SSTR2 Expression Research Articles

Histopathological Evaluation of Somatostatin Receptor 2 Expression in Myocarditis—Rationale for the Diagnostic Use of Somatostatin Receptor Imaging

Background/Objectives: Myocarditis is an inflammatory disease of the myocardium and remains to this day a challenging diagnosis. A promising novel imaging method uses the expression of somatostatin receptors (SSTRs) on inflammatory cells to visualize myocardial inflammation. However, little is known about the histopathological correlate of SSTR imaging in different forms of myocarditis. Methods: In the present retrospective histopathological study, we systematically analysed the expression of SSTR subtype 2 (SSTR2) on inflammatory cells of 33 patients with biopsy- or explant-proven myocarditis (lymphocytic myocarditis (n = 5), giant-cell myocarditis (n = 11), and cardiac sarcoidosis (n = 17)), and in eight controls (multi-organ donors) without signs of myocardial inflammation and/or scars. Results: In all patients, immunohistochemical staining for SSTR2 was positive in areas with CD68-positive macrophages and multinucleated giant cells. Staining for SSTR2 was most prominent in the presence of multinucleated giant cells. The colocalization of both SSTR2 and CD68 on the same cell could be confirmed using immunofluorescence microscopy. Western blotting confirmed the upregulated expression of SSTR2 in cases of granulomatous inflammation (sarcoidosis) of the skeletal and heart muscle, in comparison with controls. Conclusions: In conclusion, our findings demonstrate the expression of SSTR2 on the protein level on CD68-positive macrophages and multinucleated giant cells in various forms of myocarditis, which provides a clear rationale for the diagnostic use of SSTR imaging in this patient group.

6774 Recurrent Hypoglycemia In Malignant Insulinoma With Multiple Liver Metastases Successfully Managed With Octreotide

Abstract Disclosure: K. Kim: None. S. Mascarell: None. Introduction: Insulinoma is a rare functional pancreatic neuroendocrine tumor (pNET) with the incidence of 1-4/million person-years. Malignant insulinomas with locoregional invasion or metastases consist 10% among insulinomas. While the treatment of a single insulinoma is surgical resection, treatment of malignant insulinoma requires a comprehensive approach. Due to the low prevalence of the disease, data on therapeutic modalities of malignant insulinomas are limited. We hereby present a case of malignant insulinoma in which recurrent hypoglycemia was successfully managed with octreotide. Case: A 36 year old female diagnosed with grade III well differentiated pNET with multiple metastases to the liver and abdominal lymph nodes 1 year ago was admitted for recurrent hypoglycemic episodes. She reported progressively worsening hypoglycemia for the past 1 month. She was eating every 2 hours including her sleeping hours to prevent hypoglycemia. Due to recurrent hypoglycemia she required hospitalization with IV dextrose. After 13 hours of fasting in the ICU, hypoglycemia due to insulin hypersecretion was confirmed with blood glucose 51 mg/dL and elevated serum insulin 51.11 uIU/mL (1.9-23uIU/mL). She underwent the short octreotide test which showed suppressed insulin (5.25 uIU/mL) 6 hours after receiving 100 mcg of octreotide. She was started on octreotide 50 mcg every 12 hours and monitored for further hypoglycemic episodes. She tolerated octreotide without any side effects including hypoglycemia. She was discharged home with a continuous glucose monitor (CGM) and transitioned to intramuscular lanreotide 20mg injections every 4 weeks as an outpatient. No further hypoglycemic episodes occurred. Discussion: Few cases report treatment of hypoglycemia in malignant insulinoma with octreotide. Octreotide has the dual effect of suppressing insulin secretion and tumor growth on insulinomas that express SSTR2 receptors. However, because somatostatin agonists also inhibit the secretion of glucagon, in insulinomas without SSTR2 expression, octreotide can aggravate hypoglycemia. This was especially a concern for our patient with a large tumor burden. Thus the short octreotide test was conducted. We suggest that the octreotide test of 100 mcg SQ octreotide injection followed by hourly measurements of glucose and insulin levels is a useful and convenient test to predict efficacy while monitoring for octreotide induced hypoglycemia. Finally the use of CGM in the outpatient setting enabled successful transition to octreotide LAR which improved the patient’s quality of life greatly by enabling once a month injections. Presentation: 6/3/2024

8785 Does Somatostatin Receptor Expression Intensity Impact Prognosis in Non Pituitary Neuroendocrine Tumors Treated with Somatostatin Analogues?

Abstract Disclosure: N. Saleh Jouneghani: None. S. Fazeli: None. S. Chang: None. A. Hosseini: None. R. Marandi: None. A. Siddiqui: None. M. Talley: None. B. Salehian: None. Does Somatostatin Receptor Expression Intensity Impact Prognosis in Non Pituitary Neuroendocrine Tumors Treated with Somatostatin Analogues? Introduction: Non-pituitary neuroendocrine tumors (NETs) show different somatostatin receptor subtype (SSTR) expression, but their role in tumor progression and prognosis is not well known. We hypothesized that NETs with higher expression of SSTR2, SSRT5, or co-expression of SSTR2 and SSTR5 will have better outcome when treated with Somatostatin Analogues (SSA). Method: Retrospectively, patients with non-pituitary neuroendocrine tumors, followed for more than one year between 1985 and 2022, and treated with SSA (Octreotide or Lanreotide) who had available tissue were selected. Tissue immunostaining performed for SSTR2 and SSTR5 with use of monoclonal antibodies. Expression analysis of the SSTR2 and SSTR5 were evaluated by the validated semi-quantitatively method, reported by an intensity score of 0 -3. The progression free survival and overall survival were calculated by Kaplan Meier and compared in different subgroups with SSTR expression intensity. Response evaluation was assessed using RECIST v1.1. Results: Of 279 non-pituitary neuroendocrine tumors, 51 meet the criteria and tissue sent for analysis. The median age at diagnosis was 62; male 49%, with median follow up 7 years, 85% stage IV at diagnosis, most common primary tumor was in gut 54% followed by pancreas 33%. Positive SSRT5 tumors had 93% SSRT2 co-expression. There were no significant differences in progression-free survival (PFS) observed between tumors with low or high SSTR2 intensity expression (P=0.62). The presence or absences of SSRT5 expression did not have any impact on PFS (p=0.57) or overall survival (p=0.3). Conclusion: in the patient with non-pituitary neuroendocrine tumors, higher SSTR2 expression intensity or having SSRT5 co-expression, did not correlate with a better PFS or overall survival in response to SSA, in our study. Further prospective studies are needed to clarify if higher expression intensity of SSRTs correlates with better response to SSAs in NETs. Presentation: 6/1/2024

Lenticulostriatal Ischemia Shows Relevant SSTR Expression on PET/CT Imaging Using the Novel SSTR-Targeting Peptide 18F-SiTATE.

A 64-year-old woman with meningioma presented with left-sided lenticulostriatal ischemia following craniotomy and debulking of a sphenoid wing meningioma. For subsequent radiotherapy planning, an SSTR-targeted PET/CT using the novel ligand 18F-SiTATE was performed 2.5 months thereafter. The meningioma remnants showed transosseous, intrasellar, and perivascular extension around the internal carotid artery with strong SSTR expression. Moreover, there was focal 18F-SiTATE uptake in the left caudate and corresponding contrast enhancement due to postischemic blood-brain barrier disruption and reactive SSTR expression. Therefore, increased cortical or subcortical SSTR PET signal may be related to ischemic changes even in the subacute stage after initial stroke.

Immune Cell Molecular Pharmacodynamics of Lanreotide in Relation to Treatment Response in Patients with Gastroenteropancreatic Neuroendocrine Tumors.

The CLARINET trial led to the approval of lanreotide for the treatment of patients with gastroenteropancreatic neuroendocrine tumors (NETs). It is hypothesized that lanreotide regulates proliferation, hormone synthesis, and other cellular functions via binding to somatostatin receptors (SSTR1-5) present in NETs. However, our knowledge of how lanreotide affects the immune system is limited. In vitro studies have investigated functional immune response parameters with lanreotide treatment in healthy donor T cell subsets, encompassing the breadth of SSTR expression, apoptosis induction, cytokine production, and activity of transcription factor signaling pathways. In our study, we characterized in vitro immune mechanisms in healthy donor T cells in response to lanreotide. We also studied the in vivo effects by looking at differential gene expression pre- and post-lanreotide therapy in patients with NET. Immune-focused gene and protein expression profiling was performed on peripheral blood samples from 17 NET patients and correlated with clinical response. In vivo, lanreotide therapy showed reduced effects on wnt, T cell receptor (TCR), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) signaling in CD8+ T cells in responders compared to non-responders. Compared to non-responders, responders showed reduced effects on cytokine and chemokine signaling but greater effects on ubiquitination and proteasome degradation genes. Our results suggest significant lanreotide pharmacodynamic effects on immune function in vivo, which correlate with responses in NET patients. This is not evident from experimental in vitro settings.

Predicting Response to Medical Treatment in Acromegaly via Granulation Pattern, Expression of Somatostatin Receptors Type 2 and 5 and E-Cadherin.

Resistance to first-generation somatostatin receptor ligand (fgSRL) treatment in acromegaly is common, making the identification of biomarkers that predict fgSRL response a desired goal. We conducted a retrospective analysis on 21 patients with acromegaly who underwent surgery and subsequent pharmacological treatment. Through immunohistochemistry (IHC), we assessed the expression of the somatostatin receptor subtypes SSTR2 and SSTR5, E-Cadherin, and cytokeratin granulation pattern (sparsely or densely). Patients were divided into responders and non-responders based on their biochemical response to fgSRL and/or the newer agent, Pasireotide, or the GH-blocker, Pegvisomant. Patients resistant to fgSRL (n = 12) exhibited lower SSTR2 and E-Cadherin expressions. Sparsely granulated tumors were more frequent in the non-responder group. SSTR2 (p = 0.024, r = 0.49) and E-Cadherin (p = 0.009, r = 0.64) positively correlated with the Insulin-like Growth Factor 1 (IGF-1) decrease after fgSRL, while SSTR5 (p = 0.107, r = -0.37) showed a trend towards negative correlation. SSTR5 positivity seemed to be associated with Pasireotide response, albeit the number of treated patients was too low (n = 4). No IHC markers correlated with Pegvisomant response. Our findings suggest that densely granulated tumors, with positive SSTR2 and E-Cadherin seem to be associated with favorable fgSRL responses. The strongest predictive value of the studied markers was found for E-Cadherin, which seems to surpass even SSTR2.

Novel Detection of Pleomorphic Adenomas via Analysis of 68Ga-DOTATOC PET/CT Imaging.

Currently, the diagnosis of salivary gland tumors using imaging techniques is unreliable. In this monocentric retrospective study, we examined patients who received a 68Ga-DOTATOC PET/CT and subsequently underwent a salivary gland tumor resection between 1 January 2010 and 31 December 2021. PET/CT image assessment was compared with somatostatin receptor (SSTR) expression and histology. Thirteen patients (five pleomorphic adenoma (PA) and eight other parotid lesions (OPL)) received a 68Ga-DOTATOC PET/CT. Imaging displayed strong focal tracer uptake in all PA except for one with strong tumor to background discrimination. PA revealed higher SUVmax, SUVmean, liver and blood pool quotients than those of Warthin tumors (WT) and of OPL. In comparison to the contralateral parotid, SUVmax (p = 0.02), SUVmean (p = 0.02), liver quotient (p = 0.03) and blood pool quotient (p = 0.03) were all significantly higher. In contrast, WT and OPL showed in relation to the contralateral parotid no significant differences of SUVmax (WT p = 0.79; OPL p = 0.11), SUVmean (WT p = 1.0; OPL p = 0.08), liver quotient (WT p = 0.5; OPL p = 0.08) and blood pool quotient (WT p = 0.8; OPL p = 0.19). Two PA and one granuloma were not available for examination. In the immunohistochemal analysis, all PA demonstrated the highest intensity of SSTR2 expression (grade 3). Furthermore, PA had a high percentage of cells expressing SSTR2 (20%, 80% and 55%). A strong tracer uptake in PA was shown in 68Ga-DOTATOC PET/CT. This may allow physicians to utilize radioligated somatostatin analogue PET CT/MR imaging to accurately diagnose PA. Additionally, it may be possible in the future to treat the PA with a noninvasive peptide receptor radionuclide therapy or with somatostatin analogues.

Somatostatin receptors in fibrotic myocardium.

A patient with a neuroendocrine tumor and history of coronary artery disease underwent PET with 68Ga-DOTATATE PET tracer for tumor visualization. Analysis of the scan showed uptake of 68Ga-DOTATATE in the left ventricle corresponding to previous myocardial infarct. 68Ga-DOTATATE binds by somatostatin receptors (SSTR) and it has been proposed that it may be useful for the detection of cardiac inflammatory lesions. We aimed to test whether SSTR could be upregulated in cardiac fibrotic scar. We analyzed SSTR in cardiac samples from patients with end-stage ischemic cardiomyopathy (ICM, n = 8) and control hearts (n = 5). In mature ICM tissue, SSTR1 and SSTR2 expression was unchanged and SSTR5 expression was significantly decreased in ICM samples vs. control. Immunohistochemistry showed increased SSTR1 and SSTR2 in ICM. Areas with SSTR1 or SSTR2 staining were often adjacent to fibrotic areas. The majority of SSTR1 and SSTR2 staining localized in cardiomyocytes in fibrotic scar-rich areas where CD68 macrophage staining was not present. SSTR are occasionally upregulated in cardiac fibrotic areas. When using 68Ga-DOTATATE PET tracer to detect cardiac sarcoidosis or atherosclerotic plaque, the possibility of tracer uptake in fibrotic areas should be considered.

Expression of somatostatin receptors in canine and feline meningioma.

The standard treatment for canine and feline meningiomas includes radiotherapy, surgical excision or combined therapy. However, new therapeutic approaches are required due to the possible recurrence or progression of meningiomas despite initial therapy. Adjunctive therapy with synthetic long-acting somatostatin (SST) analogues has been described in humans with SST-expressing tumours. The expression of SST receptors (SSTRs) by feline meningiomas is currently unknown, and there are little data about canine meningiomas. We hypothesized that SSTR is expressed by canine and feline meningiomas (S1). Seven canines and 11 felines with histologically confirmed meningiomas underwent STTR screening. RNA expressions of SSTR1, SSTR2, SSTR3 and SSTR5 (canine) and SSTR1-SSTR 5 (feline) in fresh frozen and formalin-fixed and paraffin-embedded (FFPE) samples were investigated using real-time (RT)-qPCR. The expression of SSTR1 and SSTR2 in FFPE samples was evaluated using immunohistochemistry (IHC). The specificity of applied antibodies for canine and feline species was confirmed by western blotting. In canine meningiomas (n=7), RNA expression of SSTR1, SSTR2 and SSTR5 was detected in all samples; SSTR3 RNA expression was detected in only 33% of samples. In feline meningiomas (n=12), RNA expression of SSTR1, SSTR4, SSTR5 and SSTR2 was detected in 91%, 46%, 46% and 36% of samples, respectively; SSTR3 was not expressed. Overall, the detection rate was lower in FFPE samples. IHC revealed the expression of SSTR1 and SSTR2 in all samples from both species. However, it is important to exercise caution when interpreting IHC results due to the presence of diffuse background staining. SSTRs are widely expressed in canine and feline meningiomas, thereby encouraging further studies investigating SSTR expression to conduct trials about the effect of adjunctive therapy with long-acting SST-analogues.

Clinical Evaluation of Response to Octreotide and Chemotherapy in High-Grade Malignant Neuroendocrine Tumors and Promising In Vitro Preclinical Results with Pasireotide.

Background and Objectives: High-grade malignant neuroendocrine tumors (G3 NETs) and neuroendocrine carcinomas (NECs) are characterized by rapid proliferation, high metastatic capacity, and strong expression of somatostatin receptors (SSTRs). We aimed to analyze the presence of SSTRs in NET G3 and NEC, and to correlate their expression with the use of octreotide and pasireotide. Materials and Methods: For this purpose, we first performed a retrospective study of G3 NET and NEC patients, which included the determination of SSTR expression and response to octreotide treatment. Second, we selected the H69 small cell lung cancer cell line to determine the effect of octreotide and pasireotide. Results: Our results showed the traditional somatostatin analog (SSA) octreotide was ineffective in patients with NET G3 and NEC. On the other hand, RT-qPCR showed a high expression of SSTR2 and SSTR5 in H69 cells. Interestingly, while octreotide did not modify H69 cell proliferation, a strong inhibition of proliferation was detected with the use of pasireotide. Conclusions: In view of these results, a clinical trial in NET G3 and NEC patients using pasireotide is necessary to determine the usefulness of this drug in improving patient treatment.

Circulating levels of mir-375 in cushing's disease patients and evaluation of its role in the regulation of sstr2 expression in murine pituitary corticotroph tumor cell model

Circulating levels of mir-375 in cushing's disease patients and evaluation of its role in the regulation of sstr2 expression in murine pituitary corticotroph tumor cell model

Characterization of circRNA expression profiles associated with non-Mendelian inheritance in feather growth of chickens

ABSTRACT 1. Non-coding RNAs, such as miRNAs, play a crucial role in chicken feather growth rate. However, circular RNA (circRNA) expression profiles in fast- and slow-feathering chickens that follow and do not follow Mendelian inheritance are unclear. 2. The circRNA expression profiles was analysed by RNA sequencing of hair follicles of slow-feathering chickens that follow genetic rules and fast-feathering chickens that did not follow genetic rules. Differentially expressed circRNA-miRNA-mRNA competing endogenous RNA (ceRNA) network was then constructed and the key factors and regulation mechanisms controlling feather growth rate were identified. 3. The results revealed that 67 circRNAs were significantly differentially expressed in hens, including 22 up-regulated and 45 down-regulated circRNAs in non-Mendelian inheritance-mediated fast-feathering hens compared with Mendelian inheritance-mediated slow-feathering hens. In addition, 16 significantly differentially expressed circRNAs were identified in cockerels, including nine up-regulated and seven down-regulated circRNAs in non-Mendelian inheritance-mediated fast- compared with Mendelian inheritance-mediated slow-feathering cocks. Moreover, circRNA-mediated ceRNA regulation of hair follicle formation was particularly abundant in the Jak-STAT, Wnt and Toll-like receptor signalling pathways. Furthermore, circABI3BP was seen to be a crucial circRNA in regulating feather growth rate, by binding with gga-miR-1649-5p to regulate SSTR2 expression. 4. In conclusion, this study analysed circRNA expression profiles in fast- and slow-feathering chickens that follow and do not follow Mendelian inheritance, which laid the foundation for understanding the role of circRNA in chicken feather growth rate.

Clinicopathological and Molecular Profile of Sellar Neurocytoma

Abstract Objective To investigate the clinical features, imaging characteristics, and molecular profile of sellar neurocytoma (SN). Methods Clinical, imaging, and pathological features of 11 cases of SN were retrospectively analyzed. Electron microscopy was performed in 5 cases. Molecular features were detected in tumor tissue by RNA sequencing, quantitative polymerase chain reaction, and immunohistochemistry. Results The clinical features of SN patients showed a high incidence of hyponatremia (73%, 8/11), and the tumors tended to invade the lateral side of the saddle area from preoperative imaging analysis. The tumors had positive NeuN, synaptophysin, neurofilament, somatostatin receptor 2 (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. Fifteen differentially expressed genes were verified for quantitative polymerase chain reaction verification. SSTR2 has been verified by immunohistochemistry. Conclusion 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.

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.

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

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

Immunological signatures and predictive biomarkers for first-generation somatostatin receptor ligand resistance in Acromegaly.

Predicting resistance to first-generation Somatostatin Receptor Ligands (fg-SRL) in Acromegaly patients remains an ongong challenge. Tumor-associated immune components participate in various pathological processes, including drug-resistance. We aimed to identify the immune components involved in resistance of fg-SRL, and to investigate biomarkers that can be targeted to treat those drug-resistant Acromegaly. We conducted a retrospective study involving 35 Acromegaly patients with somatotropinomas treated postoperatively with fg-SRL. Gathering clinicopathological data, SSTR2 expression, and immunological profiles, we utilized univariate, binary logistic regression, and ROC analyses to assess their predictive roles in fg-SRL resistance. Spearman correlation analysis further examined interactions among interested characteristics. 19 patients (54.29%) exhibited resistance to postoperative fg-SRL. GH level at diagnosis, preoperative tumor volume, T2WI-MRI intensity, granularity, PD-L1, SSTR2, and CD8 + T cell infiltration showed association with clinical outcomes of fg-SRL. Notably, T2WI-MRI hyperintensity, PD-L1-IRS > 7, CD8 + T cell infiltration < 14.8/HPF, and SSTR2-IRS < 5.4 emerged as reliable predictors for fg-SRL resistance. Correlation analysis highlighted a negative relationship between PD-L1 expression and CD8 + T cell infiltration, while showcasing a positive correlation with preoperative tumor volume of somatotropinomas. Additionally, 5 patients with fg-SRL resistance underwent re-operation were involved. Following fg-SRL treatment, significant increases in PD-L1 and SSTR5 expression were observed, while SSTR2 expression decreased in somatotropinoma. PD-L1 expression and CD8 + T cell infiltration, either independently or combined with SSTR2 expression and T2WI-MRI intensity, could form a predictive model guiding clinical decisions on fg-SRL employment. Furthermore, targeting PD-L1 through immunotherapy and embracing second-generations of SRL with higher affinity to SSTR5 represent promising strategies to tackle fg-SRL resistance in somatotropinomas.

212P Correlation of 68Ga-SSO120 PET with SSTR2 expression and prognostic value in patients with small cell lung cancer

212P Correlation of 68Ga-SSO120 PET with SSTR2 expression and prognostic value in patients with small cell lung cancer

Loss of function in somatostatin receptor 5 has no impact on the growth of medaka fish due to compensation by the other paralogs

Somatic growth in vertebrates is regulated endocrinologically by the somatotropic axis, headed by the growth hormone (GH) and the insulin growth factor-I (IGF-I). Somatostatin (Sst), a peptide hormone synthesized in the hypothalamus, modulates GH actions through its receptors (Sstr). Four Sstr subtypes (Sstr 1–3 and 5) have been identified in teleosts. However, little is known about whether they have a specific function or tissue expression. The aim of this study was to determine the role of sstr2 and sstr5 in the growth of the medaka (Oryzias latipes). The assessed expression pattern across diverse tissues highlighted greater prevalence of sstr1 and sstr3 in brain, intestine and muscle than in pituitary or liver. The expression of sstr2 was high in all the tissues tested, while sstr5 was predominantly expressed in the pituitary gland. A CRISPR/Cas9 sstr5 mutant with loss of function (sstr5-/-) was produced. Assessment of sstr5-/- indicated no significant difference with the wild type regarding growth parameters such as standard length, body depth, or peduncle depth. Furthermore, the functional loss of sstr5 had no impact on the response to a nutritional challenge. The fact that several sstr subtypes were upregulated in different tissues in sstr5-/- medaka suggests that in the mutant fish, there may be a compensatory effect on the different tissues, predominantly by sstr1 in the liver, brain and pituitary, with sstr2 being upregulated in pituitary and liver, and sstr3 only presenting differential expression in the brain. Analysis of the sstr subtype and the sstr5-/- fish showed that sstr5 was not the only somatostatin receptor responsible for Sst-mediated Gh regulation.

Somatostatin receptor 1 (SSTR1) expression as a potential predictive biomarker for response to androgen receptor signaling inhibitor (ARSI) therapy in metastatic castration-resistant prostate cancer (mCRPC).

180 Background: Overcoming ARSI resistance is an unmet need for mCRPC patients. Known resistance mechanisms include genetic alterations augmenting androgen receptor (AR) function (e.g., amplifications of the AR gene and its enhancer and AR mutations) and treatment-emergent evolution from an AR-driven to an AR-indifferent phenotype such as small cell neuroendocrine prostate cancer. Other mechanisms remain unexplored. Methods: To phenotype ARSI-resistant prostate cancer, we compared the RNA-seq profiles of paired metastatic biopsies from 31 mCRPC patients obtained before the initiation of first-line abiraterone or enzalutamide, and upon radiographic progression. The patient samples were obtained from two independent cohorts, the Stand Up To Cancer/Prostate Cancer Foundation (SU2C/PCF) West Coast Prostate Cancer Dream Team (WCDT) and a multi-institutional cohort from the Netherlands sequenced through the Hartwig Medical Foundation. We first evaluated RNA-seq data to identify the most differentially expressed genes and then performed survival analysis in the retrospective WCDT cohort (n=115, including 54 ARSI-naïve and 61 ARSI-experienced tumors) to assess the association between gene expression and overall survival, defined as the time interval from biopsy to death from any cause. Results: In the analysis of paired RNA-seq data from 31 mCRPC patients, SSTR1 was identified as the most significantly altered gene; SSTR1 expression was consistently decreased in post-treatment, ARSI-resistant tumors (log2[fold change]=-2.5, p=1.08×10-16). SSTR1 encodes somatostatin receptor 1, a G-protein coupled receptor that, when activated by the endogenous peptide hormone somatostatin or exogenous somatostatin analogues, mediates anti-proliferative, anti-migratory, and anti-secretory effects on target cells. Retrospective analysis in the 115 WCDT patients demonstrated that low SSTR1 expression was associated with worse overall survival ( p=0.047); ARSI treatment improved survival for patients with SSTR1-high (≥ median) tumors (HR=0.29, p=0.0002) more significantly than those with SSTR1-low (&lt; median) tumors (HR=0.67, p=0.17), with an interaction ( SSTR1 expression * ARSI treatment) towards statistical significance ( p=0.0598). A differential survival benefit of ARSI therapy with respect to SSTR1 expression was observed only among the 61 ARSI-experienced patients. Conclusions: SSTR1 expression is a potential predictive biomarker for response to ARSI in mCRPC, with higher SSTR1 expression predicting better response. This observation could be explained by an anti-tumor effect of SSTR1 signaling. Further work is warranted to prospectively validate these findings and to investigate SSTR1 as an actionable drug target to overcome ARSI resistance.

Mutual associations among responsiveness to differential diagnostic tests for Cushing's disease, tumor size, and somatostatin receptor 5 expression in corticotroph tumors.

There are differences in the responsiveness to differential diagnostic tests for Cushing's disease (CD), corticotroph tumor size, and the somatostatin receptor (SSTR) 5 expression in corticotroph tumors between CD patients. The differences in SSTR5 expression are particularly significant for identifying therapeutic targets for CD. However, prospective predictors of SSTR5 expression remain unclear. Thus, our objective was to elucidate the relationships among these clinical characteristics of CD, including SSTR5 expression. In 27 hospitalized patients with CD at Osaka University Hospital, Osaka, Japan, associations between corticotroph tumor diameter, the response of ACTH and cortisol to differential diagnostic tests for CD (CRH, desmopressin [DDAVP], and high-dose dexamethasone suppression test [HDDST]), the ACTH/cortisol index, and the SSTR5 immunoreactive score were retrospectively investigated. The response to differential diagnostic tests, ACTH/cortisol index, tumor diameter, and SSTR5 expression were significantly related (vs. tumor diameter [CRH: r = -0.54; DDAVP: r = -0.54; HDDST r = -0.67; ACTH/cortisol index: r = 0.76; SSTR5: r = -0.61], vs. CRH [DDAVP: r = 0.63, HDDST: r = 0.72, ACTH/cortisol index: r = -0.45; SSTR5: r = 0.56], vs. DDAVP [HDDST: r = 0.66; ACTH/cortisol index: r = -0.46; SSTR5: r = 0.76], vs. HDDST [ACTH/cortisol index: r = -0.62; SSTR5: r = 0.77], ACTH/cortisol index vs. SSTR5: r = -0.67). The areas under the receiver operating characteristic curve for the prediction of high SSTR5 expression via the CRH test, DDAVP test, HDDST, ACTH/cortisol index, and tumor diameter were 0.79, 0.87, 0.80, 0.71, and 0.71, respectively. Tests for differential diagnosis of CD, the ACTH/cortisol index, and the corticotroph tumor diameter have the potential for identifying SSTR5 expression in corticotroph tumors. These parameters may reflect the biological characteristics of corticotroph tumors.