRP3 inflammasome activation-mediated pyroptosis and alleviating sepsis-induced myocardial injury.

The value of digital quantification of somatostatin receptor subtypes 2 and 5 immunostaining in GH-secreting pituitary tumors

The value of digital quantification of somatostatin receptor subtypes 2 and 5 immunostaining in GH-secreting pituitary tumors

In-vivo inhibition of neutral endopeptidase 1 results in higher absorbed tumor doses of [177Lu]Lu-PP-F11N in humans: the lumed phase 0b study

BackgroundA new generation of radiolabeled minigastrin analogs delivers low radiation doses to kidneys and are considered relatively stable due to less enzymatic degradation. Nevertheless, relatively low tumor radiation doses in patients indicate limited stability in humans. We aimed at evaluating the effect of sacubitril, an inhibitor of the neutral endopeptidase 1, on the stability and absorbed doses to tumors and organs by the cholecystokinin-2 receptor agonist [177Lu]Lu-PP-F11N in patients. In this prospective phase 0 study eight consecutive patients with advanced medullary thyroid carcinoma and a current somatostatin receptor subtype 2 PET/CT scan were included. Patients received two short infusions of ~ 1 GBq [177Lu]Lu-PP-F11N in an interval of ~ 4 weeks with and without Entresto® pretreatment in an open-label, randomized cross-over order. Entresto® was given at a single oral dose, containing 48.6 mg sacubitril. Adverse events were graded and quantitative SPECT/CT and blood sampling were performed. Absorbed doses to tumors and relevant organs were calculated.ResultsPretreatment with Entresto® showed no additional toxicity and increased the stability of [177Lu]Lu-PP-FF11N in blood significantly (p < 0.001). Median tumor-absorbed doses were 2.6-fold higher after Entresto® pretreatment (0.74 vs. 0.28 Gy/GBq, P = 0.03). At the same time, an increase of absorbed doses to stomach, kidneys and bone marrow was observed, resulting in a tumor-to-organ absorbed dose ratio not significantly different with and without Entresto®.ConclusionsPremedication with Entresto® results in a relevant stabilization of [177Lu]Lu-PP-FF11N and consecutively increases radiation doses in tumors and organs.Trial registration clinicaltrails.gov, NCT03647657. Registered 20 August 2018.

Correlation between tumor invasion and somatostatin receptor subtypes in acromegaly.

The low expression of somatostatin receptor (SSTR) subtypes in somatotropinoma is associated with a poor response to somatostatin analogs (SSAs). However, the correlation between SSTRs and tumor invasion has not yet been clarified. Therefore, the authors aimed to investigate the relationship between SSTRs and tumor invasion, as well as the correlation between tumor invasiveness and pharmacological response to SSAs. A total of 102 patients with acromegaly who underwent surgery between December 2016 and December 2021 at the largest pituitary tumor surgery center in southern China were included in this retrospective study. Patients were divided into the noninvasive tumor group (Knosp grades 0-2 and Hardy-Wilson grade I or II) and invasive group (either Knosp grade 3 or 4 or Hardy-Wilson grade III or IV). The positive response to SSAs was defined by the following criteria after at least 3 months of SSA treatment: 1) ≥ 50% reduction or age- and sex-adjusted normal range of insulin-like growth factor-1 (IGF-1) level; 2) ≥ 80% reduction in or normal range of growth hormone (GH) level; or 3) > 20% reduction in tumor volume. The reference for the normal range of age- and sex-adjusted serum IGF-1 levels was derived from a survey of 2791 healthy adults (1339 males and 1452 females) in China. Demographics and clinical characteristics including tumor size, biochemical assessment, expression levels of SSTRs, and response to preoperative SSAs were compared between the invasive group and noninvasive group. Receiver operating characteristic (ROC) curve analysis was performed to assess the association between SSTR2 and tumor invasion. Compared with the noninvasive group, the invasive group presented with a larger tumor size (9.99 ± 10.41 cm3 vs 3.50 ± 4.02 cm3, p < 0.001), relatively lower SSTR2 expression (p < 0.001), and poorer response to SSAs (36.4% vs 91.7%, p < 0.001). In addition, there was a significant negative correlation between SSTR2 mRNA level and tumor size (r = -0.214, p = 0.031). However, there were no statistically significant differences in the expression of SSTR1, SSTR3, and SSTR5 between the groups. ROC analysis revealed that the low SSTR2 mRNA level was closely associated with tumor invasion (area under the curve 0.805, p < 0.0001). Tumor invasion is negatively correlated with SSTR2 level but is not associated with other SSTR subtypes. Patients with invasive tumors have a poorer response to SSA therapy, which may be due to the low level of SSTR2 expression. Therefore, SSTR2 could be considered as a routine investigative marker for aiding management of postoperative residual tumors.

Oral SSTR5 Antagonist SCO-240 for Growth Hormone Stimulation: A Phase I Single-Dose Study in Healthy Individuals.

Somatostatin inhibits endocrine and exocrine secretion in various tissues by acting on five somatostatin receptor subtypes (SSTR1-5). The clinical effects of SSTR5 antagonism remain unknown. Herein, we evaluated the effects of SCO-240, an oral SSTR5 antagonist, in healthy individuals. This randomized, single-center, double-blind, placebo-controlled, phase I study included healthy Japanese and White individuals. The effects of ascending single oral doses of SCO-240 were evaluated in healthy individuals. The main outcome measures were safety, tolerability, pharmacokinetics, and pharmacodynamics (gallbladder contractions and levels of serum insulin and plasma glucagon-like peptide-1 (GLP-1)). The levels of pituitary hormones were evaluated in our exploratory analysis. The results indicated that SCO-240 was safe and well-tolerated at all tested doses. Oral SCO-240 was readily absorbed, with its systemic exposure increasing in a dose-dependent manner. The median time to maximum concentration and mean terminal half-life of SCO-240 were 3-4 and 10.2-12.6 hours, respectively, in the ascending dose section. No clinically meaningful changes in SCO-240 pharmacokinetic profiles were observed between fed and fasted or between Japanese and White individuals. No increase in gallbladder contractions or levels of insulin and GLP-1 were detected. SCO-240 induced robust growth hormone (GH) secretion without altering the levels of other pituitary hormones. In conclusion, the study is the first to demonstrate that SSTR5 antagonism stimulates GH secretion in humans. SCO-240 was safe and well-tolerated and exhibited once-daily oral dosing potential. The robust effects of SCO-240 on GH secretion suggest that it may be a treatment option for GH-related disorders.

Hydrogel-fiber-mesh-based 3D cell cultures: A new method for studying pituitary tumors

Acromegaly is a challenging medical condition that arises from the excessive production of growth hormones and the insulin-like growth factor 1 in the pituitary gland. While surgery is the primary treatment for acromegaly, medication is increasingly being used in patients who are unsuitable for surgery or have experienced treatment failure. Despite advancements in medical and surgical therapies, the treatment of acromegaly remains challenging. In this research, a three-dimensional (3D) in-vitro cell culture model for pituitary adenoma research was developed using hydrogel fiber meshes (HFMs) and GH3 cells. Electrospun nanofibers based on polyvinyl alcohol and polyacrylic acid were converted into HFMs by hydrogelification with the leaching of electrosprayed cellulose acetate beads for porosity enhancement. GH3 cells grown in the 3D model exhibited increased dispersion and upregulation of the somatostatin receptor subtypes 2 and 5 compared to those grown in traditional 2D cultures, as well as high sensitivity to somatostatin analogs and tumor-like profiles (as indicated by functional assays and transcriptome analysis, respectively). Therefore, the proposed 3D model accurately represents the physiological response to pituitary-adenoma therapeutic agents. This study highlights the potential of HFMs as a versatile platform for 3D in-vitro cell culture models that can be employed for pituitary adenoma research. Moreover, the proposed 3D cell culture model may contribute to a deeper understanding of tumor biology and facilitate the development of effective therapeutic strategies for acromegaly.

Abstract 5165: Development and validation of an assay for the characterization of SSTR2 expression on CTCs from liquid biopsies

Abstract Background: Expression of Somatostatin Receptor subtype 2 (SSTR2) is observed in multiple cancers, including breast and colorectal cancer. Its role as a prognostic or predictive marker is cancer-type dependent. Recently, there has been renewed interest in assessing this biomarker since it plays a critical role as a target for radiotherapeutics (peptide receptor radionuclide therapy - PRRT) in patients with neuroendocrine tumors (NETs). Blood-based liquid biopsies are a non-invasive tool with proven effectiveness in characterizing cancer biomarker expression in patients. In this study, we describe the development and validation of a novel assay to analyze circulating tumor cells (CTCs) for expression of SSTR2 using the RareCyte platform. Experimental Procedures: Using AccuCyte®, an unbiased density-based method for collecting nucleated cells from whole blood, we transferred nucleated cells to slides and stained for SSTR2, CD45, and CK/EpCAM to identify CTCs (CK+/EpCAM+, CD45-), and evaluate SSTR2 expression. Slides were imaged with CyteFinder®, an automated multiparameter immunofluorescent (IF) microscopy system that applies machine learning algorithms for rare cell identification. Both clinical and spike-in samples were used for assay validation. Single-cell SSTR2 mean fluorescence intensities (MFI) were analyzed to determine protein expression levels. Colorectal cancer with neuroendocrine features and Merkel cell cancer (neuroendocrine tumor of the skin) patient samples were evaluated for CTC enumeration and SSTR2 expression. Results: The assay’s performance metrics for SSTR2 expression were 90+% accuracy, 85% sensitivity, 100% specificity with repeatability and intermediate precision CVs of 14.4% and 16.4%, respectively. A small cohort of colorectal cancer (1) and Merkel cell cancer (2) patient blood samples were tested using the assay. All 3 patients had high CTC levels (300+ per 7.5 mL). The percentage of SSTR2-positive CTCs ranged from 20-60%, reflective of tumor heterogeneity. Conclusions: SSTR2 is an important target now in the advent of theranostics - PRRT. Prognostic and therapeutic implications of SSTR2 expression is an area of active clinical research. SSTR2 targeted therapeutics like 177Lu-dotatate illustrate the possible utility of SSTR2 as a predictive biomarker of treatment response. To date, most of the work has been focused on assessing SSTR2 on tissue. Herein, we show how a CTC platform can be adapted to assess a clinically relevant cell surface protein biomarker. This is now included as an important correlative in a clinical trial for Merkel Cell Cancer patients called iPRRT that is actively accruing (NCT05583708). Citation Format: Erin G. Bayer, Rachel N. Ponting, Ciara M. Kelly, Areeb Lutfi, Maaz K. Afghan, Arturo B. Ramirez, Pashtoon M. Kasi. Development and validation of an assay for the characterization of SSTR2 expression on CTCs from liquid biopsies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5165.

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 invitro 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.

First-in-human administration of terbium-161-labelled somatostatin receptor subtype 2 antagonist ([161Tb]Tb-DOTA-LM3) in a patient with a metastatic neuroendocrine tumour of the ileum.

First-in-human administration of terbium-161-labelled somatostatin receptor subtype 2 antagonist ([161Tb]Tb-DOTA-LM3) in a patient with a metastatic neuroendocrine tumour of the ileum.

Somatostatin Receptor Subtype-2 Targeting System for Specific Delivery of Temozolomide.

Temozolomide (TMZ) is a DNA alkylating agent that produces objective responses in patients with neuroendocrine tumors (NETs) when the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is inactivated. At high doses, TMZ therapy exhausts MGMT activity but also produces dose-limiting toxicities. To reduce off-target effects, we converted the clinically approved radiotracer 68Ga-DOTA-TOC into a peptide-drug conjugate (PDC) for targeted delivery of TMZ to somatostatin receptor subtype-2 (SSTR2)-positive tumor cells. We used an integrated radiolabeling strategy for direct quantitative assessment of receptor binding, pharmacokinetics, and tissue biodistribution. In vitro studies revealed selective binding to SSTR2-positive cells with high affinity (5.98 ± 0.96 nmol/L), internalization, receptor-dependent DNA damage, cytotoxicity, and MGMT depletion. Imaging and biodistribution analysis showed preferential accumulation of the PDC in receptor-positive tumors and high renal clearance. This study identified a trackable SSTR2-targeting system for TMZ delivery and utilizes a modular design that could be broadly applied in PDC development.

Somatostatin receptor subtype 2A expression and genetics in 184 paragangliomas: a single center retrospective observational study.

Adrenal and extra-adrenal paragangliomas (PGLs) are a group of neuroendocrine tumors (NETs) with strong heterogeneity, which often express somatostatin receptor subtype 2 A (SSTR2A). However, the association between SSTR2A expression and genetic status of PGLs remains unclear. The purpose of the study was to identify whether various pathogenic variants (PVs) had an impact on SSTR2A expression in PGLs. This retrospective study included 184 patients with pathologically confirmed PGLs. The immunohistochemical expression of SSTR2A were studied in 184 tumors and PVs were tested in 159 tumor samples. Clinical and genetic data were compared in SSTR2A positive and negative PGLs. SSTR2A was positive in 63.6% (117/184) of all tumors. PGLs with negative SSTR2A were more likely to be extra-adrenal (37.0% vs 18.0%; P = 0.005) and exhibited a considerably greater proportion of PVs (75.4% vs. 49.0%; P = 0.001) than those with positive SSTR2A. Compared to those without PVs, a higher proportion of PGLs with PVs in cluster 1B (P = 0.004) and cluster 2 (P = 0.004) genes, especially VHL (P = 0.009), FGFR1 (P = 0.010) and HRAS (P = 0.007), were SSTR2A negative. SSTR2A was positive in all tumors (4/4) with SDHx PVs and in 87.5% (7/8) of metastatic PGLs. SSTR2A negativity was correlated with extra-adrenal tumor location and PVs in cluster 1B and cluster 2 genes such as VHL, FGFR1 and HRAS. Immunohistochemistry of SSTR2A should be taken into consideration in the personalized management of PGLs.

Direct and Indirect Chimeric Antigen Receptor T-Cell Imaging with PET/MRI in a Tumor Xenograft Model.

Background Chimeric antigen receptor (CAR) T cells are a promising cancer therapy; however, reliable and repeatable methods for tracking and monitoring CAR T cells in vivo remain underexplored. Purpose To investigate direct and indirect imaging strategies for tracking the biodistribution of CAR T cells and monitoring their therapeutic effect in target tumors. Materials and Methods CAR T cells co-expressing a tumor-targeting gene (anti-CD19 CAR) and a human somatostatin receptor subtype 2 (hSSTr2) reporter gene were generated from human peripheral blood mononuclear cells. After direct labeling with zirconium 89 (89Zr)-p-isothiocyanatobenzyl-desferrioxamine (DFO), CAR T cells were intravenously injected into immunodeficient mice with a CD19-positive and CD19-negative human tumor xenograft on the left and right flank, respectively. PET/MRI was used for direct in vivo imaging of 89Zr-DFO-labeled CAR T cells on days 0, 1, 3, and 7 and for indirect cell imaging with the radiolabeled somatostatin receptor-targeted ligand gallium 68 (68Ga)-DOTA-Tyr3-octreotide (DOTATOC) on days 6, 9, and 13. On day 13, mice were euthanized, and tissues and tumors were excised. Results The 89Zr-DFO-labeled CAR T cells were observed on PET/MRI scans in the liver and lungs of mice (n = 4) at all time points assessed. However, they were not visualized in CD19-positive or CD19-negative tumors, even on day 7. Serial 68Ga-DOTATOC PET/MRI showed CAR T cell accumulation in CD19-positive tumors but not in CD19-negative tumors from days 6 to 13. Notably, 68Ga-DOTATOC accumulation in CD19-positive tumors was highest on day 9 (mean percentage injected dose [%ID], 3.7% ± 1.0 [SD]) and decreased on day 13 (mean %ID, 2.6% ± 0.7) in parallel with a decrease in tumor volume (day 9: mean, 195 mm3 ± 27; day 13: mean, 127 mm3 ± 43) in the group with tumor growth inhibition. Enhanced immunohistochemistry staining of cluster of differentiation 3 (CD3) and hSSTr2 was also observed in excised CD19-positive tumor tissues. Conclusion Direct and indirect cell imaging with PET/MRI enabled in vivo tracking and monitoring of CAR T cells in an animal model. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Bulte in this issue.

Somatostatin and Somatostatin Receptors in Tumour Biology.

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

18F-labeled somatostatin analogs for somatostatin receptors (SSTRs) targeted PET imaging of neuroendocrine tumors (NETs)

A novel 18F-radiolabeled somatostatin analogue, [Al18F]NODA-MPAA-HTA, was synthesized and evaluated for positron emission tomography (PET) imaging of Neuroendocrine tumors (NETs). [Al18F]NODA-MPAA-HTA was designed and synthesized by conjugating 18F nuclide with a modified KE108 peptide, a somatostatin analog with high affinity for all five subtypes of somatostatin receptors (SSTR 1-5), through coupling a bifunctional chelator (NODA) to target somatostatin receptor (SSTR) positive tumors. The amino group of KE108 peptide, a SSTRs-targeting pharmacophore, was conjugated with the carboxyl group of NODA by a condensation reaction to obtain the labeling precursor of [Al18F]NODA-MPAA-HTA, in which its precursor was obtained through Fmoc solid-phase methods. A novel methodology for Al18F labeling of chelating agent-biomolecule conjugates was used to synthesize [Al18F]NODA-MPAA-HTA. In vitro stabilities of [Al18F]NODA-MPAA-HTA were evaluated by incubating it in saline or bovine serum for 2h. Ex vivo biodistribution and in vivo imaging of [Al18F]NODA-MPAA-HTA were further investigated to evaluate its SSTRs targeting ability and feasibility for the diagnosis of NETs using PET imaging. [Al18F]NODA-MPAA-HTA was synthesized using a one-step 18F-AlF labeling procedure resulting in moderate radiochemical yield (60-80%, non-decay corrected) and high radiochemical purity (>95%). It exhibited good hydrophilicity and excellent stability in vitro, with a molar activity of 122 GBq/μmol. At 30min and 60min, the uptake of [Al18F] NODA-MPAA-HTA by HEK293-SSTR2 cells was 5.47±0.97%/105 cells and 12.11±0.32%/105 cells, respectively. The affinity of [Al18F]NODA-MPAA-HTA for SSTR2 was determined to be 8.77±1.14nM. In micro-PET imaging of HEK293-SSTR2 tumor-bearing mice, [Al18F]NODA-MPAA-HTA showed high tumor uptake of radioactivity and a high tumor-to-muscle ratio. Biodistribution results confirmed that radioactivity uptake in the tumor was significantly higher than that in the muscle by more than five-fold (P<0.001). Furthermore, the relatively low bone uptake of [Al18F]NODA-MPAA-HTA suggested that defluorination did not occur in vivo. These preliminary results provide experimental evidence for further study of Al18F-labeled somatostatin analogues as tumor probes for PET imaging of NETs. Fluorine-18 is widely used as a radionuclide for the production of radiopharmaceuticals for positron emission tomography (PET). Due to its short half-life (T1/2,109.8min), its ease of production will facilitate the widespread dissemination of this radiopharmaceutical. A high-quality [Al18F]NODA-MPAA-HTA was synthesized with satisfactory yield. This radiopharmaceutical demonstrated higher tumor uptake and better tumor-to-muscle contrast, resulting to excellent image quality. These findings suggest that the novel 18F-labeled somatostatin analogue, [Al18F]NODA-MPAA-HTA, is a promising tool for PET imaging of NETs.

Effect of hepatic impairment on pharmacokinetics, safety, and tolerability of oral paltusotine, a small-molecule, selective somatostatin receptor subtype 2 agonist

Effect of hepatic impairment on pharmacokinetics, safety, and tolerability of oral paltusotine, a small-molecule, selective somatostatin receptor subtype 2 agonist

Discovery and exploration of novel somatostatin receptor subtype 5 (SSTR5) antagonists for the treatment of cholesterol gallstones

The shortage of cholesterol gallstones treatment intensifies the need to discover of effective small molecule drugs. Clinical follow-up and studies have found that activation of somatostatin receptor subtype 5 (SSTR5) reduce gallbladder contraction and thus increase the risk of cholesterol gallstones, implying that antagonizing SSTR5 may promote gallbladder emptying and reduce the formation of gallstones. Herein, we discovered novel SSTR5 antagonists and firstly investigated its effects on cholesterol gallstone. From loperamide, a reported seed structure with micromole activity, we identified optimal compound 23 as an SSTR5 antagonist exhibiting single-digit nanomolar potency, low hERG inhibition and oral availability. Further in vivo evaluation revealed that 23 significantly promoted gallbladder emptying. Moreover, in a mouse cholesterol gallstone model, 23 (3 mg/kg) effectively reduced the cholesterol gallstones formation, showing better efficacy than the clinical first-line drug UDCA (60 mg/kg), providing a new insight into the development of anti-gallstone drugs.

Influence of the Molar Activity of 203/212Pb-PSC-PEG2-TOC on Somatostatin Receptor Type 2-Binding and Cell Uptake.

(1) Background: In neuroendocrine tumors (NETs), somatostatin receptor subtype 2 is highly expressed, which can be targeted by a radioactive ligand such as [177Lu]Lu-1,4,7,10-tetraazacyclododecane-N,N',N″,N‴,-tetraacetic acid-[Tyr3,Thr8]-octreotide (177Lu-DOTA-TOC) and, more recently, by a lead specific chelator (PSC) containing 203/212Pb-PSC-PEG2-TOC (PSC-TOC). The molar activity (AM) can play a crucial role in tumor uptake, especially in receptor-mediated uptake, such as in NETs. Therefore, an investigation of the influence of different molar activities of 203/212Pb-PSC-TOC on cell uptake was investigated. (2) Methods: Optimized radiolabeling of 203/212Pb-PSC-TOC was performed with 50 µg of precursor in a NaAc/AcOH buffer at pH 5.3-5.5 within 15-45 min at 95° C. Cell uptake was studied in AR42 J, HEK293 sst2, and ZR75-1 cells. (3) Results: 203/212Pb-PSC-TOC was radiolabeled with high radiochemical purity >95% and high radiochemical yield >95%, with AM ranging from 0.2 to 61.6 MBq/nmol. The cell uptake of 203Pb-PSC-TOC (AM = 38 MBq/nmol) was highest in AR42 J (17.9%), moderate in HEK293 sstr (9.1%) and lowest in ZR75-1 (0.6%). Cell uptake increased with the level of AM. (4) Conclusions: A moderate AM of 15-40 MBq/nmol showed the highest cell uptake. No uptake limitation was found in the first 24-48 h. Further escalation experiments with even higher AM should be performed in the future. It was shown that AM plays an important role because of its direct dependence on the cellular uptake levels, possibly due to less receptor saturation with non-radioactive ligands at higher AM.

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

PurposeThe 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.MethodsNew 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.ResultsThe 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.ConclusionStructural 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.

Abstract 12853: [ 64 Cu]Cu-DOTATATE is Superior to [ 68 Ga]Ga-NODAGA-E[c(RGDyK)]2 (RGD) PET/CT Imaging In Detection and Quantification of Atherosclerosis: A Retrospective Analysis of a Phase 2 Trial Cohort

Introduction: Inflammation and angiogenesis are central to development of atherosclerosis. [ 64 Cu]Cu-DOTATATE and [ 68 Ga]Ga-NODAGA-E[c(RGDyK)]2 (RGD) are PET tracers that can non-invasively visualize somatostatin receptor subtype 2 (SSTR 2 ) and α v β 3 integrin expression that represent inflammation and angiogenesis respectively. Hypothesis: Whether an imaging tracer of inflammation can be compared with a tracer of angiogenesis for detection and quantification of the atherosclerotic process in patients from a Phase II cancer trial cohort. Methods: A cohort of patients from Phase II trial were divided in three groups as controls (N=7), at risk (N=6) &amp; diseased (N=7). PET/CT scans with two different tracers were performed in all subjects. The scans were retrospectively analyzed, and tracer uptake (mean of maximum target-to-background ratios (mTBRmax)) were determined in 6 arterial segments. In addition, plaques from patients (N=7) undergoing carotid endarterectomy (CEA) were studied with autoradiography and immunohistochemistry. Results: [ 64 Cu]Cu-DOTATATE uptake in the disease group was significantly higher compared to the control group in the abdominal aorta (4.4 vs 2.1, p=0.02), thoracic aorta (3.0 vs 2.2, p=0.02), aortic arch (2.8 vs 2.2, p=0.03), left carotid artery (2.2 vs 1.3, p=0.02) and the average of all six aortic segments (2.7 vs 2.0, p=0.01) whereas all aortic segments in the disease group showed a higher but a non-significant difference compared to the control group with RGD uptake. A moderate correlation was found between the mean aortic uptake of [ 64 Cu]Cu-DOTATATE &amp; RGD (r=0.41, p=0.01) in patients from the disease group. SSTR 2 and α v β 3 expression was confirmed on ex vivo plaques along with tracer binding. Conclusions: An in vivo imaging marker of inflammation was superior to a marker of angiogenesis in discriminating levels of atherosclerosis. The two markers were weakly correlated in patients with known cardiovascular disease.

FRI265 I123-MIBG Positive, CU64-Dotatate PET Negative Pheochromocytoma In A Patient With Bilateral Adrenal Incidentalomas

Abstract Disclosure: P. Pagadala: None. V. Patel: None. Bilateral incidental adrenal nodules represent 10-23% of all incidental adrenal nodules. Most are benign nonfunctioning adenomas however these can be catecholamine-secreting tumors that arise from chromaffin cells of the adrenal medulla called pheochromocytomas. Identifying pheochromocytoma using anatomic imaging alone in cases of bilateral adrenal nodules is challenging. Functional imaging with radioisotope tracers can be helpful such as MIBG (meta-iodobenzylguanidine) and DOTATATE scans. We describe a case of pheochromocytoma, which was negative on DOTATATE but positive on MIBG scan which localized the pheochromocytoma. A 65-year-old male with a history of hypertension, chronic kidney disease and obstructive sleep apnea was found to have bilateral adrenal nodules on routine imaging. MRI abdomen showed a right adrenal nodule 1.7cm x 1.8cm x 1.7cm and a left adrenal nodule 2.3 cm in maximum dimension. He had no apparent symptoms of catecholamine excess. Biochemical testing revealed elevated total plasma metanephrines on serial assessments along with elevated 24-hour urine dopamine levels. A CT scan with adrenal protocol further characterized the right adrenal nodule with precontrast density of 43 Hounsfield Units (HU) with a rapid washout of 75% within 5 minutes, consistent with benign adrenal adenoma. The left adrenal gland had 2 nodules. A smaller superior nodule 1.3 cm AP x 1.0 cm transverse x 0.9 cm craniocaudal in size, density of -3 HU on the precontrast images, with approximately 85% washout most consistent with a benign adrenal adenoma. A larger inferior nodule was 2.3 cm AP x 2.2 cm transverse x 2.3 cm craniocaudal in size and precontrast density of 32 HU, rising to 58 HU during the portal venous phase and remaining at about 58 HU on the delayed images, indicating no significant washout and is indeterminate. A Cu64 labeled DOTATATE scan showed the 1.6 cm right adrenal nodule demonstrated activity similar to that of contralateral background adrenal activity. There was no comment regarding the two left adrenal nodules. A I123 MIBG scan showed the larger of the two left adrenal nodules had a strong uptake of the MIBG highly likely to be a pheochromocytoma. The smaller left adrenal nodule and the right adrenal nodule had no significant MIBG uptake, making these adrenal adenomas. The patient underwent left robotic adrenalectomy and pathology confirmed a 2.3 cm pheochromocytoma in addition to adrenocortical nodular disease. Three months post-surgery, plasma and 24-hour urinary measurements for metanephrines and catecholamines had normalized. Further research is needed to assess the benefit of I123MIBG when DOTATATE is negative. A potential cause of false negatives on DOTATATE is variability in somatostatin receptor subtype expression. Better imaging modalities for pheochromocytomas and guidelines for the management of bilateral adrenal nodules would assist in treatment decisions. Presentation: Friday, June 16, 2023